WO2009027255A2

WO2009027255A2 - A method and system that are used to determine the service life endpoint and evaluate the current historical service life

Info

Publication number: WO2009027255A2
Application number: PCT/EP2008/060789
Authority: WO
Inventors: Wen Gang Shi; Xi Hu; Qing Gang Wang; Jian Hui Xing
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-08-24
Filing date: 2008-08-18
Publication date: 2009-03-05
Also published as: CN101373495A; WO2009027255A3; CN101373495B

Abstract

The present invention discloses a method and system that are used to determine the service life endpoint and evaluate the current historical service life. The current historical service life evaluation method comprises: generating the load waveform of the driver according to the load information and movement position information of the transmission mechanism; obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said load waveform of the driver, and using the weighted coefficient to perform the weighted calculation on the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism. In the method to determine the service life endpoint of the transmission mechanism, the initial value of the previous cumulated historical service life is preset; the current historical service life is added to the previous cumulated historical service life, and the resulting value is compare with the preset estimated service life of the transmission mechanism to determine whether this transmission mechanism reaches its service life endpoint. The technical solution of the present invention can increase the accuracy of the estimation made on the historical service life of the transmission mechanism.

Description

A method and system that are used to determine the service life endpoint and evaluate the current historical service life

Field of Invention

The present invention relates to the mechanical field, and more particularly to a method and system used to determine the service life endpoint of the transmission mechanism and a method and system for estimating the current historical service life of the transmission mechanism.

Background Technology

In the process of machining, the transmission mechanism is subject to huge workload. As a result, the wearing and fail- ure of the transmission mechanism will directly reduce its service life. The transmission mechanism has to be replaced immediately when it reaches its service life endpoint, or it may impact the stability of the machining quality and cause damages to other components that are connected to it. There- fore, it is necessary to set the expected service life of the transmission mechanism in advance and calculate the historical service life, or the used service life, of the transmission mechanism in a real-time manner. When the historical service life of the transmission mechanism reaches the ex- pected service life, it means the transmission mechanism needs to be replaced promptly.

Taking the ball screw as an example, the term fatigue life is usually used to describe the service life of the ball screw in the machine tool field, and the fatigue life is expressed as total number of rotations, total duration and total travel .

However in various applications of the ball screw, on one hand, the axial load or feeding rate usually changes with time, and on the other hand, the ball screw will experience an early fatigue due to incorrect installation and improper lubrication of the ball screw as well as contamination, which shorten the service life of the ball screw. The fact that the ball screw works under varied conditions makes it very difficult to accurately predict whether the ball screw is reaching its expected service life by simply calculating the number of rotations, duration or travel of the ball screw.

At present, the prediction of historical fatigue life of the ball screw in a machine tool is mainly based on dynamic load level, axial load and RPM applied to the ball screw. The US Patent US6332355 has disclosed a method to evaluate the ball screw in an electronic plastic jetting-molding machine, wherein the energy applied to the ball screw in unit time is obtained by multiplying the running speed of the ball screw in this unit time by operating current or torque, wherein the amount of the operating current or the torque is a specific manifestation of the load, and then the energy applied to the ball screw in each unit time is accumulated to obtain the total historical energy applied to the ball screw, and when this total historical energy reaches the energy corresponding to the expected service life of the ball screw, it can be determined that the ball screw is reaching its service life endpoint.

In addition, the US Patent US6615203 has disclosed a method to estimate the historical service life of a bearing, which is similar to the above example of the ball screw, wherein the digital controller collects the load and RPM every 10 seconds and accumulates these loads and RPMs to obtain the cumulated wearing level of the bearing, which is compared with the wearing level corresponding to the expected service life to determine whether the bearing is reaching its expected service life endpoint.

However, the existing technologies for estimating the historical service life take into account only the external fac- tors such as load and RPM applied to the transmission mechanism, and overlook the depreciation in the entire historical service life of the transmission mechanism due to the local defects of the transmission mechanism itself (such as indi- vidual tooth wearing, corrosion or cracking) . Further, as the local defects of the transmission mechanism itself often cannot be reflected in the external factors such as load and RPM, or even can reduce the external load or RPM to lower than their normal levels, the estimation of the historical service life is affected. Consequently, it is very hard to accurately estimate the historical service life of the transmission mechanism by replying on only the external factors such as load and RPM applied to the transmission mechanism.

Description of Invention

The present invention provides a method to determine the service life endpoint of the transmission mechanism in one respect, and provides a system to determine the service life endpoint of the transmission mechanism in another respect, so as to improve the accuracy for estimating the historical ser- vice life endpoint.

In addition, the present invention also provides a method and system to predict the current historical service life, so as to increase the accuracy in a single estimation of the historical service life.

The present invention discloses a method to determine the service life endpoint of transmission mechanism, comprising:

A. presetting the initial value of the previous cumulated historical service life;

B. generating the load waveform of the driver according to the load information and movement position information of the transmission mechanism when the preset time interval is reached; obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said load waveform of the driver, and using the weighted coefficient to perform the weighted calculation on the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism.

C. adding the current historical service life to the previous cumulated historical service life to obtain the current cumulated historical service life;

D. determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism, and if yes, determining the transmission mechanism is reaching its service life endpoint, and if not, recording the current cumulated historical service life for use as the previous cumulated historical service life in the next cycle of historical service life estimation, and re- turning to execute Step B.

Said method of obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said driver's load waveform is: separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism's driver to generate the load waveform component of the transmission mechanism; performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain the current waveform characteristics pa- rameters that are related to the wearing of the transmission mechanism; generating the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters.

Preferably the method further comprises: generating the load waveform of the transmission mechanism' s driver based on the load information and movement position information of the transmission mechanism when in the initial operation under the preset working conditions; separating the components that are related to the transmission mechanism from the load wave- form of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism; performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain the initial waveform characteristics parameters that are related to the wearing of the transmission mechanism;

As described in Step B, said method of generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism is: generating the load waveform of the transmission mechanism's driver according to the load information and movement position information of the transmission mechanism under the preset working conditions that are the same as those when the transmission mechanism worked initially;

As described in Step B, said method of generating the current historical service life weighted coefficient of the transmission mechanism according to said current waveform characteristics parameters is: generating the current historical service life weighted coefficient of the transmission mechanism according to changes of said current waveform characteristics parameters relative to said initial waveform characteristics parameters .

Said method of separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism's driver is: using the wavelet transform or empirical mode decomposition or filtering method to decompose the load waveform of said transmission mechanism' s driver and separating the components that are related to the transmission mechanism.

Said fractal dimension is: fractal box dimension or fractal dimension or Hausdorff dimension, or the information dimension or multi-fractal dimension.

Said method of determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: determining whether the current cumulated historical service life of said transmission mechanism is greater than or equal to said expected service life, and if yes, determining the transmission mecha- nism is reaching its service life endpoint;

or is: subtracting the current cumulated historical service life of said transmission mechanism from said expected service life to obtain the current remaining service life, determining whether the current remaining service life is less than or equal to zero, and if yes, determining the transmission mechanism is reaching its service life endpoint.

Preferably, the cumulated historical service life pre-warning threshold is preset to less than said expected service life; said determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: determining whether the current cumulated historical service life of said transmission mechanism is greater than or equal to said expected service life pre-warning threshold, and if yes, determining the transmis- sion mechanism is reaching its service life endpoint; if not, determining the transmission mechanism has not reached its service life endpoint;

or, the remaining service life pre-warning threshold is preset to a value greater than zero; said determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: subtracting the current cumulated historical service life of said transmission mechanism from said expected service life to obtain the current remaining service life, determin- ing whether said current remaining service life is less than or equal to said remaining service life pre-warning threshold, and if yes, determining the transmission mechanism is reaching its service life endpoint; if not, determining the transmission mechanism has not reached its service life end- point. In the above, the service life of the transmission mechanism is expressed as service life parameters;

Said current initial historical service life is: setting the weighted coefficients respectively according to the different working conditions of the transmission mechanism, and recording the service life of the transmission mechanism under different working conditions, using the weighted coefficients of said different working conditions to perform the weighted calculation on the service life recorded under the corre- sponding working conditions, and accumulate the results from the weight calculations for all conditions to obtain said current initial historical service life.

Said service life parameters comprise: number of rotations, duration and travel.

Said working conditions are: working conditions of feeding at constant speed, or at accelerated speed or at extra accelerated speed.

Said load information of said transmission mechanism includes: operating current and torque of the transmission mechanism's driver.

The present invention discloses a method to evaluate the current historical service life for transmission mechanism, comprising:

generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism;

obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said load waveform of said driver;

using said weighted coefficient to perform the weighted calculation on the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism.

Said obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said load waveform of said driver is:

separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism;

performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism;

generating the current historical service life weighted coefficient of the transmission mechanism according to said cur- rent waveform characteristics parameters.

Preferably, the method further comprises: generating the load waveform of the transmission mechanism' s driver based on the load information and movement position information of the transmission mechanism when in the initial operation under the preset working conditions; separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism; performing the fractal dimension calculation on the load wave- form component of said transmission mechanism to obtain the initial waveform characteristics parameters that are related to the wearing of the transmission mechanism;

said generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism is: generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism under the preset working conditions that are same as those when the trans- mission mechanism worked initially;

said generating the current historical service life weighted coefficient of the transmission mechanism according to said current waveform characteristics parameters is: generating the current historical service life weighted coefficient of the transmission mechanism according to the variations of said current waveform characteristics parameters from said initial waveform characteristics parameters.

Said generating the current historical service life weighted coefficient of the transmission mechanism according to the variations of said current waveform characteristics parameters from said initial waveform characteristics parameters is :

predefining the transfer function between said initial wave- form characteristics parameters and said current waveform characteristics parameters; substituting the obtained said current waveform characteristics parameters and said initial waveform characteristics parameters into the transfer function to obtain the calculated value of the transfer function, and using the calculated value of the transfer function as the current historical service life weighted coefficient of the transmission mechanism.

Said separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism's driver is: using the wavelet transform or empirical mode decomposition or filtering method to decompose the load waveform of said transmission mechanism' s driver and separating the components that are related to the transmission mechanism.

If said transmission mechanism is ball screw, then said components that are related to transmission mechanism comprise: the trend component of said load waveform, load waveform component that is related to the rotating frequency of the ball screw, the load waveform component that is related to the pass frequency at which the balls in the screw nut pass through a point of the leading screw, and the load waveform component that is related to the frequency of the axial bearing of the leading screw, or any one or any combination of the above;

or, if said transmission mechanism is a wheel gear, said components that are related to transmission mechanism comprise: either of or combination of the components related to the engaging frequency of individual wheel gears and the load wave- form component related to the rotation frequency of individual shafts in the gearing transmission mechanism.

The service life of the transmission mechanism is expressed as service life parameters;

Said current initial historical service life is: setting individual weighted coefficients according to different working conditions of the transmission mechanism, and recording the service life of the transmission mechanism under different working conditions, using the weighted coefficients of said different working conditions to perform the weighted calculation on the service life recorded under the corresponding working conditions, and accumulating the results from the weight calculations for all conditions to obtain said current initial historical service life.

Said transmission mechanism is: ball screw or guide or bearing or wheel gear. The present invention discloses a system to determine the service life endpoint for transmission mechanism, comprising:

a process monitoring module, which is used to monitor the running process of the transmission mechanism, and provide the parameters required for calculating the current initial historical service life to the current initial historical service life calculation module;

a current initial historical service life calculation module, which is used to calculate the current initial historical service life according to said parameters provided by said process monitoring module;

wherein, the system further comprises: a waveform recording module, a weighted coefficient calculation module, a current historical service life calculation module, a current cumu- lated historical service life calculation module and a service life endpoint determination module;

wherein, said process monitoring module further provides the load information and movement position information of the transmission mechanism that it collects to the waveform re- cording module;

Said waveform recording module generates the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism sent from the process monitoring module;

Said weighted coefficient calculation module obtains the current historical service life weighted coefficient of the transmission mechanism according to the load waveform generated by said waveform recording module;

Said current historical service life calculation module ob- tains the current historical service life of the transmission mechanism by performing the weighted calculation on the current initial historical service life sent from the current initial historical service life calculation module by using said current historical service life weighted coefficient sent from the weighted coefficient calculation module;

Said current cumulated historical service life calculation module obtains the current cumulated historical service life by adding the stored previous cumulated historical service life to the current historical service life calculated by said current historical service life calculation module, and stores said current cumulated historical service life for use as the previous cumulated historical service life in the next cycle of historical service life estimation; wherein the initial value of previous cumulated historical service life is a preset value;

The life endpoint determination module determines whether the current cumulated historical service life of the transmission mechanism obtained by the current cumulated historical service life calculation module reaches the preset expected service life of the transmission mechanism, and if yes, determines the transmission mechanism is reaching its life end- point, and if not, notifies the process monitoring module to continue with the monitoring.

Said weighted coefficient calculation module comprises:

a waveform component extraction sub-module, which is used to separate the components related to the transmission mechanism from the load waveform of the transmission mechanism' s driver generated by said waveform recording module to generate the load waveform component of the transmission mechanism;

a fractal dimension calculation sub-module, which is used to perform the fractal dimension calculation on the load waveform component of the transmission mechanism generated by said waveform component extraction sub-module to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism;

a weighted coefficient calculation sub-module, which is used to generate the current historical service life weighted co- efficient of the transmission mechanism according to the current waveform characteristics parameters obtained by said fractal dimension calculation sub-module.

Said service life endpoint determination module comprises:

a current remaining service life calculation module, which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumulated historical service life calculation module from the preset expected service life of the transmission mechanism;

a life endpoint determination module, which is used to determine whether the current remaining service life obtained by said current remaining service life calculation module is less than or equal to zero, and if yes, determine the trans- mission mechanism is reaching its service life endpoint.

Said service life endpoint determination module comprises: a current remaining service life calculation module, which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumulated historical service life calculation module from the preset expected service life of the transmission mechanism;

a pre-warning module, which is used to determine whether the current remaining service life obtained by said current re- maining service life calculation module is less than or equal to the remaining service life pre-warning threshold that is preset to greater than zero, and if yes, determine the transmission mechanism is reaching its service life endpoint.

In addition, the present invention discloses a method to es- timate the current historical service life of transmission mechanism, comprising:

wherein the system further comprises: a waveform recording module, a weighted coefficient calculation module and a cur- rent historical service life calculation module;

wherein, said process monitoring module further provides the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism that it detects to the waveform recording module;

said waveform recording module generates the load waveform of the transmission mechanism' s driver according to the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism provided by the process monitoring module;

said current historical service life calculation module ob- tains the current historical service life of the transmission mechanism by performing the weighted calculation on the current initial historical service life sent from the current initial historical service life calculation module by using said current historical service life weighted coefficient sent from the weighted coefficient calculation module.

Said weighted coefficient calculation module comprises:

a weighted coefficient calculation sub-module, which is used to generate the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters obtained by said fractal dimension calculation sub-module.

From the above solution we can see that the embodiments of the present invention describe the wearing of the transmission mechanism by generating the load waveform of the transmission mechanism' s driver and separate the load waveform component of the transmission mechanism from the load waveform of transmission mechanism's driver; obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism according to the load waveform component of the transmission mechanism, and use the current waveform characteristics parameters to generate the current historical service life weighted coefficient of the transmission mechanism; perform the weighted calculation on the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism; thereby more accurately estimating the current historical service life, thus further increasing the accuracy of the estimation of the total historical service life, and in turn improving the accuracy in the prediction of the service life endpoint of the transmission mechanism. Description of Drawings

The following will describe in detail the exemplary embodiments of the present invention with reference to the attached Figures, so that the those of ordinary skill in the art will more clearly understand the above-described and other features and advantages of the present invention. In the attached Figures:

Figure 1 (a) shows the load waveform of the driver when the ball screw is in healthy conditions;

Figure 1 (b) shows the load waveform of the driver when the ball screw is in more serious wearing conditions;

Figure 2 is an exemplary flow chart of the method to determine the service life endpoint of the transmission mechanism described in embodiment 1 of the present invention;

Figure 3 is an exemplary structural diagram of the system to determine the service life endpoint of the transmission mechanism described in embodiment 1 of the present invention;

Figure 4 is a diagram showing the internal structure of the weighted coefficient calculation module in the system shown in Figure 3;

Figure 5 (a) is a diagram illustrating an internal structure of the system shown in Figure 3 using a service life endpoint determination module;

Figure 5 (b) is a diagram illustrating another internal struc- ture of the system shown in Figure 3 using a service life endpoint determination module;

Figure 6 is a diagram showing the load waveform of the driver when the ball screw is in healthy conditions as described in embodiment 2 of the present invention;

Figure 7 is a diagram showing the load waveform component when the ball screw is in healthy conditions as described in embodiment 2 of the present invention;

Figure 8 is a schematic diagram showing the calculation of the initial waveform characteristics parameters when the ball screw is in healthy conditions as described in embodiment 2 of the present invention;

Figure 9 shows the flow chart of the method to determine the historical service life endpoint of the ball screw as described in embodiment 2 of the present invention;

Figure 10 shows the load waveform chart of the driver after the ball screw has been operating for a period as described in embodiment 2 of the present invention;

Figure 11 shows the load waveform component chart after the ball screw has been operating for a period as described in embodiment 2 of the present invention;

Figure 12 is a schematic diagram illustrating the calculation of the initial waveform characteristics parameters after the ball screw has been operating for a period as described in embodiment 2 of the present invention.

Embodiments

Because the service life of the transmission mechanism is usually estimated at preset time intervals, and the total historical service life is obtained by accumulating the service life already consumed in each time interval, it is determined that the transmission mechanism is reaching its ser- vice life endpoint when the total historical service life reaches the expected service life that is preset. The preset time intervals can be identical or different. Therefore, for convenience of description herein, the consumed service life in the current time interval obtained by using the calcula- tion of the present invention solution is called the current historical service life, and accordingly, the consumed service life of the transmission mechanism in the current time interval estimated by using the conventional method is called the current initial historical service life. Furthermore, the historical service life calculated by adding up each current historical service life estimated at individual time intervals before the current time interval is called the previous cumulated historical service life, and the previous cumulated historical service life is added to the current historical service life to obtain a total consumed service life which is called the current cumulated historical service life.

In addition, the method to determine whether the transmission mechanism reaches its service life endpoint can also be: subtracting the expected service life from the cumulated historical service life to obtain the remaining service life and determining that the transmission mechanism reaches its service life endpoint when the remaining service life approaches or is less than or equal to zero. Therefore, for convenience of description herein, the remaining service life obtained by subtracting the current cumulated historical service life from the expected service life is called the current remaining service life, and likewise, the remaining service life obtained by subtracting the previous cumulated historical service life from the expected service life is called the previous remaining service life.

In this embodiment of the present invention, we found through experiment that the local defects of transmission mechanism can be reflected in its load waveform. When defects occur, the load waveform will fluctuate abnormally, becoming complex and irregular, and the complexity and irregularity of load waveform change depending on the severity of the defects. As shown in Figures 1 (a) and 1 (b) which use the ball screw as an example, Figure 1 (a) shows the driver's load waveform when the ball screw is in a healthy condition and Figure 1 (b) shows the driver' s load waveform when the ball screw is in a more serious wearing condition. The load waveform chart is generated by the torque of the driver and the movement posi- tion information of the transmission mechanism. The movement position information of the transmission mechanism can be ei- ther the position information of the corresponding motor encoder or the position information directly recorded in the transmission mechanism, for instance, the position information recorded by the grating scale installed on the work ta- ble. The load waveform chart records the driver's torque values when the transmission mechanism is at different positions. From a comparison between Figure 1 (a) and Figure 1 (b) we can find that, the load waveform of the driver shown in Figure 1 (b) describes major wearing of the ball screw. There- fore, we can use the load waveform of the transmission mechanism's driver to describe its local defects, and further leverage the fractal dimension to describe the complexity and irregularity of the load waveform. Changes in complexity and irregularity are used to perform the weighted calculation on the current initial historical service life of the transmission mechanism to obtain the current historical service life.

There is more than one process for performing the weighted calculation on the current initial historical service life of the transmission mechanism according to changes in the com- plexity and irregularity of the load waveform after the driver' s load waveform is obtained from the load information and movement position of the transmission mechanism. We can either directly use the complexity and irregularity of the driver' s load waveform to calculate the current historical service life weighted coefficient through experiments and by using empirical values, or we can separate the components related to the transmission mechanism from the driver' s load waveform to generate the load waveform component of the transmission mechanism and perform the fractal dimension cal- culation on the load waveform component to obtain current waveform characteristics parameters that are related to the wearing of the transmission mechanism and then generate the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters.

In order to make more apparent the purposes, technical solu- tion and advantages of the present invention, the following further describes the present invention by referring to the drawings .

Embodiment 1 :

Figure 2 shows an exemplary flow chart of the method to determine the service life endpoint of the transmission mechanism as described in embodiment 1 of the present invention. The flow includes the following steps, as shown in Figure 2:

step 201, monitoring the parameters during the course of the transmission mechanism operation, and, when the preset time interval is reached, generating the load waveform of the transmission mechanism driver according to the operating current or torque of the transmission mechanism driver and the movement position information of the transmission mechanism.

In this step, the load waveform information during the operation of the transmission mechanism can be reflected in the operating current or torque of the transmission mechanism' s driver, and the transmission mechanism' s movement position information can be obtained from the feedback of the position measurement system in the transmission mechanism, and then the load waveform of the transmission mechanism driver is generated according to the obtained operating current or torque of the transmission mechanism driver and the movement position information of the transmission mechanism.

Step 202, separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism.

As the load waveform of the transmission mechanism driver in- eludes the waveform components of all components of the transmission system, it is necessary to separate the components related to the transmission mechanism from the load waveform of the transmission mechanism driver in order to accurately estimate the historical service life of the trans- mission mechanism. In a specific embodiment, we can use the wavelet transform or empirical mode decomposition (EMD) or other methods to decompose the load waveform of the transmission mechanism driver to obtain multiple components, hence separating the components related to the transmission mechanism. The components related to the transmission mechanism can be obtained through experiments, or by experience. Considering a gear transmission mechanism, the abovementioned method can be used to extract the load waveform components that are related to the engaging frequency of the wheel gears and the rotation frequency of the shafts in the gearing transmission mechanism, or only extract the components related to the engaging frequency of the wheel gears, or only separate the load waveform component that is related to the rotation frequency of the shafts in the gearing transmission mechanism. Considering a ball screw, we can extract the trend component (i.e. low frequency) of the load waveform, load waveform component that is related to the rotating frequency of the ball screw, the load waveform component that is re- lated to the pass frequency at which the balls in the screw nut pass through a point of the leading screw, and the load waveform component that is related to the frequency of the axial bearing of the leading screw, or any one or any combination of the above.

Step 203, performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism.

In a specific embodiment, the fractal dimension can be frac- tal box dimension or fractal dimension or Hausdorff dimension, information dimension or multi-fractal dimension or fractal dimension of other forms.

Because the fractal dimension calculation is to describe the changes in the characteristics of the waveform such as com- plexity and irregularity, we can do a test in advance on the waveform of the transmission mechanism during the initial running, that is, generate the load waveform of the transmission mechanism' s driver according to the operating current or torque of the transmission mechanism driver and the movement position information of the transmission mechanism; separate the components related to the transmission mechanism from the load waveform of the transmission mechanism' s driver and generate the load waveform component of the transmission mechanism; perform the fractal dimension calculation on the transmission mechanism load waveform, and obtain the initial wave- form characteristics parameters related to the wearing of the transmission mechanism in healthy conditions for use as the benchmark for comparison. Further, in order to establish a universal estimation standard, it is preferred that the transmission mechanism is monitored and that the load wave- form of the transmission driver during initial operation and that of the transmission mechanism driver during the course of operation are generated. The waveform can be a waveform generated in a period within this time interval, e.g., the last period of time within this time interval, or in a period of time within this time interval when the operation of the transmission mechanism is monitored and the working conditions of the transmission mechanism are identical to those when the waveform of the transmission mechanism is tested in the healthy conditions. The identical conditions can be iden- tical load and identical running speed and others.

Step 204, generating the current historical service life weighted coefficient of transmission mechanism according to the current waveform characteristics parameters and using this weighted coefficient to calculate the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism.

The current initial historical service life of the transmission mechanism is the service life consumed by transmission mechanism after the previous historical service life estimation and this current initial historical service life can be calculated using any of existing methods. For instance, the energy applied to the transmission mechanism during the time period can be calculated by multiplying the running speed of the transmission mechanism by the operating current or torque to obtain the current initial historical service life.

Alternatively, the current initial historical service life of the transmission mechanism can also be generated using the following methods: setting the individual weighted coefficients according to different working conditions of the transmission mechanism, and recording the number of rotations/duration/travel of the transmission mechanism in different working conditions within this period of time, using the weighted coefficients of said different working conditions to perform the weighted calculation on the number of rotations/duration/travel recorded in the corresponding working conditions, and accumulating the results from the weight calculations for all conditions to obtain said current initial historical service life.

The different working conditions can be various states of different performance parameters, including the respective state of individual factors such as temperature, current, pressure, feeding speed, or states of combination of some of these factors. For instance, the states of feeding can include constant feeding, accelerated feeding or extra acceler- ated speed and so on.

When generating the weighted coefficient of the current historical service life of the transmission mechanism according to the waveform characteristics parameters, the wearing- related, initial waveform characteristics parameters of the transmission mechanism in healthy conditions and the wearing- related, current waveform characteristics parameters of the current transmission mechanism, as well as the determined transfer function can be used to perform a calculation to obtain the weighted coefficient of current historical service life as described in Step 203, and then this weighted coefficient can be used to perform the weighted calculation on the current initial historical service life to obtain the current historical service life of the transmission mechanism.

This concludes the calculation of the historical service life within this time interval.

Step 205, adding the current historical service life to the previous cumulated historical service life to obtain the current cumulated historical service life.

The previous cumulated historical service life is the accumulation of the calculated historical service life within all the time intervals before calculating the historical service life within this time interval, and the historical service life within each time interval can be calculated according to the flow described in Step 201 to Step 204, or, if the transmission mechanism is in a healthy condition during its ini- tial operation, we may only calculate the current initial historical service life, and use the current initial historical service life for accumulation, and at this point in time, the weighted coefficient of the current initial historical service life is equivalent to 1. The previous cumulated his- torical service life can be preset to zero, or a safety coefficient is preset so that the previous cumulated historical service life can be preset to an allowance, or the previous cumulated historical service life is preset to an initial value according to other standards.

This concludes the calculation of the current cumulated historical service life, that is, the consumed service life of the transmission mechanism.

Step 206, determining whether the service life of the transmission mechanism reaches its endpoint according to the pre- set expected service life of the transmission mechanism, and if not, recording the current cumulated historical service life for use as the previous cumulated historical service life in the next cycle of historical service life estimation, and returning to execute Step 201; if yes, terminating the servi ce .

The specific determination process can be: if the current cumulated historical service life of the transmission mechanism is greater than or equal to the expected service life, it is determined that the transmission mechanism is reaching its service life endpoint; if not, the transmission mechanism has not reached its service life endpoint. In addition, the cumulated historical service life pre-warning threshold can be preset to lower than the expected service life so that when the current cumulated historical service life of said transmission mechanism is greater than or equal to the cumulated service life pre-warning threshold, a warning is provided indicating that the transmission mechanism is approaching its service life endpoint and that the user needs to prepare to replace the transmission mechanism in a timely manner, or in other words, the transmission mechanism is reaching its service life endpoint.

Also, the specific determination process can be: subtracting the current cumulated historical service life of said trans- mission mechanism from its expected service life to obtain the current remaining service life. When the current remaining service life is less than or equal to zero, it is determined that the transmission mechanism is reaching its service life endpoint; otherwise, it does not reach its service life endpoint. Similarly, we can also preset the remaining service life pre-warning threshold to a value greater than zero, and when the current remaining service life is less than or equal to the preset remaining service life pre-warning threshold, we can determine the transmission mechanism is approaching its service life endpoint and we should prepare to replace the transmission mechanism in a timely manner, or in other words, the transmission mechanism reaches its service life endpoint .

The above embodiments give a detailed description of the method for determining the transmission mechanism service life endpoint of the present invention. The following will describe the system for determining the service life endpoint of the transmission mechanism in embodiments of the present invention .

Figure 3 shows an exemplary structure of the system to deter- mine the service life endpoint of the transmission mechanism presented in embodiment 1. As shown in Figure 3, this system comprises: a process monitoring module 310, a current initial historical service life calculation module 320, a waveform recording module 330, a weighted coefficient calculation mod- ule 340, a current historical service life calculation module 350, a current cumulated historical service life calculation module 360 and a service life endpoint determination module 370.

The process monitoring module 310 is used to monitor the run- ning process of the transmission mechanism, and provide the parameters required for calculating the current initial historical service life to the current initial historical service life calculation module 320.

The current initial historical service life calculation mod- ule 320 is used to calculate the current initial historical service life according to the parameters provided by the process monitoring module.

The parameters required for calculating the current initial historical service life can be either the running speed of the transmission mechanism, the operating current or torque or be the number of rotations, duration and travel. In the specific calculation, various methods of existing technologies can be used. For instance, it can be identical to the method and flow described in Figure 2.

Additionally, the process monitoring module 310 further provides the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism that it detects to the waveform recording module 330. The waveform recording module 330 is used to generate the load waveform of the transmission mechanism' s driver according to the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism sent from the process monitoring module 310.

The weighted coefficient calculation module 340 is used to obtain the current historical service life weighted coefficient of the transmission mechanism according to the load waveform generated by said waveform recording module 330.

The current historical service life calculation module 350 is used to obtain the current historical service life of the transmission mechanism by performing the weighted calculation on the current initial historical service life sent from the current initial historical service life calculation module

320 using the current historical service life weighted coefficient sent from the weighted coefficient calculation module 340.

The current cumulated historical service life calculation module 360 is used to obtain the current cumulated historical service life by adding the stored previous cumulated historical service life to the current historical service life calculated by the current historical service life calculation module 350, and store said current cumulated historical ser- vice life for use as the previous cumulated historical service life in the next cycle of historical service life estimation; wherein the previous cumulated historical service life is preset to an initial value. This preset initial value can be either zero or a preset safety factor.

The service life determination module 370 is used to determine whether the transmission mechanism is reaching its service life endpoint according to the current cumulated historical service life of transmission mechanism obtained by the current cumulated historical service life module 360 and the preset expected service life of the transmission mecha- nism. If it has not reached the endpoint, the process monitoring module 310 will be notified to continue with the monitoring and each module repeats each of the functions mentioned above; otherwise, a notification will be given to re- place the transmission mechanism.

In actual implementation of the weighted coefficient calculation module 340, one form of the implementation is shown in Figure 4, which illustrates the internal structure of the weighted coefficient calculation module. It comprises: a waveform component extraction sub-module 341, a fractal dimension calculation sub-module 342 and a weighted coefficient calculation sub-module 343.

The waveform component extraction sub-module 341 is used to separate the components related to the transmission mechanism from the load waveform of the transmission mechanism' s driver generated by said waveform recording module to generate the load waveform component of the transmission mechanism.

The fractal dimension calculation sub-module 342 is used to perform the fractal dimension calculation on the load wave- form component of the transmission mechanism generated by the waveform component extraction sub-module to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism.

The weighted coefficient calculation sub-module 343 is used to generate the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters obtained by said fractal dimension calculation sub-module 342.

The specific determination process of the life endpoint de- termination module 370 can be the same as the method and flow described in the Figure 2. For instance, Figure 5 (a) presents one of the internal structures of the service life endpoint determination module 370. As shown in Figure 5 (a) , the service life endpoint determination module 370 may comprise: a current remaining service life calculation module 371, which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumu- lated historical service life calculation module from the preset expected service life of the transmission mechanism; a service life determination module 372, which is used to determine whether the current remaining service life obtained by the current remaining service life calculation module is less than or equal to zero, and if less than or equal to zero, it determines the transmission mechanism reaches its service life endpoint and if not, it determines the transmission mechanism has not reached its service life endpoint.

Figure 5 (b) presents another internal structure of the ser- vice life endpoint determination module 370. As shown in Figure 5 (b) , the service life endpoint determination module 370 may comprise: a current remaining service life calculation module 371, which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumulated historical service life calculation module from the preset expected service life of the transmission mechanism; a pre-warning module 373, which is used to determine whether the current remaining service life obtained by the current remaining service life calculation module is less than or equal to the preset remaining service life pre- warning threshold which is greater than zero, and if so, it gives an alarm indicating that the transmission mechanism is approaching its service life endpoint and that the user should prepare to replace the transmission mechanism in a timely manner, or in other words, the transmission mechanism reaches its service life endpoint.

In practical application, the process monitoring module 310, the current historical service life calculation module 320, the waveform recording module 330, the waveform component extraction sub-module 341, the fractal dimension calculation sub-module 342 and the current historical service life calculation module 350 can independently form a system for a single estimation of the historical service life of the transmission mechanism, which is used to calculate the historical service life within each time interval.

The specific implementation of each module mentioned above can be the same as the method and flow described in Figure 2 and is not further described herein.

Embodiment 2 :

This embodiment gives a detailed description of the above method and system in a specific case of application.

This embodiment uses the ball screw in a digitally controlled machine tool as an example. When the ball screw initially runs in a healthy condition, the machine tool is kept in op- eration without load and at the preset feeding rate. Then the load waveform of the driver when the ball screw is in a healthy condition is generated by monitoring the torque of the driver and the movement position information of the ball screw feedback by the position measurement system of the ball screw, as shown in Figure 6. Figure 6 shows the load waveform of the driver when the ball screw is in a healthy condition and the load waveform is generated by the torque of the driver and the position information of the ball screw. Because the machine tool runs without load when it is just put into use, the service life depreciation of the ball screw can be ignored during this test, that is, it is not added to the previous cumulated historical service life during this test. Otherwise, if the test occurs during the subsequent use of the digital controlled machine tool, the time length of the test should be recorded, and this recorded time length should be taken into account in the estimation of previous cumulated historical service life.

Next, the wavelet transform is used to separate the component related to the ball screw from the load waveform of the ball screw' s driver, and to generate the load waveform component of the ball screw, as shown in Figure 7. Figure 7 shows the load waveform component when the ball screw is in a healthy condition. The components related to the transmission mecha- nism can be obtained through experiments, or experience.

The fractal box dimension calculation is performed on the load waveform component of said ball screw to obtain the initial waveform characteristics parameters that are related to the wearing of the ball screw, as shown in Figure 8. Figure 8 is a schematic diagram showing the calculation of the initial waveform characteristics parameters when the ball screw is in a healthy condition in this embodiment and this schematic diagram is obtained from the ratio of the logarithm value of the box quantity (1(XJ₂N) to that of the reciprocal of the box side length ( log₂ ( 1 /δ) ) . Said calculated initial waveform characteristics parameter is 1.73, or in other words, the fitting gradient of the curve is 1.73.

Figure 9 is a flow chart of the method to determine the historical service life endpoint of the ball screw in embodiment 2 of the present invention. The flow comprises the following steps as shown in Figure 9:

Step 901, the digital controlled unit monitors the parameters during the running of the ball screw such as operating current or torque of the driver, position information of the ball screw and feeding rate.

The position information of the ball screw can be obtained from the feedback provided by the position measurement system of the ball screw. This feeding rate can be feeding at constant speed, at accelerated speed or at extra accelerated speed and so on.

Step 902, when the preset time interval is reached, the machine tool is kept in operation without load and at the preset feeding rate. Then the monitored torque of the driver and the movement position information of the ball screw is used to generate the current load waveform of the ball screw' s driver .

To standardize the estimation basis, both measurement of the current load waveform of the ball screw' s driver and measure- ment of the load waveform of the driver when the ball screw is in a healthy condition are performed when the machine tool runs without load and at the preset feeding rate. The service life depreciation of the ball screw during the test period may be taken into consideration, and the time length of the test should be recorded and the depreciated life during this time length should be added to the current initial historical service life.

Figure 10 shows the current load waveform of the ball screw's driver in this embodiment. This load waveform is generated from the torque of the driver and position information of the ball screw.

Step 903, the wavelet transform is used to separate the component related to the ball screw from the load waveform of the ball screw' s driver, and generate the load waveform com- ponent of the ball screw.

Figure 11 shows the current load waveform of the ball screw in this embodiment. The components related to the ball screw can be obtained through experiment, or experience. For example, we can extract the trend (low frequency) component of said load waveform and the load waveform component that is related to both rotation frequency of the ball screw and the frequency at which the balls in the screw nut pass through a point of the leading screw.

Step 904, the fractal dimension calculation is performed on the load waveform component of the ball screw to obtain current waveform characteristics parameters that are related to the wearing of the ball screw.

Figure 12 is a schematic diagram showing calculation of the current initial waveform characteristics parameters of the ball screw. This schematic diagram is obtained from the ratio of the logarithm value of the box amount (log₂N) to that of the reciprocal of the box side length ( log₂ ( 1 /δ) ) . The calculated initial waveform characteristics parameter is 1.68, that is, the fitting gradient of the curve is 1.68.

Step 905, the ball screw's current historical service life weighted coefficient is generated according to the current waveform characteristics parameters and this generated weighted coefficient is used to calculate the current initial historical service life of ball screw to obtain the current historical service life of the ball screw.

The current initial historical service life in this embodiment can be calculated using the following method:

Individual weighted coefficients are set according to differ- ent working conditions of the ball screw. Assuming the working conditions of the ball screw α in this embodiment mainly involve the feeding states, that is, feeding at constant speed, at accelerated speed and at extra accelerated speed, there are three weighted coefficients, cxi, α₂ and α₃. The val- ues of cxi, α₂ and α₃ can be obtained based on tests and experience. For instance, tests are performed to measure the axial load on the ball screw in the three feeding states, i.e. feeding at constant speed, at accelerated speed and at extra accelerated speed, and determine the values of cxi, α₂ and α₃ according to the maximum peak of the axial load in these three feeding states. In other words, make cxi=l . If the maximum peak of the axial load at accelerated feeding speed increases to 1.2 times of that at the constant feeding speed, then α₂=l .2³=1.728. Similarly, if the maximum peak of the ax- ial load at extra accelerated feeding speed increases to 2 times of that at the constant feeding speed, then α₃=2³=8.

Record the working hours under different working conditions of the ball screw from the previous evaluation of the historical service life up to the present. Assuming that the working hours are T₁ under the condition of feeding at con- stant speed, T₂ under the condition of feeding at accelerated speed, T₃ under the condition of feeding at highly- accelerated speed, and the current initial historical service life is Li_n.

The current initial historical service life is calculated

When the current historical service life weighted coefficient of the ball screw is generated according to the current waveform characteristics parameters, the transfer function f/ (D, Di) can be generated according to the initial waveform characteristics parameters obtained when the ball screw is in a healthy condition and the current waveform characteristics parameters which are calculated in this cycle of estimation, and this transfer function can be determined through experience or test. For example, the transfer function

can be defined by comparing the fractal dimension difference between the initial state of the ball screw and the current load waveform of the ball screw. Then, the value of this transfer function f (D, Di) is used as the weighted coefficient of the current historical service life. Wherein, D is the initial waveform characteristics parameter which is obtained when the ball screw is in a healthy condition; Di is the current waveform characteristics parameter which is calculated in this cycle of estimation. As shown in Figure 8 and 12, if the initial load waveform characteristics parameter of the ball screw is 1.73, and the current waveform characteristics parameter which is calculated in this cycle of estimation is 1.68, the value of the transfer function can be calculated from the above formula:

Assuming that the current historical service life is Li, the current historical service life of the ball screw can be calculated from the formula: Li=f (D , Di) ^• (αiT₁+α₂T₂+α₃T₃) .

Step 906, the current historical service life is added to the previous cumulated historical service life to obtain the current cumulated historical service life.

Wherein, the current cumulated historical service life L_act can be expressed as :

L_a* = Σ f (D, D₁) - {a_λT_Xi + (Z₂T₂₁ + a₃T_3i)

1=1

Wherein, i represents the serial number of each estimation of the historical service life during the entire working period of the ball screw. Tn is between the i^th estimation of historical service life and the (i-l)^th estimation of historical service life, that is, the time length when the ball screw works at a constant feeding speed as measured in the i^th time interval; T₂i is the time length when the ball screw works at accelerated feeding speed as measured in the i^th time interval; T₃i is the time length when the ball screw works at extra accelerated feeding speed as measured in the i^th time interval. N is the total number of cycles of the historical service life estimation.

Step 907, the current remaining service life of the ball screw can be obtained by subtracting the current cumulated historical service life of the ball screw from the preset expected service life of the ball screw.

The expected service life, Lmax, of the ball screw can be calculated from the formula:

Wherein, C₃ is the basic dynamic load rating in Newton (N) ; F_m is the average effective load in N; N_n, is the average RPM in 1/min; and f_w is the load coefficient.

Then, the current remaining service life is:

Step 908, it is determined whether the current remaining service life of the ball screw reaches the remaining service

life pre-warning threshold, and if yes, an alarm is provided to warn that the ball screw is approaching its service life endpoint and should be replaced as soon as possible; if not, return to execute Step 901.

The system to determine the historical service life endpoint of the ball screw in this embodiment is similar to the system described in Figure 3, and the specific operating process of each module is the same as the corresponding steps in the method to determine the historical service life endpoint of the ball screw as shown in Figure 9, and therefore they are not further described herein.

The above description uses the ball screw as an example of transmission mechanism and it is also applicable to other transmission mechanisms such as ball screw, guide, bearing and wheel gear.

It is apparent from the above embodiments that the technical solution of the present invention can accurately estimate the service life of the transmission mechanisms. On one hand, the technical solution of the present invention take into account the impact of the wearing and defect of the transmission mechanism itself on its service life. As the wearing and defect of the transmission mechanism itself often appear in a local area of the transmission mechanism and are instantaneous fluctuation or minor interference when reflected in the load waveform, it is possible to discover at an early stage the local wearing and defect of the transmission mechanism and their impact on the remaining service life of the transmission mechanism by analyzing the load waveform. On the other hand, the technical solution of the present invention also considers the impact on the service life of the transmission mechanism when it works in various conditions. By separately estimating the historical service life of the transmission mechanism when working in different conditions, it is possible to predict more accurately the service life of the transmission mechanism. Therefore, it can be understood that the above are only preferred embodiments of the present invention, and is not intended to restrict the protection range of this invention. Any modifications, equivalent substitutions and improvements within the philosophy and principle of the present invention are included in the protection of the present invention.

Claims

Patent claims

1. A method to determine the service life endpoint of transmission mechanism, wherein the method comprises:

C. adding the current historical service life to the previous cumulated historical service life to acquire the current cumulated historical service life;

D. determining whether said current cumulated historical ser- vice life reaches the preset expected service life of the transmission mechanism; and if yes, determining whether the transmission mechanism is reaching its service life endpoint; if not, recording the current cumulated historical service life for use as the previous cumulated historical service life in the next cycle of historical service life estimation, and returning to execute Step B.

2. The method as claimed in claim 1, wherein said method of obtaining the weighted coefficient of the current historical service life of the transmission mechanism according to said driver's load waveform is: separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism; conducting the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain current waveform characteristics parameters that are related to the wearing of the transmission mechanism; generating the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters.

3. The method as claimed in claim 2, wherein the method further comprises: generating the load waveform of the transmis- sion mechanism's driver based on the load information and movement position information of the transmission mechanism during the initial operation of the transmission mechanism under the preset working conditions; separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism; conducting the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain initial waveform characteristics parameters that are re- lated to the wearing of the transmission mechanism;

as described in Step B, said method of generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism is: generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism under the preset working conditions that are the same as those when the transmission mechanism worked initially;

4. The method as claimed in claim 2, wherein said method of separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism's driver is: using the wavelet transform or empirical mode decomposition or filtering method to decompose the load waveform of said transmission mechanism' s driver and separating the components that are related to the transmission mechanism from the decomposed components.

5. The method as claimed in claim 2, wherein said fractal dimension is: fractal box dimension or fractal dimension or Hausdorff dimension, or the information dimension or multi- fractal dimension.

6. The method as claimed in claim 1, wherein said method of determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: determining whether the current cumulated historical service life of said transmission mechanism is greater than or equal to said expected service life, and if yes, determining the transmission mechanism is reaching its service life endpoint;

or: subtracting the current cumulated historical service life of said transmission mechanism from said expected service life to obtain the current remaining service life, and deter- mining whether the current remaining service life is less than or equal to zero, and if yes, determining the transmission mechanism is reaching its service life endpoint.

7. The method as claimed in claim 1, wherein the method of presetting a cumulated historical service life pre-warning threshold to less than said expected service life, wherein said determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: determining whether the current cumulated historical service life of said transmission mecha- nism is greater than or equal to said expected service life pre-warning threshold, and if yes, determining the transmission mechanism is reaching its service life endpoint; if not, determining the transmission mechanism has not reached its service life endpoint;

or, presetting the remaining service life pre-warning threshold to greater than zero, wherein said method of determining whether said current cumulated historical service life reaches the preset expected service life of the transmission mechanism is: subtracting the current cumulated historical service life of said transmission mechanism from said expected service life to obtain the current remaining service life, and determining whether said current remaining service life is less than or equal to said remaining service life pre-warning threshold, and if yes, determining the transmission mechanism is reaching its service life endpoint, and if not, determine the transmission mechanism has not reached its service life endpoint.

8. The method as claimed in claim 1, wherein said method of calculating said current initial historical service life is: setting individual weighted coefficients according to different working conditions of the transmission mechanism, and recording the service life of the transmission mechanism under the different working conditions, using the weighted coeffi- cients of said different working conditions to perform the weighted calculation on the service life recorded under the corresponding working conditions, and accumulating the results from the weight calculations for all conditions to obtain said current initial historical service life.

9. The method as claimed in claim 8, wherein the service life of the transmission mechanism is expressed as service life parameters and said service life parameters comprise: number of rotations, duration and travel.

10. The method as claimed in claim 8, wherein said working conditions are: working conditions of feeding at constant speed, or at accelerated speed or at extra accelerated speed.

11. The method as claimed in one of claims 1 to 10, wherein the load information of said transmission mechanism includes: operating current and torque of the transmission mechanism' s driver.

12. The method as claimed in one of claims 1 to 10, wherein the position information of said transmission mechanism includes: the information of position corresponding to the motor encoder and position information recorded in the trans- mission mechanism.

13. A method to evaluate current historical service life for transmission mechanism, wherein the method comprises:

generating the load waveform of the transmission mechanism' s driver according to the load information and movement posi- tion information of the transmission mechanism;

using said weighted coefficient to perform the weighted cal- culation on the current initial historical service life of the transmission mechanism to obtain the current historical service life of the transmission mechanism.

14. The method as claimed in claim 13, wherein said method of obtaining the weighted coefficient of the current histori- cal service life of the transmission mechanism according to said load waveform of said driver is:

performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain current waveform characteristics parameters that are related to the wearing of the transmission mechanism;

15. The method as claimed in claim 14, wherein said method further comprises: generating the load waveform of the transmission mechanism' s driver based on the load information and movement position information of the transmission mechanism when in the initial operation under the preset working conditions; separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism' s driver to generate the load waveform component of the transmission mechanism; performing the fractal dimension calculation on the load waveform component of said transmission mechanism to obtain initial waveform characteristics parameters that are related to the wearing of the transmission mechanism;

said method of generating the load waveform of the transmis- sion mechanism's driver according to the load information and movement position information of the transmission mechanism is: generating the load waveform of the transmission mechanism' s driver according to the load information and movement position information of the transmission mechanism under the preset working conditions that are same as those when the transmission mechanism worked initially;

said method of generating the current historical service life weighted coefficient of the transmission mechanism according to said current waveform characteristics parameters is: gen- erating the current historical service life weighted coefficient of the transmission mechanism according to changes of said current waveform characteristics parameters relative to said initial waveform characteristics parameters.

16. The method as claimed in claim 15, wherein said method of generating the current historical service life weighted coefficient of the transmission mechanism according to changes of said current waveform characteristics parameters from said initial waveform characteristics parameters is:

predefining the transfer function of said initial waveform characteristics parameters and said current waveform characteristics parameters; substituting the obtained said current waveform characteristics parameters and said initial waveform characteristics parameters into the transfer function to ob- tain the calculated value of the transfer function, and using the calculated value of the transfer function as the current historical service life weighted coefficient of the transmission mechanism.

17. The method as claimed in claim 14, wherein said method of separating the components that are related to the transmission mechanism from the load waveform of said transmission mechanism's driver is: using the wavelet transform or empirical mode decomposition or filtering method to decompose the load waveform of said transmission mechanism' s driver and separating the components that are related to the transmission mechanism from the decomposed components.

18. The method as claimed in claim 14, wherein said transmission mechanism is ball screw, and said components that are related to transmission mechanism comprise: the trend compo- nent of said load waveform, load waveform component that is related to the rotating frequency of the ball screw, the load waveform component that is related to the pass frequency at which the balls in the screw nut pass through a point of the leading screw, and the load waveform component that is re- lated to the frequency of the axial bearing of the leading screw, or any one or any combination of the above.

or, said transmission mechanism is wheel gear, said components that are related to transmission mechanism comprise: either of or combination of the component related to the en- gaging frequency of individual wheel gears and the load wave- form component related to the rotation frequency of individual shafts in the gearing transmission mechanism.

19. The method as claimed in claim 14, wherein said fractal dimension is: fractal box dimension or fractal dimension or Hausdorff dimension, or the information dimension or multi- fractal dimension.

20. The method as claimed in claim 13, wherein the service life of the transmission mechanism is expressed as service life parameters;

21. The method as claimed in claim 20, wherein said service life parameters comprise: number of rotations, duration and travel .

22. The method as claimed in claim 20, wherein said working conditions are: working conditions of feeding at constant speed, or at accelerated speed or at extra accelerated speed.

23. The method as claimed in any of claims 13 to 17 and 19 to 22, wherein said transmission mechanism is: ball screw or guide or bearing or wheel gear.

24. A system to determine the service life endpoint of transmission mechanism comprises:

a process monitoring module (310), which is used to monitor the running process of the transmission mechanism, and pro- vide the parameters required for calculating the current initial historical service life to the current initial historical service life calculation module (320);

a current initial historical service life calculation module (320), which is used to calculate the current initial historical service life according to said parameters provided by said process monitoring module;

wherein the system further comprises: a waveform recording module (330), a weighted coefficient calculation module (340), a current historical service life calculation module (350), a current cumulated historical service life calculation module (360) and a service life endpoint determination module (370) ;

wherein, said process monitoring module (310) is further used to provide the load information and movement position information of the transmission mechanism that it collects to the waveform recording module (330);

said waveform recording module (330) is used to generate the load waveform of the transmission mechanism' s driver accord- ing to the load information and movement position information of the transmission mechanism sent from the process monitoring module (310);

said weighted coefficient calculation module (340) is used to obtain the current historical service life weighted coeffi- cient of the transmission mechanism according to the load waveform generated by said waveform recording module (330);

said current historical service life calculation module (350) is used to obtain the current historical service life of the transmission mechanism by performing the weighted calculation on the current initial historical service life sent from the current initial historical service life calculation module (320) by using said current historical service life weighted coefficient sent from the weighted coefficient calculation module (340) ; said current cumulated historical service life calculation module (360) is used to obtain the current cumulated historical service life by adding the stored previous cumulated historical service life to the current historical service life calculated by said current historical service life calculation module (350), and store said current cumulated historical service life for use as the previous cumulated historical service life in the next cycle of historical service life estimation, wherein the initial value of previous cumulated historical service life is a preset value;

the life endpoint determination module (370) is used to determine whether the current cumulated historical service life of the transmission mechanism obtained by the current cumulated historical service life calculation module is reaching the preset expected service life of the transmission mechanism, and if yes, determine the transmission mechanism is reaching its life endpoint, and if not, notify the process monitoring module (310) to continue with the monitoring.

25. The system as claimed in claim 24, wherein said weighted coefficient calculation module (340) comprises:

a waveform component extraction sub-module (341), which is used to separate the components that are related to the transmission mechanism from the load waveform of the transmission mechanism' s driver generated by said waveform re- cording module (330) to generate the load waveform component of the transmission mechanism;

a fractal dimension calculation sub-module (342), which is used to perform the fractal dimension calculation on the load waveform component of the transmission mechanism generated by said waveform component extraction sub-module (341) to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism;

a weighted coefficient calculation sub-module (343) , which is used to generate the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters obtained by said fractal dimension calculation sub-module (342).

26. The system as claimed in claim 24, wherein said service life determination module (370) comprises:

a current remaining service life calculation module (371), which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumu- lated historical service life calculation module (360) from the preset expected service life of the transmission mechanism;

a life endpoint determination module (372), which is used to determine whether the current remaining service life obtained by said current remaining service life calculation module (371) is less than or equal to zero, and if yes, determine the transmission mechanism is reaching its service life end- point .

27. The system as claimed in claim 24, wherein said service life determination module (370) comprises:

the current remaining service life calculation module (371), which is used to obtain the current remaining service life by subtracting the current cumulated historical service life of said transmission mechanism obtained by said current cumu- lated historical service life calculation module (360) from the preset expected service life of the transmission mechanism;

a pre-warning module (373), which is used to determine whether the current remaining service life obtained by said current remaining service life calculation module (371) is less than or equal to the remaining service life pre-warning threshold which is preset to greater than zero, and if yes, determine the transmission mechanism is reaching its service life endpoint.

28. A system to evaluate the current historical service life for a transmission mechanism comprising:

the process monitoring module (310), which is used to monitor the running process of the transmission mechanism, and pro- vide the parameters required for calculating the current initial historical service life to the current initial historical service life calculation module (320);

the current initial historical service life calculation module (320), which is used to calculate the current initial historical service life according to said parameters provided by said process monitoring module;

wherein the system further comprises: the waveform recording module (330), weighted coefficient calculation module (340), and current historical service life calculation module (350);

wherein, said process monitoring module (310) is further used to provide the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism that it detects to the waveform recording module (330);

said waveform recording module (330) is used to generate the load waveform of the transmission mechanism' s driver according to the operating current or torque of the transmission mechanism' s driver and movement position information of the transmission mechanism sent from the process monitoring mod- ule (310);

said weighted coefficient calculation module (340) is used to obtain the current historical service life weighted coefficient of the transmission mechanism according to the load waveform generated by said waveform recording module (330);

said current historical service life calculation module (350) is used to obtain the current historical service life of the transmission mechanism by performing the weighted calculation on the current initial historical service life sent from the current initial historical service life calculation module (320) by using said current historical service life weighted coefficient sent from the weighted coefficient calculation module (340) .

29. The system as claimed in claim 28, wherein said weighted coefficient calculation module (340) comprises:

the waveform component extraction sub-module (341), which is used to separate the components that are related to the transmission mechanism from the load waveform of the trans- mission mechanism's driver generated by said waveform recording module (330) to generate the load waveform component of the transmission mechanism;

the fractal dimension calculation sub-module (342), which is used to perform the fractal dimension calculation on the load waveform component of the transmission mechanism generated by said waveform component extraction sub-module (341) to obtain the current waveform characteristics parameters that are related to the wearing of the transmission mechanism;

the weighted coefficient calculation sub-module (343) , which is used to generate the current historical service life weighted coefficient of the transmission mechanism according to the current waveform characteristics parameters obtained by said fractal dimension calculation sub-module (342).