CN102873638B - Workpiece radius online detection method in excircle cutting in grinding feeding process - Google Patents

Abstract

The invention relates to a workpiece radius online detection method in the excircle cutting in grinding feeding process. The workpiece radius online detection method is characterized in that a sound emission sensor is arranged at any position in a machine tool processing area, and a sound emission signal RMS value in the stable grinding state is measured to obtain a stable coefficient Ks value; a sound emission signal in the grinding feeding process is divided according to a certain time interval, and the variable quantity of the sound emission signal RMS value at different intervals and the stable coefficient Ks value are adopted to calculate a grinding system time constant; and the sound emission signal RMS value is remarkably improved to a mark from the initial signal state, the grinding time of the current feeding process is obtained in real time and is substituted into a workpiece radius change formula, the workpiece radius change quantity is calculated on line, and the workpiece radius size in the feeding process is obtained on line. The sound emission sensor is arranged at any position in the machine tool processing area so that the defect of a displacement sensor is effectively overcome. The workpiece radius online detection method can effectively simplify the production process flow of large-scale precise shaft parts and improves production efficiency.

Description

The workpiece radius online test method of cylindrical crush grinding feeding process

Technical field

The present invention relates to a kind of workpiece radius detection method, particularly relate to a kind of workpiece radius for cylindrical plunge-cutting change online test method.

Background technology

Grinding is precision machined critical process, and grinding quality often decides the Accuracy of finish of workpiece.Wherein cylindrical plunge-cutting is a kind of important Machining of Shaft-type Parts method, can obtain very high surface quality and geometric accuracy.And carrying out in cylindricalo grinding precision machining processes at present, the technical merit of the grinding quality of workpiece and efficiency depend primarily on machine operation person, in order to improve and improve Cylindrical Grinding Processes technological process, can carry out Real-Time Monitoring to process.Usual workpiece dimension information (i.e. workpiece radius) implements to have great meaning to grinding on-line monitoring, it can for evaluating working (machining) efficiency, improve processing technology important evidence be provided.At present, main online test method is arranged on by non-contact displacement transducer on the corresponding position of lathe, alignment pieces axis direction, the variable quantity of real-time measuring workpieces.But this method exists certain deficiency, first displacement transducer is arranged on cylindrical grinder, must very as far as possible near workpiece, so harsher to the designing requirement of displacement transducer clamp structure; Secondly, the necessary accurately alignment pieces axis direction of displacement transducer gauge head, just can accurately measure the variable quantity in workpiece radius.And these limiting factors make the method reduce working (machining) efficiency in actual production process, add processing cost.In order to overcome the shortcoming of above-mentioned detection method, the present invention proposes a kind of workpiece radius detection method utilizing acoustic emission signal to realize cylindrical plunge-cutting.

Summary of the invention

The present invention is in order to overcome the dependence to displacement transducer in existing cylindricalo grinding, a kind of workpiece radius online test method of cylindrical crush grinding feeding process is provided, the method adopts calibrate AE sensor workpiece radius to be carried out to the method detected in real time, by measuring the acoustic emission signal of grinding process in real time, obtain workpiece size information.

The technical solution used in the present invention is: a kind of workpiece radius online test method of cylindrical crush grinding feeding process, and step comprises:

1. stable state acoustic emission signal RMS pH-value determination pH

First processing is once tried, when entering stable grinding state after emery wheel contact workpiece a period of time, during Measurement sensibility grinding state, sound emission rms signal, averages to all sampled points, this value as stable state sound emission rms signal, thus obtains coefficient of stability K _svalue;

2. grinding system time constant calculates

1. carry out second time and try processing, when sound emission rms signal is continued to improve by original state, represent that emery wheel touches workpiece, it is grinding time started T that record improves the starting point moment _start;

2. T at set intervals _intervalthe variable gradient of sound emission rms signal in this time period of real-time measurement in conjunction with coefficient of stability K _svalue, utilizes obtain the calculated value τ of this section of time τ _i, i is the number of times calculated;

3. by τ _ithe grinding time T of start time is calculated with this _interval× i compares second, they is subtracted each other and takes absolute value, and then absolute difference and threshold value given in advance is compared, and when absolute difference is greater than given threshold value, repeat to enter the and 2. walk, when absolute difference is less than or equal to given threshold value, then this calculates the τ asked _ivalue is final grinding system time constant value τ;

3. workpiece radius variable quantity calculates in real time

Enter formal grinding, continue to rise to processing opening flag from initialize signal state with sound emission rms signal, obtain current grinding time t and be updated to workpiece radius change formula, online calculate workpiece radius variation delta r, again by workpiece original radius values, obtain the radius value of current workpiece in real time.

Before aforementioned stable state acoustic emission signal RMS pH-value determination pH starts, the sound emission primary signal that grinding detects is converted to root mean square rms signal AE _rMS, its expression formula is:

${\mathrm{AE}}_{\mathrm{RMS}}\left(t\right)=\sqrt{\frac{1}{\mathrm{\ΔT}}{\∫}_0^{\mathrm{\ΔT}}{V}^2\left(t\right)\mathrm{dt}}---\left(1\right)$ (in formula AE italic)

V in above formula---sound emission primary signal;

Δ T---the time window cycle.

The concrete calculation procedure of above-mentioned grinding system timeconstantτ is as follows:

1., in cylindrical plunge-cutting, normal grinding force can be expressed as:

$F_n=k_{c}a=\frac{k_c\stackrel{\·}{r}}{n_w}---\left(2\right)$

The feeding length that a in above formula---workpiece often turns;

K _c---grinding force coefficient;

---the reduction of workpiece radius;

N _w---workpiece rotational frequency;

Plunge-cutting has Systematical control formula to foreign round:

$\stackrel{\·\·}{r}+\frac{\stackrel{\·}{r}}{\mathrm{\τ}}=\frac{\stackrel{\·}{u}}{\mathrm{\τ}}---\left(3\right)$

In above formula ---emery wheel NC instruction feed speed;

τ---grinding system time constant.

2. sound emission rms signal becomes approximate ratio relation with normal grinding force:

AE _RMS=k _aeF _n (4)

AE in above formula _rMS---sound emission rms signal;

K _ae---the proportionality coefficient of sound emission rms signal and grinding force.

3. the grinding and feeding stage, formula (3) is solved, the expression formula of workpiece radius relative time change can be obtained:

$r\left(t\right)=\stackrel{\·}{u}(t-\mathrm{\τ}+\mathrm{\τ}{e}^{-t/\mathrm{\τ}})---\left(5\right)$

Formula (5) is substituted into formula (2), normal grinding force can be obtained relative to emery wheel NC instruction feed speed , corner of workpiece speed omega _w, grinding force coefficient k _cwith the expression formula of grinding system timeconstantτ:

$F_n=\frac{k_c\stackrel{\·}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(6\right)$

Formula (6) is substituted into the expression formula that formula (4) obtains sound emission rms signal:

${\mathrm{AE}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(7\right)$

4. formula (7) is converted:

${\mathrm{AE}}_{\mathrm{RMS}}=V_{\mathrm{AE}}^{\′}\≈\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{n_w}\≡K_s(t>>\mathrm{\τ})---\left(8\right)$

$A{\stackrel{\·}{E}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{n_w\mathrm{\τ}}{e}^{-1}=\frac{K_s}{\mathrm{\τ}}{e}^{-1}\⇒\mathrm{\τ}=\frac{K_s}{A{\stackrel{\·}{E}}_{\mathrm{RMS}}}{e}^{-1},(t=\mathrm{\τ})---\left(9\right)$

From formula (8), when the grinding time, t was much larger than timeconstantτ, acoustic emission signal RMS enters stable state, at this moment AE _rMSequal coefficient of stability K _s, so K _ssize be the sound emission rms signal after stable state;

5., when the grinding time, t just in time equaled grinding system timeconstantτ, formula (9) is utilized to calculate the size of timeconstantτ; Concrete grammar is, T at set intervals after the feeding stage starts _interval, first measure and calculate sound emission rms signal variable gradient in this time period in conjunction with coefficient of stability K _svalue, recycling formula (9) carries out the calculating of a grinding system time constant, obtains this calculated value τ _i, and compare calculated τ _iwhether equal with current grinding time t, namely whether be less than by their absolute difference the threshold value T preset _thresholdjudge, when absolute difference is less than threshold value, then the τ of this time period calculating _ivalue is final grinding system time constant size τ, otherwise T _intervalafter time, enter next computing cycle repetition said process and calculate next grinding system time constant calculated value τ _i+1.Threshold value T _thresholdthe setting of size is not less than the required precision of grinding system time constant.

The invention has the beneficial effects as follows:

The present invention adopts acoustic emission signal to carry out the real-time measurement of workpiece radius, namely adopts calibrate AE sensor as testing tool, instead of traditional displacement transducer.Because calibrate AE sensor can be arranged on any position in machine tooling region, effectively avoid many defects of displacement transducer.The present invention effectively can simplify the technological process of production of the accurate axial workpiece of scale, enhances productivity.

Accompanying drawing explanation

Fig. 1 is the basic step schematic flow sheet of the embodiment of the present invention;

Fig. 2 is the grinding system time constant calculation process schematic diagram of the embodiment of the present invention.

Detailed description of the invention

Below in conjunction with accompanying drawing and embodiment, the present invention is further elaborated.

As shown in Figure 1, the workpiece radius online test method of cylindrical crush grinding feeding process of the present invention, step comprises:

1. stable state acoustic emission signal RMS pH-value determination pH

1., before grinding starts, the sound emission primary signal that grinding detects is converted to root mean square (Root Mean Square is called for short RMS) signal AE _rMS, its expression formula is:

${\mathrm{AE}}_{\mathrm{RMS}}\left(t\right)=\sqrt{\frac{1}{\mathrm{\ΔT}}{\∫}_0^{\mathrm{\ΔT}}{V}^2\left(t\right)\mathrm{dt}}---\left(1\right)$

V in above formula---sound emission primary signal;

Δ T---the time window cycle

2. processing is once tried, when entering stable grinding state, sound emission rms signal during Measurement sensibility grinding state after emery wheel contact workpiece a period of time, average to all sampled points after stable, this value as stable state sound emission rms signal, thus obtains coefficient of stability K _svalue;

2. grinding system time constant calculates

The key step that grinding system time constant calculates as shown in Figure 2 is:

1. carry out second time and try processing, continued to rise to mark with sound emission rms signal by original state, the starting point moment that mark improves is grinding time started T _start;

2. every a bit of time T _intervalthe variable gradient of sound emission rms signal in this time period of real-time measurement again in conjunction with coefficient of stability K _svalue, utilizes formula (9) to calculate the grinding system time constant calculated value τ of this period _i, i is this calculation times;

3. the grinding system time constant calculated value τ calculated in real time _ithe grinding time t=T of start time is calculated with this _interval× i compares second, they is subtracted each other and takes absolute value, then by absolute difference and the threshold value T preset _thresholdcompare, when absolute difference is greater than given threshold value, repeat to enter the and 2. walk, when absolute difference is less than or equal to given threshold value, then this calculates gained τ _ivalue is final grinding system timeconstantτ value;

Wherein, the Computing Principle of grinding system timeconstantτ and step as follows:

1., in cylindrical plunge-cutting, normal grinding force can be expressed as:

$F_n=k_{c}a=\frac{k_c\stackrel{\·}{r}}{n_w}---\left(2\right)$

The feeding length that a in above formula---workpiece often turns;

K _c---grinding force coefficient;

---the reduction of workpiece radius;

N _w---workpiece rotational frequency.

Plunge-cutting has Systematical control formula to foreign round:

$\stackrel{\·\·}{r}+\frac{\stackrel{\·}{r}}{\mathrm{\τ}}=\frac{\stackrel{\·}{u}}{\mathrm{\τ}}---\left(3\right)$

In above formula ---emery wheel NC instruction feed speed;

τ---grinding system time constant.

2. according to long term test research, grinding process sound emission rms signal is very close with grinding force change curve, so sound emission rms signal becomes approximate ratio relation with normal grinding force:

AE _RMS=k _aeF _n (4)

AE in above formula _rMS---sound emission rms signal;

K _ae---the proportionality coefficient of sound emission rms signal and grinding force.

3. the grinding and feeding stage, formula (3) is solved, the expression formula of workpiece radius relative time change can be obtained:

$r\left(t\right)=\stackrel{\·}{u}(t-\mathrm{\τ}+\mathrm{\τ}{e}^{-t/\mathrm{\τ}})---\left(5\right)$

Formula (5) is substituted into formula (2), normal grinding force can be obtained relative to emery wheel NC instruction feed speed corner of workpiece speed omega _w, grinding force coefficient k _cwith the expression formula of grinding system timeconstantτ:

$F_n=\frac{k_c\stackrel{\·}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(6\right)$

Formula (6) is substituted into the expression formula that formula (4) obtains sound emission rms signal:

${\mathrm{AE}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(7\right)$

4. formula (7) is converted:

${\mathrm{AE}}_{\mathrm{RMS}}=V_{\mathrm{AE}}^{\′}\≈\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{n_w}\≡K_s(t>>\mathrm{\τ})---\left(8\right)$

$A{\stackrel{\·}{E}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{\·}{u}}{n_w\mathrm{\τ}}{e}^{-1}=\frac{K_s}{\mathrm{\τ}}{e}^{-1}\⇒\mathrm{\τ}=\frac{K_s}{A{\stackrel{\·}{E}}_{\mathrm{RMS}}}{e}^{-1},(t=\mathrm{\τ})---\left(9\right)$

From formula (8), when the grinding time, t was much larger than timeconstantτ, acoustic emission signal RMS enters stable state, at this moment AE _rMSequal coefficient of stability K _s, so K _ssize be the sound emission rms signal after stable state;

5., when the grinding time, t just in time equaled grinding system timeconstantτ, formula (9) is utilized to calculate the size of timeconstantτ.Concrete grammar is, T at set intervals after the feeding stage starts _interval, first measure and calculate sound emission rms signal variable gradient in this time period in conjunction with coefficient of stability K _svalue, recycling formula (9) carries out the calculating of a grinding system time constant, obtains this calculated value τ _i, and compare calculated τ _iwhether equal with current grinding time t, namely whether be less than by their absolute difference the threshold value T preset _thresholdjudge, when absolute difference is less than threshold value, then the τ of this time period calculating _ivalue is final grinding system time constant size τ, otherwise T _intervalafter time, enter next computing cycle repetition said process and calculate next grinding system time constant calculated value τ _i+1.Threshold value T _thresholdthe setting of size is not less than the required precision of grinding system time constant.

3, workpiece radius variable quantity calculates in real time

Enter formal grinding, continue to rise to mark with acoustic emission signal RMS, it is grinding time started T that record improves start time _start, to any time in grinding and feeding stage, current grinding time t is by current time t _presentdeduct grinding time started T _startobtain, i.e. t=t _present-T _start, grinding time t is updated to formula (5), calculates workpiece radius variation delta r in real time online, then current radius size can be obtained by workpiece initial radium.

Be below one embodiment of the present of invention:

(1) stable state sound emission rms signal is measured, and before processing starts, first the primary signal of calibrate AE sensor is converted to rms signal;

(2) first time tries processing, and when entering stable grinding state after emery wheel contact workpiece a period of time, the acoustic emission signal RMS value after measuring in a period of time is 1.13V, record K _sbe 1.13.

(3) grinding system time constant calculates.

1. continued to rise to mark by original state with sound emission rms signal, it is grinding time started T that mark improves start time _start;

2. every 0.1 second after from grinding, measure in real time and calculate the variable gradient of sound emission rms signal in this 0.1 second again in conjunction with coefficient of stability K _s=1.13, utilize formula (9) to calculate the grinding system time constant calculated value τ of this period _i, i is this calculation times;

3. this is calculated and obtain grinding system time constant calculated value τ _iperforms the grinding time 0.1 × i of start time compare second with calculating, when its absolute difference is greater than given threshold value 0.05 second, then calculation times i is increased by 1, return the and 2. walk and repeat.

In repetition step 2., 3., when entering into 2.8 seconds grinding time, when to calculate grinding system time constant value be 2.78 seconds, its difference is less than given threshold value 0.05 second for 0.02 second to embodiment, then determine that grinding system constant is 2.78 seconds.

4. emery wheel NC instruction feed speed 5 μm/s and grinding system time constant 2.78s is brought in formula (5), obtains the feeding stage workpiece radius change expression formula relative to the grinding time: r (t)=5 (t-2.78+2.78e ^-t/2.78).

(4), after obtaining above-mentioned workpiece radius change expression formula, can start formal processing, time emery wheel feeding touches workpiece, sound emission rms signal continues to increase, and this change initial time is designated as grinding start time T _start; Grinding time t deducts the acquisition of grinding start time by current time, i.e. t=T _present-T _start, grinding time t is brought into r (t)=5 (t-2.78+2.78e ^-t/2.78) in, calculate the workpiece radius variable quantity of current time in real time, finally calculate current radius size by workpiece initial radium.

Claims (3)

1. a workpiece radius online test method for cylindrical crush grinding feeding process, it is characterized in that, step comprises:

(1) stable state acoustic emission signal RMS pH-value determination pH

First processing is once tried, when entering stable grinding state after emery wheel contact workpiece a period of time, during Measurement sensibility grinding state, sound emission rms signal, averages to all sampled points, this value as stable state sound emission rms signal, thus obtains coefficient of stability K _svalue;

(2) grinding system time constant calculates

1. carry out second time and try processing, when sound emission rms signal is continued to improve by original state, represent that emery wheel touches workpiece, it is grinding time started T that record improves the starting point moment _start;

2. T at set intervals _intervalthe variable gradient of sound emission rms signal in this time period of real-time measurement , in conjunction with coefficient of stability K _svalue, utilizes obtain the calculated value τ of this section of time τ _i, i is the number of times calculated;

3. by τ _ithe grinding time T of start time is calculated with this _interval× i compares second, they is subtracted each other and takes absolute value, and then absolute difference and threshold value given in advance is compared, and when absolute difference is greater than given threshold value, repeat to enter the and 2. walk, when absolute difference is less than or equal to given threshold value, then this calculates the τ asked _ivalue is final grinding system time constant value τ;

(3) workpiece radius variable quantity calculates in real time

Enter formal grinding, continue to rise to processing opening flag from initialize signal state with sound emission rms signal, obtain current grinding time t and be updated to workpiece radius change formula: online calculate workpiece radius variation delta r, then by workpiece original radius values, obtain the radius value of current workpiece in real time.

2. the workpiece radius online test method of cylindrical crush grinding feeding process according to claim 1, it is characterized in that: before aforementioned stable state acoustic emission signal RMS pH-value determination pH starts, the sound emission primary signal that grinding detects is converted to root mean square rms signal AE _rMS, its expression formula is:

${\mathrm{AE}}_{\mathrm{RMS}}\left(t\right)=\sqrt{\frac{1}{\mathrm{\ΔT}}{\∫}_0^{\mathrm{\ΔT}}{V}^2\left(t\right)\mathrm{dt}}---\left(1\right)$

V in above formula---sound emission primary signal;

Δ T---the time window cycle.

3. the workpiece radius online test method of cylindrical crush grinding feeding process according to claim 1, is characterized in that: the concrete calculation procedure of grinding system timeconstantτ is as follows:

1., in cylindrical plunge-cutting, normal grinding force can be expressed as:

$F_n=k_{c}a=\frac{k_c\stackrel{.}{r}}{n_w}---\left(2\right)$

The feeding length that a in above formula---workpiece often turns;

K _c---grinding force coefficient;

---the reduction of workpiece radius;

N _w---workpiece rotational frequency;

Plunge-cutting has Systematical control formula to foreign round:

$\stackrel{..}{r}+\frac{\stackrel{.}{r}}{\mathrm{\τ}}=\frac{\stackrel{.}{u}}{\mathrm{\τ}}---\left(3\right)$

In above formula ---emery wheel NC instruction feed speed;

τ---grinding system time constant;

2. sound emission rms signal becomes approximate ratio relation with normal grinding force:

AE _RMS＝k _aeF _n (4)

AE in above formula _rMS---sound emission rms signal;

K _ae---the proportionality coefficient of sound emission rms signal and grinding force;

3. the grinding and feeding stage, formula (3) is solved, the expression formula of workpiece radius relative time change can be obtained:

$r\left(t\right)=\stackrel{.}{u}(t-\mathrm{\τ}+\mathrm{\τ}{e}^{-t/\mathrm{\τ}})---\left(5\right)$

Formula (5) is substituted into formula (2), normal grinding force can be obtained relative to emery wheel NC instruction feed speed , corner of workpiece speed omega _w, grinding force coefficient k _cwith the expression formula of grinding system timeconstantτ:

$F_n=\frac{k_c\stackrel{.}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(6\right)$

Formula (6) is substituted into the expression formula that formula (4) obtains sound emission rms signal:

${\mathrm{AE}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{.}{u}}{{\mathrm{\ω}}_w}(1-e^{-t/\mathrm{\τ}})---\left(7\right)$

4. formula (7) is converted:

${\mathrm{AE}}_{\mathrm{RMS}}=V_{\mathrm{AE}}^{\′}\≈\frac{k_{\mathrm{ae}}{k}_c\stackrel{.}{u}}{n_w}\≡K_s(t>>\mathrm{\τ})---\left(8\right)$

$A{\stackrel{.}{E}}_{\mathrm{RMS}}=\frac{k_{\mathrm{ae}}{k}_c\stackrel{.}{u}}{n_w\mathrm{\τ}}{e}^{-1}=\frac{K_s}{\mathrm{\τ}}{e}^{-1}\⇒\mathrm{\τ}=\frac{K_s}{A{\stackrel{.}{E}}_{\mathrm{RMS}}}{e}^{-1}(t=\mathrm{\τ})---\left(9\right)$

From formula (8), when the grinding time, t was much larger than timeconstantτ, acoustic emission signal RMS enters stable state, at this moment AE _rMSequal coefficient of stability K _s, so K _ssize be the sound emission rms signal after stable state;

5., when the grinding time, t just in time equaled grinding system timeconstantτ, formula (9) is utilized to calculate the size of timeconstantτ; Concrete grammar is, T at set intervals after the feeding stage starts _interval, first measure and calculate sound emission rms signal variable gradient in this time period , in conjunction with coefficient of stability K _svalue, recycling formula (9) carries out the calculating of a grinding system time constant, obtains this calculated value τ _i, and compare calculated τ _iwhether equal with current grinding time t, namely whether be less than by their absolute difference the threshold value T preset _thresholdjudge, when absolute difference is less than threshold value, then the τ of this time period calculating _ivalue is final grinding system time constant size τ, otherwise T _intervalafter time, enter next computing cycle repetition said process and calculate next grinding system time constant calculated value τ _i+1; Threshold value T _thresholdthe setting of size is not less than the required precision of grinding system time constant.