GB2577264A

GB2577264A - Dot marking machine

Info

Publication number: GB2577264A
Application number: GB1815193.6A
Authority: GB
Inventors: James Ray David
Original assignee: Edward Pryor and Son Ltd
Current assignee: Edward Pryor and Son Ltd
Priority date: 2018-09-18
Filing date: 2018-09-18
Publication date: 2020-03-25
Also published as: GB201815193D0; WO2020058670A1

Abstract

A battery-powered dot marking machine comprises a battery (110, fig 3), a voltage sensor (116, fig 3) for sensing a voltage of the battery, a stylus 114 having a tip, a solenoid (111, fig 3) arranged to drive the tip of the stylus towards a target and a control means (118, fig 3) arranged to receive an input indicative of the sensed voltage from the voltage sensor, wherein the control means is arranged to control the solenoid in dependence on the sensed voltage. The control means is preferably configured to cause a current from the battery to be applied to the solenoid for a predetermined length of time, wherein the predetermined length of time is determined by the control means in dependence on the sensed battery voltage. A method of controlling a battery-powered dot making machine is also disclosed. The method comprises controlling the acceleration time of the stylus in dependence on the sensed voltage.

Description

Dot Marking Machine This invention relates to the general technical field of dot marking for engineering components.

Aspects of the invention relate to a battery-powered dot marking machine, to a method of controlling a battery-powered dot marking machine, and to a controller. It will be understood that dot marking machines may alternatively be referred to as dot-peen machines or impression marking machines.

BACKGROUND

Traditionally, identifiable marks were added to expensive parts by hand tools, such as a hammer and stamp. In more recent times, it has become common to use dot marking machines to mark parts. These machines generally consist of a hard, sharp object being propelled towards the target with minimal user effort, producing enough pressure to plastically deform the target, leaving a permanent impression (a dot). A plurality of these dots is then produced such that they form recognizable symbols, such as letters, trademarks, machine-readable signatures such as Data Matrix identification codes, Barcodes or QR Codes (RTM).

One such machine uses a solenoid to generate a magnetic field which accelerates a stylus towards the target. Such machines are generally large, and mains powered. Battery powered handheld versions do exist, although they have flaws. The first flaw of battery powered marking machines is that as the voltage of the battery decays whilst it is being used, the magnetic field strength produced by the solenoid also decreases. This means that over the course of a working day a user must either constantly keep the machine charged, or risk having dots of different depths and diameters, degrading the quality of his signs. This is a problem for several reasons.

Firstly, it is generally high value manufactured parts that are marked in this way such that a manufacturer can trace faults to batches or check warranties or servicing requirements. Therefore, it is important for the amount of stress applied to such parts to be kept to a minimum and as such a consistent depth and diameter of dot, without the need to repeat dots would be valuable.

Another reason is that if the dot sizes are not consistent then the machine-readable codes may fail, halting the manufacturing process or preventing a part from being identified when it is serviced. Whilst manufacturing high value goods, such as airplane components, it is crucial that every safety critical part added is traceable and that the airline knows when a service of those parts is required. If the machine code cannot be read it is possible that the part will be rejected, even if it is otherwise perfectly serviceable.

Many of the machine-readable marks that may be made on parts are designed with some redundancy, such that the mark will still be readable if a certain proportion (for example 30%) of the original mark is destroyed. However, this assumes that the original mark was reproduced perfectly. Accordingly, it may be difficult to detect a substandard mark at the time that it is made, as it will still appear readable if the amount of the mark that is illegible is less than the amount of redundancy designed into the mark. However, such a mark would be more likely to become illegible as a result of wear in normal use, as compared to a mark that was perfectly reproduced and therefore had all of the intended redundancy present at the time that the part entered service. It is therefore important to ensure that the marks produced by dot marking machines reproduce the intended mark as closely as possible.

A further reason why consistency is important is that companies using such a service will require that the end result is aesthetically pleasing, particularly if the mark is a visible trademark. Inconsistent dot sizes as well as repeated dots may result in a substandard mark that may be less aesthetically pleasing.

At least in certain embodiments, the present invention seeks to address or mitigate the

problems associated with the prior art.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with an aspect of the present invention there is provided a battery-powered dot marking machine comprising: a battery; a voltage sensor for sensing a voltage of the battery; a stylus having a tip; a solenoid arranged to drive the tip of the stylus towards a target; and a control means arranged to receive an input indicative of the sensed voltage from the voltage sensor, wherein the control means is arranged to control the solenoid in dependence on the sensed voltage. A benefit of this device is that the control means can adjust certain variables in dependence on the sensed voltage such that declines in said voltage are controlled for, leading to a consistent dot size.

In an embodiment of the present invention the controller is configured to cause a current from the battery to be applied to the solenoid for a predetermined length of time, wherein the predetermined length of time is determined by the controller in dependence on the sensed battery voltage. An advantage of this embodiment is that although the voltage available cannot be controlled, the kinetic energy of the stylus can still be controlled by factoring the acceleration force produced by the solenoid in dependence on the voltage and controlling the total acceleration time.

In a further embodiment the dot marking machine further includes a user input means, and the predetermined length of time is determined in dependence on an intensity setting provided via the user input means. Including user input means allows a user to control the energy delivered each time the stylus impacts on the workpiece, thereby controlling dot size for a given material.

As will be well understood by the skilled person, softer metals such as gold will require a lower setting for the same size of dot as compared to harder metals such as steel.

In a further embodiment the user input means allows the user to select one from a discrete number of acceleration times. Users may wish to increase or decrease the acceleration time, having discrete acceleration times means that the user can select from pre-determined values, hence reducing variance between dot marks on the same mark or between marks for different parts. A suitable number of acceleration times may be provided such that the device is operable to produce small increments between a shallow, faint mark and a deep mark. A suitable number of increments may be in the range of 5-20, preferably about 7-14.

In a further embodiment the controller comprises an electronic memory having a lookup table stored thereon, the lookup table comprising a plurality of values for the predetermined length of time, each value for the predetermined length of time corresponding to a given combination of intensity setting and sensed battery voltage. Having the values predetermined may reduce the computational requirements of the controller by removing the requirement to perform a calculation to determine the required acceleration time for a given voltage. This will also improve consistency between dots and marks overall.

In a further embodiment the controller is programmable to adjust the predetermined length of time corresponding to each of the intensity settings at a baseline value of the sensed battery voltage.

In a further embodiment the controller is configured to perform an interpolation between values in the lookup table to determine the predetermined length of time corresponding to an intensity setting if the predetermined length of time corresponding to the intensity setting has been adjusted and the sensed voltage is different from the baseline value. An advantage of this embodiment is that if there are, for example, 10 force settings available to the user, when working on a relatively hard material the first 5 force settings may be incapable of generating a dot of appropriate size. By adjusting the force settings in dependence on a baseline the user will be able to select any force setting since the force settings will have been adjusted such that the minimum force setting still produces a dot.

In a further embodiment the machine comprises a biasing means arranged to bias the stylus towards a neutral position. An advantage of this embodiment is that the machine is automatically readied after a dot has been made, without the user being required to actively do anything.

In a further embodiment, the biasing means comprises one or more springs. An advantage of using springs is that they are lighter and cheaper than other potential alternatives, as well as being easy to replace.

In an embodiment, the machine is arranged wherein: if the sensed voltage is greater than a baseline voltage, the predetermined length of time is selected based on a first linear relationship between the sensed voltage and the predetermined length of time; and if the sense voltage is less than the baseline voltage, the predetermined length of time is selected based on a second linear relationship between the sensed voltage and the predetermined length of time. Optionally, if the sensed voltage is equal to the baseline voltage, the predetermined length of time is selected to be equal to a baseline length of time.

Advantageously, such linear relationships may be selected to substantially match empirically-determined values of acceleration time to give consistent-sized marks across the entire voltage range for a given force setting. Furthermore, such relationships are computationally inexpensive, and interpolation or extrapolation may be performed to obtain the required constants for the linear relationships to use for user-defined force settings.

A further aspect comprises a method of controlling a battery-powered dot marking machine, said dot marking machine comprising: a battery and a voltage sensor for sensing the voltage of the battery; a stylus with a tip; and an electric solenoid for driving the tip of the stylus towards a target, the method comprising: controlling the acceleration time of the stylus in dependence on the sensed voltage.

An advantage of this aspect is that the resulting dots will be of a consistent size and shape due to the controller determining the acceleration time in dependence on a number of factors, including the voltage of the battery.

A further embodiment includes a controller for performing the above method.

BRIEF INTRODUCTION OF THE DRAWINGS

An embodiment of the invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of dot marking machine (Prior Art); Figure 2 is an image of a piece of metal that has been marked by a prior art battery powered dot marking machine, with the battery at various voltages and with 9 different user settings applied; Figure 3 is a block diagram of the components of an embodiment of the present invention Figure 4 is a block diagram of the components of an embodiment of the present invention Figure 5a is a lookup table of data for determining appropriate force application times for various detected voltages; Figure 5b is an alternate lookup table of data for determining appropriate force application times for various detected voltages; Figure 6a is a graph of the data from the lookup table shown in figure 5a; Figure 6b is a graph of the data from the lookup table shown in figure 5b; Figure 7 is an image of a piece of metal that has been marked by dot marking machine in an embodiment of the present invention, with the battery at various voltages and with 9 different user settings applied; Figure 8 a graph of how dot diameter varies with force applied for various stylus gaps; Figure 9 is a flow chart showing a method of controlling a dot marking machine in an embodiment of the present invention.

DETAILED DESCRIPTION

Figure 1, is an example of a prior art handheld, battery-powered, dot marking machine 10. The dot marking machine 10 comprises a housing 13 having a handle 28 attached thereto. A frame 27 defining a foot 26 is also connected to the housing. A bottom surface of the foot is provided with a high-friction coating 29, which is a layer of rubber in the illustrated embodiment. The frame 27 is attached to the housing 13 via an adjustable mechanism, which allows the distance between the foot 26 and the rest of the housing to be adjusted. In the illustrated embodiment, the adjustable mechanism comprises a frame 27 having slots (not shown), which frame can slide within the slots to move relative to the housing 13, and which may be fixed to the housing by tightening a plurality of bolts (not shown). Graduation marks are provided adjacent to the slots to aid a user in adjusting the distance between the foot 26 and the housing 13.

The housing 13 contains a solenoid assembly 11 having a stylus 14 extending from a solenoid housing 11. The solenoid housing 11 encloses a solenoid and a biasing means comprising a spring arranged to bias the stylus 14 towards a neutral position. The solenoid can be selectively energized by a controller (not shown) connected to a battery (not shown).

The solenoid assembly 11 is mounted on an X-Y actuation mechanism 24. The controller is operable to communicate with the X-Y actuation mechanism to adjust the position of the solenoid assembly 11. A user input means (not shown) is provided to allow the user to program the machine to produce a desired mark made up of a plurality of dots at different X-Y positions. The user input means may also allow the user to select one of a plurality of power settings, thereby allowing the depth of the dots produced by the machine when used on a workpiece of given hardness to be varied.

In use, the foot 26 is placed on to the workpiece such that the stylus 14 is a predetermined distance away from the surface to be marked, the predetermined distance being determined by the adjustable mechanism attaching the foot 26 to the housing 30. With the foot 26 in place on the workpiece, the user initiates marking via a further user interface means, which may be a button (not shown). Upon receipt of a user input indicating that it is desired to commence marking, the controller is configured to actuate the X-Y actuation mechanism 24 to move the solenoid assembly 11 to a position corresponding to the first dot to be made in the programmed mark. The solenoid is then activated by connecting the coil of the solenoid to the battery for a predetermined amount of time, which amount of time is determined based upon the currently-selected power setting. The connection of the coil to the battery may pass through the controller, which controller may be operable to selectively close the connection between the solenoid and the battery for a predetermined length of time. Activation of the solenoid causes a metallic slug that is located within the coil and that is attached to the stylus 14 to be accelerated towards the target. The stylus impacts on the target, causing an indent, and is then returned to its original position by the biasing means. The X-Y actuation mechanism 24 then moves the stylus to the next user defined position and the process is repeated. The handle 28 may be employed by a user to make coarse X-Y position changes by simply moving the whole machine, although it is of course necessary for the user not to move the machine during the production of a particular mark.

Whilst the device is being used the energy available in the battery will decrease. The decreasing battery power will result in lower voltage and therefore the magnetic field strength produced by the solenoid will be lower. The present inventors have recognized that this can lead to a degradation in the quality of marks produced by a battery-powered dot marking machine.

Figure 2 shows a metal workpiece that has been marked by a battery-powered dot marking machine. The numbers descending vertically show the sensed battery voltage in volts. The increasing horizontal numbers show the user defined force setting (with arbitrary values, which may correspond to the numbers on a force setting dial of the dot marking machine 100). The sensed voltage decreases as the dot marking machine is used and as a consequence the diameter of the dots created by the machine decreases. As shown in figure 2, the degradation of mark quality is particularly significant for lower power settings, as the machine does not mark the workpiece at all when a low power setting is selected and the voltage is low. However, it will be observed that a noticeable change in dot size between the minimum and maximum battery voltage occurs at all of the power settings shown in figure 2.

It is known to use a DC-DC converter to maintain a voltage output at a desired level, irrespective of changes in the input voltage provided by the battery to the DC-DC converter.

However, including a DC-DC converter will inevitably add weight and cost to the dot marking machine, which is undesirable for handheld devices.

Figure 3a is a block diagram, showing the connections between various components of a battery-powered dot marking machine 101 according to an embodiment of the present invention.

The dot marking machine 101 comprises a controller 118 arranged to receive electrical power from a battery 110. The controller 118 comprises input means 118i arranged to receive signals from a user interface means 120 and from a voltage sensor 116. The controller also comprises output means 118o arranged to send control signals to an X-Y actuation mechanism 124 and to selectively power a coil of a solenoid assembly 111. In this way, the connection between the battery 110 and the solenoid assembly 111 is controlled by a controller 118. The controller 118 is configured to control the X-Y actuation mechanism 124 to control the position of the solenoid assembly 111.

As shown in figure 3b, many of the components of the dot marking machine 101 are provided inside a housing 113, which may be similar to the housing 13 shown in figure 1. The housing 113 is connected to a foot 126 and a frame 127 via an adjustable mechanism, in the same manner as the foot, frame and adjustable mechanism described in relation to figure 1. The adjustable mechanism connecting the foot 126 to the housing 113 allows the machine to be accurately positioned relative to a workpiece, thereby to allow the distance between the tip of the stylus 114 and the workpiece to be adjusted.

In use, the machine 101 is positioned with the foot 126 against a workpiece, and the user provides an instruction to commence marking of the workpiece via user interface means 120. The controller 118 then controls the X-Y actuation mechanism to move the solenoid assembly 111 to a position corresponding to the first dot in the required mark. The controller then connects the coil of the solenoid assembly 111 to the battery for an amount of time that is determined in dependence on data received from the voltage sensor 16 and the user settings inputted via the user interface 120. The calculation of the appropriate acceleration time will be discussed in more detail below.

Figure 4 is a schematic diagram showing some of the components of the dot marking machine 101. The solenoid assembly 111 comprises a stylus having a tip 114, a slug 115, having solenoid coil 112 wound therearound, and a biasing means in the form of a spring 122, which is an extension spring in the illustrated embodiment. It will be understood that an appropriately-positioned extension spring could be used in alternative embodiments. The slug 115 is rigidly connected to the stylus 114, and the slug is free to move axially within the coil 112.

As discussed above, the connection between the battery 110 and the solenoid coil 112 is controlled by the controller 118. When the solenoid coil is energized this generates a magnetic field which accelerates the stylus towards the target. The biasing means 122, which is a spring 122 in the illustrated embodiment, opposes the forces applied by the solenoid coil 112, although this does not prevent the tip of the stylus from impacting on the target. When the solenoid 112 is not energized, the spring 122 biases the stylus 114 and slug 113 back into a neutral position in which a rear face of the stylus bears against a stop surface of the solenoid assembly (not shown).

The controller 118 is configured to receive information about the voltage of the battery and a currently-selected power setting provided via the user interface means 120, and to determine the acceleration time for which the coil of the solenoid assembly 111 is energized in dependence on the sensed voltage and the power setting.

The controller 118 is provided with a lookup table relating the detected voltage and force setting to the acceleration time. Figure 5a is a lookup table which gives an example of how the acceleration time could vary with force settings and detected voltage. The acceleration time increases with force setting as per usual, but the lookup table allows for different relationships between acceleration time and force setting a specific voltage is detected. For example, when a battery voltage of 37 V is detected and force setting 1 is requested by the user, an acceleration time of 2 milliseconds is used to get a dot size similar to that observed when a battery voltage of 42 V is detected and an acceleration time of 1.76 milliseconds is used. This table is for exemplary purposes and it will be understood that in some embodiments a different number of force settings, acceleration times or range of detected voltages may be used, and it will be understood that various factors will affect the required acceleration times at different combinations of detected voltage and force setting.

Although the values in the lookup table shown in figure 5a could be obtained analytically, in this case they were obtained empirically through experimentation, with the given values being determined to ensure consistent dot size for a given force setting. The values shown in figure 5a have been shown to produce consistently-sized dots for a given force setting and material to be marked, across the full range of possible voltages.

Figure 6a shows data from the lookup table in figure 5a in a graphical form. The trend line for force setting 1 is the lowest, with data points denoted by a + sign, the trend line for force setting 2 is the second lowest, with data points denoted by circles, setting 3 the next highest with a dotted trend line, force setting 4 is the next highest with a dashed trend line and circular data points, force setting 5 is the next highest and is represented by a double trend line with triangular data points, force setting 6 is the next highest with data points represented by a an x, force setting 7 is the next highest with a singular trend line and triangular data points force setting 8 is the next highest with data points represented by a diamond shape, force setting 9 is the highest on the graph with data points represented by a square.

Due to factors such as air resistance and the presence of the biasing means, the relationship between the voltage and the acceleration times required to get the same dot size for a given force setting is not linear.

Figure 6b shows data from the lookup table in figure 5b in a graphical form. The trend line for force setting 1 is the lowest, with data points denoted by a + sign, the trend line for force setting 2 is the second lowest, with data points denoted by circles, setting 3 the next highest with a dotted trend line, force setting 4 is the next highest with a dashed trend line and circular data points, force setting 5 is the next highest and is represented by a double line with triangular data points, force setting 6 is the next highest with data points represented by an x, force setting 7 is the next highest with a singular trend line and triangular data points force setting 8 is the next highest with data points represented by a diamond shape, force setting 9 is the highest on the graph with data points represented by a square.

Due to factors such as air resistance and the presence of the biasing means, the relationship between the voltage and the acceleration times required to get approximately the same dot size for a given force setting is determined by solving a linear equation which varies depending on whether the measured battery voltage is above or below the baseline voltage of 34V.If the measured voltage is 34V the values are predetermined standard values.

If the measured voltage is below 34V the acceleration time adjustment for a given force setting is calculated by subtracting the measured voltage from 34 and then multiplying that value by a first correction factor. For example, if the measured voltage is 32V the adjustment value would be (34 -32) * C1 where C1 is a value of the first correction factor. The acceleration time is calculated by adding the calculated adjustment value to the standard acceleration time for use when the voltage is 34V. ;If the measured voltage is greater than 34V but below 42V the acceleration time adjustment for a given force setting is calculated by performing a standard linear interpolation between the empirically-determined timing for the given force setting at a baseline value of 34V and the empirically-determined timing for the same force setting at the maximum rated voltage of 42V. ;To perform the interpolation, the acceleration time for the force setting at 34V is reduced by a correction factor C2. C2 is calculated by multiplying the difference between the acceleration time at 34V and at 42V for the required force setting by the difference between 34V and the measured voltage, then dividing by the difference between 34V and 42V (i.e. 8V). For example, the acceleration time at 39V for force setting 4 is 2.4ms -((2.4ms -1.85ms) * (39V -34V)) / (42V -34V) = 2.05625ms. The values of 2.4ms at 34V and 1.85ms at 42V are empirically determined to give approximately the same size of mark. In this embodiment, 39V is the measured voltage, 34V is the baseline voltage and 42V is the maximum rated voltage.

However, it will be understood that the method would be the same for other baseline and maximum rated voltages.

This method of determining an appropriate acceleration time allows for extrapolation beyond force setting 9, even if empirical values for the baseline voltage are not available. In this case, the baseline acceleration times, and the acceleration times at the maximum rated voltage may be determined by extrapolation, as can be seen in the "Extrapolated" portion of the table in figure 5b. The baseline acceleration times, and the acceleration times for the maximum rated voltage may also be determined for user-defined force settings in which the baseline acceleration time is between the baseline acceleration times for two of the defined values. In this case interpolation between the defined acceleration time values may be performed. Given the baseline acceleration times and the acceleration times for the maximum rated voltage, the values for intermediate voltages can then be determined by the same interpolation process described above.

Figure 7 shows a piece of metal that has been marked by a battery-powered dot marking machine 101 in an embodiment of the present invention. As can be clearly seen, the dots in different force settings are consistent because the compensation algorithm is used to adjust the acceleration time in dependence on the force setting and the sensed voltage, using the lookup table shown in figure 5a.

Figure 8 is a graph of how the dot diameter produced by a battery-powered dot marking machine varies with force setting. The different series labelled "stylus gap" are various initial distances between the target and the tip of the stylus. The trend line for a 1mm stylus gap is the lowest at force 20 and is denoted by a solid line with data points marked as squares. The second lowest at force 20 is the 2mm stylus gap which is denoted by a solid line with data points marked as diamonds. The next highest at force 20 is the 3 mm stylus gap denoted by a solid line with triangular data points. The next highest at force 20 is stylus gap 4mm denoted by a solid line with an x marking each data point. The next highest at force 20 is stylus gap 5mm which is denoted by a solid trend line with an x with a vertical line through it denoting the data points. The next highest at force 20 is stylus gap 6 mm which is denoted by a solid line with circles marking the data points. The next highest at force 20 is stylus gap 7mm which is denoted by a double line with squares marking the data points. The next highest at force 20 is stylus gap 8mm which is denoted by a dotted line with diamonds marking the data points. The next highest at force 20 is stylus gap 9mm which is denoted by a dashed line with squares marking the data points. The next highest at force 20 is stylus gap 10mm, which is denoted by a dashed line with triangular data points. The next highest at force 20 is 11mm stylus gap which is denoted by a dotted line with data points marked by an x. The variations occur due to two factors. The first is that when the stylus is too close to the target, it does not accelerate over the full acceleration time. If the stylus will contact the target within 1 millisecond of the initial force being applies, and the acceleration time is 2 milliseconds, the stylus will have less energy to work the target upon impact. After impact the remaining acceleration force applied by the solenoid 112 will not cause a larger diameter since the energy needs to be delivered as a pulse rather than over time in order to cause permanent deformation. Therefore, for a given stylus gap the dot diameter increases with increasing force setting up to a maximum level, after which the dot diameter remains substantially constant.

The second factor that affects the relationship between dot diameter, force setting, and stylus gap is the spring that biases the stylus towards the neutral position and away from the workpiece. The amount of energy required to overcome the spring and bring the stylus tip into contact with the workpiece increases with increasing stylus gap. Accordingly, if the stylus gap is large and the force setting is low then the energy required to overcome the spring may significantly reduce the amount of energy available to mark the workpiece. As shown in figure 4, this can lead to no mark being made at all for certain combinations of stylus gap and force setting. For example, no dot was observed with an 11mm stylus gap and force settings of 1-7.

Although the lookup table shown in figure 5a has been found to be effective across a wide range of stylus gaps, it will be understood that in some embodiments, the controller 118 may be further configured to receive an input indicative of the stylus gap from a sensor arranged to detect the condition of the adjustable assembly, and the lookup table may provide acceleration times in dependence on the power setting, the detected voltage and the stylus gap.

In the embodiment illustrated above, the controller 118 is arranged to round the detected voltage to the nearest whole number of volts, and only discrete force settings can be provided via the input means. Accordingly, the controller is always able to select one of the values shown in the lookup table in figure 5a. However, in another embodiment, the controller 118 is arranged to interpolate between the values given for different voltage levels. This may improve the uniformity of the dots produced by the marking machine 101, although it may also make the marking operations more time consuming as it may be computationally expensive to perform such an interpolation. Furthermore, it may be possible for the user to program the machine 101 to adjust the acceleration times provided by the force settings so as to provide finer control of the acceleration time (and therefore the dot size) within a particular range. This may be useful if the material to be marked is particularly hard or soft, so that it is desirable to have more control of the acceleration time close to the maximum or minimum values that the machine is able to output. In this case, the user-defined values may correspond to the acceleration times for a baseline voltage level of 34V. As the user-defined values for the different force settings may not be equal to values in the lookup table shown in figure 5a, it will be necessary to interpolate between the values that are provided to calculate the acceleration times for the user-defined force settings when the detected voltage is different from the baseline voltage level. Figure 5a shows nine force settings per detected voltage. In the case where a user is dot marking steel and the voltage is at or below the baseline value of 34 volts, the first 5 force settings may not cause a dot in the steel as they cannot deliver enough force. In this case the user has less choice for his range of dot sizes, lowering the number of variations of marks that can be made.

Advantageously, the present invention can interpolate between force setting acceleration times such that if settings 1 -4 do not cause a mark or only cause a very faint mark, the user can redefine the acceleration times at the baseline voltage (which is 34V in the present embodiment). For example, this may allow a user in the situation described above to define nine separate acceleration times evenly spaced between the acceleration times for force setting 5 and force setting 9 in the standard lookup table. If the user has redefined the acceleration times at the baseline voltage, then values of acceleration time can be interpolated between the values defined in the standard lookup table when the acceleration time is user-defined and the voltage is different from the baseline voltage. It will be understood that in some embodiments most or all of the force settings may be re-defined, such that interpolation between values in the lookup table is necessary at all force settings. Furthermore, force settings above the maximum defined force setting or below the minimum defined force setting may be programmable by the user. In this case, the controller 118 may be configured to extrapolate the required acceleration times from the values given in the table. For example, linear or polynomial extrapolation may be employed to determine the required acceleration times for values beyond the maximum or minimum force setting.

Allowing the acceleration times at the baseline voltage for each force setting to be redefined gives the user with a wider range of possible dot sizes than would otherwise be available. A further advantage of this method is that the interpolated values can be calculated instantly by the onboard controller, without the user being required to spend time filling in a new lookup table with different values.

Figure 9 is a flow chart depicting a method 200 of marking using a battery-powered dot marking machine, in an embodiment of the present invention. After initializing the battery-powered dot marking machine, the method begins at step 202 in which the controller 118 receives instructions to commence marking from a user interface means. The method then proceeds to step 204, in which the controller 118 controls the X-Y actuation mechanism 24 to move the solenoid assembly 111 into a position corresponding with the location of the first dot to be made. It will be understood that a user may have programmed a mark to be made into the memory of the controller 118 prior to commencing of the method 200. The method then proceeds to step 206, in which the controller 118 receives measured values for the voltage of the battery and the force setting. In step 208, the controller determines whether or not a user defined force setting has been provided. If such user-defined values have been provided then the method proceeds to step 210, in which the controller 118 performs interpolation between values in a lookup table for the given voltage to determine the required acceleration time at the present, user-defined, force setting. If a user defined force setting has not been provided then the method proceeds to step 212, in which the controller 118 determines the required acceleration time by reference to the lookup table. In either event, once the required acceleration time has been obtained, in step 213, the solenoid 112 is energized by electrically connecting the battery to the coil of the solenoid 112 for the acceleration time. The connection of the coil to the battery may pass through the controller, which controller may be operable to selectively close the connection between the solenoid and the battery for a predetermined length of time corresponding to the acceleration time. Energizing the coil of the solenoid causes the stylus to accelerate towards the workpiece, thereby producing a dot on the workpiece.

In step 214, the solenoid assembly is moved to a location corresponding with the next dot to be marked and the solenoid coil is again energized for the required acceleration time in step 218. The method then proceeds to step 220, in which it is determined whether or not the mark has been completed. If the mark is complete, then the method ends and the user may remove the machine from the workpiece. Optionally, a notification means may produce a visible, audible or tactile indication that the mark is finished after the controller determines that the mark is complete. If it is determined that the mark is not complete, then steps 216 and 218 are repeated until the mark has been completed until the mark is complete.

It will be understood that the biasing means may be a spring, or the solenoid 112 generating a reversed magnetic field, or some other biasing means capable of returning the stylus to its starting position after indenting the target.

A handheld dot marking machine will be understood to be a machine having appropriate dimensions and weight such that it can be relatively easily maneuvered by the user. A dot 35 marking machine having a size of less than 400x400x500mm, preferably less than 290x270x400 mm and/or weighing less than 15kg, preferably less than 13kg could be considered to be a handheld device.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one. or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS1. A battery-powered dot marking machine comprising: a battery; a voltage sensor for sensing a voltage of the battery; a stylus having a tip; a solenoid arranged to drive the tip of the stylus towards a target; and a control means arranged to receive an input indicative of the sensed voltage from the voltage sensor, wherein the control means is arranged to control the solenoid in dependence on the sensed voltage.
2. The dot marking machine of claim 1 wherein the control means is configured to cause a current from the battery to be applied to the solenoid for a predetermined length of time, wherein the predetermined length of time is determined by the control means in dependence on the sensed battery voltage.
3. The dot marking machine of claim 2, wherein the dot marking machine further includes a user input means, and the predetermined length of time is determined in dependence on an intensity setting provided via the user input means.
4. The dot marking machine of claim 3, wherein the user input means allows the user to select one from a discrete number of acceleration times.
5. The dot marking machine of claim 4, wherein the control means comprises an electronic memory having a lookup table stored thereon, the lookup table comprising a plurality of values for the predetermined length of time, each value for the predetermined length of time corresponding to a given combination of intensity setting and sensed battery voltage.
6. The dot marking machine of claim 4 or claim 5, wherein the control means is programmable to adjust the predetermined length of time corresponding to each of the intensity settings at a baseline value of the sensed battery voltage.
7. The dot marking machine of claim 6 where dependent on claim 5, wherein the control means is configured to perform an interpolation between values in the lookup table to determine the predetermined length of time corresponding to an intensity setting if the predetermined length of time corresponding to the intensity setting has been adjusted and the sensed voltage is different from the baseline value.
8.The dot marking machine of any preceding claim, wherein the machine comprises a biasing means arranged to bias the stylus towards a neutral position.
9.The dot marking machine of claim 8, wherein the biasing means comprises one or more springs.
10. The dot marking machine of any preceding claim wherein, the dot marking machine comprises a housing for the solenoid, and the stylus having a tip, the housing comprising a face with a hole.
11. The dot marking machine of claim 10 wherein the housing is transparent.
12. The dot marking machine of claim 10 wherein the face of the housing comprises a high friction material.
13. The dot marking machine of claim 2, or any one of claims 3-12 where dependent on claim 2, wherein: if the sensed voltage is greater than a baseline voltage, the predetermined length of time is selected based on a first linear relationship between the sensed voltage and the predetermined length of time; and if the sense voltage is less than the baseline voltage, the predetermined length of time is selected based on a second linear relationship between the sensed voltage and the predetermined length of time.
14. The dot marking machine of claim 13, wherein if the sensed voltage is equal to the baseline voltage, the predetermined length of time is selected to be equal to a baseline length of time.
15. A method of controlling a battery-powered dot marking machine, said dot marking machine comprising: a battery and a voltage sensor for sensing the voltage of the battery; a stylus with a tip; and an electric solenoid for driving the tip of the stylus towards a target, the method comprising: controlling the acceleration time of the stylus in dependence on the sensed voltage.
16. A controller for a dot marking machine arranged to implement the method of claim 15.