Machine tool analysis device and method
The invention relates to a device and method for analysis of a tool 50 e.g. used on a machine tool. A tool detector 5 includes a light emitter 12 and a light receiver 34. Tool 50 when progressed into a beam 20 of light emitted from the emitter 12 will cause a signal from the receiver to change. Circuitry 32 includes a digital signal processor which processes the signal from the receiver and produces an output only if the signal conforms to a predetermined condition. Preferably this predetermined condition could be e.g. a characteristic shape of the signal from the receiver, a change in a value derived from a succession of such signals or a change in the minimum or maximum values of a succession of signals from the receiver.
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This is a continuation of application Ser. No. 10/535,716 filed May 20, 2005, which is a National Stage Application of PCT Application No. PCT/GB2003/005538, filed Dec. 18, 2003 that claims priority to United Kingdom Patent Application 0229459.3 filed Dec. 19, 2002. The entire disclosures of the prior applications are hereby incorporated by reference herein in their entirety.
BACKGROUNDThis invention relates to a device and method usable for analysis of a tool during its use with a machine tool, in particular but not exclusively for determination of the position of a tool.
Toolsetting devices for determining the position of a tool, which use a break beam system are known. EP1050368 A1 describes in detail one system which has a light transmitter and receiver. The transmitter produces a beam of light and a receiver has circuitry which produces a signal when obstruction of the beam is detected. When a predetermined level of beam obstruction e.g. 50% is reached then the signal strength from the receiver is reduced such that a trigger is produced. The trigger occurs when a tool is present in the beam path.
A toothed cutting tool has to be rotated in order to find its cutting diameter. Usually it will have at least two teeth, one of which may be taller than the other and so that tooth will circumscribe a larger diameter than the other(s). When the tool is brought into the beam path the tallest tooth may be at any point and so the repeatability of the trigger will vary. For example if a tool rotating at 1500 rpm is moving towards the beam at 6 mm per minute then the feed per revolution would be 6÷1500 which equals 0.004 mm. So, the repeatability of the trigger will be no better than 4 microns because the largest tooth may break the beam anywhere in that feed per revolution distance. The feed per revolution of the measurement limits the speed at which the tool can be driven into the beam and so slows the detection rate. Detection speed needs to be maximized for quick operation of the machine tool, whilst repeatability needs to be maximized also, requiring slow feed rates.
SUMMARYOne known way to increase detection speed is to move the tool quickly toward the tool setting device and once detected to back off and then move in slowly to determine the tool's position. This procedure, whilst saving some time, is still relatively time consuming.
According to a first aspect the present invention provides a tool analysis device for use on a machine tool comprising a light emitter and a light receiver, the light receiver in use receiving light from the emitter and producing a signal indicative of the amount of light being received, wherein the device further comprises a converter for providing data having a numerical representation of the signal produced by the receiver and comprising also a processor for processing that data and for producing an output when the data conforms to a predetermined condition.
The processor may be a digital signal processor (DSP) operative to process the data according to an algorithm.
According to a second aspect the invention provides a method for processing an analogue signal resulting from light falling on a light receiver of a tool analysis device for use on a machine tool, comprising the steps of:
converting the analogue signal into data having a numerical form which represents the signal; and
processing the data according to an algorithm.
Preferably the method provides a further step of:
producing an output signal when instructed by the algorithm when the data conforms to a predetermined condition.
Preferably the method employs a DSP to process the data and the algorithm is executed within the DSP.
According to both aspects the predetermined condition may be the data obtained when the light falling on the light receiver is altered e.g. in such a way that the tooth of a tool momentarily moves into and then out of the light falling in the light receiver, or a series of such events that conform to a predetermined pattern. The pattern could be deviations in the amount of that light such or a definable change in the magnitude of those deviations, e.g. a decrease in magnitude from one deviation to the next or a maximum followed by a minimum followed by another maximum in that magnitude.
BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments of the invention will now be described in detail with reference to the drawings, wherein:
FIGS. 4,5,7 and 8 show simplified graphical representations of signals produced during use of the detector shown in
The tool detector 5 includes a laser light transmitter 12 (IR light is used in this instance), at transmitter portion 10, a light receiver 34 at receiver portion 30 and a base 40 for mounting the transmitter and receiver portions. A light beam 20 is created in use which can be obstructed by the tool 50. Additional circuitry 32 is used also for processing the signal issued by the light receiver 34. Whilst the circuitry is shown in the receiver portion 30 some or all of it may be located off the detector, e.g. as a PC interface card.
Prior to tool detection a calibration pin is detected by the detector. A pin, in this instance similar in size to the tool to be detected is brought into the beam 20 by a program running in the CNC at a feed rate of approximately 4 mm/sec. The pin may be rotating or non-rotating. The light receiver output will follow a curve similar to that shown in
When the tool 50 is brought into the beam at about the same feed rate as the pin, whilst it is rotating, it will have teeth which temporarily obscure a part of the beam and these teeth cause voltage deviations s in the signal from the receiver 34 as shown in
It has been found that the minima and maxima of the deviations shown in
The deviations present will differ in shape depending on the tool type but the minima and maxima will still lie on the calibration curve c.
Another set of deviations is shown in
Yet another set of deviations is shown in
In each of the graphs of
Now, in this embodiment of the invention the voltage signals from the light receiver are conditioned using the circuitry shown schematically in
In this example the predetermined condition is the data obtained when the beam is obstructed by the tool.
The processing of the digitized signal by the DSP can be carried out in a number of ways. The DSP is an ideal device for carrying out such processing because it is very fast and processes the data in real time, thus enabling short response times.
One method of processing the sampled data involves deriving a polynomial e.g. cubic expression for the calibration curve c shown in
Alternatively an approximate straight line or polynomial can be generated using the minima as points on that line. No calibration curve(s) is (are) required but rather, a threshold value can be predetermined and when the straight line or polynomial line is calculated to have crossed (or will cross when extrapolated) that threshold then a trigger signal can be generated. The calculations necessary for the line generation again can be performed in the DSP. The accuracy of the estimated threshold crossing point can be improved if more than the minimum number of points are used. A gradient method can be used to determine minima or maxima and hence determine a threshold value. The increase p can be used also to predict a threshold crossing if required.
Drips or similar obstructions to the beam may give rise to false readings during the use of the technique mentioned immediately above. There are a number of ways in which these false readings can be ignored. One such way is to look for periodic voltage deviations from the receiver 34 and then to open time periods around the time when another deviation is expected. Only in this period will digitizing of the signal take place. Thus, the chance of a drip occurring within that period will be relatively small.
Another way to reject drips etc is to reject any voltage deviation minima or maxima whose values lie outside a band within which the next successive value for a predetermined curve would be expected.
The above examples for processing of sampled data can be used for non-rotating or rotating tool detection including the detection of the lengths of rotating drills etc which, when brought into the beam on axis may appear to be non-rotating.
Another method of processing the sampled data from the edge of a rotating tool is to look for voltage deviations which have a distinctive character. A detail of one such voltage deviation is shown in
The characteristic shape mentioned above may be a min-max-min as well as the max-min-max described.
A method of rejecting drips when detecting rotating tools is to ignore voltage deviations which do not have the expected distinctive character i.e. either min-max-min or max-min-max e.g. as shown in
The techniques mentioned above for determining the position of a tool rely on the calculation of the minima and maxima of the voltage deviations s which occur when a tooth obstructs the beam. There are a number of well-known techniques for estimating the zero slope part of a curve from points on either side of minima or maxima which may be used.
A calibration pin has been brought into the beam and has caused the characteristic curve c which is shown in
Various typical shapes of the data plots at points F 11 to F14 along the curve are shown in more detail in FIGS. 11 to 14 respectively. In each of the graphs shown in
In
Tools which are brought into the beam along their axis of rotation e.g. drills brought in tip first also have this characteristic “c” shape.
Thus it can be seen that the voltage deviation that is detected by the algorithm in the DSP develops as the tool is progressed into the beam. As mentioned above, there are many ways in which the sampled data can be used to determine a trigger point.
The max-min-max signal shown in
It has been found that the curve c shown in
Thus it can be seen that there are a number of ways in which data derived from receiver 34 can conform to a predetermined condition indicative of a tool present in the beam 20 e.g.:
a number of repeated signals e.g. max,min,max which have a characteristic profile;
the shape of curve c may conform to a calibration curve or may have an expected shape;
the time t (
successive peaks h (
A DSP has been utilized in the embodiment described, however many alternatives exist. Processing of the digitized signal could be carried out using e.g. a Field-Programmable Gate Array, an application-specific integrated circuit or a general-purpose microprocessor e.g. a PIC or a PC based system.
The tool detector is shown as a break beam type, but could be a reflective type.
Any edge of a tool can be detected e.g. side or end. Usually a calibration curve will be generated for each edge which is to be detected, but such a curve is not essential for edge detection.
The graphs show generally voltage output of a light receiver but any other variable can be employed. The voltage etc may not drop fully to zero, particularly if a very small tool is to be detected and where only a portion of the beam is obstructed.
Detection can be made when the tool is coming out of the beam as well as going into the beam. In such circumstances the effects detailed above will be reversed. Tools or other items to be detected need not be rotating to be detected.
As described above the minima or maxima of voltage deviations or deviations of variables can be fitted to a curve or simply used to plot a line. In either instance a trigger point equivalent to a voltage (etc) threshold can be set.
Claims
1. A method of analyzing a rotating tool, comprising the steps of:
- (i) taking a light emitter and a light receiver,
- (ii) passing a light beam from the light emitter to the light receiver, wherein the light receiver produces a signal indicative of the amount of light being received,
- (iii) moving a rotating cutting tool having at least one tooth through the light beam,
- (iv) determining characteristic deviations in the signal output by the light receiver as the at least one tooth of the rotating cutting tool interrupts the light beam,
- (v) comparing a series of the characteristic deviations determined in step (iv) to a predetermined pattern; and
- (vi) issuing a trigger signal when the series of characteristic deviations conform to the predetermined pattern.
2. A method according to claim 1 wherein each of the characteristic deviations comprise at least one of a maxima and a minima in the signal.
3. A method according to claim 1 wherein each of the characteristic deviations comprise a minima followed by a maxima followed by a minima.
4. A method according to claim 1 wherein a characteristic deviation is produced during each rotation of the rotating cutting tool.
5. A method according to claim 1 wherein step (v) comprises fitting the series of characteristic deviations to a polynomial expression.
6. A method according to claim 1 comprising the step of using temporal changes in a series of characteristic deviations to determine the position of the cutting tool relative to the beam.
7. A method according to claim 6 comprising the step of moving the cutting tool relative to the light beam at a known velocity such that, when the cutting tool reaches a predetermined position relative to the light beam, cutting tool geometry can be determined.
8. A method according to claim 1 comprising the step of issuing the trigger signal when the cutting tool reaches a predetermined position relative to the light beam.
9. A method according to claim 1 comprising the steps of rotating the cutting tool with constant angular velocity and determining the diameter of the cutting tool.
10. A method according to claim 1 wherein step (v) comprises the step of determining how many characteristic deviations that conform to the predetermined pattern are present in a predetermined time period and step (vi) comprises issuing the trigger signal when a predetermined number of such characteristic deviations are present in the predetermined time period.
11. A method according to claim 1 comprising the step of determining the position of the edge of the cutting tool.
12. A method according to claim 1 in which the rotating cutting tool provided in step (iii) comprises at least a first tooth and a second tooth, wherein step (iv) comprises determining first characteristic deviations in the signal output by the light receiver as the first tooth interrupts the light beam and second characteristic deviations in the signal output by the light receiver as the second tooth interrupts the light beam.
13. A method according to claim 12 wherein step (v) comprises comparing a series of the first characteristic deviations to a first predetermined pattern and comparing a series of the second characteristic deviations to a second predetermined pattern.
14. A method according to claim 1 in which any deviations in the signal are ignored that do not have an expected characteristic deviation.
15. A method according to claim 1 wherein step (iii) comprises moving the rotating cutting tool into the light beam and step (iv) comprises determining the characteristic deviations as the cutting tool enters the light beam.
16. A method according to claim 1 wherein step (iii) comprises moving the rotating cutting tool out of the light beam and step (iv) comprises determining the characteristic deviations as the cutting tool leaves the light beam.
17. A method of analyzing a rotating tool, comprising the steps of;
- (i) taking a light emitter and a light receiver,
- (ii) passing a light beam from the light emitter to the light receiver, wherein the light receiver produces a signal indicative of the amount of light being received,
- (iii) moving a rotating cutting tool having at least one tooth into said light beam,
- (iv) determining at least one of minimum values and maximum values in the signal output by the light receiver as the at least one tooth of the rotating cutting tool interrupts the light beam,
- (v) comparing a plurality of said at least one of minimum values and maximum values determined in step (iv) to a predetermined condition, and
- (vi) issuing a trigger signal when said at least one of minimum values and maximum values conform to said predetermined condition.
18. A tool analysis device for analyzing a rotating cutting tool, comprising;
- a light emitter for emitting a beam of light,
- a light detector for receiving light from the light emitter and producing a signal indicative of the amount of light received,
- a processor for analyzing the signal, the processor determining characteristic deviations in the signal and comparing a series of such characteristic deviations to a predetermined pattern,
- wherein the processor issues a trigger signal when the series of characteristic deviations conform to the predetermined pattern.
19. A device according to claim 18 wherein the processor issues the trigger signal when the cutting tool reaches a predetermined position relative to the light beam.
20. A tool analysis device for analyzing a rotating cutting tool, comprising;
- a laser for emitting a beam of light,
- a photodiode for receiving light from the laser and producing a voltage signal indicative of the amount of light received,
- an analogue-to-digital converter for converting the voltage signal into a numerical representation of the voltage signal,
- a digital signal processor for receiving and analyzing the numerical representation of the voltage signal, the digital signal processor determining characteristic voltage deviations in the voltage signal and comparing a series of such characteristic voltage deviations to a predetermined pattern,
- wherein the digital signal processor issues a trigger signal when the series of characteristic deviations conform to the predetermined pattern.
Type: Application
Filed: Nov 15, 2007
Publication Date: Mar 20, 2008
Applicant: RENISHAW plc (Gloucestershire)
Inventors: Sharon Ashton (Bristol), Victor Stimpson (Avening), Jonathan Fuge (Bristol), David McMurtry (Dursley)
Application Number: 11/984,289
International Classification: G06K 9/00 (20060101);