GB2042726A

GB2042726A - Pattern Logging Device

Info

Publication number: GB2042726A
Application number: GB7908004A
Authority: GB
Original assignee: BRANSBURY R
Current assignee: BRANSBURY R
Priority date: 1979-03-07
Filing date: 1979-03-07
Publication date: 1980-09-24

Abstract

A device for logging the coordinates of a curve (21) on a sheet (1) comprises a stylus (13) incorporating an ultrasonic transmitter transducer and at least two fixed transducers (3-6 and 12) arranged on the surface of the sheet. The curve to be logged can be projected onto the sheet from below. Ultrasonic pulse transit times between the transducers are evaluated. <IMAGE>

Description

SPECIFICATION Pattern Logging Device In certain industrial applications it is necessary to be able to reproduce a curved line and to assist in doing this it is known to convert spaced-apart positions on the curved line into pairs of coordinates of a planar frame of reference, so that reproduction of the curved line can be effected using successive pairs of coordinates. For example if an automatically controlled machine is to act on material in some way (e.g. to cut it or stitch it) along a curve of desired shape, a sequence of coordinate points closely spacedapart along the desired curve has to be fed to the machine to define that curve.

This invention is concerned with an improved method of determining the coordinates of a point on a curve and with a pattern logging device which permits a programme of coordinates of a curve to be produced quickly and easily by an unskilled operator.

The invention finds applications in the textile and sheet metal industries, for example, in the programming of automatic machines, for verifying signatures as they are written and for the transmission of information as it is being written, to a remote location.

Pattern logging devices are known (see for Example U.K.Patent Specification No. 1,335,664) which rely on an operator moving a pointer over a surface of a board along a line representing the curve to be logged and periodically deducing from the position of the pointer relative to the board what are the coordinates of points spaced-apart along the curve. The prior art method of determining these coordinates requires a mechanical interconnection between the pointer and the board which makes thb logging device somewhat cumbersome to use and expensive to manufacture.

This invention relates to the type of logging device which uses a pointer for tracing along a curve represented on a board, but employs an improved method for determining the coordinates of the curve from the positions of the pointer on the board surface.

According to one aspect of the invention, a method of determining the coordinates of a point on a curve relative to the two components of a frame of reference in a plane containing the curve (e.g. the x-axis and the y-axis of a cartesian coordinate system) comprises transmitting energy in the form of vibrations at ultrasonic frequency between the point in question and fixed transducers in the said plane and determining from the transit times of the energy in passing between the point and at least two different fixed transducers what are the coordinates of the point.

If the frame of reference represents the first quadrants of a cartesian coordinate system, two elongate transducers can be fixed at right angles adjacent to the bottom and left-hand edges of a rectangular "drawing board" to represent the xand y-axis of the system, and the curve can be traced on the board surface with an ultrasonic generator in the form of a stylus, the boardengaging tip of which forms the final part of the output from the generator.

The energy may be transmitted through a sheet of material, the fixed transducers being fixed adjacent to the edges of the sheet and the movable stylus used on the upper surface of the sheet to feed energy into the material at the point in question or to extract energy from the material at that point.

In a particularly simple arrangement, the stylus is made as a transmitter and two orthogonal edges of the sheet are provided with elongate fixed transducer/receivers or lines of closely spaced discrete transducer/receivers. Clock controlled counters can be used to time the interval between firing an ultrasonic energy burst into the sheet at the point in question and first receiving it at the respective sheet edges. Where separate transducers are used in lines along the sheet edges the spacing is around 10 wavelengths of the energy wave at the frequency transmitted.

In another arrangement, four fixed transducers are used (one adjacent to each corner of a rectangular sheet) and a transducer is used in association with the tip of a movable stylus probe.

Two of the fixed transducers can be transmitters and the movable transducer and the other two fixed transmitters can act as receivers. A pulse sent out by a first of the two transmitters is picked up by the three separate receivers and then a pulse is sent out from the second of the two transmitters and again picked up by the two stationary receivers and the movable receiver. The transit times for the pulses from the first and second transmitter to the movable receiver give an indication of the coordinates of the movable receiver and the transit times of these pulses to the fixed receivers enables estimates to be made of the speed of the ultrasonic waves in the sheet material.A constant checking of wave velocity in the sheet material is important for high accuracy since stresses in the sheet caused by hand pressure or changes in temperature can affect the velocity and introduce errors if an average value for the velocity is assumed.

A further modification involves the use of a fifth fixed transducer located (e.g. centrally along one side) on the sheet. The four corner transducers are used as receivers and the movable transducer and fifth fixed transducer are used as transmitters. With such an arrangement the fifth fixed transducer can be used with one or more of the four corner transducers to assess the wave velocity in the sheet an instant before (and optionally also an instant after) the movable transmitter fires energy into the sheet for transit time assessments (and thus coordinates computation) with respect to the corners of the sheet.

A still further arrangement uses one corner transducer as a transmitter and three other corner transducers as receivers. The moving transducer can also be a transmitter and its firing of energy into the sheet perturbs the standing wave pattern generated by the corner transmitter, so that the position of the moving transmitter relative to the corners can be deduced.

The resolving power of the method of this invention is a function of the frequency of the ultrasonic vibrations generated and I prefer to use a frequency of at least 20 Kilohertz and preferably a few Megahertz. With an exciting frequency of 100 megahertz in a plate glass sheet definitions of the order of about +25 u are theoretically possible.

According to a further aspect of the invention a pattern logging device comprises a plane sheet of compliant material, at least three electrical/ultrasonic mechanical transducers, two being fixed to the sheet and one movable over a surface of the sheet, means to indicate a curve to be logged on said surface of the sheet, electrical means to energise at least one of the transducers as a transmitter of ultrasonic energy and at least two of the transducers as receivers of ultrasonic energy, timer means to deduce transit times of ultrasonic energy between the movable and at least two different fixed transducers, and logic means to obtain from said transit times an assessment of the coordinates of the movable transducer relative to fixed coordinate axes on the sheet.

Suitably the sheet is of transparent or translucent material. The curve can be physically marked on the sheet, projected onto the said surface of the sheet (from above or below), or marked on a film (e.g. of paper) which is rested on the sheet.

Conveniently there is a fixed transducer at each corner of a rectangular sheet, the moving transducer being a transmitter in a stylus which passes ultrasonic energy to a ball forming the tip of the stylus.

The invention finds particular, but not exclusive, application in the textile patternmaking industry.

Embodiments of the invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of the pattern-supporting part of a pattern logging device in accordance with the invention, Figure 2 is an enlarged sectional view of one of the fixed transducers shown in Figure 1, Figure 3 is an enlarged sectional view of the movable transducer shown in Figure 1, Figure 4 is a schematic of the circuits used with the part of the device shown in Figure 1, Figure 5 is a perspective view of the sensitive plate of modified form of device in accordance with the invention, and Figure 6 is a schematic view of the underside of the sensitive plate shown in Figure 5.

Referring to Figures 1 and 3, the pattern logging device shown comprises a 6 mm thick lead glass plate 1 frosted on its top face and some 1 mx600 cm in transverse dimensions, mounted at its edges on bitumenised fibre with a 10 cm wide frame 2 of 3 mm lead sheet overlapping the edges of the plate 1. A 2 mm layer of leaded putty (litharge and linseed oil) is disposed as sealant between the frame 2 and the plate 1. The outer edges of the sealant are filled with standard putty for safety reasons and the lead frame 2 is coated with an epoxy resin based paint.

Piezo-ceramic transducers 3, 4, 5 and 6 are mounted just inside the frame 2 at each corner thereof. Figure 2 shows a section through one such transducer. It comprises a bimorph 7 attached to a steel weight 8 with silver loaded cyano-acrylate adhesive for contact purposes.

Between the plate 1 and the transducer bimorph 7 is a 1 mm diameter tungsten carbide ball 9 suspended in a drop of watch oil or other nonspreading lubricant. The corner transducers are located on a diagonal of the plate 1 about 11 cm from each corner, each steel weight 8 being pressed against the plate 1 by a foam rubber pad 10 in a protective casing 11.

At the centre of one edge of the plate is mounted a fifth transducer 12 (the reference transducer) which is similar in design to that shown in Figure 2. The polarisation of all transducers 3-6 and 12 is arranged so that shear stress in the plate 1 produces very little output from the bimorph 7, whereas flexural stress produces the maximum response.

A stylus 1 3 containing a piezo-ceramic transducer 14 is used to trace curves to be logged on the plate 1. The transducer 14 includes a steel block 1 5 and a bimorph 1 6 and employs a quartz rod 1 7 to transmit vibrations from the bimorph to a 1 mm diameter tungsten carbide ball 18 which contacts the plate 1. A spring 19 bears against a mass 20 fixed in the stylus body and urges the bimorph 1 6 against the rod 1 7. The curve to be logged is represented on the plate 1 at 21 and can be formed on thin draughting film attached to the plate, or (as shown) a slide of the required pattern is projected onto the plate from below.

One of a number of points on the curve 21 to be digitized is selected and the stylus 1 3 applied to it. Pressure is put on the stylus and the D.C.

component of the output from the stylus bimorph 17 is monitored to give a measure of the stylus/plate pressure.

The equipment described in Figures 1 to 3 will be used with the simplified circuit shown in Figure 4. The outputs from the transducers 3-6 are, respectively, fed to amplifiers 22-25 and from there to flip-flops 26-29. The outputs from these flip-flops are gated with a reference clock 30 and the gated outputs (31 c-34c) are used tb drive four counters 31 to 34. When a pulse arrives at a transducer, it toggles the relevant flip-flop and stops the count. Each flip-flop has an output (31b-34b) to a central processor to signal that a count has finished.Each counter also has an output (31 d-34d) from its final section which, if activated, indicates to the processor, via a gate A, that is has overflowed and thus that a fault condition exists and another pulse should be launched from the sending transducer. The outputs from each counter are sent to the processor from the twelve terminals 31a-34a, on each counter.

A divider unit 47 (e.g. dividing by the factor five) generates a basic clock frequency for the processor from the output of the clock 30, this frequency signal being led off on a line 47d.

A timing circuit 41 is employed to generate a single square pulse when the processor is ready for a sample. The positive-going edge of this pulse sets all counters to zero via a line 41 a and resets the flip-flops 26-29, via line 41 b. The following negative-going edge of the pulse then starts the counts.

In use the transducer 7 transmits a train of pulses which are picked up by the corner transducers 3-6 and the transducer 1 6 when the stylus contacts the plate 1 with sufficient contact pressure. A level discriminator 42 senses the stylus pressure by measuring the D.C.

component of the output from the transducer 1 6 taken from a low pass filter 43, and feeds a signal to the processor on the line 42a. The input to the filter 43 is taken from a stylus preamplifier 44 which also feeds a high pass filter 45 and, via this, a rectifier 45a.

The high pass filter 45 produces an output on a line 45b to the processor by picking up the signal in the glass from the reference transducer 7, and indicates that the stylus is indeed in contact with the plate 1. When the stylus is pressed with sufficient force against the plate 1, the processor allows one more pulse to occur from the circuit 41 via the transducer 7 to the plate 1 and estimates the sonic velocity in the glass using the counters in the usual way. When the echo signals from this pulse are no longer sensed by the transducer 16, a relay coil 50 changes over a contact 50a and the actual sampling pulse can be generated.

Thus when the D.C. output from the transducer 16 indicates a sufficient manual pressure is being applied for a logging operation to be undertaken, transducer 7 is switched off and a single pulse is generated from the transducer 1 6.

The output of the stylus transducer 1 6 is used to stop the output of the transducer 7 at a short time before the initiation of the pulse and the timing of the associate circuitry is arranged so that only when the vibrations of the reference have died down owing to absorption at the edges of the plate 1 is the sampling pulse from 16 allowed to occur.

The sampling pulse starts the high frequency clock 30 which is applied to four counters 31 34 which have previously been cleared by the switching off of the transducer 7.

Each counter 31-34 counts the pulses from the clock 30 until the wavefront of the sampling pulse arrives at its respective transducer 3-6 and stops the counters via a conduction path through the respective flip-flop. At this point each counter stops and then signals to the central processor via output A that its output is ready.

The state of the four counters 31-34 is then read from the outputs 31a-34a and calculation of the position of the stylus when the sampling pulse was generated is calculated.

While the stylus 13 is in contact with the plate 1 and receiving the reference output, the velocity of the wave in the glass plate 1 is monitored using the counters 31-34 as has previously been described, so that short-term variations in this velocity from temperature changes, hand or arm damping, etc., are compensated for. In theory, only two transducers 3-6 are necessary to determine the position of the stylus 13 at the point of transmission. However, this would require that the plate 1 be perfectly flat since circular wavefront propagation would then have to be assumed.Since the plate is not perfectly flat, the 6 relevant calculations from pairs of transducers (adjacent corners (3-4, 3-6, 5-6, 5-4) are diagonals (3-5, 4-6)) can be used and the mean taken.

If still greater accuracy is required, a calibration procedure can be adopted using a grid of the desired accuracy projected onto the (top) face of the plate 1. Sufficient mesh points of the grid are then sensed with the stylus and these are at known coordinates. These coordinates are then stored as an array in the processor memory and serve as a look up table of corrections for any input position subsequently taken.

The degree of accuracy attainable with the equipment described is determined by the rise time of the transmitter medium and detectors.

Since the impedance match of piezo-electric transducers to glass is reasonably good, the power content of the stylus pulse needed to attain reasonable bandwidth in the detecting amplifier is not great.

The speed of the system requires that the rise time of the transmitter-medium-receiver needs to be about 100 nS for 0.26 mm (11 thou) definition (assuming the velocity of flexural waves in lead glass to be about 2.6 x 1 Off m/sec) which for applications in the textile pattern making industry is quite acceptable.

To calculate the cartesian coordinates of the stylus 13, fast algorithms using hardware multiply are employed, the velocity of the wave being deduced from the known distances between the various pairs of receivers 3, 4, 5 and 6. However, this does reduce the accuracy since the squares of the times taken for the energy pulse to reach the transducers 3-6 are used. More complex solutions are also possible but these will be slower. In the application of pattern manufacture in the textile industry, the speed of coordinate solution only requires standard hardware since the rate of coordinate input is unlikely ever to exceed one/sec.

A modification of the technique described above which eliminates the reference transducer 12 is to mount only the four transducers 3-6 as before in the corners of the plate. Two of these function as transmitters and the others (including the stylus transducer 16) act as receivers. A pulse is sent out by one transmitter and is picked up by the three receivers. The transit times of the wave front to the stylus transducer enables the calculation of a first stylus coordinate to be undertaken, the value for the wave velocity in the sheet being deduced from the transit times of this wave front to the fixed receivers. The reception of the first pulse at the corner transducers causes a second pulse to be generated by the second transmitter and zeros the counters again.On reception, the processor is signalled that the coordinate information is available and calculation of the full position of the stylus can be completed. Calculation of the position is simpler in this system but suffers from the presence of reflections from the corners where the transmitter transducers are mounted which complicate the circuitry of the receiver amplifiers which have to discriminate between the three sources, one real and the other two images of the transducer produced by the corner edge mismatches. Owing to the damping at the edge of the plate 1 and the use of only the vertical component of the wavefront, the ratio of real to imaginary pulses can be as great as 20 dB so the first pulse to be received will always be the greater amplitude real pulse.

In a further example of the principle, one corner transducer (say 3) is used as a transmitter with an approximately sinewave output at about 10 MHz.

The other three transducers (4, 5 and 6) pick up this signal and from the instantaneous phase difference between the input and each output, values are derived for the instantaneous damping load, (e.g. by hand or arm pressure) on the plate.

The stylus 13 is then applied to the required point on the curve 21. The stylus pressure is measured from the D.C. output of the transducer 1 6 and when the required value is reached, the stylus is made to transmit a burst of ultrasonic energy at the same frequency as the transmitter 3. The perturbation in the phase pattern produced as measured by the transducers 4 6 gives a measure of the stylus position.

This method produces 45 solutions to the position of the stylus, one real and 44 imaginary caused by the reflections in the edges of the plate by each transducer.

The real solutions for the stylus (those solutions which are within the known bounds of the plate) are accepted, leaving 9 possible solutions for each of the three transducers 4-6.

Since the fixed transducers are mounted more or less symmetrically in each corner and more than 10 wavelengths away from the actual corner of the glass, but in each case are more or less the same, the solutions will form a set of regular matrices which will have a degree of correlation dependant on the degree of symmetry of the system. Inspection of the matrices and combining of the like solutions will yield a matrix of the 5 mean solutions, the central one being taken.

The amount of processing power to implement this embodiment of the principle is seen to be of a much greater order than the first, if a reasonable rate of coordinate input is required. However with increase in exiting frequency, the definition of the system can be improved. A 100 MHz exiting signal can yield a definition of the order of 26 y.

The input power required to yield a reasonable signal to noise ratio at the output of the amplifiers 23-25 will however become a significant limiting factor and non-linearity in the interface between the transducer 3 and the glass will become a serious consideration since this will give rise to other images of the stylus at points outside the consideration of the software.

A further embodiment of the principle is proposed where two orthogonal edges of the plate 1 are each mounted with an array of transducers spaced at (say) 10 wavelength intervals. Correlation of the outputs of these transducers yields the x and y coordinates directly and excitation is by either a pulse or by a steady state signal from the transducer 1 6. In each case, each embodiment yields a price-performance ratio which can be made to suit its application. If the steady state four transducer and stylus is to be used for on-line manual data entry to a mainframe, the software overhead will be insignificant, and the accuracy can be fully used.

Figures 5 and 6 show a modified arrangement which has use as a point of sale terminal or as a device for transmitting drawn or written information to a remote station.

Figure 5 shows a stylus 53 working on a plate 51, the stylus generating rapid pulses of ultrasonic energy which is transmitted through the plate 51 to rows of transducers 52 and 54 (see Figure 6). By making the plate 51 of a piezoceramic material the receivers in the rows 52 and 54 can simply be metalized areas formed in edge regions of the plate. Two analogue shift registers 55 and 56 are mounted on the back of the plate 51 and the appropriate connecting circuitry to the metalized edge areas and x- and y-output contacts 57 and 58 can be provided on the back of the plate by normal printed circuit techniques.

The unit shown in Figure 5 could be a point of sale terminal for verifying a signature as being genuine, the plate 51 being some 10x20 cm in size.

By making the output from the stylus 53 a series of pulses, a follower can be employed to digitize the continuous movement and transmit the digital information to a remote location where the comparison of the digital train with stored information relating to the signature in question can be used to confirm its authenticity. The inter pulse strain on the stylus transducer can be measured to ensure that sufficient pressure is being placed on the plate 51 or a pressure sensing element can be included in the stylus body. A coloured lubricant can be used around the stylus' ball to yield a pen with a pulsed acoustic output. As well as verifying a signature as a credit card point of sale terminal, the unit in Figure 5 can be used to transmit free hand writing and/or drawing to a remote place where it will be reproduced by a suitable machine-controlled drawing instrument.

Claims

1. A method of determining the coordinates of a point on a curve relative to the two components of a frame of reference in a plane containing the curve comprising transmitting energy in the form of vibrations at ultrasonic frequency between the point in question and fixed transducers in the said plane and determining from the transit times of the energy in passing between the point and at least two different fixed transducers what are the coordinates of the point.

2. A method as claimed in claim 1, in which the energy is transmitted through a sheet of material, the fixed transducers being fixed adjacent to the edges of the sheet and a movable stylus being used on the upper surface of the sheet to feed energy into the material at the point in question or to extract energy from the material at that point.

3. A method as claimed in claim 2, in which the stylus is made as a transmitter and two orthogonal edges of a rectangular sheet are provided with elongate fixed transducer/receivers or lines or closely spaced discrete transducer/receivers.

4. A method as claimed in claim 2 or claim 3, in which clock controlled counters are used to time the interval between firing an ultrasonic energy burst into the sheet at the point in question and first receiving it at the respective sheet edges.

5. A method as claimed in claim 1, in which four fixed transducers are used one adjacent to each corner of a rectangular sheet and a movable transducer is used in association with the tip of a movable stylus probe to define the said point.

6. A method as claimed in claim 5, in which two of the fixed transducers are transmitters and the movable transducer and the other two fixed transmitters act as receivers.

7. A method as claimed in claim 6, in which a pulse of energy is sent out by a first of the two transmitters, is picked up by the three separate receivers and then a pulse is sent out from the second of the two transmitters and again picked up by the two stationary receivers and the movable receiver.

8. A method as claimed in claim 7, in which the transit times for the pulses from the first and second transmitter to the movable receiver are used to give an indication of the coordinates of the movable receiver and the transit times of these pulses to the fixed receivers are used to estimate the speed of the ultrasonic waves in the sheet material.

9. A method as claimed in claim 5, in which a fifth fixed transducer is located on the sheet, the four corner transducers being used as receivers and the movable transducer and the fifth fixed transducer being used as transmitters.

10. A method as claimed in claim 9, in which the fifth fixed transducer is used with one or more of the four corner transducers to assess the wave velocity in the sheet at least an instant before the movable transmitter fires energy into the sheet for transit time assessments with respect to the corners of the sheet.

11. A method as claimed in claim 5, in which one corner transducer is used as a transmitter and three other corner transducers are used as receivers, the moving transducer also serving as a transmitter and its firing of energy into the sheet perturbing the standing wave pattern generated by the corner transmitter, so that the position of the moving transmitter relative to the corners can be deduced.

12. A method as claimed in any preceding claim in which the frequency of the ultrasonic vibrations generated is at least a few Megahertz.

1 3. A pattern logging device comprising a plane sheet of compliant material, at least three electrical/ultrasonic mechanical transducers, two being fixed to the sheet and one movable over a surface of the sheet, means to indicate a curve to be logged on said surface of the sheet, electrical means to energise at least one of the transducers as a transmitter of ultrasonic energy and at least two of the transducers as receivers of ultrasonic energy, timer means to deduce transit times of ultrasonic energy between the movable and at least two different fixed transducers, the logic means to obtain from said transit times an assessment of the coordinates of the movable transducer relative to fixed coordinate axes on the sheet.

14. A device as claimed in claim 13 in which the sheet is of transparent or translucent material.

1 5. A device as claimed in claim 14, in which means is provided to project the curve onto a surface of the sheet.

16. A device as claimed in claim 13, 14 or 15, in which the sheet is rectangular and a fixed transducer is located adjacent to each corner of the sheet, the moving transducer being a transmitter in a stylus which passes ultrasonic energy to a ball forming the tip of the stylus.

17. A device as claimed in claim 16, in which a fifth fixed transducer is employed at the centre of one edge of the sheet.

18. A device as claimed in claim 1 6 or 17, in which each corner transducer is spaced from the actual corner of the sheet by more than, ten wavelengths of the ultrasonic energy transmitted by the transmitter.

19. A device as claimed in claim 16, 17 or 18, in which the transmitter in the stylus is controlled in response to pressure of the stylus tip on the sheet.

20. A device as claimed in claim 19, in which the stylus pressure on the sheet is measured by monitoring the d.c. output of a bimorph forming a component part of the moving transducer.

21. A pattern.logging device substantially as herein described with reference to, and as illustrated in Figures 1 to 4 of the accompanying drawings.

22. A device for transmitting drawn or written information to a remote station substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.