TRACER CONTROL EQUIPMENT

Abstract: The equipment has a memory MEM holding both tracer operation and numerical command data. Processor CPU reads out numerical command data from MEM to buffer regis­ ter BFR, for supply to digital-to-analog converter DA and con­ version to an analog velocity command signal. An analog gate circuit GC receives the analog velocity command signal and tracer control signals (from tracer arithmetic unit ART). The gate circuit GC is selectively operable, under processor con­ trol, to pass on the analog velocity command signal or a tracer control signal, to command a cutter driving servo motor MX of a tracer machine, providing either numerical control, or tracer control. For example, for position control, reversible counter CNTX maintains a count of movement-indicating pulses, from position detector PCX, representing the current position of cutter CT. The processor compares the count with desired cutter position data and zero's the content of buffer register BFR when the desired position is attained.

Description: Tracer Control Equipment This invention relates to tracer control equipment. racer controlled machining may in some cases require relatively simple numerical control, for positioning for example, using a numerical command according to a workpiece being machined. A method that has been employed in the past to meet such a requirement is to combine tracer control equipment with numerical control equipment, to share a motor drive circuit and to perform selectively numerical control and tracer control by switching appropriate commands to the motor drive circuit for each particular operation to be effectea. With this method, however, during tracer control the expensive numerical control equipment is completely unused, and both tracer control and numerical control equipments provide facilities for jog feed, rapid feed, handle feed and so forth; so that this method is very wasteful in many respects. According to thepresent invention there is provided tracer control equipment in which trace direction and trace velocity are calculated using signals from a tracer head tracing a model surface, when the equipment is in use, and the equipment effects tracer control in accordance with the calculation results, the equipment being characterised by: a processor; a memory for storing numerical commana data; and means whereby the processor can read out the stored numerical command data and such that the equipment can effect as an alternative to tracer control, numerical control in accordance with the storea numerical command data. Tracer control equipment embodying the present invention is proviaed with a processor and#is designed to perform a relatively simple numerical control function for positioning control and the like through utilization of the processor so that both tracer control and numerical control may be effected by means of an economical arrangement of the tracer control equipment alone. Briefly, in tracer control equipment embodying this invention, there are provided a memory for storing numerical command data and means for reading out the numerical command data from the memory under the control-of a processor, for the performance of positioning control of a tracing machine in accordance with the stored data. Thus, the equipment has both ordinary tracer control functions and a relatively simple numerical control function. reference is made, by way of example, to the accompanying drawing which illustrates in a schematic block diagram principal parts of equipment embodying the present invention. In the drawing, ART is a tracer arithmetic unit including a composite displacement calcu-lation circuit, a velocity calculation circuit and a distribution circuit, GC is an analog gate circuit; DAVX is an amplifier; MX is a servo motor; MAC is a tracing machine; rEDL is a model; TR is a tracer head; ST is a stylus; CT-is a cutter; W is a workpiece; PCX is a position detector; CNTX is a reversible counter for counting pulses available from the position detector; DO is a data output unit; BFR is a buffer register; DA is a D-A (digital to analog) converter; MEM is a memory having a control program memory part MO, a data memory part MI and a work memory part M2; DI is a data input unit; KB is a keyboard; and CPU is a processor. in the drawing, only one drive axis (the X-axis, of three drive axes X, Y and Z) is illustrated (i.e. only the X-axis amplifier DEVX, the X-axis servo-motor MX, the X-axis position detector PCX and the X-axis reversible counter CNTX are shown) for convenience of description. When the stylus ST is brought into contact with the model MDL ana traces over the surface of the model, driven by the servo motor MX, the tracer head TR provides to the tracer arithmetic unit ART displacement signals # x' # y and Ge Zcorresponding to the displacement of the stylus ST. The tracer arithmetic unit ART derives from the displacement signa a composite displacement signal, E EMI3.1 and displacement direction signals sin e and cos 8 and produces a velocity command signal based on the thus obtained signals and on a reference displacement signal ± applied separately (not shown) from the abovesaid displacement signals exn & The velocity command signal thus obtained is supplied to the analog gate circuit GC. Since the analog gate circuit GC applies the velocity command signal to a selected one of the X, Y and z axis amplifiers (of which only the X-axis amplifier is shown), corresponding respectively to the X, Y ana Z drive axes, the appropriate servo motor is driven in response to tne velocity command signal amplified by the selected amplifier thereby bodily to feed the cutter and the tracer head TR. These operations are well-known in the art. Data defining a tracer operation is entered from the keyboard KB, for example, and stored in the memory ME. The processor CPU reads out the operation defining data from the memory MEM when the tracer operation is effected and controls the tracing path in accordance with that data. For example, decisions as to whether or not the stylus ST has reachea a trace turning position or a trace end position for example are checked by making a comparison between stylus position information, from the reversible counter CNTX for example, and set position information stored in the data memory part Ml of memory MEM. In an embodiment of the present invention, in such tracer control equipment provided with a processor for controlling the tracing path and the like, there are provided buffer register BFR, for storing velocity command and like numerical command data, and D-A converter DA for converting the output from the buffer register BFR to analog form for input to the analog gate circuit GC. The buffer register BFR and the D-A converter DA are placed under the control of the central processor CPU so as to perform positioning control using the numerical command data. For positioning control, numerical command data such as distance, direction and velocity of movement of the cutter and so forth are. entered, from the keyboard KB for example, to be prestored in the data memory part Ml of the memory MEM via the data input unit DI. When the cutter CT is placed at its initial start point and a start-button (not shown) depressed, the processor CPU changes over the analog gate circuit GC and, at the same time, reads out feed rate data and the data representing feed direction, stored in the memory MEM, and writes that data into the buffer register BFR via the data output unit DO. In this case, the feed direction is written in the buffer register BFR with a positive or negative sign. The output from the buffer register BFR is converted by the D-A converter into an analog signal, which is applied as a velocity command signal via the analog gate circuit GC to the amplifier DRVX. The servo motor MX is driven in correspondence with the velocity command signal to shift the cutter CT and the stylus ST. The distance of movement of the cutter CT and the stylus ST can be detected from the content of the reversible counter CNTX which counts output pulses available from the position detector PCX mounted on the servo motor lIX. The processor CPU reads out the content of the reversible counter CNTX via the data input unit DI with a constant period (the content is read repeatedly at predetermined intervals) and adds the count content of the reversible counter CICX to the previous stored content (the content accumulateu up to the last reading) and stores the sum in some area of the work memory part M2 of memory MEM. The distance of movement of the cutter CT as represented by the sum stored in the work memory M2 and the desired distance-of-movement data prestored in the data memory part Ml (fed in from the keyboard KB or the like) are read out by the processor CPU with a constant period and compared with each other (repeated comparisons are made at regular intervals). When it is determined by this comparison that the actual distance of movement of the cutter CT matches the preset desired distance, the processor CPU zeros the content of the buffer regisrer BFR via the data output unit DO to stop servo motor operation, thus completing positioning control. The reversible counter CNTX is reset by a reset signal RST after its content has been read out, and therefore it need have a capacity sufficient only to count output pulses from the position detector PCX over a certain period of time; thus, the reversible counter CNTX can be formed of a register of relatively small capacity. In positioning as described above, the desired distance of movement of the cutter CT is specified in advance. However, positioning can also be performed by increasing the capacity of the reversible counter CNTX so that its content indicates the current position-of the cutter CT at all times, storing in the memory MEM data on a desired final position of the cutter CT and comparing this data with the current position data from the reversible counter CNTX by means of the processor CPU. When carrying out, by such positioning control, what is called straight-line cutting, which involves effecting a cutting operation even whilst the cutter moves in parallel to its axial direction, the accuracy of the cutter feeding speed is also important in addition to the distance of movement of the cutter, and the cutter must be fed faithfully at a specified feed rate. However, if there is in the servo system or the like an offset of, for example, several millimeters per minute in terms of the feed rate, then the cutter may not be fed at a specified velocity; this error poses a problem especially when the feeding speed is low, for instance, five to ten-odd millimeters per minute. Embodiments of the present invention can provide for correction of such a feed rate error as described hereunder. After writing into the buffer register BFR feed velocity data stored in the memory MEM, to start up feeding by the servo motor MX, the processor CPU reads out the content of the reversible counter CNTX to calculate therefrom the actual velocity of movement of the cutter CT, compares the calculated cutter movement velocity with the abovementioned- feed velocity data and rewrites the content of the buffer register BFR so that the two velocities may be caused to match one another. For such rewriting of the content of BFR, use can be made of feed velocity correction data prestored in the memory MEM. As has been described above, tracer control equipment embodying the present invention is equipped with a relatively simple numericai-c#ontrol function through utilization of a processor controlling the tracing path and so forth. Accordingly, tracer control equipment embodying the invention is capable of effecting both tracer control and numerical control with an economical arrangement, as compared with an arrangement in which full tracer control equipment and a numerical control equipment are merely combined as has heretofore been employed. Thus, an embodiment of the invention provides tracer control equipment in which a trace direction and a trace velocity are calculated using signals from a tracer head tracing a model surface and in which tracer control is performed in accordance with the calculation results. The equipment has a memory for storing numerical command data and means whereby a processor can read out the stored numerical command data from the memory, thereby to add a numerical control function for positioning control to the capabilities of the tracer control equipment.

Claims: Claims 1. Tracer control equipment in which trace direction and trace velocity are calculated using signals from a tracer head tracing a model surface, when the equipment is in use, and the equipment effects tracer control in accordance with the calculation results, the equipment being characterised by: a processor; a memory for storing numerical command data; and means whereby the processor can read out the stored numerical command data and such that the equipment can effect as an alternative to tracer control, numerical control in accordance with the stored numerical command data. 2. Equipment as claimed-in claim 1, further including:- a buffer register, into which numerical command data read out by the processor is set, a digital to analog converter, arranged for converting data set into the buffer register into an analog signal for use as a command signal for a servo motor of a tracer machine controlled by the tracer control equipment when it is in use. 3. Equipment as claimed in claim 2, further including a position detector arranged to produce output pulses indicative of changes in position of the servo motor, and a reversible counter for counting output pulses from the position detector, wherein the processor is operable to read out the count content of the reversible counter and to compare a quantity based on the read out count content with numerical command data stored in the memory, thereby to effect control in accordance with the stored numerical command data. 4. Equipment as claimed in claim 3, wherein the said analog signal is for use as a velocity command signal for the servo motor of the tracer machine, and wherein the count content of the reversible counter is read out, by the processor, at regular intervals, the count content being reset to zero after each read out, and the processor is operable to set in the memory an accumulated count, the sum of the read out count contents, and to compare that accumulated count with distance-of-movement data, thereby to effect positioning control. 5. Equipment as claimed in claim 3, wherein the said analog signal is for use as a velocity command signal for the servo motor of the tracer machine, and wherein the count content of the reversible counter represents the current position of a cutter of a tracer machine driven in accordance with the said servo motor, and the processor is operable to compare the count content with desired final position data, thereby to effect positioning control. 6. Equipment as claimed in claim 3, wherein the said analog signal is for use as a velocity command signal for the servo motor of the tracer machine and wherein the processor is operable to calculate from read out counts of the reversible counter the velocity of movement of a cutter of the tracer machine driven in accordance with the servo rotor, to compare the calculated velocity with a desired cutter feed velocity and to rewrite the numerical command data set into the buffer register as appropriate to match the calculated velocity with the desired feed velocity. 7. Equipment as claimed in any one of claims 3 to 6, comprising an analog gate circuit to which the said analog signal is supplied, which analog gate circuit is arranged also to receive tracer control signals and is selectively operable, under processor control, to deliver either the said analog signal or a tracer control signal as a command signal for the servo motor. 8. Equipment as claimed in any preceding claim, wherein the memory is for storing also tracer operation-defining data and the processor is operable to read out that data to effect tracer control in accordance with a tracing path defined by that data.

Inventors: IMAZEKI, RYOJI, YAMAZAKI, ETUO
Applicants: FANUC LTD
Application year: 1980
Main classification: B23Q35
IPC codes: B23Q35, G05B19