PROFILE CONTROLLER

Abstract: A deceleration control circuit (18) is provided for a profile controller which controls motors (12X to 12Z) relying upon displacement signals (εX to εZ) from a tracer head (1) that traces the surface of a model, in order to control a relative feed between the tracer head and the model, thus making it possible to control the deceleration depending upon the shape of a point where the model changes abruptly. The dec­ eleration control circuit compares a plurality of threshold values with variations of displacement signals (εX to εZ) per unit time, and controls a relative feed speed between the tra­ cer head and the model depending upon to which area deter­ mined by said plurality of threshold values said variations belong.

Description: The present invention relates to improvements in tracer control equipment, and more particularly to tracer control equipment which enables deceleration control at a jerk point in the configuration of a model to be optimum to the configuration of the model at that particular point. In the case of tracing a model M of such a configuration as shown in Fig. 4, if the jerk points (a) to (c) in the configuration of the model are traced at the same speed as that for flat surfaces of the model, a cutter can bite into the workpiece at the jerk point (a) and a stylus ST can move out of contact with the surface of the model M at the jerk points (b) and (c). To avoid this, it is a general practice in the prior art to compare the variation of a deflection signal from a tracer head per unit time with a preset value and reduce the feed rate to a predetermined value while the former is greater than the latter. That is, since the deflection signal from the tracer head undergoes an abrupt change at each jerk point in the configuration of the model and the variation of the deflection signal per unit time also varies abruptly at the jerk point, it is possible to prevent the biting of the cutter into the workpiece and other similar trouble by controlling the feed rate as mentioned above. According to the above-mentioned prior art example, however, when the changing ratio of the deflection signal exceeds a predetermined value, the feed rate is reduced to a predetermined value regardless of the configuration of the model at the jerk point; so that it is impossible to perform optimum deceleration control corresponding to the configuration of the model at the jerk point. Namely, according to the prior art example, the feed rate during deceleration must be set low so that the cutter will not bite into the workpiece even when the stylus traces a sharp corner of the model. Consequently, when deceleration control takes place at a gentle corner portion, the feed rate undergoes an abrupt change, which results in the problem of deterioration of the workpiece surface. Other prior attempts at providing deceleration control at jerk points are disclosed in EP-A-080513 and US-A-3743910. The former employs data defining the positions of jerk points stored in memory, while the latter provides tracer control equipment according to the precharacterising part of the attached claim 1, which changes feed rate according to a predetermined deceleration characteristic. According to the present invention there is provided tracer control equipment for controlling the relative feed rate between a model and a tracer head tracing the surface of the model in accordance with a deflection signal generated by the tracer head, wherein a deceleration control circuit is provided for controlling the feed rate in accordance with the configuration of the model, as indicated by a time derivative of the deflection signal, so that at abrupt corners in the model configuration signalled by an abrupt change in the deflection signal, the feed rate will firstly be reduced as the corner is first encountered, and will be subsequently restored as the corner is traversed, characterised in that the deceleration control circuit comprises comparison means for comparing said time derivative with various successive threshold values, signalling means for providing a distinct signal each time the time derivative rises above one of the threshold values, further signalling means for providing a distinct signal each time the time derivative falls below one of the threshold values, and counting means for counting on the one hand the distinct signals issued by the first-mentioned signalling means when the time derivative increases in value, and on the other hand the distinct signals issued by the further signalling means when the time derivative subsequently decreases in value, the feed rate being reduced and then restored in dependence upon the count in the counting means. Embodiments of the present invention provide an optimum deceleration control corresponding to the configuration of a model at jerk points therein. According to the tracer control equipment of the present invention, the feed rate for deceleration control is determined depending upon which of the regions defined by the plurality of threshold values, the variation of the deflection signal per unit time belongs to. Thus, optimum deceleration control can be achieved corresponding to the configuration of the model at the jerk point. Furthermore, since in a development the deceleration control circuit continues its deceleration control until the variation of the displacement signal becomes smaller than the threshold value of the lowest level again after having exceeded it, deceleration and its removal will not be repeated. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of an embodiment of the present invention; Fig. 2 is a block diagram illustrating an example of the arrangement of a deceleration control circuit 18 of Fig. 1; Fig. 3 is a diagram for explaining the operation of the circuit shown in Fig. 3; and Fig. 4 is a diagram for explaining a defect of a prior art example. Fig. 1 illustrates in block form an embodiment of the present invention. Reference numeral 1 indicates a tracer head, 2 a stylus, 3 a composite deflection signal generator, 4 an adder, 5 and 6 velocity calculation circuits, 7 a distribution circuit, 8 a gate circuit, 9 a change-over-circuit, 10 an indexing circuit, 11X, 11Y and 11Z amplifiers in the X, Y and Z axes, 12X, 12Y and 12Z motors in the X, Y and Z axes, 13 a microprocessor, 14 a memory, 15 an output port, 16 and 17 DA converters, and 18 a deceleration control circuit. The tracer head 1 outputs deflection signals ε X , ε Y and ε Z corresponding to the deflection of the stylus 2 in the X-, Y- and Z-axis directions,which stylus moves in contact with a model. The deflection signals ε X , ε Y and ε Z are provided to the composite deflection signal generator 3, the changeover circuit 9, and the deceleration control circuit 18. The composite deflection signal generator 3 yields a composite deflection signal, ε = √ ε X ² + ε Y ² + ε Z ² , which is applied to the adder 4. The adder 4 obtains a difference, Δε = ε - ε₀, between the composite deflection signal ε and a reference deflection signal ε₀ which is provided via the output port 15 and the DA converter 16. The difference Δε thus obtained is applied to the velocity calculation circuits 5 and 6. Based on the difference Δε, the velocity calculation circuits 5 and 6 obtain a normal-direction velocity signal V N and a tangential-direction velocity signal V T , which are provided to the distribution circuit 7. The changeover circuit 9 supplies the indexing circuit 10 with that one of the deflection signals ε X , ε Y and ε Z from the tracer head 1 which corresponds to the tracing axis. The indexing circuit 10 produces displacement-direction signals sinϑ and cosϑ on the basis of the deflection signals which are applied via the change-over circuit 9. Incidentally, when the plane of tracing is the X-Z plane, the X- and Z-axis deflection signals ε X and ε Z are provided via the change-over circuit 9 to the indexing circuit 10. The distribution circuit 7 generates a velocity command signal, based on the normal-direction and tangential-direction velocity signals V N and V T from the velocity calculation circuits 5 and 6 and the displacement-direction signals sinϑ and cosϑ from the indexing circuit 10. The velocity command signal is applied to the amplifier selected by the gate circuit 8 , and the resulting amplified output drives the corresponding motor, feeding the tracer head 1 and the model relative to each other. Since the above-described operation is well-known as tracer control, no further detailed description thereof will be given. Fig. 2 illustrates in block form an example of the arrangement of the deceleration control circuit 18 which controls the feed rate in accordance with the configuration of the model. Reference numerals 21 to 23 designate differentiation circuits, 24 an arithmetic circuit, 25 to 27 comparators, 28 to 30 rise detectors, 31 to 33 fall detectors, 34 and 35 counters, 36 a comparator, 37 a zero detector, 38 an attenuator, 39 an acceleration/deceleration circuit, 40 a coincidence detector, 41 a comparator, OR1 and OR2 OR gates, and AND an AND gate. The differentiation circuits 21 to 23 in the deceleration control circuit 18 differentiate the deflection signals ε X , ε Y and ε Z which are applied thereto from the tracer head 1, the differentiated outputs being provided to the arithmetic circuit 24. The arithmetic circuit 24 produces a signal, ε' = √ ε X '² + ε Y '² + ε Z '² , based on the output signals ε X ', ε Y ' and ε Z ' from the differentiation circuits 21 to 23. The comparators 25 to 27 compare the output signal ε' from the arithmetic circuit 24 with predetermined threshold values L1, L2 and L3 (where L1 < L2 <L3), respectively, and make their output signals a, b and c "1s" while the output signal ε' from the arithmetic circuit 24 is greater than the respective threshold values. The rise detectors 28 to 30 make their output signals "1s" for only a predetermined period of time T at the rise of the output signals a to c from the comparators 25 to 27, respectivley. The fall detectors 31 to 33 make their output signals "1s" for only the predetermined period of time T at the fall of the output signals a to c from the comparators 25 to 27, respectively. The counter 34 increments its count value CA by one each time the output signal d of the OR gate OR1 (which ORs the output signals from the rise detectors 28 to 30) goes to a "1", and it is reset when the output signal i of the AND gate AND goes to a "1"; namely, its count value CA is made a "0". The counter 35 increments its count value CB by one each time the output signal d of the OR gate OR1 which is applied to its + terminal goes to a "1", and it decrements its count value CB by one each time the output signal e of the OR gate OR2 (which is applied to its - terminal) goes to a "1". The comparator, 36 compares the count values CA and CB of the counters 34 and 35 and makes its output signal f a "1" when the condition CA > CB is satisfied. The zero detector 37 makes its output signal g a "1" when the count value CB of the counter 35 is a "0". The attenuator 38 attenuates a velocity command signal Vcmd which is provided thereto via the DA converter 17 from the microprocessor 13, with an attenuation factor corresponding to the count value CA of the counter 34 (which attenuation factor is zero when the count value is a "0", and increases as the count value CA increases). The acceleration/deceleration circuit 39 operates as a filter with a time constant τ₁ when the output signal k of the comparator 41 is a "1" and, as a filter with a time constant τ₂ (where τ₂ >> τ₁) when the output signal k is a "0", the output signal Vb being applied to the velocity calculation circuit 6. The comparator 41 compares the output signal Va of the attenuator 38 and the output signal Vb of the acceleration/deceleration circuit 39 and makes its output signal k a "1" while Vb > Va. Accordingly, the acceleration/deceleration circuit 39 operates as the filter with the time constant τ₁ during deceleration and as the filter with the time constant τ₂ during tracing at the normal feed rate. The coincidence detector 40 makes its output signal h a "1" when detecting coincidence between the output signal Va of the attenuator 38 and the output signal Vb of the acceleration/deceleration circuit 39. The velocity calculation circuit 6 varies its input/output characteristic in accordance with the level of the output signal Vb from the acceleration/deceleration circuit 39 in such a manner that the lower the level of the signal Vb becomes, the more the output level (the tangential-direction velocity signal V T ) for the same input level is lowered. Accordingly, assuming that the stylus has reached a jerk point in the configuration of the model, for example, at a time t1, the output signal ε' of the arithmetic circuit 24 abruptly rises in level at the time t1, as shown in Fig. 3(A). In response to this, the output signals a to c of the comparators 25 to 27 go to "1s" in succession, as depicted in Figs. 3(B) to (D), with the result that the output signal d of the OR gate OR1 (which ORs the output signals of the rise detectors 28 to 30) goes to a "1" at the rise of each of the signals a to c, as shown in Fig. 3(E). As the output signal d of the OR gate OR1 undergoes such variations as depicted in Fig. 3(E), the count values CA and CB of the counters 34 and 35 are gradually incremented in the order "0", "1", ... , as shown in Figs. 3(G) and (H), respectively. The increase in the count value CA of the counter 34 increases the attenuation factor of the attenuator 38, and consequently its output signal Va diminishes stepwise, as indicated by the solid line in Fig. 3(K). At the same time, the output signal Vb of the acceleration/deceleration circuit 39 also gradually diminishes from the level Vcmd, with the time constant τ₁, as indicated by the broken line in Fig. 3(K). As a result of this, the level of the tangential-direction velocity signal V T , which is provided from the velocity calculation circuit 6, drops in proportion to the decrease in the level of the output signal Vb of the acceleration/deceleration circuit 39, thus decreasing the feed rate. Then, when the output signal ε' of the arithmetic circuit 24 diminishes, the output signals c, b and a of the comparators 27, 26 and 25 go to "0s" in succession, as depicted in Figs. 3(D), (C) and (B), respectively. In consequence, the output signal e of the OR gate OR2, which ORs the output signals of the fall detectors 31 to 33, goes to a "1" at the fall of each of the signals c to a, as shown in Fig. 3(F). As the output signal e of the OR gate OR2 varies, as shown in Fig. 3(F), the count value CB of the counter 35 gradually decreases, as depicted in Fig. 3(H). When the count value CB has reached "2", the output f of the comparator 36 goes to a "1", as depicted in Fig. 3(I), and when the count value CB has reached "0" (at a time t2), the output signal g of the zero detector 37 goes to a "1", as shown in Fig. 3(J). When the output signal g of the zero detector 37 has thus risen to the "1" level at the time t2, the output signal i of the AND gate AND, by which are ANDed the output signal f of the comparator 36, the output signal g of the zero detector 37, and the output signal h of the coincidence detector 40, shown in Figs. 3(I), (J) and (L), respectively, goes to a "1", as depicted in Fig. 3(M). The output signals i resets the counter 34 to make its count value CA a "0", in consequence of which the attenuation factor of the attenuator 38 is reduced to zero and its output signal Va assumes the level Vcmd, as indicated by the solid line in Fig. 3(K). Furthermore, the increase in the level of the output signal Va of the attenuator 38 causes an increase in the level of the output signal Vb of the acceleration/deceleration circuit 39, as indicated by the broken line in Fig. 3(K). In this case, however, since Va > Vb and the output signal k of the comparator 41 remains at the "0" level, the signal Va gradually increases with the time constant τ₂. Then, as the level of the output signal Vb of the acceleration/deceleration circuit 39 rises, the level of the tangential-direction velocity signal V T from the velocity calculation circuit 6 rises, ceasing deceleration control. As described above, according to this embodiment, since the output signal ε' of the airthmetic circuit 24 is compared with the plurality of threshold values L1 to L3 (where L1 < L2 < L3) and the feed rate is reduced to a value corresponding to the level of the signal ε', it is possible to perform optimum deceleration control corresponding to the configuration of the model at a jerk point therein. Moreover, once the signal ε' exceeds the threshold value L, the deceleration control is continued until the signal ε' returns to the threshold value L1, and consequently deceleration and its removal will not be repeated during deceleration control. While in the above embodiment the threshold values are described to be three, i.e. L1 to L3, they are not limited specifically thereto as long as they are plural. As described above, the present embodiment of the invention is provided with detecting means (which comprises the differentiation circuits 21 to 23 and the arithmetic circuit 24 in the embodiment) for detecting the variation of a displacement signal from the tracer head per unit time, decision means (which comprises the comparators 25 to 27 in the embodiment) for comparing the detected variation of the displacement signal and a plurality of threshold values of different levels and deciding which of regions defined by the threshold values the detected variation of the displacement signal belongs to, and deceleration control circuitry (which comprises the rise and fall detectors 28 to 33, the OR gates OR1 and OR2, the counters 34 and 35, the comparator 36, the zero detector 37, the AND gate AND, and the attenuator 38) whereby the relative feed rate between the tracer head and a model is reduced to and held at a value corresponding to the result of decision by the decision means during a period from the time when the variation of the displacement signal is decided by the decision means to have exceeded the threshold value of a level lower than those of the other threshold values to the time when it is decided to have returned to a value smaller than the threshold value of the lowest level. Since the feed rate during deceleration can be changed in accordance with the variation of the displacement signal per unit time, that is, according to the configuration of the model at a jerk point therein, the present invention possesses the advantage that optimum deceleration control can be effected in accordance with the configuration of the model at the jerk point. Furthermore, since the deceleration control means continues deceleration control over the entire period from the time when the variation of the displacement signal exceeds the threshold value of a level lower than those of the other threshold values to the time when it returns to a value smaller than the threshold value of the lowest level, the present invention has another advantage that deceleration and its removal will not be repeated during deceleration control.

Claims: Tracer control equipment for controlling the relative feed rate between a model and a tracer head (1) tracing the surface of the model in accordance with a deflection signal (ε) generated by the tracer head (1), wherein a deceleration control circuit (18) is provided for controlling the feed rate in accordance with the configuration of the model, as indicated by a time derivative (ε') of the deflection signal (ε), so that at abrupt corners in the model configuration signalled by an abrupt change in the deflection signal (ε), the feed rate will firstly be reduced as the corner is first encountered, and will be subsequently restored as the corner is traversed, characterised in that the deceleration control circuit comprises comparison means (25,26,27) for comparing said time derivative (ε') with various successive threshold values (L1,L2,L3), signalling means (28,29,30,OR1) for providing a distinct signal each time the time derivative (ε') rises above one of the threshold values (L1,L2,L3), further signalling means (31,32,33,OR2) for providing a distinct signal each time the time derivative (ε') falls below one of the threshold values (L1,L2,L3), and counting means (34,35) for counting on the one hand the distinct signals issued by the first-mentioned signalling means (28,29,30,OR1) when the time derivative (ε') increases in value, and on the other hand the distinct signals issued by the further signalling means (31,32,33,OR2) when the time derivative (ε') subsequently decreases in value, the feed rate being reduced and then restored in dependence upon the count in the counting means (34,35). Tracer control equipment according to claim 1, wherein said counting means (34,35) comprises a first counter (34) for counting the distinct signals issued by said first-mentioned signalling means (28,29,30,OR1) when said time derivative increases in value, and a second counter (35) for counting the distinct signals used by said further signalling means (31,32,33,OR2) when said time derivative subsequently decreases in value, the feed rate is reduced in dependence upon the count in the first counter (34) increasing, and is then restored in dependence upon the count in the second counter (35). Tracer control equipment according to claim 2, wherein each of the first and second counters (34 and 35) is arranged to count up the distinct signals issued by said first-mentioned signalling means (28,29,30,OR1) when said time derivative increases in value, the second counter is arranged then to count down the distinct signals issued by said further signalling means (31,32,33,OR2) when said time derivative subsequently decreases in value, and the first counter (34) is arranged to be reset when the second counter (35) has counted down to zero, it being the content of the first counter (24) which controls the feed rate as aforesaid, so that when it is reset the feed rate is thereby restored by means of a single step. Tracer control equipment according to any preceding claim, wherein the first-mentioned signalling means comprises a plurality of rise detectors (28,29,30) having inputs connected to the comparison means (25,26,27) and outputs connected to inputs of an OR gate (OR1), and the further signalling means comprises a plurality of fall detectors (31,32,33) having inputs connected to the comparison means (25,26,27) and outputs connected to inputs of an OR gate (OR2). Tracer control equipment according to any preceding claim, wherein the feed rate is reduced and then restored by means of an attenuator (38) controlled by the counting means (34,35).

Inventors: YAMAZAKI, ETUO
Applicants: FANUC LTD.
Application year: 1986
Main classification: B23Q33
IPC codes: B23Q35, B23Q33