SYSTEM FOR CONTROLLING PROFILING OPERATION IN ARBITRARY DIRECTION

Abstract: In a system for controlling a profiling operation in an arbitrary direction, in which a model and a tracer head are moved relatively at an arbitrary angle with respect to a refer­ ence axis X, a reference point K is determined with respect to the model, and first and second profiling borders L1, L2 at which the profiling operation is turned back are determined, the profiling direction being always set on the radial lines a-b, c-d, e-f, g-h extending from the reference point K. Pre-­ determined quantities of pick feed operations b-c, f-g are car­ ried out on the profiling borders L1, L2 so as to make profiling feed actions always in the direction which is at right angles to the curved surfaces of the model, whereby the curved sur­ faces can be profiled with a high accuracy.

Description: The present invention relates to improvements in or relating to arbitrary-direction tracer control which permits free setting of the direction in which a tracer head and a model are fed relative to each other, and more particularly to an arbitrary-direction tracer control method which enables highly accurate tracing of a model with a curved surface. Heretofore there has been proposed an arbitrary-direction tracer control system which makes it possible to feed a tracer head and a model relative to each other at an arbitrary angle to the X- or Y-axis (EP-A-0015650). By such setting of the direction of feed at an arbitrary angle to the X- or Y-axis, even four corners of a square model could be traced with high accuracy. Even with the arbitray-direction tracer control system, however, there are cases where models cannot be traced with high accuracy according to their configurations. For example, assuming that a model M, whose cross-sectional and top plan views are shown in Figs. 8(A) and (B), is traced along a path depicted in Fig. 8(B), portions (a) to (d) of the model M where the angle between its curved surfaces and the path is small cannot be traced with high accuracy because the tracer head yields only small displacement signals in these portions. The present invention offers a solution to the above-noted problem and has for its object to permit highly accurate tracing of a model with curved surfaces. According to the present invention there is provided an arbitrary-direction tracer control method in which relative movement takes place between a model and a tracer head in a 2-d tracing plane OXY of a 3-d coordinate system OXYZ, the relative movement taking place initially at an arbitrary angle to the X-axis; the method comprising inputting the coordinate values of a reference point in the OXY plane, setting first and second tracing stroke limits from where tracing feed is returned, and controlling the relative movement of the model and the tracer head, wherein the tracer head is moved from the first tracing stroke limit to the second one along a first tracing path extending along a line which passes through the reference point and has a first angle to the X-axis, when the tracer head reaches the second tracing stroke limit a predetermined amount of pick feed is carried out transversely to the first tracing path, upon completion of the pick feed the tracer head is moved back to the first tracing stroke limit along a second tracing path extending along a line joining the current position of the tracer head after the pick feed and the reference point, and when the tracer head reaches the first tracing stroke limit it is moved along a third tracing path extending along a line which passes through the reference point and has a predetermined angle to the second tracing path, tracing being repeated in this manner between the first and second tracing stroke limits until this mode of tracing is complete. In the case of tracing a model with a curved surface, for instance a hemispherical model, the coordinate value of the center of the model is input as the coordinate value of the reference point through input means, the first tracing stroke limit is set as the reference point by setting means, and the second tracing stroke limit is set to be a curve parallel to the perimeter of the model. This ensures that tracing feed is always performed at right angles to the curved surface of the model, enabling the curved surface to be traced with a high degree of accuracy. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a tracer controller embodying the present invention; Figs. 2, 4, 6 and 7 are plan views showing tracing paths in different methods of the present invention; Figs. 3 and 5 are flowcharts showing the contents of processing by a microprocessor 15; and Fig. 8 is a diagram explanatory of a prior art example. Fig. 1 is a block diagram illustrating the arrangement of a tracer controller embodying the method of the present invention. Reference numeral 1 indicates a tracer head, 2 a stylus, 3 a composite displacement (ie deflection) signal generator, 4 an adder, 5 and 6 velocity signal generators for generating normal-direction and tangential-direction velocity signals V N and V T , 7 a distribution circuit, 8 and 12 coordinate transformers, 9X to 9Z X- to Z-axis servo drive circuits, 10X to 10Z X- to Z-axis motors, 11X to 11Z X- to Z-axis position sensors, 13 an indexing circuit, 14X to 14Z counters, 15 a microprocessor, 16 a memory, 17 a keyboard, 18 an output port, and 19 to 21 DA converters. The velocity signal generator 6 yields the tangential-direction velocity signal V T with a sign + or - depending upon whether a signal a which is applied thereto via the output port 18 is "high" or "low". That is, the tracer feed direction can be changed 180 degrees depending upon whether the signal a is made "high" or "low". Displacement (ie deflection) signals ε x , ε y and ε z from the tracer head 1 are provided to the composite displacement signal generator 3, from which the displacement signals ε x and ε y are applied to the coordinate transformer 12 and the displacement signal ε z is applied to the indexing circuit 13. The composite displacement signal generator 3 produces a composite displacement signal, ε = √ ε x ² + ε y ² + ε z ² , which is provided to the adder 4. The adder 4 obtains the difference, Δε = ε - ε₀ , between the composite displacement signal ε and a reference displacement signal ε₀ which is applied thereto via the DA converter 21 from the microprocessor 15, the difference thus obtained being provided to the velocity signal generators 5 and 6. The velocity signal generator 5 produces the normal-direction velocity signal V N on the basis of the difference Δε, and the velocity signal generator 6 produces the tangential-direction velocity signal V T on the bases of the difference Δε and the signal a . The coordinate transformer 12 creates signals ε α and ε α+90° given by the following expressions (1) and (2), on the bases of the displacement signals ε x and ε y from the tracer head 1 and signals cosα and sinα which are applied from the microprocessor 15 via the DA converters 19 and 20, respectively. In the above α is the angle between the tracer feed direction and the X-axis. For example, a coordinate transformer 22 set forth in EP-A-0015650 can be employed as the coordinate transformer 12. When a signal b which is applied thereto via the output port 18 from the microprocessor 15 is "high", the indexing circuit 13 indexes an angle of displacement β in a plane containing an axis which forms an angle α with the X-axis and the Z-axis, on the bases of the displacement signal ε z from the tracer head 1 and the signal E α from the coordinate transformer 12, and yields a cosine signal cosβ and a sine signal sinβ in the direction of displacement which are given by the following expressions (3) and (4). When the signal b is "low", the indexing circuit 13 indexes the angle of displacement β in a plane containing an axis which forms an angle (α + 90°) with the X-axis and the Z-axis, on the bases of the displacement signal ε z and the signal ε α+90° from the coordinate transformer 12, and yields a cosine signal cosβ and a sine signal sinβ which are given by the following expressions (5) and (6). cosβ = ε α ² ÷ (ε α ² + ε z ²) (3) sinβ = ε z ² ÷ (ε α ² + ε z ²) (4) cosβ = ε α+90° ² ÷ (ε α+90° ² + ε z ²) (5) sinβ = ε z ² ÷ (ε α+90° ² + ε z ²) (6) The distribution circuit 7 creates a velocity signal V α in the tracer feed direction and a velocity signal V z in the Z-axis direction on the bases of the velocity signals V N and V T from the velocity signal generators 5 and 6 and the output signals coss and sinβ from the indexing circuit 13. The velocity signal V z in the Z-axis direction is applied to the servo drive circuit 9Z, by the output of which the motor 10Z is driven. The velocity signal V α in the tracer feed direction is applied to the coordinate transformer 8, which in turn produces velocity signals V x = V α · cosα and V y = V α · sinα in the X- and Y-axis directions. The velocity signals V x and V y in the X- and Y-axis directions are provided to the servo drive circuits 9X and 9Y, the output signals from which are applied to the motors 10x and 10Y to drive them, feeding the tracer in the tracer feed direction. A coordinate transformer 23 used in EP-A-0015650 can be employed as the coordinate transformer 8. The position sensors 11X to 11Z yield a + pulse each time the motors 10X to 10Z rotate through a predetermined angle in the forward direction, and yield a - pulse each time the motors 10X to 10Z rotate through a predetermined angle in the backward direction. The counters 14X to 14Z are each incremented by one upon each application of the + pulse and decremented by one upon each application of the - pulse. In short, the count values of the counters 14X to 14Z indicate the X-, Y- and Z-coordinates of the current position of the tracer head 1, respectively. Fig. 2 is a plan view showing the tracing path along which was traced the model M of the same configuration as the model M depicted in Figs. 8(A) and (B). In Fig. 2, reference character L indicates a tracing stroke limit where the tracing stroke is returned, and K a reference point (which is the center of curvature of the model M, in this case, and the coordinate value of which is input from the keyboard 17 in advance). The tracing stroke limit L is set by, for instance, attaching a potential wire on the model surface, or inputting from the keyboard 17 an equation corresponding to the tracing stroke limit L. Fig. 3 is a flowchart showing the contents of processing by the microprocessor 15 in the case of employing the cutting path depicted in Fig. 2. The tracing operation will hereinbelow be described with reference to Fig.3. When directed to start its processing, the microprocessor 15 first applies the signals cosα₀ and sinα₀ to the coordinate transformers 8 and 12 via the DA converters 19 and 20 (steps S1 and S2). Here, α₀ is the angle between the tracer feed direction and the X-axis, which angle is calculated from the coordinate values of the current position of the tracer head 1 and the reference point K and is prestored in the memory 16. Next, the microprocessor 15 provides a control signal to the output port 18 to make its output signals a and b "high" (steps S3 and S4) and then starts tracing (step S5). In this way, tracing along a path K - a is initiated. When it is detected from the count values of the counters 14X and 14Y that the tracer head 1 has reached the tracing stroke limit L (step S6), the microprocessor 15 applies a control signal to the output port 18 to make its output signal b "low" (step S7). By this, the tracer feed direction is changed 90 degrees, and then a pick feed is carried out along a path a - b. When it is detected from the count values of the counters 14X and 14Y that the pick feed has been effected by a predetermined amount (a predetermined angle α₁, for instance) (step S8), the microprocessor 15 outputs signals cos(α₀ + α₁) and sin(α₀ + α₁) (step S10) and then provides a control signal to the output port 18 to make its output signals a and b "low" and "high", respectively (steps S11 and S12). By this, tracing along a path b - K is performed. Then, when it is detected from the count values of the counters 14X and 14Y that the tracer head 1 has reached the reference point K (the center of curvature of the model M, in this instance), the microprocessor decides whether the tracing has ended or not (step S14). In this case, since the result of decision in step S14 is "NO", the microprocessor 15 outputs signals cos(α₀ + 2α₁) and sin(α₀ + 2α₁) (steps S15 and S16) and then applies a control signal to the output port 18, making its output signal a "high". As a result of this, tracing is carried out along a path K - c. Thereafter, the microprocessor 15 repeats the processing of each of steps S6 to S17 until the tracing has been completed. As described above, this method ensures tracing in the direction perpendicular to the curved surface of the model M at all times, and hence permits highly accurate tracing of the model M. Fig. 4 is a plan view showing the path for tracing a doughnutshaped model M according to a method of the present invention. In Fig. 4, reference characters L1 and L2 indicate tracing stroke limits where the tracing stroke is returned, and K a reference point (the center of curvature of the model M, in this case). Fig. 5 is a flowchart showing the contents of processing by the microprocessor 15 in this instance. The tracing operation will hereinbelow be described in respect of Fig. 5. When directed to start its processing, the microprocessor 15 applies the signals cosα₀ and sinα₀ to the coordinate transformers 8 and 12 via the DA converters 19 and 20 (steps S51 and S52) and provides a control signal to the outpout port 18 to make its output signals a and b "high" (steps S53 and S54), thereafter initiating the tracing (step S55). By this, the tracing is performed along a path a - b. When it is detected from the count values of the counters 14X and 14Y that the tracer head 1 has reached the tracing stroke limit L1 (step S56), the microprocessor 15 provides a control signal to the output port 18 to make its output signal b "low" (step S57). By this, a pick feed is carried out along a path b - c. When it is detected from the count values of the counters 14X and 14Y that the pick feed has been effected by a predetermined amount (a predetermined angle α₁ in this case) (step S58), the microprocessor 15 yields the signals cos(α₀ + α₁) and sin(α₀ + α₁) (steps S59 and S60) and applies a control signal to the output port 18, making its output signals a and b "low" and "high", respectively (steps S61 and S62). By this, the tracing is performed along a path c - d. When it is detected from the count values of the counters 14X and 14Y that the tracer head 1 has reached the tracing stroke limit L2 (step S63), the microprocessor 15 decades whether the tracing has been completed or not (step S64). In this instance, since the result of decision in step S64 is "NO", the microprocessor 15 provides a control signal to the output port 18 to make its output signal b "low". As a result of this, a pick feed takes place along a path d - e. When it is detected from the count values of the counters 14X and 14Y that the pick feed has been carried out by a predetermined amount (the predetermined angle α₁ in this case) (step S66), the microprocessor 15 yields the signals cos(α₀ + 2α₁) and sin(α₀ + 2α₁) (steps S67 and S68) and applies a control signal to the output port 18 to make its output signals a and b "high" (steps S69 and S70). In consequence, the tracing is performed along a path e - f. Following this, the microprocessor 15 repeats the processing of each of steps S56 to S70 until the tracing has been completed. As described above, according to this method, the tracing of the model M always takes place in the direction perpendicular to its curved surface, and hence is highly accurate. Also in the case of tracing a model M of such a configuration as shown in Fig. 6, the tracing feed can always be held perpendicular to the curved surface of the model M, by setting the tracing stroke limits L1 and L2 and the reference point K and executing the processes shown in the flow-chart of Fig. 5. Furthermore, a model M whose curved surface meanders in the X-Y plane as shown in Fig. 7 can also be traced continuously and accurately, by prestoring first and second reference points K1 and K2 and first and second incremental angles α₁ and α₂ in the memory 16 and switching between the reference points and between the incremental angles at the bending point A. While in the above-described methods the pick feed is performed in terms of a predetermined angle, alternatively it may also be effected in terms of distance, of course. As described above, according to the present invention, the tracing feed direction can always be held perpendicular to the curved surface of a model simply by setting a refernce point (the center of curvature in the embodiments) and a tracing stroke limit, and accordingly, the model with the curved surface can be traced with a high degree of accuracy.

Claims: An arbitrary-direction tracer control method in which relative movement takes place between a model (M) and a tracer head (1) in a 2-d tracing plane OXY of a 3-d coordinate system OXYZ, the relative movement taking place initially at an arbitrary angle (α₀) to the X-axis; the method comprising inputting the coordinate values of a reference point (K) in the OXY plane, setting first (K,L) and second (L2,L1) tracing stroke limits from where tracing feed is returned, and controlling the relative movement of the model (M) and the tracer head (1), wherein the tracer head (1) is moved from the first tracing stroke limit (K or L2) to the second one (L or L1) along a first tracing path extending along a line which passes through the reference point (K) and has a first angle (α₀) to the X-axis, when the tracer head (1) reaches the second tracing stroke limit (L or L1) a predetermined amount of pick feed is carried out transversely to the first tracing path, upon completion of the pick feed the tracer head (1) is moved back to the first tracing stroke limit (K or L2) along a second tracing path extending along a line joining the current position of the tracer head (1) after the pick feed and the reference point (K), and when the tracer head (1) reaches the first tracing stroke limit (K or L2) it is moved along a third tracing path extending along a line which passes through the reference point (K) and has a predetermined angle (α₁) to the second tracing path, tracing being repeated in this manner between the first (K,L) and second (L2,L1) tracing stroke limits until this mode of tracing is complete.

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