JPS6260222B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a copying control device.

In conventional tracing control devices, a stylus moves along and in contact with a model having a predetermined contour. When this stylus comes into contact with the above model and is displaced, a composite value of two-dimensional or three-dimensional normal vector component signals generated by a normal vector signal generator mechanically connected to the stylus and representing the above displacement of the stylus is generated. It is controlled to be equal to a reference displacement amount given from the outside, and the direction of movement of the stylus is determined by the ratio of the component signals. The speed at which the stylus moves is determined by a reference tangential velocity for the stylus model that is separately given from the outside. A vector in which each component ratio is equal to the above-mentioned ratio and whose composite value is equal to the above-mentioned reference tangential velocity is the tool speed vector. First, a conventional copying device will be explained with reference to FIGS. 1, 2, 3, and 4. FIG. 1A illustrates the movement of a stylus S around a model M.
The stylus S is moving along the contour M2 of the model M in the XY plane, and is moving along the contour M1 of the model M in the Z direction. FIG. 1B shows a workpiece W, and shows how a tool T (an end mill in FIG. 1B) having the same shape as the stylus S moves while cutting the workpiece W. In the copying device, the reference point of the stylus S and the reference point of the tool T are relatively fixed, and the relative positions of the model M and the workpiece W are determined in the same way as the relative positions of S and T. ing. Therefore, when the stylus S is moved along the model M, the tool T will be moved along the material W, and since its movement trajectory is equal to the movement trajectory of S, the cutting effect obtained while T is moving Machining into a shape corresponding to model M is performed on W, and "copying" is performed.

FIG. 2 is a diagram showing an example of a conventional tracer head that generates signals for controlling movement of a stylus S. In Fig. 2A, the outer cylinder B2 is equipped with a differential transformer (movable iron core AZ, coil CZ) for detecting displacement in the Z direction, and an inner cylinder B1, so that B2 itself can be attached to a separate support structure. It's summery. The inner cylinder B1 is attached to B2 via the ball BL and is restrained so that it cannot be displaced in the XY plane, but in the Z direction, a spring L3
displacement is possible until it is balanced. Inside the inner cylinder B1, there is an arm R that can be tilted about a fulcrum P by means of a lever spring L1 and a bellows L2.
An iron core E, which forms part of a detector that detects displacement in the XY plane in the A' section, is attached. When the stylus S contacts the model, an external force is applied to the stylus S. Its Z component displaces the stylus S in the Z direction until it balances with the spring L3, and this displacement is equal to the displacement of the movable iron core AZ. In this way, a displacement component signal of the stylus S in the Z direction is obtained from the coil CZ. The XY components of the external force tilt the stylus S about the fulcrum P until it is balanced with the bar spring L1. The tilt of the stylus S is expressed as a displacement of the movable iron core E in the XY plane. In FIG. 2B, around the iron core E there are iron cores AX and AX' on the X axis, and iron cores AY and AY' on the Y axis, each having coils CX and CY. Iron core E and AX, AX', and CX constitute a first differential transformer, and iron core E and AY, AY', and CY constitute a second differential transformer. Thus, the iron core E
According to the displacement of coils CX and CY,
A displacement component signal in the direction is obtained.

FIG. 3 is a diagram illustrating a configuration example of a conventional copying apparatus using the tracer head of FIG. 2. As an example of the operation of the copying device, a synthetic three-dimensional copying operation of the XY plane contour and the Z axis will be described below. A tracer head TH, which has a signal detection section equipped with displacement detection coils CX, CY, and CZ, and a stylus S, is fixed to a table TZ together with a spindle head SP for rotating a tool T. Table TZ is moved in the Z direction by feed motor MZ. Furthermore, the model M and the workpiece W are fixed on the table TY. Table TY is provided on table TX and can be moved in the Y direction and X direction by feed motors MY and MX, respectively. As a result,
The stylus S and tool T can move in the Z direction,
Since the model M and the material W can move in the XY plane, the stylus S is relative to the model M, and the tool T is relative to the material W in X, Y, Z3.
Can move dimensions.

Now, the signals eX, eY, and eZ indicating the displacement of the components are obtained from the coils CX, CY, and CZ, and the control circuit
Guided by CL. An example of an explanation of such a circuit CL is "Automatic Control of Machine Tools" by Den Mochizuki, published by Sanpo Publishing.
It is shown in the control mechanism and related explanatory text on page 197, or the control mechanism and related explanatory text on page 578 of Automatic Control Express, edited by Automatic Control Study Group, Corona Publishing, etc.

Now, the reference displacement amount Δ and the reference tangential velocity Fe are given to the control circuit CL from the outside. In other words, in the composite three-dimensional scanning of the
The deviation amount in the Z direction is 0), and the combined feed rate in the XYZ directions indicates Fc. When the signals ex and ey are generated, the stylus S is tilted along the normal direction NOR with respect to the model M, as explained using FIG. The stylus S is in contact with the model M at the contour M', and the iron core E is displaced via the fulcrum P in Fig. 2, and displacement component signals ex and ey are obtained from the detection coils CX and CY according to the inclination. It is.

The circuit CL is designed for ^the X-axis, Y- ^axis , and Signals to axis motor drive circuit Rx, Ry is being applied. K ₁ is a constant. Based on this applied signal, circuits Px, Py are connected to feed motors Mx, My
As a result, the position of the stylus S is corrected with respect to the model M along the normal NOR direction in FIG. In response to this position correction, ex and ey change, and thus (1) is maintained.

Next, the reference tangential velocity Fc of the stylus S is determined by the circuit
CL, the stylus S is controlled to move in the direction of the tangent line TAN in FIG. 4 at component velocities of Fx and Fy in FIG. In this case, Z
If the component velocity in the axial direction is Fz, then Fc=√ ² + ² + ² ...(4) is required. From (2), the resultant velocity in the x, y plane is √ ² + ² = √ ² − ² ...(5) and Fx:Fy=ey:-ex ...(6) (in the case of Fig. 4) The circuit CL is for the motor drive circuit Px, Py. Apply a signal accordingly. Note that the component velocity Fz is given as follows. In other words, the displacement component signal
The circuit CL applies a Z-axis motor drive circuit Pz signal (O-K ₁ ez) so that Fz=O-K ₁ ez is established according to ez.

As a result, the feed rate component Fz of the stylus S in the Z direction becomes -K ₁ ez. After all, in the copying device shown in Fig. 3, the movement vector component signals of the stylus S are applied to the motor drive circuits Px, Py, and Pz.
SX, SY, SZ are respectively, sz=-KAez...(11) The first term of SX, SY is the component of the tangential velocity vector of size √ ² - ( ₁ ^{2 2} ) in the X, Y plane of the stylus S, and the second term is the component of the tangential velocity vector of the stylus S in the X, Y plane. S is the reference displacement amount Δ
It shows the components of the normal velocity vector to maintain a displacement of the magnitude of .

As described above, the stylus S can trace the model M at the standard tangential velocity Fc while maintaining the standard displacement amount Δ in the normal direction within the XY plane. The shortcomings of the conventional devices exemplified above are summarized as follows. () Poor accuracy or low feed rate. As is well known, an example of the characteristics of a feed control system consisting of a motor drive and a feed motor for obtaining a good machined surface is a first-order lag characteristic with respect to the command speed as shown in FIG. It is especially important that there is no overshoot (excessive response).

Also, at this time, a following error (positional deviation) (hereinafter referred to as droop) occurs that is proportional to the feed rate, and the relationship is known as feed rate = KS x droop (12). Here, KS is a gain indicating the characteristics of the servo system and has a dimension of [1/time].

Droop is the difference between the command position obtained by integrating the command speed over time and the response position obtained by integrating the response speed over time, and has the dimension of [length]. A large droop corresponds to poor accuracy, and a small (KS x droop) corresponds to a low feed rate. A low feed rate indicates low productivity and, in reality, is not economical. For this reason, in the past, when implementing copying that placed emphasis on accuracy, one had no choice but to endure low productivity, and when emphasis was placed on productivity, it was unavoidable to sacrifice accuracy.

On the other hand, an example of an effort to get as close to NC as possible was to introduce a feed control system with a large gain KS.

However, the large feed control system of the KS had the disadvantage that the motor drive circuit was complex and expensive. Mata KS
A large value indicates that the feed control system is easily affected by mechanical vibration during cutting, so depending on the cutting conditions and resonance characteristics of the mechanical system, the great features of KS may not be fully utilized.

It has been said that even with such efforts, copying control is inevitably inferior to NC in terms of accuracy and productivity. Here, the reason why a feed control system with a normal NC value of KS can achieve good accuracy or high productivity will be explained with reference to FIGS. 9 and 10. Figure 6 shows the command position PC and response position in NC.
It is a figure showing the relationship of PR. In NC, the position
The PC's NC calculation unit calculates every moment along the curve CV1 to be tracked. And position PC is always position PR
is ahead of The difference between position PC and position PR is X
Droop X component DX, Y in axis and Y axis direction respectively
Indicated by the component DY. (This vector is DV).

Position PR indicates the position of the tool. Position PC corresponds to the predicted position of position PR. Simply put
Since NC is a method in which the position PR always follows the position PC, the accuracy is good even if the droop is large to some extent.

On the other hand, the case of tracing control will be explained with reference to FIGS. 7A and 7B. CV2 indicates a curve that conforms to the model.
PP indicates the stylus position. The signal obtained by the tracer bed depending on the position of this stylus
Vector SV indicating the direction and movement speed of the stylus position PR by ex, ey, es (omitted in Figure 7)
is obtained (the components of SV are given by equations 9 and 10). The position PP plays the role of the position PC in FIG.

On the other hand, the tool position PT is a position moved by the vector SV, and the curve CV3 is the locus of the tool position PT, which is obtained by moving the curve CV2 in parallel. The tool position PT corresponds to the response position PR in FIG. Therefore, when CV2 and CV3 are overlapped, Figure 7B
It will be like this. In other words, the curve CV2 (=CV3)
Above, position PP and position PT overlap. CV1 and
In the case of a curve with constant curvature such as CV2 (=CV3), vector DV in Figure 6 and vector SV in Figure 7
are almost the same, and in this case, NC and copying control can achieve almost the same accuracy and productivity.

However, let us consider a case as shown in FIG. FIG. 8A is a diagram showing the relationship between the position PR tracing the curves CV4 and CV5 and the vector DV, and corresponds to the case of NC. Figure 8B shows the position following curves CV4 and CV5.
This is a diagram showing the relationship between PT and vector SV, and corresponds to the case of copying control. In part 1, position PR is position
Vector DV corresponds to PT, and vector DV corresponds to vector SV, and can be equal to each other. However, in Part 2, Vector DS and Vector SV are very different.

As a result, as shown in Figure 9, the curves CV6 and CV
7. The locus of the position PT tracing the contour consisting of CV8 looks like a broken line depending on the direction of the tracing. Significant overshooting or digging occurs as shown by the hatch. On the other hand, in the case of NC, part 2 of Figure 8A
As shown in Figure 5, the direction of the vector DV changes as it moves from curve CV4 to curve CV5, so the position PR is determined by the primary feed characteristics of the feed control system (see Figure 5).
follows curve CV4 with high fidelity and moves to curve CV5. That is, when the vector DV is large (the feed speed is large), the position PR passes near the end point of the curve CV4 (the starting point of the curve CV5) and has a somewhat "rounded corner", but its value is very small. 8th
As shown in the figure, the difference between the vectors DV and SV is that DV has predictability and SV does not. This difference is the reason why profiling control is said to be less accurate or less productive than NC.

An object of the present invention is to propose a new method that eliminates the drawbacks of such tracing control.

The configuration of the tracer head and related circuits of the present invention adds predictability to the stylus movement vector SV compared to the conventional tracer head, so that the stylus contacts the model while maintaining a predetermined deviation amount and moves parallel to the tip of the vector SV. It has a movement mechanism.

The effects of the present invention are that by simply adding simple means to the conventional tracer head and copying device, the above-mentioned drawbacks of copying control can be eliminated, and the accuracy and productivity of copying control can be improved.
The aim is to dramatically improve it to the same level as NC.

The effect of the tracer head shown in Figure 11 is
This is also noticeable when tracing a complex model using so-called 2-dimensional NC + 1-dimensional scanning control, in which the trajectory of the Y plane is NC and vertical changes are controlled using scanning control. That is, the stylus can be advanced by a two-dimensional droop component (see FIG. 6) by utilizing the stylus movement mechanism. By doing this, the vertical deviation detection signal for one-dimensional scanning control becomes a signal equivalent to the droop in three-dimensional NC, so Z controlled by this signal.
The accuracy and productivity of 2D + 1D scanning control that takes the axes into account is as high as that of 3D NC.

Next, the present invention will be explained. FIG. 10 is a diagram illustrating a stylus moving element (for one axis) of the present invention. A motor 9, a hole screw 4, and a hole guide 5 are attached to the frame 1, and the hole nut 3 is combined with the hole screw 4, and the hole slide 6 is combined with the hole guide 5, and each is connected to the table 2. A gear 7 is attached to the motor 9, and this gear meshes with a gear 8 attached to the hole screw 4. Now, when drive power is supplied to the motor, the rotation of motor 9 is caused by gears 7 and 8.
Turn the hole screw 4 through the . As the screw 4 rotates, the nut 3 slides back and forth, and eventually the table 2 moves in the direction of the arrow in accordance with the amount of rotation of the motor. A resistor section 12 of a potentiometer 11 is attached to the table 2. Both ends of the slider 13 and the resistor section 12 are electrically connected to the socket 10. A signal indicating the position of table 2 can then be taken out from socket 10.

Figure 11 shows the stylus movement elements in Figure 10.
2 is a diagram showing an embodiment of the present invention in which the axes (X-axis, Y-axis) are combined with the tracer head TH explained in FIG.
Corresponding to the numbers in the figure, X indicates an X-axis stylus movement element. 1Y, 2Y,..., 7Y, 8Y
The same is true). In FIG. 11, a table 2X of an X-axis stylus moving element is fixed to the tracer head support arm SA. Also, frame 1
A Y-axis table 2Y is fixed to X, and a tracer head TH is fixed to frame Y. Thus, when drive power is applied to the motors 9X, 9Y, the tracer head TH and therefore the stylus S can be moved in parallel.

Next, an example of the tracer head and stylus moving mechanism drive circuit shown in FIG. 11 according to the present invention will be explained with reference to FIG. 12. The elements shown in FIG. 12, except for the conventional tracer head TH, are elements added to the conventional tracing control device of FIG. The speed component signal SX in FIG.
Applied to a circuit consisting of 4X. amplifier 101x
The output is a signal with a value corresponding to SX/KS (KS is the gain constant of the feed control system shown in (12)) determined by the ratio of resistors 101X and 102X, and this is supplied to the drive amplifier 100X of the motor 9X. Potentiometer slider 13 for drive amplifier 100X
The position detection signal of the table 2X consisting of X is fed back. The same applies to signals SY and below.

In the devices shown in Figures 3 and 12, the motor
Contour tracking control is performed on MX and MY using NC to control the motor.
It is also possible to control the MZ by following the signal ez. In other words, if the droop signals DX and DY of the X-axis feed control generated by the NC device (omitted in Fig. 3) are applied in place of the signals SX/KS and SY/KS in Fig. 12 in so-called 2-dimensional NC + 1-dimensional copying control, 12th
The stylus moves by the vector DV to the command position PC in Figure 6, and the motor responds to the position PR.
precedes. In this case, since ez is a signal corresponding to the position PC, high precision and high production equivalent to 3D NC is expected during 2D NC + 1D scanning control using such ez.

In the 2D contour and 1D up/down 3D scanning control of the present invention, the stylus S takes the lead unlike in Fig. 7, so the detection position PP and tool position PT are at the 13th position.
It will look like the figure. At this time, vector SV whose components are signals SX and SY is ideal for position PR, but
PT has too good a degree of prediction, and if things continue as they are, the position
The trajectory of PT may deviate slightly from the curve CV2 (=CV3), resulting in loss of accuracy. The time constant circuits 104x and 104y shown in Fig. 12 are used to improve this problem, and by appropriately selecting the time constants, it is possible to realize SV' instead of the velocity vector SV at the position PT, further improving accuracy and productivity. be able to.

Further, in the tracing control using FIG. 12, overshooting or digging, which is caused by the conventional method shown in FIG. 9, can be completely eliminated.
Furthermore, even when the contour as shown in Fig. 14 undergoes a sudden change in direction, such as moving from curve CV9 to curve CV10, the detection position PP in Fig. 7 reaches position PE (at this time, the tool signal Pr is at position PF). Hour position PP
The velocity vector SV1 at SV1 suddenly changes to SV2. If this change is detected by the change in SX, SY and the signals SX, SY applied to the feed control system are clamped to zero for a predetermined time corresponding to the response time constant of the feed control system Px-Mx, Py-My. The position PT reaches the position PE while the speed decreases as shown in the falling part of FIG. After that, when the clamp is stopped, the position PT curves as the speed increases, as shown in the rising part of Fig. 5, based on the vector SV2.
Can move on CV10. In this way, when the position PT moves from CV9 to CV10, a sharp angle can be produced.

As described above, according to the present invention, accuracy and productivity can be dramatically improved compared to conventional scanning control.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the concept of copying control, Fig. 2 is a diagram showing an example of a tracer head of a conventional copying control device, Fig. 3 is a diagram showing an example of the configuration of a conventional copying control device, and Fig. 4 is a diagram showing an example of the configuration of a conventional copying control device. Figure 5 shows an example of the response characteristics of the feed control system, Figure 6 shows the command position and response in NC. Figure 7 is a diagram showing the relationship between the positions, Figure 7 is a diagram showing the relationship between stylus position and tool position in copying control, Figure 8 is a diagram comparing NC and copying control, Figure 9
10 is a diagram illustrating a moving mechanism provided in a tracer head according to the present invention. FIG. 11 is a diagram illustrating a tracer head according to the present invention. FIG. 12 is a diagram showing a stylus moving mechanism drive circuit of the present invention, and FIGS. 13 and 14 are diagrams for explaining the effects of the tracing control device of the present invention.

Claims (1)

[Claims] 1. (a) A stylus that can be displaced by contacting the model surface; (b) When the stylus comes into contact with the model and is displaced, the direction of the normal to the surface of the model and the direction of the stylus a tracer head that generates a normal vector signal representing the magnitude of displacement, (c) a tool that performs machining on the workpiece, and (d) the tool and tracer head that are integrated into each of the processing machines. (e) a method for coordinating the direction of the normal vector and making the displacement of the stylus equal to a reference displacement given as a constant from the outside; A velocity vector that is a composite of a linear velocity vector and a tangential velocity vector that gives the tool a velocity that matches the tangential direction of the model orthogonal to the normal vector and whose magnitude is equal to the reference tangential velocity given as a constant from the outside. (f) a control device that is provided between the tracer head and the tool and moves the relative position of the two along the respective coordinate axis directions; a plurality of moving mechanisms; (g) a plurality of detectors for detecting relative movement amounts of the tracer head and the tool in the respective coordinate axis directions; and (h) for each of the components of the velocity vector in the respective coordinate axis directions. a calculation means for calculating a tracking error amount; (i) each tracking error amount calculated by the calculation means is set as a target value; A tracing control device comprising a plurality of driving means for driving each moving mechanism in a direction that eliminates tracking errors.