JPS5890442A - Precision cutting system - Google Patents

Abstract

PURPOSE:To restrict the amount of compensation to the inside of a prescribed value by driving a tool supporting part provided on a cutter holder with a micro-displacement driving part, measuring a tool position with a laser measuring machine, and compensating a difference between the measured and theoretical values thereof while driving the cutter holder every time the amount of compensation exceeds the prescribed value. CONSTITUTION:The XY positions of a tool supporting part 4 are measured with a laser measuring mchine, and the theoretical positions Y on a Y axis responding to the cut curved surface is estimated from detected X axis position with an arithmetic circuit 15. By comparing an actual measured value y with a theoretical one Y on the Y axis with the first comparator to control a micro-displacement element 6 by the difference thereof, while by comparing said actual measured value y with said theoretical one which were held in a hold circuit 20 with the second comparator 18 to output DELTAY to an NC control part 8 every time the difference exceeds the prescribed value DELTAY, the cutter holder is stepwise driven in the Y axis direction by the DELTAY.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a precision cutting system for finishing an axially symmetric quadratic curved surface into a mirror surface.

Recently, in the field of precision machining, processing machines with a processing accuracy of 0.1 micron or more are desired due to changes in radar technology, VLSI technology, etc. However, with conventional processing machines, 0.1
Machining precision of microns or higher is mainly achieved by grinding, and the objects to be machined are limited to simple planes or circumferential surfaces obtained by grinding the outer periphery of rod-shaped members.

For this reason, it is possible to machine paraboloids, hyperboloids, etc. to a mirror finish, and the technical problem of doing so by cutting has not been solved with conventional processing machines.

The reason for this is that, apart from the fact that there was limited demand for mirror-finishing quadratic surfaces, etc., from a purely technical standpoint, the temperature of the machine parts of the processing machine affects the processing accuracy, and the The influence of the feed drive system on the machining accuracy, such as the accuracy of the guide surface, the resolution of the drive motor itself,
Possible error factors include the accuracy of the feed screw, the accuracy of the position feedback detector, or the responsiveness of the drive system. In particular, the latter problem is caused by the fact that the aforementioned grinding of flat surfaces, circumferential surfaces, etc. is basically aimed at controlling the relative movement between a tool such as a grindstone and a workpiece in a uniaxial direction. Cutting of curved surfaces requires simultaneous control in two axial directions.

Conventionally, feed drive control that performs two-axis (x, y) control simultaneously has been realized by a so-called NC machine tool, if machining accuracy is not considered. However, in NC machine tools, the accuracy of detecting the amount of movement of a table, etc. is 1 micron even with a high precision machine tool, and about ±0.5 micron even with a special machine tool. Regarding the NC machine tool itself, if the minimum disassembly command value is set to 0.01 (microns/pulse) and the maximum cutting feed speed is set to 600 II+/min, the dispensing speed of the gusset is high. This makes it difficult for NC machine tools to perform interpolation calculations, etc.

Furthermore, the position detector for feedback control can measure a certain amount of movement, and o, o
At present, only radar length measuring instruments are capable of achieving accuracy on the order of t microns. However, even when such a radar length measuring device is used, there is a problem in that the drive system cannot respond to the error signal obtained.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a precision cutting system capable of cutting a quadratic curved surface with a processing accuracy of 0.1 micron or more.

The present invention holds a cutter tool through an X-axis drive system and a minute displacement drive section that positions the tool post at high speed and with high precision along the Y-axis, which is driven to any position on the xy plane by the X-axis drive system. The position of the tool holder is measured using an optical length measuring device, and the difference between this measured length value and the theoretical value is compensated for by the minute displacement drive section. The present invention is characterized in that each time the amount of compensation in the displacement drive unit exceeds a predetermined set value, the X-axis drive system is driven to bring the amount of compensation within a predetermined value.

An embodiment of the present invention is shown in FIG. 1 below! Tip 2 This will be explained in detail with reference to Figure 2. In the figure, reference numeral 1 denotes a cutting tool which comes into contact with a workpiece 3 that is held on a rotary shaft 2 and is driven to rotate, thereby cutting the workpiece. The cutting tool 1 is then driven to move relative to the workpiece 3 to cut its surface into a desired shape. In the following description, the driving direction of the cutting tool I is assumed to be an orthogonal coordinate system consisting of a Y axis parallel to the rotation axis 2 and an X axis perpendicular to the rotation axis 2. The cutting tool 1 is held in a tool holder 4, and the tool holder 4 is held in a tool rest 5 via a minute displacement element 6.

2 to 4 are a plan view, a side view, and a #br plane IA shown in FIG. That is, the tool holding part 4 is held with respect to the tool post S via a hydrostatic bearing so that it can move forward and backward in the Y-axis direction shown in the figure. The cutting tool 1 is attached to the front end of the tool holder 4, and a minute displacement cable 6 is interposed between the rear end and the end wall 5A protruding from the end of the tool rest 5, and both ends of the cutting tool 1 are attached. It's stuck.

Fig. 5 is a side view showing an example of the minute displacement element 6.
For example, three piezoelectric elements 61 are stacked in a layer with electrodes 62, 63, 64, 65 such as silver foil interposed at both ends and between the layers, and an insulator 66.
A connecting member 67 is provided via a connecting member 66. Then, the electrodes 63 and 64 are grounded, and one pole 62°6 is connected to this ground potential.
A voltage of several hundred delts is applied between the piezoelectric element 61 and the piezoelectric element 61 in the stacking direction.

FIG. 6 is a diagram showing an example of the relationship between the voltage applied to the minute displacement cord 6 and the amount of extension Δt. For example, when the thickness 4=1
Applying a voltage of =500V to the piezoelectric element of m
．． Suppose that it is possible to give an elongation of 25μ. Here, the applied voltage is controlled in the range of 500±300v, and the piezoelectric element 1
If a displacement of ±0.15μ is produced for each piezoelectric element, the total displacement is 0.3μ to 1.2μ by stacking three piezoelectric elements.
The thickness can be controlled within the μ range. On the other hand, the change in thickness of such a minute displacement element with respect to the applied voltage becomes approximately linear when the voltage is controlled within an appropriate range, and the response is also extremely good.

Therefore, by controlling the voltage applied to the minute displacement element 6, the tool holder 4 can be driven in the Y-axis direction relative to the tool rest 5, and the position of the cutting tool I can be controlled.

In FIG. 1, reference numeral 7 denotes an X-axis drive mechanism for driving the tool rest 5 in the X-axis direction, which is rotatably driven by, for example, a drive motor, and is provided with a feed screw screwed into the tool rest 5. ing. And this X-axis drive mechanism 7
is X according to the X-axis control signal given from the NC control section 8.
The turret 5 is driven in the X-axis direction by the shaft overpass amplifier 9. Reference numeral 10 denotes a Y-axis drive mechanism for driving the tool rest 5 in the Y-axis direction, and includes, for example, a drive motor and a feed screw that is rotationally driven by the motor and is screwed into the tool rest 5.

The drive motor is controlled by the Y-axis knob 11 and drives the tool rest 5 in the Y-axis direction.

12.13 is an X-axis side long machine and a Y-axis side long machine that non-contact detects the position of the tool holding part A, such as a radar
It is a side-long machine that uses light interference to travel. Here, since the cutting tool I is stacked on the tool holding part 4, the position of the cutting edge at the tip of the cutting tool can be known from the position of the tool holding part 4. Then, as the tool holder 4 moves in the X-axis direction, an irradiation signal is output from the X-axis side length machine 12 at regular intervals, for example every 0.01μ.

In addition, in response to movement in the Y-axis direction, the Y-axis side length machine 13 similarly outputs a y-rus. Then, the X-axis position counter 14 counts output pulses of the X-axis side long machine 12 that detects the position in the X-axis direction, and detects the position of the tip of the cutting tool AI in the X-axis direction.

Then, the count value X of this X-axis position counter 14 is set to f
(X) Provided to the arithmetic circuit 15. This f(→operating circuit 15
(corresponding to the position X on the X-axis of the cutting tool 1 and the theoretical position f on the Y-axis) is calculated according to the desired cutting surface. Then, the calculated value of the f((rotation) calculation circuit 15 is applied to the data register 16, and the output of 13 is counted by the Y-axis position counter 19, and the count value corresponding to the value assigned to the cutting edge of the cutting P3u tool 1 is obtained. That is, the Y-axis actual measured value y is sent to the second comparator 1 via the first comparator 17 and the hold circuit 20.
Give to 8. The output of the first comparator 17 is converted into a voltage at a predetermined ratio by a minute displacement element drive circuit 21 and applied to the minute displacement element 6.

Further, the count value of the Y-axis position counter 19 held in the hold circuit 2o, that is, the actual value y, and the theoretical value Y of the data register 16 are given to the second comparator I8, and the contents are compared and the difference is calculated. Every time a predetermined value Δy is exceeded, a drive signal ΔY is given to the NC control unit 8 to drive the drive a certain distance in the Y-axis direction. and second comparator 18
The NC control unit 8, which is supplied with the drive signal ΔY, drives the tool rest 5 by a predetermined amount ΔY in response to the drive signal ΔY. Therefore, by setting this predetermined value ΔY to an appropriate value, the control voltage for the minute displacement cable 6 can be maintained within an appropriate range, and iii? ! Care is taken not to impair M properties or apply excessive voltage.

FIG. 7 is a block diagram showing the main parts of the NC control unit 8, and the Y-axis and Y-axis position signals are transmitted to each interpolation calculation unit 8ax.
, each command counter gbx via Shy,
This output is sent to each D/A converter 8ex,
Each signal is converted to an analog signal by 8cy and sent to amplifier 9,
11. The drive signal ΔY given from the second comparator I8 is applied to the command counter 8b on the Y-axis side.
y and is added to the output of the interpolation calculation unit gay.

With such a configuration, before the start of cutting, N
The C control unit 8 moves the cutting tool 1 to the machining origin Xo of the workpiece 3,
Drive to Yo and reset all counters and registers. Then, when the cutting process starts, the X-axis is
The cutting tool 1 is moved to the workpiece 3 by the X-axis drive mechanism 7 via the
Drive from the outer periphery toward the center at a set speed.

Then, depending on the position in the X-axis direction of the tool rest 4 that holds the cutting tool 1, a 0.01μ
The elbow is output every time. Then, this noggle is counted by the X-axis position counter 14 to obtain the actual measured value X of the cutting tool 1 with respect to the machining origin XolC. This measured value X is f((
(2) The theoretical value Y in the Y-axis direction corresponding to the calculated value is outputted from the data register 16. Note that in this case, the actual measurement value X is given as a digital value from the X-axis position counter 14, so it is the accuracy of the drive system.

The calculation is performed by updating the actual measurement value X given to the f(transform) calculation circuit I5 every fixed movement amount Δχ, for example every 5μ, depending on the responsiveness and the like.

On the other hand, depending on the position of the cutting tool lOY-axis direction, the Y-axis side length machine 1
3 is counted by the Y-axis position counter 19, and this measured value y is counted by the first comparator 17 and the above-mentioned demonstration January surface in synchronization with the update of the output data of the X-axis position counter 14. A hold circuit 2o is provided to hold y.

The actual measured value y outputted from the hold circuit 2o and the theoretical value Y given from the data register 16 are then given to the second comparator 18 for comparison, and each time the difference exceeds a predetermined value Δγ, the value is sent to the NC control section 8. Give this output -? The cutting tool 1 is driven by the X-axis drive mechanism 10 via the amplifier 11.
The position in the Y-axis direction is driven step by step by ΔY.

At the same time, the first comparator 17 outputs the measured value y and the theoretical value Y.
and the minute displacement element drive circuit 2 according to this value.
The position of the tool holder 4 is controlled by controlling the voltage applied to the minute displacement element 6.

Here, in FIG. 1, the second comparator 18 and the hold circuit 20 are not provided, and the output of the data register 16 is
The Y-axis is connected via the comparator 17 and the NC control section 8. Consider what is to be applied to the amplifier 11. In this case, for example, as shown in FIG. 8, the cutting tool 1 is moved to the machining origin (Xo
, Yo) in the X-axis direction, f
(From the xJ calculation circuit 15, the theoretical values f(xo), f(
xl) and f(x2) − are given. Note that this theoretical value f(x) is the ideal curve F that is the target of the desired machining surface.
The X-axis drive mechanism 10 is driven via the Y-axis gear amplifier 11 according to the theoretical value f((x), and the actual value y gradually becomes the theoretical value f(x).
Approach J.

In this process, the first comparator 17 obtains the difference between the measured value y and the theoretical value f ((transformation)), and this value Yσ is applied to the minute displacement element 6 via the minute displacement element drive circuit 21 to drive it. However, in such a device, when the difference between the measured value y and the theoretical value f ((rotation) becomes significantly large, as shown at position 11 on the X-axis in the figure, the signal Yσ for controlling the minute displacement element 6 may become significantly large, deviating from its proper control range, resulting in loss of linearity or even loss of control.

On the other hand, in the embodiment described above, as shown in FIG. The exponent drive signal ΔY is supplied to the NC control section 8.

Therefore, the Y-axis S-♂ Ang 11 has the theoretical value f(x)
A signal obtained by adding the above drive signal ΔY to Since the X-axis drive mechanism 10 is driven, the actual measured value y
quickly approaches the theoretical value f(-. Therefore, the drive signal Yσ for the minute displacement element 6 falls within a predetermined appropriate range ±σm
ax can be controlled, and good linearity and accurate control can be achieved.

Therefore, the error caused by the mechanical drive mechanism regarding the position of the cutting tool in the direction of cut is corrected by a micro-displacement element that utilizes an electric piezoelectric effect, and when the voltage applied to this micro-displacement element exceeds the appropriate range, the above-mentioned drive Since the cutting tool is driven by the mechanism to reduce the amount of correction, the minute displacement element always operates within an appropriate range.

It should be noted that the present invention is not limited to the above-mentioned embodiment. For example, the actual measurement value X obtained from the output pulse of the X-axis side machine 12 is calculated by a separate f ( Alternatively, the signals may be supplied to the second comparators 17 and 18, respectively.

Furthermore, the f((rotation)) calculation circuit is not limited to one that rapidly calculates the theoretical value Y in the Y-axis direction of a desired cutting surface from the given actual measurement value A memory may be provided and the stored contents may be read out sequentially.

Furthermore, the minute displacement element 6 has extremely good responsiveness to the drive signal, so if it is sensitive, the output of the first comparator 17 and the minute displacement element drive circuit 2 are connected as shown by the broken line in FIG.
1, an integrating circuit 22 may be inserted between the two.

FIG. 10 is a diagram showing an example of such an integrating circuit 2I,
For example, a digital signal of a plurality of pits provided from the first comparator 17 is converted into an analog signal by the digital-to-analog converter DA, and the resistor R1 and the first switch SWl are converted into analog signals.
is input to operational amplifier OP1 via. This operational amplifier OP1 has an integrating capacitor C and a discharge resistor R between input and output.
, and a second switch SW are connected in parallel 9, and the first switch fft selects the resistor R1, and the second switch Sh is opened to integrate the above analog signal, and the integration is completed. The second switch SW1 selects the ground potential side, closes the second switch SW, and discharges the charge in the integrating capacitor C.

FIG. 11 is a circuit diagram showing an example of the minute displacement element drive circuit 22, in which three transistors Trl and T are used to control the applied voltage of several hundred volts to the minute displacement element 6.
The collector and emitter of ry and Trl are connected in cascade. That is, the signal Yσ applied to the input terminal T is passed through the buffer amplifier OP to the transistor T.
Depends on the base of rl. On the other hand, the transistor Tr1,
The emitters and collectors of Trs and Trl are connected in cascade, and resistors R1 + Rm + Rj are inserted between the collector and the pace of the transistor Try, between the pace of the transistor "l*Try, and between the pace of the transistor Tr1 and the emitter of the transistor Trl, respectively. ing.

and the emitter of transistor Trl and transistor T
A power supply P of several hundred volts and a series circuit of a minute displacement element 6 are connected between the collector of the ry.

In this way, each transistor, Trl, Tr)
.

The voltage applied between the emitter and collector of Try is approximately V3, which is the power supply voltage.9) Transistor Tr1゜Trl,
The requirement for collector breakdown voltage of Trs can be relaxed.

Furthermore, in the above embodiment, the f(d calculation circuit 15
The theoretical value Y for o is output, but it is not limited to this, and the previous position Xn-1 in the X-axis direction
The theoretical value yn corresponding to , and the position X in the X-axis direction at the relevant time
The difference Yn-Yn-1 from the theoretical value Yn corresponding to n may be outputted.As described in detail above, according to the present invention, the position error in the cutting direction of the cutting tool caused by the mechanical drive mechanism is corrected by a micro-displacement element whose displacement is electrically controlled, and when the voltage applied to the micro-displacement element exceeds an appropriate range, the cutting tool is driven by the drive mechanism to reduce the correction amount. It is something.

Therefore, it is possible to provide a precision cutting system that can cut a quadratic curved surface with extremely high precision and can always operate the minute displacement element within an appropriate range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
3 and 4 are a plan view, a side view, and a view taken along the line IV-■ in FIG. 2, and FIG. 5 is a side view showing an example of the minute displacement element of the above embodiment. , FIG. 6 is a diagram showing the relationship between the applied voltage and the amount of extension of the minute displacement element,
FIG. 7 is a block diagram showing the main parts of the control section, FIG. 8 is a diagram explaining the operation of the conventional device, FIG. 9 is a diagram explaining the operation of the device of the present invention, and FIG. FIG. 11 is a diagram showing an integration circuit according to another embodiment of the present invention, and FIG. 11 is a diagram showing an example of a minute displacement element drive circuit according to the present invention. 1... Cutting tool, 2... Rotating shaft, 3... Workpiece,
d...Tool holding part, 5...Turret, 6...Minute displacement element, 2...X-axis drive mechanism, 8...NC control unit, 1
0...Y-axis drive mechanism, 12...X-axis side length machine, 13...
・Y-axis side length machine, 15...f (XI calculation circuit, I7...
- First comparator, 18... second comparator.

Claims (1)

[Claims] A workpiece that is held on a rotating shaft and rotationally driven, a tool holder that holds a cutting tool for cutting this workpiece, a tool rest that holds this tool holder, and a tool rest that holds the tool rest for cutting the cutting tool. an X-axis drive mechanism that drives the tool post in a direction perpendicular to the cutting direction of the cutting tool; Axial drive mechanism and
an NC control section that controls the shaft drive mechanism; a minute displacement element that is interposed between the tool holding section and the tool post and drives the tool post in the cutting direction with respect to the tool holding section; The X-axis side long line and Y-axis side long side line detect the position in the axial and Y-axis directions without contact, and the theoretical value of the Y-axis direction of the desired cutting surface according to the actual measured value given from the X-axis side long line. f(xJ arithmetic circuit), and this f(xJ arithmetic circuit) produces a minute displacement that displaces the minute displacement element in the cutting direction according to the difference between the theoretical value given from the xJ arithmetic circuit and the actual value given from the Y-axis side long story. It includes an element drive circuit and a second comparator that drives the X-axis drive mechanism via the NC control unit to maintain the displacement amount in the minute displacement element within a predetermined range every time the difference exceeds a predetermined value. Precision cutting system.