JPH02160457A - Correcting device for straightness of machine tool - Google Patents

Abstract

PURPOSE:To mutually correct the combined error of each slide base at real time with high accuracy by forming a structure of driving 2nd or 3rd servomotor by correcting it based on the respective correction amt. in case of the moving locus of a 1st slide base and the deviation amt. of a 1st or 2nd reference face becoming more than an allowable value. CONSTITUTION:A measuring device 36 is fitted to the lower face of a table 27, the gap in Y axial direction with the reference block 37 of the right side face of a saddle 25 is measured, the correction pulse is fed to a Y axial servomotor 31 to move a main shaft head 30 by the correction amt. and the error in Y axial direction accompanied by the movement in Z axial direction of the table 27 is corrected. Similarly, the correction of the error in X axial direction accompanied by the movement in Z axial direction of the table 27 and the error in X axial direction accompanied by the vertical movement in Y axial direction of the main shaft head 30, is performed by moving the saddle 25 by the correction amt., and the correction in Z axial direction accompanied by the vertical movement in Y axial direction of the main shaft head 30 is performed by moving the table 27 by the correction amt. Thus, the errors in all directions at the slide base moving time can correctly be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION In order to maintain the straightness and parallelism of the slide tables of a numerically controlled machine tool and the perpendicularity of the motion between the slide tables, This invention relates to a straightness correction device for a machine tool that improves the machining accuracy of the machine tool by measuring the displacement of the machine tool and feeding the results back to the control unit that controls the drive of the servo motor of the machine tool. . - Machining errors of machine tools that carry blades or workpieces on boats and slide them back and forth include manufacturing errors in guide surfaces, gaps between guide surfaces and slide tables, etc. This error occurs due to deformation due to cutting force during machining, wear, etc., but it is impossible to completely eliminate this error.
There is a limit to how much accuracy can be achieved beyond that of a room.

In recent years, with the development of electronic control technology such as numerical control (NC) and optical control technology, it has become possible to control machines with high precision. In order to perform highly accurate feeding and positioning, the accuracy of the machine itself must also be high. However, although it is not impossible to manufacture a machine with a high precision of 1 micron or more, it is actually uneconomical because the manufacturing cost is too high, and the mechanical It is difficult to manufacture a product that takes even the complicated deformation of the material into consideration.

Therefore, it has been proposed for some time that it would be better to adopt another method that does not require highly accurate straightness and parallelism of the machine itself. One way of achieving this is by continuously measuring the deviation of the slide table from the theoretically required path and feeding the results to the servo motor control unit to issue control commands to satisfy the required accuracy. The basic idea of correcting the oil has been proposed, but there are problems with the measurement method and the processing of constant values, so
The current situation is that nothing practical has been created yet.

The present invention was invented to provide a practical machining error correction device that solves the above-mentioned problems. In other words, a means for forming an ideal straight line as a reference for sliding of the sliding table is provided on either the sliding table or the fixed side, and a means for forming an ideal straight line with the sliding table on the other side. A measuring device is installed to measure the distance between the sliding tables, and each time the deviation of the fixed value measured by the measuring device on one sliding table exceeds a set reference value, a correction signal is sent to drive the other sliding table. By providing a correction signal generator that sends to the servo motor controller that controls It is an object of the present invention to provide a straightness correction device for a machine tool that performs mutual correction with high precision.

In the embodiment of the present invention, a highly precisely finished reference block is used as a means for forming an ideal straight line,
Its position can be precisely adjusted using an adjustment screw. Of course, there are other means for forming an ideal straight line, such as a laser beam, and the method is selected depending on the balance between the required degree of accuracy and cost. The effects of using such means for forming highly accurate straight lines as a reference for guiding the sliding table are as follows.

A. Since the shape is simpler than that of a guide surface, it is easy to manufacture a highly accurate one.

B. Since the length only needs to be equal to the net stroke amount of the slide table, the length can be shorter than that of the guide surface.

C6 Since no cutting force is applied to the means for forming the ideal straight line, no wear or deformation occurs. Therefore, high accuracy can be maintained for a long time.

D. Easy to replace and modify.

E9 For example, in the case of face milling on a machining center, when processing square objects, it is often necessary to finish the product at an accurate right angle, but since the intersecting angle between the means to form an ideal straight line can be adjusted arbitrarily, it is easy to achieve accurate A surface angle can be obtained.

The measuring device used in the present invention is required to be highly accurate. If a measuring device that measures displacement in a non-contact manner is used, it is possible to measure the displacement in units of 0.1 micron, and although it is a contact type, an electric micrometer can also be used to measure the same degree.

In order to make the principle of the present invention easier to understand, an example of simultaneous two-axis control applied to a numerically controlled lathe will be shown and explained below. Fifth
The figure shows an embodiment of the invention, in which a headstock I-tsuk 2 is placed on a bed 1, a chuck 4 is attached to the front end of a main shaft 3 rotatably supported on the headstock 2, The workpiece W is gripped. A saddle 6 is placed on guide surfaces 5A and 5B formed on the bed 1 so as to be slidable in the direction of the spindle axis, and guide surfaces 7A and 7B formed on the saddle 6 in a direction perpendicular to the spindle axis. A cross slide 8 is slidably mounted on the top.

The saddle 6 is caused to reciprocate and slide parallel to the main shaft axis via a nut 11 by a screw 10 driven by a Z-axis servo motor 9. In addition, the Sloss slide 8 is
Screw 1 driven by X-axis servo motor 12
3 allows reciprocating sliding at right angles to the main shaft axis via the nut 14. A reference block 1 is placed on the front overhang IA from the bed 1 as a means of forming an ideal straight line.
5 is attached by fixing means such as bolts, and the adjusting screw 17 screwed into the block 16 is applied to the reference block 15, and the reference block 15 is slightly swung, and the accurately finished reference surface 15A is fixed to the main shaft. Set correctly parallel to the axis. The aforementioned non-oxidation measuring device 18 is attached to the saddle 6 facing the reference surface 15A, and the gap between the non-oxidizing measuring device 18 and the reference surface 15A is measured in the Z-axis direction of the saddle. Measure over the entire stroke. Similarly, a reference block 19 is mounted on the saddle 6, and an adjustment screw 21 screwed into the block 20 allows the reference plane 19A to be correctly set perpendicular to the spindle axis. The cross slide 6 has a reference surface 19A.
A non-oxidation type measuring device 22 is attached opposite to the measuring device 22, and measures the gap between the measuring device 22 and the reference surface 19A over the entire stroke of the cross slide 8 in the X-axis direction. The reference block 15.1 has a simple shape with a rectangular cross section.

The reference block 15 has a stroke amount in the Z-axis direction, and the reference block 19 has a length equal to the stroke amount in the X-axis direction.
Each measuring device 18.22 and reference block 15.1 are preferably covered with a cover or the like to protect the reference surface from chips, cutting oil, etc. A tool rest 23 is mounted on the cross slide 8, and a cutter T is set on the tool rest 23. As shown in FIG. 5, the measuring device 18 is aligned with the cutting edge position of the cutter T in the Z-axis direction, and
If it is set to match the position of the cutting edge of the cutting tool T in the X-axis direction, the error at the cutting point can be accurately measured.

Figures 3(a) and 3(b) show diagrams of the principle of correction.

Now, do not give any movement command to the 2-axis servo motor,
When a movement command is given to the axis servo motor, the measured value obtained from the measuring device 22 as the X axis moves is the gap distance (L → curve A in Figure 2 is obtained. When a movement command is given to the Z-axis servo motor without giving a command, the measurement value obtained from the measuring device 18 as the Z-axis moves is the gap distance (L), and the curve A in Fig. 3 (a) is can get.

As shown in FIG. 3(A), the measured values of the gap measured by the measuring devices 18 and 22 are generally analog quantities as shown by curve A, which are digitized into correction units by an AD converter. Convert to a step-like curve. Then, it is calculated by a data calculation unit, which will be described later, to calculate the gap at the time of tape start. (!.) Each time the gap increases or decreases by a correction unit amount (for example, 1 micron), as shown in Figure 3 (b), 1
A correction pulse on the plus or minus side is generated pulse by pulse, and this correction pulse is sent to the Z-axis servo motor 9 (X-axis servo motor 12) and
The axis servo motor 12) is driven with the command value from the tape corrected by the correction pulse.

For simplicity, assuming that there is no command from the tape for the Z-axis, the only pulse sent to the Z-axis servo motor 9 is a correction pulse, and therefore, the saddle 6 is moved by the correction unit amount each time a correction pulse is generated. , the error in the movement of the cutting edge is reduced as shown in Figure 4.

FIGS. 1 and 2 show an embodiment in which the present invention is applied to a cross-boring milling cutter. A saddle 25 is mounted on the bed 24 so as to be slidable in the X-axis direction, and is driven by an X-axis servo motor 26. A table 27 is placed on the saddle 25 so as to be slidable in the Z-axis direction, and is driven by a Z-axis servo motor 28. A spindle head 30 is mounted on two columns attached to the side surface of the bed 24 so as to be vertically slidable in the Y-axis direction, and is driven by an X-axis servo motor 31.

As shown in FIG. 1, a measuring device 32 similar to that described above is attached to the front surface of the bed 24 corresponding to the position in the X-axis direction of the center of the spindle, and a reference block 33 attached to the front surface of the saddle 25 is attached to the same measuring device 32 as described above. Gap in the Z-axis direction! -ノ. +Δ is measured, and the correction pulse is sent to the Z-axis servo motor 28 to move the table 27 by a correction amount to correct the error in the Z-axis direction due to the movement of the saddle 25 in the X-axis direction.

As shown in FIG. 2, a measuring device 34 is attached to the rear surface of the bed 24 corresponding to the position in the X-axis direction of the center of the spindle, and a reference block 35 is attached to the rear surface of the saddle 25.
The gap in the Y-axis direction is measured and the correction pulse is sent to the X-axis servo motor 31 to move the spindle head 30 by a correction amount to correct the error in the Y-axis direction caused by the movement of the saddle 25 in the X-axis direction. let

As shown in FIG. 1, a measuring device 36 is attached to the lower surface of the table 27, which measures the gap in the Y-axis direction with a reference block 37 attached to the right side of the saddle 25, and transmits the correction pulse to the X-axis. Send it to the servo motor 31 and spindle head 3
0 by a correction amount to correct the error in the Y-axis direction due to the movement of the table 27 in the Z-axis direction.

Furthermore, as shown in FIG. 2, a measuring device 38 is attached to the left side of the table 27, and measures the gap in the X-axis direction between the table 27 and a reference block 39 housed on the upper surface of the saddle 25. is sent to the X-axis servo motor 26 to move the saddle 25 by a correction amount to correct the error in the X-axis direction due to the movement of the table 27 in the Z-axis direction.

Further, as shown in FIG. 1, a measuring device 40 is attached to the left side of the spindle head 30 corresponding to the position in the Y-axis direction of the center of the spindle. The gap in the axial direction is measured, and the correction pulse is sent to the X-axis servo motor 26 to move the saddle 25 by a correction amount to correct the error in the X-axis direction caused by the vertical movement of the spindle head 30 in the Y-axis direction.

Further, as shown in FIG. 2, a measuring device 42 is attached to the rear surface of the spindle head 30 corresponding to the Y-axis direction position of the center of the spindle, and a measuring device 42 is attached to the rear surface of the spindle head 30 in correspondence with the Z-axis direction position of the reference block 43 attached to the rear surface of the column 29. The gap in the direction is measured, and the correction pulse is sent to the Z-axis servo motor 28 to move the table 27 by a correction amount to correct the error in the Z-axis direction due to the vertical movement of the spindle head 30 in the Y-axis direction.

In other words, the error in the direction perpendicular to the direction of movement between two slides that can slide in directions perpendicular to each other and whose guide surface is parallel to the plane containing one guide surface. By correcting each other, it is possible to accurately correct errors in all directions during slide table movement.

FIG. 6 shows a control block diagram for the X-axis and Z-axis of the lathe with simultaneous two-axis control shown in FIG. 5, which is an embodiment of the present invention.

Furthermore, when applied to the cross-boring slicing machine of the embodiment shown in Fig. 1.2, the same principle can be applied to the X-axis and Z-axis. The same applies to the X-axis and Y-axis, as well as the Y-axis and Z-axis.

The control data punched on the command tape is read by a tape reader, passes through the data control section, and enters the sequential interpolation calculation section.
Arithmetic processing necessary for normal numerical control is added, and the pulse generator enters the X-axis or Z-axis pulse generation section as necessary. The pulses generated by each pulse generation section pass through an acceleration/deceleration section, a droop amount detection section, a D-A conversion section, a speed amplification section, and a servo drive section.
It generates a voltage determined by the direction of movement, distance and set speed, and rotates the X-axis or Z-axis servo motor.

A pulse generator and a tacho generator are connected to each servo motor, and the tacho generator generates a voltage proportional to the rotation speed of the servo motor, and feeds this back to the speed amplifier to increase the rotation speed of the servo motor. It's in control. In addition, the pulse generator generates a pulse proportional to the rotation angle of the servo motor, and feeds this back to the droop amount detection unit via the direction feedback pulse generation unit, thereby rotating the servo motor to the commanded rotation angle position. , it is now possible to hold it.

Next, a control operation in which the Z-axis servo motor 9 corrects an error in a direction perpendicular to the direction of movement when the cross slide 8 moves in the X-axis direction will be described. When t=tn, the analog signal V2tn output from the greenhouse device 22 is A
After amplifying to V z t n, A-D conversion is performed,
Outputs the digital quantity Dz tn. Next, in the data transfer section, when t=tn, the output digital quantity 1) zt
At the same time as n is stored in the shift register S1, the digital quantity Dztn-1, which was stored in Sl and was output when t=t, n-1, is transferred to the shift register S2. Next, in the data calculation section, the difference Δ between Dztn-1 and Dztn
Detect D2. ΔD2 is output from the correction data output section. Of course, there are two types of ΔDZ: positive and negative.

The output ΔDz from the correction data output section is further sent to the Z-axis drive pulse generation section, and the command data D from the interpolation calculation section is sent to the Z-axis drive pulse generation section.
A drive pulse is generated and corrected so that ΔDZ becomes zero while matching with z. This correction operation corrects the error in the direction perpendicular to the direction of movement when the saddle 6 moves in the Z-axis direction.
The case of correction using the X-axis servo motor 12 is also completely the same.

As another correction method, as shown by the broken line, the correction signal ΔD2 from the correction data output section is sent to the direction feedback pulse generation section, and the direction feedback pulse generation section matches the feedback pulse from the pulse generator. , ΔDz
It is also possible to correct by generating a drive pulse so that the value becomes zero.

Further, although a control block diagram for simultaneous three axes is not shown, control can be performed on the same principle as the simultaneous two axes control.

As mentioned above, the present invention is not limited to the configurations shown in the embodiments, and modifications are expected without departing from the technical idea of the present invention as set forth in the claims. By the way.

[Brief explanation of the drawing]

1 and 2 are perspective views showing an embodiment in which the present invention is applied to a numerically controlled tank boring and milling machine, and FIG. 3 is a correction principle diagram;
Fig. 4 is a graph showing the movement of the cross slide when correction is applied, Fig. 5 is an example showing the principle applied to a numerically controlled lathe, and Fig. 6 is the simultaneous two-axis X-axis and Z-axis of the present invention. It is a control block diagram in the case of.

Claims (1)

[Claims] a first sliding table provided so as to be slidable in a first direction along a first guiding surface on the first guiding member; and a first sliding table that is perpendicular to the sliding direction of the first sliding table. a second sliding table provided so as to be slidable in a second direction along a second guiding surface on the second guiding member; and each of the first sliding table and the second sliding table. a third sliding table provided so as to be slidable in a third direction along a third guiding surface on a third guiding member perpendicular to the sliding direction of the first sliding table; a first servo motor that slides the first servo motor along the first guide surface; a first control section that controls the first servo motor; a second servo motor for sliding, a second control section for controlling the second servo motor, and a third servo motor for sliding the third sliding table along a third guide surface. and a third control unit that controls the third servo motor, and a numerical control machine that processes a workpiece with a tool by a combination of relative movements of the first, second, and third slide tables. In the machine, the first sliding table or the first sliding table
The reference forming means is provided on either one of the guide members and has a first reference surface in the second direction of the first sliding table and a second reference surface in the third direction of the first sliding table. and a first reference surface of the reference forming means provided on the other of the first slider or the first guide member of the first slider and the movement locus of the first slider and the first reference surface of the reference forming means. a first measuring device that measures distance;
The distance between the movement locus of the first sliding table and the second reference plane of the reference forming means is provided on the other of the first sliding table or the first guide member of the first sliding table. When the measured value of the second measuring device and the first measuring device exceeds the reference value in the second direction, a correction value is calculated and sent to the second control unit, and the measured value of the second measuring device is a correction calculation unit that calculates a correction value when the value exceeds a reference value in a third direction and sends it to a third control unit, and the correction calculation unit calculates a correction value when A straightness correction device for a machine tool, characterized in that when a surface deviation amount exceeds an allowable value, a second servo motor or a third servo motor is driven for correction based on the respective correction amounts.