JP3897884B2 - Method and apparatus for correcting thermal displacement of machine tool - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for correcting thermal displacement of a machine tool during workpiece machining.
[0002]
[Prior art]
When machining a workpiece (workpiece) with a machine tool, the position of the blade position measurement sensor may be displaced due to expansion / contraction due to temperature changes or expansion due to cutting heat in each component of the drive system on the machine tool side. In many cases, a relative displacement occurs between the workpiece and the machine tool, and the machining accuracy of the workpiece decreases.
[0003]
Various temperature compensation methods have been proposed in order to prevent a reduction in machining accuracy due to such temperature changes at various sites. For example,
a) A method of obtaining a correction value by estimating and calculating displacement due to temperature based on the temperature detected by the temperature sensor,
b) A method of measuring a temporal change tendency of the thermal displacement amount in advance and correcting an actual measurement value based on the measured tendency.
c) A method in which the position of a processed workpiece is directly measured by a touch sensor to obtain a correction value;
d) A method of measuring the cutting edge position directly with a tool setter or the like to obtain a correction value,
And so on.
[0004]
[Problems to be solved by the invention]
Each of the conventional thermal displacement correction methods described above has advantages and significance, but each correction method has insufficient error correction, complicated handling of the equipment for error correction, and skill. And the correction value varies, and it is not always sufficient.
[0005]
Accordingly, it is an object of the present invention to provide a machine tool thermal displacement correction method and apparatus that can be easily handled and that can further reduce machining errors due to thermal displacement.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 is a position measuring step for measuring a relative position between a spindle to which a workpiece is attached and a turret head to which a cutting tool is attached, a temperature measuring step for measuring the temperature of the turret head, the position measuring step, and Correction amount calculation for calculating a correction amount for correcting the relative position in the measurement after the start of processing based on the temperature at that time based on the relationship between the relative position and the temperature measured before the start of processing as the temperature measurement step. And measuring the temperature of the temperature simulation block arranged in thermal contact with the circulating cutting fluid for indirectly measuring the temperature of the turret head in the temperature measuring step. By doing so, temperature measurement for measuring the temperature of the turret head is executed.
[0007]
The invention according to claim 2 estimates the light weight of the cutting load on the basis of the temperature measured in the temperature measurement step and calculates a coefficient representing the light weight when calculating the correction amount in the correction amount calculation step. Configured as
[0008]
According to a third aspect of the present invention, there is provided a position sensor for measuring a relative position between a spindle to which a workpiece is attached and a turret head to which a cutting tool is attached, temperature measuring means for measuring the temperature of the turret head, the position sensor, and the temperature. A correction amount calculating means for calculating a correction amount for correcting the relative position in the measurement after the start of processing from the temperature at that time, based on the relationship between the relative position and the temperature obtained by the measurement performed before the start of processing by the measuring means; A temperature simulation block arranged to be in thermal contact with the circulating cutting fluid for indirectly measuring the temperature of the turret head, and the temperature of the temperature simulation block And a temperature sensor that measures the temperature of the turret head.
[0009]
According to a fourth aspect of the present invention, the correction amount calculation means estimates a light weight of a cutting load based on a temperature measured by the temperature sensor when calculating the correction amount, and adds a coefficient representing the light weight. Configured as
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 shows the overall configuration of a machine tool to which the present invention is applied. The machine tool shown in the figure is a numerically controlled machine tool, that is, an NC machine tool. The work 4 attached to the spindle of the spindle head 2 is assisted by a numerical controller (NC) 10 by means of a blade 8 attached to the turret head 6. It is a machine that borrows and performs digital control processing. The spindle head 2 is driven to rotate by a spindle motor 12. The turret head 6 is attached to the turret box 14. The turret box 14 is moved in the X-axis direction via the X-axis ball screw 17 by the X-axis servo motor 16 in order to adjust the distance between the axis of the work 4 and the tip of the cutting tool 8 according to the processing content of the work 4. A displacement operation is possible, and a displacement operation in the Z-axis direction can be performed by the Z-axis servomotor 18 via the Z-axis ball screw 19 in order to adjust the position of the cutting tool 8 in the axial center direction with respect to the workpiece 4. In order to process the workpiece 4 into a predetermined shape and size according to a predetermined program, the turret box 14 and the spindle head 2 are controlled by the NC 10 via the X-axis servo motor 16, the Z-axis servo motor 18 and the spindle motor 12, respectively. The
[0013]
The X-axis direction position detected by the X-axis servomotor 16 is detected by the X-axis direction position detection pulse coder 20, and the Z-axis direction position detected by the Z-axis servomotor 18 is detected by the Z-axis direction position detection pulse coder 22. In the spindle head 2 and the turret box 14, a position sensor reflector 24 is attached to one of the mutually opposing portions (spindle head 2 in the illustrated example), and the non-contact type position sensor 26 is attached to the other (turret box 14). Is attached.
[0014]
In order to release cutting heat generated between the cutting tool 8 and the workpiece 4 and reduce friction, a cutting fluid 56 (see FIG. 6), for example, cutting oil, is injected from the nozzle 28 to the cutting portion of the workpiece 4. Is done. The nozzle 28 is supplied with a cutting fluid in a pressurized state from a liquid pump 34 driven by a liquid motor 32 via a liquid pipe 36, and jets the cutting fluid from the nozzle 28 to the cutting portion. The cutting fluid sprayed from the nozzle 28 is subjected to a given operation (cooling, anti-friction, coating, washing) in the cutting portion and then collected in the liquid tank 50 (FIG. 4) as will be described later. After processing such as the above, the liquid is returned to the liquid pump 34 and reused for reuse.
[0015]
Since the turret head 6 rotates, it is difficult to directly measure its temperature. Therefore, in order to indirectly measure the temperature of the turret head 6, a temperature simulation block 30 having a heat capacity close to the heat capacity of the turret head 6 and arranged close to the turret head 6 is prepared, and before the injection through the pipe 36. In contact with the cutting fluid. The temperature of the cutting fluid in the pipe 36 is lower than the temperature immediately after the cutting work part. However, since the cutting fluid sprayed from the nozzle 28 cools the tool 8 and also the turret head 6 and the tool (tool post), it is rather empirical to use the cutting fluid before work rather than the turret head 6. It was found that a temperature close to the temperature was obtained. Thus, the temperature of the turret head 6 is estimated by simulating the temperature of the turret head 6 by the block 30 and measuring the temperature by the temperature sensor 38.
[0016]
FIG. 3 is an explanatory diagram for explaining the internal structure of the turret box 14 and the turret head 6 with respect to the movement of the turret head 6 in the X-axis direction. When the servo motor 16 rotates, the ball screw 17 rotates through the coupling 40. The ball screw 17 is supported by tack bearings 44 and 46 at both ends thereof. As the ball screw 17 rotates, the nut 48 screwed together moves in the axial direction. Therefore, the turret head 6 can be moved in the axial direction of the spindle 54 by connecting the nut 48 and the turret box 14 so as to move integrally and rotating the ball screw 17 by the servo motor 16. .
[0017]
In that case, the ball screw 17 and the nut 48 slide to generate heat, and the ball screw 17 extends. The extending direction is determined by how the tack bearings 44 and 46 are assembled. In the case of illustration, it is the direction of the arrow P. As described above, when the ball screw 17 is extended due to heat generation, the actual movement amount is shifted toward the servo motor 16 with respect to the NC command value from the NC 10.
[0018]
The heat transfer system and thermal displacement of the machine tool will be described with reference to FIG. The heat generated by the cutting process on the workpiece 4 is accumulated in the liquid tank 50 through the cutting fluid. Therefore, the liquid tank 50 serves as a heat source for the leg 52 formed with the C surface, which is a mounting surface on which the spindle head 2 and the turret box 14 are mounted, and from the A surface facing the liquid tank 50 to the leg 52. And heat is conducted. At this time, the temperature of the A surface is naturally higher than that of the B surface, which is the opposite surface. As a result, the A surface side of the leg 52 is pushed up, and the C surface on which the spindle head 2 is placed is deformed into a C ′ surface as indicated by a broken line. This deformation reduces the distance D between the turret box 14 and the spindle head 2. In this state, the cutting tool 8 comes closer to the workpiece 4 than the NC command value. This influence becomes larger as the temperature difference between the A surface and the B surface increases, and the distance D between the cutting tool 8 and the workpiece 4 becomes narrower.
[0019]
In addition to this, as heat factors for the legs 52, there are heat generation of the spindle motor 12, heat generation of the spindle 54, heat generation of the cutting fluid, etc., and these are added to the legs 52 from different parts / locations in combination. The legs 52 are complicatedly deformed. Therefore, it is almost impossible to accurately capture the displacement amount of each part of the leg 52 by calculation.
[0020]
Next, the displacement of the turret box 14 and the turret head 6 will be described with reference to FIG. The turret box 14 extends in the Q direction, that is, in the axial direction with the nut 48 as a base point due to the temperature rise. The turret head 6 extends in the R direction parallel to Q with the turret axis X as a base point by the temperature of the cutting fluid, for example, cutting oil, or the conduction heat from the cutting tool 8 in addition to the outside air temperature.
[0021]
As shown in FIG. 6, the cutting heat generated by cutting the workpiece 4 with the cutting tool 8 is conducted in three directions. That is,
1) Conducted heat H1 toward the turret head 6 through the blade 8
2) Conducted heat H2 toward the spindle 54 via the workpiece 4
3) Heat conduction H3 conducted through the working cutting fluid
That is it.
[0022]
In order to calculate the amount of displacement due to thermal expansion of the turret head 6, the temperature of the turret head 6 must be detected. However, since the turret head 6 rotates, a temperature sensor cannot be directly attached thereto. Then, it substitutes by measuring the temperature of the cutting fluid in connection with the third conduction heat H3 among the heat conducted in the three directions.
[0023]
FIG. 1 is a block diagram of a thermal displacement correction device 70 according to the present invention. This thermal displacement correction device 70 calculates a thermal displacement correction value and gives it to the NC 10, and includes a position correction calculation means 702 having a reference position storage means 701, a temperature correction calculation means 704 having a reference temperature storage means 703, both Correction value calculation means 705 for calculating the temperature correction value and position correction value based on the calculation results of the correction calculation means 702 and 704, correction value storage means 706 for storing the temperature correction value and position correction value, and their correction values Whether or not manual correction has been performed is determined. When it is determined that manual correction has been performed, a manual correction determination unit 707 is fed back and updated to the reference position storage unit 701 and the reference temperature storage unit 703. I have. Position detection information of the position sensor 26 is introduced into the position correction calculation means 702 via the AD converter 62, and temperature detection information of the temperature sensor 38 is introduced into the temperature correction calculation means 704 via the AD converter 64. Introduced.
[0024]
In order to carry out the present invention, the following a and b are prepared as detection ends.
a) A position sensor 26 for measuring the relative distance between the turret head 6 (the blade 8) and the spindle head 2 (the spindle 54) is attached to the turret box 14 side, and the reflector 24 is attached to the spindle head 2 side ( Fig. 2),
b) In order to estimate the temperature of the turret head 6, a block 30 that simulates the temperature of the turret head 6 and a temperature sensor 38 that measures the temperature are attached.
[0025]
In FIG. 2, by measuring the distance between the turret box 14 and the spindle head 2 by the position sensor 26, a displacement amount mainly including the following displacements can be obtained. Note that the measurement position is always a fixed position from the origin in accordance with a command from the NC 10.
1) Displacement of ball screw 17 (see FIG. 3)
2) Displacement of leg 52 (see FIG. 4)
3) Displacement of the spindle 54 (effect of displacement of the leg 52 mainly due to heat transfer to the leg 52)
4) Displacement of turret box 14 (see FIG. 5)
Next, a method for estimating the temperature of the turret head 6 using the temperature measurement result of the block 30 by the temperature sensor 38 and calculating the displacement of the turret head 6 by using the temperature measurement result will be described.
[0026]
The heat generated by the cutting is conducted to the turret head 6 side in the direction of conduction heat H1 in FIG. In that case,
a) When the amount of heat for cutting is small due to a light load, the heat dissipation amount of (the cutting tool 8 + tool + turret head 6) is large, so the temperature rise of the (cutting tool 8 + tool + turret head 6) relative to the temperature of the turret box 14 Are small and these displacements can be ignored. Incidentally, since the position measurement already described is performed on the spindle 54 side of the turret box 14, these displacements are included in the position measurement result.
b) When the amount of heat of cutting is large due to heavy load, the temperature rise of (the cutting tool 8 + tool + turret head 6) increases with respect to the temperature of the turret box 14, and their displacement increases. In that case, the displacement of the turret head 6 system is
Displacement = (Turret head radius) x (Expansion coefficient) x (Current temperature-Reference temperature) x (Load coefficient)
Can be calculated as
[0027]
The temperature measurement of the turret head 6 is as described with reference to FIG. The load coefficient in the equation is estimated based on the temperature measured by the temperature sensor 38. That is, the light weight of the cutting load can be estimated by the temperature increase of the turret head 6 after a predetermined time from the start of cutting, for example, 30 minutes, that is, the temperature increase of the block 30. This temperature rise amount is determined by multiplying by a coefficient obtained experimentally in advance. According to experiments, about 1 / 2.93 was appropriate as this coefficient.
[0028]
Next, the procedure of the present invention performed by the thermal displacement correction apparatus of FIG. 1 will be described with reference to FIG.
First, at the beginning of the machining cycle, the turret is moved to the measurement position by an NC program command (step 101). Next, the distance between the turret box 14 and the spindle head 2 is measured by the position sensor 26, and the measurement data is taken into the thermal displacement correction device 70 via the AD converter 62 as shown in FIG. In order to estimate the temperature of the turret head 6, the temperature of the block 30 is measured by the temperature sensor 38, and the measurement data is also taken into the thermal displacement correction device 70 via the AD converter 64 (step 102). When the measurement value has been taken in, the turret is temporarily retracted from the position sensor measurement position (step 103). Here, the variable i for counting the number of correction groups is cleared to zero (step 104). Assuming that the maximum value of the variable i representing the number of correction groups, that is, the number of offset correction groups of the turret head 6 to be corrected is “32”, the next step is to check whether “i = 32”. (Step 105). Here, since i = 0 at the beginning, “NO”. In order to determine whether or not manual correction described later has been performed, it is checked whether or not the i + 1th offset of NC10 is the same as the i + 1th correction stored value (step 106). If “YES”, it means that manual correction has not been performed, so the displacement amount from the (i + 1) th reference position is calculated (step 107), and the deviation from the (i + 1) th reference temperature is calculated (step 108). Based on the calculation result, the i + 1-th offset correction of NC10 is performed (step 109), and the correction value is stored (step 110). This completes the correction process for the first point. If “NO” in the step 106, the manual correction is performed, so that the update storage of the i + 1th reference position and the reference temperature is performed (step 111) and the correction value storage (step 110) is performed. . After storing the correction value, i = i + 1 processing is performed (step 112) to return to step 105 in order to perform correction processing for the next correction point. Thereafter, steps 106 to 112 are repeated, and after i = i + 1 in step 112, if i = 32 is confirmed in step 105, it means that the correction processing for all correction points has been completed. A predetermined cutting work is performed (step 113), and the process ends.
[0029]
The features of the present invention described above can be summarized as follows.
1) Position correction data is obtained by a combination of the position sensor 26 and the temperature sensor 38.
a) By measuring the distance between the turret box 14 and the spindle 54 with the position sensor 26, the displacement from the following reference position can be obtained in total.
* Leg 52 displacement due to changes in cutting fluid temperature and outside air temperature,
* The amount of displacement due to the extension of the ball screw 17 due to the sliding nut 48 sliding,
* Displacement amount of the spindle head 2 due to heat conduction to the legs 52 due to heat generated by the rotation of the spindle 54, and * calculation errors due to heat transfer delay of each displacement amount.
b) By estimating the temperature of the turret head 6 with high accuracy via the temperature simulation block 30 and the temperature sensor 38, the displacement amount (expansion amount) of the turret head 6 and the tool or the cutting tool 8 relative to the position at the reference temperature is obtained. calculate.
c) The correction displacement amount of the workpiece 4 is grasped by adding the values a and b.
[0030]
2) The temperature and position when the operator manually corrects the control by the NC 10 are set as the reference temperature and reference position of the offset number corrected manually.
a) When the operator performs manual correction, naturally, the dimension of the processed product is checked, and the processing error is manually corrected. By performing this correction, it can be considered that the machining error has become zero. Therefore, the above temperature and position at this time are used as a reference for calculation (reference temperature, reference position).
b) When continuous machining is performed, it is checked whether manual correction has been performed by the manual correction determination means 707 every time position measurement and temperature measurement are performed. If it is determined that manual correction has been performed, the reference temperature and the reference position are updated. To do.
c) In the case of continuous processing, the product, that is, the workpiece 4 undergoes a dimensional change due to wear of the blade 8. Therefore, the operator usually checks the dimensions periodically and manually corrects processing errors including wear. This periodically calibrates the reference temperature and reference position to the latest data. Therefore, more accurate correction can be realized.
[0031]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a machine tool thermal displacement correction method and apparatus that are relatively easy to handle and that can further reduce a workpiece machining error due to thermal displacement of the machine tool.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a thermal displacement correcting device for a machine tool according to the present invention.
FIG. 2 is a layout view showing the overall configuration of a machine tool to which the present invention is applied and the mounting positions of position sensors and temperature sensors.
FIG. 3 is an explanatory view for explaining the displacement of a ball screw included in the turret box.
FIG. 4 is an explanatory diagram for explaining displacement of a leg on which a turret box and a spindle head are placed.
FIG. 5 is an explanatory diagram for explaining thermal displacement of a turret box and a turret head.
FIG. 6 is an explanatory diagram for explaining a cutting heat conduction direction and temperature measurement of the turret head.
FIG. 7 is a flowchart for explaining a thermal displacement correction method and apparatus according to the present invention.
[Explanation of symbols]
2 Spindle head 4 Work 6 Turret head 8 Cutting tool 10 Numerical controller (NC)
12 Spindle motor 14 Turret box 16 X-axis servo motor 17 X-axis ball screw 18 Z-axis servo motor 19 Z-axis ball screw 20 Pulse coder 22 Pulse coder 24 Position sensor reflector 26 Non-contact position sensor 28 Nozzle 30 Temperature simulation block 32 Liquid Motor 34 Liquid pump 36 Liquid piping 38 Temperature sensor 40 Coupling 44 Tuck bearing 46 Tuck bearing 48 Nut 50 Liquid tank 52 Leg 54 Spindle 56 Cutting oil 62 AD converter 64 AD converter 70 Thermal displacement correction device 701 Reference position memory Means 702 Position correction calculation means 703 Reference temperature storage means 704 Temperature correction calculation means 705 Correction value calculation means 706 Correction value storage means 707 Manual correction determination means

Claims (4)

A position measuring step for measuring a relative position between the spindle with the workpiece and the turret head with the cutting tool;
A temperature measuring step for measuring the temperature of the turret head;
Based on the relationship between the relative position and the temperature by the measurement performed before the start of machining as the position measurement step and the temperature measurement step, a correction amount for correcting the relative position in the measurement after the machining start is determined from the temperature at that time. A correction amount calculating step to calculate,
With
In the temperature measuring step, by measuring the temperature of a temperature simulation block arranged to be in thermal contact with the circulating cutting fluid for indirectly measuring the temperature of the turret head, A temperature measurement is performed to measure the temperature of the head,
Machine tool thermal displacement correction method.   The heat of the machine tool according to claim 1, wherein when calculating the correction amount in the correction amount calculation step, a light weight of the cutting load is estimated based on the temperature measured in the temperature measurement step, and a coefficient representing the light weight is taken into account. Displacement correction method. A position sensor that measures the relative position between the spindle with the workpiece and the turret head with the blade;
Temperature measuring means for measuring the temperature of the turret head;
Based on the relationship between the relative position and the temperature measured before the start of processing by the position sensor and the temperature measuring means, a correction amount for correcting the relative position in the measurement after the start of processing is calculated from the temperature at that time. Correction amount calculating means for
The temperature measuring means is
A temperature simulation block arranged to be in thermal contact with the circulating cutting fluid for indirectly measuring the temperature of the turret head ;
A temperature sensor for measuring the temperature of the turret head by measuring the temperature of the temperature simulation block;
Consists of
Thermal displacement compensation device for machine tools.   The heat of the machine tool according to claim 3, wherein the correction amount calculation means estimates a light weight of a cutting load based on a temperature measured by the temperature sensor when calculating the correction amount, and takes into account a coefficient representing the light weight. Displacement correction device.

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