JP2006116654A - Thermal deformation correction method and thermal deformation correcting device of nc machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal deformation correction method of an NX machine tool, machining with good accuracy without setting an environment temperature to an ordinary temperature even when a coefficient of thermal expansion of a machine tool is remarkably different from a coefficient of thermal expansion of a workpiece, and implemented at a low cost. <P>SOLUTION: An NC machine tool has a pitch error correcting function of correcting a pitch error of a feed system. This thermal deformation correcting method of the NC machine tool includes: a process S1 of measuring room temperature; a process of operating a difference between a thermal deformation amount of the NC machine tool to the ordinary temperature per stroke length and thermal deformation amount of the workpiece; a process S3 of setting a secondary correction amount of the respective correction points of the pitch error correcting function on the basis of the difference; and a process S4 of subtracting or adding the second correction amount from and to the pitch error correction amount of each correction point of the pitch error correcting function to adjust the pitch error correction amount. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermal deformation correction method and a thermal deformation correction apparatus that perform correction based on a difference in thermal deformation between an NC machine tool and a workpiece.

  In general, an NC machine tool has a pitch error correction function for correcting a pitch error of a feed system such as a ball screw in order to correspond to the room temperature (environmental temperature) of the installation place. If the coefficient of thermal expansion of the NC machine tool made of ceramics is significantly different from that of the cast NC machine tool, the pitch error is corrected with the conventional pitch error correction function and the NC machine tool positioning scale is set to the ambient temperature. Even if correspondingly correct, the positioning scale and the scale of the workpiece are different, so that the workpiece cannot be processed with high accuracy.

  For this reason, conventionally, when the thermal expansion coefficient of the workpiece and the thermal expansion coefficient of the NC machine tool are significantly different from each other, it is necessary to keep the environmental temperature at room temperature (20 ° C.), which increases the equipment cost. There was a problem.

Therefore, in order to solve such a problem, as disclosed in, for example, Patent Document 1, the dimensions of the workpiece are measured with a measurement probe, and the temperature of the NC machine tool and the temperature of the workpiece are respectively set to temperature. It has been proposed to measure with a sensor, determine the actual dimension of the workpiece from these measured values, and process the workpiece based on this actual dimension.
JP 2001-269841 A

  However, the above proposal requires not only a temperature sensor but also a measurement probe, and the control program for machining the workpiece based on the actual dimension of the workpiece becomes complicated, and it can be processed at high speed. Need to be equipped with a high-performance computer. For this reason, there exists a fault that NC machine tool itself will become expensive.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and the object of the present invention is to improve the conventional pitch error correction function so that the positioning scale of the machine tool matches the scale of the workpiece. Even if the thermal expansion coefficient of the workpiece and the thermal expansion coefficient of the workpiece are significantly different, thermal deformation of the NC machine tool that can be processed accurately without reducing the ambient temperature to normal temperature and can be carried out at low cost. A correction method and a thermal deformation correction apparatus are to be provided.

  In order to solve the above-mentioned problems, the invention according to claim 1 measures the room temperature at the installation place of the NC machine tool as a thermal deformation correction method of the NC machine tool having a pitch error correction function for correcting the pitch error of the feed system. The amount of thermal deformation of the NC machine tool and the amount of thermal deformation of the workpiece with respect to the room temperature per stroke length of the feed system from the measured room temperature, the linear expansion coefficient of the NC machine tool, and the linear expansion coefficient of the workpiece Among the correction points of the pitch error correction function, the secondary correction amount of the correction point that is also the reference point of the feed system is set to zero, and the correction point at the stroke end opposite to the reference point is calculated. Each correction point is set so that the secondary correction amount is the value of the difference and the secondary correction amount of the intermediate correction point is a value corresponding to the ratio of the length from the reference point to the correction point with respect to the stroke length of the difference. The step of setting the secondary correction amount of Secondary correction amount to the structure and a step of correcting the pitch error correction amount, respectively subtracting or adding to the pitch error correction amount of the correction point of the pitch error correction function.

  In this configuration, when the room temperature of the installation location of the NC machine tool is different from the normal temperature, the NC relative to the normal temperature per stroke length of the feed system is calculated from the room temperature, the linear expansion coefficient of the NC machine tool, and the linear expansion coefficient of the workpiece. The difference between the amount of thermal deformation of the machine tool and the amount of thermal deformation of the workpiece is calculated, and as a secondary correction amount for the pitch error correction amount of each correction point of the pitch error correction function, the correction point that is also the reference point of the feed system The secondary correction amount is zero, the secondary correction amount of the correction point at the stroke end opposite to the reference point is the difference value, and the secondary correction amount of the intermediate correction point is the reference point for the stroke length of the difference. Is set to a value corresponding to the ratio of the length from the correction point to the correction point, that is, a linear function value, and the secondary correction amount is subtracted or added to the pitch error correction amount at each correction point, respectively. The error correction amount will be corrected Ri, feed system positioning scale is to match the length scale of the workpiece. For this reason, even when a workpiece such as ceramics having a significantly different thermal expansion coefficient or linear expansion coefficient is processed with an NC machine tool, it can be processed with high accuracy without bringing the room temperature to room temperature.

  The invention according to claim 2 is an embodiment suitable as a thermal deformation correction method for an NC machine tool according to claim 1, particularly when the feed system has an extended shaft portion having a predetermined length outside the stroke reference point. Is to provide. That is, in the pitch error correction function, the pitch error correction amount is set with the end of the extended shaft portion as a true reference point. In the secondary correction amount setting step, the amount of thermal deformation of the extended shaft portion is taken into account. The secondary correction amount for each correction point is set. In this configuration, the pitch error correction amount is set corresponding to the thermal deformation of the extension shaft portion of the feed system, and the secondary correction amount of each correction point is set in consideration of the thermal deformation amount of the extension shaft portion. Therefore, the positioning scale of the feed system coincides with the length scale of the workpiece including the extension shaft portion.

  The invention according to claim 3 provides an apparatus suitable for carrying out the thermal deformation correction method for an NC machine tool according to claim 1. That is, as a thermal deformation correction device for an NC machine tool having a pitch error correction function for correcting a pitch error of a feed system, a temperature sensor that measures the room temperature at the place where the NC machine tool is installed, and the room temperature and NC measured by this temperature sensor A difference calculating means for calculating a difference between the amount of thermal deformation of the NC machine tool and the amount of thermal deformation of the workpiece with respect to room temperature per stroke length of the feed system from the linear expansion coefficient of the machine tool and the linear expansion coefficient of the workpiece; Of the correction points of the pitch error correction function, the secondary correction amount of the correction point that is also the reference point of the feed system is set to zero, and the secondary correction amount of the correction point at the stroke end opposite to the reference point is set to the difference. The secondary correction amount of each correction point is set to a value corresponding to the ratio of the length from the reference point to the correction point with respect to the stroke length of the difference. Secondary correction amount setting means And the secondary correction amount to the structure and a pitch error correction amount correction means for correcting the pitch error correction amount, respectively subtracting or adding to the pitch error correction amount of the correction point of the pitch error correction function.

  As described above, according to the thermal deformation correction method and the thermal deformation correction apparatus for an NC machine tool of the present invention, the positioning scale of the feed system matches the length scale of the workpiece even when the room temperature is different from the normal temperature. Even if the workpiece has a significantly different coefficient of thermal expansion than a machine tool such as ceramics, it can be processed with high accuracy. Moreover, not only does it require equipment for bringing the room temperature to room temperature, but it does not require a measurement probe and a high-speed, high-performance computer, and can be implemented at low cost and has excellent practicality. It is what you have.

  In particular, in the invention according to claim 2, in the case where the feed system has an extension shaft portion having a predetermined length outside the stroke reference point, the positioning scale of the feed system includes the extension shaft portion, and the length scale of the workpiece. Therefore, it is possible to further improve the processing accuracy for a workpiece having a thermal expansion coefficient significantly different from that of the machine tool without bringing the room temperature to room temperature.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments that are the best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of an NC machine tool A according to a first embodiment of the present invention. This NC machine tool A mainly comprises a machine body 1 and an NC device 2 for controlling the operation thereof.

  The machine body 1 includes a bed 10, an X-axis table 12 that moves in the X-axis direction, which is one direction of the bed 10, by the operation of the X-axis feeding device 11, and a moving region of the X-axis table 12. A columnar column 13 erected on the bed 10 and a spindle head 15 supported on the column 13 via a Y-axis saddle 14 are provided. The X-axis feeding device 11 includes a ball screw 17 disposed along the X-axis direction of the bed 10, a servo motor 18 connected to one end of the ball screw 17, a ball screw 17, and an X-axis table 12. The ball screw nut portion 19 is fixed to the X axis table 12 and the servo motor 18 rotates the ball screw 17 to move the X axis table 12 in the X axis direction of the bed 10. The Y-axis saddle 14 moves the spindle head 15 in the Y-axis direction orthogonal to the X-axis direction of the bed 10, and the spindle head 15 has a configuration in which the tool mounting portion 15a moves in the vertical direction, that is, the Z-axis direction. It has become. A workpiece w (see FIG. 3) is fixed on the X-axis table 12, and a tool (not shown) mounted on the tool mounting portion 15a of the spindle head 15 is attached to the workpiece w in the three-axis direction. Processing is performed with relative movement. Note that the Y-axis saddle 14 and the Z-axis feeding device, which are the feeding device for the Y-axis saddle 14 and the spindle head 15, are not shown, but have substantially the same configuration as the X-axis feeding device 11. ing.

  On the other hand, the NC device 2 is based on an input unit 21 including a keyboard, an arithmetic control unit 22 that executes various controls based on input data from the input unit 21, and the commands of the arithmetic control unit 22. And a servo motor control unit 23 for controlling each servo motor 18 of the X-axis, Y-axis, and Z-axis feeding device 11 of the machine main body 1. The arithmetic control unit 22 includes pitch error correction control for correcting the pitch error of each feeder 11 in the control to be executed, and has a pitch error correction function for executing this control. In this case, the pitch error correction amount at each correction point of the pitch error correction function is stored in advance in the calculation control unit 22.

  As a feature of the present invention, the NC machine tool A includes a temperature sensor 25 that measures the room temperature of the installation location, and the temperature signal of the temperature sensor 25 is arithmetically controlled through the input unit 21 of the NC device 2. Input to the unit 22. The arithmetic control unit 22 corrects the pitch error correction amount at each correction point of the pitch error correction function based on this temperature signal. The arithmetic control unit 22 and the temperature sensor 25 constitute a thermal deformation correction device 30 according to the present invention. Hereinafter, correction control for the pitch error correction amount at each correction point of the pitch error correction function will be described with reference to the flowchart shown in FIG.

  That is, in the correction control, first, the room temperature is measured by the temperature sensor 25 (step S1), and then the measured room temperature and the linear expansion coefficient of the machine body 1 of the NC machine tool A (specifically, the X-axis feeder 11). NC machine tool A with respect to room temperature per stroke length of the X-axis feeder 11 from the linear expansion coefficient of the ball screw 17 serving as a reference for the positioning scale and the linear expansion coefficient of the workpiece w constituting the linear scale) The difference between the amount of thermal deformation of the machine body 1 and the amount of thermal deformation of the workpiece w is calculated (step S2).

As a method of calculating this difference, for example, in FIG. 3, the stroke L1 of the X-axis feeder 11 is 2000 mm, the length L2 of the workpiece w is 500 mm, the room temperature is 30 ° C., and the linear expansion coefficient of the casting (machine body 1) is When the linear expansion coefficient of the work w is 12 × 10 ⁻⁶ / ° C. and 7 × 10 ⁻⁶ / ° C., first, the X-axis feeder 11 of the NC machine tool A with respect to room temperature (20 ° C.) at room temperature. A thermal deformation amount (elongation amount) e1 per stroke length L1 is calculated. This thermal deformation amount e1 is 240 μm. Next, the thermal deformation amount e <b> 2 is calculated when the workpiece w is considered to be the same as the stroke length L <b> 1 of the X-axis feeding device 11 with respect to room temperature at room temperature. This thermal deformation amount e2 is 140 μm. Thereafter, the difference Δe is calculated from the two heat deformation amounts e1 and e2. This difference Δe is 100 μm. The difference calculation means 31 which is a component of the thermal deformation correction apparatus 30 of the present invention is configured by step S2 for executing the calculation of the difference Δe.

  Next, a secondary correction amount is set as a correction amount for the pitch error correction amount at each correction point of the pitch error correction function (step S3). In the setting of the secondary correction amount, for example, as shown in FIG. 4, in the pitch error correction function, five correction points X1 to X5 are set at equal intervals between the reference point of the X-axis feeder 11 and the stroke end. When the difference Δe is 100 μm as shown in the above example, the secondary correction amount at the correction point X1, which is also the reference point of the X-axis feeding device 11, is set to zero, and the secondary correction amount at the stroke end correction point X5 is set as the difference. The value of Δe is 100 μm, and the secondary correction amount at each of the intermediate correction points X2 to X4 is set according to the ratio of the length from the reference point to each correction point X2 to X4 with respect to the stroke length L1 of the difference Δe. The values are set to 25 μm, 50 μm, and 75 μm, respectively. By the step S3 for executing the setting of the secondary correction amount, the secondary correction amount setting means 32 that is a component of the thermal deformation correction device 30 of the present invention is configured.

  Subsequently, the pitch error correction amount is corrected by subtracting or adding the secondary correction amount to the pitch error correction amount at each of the correction points X1 to X5 of the pitch error correction function (step S4). In this correction, as shown in FIG. 3, when the thermal deformation amount e1 of the machine body 1 is larger than the thermal deformation amount e2 of the workpiece w, the secondary correction amount is the direction of the difference Δe between the deformation amounts e1 and e2. If the amount of thermal deformation e1 of the machine body 1 is smaller than the amount of thermal deformation e2 of the workpiece w, the secondary correction amount is reversed. Is added in the direction of increasing the pitch error correction amount. Here, the pitch error correction function corrects the pitch error in accordance with the thermal deformation of the machine body 1, and the pitch error correction amount at each correction point is determined from the reference point of the machine body 1 shown in FIG. It corresponds to the amount of thermal deformation up to the stroke end. Therefore, correcting the pitch error correction amount by subtracting or adding the secondary correction amount to the pitch error correction amount at each correction point of this pitch error correction function is effective for the thermal deformation of the workpiece w. It means changing to the corresponding value. The pitch error correction amount correcting means 33, which is a component of the thermal deformation correction apparatus 30 of the present invention, is configured by step S4 for executing the correction of the pitch error correction amount.

  Thereafter, the servo motor 18 of the X-axis feeder 11 is controlled via the servo motor control unit 23 based on the corrected pitch error correction amount (step S5). Thus, one correction control is completed. This correction control may be performed only before the machining of the workpiece w is started, or may be repeatedly performed every predetermined time during machining by a timer or the like built in the NC device 2.

  Therefore, in the NC machine tool A, even when the room temperature of the installation location is different from the room temperature, the pitch error correction amount is adjusted by performing correction control on the pitch error correction amount at each correction point of the pitch error correction function. The workpiece w is changed to a value corresponding to the thermal deformation of the workpiece w, and the positioning scale of each feeder 11 of the machine body 1 matches the length scale of the workpiece w. Even those with significantly different expansion rates can be processed with high accuracy. In addition, it does not require equipment for bringing the room temperature to room temperature, and does not require a measurement probe and a high-speed, high-performance computer unlike the conventionally known one disclosed in Patent Document 1, so that it can be implemented at low cost. Can do.

  FIG. 5 shows the configuration of the X-axis feed device 51 of the NC machine tool according to the second embodiment of the present invention. In the case of this second embodiment, the X-axis feed device 51 rotates the ball screw 53 by the servo motor 52 in the same manner as the X-axis feed device 11 of the NC machine tool A according to the first embodiment. 54 is moved between the reference point X1 in the X-axis direction and the stroke end Xn, but has a relatively long extension shaft portion 55 outside the reference point X1, that is, closer to the servo motor 52. .

  The extension shaft portion 55 is made of a part of the ball screw 53 or a member made of the same material (casting). When the room temperature is different from the room temperature, the extension shaft portion 55 is also connected to the stroke reference point X1 of the X-axis feeding device 51. As shown in FIG. 5, the actual thermal deformation amount e of the X-axis feeding device 51 is set to the true reference point X0 at the end of the extended shaft portion 55, and the reference point X0. It becomes a linear function value in proportion to the distance from. Correspondingly, in the pitch error correction function, the pitch error correction amount of each of the correction points X1 to Xn is set to a linear function value with the end of the extended shaft portion 55 as the true reference point X0.

  The correction control for the pitch error correction amount at each correction point of the pitch error correction function is basically the same as in the first embodiment, but when setting the secondary correction amount (see FIG. 2). Step S3), a secondary correction amount is set in consideration of the amount of thermal deformation of the extension shaft portion 55. Specifically, the amount of thermal deformation of the extension shaft portion 55 is set as an offset amount Δe0, and the correction amount Δe1 determined by the position of each correction point from the stroke reference point X1 (in the case of the first embodiment). A value obtained by adding a value corresponding to the secondary correction amount is set to a secondary correction amount Δe (= Δe1 + Δe0). The offset amount Δe0 is L3 as the length of the extension shaft portion 55, ΔT as the temperature difference between room temperature and normal temperature, and α as the linear expansion coefficient of the casting.

Δe0 = L3 × ΔT × α
It is.

  In the second embodiment, when the X-axis feeding device 51 has a relatively long extending shaft portion 55 outside the stroke reference point X1, the positioning scale of the X-axis feeding device 51 is the extending shaft portion 55. Therefore, the processing accuracy for a workpiece having a significantly different thermal expansion coefficient from that of the machine body can be further improved without bringing the room temperature to room temperature.

  The present invention is not limited to the first and second embodiments described above, but includes other various embodiments. For example, in the first embodiment, in the correction control for the pitch error correction amount at each correction point of the pitch error correction function, the room temperature measured by the temperature sensor 25 and the linear expansion coefficients of the NC machine tool A and the workpiece w are calculated. From the above, the amount of thermal deformation of the NC machine tool A and the amount of thermal deformation of the workpiece w with respect to the room temperature per stroke length of the feeder 11 is calculated separately, and the difference between the two heat deformation amounts is calculated. In the present invention, in order to increase the calculation speed and hence the control speed, the control table for determining the difference between the thermal deformation amount of the machine tool A and the thermal deformation amount of the work w in advance for each temperature of room temperature is arithmetically controlled. If the room temperature is measured and the room temperature is measured, the difference is immediately calculated from this comparison table, or the difference obtained from the calculation formula is integrated with the correction factor according to the actual machine to determine the difference. Good.

  Further, in each of the above embodiments, all correction control for the pitch error correction amount of each correction point of the pitch error correction function is automatically performed by the arithmetic control unit 22 of the NC device 2. As an invention of a thermal deformation correction method for a machine, an operator may perform part of the correction control. For example, the operator measures the room temperature of the installation location of the NC machine tool with a thermometer, and inputs the measured temperature to the input unit 21 of the NC device 2, or not only the temperature measurement but also the amount of thermal deformation of the machine tool A. The operator may calculate a difference from the amount of thermal deformation of the workpiece w, and the difference may be input to the input unit 21 of the NC device 2.

1 is a schematic configuration diagram of an NC machine tool according to a first embodiment of the present invention. It is a flowchart figure of correction control with respect to the pitch error correction amount of each correction point of a pitch error correction function. It is explanatory drawing for demonstrating the calculation method of the difference of the thermal deformation amount of a machine main body, and the thermal deformation amount of a to-be-processed object. It is explanatory drawing for demonstrating the setting method of the secondary correction amount with respect to the pitch error correction amount of each correction point of a pitch error correction function. FIG. 5 is a view corresponding to FIG. 4 showing a second embodiment.

Explanation of symbols

A NC machine tool w Workpiece 11, 51 X-axis feed device 22 Calculation control unit 25 Temperature sensor 30 Thermal deformation correction device 31 Difference calculation means 32 Secondary correction amount setting means 33 Pitch error correction amount correction means

Claims (3)

An NC machine tool thermal deformation correction method having a pitch error correction function for correcting a pitch error of a feed system,
A process of measuring the room temperature of the NC machine tool installation location;
Calculate the difference between the amount of thermal deformation of the NC machine tool and the amount of thermal deformation of the workpiece with respect to the room temperature per stroke length of the feed system from the measured room temperature, the linear expansion coefficient of the NC machine tool, and the linear expansion coefficient of the workpiece. And a process of
Among the correction points of the pitch error correction function, the secondary correction amount of the correction point that is also the reference point of the feed system is set to zero, and the secondary correction amount of the correction point at the stroke end opposite to the reference point is set to the difference. The secondary correction amount at each correction point is set so that the secondary correction amount at the intermediate correction point is a value corresponding to the ratio of the length from the reference point to the correction point with respect to the stroke length of the difference. Process,
And a step of correcting the pitch error correction amount by subtracting or adding the secondary correction amount to the pitch error correction amount of each correction point of the pitch error correction function. Correction method.   When the feed system has an extended shaft portion of a predetermined length outside the stroke reference point, the pitch error correction function has a pitch error correction amount set with the end of the extended shaft portion as a true reference point. 2. The NC deformation correction method for an NC machine tool according to claim 1, wherein in the secondary correction amount setting step, the secondary correction amount at each correction point is set in consideration of the thermal deformation amount of the extension shaft portion. . A thermal deformation correction device for an NC machine tool having a pitch error correction function for correcting a pitch error of a feed system,
A temperature sensor that measures the room temperature of the NC machine tool installation location;
The amount of thermal deformation of the NC machine tool and the amount of thermal deformation of the workpiece with respect to the room temperature per stroke length of the feed system based on the room temperature measured by this temperature sensor, the linear expansion coefficient of the NC machine tool, and the linear expansion coefficient of the workpiece. Difference calculating means for calculating the difference between
Of the correction points of the pitch error correction function, the secondary correction amount of the correction point that is also the reference point of the feed system is set to zero, and the secondary correction amount of the correction point at the stroke end opposite to the reference point is set to the difference The secondary correction amount of each correction point is set so that the secondary correction amount of the intermediate correction point is a value corresponding to the ratio of the length from the reference point to the correction point with respect to the stroke length of the difference. Secondary correction amount setting means;
An NC comprising: pitch error correction amount correcting means for correcting the pitch error correction amount by subtracting or adding the secondary correction amount to the pitch error correction amount at each correction point of the pitch error correction function. Machine tool thermal deformation correction device.

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