JPH0970739A - Dynamic thermal displacement correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform working with high accuracy higher than a predetermined level by correcting thermal displacement corresponding to the rotational frequency and time with a predetermined time pitch on real time on the basis of a thermal displacement table of the rotational frequency-time while continuing the working. SOLUTION: By obtaining the thermal displacement σ value in a working position in a predetermined pattern, a thermal displacement table of the rotational frequency-time of a spindle 6 is prepared. In the actual working based on this pattern, a workpiece can be worked with high accuracy under the non- thermal displacement condition by correcting the displacement of amount σin the X, Y, Z directions in the working position by a control section of an NC machine tool 1 for example. Further, either method of changing the workpiece coordinate system by a correcting amount or method of correcting the move amounts of the X, Y, Z axes by the correcting amount may be used for the control method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic thermal displacement correction method which enables real-time correction of thermal displacement during machining in a numerically controlled machine tool having a rotating mechanism such as a spindle to enable highly accurate machining.

[0002]

2. Description of the Related Art In a machine tool or the like, each part generates heat as the main shaft rotates, causing thermal displacement in the X, Y, and Z directions.
This thermal displacement affects the processing tool mounted on the spindle. Therefore, if the processing part of the processing tool is not corrected in the X, Y, and Z directions by the amount of thermal displacement, the processing size is deviated by that amount. In the prior art, various cooling means or the like are adopted to suppress the temperature rise of the rotating mechanism section or the like to minimize the heat change, and at the same time, the thermal displacement of each part of the machine is corrected based on the information from the detector such as the temperature sensor. The method was adopted.

[0003]

In a machine tool or the like, a headstock, which is one of the rotating mechanism parts, has a complicated structure and serves as a heating element. Various types of cooling means have been adopted, but all of them are expensive. Further, it is difficult to keep the inside of the headstock always at room temperature by the cooling means. On the other hand, it is possible to improve the working accuracy by grasping the heat generation state of the spindle with a temperature sensor or the like and performing thermal displacement correction corresponding to this. However, this method is an intermittent correction, and it is not possible to correct the thermal displacement in the machining site that changes in various ways. Therefore, there is a problem that high-precision processing of a predetermined level or higher cannot be performed.

The present invention solves the above problems, and provides a dynamic thermal displacement correction method in which thermal displacement correction is performed in real time and which is capable of high precision machining of a fraction of the prior art. To aim.

[0005]

According to the present invention, there is provided a characteristic of a machine in which a change in thermal displacement when rotating for a certain number of revolutions in a target processing machine and a change in thermal displacement after stopping rotation are constant. A method for correcting thermal displacement in a processing machine in which at least the machined part of the machine is thermally displaced in the X, Y, and Z directions due to temperature changes caused by rotation or stop of the rotation mechanism section. That is, the processing machine is rotated at various rotational speeds (RPMs) for an appropriate period of time, or stopped after rotation, and the thermal displacement of the processed portion in each of the X, Y, and Z directions is measured to measure the thermal speed-time of heat. After creating a displacement table in advance and recording it in the control unit that controls the coordinate position of the machining site, the machining machine is caused to perform predetermined machining under appropriate machining conditions, and the rotation speed and The elapsed time in the rotation, the elapsed time after the rotation is stopped, and the change in the number of revolutions are detected, and the thermal displacement corresponding to the number of revolutions and the time is corrected at a predetermined time pitch based on the thermal displacement table of the number of revolutions-time. It is characterized by a dynamic thermal displacement correction method in which the processing is continued while being performed in real time. Further, a dynamic thermal displacement correction method for selectively switching the thermal displacement correction by the control unit between changing the work coordinate system and correcting the movement amounts of the X, Y, and Z axes in the processing region. It is characterized by.

An elapsed time thermal displacement table at a certain number of rotations is created in advance for each target processing machine, and an elapsed time thermal displacement table is created when the rotation is stopped at that rotation and then both tables are created. Record in the controller. Next, the number of revolutions during actual machining, the elapsed time in that revolution, the elapsed time after the rotation is stopped, and the state of change in the number of revolutions are obtained, and the thermal displacement amount corresponding to the state is obtained based on the table. Make a correction. This correction is performed in real time at a predetermined time pitch. As a result, the thermal displacements in the X, Y, and Z directions of the processing portion of the processing machine are corrected in real time, and high-precision processing is performed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a dynamic thermal displacement correction method according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, a numerically controlled machine tool 1 such as a machining center comprises a column 3 and a table 4 placed on a bed 2, and a headstock 5 supported by the column 3 so as to be movable in the Y direction. . The column 3 moves along the Z direction, and the table 4 moves along the X direction. A spindle 6 is mounted on the spindle stock 5, and a work (not shown) is mounted on the table 4. The work is processed by a processing tool (not shown) attached to the spindle 6. From the above structure, by estimating the thermal displacement state between the mounting position B of the processing tool on the spindle 6 and the mounting position A of the work on the table 4, a thermal displacement amount substantially equal to the thermal displacement at the processing site can be estimated. You can The method for actually measuring the thermal displacement at this processed portion is as follows. That is, the ball 7 is mounted at the mounting position B, the flat surface 8 of the gap sensor is provided at a position opposite to the ball 7, and the flat surface 8 is set in association with the mounting position A. The thermal displacement can be obtained by detecting the change in the gap δ between the ball 7 and the flat surface 8 and measuring it with the measuring device 9.

The thermal displacement characteristics of the numerically controlled machine tool 1 are obtained in advance as follows. For example, the spindle 6 has a rotational speed of 20,
000RPM, 18,000RPM, 16,000RP
Rotate at M, 14,000 RPM ... And measure the value of thermal displacement δ with the passage of time. In this example, it is performed every 5 minutes. Next, when the value of the thermal displacement δ reaches the saturated state (stable state), the rotation of the main shaft 6 is stopped, and the change in the thermal displacement δ with the lapse of time is obtained as in the above. By the above measuring method, the thermal displacement table of rotation speed-time as shown in FIGS. 2 and 3 is created. This table is input to and recorded in the control unit that controls the position of the spindle 6 of the numerically controlled machine tool 1 in the X, Y, and Z directions.

FIG. 2 is a rotational thermal displacement correction table showing thermal displacement δ during rotation of the main shaft 6. When the main shaft 6 is rotating at 20,000 RPM as shown in the figure, there is a thermal displacement of a at the elapsed time of 5 minutes, b at the next 10 minutes, below, the next 15 minutes, 20 minutes, 25 minutes, At 30 minutes ..., Thermal displacement of c, d, e, f ... occurs. Similarly, the rotation speed RPM of the spindle 6 is 18,000 RPM, 16,000 RPM.
In the case of RPM, 14,000 RPM, the elapsed time is 5 minutes to 30 minutes ... The thermal displacement is g, h, i, j, k, l ...
., M, n, o, p, q, r ..., s, t, u, v,
w, x ...

FIG. 3 shows that the spindle 6 has a constant RPM for a certain time.
The following table shows a thermal displacement correction table during stop when the main shaft 6 is rotated in a state where the thermal displacement is saturated and the rotation of the main shaft 6 is stopped and left as it is. Rotation speed 20,000R as shown
The values of the thermal displacement δ every 5 minutes after the spindle 6 rotating at PM stopped are a ', b', c ', d', e ', f'.
Indicated by. Similarly, 18,000 RPM, 1
The value of the thermal displacement δ for each elapsed time divided into 6,000 RPM, 14,000 RPM, ... Is g ′, h ′, i ′,
j ', k', l '..., m', n ', o', p ',
q ', r' ... s ', t', u ', v', w ', x'
Indicated by. In addition, in FIG. 5, 20,000 RPM
And the time-thermal displacement curve at 15,000 RPM is shown.

Next, the operation of this example will be described. In machining a workpiece, the RPM RPM of the spindle 6 changes depending on the shape, size, and machining method of the workpiece, and the machining time (elapsed time) at a constant revolution also varies. Therefore,
It is complicated and difficult to understand to show the operation of this example in actual processing. Therefore, FIG. 5 shows a simulated pattern for explaining the operation of this example. That is, the spindle 6 starts to rotate at 20,000 RPM from the start of rotation (t ₀ ) of the spindle 6, and stops after a lapse of time t ₁ . Next, when t _{2 has} passed, the spindle 6 is again rotated by 15,000.
Rotate at RPM. Then, when the time t _{3 has} elapsed, the rotation of the spindle 6 is stopped again and the spindle 6 is left standing. At the elapsed time t ₄ , the spindle 6 returns to the state at the original rotation start time.
By obtaining the value of the thermal displacement δ in the processed portion in the above pattern, the thermal displacement table as shown in FIGS. 2 and 3 can be created. In the actual machining based on the pattern, for example, the controller of the numerically controlled machine tool 1 corrects the displacement in the X, Y and Z directions in the machining portion by the thermal displacement δ shown in FIG. Workpiece machining is performed in a state where it does not occur, and high precision machining is possible. As the control method, either of the control methods of changing the work coordinate system by the correction amount as described above or correcting the movement amounts of the X, Y, and Z axes by the correction amount may be used.

Next, the process of the thermal displacement correction method of this embodiment will be described with reference to the flowchart of FIG. First, the elapsed time and the rotation speed RPM in the processing state are calculated each time (steps 100 and 101). Next, it is confirmed that the spindle is rotating (step 102), and if it is rotating (yes).
The stop flag is set to OFF (step 103). On the other hand, if it is not rotating (no), the process proceeds to the rotation flag OFF setting (step 104). If it is confirmed that the flag during stop is off, yes or no that the flag during rotation is off
Is determined (step 105), and if yes, the process proceeds to time reset (step 106) and time measurement is performed (step 107). If no, step 10 directly
Time measurement of 7 is performed. Next, the previous RPM and the current RPM are compared (step 108), and if they match (yes), thermal displacement correction based on the correction data is performed (step 109). On the other hand, if they do not match (no), the current RPM is reset by turning on the rotating flag (step 110), and the process returns to step 108 again. On the other hand, if the step 104 for confirming that the rotation flag is off is performed, the stop flag is continuously turned off yes, no.
Is determined (step 111), and if yes, the time is reset (step 112) and the time is measured (step 113). If no, step 11 directly
Measure the time of 3. Next, the thermal displacement correction based on the thermal displacement correction data during stop is performed (step 114).

Specifically, according to this example, it was verified that the processing system was improved by about 1/3. Further, the time pitch of the thermal displacement correction is every 10 seconds in this example, but it is not limited to this.

[0014]

The dynamic thermal displacement correction method according to the present invention has the following remarkable effects. 1) Since the thermal displacement correction according to the processing mode is performed in real time by the recording table that is measured in advance, high-precision processing becomes possible. 2) The actual processing machine itself is operated to create a thermal displacement correction table at the processing site, and corrections are made at appropriate time intervals during processing based on this correction table, which is extremely effective compared to conventional methods. Correction is performed. 3) A temperature sensor, a control device that operates based on the detection signal, and the like are unnecessary, and the cost of the control system can be reduced. 4) It is applicable to all kinds of processing machines and has a wide range of applications.

[Brief description of drawings]

FIG. 1 is an explanatory view for explaining a measuring method for creating a thermal speed-time thermal displacement table of the present invention in a machine tool in advance.

FIG. 2 is a diagram showing an example of a thermal displacement correction table during rotation according to the present invention.

FIG. 3 is a table showing an example of a thermal displacement correction table during stop in the present invention.

FIG. 4 is a diagram showing a time-thermal displacement curve in the present invention.

FIG. 5 is a diagram showing a time-thermal displacement curve in the present invention.

FIG. 6 is a flowchart for explaining thermal displacement correction of the present invention.

[Explanation of symbols]

 1 Numerical control machine tool 2 Bed 3 Column 4 Table 5 Spindle base 6 Spindle 7 Ball 8 Flat surface 9 Measuring device

Claims (2)

[Claims] 1. A method for correcting thermal displacement in a processing machine, wherein at least a machined part of the machine is thermally displaced in X, Y, and Z directions due to a temperature change caused by rotation or stop of a rotating mechanism.
The processing machine is rotated at various rotational speeds (RPM) for an appropriate period of time, or stopped after the rotation so that X, X
After measuring the thermal displacement in each of the Y and Z directions with time, a thermal displacement-time thermal displacement table is created in advance, and the thermal displacement table is recorded in the control unit that controls the coordinate position of the machining site. Perform predetermined processing under the processing conditions, detect the number of revolutions during the machining, the elapsed time in the rotation, the elapsed time after rotation stop and the change in the number of revolutions, and determine based on the thermal displacement table of the number of revolutions-time. A dynamic thermal displacement correction method, characterized in that the machining is continued while correcting the amount of thermal displacement commensurate with the rotational speed and time in real time at the time pitch of. 2. The thermal displacement correction by the control unit changes the work coordinate system, or X,
2. The dynamic thermal displacement correction method according to claim 1, wherein whether or not to correct the movement amounts of the Y and Z axes is selectively switchable.