JPH0839399A - Thermal displacement correcting device for machine tool - Google Patents

Abstract

PURPOSE:To precisely eliminate an influence of mechanical thermal displacement on the working accuracy in actual working by detecting a thermal displacement in designated timing to obtain an accurate correction value during idling according to a working program. CONSTITUTION:In advance of actual working on a work, a machine tool is idled according to the same working program. At this time, a test bar 3 is fitted to a spindle 2, and the thermal displacement of the spindle is detected by a displacement detector 4 in a designated timing of the working program. According to the thermal displacement, the relative position correction value of the spindle 2 to the work is calculated and stored. At the time of working a work, the relative position of the spindle 2 the work is corrected by each block of the working program according to the correction value. The correction value may be interpolated in such a manner as to be changed step by step at designated detecting intervals so that at the time of working, correction may be made by subdivided correction values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for correcting thermal displacement of a spindle in a machine tool for cutting or grinding a work.

[0002]

2. Description of the Related Art Generally, thermal displacement of a spindle has a great influence on the machining accuracy of a work, and particularly when a machining failure occurs in a work that is expensive and requires high accuracy, such as a die, it causes a great economic loss. Suffer. Therefore, various countermeasures against thermal displacement have been proposed in the past, and one of them is known as a device that estimates the thermal displacement amount based on the temperature of the main spindle and corrects it. There is also known a method in which the work is sampled, its dimensions are measured, and correction is performed at appropriate times.

[0003]

However, according to the former conventional device, since the thermal displacement amount is indirectly estimated based on the temperature, the distance from the heat generating portion to the processing portion and the thermal conductivity of inclusions are high. It is difficult to accurately detect the thermal displacement amount including such factors as fluctuations, and accurate correction is impossible. Further, according to the latter conventional method, particularly when the machining such as the die machining by the machining center takes a long time, the amount of thermal displacement continuously changes due to the continuous machining, so that it is also difficult to make an accurate correction.

Therefore, an object of the present invention is to provide a novel apparatus capable of accurately and easily correcting thermal displacement.

[0005]

In order to solve the above-mentioned problems, a thermal displacement correction device of the present invention comprises a displacement detector for detecting the thermal displacement amount of a spindle during idle operation in a machining program of a machine tool, A detection program storage unit that stores the thermal displacement amount detection program by the displacement detector, a detection time storage unit that stores the timing for detecting the thermal displacement amount for the machining program, and the relative position between the spindle and the workpiece based on the thermal displacement amount. A correction value calculation unit that calculates a correction value and a control unit that corrects the relative position between the spindle and the workpiece based on the correction value at the timing of the machining program during machining of the workpiece are provided.

Here, preferably, the displacement detector detects the thermal displacement amount at the timing, and calculates the relative position correction value by performing an interpolation process so as to change stepwise with respect to the detection interval of the timing. An interpolation correction value calculation unit is provided, and the control unit is configured to correct the relative position between the spindle and the work on the basis of the correction value subdivided at the time of machining the work.

[0007]

According to the thermal displacement compensating device of the present invention, prior to actual machining, the machine tool is idled according to the same machining program as during machining, and the thermal displacement amount of the spindle at that time is detected using the displacement detector. Therefore, under almost the same conditions as during processing, it is possible to accurately detect a thermal displacement caused by various factors including environmental factors such as room temperature at a predetermined timing and obtain a correction value. Therefore, if a correction is applied at the time of processing with this correction value, it is possible to eliminate or reduce the influence of mechanical thermal displacement on the processing accuracy. Moreover, since it is not necessary to sample the work when measuring the amount of thermal displacement, the detection and correction work can be accurately and easily performed at a predetermined timing even when the processing time is long.

Further, if the correction value is interpolated at the detection interval and the correction value is subdivided at the time of machining, the measurement time of the thermal displacement amount can be suppressed to the necessary minimum. It becomes possible to machine the machined surface smoothly by adding precise correction.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the configuration of a machine tool. 1 is a machine body, 2 is a spindle, 3 is a test bar attached to the spindle 2, 4 is the position of the test bar 3 and the heat of the spindle 2 is measured. A displacement detector, such as a gap sensor or a laser length measuring device, for detecting the amount of displacement, 5 is a control device for electrically controlling each part of the machine tool during machining and detection, and 6 is an operation panel.

FIG. 2 shows the configuration of the control unit 5, which is 8
Is a machining program storage unit for storing a machining program. 9 is a detection program storage unit for storing a thermal displacement amount detection program by the displacement detector,
A measurement program storage unit that can store a measurement program, and 10 is a detection time storage unit that stores a timing for detecting a thermal displacement amount for a machining program, and sets a time interval during detection and correction. It is an interval storage unit capable of storing a value. Also, 11
Is a program analysis unit that analyzes the machining program and the measurement program. 12 is a function generator that generates a predetermined function based on the program analysis value; 13 is an adder;
Is a servo control unit. Then, the servo control unit 14 controls the drive unit 15 of each part of the machine tool according to the machining program to machine the work (not shown) with the tool attached to the spindle 2.

In FIG. 2, 16 is a time counter, and 17 is a timing judgment unit for judging the detection timing and the correction timing based on the set value in the interval storage unit 10. Reference numeral 18 is a displacement amount calculation unit that calculates the thermal displacement amount of the spindle 2 from the detection data of the displacement detector 4, and 19 is the spindle 2
And a correction value calculation unit that calculates a correction value of the relative position of the work in association with the thermal displacement amount, 20 is a correction value storage unit that stores the correction value, and 21 is a correction interval that is set in the interval storage unit 10. The interpolation correction value calculation unit calculates a plurality of interpolation correction values by performing an interpolation process so that the values change stepwise.

Next, a first embodiment of a thermal displacement correction method using the apparatus configured as described above will be described with reference to the flow charts of FIGS. 3 and 4. FIG. 3 is a flow chart showing a thermal displacement amount measuring process. In this measuring process, the machine tool is idle-operated according to the same machining program as when machining a workpiece. That is, when processing is started in step S1,
The time counter 16 is activated, and in step S2, the timing determination unit 17 determines whether or not the count value of the time counter 16 has reached the set value of the interval storage unit 10. If the count value reaches the set value, step S3
Then, the machining is interrupted, the time counter 16 is stopped, and the block number of the machining program at this time is stored.

In step S4, the measurement program is read, the test bar 3 is attached to the spindle 2 on the machine side, and the displacement detector 4 is positioned at a predetermined position facing the test bar 3. Then, in step S5, the position of the test bar 3 is measured by the displacement detector 4, and the displacement amount calculator 18 detects the thermal displacement amount of the spindle 2. In step S6, the correction value calculation unit 19 calculates the correction value of the relative position of the spindle 2 and the work in association with the thermal displacement amount, and in step S7, the correction value is stored in the correction value storage unit 20.

In step S8, with the spindle 2 and the workpiece positioned at the end point of the block number before the machining is interrupted, the time counter 16 is restarted to restart the machining, and in step S9, the blocks are block by block. Is read and the processing is executed. Then, in step S10, it is determined whether or not the processing is completed based on the presence or absence of a command in the processing program, and if the processing is continued, the process returns to step S2. If the machining is completed, the presence or absence of the next work or machining program is confirmed in step S11. If there is the next machining, the process returns to step S1. If not, the measuring process is terminated.

FIG. 4 is a flow chart showing a working process of the work after the thermal displacement measuring process is completed.
When the processing is started in 12, the time counter 16 is activated, and in step S13, it is determined whether or not the count value of the time counter 16 has reached the set value of the detection interval. When the count value reaches the set value, that is, at the same timing as when the thermal displacement amount is detected, the correction value corresponding to the count value is read from the correction value storage unit 20 in step S14.
Then, in step S15, based on the correction value and the output of the function generating unit 12, the servo control unit 14 controls the driving device 15 of each unit of the machine tool, and the processing of each block is executed. After that, in step S16, it is determined whether the processing is completed or continued, and if it is continued, the process returns to step S13. In the case of the end, in step S17, the presence or absence of the next work or machining program is confirmed, and if there is the next machining, the process returns to step S12, and if not, the machining process ends.

According to the thermal displacement correction method of this first embodiment, prior to the actual machining, the machine tool is idled according to the same machining program as during machining, and the thermal displacement amount of the spindle 2 at that time is detected by the displacement detector 4. Since it is detected by using, the thermal displacement generated by various factors including environmental factors such as room temperature can be accurately detected and the correction value can be obtained under almost the same conditions as during processing. Therefore, if a correction is applied at the time of processing with this correction value, the effect of mechanical thermal displacement on the processing accuracy can be removed or reduced for each block in actual processing, and expensive and highly accurate molds and the like are required. It is possible to surely prevent machining defects of a workpiece, thereby avoiding economic damage. Further, unlike the conventional case, since it is not necessary to sample the work, there is an advantage that even if the machining program is composed of a plurality of blocks, the detection and correction work can be accurately and easily carried out for each block.

FIG. 5 is a flowchart showing a second embodiment of the thermal displacement correction method, in which the measuring process and the machining process of the first embodiment are integrated into a series of programs.
When processing is started in step S18, step S19
Then, it is confirmed whether or not there is a correction value corresponding to the machining program. Here, the correction data file corresponding to the machining program is determined under a specific condition, and it is determined whether or not there is a file that meets this condition. If there is no file, the correction value file is automatically created in step S20. Later,
After step S21, the same measurement program as that of the first embodiment is executed. If the correction value already exists, re-measurement is not necessary, and therefore, the processing program similar to that of the first embodiment is executed in step S31 and subsequent steps.

According to the thermal displacement correction method of the second embodiment, when a work is automatically carried in and out by a pallet changer or a loader, if there is no correction value, the work is not carried in first and If the amount of thermal displacement is detected, and if there is a correction value, the machining program is stored in the control device 5 such that the work is immediately carried in and the actual machining is performed. It has the advantage that it can be automatically implemented by the program. In addition, the function to judge the presence or absence of the correction value,
The timing determination unit 17 may be configured to have the same function, or this functional unit may be provided between the determination unit 17 and the correction value storage unit 20.

By the way, according to the correction methods of the first and second embodiments, there is a possibility that the correction value may change during processing in the case of a work having a long processing time. The degree of change is small if the detection interval (also the correction interval) is short, but if so, the time required for measurement becomes very long. On the contrary, if the detection interval is lengthened, the required measurement time will be shortened, but the degree of change in the correction value will be large, and there will be a possibility that a step will be formed on the processing surface when processing a gently curved surface such as a mold. is there. In order to solve these problems, the thermal displacement correction device of the present invention includes an interpolation correction value calculation unit 21. That is, in the above-described embodiment, the correction is performed at the same timing as the detection, but in the third embodiment disclosed below, the interpolation correction value calculation unit 21 changes the plurality of correction values stepwise in one detection interval. The servo control section 1
4 corrects the thermal displacement by the subdivided correction value.

This correction value interpolation processing will be described with reference to the flowchart of FIG. 6. First, prior to the measurement step, the operator sets the detection interval a and the correction interval b in advance on the operation panel 6, and the set values are set to the interval. It is stored in the storage unit 10. Then, the thermal displacement amount is detected for each block in the same manner as in the above embodiment. Next, the interpolation processing program of FIG. 6 is started, and the thermal displacement amount Xt at the time of initial detection is read into the interpolation correction value calculation unit 21 in step S35. In step S36, the presence or absence of the thermal displacement amount Xt + 1 at the time of the next detection is confirmed, and if there is the next time, the thermal displacement amount Xt + 1 is read by the interpolation correction value calculation unit 21 in step S37.

Then, in steps S38 to S41, the interpolation correction value Xn at the correction interval b is calculated using the following equation, and the value is stored in the correction value storage unit 20. Xn = Xt + Xt + 1 (b / a) n (1≤n≤
[A / b]) Here, the interpolation correction value Xn is obtained for each correction interval b within a range in which a multiple of b exceeds a, and then step S4.
In step 2, the t is updated to t + 1 and the process returns to step S35.
The interpolation correction value corresponding to the thermal displacement amount at the time of the next detection is similarly obtained, and if the thermal displacement amount data is lost, step S
At 43, n and t are set to 0, respectively, and the interpolation process ends. The correction interval b can be set to a value obtained by equally dividing the detection interval a.

FIG. 7A shows the correction values obtained in the first and second embodiments, and FIG. 7B shows the correction values obtained in the third embodiment. As is clear from a comparison of both figures, according to the correction device of the third embodiment, the correction value is subdivided into a plurality of values in one detection interval, so the measurement time of the thermal displacement amount is kept to the minimum necessary. In addition, it is possible to process the processed surface smoothly by adding precise correction.

The present invention is not limited to the above embodiment, and for example, the thermal displacement amount may be detected and the correction may be added immediately after the tool is replaced. In this case, in step S2 of FIG. 3, step S13 of FIG. 4, and steps S21 and S31 of FIG. 5, it is determined whether or not there is a tool replacement command in the machining command, and if there is a tool replacement command, detection and correction are performed. Also, if the machining conditions change significantly due to tool change, it is highly possible that the amount of thermal displacement will change rapidly immediately after the start of machining, so in order to handle this, start the time counter with the tool change command, The detection and correction may be performed a predetermined number of times at regular intervals immediately after the tool is replaced.

[0024]

As described above in detail, according to the first aspect of the invention, since the device for correcting the correction value obtained at the predetermined timing during the idle operation is added at the time of the processing, it is almost the same as that at the time of the processing. In the same situation, the amount of thermal displacement is accurately detected at a predetermined timing to obtain a correction value, and the effect of mechanical thermal displacement on the machining accuracy can be accurately and easily removed in actual machining.

According to the second aspect of the present invention, since the apparatus for interpolating the correction value at the detection interval and adding the correction value at the time of processing with the subdivided correction value is adopted, the measurement time for the thermal displacement amount is required. The effect is that it can be minimized and that the machined surface can be machined smoothly by adding precise correction.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing the configuration of a machine tool.

FIG. 2 is a block diagram showing a thermal displacement correction device of the present invention.

FIG. 3 is a flowchart showing an idle operation program of the thermal displacement correction method of the first embodiment.

FIG. 4 is a flowchart showing a machining operation program of the thermal displacement correction method of the first embodiment.

FIG. 5 is a flowchart showing a thermal displacement correction method of a second embodiment.

FIG. 6 is a flowchart showing a thermal displacement correction method of a third embodiment.

FIG. 7 is an explanatory diagram showing comparison of effects of the thermal displacement correction methods of the first to third embodiments.

[Explanation of symbols]

1 ・ ・ Machine body 2 ・ ・ Spindle 3 ・ ・ Test bar 4 ・
・ Displacement detectors, 5 ・ ・ Control devices, 6 ・ ・ Operating panels, 8 ・ ・
Machining program storage unit, 9 ... Measurement program storage unit,
10 ... Interval storage, 12 ... Function generator, 1
4 ... Servo control unit, 16 ... Time counter, 17 ...
・ Timing judgment unit, 18 ・ ・ Displacement amount calculation unit, 19 ・ ・
Correction value calculation unit, 20 ... Correction value storage unit, 21 ... Interpolation correction value calculation unit.

Claims (2)

[Claims] 1. A displacement detector for detecting a thermal displacement amount of a spindle during idle operation in a machining program of a machine tool, a detection program storage section for storing a thermal displacement amount detection program by the displacement detector, and a machining program. A detection time storage unit that stores the timing for detecting the thermal displacement amount, a correction value calculation unit that calculates the relative position correction value between the spindle and the workpiece based on the thermal displacement amount, and the correction at the timing of the machining program when machining the workpiece. A thermal displacement correction device for a machine tool, comprising: a control unit that corrects a relative position between a spindle and a workpiece based on a value. 2. The interpolation correction value calculation, wherein the displacement detector detects a thermal displacement amount at the timing, and interpolates the relative position correction value so as to change stepwise with respect to the detection interval of the timing. 2. The thermal displacement of the machine tool according to claim 1, further comprising: a part, wherein the control part is configured to correct the relative position between the spindle and the work based on the correction value subdivided at the time of machining the work. Correction device.