JPS6288547A - Thermal displacement compensating device - Google Patents

Abstract

PURPOSE:To make possible to limit a thermal displacement to a minimum value, by receiving the output of a temperature difference measuring means at every predetermined time to compare the present value with the previously received value, and by compensating the movements of movable parts in a machine tool in accordance with a value which is calculated or selected in accordance with the result of the comparison. CONSTITUTION:When an X-axis compensating instruction is delivered, a CPU initiates time-counting, and issues a READY signal when a time-up occurs after a predetermined time elapses to store values A-D measured and delivered by a temperature difference measuring circuit 20 or temperature differences between detecting sections and the room temperature in a buffer memory. Then, comparison is made between the present delivered value and the previously delivered value to obtain a temperature variation DELTAT, and a compensating value corresponding to the temperature variation DELTAT is calculated. Then, the number of pulses corresponding to the compensating value DELTAX is transmitted from a compensating pulse generating circuit 35, and is interrupted into the interrupting section of a manual pulse generator 34 to control an X-axis drive circuit DUX for driving an X-axis servomotor 15 so that the position of the table is compensated by an amount corresponding to a thermal displacement. Accordingly, a thermal displacement may be limited to a minimum value.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thermal displacement correction device capable of correcting thermal displacement of a machine tool or the like at regular intervals.

<Prior art> In general, in a thermal displacement correction device for a machine tool, a thermal displacement correction command is programmed in numerical control data, and each time the thermal displacement correction command is read, it interrupts the program to control the moving parts. A method that corrects thermal displacement by moving the sensor according to temperature changes, and a method that corrects thermal displacement every time the temperature of the detection section changes by unit temperature.
There is a method of correcting thermal displacement by moving the movable part of the machine tool by a unit amount.

<Problems to be Solved by the Invention> However, in the former method, it is not only necessary to program thermal displacement correction commands at key points in the numerical control data, but also when the execution time of one block of programs is long. Since thermal displacement cannot be corrected during the process, there is a problem that thermal displacement correction cannot be immediately performed.

In addition, in the latter method, if the temperature increases by a unit amount, correction is performed in the child direction, and if the temperature decreases by a unit amount, correction is performed in one direction, so the temperature change that occurs during operation is corrected. Even if it is possible to correct the thermal displacement caused by the stoppage, if a temperature change occurs when the operation is stopped, it will not be possible to correct the thermal displacement that occurred during the stoppage at the start of operation unless special measures are taken. There is a problem in that proper thermal displacement correction cannot be performed using only the temperature of the detection section due to the influence of room temperature and the like.

Means for Solving the Problems> The present invention has been made in view of the above-mentioned conventional problems, and its configuration is such that the temperature of the detection part of a machine tool etc. and the room temperature or the base temperature of the machine tool etc. A temperature difference measuring means is provided to measure the temperature difference, and when a thermal displacement correction command is given,
Comparison calculation means is provided for inputting the output of the temperature difference measuring means at regular time intervals and performing a comparison calculation with the previous input, and a correction value calculation for calculating or selecting a correction value based on the comparison calculation result by the comparison calculation means. A correction moving means is provided for correctively moving a movable part of a machine tool or the like in accordance with the correction value calculated or selected by the correction value calculating means.

With the above configuration, when a thermal displacement correction command is given, the temperature difference measured by the temperature difference measuring means is input at fixed time intervals, and compared with the previously input temperature difference, the change temperature Δ is calculated.
T is required. A correction value is calculated or selected based on this temperature change, and a pulse corresponding to this correction value is given to a servo motor by interrupt processing, and a movable part of a machine tool or the like is moved for correction. Such a correction operation is executed at regular intervals until a correction completion command is given, and the thermal displacement is corrected in-process.

<Example> Embodiments of the present invention will be described below based on the drawings.

1 and 2 show a numerically controlled machine tool to which the present invention is applied, and a table 1 is mounted on the bed 10 of this machine tool.
1 and a column 12 are mounted so as to be movable in the X-axis (left-right) direction and the Z-axis (front-back) direction, which are perpendicular to each other. The spindle head 13 is attached to the column 12 on the Y axis (up and down)
A main shaft (not shown) on which a tool is removably attached to the main shaft head 13 is rotatably supported around a horizontal axis parallel to the two axes. Therefore, the table 11, the spindle head 13 and the column 12
is controlled to feed in each axial direction by servo motors 15, 16, and 17, and the workpiece on the table 11 is machined by a tool attached to the main shaft.

In a numerically controlled machine tool having such a configuration, thermistors SA and SB are installed at two locations on both sides of the tip of the spindle bend 13 in order to detect the temperature of the movable part, and thermistors SA and SB are installed at two locations on the front and rear surfaces of the column 12. Thermistors SC and SD are attached to the. Further, a thermistor SE for detecting room temperature (base temperature) is attached to the rear surface of the bed 10, which is away from the processing section. Each thermistor 5 attached to these detection parts
A-SD and room temperature detection thermistor SE are connected to each other and the temperature difference therebetween is measured.

FIG. 3 shows a temperature difference measuring circuit 20 that measures the temperature difference between the temperature TA of the detection section to which the thermistor SA is attached and the room temperature TE. a temperature detection circuit 21; a temperature detection circuit 22 incorporating a thermistor SE that detects room temperature TE;
A differential amplifier 23 inputs the re-outputs of these temperature detection circuits 21 and 22 and performs subtraction processing, and the output of the differential amplifier 23 is AD converted by an AD converter 24, and then read When the signal is output, it is input to the numerical control device 30.

A temperature difference measurement circuit with a similar configuration is used to measure the temperature difference (TB
-TE), the temperature difference (TC-TE) between the temperature TC of the detection part detected by the thermistor SC and the room temperature TE, and the temperature TD of the detection part detected by the thermistor SD and the room temperature T
They are provided to measure the temperature difference (TD-TE) with E.

In the following explanation, the temperature difference (TA - TE) between the temperature TA of the detection section detected by the thermistor SA and the room temperature TE detected by the thermistor SE will be referred to as the measured value A, and Part temperature TB.

Each temperature difference between TC, TD and room temperature TE (TB-TE).

TC-TE, TD-TE) will be referred to as measured values B, C, and D.

Here, thermal displacement of the machine tool occurs in the X-axis direction due to the tilt of the spindle head 13 due to the temperature difference between measured values A and B, and thermal displacement in the Y-axis direction and due to the tilt of the column 12 due to the temperature difference between measured values C and D. A thermal displacement occurs in the Z-axis direction, a thermal displacement occurs in the Z-axis direction based on the absolute value of measured values A and B, and a thermal displacement in the Y-axis direction occurs based on the absolute value of measured values C and D. Therefore, in the following embodiment, an example will be described in which the thermal displacement of the X-axis, Y-axis, and Z-axis is corrected based on the table below.

FIG. 4 shows the configuration of a numerical control device 30 that controls the numerically controlled machine tool, and this numerical control device 30 includes a microprocessor MPU, a continuous memory ROM,
It is mainly composed of a central processing unit CPU consisting of a random access memory RAM, and this central processing unit CPU
A pulse generating circuit 31 is connected via an interface 32 to supply command pulses to drive circuits DUX, DUY, and DUZ that respectively drive the aforementioned servo motors 15, 16, and 17 for each axis. Also, the central processing unit CPU
A for AD converting the output of the temperature difference measuring circuit 20.
A D converter 24 is connected via an interface 33, and a manual pulse generator 34 and a correction pulse generating circuit 35 are also connected via an interface 36.

The random access memory RAM stores the measured value A measured by the temperature difference measuring circuit 20 as shown in FIG.
, B, C, and D data area T for temporarily storing each data.
AA, TBA, TCA, TDA, and a data area NCDA for storing a numerical control program are formed.

Next, the numerical control execution routine will be explained based on FIGS. 6 and 7.

When a processing start command is given, the central processing unit CPU,
As shown in Fig. 6, the numerical control data stored in the numerical control data area NCDA of the random access memory RAM is read out one block at a time, and auxiliary functions are processed accordingly, while at the same time pulse distribution for each axis is performed. conduct,
Control processing.

Here, as an auxiliary function regarding correction of thermal displacement, rM80
J is the X-axis correction command, rM81J is the Y-axis correction command, r
M82J indicates a Z-axis correction command, "M2S," indicates a simultaneous 3-axis correction command, and rM84J indicates a correction completion command, which are selectively programmed in the numerical control data according to the machining content. .

However, in the numerical control execution routine shown in FIG.
Auxiliary function M is included in one block of numerical control data read out.
80 to M83, the numerical control execution routine shown in FIG. 7 is executed as M code processing. Below, as an example, an execution routine when the X-axis correction command M80 is issued will be described.

When the X-axis correction command M80 is given, the central processing unit CP
As shown in FIG. 7, the U starts time counting in step 50, and when the time is up after a certain period of time has elapsed, it outputs a READY signal in step 51. Next, in step 52, the measured values A-D measured by the temperature difference measuring circuit 20, that is, the temperature difference between each detection section and the room temperature (TA-TE, TB-TE, TC-TE,
TD-TE) are input and stored in the buffer memory of the circuit, respectively. Subsequently, in step 53, a comparison calculation with the previously input measured value is performed to determine the temperature change ΔT. Here, if the input in step 52 is the first time, the previous input becomes the initial value O, and the calculation result becomes the input value, and if the input in step 52 is the nth time, the temperature change ΔT is as follows. It is calculated as follows.

ΔTA= An-A(n-+) =TAn-TEn-(TA(n-+)-TE(n
-+))ΔTB= On-B(n-r) = TBn -TEn -(TB (n-+)-TE
(n-+)) ΔTC=Cn-C(n-+) = TCn-TEn-(TC(n-+)-TE (
n-+))ΔTD=On-D(n-+on=TDn-THn-(TD cn-+)-TH(n-
+)) After such a comparison operation, the data areas TAA, TBA, TCA of said random access memory RAM.

The current input value is written to TDA in place of the previous input value.

Next, in step 54, a correction value corresponding to the changed temperature ΔT calculated as described above is calculated. In the case of X-axis correction, this correction value is obtained from the following formula.

ΔX=kt(ΔTA−ΔTB) Here, is a constant or function determined in advance through experiments.

Next, in step 55, the number of pulses corresponding to the correction value ΔX is transmitted from the correction pulse generation circuit 35 to the interrupt section of the manual pulse generator 34, thereby controlling the X-axis drive circuit DUX and driving the X-axis servo motor. 5 is driven to correct the movement of the table 11 by the amount of thermal displacement of the spindle head 13. Subsequently, in step 56, it is determined whether the correction completion command M84 has been output, and if the correction completion command M84 has not been output, the process returns to the first step 50 and the above-mentioned thermal displacement correction operation is performed at fixed time intervals. Execute. Although the time interval can be set arbitrarily, it is best to set it within a range that does not cause large thermal changes due to temperature changes during processing, and for example, an interval of about 30 seconds is appropriate.

In the above, I talked about the X-axis correction, but the X-axis correction (
MB2) or Z-axis correction (MB2), the formula for calculating the correction value ΔY or ΔZ in step 54 is as follows.

Here, 2 to 5 are constants or functions determined in advance through experiments in the same way as described above.

In the above embodiment, an example was described in which the correction value was calculated using a constant or a function.
It is also possible to register a correction value corresponding to the temperature change ΔT in the read-only memory ROM, and read out the correction value corresponding to the temperature change ΔT in order to correct the thermal displacement.

In addition, in the above embodiment, an example was described in which correction is possible on three axes: It is also possible to calculate or read the correction value based on the changing temperature of the two temperature difference measuring circuits.

Further, in the above embodiment, the thermal displacement correction of a machine tool was described, but it goes without saying that the present invention can also be applied to thermal displacement correction of a measuring machine.

<Effects of the Invention> As described above, the present invention, when a thermal displacement correction command is given, inputs the output of the temperature difference measuring means at regular intervals and calculates the change in temperature by comparing it with the previous input. Since the configuration is such that thermal displacement correction is performed by calculating a correction value based on this temperature change, even if the execution time of a program for one block of numerical control data is long, a certain period of time during the execution of the program The thermal displacement can be corrected at each time, which has the effect of minimizing the thermal displacement.

Furthermore, the present invention corrects thermal displacement based on the temperature difference between the temperature of the detection part of the machine tool and the room temperature or the base temperature of the machine tool, so the thermal displacement can be accurately calculated regardless of changes in the room temperature, etc. An effect that can be corrected is also produced.
.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a front view showing an outline of a numerically controlled machine tool, FIG. 2 is a side view of the same, and FIG.
The figure shows the temperature difference measurement circuit, Figure 4 is a block diagram showing the configuration of the numerical control device, Figure 5 shows the state of data storage in the memory, and Figure 6 shows the processing control execution routine. The flowchart, FIG. 7, is a diagram showing an execution routine for thermal displacement correction. 15.16.17... Servo motor, 20... Temperature difference measuring circuit, 30... Numerical control device.

Claims (2)

[Claims] (1) A temperature difference measuring means for measuring the temperature difference between the temperature of a detection part of a machine tool, etc. and the room temperature or the base temperature of the machine tool, etc.; Comparison calculation means for inputting an output at regular intervals and performing a comparison calculation with the previous input; correction value calculation means for calculating or selecting a correction value based on the comparison calculation result by the comparison calculation means; A thermal displacement correction device comprising a correction moving means for correcting and moving a movable part of a machine tool or the like according to a correction value calculated or selected by the means. (2) A plurality of the temperature difference measuring means are provided to measure temperature differences between different detection parts of a machine tool, etc., and a correction value is calculated based on the difference or sum of changing temperatures of these temperature differences. A thermal displacement correction device according to claim 1.