JPH10156663A - Method for correcting thermal deformation of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control correction errors by substantially shortening the correction intervals without increasing load of a computing circuit. SOLUTION: In a method for correcting thermal displacement, in which correction based on the temperature of a machine body is intermittently repeated at the prescribed intervals, the intermediate correction is performed in a correction interval. In the intermediate correction, the correction speed is calculated by dividing the difference between the thermal displacement correction amounts of a part subjected to correction, calculated from the last and this temperatures by the preset correction interval. The times and the intervals of the intermediate correction are found on the basis of the correction speed. The intermediate correction amount for the correction times is calculated by using the corruption speed and the correction coefficient. As the correction factor, a value to be inversely proportional to the correction times and to be accumulated according to the correction times is used. The intermediate correction amount of the N time is found from the product of the factor, the correction speed and N, and the part subjected to correction is controlled according to the intermediate correction amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a thermal displacement of a machine tool.

[0002]

2. Description of the Related Art Factors of thermal deformation that deteriorate the processing accuracy of a machine tool include a change in the ambient temperature of the machine tool, the heat generated by the machine itself, a change in the cutting fluid temperature due to the processing heat, and the like. As a countermeasure for suppressing thermal deformation, a mechanical structure method of cooling the vicinity of a heat receiving portion or a heat generating portion (for example, a rolling bearing of a main shaft), controlling a cutting fluid temperature, or detecting a thermal displacement from machine temperature information. An electric control method for estimating and correcting is known. As the latter thermal displacement correction method, the temperature of each part of the machine tool is measured by a temperature sensor, a thermal displacement correction amount is calculated based on a temperature rise value or a temperature difference between two relative points, and the correction target portion is calculated using the correction amount. Techniques for controlling and correcting thermal displacement are known.

[0003]

However, this thermal displacement correction is generally performed intermittently and repeatedly at a correction interval of a predetermined time during the operation of the machine tool. Therefore, according to the conventional method, as shown in FIG. When the thermal displacement changes continuously, the correction error becomes maximum immediately before the axis movement of the correction target portion at each correction interval. For this reason, there has been a problem that the position of the tool edge greatly changes immediately after the axis movement, which adversely affects machining accuracy. In order to avoid this problem, it is conceivable to shorten the correction interval, but in this case, temperature measurement,
Another problem arises that the number of estimation calculations increases and the load on the calculation circuit increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for correcting a thermal displacement of a machine tool, which can reduce a correction error by substantially shortening a correction interval without increasing a load on an arithmetic circuit.

[0005]

In order to solve the above-mentioned problems, a thermal displacement correction method according to the present invention comprises the steps of measuring the temperature of each part of a machine tool and calculating a thermal displacement correction amount based on the measured temperature. And the step of controlling the correction target part in accordance with the calculated thermal displacement correction amount are repeatedly executed at predetermined correction intervals, and during the correction interval, the unit time is calculated from the previous thermal displacement correction amount and the correction interval. Calculating the thermal displacement correction amount per unit, calculating the intermediate correction amount at intervals obtained by dividing the correction interval based on the thermal displacement correction amount per unit time, and according to the intermediate correction amount at the divided interval. And a step of controlling the correction target portion.

Here, in order to improve the correction accuracy by subdividing the correction interval, the number of corrections controlled according to the intermediate correction amount may be increased or decreased in proportion to the previous thermal displacement correction amount.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a thermal displacement correction system for a machining center. A moving table 2 and a column 3 are provided on a bed 1 of the machining center, and a column 3 supports a spindle head 5 having a spindle 4. A first temperature sensor 6 for detecting a heating temperature of the main shaft 4 is attached to an outer periphery of a bearing portion of the main shaft 4, and a second temperature sensor 7 for detecting a reference temperature is attached to the bed 1.

The electrical control system of the machining center includes a temperature measuring device 8 for digitizing and measuring the spindle temperature and the reference temperature based on the outputs of the sensors 6 and 7, and a correction value calculation for calculating a thermal displacement correction amount based on the measured temperature. Device 9, an intermediate correction arithmetic device 10 for executing arithmetic processing required for intermediate correction, and an NC for controlling a correction target portion in accordance with the output of each arithmetic device 9, 10.
An apparatus 11 is provided.

FIG. 2 is a flowchart showing a method for correcting thermal displacement by the above system. In correcting the thermal displacement of the machining center, first, the outputs of the temperature sensors 6 and 7 are converted from analog signals to digital signals, and the temperatures of the respective parts of the machine are measured as numerical values (step S1). Then, a thermal displacement correction amount is calculated based on the measured temperature value by a known method (step S2), and the correction target unit (for example, the spindle head 5) is controlled according to the calculated thermal displacement correction amount (step S3).

Next, in the intermediate correction arithmetic unit 10,
By dividing the difference between the thermal displacement correction amount of the correction target portion calculated from the temperature difference of the previous time and the current time by the preset correction interval,
An amount of change per unit time, that is, a correction speed is calculated (step S4). Further, the number of intermediate corrections is obtained from Expression 1 based on the correction speed (step S5). Further, the interval of the intermediate correction is calculated from Equation 2 as, for example, an equal interval (Step S6). Number of intermediate corrections = F (correction speed) Equation 1 Intermediate correction interval = Thermal displacement correction interval / (Number of intermediate corrections +1) Equation 2

Next, an intermediate correction amount for the number of corrections is calculated using the correction speed and the correction coefficient (step S8). Here, as the correction coefficient, a value that is inversely proportional to the number of corrections and progresses in accordance with the number of corrections is used. Therefore, the N-th intermediate correction amount is obtained from Expressions 3 and 4. Correction coefficient = Setting coefficient / Number of corrections Equation 3 (Setting coefficient: value preset and stored) Nth intermediate correction amount = N × correction coefficient × correction speed Equation 4

Subsequently, the intermediate correction value is transmitted to the NC unit 11, the portion to be corrected is controlled in accordance with the intermediate correction value (step S9), and the required number of intermediate corrections is performed. When the last intermediate correction is completed (step S
7), continuation of the thermal displacement correction is determined (step S1)
0), the above series of processing is repeatedly executed at predetermined correction intervals until the thermal displacement converges. Therefore, according to the correction method of this embodiment, as shown in FIG. 3, the number of intermediate corrections is increased at a correction interval with a large correction speed, and the number of intermediate corrections is reduced at a correction interval with a small correction speed. The correction error can be suppressed uniformly throughout the period.

In the above-described embodiment, the number of intermediate corrections and the amount of correction are obtained by calculation, but these are stored in advance in a memory in a correction speed-correction number relationship table or a correction speed-correction number-correction amount relationship. It can also be obtained from a table. Further, the correction coefficient used for calculating the intermediate correction amount may be obtained from a non-linear equation. Further, in the above embodiment, the intermediate correction amount is determined based on the correction speed. However, the present invention is not limited to the above embodiment, and for example, the intermediate correction amount is obtained from the difference between the previous and current correction amounts obtained from the temperature. The amount may be determined.

[0014]

As described above in detail, according to the first aspect of the present invention, the thermal displacement correction amount per unit time is calculated from the previous thermal displacement correction amount and the correction interval, and the intermediate correction is performed. There is an excellent effect that the correction interval can be substantially shortened without increasing the load on the arithmetic circuit, the correction error can be suppressed, and the processing accuracy can be improved.

According to the second aspect of the present invention, since the intermediate correction is performed a number of times corresponding to the previous thermal displacement correction amount, the correction interval can be subdivided and the correction accuracy can be efficiently improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a machining center showing a system for implementing a thermal displacement correction method according to the present invention.

FIG. 2 is a flowchart illustrating an embodiment of a thermal displacement correction method according to the present invention.

FIG. 3 is a model diagram showing an implementation result of the correction method.

FIG. 4 is a model diagram showing an implementation result of a conventional thermal displacement correction method.

[Explanation of symbols]

1. Bed, 2. Moving table, 3. Column, 4.
..Spindle, 5 ... Spindle head, 6 ... First temperature sensor,
7 second temperature sensor, 8 temperature measurement device, 9 correction value calculation device, 10 intermediate correction calculation device, 11 N
C device.

Claims (2)

[Claims] Measuring the temperature of each part of the machine tool;
A method of correcting a thermal displacement by repeatedly executing a step of calculating a thermal displacement correction amount based on a measured temperature and a step of controlling a correction target portion according to the calculated thermal displacement correction amount at a correction interval of a predetermined time. During the interval, calculating the thermal displacement correction amount per unit time from the previous thermal displacement correction amount and the correction interval, and calculating the intermediate correction amount at intervals obtained by dividing the correction interval into the thermal displacement correction amount per unit time. And a step of controlling the correction target portion in accordance with the intermediate correction amount at the divided intervals. 2. The method according to claim 1, wherein the number of corrections controlled in accordance with the intermediate correction amount is increased or decreased in proportion to the previous thermal displacement correction method.