KR100427326B1 - Method of compensating thermal displacement of main spindle for a machine tool - Google Patents

Abstract

Disclosed is a method for correcting thermal displacement of a machine tool spindle system. The disclosed method for correcting the thermal displacement of a spindle of a machine tool includes measuring the temperature change characteristic of the spindle system of a target machine tool by operating conditions and obtaining a maximum temperature change amount and a time constant according to each operating condition. A mathematical model for the temperature change (θ) of the main shaft is constructed as shown in Equation 1 and 2 below, and built into the controller of the thermal displacement compensator of the machine tool to compensate for the thermal displacement of the spindle of the machine tool. It is characterized by what was made possible.

When starting the spindle or increasing the number of revolutions

θ = (ax rpm)

When spindle speed decreases or stops

θ = (ax rpm)

In Equations 1 and 2 described above,

rpm: spindle speed,

t: driving time,

T: temperature time constant by spindle speed,

a: correction factor for spindle speed

According to the present invention, it is possible to exhibit the same performance as the existing technology without additional hardware, there is an advantage of cost reduction.

Description

Heat displacement compensation method of machine tool spindle system {METHOD OF COMPENSATING THERMAL DISPLACEMENT OF MAIN SPINDLE FOR A MACHINE TOOL}

The present invention relates to a method for correcting the thermal displacement of a machine tool spindle system, and more particularly, to a cost reduction, and to a method for correcting the thermal displacement of a machine tool spindle system improved to enable precision and precision of a machine tool. will be.

The degree of machining of the machine tool is primarily influenced by the positional error, the angular displacement error, the straightness, and the squareness caused by the assembly and geometrical states of the components constituting the machine tool. In addition, the degree of cutting is directly affected by cutting heat generated during machining, heat generated by high-speed rotation of the spindle, and heat deformation errors caused by frictional heat and ambient temperature changes caused by repeated feeding of the feed shaft.

In general, based on the results of many experiments, the thermal deformation error has a greater effect on the machining accuracy than the geometrical error of the machine tool, and 40-70% of the error in the machine tool is caused by the thermal deformation error.

The geometric error of the machine tool is maintained after the assembly through the quality control and position error compensation, but the thermal deformation error due to the generated heat is directly affected by the working conditions and processing characteristics. The error correction is difficult because it appears in a complicated form by temperature.

In order to minimize the thermal deformation error of the machine tool, a method of improving the thermal stiffness or separating the heat source to increase the structural thermal stability has been developed mainly in Japan and Germany.

The machine tool is designed to have a thermally symmetrical structure, or to minimize the heat generated by installing a cooling jacket on the outside of the motor and bearing of the spindle head cooling oil, the motor built-in spindle, and the forced cooling by air or oil cooling. A method is proposed.

Even if such a system is applied, heat deformation inevitably occurs, so that a displacement sensor is attached to the main axis to measure the heat deformation error, or as shown in FIG. 1, at a specific part of the machine tool 10 in which the main axis 11 is installed. A system for mounting a temperature sensor 12 and predicting thermal deformation using a temperature value detected therein has been proposed and applied to a commercial machine tool. 2 is a block diagram illustrating a thermal distortion correction algorithm.

As a method for minimizing the thermal deformation error, the method of heat source cooling, the method using a material without thermal deformation or a material with low thermal conductivity, and the method of measuring and correcting the thermal deformation error generated are applied. have.

Recently, a method of minimizing the thermal strain error of a machine tool has been applied to the measurement of the thermal strain error through measurement, and a neuropurge algorithm is applied to the machining center to predict and correct the thermal strain error in the Z-axis direction. Is being proposed.

However, there are limitations in the cost and material development to reduce the thermal deformation error through the optimum design, and the method of directly measuring and correcting the thermal deformation error or predicting and correcting the thermal displacement using the temperature change value obtained from the temperature sensor. To build a system, additional hardware such as a separate measuring device and data collection device (A / D board) is required, which increases the cost of machine tools.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thermal displacement correction method of a machine tool spindle system, which enables cost reduction by performing thermal displacement correction without adding additional hardware. .

1 is a view showing a thermal displacement correction apparatus of a machine tool spindle system according to the prior art.

Figure 2 is a block diagram showing a heat distortion correction algorithm according to the prior art.

3A and 3B are graphs showing temperature change characteristics of the main shaft system.

4 is a graph showing the results of experiments with temperature changes according to the spindle operating conditions.

5 is a block diagram of a thermal displacement prediction model proposed by the thermal displacement correction method of the machine tool spindle system according to the present invention.

6 is a view showing an embodiment of a thermal displacement correction method of the machine tool spindle system according to the present invention.

<Description of Symbols for Main Parts of Drawings>

20. Machine tool

21. Spindle

30. Controller

Thermal displacement correction method of the machine tool spindle system of the present invention for achieving the above object, by measuring the temperature change characteristics of the spindle system of the target machine tool for each operation condition to determine the maximum temperature change amount and time constant according to each operation condition By constructing, a mathematical model of the temperature change (θ) of the main shaft whose operating condition is a parameter is constructed as shown in Equation 1, 2, and built into the controller of the thermal displacement compensator of the machine tool. It is characterized by the fact that the thermal displacement of the machine tool spindle system can be compensated.

[ Equation 1 ]

When starting the spindle or increasing the number of revolutions

θ = (ax rpm)

[ Equation 2 ]

When spindle speed decreases or stops

θ = (ax rpm)

In Equations 1 and 2 described above,

rpm: spindle speed,

t: driving time,

T: temperature time constant by spindle speed,

a: correction factor for spindle speed

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The method of correcting the thermal displacement of a spindle of a machine tool according to the present invention is a means for obtaining a temperature change value of a spindle of a machine tool. The thermal displacement compensation method of the machine tool spindle system which is replaced by a mathematical model.

As described above, the thermal deformation characteristic of the main shaft system of the machine tool is shown in FIG. The driving conditions of the spindle unit are most affected by, for example, the number of revolutions and the operating time. During spindle operation, the temperature of the spindle system changes naturally logarithmically with an increase in the heat source, for example, starting or rotating the spindle, or decreasing the heat source, for example, decreasing or stopping the spindle.

In this aspect, the thermal displacement correction method of the spindle of the machine tool according to the present invention, by measuring the temperature change characteristics of the operating condition of the spindle system of the target machine tool through an experimental method, as shown in Figure 4, each operating condition ( By calculating the maximum temperature change amount (A) and time constant (T) according to the spindle speed and operating time), a mathematical model for the temperature change (θ) of the main axis whose operating conditions are parameters is constructed.

The mathematical model of the main shaft temperature change of this proposal is as follows. First, when starting or increasing the number of revolutions of the main axis is constructed as shown in Equation 1 below.

[ Equation 1 ]

When starting the spindle or increasing the number of revolutions

θ = (ax rpm)

Second, when the rotational speed of the main shaft is reduced or stopped, it is constructed as shown in Equation 2 below.

[ Equation 2 ]

θ = (ax rpm)

In Equations 1 and 2 described above,

rpm: spindle speed

t: driving time

T: Temperature time constant by spindle speed

a: correction factor for spindle speed

to be.

In addition, after the measurement of the relationship between the thermal displacement of the main axis and the main axis temperature change by the experimental method, a mathematical model is constructed using the statistical method, the progressive method.

By integrating the two models thus constructed, as shown in FIG. 5, a thermal displacement prediction model according to the operating conditions of the main axis may be constructed.

And, as shown in Figure 6, by embedding in the controller (PC-NC) 30 of the thermal displacement correction apparatus of the machine tool 20, the spindle 21 is installed, a separate temperature sensor (Fig. Thermal displacement of machine tool spindle system can be compensated without the need of A / D board.

As described above, the thermal displacement correction method of the machine tool spindle system according to the present invention has the following effects.

By constructing a mathematical model of thermal displacement according to the spindle operating conditions and embedding it in the controller (PC-NC), it can show the same performance as the existing technology without additional hardware. Therefore, there is a cost reduction effect.

In addition, it can secure external competitiveness in terms of precision and precision of machine tools.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (2)

Mathematical model of the temperature change (θ) of the main shaft whose parameters are the operating conditions by measuring the temperature change characteristic of the main shaft system of the target machine tool by the operating conditions and obtaining the maximum temperature change amount and time constant according to each operating condition. Is constructed as shown in Equation 1 and 2 below, and built into the controller of the thermal displacement compensator of the machine tool to compensate for the thermal displacement of the machine tool spindle system. Thermal displacement correction method. [ Equation 1 ] When starting the spindle or increasing the number of revolutions θ = (ax rpm) [ Equation 2 ] When spindle speed decreases or stops θ = (ax rpm) In Equations 1 and 2 described above, rpm: spindle speed, t: driving time, T: temperature time constant by spindle speed, a: correction factor for the spindle speed, The method of claim 1, And said operation condition comprises a speed and an operation time of said main shaft.