CN101825453A - Temperature error compensation method for three-coordinate measuring machine with cylindrical-coordinate system - Google Patents

Abstract

The invention belongs to the field of testing technology and instruments. In order to realize temperature error compensation, the technical solution adopted by the present invention is: 1. According to the situation of the workpiece to be measured, design and manufacture the reference parts at the upper and lower ends; 2. Accurately calibrate the inner and outer diameters and heights of the reference parts; 3. Establish a mathematical model for temperature error compensation; 4. Write an error compensation program based on the established mathematical model for temperature error compensation, and add it to the data processing program for workpiece measurement results; Add it to the measurement program, and measure the cross-section required for error compensation during the process of measuring the workpiece; 6. Perform data processing of the measurement results to complete temperature error compensation. The invention is mainly applied to the measurement of rotary parts.

Description

The Temperature Error Compensation Method of Cylindrical Coordinate System Three Coordinate Measuring Machine

technical field

The invention relates to a temperature error compensation technology for a three-coordinate measuring machine of a cylindrical coordinate system, which can effectively compensate the measurement error caused by the deformation of the measuring machine and workpiece caused by temperature changes under the working condition of a workshop, and improve the measurement accuracy. It belongs to the field of testing technology and instruments.

Background technique

Rotary parts occupy a large proportion in various parts of industrial production, especially in military production. As the key parts of machines, they are widely used in the fields of industry, aviation, aerospace, national defense and so on. The generatrix of the rotary workpiece can be a straight line or an arc, and the shape of the surface can be cylindrical, conical, spherical, torus, plane, etc. Although the structure and size of revolving parts vary with their uses, their structures generally have the following characteristics: there are high requirements for the roundness of each section, there are multiple inner and outer circular revolving surfaces that need to be tested, and their The coaxiality requirement is higher. These parts are often the key parts of machines and equipment, and the batches are large, requiring 100% inspection. The high precision and high efficiency of rotary parts have become the urgent needs of many departments in the national economy and national defense.

The three-coordinate measuring machine with cylindrical coordinate system is especially suitable for the detection of rotating parts. The overall composition and working principle of the cylindrical coordinate system three-coordinate measuring machine are shown in Figure 1. The measuring machine consists of a rotary table and several measuring frames. The workpiece is installed on the rotary table, clamped and centered by the fixture, and driven by the rotary table to rotate continuously. Various probes are installed on the measuring frame to measure the axial and radial dimensions, shape and position error of the inner and outer surfaces of the workpiece.

The cylindrical coordinate system CMM has the following advantages.

1) High measurement efficiency When measuring, the workpiece rotates continuously, the probe is fixed, and the workpiece rotates one circle to complete the measurement of a section. In the traditional orthogonal three-coordinate measuring machine, it needs to measure point by point, which is very time-consuming.

2) The measurement accuracy of form and position is high. It is measured during the rotation process. Only the motion error of the rotary table and the measurement uncertainty of the probe affect the accuracy of measuring form and position errors such as roundness, circular runout, and coaxiality. The motion errors of the individual components on the stand have little effect on the accuracy of these form and position measurements, since they do not move when measuring a section.

3) The movement of the measuring head is simple, and the problem of anti-collision is relatively easy to solve.

But the CMM has its own problems. This is mainly because the size of the workpiece to be measured cannot be read directly from the scales that determine each measuring frame. What is read from the ruler is only the relative displacement of each mobile frame. In order to determine the absolute size of the workpiece to be measured, it is necessary to know the position of the coordinate origin of each measuring frame relative to the origin of the coordinate system of the rotary table, as well as the clamping distance between the directions of the coordinate axes. Angular relationship, that is, to realize the unification of each measuring frame and the coordinate system of the rotary table. The unification of this coordinate system is usually achieved through the calibration of the reference parts.

However, as shown in Figure 1, due to temperature changes, the position and coordinate axis direction of each measuring frame will change relative to the rotary table, causing measurement errors. Especially for the cylindrical coordinate measuring machine used in the workshop, the measurement error caused by the temperature change will be very large, often reaching tens to hundreds of microns. In addition, the temperature conditions in the workshop are complex, and it is difficult to obtain good results by using the method of establishing a temperature field model for temperature error compensation.

Contents of the invention

In order to overcome the deficiencies of the prior art, in order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: for this purpose, some sleeves need to be used as related parts of the simulation to measure the runout of the extended part at a certain position away from the part. The measuring machine should be able to measure parameters with extended tolerances. In temperature error compensation, they can be used as reference parts to realize temperature error compensation.

In order to achieve the above object, the technical solution adopted by the present invention is that the temperature error compensation method of a three-coordinate measuring machine in a cylindrical coordinate system comprises the following steps:

1. According to the condition of the workpiece to be tested, design and manufacture the reference parts at the upper and lower ends. The reference parts are required to meet the technical requirements of general gauges, with small cylindricity shape errors, small end surface flatness errors, and good long-term stability;

2. Accurately calibrate the inner and outer diameters and heights of the reference parts: the inner and outer diameters need to be calibrated on at least two sections, and the two sections should be far apart to obtain a more accurate angle change value, height The number of positions measured depends on the need;

3. Establish a mathematical model for temperature error compensation;

4. Write the error compensation program on the basis of the established mathematical model of temperature error compensation, and add it to the data processing program of the workpiece measurement results;

5. Add the section to be measured for error compensation into the measurement program, and add the section to be measured for error compensation during the process of measuring the workpiece;

6. Perform data processing of measurement results and complete temperature error compensation.

The reference part is a sleeve.

The present invention has the following technical effects:

1. Improve the measurement stability of the cylindrical coordinate measuring machine.

2. Simple and accurate.

Description of drawings

Figure 1 is a schematic diagram of the working principle of a cylindrical coordinate measuring machine. In the picture:

1-rotary table 2-fixture 3-lower sleeve 4-probe 5-outer measuring frame for axial parameters 6-workpiece 7-inner measuring frame 8-upper sleeve 9-probe 10-probe 11-radial Parameter external measuring frame 12-probe.

Figure 2 is a schematic diagram of error compensation measurement.

Detailed ways

The purpose of the present invention is to provide a temperature error compensation technology based on the size of the measurement reference part, so as to improve the measurement stability of a cylindrical coordinate measuring machine.

The temperature error of measuring workpiece size on a cylindrical coordinate measuring machine is mainly caused by the following three factors.

1. The measuring frame moves in translation relative to the rotary table.

2. The direction of the movement axis of the measuring frame is deflected relative to the rotation axis.

3. The thermal expansion of the workpiece itself.

In practice, it is found that a considerable part of the rotating body parts need to be connected to the related parts through threads, and to ensure that the connected related parts have accurate positions and directions. For this reason, it is necessary to use some sleeves as the simulated related parts to measure their The amount of runout in an extension at a certain location away from the part. The measuring machine should be able to measure parameters with extended tolerances. In temperature error compensation, they can be used as reference parts to realize temperature error compensation.

Figure 2 shows the situation where a sleeve is screwed on each of the two ends of the workpiece. The size of the sleeve in the standard state is determined and known by calibration. Using the external probe to measure the outer diameter of the sleeve on section A, the difference ΔD _A between the measured outer diameter on section A and its calibration value can be obtained. It is caused by the change of the zero position of the scale relative to the axis of the rotary table when the measuring frame measures the A section under the influence of temperature changes, and the thermal deformation of the workpiece and the reference piece itself. Generally speaking, the distance between the zero position of the measuring frame scale and the axis of the rotary table is much larger than the outer diameter of the workpiece; at the same time, the temperature of the workpiece and the reference part are close, if their linear expansion coefficient and outer diameter are also close, then Their thermal deformations are also very close, and their effects cancel each other out. It can be considered that ΔD _A is mainly caused by the change of the zero position of the scale relative to the axis of the rotary table when the measuring frame measures the A section.

Subsequently, the outer diameter of the sleeve on the B-section is measured by the external probe, and the difference ΔD _B between the outer diameter on the B-section and its calibration value can be obtained. ΔD _B - ΔD _A is mainly caused by the deflection of the movement axis direction of the measuring frame relative to the rotation axis. The angle change between them

After measuring ΔD _A and ΔD _B , the measurement error of outer diameter caused by temperature change at any section can be compensated.

Similarly, the difference Δd C and Δd D between the measured value and the calibration value can be obtained by measuring the inner diameter of the sleeve at the cross-sections _C and _D. After the Δd _C and Δd _D are obtained according to the measurement, the measurement error of the inner diameter caused by the temperature change at any section can be compensated.

When the workpiece does not have an extension tolerance item to be measured, so that the threaded sleeve shown in Figure 2 is not needed, the lower sleeve can be replaced by the outer surface of the rotary table, that is, ΔD _A is obtained by measuring the outer diameter of the rotating body . In order to obtain ΔD _B and Δd _C , Δd _D , special sleeves are required.

In order to compensate the temperature error for the measurement of the axial dimension, it is necessary to use some axial dimensions L _E and L _F of the inner and outer probes to measure the sleeve, and the measured values L _E and L _F are respectively compared with those obtained by calibration under the standard state Compare the values of L _E0 and L _F0 to obtain their difference ΔL _E and ΔL _F , and then introduce compensation according to linear interpolation.

The temperature error compensation for the measurement of the axial dimension above is discussed for the columnar workpiece, that is, the case where the height is much larger than the diameter. For disc-shaped workpieces, that is, the diameter is much larger than the height, it is necessary to consider the influence of the change of the horizontal movement direction of the measuring frame relative to the axis of the rotary table. To do this, it is necessary to carry out the above-mentioned measurements on two cross-sections with different x, and then to introduce error compensation.

Below in conjunction with embodiment further illustrate the present invention.

1. According to the condition of the workpiece to be tested, design and manufacture the reference parts at the upper and lower ends. The reference part (sleeve) is required to meet the technical requirements of general gauges, with small cylindricity shape errors, small end face flatness errors, and good long-term stability.

2. Accurately calibrate the inner and outer diameters and heights of the reference parts. Both inner and outer diameters need to be calibrated on at least two sections. The two sections should try to be far apart to obtain a more accurate angle change value. The number of positions for height measurement is as required.

3. Establish the mathematical model of temperature error compensation.

4. Write the error compensation program based on the established mathematical model of temperature error compensation, and add it to the data processing program of the workpiece measurement results.

5. Add the section to be measured for error compensation into the measurement program, and add the section to be measured for error compensation during the process of measuring the workpiece.

6. Perform data processing of measurement results and complete temperature error compensation.

Claims (2)

1. A temperature error compensation method of a cylindrical coordinate system three-coordinate measuring machine, characterized in that, comprising the following steps: 1) According to the condition of the workpiece to be tested, design and manufacture the reference parts at the upper and lower ends. The reference parts are required to meet the technical requirements of general gauges, with small cylindricity shape errors, small end surface flatness errors, and good long-term stability; 2) Accurately calibrate the inner and outer diameters and heights of the reference parts: the inner and outer diameters need to be calibrated on at least two sections, and the two sections should be far apart to obtain a more accurate angle change value, height The number of positions measured depends on the need; 3) Establish a mathematical model for temperature error compensation; 4) Write the error compensation program on the basis of the established mathematical model of temperature error compensation, and add it to the data processing program of the workpiece measurement results; 5) Add the section to be measured for error compensation into the measurement program, and add the section to be measured for error compensation during the process of measuring the workpiece; 6) Perform data processing of the measurement results and complete temperature error compensation. 2. A method for compensating temperature errors of a three-coordinate measuring machine with a cylindrical coordinate system according to claim 1, wherein the reference member is a sleeve.

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