CN107607070A - A kind of articulated arm coordinate measuring machine thermal deformation errors recognize bearing calibration - Google Patents

Abstract

The invention discloses a method for identifying and correcting thermal deformation errors of an articulated arm type coordinate measuring machine. Thermal monitoring points are respectively set at the base of the articulated arm, the measuring arm, the joint, and the measuring head, and the temperature rise-time changes of each monitoring point are recorded. Curve; operate the coordinate measuring machine to measure the standard gauge block, each thermal monitoring point is equivalent to the temperature rise value of the laboratory temperature, and the measurement error, according to the multiple linear regression algorithm, the temperature rise value and thermal deformation error value of the seven thermal monitoring points of the joint arm Establish the experimental error compensation model. The undetermined parameters are determined by the least square method, and the measurement results of the articulated arm coordinate measuring machine are compensated. The present invention can obtain the mapping relationship between the length measurement error of the articulated arm type coordinate measuring machine and the temperature rise change between the corresponding temperature monitoring points; based on the mapping relationship, a thermal deformation error compensation model of the body based on multivariate linear fitting is established to realize the thermal deformation error Compensation to improve the measurement accuracy of the articulated arm.

Description

A thermal deformation error identification and correction method for an articulated arm coordinate measuring machine

technical field

The invention relates to the field of articulated arm coordinate measuring machines, in particular to a method for identifying and correcting thermal deformation errors of articulated arm coordinate measuring machines.

Background technique

The articulated arm coordinate measuring machine (hereinafter referred to as the articulated arm) is a high-precision instrument for coordinate measurement. During the coordinate measurement process, due to the thermal deformation of the body due to the change of the internal circuit of the articulated arm and the ambient temperature, the measurement force error is introduced. The thermal deformation of the body is an important factor affecting the measurement accuracy of the articulated arm. Due to the existence of thermal deformation, the real structural parameters of the articulated arm do not match its kinematic equations, resulting in large measurement errors. Although the probe error can be reduced by regular calibration of the articulated arm, the influence of the internal heating factor of the body is usually ignored in the calibration and measurement process. In order to improve the measurement accuracy of the articulated arm, it is necessary to master the internal heating The mechanism of generating thermal errors helps to further improve its measurement accuracy.

Contents of the invention

The purpose of the present invention is to design a method for identifying and correcting thermal deformation errors of an articulated arm type coordinate measuring machine.

In order to achieve the purpose of the above invention, the technical solution of the present invention is: a thermal deformation error identification and correction method of an articulated arm type coordinate measuring machine, comprising the following steps:

Step 1) Control the laboratory temperature at about 20°C, and monitor the laboratory temperature in real time;

Step 2) Set up m thermal monitoring points at the base of the articulated arm, the measuring arm, the joint and the measuring head respectively, equip the above m thermal monitoring points with a real-time temperature recording module, and record each monitoring point of the articulated arm from startup to thermal equilibrium. The temperature change of each monitoring point is obtained, and the temperature rise-time change curve of each monitoring point is obtained;

Step 3) Operate the coordinate measuring machine to perform random measurements on the standard gauge blocks in chronological order, and use random measurements for multiple times each time, and take the average value as the measured distance, that is, the measured value, and the difference between the measured value and the standard value of the standard gauge block is is the measurement error of the articulated arm;

Step 4) at regular intervals, record the temperature measurement of the thermal monitoring point in step 2), and measure the standard distance in step 3); draw n groups of test data, including each thermal monitoring point being equivalent to the temperature of the laboratory temperature Temperature rise value ΔT _ij (i=1, 2,..., m; j=1, 2,..., n), measurement error ΔE _j (j=1, 2,..., n) of the joint arm to the standard distance;

Step 5) Establish an experimental error compensation model for the temperature rise and thermal deformation error values of the seven thermal monitoring points of the articulated arm according to the multiple linear regression algorithm. The form of the model is:

E＝A ₀ +A ₁ ΔT _1j +A ₂ ΔT _2j +…+A _m ΔT _mj

In the formula, j=1, 2,...,n; ΔT _1j , ΔT _2j ,..., ΔT _mj respectively represent the temperature rise value of 1, 2,..., m thermal monitoring points at time j and the laboratory temperature; A ₀ , A ₁ ,..., A _m are undetermined parameters respectively;

Step 6) According to the n groups of test data in step 4), use the least squares method to determine the undetermined parameters A ₀ , A ₁ ,..., A _m , bring them into the test error compensation model in step 5), and obtain the heat of the articulated arm coordinate measuring machine Deformation error compensation model;

Step 7) Compensate the measurement results of the articulated arm coordinate measuring machine by using the error compensation formula obtained in step 6).

The beneficial effects of the present invention are:

1) This method can obtain the mapping relationship between the length measurement error of the articulated arm coordinate measuring machine and the temperature rise change between the corresponding temperature monitoring points;

2) Based on the mapping relationship, a thermal deformation error compensation model of the body based on multiple linear fitting is established to realize thermal deformation error compensation and improve the measurement accuracy of the articulated arm.

Description of drawings

Figure 1 is a distribution diagram of the articulated arm coordinate measuring machine and thermal monitoring points;

Fig. 2 is the temperature-time variation curve of each thermal monitoring point;

Fig. 3 measurement error and prediction error curve diagram of compensation model;

Fig. 4 adopts step 6) measurement accuracy curve before and after compensation model compensation;

Table 1 shows the temperature rise and measurement error data of each thermal monitoring point;

Table 2 shows the extreme value and average value of measurement accuracy before and after measurement error compensation.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

The present invention analyzes the detection method for the thermal deformation error caused by the temperature of the articulated arm. By designing a simple measurement method, the coordinates of the articulated arm are measured in consideration of the thermal deformation. The measurement accuracy of the measuring machine is greatly affected, and the error caused by the thermal deformation of the body is compensated. The invention fully takes into account the influence of thermal deformation of the body of the articulated arm coordinate measuring machine on the measurement accuracy, and provides a detection method for subsequent improvement of the measurement accuracy of the articulated arm coordinate measuring machine.

As shown in Figure 1, a thermal deformation error identification and correction method of an articulated arm coordinate measuring machine, the main components of an articulated arm coordinate measuring machine (hereinafter referred to as the articulated arm) include a base 1, a measuring arm 2, a measuring joint 3 and Probe 4.

Step 1) Control the laboratory temperature at about 20°C, and monitor the laboratory temperature in real time;

Step 2) Set 7 thermal monitoring points at the base 1 of the articulated arm, the measuring arm 2, the joint 3 and the measuring head 4 respectively, and mark them as P1, P2, P3, P4, P5, P6 and P7 respectively, and give The above-mentioned 7 thermal monitoring points are equipped with real-time temperature recording modules, which record the temperature changes of each monitoring point when the joint arm starts to reach thermal equilibrium, record the laboratory temperature synchronously, and mark it as P8, and calculate and calculate the temperature of each thermal monitoring point. The temperature-time change curve is shown in Figure 2.

Step 3) In this embodiment, a standard gauge block with cone dimples is used as a standard measuring tool, and the standard distance between cone dimples is 361.910 mm. Operate the coordinate measuring machine to randomly measure the cone-dimple distance of the standard gauge block in chronological order, and take 5 random measurements each time, and take the average value as the actual measured distance, that is, the measured value, the difference between the measured value and the standard distance of the cone-dimple distance is the measurement error of the articulated arm;

Step 4) Every 5 minutes, record the temperature measurement of the heat monitoring point in step 2), and measure the distance of the cone dimple in step 3); the test lasts for 150 minutes, and 30 groups of test data are obtained, as shown in Table 1 , including the temperature rise value ΔT _ij (i=1, 2,...,7; j=1, 2,...,30) of each thermal monitoring point equivalent to the laboratory temperature, and the measurement error ΔE _j (j = 1, 2, ..., 30).

Table 1 Temperature rise and measurement error data of each thermal monitoring point

Step 5) Thermal deformation error compensation model based on multiple linear regression.

The mathematical model of thermal error and temperature rise of each monitoring point is established by multiple linear regression method. The principle of multiple linear regression is: if the internal relationship between the dependent variable y and other m variables x ₁ , x ₂ ,…,x _m is linear, and the observed data (x ₁ ,x ₂ ,…, x _m ; y), then the observed data can have the following structure:

y=β ₀ +β ₁ x ₁ +β ₂ x ₂ +,…,+β _m x _m

In the formula, β ₀ , β ₁ ,..., β _m are m+1 parameters to be estimated; x ₁ , x ₂ ,..., x _m are m general variables that can be measured or controlled.

According to the multiple linear regression algorithm, the experimental error compensation model is established for the temperature rise and thermal deformation error values of the seven thermal monitoring points of the articulated arm. The form of the model is:

E＝A ₀ +A ₁ ΔT _1j +A ₂ ΔT _2j +…+A ₇ ΔT _7j

In the formula: j=1,2,…,30; E is the thermal deformation error; ΔT _1j , ΔT _2j ,…, ΔT _7j respectively represent the thermal monitoring points P1, P2, P3, P4, P5, P6, P7 at time j Relative to the temperature rise value of the laboratory temperature P8; A ₀ , A ₁ ,..., A ₇ are parameters to be determined respectively.

Step 6) According to the 30 sets of test data in Step 4) Table 1, the undetermined parameters A ₀ , A ₁ , ..., A ₇ are determined by least square method. Bring it into the step five) test error compensation model to obtain the compensation formula for the thermal deformation error of the articulated arm.

To determine the parameters A ₀ , A ₁ , ..., A ₇ , use the mathematical optimization analysis comprehensive tool software 1stOPt developed by Qiwei Hi-Tech Co., Ltd. to input the undetermined parameters (Parameters) A ₀ , A ₁ , ..., A ₇ , Temperature rise variation values of each sensor ΔT ₁ , ΔT ₂ ..., ΔT ₇ and measurement error value (Variable) ΔE _j (j=1, 2, ..., 30). And to determine the model function (Function) E=A ₀ +A ₁ ΔT _1j +A ₂ ΔT _2j +...+A ₇ ΔT _7j , and bring in the experimental data in Table 1.

Set the optimization algorithm, use the simulated annealing algorithm, and set the algorithm parameters (choose the default). Click Run to obtain the identification results of A ₀ , A ₁ ..., A ₇ as follows:

A ₀ =-0.118, A ₁ =0.092, A ₂ =0.010, A ₃ =0.164, A ₄ =0.213, A ₅ =-0.207, A ₆ =-0.008, A ₇ =-0.129

Therefore, the thermal deformation error compensation model of the articulated arm coordinate measuring machine based on multiple linear regression is established as follows:

E＝-0.118+0.092ΔT ₁ +0.010ΔT ₂ +0.164ΔT ₃ +0.213ΔT ₄

-0.207ΔT ₅ -0.008ΔT ₆ -0.129ΔT ₇

Step 7) The error compensation model obtained in step 6) is used to compensate the measurement results of the articulated arm coordinate measuring machine.

In order to verify the effectiveness of the compensation model, the compensation model obtained from the experiment is verified, and the comparison between the experimental measurement error and the estimation error of the compensation model (that is, the error calculated using the compensation model) is shown in Figure 3. And according to the error compensation model, error compensation is performed on the measurement data, that is, the measurement error of the articulated arm coordinate measuring machine is subtracted from the estimation error of the compensation model, so as to obtain the measurement accuracy after compensation. The comparison of the effects before and after compensation is shown in Figure 4 and Table 2 .

Before error compensation After error compensation percentage(%) Max(mm) 0.179 0.0936 47.7% Minimum value (mm) 0.002 0.00064 68% Average value(mm) 0.0715 0.0335 53.15%

Table 2 Measurement accuracy extreme value and average value before and after measurement error compensation

It can be seen from Figure 4 and Table 2 that the maximum, minimum and average values of the measurement errors after error compensation of the articulated arm are all reduced, and the maximum measurement error is reduced from 0.179mm to 0.0936mm, which is a decrease of 47.7%. The error is reduced from 0.0715mm to 0.0335mm, effectively improving the measurement accuracy of the articulated arm.

The described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Claims (1)

1. a kind of articulated arm coordinate measuring machine thermal deformation errors recognize bearing calibration, it is characterised in that comprise the following steps：

Step 1) control laboratory temperature to be monitored in real time at 20 DEG C or so, and to laboratory temperature；

Step 2) m hot monitoring points are set at the pedestal of joint arm, measuring arm, joint and gauge head respectively, to above-mentioned m heat Monitoring point be equipped with real time temperature logging modle, record joint arm from start reach thermal balance when each monitoring point temperature change, And draw temperature rise-time changing curve of each monitoring point；

Step 3) operation coordinate measuring machine carries out random measurement in chronological order to standard gauge block, and it is random more using measuring every time It is secondary, average as measured distance, i.e. measured value, the difference of measured value and standard gauge block standard value is that the measurement of joint arm misses Difference；

Step 4) every the set time, to step 2) in hot monitoring point temperature measuring and recording, and to step 3) Plays distance Carry out one-shot measurement；Draw n group test datas, including each hot monitoring point equivalent to the temperature rise value Δ T of laboratory temperature_ij(i=1, 2 ..., m；J=1,2 ..., n), measurement error Δ E of the joint arm to gauged distance_j(j=1,2 ..., n)；

Step 5) temperature rise value and thermal deformation errors value of seven hot monitoring points of joint arm are established according to arithmetic of linearity regression Experimental error compensation model, the form of institute's established model are：

E=A₀+A₁ΔT_1j+A₂ΔT_2j+…+A_mΔT_mj

J=1,2 in formula ..., n；ΔT_1j, Δ T_2j..., Δ T_mj1,2 is represented respectively ..., m hot monitoring points are at j moment and experiment The temperature rise value of room temperature；A₀, A₁..., A_mRespectively undetermined parameter；

Step 6) according to step 4) in n group test datas, undetermined parameter A is determined using least square method₀, A₁..., A_m, bring into Step 5) in test error compensation model, obtain articulated arm coordinate measuring machine thermal deformation error compensation model；

Step 7) use step 6) obtained error compensation model, the measurement result of articulated arm coordinate measuring machine is mended Repay.