Calibration method of angle encoder eccentricity and structure parameters of joint coordinate measuring machine

Abstract

The invention discloses a high-accuracy calibration method of a joint coordinate measuring machine. The method comprises the steps that a to-be-calibrated machine is placed in a measuring space of a reference machine by taking the six-freedom-degree joint coordinate measuring machine as the to-be-calibrated machine and a higher-accuracy three-coordinate measuring machine as the reference machine; calibration plates with taper holes are sequentially placed according to six bisectrices of a circle; the measuring machine measures the taper holes in the calibration plates with a plurality of poses in each position; each pose corresponds to a measuring coordinate of one taper hole under a to-be-calibrated coordinate system and a group of joint angle values; the high-accuracy three-coordinate machine measures coordinates of the taper holes in the positions under a reference coordinate system; the joint angle values and reference coordinates corresponding to measuring points serve as sampling data; a multi-target search problem is converted into a single-target nonlinear programming problem based on the sampling data; and a structure parameter error value of the to-be-calibrated machine and an eccentricity parameter of an angle encoder are obtained by identification of a sequential quadratic programming algorithm.

Description

technical field [0001] The invention relates to the technical field of coordinate measurement, in particular to a calibration method for structural parameters of a six-degree-of-freedom articulated coordinate measuring machine and an eccentricity error of an angle encoder. Background technique [0002] Articulated coordinate measuring machine is a multi-degree-of-freedom non-orthogonal coordinate measuring machine, usually with 6 degrees of freedom. It is modeled on the joint structure of the human body, and consists of three measuring arms and a measuring head connected in series through six (rotation) joints to form a space open chain structure, thereby replacing the length measurement reference with the angle measurement reference. When measuring with a measuring machine, the probe coordinates are a function of the kinematic parameters of the measuring machine and the angles of its six joints. Compared with the traditional three-coordinate measuring machine with orthogon...

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Problems solved by technology

The above methods can realize the identification of structural parameters, but before the calibration, the six angle encoders must be calibrated to determine the eccentric parameters of the angle encoders, so as to compensate the joint rotation angle of the measuring machine; at the same time, most of these methods use traditional numerical analysis methods ( Such as the least squares method, singular value decomposition method) to obtain analytical solutions, this type of method has high requirements for the initial value, in the case of inappropriate selection of the initial value, often only a partial solution can be obtained, which affects the measurement accuracy of the measuring machine

[0005] In addition, some literatures have been published in recent years to propose different calibration methods: "Research on Calibration Technology of Multi-joint Flexible Three-coordinate Measuring System" (Journal of Harbin Institute of Technology, 2008) uses a calibration ball to measure the center of ten balls and uses the least squares method Carry out calibration; "Parameter Calibration of Articulated Coordinate Measuring Machine Based on Laser Tracker" (Journal of University of Science and Technology of China, 2009) uses laser tracker to calibrate, and uses special fixture to fix the attitude of measuring machine during calibration, and measures 30 points. Gauss-Newton method to find the least squares solution; "Mathematical Modeling and Calibration Method of Humanoid Articulated Coordinate Measuring Machine" (Journal of Huazhong University of Science and Technology, 2007) When calibrating, use high-precision three-coordinate machine to establish the world coordinate system and calculate the error , collect 30 points for calibration; "Design of Calibration System for Jointed Arm Coordinate Measuring Machine" (Computer Measurement and Control, 2009) uses the inversion method to indirectly measure the structural parameters of the measuring machine, but the experimental process is complicated and requires complex Clamping tools and high-precision orthogonal coordinate measuring machines; "High-precision calibration method for six-degree-of-freedom joint-type flexible coordinate measuring machines" (patent, 2007) also uses high-precision instruments and special fixtures to complete the calibration, and the calibration posture is fixed. Consider repeated measurement of a single point; "Flexible Coordinate Measuring Machine Parameter Identification Method" (Journal of Agricultural Machinery, 2007) adopts the calibration method of single-point cone dimples, fixing a cone dimple at a position in the measurement space, using joint flexible The coordinate measuring machine continuously samples 200 points at the apex of the cone dimple; "A Portable Articulated Coordinate Measuring Machine Structural Parameter Calibration Optimal Sampling Strategy" adopts a quartz rod with cone dimples at both ends for calibration, and the quartz rod is placed on the measuring machine for On the six circumferential positions of the center of the circle, measure 500 sets of data by rotating the quartz rod in different planes at each position, a total of 3000 sets of data

[0006] The above methods still have deficiencies in calibration. For example, most of the methods do not consider the spatial distribution of measuring machine errors, and there are phenomena of single attitude of measuring machine and narrow measurement area in sampling, and the calibration results are only locally optimal; Only one of the repeatability accuracy and length measurement accuracy indicators of the measuring machine accuracy is considered, which makes the calibration results unsatisfactory when evaluating the accuracy of the measuring machine; these calibration methods also need to calibrate and compensate the eccentricity error of the angle encoder in advance

The above methods have proposed their own joint angle error compensation models and carried out parameter identification, but they all place individual joints on auxiliary equipment for measurement instead of on a fully assembled measuring machine. The measurement data is large and difficult to operate. complex

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