High-accuracy calibration method of joint coordinate measuring machine

Abstract

The invention discloses a high-accuracy calibration method of a joint coordinate measuring machine, which comprises the following steps that the measuring machine acquires a plurality of pairs of taper holes in each calibration plate with different poses for many times; each pose corresponds to a group of joint angles and a measuring head coordinate; a plurality of groups of joint angle vectors and measuring head coordinates are obtained; a plurality of groups of two-point distance values between the taper holes in the calibration plates are calculated; a standard deviation formula of x, y and z coordinates of each measuring point is obtained; standard deviations of the measuring points are summed; the two-point distance value Li of each calibration plate at the measuring point i subtracts a point distance truth value Lr; standard deviations are obtained and summed; delta xyz and delta L are summed to serve as an objective function of a nonlinear quadratic programming problem; and a structure parameter error value of the joint coordinate measuring machine is obtained by a sequential quadratic programming algorithm.

Description

technical field [0001] The invention relates to the technical field of coordinate measurement, in particular to a high-precision calibration method for a six-degree-of-freedom articulated coordinate measuring machine. 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 orthogonal coordinate system, it has the advantages of large mea...

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Problems solved by technology

"Flexible Coordinate Measuring Machine Parameter Identification Method" (Journal of Agricultural Machinery, 2007) adopts the single-point cone dimple calibration method, fixes a cone dimple at a position in the measurement space, and uses an articulated flexible coordinate measuring machine to continuously measure the apex of the cone dimple. Sampling 200 points, this method does not require other precision instruments, but only single-point repeatability is considered during calibration, and length measurement accuracy is not considered; at the same time, the fixed measurement area also affects the calibration results

"An Optimal Sampling Strategy for Structural Parameter Calibration of a Portable Articulated Coordinate Measuring Machine" uses a quartz rod with cone dimples at both ends for calibration. 500 sets of data were measured by rotating the quartz rod on different planes according to a certain division, a total of 3000 sets of data; although such a sampling strategy can satisfy the entire measurement space, the implementation process is complicated, and at the same time, the single-point repeatability is not considered in the calibration. Accuracy index

[0005] 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 measuring machine accuracy is considered, which makes the calibration results unsatisfactory when evaluating the accuracy of measuring machines; and the calibration implementation depends on other high-precision measuring instruments, which cannot be calibrated on site

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