Virtual-Point Kinematics Calibration for Five-Axis Motion Accuracy
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Solution Overview
Problem
Existing kinematics calibration methods face issues with introducing too many clamping errors and interrupted light continuity errors, leading to a tedious and complex calibration process due to the need for multiple reflecting heads and repeated positioning errors in high-precision motion mechanisms like five-axis machine tools and robots.
Innovation Solution
A dimensionless kinematics calibration method based on a virtual point is introduced, where virtual points are arranged at the tail end of the motion mechanism, allowing for a single round of motion with a six-degree-of-freedom reflecting head, avoiding extra clamping errors and reducing the need for multiple measurements, and converting the measurement coordinate system to align with the motion mechanism's coordinate system for accurate calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple reflecting heads are used to obtain positions of four points, then measurement completeness is improved, but interrupted light continuity error is introduced
Solution Approach 1:
A single six-degree-of-freedom reflecting head is designed to perform multiple measurement functions simultaneously. The reflecting head can measure positions of multiple virtual points (P1, P2, P3, P4) and capture both position and orientation information in one continuous measurement process, eliminating the need for multiple separate reflecting heads and avoiding light interruption errors.
Solution Approach 2:
The patent combines multiple measurement functions into a single integrated measurement system. By merging the measurement of four different points and six-degree-of-freedom information into one reflecting head, the system achieves complete measurement data without interrupting the laser tracker's light beam, thus resolving the contradiction between measurement completeness and measurement continuity.
2Device complexity
If one reflecting head is used to obtain positions of four points, then device complexity is reduced, but repeated positioning error and secondary clamping error are introduced
Solution Approach 1:
The patent introduces virtual points (P1, P2, P3, P4) in three-dimensional space at the tail end of the motion mechanism, allowing a single reflecting head to measure positions across multiple spatial locations simultaneously. This dimensional approach enables one reflecting head to capture equivalent data that would traditionally require multiple reflecting heads at different physical locations, eliminating repeated positioning errors while maintaining measurement precision.
3Adaptability or versatility
If traditional kinematics calibration is performed with three positions and three poses, then calibration coverage is improved, but uneven distribution in optimization occurs
Solution Approach 1:
The patent transforms the calibration parameters from traditional three positions and three poses into six-dimensional position and orientation parameters (x, y, z coordinates and α, β, γ angles) of virtual points. This parameter transformation ensures uniform distribution in the optimization process while maintaining comprehensive calibration coverage, as all six degrees of freedom are measured simultaneously at each virtual point location.
Data Source
AI summary
A dimensionless kinematics calibration method based on a virtual point and a related apparatus thereof. The method comprises: establishing a kinematics model of a motion mechanism, and arranging a plurality of virtual points at a tail end of the motion mechanism to establish a dimensionless kinematics model and a dimensionless error model; converting a measurement coordinate system into a motion mechanism coordinate system, acquiring a rotation matrix and a translation matrix of a target virtual point measured by the measurement device, and calculating actual coordinates of all virtual points to obtain a measured value of the dimensionless kinematics model; calculating a theoretical value of the dimensionless kinematics model according to a spatial relationship between a reflecting head and the tail end of the motion mechanism; and optimizing the dimensionless error model according to the measured value and the theoretical value to obtain a calibration result.