6-Axis Robot Inter-Axis Offset Calibration via LED Trajectory Measurement
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Solution Overview
Problem
Current methods for improving the absolute position accuracy of 6-axis robots fail to account for inter-axis offsets, leading to deviations in the end effector's position due to assembly and working errors, which are not effectively compensated by existing error correction techniques.
Innovation Solution
A method involving the measurement and correction of inter-axis offsets by arranging a measurement point on the end effector, rotating it around the first rotation joint, and measuring multiple positions on a rotation trajectory using a three-dimensional gauge to determine the inter-axis offset, which is then used to adjust the DH parameters for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional error compensation methods are used to improve absolute position accuracy, then link length errors, twist angle errors, motor origin position errors, and driving system deflections are corrected, but inter-axis offset errors remain uncorrected, causing the end effector to deviate from the indicated position
Solution Approach 1:
The patent applies preliminary action by measuring and compensating for inter-axis offset errors before they cause positioning inaccuracies. The method involves rotating the robot arm around the first rotation joint, measuring the rotation trajectory of a measurement point on the end effector using a three-dimensional gauge, and calculating the inter-axis offset based on the measured trajectory. This offset is then compensated for in advance, ensuring that the end effector accurately reaches the indicated position without being affected by assembly and working errors in the rotation joints.
Solution Approach 2:
The patent replaces traditional mechanical alignment and calibration methods with a measurement-based approach. Instead of relying on precise mechanical assembly to minimize inter-axis offsets, the invention uses a three-dimensional gauge to measure the actual rotation trajectory and calculates the offset mathematically. This substitution of mechanical precision requirements with measurement and computation allows for effective compensation of assembly and working errors in the rotation joints.
2Ease of operation
If the position of second, third, and fifth rotation joints is deviated from normal position due to assembly and working errors, then the end effector moves to an incorrect position, but existing compensation methods do not address this specific deviation
Solution Approach 1:
The patent implements feedback by using a three-dimensional gauge to continuously measure the actual position of the end effector during rotation around the first rotation joint. The measured rotation trajectory provides feedback information about the inter-axis offset, which is then used to calculate and compensate for the positioning error. This closed-loop feedback mechanism ensures that assembly and working errors in the rotation joints do not result in inaccurate end effector positioning.
Solution Approach 2:
The patent applies parameter changes by modifying the DH parameters (Denavit-Hartenberg parameters) based on the measured inter-axis offset. The method involves calculating the offset from the measured rotation trajectory and then adjusting the relevant DH parameters (specifically the d parameters representing link lengths along the rotation axes) to compensate for the offset. This parameter adjustment corrects the mathematical model of the robot, ensuring accurate positioning despite physical deviations in the rotation joints.
3Manufacturing precision
If a measurement point is arranged on the end effector and the robot arm is rotated around the first rotation joint to measure multiple positions, then the inter-axis offset can be detected, but the measurement and correction process requires additional time and complexity
Solution Approach 1:
The patent applies partial action by focusing the measurement process specifically on detecting inter-axis offset errors, rather than performing a comprehensive calibration of all robot parameters. The method rotates the robot arm only around the first rotation joint and measures the trajectory of a single measurement point on the end effector, which is sufficient to detect the inter-axis offset. This targeted approach reduces measurement time and complexity compared to full system calibration, while still achieving accurate offset detection and compensation.
Data Source
AI summary
In a 6-axis robot, as an example, an inter-axis offset can be measured and calibrated. A light emitting diode is installed on an end effector, and the end effector is located on a plurality of target positions of movement on the axis X (Xb) of a robot coordinate. Then, the position of the light emitting diode is measured by a three-dimensional gauge, and an inter-axis offset F is detected based on an error between the target positions of movement and actually moved positions. For the inter-axis offset F, DH parameters are calibrated.