Robot Joint Error Compensation Using Constant-Torque Speed Fluctuations
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Solution Overview
Problem
Existing methods for reducing kinematic error in articulated robot arms are complex and costly, and existing compensation techniques do not effectively account for imperfections in motor and gear manufacturing, leading to inaccuracies in position and speed control.
Innovation Solution
A method and system for assessing kinematic error by controlling a robot joint to rotate at a constant speed under a constant gravity-induced torque, using sensors to detect speed fluctuations, and compensating for these errors by estimating and correcting the kinematic error based on these fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing compensation techniques are used to reduce kinematic error, then manufacturing precision is improved, but device complexity increases and cost increases
Solution Approach 1:
The system uses the robot arm's own operational data (motor position, joint position, speed measurements during normal operation) to self-assess and self-compensate for kinematic errors. The controller performs regression analysis on collected data to generate compensation values without requiring external assessment equipment, making the system self-sufficient and cost-effective.
Solution Approach 2:
The system implements a feedback mechanism where the controller continuously collects operational data from sensors, analyzes the relationship between motor position and joint position through regression analysis, and uses the assessed kinematic errors to correct future position commands. This closed-loop feedback enables ongoing improvement of positioning accuracy.
2Manufacturing precision
If existing compensation techniques are used to reduce kinematic error, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The system performs kinematic error assessment during normal robot operation by collecting data from routine movements, rather than requiring separate dedicated measurement procedures. The controller accumulates operational data and performs regression analysis in the background, preparing compensation values ahead of time for future operations.
Solution Approach 2:
The system continuously collects operational data during normal robot operation and continuously refines compensation values through ongoing regression analysis. This eliminates idle measurement time and ensures the robot is productive while the system learns and improves accuracy.
3Measurement precision
If sensors are used to detect joint rotation and speed fluctuations, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system uses existing sensors already present in the robot arm (motor position sensors and joint position sensors) to measure speed fluctuations. No additional specialized measurement equipment is required - the existing sensor infrastructure is leveraged for kinematic error assessment, reducing overall system complexity.
Solution Approach 2:
The existing sensors serve multiple functions: they provide feedback for basic motor control, enable kinematic error assessment, and support the regression analysis process. This multi-functionality eliminates the need for dedicated measurement sensors and reduces overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise and cost-effective compensation of kinematic errors, improving the accuracy of robot arm movement by reducing fluctuations due to gear imperfections.
Implementation Method 1
a sensor for measuring the rotation of the joint
Implementation Method 2
a transmission gear... for driving rotation of the joint by a transmission gear
Implementation Method 3
Rotation of such a joint is driven by a motor, typically via a transmission gear
Implementation Method 4
the joint, while being rotated from a start angle to an end angle, is subject to a constant gravity-induced torque
Data Source
Figure 1~2
Figure 3~6
AI summary
A method is provided for assessing kinematic error in a joint (5a, 5b, 5c, 5d) which rotatably connects a proximal portion (15b, 15c) and a distal portion (14b, 14c) of a robot arm (1), the joint (5a, 5b, 5c, 5d) having associated with it a motor (9b, 9c, 9d) mounted in one of said portions (14b, 14c; 15b, 15c) and coupled to the other one (15c, 15b; 14b, 14c) of said portions for driving rotation of the joint (5a, 5b, 5c, 5d) by a transmission gear (10b, 10c, 10d), and a sensor (18b, 18c) for measuring the rotation of the joint (5a, 5b, 5c, 5d). The method comprises the steps of: a) determining a movement of the robot arm (1) in which the joint (5a, 5b, 5c, 5d), while being rotated from a start angle to an end angle, is subject to a constant gravity-induced torque; b) controlling execution of said movement, and, in said movement, controlling the joint (5a, 5b, 5c, 5d) to rotate from the start angle to the end angle at a constant speed, c) detecting speed fluctuations of the joint (5a, 5b, 5c, 5d) while it is being rotated from the start angle to the end angle; and d) estimating the kinematic error based on the speed fluctuations.