Robot Joint Speed Feedback for Kinematic Error Estimation
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Solution Overview
Problem
Articulated robot arms experience kinematic errors due to imperfections in motor and gear manufacturing, leading to inaccuracies in position and speed control of the end effector.
Innovation Solution
A method is described to assess and compensate kinematic errors in robot joints by determining a movement where the joint is subject to a constant gravity-induced torque, controlling the joint to rotate at a constant speed, detecting speed fluctuations, and estimating kinematic error based on these fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a transmission gear is used to drive the robot joint, then the reduction ratio is increased and backlash is reduced, but kinematic error due to gear imperfections (eccentricity of gearwheel or spline) still causes rotation speed fluctuations
Solution Approach 1:
The patent uses a sensor to detect the actual rotation speed of the joint and feeds this information back to the controller. The controller compares the actual speed with the commanded constant speed and uses this feedback to estimate and compensate for kinematic errors caused by gear imperfections, thereby maintaining accurate position control despite transmission gear inaccuracies.
Solution Approach 2:
The patent replaces purely mechanical position calculation (based on motor position and reduction ratio) with a hybrid approach that incorporates sensory feedback and computational estimation. By substituting mechanical precision requirements with sensor-based measurement and software-based compensation, the system achieves accurate control without requiring perfectly precise mechanical components.
2Ease of operation
If the robot arm moves under gravity influence, then the movement is more realistic for operation, but gravity-induced deformation of the robot arm biases the speed fluctuations and complicates kinematic error assessment
Solution Approach 1:
The patent identifies and utilizes movement configurations where the robot arm operates in a gravitational equipotential state, specifically when the arm is horizontal or when the center of gravity of the distal portion lies on the rotation axis. In these configurations, gravity-induced torque is constant or zero, eliminating gravity-induced deformation effects and enabling accurate isolation and measurement of pure kinematic errors from the transmission gear.
Solution Approach 2:
The patent segments the sources of speed fluctuations into distinct components: those caused by transmission gear imperfections and those caused by gravity-induced deformation. By carefully selecting measurement configurations where gravity effects are constant or absent, the method isolates the gear-related kinematic errors for accurate assessment, while gravity effects can be separately characterized and compensated in operational conditions.
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 accurate assessment and compensation of kinematic errors, improving the precision of robot arm movement by isolating speed fluctuations caused by gear imperfections from those influenced by gravity-induced deformations.
Implementation Method 1
determining a movement of the robot arm in which the joint, while being rotated from a start angle to an end angle, is subject to a constant gravity-induced torque
Data Source
AI summary
A method includes determining a movement of a robot arm in which a joint while being rotated from a start angle to an end angle, is subject to a constant gravity-induced torque; controlling execution of the movement, and, in the movement, controlling the joint to rotate from the start angle to the end angle at a constant speed; detecting speed fluctuations of the joint while it is being rotated from the start angle to the end angle; and estimating the kinematic error based on the speed fluctuations.