Manipulator Calibration Using Constrained Motion and Friction Feedback
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Solution Overview
Problem
Industrial robots face challenges in achieving high accuracy due to non-rigid joints and links, non-linear effects like friction and backlash, which current calibration methods fail to adequately address, leading to deviations in end-effector positioning and motion accuracy.
Innovation Solution
A method and system that use internal sensors to determine geometric properties of manipulators by constraining motion with a constraining device, performing friction-aware control, and identifying kinematic parameters for an elasto-kinematic model to account for elasticity and other non-geometric effects, allowing for improved accuracy in end-effector positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional kinematic calibration methods are used, then the calibration process is simple, but the accuracy of end-effector positioning is insufficient due to unaccounted elasticity and non-linear effects
Solution Approach 1:
A constraining device is introduced as an intermediary element between the manipulator and the environment. This device provides known geometric constraints that enable accurate determination of geometric properties while accounting for elasticity and non-linear effects, without requiring complex external measurement systems
Solution Approach 2:
The manipulator performs self-calibration by executing constrained motions under its own control. Internal sensors monitor motor torques and angles during these motions, allowing the system to determine its own geometric properties without external intervention or complex calibration equipment
2Measurement precision
If friction-aware control is implemented, then the accuracy of geometric property determination is improved, but the control complexity increases
Solution Approach 1:
Internal sensors provide feedback on motor torques and angles during constrained motions. This feedback is used in friction-aware control algorithms to compensate for friction and other non-linear effects, enabling accurate determination of geometric properties through iterative refinement
Solution Approach 2:
The control system dynamically adjusts control parameters based on monitored motor torques and angles. Friction-aware control modifies motion profiles and torque compensation parameters in real-time to account for friction effects, improving measurement accuracy without requiring complex hardware changes
3Measurement precision
If elasto-kinematic models are used to account for elasticity, then the accuracy of kinematic parameters is improved, but the computational complexity increases
Solution Approach 1:
The manipulator system is segmented into distinct components (joints, links, constraining device) with separate geometric and elastic properties. This segmentation allows the elasto-kinematic model to systematically account for elasticity in each component while maintaining computational tractability through modular parameter identification
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 enables more accurate determination of geometric properties and reduced deviations in end-effector motion, enhancing the precision of industrial robots by explicitly managing non-geometric properties and improving the accuracy of kinematic calibration.
Implementation Method 1
constraining motion of the manipulator by means of a constraining device such that the motion of the manipulator is physically constrained in at least one degree of freedom
Implementation Method 2
performing friction-aware control of the constrained manipulator motion for a period of time while monitoring quantities related to motor torque and to motor angle
Implementation Method 3
performing an identification of a set of kinematic parameters for an elasto-kinematic model that includes at least one known quantity representing the at least one elasticity
Data Source
AI summary
A method and system for determining geometric properties of a manipulator (2). The manipulator (2) is controlled to perform constrained motions exhibiting force interaction with the environment, or between different links of the manipulator (2), such that a kinematic chain is formed mechanically. The chain may include peripherals and external axes of motion. A constraining device, enables motions that facilitate the determination of geometric properties. A unified model of joint and link compliances facilitates determination of stiffness parameters. The force interaction is controlled with awareness of friction such that non-geometric properties are possible to identify, thereby enabling separation of non-geometric effects from the geometric ones, which improves accuracy.