Manipulator Calibration Using Constrained Elasto-Kinematic Modeling
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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 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 motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional rigid-body kinematic calibration is used, then the calibration process is simple and fast, but the accuracy is limited due to unmodeled elastic effects and non-linearities
Solution Approach 1:
The patent transitions from rigid-body kinematic parameters to elasto-kinematic parameters that include elastic deformation effects. By changing the parameter model to account for flexibility in joints and links, the system achieves higher accuracy without requiring complex external measurement equipment.
Solution Approach 2:
The patent replaces traditional mechanical measurement systems (external sensors, laser trackers) with an internal sensor-based approach that uses the robot's own motors and encoders. This substitution eliminates complex external hardware while achieving superior accuracy through elasto-kinematic modeling.
2Measurement precision
If friction-aware control is implemented, then the accuracy of motor angle measurements is improved, but the control complexity increases
Solution Approach 1:
The patent introduces friction models as intermediary elements that mediate between the motor commands and the actual joint angles. By modeling friction effects and compensating for them, the system retrieves accurate motor angle measurements without requiring complex hardware modifications.
3Measurement precision
If elasto-kinematic models with multiple parameters are used, then the accuracy of geometric property determination is improved, but the identification process becomes more complex and time-consuming
Solution Approach 1:
The patent performs preliminary identification of friction parameters and elastic properties before the main geometric calibration. By pre-characterizing these non-geometric effects, the system reduces the complexity and time of the subsequent geometric parameter identification process.
Solution Approach 2:
The patent segments the calibration process into distinct phases: friction parameter identification, elastic property identification, and geometric parameter identification. This segmentation allows each phase to be optimized independently, reducing overall calibration time while maintaining accuracy.
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, reducing deviations and improving the precision of end-effector positioning and motion, achieving accuracy closer to the repeatability limits of industrial robots.
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
joint friction, which is separated from the identification of the geometric properties
Implementation Method 3
at least one axis comprises at least one elasticity
Data Source
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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.