Haptic Mapping for Joint Simulator Force Convergence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Joint testing machines face challenges in accurately reproducing intermittent contact conditions, which are characterized by near-impulsive forces with high-frequency spectral content, leading to difficulties in converging actual testing forces and displacements to prescribed values during cyclic testing.
Innovation Solution
A haptic mapping technique is employed in conjunction with an impedance-mode servo controller, using a system comprising a simulator stage, drive system, force sensor, displacement sensor, and digital control system, including an iterative learning control (ILC) system and waveform compensation, to generate a haptic map that pre-compensates for drive system lag and attenuation, improving the convergence of testing forces and displacements to prescribed values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard cyclic testing is performed without haptic mapping, then the testing protocol can be implemented, but the convergence rate of actual testing forces to prescribed forces is slow
Solution Approach 1:
The haptic mapping technique performs preliminary characterization of the drive system's dynamic behavior by measuring its frequency response function. This pre-acquired information is then used to pre-compensate control signals, allowing the system to anticipate and correct for lag and attenuation effects before they degrade performance. This resolves the contradiction by preparing the system in advance rather than reacting to convergence issues during actual testing.
Solution Approach 2:
The system employs iterative learning control that uses feedback from actual testing forces and displacements to continuously refine the haptic map. By comparing prescribed forces with actual measured forces and updating the compensation parameters accordingly, the system accelerates convergence over multiple test cycles. This feedback mechanism directly addresses the slow convergence problem by learning from past performance.
2Productivity
If drive system operates at high speed, then testing efficiency is improved, but drive system lag and attenuation increase
Solution Approach 1:
The system characterizes the drive system's dynamic parameters (lag and attenuation) as functions of frequency through haptic mapping. By understanding how these parameters change with operating speed, the control system can apply frequency-dependent compensation. This allows the drive system to operate at high speeds while maintaining accuracy, as the compensation parameters are specifically tuned to counteract the speed-related degradation.
Solution Approach 2:
The haptic mapping technique applies preliminary anti-action by pre-compensating control signals with inverse characteristics of the drive system's lag and attenuation. Before the drive system processes commands at high speed, the control signals are pre-adjusted to counteract the expected dynamic errors. This proactive compensation enables high-speed operation without sacrificing force and displacement reproduction accuracy.
3Reliability
If intermittent contact conditions are reproduced, then realistic joint testing is achieved, but near-impulsive forces with high-frequency content cause control difficulties
Solution Approach 1:
The haptic map serves as an intermediary that mediates between the control system and the drive system during intermittent contact conditions. By pre-characterizing the drive system's response to high-frequency content, the haptic map provides a buffer that smooths out the control difficulties associated with near-impulsive forces. This intermediary layer enables realistic intermittent contact testing while simplifying the control problem.
Data Source
AI summary
The present invention relates to joint simulators, and in particular, to methods and systems for controlling joint simulators by using a haptic mapping technique. A joint simulator is used to closely approximate the conditions within the body, particularly with respect to human and animal joints, and can be used to test and evaluate prosthetics for use in various parts of a human or animal body. The haptic mapping technique improves the rate of convergence of the actual testing forces to the prescribed forces during repetitive performance and life testing. The method is used in conjunction with an impedance-mode servo controller.