Manipulator Joint Hard-Stop Control for Vibration-Free Limit Approach
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Solution Overview
Problem
Robotic manipulator systems face issues with mechanical limits on joint mechanisms, leading to vibrations, errant motion, and potential damage due to impacts or excessive force when approaching these limits.
Innovation Solution
A control system that detects when joint velocities exceed thresholds and applies resistance proportional to the velocity excess, dissipating kinetic energy and preventing impacts by resisting joint movement near mechanical limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical limits are implemented to limit joint motion range, then joint mechanism protection is improved, but vibrations and errant motion occur when approaching limits
Solution Approach 1:
The control system applies resistance torque before the joint reaches the mechanical limit position. By detecting the joint position and velocity, the controller proactively applies counteracting torque to prevent excessive velocity and impact, thereby eliminating vibrations and errant motion before they occur.
Solution Approach 2:
The patent converts the potentially harmful kinetic energy of the joint into useful work by applying controlled resistance torque. This resistance dissipates the kinetic energy through controlled deceleration, transforming the harmful impact energy into controlled motion reduction, preventing vibrations while maintaining system reliability.
2Reliability
If resistance is applied to prevent impact at mechanical limits, then joint mechanism protection is improved, but kinetic energy must be dissipated
Solution Approach 1:
The kinetic energy that would otherwise be wasted as impact energy is converted into controlled deceleration work. The resistance torque applies controlled friction and damping forces that dissipate kinetic energy in a controlled manner, protecting the joint while managing energy loss through predictable dissipation rather than destructive impact.
Solution Approach 2:
The control system applies resistance torque in advance of the mechanical limit, creating a cushioning effect. This progressive resistance builds up as the joint approaches the limit, smoothly dissipating kinetic energy before impact occurs, thereby protecting the joint mechanism while managing energy dissipation in a controlled, gradual manner.
3Object-affected harmful factors
If velocity threshold control is applied near mechanical limits, then vibrations are reduced, but control complexity increases
Solution Approach 1:
The control system continuously monitors joint position and velocity, comparing actual values against threshold criteria. Based on this feedback, the controller dynamically adjusts resistance torque application. This closed-loop feedback mechanism effectively reduces vibrations by responding to actual joint state while maintaining manageable control complexity through algorithmic decision-making.
Solution Approach 2:
The velocity threshold is not a fixed value but varies dynamically based on joint position relative to the mechanical limit. As the joint approaches the limit, the threshold velocity decreases, creating a dynamic control profile that adapts to the situation. This dynamic approach reduces vibrations effectively while keeping control logic manageable through position-based threshold adjustment.
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
Prevents mechanical limit overrides, reduces vibrations, and manages kinetic energy dissipation, protecting joint mechanisms and allowing controlled movement near limits.
Implementation Method 1
instruct an actuator to resist movements of the joint above the threshold velocity... apply increasing amounts of resistance in proportion to an amount the actual velocity of the joint exceeds the threshold velocity to dissipate kinetic energy
Data Source
AI summary
Disclosed herein are apparatus and method for resisting external articulation of one or more joints of a manipulator assembly when the joints are approaching mechanical limits. For example, an articulable system may include a joint mechanism, an actuator coupled to the joint mechanism, a sensor system for sensing a joint state and a controller. The controller can operate the articulable system in an external articulation facilitation mode. The controller can command the actuator to resist movement of the joint in response to the joint state indicating the joint is moving toward a mechanical limit location with a joint velocity meeting a first velocity criterion. The controller can also command the actuator resist movement of the joint at a second joint position when the joint velocity meets a second criterion.