Manipulator Joint Resistance Control Near Mechanical Limits
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Solution Overview
Problem
Robotic manipulator systems face issues with joint mechanisms experiencing vibrations, errant motions, and overloading due to mechanical limits, which can lead to damage when external articulation exceeds the joint's range of motion.
Innovation Solution
A control system that detects joint velocity thresholds and applies resistance proportionally to dissipate kinetic energy, allowing un-resisted movement below certain thresholds and resisting external articulation near mechanical limits to prevent overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the joint mechanism allows free movement to assist external articulation, then ease of operation is improved, but the joint mechanism may experience overload and damage when approaching mechanical limits
Solution Approach 1:
The control system dynamically changes the resistance parameter based on joint position and velocity. As the joint approaches mechanical limits or exceeds velocity thresholds, the system increases resistance torque to prevent overload while maintaining ease of operation within safe parameters. This is achieved by continuously monitoring joint state and adjusting actuator output torque accordingly.
Solution Approach 2:
The system employs feedback control by continuously monitoring joint position, velocity, and acceleration through sensors. The control system uses this feedback to determine when to apply resistance torque and adjusts the resistance level based on real-time joint state, ensuring reliable protection while maintaining operational ease when conditions are safe.
2Reliability
If the control system applies resistance to prevent mechanical limit overload, then joint mechanism reliability is improved, but kinetic energy dissipation may cause vibrations and errant motions
Solution Approach 1:
The resistance torque is dynamically adjusted based on real-time joint velocity and position. Rather than applying constant resistance, the system modulates the torque level to match the kinetic energy that needs to be dissipated. This dynamic approach prevents sudden stops that cause vibrations while still protecting against mechanical limit overload.
Solution Approach 2:
The control system applies resistance torque in advance as the joint approaches velocity thresholds or mechanical limits, rather than waiting for the impact to occur. This gradual cushioning effect dissipates kinetic energy smoothly before it can cause damaging impacts, vibrations, or errant motions.
3Reliability
If the system applies resistance torque to dissipate kinetic energy, then mechanical limit protection is improved, but energy consumption increases
Solution Approach 1:
The control system applies resistance torque only partially and selectively—specifically when joint velocity exceeds thresholds or when approaching mechanical limits. Rather than continuous resistance, the system intervenes only when necessary to dissipate excess kinetic energy, minimizing unnecessary energy consumption while maintaining protection.
Solution Approach 2:
The resistance torque parameter is dynamically adjusted based on joint state. The system varies the torque level from zero (when safe) to maximum (when protection is critical), optimizing energy consumption by applying resistance only when and to the extent needed for mechanical limit protection.
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
The system effectively protects joint mechanisms from overload and dissipates kinetic energy efficiently, preventing damage and ensuring smooth operation near mechanical limits, even with high mass links.
Implementation Method 1
instruct the actuator to 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.