Dynamic stability of a robot manipulator
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Solution Overview
Problem
Robot manipulators face challenges in maintaining dynamic stability when encountering unexpected external forces, such as bumps from people or objects, which can compromise their safety and operational effectiveness.
Innovation Solution
A control system for a robot manipulator that determines how to respond to external forces by prioritizing dynamic stability, using a force selector to calculate and apply forces that counteract the motion of the Zero Moment Point (ZMP) or move it back within a predetermined support region, while also considering external forces applied to the base.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the robot manipulator prioritizes maintaining dynamic stability by counteracting ZMP motion in response to external forces, then the robot's stability and safety are improved, but the ability to execute the target trajectory accurately deteriorates
Solution Approach 1:
The control system calculates a virtual ZMP force that represents the force needed to counteract observed ZMP motion and maintain stability. This preliminary anti-action is computed before executing trajectory commands, allowing the system to preemptively counteract destabilizing forces while minimizing impact on trajectory execution. The virtual ZMP force is derived from the relationship between ZMP position and required counteracting force, enabling proactive stability maintenance.
Solution Approach 2:
The system dynamically adjusts the base motion by applying forces calculated from real-time ZMP measurements. The control approach transitions from static trajectory following to dynamic adaptation where the base can move in response to external forces. The system continuously updates the virtual ZMP force based on current ZMP position and applies appropriate counteracting forces, allowing the robot to adapt its behavior dynamically while maintaining both stability and trajectory accuracy.
2Reliability
If the robot manipulator responds to external forces by moving the base to counteract applied forces, then the robot's dynamic stability is improved, but the complexity of the control system increases
Solution Approach 1:
The virtual ZMP force serves as an intermediary that simplifies the control architecture. Instead of directly complex multi-variable control of base motions and arm positions, the system uses the virtual ZMP force as a mediating quantity that encapsulates the relationship between ZMP position and required counteracting force. This intermediary simplifies the control logic by providing a clear computational pathway: measure ZMP, calculate virtual ZMP force, apply counteracting force to base.
3Adaptability or versatility
If the robot manipulator uses a force selector to determine target force based on multiple force components, then the robot's ability to maintain stability under various conditions is improved, but the device complexity increases
Solution Approach 1:
The control system segments the total target force into distinct components: the virtual ZMP force for stability maintenance and the effective force for trajectory execution. The force selector acts as a segmentation mechanism that separates these functional requirements into manageable parts. By dividing the control task into discrete force components with specific purposes, the system achieves versatile stability response while keeping each component's computation relatively simple and modular.
Data Source
AI summary
A robot manipulator has a base with a connected arm by a shoulder joint, and a control system and force selector. Based on a target trajectory for a distal end of the arm instructions, a target motion and an effective force applied to the base that causes the base to execute the target motion is determined. An applied force on the robot manipulator results in a determination of a virtual ZMP force applied to the base that would either counteract an observed motion of a ZMP of the robot manipulator or act to move the ZMP back to within a predetermined support region, and/or an external force applied. Data defining the effective force and the virtual ZMP force and/or the external force applied to the base and determines a target force based on the data is received. The base executed a motion in response to the target force.