Robot End Effector Control via Dynamic Impedance Constraints
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Solution Overview
Problem
Robot end effectors face operational limitations due to environmental impedance from objects, leading to issues like motor overheating, stiction, and unstable grasping when attempting to achieve precise grasp forces and positions, as the difference between desired and potential grasp torque values can strain actuators and joints.
Innovation Solution
Implementing end effector constraints such as deadbands to ignore or reduce position and grasp force errors within specific ranges, allowing the robot to operate within safe limits and avoid corrective actions that could lead to adverse outcomes, using force signals from sensors to determine these constraints dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the robot attempts to achieve precise grasp forces and positions by correcting position and force errors, then the precision of end effector positioning and force control is improved, but the actuators and joints may overheat and the system becomes unstable due to strain on operational limits
Solution Approach 1:
The patent applies dynamics by making the end effector constraints adaptive and dynamic rather than static. The controller dynamically adjusts position and force constraints based on the object's impedance characteristics, allowing the system to adapt its control behavior to match the physical properties of the manipulated object, thereby achieving precise control without overstraining actuators
Solution Approach 2:
The patent changes control parameters by introducing impedance-based adjustments to position and force constraints. The controller modifies the acceptable ranges for position and force errors based on the measured impedance of the object, allowing larger tolerances when object impedance is high and tighter control when impedance is low, preventing actuator overheating while maintaining necessary precision
2Force
If the robot applies high grasp torque to overcome object impedance and achieve desired grasp force, then the grasp force control is improved, but the joints and actuators may overheat or stall due to excessive strain
Solution Approach 1:
The patent applies preliminary anti-action by pre-establishing force constraints based on object impedance before attempting to achieve the desired grasp force. The controller proactively limits the maximum force corrections that can be applied, preventing the actuators from being strained beyond their thermal capacity while still achieving acceptable grasp force control within safe operational limits
Solution Approach 2:
The patent applies partial action by accepting that the desired grasp force may not be fully achieved when object impedance is high. The controller applies force corrections only within the safe operational range defined by the force constraints,宁愿接受部分达成目标力也不愿过度驱动导致过热，从而在保证安全运行的前提下获得可接受的抓取力控制
3Speed
If the robot uses aggressive error correction to eliminate position control errors quickly, then the position control speed is improved, but the system experiences stiction and unstable oscillation
Solution Approach 1:
The patent applies beforehand cushioning by pre-defining position constraints that act as buffers against aggressive corrections. The position constraints establish acceptable tolerance ranges before control actions are taken, cushioning the system against excessive correction movements that would cause stiction and oscillation, thereby enabling faster response while maintaining stability
Solution Approach 2:
The patent applies universality by creating a unified constraint framework that simultaneously addresses position and force control. The impedance-based constraints serve multiple functions: they define acceptable position tolerances, limit force corrections, and prevent unstable interactions, providing a comprehensive solution that improves both speed and stability across different operating conditions
Data Source
AI summary
Techniques are provided for achieving stable tracking and/or manipulation by robots of objects. In various implementations, it may be detected, based on force signal(s) from force sensor(s), that an end effector of the robot has made physical contact with an environmental object. Based on the force signal(s), end effector constraint(s) may be identified. These constraint(s) may include a position constraint associated with position control of the end effector and/or a grasp force constraint associated with grasp force control of the end effector. Error measure(s) may be determined based on a measured position/force of the end effector. The error measure(s) may include a position control and/or grasp control error. The measured position and/or force may be compared with the end effector constraint(s) to reduce an impact of the error measure(s) on operation of the robot.