Adaptive Stiffness Control for Robotic Arms via H-Infinity Law
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Solution Overview
Problem
Existing robotic arm control methods require rigid structures and specific controller types, making it difficult to adapt stiffness for tasks with imperfect knowledge of target positions, especially when dealing with contact tasks like insertion, where precise position servo-control is not feasible.
Innovation Solution
A method to control the robotic arm's apparent stiffness by estimating its inertia and synthesizing an H∞ control law that adjusts the transfer function between speed and external force, allowing the arm to behave like an object with desired mass, stiffness, and damping, while meeting performance objectives and constraints such as sensitivity and pole placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position servo-control is used, then positioning precision is improved, but adaptability to imperfect target position knowledge deteriorates
Solution Approach 1:
The patent applies impedance control to dynamically adjust the robot arm's stiffness characteristics during operation. By modifying the apparent inertia and damping through control laws rather than physical structure, the system transitions from rigid position control to adaptive dynamic control, enabling high stiffness during insertion while allowing position deviations during exploration
Solution Approach 2:
The patent changes the dynamic parameters (inertia, damping, stiffness) of the robot arm through control law synthesis rather than physical modification. The H∞ control law adjusts these parameters in real-time to match task requirements, allowing the same robot to exhibit different mechanical characteristics for different phases of the insertion task
2Device complexity
If rigid structure hypothesis is used, then control implementation is simplified, but applicability to flexible robots deteriorates
Solution Approach 1:
The patent replaces the mechanical rigidity assumption with a control-based solution. Instead of requiring physically rigid robots, the H∞ control law synthesizes virtual stiffness and damping characteristics that achieve the same effect as mechanical rigidity, thereby extending applicability to flexible and compliant robots while maintaining control simplicity
3Measurement precision
If analytical calculation is used, then control precision is improved, but applicability to non-rigid robots deteriorates
Solution Approach 1:
The patent transforms the control approach from precise analytical calculation based on rigid body dynamics to H∞ robust control that accounts for parameter variations and uncertainties. The control law is synthesized to maintain precision across a range of inertial parameters, making it applicable to both rigid and flexible robots without requiring exact knowledge of the robot's dynamic parameters
Data Source
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AI summary
The invention relates to a method of controlling an actuator (1) of an articulated segment (5) comprising the steps of estimating an inertia J of the segment; estimating or measuring a speed of displacement (I) of the segment; synthesizing a control law of type (II) generating a control torque for the segment on the basis of these estimates or measurements and meeting a performance objective pertaining to the loading sensitivity function: (III) K being the desired stiffness, and c a desired damping rate, ε a mathematical artifact, (IV), where G(s) is the transfer function (V) for going between the speed (I) (linear or angular) of the segment and an external force F experienced by the segment; and controlling the actuator of the articulated segment according to the control law thus synthesized.