Robotic Manipulator Admittance Control Without Contact Localization
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Solution Overview
Problem
Conventional admittance control methods for robotic manipulators face challenges in accurately determining the exact location of physical interaction with objects, leading to inefficient and unsafe interactions, especially when interacting with humans or inanimate objects, due to the need for representation of interaction wrench in task space and inability to react to wrenches applied above force-torque sensors.
Innovation Solution
A generalized admittance control system that eliminates the need for determining the exact location of physical interaction by sampling a set of interaction points on the robotic manipulator's surface, computing a generalized velocity through a cost function that models contact force measurements, and generating joint control instructions to control the robotic manipulator's motion without converting interaction wrench in task space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional admittance control methods are used to determine the exact location of physical interaction, then the control accuracy is improved, but the system complexity and computational burden increase due to the need for inverse kinematics algorithms and task space transformation
Solution Approach 1:
The effector surface is segmented into multiple discrete interaction points rather than treating it as a continuous surface. This segmentation allows the system to sample contact forces at specific locations and compute generalized velocity without requiring exact interaction location determination, thereby reducing computational complexity while maintaining control accuracy
Solution Approach 2:
The patent replaces the traditional mechanical control approach (inverse kinematics and task space transformation) with a direct generalized velocity computation method. By formulating the admittance control in terms of generalized velocities and using cost function minimization, the system eliminates the need for complex kinematic calculations while achieving the same control objectives
2Measurement precision
If the exact location of physical interaction is determined to achieve accurate admittance control, then the control performance is improved, but the response time to contact forces decreases due to computational delays
Solution Approach 1:
The interaction points are pre-defined on the effector surface before contact occurs. This preliminary setup allows the system to immediately map contact forces to the nearest interaction points without requiring real-time location determination, thereby reducing computational delay and improving response time to contact forces
Solution Approach 2:
The system computes generalized velocity based on a sampled set of interaction points rather than calculating the exact interaction location. This partial action approach provides sufficiently accurate control response without the computational burden of exact location determination, achieving a balance between accuracy and response time
3Measurement precision
If additional sensors are added to improve contact force measurement accuracy, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The existing force-torque sensor at the effector is made multi-functional by using its measurements to infer contact forces at multiple interaction points through the generalized velocity formulation. This eliminates the need for additional sensors while maintaining measurement accuracy, as the same sensor data is utilized in a more versatile manner
Solution Approach 2:
The system uses the existing force-torque sensor measurements to serve multiple purposes: determining contact forces at interaction points, computing generalized velocity, and achieving admittance control. This self-service approach eliminates the need for additional sensors by maximizing the utility of the existing sensor system
Data Source
AI summary
A control system and method for generalized admittance control (AC) is provided. The control system includes circuitry communicatively coupled to a robotic manipulator. The circuitry receives, from a sensor system of the robotic manipulator, contact force measurements associated with a physical interaction of the robotic manipulator with an object. The circuitry determines a surface portion of the robotic manipulator on which the physical interaction with the object occurs and samples a set of interaction points from the surface portion. The circuitry computes a generalized velocity for AC of the robotic manipulator by minimizing a cost function. The cost function includes a relationship between the contact force measurements and an approximation term which models application of an actual contact force of the physical interaction on the sampled set of interaction points. The circuitry generates a set of joint control instructions based on generalized velocity to control motion of the robotic manipulator.