Robotic End Effector Trajectory Recovery Under Unknown Loads
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Solution Overview
Problem
Impedance control in robotic devices is challenged by unknown loads causing errors in the desired position of the end effector, particularly when interacting with human environments, leading to deviations from the reference trajectory.
Innovation Solution
A method that applies impedance control, detects external forces and torques, estimates joint forces and torques using sensorless methods, calculates adjustments to compensate for these forces, and applies preload torques to recover the reference trajectory while maintaining the stiffness of the robotic device's movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance control is applied to the robotic device, then the robotic device can interact safely with human environments and maintain controlled force output, but unknown loads cause errors in the desired position of the end effector and deviation from the reference trajectory
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors the actual position of the end effector, compares it with the reference trajectory, detects deviations caused by external forces, and dynamically adjusts the control signals to compensate for these deviations. This closed-loop feedback system maintains positional accuracy while preserving the safe interaction capabilities provided by impedance control.
Solution Approach 2:
The patent dynamically changes the impedance parameters (stiffness, damping) based on the detected external forces and deviation from reference trajectory. By adjusting these parameters in real-time, the system can maintain stable interaction with unknown loads while recovering the reference trajectory, thus resolving the contradiction between safety and precision.
2Manufacturing precision
If the robotic device compensates for unknown loads, then positional accuracy is maintained, but the complexity of the control system increases
Solution Approach 1:
The patent employs a self-service approach where the robotic system uses its own sensors and controllers to detect external forces and automatically compensate for unknown loads without requiring external intervention or complex additional hardware. The controller leverages existing impedance control infrastructure and adds adaptive compensation algorithms, maintaining simplicity while achieving high positional accuracy.
3Stability of the object's composition
If the robotic device maintains stiffness of movement, then the perceived stiffness is retained for safe interaction, but external forces cause static errors in position that need correction
Solution Approach 1:
The patent introduces dynamic adjustment to the control system where the stiffness and damping parameters are not fixed but adapt in real-time based on detected external forces and trajectory deviations. This dynamic approach allows the system to maintain perceived stiffness for safe interaction while simultaneously correcting static position errors, as the controller modulates impedance parameters to balance both requirements.
Data Source
AI summary
Certain examples described herein provide a method of controlling a robotic device including a body, an end effector coupled to the body by one or more joints and a propulsion system to drive the one or more joints to control a state of the robotic device. Example methods include applying impedance control to the robotic device; determining a reference trajectory of the end effector; detecting an applied external force and/or torque acting on the robotic device causing a departure from the reference trajectory; calculating an adjustment to be applied to one or more of the one or more joints to compensate for the detected applied external force and/or torque; and using the calculated adjustment to control the one or more joints to actuate the end effector and recover the reference trajectory of the end effector.