Robot Motor Torque Control for Safe Human Contact
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Solution Overview
Problem
Current robot systems collaborating with humans face challenges in safely operating without applying large forces during contact, as they rely on expensive external force measurement sensors, and struggle to detect contact accurately due to low back drivability and limited current information from motor sensors.
Innovation Solution
Implementing a robot system that controls motor torque to prevent harm to humans by executing torque control instead of position control, allowing safe operation without external force measurement sensors, using a robot controller that stores and executes torque commands to manage motor operations and detect contact through positional deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If position control is used for motor control in collaborative robots, then positioning accuracy is improved, but safety during human contact deteriorates due to large applied forces
Solution Approach 1:
The system dynamically switches between position control mode (for normal operation requiring high positioning accuracy) and torque control mode (for safety during human contact). This dynamic adjustment of control characteristics allows the robot to adapt its behavior based on operational context, resolving the contradiction between positioning accuracy and contact safety.
Solution Approach 2:
The control system changes the fundamental control parameter from position commands to torque commands when contact is detected. By changing the control mode parameter, the robot transitions from prioritizing positioning accuracy to prioritizing force limitation, thereby resolving the contradiction between these two requirements.
2Measurement precision
If external force measurement sensors are added to detect contact, then contact detection accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The motor's existing current sensor serves dual purposes: it continues to provide current information for motor control while also enabling contact detection through analysis of current deviations. This self-service approach allows the sensor to perform multiple functions, eliminating the need for separate external force measurement sensors and reducing system complexity.
Solution Approach 2:
The current sensor is made multi-functional by using it both for motor control and for contact detection. This universal utilization of existing components avoids adding separate sensing systems, thereby reducing device complexity while maintaining contact detection capability.
3Device complexity
If torque control is implemented without external force sensors, then system cost is reduced, but contact detection capability deteriorates
Solution Approach 1:
The system implements feedback-based contact detection by continuously monitoring current information from the motor and comparing it against expected values. When deviations exceed thresholds, contact is inferred. This feedback mechanism enables accurate contact detection using only existing motor sensors, eliminating the need for expensive external force sensors.
Solution Approach 2:
The patent replaces the mechanical/physical force measurement system (external force sensors) with an electrical measurement system (current sensor analysis). By substituting the sensing mechanism from mechanical to electrical domain, the system achieves contact detection capability without requiring additional mechanical sensors, thereby reducing cost while maintaining detection accuracy.
Data Source
AI summary
A robot system includes: a robot comprising a joint driven by a motor; and a circuitry configured to: execute position control of the motor based on position commands; store torque commands generated based on the position commands during execution of the position control of the motor; and execute torque control of the motor based on the stored torque commands.