Robot Torque Estimation for External Force Safety Control
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Solution Overview
Problem
Existing robot systems lack effective mechanisms to prevent excessive external forces from causing injury to operators by not adequately estimating and managing torque limits, leading to potential harm during physical interactions.
Innovation Solution
A robot system with a control device that includes torque detectors and an external-force upper-limit-value estimator, which calculates and compares estimated external-force upper limit values with predetermined thresholds, triggering stopping or retraction operations to prevent excessive force application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the robot stops only when detected torque exceeds a fixed upper limit value, then the control system is simple, but it cannot reliably prevent excessive external forces from causing injury to operators
Solution Approach 1:
The patent changes the parameter from a fixed torque upper limit to a dynamically calculated external-force upper limit value. This value is derived by dividing the detected torque by the minimum radius from the rotation axis to the contact point, allowing the system to adapt to different contact geometries and reliably prevent excessive forces while maintaining operational flexibility
Solution Approach 2:
The patent introduces an intermediary calculation step between torque detection and stop control. The external-force upper limit value acts as a mediator that translates raw torque data into a meaningful safety metric by incorporating geometric information (minimum radius), enabling more reliable safety assessment without requiring complex additional sensors
2Measurement precision
If the robot uses a fixed torque threshold for stopping, then the control logic is simple, but it cannot accurately estimate actual external forces acting on the robot
Solution Approach 1:
The patent transforms the measurement parameter from torque alone to external force by introducing a geometric parameter (minimum radius). This allows accurate estimation of external forces by dividing detected torque by the minimum radius, providing precise safety assessment without requiring direct force sensors
Solution Approach 2:
The patent replaces direct mechanical force measurement with a calculated estimation based on torque detection and geometric parameters. This substitution achieves accurate external force estimation using existing torque sensors and radius calculations, avoiding the need for complex additional measurement systems
Data Source
AI summary
A robot system including a robot and a control device that controls the robot. The robot includes a first member, a second member that is rotationally driven around a predetermined first axis relative to the first member, and a first torque detector that detects a torque around the first axis. The control device includes an external-force upper-limit-value estimator that estimates an external-force upper limit value serving as an assumable upper limit value for an external force acting on the second member based on the torque detected by the first torque detector, and controls the robot to avoid an increase in the external force when the estimated external-force upper limit value is larger than a predetermined threshold value.