External Force Detection in Collaborative Robots via Motor Current
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Solution Overview
Problem
Existing methods for detecting external forces on human-collaborative industrial robots are not precise due to the nonlinear characteristics of deceleration mechanisms, such as backlash and friction, which affect torque estimation.
Innovation Solution
An external force judgment method and device that acquire a reference value of the relative position or angle of a robot's components under no external force or a known force, and compare it with a measured value during operation, using a detection unit and a detected unit arranged on non-relatively moving parts to judge the presence of an external force based on a threshold value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque is estimated based on the difference between motor rotation angle and decelerator output shaft rotation angle, then external force detection is enabled, but measurement precision deteriorates due to nonlinear characteristics of the decelerator
Solution Approach 1:
The patent replaces the mechanical torque estimation method (based on rotation angle differences through the decelerator) with an electrical current-based detection method. The external force detection unit measures the current consumed by the motor, and since motor current is linearly proportional to torque, this provides precise external force detection without being affected by the decelerator's nonlinear mechanical characteristics such as backlash and friction.
2Power
If decelerator is used to amplify torque for robot operation, then robot operation capability is improved, but external force detection precision deteriorates due to backlash and friction
Solution Approach 1:
The patent substitutes the mechanical torque measurement approach with an electrical measurement approach. By monitoring the motor's current consumption, the system can detect external forces with high precision while the decelerator continues to provide torque amplification for robot operation. The current-based measurement bypasses the decelerator's mechanical nonlinearities entirely.
Solution Approach 2:
The patent introduces motor current as an intermediary parameter for external force detection. Instead of directly measuring torque through the mechanical decelerator system, the system uses electrical current as a mediator that linearly reflects torque while avoiding the nonlinear mechanical transmission path. This intermediary measurement enables precise external force detection independent of decelerator characteristics.
Data Source
AI summary
An external force judgment method including a reference value acquisition step of acquiring a reference value of a relative position or angle of a second member with respect to a first member when a robot on which no external force is acting or on which a known external force is acting is assumed to be operated by a predetermined command in advance; a measured value acquisition step of acquiring a measured value of a relative position or angle of the second member with respect to the first member when the robot is operated by the predetermined command; and a judgment step of judging the presence or absence of an external force acting on the robot based on a difference between the reference value and the measured value and a predetermined threshold value.