Speed-Based Current Limiting for Robot Drive Torque Output
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Solution Overview
Problem
Conventional robots with speed reducers face issues in maintaining desired torque output due to increased torque losses and decreased motor torque generation as rotation speeds increase, leading to potential damage and inefficiencies.
Innovation Solution
A current limiting device that adjusts the limit value of current based on the speed of the drive to compensate for torque losses and changes in motor torque, ensuring desired force or moment output even at increased speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant upper limits are set for currents to be carried to motors, then it is possible to appropriately limit driving torques applied to joints according to the posture of the robot, but desired torques cannot be output from speed reducers due to increased torque losses and decreased motor torques at higher rotation speeds
Solution Approach 1:
The current upper limit value is changed dynamically according to the rotation speed of the motor. As rotation speed increases, the upper limit value is increased to compensate for the decreased torque generation capability of the motor and increased torque losses in the speed reducer, thereby maintaining desired torque output capability across different operating speeds
Solution Approach 2:
The parameter being changed is the current upper limit value, which is adjusted based on the rotation speed parameter. This parameter change allows the system to adapt to varying torque requirements and losses at different speeds, resolving the contradiction between maintaining accurate current limits and preserving torque output capability
2Productivity
If the rotation speed of motors increases, then productivity is improved, but torque losses of speed reducers increase and torques generated by motors decrease
Solution Approach 1:
The system uses feedback from the rotation speed detection to adjust the current upper limit value. The rotation speed information feeds back to the control unit, which then modifies the current limit accordingly, creating a closed-loop system that compensates for speed-related torque losses and maintains effective torque output
Data Source
AI summary
A current limiting device includes a current limiter to limit a current to be carried to a drive within a range of a limit value. The limit value is set to change according to a speed of the drive.