Robot Control Device for Vibration-Free Touch Sensing
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Solution Overview
Problem
Industrial robots experience vibration when abruptly stopped during touch sensing, leading to inaccurate workpiece position detection and increased sensing time, especially when the stop position is not predetermined.
Innovation Solution
A robot control device that includes a joint-angle command calculating unit, axial-force torque calculating unit, elastic deformation compensation unit, stop position detecting unit, and command angle switching unit to calculate and output motor commands that compensate for joint deflection and vibration, allowing for precise and vibration-free stopping at a desired position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the robot is abruptly stopped upon contact detection, then the sensing time is reduced, but vibration occurs leading to inaccurate position detection
Solution Approach 1:
The system pre-calculates a deceleration trajectory before the robot makes contact with the workpiece. When contact is detected, the robot is already in a controlled deceleration phase rather than abrupt stopping, which prevents vibration while maintaining quick sensing. The deceleration profile is prepared in advance based on predicted contact timing.
Solution Approach 2:
The robot's motion control transitions from static positioning to dynamic trajectory control upon contact detection. The system adjusts the deceleration profile in real-time based on the actual contact moment, creating a smooth transition that eliminates vibration while maintaining accuracy. The motion parameters are dynamically modified rather than abruptly changed.
2Productivity
If the robot operates at high speed during touch sensing, then productivity is improved, but the position detection accuracy deteriorates due to wire movement during delay time
Solution Approach 1:
The system pre-calculates the deceleration trajectory and prepares the control profile before contact occurs. This allows the robot to maintain high speed during the approach phase, then smoothly transition to deceleration upon contact detection, eliminating the need for continuous low-speed operation while ensuring accurate position capture.
Solution Approach 2:
The system uses real-time feedback from contact detection to adjust the motion profile. When contact is detected, the feedback signal triggers the pre-prepared deceleration trajectory, allowing the system to maintain high speed during non-contact phases while ensuring accurate positioning at the moment of contact.
3Measurement precision
If the robot operates at low speed during touch sensing, then position detection accuracy is improved, but sensing time increases reducing productivity
Solution Approach 1:
The system prepares a deceleration trajectory in advance that can be activated at the moment of contact detection. This eliminates the need to operate at low speed throughout the entire sensing process - the robot maintains high speed during approach, then transitions to controlled deceleration only when needed, achieving both speed and accuracy.
Solution Approach 2:
The robot operates in different speed phases: high speed during the approach phase and controlled deceleration during the contact phase. This periodic variation in speed allows the system to maintain high productivity during non-critical phases while ensuring accuracy during the critical contact detection moment.
Data Source
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Figure 5~6A
AI summary
A control device (10) of a robot (R) for controlling the angle of a joint (J) of the robot (10) that is driven by a motor (M). The control device (10) is equipped with: a joint angle command-calculating unit (11) for calculating a joint angle command value; an axial force torque-calculating unit (12) for calculating the axial force torque generated in the joint axis; an elastic deformation-compensating unit (13) for calculating a motor command angle by adding a joint deflection, which is calculated from the axial force torque and a joint spring constant, to the joint angle command value; a stopping position-detecting unit (15) for detecting the angle of the motor (M) when the robot (R) contacts an external structure; and a command angle-switching unit (16) for outputting the motor (M) angle detected by the stopping position-detecting unit (15) instead of the joint angle command value when the stopping position-detecting unit (15) outputs the angle of the motor (M).