Robot Fitting Apparatus with Dynamic Force Control
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Solution Overview
Problem
Conventional compliance control or force control methods for robot-assisted assembly are limited by increased vibration and oscillation due to high force control gains, leading to slow error correction in positioning and orientation of workpieces with initial errors.
Innovation Solution
A fitting apparatus with a robot arm, force detector, and controller that generates and corrects operation commands to reduce detected forces and moments to predetermined thresholds, allowing for larger force control gains without being affected by noise, enabling quicker and more stable fitting operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the force control gain is increased to achieve quicker error correction, then the productivity is improved, but the robot arm and workpiece vibrations are amplified causing oscillation
Solution Approach 1:
The patent segments the control into two distinct parts: a high-gain position control for rapid error correction and a separate vibration suppression control for stability. This segmentation allows each control to be optimized independently without the trade-off that plagues conventional single-loop force control.
Solution Approach 2:
The patent dynamically adjusts control parameters based on the operational phase. During the approach phase, high position control gain is applied for rapid correction. During the contact phase, the system transitions to vibration suppression mode with adjusted gains to minimize oscillations while maintaining fitting accuracy.
2Loss of time
If the force control gain is increased to reduce error correction time, then the time required for fitting is reduced, but the operation of the robot arm becomes unstable
Solution Approach 1:
The patent employs dual feedback loops: position feedback for rapid error correction and vibration feedback for stability maintenance. The position feedback uses high gain to quickly reduce positioning errors, while the vibration feedback continuously monitors and suppresses oscillations, allowing high gains to be used without compromising stability.
Solution Approach 2:
The control parameters are changed based on the operational state. The position control gain is set high during approach to minimize correction time, while vibration suppression parameters are adjusted during contact to maintain stability. This dynamic parameter adjustment resolves the contradiction between speed and stability.
Data Source
AI summary
A fitting apparatus includes a robot arm having, at the forward end thereof, a gripper for holding a workpiece, a force detector for detecting a force and moment received by the workpiece held by the gripper, and a controller for controlling an operation of the robot arm. The controller includes a motion command generating unit for generating an operation command to fit two workpieces to each other, and an operation command correcting unit for correcting the operation command so as to correct the position of the gripper in a direction perpendicular to the fitting direction and the orientation of the gripper around an axis perpendicular to the fitting direction until the detected force and moment become less than or equal to a threshold value, based on either maximum values of the force and moment detected by the force detector while the two workpieces are in contact with each other or the force and moment detected by the force detector when the two workpieces first come into contact with each other.