Robot Contact Force Control Using Stiffness-Based Braking
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Solution Overview
Problem
Robots experience after-running and increased reaction force due to mechanical, electrotechnical, and control-related inertias, leading to unwanted penetration and deformation in unknown or varying environments, which existing methods attempt to mitigate by reducing speed before contact but with limited success.
Innovation Solution
A method that involves specifying a setpoint force and measuring contact stiffness to slow down the robot using its drives and brakes, starting the slowing process before the setpoint force is reached, thereby reducing excessive after-running and ensuring the application of the setpoint force within a tolerance, based on the measured stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the robot reduces speed before contact to reduce impulse and after-running, then the reaction force beyond setpoint force is reduced, but the productivity and operation speed are decreased
Solution Approach 1:
The control system performs preliminary actions by reducing robot speed before the setpoint force is actually reached, based on prediction of contact stiffness and after-running compensation. This proactive speed reduction prevents excessive force application while allowing higher overall operation speeds.
Solution Approach 2:
The system uses feedback from measured contact stiffness and detected contact points to continuously adjust robot speed. The control monitors the reaction force and modifies the speed profile in real-time to compensate for after-running effects, ensuring precise force control without permanently reducing operation speed.
2Productivity
If the robot maintains high speed near contact point to improve productivity, then the clock interval is reduced, but the after-running causes excessive penetration and deformation
Solution Approach 1:
The system performs preliminary speed reduction before contact based on predicted contact stiffness and after-running characteristics. This allows the robot to maintain high speeds during most of the operation while proactively slowing down only when necessary to prevent excessive penetration.
Solution Approach 2:
The control system dynamically changes the speed parameter based on the robot's proximity to contact points and predicted contact stiffness. By adjusting speed as a variable parameter rather than maintaining constant high speed, the system achieves both high productivity and precise contact control.
3Reliability
If the robot slows down after detecting setpoint force to prevent excessive reaction force, then the force control is improved, but the delay increases and penetration deepens
Solution Approach 1:
Instead of waiting to detect the setpoint force before slowing down, the system performs preliminary speed reduction based on prediction of when the setpoint force will be reached. This anticipatory approach eliminates the detection-to-action delay and prevents excessive penetration before it occurs.
Solution Approach 2:
The system applies preliminary anti-action by reducing speed before the excessive force condition occurs. By compensating for predicted after-running effects in advance, the system prevents the harmful penetration and deformation rather than reacting after they have already occurred.
Data Source
AI summary
A method for controlling a robot includes applying a setpoint force to a contact point; measuring a contact stiffness at the contact point; and slowing down the moving robot using its drives and/or braking the robot to apply the setpoint force to the contact point by the slowing down and/or slowed down robot depending on the measured contact stiffness, wherein the robot is slowed down before the setpoint force is reached.