Robot Contact Force Control Using Measured Contact Stiffness
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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 unintended penetration and deformation in unknown or varying environments, as they slow down to apply a setpoint force.
Innovation Solution
A method that involves measuring contact stiffness and slowing down the robot before reaching the setpoint force, using this information to control the robot's drives and brakes to apply the setpoint force within a tolerance, thereby reducing after-running and maintaining the specified force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the robot slows down to apply the setpoint force, then the reaction force accuracy is improved, but the productivity decreases
Solution Approach 1:
The robot performs a preliminary movement phase at high speed to approach the contact point, then transitions to a slowing down phase. This preliminary high-speed movement allows the robot to maintain productivity while preparing for the subsequent force-controlled phase, thus resolving the contradiction between speed and force accuracy.
Solution Approach 2:
The robot dynamically adjusts its speed based on the contact stiffness measurement. The control system modifies the robot's velocity in real-time during the approaching phase, enabling high speed when contact is not yet detected and automatic deceleration when contact stiffness indicates proximity to the contact point, thereby maintaining both productivity and force accuracy.
2Productivity
If the robot maintains high speed near contact points, then the productivity is improved, but the after-running and excessive force increase
Solution Approach 1:
The robot performs a preliminary measurement of contact stiffness during the approaching phase before actual contact occurs. This preliminary action allows the control system to predict the contact characteristics and pre-calculate the appropriate deceleration profile, enabling the robot to maintain high speed longer while preventing excessive force and after-running through proactive speed adjustment.
Solution Approach 2:
The robot continuously monitors contact stiffness during the approaching phase and uses this feedback to dynamically adjust its speed. When contact stiffness increases indicating proximity to the contact point, the feedback loop triggers automatic deceleration, preventing after-running and excessive force while allowing high-speed operation during the approach, thus resolving the contradiction between productivity and harmful effects.
3Object-generated harmful factors
If the robot reduces speed before contact, then the after-running is reduced, but the clock interval increases
Solution Approach 1:
The robot performs preliminary high-speed movement to quickly approach the contact point, minimizing the clock interval. Only when contact stiffness measurement indicates proximity to contact does the robot initiate deceleration. This preliminary high-speed phase reduces the overall time loss while the subsequent controlled deceleration prevents after-running, resolving the contradiction between time efficiency and harmful effects.
Solution Approach 2:
The robot dynamically transitions from high-speed approach to controlled deceleration based on real-time contact stiffness measurement. This dynamic speed adjustment allows the robot to maintain high speed for most of the approach phase (reducing clock interval) while automatically decelerating only when necessary to prevent after-running, thus optimizing both time efficiency and harmful effect reduction.
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.