Robot Force Control Using Filtered Collision Torque Shares
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Solution Overview
Problem
Industrial robots experience instability and 'hammer' or 'knock' effects during collisions due to inadequate control of drive forces, leading to potential damage and inefficiency in tasks like grasping or editing components.
Innovation Solution
The system commands robot drives based on a combination of first and second target shares, using low-pass filtering and proportional-integral control to determine target drive forces, allowing for precise and stable operation by absorbing collision forces and evading reaction forces through calculated torque adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional force control is used during robot collisions, then the robot can maintain basic operational capability, but instability and hammering effects occur leading to potential damage
Solution Approach 1:
The control deviation is segmented into two distinct components: a low-pass filtered component for stable force control and a differential component for collision response. This segmentation allows each component to handle specific aspects of collision management independently, preventing the harmful hammering effects while maintaining operational stability.
Solution Approach 2:
The patent changes the parameters of the control system by applying different filtering characteristics to different components of the control deviation. The first component uses low-pass filtering to attenuate high-frequency collision impulses, while the second component captures the differential effects. This parameter differentiation resolves the contradiction by allowing stable control while eliminating harmful collision effects.
2Measurement precision
If high force control precision is maintained during collisions, then accurate force control is achieved, but the robot becomes unstable and produces knocking effects
Solution Approach 1:
The force control signal is segmented into two precision levels: the low-pass filtered component provides stable, precise force control by attenuating high-frequency noise, while the differential component handles rapid collision transients. This segmentation maintains measurement precision while ensuring control stability during collisions.
Solution Approach 2:
The low-pass filter acts as an intermediary between the raw control deviation and the force control output. It mediates by selectively attenuating high-frequency collision impulses while preserving the essential force control information, thus maintaining precision without sacrificing stability.
3Speed
If the robot responds quickly to collision forces, then collision damage is reduced, but instability and bouncing effects are induced by the controller
Solution Approach 1:
The control response is segmented into two speed components: the low-pass filtered component provides a stable, moderated response that prevents controller bouncing, while the differential component delivers rapid collision response. This segmentation enables the system to respond quickly to collisions without inducing instability.
Solution Approach 2:
The patent applies partial action by using only the necessary portion of the control deviation for each purpose. The low-pass filtered component handles the stable, continuous force control, while the differential component handles only the collision-related transients. This partial differentiation allows rapid collision response without excessive controller action that would cause bouncing.
Data Source
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AI summary
According to a claimed method for controlling the force of a robot (10), drives (26) of the robot are actuated based on a first target component (T cmd, 1) and a second target component (T cmd,2), the first target component being determined based on a first control difference component (ΔF 1), which is determined based on at least one low-pass filter (28) of a control difference (ΔF) between a target load (F cmd) to be exerted by the robot and an actual load that is detected by the robot, and the second target component (T cmd, 2) is determined based on a second control difference component (ΔF 2) which is determined based on a difference load between the control difference and the first control difference component.