Robot Force Control with Dual Low-Pass Filters for Stable Fitting
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Solution Overview
Problem
Industrial robots with force detectors face instability in trajectory correction control due to noise during fitting operations, leading to potential overload and delayed stopping, while high-sensitivity filtering for reached position sensing control can result in unstable trajectory correction.
Innovation Solution
A robot apparatus with a multi-joint arm and force detector uses separate low-pass filters for trajectory correction and reached position sensing control, with a first filter having a lower cutoff frequency for trajectory correction and a second filter with a higher cutoff frequency for reached position sensing, allowing for stable displacement correction and quick position sensing in the direction of the distal end shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a single low-pass filter is used for both trajectory correction control and reached position sensing control, then noise is reduced for stable trajectory correction, but the reached position sensing sensitivity decreases and stopping timing is delayed
Solution Approach 1:
The patent divides the force detection signal processing into two separate filtering paths: one low-pass filter for trajectory correction control and another low-pass filter for reached position sensing control. This segmentation allows each filter to be optimized independently for its specific purpose, resolving the contradiction between stability and sensitivity.
Solution Approach 2:
The patent applies different filtering characteristics to different control functions. The first low-pass filter uses a lower cutoff frequency optimized for noise reduction in trajectory correction, while the second low-pass filter uses a higher cutoff frequency optimized for sensitivity in reached position sensing. This local differentiation of filter properties resolves the contradiction.
2Measurement precision
If the filter cutoff frequency is increased for quick reached position sensing, then sensing sensitivity improves, but trajectory correction becomes unstable due to insufficient noise removal
Solution Approach 1:
The patent segments the signal processing into two independent filtering paths, allowing the second filter (for reached position sensing) to use a higher cutoff frequency for improved sensitivity without affecting the stability of the first filter (for trajectory correction) which maintains a lower cutoff frequency.
Solution Approach 2:
The patent applies different filtering characteristics locally to different control functions. The first low-pass filter maintains a lower cutoff frequency for stable trajectory correction, while the second low-pass filter applies a higher cutoff frequency locally to the reached position sensing path, achieving both stability and sensitivity simultaneously.
3Device complexity
If only position control is performed without force control, then the control system is simpler, but fitting failure or operating object acquiring error occurs due to positional displacement
Solution Approach 1:
The patent introduces force detection as an intermediary mechanism between position control and the fitting operation. The force detector monitors contact forces and provides feedback that enables automatic trajectory correction, ensuring reliable fitting without requiring complex manual intervention or overly complex control systems.
Solution Approach 2:
The patent implements force-based feedback control where the force detector continuously monitors forces during the fitting operation and provides feedback to the control device. This feedback enables automatic trajectory correction, improving fitting reliability while maintaining reasonable system complexity through automated closed-loop control.
Data Source
AI summary
A force detector provided between a robot arm and a robot hand detects forces Fx, Fy, and Fz. A robot controller performs a filtering process for the forces Fx and Fy by a first low-pass filter of a cutoff frequency Fc1, moves the robot hand so that the forces Fx and Fy become smaller, corrects a trajectory of the robot arm, performs a filtering process for the force Fz by a second low-pass filter of a cutoff frequency Fc2 having a frequency higher than the cutoff frequency Fc1, performs a threshold value determination for the force Fz, and stops the movement of the robot hand when the force Fz exceeds a threshold value during a fitting operation.