Robot Contact Detection via Joint-Angle Force Correction
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Solution Overview
Problem
Existing robot control systems fail to precisely detect contact with an external environment due to forces generated by umbilical members, leading to incorrect determinations of contact status, which can result in unsafe operations.
Innovation Solution
A robot control device that estimates internal forces and stores force correction amounts for each joint angle, allowing for precise calculation of contact forces by subtracting internal and correction forces from sensor outputs, and includes a stop command unit to halt the robot when contact forces exceed a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If force correction is based only on tip position, then the system is simple, but detection precision deteriorates when robot attitude changes
Solution Approach 1:
The patent segments the force correction approach by dividing the robot arm's operational space into multiple discrete regions based on joint angles. Instead of using a single correction value for all positions, the system creates region-specific correction values that account for attitude variations. This segmentation allows the system to maintain simplicity while improving precision by selecting appropriate correction values based on current joint angle measurements.
Solution Approach 2:
The patent transitions from one-dimensional position-based correction to multi-dimensional correction by incorporating joint angle information. The correction system now considers not just the tip position but also the rotational angles of multiple joints, creating a higher-dimensional correction space. This dimensional expansion enables accurate differentiation between position-only changes and attitude changes, resolving the precision issue.
2Measurement precision
If force correction is applied for each joint angle region, then detection precision improves, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing force correction values for various joint angle regions before actual operation. The correction values are determined in advance based on simulated or measured internal forces at different attitudes, and stored in a lookup table. During operation, the system simply retrieves the appropriate correction value based on current joint angles, avoiding complex real-time calculations while maintaining high precision.
Solution Approach 2:
The system achieves self-service by using the robot's own joint angle measurements to automatically select the appropriate correction value. The control device monitors joint angles, determines the current region, and applies the corresponding pre-stored correction value without requiring external intervention or complex decision-making processes. This self-service mechanism simplifies the overall system while maintaining precision.
3Reliability
If internal force estimation is used, then contact detection is enabled, but false positives occur due to umbilical member forces
Solution Approach 1:
The patent extracts and separates the internal force component from the total force measurement. By calculating internal forces based on joint angles and robot configuration, the system isolates this component and subtracts it from the force sensor output. This extraction process removes the harmful influence of internal forces including umbilical member forces, leaving only the external contact force for accurate detection.
Solution Approach 2:
The patent introduces joint angle measurements as an intermediary parameter to bridge the relationship between robot configuration and force measurements. By using joint angles to determine the current operational region and select appropriate correction values, the system creates an intermediary layer that enables accurate compensation for internal forces without directly measuring them, thereby improving both reliability and precision.
Data Source
AI summary
A robot control device includes: an internal force estimating unit; a storage unit in which, in each small region of a rotational operation region of a plurality of joints of a robot arm, an internal force estimated by the internal force estimating unit is subtracted from an output of the force sensor in a state in which the robot arm is not in contact with an external environment, thereby storing a force correction amount; a force correction amount determining unit in which a force correction amount corresponding to each of the current angles of the plurality of joints of the robot arm is determined; and a contact force calculating unit in which a contact force when the robot arm is in contact with an external environment is calculated by subtracting an internal force and the force correction amount from a current output of the force sensor.