Robot Motion Control After Emergency Stop Force Detection
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Solution Overview
Problem
Existing robot systems face issues with unintended movements of movable members due to erroneous torque sensor readings or initial settings, leading to continued movement after external force removal, which can interfere with workers.
Innovation Solution
A robot system with a control apparatus that includes an emergency stop controller, direction calculator, and speed calculator to manage external forces, switching between modes to adjust movement based on force magnitude and time elapsed since halt, using a point mass model and torque sensors for accurate force estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the robot moves movable members to follow external force after emergency stop, then worker assistance is improved, but unintended movement occurs due to erroneous torque sensor readings
Solution Approach 1:
The system continuously monitors external force magnitude through torque sensors and uses this feedback to dynamically adjust movement behavior. The control apparatus calculates external force in real-time and compares it against threshold values to determine whether to assist movement or maintain emergency stop state, creating a closed-loop control system that responds to actual physical conditions.
Solution Approach 2:
The patent changes the parameter of movement speed from a fixed value to a variable that depends on external force magnitude. The speed calculation formula incorporates external force as a variable, allowing the system to adapt movement characteristics based on real-time force conditions. This parameter change enables differentiated response: full assistance when force is high, limited movement when force is low or erroneous.
2Reliability
If the robot maintains emergency stop state, then safety is improved, but worker freedom of motion is restricted
Solution Approach 1:
The system transitions from a static emergency stop state to a dynamic assisted movement state based on external force conditions. The control apparatus continuously evaluates force magnitude and adjusts the robot's response in real-time, allowing smooth transition between safety-critical stop and worker-assisted movement. This dynamic behavior optimizes both safety and worker freedom depending on actual conditions.
Solution Approach 2:
The system prepares counter-actions in advance: when external force is detected, the robot calculates the appropriate assisted movement in opposition to the force direction to prevent sudden jerks or unintended movements. The control apparatus pre-computes movement parameters based on detected force, ready to execute smooth counter-balancing motion that protects both worker and equipment.
3Measurement precision
If torque sensor sensitivity is increased to detect small external forces, then detection capability is improved, but false detection of erroneous force occurs
Solution Approach 1:
The system applies partial action by setting a threshold for external force magnitude. Instead of responding to all detected forces equally, the robot only assists movement when force exceeds the threshold value, filtering out small erroneous readings. This partial response strategy maintains sensitivity to genuine external forces while ignoring noise from sensor errors or initial setting inaccuracies.
Solution Approach 2:
The control apparatus uses feedback from torque sensor readings to continuously monitor force magnitude and compare it against predetermined thresholds. This feedback mechanism enables the system to distinguish between significant external forces requiring assistance and minor fluctuations representing sensor errors, maintaining both detection sensitivity and reliability through adaptive threshold-based decision-making.
Data Source
AI summary
A robot system includes a robot and a control apparatus programmed to control the operation of the robot. The control apparatus is programmed to implement an emergency stop controller configured to stop the operation of movable members of the robot in response to an external force imposed on the movable members during operation. The control apparatus is further programmed to implement a direction calculator configured to determine a moving direction to be adopted by the movable members. The control apparatus is further programmed to implement a speed calculator configured to determine a moving speed to be adopted by the movable members. The control apparatus is further programmed to implement a movement controller configured to move the movable members in the determined moving direction at the determined moving speed.