Robot E-Stop Control Using Position Lag Deceleration
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Solution Overview
Problem
Emergency stop events in moving robotic assembly lines can cause abrupt disruption of synchronized motion between robots and products, leading to undesirable impact forces during the contact phase, potentially resulting in damage to both the product and the robot.
Innovation Solution
A system comprising an assembly robot, a tracking sensor, and a controller that calculates a lag value of the robot's position relative to a carrier and selectively transmits a speed signal to decelerate the platform only when the calculated lag value exceeds a threshold, minimizing contact forces during an emergency stop event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the robot stops immediately upon e-stop event during contact phase, then the robot stops quickly and safety is improved, but abrupt disruption of synchronized motion causes collision and impact forces between end effector and product
Solution Approach 1:
The system performs preliminary action by detecting the e-stop event and calculating the position lag value before actually stopping the robot. The controller evaluates the lag value (comparing robot position to carrier position) and only then decides whether to initiate deceleration, preventing abrupt stopping when not necessary and maintaining safety while avoiding impact forces.
Solution Approach 2:
The system applies dynamics by transitioning from a static stop command to a dynamic, conditional stopping process. The robot's deceleration is not immediate but is modulated based on real-time position lag calculations, allowing the system to adapt the stopping behavior to the current synchronized motion state and minimize impact forces.
2Object-affected harmful factors
If the robot maintains synchronized motion with the carrier during e-stop, then impact forces are minimized, but the robot cannot stop quickly enough for safety
Solution Approach 1:
The system implements feedback by continuously monitoring the position lag value (difference between robot position and carrier position) and using this information to control the deceleration process. The controller adjusts the robot's stopping behavior based on real-time feedback from the position lag calculation, ensuring both safety and minimal impact forces.
Solution Approach 2:
The system applies parameter changes by modifying the robot's speed parameter dynamically during the e-stop event. Instead of a fixed immediate stop, the controller changes the speed parameter based on the position lag value, creating a variable deceleration profile that balances safety requirements with impact force minimization.
3Object-affected harmful factors
If the robot decelerates at a calibrated rate based on position lag, then synchronized motion is maintained and impact forces are reduced, but the stopping time increases
Solution Approach 1:
The system applies partial action by implementing selective deceleration based on the position lag value. The robot does not always decelerate at the calibrated rate - only when the position lag exceeds a threshold. This partial application of deceleration reduces unnecessary stopping time while still preventing impact forces when needed.
Data Source
AI summary
A system for a work cell having a carrier that moves a product along an assembly line includes an assembly robot, sensor, and controller. An arm of the robot moves on the platform adjacent to the carrier. The sensor measures a changing position of the carrier and encodes the changing position as a position signal. The controller receives the position signal and calculates a lag value of the robot with respect to the carrier using the position signal. The controller detects a requested e-stop of the carrier when the arm and product are in mutual contact, and selectively transmits a speed signal to the robot to cause a calibrated deceleration of the platform before executing the e-stop event. This occurs only when the calculated tracking position lag value is above a calibrated threshold. A method is also disclosed for using the above system in the work cell.