Robot control during an e-stop event

A method for use in a work cell having a carrier that moves a product along an assembly line, the method comprising:

• moving a robotic arm of an assembly robot on a moveable platform that is positioned adjacent to the carrier;
• measuring a changing position of the carrier using a tracking sensor;
• encoding the changing position as a position signal;
• transmitting the position signal to a controller;
• calculating a lag value of the assembly robot via the controller with respect to the carrier as a function of the position signal;
• detecting a requested emergency stop (e-stop) event of the assembly robot when the arm and the product are in mutual contact;
• and
• selectively transmitting a speed signal from the controller to a motor of the assembly robot only when the calculated tracking position lag value is above a calibrated threshold, wherein the speed signal causes a calibrated deceleration of the platform to occur via the motor, thereby minimizing contact forces between the robot arm and the product during the e-stop event.

A system for use in a work cell having a carrier that moves a product along an assembly line, the system comprising:

• an assembly robot having a robotic arm, a platform that transports the robotic arm, and a rail motor that propels the platform on a rail adjacent to the assembly line in a synchronous manner with respect to motion of the carrier;
• an electro-optical tracking camera positioned with respect to the carrier that electro-optically images the carrier as the carrier moves the product;
• and
• a controller in communication with the assembly robot and the camera;
• wherein the controller is configured to:
• receive a position signal from the tracking camera describing the changing position of the carrier;
• calculate an average speed of the carrier using the position signal;
• calculate a lag value of the platform with respect to the carrier using the position signal;
• detect a requested emergency stop (e-stop) event of the carrier when the arm and the vehicle component are in mutual contact;
• selectively transmit a first speed signal to the rail motor to cause a calibrated deceleration of the platform to occur only when the calculated tracking position lag value is above a calibrated threshold, thereby minimizing contact forces between the robot arm and the product during the e-stop event;
• and
• selectively transmit a second speed signal to the rail motor to move the platform at an average speed of the carrier when the calculated tracking position lag value is below the calibrated threshold.