Systems and methods for updating the correction coefficient of an industrial robot force sensor

A method for automatically calibrating an external force measuring device of an industrial robot, the industrial robot comprising a multi-axis robot arm, the robot arm comprising, for each joint axis, an electric actuator and a position sensor able to measure a joint position of the corresponding joint, the robot comprising a force measuring device, the force measuring device comprising at least one measuring sensor capable of measuring the forces applied to the robot arm, the method comprising the steps of:

• for a plurality of successive measurement cycles, storing the joint position of the robot arm and calculating an external force exerted on the external force measuring device, the external force exerted being equal to the external force measured by the external force measuring device minus a drift correction coefficient of the external force measuring device applied to the robot arm and a mass effect of the robot;
• after a predefined number n of successive measurement cycles, for each subsequent cycle,
• calculating an indicator of variation in external force exerted and a motion indicator, the indicator of variation in external force exerted being representative of a variation in external force exerted during a last n measurement cycles, the motion indicator being representative of a variation in joint position during the measurement cycles;
• calculating an average force of the external forces exerted during the last n measurement cycles;
• updating the correction coefficient by incrementing it with a value proportional to the average force of the external forces exerted if the following conditions are met:
• the motion indicator is below a vector of predetermined positional variation thresholds, and
• the indicator of variation in external force exerted is below a vector of predetermined force variation thresholds, and
• the average force of the external forces exerted is, as an absolute value, less than a vector of predetermined thresholds on the average force.