Method for controlling a robotic gripper using friction estimation

A gripper, comprising:

• a gripper body;
• at least two gripping jaws, at least one of which is movable with respect to another one between a jaw opening position and a jaw closing position;
• an actuation group housed inside the gripper body;
• a transmission group housed inside the gripper body, the actuation group being operatively coupled to the at least one movable jaw by the transmission group to move said at least one movable jaw between the jaw opening position and the jaw closing position;
• a jaw position sensor, suitable to measure an absolute position of the gripping jaws;
• a gripping force sensor suitable to measure a gripping force applied by the gripping jaws to an item;
• a processing unit operatively connected to said sensors and to said actuation group and comprising a friction estimation module and a friction compensation module, wherein:
• the friction estimation module is configured to estimate static and dynamic friction forces acting on components of the transmission group and on the gripping jaws, the static friction force being calculated by the friction estimation module based on constraining reactions to which the components of the transmission group and the gripping jaws are subjected, the constraining reactions being calculated at least as a function of an actuation force applied by the actuation group and/or the gripping force measured by the gripping force sensor, a friction coefficient (μi) of materials of the gripper and/or of lubricant used being known, the dynamic friction force being calculated based on speed of the gripping jaws, width of sliding surfaces of the gripping jaws, and distance between said sliding surfaces, viscosity of the lubricant used being known;
• and the friction compensation module is configured to control the actuation group based on signals from the sensors and on estimation of the friction forces from the friction estimation module.