Force Control

力控Essential

Controlling how much force a robot applies to an object, rather than just where it moves.

Force control means controlling how much force a robot applies to an object or its environment, rather than simply driving it to a target position. Pure position control responds to any deviation by pushing harder and harder to reach the commanded position, so if it meets a surface higher than expected it can crush the workpiece; force control instead keeps the contact force near a set value. There are two implementation approaches. Direct force control makes the target force itself the feedback setpoint, typically hybrid force/position control, which splits the directions so some axes control force and others control position. Indirect force control means impedance control and admittance control, which set a stiffness, damping, and inertia to decide how soft the robot feels when pushed. Force control requires knowing the actual force applied, usually from a wrist-mounted six-axis force-torque sensor, joint torque sensors, or motor current estimates. Contact-rich tasks — sanding, assembly, wiping a table, plugging in a cable — all depend on it.

ExampleA robot arm wiping a whiteboard: under pure position control, a height difference of just a few millimeters would make it either miss the board or press too hard; switching to force control and setting a fixed pressure in the direction perpendicular to the board lets it keep contact and wipe evenly even where the surface isn't perfectly flat.

Also called: Force-Based Control
Related: Impedance Control · Admittance Control · Hybrid Force/Position Control · Six-Axis Force/Torque Sensor · Joint Torque Sensor · Contact-rich Manipulation
Sources: Wikipedia: Force control