force control

Force control is making a robot care about how hard it pushes rather than exactly where it is. In ordinary position control the robot chases a target spot and ignores what it bumps into; that is fine in open air but disastrous on contact — press a polishing pad against a surface by position alone and a millimetre too far means either no contact or a cracked workpiece. Force control flips the goal: the robot is told to maintain, say, a steady ten newtons of push, and it continuously adjusts its motion to keep that force right, easing off where the surface bulges and pressing in where it dips.

The robot needs a sense of touch to do this — usually a force/torque sensor (a wrist gauge that measures pushes and twists) or joints that can feel resistance directly. The controller compares the felt force to the wanted force and nudges the robot to close the gap, exactly the way you sand wood: you do not think about the precise height of your hand, you think about pressing 'just hard enough' and let your hand ride up and down over the grain. This yielding, touch-guided behaviour is why force control is also called compliant control.

Pure force control is rarely used everywhere at once. In real tasks a robot mixes it with position control along different directions — holding position sideways while regulating force into the surface — and impedance or admittance control are the popular, well-behaved ways to blend the two. Force control is the heart of any job where the robot must work with the world rather than blindly against it: assembly, grinding, gentle grasping, or safe physical contact with people.