joint torque

Joint torque is the twisting force a robot applies at one of its joints to make that joint turn — the rotational cousin of an ordinary push. Where a plain force shoves something in a straight line, a torque tries to spin it around a pivot. You feel the difference every time you open a door: pushing near the hinge does almost nothing, but pushing at the far edge swings it easily. Torque is that turning effect, and it grows both with how hard you push and how far from the pivot you push. At a robot's joint, the motor supplies exactly this twist.

Torque is what actually drives a robot's motion. To get a joint moving — to overcome the weight of the arm hanging off it, to fight the friction in its gears, to accelerate the links into a swing — the motor must deliver enough torque. Too little and the arm sags or stalls; too much and it whips around and overshoots. A robot's controller spends much of its life deciding, moment by moment, precisely how much torque to send to each joint, and the robot's equation of motion is the very tool that tells it the right amount.

Because torque is so central, robots often measure it as well as command it. By sensing the actual torque at each joint, a robot can feel how hard it is pressing on the world — letting it shake your hand gently, insert a peg without jamming, or stop the instant it bumps a person. This is the heart of force-aware, collaborative robots: torque is both the language they use to move and the sense they use to feel.