gravity compensation

Gravity compensation is the trick of calculating exactly how hard gravity is pulling down on each part of a robot arm at this very moment, and then telling the motors to push back with precisely that much force — no more, no less. The result is an arm that feels weightless: it neither sags toward the floor nor drifts upward. Imagine holding a heavy ladder perfectly still in mid-air. Most of your effort is not about moving it; it is just spent fighting gravity so the ladder stops where you let go. Gravity compensation hands that exact 'holding' effort to the robot's own motors, so they hold the arm up on their own.

Why does this matter so much? A robot arm is a chain of heavy links, and the pull of gravity on each link depends on how the arm is currently folded — an outstretched arm needs far more holding torque at the shoulder than a tucked-in one. The robot uses a math model of its own masses and lengths to work out, joint by joint, the steady torque needed just to stay put against gravity. Once that baseline torque is supplied automatically, any extra command from the controller goes purely into the motion you actually want, instead of being wasted on holding weight up. This makes the arm easier to control precisely, and it lets a person grab the arm and guide it by hand as if it floated, which is how many robots are 'taught' new motions.