Force-Sensorless Friction and Gravity Compensation for Robots

In this paper we present two controllers for robots that combine terms for the compensation of gravity forces, and the forces of friction of motors and gearboxes. The Low-Friction Zero-Gravity controller allows a guidance of the robot without effort, allowing small friction forces to reduce the free robot motion. It can serve to aid users providing kinesthetic demonstrations while programming by demonstration. In the present, kinesthetic demonstrations are usually aided by pure gravity compensators, and users must deal with friction. A Zero-Friction Zero-Gravity controller results in free movements, as if the robot were moving without friction or gravity influence. Ideally, only inertia drives the movements when zeroing the forces of friction and gravity. Coriolis and centrifugal forces are depreciated. The developed controllers have been tuned and tested for 1 DoF of a full-sized humanoid robot arm.