AN ACTIVE VERTICAL-DIRECTION GRAVITY COMPENSATION SYSTEM

To perform simulations of partial or microgravity environments on eart h requires some method of compensation for the earth's gravitational f ield. This paper discusses an active compensation system that modulate s the tension in a counterweight support cable in order to minimize st ate deviation between the compensated body and the ideal weightless bo dy. The system effectively compensates for inertial effects of the cou nterweight mass, viscous damping of all pulleys, and static friction i n all parts of the gravity compensation (GC) system using a hybrid PI (proportional plus integral)/fuzzy control algorithm. The dynamic comp ensation of inertia and viscous damping is performed by PI control, wh ile static friction compensation is performed by the fuzzy system. The system provides a very precise gravity compensation force, and is cap able of nonconstant gravity force compensation in the case that the pa yload mass is not constant.