CONTROL OF FREE-FLYING UNDERACTUATED SPACE MANIPULATORS TO EQUILIBRIUM MANIFOLDS

Underactuated mechanisms will provide low cost automation and will eas ily overcome actuator failures. These mechanisms will be particularly useful for space applications because of their reduced mass and lower power consumption. In space underactuation can be effectively introduc ed in robot manipulators. Such mechanisms will however be difficult to control because of the fewer number of actuators in the system. Of th eoretical interest to us, is the problem where the unactuated joints d o not have brakes. It is shown that in such a situation it is possible to bring the system to a complete rest and converge the actuated join ts to their desired values, provided the system maintains zero momentu m and none of the unactuated joints are cyclic coordinates. Our main i nterest is to converge both the actuated and the unactuated joints to their desired set of values. For this purpose, we assume that the numb er of actuated joints are more than the number of unactuated joints, a nd the unactuated joints have brakes. It is shown that if there exists sufficient dynamical coupling between the set of actuated and unactua ted joints it is possible to converge all the manipulator joints to th eir desired values. In the paper, the orientation of the space vehicle is not controlled because this task can be accomplished after the man ipulator has been reconfigured, using methods already developed.