The question of control and stabilization of flexible space robots is
considered. Although, this approach is applicable to space robots of
other configurations, for simplicity, a flexible planar two-link robot, mounted
on a rigid floating platform, is considered. The robotic arm
has two revolute joints and its links undergo elastic deformation
in the plane of rotation. Based on nonlinear inversion technique,
a control law is derived for controlling output variables describing
the position and orientation of the platform and the joint
angles of the robot. Although, the inverse controller accomplishes reference
trajectory tracking, it excites the elastic modes of the arm.
For the vibration suppression, three different stabilizers are designed. Using
linear quadratic optimal control theory, a composite stabilizer for stabilization
of the rigid and flexible modes and a decoupled flexible
mode stabilizer are designed for regulating the end point of
the robot to the target point and vibration suppression. Stabilization
using only elastic mode velocity feedback is also considered. For
large maneuvers, first the inverse controller is active, and the
stabilizer is switched for regulation when the motion of the
robot lies in the neighborhood of the terminal equilibrium state.
Simulation results are presented to show that in the closed-loop
system including the inverse controller and each of the stabilizers,
trajectory tracking and stabilization of elastic modes are accomplished.