| Flexible robots have given
rise to numerous investigations, and their use is easily justified in two
main cases: (1) when the weight of the robot has to be minimized and (2)
when collisions of the robot with the environment are foreseen, as a flexible
lightweight robot delivers less impact energy. Much work has been done by
different authors on the position control of flexible robots using feedback
of the tip position or tip acceleration. However, the use of these sensing
devices is problematic in practical applications of flexible arms: three-dimensional
tip position sensing is expensive, and occlusions appear at some arm configurations.
Accelerometers cannot be used when contact of the tip with the environment
is expected because these sensors cannot stand the high negative accelerations
produced at the impact (unless very low speed motions are performed). This
paper studies the possibility of carrying out the tip position control of
a three-degree-of-freedom flexible arm using sensing devices placed far
away from the tip (where contact is expected) in such way that they can
easily stand the impact, which will be needed in the development of a position/force
control for flexible robots. A control scheme based on motor position sensing
plus some strain gauges placed on the arm structure is proposed. Stability
of this control scheme is proven and is experimentally verified on a flexible
manipulator prototype that was developed in the authors' laboratory. |
