| Summary: | This thesis reports on the development of strategies for the control of contact forces exerted
by a structurally flexible robotic manipulator on surfaces in its working environment. The
controller is based on a multivariable, explicitly adaptive, long range predictive control
algorithm. A static equilibrium bias term which is particularly applicable to the contact
force control problem has been incorporated into the control algorithm cost function. A
general formulation for the discrete time domain characteristic polynomial of the closed
loop system has been derived and shown useful in tuning the controller.
Kinematic and dynamic models of a robotic manipulator with structurally flexible links
interacting with its working environment are derived. These models include inertia and
damping effects in the contact dynamics in addition to the contact stiffness employed in
most previous work. Linear analyses of the dynamic models for a variety of manipulator
configurations reveal that the controlled variable, the contact force, is dominated by different
open ioop modes of the system depending on the effective stiffness of the contacting surfaces.
This result has important implications for the selection of the controller parameters.
The performance of the controller has been evaluated using computer simulation. A
special purpose simulation program, TWOFLEX, which includes the dynamics models of the
manipulator and the environment as well as the control algorithm was developed during
the research. The configurations investigated using the simulation include a single flexible
manipulator link, two link manipulators with both rigid and flexible links, and a two link
prototype model of the Mobile Servicing System (MSS) manipulator for the proposed Space
Station, Freedom. The results show that the controller can be tuned to provide fast contact
force step responses with minimal overshoot and zero steady-state error. The problem of
maintaining control through the discontinuous situation of unexpectedly making contact
with a surface is addressed with the introduction of a contact control logic level in the
control hierarchy.
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