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Bearing traction torque is an important factor to a precision
po sitioning system. The performance of precision controllers
may be greatly improved if the bearing traction torque can be
accurately estimated. In the conventional PID controllers,
integrator are us ed to eliminate small steady state errors;
however, they may creat e small stick-slip oscillations on the
controller outputs if bear ing traction torque are presented.
To improve the controller accuracy, one can either compute the
be aring traction torque precisely or use a special control
methodology. In this thesis, the boundary lubrication and
partial thesis, the boundary lubrication and partial
lubrication friction models are discussed to gain the knowledge
on friction models. The full lubrication model was excluded
because the angular velocity of the problem we are considering
is too small to use th is model. The result shows that only
boundary lubrication model is applied when stick-slip problems
are considered. A new controller algorithm is also proposed in
this thesis. It is named ``kick-and-go''controller. This
controller tries to estimate the bearing traction torque at the
current position, and send a up and down torque pulse to the
output of the motor. This ``kicks'' the motor into a higher
precision location. An adaptive scheme is also proposed once
the traction torque estimation needs to be modified.
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