The main control problem
of visual servoing is to cope with the delay introduced by image acquisition
and image processing. This delay is the main reason for limited tracking
velocity and acceleration. Predictive algorithms are one solution to handle
the delay. The drawback of prediction algorithms is the bad prediction
behavior for the discontinuity in the target motion, for example, a velocity
step. In this paper, a switching Kalman filter (SKF) is proposed to overcome
this problem. The SKF introduces three cooperating components. A prediction
monitor supervises the prediction quality of an adaptive Kalman filter
(AKF). If a discontinuity is detected, a transition filter switches to
an appropriate steady-state Kalman filter (alpha beta or alpha beta gamma),
which handles a discontinuity better than the AKF. During this transition,
an auxiliary controller ensures that overall control is continuous. This
new prediction algorithm is able to achieve a good prediction quality
for smooth and for discontinuous motions. It is evaluated using a pan/tilt
unit to track a colored object. The SKF and its components are compared
to the classical AKF with four different target motions. |