| By the extrapolation of movement
increments detected by differential encoders, the position of a mobile robot
can be easily computed. However, the encoders suffer fromvarious systematic
errors resulting in an increasing error of the obtained robot position.
This problem is also known from the scope of inertial navigation, but the
transfer of the respective concepts of maintaining merely errors to mobile
robot localization has, with few exceptions, been neglected so far. In this
paper, the position error is related to the encoder errors in an augmented
state-space system. As done in inertial guidance, the position error is
estimated by an error-state Kalman filter making use of general complementary
sensor information as, for example, absolute position measurements or redundantly
detected movement increments. Specifically, the usage of a rate gyroscope
as a complementary sensor is examined. This case is somehow special, as
it implies a correlation of the overall error model and the observation,
demanding a modification of the Kalman filter equations. The derived filter
is embedded in the localization scheme of the robot in partly closed-loop
mode allowing a mutual online-correction of the encoder readings and the
gyroscope output. As demonstrated by exemplary trajectories, the proposed
localization scheme can substantially improve the position estimation. Furthermore,
it can easily be modified to accept, for example, absolute position measurements
as a complement to its own position estimation. |
