Vertical Position Estimation of a Constrained Link Using IMU Signals and Kinematic Constraint

Vertical position is often estimated using global positioning systems (GPSs) or barometers. Also they are commonly integrated with inertial measurement units (IMUs) for better estimation performance. However, when the GPS or barometer signals are not accurate enough, the degradation in the estimated vertical position is unavoidable. This research proposes a new approach that uses IMU alone without GPS or barometer, when a link is constrained by a joint. The underlying concept is that the vertical position of the constrained link can be estimated from the orientation of the link and the pre-defined position vector. In this research, the uncertainty of orientation estimation is eliminated by utilizing the kinematic constraint derived by a spherical constraint. Due to the augmentation of the kinematic constraint to the orientation estimation algorithm, the proposed method can use very accurate orientation information, which accordingly yields very accurate vertical position estimation. Experimental results show the proposed method outperformed the barometer-based methods.