This paper proposes a passivity-based nonlinear disturbance observer (DOB) design for a powered upper-limb robot control. The proposed DOB allows for the nonlinearities of the robot dynamics, whereas the typical DOB designs cannot. Moreover, by virtue of the passivity property, human operator and environmental interactions can be embedded in the control loop. As a DOB, the proposed approach has a disturbance observation property that makes the actual robot behave like a nominal model selected by the user. Performance analysis proposes a gain tuning rule. In experimental validation, actual powered upper-limb robot is used to perform unknown payload carrying applications.

The use of conventional kinematic equations for Mecanum wheel based omni-directional mobile robot suffers from position errors mainly because of slips on the wheels. To overcome the problem, we first identify the sources that originate position errors and then introduce the wheel parameter adjustment to reduce the position errors of the robot system. The experimental results show that the presented wheel parameter adjustment indeed reduces position errors and provides a good calibration mechanism.