Power assist method for a nonholonomic mobile robot using both ZMP criterion and impedance control

In this paper, we describe a power assist method for a nonholonomic mobile robot designed to carry out office-oriented services. We developed a new mechanism for obtaining an approximate measurement of the zero moment point (ZMP) using three single-axis force sensors so that a robot pushed from any direction by a human can detect the direction and magnitude of the external force. We also propose impedance control to generate translational and rotational motion in accordance with ZMP displacement. This control method achieves a function whereby a robot that has been given an external force from a direction differing from its translation direction will follow the direction of the external force while rotating. The robot can also return automatically to its initial pose once the external force has been released. We show though experiments that our power assist method is effective in improving the operability and usability of an office-oriented robot.