Zero-Moment Point Feedforward Balance Control of Leg-Wheel Hybrid Structures by using Input/Output Linearization

This paper proposes a balance-control algorithm which uses the Zero-Moment Point (ZMP) in order to maximize the dynamic stability of leg-wheel hybrid structures on hard, flat surfaces. The algorithm constrains the control input to satisfy the condition in which the ZMP stays at the geometric center of the contact area. This restriction of the control input changes the original fully actuated system into an under-actuated system and generates a problem with the internal dynamics. To solve this issue, we found output variables which reduce and stabilize the internal dynamics by means of an Input/Output Linearization (IOL) process. We tested the effectiveness of the proposed algorithm by comparing three cases in a simulation - no balance control, ZMP feedback balance control, and ZMP feedforward balance control.