Biped Walking Pattern Generation Using an Analytic Method for a Unit Step With a Stationary Time Interval Between Steps

In this paper, an analytic method for generating a unit step pattern using a center of mass (COM) constraint is presented. Using a unit step pattern with the COM position constrained in the supporting polygon at the end of each step, a robot can have a stationary time interval between steps to control and stabilize its posture. The walking pattern is based on the linear inverted pendulum model. Assuming radical zero moment point (ZMP) trajectories, a simple solution form of the COM trajectories is formulated. Three types of case studies are presented for an analytic solution, which is based on different constraints on ZMP references, COM, and time differences. The unknown parameters of the COM trajectories in the solution form are formulated for the different cases. One of the cases was tested for long-stride walking with the DRC-HUBO robot developed at the Korea Advanced Institute of Science and Technology for the Defense Advanced Research Project Agency Robotics Challenge. Experiments of long-stride walking on bricks were successfully performed using the unit step pattern with several previous controllers of HUBO.