Circular arc-shaped walking trajectory generation for bipedal humanoid robots

The design of a controller which can achieve a steady and stable walk is crucial in bipedal humanoid robotics. Reference trajectory generation is central in the walking control. The Zero Moment Point (ZMP) criterion is the most widely used stability criterion for trajectory generation. It is most successfully used when the ZMP equations are coupled with the dynamics equations of a simple mechanism, the Linear Inverted Pendulum Model (LIPM) which approximates the humanoid model. In a number of approaches the position reference for the Center of Mass (CoM) of the robot body is computed from predefined ZMP references. After the computation of the CoM, the joint references are computed by inverse kinematics. A natural ZMP reference trajectory and a Fourier series approximation based method for computing the CoM reference from it, was previously proposed for the humanoid robot SURALP (Sabanci University Robotics ReseArch Laboratory Platform), for a straight walk This paper improves these techniques by modifying the straight walk reference trajectory into an arc-shaped one. In principle the straight walk is projected into a walk reference on an arc with a desired radius. On-line smooth change of the walking direction is achieved by adjusting the arc radius command. The proposed reference generation algorithm is tested on SURALP. Experiments indicate that the method is successful in generating a stable walk following an arc.