Adjustment of home posture of a biped humanoid robot using an inertial sensor and force torque sensors

In the walking control of a biped humanoid robot, the walking performance is seriously affected by the initial home posture. An important thing is that the initial home posture of real robot is slightly different at every setting because a zero position of joint is not exactly the same. Accurate and consistent initial home posture is essential when we compare and analyze walking control algorithms. In general, the conventional method for electric motor uses an incremental encoder with a limit switch or an absolute encoder such as potentiometer to make a zero position. However, this method for the multi-axis humanoid robot is difficult, time-consuming, and inaccurate. Furthermore, it has the disadvantage that additional limit switch or absolute encoder can interfere with the design objective of compactness. This paper describes a novel adjustment method of home posture for a humanoid robot utilizing incremental encoders, an inertial sensor and force torque sensors. Four kinds of controllers are proposed and adjusted offsets are measured when outputs of the controllers are converged. The experimental results from KHR-2 show the effectiveness of the proposed algorithm.