Abstract

This study presents the development of Sit to Stand (STS) motion control method. The main challenge in STS is in addressing the lift-off from chair problem. In solving the problem, the main components of the humanoid STS motion system involved are the (1) phase and trajectory planning and (2) motion control. These components should be designed so that the Zero Moment Point (ZMP), Centre of Pressure (CoP) and Centre of Mass (CoM) is always in the support polygon. Basically, in STS motion control there are two components, 1. Action selector and 2. Tracking controller. The STS motion control should able to operate in real time and continuously able to adapt any change in between the motion. In this way, the accuracy of the controller to rectify the motion error shall increase. The overall proposed method to perform the STS motion is designed to have two main phases. (1) CoM transferring that implements Alexander STS technique and (2) Stabilization Strategy that used IF-THEN rules and proportional velocity controller. This study focuses on the presentation of the development of second phase which are 1. The development of the IF-THEN rules as the action selector that operates in real time to assists the proportional controller in making the best decision and, 2. The development of Proportional Gain Identification for the proportional velocity controller that is capable to change the gain implementation by referring to the define region that represent the motion condition. The validation of the proposed method is done experimentally using NAO robot as the test platform. The coefficient of the gain identification for the proportional controller was tuned using NAO robot that was initially set at sitting position on a wooden chair. The inclination of the body from a frame perpendicular with the ground, angle y is observed. Coefficient that gives the lowest RMSE of angle y trajectory is taken as a constant. Results show the proposed control method has reduce the (Root Mean Square Error) RMSE of the motion from 6.6858° after the coefficient at all defined region have been identified.

Keywords:

Alexander technique , control method , NAO robot , STS,

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