Investigating the relation between standing period and stability of humanoid robot when performing STS motion

The main challenge in STS is addressing the lift-off from chair problem. In solving the problem, two method was proposed, 1) phase and trajectory planning based on the Alexander STS technique and 2) motion control which applied IF-THEN rules to control the action given (direction and gain) with aid of proportional velocity control. This paper discussed on the trajectory planning to perform STS motion by, 1) Observation of the relationship between standing velocity i.e standing period, Ts with the stability of the STS motion and 2) Introduce a limitation on body's angular direction in y-axis on saggital plane, angle y. Nao humanoid robot is used to perform the task. Angle y trajectory and centre of pressure, CoP reading was measured to validate the proposed method. The results show that Standing period, Ts plays important role in order to perform a stable STS motion where stability increased as Ts increased. The lowest RMSE is 8.83° when Ts = 3.0. When the forward momentum decreasing with the implementation of angle y trajectory limitation, the results shows RMSE increased as Ts increased. However, the lowest RMSE is 7.07° when Ts = 1.5 where RMSE was decreased while using much lower standing period, Ts. The proposed angle y limitation has improved the motion stability and able to perform the task faster.