| Summary: | 碩士 === 中華大學 === 電機工程學系碩士班 === 100 === The hierarchical sliding mode control (HSMC) has been proposed to achieve the position control of a spherical robot driven by Omni wheels. The two-direction movement can be accomplished by the cross type arrangement of driving wheels. Based on the two-layer architecture of HSMC and the Lyapunov stability theorem, at first, the equivalent control of each subsystem is deduced, and then the total control law is derived. The switching scheme of the HSMC is dependent on the state of the spherical robot, so it usually causes that the body converges too fast to be upright and still before the spherical wheel becomes still and at the desired position. In this thesis, a periodic hierarchical sliding mode control (PHSMC) is proposed to solve the spherical wheel which is at the constant speed or is still but not in correct position situation. Basically, the periodic switching scheme instead of state can slow down the body convergent rate. The position control can be achieved by various duration of the period. The shorter the duration is, the smoother the trajectory is. For the long duration of the periodic switching, the hardware requirement is easy at the cost of slow body convergent rate. Therefore, the cubic of body angle term, which can result in fast convergent rate outside the designated body angle but in slow convergent rate within the designated body angle, is proposed to be included. By adding the cubic term, the body can become still and upright only when the spherical wheel reaches the desired position with slow speed.
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