Control System Design and Experimental Verification of Capsubot

This paper presents theoretical analysis and experimental verification of the locomotion for the capsule-type robot which is called the Capsubot. The Capsubot as no external driving parts and its input force is applied to the inner mass. Then, the Capsubot moves by utilizing a reaction force and a friction. Control algorithm is constructed depending on the mode of the outer shell: slip and stick mode. In the slip mode, the Capsubot moves forward when inner mass is accelerated in backward. The control input in the slip mode is assigned to minimize the input power by optimal control method. In the stick mode, the inner mass returns to the start position in the outer shell with slow velocity so that the outer shell does not move under the friction. In this paper, we verified the control algorithm through numerical simulations and the motion of the Capsubot is compared with theoretical model in the experiment. By designing the controller to identify a friction coefficient, the perfect implementation was achieved as we expected. Because it is not easy to control the position of the inner mass in the slip mode, several trials are performed to locate it at right position by adjusting some parameters. As a result of the experiment, the average speed of the Capsubot was 13 mm/s.