Manipulation control of an armed Ballbot with stabilizer

Abstract

Combination of a mobile platform and a manipulator which is known as a mobile manipulator can be used in lots of applications. Motion control with respect to stability of dynamically stable mobile manipulators is one of the interesting challenges in robotics. In addition, servant robots are becoming widespread, from local uses as robotic cleaner to field applications as flexible robots, also for farming, martial, and space exploration. One of the servant robots that are designed to operate specially in indoor places is the Ballbot. A Ballbot is an under-actuated system with non-holonomic dynamic constraints. It is as tall as human height until it could interact by people. Moreover, it can be equipped with a manipulator for grasping and manipulating objects. So, manipulation control of such system is highly complicated due to severe under-actuated condition and non-linear dynamics which is considered in this article. Therefore, developing a compact dynamic model is highly practical for controller design, developing simulation studies in support of design improvement, and for useful applications. To this end, the Ballbot has been equipped with a Programmable Universal Machine for Assembly–type manipulator. This manipulator adds new advantages to the Ballbot such as an object manipulation operation and better stability. So, the dynamic model of the proposed system without any simplicity is presented, and then, the validation of this extracted model is studied. Next, the manipulator reconfiguration is used to help the system move without flutter. Because of the passive joints, the Ballbot cannot maintain its stability and follows the desired end-effector trajectory. Therefore, a stabilizing pendulum is proposed to help the stability of the system when the manipulator handles an object on the desired path. Finally, a manipulation control algorithm is proposed to reach the system to its desired position. Simulation results show the capability of the presented controllers.