Study On A Dual-Drive Spherical Robot And Its Motion Control System

Spherical robot, belonging to mobile robot category, is an independent movement unit with sphere or approximate sphere shape, and its main motion is characterized by rolling style. Spherical robot attracts robot researchers'universal attention at once since it appeared in the world, not only because of its novel configuration and movement mechanism, but also because its special advantages in engineering application with respect to the other mobile robots.This study develops mechanic modeling and controller design of a new dual-drive spherical robot. The methods applied in research are theoretical analysis, simulation and experimental verification. The contents can be expressed as follow,Based on summarizations of the present spherical robots in view of structure, a new dual-drive spherical robot has been proposed. The main character is that the axial lines of two DC motors have been placed on the same straight line. Without a relative stable platform in the robot, the output torque of driving motor would lead robot's gravity center to deviate from sphere's center, and then, the gravity torque with regard to point of contact would cause the robot rolling forward. The turning motor leads inner components to change direction steering by rack and pinion to transfer torque.In order to understand and analyze the dual-drive spherical robot better, it is necessary to study its situation and orientation description on arbitrary time. The individual variables can be divided into two parts, inner and outer character, when describing movement states of the robot rolling on a plane. The outer character variables define postures of plate-ball system, and the inner character variables decide positional relationship of the component. Those variables can be transformed each other by transition matrix.Because the spherical robot involves some problems of nonholonomic constraints, strongly coupled manner, underactuated and nonlinear property, dynamic equations described the whole character variables entirely appear extraordinary complex and tedious. Based on those dynamic equations, the problems of system analysis and controller design become more difficult, which would greatly limit application of the robot. Therefore, a movement strategy, executing turning direction and rolling forward alternatively, has been proposed. Here, the system suffered by nonholonomic constraints has been transformed into two subsystems suffered only by holonomic constraints, and then, difficulty of controlling design has been decreased. Furthermore, the spherical robot can realize a straight arbitrary-length path, and can approach an enclosed trajectory approximately through the proposed trajectory planning method, named'point-to-point straight-line interpolation'. At last, in order to verify the proposed method, experiment platform has been built up to tracking an ellipse trajectory. The results illustrate that when tracking precision doesn't be restricted strictly, the dual-drive spherical robot can fulfill some generally explore assignments applied the above strategies and methods.Rolling forward is the main movement of the dual-drive spherical robot. Hence, the dynamic of this motion should be investigated carefully because its driving mechanism using gravity torque is more differently than other mobile manners. Firstly, the dynamic equation has been obtained from Lagrangian function based on energy dissipation. Then, changeable curves of state variables have been analyzed by simulation method. Secondly, the dynamic equation forms, suffered by rolling frictional resistance and climbing state, have been unified. Such makes the derived equation more universality. Lastly, dynamic equation has been transformed into state space form with linear invariant property at new equilibrium point of system, which is relative to critical pendulum angle.A series of research work about controller design and simulation analysis has been developed base on the derived state-space form equation. The contents are as followings: analysis about stabilization of the robot system; resolve tracking a reference input problem by means of expending state variables; study controller design method to estimate unmeasurable state using state observer; develop optimal controller for a special objective function constructed from some performance indexes. Experiment data prove existence of the critical pendulum angle and validity of state gain controller.In addition, this paper has also studied some other problems related to the spherical robot, such as, smooth time-variable controller to nonholonomic system, mechanism of rolling friction, and so on.