| A modular serial robot consists of a chain of links and joints such that its configuration can be changed by the order and number of links and joints. Although theoretically a modular robot can take any configuration, the weight of the modules is usually the limiting factor in the number of modules that can be chained together. Since the actuator often contributes a significant portion of the module weight, this is reduced in the proposed design by replacing the actuator with a pair of clutches. Drive torque for the module is tapped from a central rotating shaft using these clutches, the central shaft being continuously driven by a single base-mounted motor. The position and velocity of the modules are regulated by controlling the engagement time of the clutches using the Pulse Width Modulation (PWM) technique. An experimental 2-axis gantry robot based on the uni-drive modular robot concept has been designed and fabricated. The mathematical model of the gantry robot is developed; then, experimental and simulation results are compared. Based on the theory of variable structure systems and nonlinear PWM controller, a local controller is designed and tested on the gantry robot. In the modeling and control of an articulated uni-drive modular robot, a self expansion formula is first developed to generate the equations of motion for a uni-drive planar modular robot only based upon the number of modules. The principal design of local controllers and path planner for the articulated uni-drive modular robots is introduced next. For local controllers, with the combination of independent joint control and sliding mode control, a new robust design methodology against parametric uncertainty, disturbances and the frequency range of unmodeled dynamics is developed. The elastic model method is used for the structure of the path planner; then, the performance of the designed local controllers and path planner is presented by simulation of a uni-drive three-module robot. |
