Cartesian Parallel Manipulator Modeling, Control and Simulation

The research presented in this chapter establishes the CPM as a viable robotic device for three degrees of freedom manipulation. The manipulator offers the advantages associated with other parallel manipulators, such as light weight construction; while avoiding some of the traditional disadvantages of parallel manipulators such as the extensive use of spherical joints and coupling of the platform orientation and position. The CPM employs only revolute and prismatic joints to achieve translational motion of the moving platform. The main advantages of this parallel manipulator are that all of the actuators can be attached directly to the base, closed-form solutions are available for the forward and inverse kinematics, and the moving platform maintains the same orientation throughout the entire workspace. From simulations done in this research, performance of various motion controllers are studied and compared. Although the simple PD controller with only position and velocity reference is easy to implement and no knowledge of the system is needed to develop this type of controller, the tracking ability is very poor compared to the rest of the controllers used in this thesis. At the next step, when partial dynamic modeling information is incorporated into the controller, the PD controller with gravity compensation is implemented. The simulation results show a significant improvement in tracking ability from a simple PD controller. Next, the verification is needed to determine if complete mathematical modeling knowledge is needed to give the controller complete advantage in motion control. Hence, the PD controller with full dynamic feedforward terms and computed torque controller are implemented and put to the test. The model based controllers such as computed torque and PD control with full dynamic feedforward terms can generate force commands more intelligently and accurately than simple non-model based controllers. Hence, the need for studying dynamics of robot manipulator as well as having a good understanding of various basic motion controller theories are important in designing and controlling motion of the robot to achieve the highest quality and quantity of work. The simulation results show that the computed torque controller gives the best.