The Key Technologies And Prototype Development Of A High-speed And Light-weight Parallel Manipulator

This dissertation is focused upon the development of a complete theoretical package in terms of the conceptual design,dimensional optimization synthesis,servomotor parameters estimation,control parameters setting and kinematic calibration of a novel 2-DOF translational parallel robot for rapid pick-and-place operations. As a result, a prototype machine for automatic sorting of rechargeable batteries has been developed. The following creative works have been completed. Utilizing the properties of parallelograms, a 2-DOF revolute-jointed translational parallel robot patented with the name Diamond has been proposed. The light-weight component design and the base-mounted actuator arrangement allow the robot to achieve very high velocity and acceleration. This device can also be integrated with a 1-DOF feed mechanism, enabling a 3-DOF translational hybrid robot to be created. The integration is particularly useful for transporting workpieces at very high speed in a plane together with a relatively slow or step-by-step long distance motion in the direction normal to that plane. It has been found that the mean value of condition number of the Jacobian matrix is not suitable for evaluating the kinematic performance of the parallel mechanisms driven by external actuators. A global and comprehensive cost function is proposed by considering both the mean value and fluctuation of the condition number of Jacobian matrix. Meanwhile, a set of appropriate constraints has been considered in terms of the force transmission behavior, the workspace/machine volume ratio, and the feasibility in practical implementation. With the aid of the principle of virtual work, the dynamic model of the robot has been formulated. An approach to estimate the servomotor parameters is proposed using the singular value decomposition technique, resulting in the mapping function between the maximum value of joint variables and the unit operation variables. This makes it possible to the upper bounds of the servomotor parameters to be estimated in an effective manner. These parameters include the moment of inertia, the maximum speed, torque, and power. A method for the fixed-parameter PID controller tuning is proposed by taking into account of the nonlinearity and structural stiffness. The method can be implemented by two steps, (1) Tune the PID parameters of the velocity control loop by the CHR method, and (2) Tune the position control gain according to the matching principle of the dynamic characteristics of the control and mechanical subsystems. It has also been shown that the velocity tracking error can be dramatically reduced by using the feedforward control strategy. An effective kinematic calibration approach has been presented by taking the initial position of the reference point of the moving platform as the origin of the calibration frame. The method can be implemented by identifying the home errors of the active proximal links in the first place and followed by identifying the rest geometrical errors. The above outcomes have been used for the development of a prototype machine for automatic sorting of rechargeable batteries. It has been shown that the device is of simple structure, low cost, and high productivity. The gripper velocity is up to 4.5m/sec and the acceleration to 60m/sec2. The point-to-point positioning accuracy is 0.05mm. Another prototype has been developed for the University of Warwick in the UK for teaching and research.