A Novel Hybrid Machine Tool Integrating a Symmetrical Redundantly Actuated Parallel Mechanism: Design, Kinematics, Prototype and Experiment

Inverse Kinematics of a 5-Dof Hybrid Manipulator

The kinematics of 3-PRS parallel mechanisms (PMs), an important category of 2R1T PMs, is very important for the motion control and error compensation of PMs. In order to produce a spindle head that could meet the requirements of various machining accuracy levels, a definite kinematics analysis of the PMs par should be taken with caution firstly. Here, the mathematical models of two 3-PRS PMs with different branch chain arrangements were established using the Euler angle. The kinematic equations of two 3-PRS PMs were obtained by establishing the closed-vector loop equation according to structural conditions. Parasitic motions that would cause a great effect were obtained, and their variations with structural and kinematic parameters were also obtained through MATLAB. Since the relationship between parasitic motions, and the given structural and kinematic parameters, is inextricable, an analysis is performed for the purpose of reducing or eliminating parasitic motion to ensure the accuracy of end-effector movement. The caused effect of parasitic motion can be improved with scale optimization and precision compensation. Lastly, two improved 3-PRS PMs without the parasitic motion of different branch chain arrangements used as the spindle head were obtained. Parasitic motion was related to the mechanism configuration and could be avoided in the configuration design stage with the comprehensive optimization of the structural and kinematic parameters, which provides a reference to obtain a sufficient workspace and improve the precision of traditional five-axis CNC machine tools.

Parasitic Motions of 3-PRS Parallel Mechanisms with Two Different Branch Chain Arrangements

Numerical control (NC) system is the core functional module of 5-axis machining devices. The paper presents a dispersing NC system for a novel hybrid machining robot. For this purpose., three issues are clarified., i.e. the architecture., the control strategy and the software of NC system. Firstly., by adopting a multi-axis motion control unit (MCU)., the architecture of a dispersing NC system is designed. Secondly., a control strategy is presented based on tool-path smooth algorithms., kinematics model and kinematic calibration method. By embedding above control strategy., a post-processing software and a human-machine interaction (HMI) software are developed. Finally., a NC system is developed to construct a hybrid machining robot system. A set of kinematic accuracy tests and machining tests are carried out to verify the feasibility of the developed NC system.

P.C. López-Custodio

Papers

Compliance model of Exechon manipulators with an offset wrist