Development of a PKM control system by design, modelling, simulation and integration

Abstract: PKM (ParallelKinematicMechanism) machines have received increasing interestfrom industries. Nevertheless, they didn't turn out goodresults in control performances as desired. One of the reasonsis the unsuitability of the available control systems for theparallel mechanisms.This thesis presents a process to develop a PKM controlsystem. The process is fulfilled by three developing groups:the control supplier, the machine builder and the machine user.By making use of the axiomatic design principle, a conceptualcontrol system is designed to meet the functional requirementsof these three groups. The design is especially focused on thetransformation module within the motion controller since thismodule mainly makes PKM control system different from othercontrol systems.Kinematic transformations are needed in the transformationmodule to control the PKM machines. Therefore, a transformationtheory for control is proposed to perform all computations ofthe transformations in the motion controller. The theoryincludes two parts. Part 1 introduces the inverse and forwardtransformations and the roles of singularity and dexterity inmotion control. Part 2 describes how to integrate the kinematicmodels into a control system to realise the transformationfunctions. The integration process takes place on thetransformation platform and makes it possible for a controlsupplier to co-operate with the machine builders and users.A new method, named a connection method, is created in thisthesis to establish the dynamic models of the PKM machines. Thepurpose is to reveal the dynamic behaviours of the PKM machinesand to design a better control model via the dynamic modelstogether with the kinematic models. This method is successfullyapplied to a planar PKM machine, PAMELA (PArallelMEchanism withLinearActuators).By simulation, a control model, called ISF (IntermediateStateFeedback), is suggested to eliminate the control-errorscaused by the inexact kinematic models. The simulation alsoshows that the good dexterity obtained in the machine designcan lead to good control performances. Together with thekinematic compensation, the ISF control model can improve thepositioning accuracy.This thesis demonstrates the whole development process ofthe PKM control system by taking the PAMELA machine as anexample. It helps to verify the development process and gives astudy case to develop other machine control system.Keywords: Control System Design, PKM machines, KinematicTransformation, Dynamic Modelling, Motion ControlSimulation