Design And Research Of A Six-Degree-of-Freedom Haptic Device

With the development of virtual reality technology,the important status of the haptics is also growing.As an indispensable role in Interactive exploration system,the haptic device can transmit motion and force between human and virtual environment,increasing the telepresence in virtual reality.Aiming at the problems about low stiffness,limited output ability and application fields,this thesis shows a new six degree-of-freedom haptic device with focus on designs offering high force capability and general applicability.According to the requirements of haptic device,the mechanism of haptic device consists of two types parallel mechanism,which have been improved for better operating performance.The forward and inverse kinematics of the mechanism are then analyzed.Based on the results,to guarantee transmit performance and compact structure,a combined index with dexterity index and volume index is presented as the goal of parameters optimization.Considering the inertia of moving parts,the inverse dynamic model of the translational joints is build using Newton-Euler method,and is proved to be correct via simulation in ADAMS and Simulink.Considering the resistance existing in the process of backdrive operation,a compensation method consists of dynamic part and friction part is presented.In the part of dynamic compensation,the Time Delay Estimation(TDE)method is used for estimate the joint force caused by dynamic characteristics,and in the part of friction compensation,the static friction + coulomb friction + viscous friction model is used.In order to obtain the parameters in friction model,a series identification experiments are conducted on the prototype.Then the calculated compensation force is added into to the controller as the feedforward.Experiment result shows that backdrive force is reduced over 70% after using the compensation method.During the operation process,controllers are respectively designed in teleoperation phase and in force feedback phase.During the teleoperation phase,presented compensation method is used to increase compliance of backdrive.During the force feedback phase,the impedance control based on position is used to simulate dynamic relationship between human and environment.In general,heterogeneous mapping is often used in the master-slave operation,therefore,it is necessary to study the kinematic mapping method,and a variable ratio mapping method based on position and velocity of haptic device is presented.Finally,experiments are conducted to verify the effectiveness of the controllers.Experiment results show that the backdrive force is reduced dramatically after using the compensation method during free motion,and the haptic device can output accordingly force under the given impedance parameters during the force feedback phase.