The Monash Epicyclic Parallel Manipulator: a novel six-degree-of-freedom impedance-type haptic device
thesisposted on 22.02.2017 by Abeywardena, Sajeeva Niranta Yapa
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Force-feedback haptic devices are human operated mechanisms which manipulate objects in a remote environment and relay back the interaction experienced by the object to the user. The structure of force-feedback devices resemble that of robotic mechanisms, employing either a serial, parallel or hybrid architecture. In the study discussed in this thesis, the Monash Epicyclic Parallel Manipulator (MEPaM), a novel three-legged six degree-of-freedom (dof) parallel mechanism with base mounted actuators is introduced. The characteristics of MEPaM are suitable for use as an impedance-type haptic device–that is, a device in which the user has control over motion and force is applied by the device motors. Before the mechanism was used as a haptic device, a theoretical investigation into the geometric models, singularities and dynamics of MEPaM was conducted. This showed that the mechanism has simpler geometric and dynamic features when compared with existing six-dof parallel mechanisms. Accurate pose estimation is paramount in haptic situations, with the correct geometric parameters required. The geometric parameters of MEPaM were found experimentally through a geometric calibration, such that the identified parameters minimised errors between estimates from the geometric models and measurements. The suitability of MEPaM as a haptic device was investigated using the concepts of Z-Width and transparency. Three control strategies–open loop impedance control, open loop impedance control with model feedforward and impedance control with force feedback–were implemented, with the best performance found when the impedance control with force feedback strategy was used. Further, it was found that the force capabilities and maximum limits of Z-Width of MEPaM are comparable or superior to commercially available devices. Future investigation into the use of MEPaM as a haptic device in virtual environments which simulate needle punctures or tools in trocars used in minimally invasive surgery for purpose of medical training is recommended.