Variable Stiffness Actuators Towards Passive Haptic Interfaces

Abstract

The main purpose of haptic devices is to enhance the interaction between the user and virtual or remote environments through the sense of “touch”, allowing them to perceive information more efficiently. Research has been oriented around the creation and the control of new haptic interfaces. Haptics nowadays are found in numerous applications, starting from joysticks in entertainment devices, to cellphones, medical applications and industrial applications where interaction between user and the virtual or remote environment is needed. The classifications of haptic interfaces go into two folds based on the nature of their actuation system; “Active” or “Passive”. Passive haptics is the category of haptic interfaces that incorporate passive actuation systems that either dissipate, redirect or store energy, (i.e. brakes, clutches, springs… etc.). The main advantage of using passive haptic devices lies in their intrinsic stability, which reflects their safety. Two main limitations hinder the capabilities of passive haptic devices. One lies in their inability to generate desired forces in any arbitrary direction and magnitude. The other one lies in their inability to fully simulate the interaction between the virtual tool and the deformable elastic body. The ideal solution for the latter limitation lies in incorporating variable stiffness mechanisms that are able to alter the stiffness of the haptic interface to equate (relate to) the level of stiffness of remote/virtual elastic body. This had become the main driver of this research. In this thesis, three novel passive variable stiffness joints were invented and their design, modeling and characterization for passive haptic interfaces are presented. The design criteria of these joints lie in their ability of moving freely at zero stiffness level, with several ranges of stiffness that can be achieved, taking account of the simplicity of the design, the energy consumption, and the speed of stiffness altering.

Keywords: Haptic Devices, Passive Haptic Interfaces, Variable Stiffness Mechanisms, Passive Variable Stiffness Joint (pVSJ)