Geodesic Haptic Device for Surface Rendering

Abstract

This paper describes a haptic device whose aim is to render the contact with a continuous and developable surface by means of the representation of a geodesic trajectory. Some preliminary tests conducted with industrial designers have showed that the trajectories performed while exploring the surface of a style product, for a qualitative evaluation, follows some particular trajectories that may be mathematically described as geodesic curves. In order to represent these particular curves a haptic strip based on a modular servo-controlled mechanism has been developed. Each module of mechanism allows us to control both the curvature and the torsion. This device, in respect to the commercial existing haptic devices, allows a hand-surface contact with the virtual model in real scale without artifacts, by self-deforming its shape in order to conform to the mathematical curve to render. The strip is 900 mm long and has 9 control points for bending and 8 control points for torsion. Due to these characteristics, it allows us to render exploration trajectories of several kinds of product shapes and dimensions. In order to allow users to fully explore an object surface, we have mounted the strip on a platform consisting of two MOOG-FCS HapticMaster devices, which permits 6DOF orientation of the strip and force feedback control. The paper describes the mechanism of the strip and the 6DOF platform starting from the empirical observations of the exploration of surfaces and highlights the problems encountered and the solutions adopted.