A Linear Haptic Interface for the Evaluation of Shapes

The paper presents a haptic device that allows a user to explore a virtual object along a continuous line. In particular the device is developed with the aim of supporting designers during the evaluation of the aesthetic quality of a virtual product. This is generally done by means of the global and local analysis of the shape in terms of curvature characteristics, presence of inflections points and discontinuities. In order to evaluate such features, designers are used to work on physical prototypes, relying on their skilled sense of touch. It is known that physical prototypes are expensive in terms of cost and time for their realization, and a modification on a physical prototype implies a reverse engineering process for appling such modifications on the virtual model. A linear haptic interface, that adapts its shape reproducing a generic curve on a surface, has been developed to replicate the behavior of a physical strip. This is the way to replace real prototypes with virtual ones without changing the evaluation paradigms that designers are used to. The physical limitations encountered in representing discontinuities in position, tangency and curvature, not renderable by bending and deforming a physical strip, have been overcome thanks to the application of some principles of the theory of haptic illusions by means of sonification of some curve characteristics. The paper describes the linear haptic interface developed and the solution based on haptic illusion that has been implemented to overcome the strip limitations.