This paper describes a multimodal system whose aim is to replicate in a virtual reality environment some typical operations performed by professional designers with real splines laid over the surface of a physical prototype of an aesthetic product, in order to better evaluate the characteristics of the shape they are creating. The system described is able not only to haptically render a continuous contact along a curve, by means of a servo controlled haptic strip, but also to allow the user to modify the shape applying force directly on the haptic device. The haptic strip is able to bend and twist in order to better approximate the portion of the surface of the virtual object over which the strip is laying. This device is 600mm long and is controlled by 11 digital servos for the control of the shape (6 for bending and 5 for twisting) and by two MOOG-FCS HapticMaster devices and two additional digital servos for 6-DOF positioning. We have developed additional input devices, which have been integrated with the haptic strip, which consist of two force sensitive handles positioned at the extremities of the strip, and a capacitive linear touch sensor placed along the surface of the strip, and four buttons. These devices are used to interact with the system, to select menu options, and to apply deformations to the virtual object. The paper describes the interaction modalities and the developed user interface, the applied methodologies, the achieved results and the conclusions elicited from the user tests.

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