Design guidelines for generating force feedback on fingertips using haptic interfaces
Carlo Alberto Avizzano, Antonio Frisoli and Massimo Bergamasco
Manipulation and grasping have key importance in most types of interactions between humans and the world surrounding them [1, 2]. Even if almost all existing haptic interfaces provide a user interaction based on a single contact point, an increased number of contact points, not only allows to display a more natural haptic interaction [3, 4], but also improves the quality of interaction that users can perform in the environment. Haptic exploration is highly dependent on the number of fingers used for exploration of common objects , the largest difference appearing between the ‘one finger’ and the ‘two fingers’ conditions , and as proven by Jansson et al.  by the ability to discriminate a precise tactile pattern during the exploration. In , we found an experimental confirmation of this hypothesis: the haptic exploration do not improve with the increase of contact points, from one to two fingers. This suggests that the restriction imposed on the fingerpad contact region can blunt the haptic perception of shape and so indicates that local haptic cues play an important role in haptic perception of shape. Factors that can account for the observed performance in these experiments are lack of physical location of the contact on the fingerpad and lack of geometrical information on the orientation of the contact area, that constitute interesting insights and suggestions for the design of haptic displays.
Multipoint haptics [9, 10] are devices that can simultaneously interact with the user through more than one contact point. These systems allow both force and torque feedback during the simulation of dexterous manipulation and complex manoeuvring of virtual objects and can improve the interaction in several applications, e.g., assembly and disassembly in virtual prototyping [11, 12], medical palpation during simulated physical examination of patients  and many other ones.
In this chapter we present different approaches to improve the quality of haptic feedback during virtual manipulation of objects. Four different aspects of modelling perception and manipulation are proposed and investigated through conducted experimental studies.
Initially we investigate the capabilities of using a haptic system for grasping and manipulating virtual objects, by means of a two contact points haptic device. The work also investigates the relationship between human prehension and features of the physical model of the grasped object, finding out how grasping in virtual conditions present higher forces and safety margins than in real conditions. A possible motivation of this observed difference is due to the limitations of kinesthetic devices in stimulating local mechanoreceptors.
<link>contents «Human Haptic Perception», Grunwald (Ed.)
<link>« Haptic shape cues, invariants, priors and interface design
<link>» Haptic rendering and control
<link>references: Design guidelines for generating force feedback on fingertips using haptic interfaces
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