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Since its introduction in the early 50's, teleoperation systems have expanded their reach, to address micro and macro manipulation, interaction with virtual worlds and the general field of haptic interaction. From its beginnings, as a mean to handle radioactive materials and to reduce human presence in dangerous areas, teleoperation and haptics have also become an interaction modality with computer generated objects and environments. One of the main goals of teleoperation is to achieve transparency, i.e. the complete perception by the human operator of the virtual or remote environment with which he/she is interacting (Lawrence, 1993). The ability of a teleoperation system to provide transparency depends upon the performance of the master and the slave, and of its control system. Ideally, the master should be able to emulate any environment, real or simulated, from freespace to infinitely stiff obstacles. The design of a transparent haptic interface is a quite challenging engineering task, since motion and sensing capabilities of the human hand/arm system are difficult to match. Furthermore, recent studies are providing more and more evidence that transparency is not only achieved by a good engineering design, but also by a combination of perceptual and cognitive factors that affect the operator ability to actually perceive the stimuli provided. The current knowledge on operator models reflects two separate groups of results. On one hand, there are guidelines for the design of an effective interface, from a human factors points of view, which include perceptual issues related to the cognitive and information processing of the human operators (see Subsection 2.4). On the other hand, there are several operator models related to biomechanical, bandwidth and reaction time issues (see Subsection 2.5). In this work we survey the main human factors that concur to the effectiveness of a haptic interface, and we present a series of psychophysical experiments, which can enrich performance in haptic systems, by measuring the mechanical effectiveness of the interface, providing a measure of the perception of a human operator. In addition the experiments are useful to represent the complex behavior of the human perception capabilities, and to propose new ways for enhancing the transparency of the virtual environment, by proposing suitable force scaling functions. In addition, our experience with psychophysics procedures highlights the needs of non-classical approaches to the problem, but the design of this type of experiments is not trivial, thus the need of a dedicated software tool or library arises. 22 |
