Haptic interfaces that include tactile shape displays must correlate small-scale shape information with finger position. High temporal bandwidth of the display actuators is required to provide realistic sensation during rapid finger motions. To characterize finger speeds during surgical palpation, we performed an experiment where subjects used the tip of the index finger to search for 4 mm lumps embedded in flat rubber models. The models were 15 to 25 mm thick soft silicone rubber with mechanical characteristics approximating lung or breast tissue. Average fingertip speed while in contact with the rubber was approximately 38±16 mm/s (mean ± standard deviation), and average maximum speed was 90±31 mm/s. While moving between contact intervals, the average finger tip speed was approximately 76±18mm/s, and average maximum speed was 146±37 mm/s. There were no significant speed differences between experienced surgeons and subjects who had no medical training. The results indicate that a 30 Hz bandwidth is necessary for shape displays used in haptic interfaces for lump localization in surgery. A shape display design meeting this specification is also presented.

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