Toward realistic haptic interactions with virtual rigid objects: Low-level dynamics and event-based algorithms

Many tasks in medical diagnosis and treatment require the doctor to use his or her sense of touch to make judgments about the material properties of various tissues and structures. As training physicians to perform these tasks on live patients is both costly and risky, interest has recently emerged in the area of high-fidelity simulation of such procedures. One of the most challenging aspects of creating a virtual environment for training of manual tasks is the need to provide realistic force feedback to the operator. Examination of the forces and accelerations produced when a hand-held instrument or probe is brought into contact with a hard surface such as bone or metal shows that the mechanical properties of the surface, probe, and hand dictate the shape and amplitude of the resulting high-frequency transient impact acceleration. Devoid of this high-frequency response, a virtual rendering of such a surface would never be capable of faithfully reproducing the dynamics and appropriate feel of the real interaction.; The majority of today's haptic simulation systems rely on quasi-static algorithms for the determination of surface forces; however, numerous limitations restrict the displayable stiffness to well below the level necessary to represent even moderately hard objects. As such, the first component of this thesis seeks to increase this limit by focusing on the lower-level dynamics of the typical haptic system, including a novel third-order switching controller design which has demonstrated potential to overcome many of the limits of the traditional approach. The second component of this work investigates a higher-level approach to augment standard feedback with open-loop transients. Extensive user tests comparing the perceived realism of tapping on real and virtual surfaces demonstrate that the inclusion of a contact transient significantly improves the realism of virtual rendering. To support this new technique, an investigation of the dynamics of real tapping elucidates the relationships between material properties, user-controllable parameters, and the transient response. Integrating this knowledge of how transient magnitude is affected by user parameters, the open-loop rendering technique produces virtual renderings of hard surfaces which feel nearly indistinguishable from real interactions.