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Haptic emulation of hard surfaces with applications to orthopaedic surgery

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Title: Haptic emulation of hard surfaces with applications to orthopaedic surgery
Author: Hungr, Nikolai Anthony
Degree Master of Applied Science - MASc
Program Mechanical Engineering
Copyright Date: 2008
Publicly Available in cIRcle 2008-04-03
Subject Keywords Haptic devices; Virtual fixtures; Knee surgery; Computer assisted surgery; Bone conserving implants; Bone sculpting
Abstract: A generally accepted goal in orthopaedic surgery today is to maximize conservation of tissue and reduce tissue damage. Bone-conserving implants have bone-mating surfaces that reproduce the natural curvature of bone structures, requiring less bone removal. No small, reliable, inexpensive and universal bone sculpting technique currently exists, however, that can both create and accurately align such complex surfaces. The goal of this thesis was to develop a haptic hard surface emulation mechanism that could be applied to curvilinear bone sculpting using a surgical robot. A novel dynamic physical constraint concept was developed that is able to emulate realistic hard constraints, smooth surface following, and realistic surface rigidity, while allowing complete freedom of motion away from the constraints. The concept was verified through the construction of a two-link manipulator prototype. Tests were run on nine users that involved each user tracing out five different virtual surfaces on a drawing surface using the prototype. The primary purposes of prototype testing were to obtain subjective data on how effectively the dynamic physical constraint concept simulates simple surfaces, to assess how it reacts to typical user interactions and to identify any unexpected behaviour. Users were 100% satisfied with the prototype’s ability to emulate realistic and stiff hard surfaces and with its ease of manipulation. The amount of incursion into each of the virtual surfaces by all the users was measured to assess the precision of the system with the goal of deciding whether this new haptic concept should be further developed specifically for precision applications such as surgery. For curvilinear surfaces, 90% of the cumulative distribution of the measured data was less than 2mm, while for linear surfaces it was less than 6mm. Four behavioural effects were noticed: lateral deflection, reverse ‘stickiness’, hysteresis and instability in certain areas. These effects were studied in detail to determine how to either eliminate them or to minimize them through system design optimization. A computer simulation was also used to model the behaviour of the prototype and to gain further understanding of these effects. These analyses showed that the concept can be successfully used in curvilinear bone sculpting.
URI: http://hdl.handle.net/2429/639

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