A Haptic Simulator for Gastrointestinal Endoscopy : Design Development and Experiments

Abstract

Endoscopy is an involved clinical practice requiring considerable skill in performing the procedure. Virtual reality together with haptics offers immersive, flexible, and cost-effective platform for training in endoscopic procedures. In this thesis, we present mechanical design, control, characterization, and integration of a novel endoscopic haptic simulator with three degrees of freedom. Related ideas, computations, and experiments that support endoscopy and endoscopic simulator are also investigated in this thesis. The haptic device is designed to reflect forces in the three important directions, namely, longitudinal, rotational, and radial directions. The mechanical design of the haptic device overcomes some of the limitations of the existing systems. The device provides large sustained output force and possesses low friction, low inertia and zero backlash. Dynamics-based feed-forward control algorithm is developed to achieve high fidelity and transparency in force-feedback. Tracking performance, transparency, and nonlinearity are all quantified using experiments designed to validate the control structure and to characterize the developed haptic device. The device is shown to apply a maximum continuous force of 11 N in the longitudinal direction, maximum continuous torque of 196 mN.m in the rotational DoF, and a maximum force of 1.5 N (at each of the four radial pads) in the radial direction. Furthermore, we also present the design of a novel compliant mechanism for the radial DoF. The circumferentially actuated compliant (CAC) mechanism is a planar, reversible, and single degree-of-freedom compliant mechanism that emulates controlled and responsive circularly shaped opening. The mechanism is designed in view of the anatomy of the throat and the special manoeuvre required for intubation of the endoscope into the oesophagus by avoiding the trachea. As part of the auxiliary work for the endoscopic simulator, we developed a computational technique for simulating the shape of the entire endoscope during endoscopy. Strain measurements made at discrete locations along the length of endoscope are used in the method. Strain measurement, stain interpolation, and shape reconstruction based on strain information are discussed. Furthermore, a method to predict the location of point forces acting on the endoscope tube during endoscopy is proposed. A novel concept of haptic playback for endoscopy is also investigated in this work. Haptic playback aids the endoscopists to recall both visual as well as haptic information from an earlier endoscopic session. The endoscopic playback concept is evaluated using psychophysical experiments. Through these experiments, we quantified haptic perception through the endoscope, the effect of temporal separation on haptic memory, and the interaction between haptic and visual information in sensory processing.