Abstract

This master thesis is divided into two major sections. First, anatomic characterization and profilometry of tissues with natural shape: a real-time approach for robotic-assisted minimally invasive surgery (RMIS); and second, design and characterization of a novel tactile array sensor capable of differentiating among different viscoelastic tissues that exhibit time-dependent behaviour.
The first part of this thesis is focused on a tissue characterization system for RMIS applications. RMIS has gained immense popularity with the advent of high-precision robotic systems. The lack of haptic feedback, however, is considered as being one of the main drawbacks of present-day RMIS systems. In order to compensate for this deficiency, a novel tissue characterization system is proposed which is inspired from the human haptic system. Hence, kinesthetic and tactile feedback which are constitutive components of human haptic system are used to characterize naturally shaped tissues. Toward this goal, a 5-degree-of-freedom robot which is called Catalys5 is equipped with a ball caster force-cell. The system is used to simulate robotic surgery maneuvers in which an admittance control approach is implemented to design the force feedback controller. The proposed method characterizes naturally shaped tissues, which is capable of touching and palpating to: a) Identify the 2D or 3D surface profile of the target tissue (profilometry), b) Measure the modulus of elasticity of any desired point on the tissue’s surface, c) Find and map the location of any lump in the tissue, and d) Map hardness distribution around the lump.
Initially, silicon-rubber materials were used to build tissue phantoms with different curvatures and degrees of softness. The surface profiles were obtained using the developed profilometry algorithm and validated using a 3D scanner. In addition, several experiments were conducted on bovine tissues to evaluate all above mentioned capabilities of the system. The results of experiments on real tissues were also compared to those that are available in current literature. The results indicate that the proposed approach can be used for reliable material characterization for RMIS application.
The second part of this thesis is focused on developing an array tactile sensor for distinguishing softness of viscoelastic tissues with time-dependent behaviour for use in MIS and RMIS. Review of literature on tactile sensors reveals that the vast majority deals with determining the applied contact force and object elasticity. In this research, a novel idea is proposed in which a tactile sensor array can measure rate of displacement in addition to force and displacement of any viscoelastic material during the course of a single touch. In order to verify this new array sensor, several experiments were conducted on a range of biological tissues. It was concluded that this novel tactile sensor can distinguish among the softness of real biological tissue with time-dependent behaviour.