Indika B. Wanninayake

The lack of tactile and force perception during robot-assisted surgeries could lead to application of inadvertent forces resulting in tissue trauma and accidental tissue damage. In order to perform surgical procedures within tight spaces surrounded by sensitive soft tissues, surgeon's ability to manoeuvre instruments with precision and control must be enhanced. Further, the tools with built-in tactile and force sensors enable surgeons to investigate surrounding tissues to determine surgical margins for dissection. This paper proposes a novel optical fibre based tactile probe capable of modelling tool tissue interactions to estimate tissue abnormalities. Tissue stiffness is estimated through an indentation technique. The proposed method allows rapid acquisition of tactile data as the instrument rolls over tissue surface in a near frictionless manner. The probe can concurrently measure both indentation force and indentation depth, which can be combined to develop a pseudo-colour stiffness image of the investigated tissue with abnormal regions clearly highlighted.

Optical-fiber-based contactless sensing techniques are used in a wide range of sensing applications in many industries to measure physical parameters such as displacement, torque, strain, and vibration. Due to extremely small diameters, flexibility, and the light weight of optical fibers, these sensors can be employed to provide accurate contactless sensing in areas where space is a major limitation. Although many different modulation schemes are possible through optical fibers, the intensity modulation (IM) scheme is very popular due to low cost, simplicity of the sensing structure, and its compatibility with multimode fibers. However, in comparison with other optical modulation schemes, the main drawback of IM is the limited sensitivity. Further, the optical fiber tips must be mounted very close to the reflective element (required to modulate the light intensity as a function of the measured physical quantity) to achieve the highest sensitivity and linearity. The aim of this paper is to mathematically model the output characteristics of IM optical fiber sensors under a number of different sensing configurations. These include IM sensors, utilizing planar, concave or convex reflective elements. Furthermore, a novel sensing configuration is proposed: an IM sensor employing a converging lens in between the fiber tips and the reflective element. In this configuration, the output sensitivity can be increased significantly simply by altering the gap between the lens and fiber tips. A nonlinear mathematical expression is developed for each configuration, and with that, once the output response for a planar reflector is known, sensing characteristics for other sensor configurations can be derived. Hence, this paper is a useful tool for predicting sensor characteristics and optimizing sensor design.