Realization and development of an optic based prototype tactile sensor

Due to the advancements in science and technology, practical use of machinery in daily life gained a greater role as the time passed leading the invention of so called "smart machines". Since then the development of these smart machines are still in progress parallel to the latest technological advancements. Software, electronics and mechanics are three fundamental components of these developments. Mechatronics is the main roof that gathers and coordinates these factors. Sensor technology is one of the main and important topics of mechatronic systems. Recently there has been an increased interest on tactile sensing. Tactile sensing is one of the Five Senses of Human Nature. It is estimated that the density of low threshold mechanoreceptive units that are all individual tactile sensor cells at the fingertip is approximately 241 units per centimeter square. Human fingertips have the sensitivity of 1 mm spatial resolution with 1.4 millisecond speed. Tactile sensing usually refers to a transducer that is sensitive to touch, force, or pressure like human skin. A tactile-sensing array can be considered as a coordinated group of touch sensing receptors. Recently, there has been an increased interest in tactile sensors, yet, the desired level, which is the resolution of human's tactile sense could not have been reached in terms of number of receptors at a certain area. The unique and the most important contribution of this dissertation to the related field of study and literature are to use a patented design (WO 2014011126 A1) in order to increase the number of sensory receptors per centimeter square up to millions. The xx second contribution is the development of a method that can acquire millions of data at low costs. This dissertation uses the main idea of a patented design by Dr. Utku Buyuksahin (advisor of the thesis) named 'Multi point, high sensitive tactile sensing module for robots and devices', (WO 2014011126 A1). A prototype design is made and realized where this patent is taken as a basis and accordingly further research, production, analysis, development and experiments are done on this fundamental approach. The main goal and the unique outcome of this dissertation which also separates this work from the patent is to describe the relation that is between the measurements of the sensor with the materials used within when this patented design is manufactured. One can select the materials due to the intended features of the measurements. Tactile sensors usually measure one or more of the following mechanical features of an external stimulus; displacement, force, pressure, indentation, mass, temperature, vibration, geometry. Tactile sensors are employed for automation, robotic, medical and space technology applications. The desired level for tactile sensing in robotics and devices compared to the humans tactile sensing ability still could not be reached in terms of receptors per measurement area. In this dissertation a new and novel tactile sensor system is developed that measures the displacement, force and pressure that arise from an external stimulus. The design illustrated in this study proposes using change of intensity of the reflected light due to the deformation on the contact surface of the elastic medium. In this novel sensory system that is presented in this study is designed to achieve the consistency and spatial resolution of human fingertip. An elastic and transparent structure that has similar consistency with humans' fingertip tissue is produced by using elastomeric silicone substance. A high resolution and highly sensitive tactile senor system is manufactured by fiber optic cables carrying light embedded within the silicone pad, that mimics the transmission of the human nervous system. The best mathematical model is selected due to the experimental and theoretical approaches on the silicone pad. The intensity/brightness data of the reflected light beams that are carried by fiber optic cables enter this sequent mathematical model as the input, and step by step, displacement and force map of the contact surface is evaluated as the output. The purpose of this dissertation is to realize and develop a prototype that has the same tactile spatial resolution of a human fingertip and to examine and define this technology scientifically.