ABOUT TACTILE SENSING
WHAT WE SHOULD KNOW
Tactile sensing research has been frequently misinterpreted with sensor research. A variety of research efforts were directed to develop a sensor or combinations of sensors to function as human touch sense. The reason for the variety of interests in sensor research is embedded in the variety of questions tried to be answered. In order to find the right answer, the right question is required. The first question is “why do we need an artificial tactile sensing system?”
Let’s consider a few eligible answers. First of all, we require robots to interact with human being considering the softness of body tissue. Therefore, the robots have to be able to detect soft tissue from bones. Secondly, we require minimally invasive surgery tools to provide information about the soft tissues of organs during surgery. Third, we need artificial tactile sensing to compensate for the deficiency of human tactile sensing in order to provide precisely quantified properties of soft tissues/materials. For this end, the tactile sensing should be much more capable than human sense to characterize soft tissue.
The next right question emerging from the abovementioned answers is “what is the characteristics of soft tissue specifically and soft materials generally?” or “what is the characteristics of soft tissue/materials for which human sense is deficient to sense?”
To answer this question, we enter the discipline of material engineering. The characteristic of soft materials has been categorized into three types: hyperelastic, plastic and viscoelastic. Viscoelasticity is a complex behavior which had been approached by different models but none has successfully provided an analytical solution. The soft tissue and most of the soft materials in natural are viscoelastic. Lack of a reliable analytical solution for viscoelastic material is one of the challenges in sensing soft tissues. The solution of viscoelasticity for tactile sensing soft tissue is explained in a separate page.
The next right question to be answered by tactile sensing is “what is the desired precision and the accuracy of characterization of soft tissues?”
In material science the characteristics are expressed in terms of properties of material such as elasticity, elongation, thermal capacity, etc. most of the properties are either linear or consider linear within a certain range otherwise a curve of a property based on the depending factors is demonstrating the behavior of the material. The elasticity modulus of steel is a common example of linearization of a nonlinear property due to linear behavior of steel within the range of industrial application. On the contrary, soft materials which undergo large deformation (more than 5%) demonstrate nonlinear behavior in most of the properties. The nonlinearity of soft tissue is another challenge which tactile sensing has to face. We discuss in another page the nonlinearities and their importance in characterization of soft materials.
For more information refer to “Method and system for real time characterization of soft materials and biological tissues based on nonlinear properties, Patent No. 10126219”.