Analysis of Different Possible Designs for Fingertip Sensor Cantilever Beams

Abstract

Prosthetic hand is an artificial device used for the functioning of a hand. There are some prosthetic hands which are controlled by using myoelectric signal (nearly 1mV) of the body. These signals are extracted with the help of electrodes which is analyzed and necessary actions like amplification, filtering is taken. These signals are further feed to microcontroller (PIC) to guide the servo motors of the hand for the control functions like wrist rotation, fingers movement, etc. In the case of a prosthetic hand, the user is unable to „feel‟ an item held by the hand. For example, the user would be unaware if he holds a very hot or very cold item, possibly resulting in damage to the prosthesis or to the user. Another example, the lack of feedback on the force exerted during a grip posture could result in the crushing of a gripped item. A possible solution to these problems is to include some form of multi-parameter sensing system within the prosthetic device. For the prosthetic hand, such a system might comprise a number of force sensors to monitor and adjust the grip strength and also include thermal sensors to measure the temperature of a grasped object. There are different static and dynamic sensors into use which are prepared by using thick-film technology. They are very suitable to measure the grip forces exerted upon an object held by a prosthetic hand. The static force sensors exploit the piezoresistive characteristics of commercially available thick-film pastes while the dynamic slip sensors utilize the piezoelectric behavior of PZT pastes. In the present dissertation an analysis of different possible structures of cantilever beams have been carried out for the purpose of enhancing sensitivity and life of sensor. Different aspects like stress, strain, life, safety factor, deformation and hysteresis were considered for various possible shapes for the prosthetic arm.