Characterization of an Elastomer Based Autonomous Sensing-Actuating System

Abstract

Elastomers are materials which exhibit variable stiffness with respect to temperature. This property can be utilized in designing a system to sense the temperature and act according to a pre-design, autonomously. The stiffness change is remarkable near to the glass transition temperature. Hence to get the best effect of design, the device can be designed by the proper selection of the type of elastomer so that the glass transition temperature can be shifted to the desired value. The present paper describes an elastomer based sensing-actuating system in the form of a bender which is designed using a spring steel strip with cured elastomer layer bonded to it and pre-loaded. The paper gives the details of characterization of the device with reference to temperature and with various degrees of pre loading. The experiments are also carried out with different elastomer materials. The results are recorded for all the configurations and analysed. The studies are also carried out at different humidity conditions. The pre loading is carried out by winding the spring steel strip around a cylinder and bonding the elastomer layer around that. The bonding agent has been selected based on the temperature range required to be sensed and the materials to be bonded. An environmental chamber is used to obtain the different temperature conditions. This unit has a programmable controller where temperature and humidity can be set. The chamber has a cut out to access the device at different temperatures. The bender type system is positioned in the environmental chamber with one end fixed to the base. The other end is connected to a link which is taken through the access point. The temperature at the device is recorded using a thermocouple fixed to it. The measurements are carried out using a strain-gauged link, which is calibrated prior to the experiment. A precision Linear Variable Differential transformer (LVDT) is also connected to the free end in order to measure the displacement. The measurements are made through out the temperature range. The calibrated sensing-actuating system can be used for sensing the temperature and to trigger a desired action in various applications. Some of the typical applications are sensing and actuating in hostile conditions, space applications, operation of self sensing thermal valves.