LS 2

 

A new test method comprising a modular set of indentation devices has been designed, which is expected to provide more information about the mechanical comfort properties of the seat and bed system well correlating to the subjective assessment of total comfort. The indentor is equipped with pressure sensors along the surface to determine the magnitude and distribution of the contact pressure at the indentor/support interface in order to understand the concept of mechanical comfort properties by knowing the interaction of forces between persons and the bed in which they lie or the seat, including body contact pressure and subjective ratings of comfort. Subjects found all of the mattresses tested to be significantly more comfortable than an incompressible wooden reference surface. In this regard a new indentor has been designed to enhance the accuracy of the softness measuring system.


Introduction


The standard method of determining firmness has been usually carried out by measuring the compressibility as a function of load, using a flat circular indentor. This method has, however, been criticized for two reasons. The first being that it is the contact pressure against the human body and not the compressibility due to a certain load, determines the sensation of firmness. The second point is that a flat circular plate pressed against a flexible medium, larger than the plate, will result in an uneven force distribution along the surface, thus making any calculation of contact pressure meaningless. To overcome this new loading pad is suggested.


Mechanical comfort is defined as the part of the total comfort that depends on the contact pressure distribution over the human body parts in contact with the seat or bed. Contact pressure, pressure distribution and loading time are the main parameters affecting the mechanical comfort. There is an inverse relationship between acceptable level of pressure and the length of time spent lying in bed. Apart from tests with human subjects, not much has been published regarding the objective measurement methods for testing comfort. A number of mechanical properties are tested using standard methods. Most of these methods are intended to test the durability of seats but not the comfort. So an attempt has been made to study the comfort of mattress objectively and compare it with the subjective method.


Material and method


In this study two methods were used to find the comfort properties of different mattresses, namely objective method and subjective method. In the objective method the special design of indentor is used to test the comfort of mattresses. An elliptical indentor with 9 segments was made using aluminium. The objective method is done using an instron. And in the subjective method six differences places were chosen to rate the comfort of mattresses. In this method the general comfort rating scale was used. Nearly 120 subjects were involved in analysis of comfort of mattresses. Average weight of subject was 60kg. Here, five mattresses were used to find the comfort, namely foam, fur coir/foam, cotton, kapok. The duration of the subjective method was 40 days. After using of mattress for 40 days their option was taken has the result.