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.

Result and discussion

 

Objective method


Here, the indentor was used to test the comfort characteristic of mattresses with help of nine individual sensors in each segment of indentor. The distribution of weight in the mattress occurs by designed indentor. The result obtain from the objective method is in kg which is displayed in sensor.



Test result shows that the lower average value gives good comfort when compared to higher value mattress. The formation of soft bulkiness of the mattress is higher in lower reading mattress.



The graph shows the result of mattress comfort, the higher peak is uncomfort and the lower peak shows comfort mattress. Depending upon the weight distribution in the mattress the peak of graph is plotted.

Subjective method


Six places were choosing to test the five mattresses with help subjects. The subject result is converted into ranking. The subjective method result is proved by statistical way called Kendalls ranking. The ranking method give a result in rank order that is the first comfortable mattress is kapok, second is foam, third is coir/foam, fourth is cotton and fifth is fur.


Conclusions


In order to evaluate the seat and mattress comfort by subjective and objective method. The experiment was carried out to evaluate mattress comfort. In the comfort evaluation, it was found that seat compliance become an effective index as a human body response to the stimulation through cutaneous sensation. The objective and subjective were proved statistically. The comfort mattresses order was kapok, foam coir, cotton, and fur. The both method shows the same result. The conclusion of this study was objective method is better correlate to subjective method.


References

  • American Society for Testing and Materials, Standard Methods of Testing Slab Flexible Urethane Foam, ASTM Designation, D1564-71.

  • American Society for Testing and Materials, Standard Specifications and Test for Latex Foam Rubbers, ATSM Designation, D1055-69.

  • Brattga S Carlsoo and Severinson k, Temperature and Humidity in the Sitting Area, Kenedi, 1976.

  • Cochran, George Van B and Glen Slater, Experimental Evaluation of Wheelchair Cushions, Report of a Pilot Study, Bull, Prosth, Res.10-20, pp.29-61, fall 1973.

  • Dartman T, Hanel S-E and Linden J, TEFO resilience evaluation system. Beds and cushion. Determination of resilience. Development of a new method and a new testing equipment (in Swedish), Research report BM878004 FR, the Swedish Institute for Textile Research (TEFO) 1988.