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, a 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 an 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 mattresses objectively and compare it with the subjective method.
Material and method
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.
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
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American Society for Testing and Materials, Standard Methods of Testing Slab Flexible Urethane Foam, ASTM Designation, D1564-71.
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American Society for Testing and Materials, Standard Specifications and Test for Latex Foam Rubbers, ATSM Designation, D1055-69.
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Brattga S Carlsoo and Severinson k, Temperature and Humidity in the Sitting Area, Kenedi, 1976.
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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.
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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.
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