Studies confirm that pressure in healthy blood vessels of the skin amounts to 32 mmHg (4.3 kPa) and enables proper blood circulation (Krutul 2004). By examining the stresses on muscle tissue, it was found that stresses up to 34.6 kPa lasting for 35 min cause its stiffening, which leads to pressure pain (Gefen et al. […]
Category: The History of Furniture Construction
Model of Interaction of the Human-Bed System
The development of mechanical models of interaction of the human-bed systems aims to determine the distribution of forces of mutual effect of the technical item and the human body. By using mesh phantoms, which are a reflection of the human body of the 5th, 50th and 95th centile (Fig. 8.55), the distribution of forces working […]
Numerical Modelling of Human-Seat Systems
Bedsores are a major problem for people who are physically handicapped and forced to stay lying down or in a reclining position permanently. The practice of dermatology shows that ulceration begins in the deeper tissues and spreads fromthere outwards to the surface of the skin (Krutul 2004). At the same time, cracking of the skin […]
Model of Interaction of the Human-Seat System
Due to human physiology, maintaining sitting position for a couple of hours is not beneficial for the nervous and musculoskeletal systems. Despite the fact that maintaining such a position is physically less tiring compared to the standing position, then with an incorrect position of the body it can cause a much greater (by approx. 40 […]
Experimental Testing of Stiffness of Seats
Most furniture pieces designed for sitting, especially office chairs, cafe chairs, cinema chairs or house chairs, have soft, upholstered seats and/or backrests. Usually these parts of the furniture, on an industrial scale, are made from flexible polyurethane foams, latex foams and spring systems covered by layers of polyurethane foam or coconut mats, as well as […]
Stiffness of Spring Units
When designing furniture for lying down of sitting (with sleep and relaxation functions), anthropometric and physiological rules should be taken into account arising from their use. Mattresses, especially those of orthopaedic character, constitute one of the essential factors of the quality of life for people with musculoskeletal dysfunction. Rehabilitation of such patients is an ongoing […]
Parallel Systems of Springs of Various Stiffness
In upholstered furniture, there are several construction solutions used for spring units, which constitute the main spring layer. Biconical springs and cylindrical springs (Fig. 8.33a, b) are used in many designs of mattresses. However, the latest solutions tend towards a serial or parallel connection of springs of varying geometry (Fig. 8.33c). Such a compilation of […]
Modelling of Stiffness of Conical Springs
The variable stiffness of the spring during operational loads should ensure high softness of the system at surface loads and significant stiffness when exposed to concentrated forces or forces of high intensity. For such exploitation conditions, a construction minimum is a biconical spring consisting of two conical springs differing in stiffness coefficients, but made from […]
Stiffness of Conical Springs
For biconical springs, which are applied in the Bonnell-type spring systems, the torsion moment Ms is not a value dependent only on the load, but a function of the changing length of the coil radius Ms = f(R). This radius depends on the angle of the unstretching of the spring a, R = f(a) (Fig. […]
Stiffness of Upholstery Springs
8.4.1 Stiffness of Cylindrical Springs The comfort of the use of upholstered furniture is connected, to a large extent, with the softness of the spring layer. Its quality can be adjusted by choosing or designing the appropriate springs and spring units. First, let us imagine a cylindrical spring stretched with two forces P acting in […]