Sit-standing posture and chairless chair. A prototype without ground contact.

Abstract

Currently there are many types of wearable devices for unconventional sitting. The devices are named suggestively: wearable chairless chair. What all these products have in common is an additional support behind the heel. The additional support, a ground contact behind the heel, appears to add more stability and at the same time increases the complexity of the product, the weight and the difficulty of wearing it.The research assumes that there is no need for additional support nor ground contact. The working method consisted of analyzing products on the market. The analysis was followed by understanding the functioning and the biomechanical cause for the existence of the posterior support. The analysis was carried out by relating the human silhouette, its body volumes and geometry, to the shape and structure of the devices. We focused on the side view because it is the one that gives the asymmetric behavior of the body volumes. In the biomechanical analysis we kept the premises of locating the center of mass, of spatial summation of the partial centers of mass (the head, the trunk and the limbs) as well as the reference to the ground support polygon of the soles. Biomechanical and static analysis was followed by the identification and isolation of that component of body geometry responsible for the need of posterior support. The analysis was then repeated in its absence. It was necessary to correct the geometry of the body and change the degree of flexion of the knees and ankles. The verification of the hypothesis has been achieved by developing a device that corresponds to a body geometry, does not provide posterior support and at the same time eliminates orthostatic muscle stress. Tests were carried out with primitive mock-ups and prototypes, with briefly articulated parts that meet the condition of being wearable through permanent contact with the leg and the thigh. The results were encouraging from the point of view of stability but were unsatisfactory from the point of view of the comfort offered by the primitive prototypes. Refinement of the prototype was achieved by developing the design of the thigh and leg interface components as well as the design of the flexion locking subsystem. Of particular concern was the contact between the product and the surface of the thigh and calf. Refined in this way the prototype unquestionably preserved the stability of the human subject and presented an improvement in comfort criteria.In conclusion, the research confirms the hypothesis. The no ground contact prototype allows a posture in which orthostatic stress is avoided, with good stability and with enough containment to be wearable.