Patent ID: 7530143

Claim:
A hinge mechanism comprising: a main shaft having a first shaft end and an opposite second shaft end, the main shaft being provided with a stopping mechanism at the first shaft end; a cylindrical torsion spring surrounding the main shaft, the torsion spring comprising a coiled sheet forming a plurality of loops and having a substantially hollow interior and an exterior, wherein the plurality of loops are substantially concentric; and a housing being cylinder-shaped and hollow, the housing having a first housing end and a second housing end, the first housing end thereof being open and sized to receive the torsion spring therein, the second housing end having a shaft-receiving opening sized and configured to receive the main shaft therein; wherein the torsion spring is inserted into the housing, the main shaft is inserted into the torsion spring, rotatable with the interior of the torsion spring, and received in the second opening of the housing, the housing is rotatable with the exterior of the torsion spring so that the housing is rotatable relative to the main shaft and the stopping mechanism prevents the main shaft from becoming disassembled from the housing.