Patent ID: 7322654

Claim:
A bracket angle adjustment mechanism comprising: a first bracket including an external-tooth gear; a second bracket including an internal-tooth gear which has a larger number of internal teeth than that of external teeth of the external-tooth gear; a pair of wedge members fitted in an eccentric space which is defined between a large-diameter hole formed in a central region of the external-tooth gear and a small-diameter shank constituting a central portion of the internal-tooth gear, in a state when the external-tooth gear and the internal-tooth gear are partly engaged with one another; a spring member applying a biasing force to each of the pair of wedge members in a wedging direction; and a wedged-state release member disposed between respective wedging-directional leading edges of the pair of wedge members, the wedged-state release member being operable, when rotated by a control shaft associated therewith, to move the pair of wedge members together with the spring member in a wedged-state release direction around the eccentric space, whereby the small-diameter shank is eccentrically moved relative to the large-diameter hole to allow an engagement position of the internal-tooth gear relative to the external-tooth gear to be changed so as to adjust an angle of the second bracket relative to the first bracket, wherein each of the external teeth of the external-tooth gear has two arc shapes in an addendum region between a reference circle and a tip circle of the external-tooth gear, each of the two arc shapes having a center defined by a point on the reference circle and crossing a circumference of the reference circle, allowing a force for rotating the control shaft to be reduced, and each of the internal teeth of the internal-tooth gear has a shape free of interference with the addendum region in a corresponding one of the external teeth, each of the internal teeth of the internal-tooth gear having two arc shapes in a dedendum region between a reference circle and a root circle of the internal-tooth gear, each of the two arc shapes having a center defined by a point on the reference circle of the internal-tooth gear and crossing a circumference of the reference circle, a turning force of the external tooth acting on the internal tooth at a right angle in a rotation direction at an engagement point on both of the reference circles.