Patent ID: 7350221

Claim:
A height adjustment device comprising: a first chassis having an adjustment hole, an adjustment screw that stands when threadedly engaged with the adjustment hole in the first chassis, a second chassis locked by the adjustment screw so as to have a preset separation distance from the first chassis, and biasing means for biasing the first chassis and the second chassis in the direction of attaining separation therebetween, wherein the adjustment screw has a tip portion for forming a female thread in the adjustment hole when rotated and inserted into the adjustment hole, a threaded portion having a male thread threadedly engaged with the female thread formed by the tip portion, and a head portion for locking the second chassis against the direction of biasing by the biasing means, in a nearly linear state, said adjustment hole in the first chassis has a small diameter portion in which the female thread is formed and a large diameter portion having a diameter larger than the outside diameter of the tip portion of the adjustment screw, and the adjustment screw being inserted from the side of the small diameter portion to the side of the large diameter portion, a distance between one end of the threaded portion of the adjustment screw and the other end of the threaded portion is made larger than the sum of the length of the small diameter portion of the adjustment hole in which the female thread is formed, a face-to-face distance between the chassis-side end of the small diameter portion of the first chassis and the second chassis, and a thickness of the second chassis, and the threaded portion of the adjustment screw has the same pitch as that of the tip portion and is provided with thread ridges, and said tip portion has a tapping screw for forming a female thread in said adjustment hole and is formed of thread ridges having a diameter larger than that of the threaded portion.