Patent ID: 8495796

Claim:
An opening-and-closing mechanism comprising: a first supporting member and a second supporting member disposed so as to be capable of relative rotation around a rotary axis; a plurality of protruding portions provided on the first supporting member; and a plurality of depressed portions provided on the second supporting member and engaged with the plurality of protruding portions, wherein at least some of the plurality of depressed portions have different lengths in a circumferential direction centered at the rotary axis and different positions in a radial direction than others of the plurality of depressed portions; wherein, when the first supporting member and the second supporting member are in a plurality of predetermined relative alignments, a predetermined amount of the plurality of protruding portions and the same amount of the plurality of depressed portions are engaged; wherein forces required for disengaging the protruding portions and the depressed portions by rotating at least one of the first supporting member and second supporting member differ in a first rotation direction and a second rotation direction; and wherein the positions and the lengths in the circumferential direction of the depressed portions are set so that the number of protruding portions and depressed portions that are simultaneously disengaged differs depending on the relative rotating direction.