Patent ID: 8366560

Claim:
A coupling device for coupling a rotating shaft and a rotating member, comprising: a first flexible member and a second flexible member that are vertically connected to the rotating shaft having a variable length that can be varied in an inward and outward direction with respect to the rotating shaft; elastic members that are connected to the first flexible member and the second flexible member respectively, and cause the first flexible member and the second flexible member to receive an elastic force in the outward direction with respect to the rotating shaft; and a cam member that is rotatably connected to the rotating shaft and delivering a rotating force of the rotating shaft to the rotating member, wherein the cam member is formed with a first through-hole and a second through-hole passing through top and bottom surfaces of the cam member at opposite sides with respect to the rotating shaft; wherein the first flexible member and the second flexible member are formed symmetrically with respect to the rotating shaft and inserted into the first through-hole and the second through-hole respectively so that the first flexible member and the second flexible member abut inner surfaces of the first through-hole and the second through-hole due to the elastic forces of the elastic members; and wherein a first initial-position portion configured to position the first flexible member at an initial stage, and a displaced-position portion having a constant diameter smaller than the initial-position portion about the rotating shaft are formed on the inner surface of the first through-hole; wherein a second initial-position portion configured to position the second flexible member and a return-position portion having a radius decreasing with increase in distance from the second initial-position portion are formed on the inner surface of the second through-hole; wherein the first flexible member rotates free of the cam member up until an angular displacement of the first flexible member equals an arc length of the first through-hole when an external force equal to or greater than a limit torque of the coupling device is applied to the rotating member.