Bent state holding mechanism of an endoscope

1. A bent state holding mechanism for an endoscope which includes a control portion and an insertion portion extending from said control portion, said insertion portion having a bendable portion at a distal end thereof, comprising:

a bendable portion control mechanism provided on said control portion, which is operated to bend said bendable portion, and

at least two frictional resistance producing members which rotate relative to each other upon operation of said bendable portion control mechanism, to exert a frictional resistance for holding said bendable portion at any operated position,

wherein said two frictional resistance producing members include a radial plate spring made of resilient metal which includes a ring portion and a plurality of radial projections which project radially outwards from an outer periphery of said ring portion,

wherein said radial plate spring rotates with said bendable portion control mechanism about an axis of rotation; and

an annular friction member having a pressure surface which is brought to be pressed obliquely against flat surfaces of said plurality of radial projections,

wherein said annular friction member is engaged with a fixing member of said control portion to be prevented from rotating relative to said control portion.

2. The bent state holding mechanism according to claim 1 , wherein said radial plate spring is formed in a flat shape as a whole, and

wherein said pressure surface of said annular friction member is formed in an umbrella-like beveled shape.

3. The bent state holding mechanism according to claim 1 , wherein said radial plate spring is formed in an umbrella-like beveled shape as a whole, and

wherein said pressure surface of said annular friction member is formed in a flat shape.

4. The bent state holding mechanism according to claim 1 , wherein at least edges of said plurality of radial projections which are pressed against said pressure surface of said annular friction member are chamfered.

5. The bent state holding mechanism according to claim 1 , further comprising a bent state holding device which is operated to switch between an engaged state in which said plurality of radial projections and said pressure surface of said annular friction member are pressed against each other and a disengaged state in which said plurality of radial projections and said pressure surface of said annular friction member are disengaged from each other.

6. The bent state holding mechanism according to claim 5 , wherein the amount of pressure contact between said plurality of radial projections and said annular friction member can be varied by an operation of said bent state holding device.

7. The bent state holding mechanism according to claim 6 , wherein as said amount of pressure contact between said plurality of radial projections and said annular friction member increases, said plurality of radial projections are resiliently deformed by a greater amount while the area on portions of said plurality of radial projections which are pressed against said pressure surface of said annular friction member gradually increases in radially inward directions from radially outermost portions of said plurality of radial projections.

8. The bent state holding mechanism according to claim 1 , wherein said bendable portion control mechanism comprises a bendable portion control knob for controlling said bendable portion, said bent state holding mechanism being installed in an internal space of said bendable portion control knob.

9. The bent state holding mechanism according to claim 1 , wherein said annular friction member comprises a metal disk.

10. The bent state holding mechanism according to claim 1 , wherein said endoscope includes a control wire, a distal end of which is fixed to said bendable portion and which is extended to said control portion through said insertion portion.

11. The bent state holding mechanism according to claim 8 , wherein said bendable portion control device comprises a torque limiting mechanism for allowing a torque exerted on said bendable portion control mechanism to be transmitted to said bendable portion when said torque is equal to or less than a predetermined torque, and for preventing said torque from being transmitted to said bendable portion when said torque exceeds said predetermined torque, said torque limiting mechanism being installed in an internal space of said bendable portion control knob.

12. The bent state holding mechanism according to claim 5 , wherein said bendable portion control mechanism comprises a bendable portion control knob for controlling said bendable portion, and

wherein said bent state holding device includes a bent state holding knob positioned so as to be capable of being operated to rotate coaxially with said bendable portion control knob.

13. The bent state holding mechanism according to claim 6 , wherein when an amount of friction between said plurality of radial projections and said annular friction member is increasing, an area of said pressure surface becomes larger, and an average turning radius becomes smaller.