Torque limiting mechanism of bendable portion control device for an endoscope

1. A bendable portion control device for an endoscope including a control portion and an insertion portion extending from the control portion, the insertion portion having a distal end bendable portion provided at a distal end of the insertion portion, the bendable portion control device comprising:

a control wire, a distal end of which is fixed to the distal end bendable portion, and the control wire extending to the control portion through the insertion portion;

a manually-rotatable control knob provided on the control portion, the manually-rotatable control knob configured to pull the control wire so as to bend the distal bendable portion;

an operating force transmission mechanism that transmits a torque exerted on the control knob to the distal end bendable portion via the control wire, the operating force transmission mechanism having a grooved rotational plate and a seating plate, the grooved rotational plate and the seating plate being relatively rotatable with respect to each other, the seating plate being connected to one of the control knob and a proximal end of the control wire, and the grooved rotational plate being connected to the other of the control knob and the proximal end of the control wire,

the grooved rotational plate having at least one engaging groove formed in one of the outer and inner peripheral surfaces of the grooved rotational plate,

at least one spring engaging arm having an end fixed to the seating plate and positioned along the one of the outer and inner peripheral surfaces of the grooved rotational plate in which the at least one engaging groove is formed, the at least one spring engaging arm comprising a resilient material, wherein the at least one spring engaging arm is rotatable relative to the grooved rotational plate,

at least one engaging lug provided on and projecting from a free end of the at least one spring engaging arm so as to engage and disengage the at least one engaging groove;

a torque limiting mechanism defined by the interaction between the grooved rotational plate and the at least one spring engaging arm,

wherein the at least one engaging lug is positioned within the at least one engaging groove when an applied torque is one of equal to and less than a predetermined torque,

wherein the at least one spring engaging arm resiliently deforms such that the at least one engaging lug disengages the at least one engaging groove when the applied torque exceeds the predetermined torque, and

wherein the at least one spring engaging arm comprises first and second spring engaging arms which are positioned along the one of the outer and inner peripheral surfaces of the grooved rotational plate so as to be resiliently pressed against the one of the outer and the inner peripheral surfaces of the grooved rotational plate,

the first and second spring engaging arms are integrally formed so as to provide a substantially C-shaped ring,

the at least one lug is provided on the first spring engaging arm; and

a pressure projection provided on the second spring engaging arm, wherein the pressure projection slidably contacts the grooved rotational plate so as not to be positioned within a corresponding groove when that at least one spring engaging arm is engaged with the at least one engaging groove.

2. The bendable portion control device according to claim 1 , wherein the torque limiting mechanism is provided within an internal space of the control knob.

3. The bendable portion control device according to claim 1 , wherein the grooved rotational plate is provided on a member to which the control wire is connected,

wherein the at least one engaging groove is formed on an outer peripheral surface of the grooved rotational plate, and

wherein the at least one spring engaging arm is provided on another member connected to the control knob.

4. The bendable portion control device according to claim 1 , wherein, in a state where the at least one engaging lug is disengaged from the at least one engaging groove, the at least one spring engaging arm is in sliding contact with the grooved rotational plate to produce a frictional resistance between the at least one spring engaging arm and the grooved rotational plate due to resiliency of the at least one spring engaging arm when a relative rotation occurs between the grooved rotational plate and the at least one spring engaging arm.

5. The bendable portion control device according to claim 1 , wherein the torque limiting mechanism lies in a plane orthogonal to an axis of rotation of the control knob.

6. The bendable portion control device according to claim 1 , wherein the operating force transmission mechanism comprises:

a cylindrical shaft fixed to a stationary member of the control portion to extend upright coaxially with an axis of the control knob;

a tubular drive shaft positioned around the cylindrical shaft to be rotatable on an axis of the cylindrical shaft; and

a pulley fixed to the tubular drive shaft, the proximal end of the control wire being fixed to the pulley,

wherein the grooved rotational plate is fixed to the tubular drive shaft.