Fixing apparatus
A fixing apparatus to fix a toner image on a recording material includes a heating unit, a pressure member, a support member, a pressing mechanism, and an insulating member. The heating unit includes a heating member having a conductive layer, a coil having a helical structure portion having a helical axis substantially parallel to a longitudinal direction of the heating member, and a core to induce magnetic lines of force of an alternating magnetic field generated by the coil. The pressure member is in contact with a heating member outer circumferential surface and forms a nip portion between the pressure member and the heating member. The insulating member electrically interrupts a conductive path to prevent formation of the conductive path that is in a loop-shape surrounding the coil and passing through the support member and the pressing mechanism when viewed in an axial direction of the helical axis.
1 . A fixing apparatus to fix a toner image on a recording material, the fixing apparatus comprising:
a heating unit, the heating unit includes
a cylindrical belt contacting the recording material, the cylindrical belt has a conductive layer,
a coil disposed in an inner space of the cylindrical belt, the coil includes a helical structure portion having a helical axis substantially parallel to a longitudinal direction of the cylindrical belt, and the coil is configured to generate an alternating magnetic field to generate an induced current in the conductive layer,
a core disposed in an inner space of the helical structure portion and configured to guide magnetic lines of force of the alternating magnetic field,
a stay disposed in the inner space of the cylindrical belt and configured to transmit a pressing force to an entirety of the heating unit in the longitudinal direction of the belt, and
a flange disposed at a position facing an end surface of the cylindrical belt and configured to guide the belt, the flange is positioned relative to the stay;
a pressure roller configured to be in contact with an outer circumferential surface of the cylindrical belt and form a nip portion between the pressure roller and the cylindrical belt to nip and convey the recording material;
a frame made of metal, the frame includes a side plate formed with a U-shaped opening for supporting the heating unit and the pressure roller;
a support shaft fitted in a fitting hole of the side plate and fitting holes of a pressing plate so that the pressing plate is supported so as to be pivotable about the support shaft with respect to the side plate, the pressing plate being configured to press the flange toward the pressure roller to form the nip portion;
a spring configured to apply the pressing force to the pressing plate in a compression direction of the spring;
a movable plate arranged at the side plate and configured to move relative to the side plate in the compression direction of the spring;
a movable shaft fixed to the movable plate;
a movable shaft sliding member fixed to the side plate and having a long hole extending in the compression direction of the spring, the movable shaft being received in and slidable along the long hole of the movable shaft sliding member;
a movable plate reinforcement member fixed to the movable plate and having a screw thread;
an adjustment screw threaded in the movable plate reinforcement member and configured to adjust a compression amount of the spring so as to adjust the pressing force applied to the pressing plate;
a side-plate sliding member attached to the movable plate, the side-plate sliding member having a cam sliding portion and a side-plate sliding portion, the cam sliding portion being formed as a long hole extending in the compression direction of the spring and being slidable on a cam, and the side-plate sliding portion being slidable on a plane of the side plate; and
a cam fixed to a cam shaft supported by the side plate and configured to contact the cam sliding portion of the movable plate and a portion of the pressing plate so that rotation of the cam changes a force length of the spring and a position of the pressing plate between a pressing state and a pressing release state,
wherein the movable shaft sliding member and the side-plate sliding member are made of an electrical insulating material so as to interrupt a looping conductive path that would otherwise pass through the side plate, the support shaft, the pressing plate, the spring, a spacer, the adjustment screw, the movable plate reinforcement member, and the movable plate, when viewed in the axial direction of the helical axis.
2 . The fixing apparatus according to claim 1 , wherein the spacer is disposed on a side of the spring opposite to a side on where the pressing plate is provided in a pressing force apply direction of the spring, at a position receiving a reaction force of the pressing force of the spring, and configured to regulate an axial position of the spring.
3 . The fixing apparatus according to claim 1 ,
wherein the cam is made of an electric insulator so as to interrupt a looping conductive path that would otherwise pass through the side plate, the support shaft, the pressing plate, the spring, the spacer, the adjustment screw, the movable plate reinforcement member, the movable plate, and the cam, when viewed in the axial direction of the helical axis.