Fixing device and image forming apparatus

1. A fixing device, comprising:

a first rotating body;

a second rotating body configured to form a nip in combination with the first rotating body;

a frame configured to support the first rotating body and the second rotating body, the frame having an opening through which a sheet conveyed toward the nip passes;

a shutter rotatable about a first axis between a closed position in which the shutter covers the opening and an open position in which the shutter uncovers the opening;

a pressure arm configured to press the first rotating body against the second rotating body;

a cam supported by a shaft and configured to push the pressure arm, the cam and the shaft being rotatable about a second axis;

a shutter arm connected to the shutter and configured to rotate about the shaft independent of the cam, to cause the shutter to rotate between the closed position and the open position; and

an arm cam configured to rotate about the shaft to push the shutter arm at a position offset from the second axis and cause the shutter arm to rotate about the second axis.

2. The fixing device according to claim 1 ,

wherein the arm cam includes a hollow cylindrical portion in which the shaft is received, and

wherein the shutter arm has a hole in which the hollow cylindrical portion is received.

3. The fixing device according to claim 1 ,

wherein the shutter includes a protrusion, and

wherein the shutter arm has an elongated hole in which the protrusion is received.

4. The fixing device according to claim 3 ,

wherein when the shutter is in the closed position, the protrusion of the shutter is located on a side of a plane containing the first axis and the second axis, on which the nip is located, and

wherein when the shutter is in the open position, the protrusion of the shutter is located on another side of the plane, opposite to the side on which the nip is located.

5. The fixing device according to claim 1 , further comprising a shaft that supports the cam, the shaft being rotatable about the second axis,

wherein the frame comprises:

a first frame configured to support the first rotating body and the second rotating body; and

a second frame attached to the first frame and configured to hold the shaft in combination with the first frame, and

wherein the shutter is supported by the second frame via a boss.

6. The fixing device according to claim 5 , wherein the boss is located on an upstream side of the nip in a direction of conveyance of the sheet.

7. The fixing device according to claim 1 , wherein the second axis is located on a downstream side of the nip in a direction of conveyance of the sheet.

8. The fixing device according to claim 1 ,

wherein the pressure arm comprises a first pressure arm and a second pressure arm located at opposite ends of the frame apart from each other in a longitudinal direction, and

wherein the first pressure arm is located between the shutter arm and the second pressure arm in the longitudinal direction.

9. The fixing device according to claim 1 , further comprising a heater comprising a substrate and a resistance heating element disposed on the substrate,

wherein the first rotating body is an endless belt heated by the heater and configured to rotate around the heater.

10. The fixing device according to claim 9 , further comprising a connector configured to provide electricity to the heater,

wherein the heater comprises a power-supply terminal on at least one of two opposite ends of the substrate located apart from each other in the longitudinal direction, the power-supply terminal being supplied with electricity from the connector,

wherein the second rotating body is a pressure roller rotatable about a third axis, and

wherein the shutter arm is located on a side of the connector opposite to another side of the connector on which the third axis is located.

11. The fixing device according to claim 1 , further comprising a spring contactable with the shutter arm,

wherein the arm cam is configured to push the shutter arm via the spring to locate the shutter in the closed position.

12. The fixing device according to claim 11 , wherein the arm cam is configured to contact the shutter arm to locate the shutter in the open position.

13. An image forming apparatus, comprising:

a main housing;

a unit installable into and removable from the main housing; and

the fixing device according to claim 1 ,

wherein the arm cam rotates about the second axis when the unit is installed into or removed from the main housing, and

wherein the shutter arm causes the shutter to rotate from the closed position to the open position when the unit is installed into the main housing, and causes the shutter to rotate from the open position to the closed position when the unit is removed from the main housing.

14. The image forming apparatus according to claim 13 , further comprising a connection link connected to the arm cam, the connection link being movable relative to the main housing and configured move when the unit being installed into the main housing contacts the connection link.

15. The image forming apparatus according to claim 14 , further comprising a lock configured to keep the shutter in the open position or in the closed position, the lock comprising a lock arm configured to contact the connection link, and a lock spring that biases the lock arm toward the connection link,

wherein the connection link includes a link protrusion provided on a side thereof facing the lock.

16. The image forming apparatus according to claim 14 ,

wherein the unit comprises a unit shaft configured to contact the connection link when the unit is being installed into the main housing, and

wherein the main housing includes a guide rail configured to guide the unit shaft.

17. The image forming apparatus according to claim 14 , wherein the unit comprises a photosensitive drum.