Image forming apparatus including sheet passing detection

1. An image forming apparatus comprising:

a sheet feeding device performing a sheet feeding operation for feeding a sheet in a predetermined conveyance direction;

an image forming part disposed on a downstream side of the sheet feeding device in the conveyance direction and forming a toner image on the sheet fed by the sheet feeding device;

a fixing device disposed on a downstream side of the image forming part in the conveyance direction, and including a fixing member heated by a heating source and a pressing member coming into contact with the fixing member to form a pressing area between the fixing member and the pressing member, the fixing member and the pressing member being rotated to fix the image on the sheet as the sheet is passed through the pressing area after passing through the image forming part;

a conveyance path along which the sheet is conveyed from the sheet feeding device to the fixing device through the image forming part;

a first sensor disposed on the conveyance path on a downstream side of the fixing device in the conveyance direction and detecting the sheet passed along the conveyance path; and

a second sensor disposed on the conveyance path on an upstream side of the fixing device in the conveyance direction and detecting the sheet passed along the conveyance path; wherein

the fixing device stops a driving of the heating source and stops a rotation of the fixing member when the first sensor does not detect the sheet passing properly, and

the fixing device stops the driving of the heating source and stops the rotation of the fixing member after a predetermined period when the second sensor does not detect the sheet passing properly,

the predetermined period is set to be longer as a number of printed sheets in a continuous printing operation until the second sensor does not detect the sheet passing properly increases.

2. The image forming apparatus according to claim 1 , comprising an informing part informing that a sheet conveyance failure occurs, wherein

when the second sensor does not detect the sheet passing properly, after the predetermined period, the informing part informs that the sheet conveyance failure occurs.

3. The image forming apparatus according to claim 1 , wherein

the fixing member is an endless fixing belt,

the heating source is a halogen heater disposed in a hollow space of the fixing member,

the fixing device further includes a pushing member pushing the fixing member to the pressing member with lubricant from an inner circumferential side of the fixing member at the pressing area, and

the fixing member is driven by a rotation of the pressing member to be rotated.

4. The image forming apparatus according to claim 1 , further comprising a resist rollers pair disposed on the conveyance path between the sheet feeding device and the image forming part, wherein

the second sensor is disposed on the conveyance path between the sheet feeding device and the resist rollers pair.

5. The image forming apparatus according to claim 4 , wherein

the second sensor is a photo sensor which sends an ON signal when detecting the sheet and sends an OFF signal when detecting a separation of the sheet, and

the fixing device stops the driving of the heating source and stops the rotation of the fixing member after the predetermined period in a case where the second sensor does not send the ON signal after a certain period since the sheet feeding device starts a sheet feeding operation and in a case where the second sensor does not send the OFF signal after a certain period since the resist rollers pair starts to be rotated at a suitable timing after the second sensor sends the ON signal.

6. The image forming apparatus according to claim 1 , further comprising a fan cooling the fixing member and the pressing member, wherein

the fan cools the fixing member and the pressing member when the first sensor and the second sensor do not detect the sheet passing properly.