Image forming apparatus that uses temperature values to control transfer voltage applied to transfer unit of the apparatus

1. An image forming apparatus comprising:

a transfer unit having a conduct we roller member formed with a conductive elastic body on an outer peripheral surface of a shaft of the conductive roller member for transferring, to a recording medium, development images formed on an image carrier based on a transfer voltage applied thereto;

a voltage application unit for applying the transfer voltage to the transfer unit;

a voltage control unit controlling the transfer voltage to be applied from the voltage application unit to the transfer unit;

a temperature measuring unit measuring shaft temperature of the conductive roller member; and

a surrounding temperature obtaining unit for obtaining an apparatus surrounding temperature,

wherein the voltage control unit controls the transfer voltage applied to the transfer unit based on the shaft temperature measured with the temperature measuring unit and based on the apparatus surrounding temperature obtained from the surrounding temperature obtaining unit.

2. An image forming apparatus comprising:

a transfer unit having a conductive roller member formed with a conductive elastic body on an outer peripheral surface of a shaft of the conductive roller member for transferring, to a recording medium, development images formed on an image carrier based on a transfer voltage applied thereto;

a voltage application unit for applying the transfer voltage to the transfer unit;

a voltage control unit controlling the transfer voltage to be applied from the voltage application unit to the transfer unit; and

a temperature measuring unit measuring shaft temperature of the conductive roller member,

wherein the voltage control unit controls the transfer voltage applied to the transfer unit based on the shaft temperature measured with the temperature measuring unit, and

wherein the voltage control unit changes formulae used for presumption, of a temperature value of the transfer unit between a period during printing operation and a period stopping printing operation in use of the shaft temperature with the temperature measuring unit.

3. The image forming apparatus according to claim 1 ,

wherein, upon presuming the temperature of the transfer unit based on the shaft temperature measured at the temperature measuring unit and based on the apparatus surrounding temperature obtained from the surrounding temperature obtaining unit, the voltage control unit controls the transfer voltage applied to the transfer unit based on the presumed temperature of the transfer unit.

4. The image forming apparatus according to claim 3 , wherein the voltage control unit changes coefficient used for formulae for presumption of the temperature of the transfer unit according to printing speed.

5. The image forming apparatus according to claim 3 , further comprising a memory unit memorizing the shaft temperature measured, with the temperature measuring unit at a time of the end of the previous image forming operation; and

a time measuring unit counting time lapse from the end of the previous image forming operation to resuming of the image forming operation,

wherein, upon presuming the temperature of the transfer unit, based on the shaft temperature measured at the temperature measuring unit, based on the apparatus surrounding temperature obtained from the surrounding temperature obtaining unit, and based on the time lapse from, the end of the previous image forming operation to resuming of the image forming operation, the voltage control unit controls the transfer voltage applied to the transfer unit based on the presumed temperature of the transfer unit.

6. The image forming apparatus according to claim 1 , wherein the transfer unit is a type of an intermediate transfer unit.