Image forming apparatus and method for detecting separated state of transfer member

Abstract

An image forming apparatus includes a secondary transfer roller that becomes a pressed state to make an intermediate transfer belt perform a transfer process and can move between the pressed state and a separated state, a press and separation driving device for driving the secondary transfer roller to become the pressed state and the separated state, a press and separation detecting device for detecting a pressed or separated state, and a voltage applying portion for applying a voltage between the intermediate transfer belt and the secondary transfer roller. The press and separation detecting device includes a resistor for detecting a current and a determination portion for determining a pressed or separated state in accordance with the detected current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic structure of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a structure of a press and separation driving device that is in a separated state.

FIG. 3 is a diagram showing an example of a structure of the press and separation driving device that is in a pressed state.

FIG. 4 is a diagram showing a circuit of a press and separation detecting device according to a first embodiment of the present invention.

FIG. 5 is a diagram showing a circuit of a press and separation detecting device that is a variation of the first embodiment.

FIG. 6 is a timing chart for explaining a press and separation detecting operation.

FIGS. 7A and 7B are diagrams showing examples of a change of a current value in transition to the separated state.

FIG. 8 is a diagram showing a relationship between current that flows in an intermediate transfer belt and a NIP width.

FIG. 9 is a diagram showing characteristics of toner quantity detected by an IDC sensor.

FIG. 10 is a diagram showing an example of a toner patch.

FIG. 11 is a flowchart showing an example of a general control operation of the press and separation detecting device.

FIG. 12 is a diagram showing a circuit of a press and separation detecting device according to a second embodiment of the present invention.

Claims

1. An image forming apparatus having a structure in which a toner image formed in an electrophotographic process is transferred from an image carrier to a member to be transferred, the apparatus comprising: a transfer member that becomes a pressed state with respect to the image carrier to make the same perform a transfer process and can move between the pressed state and a separated state;a press and separation driving device for driving the transfer member to become the pressed state and the separated state;a press and separation detecting device for detecting the pressed state and the separated state of the transfer member; anda voltage applying portion for applying a voltage between the image carrier and the transfer member, whereinthe press and separation detecting device includes a current detecting portion for detecting a current that flows between the image carrier and the transfer member when the voltage is applied by the voltage applying portion, and a determination portion for determining the pressed state and the separated state of the transfer member in accordance with the current detected by the current detecting portion.

2. The image forming apparatus according to claim 1, wherein the determination portion determines the pressed state when a value of the current is larger than a predetermined value and determines the separated state when the value of the current is smaller than the predetermined value.

3. The image forming apparatus according to claim 1, wherein the determination portion determines the separated state when a gradient of decrease in the value of the current during a predetermined time period is larger than a predetermined value.

4. The image forming apparatus according to claim 1, wherein the press and separation driving device drives the transfer member again to become the separated state if the press and separation detecting device does not detect the separated state when a predetermined time period has passed after the press and separation driving device drove the transfer member to become the separated state.

5. The image forming apparatus according to claim 1, wherein a signal indicating an abnormal state is output if the press and separation detecting device does not detect the separated state even though a predetermined time period has passed after the press and separation driving device drove the transfer member to become the separated state or even though the press and separation driving device drove the transfer member to become the separated state a predetermined number of times.

6. The image forming apparatus according to claim 1, wherein after the press and separation driving device drives the transfer member to become the separated state, a control of a NIP width of the image carrier and the transfer member is performed in accordance with a value of the current detected by the current detecting portion.

7. An image forming apparatus having a structure in which a toner image formed in an electrophotographic process is transferred from an image carrier to a member to be transferred, the apparatus comprising: a transfer member that becomes a pressed state with respect to the image carrier to make the same perform a transfer process and can move between the pressed state and a separated state;a press and separation driving device for driving the transfer member to become the pressed state and the separated state;a press and separation detecting device for detecting the pressed state and the separated state of the transfer member; anda voltage applying portion for applying a voltage to the transfer member under a condition of constant current, whereinthe press and separation detecting device includes a voltage detection portion for detecting a voltage that is applied by the voltage applying portion, and a determination portion for determining the pressed state and the separated state of the transfer member in accordance with the voltage detected by the voltage detection portion.

8. The image forming apparatus according to claim 7, wherein the determination portion determines the separated state when a value of the voltage detected by the voltage detection portion becomes larger than a predetermined value after the press and separation driving device drove the transfer member to become the separated state.

9. The image forming apparatus according to claim 7, wherein the determination portion makes the press and separation driving device drive the transfer member to become the separated state again if the press and separation detecting device does not detect the separated state when a predetermined time period has passed after the press and separation driving device drove the transfer member to become the separated state.

10. The image forming apparatus according to claim 7, wherein a signal indicating an abnormal state is output if the press and separation detecting device does not detect the separated state even though a predetermined time period has passed after the press and separation driving device drove the transfer member to become the separated state or even though the press and separation driving device drove the transfer member to become the separated state a predetermined number of times.

11. A method for detecting a separated state of a transfer member that becomes a pressed state with respect to an image carrier and a voltage is applied between the transfer member and the image carrier for performing a transfer process in an image forming apparatus having a structure in which a toner image formed in an electrophotographic process is transferred from the image carrier to the member to be transferred, the method comprising the steps of: detecting a current that flows between the image carrier and the transfer member when the voltage is applied; anddetecting the separated state when the detected current becomes smaller than a predetermined value or a gradient of decrease in a value of the current becomes larger than a predetermined value.

12. A method for detecting a separated state of a transfer member that becomes a pressed state with respect to an image carrier and a voltage is applied under a condition of constant current in an image forming apparatus having a structure in which a toner image formed in an electrophotographic process is transferred from the image carrier to the member to be transferred, the method comprising the steps of: detecting a voltage that is applied to the transfer member; anddetecting the separated state when the detected voltage becomes larger than a predetermined value.