JP4867461B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a copying machine or a printer that forms a toner image on a recording medium by electrophotography.

  In general, in a color image forming apparatus using electrophotography, toner images of Y (yellow), M (magenta), C (cyan), and K (black) formed on a photosensitive member are primarily transferred onto an intermediate transfer member. The synthesized toner image is secondarily transferred onto a recording medium. The secondary transfer roller for the secondary transfer is arranged so as to be capable of being pressed / separated with respect to the intermediate transfer member, and it has been detected by a contact-type sensor whether it is in a pressure contact state or a separation state.

  On the other hand, in terms of cost, it is preferable to omit the contact-type sensor. In this case, a weak current is supplied to the secondary transfer roller from a power source for applying a bias voltage to the secondary transfer roller, and the pressure contact is performed. It is conceivable to detect the press contact / separation based on the voltage difference between the state and the separated state.

  However, in the method of detecting the pressure contact state and the separation state based on the voltage difference when a weak current is applied to the secondary transfer roller, when condensation occurs in the image forming apparatus, the current supplied to the secondary transfer roller is Electricity is leaked due to condensation, and a voltage difference between the pressure contact state and the separated state cannot be detected, and it cannot be determined whether the pressure contact state or the separated state.

For example, Patent Documents 1 and 2 describe methods for detecting dew condensation in the image forming apparatus. In Patent Document 1, the dew condensation state is determined based on the voltage or current of the intermediate transfer belt in which the temperature dependence of the electrical resistance is high. In Patent Document 2, the dew condensation state is determined based on whether the bias value applied to the charging roller decreases or the SOS signal (vertical synchronization signal) becomes an error.
Japanese Patent Laid-Open No. 9-311560 JP 9-325538 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of reliably detecting a pressed state and a separated state of a secondary transfer roller with respect to an image carrier with a simple structure.

  Another object of the present invention is to achieve the above object and to determine the dew condensation state, and to form an image that can detect the pressure contact state and the separation state of the secondary transfer roller to the image carrier even in the dew condensation state. To provide an apparatus.

In order to achieve the above object, the present invention provides an image forming apparatus for forming a toner image on a recording medium by electrophotography.
A secondary transfer roller for secondary transfer of the toner image primarily transferred onto the image carrier onto the recording medium;
Contact / separation means for moving the secondary transfer roller from the pressure contact state to the separation state and from the separation state to the pressure contact state with respect to the image carrier;
Bias voltage applying means for applying a bias voltage to the secondary transfer roller;
Detecting means for detecting a voltage value applied to the secondary transfer roller;
Whether a weak current is supplied to the secondary transfer roller by the bias voltage application means, and whether the secondary transfer roller is in a pressure contact state or a separated state based on the voltage value of the secondary transfer roller at the time of the weak current supply And when the voltage value at the time of supplying the weak current is not a predetermined value of either the case where the pressure state is predicted to be the pressed state or the case where the voltage value is predicted to be the separated state, the bias voltage applying unit supplies the secondary transfer roller. Control means for changing the current value to be
It is provided with.

  In the image forming apparatus according to the present invention, a weak current is supplied to the secondary transfer roller by the existing bias voltage application unit to determine the pressure contact / separation state of the secondary transfer roller. Therefore, a contact type sensor for pressure contact / separation detection is not required. When the pressure contact / separation cannot be determined, the value of the current supplied from the bias voltage applying unit to the secondary transfer roller is changed, so that the pressure contact / separation state can be reliably determined even in the dew condensation state. It becomes possible.

  When the current value supplied from the bias voltage applying unit to the secondary transfer roller is changed, the control unit is in a dew condensation state if the voltage value of the secondary transfer roller is different between the pressure contact state and the separation state. When it is determined that there is a voltage value, the separated state is determined. In this way, it is preferable to place the secondary transfer roller in a separated state when in the dew condensation state. In the dew condensation state, it is preferable to turn on the heater in the image forming apparatus and drive the fan, so that the dew condensation state can be quickly eliminated.

  In addition, when the current value supplied from the bias voltage applying unit to the secondary transfer roller is changed, the control unit determines that the voltage value of the secondary transfer roller is not different between the pressure contact state and the separated state. It is determined that the contact / separation means of the transfer roller is defective. Thus, when the contact / separation means is defective, it is preferable to warn the user to that effect.

  The control unit changes the current value supplied from the bias voltage application unit to the secondary transfer roller to a higher current value. Such a change in current value is preferably increased by a predetermined number of times by a constant current value. This is because an excessive increase in the current value can be prevented.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
FIG. 1 shows an electrophotographic color printer 10 which is an embodiment of an image forming apparatus according to the present invention. The color printer 10 is configured to synthesize four-color images in a so-called tandem system. The photosensitive drum 21, the charging device 22, the image exposure device 23, the developing device 24, and a residual toner and residual charge cleaning device. Image forming cartridges 20Y, 20M, 20C, and 20K that form YMCK (yellow, magenta, cyan, and black) images including 25 and the like are juxtaposed directly below the intermediate transfer belt 11.

  The image data is transmitted from an image reading device (scanner) (not shown) or a computer to an image memory of the controller 40 mainly composed of a CPU. The controller 40 drives the various image forming devices, forms an electrostatic latent image on each photosensitive drum 21 based on the transmitted image data, and develops the latent image to form a toner image. Such an electrophotographic process is well known and will not be described.

  The intermediate transfer belt 11 is stretched endlessly on the drive roller 12 and the support roller 13, is rotationally driven in the direction of arrow A, and is a portion facing the intermediate transfer belt 11 where the drive roller 12 is installed (secondary transfer portion). 15), the secondary transfer roller 16 is disposed so as to be able to contact and separate.

  In the lower part of the color printer 10, an automatic paper feeding unit 30 that feeds stacked sheets (recording media) one by one is installed. A toner fixing device 50 is installed immediately above the secondary transfer unit 15. The fixing device 50 is composed of a heating roller 52 having a heater 51 and a pressure roller 53. In addition, fans 55 and 56 are installed in the printer 10. When condensation occurs in the printer 10 as described below, the heater 51 is turned on and the fans 55 and 56 are driven to prevent condensation. Eliminate promptly.

  The toner images formed on the respective photosensitive drums 21 are sequentially primary-transferred onto the intermediate transfer belt 11 that is rotationally driven in the direction of arrow A by an electric field applied from the primary transfer roller 26, and four-color images are formed. Synthesized. On the other hand, the sheets are fed one by one from the automatic sheet feeding unit 30, conveyed from the conveying roller to the secondary transfer unit 15, and 2 composite images are generated from the intermediate transfer belt 11 by the electric field applied from the transfer roller 16. Next transferred. Thereafter, the sheet is conveyed to the fixing device 50 where the toner is heated and fixed, and is discharged from the discharge roller 38 onto the tray 39.

  In addition, a paper passing path 35 is provided so that double-sided printing is possible, and paper printed on one side is switched back by a paper discharge roller 38, and transport rollers 36 and 37 disposed in the paper passing path 35 are further provided. Then, the toner is conveyed again to the secondary transfer unit 15 by the conveying roller 31 and the toner image is secondarily transferred to the other surface.

  The secondary transfer roller 16 can be pressed against and separated from the intermediate transfer belt 11 (the separated state is indicated by a dotted line in FIG. 1), and is connected to a motor 54 that rotationally drives the heating roller 52 of the fixing device 50. Further, when the solenoid 17 is pressed against the intermediate transfer belt 11 for a predetermined time, the solenoid 17 is separated from the intermediate transfer belt 11, and when the solenoid 17 is in the separated state, the solenoid 17 is turned on for a predetermined time to shift to the pressure contact state. . As shown in FIG. 2, the solenoid 17 is connected to the controller 40 via the control unit 41, and the controller 40 controls the fixing motor 54 and controls the solenoid 17 on / off via the control unit 41.

  Further, as shown in FIG. 2, the secondary transfer roller 16 is connected to a high voltage power supply 43 through a voltage detection unit 42, the high voltage power supply 43 is controlled by a controller 40, and a detection signal of the voltage detection unit 42 is sent to the controller 40. Entered. The controller 40 controls the printer 10 as a whole, but performs the following control in connection with the present invention.

(Control basics)
That is, when the printer 10 is turned on or a cover (not shown) is opened or closed for maintenance, it is unclear whether the secondary transfer roller 16 is in a pressure contact state or a separated state. Therefore, a weak current is supplied from the high-voltage power supply 43 to the secondary transfer roller 16, and it is determined whether the secondary transfer roller 16 is in the pressure contact state or in the separated state based on the voltage value detected by the voltage detection unit 42. To do.

  If the voltage value at the time of weak current supply is not a predetermined value when predicted to be a pressed state or a separated state, the current value supplied from the high voltage power supply 43 to the secondary transfer roller 16 is set. Raise. When the current value supplied to the secondary transfer roller 16 is increased, if there is a difference between the voltage value of the secondary transfer roller 16 between the pressure contact state and the separated state, it is determined that the condensation state is present, and the voltage value Is determined to be a separated state. When the current value supplied to the secondary transfer roller 16 is increased, if the voltage value of the secondary transfer roller 16 is not different between the pressure contact state and the separation state, the contact / separation that makes the secondary transfer roller 16 contact / separate It is determined that the mechanism (solenoid 17 and / or motor 54) is defective, and that effect is displayed on a display panel (not shown) or warned to the user by voice.

  Specifically, the output of the high-voltage power supply 43 is set to a weak constant current I1 (10 μA), and first, the secondary transfer roller 16 is expected to be in either the pressure contact state or the separated state for a certain period of time. The voltage detection unit 42 detects the voltage V1. Next, the solenoid 17 is turned on for a predetermined time to set the secondary transfer roller 16 in a state opposite to the above, and the voltage detection unit 42 detects the voltage V2 for a predetermined time. If the detected voltage V1 is V1 ≧ C1 and V2 <C1 with respect to the reference value C1 (4 kV) for judging the contact / separation state of the secondary transfer roller 16, the voltage V1 (4.5 kV) is detected. Is determined to be in the separated state, and when the voltage V2 (3 kV) is detected, it is determined to be the pressure contact state. If V1 <C1 and V2 ≧ C1, it is determined that the pressure state is detected when the voltage V1 (3 kV) is detected, and the separated state is detected when the voltage V2 (4.5 kV) is detected. As described above, after the contact / separation state of the secondary transfer roller 16 is determined, the secondary transfer roller 16 is set to the separation state and waits for the print processing.

(Refer to Control Example 1 and FIG. 3)
Here, the control example 1 is demonstrated with reference to the flowchart of FIG. First, in step S1, the detection voltages V1 and V2 are compared with the reference value C1. As described above, if V1 ≧ C1 and V2 <C1, or if V1 <C1 and V2 ≧ C1 (NO in step S1), the contact / separation state of the secondary transfer roller 16 is clear, and this control is performed immediately. finish.

  On the other hand, if V1 <C1 and V2 <C1 (YES in step S1), there is almost no difference between the voltages V1 and V2, and the contact / separation state of the secondary transfer roller 16 cannot be determined. In this case, the output of the high-voltage power supply 43 is switched to the constant current I2 (100 μA) (step S2). The voltage V3 is detected in a state where the secondary transfer roller 16 is expected to be in either the pressure contact state or the separated state, and the solenoid 17 is turned on for a predetermined time so that the secondary transfer roller 16 is reversed. The state is set and the voltage V4 is detected. The detected voltages V3 and V4 are compared (step S3). If V4 is large with respect to V3, or if V3 is large with respect to V4 (YES in step S3), the voltage value is large. The separated state is determined (step S4).

  For example, if V3 is 2 kV and V4 is 2.1 kV, it is determined that the pressure is detected when the voltage V3 (2 kV) is detected, and the separated state is detected when the voltage V4 (2.1 kV) is detected. If V3 is 2.1 kV and V4 is 2 kV, it is determined that the voltage V3 (2.1 kV) is detected as a separated state, and the voltage V4 (2 kV) is detected as a pressure contact state.

  Then, the controller 40 determines that the inside of the printer 10 is in a dew condensation state (step S5), and energizes the heater 51 and drives the fans 55 and 56 at full speed to eliminate the dew condensation (step S6). Finally, the secondary transfer roller 16 is set to a separated state (step S7), and the print processing is waited.

  On the other hand, if there is no difference between the detection voltages V3 and V4 (NO in step S3), it cannot be determined whether the secondary transfer roller 16 is in the pressure contact state or the separation state at any voltage value. The contact / separation mechanism is determined to be defective (step S8). Then, the fact that the contact / separation mechanism is defective is displayed on a display panel (not shown) (step S9).

(Refer to Control Example 2 and FIG. 4)
Next, Control Example 2 will be described with reference to the flowchart of FIG. This control example 2 is basically the same as the control example 1, and the difference is the method of switching the constant current I2. That is, the constant current I1 (10 μA) is set as an initial value, and the current I3 (10 μA) is increased a predetermined number of times (steps S2 ′ and S3a). The other processing is the same as the processing given the same step number in FIG. 3, and redundant description is omitted.

  In the present control example 2, the current value is increased by 10 μA by a predetermined number of times and the voltages V3 and V4 are detected, so that an excessive increase in the current value can be prevented.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the configuration of the image forming portion and the paper transport mechanism in the printer is arbitrary. Of course, the specific current values and voltage values shown in the above embodiments are only examples.

1 is a schematic configuration diagram illustrating a color printer which is an example of an image forming apparatus according to the present invention. It is a block diagram which shows the outline of the control part of the said color printer. It is a flowchart figure which shows the example 1 of control. It is a flowchart figure which shows the example 2 of control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Printer 11 ... Intermediate transfer belt 16 ... Secondary transfer roller 17 ... Solenoid (contact / separation means)
DESCRIPTION OF SYMBOLS 40 ... Controller 42 ... Voltage detection part 43 ... High voltage power supply 51 ... Heater 55, 56 ... Fan

Claims (7)

In an image forming apparatus for forming a toner image on a recording medium by electrophotography,
A secondary transfer roller for secondary transfer of the toner image primarily transferred onto the image carrier onto the recording medium;
Contact / separation means for moving the secondary transfer roller from the pressure contact state to the separation state and from the separation state to the pressure contact state with respect to the image carrier;
Bias voltage applying means for applying a bias voltage to the secondary transfer roller;
Detecting means for detecting a voltage value applied to the secondary transfer roller;
Whether a weak current is supplied to the secondary transfer roller by the bias voltage application means, and whether the secondary transfer roller is in a pressure contact state or a separated state based on the voltage value of the secondary transfer roller at the time of the weak current supply And when the voltage value at the time of supplying the weak current is not a predetermined value of either the case where the pressure state is predicted to be the pressed state or the case where the voltage value is predicted to be the separated state, the bias voltage applying unit supplies the secondary transfer roller. Control means for changing the current value to be
Equipped with a,
When the current value supplied from the bias voltage application unit to the secondary transfer roller is changed, the control unit is in a dew condensation state if the voltage value of the secondary transfer roller is different between the pressure contact state and the separation state. Determining that there is a voltage value is large and determining that it is in a separated state;
An image forming apparatus. Wherein, when it is determined that the dew condensation state, the image forming apparatus according to claim 1, characterized in that the secondary transfer roller to the separated state. Wherein, when it is determined that the dew condensation state, the image forming apparatus according to claim 1 or claim 2, characterized in that to drive the fan with turning on the heater in the image forming apparatus. When the current value supplied from the bias voltage application unit to the secondary transfer roller is changed, the control unit determines that the voltage value of the secondary transfer roller is not different between the pressure contact state and the separation state. the image forming apparatus according to any one of claims 1 to 3, characterized in that the releasing means determines that defective. 5. The image forming apparatus according to claim 4 , wherein when the control unit determines that the contact / separation unit is defective, the control unit warns the user. Said control means, the image forming apparatus according to any one of claims 1 to claim 5, characterized in that to change the value of current supplied from the bias voltage applying means to the secondary transfer roller to a higher current value . It said control means, the image forming apparatus according to any one of claims 1 to 6, characterized in that for a predetermined number of times increased by a constant current value.

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