JP2006201384A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique by which rush current or the like caused with operation for opening/closing the cover of an image forming apparatus is restrained. <P>SOLUTION: The image forming apparatus comprises; a driving means constituted by including capacitive load; a power source; a switch provided on a power supply path from the power source to the driving means and made off or on with the action of the predetermined part of the image forming apparatus so as to switch whether or not power is supplied; and a power supply control circuit provided on a power supply path between the switch and the driving means and made on interlocked with the on-state of the switch so as to supply the power to the driving means. The power supply control circuit comprises a field effect transistor (81) whose source is connected to the power source side on the power supply path and whose drain is connected to the driving means side, a 1st resistance element (83) connected between the gate and the source of the field effect transistor, and a 2nd resistance element (84) and a capacitive element (85) connected in parallel with the 1st resistance element and connected in series between the gate and the source. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine.

  A conventional example of an electrophotographic image forming apparatus such as a printer, a copier, or a facsimile machine is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-54097 (Patent Document 1). In such an image forming apparatus, two or more power supply voltages are generally used as power supplies for driving internal circuits. For example, a control unit configured to include a microprocessor and the like, and a logic circuit that implements image signal processing and other functions that control the overall operation of the image forming apparatus require a low-voltage (for example, 5 V) power source. Thus, for a mechanism that requires a relatively large electric power, such as a motor for driving a photosensitive drum or a paper feed mechanism or a laser unit that serves as an exposure light source, a power source of a higher voltage (for example, 24 V) is required. It is to do.

  In a general image forming apparatus, a switch that opens and closes in conjunction with opening and closing of the cover to shut off the power supply to the motor etc. when the cover that covers the inside of the main body is opened when a malfunction (paper jam etc.) occurs Is provided on the circuit. However, after opening the switch to shut off the power supply, when closing the switch again, a large inrush current may flow to the capacitor (capacitive load) mounted on the motor control board to which power is supplied. is there. There is an upper limit for the current value that can be passed through the switch, and the inrush current may exceed the upper limit value. For such inconvenience, in addition to the switch, by providing an electronic switch such as a field effect transistor (FET) on the power supply path and dividing the power supply destination, each transistor is turned on with a time difference. Measures are taken to avoid large inrush current flowing into the switch.

  However, the above countermeasures using FETs are not perfect and leakage current may occur when the switch is turned on. If this leakage current increases, the upper limit of the current value that can be passed through the switch may be exceeded. In addition, since the FET has a relatively fast switching speed, a current flows instantaneously, which may cause a drop in power supply voltage. Therefore, an improved technique for suppressing inrush current and leakage current is desired.

JP 2003-54097 A

  SUMMARY An advantage of some aspects of the invention is that it provides a technique capable of suppressing an inrush current or the like that occurs in association with an operation of opening and closing a cover of an image forming apparatus.

  The present invention relates to an image forming apparatus for forming an image by an electrophotographic method, including a capacitive load, driving means for driving each part of the apparatus, a power source for supplying power to the driving means, and the power source. A switch provided on a power supply path to the driving unit, which is cut off or conducted in accordance with an operation of a predetermined portion of the image forming apparatus, and switches whether to supply the power to the driving unit; A power supply control circuit that is provided on the power supply path to the drive means, is turned on in conjunction with the conduction of the switch, and supplies the power to the drive means. The power supply control circuit includes: a field effect transistor having a source connected to the power supply side on the power supply path and a drain connected to the driving means; a gate of the field effect transistor; A first resistive element connected in between, and a second resistive element and a capacitive element connected in parallel with the first resistive element and connected in series between the gate and the source. Composed.

  According to such a configuration, immediately after the switch is turned on by the series circuit of the second resistance element and the capacitive element, no potential difference is generated between the gate and the source of the field effect transistor, and the on state is not achieved. Therefore, inrush current can be suppressed. Further, the switching of the field effect transistor can be relaxed, and the inrush current when the field effect transistor is on can be reduced.

  Preferably, the switch is cut off or conducted in accordance with an opening / closing operation of a cover that protects the outside of the image forming apparatus.

  Thereby, the inrush current accompanying cover opening and closing can be avoided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram for explaining the overall configuration of an image forming apparatus according to an embodiment. The image forming apparatus shown in FIG. 1 forms a full-color image by superposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K) by electrophotography. The apparatus forms a monochrome image using only the toner. In this image forming apparatus, when an image signal is given from an external device (not shown) such as a host computer, each unit operates in accordance with the control of the main controller and the engine controller, and copying paper, transfer paper, paper, and OHP transparent An image corresponding to the image signal is formed (that is, printed) on a sheet S such as a sheet.

  In the image forming apparatus shown in FIG. 1, each of the photosensitive unit 2, the developing unit 3, the intermediate transfer unit 4, and the fixing unit 5 is configured to be detachable from the apparatus main body (housing 6). In a state where these units are mounted on the apparatus main body 6, as shown in FIG. 1, the photosensitive member 21 of the photosensitive member unit 2 rotates in the direction of the arrow shown in the drawing, and the rotating direction around the photosensitive member 21. A charging unit 22, a rotary developing unit 3, and a cleaning unit 23 are arranged along the line. The rotary developing unit 3 includes four developing units corresponding to YMCK colors. The charging unit 22 is applied with a charging bias, and uniformly charges the outer peripheral surface of the photoconductor 21. The cleaning unit 23 cleans the photosensitive member 21 by scraping off the toner remaining on the outer peripheral surface of the photosensitive member 21 after the primary transfer.

  The exposure unit 8 outputs a laser beam L in accordance with an image signal from the engine controller to expose the outer peripheral surface of the photosensitive member 21, and forms an electrostatic latent image corresponding to the image signal on the photosensitive member 21. The electrostatic latent image formed in this way is developed with toner by the rotary developing unit 3. As a result, the electrostatic latent image on the photoconductor 21 is visualized by the toner of each color of YMCK. The toner image developed in this way is primarily transferred onto the intermediate transfer belt 41 of the intermediate transfer unit 4 in the primary transfer region TR1. The image formed on the intermediate transfer belt 41 is secondarily transferred onto the sheet S taken out from the cassette 9 in a predetermined secondary transfer region TR2. The sheet S on which an image has been formed in this way is conveyed via the fixing unit 5 to a discharge tray portion provided on the upper surface portion of the apparatus main body 6.

  FIG. 2 is a block diagram illustrating circuit formation centering on the power supply system of the image forming apparatus. The image forming apparatus according to the present embodiment operates by receiving supply of an AC voltage (100 V) from a commercial power supply (AC power supply).

  The low-voltage power supply 50 receives an AC voltage from a commercial power supply via a power switch and generates three types of DC voltages (3.3V, 5V, and 24V). The 3.3V, 5V, and 24V power supplies are supplied to each part of the image forming apparatus via the second main substrate 51. For example, 3.3V power is supplied to the first main board 52 including the main controller and the like. The 5V power is supplied to the thermistor unit 53, batch sensor 54, R / W module 55, photosensor 56, photoconductor drive motor unit 57, overall drive motor unit 58, and drive circuit board (DRV board) 59. The 5V power is supplied to the exposure unit 8 via the 5V interlock switch 75 in the interlock switch unit 71.

  Similarly, the 24V power source includes the photoconductor 21, the high voltage power source 60, the photoconductor drive motor unit 57, the overall drive motor unit 58, the secondary transfer roller separation clutch 61, the intermediate transfer belt cleaner separation clutch 62, and the development drive motor unit. 63, a rotary drive motor unit 64, an eraser lamp unit 65, an ozone fan unit 66, a toner fan unit 67, a cooling fan 68, a paper feed related clutch 69, and a scanner motor 70. These high-voltage power supplies 60 and the like are each configured to include a capacitive load. A switch using a bipolar transistor or a field effect transistor is appropriately provided on a power supply path (wiring) connecting each part and the 24V power source. Further, the photosensitive member 21, the high-voltage power supply 60, the photosensitive member driving motor unit 57, the entire driving motor unit 58, the secondary transfer roller attaching / detaching clutch 61, the intermediate transfer belt cleaner attaching / detaching clutch 62, the developing driving motor unit 63, the rotary driving motor. For each part of the unit 64, 24V power is supplied via each 24V interlock switch 72, 73, 74 in the interlock switch unit 71, and the entire surface cover, side cover and the like of the image forming apparatus are opened. In connection with this, each interlock switch is opened, and the supply of 24V power is stopped. The interlock switch unit 71 corresponds to a “switch” in the present invention.

  In the present embodiment, a power supply control circuit 80a including a field effect transistor is provided on a supply path connecting the high-voltage power supply 60 serving as the “driving means” and the 24V power supply. Further, the photosensitive member drive motor unit 57, the entire drive motor unit 58, the secondary transfer roller contact / separation clutch 61, the intermediate transfer belt cleaner contact / detachment clutch 62, the development drive motor unit 63, and the rotary drive motor unit 64 as "drive means". A power supply control circuit 80b configured to include a field effect transistor is provided on a supply path that connects each of the above and a 24V power source. These power supply control circuits 80a and 80b are provided on a power supply path between the interlock switch unit 71 and each drive means, and supply power to the drive means in accordance with control by the first main board 52 as the control means. Whether to supply or not is switched, and inrush current flowing to the driving means when the interlock switch unit 71 is turned on is suppressed. Accordingly, it is possible to prevent an excessive inrush current from flowing to the driving unit when opening and closing the entire surface cover, the side surface cover, and the like of the image forming apparatus. A power supply control circuit 80c including a field effect transistor is provided on a supply path connecting the scanner motor 70 and the 24V power source.

  FIG. 3 is a circuit diagram illustrating a detailed configuration of the power supply control circuit. Although the configuration of the power supply control circuit 80a is illustrated in FIG. 3, the other power supply control circuits 80b and 80c have the same configuration. The power supply control circuit 80a illustrated in FIG. 3 includes a field effect transistor 81, resistor elements 82, 83, and 84, and a capacitor element 85. The field effect transistor 81 has a source connected to the power supply (DC 24 V) side on the power supply path and a drain connected to the driving means side. In this example, a p-channel enhancement type MOSFET is used as the field effect transistor 81. The resistance element 83 (first resistance element) is connected between the gate and the source of the field effect transistor 81, and divides the voltage from the power source together with the resistance element 82, and an appropriate gate voltage (12V in this example). ) Is generated. The resistive element 84 (second resistive element) and the capacitive element 85 are connected in series, and are connected in parallel with the resistive element 83 between the gate and the source of the field effect transistor 81. The resistance value and the capacitance value of each element are, for example, 100 kΩ for the resistance elements 82 and 83, 27Ω for the resistance element 84, and 0.1 μF for the capacitance element 85.

  By providing such a power supply control circuit 80a and the like, the interlock switch unit 71 is turned on, and the field effect transistor 81 is turned on for a moment in the process in which the 24V power supply is started up. The flow can be avoided. This is because by providing a series circuit of the resistor element 84 and the capacitor element 85, when the interlock switch unit 71 is turned on, there is no potential difference between the gate and the source of the field effect transistor 81, and the switch is turned on. This is because it disappears. In addition, by providing a series circuit of the resistor element 84 and the capacitor element 85, the switching speed of the field effect transistor 81 is moderated, the inrush current when the field effect transistor 81 is on is small, and the leakage current is suppressed. be able to.

  In addition, this invention is not limited to the content of embodiment mentioned above, A various deformation | transformation implementation is possible within the range of the summary of this invention.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment. 3 is a block diagram illustrating circuit formation centering on a power supply system of the image forming apparatus. FIG. It is a circuit diagram explaining the detailed structure of a power supply control circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Photoconductor, 50 ... Low voltage power supply, 51 ... Second main board, 52 ... First main board, 53 ... Thermistor unit, 54 ... Batch sensor, 55 ... R / W module, 56 ... Photo sensor, 57 ... Photoconductor Drive motor unit, 58 ... Overall drive motor unit, 59 ... Drive circuit board (DRV board), 60 ... High-voltage power supply, 61 ... Secondary transfer roller contact clutch, 62 ... Intermediate transfer belt cleaner contact clutch, 63 ... Development drive Motor unit, 64 ... Rotary drive motor unit, 65 ... Eraser lamp unit, 66 ... Ozone fan unit, 67 ... Toner fan unit, 68 ... Cooling fan, 69 ... Feeding clutch, 70 ... Scanner motor, 71 ... Interlock switch Unit, 80 ... power supply control circuit, 81 ... field effect transistor, 8 , 83, 84 ... resistance element, 85 ... capacity element

Claims (2)

An image forming apparatus for forming an image by electrophotography,
Drive means including a capacitive load and driving each part of the device;
A power supply for supplying power to the driving means;
A switch that is provided on a power supply path from the power source to the driving unit, is cut off or conducted in accordance with an operation of a predetermined part of the image forming apparatus, and switches whether to supply the power to the driving unit;
A power supply control circuit that is provided on the power supply path between the switch and the driving means, and is conducted in conjunction with conduction of the switch and supplies the power to the driving means;
With
The power supply control circuit includes a field effect transistor having a source connected to the power supply side on the power supply path and a drain connected to the driving means, and a gate between the gate and the source of the field effect transistor. Image forming comprising: a first resistance element to be connected; and a second resistance element and a capacitor element connected in parallel to the first resistance element and connected in series between the gate and the source apparatus.   The image forming apparatus according to claim 1, wherein the switch is cut off or conducted in accordance with an opening / closing operation of a cover that protects the outside of the image forming apparatus.

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