JP2006145670A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of ensuring the safety of an operator by inhibiting emission of light of a laser diode or the like in the case where a maintenance door or the like has been opened and capable of ensuring the high adjustment accuracy of an APC circuit that adjusts an amount of light emitted by the laser diode or the like. <P>SOLUTION: The image forming apparatus comprises a power supply permission signal input blocking circuit 40 (an example of a power supply permission signal input blocking means). The power supply permission signal input blocking circuit 40 is composed such that when a power supply permission signal outputted from a CPU 31 is input, the input of the power supply permission signal to a power supply permission circuit 15 that permits the supply of power to the laser diode 11 is blocked if an open door detection circuit 20 detects that the maintenance door has been opened. This inhibits emission of light of the laser diode 11 if the maintenance door has been opened. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an image provided with an exposure device that forms an electrostatic latent image corresponding to a document image on the surface of a photosensitive drum by irradiating a charged photosensitive drum (image carrier) with laser light. More particularly, the present invention relates to a technique for prohibiting laser light irradiation when a maintenance door or the like provided in the image forming apparatus is opened.

In general, an electrophotographic image forming apparatus (printer, copier, facsimile machine, etc.) irradiates a photosensitive drum (image carrier) uniformly charged at a predetermined potential with light such as laser light. An exposure device that performs an exposure process for forming an electrostatic latent image corresponding to the original image on the surface of the photosensitive drum is provided.
The exposure apparatus includes, for example, a laser diode that irradiates the photosensitive drum with laser light, a laser diode driving circuit that controls driving of the laser diode, and the like.
FIG. 5 is a conceptual diagram showing an example of a conventional laser diode drive circuit Z1.
As shown in FIG. 5, the laser diode drive circuit Z <b> 1 corresponds to the switching circuit 102 that controls power supply to the laser diode 101 based on the input Video signal (image data), and the light emission amount of the laser diode 101. Of the laser diode 101 by controlling the amount of power supplied to the laser diode 101 according to the current value of the current Ia flowing from the photodiode 103 and the current Ia flowing from the photodiode 103 An automatic output control (APC) circuit 105 that maintains the amount of light emission set in advance, and a power supply permission circuit 106 that permits power supply to the laser diode 101 in response to an input of a power supply permission signal. Configured.
In the laser diode drive circuit Z1 configured as described above, when the power supply permission signal output from the control unit such as a CPU or ASIC when the exposure process is performed is input to the power supply permission circuit 106, The power supply to the laser diode 101 is permitted. Then, when the Video signal is input to the switching circuit 102, the power supply to the laser diode 101 by the switching circuit 102 is controlled, and the exposure process is executed. During the exposure process, the light emission amount of the laser diode 101 is adjusted by the APC circuit 105.

By the way, since the laser light emitted from the laser diode is harmful to eyes and the human body, when a maintenance door (hereinafter referred to as “maintenance door”) provided in the image forming apparatus has been opened, The laser diode is prohibited from emitting light. Accordingly, even if the operator inadvertently opens the maintenance door during the light emission of the laser diode during the exposure process, the light emission of the laser diode is stopped, so that the safety of the operator is ensured. For example, Patent Document 1 shows an example of the technique. Such a method will be described below.
FIG. 6 is a conceptual diagram of a laser diode drive circuit Z2 to which the technique disclosed in Patent Document 1 is applied.
As shown in FIG. 6, in addition to the circuit configuration of the laser diode drive circuit Z1, the laser diode drive circuit Z2 includes a transistor 104 that superimposes a current Ib on the current Ia output from the photodiode 103. . Therefore, in the laser diode driving circuit Z2, the APC circuit 105 controls the amount of power supplied to the laser diode 101 in accordance with the current value of the flowing current Iab (current Ia + current Ib). Further, the APC circuit 105 prevents the power supply in the positive direction to the laser diode 101 when the current value of the current Iab exceeds a predetermined value.
In the laser diode driving circuit Z2 configured as described above, when a door opening signal is input from the CPU or the like to the transistor 104 when the maintenance door is opened, the current Ib becomes equal to or greater than the predetermined value. Is output from the transistor 104. Therefore, the APC circuit 105 prevents the power supply in the positive direction to the laser diode 101 and the light emission of the laser diode 101 is prohibited. Thereby, even when the operator carelessly opens the maintenance door while the laser diode 101 emits light, the safety of the operator is ensured.
JP-A-8-137346

However, a minute current Ib is output from the transistor 104 provided in the laser diode driving circuit Z2 due to the characteristics of the transistor 104 even when the opening signal is not input. Therefore, the current Iab in which the minute current Ib is superimposed on the current Ia flows into the power control circuit 105 in the APC circuit 105. The minute current Ib is unstable and increases or decreases by affecting the surrounding environment (temperature, etc.) of the transistor 104. Therefore, the light emission amount of the laser diode 101 controlled by the APC circuit 105 increases and decreases under the influence of the minute current Ib, and the desired light emission amount of the laser diode 101 cannot be obtained with high accuracy. The problem arises.
Accordingly, the present invention has been made in view of the above circumstances, and its purpose is to ensure the safety of the operator by prohibiting the light emission of the laser diode or the like when the maintenance door or the like is opened. An object of the present invention is to provide an image forming apparatus capable of ensuring a high adjustment accuracy of a light emission amount of a laser diode or the like by the above-mentioned APC circuit.

In order to achieve the above object, the present invention is applied to an image forming apparatus including a light irradiating unit that irradiates an image carrier with light according to image data, and the image carrying unit by the light irradiating unit. A power supply permission signal output means for outputting a power supply permission signal for permitting power supply to the light irradiating means upon irradiation of light to the body; and input of a power supply permission signal from the power supply permission signal output means And a power supply permission unit that permits power supply to the light irradiation unit, and when one or a plurality of doors (such as a maintenance door) provided in the image forming apparatus are opened, An input of the power supply permission signal to the power supply permission means is blocked.
According to such a configuration of the present invention, when the door is opened, the power supply permission unit prohibits power supply to the light irradiation unit. Irradiation is definitely prohibited. As a result, when the door is opened, the leakage of laser light or the like harmful to the human body is prevented to ensure the safety of the operator, and the amount of light emitted by the light irradiating means is adjusted. High adjustment accuracy can be ensured.
Here, as a configuration for blocking the input of the power supply permission signal, for example, a configuration in which the power supply permission signal is guided to a path different from an input path for guiding the power supply permission signal to the power supply permission means is considered. It is done. Alternatively, the input of the power supply permission signal to the power supply permission means can also be blocked by a configuration in which the output of the power supply permission signal by the power supply permission signal output means is stopped. With such a configuration, the present invention is implemented, and the safety of the operator when the door is opened and the high adjustment accuracy of the APC circuit can be ensured.

  According to the present invention, when the door is opened, power supply to the light irradiating means is prohibited by blocking the input of the power supply permission signal to the power supply permitting means. Since irradiation of light such as laser light is surely prohibited, the safety of the operator when the door is opened is ensured, and the above-described APC circuit that adjusts the amount of light irradiated by the light irradiation means is high. Adjustment accuracy can also be ensured.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a circuit diagram relating to detection of opening of a maintenance door and drive control of the laser diode 11 in the image forming apparatus X according to the embodiment of the present invention, and FIG. 2 is a power supply permission signal input blocking in the image forming apparatus X. A circuit diagram of the circuit 40 and FIG. 3 are timing charts for explaining an example of exposure processing in the image forming apparatus X.
In the image forming apparatus X according to the embodiment of the present invention, a photosensitive drum (an example of an image carrier) that is uniformly charged to a predetermined potential by a charger is irradiated with a laser beam to respond to an electrostatic image corresponding to an original image. After an exposure process for forming a latent image on the surface of the photosensitive drum, a toner image in which the electrostatic latent image is visualized by development by a developing device is transferred and fixed on a recording sheet supplied from a paper feed cassette or the like. Thus, the electrophotographic image forming apparatus forms the original image on the recording paper. The image forming apparatus X is configured to prohibit irradiation of the photosensitive drum with laser light when a maintenance door (not shown) provided in the image forming apparatus X is opened during the exposure process. This point is described in detail below. Note that components included in a general electrophotographic image forming apparatus are not different from those in the conventional art, and thus illustration and description thereof are omitted here.

First, an outline of a circuit configuration relating to a laser diode 11 (an example of a light irradiation unit) that irradiates the photosensitive drum with laser light in the image forming apparatus X will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus X includes a laser diode 11 that irradiates the photosensitive drum with laser light, a laser diode drive circuit 10 that controls driving of the laser diode 11, and an opening of the maintenance door. The door opening detection circuit 20 (an example of door opening detecting means) that inputs a door opening signal indicating that the maintenance door has been opened to the CPU 31 described below, and the CPU 31 and peripheral devices not shown (ROM, RAM) And the like, and a control unit 30 that comprehensively controls the image forming apparatus X by executing processing according to a predetermined program stored in the ROM, and a power supply permission signal input blocking circuit 40 (power) An example of supply permission signal input blocking means). The DC power is supplied to each circuit from a power source such as an AC / DC converter (not shown) that converts AC power (for example, AC 100 V) supplied from a commercial AC power source into DC power (for example, DC 5 V). (Vcc-GND shown). The laser diode 11 will be described as an example of a light irradiation unit that is controlled by the laser diode driving circuit 10 and irradiates the photosensitive drum with light corresponding to image data. The light source may be used as another example of the light irradiation means.
In the present embodiment, the CPU 31 permits power supply to the laser diode 11 when the image forming apparatus X starts the exposure process, that is, when the laser diode 11 irradiates the photosensitive drum with laser light. For this purpose, a process for outputting a power supply permission signal to the laser diode drive circuit 10 is executed. The CPU 31 when executing such processing corresponds to power supply permission signal output means. Further, the power supply permission signal output means is not limited to the CPU 31, but is provided in the control unit 30 such as an ASIC or DSP (not shown) that executes each step of the image forming process in the image forming apparatus X. An integrated circuit (arithmetic means) may be used as another example.

  As shown in FIG. 1, the laser diode drive circuit 10 detects the light emission amount of the laser diode 11 and outputs a current having a magnitude corresponding to the detected light emission amount, and the control unit 30. A switching circuit 13 for controlling the power supplied to the laser diode 11 based on a video signal (image data) transferred from an image memory (not shown) and inputted, and a current output from the photodiode 12 An APC circuit 14 for performing an APC process for maintaining the light emission amount of the laser diode 11 at a predetermined light emission amount by controlling the amount of power supplied to the laser diode 11 according to the current value, and output from the CPU 31 Permission / non-permission of power supply to the laser diode 11 according to whether or not a power supply permission signal is input. Ri and replaced power supply permission circuit 15 (an example of the power supply permitting means), provided with is schematically configured. As shown in the figure, the power supply permission circuit 15 in the present embodiment is configured to include a transistor 151 that is activated by the input of the power supply permission signal, while the power supply permission signal is being input. Permits the power supply to the laser diode 11 (allows energization between Vcc and GND), and prohibits the power supply to the laser diode 11 while it is not input (cuts off between Vcc and GND) It is.

The door opening detection circuit 20 includes a contact switch 21 that opens a contact when the maintenance door is opened, a light emitting diode 22a that emits light when the contact of the contact switch 21 is closed and is energized, and the light emission. By monitoring the operating state of the photocoupler 22 (energized state between Vcc and GND) and the photocoupler 22 having a phototransistor 22b that operates when the diode 22a is in a light emitting state and energizes between Vcc and GND. An I / O interface 24 that detects the opening of the maintenance door and inputs a door opening signal indicating the opening of the maintenance door to the CPU 31 of the control unit 30 according to the detection is schematically configured. As the maintenance door, there is a risk that the laser light of the laser diode 11 leaks to the outside by opening the door, such as a door provided on the front, back, side or inside of the image forming apparatus X. Or one or more doors.
On the other hand, the CPU 31 that has received the opening signal from the door opening detection circuit 20 transmits the opening signal to a power supply permission signal input blocking circuit 40 described later.

Here, the power supply permission signal input blocking circuit 40 that blocks the input of the power supply permission signal from the CPU 31 to the power supply permission circuit 15 will be described with reference to FIG.
As shown in FIG. 2, the power supply permission signal input blocking circuit 40 includes NPN transistors 41 and 42, and an input path 43 and an induction path 44 that are switched according to the operating state of the transistors 41 and 42. It is prepared for. The input path 43 is a transmission path that guides the power supply permission signal output from the CPU 31 to the power supply permission circuit 15, and the guide path 44 is output from the CPU 31, unlike the input path 43. A transmission path for guiding the power supply permission signal to GND through the collector-emitter of the transistor 42, and the power supply permission signal output from the CPU 31 is not simultaneously transmitted to these transmission paths.
The transistor 41 has a base connected to the CPU 31, a collector connected to the Vcc, and an emitter connected to the base of the transistor 42. The transistor 41 operates in response to an opening signal input from the CPU 31, and Vcc and the transistor 42 are operated. This switches the energization state between the base and the base. Specifically, the transistor 41 energizes between the collector and the emitter by the inflow of the current to the base due to the input of the opening signal, and outputs the current from Vcc to the base of the transistor 42.
The transistor 42 has a base connected to the emitter of the transistor 41, a collector connected to the CPU 31, and an emitter connected to the GND. The transistor 42 operates in response to the operation of the transistor 41, and the CPU 31 and the GND are energized. The state is switched. Specifically, the transistor 42 energizes between the collector and the emitter when the current output from the transistor 41 is input to the base, that is, energizes the CPU 31 and GND. At this time, the power supply permission signal output from the CPU 31 is guided to the GND via the guide path 44.
In the power supply permission signal input blocking circuit 40 configured as described above, when an opening signal is input from the CPU 31 to the base of the transistor 41, the transistor 41 and the transistor 42 are operated, and the input path 43 And the guide path 44 are switched. As a result, the power supply permission signal output from the CPU 31 is guided to the guide path 44 different from the input path 43, and the input of the power supply permission signal to the power supply permission circuit 15 is performed. Be blocked. The power supply permission signal input blocking circuit 40 may be provided between the control unit 30 and the power supply permission circuit 15 as shown in the figure. However, it is not limited to this.
Therefore, in the image forming apparatus X, when the maintenance door is opened, the input of the power supply permission signal from the CPU 31 to the power supply permission circuit 15 is blocked by the power supply permission signal input blocking circuit 40. , Power supply to the laser diode 11 is prohibited, and irradiation of laser light by the laser diode 11 is prohibited.

Hereinafter, an example of the exposure process in the image forming apparatus X according to the embodiment of the present invention will be described with reference to FIGS. 1 and 2 and the timing chart of FIG. In addition, P1-P4 described in the following description represents the identification code at the time of operation shown in the timing chart of FIG. 3A is a power supply permission signal output from the CPU 31, FIG. 3B is a power supply permission signal input to the power supply permission circuit 15, FIG. 3C is a Video signal, and FIG. 3D is a laser. 5 is a timing chart showing a power supply state to the diode 11, (e) an APC signal, and (f) an opening signal output from the CPU 31.
First, in the image forming apparatus X, when the image forming process is started by the control unit 30 and the photosensitive drum is uniformly charged to a predetermined potential by a charger, the CPU 31 performs the exposure process when executing the exposure process. The power supply permission signal (a) is output toward the power supply permission circuit 15 (at time P1). At this time, since the maintenance door is closed, that is, the door opening signal (f) is not input to the power supply permission signal input blocking circuit 40 (before time P4), the power supply permission is determined. The transistors 41 and 42 (see FIG. 2) of the signal input blocking circuit 40 are not activated. Therefore, the power supply permission signal (a) output from the CPU 31 is guided to the power supply permission circuit 15 via the input path 43 and input to the power supply permission circuit 15 (FIG. 3B). )). As a result, the transistor 151 of the power supply permission circuit 15 is activated, and the power supply to the laser diode 11 in the laser diode drive circuit 10 is permitted (a state where power can be supplied between Vcc and GND). .

Next, the APC circuit 14 determines whether or not the light emission amount of the laser diode 11 is a predetermined light emission amount and increases or decreases the amount of power supplied to the laser diode 11 by the APC circuit 14 (P2). Of time). During the execution of this APC process (t1 in the figure), an APC signal (e) is transmitted from the APC circuit 14 to the switching circuit 13. Here, the APC signal (e) instructs the switching circuit 13 to supply power to the laser diode 11. Thus, in the switching circuit 13 to which the APC signal (e) is input, a process for supplying power to the laser diode 11 is performed while the APC signal (e) is input (FIG. 3 (d) )).
The APC process is performed at predetermined intervals, and the light emission amount of the laser diode 11 is maintained at the predetermined light emission amount. For example, the APC process in the present embodiment is executed at every interval t2 at which scanning of one line of the document image by the laser diode 11 ends. Note that the APC process executed by the APC circuit 14 may always control the light emission amount of the laser diode 11 as described in Patent Document 1.

  Subsequently, when the input of the video signal (c) to the switching circuit 13 by the control unit 30 is started (at time P3), the switching circuit 13 supplies power to the laser diode 11 based on the video signal. Control is started. As a result, as shown in FIG. 3D, the laser diode 11 repeats light emission and extinction in accordance with the supply power controlled by the switching circuit 13 based on the Video signal (c). An exposure process for irradiating the photosensitive drum with laser light according to (c) is executed.

By the way, as described above, if the maintenance door of the image forming apparatus X is inadvertently opened by the operator during the execution of the exposure process, there is a risk that harmful laser light may leak to the operator. . For this reason, the image forming apparatus X according to the present embodiment includes the power supply permission signal input blocking circuit 40, whereby the light emission of the laser diode 11 is prohibited when the maintenance door is opened.
First, when the maintenance door is opened, the opening of the maintenance door is detected by the door opening detection circuit 20 and a door opening signal is input to the CPU 31. In response to this, when the opening signal (f) output from the CPU 31 is input to the power supply permission signal input blocking circuit 40 (at time P4), the transistor of the power supply permission signal input blocking circuit 40 41 and 42 operate, and the input path 43 and the guide path 44 are switched. As a result, the power supply permission signal input from the CPU 31 to the power supply permission circuit 15 via the input path 43 is guided to the guide path 44. That is, the input of the power supply permission signal to the power supply permission circuit 15 is blocked (FIG. 3B). Therefore, since the operation of the transistor 151 of the power supply permission circuit 15 is stopped and the power supply to the laser diode 11 is prohibited, regardless of the control state by the switching circuit 13 based on the Video signal (c), The laser diode 11 stops emitting light (FIG. 3D).
Note that the power supply permission signal input blocking circuit 40 in the present embodiment guides the power supply permission signal to the guide path 44 different from the input path 43, thereby supplying the power supply permission signal 15 to the power supply permission circuit 15. The input of the power supply permission signal is blocked. However, the present invention is not limited to this. For example, the contact is opened when the maintenance door is opened, and the input of the power supply permission signal to the power supply permission circuit 15 is blocked. A circuit configuration using a contact switch, a relay, or the like may be used.

  Thereafter, the state where the input of the power supply permission signal to the power supply permission circuit 15 is stopped is continued until the maintenance door is closed (FIG. 3B). In the meantime, even if the APC signal (e) is output from the APC circuit 14 to the switching circuit 13, the power supply to the laser diode 11 is prohibited by the power supply permission circuit 15. The diode 11 does not emit light. Needless to say, if the maintenance door is opened during the execution of the APC process, the light emission of the laser diode 11 is stopped regardless of the execution state of the APC process.

As described above, in the image forming apparatus X, when the maintenance door is opened, the input of the power supply permission signal to the power supply permission circuit 15 is performed by the power supply permission signal input blocking circuit 40. Since the power supply to the laser diode 11 is blocked by the power supply permission circuit 15, the light emission of the laser diode 11 is reliably prohibited. This prevents leakage of the laser light from the laser diode 11 when the maintenance door is opened, thereby ensuring the safety of the operator.
Moreover, in the image forming apparatus X, the current that is input to the APC circuit 14, that is, the current that serves as an index for controlling the amount of power supplied to the laser diode 11 is only the current that is output from the photodiode 12. Therefore, high adjustment accuracy of the light emission amount of the laser diode 11 by the APC circuit 14 is ensured.

FIG. 4 is a circuit diagram relating to detection of maintenance door opening and drive control of the laser diode 11 in the image forming apparatus Y according to the embodiment of the present invention. Note that the same components as those of the image forming apparatus X according to the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 4, the image forming apparatus Y according to the present embodiment does not include the power supply permission signal input blocking circuit 40 in the embodiment, and is directed from the CPU 31 to the power supply permission circuit 15. The power supply permission signal output in this way is directly input to the power supply permission circuit 15.
Here, the CPU 31 in this embodiment outputs the power supply permission signal to the power supply permission circuit 15 as necessary for execution of the exposure process, etc. only when the maintenance door is closed. It is.
That is, in the image forming apparatus Y, the power supply permission signal is output from the CPU 31 when the exposure process is executed. During the exposure process, the door opening detection circuit 20 opens the maintenance door. When it is detected and an opening signal is input to the CPU 31, the CPU 31 executes a process for stopping the output process of the power supply permission signal to the power supply permission circuit 15. The CPU 31 when executing the process of stopping the output process of the power supply permission signal corresponds to the power supply permission signal input blocking means. Thereby, when the output of the power supply permission signal from the CPU 31 is stopped, the input of the power supply permission signal to the power supply permission circuit 15 is stopped. 11 is prohibited from supplying power.
Therefore, also in the image forming apparatus Y configured as described above, when the maintenance door is opened, the light emission of the laser diode 11 is surely prohibited. Without affecting the function of the APC circuit 14, it is possible to ensure high adjustment accuracy of the light emission amount of the laser diode 11 by the APC circuit 14.

3 is a circuit diagram relating to detection of opening of a maintenance door and drive control of a laser diode 11 in the image forming apparatus X according to the embodiment of the present invention. FIG. FIG. 4 is a circuit diagram of a power supply permission signal input blocking circuit 40 in the image forming apparatus X according to the embodiment of the present invention. 6 is a timing chart for explaining an example of an exposure process in the image forming apparatus X according to the embodiment of the present invention. 3 is a circuit diagram relating to maintenance door opening detection and laser diode 11 drive control in the image forming apparatus Y according to the embodiment of the present invention. FIG. The conceptual diagram which shows an example of the conventional laser diode drive circuit Z1. The conceptual diagram of the laser-diode drive circuit Z2 to which the technique shown by patent document 1 is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Laser diode drive circuit 11 ... Laser diode (an example of a light irradiation means)
DESCRIPTION OF SYMBOLS 12 ... Photodiode 13 ... Switching circuit 14 ... APC circuit 15 ... Power supply permission circuit (an example of a power supply permission means)
20 ... Door opening detection circuit (an example of door opening detection means)
DESCRIPTION OF SYMBOLS 21 ... Contact switch 22 ... Photocoupler 22a ... Light emitting diode 22b ... Phototransistor 24 ... I / O interface 30 ... Control part 31 ... CPU (an example of a power supply permission signal output means and a power supply permission signal input blocking means)
40: Power supply permission signal input blocking circuit (an example of power supply permission signal input blocking means)
41, 42, 151 ... transistor 43 ... input path 44 ... induction path

Claims (3)

A light irradiation means for irradiating the image carrier with light according to image data;
A power supply permission signal output means for outputting a power supply permission signal for permitting power supply to the light irradiation means at the time of light irradiation to the image carrier by the light irradiation means;
Power supply permission means for permitting power supply to the light irradiation means in response to an input of a power supply permission signal from the power supply permission signal output means;
Door opening detection means for detecting the opening of one or more doors provided in the image forming apparatus;
An image forming apparatus comprising:
The power supply permission signal input blocking means for blocking the input of the power supply permission signal to the power supply permission means when the door opening detection means detects the opening of the door. Forming equipment.   The power supply permission signal input blocking means guides the power supply permission signal to a path different from an input path that guides the power supply permission signal to the power supply permission means, whereby the power to the power supply permission means is The image forming apparatus according to claim 1, wherein an input of a supply permission signal is blocked.   The power supply permission signal input blocking means blocks the input of the power supply permission signal to the power supply permission means by stopping the output of the power supply permission signal by the power supply permission signal output means. The image forming apparatus according to claim 1.

Images