JPH05216331A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate failure accompanying the automatic adjustment of the emitted light quantity of a laser diode (APC) such as the wasteful consumption of toner, the soiling of a transfer part or the fatigue of a photosensitive body by executing the APC while the joining part of the photosensitive body exists at a laser exposure position. CONSTITUTION:When a synchronization mark detection signal is inputted from a synchronization mark detector 11 through an input port 33, an internal timer is started at this time. Then, when the joining part of the photosensitive body arrives at the laser exposure position, the APC is executed. After the laser diode 25 is turned on through a D/A converter 24, a D/A value when the outputs of comparators 29 and 30 respectively become 'H' is saved by increasing a value set to the converter 24 by a CPU 21 by a prescribed value at a time. Then, the APC is finished by turning off the diode 25. When the APC is finished and the joining part of the photosensitive belt arrives at a prescribed position where it is passed through the laser exposure position, the internal timer is reset and printing and writing are started at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a laser diode such as a laser printer and a digital copying machine.

[0002]

2. Description of the Related Art In the image forming apparatus as described above,
The controller converts the print data from the host device into video data and sends it as a video signal to the control unit on the engine side, and the control unit turns on and off the laser diode according to the video signal from the controller, A laser beam emitted from a laser diode is deflected and scanned by a polygon mirror, and a latent image is formed by irradiating a pre-charged photoconductor through a lens and a mirror.

The amount of light emitted from the laser diode is controlled by the current flowing through the laser diode. The relationship between the current and the amount of emitted light depends on the laser diode itself,
It cannot be specified unconditionally because it depends on temperature changes or changes over time. Therefore, in order to cause the laser diode to emit a predetermined amount of light, an automatic power control (hereinafter referred to as “A
Image forming apparatuses having a function of "PC" are now available.

This APC function is carried out by using a photodiode (which may be a phototransistor) which is arranged close to the laser diode and measures the amount of emitted light. The photodiode sends a current proportional to the amount of light emitted from the laser diode, so it is converted into a voltage, the voltage is compared with a predetermined voltage by a comparator, and the result is captured to determine the amount of light emitted from the laser diode. It can be kept constant.

[0005]

However, in the image forming apparatus as described above, the laser diode has to be turned on during the APC, so that the laser beam emitted from the laser diode is normally printed. In the same way as above, the photoconductor is scanned, and the laser-exposed portion is visualized by the developing section, so that the toner is wastefully consumed or the visualized section passes through the transfer section. As a result, the transfer portion may become dirty and appear as dirt on the back surface of the print.

Further, the exposure itself of the photosensitive member by the laser beam leads to its fatigue and deterioration, which is not preferable. Furthermore, a mirror on the laser optical path,
Since the lens, aperture (slit) plate, etc. are arranged vertically with respect to the laser optical axis, the laser light reflected there returns to the laser diode side and is incident on the photodiode close to the laser diode. There is also a problem that it may not be possible to measure a certain amount of light.

The present invention has been made in view of the above points, and it is an object of the present invention to prevent the above-mentioned inconvenience from occurring during APC and to always perform accurate APC. And

[0008]

In order to achieve the above-mentioned object, the present invention provides an image forming having a laser light quantity adjusting means for automatically adjusting the quantity of light emitted from a laser diode and a belt-shaped image carrier having a joint portion. The apparatus is provided with means for automatically adjusting the amount of light emitted from the laser diode by means of the laser light amount adjusting means while the above-mentioned joining portion is present at the laser exposure position.

Further, the laser light amount adjusting means for automatically adjusting the light emission amount of the laser diode and the movement of the aperture plate arranged on the optical path of the laser beam emitted from the laser diode and having a plurality of apertures of different sizes are formed. In the image forming apparatus having a laser beam diameter changing means for changing the size of the aperture through which the laser beam passes and changing the laser beam diameter for scanning the image carrier, A means for performing automatic adjustment during movement of the aperture plate by means of laser beam diameter changing means,
And an arrangement in which the aperture plate is arranged at a slight inclination with respect to a plane orthogonal to the optical axis of the laser beam.

[0010]

According to the first aspect of the invention, the automatic adjustment (APC) of the amount of light emitted from the laser diode is performed such that the joint portion of the photoconductor (the part where the influence of laser exposure does not appear on the photoconductor) is present at the laser exposure position. Since it is done while the conventional APC, wasteful toner consumption, dirt on the transfer part, photoconductor fatigue, etc.
The drawbacks associated with can be eliminated.

According to the second aspect of the present invention, the amount of light emitted from the laser diode is automatically adjusted during the movement of the aperture plate for switching the size of the aperture through which the laser light passes (optical path blocking state). Similar effects can be obtained. According to the third aspect of the invention, since the aperture plate is arranged so as to be slightly inclined with respect to the plane orthogonal to the optical axis of the laser beam, the reflected light thereat does not return to the laser diode side, and the APC is always accurate. Can be done.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. 2 is a schematic configuration diagram showing an internal mechanism of a laser printer which is an embodiment of the present invention, and FIG. 3 is a perspective view showing an example of the photoconductor belt.

In this laser printer, when a print sequence is started by a command from the host device, the paper feed roller 1 starts feeding paper from the paper feed cassette 2, and the leading edge of the paper is held by the registration roller pair 3. To pause. On the other hand, the photoconductor belt 4 rotates in the direction of the arrow, and a laser beam modulated according to video data emitted from a laser diode (not shown) is mainly applied to the surface charged by the charger 5 in the belt width direction. Irradiation is performed while scanning to form an electrostatic latent image.

The developing roller 6 in the developing unit 6
Toner is attached and developed by a, transferred by a transfer charger 7 to a sheet fed by the registration roller pair 3 at a predetermined timing, and thereafter, the sheet heat-fixed by a fixing roller 8 is discharged to an external sheet not shown. Output the paper to the tray. On the other hand, the toner remaining on the surface of the photosensitive belt 4 after the image transfer is removed by the cleaner 9, and the electric charges remaining on the surface are removed by the irradiation of light from the discharging lamp 10 to prepare for the next image formation.

Here, the photosensitive belt 4 is formed by joining both ends of a flat film coated with a photosensitive material to form a belt shape as shown in FIG. 3, and 4a indicates the joined portion. ing. Since it is difficult to obtain the characteristics as a photoconductor, the joint portion 4a is not normally used as a printing surface. That is, it is a portion that does not retain electric charges and is not affected by exposure to laser light or development by the developing unit 6.

Therefore, the joint portion 4a of each page is
It is necessary to form a latent image at a position that avoids. Therefore, in this laser printer, the synchronization mark 4b is formed in the vicinity of the joining portion 4a of the photoconductor belt 4, and the synchronization mark detector 11 is arranged at a position where the synchronization mark 4b passes. The detector 11 detects the synchronization mark 4a and aligns it in the sub-scanning direction.

FIG. 4 is an exploded perspective view showing an example of an aperture (slit) switching unit in this laser printer, and FIG. 5 is a schematic sectional view of the assembled state. In this aperture switching unit, reference numeral 12 is an L-shaped base having a window 12a through which a laser beam is incident, and two apertures (slits) 13 having different sizes are provided therein.
The aperture plate 13 on which a and 13b are formed is provided in the pair of guide portions 12b and 12b, and the aperture switching solenoid 1
4 are attached by a pair of bosses 12c and 12c, respectively, and the aperture switching solenoid 14 is turned on / off to move the aperture plate 13 up and down to switch the size of the aperture through which the laser beam passes. There is.

That is, the aperture switching solenoid 14
Is turned on, the aperture plate 13 is raised against the biasing force of the spring 15 by its suction force, and the aperture 13b for the high resolution mode for reducing the laser beam diameter as shown in FIG. The laser beam LB is set at the passing position. On the other hand, when the aperture switching solenoid 14 is turned off, its suction force is lost,
The aperture plate 13 is lowered by the urging force of the spring 15,
As shown in FIG. 5B, the aperture 13a for the low resolution mode for increasing the laser beam diameter is the laser beam L.
It is set at the passing position of B.

FIG. 6 is a block diagram showing the principal part of the control system of the printer engine in this laser printer. In FIG. 6, reference numeral 21 denotes a central processing unit (hereinafter referred to as "CPU").
Thus, the entire control unit is centrally controlled. 22 is R
The OM stores fixed data including a control program. A RAM 23 temporarily stores various data.

Reference numeral 24 denotes a D / A converter, which converts a video signal (digital signal) from the CPU 21 into an analog current Iop.
Is converted into a laser diode (LD) 25, and the laser diode (LD) 25 is caused to emit light. Reference numeral 26 is a photodiode (PD), which detects the amount of light emitted from the laser diode 25 and supplies a monitor current Im having a magnitude corresponding thereto. Reference numeral 27 denotes a voltage detection amplifier, which detects a potential difference generated across the resistor 28 in proportion to the current Im and outputs it as a monitor voltage Vm.

Reference numeral 29 is a comparator, which compares the monitor voltage Vm output from the voltage detection amplifier 27 with the first reference voltage Vr1 (for example, 1.2 V) to obtain Vm ≧ Vr1.
Then, the output signal Sa is set to the high level “H”, and Vm <Vr
If it is 1, set to low level "L". 30 is also a comparator, and compares the monitor voltage Vm output from the voltage detection amplifier 27 with the second reference voltage Vr2 (for example, 2.0 V), and if Vm ≧ Vr2, sets the output signal Sb to “H”, If Vm <Vr2, it is set to "L".

Reference numerals 31 to 33 are input ports, of which the input port 31 outputs the output signal Sa of the comparator 29.
The input port 32 outputs the output signal Sb of the comparator 32 to
The input port 33 is the sync mark detector 11 shown in FIG.
The output signals of the above are input to the CPU 21, respectively.

Reference numerals 34 to 36 denote drivers, of which the driver 34 turns on / off the aperture switching solenoid 14 shown in FIG. 4 in response to an on / off signal from the CPU 21. The driver 35 drives a main motor 37 that rotates each roller such as the photosensitive belt 4 and the paper feed roller 1 according to a drive signal from the CPU 21. Driver 3
6 drives a polygon motor 39 for rotating the polygon mirror 38 in response to a drive signal from the CPU 21.

Here, the light emission amount P of the laser diode 25 is controlled by the magnitude of the current Iop flowing therethrough, and this current Iop is controlled by the data set in the D / A converter 24. FIG. 11 shows the relationship between the current Iop and the emitted light amount P. This relationship differs depending on the laser diode itself, temperature changes, or changes over time, and cannot be specified in a general way. Therefore, in this laser printer, in order to cause the laser diode 25 to emit a proper amount of light, a current Io flowing through the laser diode 25 is used.
Perform APC to automatically adjust p as needed.

FIG. 1 is a flow chart showing the process according to the present invention by the CPU 21 of FIG. 6, and FIG. 7 is a flow chart showing the APC subroutine. The routine of FIG. 1 starts when a print command is input from the controller. First, the polygon motor 39 and the main motor 3 are started.
After turning on 7, it is checked whether or not there is an aperture switching instruction (command for requesting the high resolution mode) from the controller, and if there is not, the aperture switching solenoid 14 is turned on.
Wait for input of sync mark detection signal from 1 (detection of sync mark).

When the sync mark detection signal (high level signal) shown in FIG. 8A is input from the sync mark detector 11 through the input port 33, the internal timer is started at that time, and APC is executed when the timer value reaches ta shown in FIG. 8B, that is, when the joining portion 4a of the photosensitive belt 4 reaches the laser exposure position.

As shown in FIG. 7, the APC turns on the laser diode 25 via the D / A converter 24, and then the CPU 21 sets the D / A converter 24 to the set value (D / A set value). Is increased by a predetermined value and the D / A when the outputs of the comparators 29 and 30 respectively become “H”
The set value is saved, the laser diode 25 is turned off, and the APC is finished.

For example, assuming that the emitted light amount P of the laser diode 25 and the monitor current Im flowing in the photodiode 26 have the relationship shown in FIG. 12, when the laser diode 25 emits light at 3 mW, the monitor current flowing in the photodiode 26. Im is 0.6mA and resistance is 2k
As shown in FIG. 13, the potential difference across the Ω resistor 28 is 1.
It becomes 2V. In this case, since the output Sa of the comparator 29 becomes "H", the CPU 21 saves the D / A set value at this time. This is the work of a 3mW APC.
Similarly, the APC work of 5 mW can be performed by saving the D / A set value when the output Sb of the comparator 30 becomes "H".

When APC is finished and the timer value of the internal timer reaches tb shown in FIG. 8B, that is, when the joining portion 4a of the photosensitive belt 4 reaches a predetermined position after passing the laser exposure position. The internal timer is reset and printing is started. That is, when a sync signal is sent to the controller and a video signal synchronized with the sync signal is received from the controller, one of the D / A set values previously saved by the video signal is used to drive the D / A converter 24. The laser diode 25 is turned on and off via the light.

As a result, the laser beam of the proper power emitted from the laser diode 25 is deflected and scanned by the polygon mirror 38 rotated by the polygon motor 39, and is precharged through the lens 40 and a mirror (not shown). A predetermined position on the belt 4 is irradiated and a latent image is formed there. As described above, the APC is performed while the joining portion 4a of the photoconductor belt 4 is present at the laser exposure position, so that toner does not adhere to the photoconductor belt 4 and wasteful toner consumption and transfer charger 7 are performed. The stains on the surface and fatigue of the photoconductor are eliminated.

FIG. 9 is a flowchart showing the processing by the CPU 21 of FIG. 6 different from that of FIG. 1 according to the present invention.
This routine starts when a print command is input from the controller. First, the polygon motor 39 and the main motor 37 are turned on, and the aperture switching solenoid 14 is turned on as shown in FIG.
The internal timer is started, and as shown in (c) of the figure, the aperture plate 13 moves and the laser beam path is cut off by the portion between the apertures 13a and 13b, as shown in (d) of the figure. When the time tc shown in the figure is reached, the internal timer is reset and APC is performed in the same manner as described above.

After that, it is checked whether or not there is an aperture switching instruction from the controller. If there is, the aperture 13b for the high resolution mode is currently set at the laser beam passage position, and if there is not, it is the low resolution mode, so the low resolution mode. After turning off the aperture switching solenoid 14 to set the aperture 13a for use as shown in FIG. 10 (b), the sync mark detection signal is input from the sync mark detector 11 (detection of the sync mark). wait.

Then, when the sync mark detection signal shown in FIG. 8A is input from the sync mark detector 11 through the input port 33, the internal timer is started again at that time, and the timer value is changed. When tb shown in (c) of FIG. 8 is reached, the internal timer is reset and the print writing is started as described above. In this way, by performing the APC while the optical path of the laser beam is blocked during the movement of the aperture plate, the same effect as that of the above-described embodiment can be obtained.

If the aperture plate 13 is arranged at a slight inclination (angle θ) with respect to the plane S orthogonal to the optical axis L of the laser beam as shown in FIG. 14, the laser diode 25 is turned on to perform APC. When this is done, the laser beam reflected by the aperture plate 13 does not return to the laser diode 25 side, so the amount of emitted light can be accurately detected by the photodiode 26, so that accurate APC is always performed. You can

Although the embodiment in which the present invention is applied to the laser printer has been described above, the present invention is not limited to this, and various images such as a digital copying machine and a facsimile machine which form an image by using a laser diode as a light source. It is applicable to a forming device.

[0036]

As described above, according to the inventions of claims 1 and 2, wasteful toner consumption, contamination of the transfer portion,
Problems associated with APC such as photoconductor fatigue can be eliminated. According to the invention of claim 3, the APC is always accurate.
Can be done.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process according to the present invention by a CPU 21 of FIG.

FIG. 2 is a schematic configuration diagram showing an internal mechanism of a laser printer which is an embodiment of the present invention.

FIG. 3 is a perspective view showing an example of the photosensitive belt 4.

FIG. 4 is an exploded perspective view showing an example of an aperture switching unit in the laser printer of FIG.

FIG. 5 is a schematic sectional view of the assembling state in the same manner.

FIG. 6 is a main part configuration diagram showing a control system of the printer engine.

7 is a flowchart showing a subroutine of APC in FIG.

FIG. 8 is a timing chart provided for explaining the flow of FIG.

9 is a block diagram of a CPU 21 of FIG. 1 according to the present invention;
It is a flow chart showing processing different from.

FIG. 10 is a timing chart for explaining the flow.

11 is a diagram showing the relationship between the current flowing through the laser diode 25 of FIG. 6 and the amount of emitted light.

12 is a diagram showing the relationship between the amount of light emitted from the laser diode 25 of FIG. 6 and the monitor current flowing in the photodiode 26. FIG.

13 is a diagram showing the relationship between the amount of light emitted from the laser diode 25 of FIG. 6 and the monitor voltage output from the voltage detection amplifier 27.

14 is a schematic cross-sectional view showing an example different from FIG. 5 of the aperture switching unit in the laser printer of FIG.

[Explanation of symbols]

4 Photoconductor belt 4a Joint part 4b Synchronization mark 11 Synchronization mark detector 12 Base 13 Aperture plate 13a, 13b Aperture 14 Aperture switching solenoid 15 Spring 21 Central processing unit 22 ROM 23 RAM 24 D / A converter 25 Laser diode 26 Photo Diode 27 Voltage detection amplifier 28 Resistance 29,30 Comparator 37 Main motor

Claims (3)

[Claims] 1. An image forming apparatus comprising: a laser light amount adjusting means for automatically adjusting the light emitting light amount of a laser diode; and a belt-shaped image carrier having a joint portion. An image forming apparatus comprising means for performing automatic adjustment while the bonding portion is present at the laser exposure position. 2. A laser light amount adjusting means for automatically adjusting the amount of light emitted from a laser diode, and an aperture plate which is arranged on the optical path of a laser beam emitted from the laser diode and which has a plurality of apertures of different sizes. An image forming apparatus having a laser beam diameter changing means for changing a size of an aperture through which a laser beam passes by movement to change a laser beam diameter for scanning an image carrier, wherein the laser light amount adjusting means emits light from a laser diode. An image forming apparatus comprising means for automatically adjusting the amount of light during the movement of the aperture plate by the laser beam diameter changing means. 3. A laser light amount adjusting means for automatically adjusting the emitted light amount of a laser diode, and an aperture plate provided on the optical path of a laser beam emitted from the laser diode and having a plurality of apertures of different sizes. An image forming apparatus having a laser beam diameter changing means for changing a size of an aperture through which a laser beam passes by moving to change a laser beam diameter for scanning on an image carrier, wherein the aperture plate is an optical axis of the laser beam. An image forming apparatus characterized in that the image forming apparatus is arranged so as to be slightly inclined with respect to a plane orthogonal to the plane.