JPH08300727A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To form an image by processing binary and multi-gradation image data at a low cost and simply. CONSTITUTION: In a latch/conversion part 5, multi-gradation image data to be respectively input are latched and output at the starting of an image clock WCLK and binary image data are converted into the max. value of the multi- gradation image data or zero and are output by a bit number converting part 72. 'Or' circuit 73 takes 'or' of multi-gradation image data input from D-FF70 and a bit number converting part 72 by a different timing each other and outputs to an LD control plate 4 through a gate 75 which is open during the voltage of a electric source of a laser diode 2 is normal. Therefore, the LD control plate 4 inputs wholly in the same way a driving electric current Id to the laser diode 2 regardless of whether the input image data is multi- gradation-style or binary and outputs a laser light with an amt. of light accurately corresponding to the image data by means of feedback control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention scans a laser beam emitted by a laser diode which emits light in accordance with input image data to form an electrostatic latent image on a photoconductor and converts it into a toner image by development. The present invention relates to an optical scanning type image forming apparatus that transfers and fixes an image on a sheet.

[0002]

2. Description of the Related Art A laser beam emitted according to image data is deflected in a main scanning direction by rotating a polygon mirror.
The electrostatic latent image formed on the photoconductor that moves in the sub-scanning direction,
Peripheral device type or built-in type laser printers, which convert a toner image by development and transfer it onto a sheet, then fix the toner image on the sheet to form an image, due to its high resolution and high image quality. Widely used.

In general, a laser diode (hereinafter also referred to as "LD") used as a light source of laser light is simply incoherent while the drive current Id is smaller than its threshold value Ish (LED emission region), as shown in FIG. The light amount P is very small. The main wavelength of the laser light output from the LD is in the near-infrared region to the infrared region, so the energy amount (mW) is correct.

When the drive current Id exceeds the threshold value Ish (laser emission region), laser oscillation is started to output coherent laser light and the light amount P thereof sharply increases. However, since the threshold value Ish greatly changes with temperature and the variation of the light amount P with respect to the variation of the driving current Id is large, when the light is emitted at a constant driving current Id, the light amount P significantly changes as the temperature increases. Finish.

For this reason, a commercially available laser output unit is provided with a photodiode (hereinafter also referred to as "PD") for detecting the amount of light in the side opposite to the laser light output direction of the LD, and is provided in an integrated case. Since the structure is hermetically sealed, feedback control (APC: automatic power control) of the drive current Id is performed so that the monitor current Im output from the PD has a value corresponding to the image data.

Recently, not only binary images such as characters and line drawings but also multi-tone images such as photographs are required, and multi-tone color images are formed. Image forming apparatuses have become commercially available. The area modulation method has been well known for forming a multi-gradation image by on / off control for a binary image.

That is, dither processing using the most general dither matrix, a proposal to change the dot diameter by controlling the laser power as shown in JP-A-61-277259, or JP-A-63-65769. As disclosed in the publication, there is a proposal to perform pulse width (dot width) modulation by level comparison with a triangular wave which replaces the dither matrix.

However, the above area modulation method has a drawback that the resolution is lowered. As a method for forming a high-quality multi-gradation image without lowering the resolution, a density modulation method in which the light amount of laser light is changed according to image data to write an image is excellent.
It is necessary to more accurately control the light amount of, and the demand becomes more severe in the case of a color image.

Therefore, for example, Japanese Unexamined Patent Publication No. 2-253968
As in the proposal disclosed in Japanese Patent Publication No. JP-A-2004-264, the light amount detected by the monitor current Im is compared with the light amount set by the light amount setting means of the LD according to the image data, and when the light amount is out of a preset allowable range, the allowable range There has been one that controls the light amount of the LD so that it falls within the range.

As proposed in Japanese Patent Laid-Open No. 2-20885, a plurality of power outputs corresponding to image data are set, and one of the power outputs is used for APC of laser light. In some cases, a plurality of power outputs were adjusted to their respective set values by carrying out.

Alternatively, as in the proposal disclosed in Japanese Unexamined Patent Publication No. 2-175266, a light quantity value corresponding to the number of gradations designated in multi-gradation image data is compared with the light quantity detected by the monitor current Im. However, in some cases, the drive current Id is feedback-controlled so that the two coincide with each other to form an image with the correct density.

[0012]

However, in the prior art including the above-mentioned proposal, it is sufficient to control the LD of the binary image data as it is, but in the case of multi-tone image data, Since the D / A conversion takes some time, it is necessary to latch the data once and then perform the D / A conversion, and the LD modulation method after the D / A conversion also requires complicated processing.

For this reason, the processing circuit for controlling the modulation of the LD is provided with two types, one for processing binary image data and the other for processing multi-tone image data. Further, switching between the two types of processing circuits becomes complicated depending on whether the image data is binary or multi-gradation, so that an increase in cost cannot be avoided.

Further, for example, if the door of the image forming apparatus is opened or closed during operation, there is a risk that the laser beam may enter the eyes of the operator. Therefore, the laser diode is turned off, but for a short time. The operation of the feedback control system became unstable during the drop of the power supply voltage, and a surge current might flow to deteriorate the laser diode.

The present invention has been made in view of the above points, and an object thereof is to easily process binary and multi-tone image data to form an image at a low cost.

[0016]

In order to achieve the above-mentioned object, the present invention provides a laser output unit in which a laser diode and a photodiode for detecting the light quantity thereof are integrated into a unit, and the laser diode converts image data into image data. Means for forming an electrostatic latent image on the photoconductor by the laser light outputted in response, video conversion means for converting the image data into video current, and reference current output means for outputting a reference current according to the image data. , An error amplifier that outputs an error current corresponding to the difference between the monitor current output by the photodiode detecting the light amount of the laser light and output and the reference current output by the reference current output means, and the error current output by the error amplifier. Drive current output means for outputting the drive current of the laser diode by subtracting it from the video current output by the video conversion means. In an image forming apparatus for controlling the light quantity of laser light by a force means, a reference current output means and an error amplifier, a data latch means for latching and outputting multi-tone image data input in synchronization with an image clock by the image clock. , A bit number converting means for converting input binary image data into multi-tone image data and outputting the same, and a multi-tone image data output by the bit number converting means or the data latch means to a video converting means and a reference current output. And a data transfer means for transferring the data to each of the means.

In the above-mentioned image forming apparatus, when the power supply voltage of the laser diode becomes equal to or lower than a preset threshold voltage, a power supply voltage monitoring means for outputting a voltage drop signal, and a voltage drop signal output by the monitoring means It is preferable to provide a laser diode protection unit that makes the reference current output by the reference current output unit zero or disables the multi-gradation image data output by the data transfer unit.

[0018]

In the image forming apparatus constructed as described above, the laser diode of the laser output unit outputs the laser light of the light quantity according to the drive current, and the light quantity is detected to detect the monitor current and the reference current output from the photodiode. The error amplifier outputs the error current by taking the difference from the reference current output by the output means according to the image data. The drive current output means subtracts an error current from the video current converted from the image data by the video conversion means and outputs the drive current to the laser diode to form a feedback control loop for the light quantity. The means for forming an electrostatic latent image writes an image on the photoconductor by means of laser light output from a laser diode, the light amount of which is controlled.

The data latch means provided in the preceding stage of the above feedback control loop latches and outputs the input multi-tone image data by the image clock, and the bit number converting means multi-tones the input binary image data. Convert to image data and output. The data transfer means transfers the multi-gradation image data output from the data latch means or the bit number conversion means to the video conversion means and the reference current output means, respectively.

Therefore, both the multi-tone image data and the binary image data which are respectively input are converted into laser light whose light amount is controlled by only one feedback control loop, which is output from the laser diode and an image is written. However, simple and complicated switching is not required, and costs can be reduced.

Further, the power supply voltage monitoring means outputs a voltage drop signal when the power supply voltage of the laser diode becomes equal to or lower than a preset threshold voltage, and the laser diode protection means outputs the reference current output means in response to the voltage drop signal. The reference current to be set to zero or the multi-gradation image data output by the data transfer means is disabled, so that the drive current of the laser diode is suppressed and the generation of surge current due to a drop in power supply voltage is prevented, The deterioration of the laser diode can be prevented.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a schematic configuration diagram showing an internal mechanism of a laser printer which is an embodiment of the present invention.

In the laser printer shown in FIG. 2, the paper 11 is fed by the paper feed roller 12 from one of the upper and lower two paper feed cassettes 10a and 10b, for example, the paper stack 11a on the upper paper feed cassette 10a. , The paper 11
After being timed by the registration roller pair 13, the sheet is conveyed to the transfer position of the photosensitive drum 15.

The surface of the photosensitive drum 15 which is driven to rotate in the direction of the arrow by the main motor 14 is charged by the charging charger 16 and is scanned by the modulated spot from the optical writing unit 26 to electrostatically charge the surface. A latent image is formed. The formed latent image is made visible by developing unit 17 with toner attached.

The toner image is transferred by the transfer charger 18 onto the sheet 11 conveyed by the registration roller pair 13. The sheet on which the toner image has been transferred is separated from the photoconductor drum 15, then sent to the fixing unit 20 by the conveyor belt 19 and pressed against the fixing roller 20b by the pressure roller 20a, and is heated in advance with the pressure. It is fixed by the temperature of the fixing roller 20b.

The sheet 11 exiting the fixing unit 20 is discharged by a sheet discharge roller 21 to a sheet discharge tray 22 provided on the side surface of the printer. On the other hand, the toner remaining on the photosensitive drum 15 is removed and collected by the cleaning unit 23. A printed circuit board 24 having a controller and an engine driver mounted thereon is arranged above the printer.

FIG. 3 is a block diagram showing an example of a control system of this laser printer. The main part of the controller 30 includes an MPU 31, a ROM 32 that stores programs, constant data, character fonts, etc., a RAM 33 that stores temporary data and dot patterns, and an I / O 34 that controls data input / output. This is an image processing unit.

The controller 30 further includes an operation panel 35 connected to the MPU 31 via the I / O 34, and an internal interface (I / F) 36, which are mutually connected by a data bus, an address bus and the like. A host machine 38 that outputs a print command, character data, image data, etc. is also connected to the MPU 31 via the I / O 34.

The engine driver 40 includes a CPU 41 and
The ROM 42 stores programs, constant data and the like, the RAM 43 stores temporary data and the like, and the I / O 44 which controls the input / output of data. Connected by.

The I / O 44 is connected to the internal interface 36 of the controller 30. The controller 30 inputs a video signal and states of various switches on the operation panel 35, and receives status signals such as an image clock and paper end from the controller 30. Output to. Also, I / O4
4 is also connected to the optical writing unit 26 and other sequence equipment groups 46 that constitute the printer engine 45, and various sensors 47 including a synchronization sensor.

The controller 30 receives a print command, a character code, and image information from the host machine 38, edits the code and information, and if the character code is a ROM.
The character font stored in 32 is converted into a dot pattern necessary for writing an image, and the dot patterns of those characters and images (hereinafter collectively referred to as “image”) are stored in a VRAM (video RAM) area in the RAM 33. Put.

When the image clock WCLK is input together with the ready signal from the engine driver 40, the controller 3
0 indicates the dot pattern stored in the VRAM area as image data synchronized with the image clock WCLK via the internal interface 36 and the engine driver 40.
Output to.

On the operation panel 35, there are switches and indicators (not shown) for controlling data according to instructions from the operator and displaying the information in the engine driver 40.
Or display the printer status on the display.

The engine driver 40 is the controller 3
From the data from 0, the optical writing unit 26 of the printer engine 45, the charger 16, the developing unit 1
Image data necessary for controlling the sequence equipment group 46 such as 7 or writing an image is input from the controller 30 and output to the optical writing unit 26. In addition, a signal indicating the state of each part of the engine is input from a synchronous sensor or other sensors 47 and processed, and necessary information and a status signal of an error condition are output to the controller 30.

FIG. 4 is a schematic configuration diagram showing an example of a main part of the optical writing unit 26. L which is a laser output unit
The D unit 1 outputs a laser beam of a light amount corresponding to the value of the multi-gradation image data input to the LD control plate 4, and the output laser beam becomes a parallel light flux by the collimator lens 50, and a polygon motor (not shown) is provided. Is deflected in the same direction (arrow B) by the polygon mirror 51 rotating counterclockwise (arrow A) at a double angular velocity.

The deflected parallel laser light is reflected by the fθ lens 5
The image is focused as a spot on the main scanning line 15a of the photoconductor drum 15 which is condensed by 2 and rotates in the sub-scanning direction, and is scanned in the main scanning direction (arrow C) to form an electrostatic latent image. The synchronization sensor 53, which is a photodiode, is fixedly disposed below the extension of the main scanning line 15a, and outputs a synchronization signal when the synchronization sensor 53 is irradiated immediately before the spot reaches the photosensitive drum 15. .

FIG. 1 shows a main part of this embodiment, a latch /
Converter, LD unit 1 and LD control plate 4 shown in FIG.
3 is a circuit diagram showing an example of the configuration of FIG. The LD unit 1 shown in FIG. 1 is an LD (laser diode) 2 that outputs laser light according to the drive current Id housed in one case.
And a PD that detects the amount of light and outputs a monitor current Im
(Photodiode) 3.

The LD control plate 4 converts the input digital image data into an analog current signal and outputs it as a video current Iv, which is a D / A converter 60 which is a video conversion means, and a reference current which is output as a reference current Ir. It is composed of a D / A converter 61 which is an output means, a driver circuit 62 which is a drive current output means which outputs the drive current Id of the LD 2, and an error amplifier 63.

The LD 2 of the LD unit 1 emits light by the drive current Id output from the driver circuit 62 according to the image data. The actual drive current Id flows in the direction of being input from the power source LD5V to the driver circuit 62 via the LD2 as shown by the arrow, but in the present specification, the “driver circuit 62” is used.
Will output. " The PD 3 detects the light amount P of the laser light output from the LD 2 and outputs the monitor current Im.

5 bits 3 input to the LD control board 4 from a latch / converter 5 described later via a 5-line data bus.
The image data of two gradations are respectively converted by the D / A converter 6
It is converted into a current signal by 0,61. The D / A converter 60 outputs it as the video current Iv to the driver circuit 62, and the D / A converter 61 outputs it as the reference current Ir to the error amplifier 63.

The error amplifier 63 amplifies by taking the difference between the monitor current Im input from the PD 3 and the reference current Ir input from the D / A converter 61, and when the monitor current Im is larger than the reference current Ir, it is as indicated by the arrow. Error amplifier 6
The error current Ie flows from 3 to the driver circuit 62, and when it is small, the error current Ie is output to the driver circuit 62.

The driver circuit 62 includes the D / A converter 6
The error current Ie is subtracted from the input video current Iv from 0, and the difference is power-amplified to be L as the drive current Id.
Output to D2 (actual Id flows from LD2).
As described above, the monitor current Im is converted into the drive current I by the D / A converter 61 that is the reference current output unit, the error amplifier 63, and the driver circuit 62 that is the drive current output unit.
The laser light is fed back to the APC (auto
Power control) is performed.

The latch / conversion unit 5 provided in the preceding stage of the LD control plate 4 is a bit number conversion unit composed of a D-FF (flip-flop) 70 which is a data latch unit and five AND circuits 71. It is composed of a conversion unit 72, an OR circuit 73 which is a data transfer means, a comparator 74 which is a power supply voltage monitoring means, and a gate 75 which is an AND circuit which is a laser diode protection means.

The D-FF 70 is an image clock WCLK for inputting multi-gradation (5-bit 32 gradations) image data input to the D terminal to the CK terminal as a synchronization reference of the image data.
The latched multi-gradation image data is output to the D / A converters 60 and 61 of the LD control plate 4 via the OR circuit 73 and the normally open gate 75.

FIG. 5 shows the image clock WCLK, the multi-tone image data input in synchronization with the clock and latched by the D-FF 70, and the light amount P of the laser light output from the LD 2 according to the image data. It is a wave form diagram which shows an example.

The multi-tone image data is, for example, 32 bits of 5 bits.
As an example of input image data in the case of gradation data, the light amount P is 3.1 mW when the image data has a maximum value of 31 and the light amount P is 3.1 mW, that is, 1 of the data is 0.1 mW. The respective waveforms are shown.

Each of the five AND circuits 71 constituting the bit number converting section 72 has one input terminal to which binary image data is input, the other input terminal connected to the power supply Vcc, and each output terminal. Each of them is connected to the input terminal of the OR circuit 73 via any of the 5-line data buses.

Therefore, the outputs of the five AND circuits 71, that is, the outputs of 5 bits, are all 0 if the binary image data is 0, and are all 1 if the binary image data is 0. 0 or 1 is immediately converted to 0 or 31 of 5-bit multi-gradation image data and output to the OR circuit 73, and the D / A converter 60 of the LD control board 4 via the gate 75 which is normally open. It is output to 61.

FIG. 6 shows a part of the bitmap data of the binary image expanded in the bitmap area in the RAM 33 of the controller 30 (FIG. 3) on the image data output side, and the data is read and input. The waveform of the binary image data, the converted multi-tone image data of 5 bits converted by the bit number conversion unit 72, and the light quantity waveform thereof are shown respectively, and the description is omitted because it is clear from the drawing. .

In the OR circuit 73, multi-tone image data or binary image data input via mutually different data buses are latched by the D-FF 70 or converted by the bit number conversion unit 72, respectively. The OR of the image data is taken and the D / A converter 6 is passed through the gate 75.
Output to 0,61.

The input multi-tone image data and the binary image data are input timing even if a photograph (multi-tone) or a character (binary) is mixed in the image data for one page. It is impossible that the input is overlapped at the same time.

Therefore, the multi-gradation image data and the converted multi-gradation image data of the binary image are collectively output by the OR circuit 73 to the LD control plate 4 to control the light amount of the LD 1, and thus two types are obtained. It is not necessary to provide different LD control plates, and a complicated switching circuit for switching the processing circuit according to the type of image data is not required. Therefore, the configuration is simple and the cost can be significantly reduced.

FIG. 7 shows a door provided between the LD unit 1 and the common power source LD5V for the LD control plate 4 provided near the LD unit 1 as shown in FIG. 4 and the normal power source Vcc. It is a circuit diagram which shows an example of a switch. Power supply L
As shown in FIG. 7, the D5V is supplied with power from the power supply Vcc via a normally (door closed) door switch 56 provided on, for example, a front door (not shown) of the image forming apparatus.

If the door is accidentally opened during operation of the image forming apparatus, or if the LD emits light for some reason while the door is being opened for repair and inspection, the main wavelength of the laser light is in the infrared region or near. Since it is in the infrared region, even if the laser light enters the eye, it is unaware that it may cause a serious accident such as visual field loss due to burning of the fundus of the eye or serious blindness.

Therefore, the door switch 56 interlocking with the opening and closing of the door opens the line for supplying power from the power source Vcc to the power source LD5V of the LD unit 1 when the door is opened, so that the LD2 does not emit light. However, since the LD control plate 4 also uses the common power source LD5V, chattering and LD of the door switch 56 are generated in a short time while the door switch 56 opens and the power source voltage drops.
A surge current may flow in the LD 2 due to unstable operation of the control plate 4, and the LD 2 may be deteriorated.

The comparator 74 inputs the voltage of the power source LD5V input to its + terminal to the − terminal in advance.
It is constantly monitored by comparing with a threshold voltage set slightly lower than V, and while the voltage of the power supply LD5V is normal, the level output to the gate 75 is set to high and the gate 75 is opened to open the OR circuit 7.
The output of 3 is passed as it is.

When the voltage of the power supply LD5V becomes equal to or lower than the threshold voltage, the comparator 74 sets its output level to low and outputs a negative logic voltage drop signal to the gate 75. Gate 7
Reference numeral 5 immediately closes in response to the voltage drop signal and disables the multi-gradation image data output by the OR circuit 73, that is, zero, so that the video current Iv and the reference current Ir output by the D / A converters 60 and 61, respectively. It becomes zero, and the driver circuit 62 sets the drive current Id to zero to prevent the surge current from flowing through the LD2.

If the reference current Ir is set to at least zero, even if the video current Iv is not zero, if the LD 2 emits even a small amount of light and the monitor current Im flows, the error current Ie becomes extremely large, and the driver circuit 62 operates. It is also possible to prevent the surge current by the feedback effect of making the drive current Id zero.

That is, although the circuit is not shown, if the reference current for inputting to the D / A converter 61 and determining the value of the reference current Ir is set to zero according to the voltage drop signal output from the comparator 74, D / A Even if the image data is input to the A converter 61, the output reference current Ir becomes zero. Alternatively, the same effect can be obtained by connecting the negative terminal of the error amplifier 63 to the ground according to the voltage drop signal.

The comparator 74 and the gate 75 are provided in the latch / conversion unit 5, and the power supply Vcc thereof is held at 5 V regardless of whether the door switch 56 is opened. Definitely done. It goes without saying that it is better to set the reference current of the D / A converter 61 (not shown) to zero, or obtain the power source of the circuit for connecting the negative terminal of the error amplifier 63 to the ground from Vcc.

[0061]

As described above, the image forming apparatus according to the present invention can easily process binary and multi-tone image data at low cost to form an image.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a configuration of a main part of an embodiment of the present invention.

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

3 is a block diagram showing an example of a control system of the laser printer shown in FIG.

FIG. 4 is a schematic configuration diagram showing an example of a main part of the optical writing unit shown in FIG.

FIG. 5 is a waveform diagram showing an example of an image clock, multi-gradation image data synchronized with the clock, and a light amount of laser light corresponding to the data.

FIG. 6 is a diagram showing an example of a part of bitmap data of a binary image, binary image data based on the data, converted multi-tone image data, and a light quantity waveform of laser light according to the data. Is.

FIG. 7 is a circuit diagram showing an example of an arrangement of door switches that open the power source of the LD unit.

FIG. 8 is a characteristic diagram showing an example of a relationship between a drive current of a laser diode and an output light amount.

[Explanation of symbols]

1: LD unit (laser output unit) 2: LD (laser diode) 3: PD (photodiode) 4: LD control plate 5: Latch / converter 26: Optical writing unit (means for forming an electrostatic latent image) 60: D / A converter (video converting means) 61: D / A converter (reference current output means) 62: Driver circuit (driving current output means) 63: Error amplifier 70: D-FF (flip-flop; data latch means) 72: Bit number conversion unit (bit number conversion means) 73: OR circuit (data transfer means) 74: Comparator (power supply voltage monitoring means) 75: Gate (laser diode protection means) Id: Drive current Ie: Error current Im: Monitor Current Ir: Reference current Iv: Video current

Claims (2)

[Claims] 1. A laser output unit in which a laser diode and a photodiode for detecting the amount of light are integrated into a unit, and an electrostatic latent image is formed on a photosensitive member by laser light output from the laser diode according to image data. An image forming unit, a video converting unit that converts the image data into a video current, a reference current outputting unit that outputs a reference current according to the image data, and the photodiode detects the light amount of the laser light. Error amplifier that outputs an error current corresponding to the difference between the monitor current that is output by the reference current output unit and the reference current that is output by the reference current output unit, and the error current output by the error amplifier from the video current output by the video conversion unit. Drive current output means for subtracting and outputting the drive current of the laser diode, the drive current output means and the reference current output means. In an image forming apparatus for controlling the light quantity of the laser light by a force means and the error amplifier, data latch means for latching and outputting multi-tone image data input in synchronization with an image clock by the image clock, Bit number converting means for converting the binary image data into multi-tone image data and outputting the multi-tone image data, and the multi-tone image data output by the bit number converting means or the data latch means for the video converting means and the reference current. An image forming apparatus, comprising: a data transfer unit for transferring to an output unit. 2. The image forming apparatus according to claim 1, wherein a power supply voltage monitoring unit that outputs a voltage drop signal when the power supply voltage of the laser diode becomes equal to or lower than a preset threshold voltage, and the monitoring unit outputs the voltage drop signal. Laser diode protection means is provided for setting the reference current output by the reference current output means to zero or disabling the multi-gradation image data output by the data transfer means in response to the voltage drop signal. Image forming apparatus.