JPH07144432A - Image forming device - Google Patents

Abstract

PURPOSE:To ensure that a sharp, intermediate tone image can be stably output, if the emission characteristics of a light source vary due to an environmental change. CONSTITUTION:If the average intensity of light of a light beam emitted from a light source based on test data entered after the adjustment of a light output power by a system controller 129 is detected by averaging the output from a PIN photodiode 123, the system controller 129 corrects conversion data stored as internal data based on an average state of intensity of light.

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 for forming a halftone image by a light beam whose pulse width is modulated based on inputted gradation image information, and more particularly to an image forming apparatus capable of executing APC control. It is about.

[0002]

2. Description of the Related Art In recent years, laser beam printers have attracted attention in terms of quietness, high speed printing, and high quality printing. In the case of color printing, a series of steps of scanning a light beam on a photoconductor to perform a first development and then transferring to a recording paper is performed in each toner color (yellow Y, magenta M, cyan C, black). The recording is repeated every K). It should be noted that the image signal is expressed in gradation by changing the light emitting area of the light beam by performing pulse width modulation to realize full color.

FIG. 21 is a block diagram illustrating a control configuration of a conventional image forming apparatus. The configuration and operation will be described below.

An image forming unit 702 forms multivalued image data based on an image code sent from the host computer 700, and an image processing unit 703 forms a pulse width modulation representing gradation based on the multivalued image data. Then, the laser driver unit 704 performs gradation printing. A printer unit 701 is provided.

In the laser driver section 704, the semiconductor laser is driven with a constant current. The threshold value of the current at which the laser emits 100% of the light amount greatly changes due to differences in individual lasers, changes in the surrounding environment, etc., so that the laser light emission amount is not stable as it is.

Therefore, the laser is continuously turned on before printing,
APC control is performed in which the laser emission light amount at that time is detected and a current value is set so that the predetermined light amount is obtained. As a result, the amount of light emitted from the laser when the laser is continuously turned on is maintained at the print density at which the toner is sufficiently attached.

[0007]

[Problems to be Solved by the Invention] However, the APC
Since the control only controls the current value flowing to the laser, when gradation is expressed by pulse width modulation, especially when the pulse width is small, the rise of the laser drive current,
Also, the fall time cannot be ignored, and the amount of emitted light varies.

FIG. 22 is a timing chart for explaining the APC control operation in the image forming apparatus shown in FIG.

As shown in this figure, for the laser drive pulse VDO of 1), the laser drive current VD of 2)
It becomes O-I.

As shown in the figure, when the 100% emission threshold of the laser varies between A and B, the laser drive current is optimally set by APC control, but the laser drive current rises and falls. Since the characteristics do not change, in the case of APC control A, the light output of 3) is obtained,
In the case of APC control B, the optical output of 4) will be obtained. When APC control is A, T2 is black (100% printing)
On the other hand, when the APC control B is used, it becomes black (100% printing) at T1.

The transition period (gray zone) from 0% to 100% printing is also different between A and B. Especially this phenomenon is
This characteristic is remarkable when the pulse output is small such that the rise and fall of the laser drive current cannot be ignored, and the state is shown in FIG. FIG. 23 is a diagram showing the response characteristics of the light quantity and the pulse width during APC control, in which the vertical axis represents the light quantity and the horizontal axis represents the pulse width.

As shown in this figure, even if the same drive pulse is given, the light output actually emitted (that is, the print gradation)
However, there is a problem in that it greatly varies depending on individual differences and the surrounding environment.

Further, in the conventional pulse width modulation circuit, trimmer adjustment (variable resistor) is performed while observing the pulse width modulation output with an oscilloscope or the like to determine the minimum pulse width and the maximum pulse width of the pulse width modulation output. Many of them are set, and i) they are only adjusted at the time of shipment from the factory, so the pulse width changes due to changes over time, environmental changes such as temperature and humidity, and changes in print density occur. In particular, in a color printer, the change in density appears as a change in hue, which is very noticeable. ii) There is also a problem that the characteristics (variation) of the laser drive circuit and the semiconductor laser are not adjusted.

The present invention has been made to solve the above-mentioned problems, and after the APC control is performed before printing, the average light amount of the light pulse emitted from the light source is detected by the test image data. By correcting the conversion data for converting the gradation image information based on the correspondence between the detected average light intensity value and the test image data, even if the light emission characteristics of the light source change due to environmental changes or the like. An object of the present invention is to provide an image forming apparatus capable of stably outputting a clear halftone image.

[0015]

An image forming apparatus according to the present invention comprises a modulation means for pulse-width-modulating a light beam based on conversion data of input gradation image information, and a light emission power of a light source for emitting the light beam. A light amount control means for adjusting and controlling
Detecting means for detecting the average light quantity of the light beam emitted from the light source based on the test data input after adjusting the light emission power by the light quantity control means, and the conversion based on the average light quantity state detected by the detecting means. And a correction means for correcting the data.

Further, the detecting means is configured to detect the average light quantity by integrating the light quantity of the light beam emitted from the light source.

Further, the correction means is configured to correct the conversion data based on the average light amount state detected by the detection means before printing each page.

[0018]

In the present invention, when the detecting means detects the average light quantity of the light beam emitted from the light source based on the test data inputted after the light emission power is adjusted by the light quantity control means, it is based on the average light quantity state. Since the correction means corrects the converted data by using the correction means, the correspondence between the average light emission amount of the light beam and the gradation image data can be always maintained in a predetermined relationship when one pixel is pulse-width modulated.

Further, since the detecting means detects the average light quantity by integrating the light quantity of the light beam emitted from the light source, it becomes possible to correct the conversion data by catching the accurate average light quantity.

Furthermore, since the correction means corrects the conversion data based on the average light intensity state detected by the detection means before printing each page, the conversion data can be corrected immediately in response to the time change, so that continuous image formation is possible. Sometimes it is possible to output a halftone image with no density difference between pages.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view for explaining a schematic structure of an image forming apparatus showing an embodiment of the present invention, which corresponds to, for example, a color laser printer and will be described as an example of multicolor printing in the color laser printer.

In FIG. 1, a photoconductor drum 501 rotating in a direction indicated by an arrow at a predetermined speed is charged by a charger 504 to a predetermined polarity and voltage value.

Next, the recording paper P is fed from the paper feed set 515 by the paper feed roller 514 one by one at a predetermined timing. When the detector 19 detects the leading edge of the paper, the laser light L modulated by the image signal VDO is emitted from the semiconductor laser 120 toward the polygon mirror 507, and the laser light L is scanned by the polygon mirror 507. , Lens 508 and mirror 509, and is guided to the photoconductor drum 501. The signal TOP from the detector 190 arranged at one end of the optical scanning is output to an image forming apparatus (not shown) as a vertical synchronization signal TOP indicating the leading edge of the recording paper. Similarly, when the laser light L is incident on the detector 200, a beam detect signal (hereinafter, referred to as BD) which is a horizontal synchronizing signal is output. Then, in synchronization with the TOP signal and the BD signal, the image signal VDO is sequentially sent to the semiconductor laser 120, and the photosensitive drum 501 is scanned and exposed. Then, the first electrostatic latent image is developed by the developing device 503Y, and the first yellow electrostatic image is formed on the photosensitive drum 501.
A toner image is formed.

A transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer drum 516 immediately before the leading edge of the recording paper P fed at a predetermined timing reaches the transfer start position, and the first toner image is recorded on the recording paper. At the same time as being transferred to P, the recording paper P is electrostatically attracted to the surface of the transfer drum 516. 5
Reference numeral 06 is a scanner motor.

Next, by scanning with the laser beam L, a second electrostatic latent image is formed on the photosensitive drum 501, and the developing device 503.
The second electrostatic latent image is developed by M, and the photosensitive drum 501
A magenta second toner image is formed thereon. And T
By the OP signal, the second toner image is transferred to the recording paper P in alignment with the position of the first toner image previously transferred to the recording paper P.

Similarly, when the third electrostatic latent image is formed and developed by the developing device 503C, the cyan toner image is transferred onto the recording paper P in alignment with it. Next, a fourth electrostatic latent image is formed, developed by the developing device 503K, and a black toner image is transferred onto the recording paper P in alignment with it.

In this way, one page of VD for each process
The O signal is sequentially output to the semiconductor laser 120. In addition, the toner image of the final transfer is cleaned by the cleaner 510 in each transfer process.
Swept away by.

The tip of the transferred recording paper P has a separating claw 51.
When approaching the position of 2, the separating claw 512 moves the transfer drum 516.
The recording paper P is separated from the transfer drum 516 by contacting the surface of the recording paper P. The separation claw 512 returns to the original position when the rear end of the recording paper P separates from the transfer drum 516. At that time, the charger 5
The stored charge on the recording paper P is removed by 11 and the separation claw 5
The separation of the recording paper P by 12 is facilitated and the air discharge during the separation is reduced. 513 is a fixing device and 529 is a paper discharge tray.

FIG. 2 shows a first example of the image forming apparatus shown in FIG.
3 is a block diagram illustrating the image processing configuration of FIG.

In the figure, reference numeral 100 denotes multi-valued image data Video [0..0] based on an image code sent from a host computer (not shown). ． 7] for forming the multivalued image data Video [0. ． 7]
A printer engine (image printing unit) that performs halftone printing based on the above, 102, 103, and 104 are buffers, and 105
Is the 8-bit multivalued image data composed of SRAM
After correction, 9-bit γ [0. ． 9], and 106 is γ [0. ． 9] is a digital-to-analog converter, 107 is a timing control circuit that controls the timing of the γ conversion table (γ correction table) 105, 108 is a frequency divider that divides the image clock VCLK by two, and 109 is 1/2 V of the output of frequency divider 108
Triangular wave generation circuit that generates a triangular wave synchronized with CLK, 1
Reference numeral 10 is a comparator for comparing the output DA of the D / A converter 106 and the output / TRI of the triangular wave generation circuit 109, and 11
3, 114 are I / O registers, 116 is a negative logic input O
An R circuit, 119 is a D / A converter for converting the digital output of the register 114 into an analog signal, and 120 is the photosensitive drum 5.
A semiconductor laser for irradiating 01 to form an electrostatic latent image, 12
1 is a switch for turning on / off based on the output of the OR circuit 116, 122 is a current source, and 123 is the semiconductor laser 1
A PIN photodiode that detects the light quantity of 20 and converts it into a current, 124 is a resistor that converts a current into a voltage, 125
Is an analog buffer, 126 is an integrator, 127 is an A / D
A converter, 128 is an I / O register of the output of the A / D converter, and 129 is a system controller for controlling the entire image printing unit 101. In addition, 130 is a humidity sensor, 13
1 is a register.

In the image forming apparatus thus constructed, the light beam emitted from the light source based on the test data input after the light emission power is adjusted by the light amount control means (APC control according to the procedure of the flowchart shown in FIG. 9). When the average light amount of the above is detected by averaging the output of the PIN photodiode 123 by the integrator 126, the system controller 129 corrects the conversion data stored as the internal data based on the average light amount state. It is possible to always maintain the correspondence between the average light emission amount of the light beam and the gradation image data in the predetermined relationship when the pulse width is modulated.

Further, since the detecting means detects the average light quantity by integrating the light quantity of the light beam emitted from the light source, it becomes possible to correct the conversion data by catching the accurate average light quantity.

Further, since the correction means corrects the conversion data based on the average light quantity state detected by the detection means before printing each page, the conversion data can be corrected immediately in response to the time change, so that continuous image formation is possible. Sometimes it is possible to output a halftone image with no density difference between pages.

First, the signal processing during the printing operation will be described.

The image forming section 100 uses the image code sent from a host computer (not shown) to generate an M code.
Halftone multi-valued 8-bit image data Video [0. ． 7] and image clock VCLK
Is sent to the image printing unit 101.

8-bit image data Video [0. ．
7] passes through the buffer 102, and the γ correction table 105
Entered in. The γ correction table 105 is composed of a 10-bit output SRAM module, and image data Video [0. ． 7] is input and the output data corresponding to the address is subjected to γ-corrected data γ [0. ． 9]. That is, for example, when the γ curve has the characteristic shown in FIG. 3, the correction data having the characteristic shown in FIG. ． 9], the gradation of print density is secured. However, the correction degree of γ correction (contents of SRAM) is set at the time of system adjustment described later.

Correction data γ [0. ． 9] is converted into an analog value DA by the D / A converter 106. The D / A converter 106, as shown in FIG. ． 8] is "00
Corresponding to 0h to 3FFh, from 0v to R
The analog value DA synchronized with the image clock VCLK is output at a resolution of 1024 steps up to efv ″ (see 1), 3), and 4) in FIG.

On the other hand, the image clock VCLK is supplied to the frequency divider 10
It is divided by 2 by 8 and the triangular wave signal 109
A TRI is generated (see 5 in FIG. 6)). The triangular wave generation circuit 109 has a configuration as shown in FIG. 7, for example.

FIG. 7 shows a triangular wave generation circuit 10 shown in FIG.
It is a circuit diagram which shows an example of 9.

In this figure, 141 and 142 are current sources, 143 is a changeover switch, and 144 is a capacitor. The changeover switch 143 has an input clock of 1/2.
When CLK is “H”, the a terminal and the c terminal are connected to allow the current value I from the current source 141 to flow through the capacitor 144. Then, the capacitor 144 is charged with electric charges, and the (voltage value) / TRI signal (voltage value) linearly increases.

Next, the input clock 1 / 2CLK is "L".
Then, the ends a and c of the changeover switch 143 are connected. Then, the charges accumulated in the capacitor 144 are discharged, and the / YTI signal (voltage value) linearly decreases. The current value I of each of the current sources 141 and 142 is such that the output swing of the triangular wave signal / TRI is 0 (v) to Vref.
The value is [v] (or slightly smaller).

An analog value DA is applied to the positive terminal of the comparator 110.
Is input, and the triangular wave signal / TRI is input to the negative terminal. The result of comparing the two becomes the negative logic pulse width modulation signal / VDO (see 6 in FIG. 6). The pulse width modulation signal / VDO is logically inverted by the negative logic input OR circuit 116 to become the laser drive signal ON.

When the laser drive signal is "ON", the ends a and b of the switch 121 are connected and the semiconductor laser 12
A current flows to 0 and it lights up, and black printing is performed. When the laser drive signal ON is "L", the a end and the b end of the switch 121 are separated, the current is turned off to the semiconductor laser 120 and the light is turned off, and white printing is performed (see 7 in FIG. 6).

In this way, multi-valued image data Video
[0. ． Pulse width modulation according to [7].

Next, system adjustment will be described with reference to the flowchart shown in FIG.

FIG. 8 is a flow chart showing an example of a first system adjustment processing procedure in the image forming apparatus according to the present invention. Note that (1) to (4) indicate each step.

This processing is carried out at power-on or before printing one page. First, APC control for adjusting the current flowing through the semiconductor laser during continuous lighting is first carried out (1), and then the humidity value is measured. Then, a basic γ-curve light amount corresponding to the surrounding environment is set (2), the contents of the γ conversion table 105 are measured so as to match the γ-curve light amount (3), and printing is performed (4).

FIG. 9 is a flow chart showing an example of the detailed procedure of the APC control processing shown in FIG. 8, and particularly corresponds to the APC control procedure of adjusting the emitted light quantity during continuous lighting of the semiconductor laser 120 to a predetermined light quantity. . Note that (10)-
(16) indicates each step.

First, the system controller 129 writes "L" in the register 113, activates the laser compulsory lighting signal / LON ("L"), and conducts the SW circuit 121 through the OR circuit 116 of negative logic input. And the current generated in the current source 122 is applied to the semiconductor laser 120.
Turn on and turn on (10). PIN photodiode 1
Reference numeral 23 is a package which is enclosed in the same package as the semiconductor laser 120 and which accurately converts the amount of light emitted from the semiconductor laser 120 into a current value.

The current generated by the PIN photodiode 123 is converted into a voltage value through the resistor 124, passes through the buffer 125, and is integrated (noise removal) by the integrator 126.
Then, it is converted into a digital value LMON by the A / D converter 127, and is taken into the system controller 129 via the register 128. System controller 129
Is LMON indicating the amount of light emitted from the semiconductor laser 120,
It is judged whether or not the value REF (100% light amount) corresponding to the predetermined light amount matches (11). If they match, the register 113 "H" is written and the / LON signal is set to "H". Then, the forced lighting of the semiconductor laser 120 is finished (16).

If LMON and REF do not match, it is judged whether LMON is smaller than REF (1
2), until LMON becomes smaller than REF, that is,
The value LI of the register 114 is decreased to reduce the output of the D / A converter 119, the current value of the current source 122 is decreased, and the emission light amount of the semiconductor laser 120 is reduced until the emission light amount of the semiconductor laser 120 becomes smaller ( 13). Then L
Judge whether MON is REF or more (14), LMO
Until N becomes REF or more, that is, the semiconductor laser 12
Until the amount of emitted light of 0 becomes a predetermined amount of light or more, the register 11
4 is increased to increase the output of the D / A converter 119, and the current value of the current source 122 is increased.
The amount of emitted light of 20 is increased (15).

After the semiconductor laser 120 is continuously lit in this way, the emitted light amount is set to a predetermined light amount,
"H" is written in the register 113, the / LON signal is set to "H", and the forced lighting of the semiconductor laser 120 is finished (16).

FIG. 10 is a flow chart showing an example of the γ setting processing procedure shown in FIG. Note that (20)-
(25) indicates each step. In the present embodiment, the γ setting corresponds to the process of measuring the surrounding environment (humidity value) and setting the basic γ curve (relationship between light quantity and print density) according to the surrounding environment.

First, the system controller 129 reads the humidity value detected by the humidity sensor 130 via the register 131.

The gamma correction process in the image forming apparatus according to the present invention will be outlined below with reference to FIG.

FIG. 11 is a diagram for explaining the γ correction processing in the image forming apparatus according to the present invention. FIG. 11A shows the relationship between the density data and the amount of laser light. Γ curve C is selected when the humidity is high, γ curve A is selected when the humidity is low, and γ curve A is selected when the humidity is moderate.
Select curve B and match the densities. (B) is a value AD obtained by digitally converting the average light amount of the semiconductor laser 120.
A table map of (output of A / D converter 127) and density is shown, and the table map is read from a ROM (not shown).

First, the system controller 129 reads the humidity value detected by the humidity sensor 130 via the register 131 (20). If the humidity value read from the register 131 is smaller than the reference minimum value (21), the γ curve A is selected (22), and if the humidity value is larger than the reference maximum value (23), the γ curve C (24) is changed to the humidity. If the value is greater than or equal to the reference minimum value and less than or equal to the reference maximum value, the γ curve B is selected (25).

In order to correct the pulse width so as to match the relationship between the density and the light amount thus selected, the γ conversion table 1
The pulse width correction processing shown in FIG. 12 for rewriting 05 is executed.

FIG. 12 is a flow chart showing an example of a detailed procedure of the pulse width correction processing shown in FIG. In addition,
(30 to (40) indicate each step.

First, R in the system controller 129
The density flag C in AM (not shown) is set to 00h (30), the output of the γ conversion table 105 is disabled by the timing control circuit 107, and the buffer 10
4 is activated and the input of the D / A converter 106 is changed to γ
The conversion table 105 is switched to the buffer 104 (31).

Next, the data Set of the buffer 104
[0. ． 9h is set to 00h (32), and initialization is performed. From the density-light amount γ curve (FIG. 11) set in the γ setting process shown in step (2) of FIG. 8, the density flag C
The light amount Pt corresponding to is read (33).

In addition, Set [0. ． 9] to buffer 10
4 to the D / A converter 106 for pulse width modulation, and the semiconductor laser 120 at that time reads LMON (A / D converter 127 output) indicating the average amount of emitted light (34). Then, the light amount value Pt to be set is compared with the actual light emission value LMON (35), and Set [0. ．
9] is incremented to increase the light emission amount (light emission pulse width) of the semiconductor laser 120 (36).

Set [0. ．
9] is the pulse width (γ conversion data) corrected to the light quantity corresponding to the density C (currently 00h), and the address of the γ conversion table 105 is C by the timing control circuit 107.
At the address of Set [0. ． 9] is written (37).

Next, the density flag C is incremented (38), and the sequence of the density graph C from 0 to FFh is repeated (39).

In this way, the density-light amount γ curve set in the γ setting processing shown in step (2) of FIG. 8 (see FIG. 1).
According to 1), after setting the contents of the γ conversion table 105 and performing pulse width correction, the input of the D / A converter 106 is returned to the γ conversion table 105 (40), and the pulse width correction is completed. , Print.

With the above-described adjustment, the amount of light emitted from the laser when one or more pixels are fully printed is kept constant (APC control), and the average amount of light emitted from the laser when one pixel is pulse-width modulated Correspondence with multi-valued image data can always be maintained in a predetermined relationship, so it is not affected by changes in the surrounding environment such as temperature and humidity, does not change over time, and gradation is always guaranteed. Various intermediate printing and color printing can be performed. [Second Embodiment] In the first embodiment, as a method for correcting the pulse width so as to correspond to a predetermined (average) light amount, γ
By configuring the conversion table widely and finely (8-bit to 10-bit conversion) and changing the contents of the conversion,
The pulse width was corrected.

In the second embodiment, the pulse width modulation section automatically adjusts the minimum pulse width so that the predetermined minimum emitted light quantity and the predetermined maximum light quantity are obtained, and the gradation is expressed between them. is there.

FIG. 13 is a block diagram for explaining the second image processing configuration of the image forming apparatus shown in FIG.

In FIG. 1, reference numeral 1 denotes an image forming section for forming multivalued image data based on an image code sent from a host computer (not shown), and 2 denotes γ conversion of the multivalued image data sent from the image forming section 1. γ conversion table, 3
Is a system controller that controls the entire system, and 4 is adjustment 8-bit data ADJγ [0. ． 7] and the output γ [0. ． 7]] is a switching device for selecting.

Reference numeral 5 is a D / A converter for converting the output of the switch 4 into digital / analog, and reference numeral 6 is for converting the digital data SET-OFS output from the CPU 21 into analog to be the reference voltage of the D / A converter 5. A / A converter, 10 is a D / A converter that generates a DC offset voltage, and 11 is a voltage adder that adds the offset voltage generated by the D / A converter 10 and the output of the triangular wave generator 28.

Reference numeral 12 is a comparator for comparing the output of the D / A converter 5 and the output of the voltage adder 11 to generate a pulse according to the multi-valued image data, and 14 is L of the system controller 3.
Negative logic input OR circuit for forcibly turning on the semiconductor laser 18 by an ON signal, 15 is ON / OF of the semiconductor laser 18.
SW and 16 that perform F are D / A converters that set the value of the current flowing through the semiconductor laser 18.

Reference numeral 17 is a variable current source, 18 is a semiconductor laser,
Reference numeral 19 is a PIN photodiode for detecting the light amount of the semiconductor laser 18, 20 is a buffer, 21 is an integrator, 22 is an A / D converter for digitally converting the output of the integrator 21, 2
5 is a frequency divider for dividing the image clock by 2, and 26 is a frequency divider 2
5 is a triangular wave converter for converting the output of 5 into a triangular wave.

27 is a DC component removing circuit for removing the output DC component of the triangular wave converter 26, and 28 is composed of the triangular wave converter 26 and the DC component removing circuit 27.
It is a triangular wave generator that generates a triangular wave having a cycle twice that of CLK.

First, the signal processing during the printing operation will be described with reference to the timing chart shown in FIG. 14 and the table shown in FIG.

The image forming section 1 uses the MCY based on the image code sent from the host computer (not shown).
Multi-valued 8-bit image data Vi corresponding to each K toner
deo [0. ． 7] is generated. The γ conversion table 2 is
Image data Video composed of ROM, RAM, etc.
[0. ． 7] is subjected to γ conversion correction (to correct linearity of halftone density), and γ [0. ． 7] is output (3 in FIG. 14).
reference).

The switch 4 is the system controller 3
The output of the γ conversion table 2 γ [0. ． 7] is selected, and the output ADJ [0 .. ． 7]
Select. γ [0. ． 7] passes through the switch 4 and is D / A converted by the D / A converter 5.

The D / A converter 5 is based on the table shown in FIG. ． 7], Ref (v) is output from 0 (v) (see 4 in FIG. 14). This D
The output of the / A converter 5 is connected to the negative terminal of the comparator 12.

In the frequency dividing circuit 25, the image clock VCLK
Is divided by 2 into a triangular wave by the triangular wave converter 26, the direct current component is removed by the direct current component removing circuit 27, and then the direct current voltage generated by the D / A converter 10 is converted into a triangular wave. Is added as an offset voltage by the voltage adder 11 to form a triangular wave signal / TRI. This triangular wave signal / TRI is connected to the positive terminal of the comparator 12 (FIG. 1).
4-5).

The comparator 12 constantly compares the output of the D / A converter 5 with the triangular wave signal / TRI to obtain the triangular wave signal / TRI.
Is higher than the output of the D / A converter 5, "H" is output, and when the triangular wave signal / TRI is smaller than the output of the D / A converter 5, "L" is output (see 6 in FIG. 14).

The output of the comparator 12 is a negative logic laser drive pulse / VDO, and γ [0. ． 7] is small, the period of “L” is short, and γ [0. ． When the value of 7] is large, the period of "L" becomes long. That is, γ
[0. ． 7] (that is, multi-valued image signal Video [0 ..
7]), a pulse width modulation output is produced.

Negative logic laser drive pulse / VDO is O
The SW 15 is controlled through the R circuit 14. OR circuit 14
The LON signal for forcibly turning on the laser is input from the system controller 3 to the other end of the. L
ON is used during system adjustment (details will be described later). The SW 15 is turned on when the output of the OR circuit 14 is “H” to supply a current to the semiconductor laser 18 to turn on the semiconductor laser 18, and the output of the OR circuit 14 is “L”.
At the time of, the current is supplied to the semiconductor laser 18 to turn off the semiconductor laser 18 (see 7 in FIG. 14).

In this way, an electrostatic latent image is formed on the rotary drum 501 and printing is performed.

Next, system adjustment will be described with reference to the flowchart shown in FIG.

FIG. 16 is a flowchart showing an example of a second system adjustment processing procedure in the image forming apparatus according to the present invention. Note that (50) to (53) indicate each step.

This processing is performed when the power is turned on or before each page is printed. As shown in FIG. 16, APC control for adjusting the supply current of the semiconductor laser is performed (50), and then the pulse width modulation section is performed. After the adjustment of the minimum pulse width (51) and the adjustment of the maximum pulse width (52), printing is performed (53).

The APC control (1) for adjusting the amount of light emitted from the semiconductor laser 18 when the semiconductor laser 18 is continuously turned on is the same as that of the first embodiment, and the description thereof is omitted.

FIG. 17 is a flow chart showing an example of the minimum pulse width control procedure shown in FIG. 16, and the pulse width is adjusted so that the minimum light amount at the time of halftone printing becomes a predetermined light amount so that toner does not adhere. It corresponds to the process of adjusting the minimum pulse width of modulation. Note that (60) to (65) indicate each step.

First, the system controller 3 sets the 8-bit adjustment data ADJ [0. ． 7] is set to "00h" and the switch 4 is set to ADJ [0. ． 7] side, the input data of the D / A converter 5 is fixed to "00h", and the output of the D / A converter 5 is set to 0v (60). At this time, if the output of the D / A converter 5 and the triangular wave / TRI are as shown in 3) of FIG. 19, for example, the laser drive pulse / VDO as shown in 4) of FIG. 19 is generated, and the semiconductor laser 18 blinks. repeat.

At this time, the PIN photo diode 19
A pulse current similar to the blinking of the semiconductor laser 18 is generated, converted into a voltage value on the pulse by the resistor R, and the integrator 21
The A / D converter 22 digitally converts the signal integrated and averaged by the A / D converter 22 and becomes LMON indicating the average laser light amount value.

By the system controller 3, LMON indicating the average light emission amount of the semiconductor laser 18 and a value MIN-corresponding to a predetermined minimum light amount so that toner does not adhere.
It is determined whether REF and REF match (61), and if they match, the adjustment of the minimum pulse width ends, and the process proceeds to step (52) shown in FIG. 16 to perform the maximum pulse width adjustment processing.

If they do not match, LMON indicates MIN-.
Until it becomes smaller than REF (that is, the semiconductor laser 18
(Until the amount of emitted light of the light becomes smaller than the predetermined amount of light) The digital input value SET-OFS of the D / A converter 18 is reduced to reduce the DC offset voltage of the triangular wave signal / TRI to reduce the minimum pulse width (62), (63).

Then, the digital input value SET-OFS of the D / A converter 10 is increased until LMON becomes approximately equal to MIN-REF, that is, until the average emitted light amount of the semiconductor laser 18 reaches a predetermined minimum light amount. Then, the DC offset voltage of the triangular wave signal / TRI is increased and the minimum pulse width is increased (64), (65).

In this way, the DC offset voltage of the triangular wave signal / TRI is adjusted so that the average light emission of the semiconductor laser 18 becomes a predetermined minimum light quantity when the data showing the minimum density is input.

Next, the maximum amount of light at the time of halftone printing is set to a predetermined amount of light so that the toner is sufficiently adhered, as shown in FIG.
The process of adjusting the maximum pulse width of pulse width modulation shown in step (52) of 6 is executed.

FIG. 18 is a flow chart showing an example of the maximum pulse width control procedure shown in FIG. In addition, (7
0) to (75) indicate each step.

First, the system controller 3 sets the 8-bit adjustment data ADJ [0. ． 7] is set to “FFh”, and the switching SW4 is set to ADJ [0. ． 7] side, the input data of the D / A converter 5 is fixed to “FFh”, and the output of the D / A converter 5 is set to the full scale value REF (70). This REF is the reference voltage value of the D / A converter 5, and is the digital output S of the system controller 3.
It is set by the D / A converter 6 that converts ET-REF to analog.

At this time, if the output of the D / A converter 5 and the triangular wave signal / TRI are, for example, as shown in FIG. 19, the laser drive pulse / VDO as shown in 6) of FIG. 19 is generated, and the semiconductor laser 18 blinks. repeat. At this time, a pulse current similar to the blinking of the semiconductor laser 18 is generated in the PIN photodiode 19, converted into a voltage value on the pulse by the resistor R, integrated by the integrator 21, and averaged. But A /
It is the same as when the minimum pulse width is adjusted, which is digitally converted by the D converter 22 and becomes LMON indicating the average laser light amount value.

The system controller 3 controls the LMON indicating the average amount of light emitted from the semiconductor laser 18 and the value MA corresponding to a predetermined maximum amount of light sufficient to adhere the toner.
It is judged whether or not it matches with X-REF (7
1) If they match, the adjustment of the maximum pulse width ends.

If they do not match, LMON is MAX-.
Until it becomes smaller than REF (that is, the semiconductor laser 18
(Until the emission of light becomes smaller than the predetermined maximum light amount), the digital input value SET-REF of the D / A converter 6 is subtracted to obtain D
The reference voltage REF of the / A converter 5 is reduced, the output value at full scale is reduced, and the maximum pulse width is reduced (72), (73).

Then, the digital input value SET-REF of the D / A converter 6 is increased until LMON becomes approximately equal to MAX-REF, that is, until the average emitted light amount of the semiconductor laser 18 reaches a predetermined maximum light amount. By subtracting the digital input value SET-REF of the D / A converter 6,
The reference voltage REF of the converter 5 is increased, the output value at full scale is increased, and the maximum pulse width is increased (74), (75).

Thus, in step (52) shown in FIG. 16, the semiconductor laser 18 is adjusted when the reference voltage REF of the D / A converter 5 is adjusted and the multivalued data indicating the maximum density is input. After setting the average emission light amount of 1 to be the predetermined maximum light amount, the process proceeds to step (53) to perform printing.

As a result, when the characteristics of the pulse output shown in FIG. 20 and the actual amount of emitted light vary, for example, as the characteristics A and B of FIG. 20, after the above adjustment is completed, the characteristic A , B can emit light in the light amount range from Bmin to Amax.

By the above adjustments, the amount of light emitted from the laser when one pixel or more is fully printed is kept constant, and the multi-valued image data and the average amount of light emitted from the laser when pulse width modulation is performed on one pixel. Since it is possible to stabilize the correspondence with, it is not affected by changes in the surrounding environment such as temperature and humidity,
High-quality halftone printing and color printing that always guarantee gradations can be performed without aging.

As described above, according to the present embodiment, the means for detecting the laser light, the integrating means for integrating and averaging the detected pulsed laser light, and the integrated value of the laser light have a predetermined light quantity. Therefore, a means for correcting the correspondence between the multivalued image data and the generated laser drive pulse width is provided. For example, after performing APC control before printing, the light pulse emitted by the test image data is detected by the photodiode, the output is integrated, and the average light intensity value of the light pulse is obtained to obtain the test image. The correspondence between the image data and the pulse width output is corrected from the correspondence between the data and the average light intensity value of the light pulse. This makes it possible to obtain high-quality halftone images with excellent gradation and high-quality color images with excellent gradation without being affected by differences in individual laser chips, environmental changes such as temperature and humidity, and changes over time. An image is obtained.

[0105]

As described above, according to the present invention,
When the detection means detects the average light quantity of the light beam emitted from the light source based on the test data input after the light emission power is adjusted by the light quantity control means, the correction means corrects the converted data based on the average light quantity state. Therefore, the correspondence between the average emission light amount of the light beam and the gradation image data when one pixel is pulse-width modulated can always be maintained in a predetermined relationship.

Further, since the detecting means detects the average light quantity by integrating the light quantity of the light beam emitted from the light source, it is possible to correct the conversion data by catching the accurate average light quantity.

Further, since the correction means corrects the conversion data based on the average light intensity state detected by the detection means before printing each page, the conversion data can be corrected immediately in response to the time change, so that continuous image formation is possible. Sometimes it is possible to output a halftone image with no density difference between pages.

Therefore, a high-quality halftone image excellent in gradation and a high-quality image excellent in color reproducibility can be obtained without being affected by individual differences of light sources, environmental changes such as temperature and humidity, and temporal changes. The effect that a high quality color image can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a first image processing configuration of the image forming apparatus illustrated in FIG.

3 is a characteristic diagram showing a relationship between a first pulse width and print density in the image forming apparatus shown in FIG.

FIG. 4 is a diagram showing a relationship between image data and γ correction in the image forming apparatus shown in FIG.

5 is a diagram illustrating output conversion values of the D / A converter illustrated in FIG.

FIG. 6 is a timing chart illustrating the operation of FIG.

FIG. 7 is a circuit diagram showing an example of the triangular wave generation circuit shown in FIG.

FIG. 8 is a flowchart showing an example of a first system adjustment processing procedure in the image forming apparatus according to the present invention.

9 is a flowchart showing an example of a detailed procedure of the APC control process shown in FIG.

10 is a flowchart showing an example of a γ setting processing procedure shown in FIG.

FIG. 11 is a diagram illustrating a γ correction process in the image forming apparatus according to the present invention.

12 is a flowchart showing an example of a detailed procedure of the pulse width correction processing shown in FIG.

FIG. 13 is a block diagram illustrating a second image processing configuration of the image forming apparatus illustrated in FIG.

FIG. 14 is a first timing chart illustrating the operation of FIG.

15 is a diagram illustrating output conversion values of the D / A converter illustrated in FIG.

FIG. 16 is a flowchart showing an example of a second system adjustment processing procedure in the image forming apparatus according to the present invention.

17 is a flowchart showing an example of the minimum pulse width control procedure shown in FIG.

18 is a flowchart showing an example of the maximum pulse width control procedure shown in FIG.

19 is a second timing chart illustrating the operation of FIG.

20 is a characteristic diagram showing a relationship between a second pulse width and print density in the image forming apparatus shown in FIG.

FIG. 21 is a block diagram illustrating a control configuration of a conventional image forming apparatus.

22 is an APC in the image forming apparatus shown in FIG.
6 is a timing chart illustrating a control operation.

FIG. 23 is a characteristic diagram showing a relationship between a pulse width and a light amount in a conventional image forming apparatus.

[Explanation of symbols]

 100 Image Forming Section 101 Image Printing Section 105 γ Conversion Table 109 Triangular Wave Generation Circuit 120 Semiconductor Laser 126 Integrator 129 System Controller

Claims (3)

[Claims] 1. A modulation means for pulse-width-modulating a light beam based on conversion data of inputted gradation image information, a light quantity control means for adjusting and controlling emission power of a light source for emitting the light beam, and this light quantity control means. Detecting means for detecting the average light quantity of the light beam emitted from the light source based on the test data input after the adjustment of the light emission power by the light source, and correcting the conversion data based on the average light quantity state detected by the detecting means. An image forming apparatus comprising: a correction unit. 2. The image forming apparatus according to claim 1, wherein the detecting unit detects the average light amount by integrating the light amount of the light beam emitted from the light source. 3. The image forming apparatus according to claim 1, wherein the correction unit corrects the conversion data based on an average light amount state detected by the detection unit before printing each page.