JPH11188910A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably forming a dot by preventing occurrence of vertical stripes in an image even when optical quantity distributions of LED elements are varied or focal depths of lens arrays are varied. SOLUTION: In this image forming apparatus, a lens array 13 is provided at a defocus position with respect to an LED array 12 and an image forming face on a photosensitive body 10. In this condition, the optical quantity distribution is likely expanded compared to a condition that the lens array is provided to a focus position. However, as the degree of the variation in the optical quantity distribution due to variation in focal depth of the lens array 13 becomes small, the optical quantity distribution of each LED element tends to be extended, but the variation therein is reduced as a whole and occurrence of vertical stripes in the image is prevented.

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 such as a printer, a digital copying machine, and a facsimile apparatus for forming an image by electrophotography using an LED array head as an optical writing means.

[0002]

2. Description of the Related Art Generally, in a printer for forming an image by electrophotography, a laser scanning optical system including a laser light source and a polygon mirror for deflecting and scanning the laser light is mainly used as an optical writing means. In recent years, in order to reduce the size and simplification of the entire device, an L
An image forming apparatus using an LED array head in which an ED array and a lens array are combined has also attracted attention. LE
The D array is formed by arranging a large number of LED elements on one straight line, and by performing light emission control of each LED element according to image data, optical writing on the photoconductor is performed.
An electrostatic latent image is formed.

Here, it is practically impossible to manufacture an LED array so that all the characteristics of a large number of LED elements are uniform. Therefore, the dot diameter formed differs depending on each LED element. Normal. Especially,
In a printer of a method of expressing gradation by an area gradation method in a 1-dot binary (having only ON / OFF information) recording method, a variation in dot diameter appears as a variation in density, and the image quality of gradation expression deteriorates Will cause. In an LED array printer, an image is always formed by the same LED element in the sub-scanning direction. Therefore, if there is a variation in dot diameter, the image is continued in the sub-scanning direction. Vertical streaks will occur. The vertical streak includes a white streak in which an image is lost in white and a black streak (thus, a streak which is darker than other portions) due to a narrowing (overlap) between adjacent dots.

For this reason, there has been proposed an LED array printer which uses an LED array head corrected so that the light amounts of all the LED elements are all uniform (Japanese Patent Laid-Open No. 5-4376). JP-A-5-50653, etc.). JP-A-5-437
According to Japanese Patent Application Laid-Open No. 6-264, the amount of light is made constant by performing trimming with a laser beam and adjusting the resistance value. According to Japanese Patent Application Laid-Open No. 5-50653, correction data for keeping the light amount of each LED element constant is obtained in advance, and a ROM storing the correction data is provided in the LED array head. Each LED element is turned on.

[0005]

However, the writing light corresponding to the image data emitted from each LED of the LED array is irradiated on the photosensitive member through the lens array to form a latent image. LED by various methods
Even if the light amount of the element is kept constant, it can be said that it is impossible to finally make the light amount distribution of all the dots uniform due to variations in the depth of focus of the lens array. As a result,
Vertical streaks and uneven density occur on the final image. Further, even if the spot diameter at a certain threshold level is made uniform, dots with a small drop in the potential of the photoconductor also occur, and dot formation becomes unstable.

[0006] These points will be described with reference to FIG. FIG. 17A shows an example of a general structure of this type of LED array 1, in which a large number of LEs are provided on a base substrate 2.
The D elements 3 are arranged on one straight line as indicated by a straight line L, and the individual electrodes 4 are alternately drawn from each LED element 3 in the sub-scanning direction. 5 is LED
The light-emitting portion of the element 3. FIGS. 17B and 17D show the respective LEs.
4 shows an example of a light amount distribution with variation when the D element 3 emits light. Here, for example, when the gradation is expressed by the area gradation method in the one-dot binary recording method, FIG.
(B) In accordance with a certain threshold level TH as shown in (d), dots D as shown in FIGS. 17 (c) and (e) are formed. In this case, white stripes between dots D ₁ and D ₂ shown in FIG. 17C are generated due to variations in the light amount distribution, and a central dot D ₃ shown in FIG. 17C. Although the spot diameter is large, the drop in the potential of the photoconductor is smaller than that of the others, so that dot formation becomes unstable. When the spot diameter at a certain threshold level TH is made uniform as shown in FIG. 17D, the generation of white streaks can be suppressed as shown in FIG. Dot D shown in
_Since the drop in the potential of the photoconductor is smaller than that of the others as in ₃ , dot formation may be unstable.

Accordingly, the present invention provides an image forming apparatus capable of forming a stable dot by reducing the occurrence of vertical streaks on an image even if the light quantity distribution in each LED element varies. With the goal.

[0008]

According to the first aspect of the present invention,
An image is formed by electrophotography by causing an LED array head composed of an LED array and a lens array in which light emitting portions of a large number of LED elements whose light emission is controlled according to image data is arranged in an array to face an image carrier. In the image forming apparatus, the lens array is disposed at a defocus position with respect to the LED array and an image forming surface on the image carrier.

Therefore, since the lens array is disposed at the defocus position, the light amount distribution tends to be broader than when the lens array is disposed at the focus position. Since the degree of distribution variation is reduced, the light amount distribution of each LED element tends to be widened as a result, but the variation is reduced as a whole, the occurrence of vertical streaks is reduced, and dots are stably formed. Can be formed.

In this case, the lens array may be disposed at the defocus position, for example, by disposing the lens array at a defocus position away from the focus position with respect to the LED array. do it. In addition, the lens array may be disposed at a defocus position away from the focus position with respect to the image forming surface on the carrier as in the third aspect of the present invention. According to this, the optical conjugate relationship between each LED element of the lens array and the image forming plane is maintained. Alternatively, the lens array may be disposed at the defocus position closer to the LED array from the focus position. In addition, the lens array may be disposed at a defocus position closer to the image forming surface on the carrier from the focus position. Also in this case, the optical conjugate relationship between each LED element of the lens array and the image forming plane is maintained.

[0011] The invention according to claim 6 is the invention according to claims 1 to 5.
The image forming apparatus according to any one of the above, further comprising: a storage unit storing correction data for setting a desired spot diameter preset for each LED element in the LED array for each of various image forming conditions; Specifying means for specifying forming conditions, and each LE in accordance with the specified image forming conditions
A correction data reading unit that reads correction data corresponding to the D element from the storage unit; and a drive control unit that controls a lighting operation of each LED element of the LED array using the read correction data.

Therefore, when the desired spot diameter is determined, even if the image forming conditions are changed, the correction data reading means reads the corresponding correction data from the storage unit in accordance with the image forming conditions, and reads the correction data. , The driving control means controls the lighting operation of the LED element, so that optical writing with a desired spot diameter is ensured. here,
Under the condition where the lens array is disposed at the defocus position, the formed dots are generally large, but the dot diameters can be made uniform to reduce the occurrence of vertical streaks. This is the same even when the image carrier to be used is changed or when the image forming conditions are simply changed. Also, from the viewpoint of setting the correction data, it is not necessary to set the LED array and the image carrier as a pair, and the versatility of the setting operation or the setting state can be secured.

[0013] The invention according to claim 7 is the invention according to claims 1 to 5.
In the image forming apparatus according to any one of the above, a storage unit that stores correction data for setting each spot diameter for each image forming condition and each spot diameter for each LED element in the LED array, Designating means for designating image forming conditions and spot diameters; correction data reading means for reading correction data corresponding to each LED element from the storage unit according to the designated image forming conditions and spot diameters; LE using the corrected data
Drive control means for controlling the lighting operation of each LED element of the D array.

Therefore, the present invention is basically the same as the image forming apparatus according to the sixth aspect of the invention, but additionally stores correction data for each spot diameter in the storage section. Therefore, even if the desired spot diameter is changed, each LED should be uniformed at that spot diameter.
The element can be turned on.

[0015] The invention according to claim 8 provides the invention according to claims 1 to 7.
In the image forming apparatus described in any one of the above, the light emission of each LED element is controlled by image data of a one-dot binary system. Therefore, when gradation is expressed by the one-dot binary method, dots are formed based on a certain threshold level, so that the formed image can be stabilized.

[0016]

FIG. 1 shows a first embodiment of the present invention.
7 will be described with reference to FIG. The image forming apparatus of the present embodiment is applied to an LED array printer that expresses a gradation by an area gradation method (such as an error diffusion method) in a one-dot binary method.

First, FIG. 4 shows a schematic structure of a writing section of an LED array printer. An LED array head 11 is provided so as to be close to and opposed to a drum-shaped photosensitive member 10 as an image carrier. This LED array head 11 is shown in FIG.
LED array 12 and lens array 1 having the structure shown in FIG.
3. That is, in the LED array 12 used in the present embodiment, similarly to the case shown in FIG. 17A, the light emitting portions 5 of the many LED elements 3 are arranged on the main scanning line as indicated by a straight line L on the base substrate 2. Arrange in one straight line,
The individual electrodes 4 are drawn alternately in the sub-scanning direction.

For such an LED array 12, L
The ED array controller 14 is connected. The LED array control unit 14 is supplied with image data, and is connected to a controller unit 15 that controls the image data. Thus, basically, the image data from an external device, for example, a frame memory, a scanner, or the like, is transmitted by the main scanning line synchronization signal / LSYNC from the controller unit 15 as a trigger, and the LED array control unit 14 is operated for each main scanning line.
The light emitting section 5 of each LED element 3 on the LED array 12 emits light in accordance with the image data, and the emitted light is irradiated and imaged on the photoreceptor 10 through the lens array 13 to form an electrostatic latent image. An image is formed.

FIG. 5 is a block diagram showing the structure of the LED array driving section 16 which is included in the LED array control section 14 and serves as driving means. The LED array driver 16 has a well-known configuration, and includes a shift register 17 and a latch 1.
8, an AND gate 19 and an LED driver 20. The shift register 17 receives the clock signal CL
One-dot binary image data of “0” or “1” is input in order from the dot 1 by OCK, and internally each dot data is sent to each register. When all the dot data of n pieces are sent, the latch 18 latches the data, and when the strobe pulse STB is input to the AND gate 19, only the dot (LED element) to which "1" of the image data is sent Is basically emitted by the LED driver 20 for the width of the strobe pulse STB.

Next, the configuration in the LED array control unit 14 will be described with reference to the block diagram shown in FIG. First,
FIFO (First-In First-Out) memory 2 for taking in one line of binary image data for one line from outside
1 is provided on the input side of the LED array drive unit 16. The FIFO memory 21 is reset by a main scanning line synchronizing signal / LSYNC from the controller unit 15, and takes in image data for one main scanning line. Then, the LED array driving unit 16 is reset by the main scanning line synchronizing signal / LSYNC from the controller unit 15, and the clock signal CLOC generated by the oscillator 22 is reset.
By K, the image data is sequentially sent from the FIFO memory 21 to the LED array drive unit 16 from dot 1 to dot n. Further, a strobe pulse generator 23 is connected to the LED array driver 16 in the LED array controller 14. The strobe pulse generator 23 is constituted by, for example, a counter, a comparator and the like, and generates a strobe pulse STB as shown in FIG. In the LED array driving section 16, a dot whose image data is "1" emits light at the timing of the strobe pulse STB.

In such a configuration, in this embodiment, as shown in FIG. 1, the lens array 13 in the LED array head 11 is disposed at the defocus position. Specifically, the lens array 13 is positioned at the focus position (position indicated by the distance L) with respect to the light emitting unit 5 of the LED array 12.
(A distance L '= L + t)
And a position (distance L ′) that moves the lens array 13 away from the focus position (position indicated by the distance L) by a small distance t with respect to the image forming plane of the photoconductor 10.
= L + t). As a result, the light emitting unit 5 of the LED array 12 and the image forming surface of the photoconductor 10 are separated by 2t with respect to the positional relationship (distance 2L) in the focus state, but are symmetric with respect to the lens array 13. The optical conjugate relationship between the two is maintained.

In such a configuration, t = 0.1 mm
In the case of (distance L ′), t = 0 mm without defocusing
FIG. 2 shows the light amount distribution characteristics in the case (distance L). t =
In the case of the defocus arrangement, the light amount distribution tends to be broader than in the focus state of 0 mm. . As a result, as shown in FIG. 3B, the light amount distribution of each LED element 3 is easy to spread, but the variation is reduced as a whole, so that vertical streaks on the image occur as shown in FIG. 3C. Can be reduced, and a stable dot D can be formed. By the way, when the peak light amount becomes too low as compared with the focus setting and the dots become unstable, the light amount of the LED array 12 may be increased as a whole. In this case, the formed dots D are entirely large, but the generation of vertical streaks can be suppressed,
A stable dot D can be formed. Further, in the case of the present embodiment, the method is applied to the one-dot binary recording method, and only one threshold level TH needs to be considered as shown in FIG.
And the occurrence of vertical stripes can be suppressed.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those described in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted. Also in the present embodiment, as shown in FIG. 8, the lens array 13 in the LED array head 11 is disposed at the defocus position, but the defocus direction is reversed. Specifically, the lens array 13 is moved closer to the light emitting unit 5 of the LED array 12 by a small distance t from the focus position (position indicated by distance L) (position of distance L ″ = L−t).
And the focus position (position indicated by the distance L) of the lens array 13 with respect to the image forming surface of the photoconductor 10
Is located at a position (distance L ″ = L−t) that is a short distance t from the control unit.
The light emitting unit 5 of the D array 12 and the image forming surface of the photoreceptor 10 are close to each other by 2t with respect to the positional relationship (distance 2L) in the focus state, but have a symmetric relationship with the lens array 13 and the optical relationship between them Conjugate relationship is maintained.

With such a configuration, the same effect as in the above embodiment can be obtained.

A third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the LED array head 11 in which the lens array 13 is disposed at the defocus position as shown in FIG. 1 or 8, for example, is used. FIG. 9 shows a configuration example of the optical writing device 31 in the LED array printer, which is mainly configured by the LED array drive unit 16 and the like. The LED array driver 16 is shown in FIG.
However, in the present embodiment, an eight-division synchronization signal / HSYNC (a signal obtained by dividing the line synchronization signal / LSYNC into eight) for performing light quantity control as described later by lighting time control. ), The shift register 1 is used as in the drive timing shown in FIG.
Reference numeral 7 is configured to be reset by an eight-segment synchronization signal / HSYNC. This shift register 17 is set to “0” or “1” by the clock signal CLOCK.
Input dot binary image data in order from dot 1,
Internally, it operates to send each dot data to each register. When all the N dot data have been sent, the latch 18 latches the data, and the strobe pulse S
When TB is input to the AND gate 19, only the dots (LED elements) to which the image data "1" has been sent are lit by the LED driver 20 for the width of the strobe pulse STB.

A strobe pulse generator 23 is connected to such an LED array driver 16 via a selector 32. The strobe pulse generation unit 23 is configured by, for example, a counter, a comparator, and the like.
Eight types of strobe pulses STB0 to STB7 are generated. These strobe pulses STB0 to STB7
Are different, and when the width of the strobe pulse STB0 is t, STB1 = 2t, STB2 = 4t, S
TB3 = 8t, STB4 = 16t, STB5 = 32t,
STB6 = 64t and STB7 = 128t are set to a power of two relationship. When each of the divided timings obtained by dividing one line into eight by the eight-divided synchronization signal / HSYNC is T0 to T7, the selector 32
At 0, the strobe pulse STB0, at the timing T1, the strobe pulse STB1,... At the timing T7, the strobe pulse STB7 is output to the AND gate 19 to perform the select operation.

A multi-level converter 33 is connected to the LED array driver 16 via a selector 34 as a separate system. The multi-level conversion unit 33 is constituted by, for example, an AND gate, and has 8-bit data b0 to b7.
Is output to the selector 34. The selector 34 selects these 8
Bit data b0 to b7 are converted to b0 at timing T0,
.. At timing T1, b7 at timing T7
Is output to the shift register 17. On the input side of the multi-level conversion unit 33, a FIFO (First-In First-Ou) is used to take in one-bit binary image data for one line.
t) The memory 21 and the correction data storage unit 35 as a storage unit
And are connected in parallel. This correction data storage unit 3
Reference numeral 5 denotes, for example, a ROM, which stores correction data for setting a desired spot diameter D preset for each of the LED elements 3 in the LED array 12 for each of various image forming conditions by a measuring method described later. . The correction data storage unit 35 is connected to an image writing condition setting unit 36 that functions as a designating unit. Here, in the image forming operation, when an image forming condition is specified by the image writing condition setting unit 36, the correction data corresponding to each LED element 3 is stored in the correction data storage unit 35 according to the specified image forming condition. It has a function of a correction data reading means for reading from the inside and outputting it to the multi-value conversion unit 33. Further, the multi-value conversion unit 33, the selector 34, and the LED array driving unit 16
Functions as drive control means for controlling the lighting operation of each LED element 3 of the LED array 12 using the read correction data.

Here, the acquisition of the correction data written and stored in the correction data storage section 35 in advance will be described.
As shown in FIG. 11, before the factory shipment, the correction data is acquired by the optical writing device 31 and the dot diameter data measuring device 41.
And is performed using This dot diameter data measuring device 4
1 is an optical writing device 31 through an interface (not shown).
Is connected detachably to the multi-value conversion unit 33, and includes a controller 42 containing a microcomputer and each LE
Beam dot diameter (spot diameter) when D element 3 is turned on
And a measurement condition setting unit 44 for setting measurement conditions by the dot diameter measurement device 43 for measuring the measurement result and outputting the measurement result to the controller 42.
A correction data setting unit 45 for outputting 8-bit correction data to the multi-value conversion unit 33 of the optical writing device 31 under the control of the controller 42; and a data storage unit 46 for storing the correction data when the correction data is determined It is composed of

Here, the correction data of the light quantity of each LED element 3 is 8-bit data (b0 to b7) for changing the lighting time, and the lighting in one line is divided into eight divided synchronization signals / HS.
The least significant bit b0 is assigned to T0, b1 is assigned to T1,..., And the most significant bit b7 is assigned to T0 at timings T0 to T7 divided into eight according to YNC, and a bit is set in the eight bits (1 ) Is data for lighting only the strobe pulse STBx at the timing Tx. FIG. 12 is an example.
Dot 1 (LED element 3 of No. 1) is corrected data “1
28 "(=" 10000000 ") indicates the drive timing. One line synchronization signal / LSYN
While C is being output, the corresponding strobe pulses STB0 to STB7 are output from the strobe pulse generator 23 and the selector 32 according to the timings T0 to T7 of the 8-divided synchronization signal / HSYNC obtained by dividing the C into eight. The light-up signal for dot 1 is output each time the sync signal / HSYNC is divided by eight, and is subjected to AND processing by the multi-level conversion unit 33, so that the bit indicating the correction data "128" is set in b7 (= T7). Strobe pulse STB at timing
The lighting is performed with a lighting width corresponding to the number 7. In this case, if the correction data is “127” (= “01111111”), the lighting is performed with the lighting width corresponding to each of the strobe pulses STB0 to STB6 at the timing of b0 to b6 (= T0 to T6) where the bit is set. . Further, for example, when the correction data is “12”
9 "(=" 10000001 "), lighting is performed at a lighting width corresponding to each of the strobe pulses STB0 and STB7 at two timings of b0 and b7 (= T0 and T7) where bits are set. The variable light amount method is known as a method for obtaining a multi-valued light amount of one dot in the gradation method based on the multi-valued representation of one dot (see “LED array writing color electrophotographic printer”, p.
206, see Journal of the Society of Electrophotography, Vol. 24, No. 3 (1995)),
The correction data for changing the dot diameter in the one-dot binary expression of the present embodiment can be easily applied as it is.

Under such an assumption, all N LEDs
A process of acquiring light amount correction data when always obtaining a desired dot diameter (spot diameter) D for the element 3 will be described with reference to a flowchart shown in FIG. Here, the measurement condition corresponding to the image forming condition such as the exposure condition is Cy (y = y
1 to Y: Y is arbitrary). First, it is checked whether a specified dot diameter D has been set (step S1). The specified dot diameter D means a target dot diameter at the time of actual image writing. The specified dot diameter D is the measurement condition setting unit 4
4 (Y in S1), the measurement condition Cy (y
= 1) is set (S2). This condition is set because the dot diameter changes depending on which light amount is used as the threshold value, and is set by the measurement condition setting unit 44 in accordance with one of the exposure conditions at the time of actual image writing. When the measurement condition Cy (y = 1) is set (Y of S2), n = 1 is set to target the dot 1 (the LED element 3 of No. 1) (S3). Next, the correction data Mny (meaning the correction data for the n-th LED element 3 in the measurement condition Cy) is temporarily set to “128” (= “10”).
000000 ”) (S4). However, there is no meaning limited to this numerical value“ 128 ”, and any numerical value within the range of“ 1 ”to“ 255 ”indicated by 8-bit data is arbitrary. Intermediate value “128” as in the present embodiment
It is preferable to use a numerical value that is expected to be closest to a desired dot diameter D based on existing experimental data or the like. This correction data Mny
Is set in the correction data setting unit 45 and is provided to the multi-value conversion unit 33 side.

Next, dot n, here, dot 1 (N
o. The first LED element 3) is turned on by the LED array drive unit 16 (S5). The lighting timing at this time is shown in FIG.
2 is shown. At this time, the dot diameter (spot diameter) Dd of the dot n is measured by the dot diameter measuring device 43 (S
6) Send the measurement result to the controller 42. The controller 42 receiving the measurement result checks whether or not the dot diameter Dd is almost equal to the specified dot diameter D (S
7). If they are still not substantially equal (N in S7), the value of the correction data Mny is increased or decreased (for example, changed to Mny = “129” or Mny = Change it to “127”. However, the increase / decrease range is not limited to 1) (S8), the dot diameter Dd of the dot n to be lit is measured again according to the correction data (S6), and this is changed to the dot diameter Dd. This operation is repeated until the value becomes almost equal to the specified dot diameter D. Here, the determination in step S7 should originally be a determination as to whether or not the two are completely equal.
Since it is conceivable that the dot diameter Dd may not always be equal due to a measurement error or the like, the data is determined to be normal when the data is within an acceptable approximate range. The approximate range is the number of bits of the correction data Mny,
The dot diameter Dd is determined in consideration of a measurement error of the dot diameter Dd, a variation range of the dot diameter that is allowable as a target image quality when an image is actually formed, and the like.

The measured dot diameter Dd is equal to the specified dot diameter D.
(Y in S7), the measurement condition Cy
The correction data Mny for the dot n at (y = 1) is stored in the data storage device 46 (S9). The correction data Mny at this time is a numerical value set in the correction data setting unit 45 at that time. Thereafter, the dot n, here, the dot 1 (the LED element 3 of No. 1) is turned off (S1).
0), n is incremented by +1 to target the next dot n, here, dot 2 (the LED element 3 of No. 2) (S11). At this time, it is checked whether the number of new dots n exceeds the total number N (S1).
2) If not, step S for dot n
The processes from 4 to S11 are similarly repeated. This allows
The correction data Mny for setting the dot diameter Dd to the specified dot diameter D for all the dots n (n = 1 to N) under the measurement condition Cy is stored in the data storage device 46.

When this processing is completed, other measurement conditions Cy
Is checked (S13), and if so, the measurement conditions are set to Cy (y = 2), Cy (y = 3),.
(Y = Y) are set in order (S2), and the above-described acquisition and storage processing of the correction data Mny is repeated for each measurement condition.

[0034] Thus, after all measurements were completed, the data storage device 46, condition correction data _{C 1 M 11 M 21 M 31} ... M N1 C 2 M 12 M 22 M 32 ... M N2 ... C Y M _{As in 1Y} M _2Y M _3Y ... M _NY , the correction data Mny for each dot is stored in such a manner that each measurement condition Cy is used as an address. The correction data Mny stored in the data storage device 46 is written into the correction data storage unit 35 in the optical writing device 31 using a ROM writer or the like, and is put to practical use.

When optical writing is actually performed by the optical writing device 31 using the correction data storage unit 35 into which such correction data Mny for each condition is written, the image writing condition setting unit 36 Set image forming conditions. These conditions correspond to the measurement conditions. For example, when an image forming condition corresponding to the measurement condition Cy is set, the correction data Mny specified by the corresponding measurement condition Cy is read from the correction data storage unit 35. The data is output to the multi-value converter 33. For example, in the case of the measurement condition _{C 2, M 12, M 22} ,
The correction data is read out as M ₃₂ ,..., M _N2 . Now, as an example, M ₁₂ = “48” (= “0011000
0 ”), M ₂₂ =“ 49 ”(=“ 00110001 ”),
If M ₃₂ = “51” (= “00110011”),
The lighting drive timing at this time is as shown in FIG.

That is, one dot binary image data is
One line is input to the O memory 21, and the image data is repeatedly output from the FIFO memory 21 at the timing of the 8-divided synchronization signal / HSYNC. On the other hand, from the correction data storage unit 35, 8 dots for each dot (each LED element 3) are stored.
The bit correction data is repeatedly output at the timing of the 8-divided synchronization signal / HSYNC, similarly to the image data. Then, the multi-value conversion unit 33 performs an AND operation on the image data and the correction data.
D is taken and sent to the selector 34 as 8-bit data (b0 to b7). At the selector 34, the timing T0
, The least significant bit b0, the bit b1 at the timing T1,
.., At timing T7, the most significant bit b7 is output.
On the other hand, the strobe pulse generator 23 outputs the strobe pulses S having different pulse widths at the respective timings T0 to T7.
TB0 to STB7 are output and lighted at the timing when AND is taken. In the case of dot 1, the light is turned on at timings T4 and T5 according to the strobe pulses STB4 and STB5.
Strobe pulses STB0, STB4, S at T4, T5
Lights according to TB5, and in the case of dot 3, the strobe pulse STB at timings T0, T1, T4, and T5.
0, STB1, STB4, and STB5 are turned on, and as a result, the dot diameter (spot diameter) in one line.
Is controlled to be uniform at D.

Therefore, according to the present embodiment, under the condition that the lens array is disposed at the defocus position, various photoconductors can be considered as measurement conditions Cy (accordingly, image forming conditions), Light amount correction data for setting the dot diameter for each image forming condition to D, which is assumed in consideration of conditions that can be changed during formation, is stored in the correction data storage unit 35.
Therefore, even if the image forming conditions are changed to match the characteristics of the photoreceptor to be used, the corresponding correction data Mny is read from the correction data storage unit 35 in accordance with the image forming conditions, and the correction data Mny is stored. Using each LED element 3
Can be controlled, so that optical writing with a desired spot diameter D is ensured. As a result, for example, as shown in FIG. 15, in order to increase the drop in the potential of the photoconductor 10 (increase the peak light amount and increase the light amount equal to or higher than the threshold level TH), the dots D formed as a whole increase. Since the dot diameters are uniform, it is possible to form a stable dot D by suppressing the occurrence of vertical streaks. Therefore, even when a high-density gradation is expressed by an area gradation with one dot binary value, an image with good gradation expression can be obtained.
This is the same even if the photoconductor to be used is changed later or the image forming conditions are simply changed. Further, regarding the work of setting the correction data, the LED array 12
And the photoconductor need not be set as a pair.
Since the D array head 11 can be used alone, versatility of the setting operation or the setting state can be secured.

A fourth embodiment of the present invention will be described with reference to FIG. Basically according to the third embodiment, in the present embodiment, each L in the LED array 12 is stored in the correction data storage unit 35 by a measurement method described below.
For the ED element 3, correction data for setting various spot diameters Dx for various image forming conditions is stored.

Here, the acquisition of the correction data previously written and stored in the correction data storage unit 35 will be described.
The acquisition of the correction data is performed by the optical writing device 31 and the dot diameter data measuring device 41 as shown in FIG.
And is performed using Various dot diameters (spot diameters) Dx (x = 1 to X: X for all N LED elements 3)
The process of acquiring the light quantity correction data when it is desired to obtain the light quantity correction data will be described with reference to the flowchart shown in FIG. First, it is checked whether a certain prescribed dot diameter Dx (x = 1) has been set (step S1 '). The certain prescribed dot diameter Dx means one of the dot diameters targeted at the time of actual image writing. When the specified dot diameter Dx is set by the measurement condition setting unit 44 (Y in S1 '), the measurement condition C
It is checked whether y (y = 1) has been set (S2).
When the measurement condition Cy (y = 1) is set (Y in S2),
In order to target the dot 1 (the LED element 3 of No. 1), n = 1 is set (S3). Next, the correction data Mnx
y (dot diameter Dx, n-th LE in measurement condition Cy)
(Meaning the correction data for the D element 3)
(= “10000000”) (S4 ′). The correction data Mnxy is set in the correction data setting unit 45 and is provided to the multi-value conversion unit 33.

Next, dot n, here, dot 1 (N
o. The first LED element 3) is turned on by the LED array drive unit 16 (S5). At this time, the dot diameter (spot diameter) Dd of the dot n is measured by the dot diameter measuring device 43 (S6), and the measurement result is sent to the controller 42. The controller 42 receiving the measurement result checks whether or not the dot diameter Dd is almost equal to the specified dot diameter Dx (S7 '). If it is still not almost equal (S
7 'N), the correction data Mnx according to the magnitude relationship between the two.
Increase or decrease the value of y (eg, Mnx
y = “129” or Mnxy = “127” ... however, the increase / decrease range is not limited to one.)
(S8 '), the dot diameter Dd of the lighted dot n is measured again in accordance with the correction data (S6), and the dot diameter Dd is measured.
This operation is repeated until d becomes almost equal to the specified dot diameter Dx.

The measured dot diameter Dd is equal to the specified dot diameter D.
When the value is substantially equal to x (Y in S7 '), the correction data Mnxy for the dot n under the measurement condition Cy (y = 1) is stored in the data storage device 46 when the specified dot diameter Dx (x = 1).
(S9 '). The correction data Mnxy at this time is a numerical value set in the correction data setting unit 45 at that time. Thereafter, dot n, here, dot 1 (No.
The first LED element 3) is turned off (S10), and n is incremented by +1 to target the next dot n, here, dot 2 (No. 2 LED element 3) (S11). At this time, it is checked whether or not the number of new dots n exceeds the total number N (S12). If not, the processes of steps S4 'to S11 are repeated for dot n. Thereby, the correction data Mnx for setting the dot diameter Dd to the specified dot diameter Dx for all the dots n (n = 1 to N) under the measurement condition Cy.
y is stored in the data storage device 46.

When this processing is completed, other measurement conditions Cy
Is checked (S13), and if so, the measurement conditions Cy (y = 2), Cy (y = 3),..., Cy
(Y = Y) are set in order (S2), and the above-described acquisition and storage processing of the correction data Mnxy is repeated for each measurement condition.

Further, after the process is completed for a certain specified dot diameter Dx, it is checked whether or not there is another specified dot diameter Dx (S14).
x (x = 2), Dx (x = 3),..., Dx (x = X) are set in this order (S1 '), and the above-described correction data Mnxy is obtained for each specified dot diameter for each measurement condition. -The storage process is repeated.

Therefore, after all the measurements are completed, the data storage device 46 stores the specified dot diameter D ₁ ; the condition correction data C ₁ M ₁₁₁ M ₂₁₁ M ₃₁₁ ... M _N11 C ₂ M ₁₁₂ M ₂₁₂ M ₃₁₂ . M _N12 … C _Y M _11Y M _21Y M _31Y … M _N1Y Specified dot diameter D ₂ ; Condition correction data C ₁ M ₁₂₁ M ₂₂₁ M ₃₂₁ … M _N21 C ₂ M ₁₂₂ M ₂₂₂ M ₃₂₂ … M _N22 … C _Y M _12Y M _22Y M _32Y ... M _n2Y ... defining the dot diameter D _X; condition correction data _{C 1 M 1X1 M 2X1 M 3X1} ... M NX1 C 2 M 1X2 M 2X2 M 3X2 ... M NX2 ... C Y M 1XY M 2XY M 3XY ... M _{Like NXY} , the correction data Mnxy for each dot is stored in such a manner that each specified dot diameter Dx and each measurement condition Cy are used as addresses. The correction data Mnxy stored in the data storage device 46 is written into the correction data storage unit 35 in the optical writing device 31 using a ROM writer or the like, and is put to practical use.

The correction data Mnxy for each such condition
When the optical writing is actually performed by the optical writing device 31 using the correction data storage unit 35 in which is written, a desired dot diameter and image forming conditions are set by the image writing condition setting unit 36. When a desired dot diameter and image forming conditions are set, the correction data Mnxy specified by the corresponding dot diameter Dx and measurement condition Cy is read from the correction data storage unit 35 and output to the multi-value conversion unit 33. For example, in the case of the dot diameter D ₂ and the measurement condition C ₂ , M ₁₂₂ and M
_The correction data is read out as ₂₂₂ , M ₃₂₂ ,..., M _N22 . As a result, lighting control is performed such that the dot diameter (spot diameter) is uniformed at an arbitrary and desired dot diameter Dx in any one line.

Therefore, according to the present embodiment, in addition to the above embodiment, the correction data M for each spot diameter Dx
Since nxy is also stored in the correction data storage unit 35, even when the desired spot diameter Dx is changed, each LED element 3 can be turned on so that the spot diameter Dx is made uniform. As a result, in the present embodiment as well, for example, as shown in FIG. 15, in order to increase the drop in the potential of the photoconductor 10 (increase the peak light amount and increase the light amount equal to or higher than the threshold level TH), it is formed entirely. However, since the dot diameter becomes uniform at a desired dot diameter, the generation of vertical streaks can be suppressed and a stable dot D can be formed.

In the third and fourth embodiments, the light quantity correction for equalizing the spot diameter of each LED element 3 is performed by controlling the light emission time.
The driving current for the D element 3 may be varied according to the correction data.

[0048]

According to the first to fifth aspects of the present invention,
Since the lens array is disposed at the defocus position, the light amount distribution tends to be wider than when the lens array is disposed at the focus position. As a result, the light amount distribution of each LED element tends to be widened, but the variation can be reduced as a whole,
Therefore, even if the light amount distribution in each LED element varies, it is possible to reduce the occurrence of vertical streaks on the image and form stable dots.

According to the present invention, under the condition that the lens array is disposed at the defocus position, a desired spot diameter preset for each LED element in the LED array for each of various image forming conditions is set. Storage unit for storing correction data for specifying the image forming conditions, specifying means for specifying desired image forming conditions, and each L in accordance with the specified image forming conditions.
By providing correction data reading means for reading the corresponding correction data for the ED element from the storage unit, and driving control means for controlling the lighting operation of each LED element of the LED array using the read correction data, In the case where the spot diameter is fixed, even if the image forming conditions are changed, the correction data reading unit reads the corresponding correction data from the storage unit according to the image forming conditions, and the drive control unit uses the correction data to execute the correction data. Since the lighting operation of the LED element is controlled, it is possible to secure optical writing with a desired spot diameter. As a result, under the condition that the lens array is disposed at the defocus position, the dots formed as a whole are formed. Is larger, but the dot diameters can be made uniform to reduce the occurrence of vertical streaks, which means that the image carrier used has been changed. The same applies to the case where the image forming conditions are simply changed. In addition, from the viewpoint of setting the correction data, it is not necessary to set the LED array and the image carrier as a pair. Versatility can be secured.

According to the seventh aspect of the invention, under the condition that the lens array is arranged at the defocus position, each spot of each LED element in the LED array is set for each image forming condition and each spot diameter. A storage unit for storing correction data for determining the diameter, a specifying unit for specifying a desired image forming condition and a spot diameter, and a correction corresponding to each LED element according to the specified image forming condition and the spot diameter Since correction data reading means for reading data from the storage unit and drive control means for controlling the lighting operation of each LED element of the LED array using the read correction data are basically provided, The same effect as in the case of the described invention can be obtained, but in addition, since the correction data for each spot diameter is also stored in the storage unit, the desired spot diameter can be changed. The LED elements as is also uniform in the spot size in the case of Tsu can be lighting operation.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, each of the L
Since the light emission of the ED element is controlled by the image data of the one-dot binary system, when the gradation is expressed by the one-dot binary system, the dots may be formed based on a certain threshold level. Image can be stabilized.

[Brief description of the drawings]

FIG. 1 is a side view showing an arrangement relationship near an LED array head according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a light amount distribution according to the focus position / defocus position.

FIG. 3 is an explanatory diagram showing an LED array, a light emission distribution, and dots to be formed.

FIG. 4 is a perspective view showing a schematic structure of a writing unit of the LED array printer together with a control system block.

FIG. 5 is a block diagram illustrating a configuration of an LED array driving unit.

FIG. 6 is a block diagram illustrating a configuration of an LED array control unit.

FIG. 7 is a time chart showing the drive timing.

FIG. 8 is a side view showing an arrangement relationship near an LED array head according to a second embodiment of the present invention.

FIG. 9 is a block diagram of an optical writing device showing a third embodiment of the present invention.

FIG. 10 is a time chart showing the basic LED array drive timing.

FIG. 11 is a block diagram showing an optical writing device and a dot diameter data measuring device.

FIG. 12 is a time chart showing a light amount control method based on variable light emission time.

FIG. 13 is a flowchart illustrating a process for acquiring correction data.

FIG. 14 is a time chart showing an example of lighting timing of each dot according to correction data.

FIG. 15 is an explanatory diagram showing an LED array, a light emission distribution, and dots to be formed.

FIG. 16 is a flowchart illustrating a process for acquiring correction data according to the fourth embodiment of the present invention.

FIG. 17 is an explanatory view showing a conventional LED array, a light emission distribution, and dots to be formed.

[Explanation of symbols]

 Reference Signs List 3 LED element 10 Image carrier 11 LED array head 12 LED array 13 Lens array 35 Storage unit 36 Designating means

Claims (8)

[Claims] 1. An electrophotographic method in which an LED array head composed of an LED array and a lens array in which light emitting portions of a large number of LED elements whose light emission is controlled in accordance with image data is arranged in an array is opposed to an image carrier. Wherein the lens array is disposed at a defocus position with respect to the LED array and an image forming surface on the image carrier. 2. The image forming apparatus according to claim 1, wherein the lens array is disposed at a defocus position away from the focus position with respect to the LED array. 3. The image forming apparatus according to claim 1, wherein the lens array is disposed at a defocus position away from the focus position with respect to the image forming surface on the image carrier. 4. The image forming apparatus according to claim 1, wherein the lens array is arranged at a defocus position closer to the LED array from the focus position. 5. The image forming apparatus according to claim 1, wherein the lens array is disposed at a defocus position approaching the focus position with respect to the image forming surface on the image carrier. 6. A storage section for storing correction data for setting a desired spot diameter preset for each image forming condition for each LED element in the LED array, and for specifying a desired image forming condition. Designating means; correction data reading means for reading out, from the storage unit, correction data corresponding to each LED element in accordance with the specified image forming condition; and reading out each LED element of the LED array using the read out correction data. The image forming apparatus according to claim 1, further comprising: a driving control unit configured to control a lighting operation. 7. A storage section for storing correction data for setting each spot diameter for each image forming condition and each spot diameter for each LED element in the LED array, and for storing a desired image forming condition and spot diameter. Specifying means for specifying, and each LE according to the specified image forming condition and spot diameter.
Correction data reading means for reading correction data corresponding to the D element from the storage unit; and drive control means for controlling a lighting operation of each LED element of the LED array using the read correction data. The image forming apparatus according to claim 1, wherein: 8. The image forming apparatus according to claim 1, wherein light emission of each LED element is controlled by image data of a one-dot binary system.