JPH10217538A - Led array printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate fluctuation of density by making uniform the dot diameter of each LED element even if the facing distance between an LED array head and an image carrier, e.g. a photosensitive body, is varied. SOLUTION: Even when the facing distance between an LED array head and an image carrier is varied at the time of image formation through the LED array head, a corresponding correction data for obtaining a desired dot diameter for each LED element 6 is read out from a memory section 17 depending on an actual facing distance detected by a distance detecting means 19. A drive control means then controls the lighting operation of the LED element 6 using the correction data to correct the quantity of light so that a desired dot diameter is obtained. According to the arrangement, optical writing with uniform dot diameter is ensured for each LED element 6 and an image having no fluctuation of density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array printer for forming an image by electrophotography using an LED array head as 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
LED array printers using ED array heads have also attracted attention. The LED array head has a large number of LED elements arranged in a line. By controlling the lighting of each LED element according to image data, optical writing is performed on the photoconductor, and an electrostatic latent image is formed. It is formed.

Here, the LED array head has a large number of LEs.
It is practically impossible to manufacture all the characteristics of the D element so as to be uniform. Conventionally, in order to obtain better image quality, the lighting amount of each LED element must be uniform. The lighting light amount of each LED element is corrected (for example, JP-A-62-179963, JP-A-2-62257, JP-A-3-1960).
No. 70, etc.).

However, when correction is performed so that the light amount becomes uniform for all the LED elements, there is a case where the diameter of the formed dot also differs due to the difference in the spot diameter. In particular, in a printer of a method of expressing gradation by an area gradation method using a one-dot binary method (having only ON / OFF information), as the density increases, variations in dot diameter appear as variations in density. This causes deterioration in image quality of gradation expression.

[0005] For this reason, an LED array printer using an LED array head whose light amount has been corrected so as to make all the spot diameters (dot diameters) uniform regardless of the variation in the light amount of each LED element. Is described in JP-A-4-305667. To explain the outline, a target spot width of the spot width of the light amount at a predetermined threshold value is set in the controller. Therefore, each LED element of the LED array head is driven by this controller, the spot width is measured, the measured spot width is compared with the target spot width by the controller, and L is set so that the measured spot width becomes the target spot width.
The value of the resistor of the drive IC for the ED array head is set. Then, the photoconductor having digital characteristics is operated at a predetermined threshold. As a result, variations in the depth of focus of the lens array and variations in the printing density due to the mounting accuracy of the LED chips can be reduced.

As described above, since the LED array head whose light amount has been corrected so that the dot diameters of the photoreceptor having digital characteristics at a certain threshold value are all uniform is used, variations in print density can be reduced. Therefore, even when expressing high-density gradations by the area gradation method in the one-dot binary method, high-quality images can be obtained because all dot diameters are uniform.

[0007]

By the way, it is desirable that the LED array head is originally installed at a position where the surface of the photosensitive member to be written is in focus. The dot diameter increases when moving away from or close to the photosensitive member from the position, and regular dots are not formed when the distance is too far or too close.

However, in reality, when an image is optically written on the surface of a photoreceptor by using an LED array head, the LED array head or the photoreceptor is relatively moved or rotated. The facing distance between the array head and the photoconductor varies. In this regard, it is indispensable to increase the design accuracy so as not to fluctuate so that dots are not formed, but it is impossible to prevent the change in dot diameter with the design accuracy.

As a result, for example, Japanese Patent Laid-Open No.
Even if an LED array head whose light amount is corrected so that the dot diameters are all uniform by using the method of JP-A No. 5667 is used, at a certain position, all the dot diameters are uniform at a specified dot diameter. In other positions, the dot diameters are uniform but differ from the prescribed dot diameters. Therefore, variations in density occur.
Furthermore, if the manner of changing the dot diameter with respect to the distance to the photoreceptor in each LED element is different, all dot diameters are uniform at a certain position, but may vary at other positions. This causes variations in density.

In view of the above, the present invention provides that even if the facing distance between an LED array head and an image carrier such as a photoreceptor fluctuates,
An object of the present invention is to provide an LED array printer capable of making the dot diameter of each LED element uniform and avoiding variations in density.

[0011]

According to the first aspect of the present invention,
In an LED array printer that forms an image by electrophotography by causing an LED array head in which a number of LED elements whose lighting is controlled in accordance with image data is arranged in a line to face an image carrier, Distance detecting means for detecting a facing distance with respect to the image carrier,
A storage unit storing correction data of the amount of light for obtaining a desired dot diameter according to the facing distance for each of the LED elements, and correction data corresponding to each LED element according to the detected facing distance from the storage unit. Reading the correction data using the correction data reading means;
Drive control means for controlling the lighting operation of each LED element of the ED array head.

Therefore, even when the distance from the LED array head to the image carrier varies during the image formation by the LED array head, each LED element is handled in accordance with the actual facing distance detected by the distance detecting means. The correction data is read from the storage unit, and the drive control unit controls the lighting operation of the LED element using the correction data to correct the light amount to a desired dot diameter. The dot diameter of the element can be made uniform. Therefore, an image having no density variation can be obtained.

According to a second aspect of the present invention, an image is formed by electrophotography by causing an LED array head, in which a large number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier. In the LED array printer, distance detecting means for detecting a distance from the LED array head to the image carrier, and correction data of a light amount for various dot diameters according to the distance of each LED element are stored. Storage unit, a designation unit for designating a desired dot diameter, and a correction data reading unit for reading correction data corresponding to each LED element from the storage unit in accordance with the facing distance detected for the designated dot diameter. And L using the read correction data.
Drive control means for controlling the lighting operation of each LED element of the ED array head.

Therefore, in the case of the present invention, it is basically the same as the LED array printer according to the first aspect. In addition, correction data for various dot diameters according to the facing distance are also stored in the storage unit. Since the stored dot information is stored, even when a desired dot diameter is desired to be changed, each LED element can be turned on so as to be uniform at the designated dot diameter regardless of the change in the facing distance.

According to a third aspect of the present invention, an image is formed by an electrophotographic method by causing an LED array head, in which a plurality of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier. In the LED array printer, position detecting means for detecting a rotational position of the image carrier, and data of facing distance to the image carrier from the LED array head previously detected at each position in the rotation direction of the image carrier. A stored distance storage unit, a correction data storage unit storing correction data of a light amount for obtaining a desired dot diameter according to a facing distance of each of the LED elements, and a storage unit of the image carrier detected by a position detection unit. The facing distance data is read from the distance storage unit based on the rotation position, and the corresponding correction data for each LED element is read in accordance with the facing distance data. A data reading means for reading from the storage unit, using said correction data read LE
Drive control means for controlling the lighting operation of each LED element of the D array head.

Accordingly, the present invention is also basically the same as the LED array printer according to the first aspect of the present invention, but does not detect the distance from the LED array head to the image carrier during image formation. Since the countermeasure distance data stored in advance is read out from the distance storage unit based on the detection of the rotational position of the image carrier, the apparatus configuration relating to the distance detection can be simplified, and the linear velocity of the image carrier can be reduced. And it is possible to sufficiently cope with the case where it is difficult to detect the facing distance.

According to a fourth aspect of the present invention, an image is formed by electrophotography by causing an LED array head, in which a number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier. In the LED array printer, position detecting means for detecting a rotational position of the image carrier, and data of facing distance to the image carrier from the LED array head previously detected at each position in the rotation direction of the image carrier. A stored distance storage unit, a correction data storage unit storing correction data of a light amount for forming various dot diameters according to the facing distance of each of the LED elements, and a designation unit for designating a desired dot diameter. Reading the facing distance data from the distance storage unit based on the rotational position of the image carrier detected by the position detecting means, and setting the dot diameter to the designated dot diameter. Data reading means for reading out, from the storage unit, correction data corresponding to each LED element according to the facing distance data, and controlling the lighting operation of each LED element of the LED array head using the read correction data. Drive control means.

Therefore, in the case of the present invention, it is basically the same as the LED array printer according to the third aspect, but in addition, correction data for various dot diameters according to the facing distance are also stored in the storage unit. Since the stored dot information is stored, even when a desired dot diameter is desired to be changed, each LED element can be turned on so as to be uniform at the designated dot diameter regardless of the change in the facing distance.

The invention according to claim 5 is the invention according to claims 1, 2, 3
5. The LED array printer according to claim 4, wherein the distance from the LED array head to the image carrier is the LE.
Detection is performed at a plurality of locations in the main scanning direction of the D array head. Therefore, the correction accuracy is basically improved, and it is possible to appropriately cope with the case where the variation of the facing distance differs depending on the position in the main scanning direction.

[0020]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. First, FIG. 2 shows a schematic structure of a writing section of an LED array printer, in which an LED array head 2 is provided so as to be in close proximity to a drum-shaped photosensitive member 1 serving as an image carrier. Further, a distance detection sensor 3 for detecting a facing distance L from the LED array head 2 to the surface of the photoconductor 1 is provided at one end of the LED array head 2 in the main scanning direction (longitudinal direction). The distance detection sensor 3 is of an optical type. For example, when the facing distance L cannot be detected on the photoconductor 1, the detection location is set outside the image forming area or outside the effective image area on the photoconductor 1. In order to easily detect the surface of the photoreceptor 1, it is only necessary to devise.

FIG. 1 shows an example of the electrical configuration of the optical writing device 4 in such an LED array printer, which is mainly composed of an LED array drive circuit 5. The LED array drive circuit 5 includes the LED array head 2 in which a large number (for example, N) of LED elements 6 are arranged in a line, and an LED array drive unit 7 that controls lighting of each LED element 6. Have been. More specifically, the LED array driver 7 has a well-known configuration as shown in FIG. 3, and includes a shift register 8, a latch 9, an AND gate 10, and an LED driver 11.
It is composed of

In this embodiment, however, since an eight-segment 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 is used, FIG. As shown in the driving timing shown in FIG.
It is configured to be reset by the NC. The shift register 8 operates in such a manner that one-dot binary image data of "0" or "1" is inputted in order from the dot 1 by the clock signal CLOCK, and internally the dot data is sent to each register. When all the N dot data have been sent, the latch 9 latches the data, and when the strobe pulse STB is input to the AND gate 10, the dot (LE) to which "1" of the image data has been sent is sent.
Basically, only the D element) is turned on by the LED driver 11 for the width of the strobe pulse STB.

The L in such an LED array driving circuit 5
A strobe pulse generator 12 is connected to the ED array driver 7 via a selector 13. The strobe pulse generator 12 is constituted by, for example, a counter, a comparator and the like, and generates eight types of strobe pulses STB0 to STB7. These strobe pulses STB0 to STB7 are different from each other, and when the width of strobe pulse STB0 is t, STB1 =
2t, STB2 = 4t, STB3 = 8t, STB4 = 1
6t, STB5 = 32t, STB6 = 64t, STB7
= 128t. The selector 13 converts one line into eight divided synchronization signals / HSY.
The divided timings divided into eight by the NC are sequentially denoted by T0 to T
7, at timing T0, the strobe pulse ST
B0, at timing T1, the strobe pulse STB1,
.., At the timing T7, a select operation is performed so as to output the strobe pulse STB7 to the AND gate 10, respectively.

The LED in the LED array driving circuit 5
For the array drive unit 7, the multi-value conversion unit 1 is provided as a separate system.
4 is connected via a selector 15. The multi-level conversion unit 14 is configured by, for example, an AND gate, and outputs 8-bit data b0 to b7 to the selector 15. The selector 15 outputs these 8-bit data b0 to b7 to the shift register 8 every time during the timing T0 to T7. A FIFO is provided on the input side of the multi-level conversion unit 14 in order to capture 1-bit binary image data for one line.
A (First-In First-Out) memory 16 and a correction data storage unit 17 as a storage unit are connected in parallel.
The correction data storage unit 17 has, for example, a ROM configuration, and performs various image forming conditions for each LED element 6 in the LED array head 2 according to a measurement method described later.
Correction data for setting a desired dot diameter D preset for each facing distance L from the array head 2 to the photoconductor 1 is stored. The correction data storage unit 17 includes an image writing condition setting unit 18 functioning as a designating unit and a distance detecting unit 19 functioning as a distance detecting unit that converts the detection output of the distance detecting sensor 3 into data of the facing distance L. Is connected. The distance detection unit 19 sends the facing distance data to the correction data storage unit 17 at the timing of the line synchronization signal / LSYNC from the controller 20.

Here, in the image forming operation, when an image forming condition is designated by the image writing condition setting unit 18,
In accordance with the designated image forming condition and further according to the facing distance data L obtained from the distance detecting unit 19, the corresponding correction data for each LED element 6 is read out from the correction data storage unit 17 and multi-valued. It has a function of a correction data reading means to be output to the conversion unit 14. The multi-level conversion unit 14, the selector 15, and the LED array driving unit 7 use the read correction data to read the LED array head 2
Function as drive control means for controlling the lighting operation of each LED element 6.

Here, the acquisition of the correction data previously written and stored in the correction data storage unit 17 will be described.
As shown in FIG. 5, the correction data is acquired before shipment from the factory.
This is performed using the optical writing device 4 and the dot diameter data measuring device 21. The dot diameter data measuring device 21 is detachably connected to the multi-value conversion section 14 of the optical writing device 4 by an interface (not shown), and includes a controller 22 having a built-in microcomputer and each LED element 6.
The distance between the dot diameter measuring device 23 which measures the dot diameter when is turned on and outputs the measurement result to the controller 22, and the dot diameter data measuring device 21 for the LED array head 2 and the photosensitive member substitute. A distance adjusting device 24 for variably adjusting L under the control of the controller 22;
A measurement condition setting unit 25 for setting measurement conditions by the dot diameter measurement device 23; and a correction data setting for outputting 8-bit correction data to the multi-value conversion unit 14 of the optical writing device 4 under the control of the controller 22. It comprises a unit 26 and a data storage device 27 that stores the correction data when the correction data is determined.

Here, the correction data of the light quantity of each LED element 6 is 8-bit (b0 to b7) data for changing the lighting time, and the lighting in one line is divided into eight divided synchronization signals / HS.
With respect to timings T0 to T7 divided into eight according to the YNC, the least significant bit b0 is assigned to T0, b1 is assigned to T1,..., And the most significant bit b7 is assigned to T7. ) Is data for lighting only the strobe pulse STBx at the timing Tx.

FIG. 6 shows an example in which dot 1 (the LED element 6 of No. 1) is corrected with correction data “128” (= “1000”).
000 ") indicates the drive timing when the light is turned on.
While the two line synchronization signals / LSYNC are being output, the corresponding strobe pulse S in accordance with timings T0 to T7 of the eight division synchronization signal / HSYNC obtained by dividing the eight line synchronization signals / LSYNC.
TB0 to STB7 are output from the strobe pulse generator 12 and the selector 13. Lighting signal for dot 1 is 8
The multi-level conversion unit 14 performs an AND process on the divided synchronization signal / HSYNC every time, thereby correcting the correction data “1”.
At a timing of b7 (= T7) in which a bit indicating "28" is set, the lighting is performed with a lighting width corresponding to the strobe pulse STB7. In this case, the correction data is "127" (= "01").
If 11111 ″ 1), b0 with a bit set
At the timing of b6 (= T0 to T6), lighting is performed with a lighting width corresponding to each of the strobe pulses STB0 to STB6. For example, when the correction data is “129” (= “10000”).
01 "), b0 and b7 (=
(T0, T7) at two timings, with a lighting width corresponding to each strobe pulse STB0, STB7. Such a variable light amount method is known as a method of obtaining a multi-valued light amount of one dot in a gradation method based on a multi-valued representation of one dot (refer to the document “Color electrophotographic printer of LED array writing method”, p. 206, see the Journal of the Institute of Electrophotographic Engineers, Vol. 24, No. 3 (1995)), and can be easily applied to the correction data for changing the dot diameter in the one-dot binary expression of the present embodiment.

Under such an assumption, all N LEDs
A process of acquiring light quantity correction data when it is desired to always obtain a desired dot diameter D for the element 6 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 C _y (y = 1 to Y: Y is arbitrary), and the facing distance L _z (z) between the LED array head 2 and the dot diameter data measuring device 21 is set. = 1 to Z: Z is arbitrary). However, for the confronting distance _Lz , the distance and fineness to be measured are determined from the focal length and the maximum fluctuation width in an actual LED array printer, and the degree of distance fluctuation that affects the dot diameter.

First, it is checked whether a specified dot diameter D has been set (step S1). This specified dot diameter D
Means the target dot diameter at the time of actual image writing. When the prescribed dot diameter D is set by the measurement condition setting unit 25 (Y in S1), it is checked whether the measurement condition C _y (y = 1) is set (S2). This condition is set because the dot diameter changes depending on which light amount is used as the threshold, and is set by the measurement condition setting unit 25 in accordance with one of the exposure conditions at the time of actual image writing. When the measurement condition C _y (y = 1) is set (Y in S2), it is checked whether the facing distance L _z (z = 1) is set (S
3). For example, when measuring from 5 mm to 5.2 mm at 0.05 mm intervals, the facing distance L ₁ is set to 5 mm.

After completion of such various settings, the dot 1
(No. 1 LED element 6)
It is set to 1 (S4). Then, the correction data _M nyz (facing distance L _z, the n-th in the measurement condition C _y LED element 6
Tentatively) to “128” (= “1”).
000000 ”) (S5). However, there is no meaning limited to this numerical value“ 128 ”, and any numerical value within the range of“ 1 ”to“ 255 ”represented 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 M
_nyz is set in the correction data setting unit 26, and the multi-value conversion unit 1
Given to the 4 side.

Next, dot n, here, dot 1 (N
o. The first LED element 6) is turned on by the LED array drive unit 7 (S6). The lighting timing at this time is shown in FIG. The dot diameter D _d of the dot n at this time was measured by dot diameter measuring device 23 (S7), and sends the measurement result to the controller 22. Measurement results in the controller 22 has received its dot diameter D _d checks almost equal or not to the provision dot diameter D (S8). If the values are still not substantially equal (N in S8), the value of the correction data _Mnyz is increased or decreased (for example, _Mnyz is changed to "129", depending on the magnitude relationship between the two). M
_Nyz = or changed to "127" ... although varying width is not limited to one by 1) (S9), again measured dot diameter D _d of the dot n to be turned in accordance with the correction data (S
7) This is repeated until the dot diameter D _d is almost equal to the specified dot diameter D. Here, for the determination in step S8, the inherent, although both should be exactly equal to determination of whether the number of bits of the correction data M _{ny z,} the measurement error of the dot diameter D _d Since it is conceivable that the relationship is not always the same, it is determined that the data is normal when the data is within an acceptable approximation range. This approximation range, the correction number of bits of the data M _Nyz, measurement error of the dot diameter D _d, is determined by actually considering variation range of the dot diameter may be acceptable quality aim when forming an image.

The measured dot diameter _Dd is _equal to the specified dot diameter D.
(Y in S8), the measurement condition C _y
(Y = 1), dot n at facing distance L _z (z = 1)
_Is stored in the data storage device 27 (S10). The correction data M _nyz at this time is a numerical value set in the correction data setting unit 26 at that time.
Thereafter, dot n, here, dot 1 (L of No. 1)
The ED element 6) is turned off (S11), and n is incremented by +1 to target the next dot n, here, dot 2 (the LED element 6 of No. 2) (S1).
2). At this point, it is checked whether or not the new dot n exceeds the total number N (S13).
Steps S5 to S12 are repeated for dot n. Thus, the measurement condition C _y and the facing distance L
correction data M _Nyz for the dot diameter D _d for all the dots n (n = 1~N) and defining dot diameter D in _{the z} are stored in the data storage device 27.

When this processing is completed, another facing distance L _z
It is checked whether or not there is a setting (S14). If there is, the measurement conditions are set to L _z (z = 2), L _z (z = 3),
, L _z (z = Z) (S3), and the above-described acquisition and storage processing of the correction data M _nyz is repeated for each facing distance L _z . Further, a certain measurement condition C _y (y = y
After the process is finished for 1), and checks whether or not another measurement condition C _y there (S15), and their measurement conditions if _{C y (y = 2),} C y (y = 3), …, C _y (y
= Y) (S2), and the above-described process of obtaining and storing the correction data M _nyz is repeated for each measurement condition.

Therefore, after all the measurements are completed, the data storage device 27 stores the measurement condition C ₁ ; distance correction data L ₁ M ₁₁₁ M ₂₁₁ M ₃₁₁ ... M _N11 L ₂ M ₁₁₂ M ₂₁₂ M ₃₁₂ . _{N12 ... L Z M 11Z M 21Z} M 31Z ... M N1Z measurement condition C _2; distance correction data _{L 1 M 121 M 221 M 321} ... M N21 L 2 M 122 M 222 M 322 ... M N22 ... L Z M 12Z M 22Z M _32Z … M _N2Z … Measurement condition C _Y ; Distance correction data L ₁ M _1Y1 M _2Y1 M _3Y1 … M _NY1 L ₂ M _1Y2 M _2Y2 M _3Y2 … M _NY2 … L _Z M _1YZ M _2YZ M _3YZ … M _NYZ , so that the corrected data M _Nyz for each dot in the form of an address to each measurement condition C _y and the facing distance L _z are stored. The correction data _Mnyz stored in the data storage device 27 is written into the correction data storage unit 17 in the optical writing device 4 using a ROM writer or the like,
Provided for practical use.

The correction data M _{nyz for} each such condition
When optical writing is actually performed by the optical writing device 4 using the correction data storage unit 17 in which is written, the image forming conditions are set by the image writing condition setting unit 18. Then, it will initiate the writing of the image, prior to this, facing distance L _z between the LED array head 2 and the photosensitive member 1 is detected by the distance detection sensor 3, the sensor output is a distance detection unit 19 Sent to Therefore, by converting to the nearest value set value of confronting distance L _z which was used to obtain the correction data as described above, the line sync signal / LS
The distance data for each line is sent to the correction data storage unit 17 at the timing of YNC. In response to this, the corresponding measurement condition _Cy and the facing distance L are read from the correction data storage unit 17.
_The correction data _Mnyz specified by _z is read and output to the multi-level conversion unit 14.

For example, when writing an image of a certain line, when the measurement condition C ₂ and the facing distance L ₂ , M ₁₂₂ ,
M _222, M _322, ..., the correction data Mn ₂₂ as M _N22 is read. Now, as an example, M ₁₂₂ = “48” (=
“00110000”), M ₂₂₂ = “49” (= “00
110001 ”), M ₃₂₂ =“ 51 ”(=“ 00110
When 011 "), the lighting drive timing at this time is as shown in FIG. 8. Moreover, when writing the image of the next line, the measurement conditions are the same C _2, conditions opposed distance L ₃ Is changed to M ₁₂₃ , M ₂₂₃ ,
M _323, ..., the correction data Mn ₂₂ as M _N23 is read. As an example, M ₁₂₃ = “47” (= “001”)
01111 ”), M ₂₂₃ =“ 48 ”(=“ 001100 ”
00 ”), M ₃₂₃ =“ 49 ”(=“ 0011000
1 "), the lighting drive timing at this time is as shown in FIG.

That is, the 1-bit binary image data is
One line is input to the O memory 16, and the image data is repeatedly output from the FIFO memory 16 at the timing of the 8-divided synchronization signal / HSYNC. On the other hand, from the correction data storage unit 17, 8 dots for each dot (each LED element 6)
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 14 performs an AND operation on the image data and the correction data.
D is taken and sent to the selector 15 as 8-bit data (b0 to b7). In the selector 15, 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 12 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. As a result, as shown in FIG. 8, for example, in the case of the dot 1, the light is turned on at the timings T4 and T5 according to the strobe pulses STB4 and STB5, and in the case of the dot 2, the strobe is emitted at the timings T0, T4 and T5. Lights in accordance with the pulses STB0, STB4, STB5. In the case of dot 3, timings T0, TB
Strobe pulse STB0, STB at 1, T4, T5
Lights according to 1, STB4 and STB5.
In each line, lighting control is performed so that the dot diameter becomes uniform at D.

The correction data M _nyz is a line synchronization signal / LS
Reset every YNC so that the next line has the same facing distance L
If a condition _z, again, will be output to the same correction data M _Nyz, if a condition different facing distance L _z,
The different correction data _Mnyz is divided into eight synchronous signals / HSYN.
It is repeatedly output at the timing of C.

Therefore, according to the present embodiment, various photoconductors having different characteristics are taken into consideration as measurement conditions C _y (accordingly, image forming conditions), or conditions that can be changed during actual image formation are considered. For each of the various image forming conditions, and the facing distance L _z between the LED array head 2 and the photoconductor 1
In consideration of the above, light amount correction data for setting the dot diameter to D is stored in the correction data storage unit 17, so that even if the image forming conditions are changed to match the characteristics of the photoreceptor to be used, or LED arrays be facing distance between the head 2 varies, it reads correction data corresponding to M _Nyz from the correction data storage unit 17 in accordance with the image forming condition C _y or facing distance L _z, using the correction data M _Nyz against Thus, the lighting operation of each LED element 6 can be controlled, so that optical writing with a desired dot diameter D is ensured. As a result, a high-quality image without density unevenness can be obtained. 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 means that the photoreceptor used will change later,
The same applies to the case where the image forming conditions are simply changed.
Also, in the work of setting the correction data, it is not necessary to set the LED array head 2 and the photoconductor as a pair, and the individual LED array heads 2 can be used alone, so that the versatility of the setting work or the setting state can be secured. .

A second embodiment of the present invention will be described with reference to FIG. 1 to 9 are denoted by the same reference numerals, and description thereof will be omitted (the same applies to the following embodiments). In the present embodiment, the correction data storage unit 17 stores the LED using the measurement method described below.
Correction data for each LED element 6 in the array head to various dot diameter D _x for each variety facing distance condition and each type of image forming conditions is stored.

Here, the acquisition of correction data written and stored in advance in the correction data storage unit 17 will be described.
The acquisition of the correction data is executed before shipment from the factory using the optical writing device 4 and the dot diameter data measuring device 21 as shown in FIG. A process of acquiring light amount correction data when it is desired to obtain various dot diameters D _x (x = 1 to X: X is arbitrary) for all N LED elements 6 will be described with reference to the flowchart shown in FIG. First, it is checked whether a certain prescribed dot diameter D _x (x = 1) has been set (step S1 ′). Dot diameter D _x of the certain provision means one dot diameter which aim at the time of actual image writing. When the prescribed dot diameter _Dx is set by the measurement condition setting unit 25 (Y in S1 '), it is checked whether the measurement condition _Cy (y = 1) is set (S2). Measurement condition C _y
When (y = 1) is set (Y in S2), the facing distance L _z
It is checked whether (z = 1) has been set (S3).

After the completion of such various settings, the dot 1
(No. 1 LED element 6)
It is set to 1 (S4). Then, the correction data M _Nxyz (dot diameter D _x, the measurement condition C _y, facing distance L _z means a correction data for the n-th LED element 6 in) the tentatively "1
28 "(=" 1,000,000 ") (S
5 '). The correction data Mnxyz is stored in the correction data setting unit 26.
And is given to the multi-value conversion unit 14 side.

Next, dot n, here, dot 1 (N
o. The first LED element 6) is turned on by the LED array drive unit 5 (S6). The dot diameter D _d of the dot n at this time
Is measured by the dot diameter measuring device 23 (S7), and the measurement result is sent to the controller 22. In the controller 22 receiving the measurement result, the dot diameter _Dd is set to the specified dot diameter D.
_It is checked whether it is almost equal to _x (S8 '). If the values are still not substantially equal (N in S8 '), the value of the correction data _Mnxyz is increased or decreased (for example, changed to _Mnxyz = "129") according to the magnitude relationship between them. , or to change the _M nxy = "127" ... although varying width is not limited to one by 1) (S9 '), again measured dot diameter D _d of the dot n to be turned in accordance with the correction data (S7), When the dot diameter _Dd is _equal to the specified dot diameter _Dx
Repeat until it is almost equal to

The measured dot diameter _Dd is _equal to the specified dot diameter D.
_When it is almost equal to _x (Y in S8 '), correction data for the dot n at the specified dot diameter _Dx (x = 1), the measurement condition _Cy (y = 1), and the facing distance _Lz (Z = 1) _Mnxyz is stored in the data storage device 27 (S10 ').
The correction data _Mnxyz at this time is a numerical value set in the correction data setting unit 26 at that time. Thereafter, the dot n, here, the dot 1 (the LED element 6 of No. 1) is turned off (S11), and the next dot n, here, the dot 2
N is incremented by +1 in order to target (No. 2 LED element 6) (S12). at this point,
It is checked whether or not the number of new dots n exceeds the total number N (S13), and if not, the processes of steps S5 'to S12 are repeated for dot n in the same manner. Thus, facing the distance L _z, for all dots n in the measurement condition C _y (n = 1~N) the correction data M _Nxyz data storage device 27 for the dot diameter D _d the prescribed dot diameter D _x Is stored.

When this processing is completed, another facing distance L _z
It is checked whether or not there is a setting (S14). If there is, the measurement conditions are set to L _z (z = 2), L _z (z = 3),
.., L _z (z = Z) (S3), and the above-described acquisition and storage processing of the correction data M _nxyz is repeated for each facing distance L _z . Further, a certain measurement condition C _y (y = y
After the processing of 1) is completed, it is checked whether or not there are other measurement conditions C _y (S15), and if there are, these measurement conditions C _y (y = 2), C _y (y = 3),. , C _y (y =
Y) are set in order (S2), and the above-described acquisition and storage processing of the correction data _Mnxyz is repeated for each measurement condition.
Then, after the processing has been completed for a certain specified dot diameter D _x, checks whether another specified dot diameter D _x exists (S16), if any their specified dot diameter D _x (x =
2), D _x (x = 3),..., D _x (x = X) are set in order (S1 ′), and the above-described correction data M _nxyz for each measurement condition and each facing distance for each specified dot _diameter. Is repeated.

Therefore, after all the measurements are completed, the data storage device 27 stores the specified dot diameter D ₁ , the measurement condition C ₁ ; the distance correction data L ₁ M ₁₁₁₁ M ₂₁₁₁ M ₃₁₁₁ ... M _N111 L ₂ M _{1112. M 2112 M 3112 ... M N112 ...} L Z M 111Z M 211Z M 311Z ... M N11Z ... defined dot diameter D _1, the measurement condition C _Y; distance correction data _{L 1 M 11Y1 M 21Y1 M 31Y1} ... M N1Y1 L 2 M 11Y2 M _{21Y2 M 31Y2 ... M N1Y2 ... L} Z M 11YZ M 21YZ M 31YZ ... M N1YZ defined dot diameter D _2, the measurement condition C _1; distance correction data _{L 1 M 1211 M 2211 M 3211} ... M N211 L 2 M 1212 M 2212 M _{3212 ... M N212 ... L Z M} 121Z M 221Z M 321Z ... M N21Z ... defined dot diameter D _2, the measurement condition C _Y; distance correction data _{L 1 M 12Y1 M 22Y1 M 32Y1} ... M N2Y1 L 2 M 12Y2 M 22Y2 M 32Y2 _{... M N2Y2 ... L Z M 12YZ} M 22YZ M 32YZ ... M N2YZ ... specified dot diameter D _X The measurement conditions C _Y; distance as correction data _{L 1 M 1XY1 M 2XY1 M 3XY1} ... M NXY1 L 2 M 1XY2 M 2XY2 M 3XY2 ... M NXY2 ... L Z M 1XYZ M 2XYZ M 3XYZ ... M NXYZ, each defined dot diameter D _x, so that the corrected data M _Nxyz for each dot in the form of an address to each measurement condition C _y and the facing distance L _z are stored. The correction data _Mnxyz stored in such a data storage device 27 is R
The data is written into the correction data storage unit 17 in the optical writing device 4 using an OM writer or the like, and is put to practical use.

The correction data Mnxyz for each such condition
When optical writing is actually performed by the optical writing device 4 using the correction data storage unit 17 in which is written, the image writing condition setting unit 18 sets a desired dot diameter and image forming conditions. Then, writing of an image is started. Prior to this, the LED array head 2 and the photoconductor 1
Facing distance L _z between is detected by the distance detection sensor 3, the sensor output is sent to the distance detection unit 19. Therefore, facing the distance L is converted to the nearest value set value of _z, the distance data for each line in the correction data storage unit 17 at the timing of the line synchronizing signal / LSYNC used upon obtaining the correction data as described above Is sent. In response to this, the corresponding desired dot diameter D _x, the correction data Mnxyz specified by the measurement condition C _y and facing distance L _z which is output to the multi-level conversion unit 14 read from the correction data storage unit 17 You. For example, in the case of the dot diameter D ₂ , the measurement condition C ₂ , and the facing distance L ₂ , M ₁₂₂₂ , M ₂₂₂₂ , M _3222,.
The correction data is read as in _MN222 . This allows
Dot diameter both within one line are lighted controlled as uniform in any and desired dot diameter D _x.

[0049] Therefore, according to this embodiment, in addition to the above embodiment, the correction data Mnxy various per dot diameter D _x
Since z is also stored in the correction data storage unit 17, even when the desired dot diameter _Dx is changed, the dot diameter _Dx is changed.
Each LED element 6 can be turned on so that _x is equalized.

A third embodiment of the present invention will be described with reference to FIGS. In the LED array printer of the present embodiment, the distance detection sensor 3 is not required in actual use, and a position detection sensor 31 that detects the rotational position of the photoconductor 1 that is driven to rotate is provided instead. As shown in FIG. 11, the position detection sensor 31 is disposed at a predetermined position in advance, and is integrally attached to one end of the photoconductor 1 with an optical detection unit 31a having a pair of a light emitting unit and a light receiving unit. A photo interrupter is configured by a detection piece 31b that passes through the expression detection unit 31a so as to block light once per rotation. In the illustrated example of FIG. 11, the distance indicating detection sensor 3 even together, but as it will be described later, after being temporarily stored by measuring the facing distance L _m in each main scan line for each of the photosensitive member 1, unnecessary In actual use, the distance detection sensor 3
May be removed.

Further, in the optical writing device 4 of the present embodiment, as shown in FIG. 12, a distance data storage section 32 functioning as a distance storage section is provided instead of the distance detection section 19, and the distance data storage section 32 is provided. The unit 32 is connected to the correction data storage unit 17 functioning as a correction data storage unit. Each main scan line of the photosensitive member 1 in this distance data storage section 32, i.e., facing the distance L _z of the LED array head 2 for each of the line sync signal / LSYNC outputted as the photosensitive member 1
Are stored in advance. The distance data storage unit 32 receives a detection signal from the position detection sensor 31 of the photoconductor 1 and receives a detection signal from the position detection unit 3 that functions as a position detection unit.
3 and a controller 34 that outputs a line synchronization signal / LSYNC. Thereby, the sending data of the facing distance L _z at a certain position of the photosensitive member 1 by the position detection signal and the line synchronizing signal / LSYNC on the correction data storage unit 17. Further, when actually writing an image, first, the photoconductor 1 is rotated so that the position detection sensor 31 detects the detection piece 31b of the photoconductor 1 and then starts writing. This stores the data of the facing distance L _z of the position of the photosensitive member 1 with respect to the photoreceptor position when the position detecting sensor 31 detects the detecting piece 31b (the main scanning line) in the distance data storage section 32 It is because.

Here, in the image forming operation, when the image forming condition is designated by the image writing condition setting unit 18,
According to the specified the image forming conditions, and further, depending on the facing distance L _m read from the distance data storage section 32 in accordance with the rotational position data obtained from the position detection unit 33, for each LED element 6 It has a function of a correction data reading means for reading out the corresponding correction data from the correction data storage unit 17 and outputting it to the multi-value conversion unit 14. Further, the multi-level conversion unit 14, the selector 15, and the LED array driving unit 7 function as drive control means for controlling the lighting operation of each LED element 6 of the LED array head 2 using the read correction data.

Meanwhile, a process of pre-measuring the facing distance L _m between the LED array head 2 and the photosensitive member 1, and stores the data of the facing distance L _m in the distance data storage section 32, FIG. 13
This will be described with reference to the flowchart shown in FIG. First, the photoconductor 1 is rotated. In order to increase the distance detection accuracy,
The rotation speed may be sufficiently lower than the speed at the time of actual image writing. In that case, the line synchronization signal / LSYN
C also becomes slower (longer). After the start of rotation, it is checked whether the position detection sensor 31 has detected the photoconductor 1 (detection piece 31b) (step S21). Once detected, it is set to m = 1 in order to measure the data of confronting distance L _m from the detection of the first line synchronizing signal / LSYNC (S22). Thereafter, it is checked whether or not the first line synchronization signal / LSYNC has been detected after the position detection sensor 31 has detected (S23). When detecting the storage was measured by confronting distance L _m (m = 1) the distance detection sensor 3 at that time (S24), the data of the facing distance L ₁ when m = 1 in the distance data storage section 32 (S25). Then, in order to target the next line synchronization signal / LSYNC, m is incremented by +1 (S26), and until the position detection sensor 31 detects the photoconductor 1 (detection piece 31b) again (ie, completes one rotation). up) (S27), stores the data of the facing distance L _m of each line sync signal / LSYNC sequential distance data storage section 32.

Therefore, after all the measurements are completed, the distance data storage unit 32 stores As described above, the data of the facing distance at that time is stored in advance in the form of using the number of times of detection of the line synchronization signal / LSYNC as an address.

FIG. 14 shows the LED array head 2 and the photoconductor 1
Is a graph which shows exaggeratedly a variation of confronting distance L _m by the photosensitive member rotation position of the data of the facing distance stored in the distance data storage section 32 as described above, the position detecting sensor 31 is first detected It becomes data for each main scan line for one rotation from the detected position to the next detected position.

Next, actual processing will be described when an image written by the optical writing device 4 by using the distance data storage section 32 the data of the facing distance L _m of each line is stored. Basically, the same result as in the first embodiment described above is obtained. However, at the time of writing an image, the position (position) when the position detection sensor 31 detects the photoconductor 1 (detection piece 31b) is used as a reference. The difference is that the write operation is controlled.
For example, the position detection sensor 31 detects the photoconductor 1, and in response to this, the position detection unit 33 sends the position information of the photoconductor 1 to the distance data storage unit 32, so that the first line synchronization signal / LSYNC is used. reads data L ₁ of confronting distance corresponding to if any sends the correction data storage unit 17, if the second line of the line synchronizing signal / LSYNC reads data L ₂ of the facing distance corresponding correction data storage This is sent to the unit 17 and thereafter, the same is repeated for each line. Sends the correction data corresponding to a desired image forming condition C _y and receiving with both conditions from the correction data storage unit 17 in confronting distance data L _m and the image writing condition setting section 18 in the multi-level conversion unit 14 . As a result, similarly to the above-described embodiment, the light amount correction for each LED element 6 is properly performed, and the dot diameters are made uniform.

Therefore, according to the present embodiment, at the time of image formation, the detection of the facing distance from the LED array head 2 to the photosensitive member 1 is not performed, and the facing distance stored in advance based on the rotation position of the photosensitive member 1 is detected. since it addressed by reading the data L _m from the distance data storage section 32, together can simplify the device configuration for distance detection, fast linear velocity of the photosensitive member 1 even when it is difficult detection of the facing distance That will be enough to deal with.

Although the present embodiment has been described as an example applied to the first embodiment, it is apparent that the present embodiment can be similarly applied to the second embodiment.

A fourth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, two distance detection sensors 3a and 3b are provided at both ends of the LED array head 2 in the main scanning direction for detecting a facing distance from the LED array head 2 to the photoconductor 1. This is different from the embodiment described above. That is, the facing distance is set to LE
The detection is performed at a plurality of locations (two locations) of the D array head 2 in the main scanning direction. Now, the distance detection sensor 3a
The distance detected based on the distance is L _1m , and the distance detection sensor 3
detected are opposed distance on the basis of b as L _2m, each LED
The process of calculating the facing distance for each element 6 and storing it in the distance data storage unit 32 will be described with reference to the flowchart shown in FIG. First, it is checked whether the photoconductor 1 is rotated and the position detection sensor 31 detects the photoconductor 1 (detection piece 31b) (step S31). If detected, the confronting distance L in the first line synchronization signal / LSYNC after detection
_In order to measure _m data, m = 1 is set (S3
2). Thereafter, it is checked whether or not the first line synchronization signal / LSYNC has been detected after the position detection sensor 31 has detected (S33). If detected, the facing distance L at that time
_1m and _L2m (m = 1) are measured by the distance detection sensors 3a and 3b (S34). Then, these two data L _1m ,
L _2m by obtaining the inclination of the main scanning direction based on the difference between the calculated individual confronting distance L _mn (m = 1) at the position of each LED element for each 6 (S35). Calculated m =
The data of the facing distance L _1n (n = 1 to N) at the time of 1 is stored in the distance data storage unit 32 (S36).

Then, the next line synchronizing signal / LSYNC
Is targeted, m is incremented by +1 (S
37), the position detection sensor 31 detects the photosensitive member 1 (detection piece 3) again.
Until 1b) is detected (that is, until one rotation is completed)
(S38) The data of the facing distance L _mn calculated for each line synchronization signal / LSYNC is sequentially stored in the distance data storage unit 32.
To be stored.

[0061] Thus, after all of the measurement and calculation were completed, the distance data in the storage unit 32, / number of detections LSYNC confronting distance data _{1 L 11, L 12, L} 13, ..., L 1N 2 L 21, _{L 22, L 23, ...,} L 2N ... M L M1, L M2, L M3, ..., as L _MN, the data of the facing distance when the detected number of line synchronizing signal / LSYNC in the form of an address Each LED
This is stored in advance for each element 6.

The facing distance L for each LED element 6
_The image writing is actually performed by the optical writing device 4 using the distance data storage unit 32 in which the data of _mn is stored, but the control at that time is such that the data of the facing distance is individual for each LED element 6. Is the same as in the case of the third embodiment described above.

Therefore, according to the present embodiment, the facing distance L _mn for each LED element 6 is estimated from the facing distance data measured at two points in the main scanning direction using the plurality of distance detecting sensors 3a and 3b. Since this is stored in advance, the light amount can be corrected under more accurate facing distance data, and more appropriate correction can be performed. In particular, it is possible to appropriately cope with the case where the change in the facing distance differs depending on the position in the main scanning direction.

In the present embodiment, an example of application to the embodiment using the distance data storage unit 32 has been described. However, the present invention can be applied to the first and second embodiments.

In these embodiments, each LED
Although the light amount correction for making the dot diameter of the element 6 uniform is performed by controlling the light emission time, a method in which the drive current for each LED element 6 is varied according to the correction data may be used.

[0066]

According to the first aspect of the present invention, an LED array head, in which a large number of LED elements whose lighting is controlled in accordance with image data, is arranged in a line, is opposed to an image carrier. An LED array printer for forming an image by using the distance detecting means for detecting a distance from the LED array head to the image carrier;
A storage unit that stores correction data of the light amount for obtaining a desired dot diameter according to the facing distance for the ED element, and a correction that reads out the correction data corresponding to each LED element from the storage unit according to the detected facing distance. Since data read means and drive control means for controlling the lighting operation of each LED element of the LED array head using the read correction data are provided, when the LED array head forms an image, Even if the facing distance to the image carrier varies, the desired dot diameter is set and each LE
The dot diameter of the D element can be made uniform, so that an image having no variation in density can be provided.

According to the second aspect of the present invention, an LED array head in which a large number of LED elements whose lighting is controlled in accordance with image data is arranged in a line shape is opposed to an image carrier and an image is formed by electrophotography. A distance detecting means for detecting a facing distance from the LED array head to the image carrier;
A storage unit for storing light amount correction data for various dot diameters in accordance with the facing distance for the D element, a designating means for designating a desired dot diameter, and a confrontation detected for the designated dot diameter Correction data reading means for reading correction data corresponding to each LED element from the storage unit in accordance with the distance, and drive control means for controlling the lighting operation of each LED element of the LED array head using the read correction data In addition to the effects of the invention described in claim 1, in addition to the effect of the first aspect, even when a desired dot diameter is desired to be changed, each dot can be uniformed at the designated dot diameter irrespective of a change in the facing distance. The LED element can be turned on.

According to the third aspect of the present invention, an LED array head in which a large number of LED elements whose lighting is controlled in accordance with image data is arranged in a line is opposed to an image carrier, and an image is formed by electrophotography. And a position detecting means for detecting a rotational position of the image carrier, and a distance from the LED array head, which is detected in advance at each position in the rotation direction of the image carrier, to the image carrier. A distance storage unit storing data, and each of the LEDs
A correction data storage unit that stores light amount correction data for a desired dot diameter according to the facing distance for the element,
Data for reading facing distance data from the distance storage unit based on the rotational position of the image carrier detected by the position detecting means, and reading corresponding correction data for each LED element from the storage unit according to the facing distance data. Since the apparatus includes the reading means and the drive control means for controlling the lighting operation of each LED element of the LED array head using the read correction data, the LED array head is used as in the first aspect of the present invention. Even when the facing distance from the LED array head to the image carrier varies during image formation, the desired dot diameter can be obtained and the dot diameter of each LED element can be made uniform, thereby providing an image without density variation. In order to obtain such an effect, the LED array head can move the image carrier at the time of image formation. Since the confronting distance is not detected, the confronting distance data stored in advance is read out from the distance storage unit based on the detection of the rotational position of the image carrier, so that the apparatus configuration related to the distance detection is simplified. Accordingly, it is possible to sufficiently cope with the case where the linear velocity of the image carrier is high and it is difficult to detect the facing distance.

According to the fourth aspect of the present invention, an LED array head in which a large number of LED elements whose lighting is controlled in accordance with image data is arranged in a line is opposed to an image carrier, and an image is formed by electrophotography. And a position detecting means for detecting a rotational position of the image carrier, and a distance from the LED array head, which is detected in advance at each position in the rotation direction of the image carrier, to the image carrier. A distance storage unit storing data, and each of the LEDs
A correction data storage unit that stores correction data of light amounts for various dot diameters according to the facing distance for the element,
Designating means for designating a desired dot diameter, and reading the facing distance data from the distance storage unit based on the rotational position of the image carrier detected by the position detecting means, and setting the facing distance for the designated dot diameter. Data reading means for reading correction data corresponding to each LED element from the storage unit in accordance with data, and drive control means for controlling a lighting operation of each LED element of the LED array head using the read correction data. So that
In addition to the effect of the third aspect of the present invention, even when a desired dot diameter is desired to be changed, each LED element is turned on so as to be uniform at the designated dot diameter regardless of a change in the facing distance. be able to.

According to the invention of claim 5, claim 1,
2. The LED array printer according to 2, 3, or 4,
Since the facing distance from the ED array head to the image carrier is detected at a plurality of points in the main scanning direction of the LED array head, the correction accuracy can be basically improved, and the variation of the facing distance is mainly affected. It is possible to appropriately cope with the case where the position differs in the scanning direction.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical writing device according to a first embodiment of the present invention.

FIG. 2 is a side view showing a schematic configuration of the LED array printer.

FIG. 3 is a block diagram illustrating a basic configuration of an LED drive circuit.

FIG. 4 is a time chart showing the basic LED array driving timing.

FIG. 5 is a block diagram showing an optical writing device and a dot diameter data measuring device.

FIG. 6 is a time chart showing a light amount control method based on variable light emission time.

FIG. 7 is a flowchart illustrating a process for acquiring correction data.

FIG. 8 is a time chart showing an example of lighting timing of each dot according to correction data.

FIG. 9 is a time chart showing an example of different lighting timing of each dot according to correction data.

FIG. 10 is a flowchart illustrating a process for acquiring correction data according to the second embodiment of the present invention.

11A and 11B show a third embodiment of the present invention, wherein FIG. 11A is a schematic front view of an LED array printer, and FIG. 11B is a schematic perspective view thereof.

FIG. 12 is a block diagram showing the optical writing device.

FIG. 13 is a flowchart showing a process of detecting and storing a facing distance.

FIG. 14 is a graph exaggeratingly showing how the facing distance varies.

FIG. 15 is a side view illustrating a schematic configuration of an LED array printer according to a fourth embodiment of the present invention.

FIG. 16 is a flowchart showing a process of detecting and storing a facing distance for each LED element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier 2 LED array head 6 LED element 17 storage unit, correction data storage unit 18 specifying unit 19 distance detection unit 32 distance data storage unit 33 position detection unit

Claims (5)

[Claims] An LED array printer that forms an image by electrophotography by causing an LED array head, in which a number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier, A distance detecting means for detecting a facing distance from the LED array head to the image carrier; a storage unit for storing correction data of a light amount for obtaining a desired dot diameter according to the facing distance for each of the LED elements; Correction data reading means for reading out, from the storage unit, correction data corresponding to each LED element in accordance with the detected facing distance; and controlling the lighting operation of each LED element of the LED array head using the read correction data. An LED array printer comprising: a drive control unit. 2. An LED array printer which forms an image by electrophotography by making an LED array head, in which a large number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, face an image carrier, A distance detecting means for detecting a facing distance from the LED array head to the image carrier; a storage unit for storing light amount correction data for various dot diameters for each of the LED elements according to the facing distance; Designation means for designating the dot diameter of the correction data; and correction data reading means for reading the correction data corresponding to each LED element from the storage unit according to the facing distance detected for the designated dot diameter. Drive control means for controlling the lighting operation of each LED element of the LED array head using the correction data. LED array printer for. 3. An LED array printer that forms an image by electrophotography by causing an LED array head, in which a number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier, Position detecting means for detecting a rotation position of the image carrier; and a distance storage unit for storing facing distance data for the image carrier from the LED array head detected in advance at each position in the rotation direction of the image carrier. A correction data storage unit storing correction data of a light amount for obtaining a desired dot diameter according to a facing distance for each of the LED elements, and the distance based on a rotation position of the image carrier detected by position detection means. While reading the facing distance data from the storage unit, the correction data corresponding to each LED element is read from the storage unit according to the facing distance data. LED array printer, wherein the data reading means out seen, drive control means for controlling the lighting operation of the LED elements of the LED array head using the correction data read, further comprising: a. 4. An LED array printer that forms an image by electrophotography by causing an LED array head, in which a number of LED elements whose lighting is controlled in accordance with image data is arranged in a line, to face an image carrier, Position detecting means for detecting a rotation position of the image carrier; and a distance storage unit for storing facing distance data for the image carrier from the LED array head detected in advance at each position in the rotation direction of the image carrier. A correction data storage unit storing correction data of light amount for forming various dot diameters according to the facing distance for each of the LED elements; a designation unit for designating a desired dot diameter; The facing distance data is read out from the distance storage unit based on the rotation position of the image carrier, and the facing distance is read for a designated dot diameter. Data reading means for reading correction data corresponding to each LED element from the storage unit in accordance with data, and drive control means for controlling a lighting operation of each LED element of the LED array head using the read correction data. And an LED array printer. 5. The LED array printer according to claim 1, wherein a facing distance from the LED array head to the image carrier is detected at a plurality of positions in the main scanning direction of the LED array head.