JPH11254737A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a dot stably by suppressing occurrence of longitudinal streaks on an image regardless of fluctuation in the distribution of quantity of light among respective LED elements. SOLUTION: An image is formed using a group of two adjacent LED elements in an LED array 12 as the minimum unit of image information (1 dot). Even if a dot is formed unstably using only one LED element 3, peak quantity of light can be increased by summing the quantity of light of the LED elements 3 forming a group continuously and enlarging the distribution of quantity of light in the main scanning direction. Consequently, occurrence of longitudinal streaks is suppressed and dots D are formed stably.

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. 13A 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. 13B and 13D 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, in the case of expressing a gradation by an area gradation method in a one-dot binary recording method, FIG.
In accordance with a certain threshold level TH as shown in FIGS. 13B and 13D, dots D as shown in FIGS. 13C and 13E are formed. In this case, white streaks like those between dots D ₁ and D ₂ shown in FIG. Although the spot diameter is large as in the center of the dot D ₃ shown in FIG. 13 (c) for the drop in potential of the photoreceptor is less than the other, the dot formation becomes unstable. When the spot diameter at a certain threshold level TH is made uniform as shown in FIG. 13D, 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 forming apparatus that forms an image by electrophotography using an LED array in which a large number of LED elements whose light emission is controlled in accordance with image data is arranged in an array,
A plurality of continuous LED elements in the D array are grouped into one group, and an image is formed using this group as a minimum unit of image information.

Therefore, a plurality of continuous LED elements are
One group is set as the minimum unit of image information, and even if it is unstable with only one LED element, the light quantity distribution is expanded in the main scanning direction by adding the light quantities of the LED elements forming the group. Can increase the peak light amount, and as a result, the occurrence of vertical streaks is reduced,
Dots can be formed stably.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, two adjacent LED elements are grouped. Therefore, since the minimum unit of image information is formed by two adjacent LED elements, the effect of the first aspect of the present invention can be secured without lowering the resolution as much as possible.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, one dot is formed by the LED elements forming each group in the LED array, and the LED element for each dot is formed. A storage unit for storing correction data for obtaining a desired spot diameter preset for each of various image forming conditions, a specifying unit for specifying a desired image forming condition, Correction data reading means for reading correction data corresponding to each LED 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. .

Therefore, when a desired spot diameter is determined for a dot formed by a plurality of LED elements, even if the image forming conditions are changed, the correction data reading means responds to the correction data reading means in accordance with the image forming conditions. The data is read from the storage unit, and the drive control unit controls the lighting operation of the LED element using the correction data, so that light writing with a desired spot diameter is ensured. Here, even 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.

According to a fourth aspect of the present invention, in the image forming apparatus of the first or second aspect, one dot is formed by the LED elements forming each group in the LED array, and the LED element for each dot is formed. A storage unit storing correction data for setting each spot diameter for each of various image forming conditions and each spot diameter, a specifying unit for specifying a desired image forming condition and a spot diameter, and a specified image Each LED according to the forming condition and spot diameter
A correction data reading unit that reads correction data corresponding to the 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, the present invention is basically the same as the image forming apparatus according to the third aspect of the present invention. In addition, correction data for each spot diameter is also stored 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 5 is based on claims 1, 2, 3
In the image forming apparatus described in Item 4, the minimum unit of the image information is controlled to emit light by one-dot binary image data. Therefore, in the case where the gradation is expressed by the one-dot binary method, one dot which is the minimum unit of image information is 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.
A description will be given 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. 2 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, the light emitting portions 5 of the large number of LED elements 3 are arranged on the main scanning line as indicated by a straight line L on the base substrate 2 as in the case shown in FIG. 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. 3 is a block diagram showing the structure of the LED array drive section 16 which is included in the LED array control section 14 and serves as drive 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 of the N (P dot) 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 emit light 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 P. 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, etc., and generates a strobe pulse STB as shown in FIG. In the LED array driving section 16, the element whose image data is "1" emits light at the timing of the strobe pulse STB.

Here, the minimum unit of image information is 1 dot,
1 line = P dot, LED in LED array 12
Assuming that the number of elements 3 is N, in the present embodiment, 2P =
N is set. More specifically, adjacent two
One LED element 3 forms one group, and one dot is formed by this group, that is, a combination of two LED elements.

In such a configuration, FIG. 1 shows two adjacent LED elements 3 as one group, and the light quantity distribution and the dots D formed when the group is the minimum unit (= 1 dot) of image information. Are shown. In the dot formation using each LED element 3 as a minimum unit as shown by a broken line, the shape of the dot becomes unstable with the occurrence of vertical streaks and a decrease in the peak light amount, but as in the present embodiment shown by a solid line,
If the light amounts of the two LED elements 3 are added, the light amount distribution expands in the main scanning direction and the peak light amount increases, so that the occurrence of vertical streaks is reduced, and stable dots D can be formed.

In this embodiment, two adjacent LED elements 3 are grouped to form one dot of image information, so that the resolution of the output image is not reduced as much as possible. However, a group is formed two-dimensionally, and 2 × 2 = 4 LED elements 3 (LED
One dot, which is the minimum unit, may be formed by using two (when viewed from the array 12 itself). According to this, although the resolution in the sub-scanning direction is also reduced similarly to the resolution in the main scanning direction, it is possible to reduce the occurrence of vertical streaks,
The formed dots are more stable. Furthermore, by forming three or more adjacent LED elements 3 as one group to form one dot of image information, the occurrence of vertical streaks can be further reduced. Further, in the case of the present embodiment, the present invention is applied to a one-dot binary recording method, and FIG.
As shown in (b), only one threshold level TH needs to be considered, so that it is possible to suppress the occurrence of vertical streaks while stabilizing the formed dots D.

A second embodiment of the present invention will be described with reference to FIGS. The same parts as those described in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.
In the present embodiment, for example, the LED array 12 shown in FIG. 1A is used. FIG. 6 shows an example of the configuration of the optical writing device 31 in the LED array printer.
It is mainly composed of the D array drive section 16 and the like. LED
Although the array driving section 16 has a well-known configuration as shown in FIG. 3, in the present embodiment, an eight-division synchronization signal / signal for performing light quantity control as described later by lighting time control is used.
Since HSYNC (a signal obtained by dividing the line synchronization signal / LSYNC into eight) is used, the shift register 17 uses the eight division synchronization signal / HSYNC as the drive timing shown in FIG.
It is configured to be reset by The shift register 17 operates to input binary image data of one dot “0” or “1” in order from the dot 1 in response to the clock signal CLOCK, and internally transmit each dot data to each register. When all the P dot data have been sent, the latch 18 latches the data, and when the strobe pulse STB is input to the AND gate 19, only the element to which the image data "1" has been sent becomes L.
Basically, the ED driver 20 turns on the light 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-value conversion unit 33, a FIFO (First-In First-Ou) is used to capture one line of 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 configuration, and correction data for setting a desired spot diameter D preset for each image forming condition with respect to each LED element 3 for each dot in the LED array 12 by a measuring method described later. It is remembered. 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. Multi-value conversion unit 3 read from inside
3 is provided with a function of a correction data reading means for outputting the correction data to the output unit 3. Further, the multi-value conversion unit 33, the selector 34, and the LED array driving unit 16 perform LE LE using the read correction data.
It functions as drive control means for controlling the lighting operation of each LED element 3 of the D array 12.

Here, the acquisition of the correction data previously written and stored in the correction data storage unit 35 will be described.
As shown in FIG. 8, the acquisition of the correction data is performed before shipment from the factory.
This is executed using the optical writing device 31 and the dot diameter data measuring device 41. The dot diameter data measuring device 41 is detachably connected to the multi-value conversion section 33 of the optical writing device 31 by an interface (not shown), and includes a controller 42 having a built-in microcomputer and one group for one dot. A dot diameter measuring device 43 that measures a beam dot diameter (spot diameter) when two adjacent LED elements 3 forming a dot are lit, and outputs the measurement result to a controller 42, and measurement conditions by the dot diameter measuring device 43. Condition setting unit 44 for setting the
A correction data setting unit 45 that outputs 8-bit correction data to the multi-value conversion unit 33 of the optical writing device 31 under two controls; and a data storage device 46 that stores the correction data when the correction data is determined. It consists of.

Here, the correction data of the light quantity of each LED element 3 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.
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. 9 shows, as an example, the drive timing when the dot 1 (the LED elements 3 of Nos. 1 and 2) is turned on with the correction data “128” (= “10000000”). One line synchronization signal / LS
While the YNC is being output, the corresponding strobe pulses STB0 to STB7 are output from the strobe pulse generator 23 and the selector 32 in accordance with the timings T0 to T7 of the 8-divided synchronization signal / HSYNC obtained by dividing the YNC 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 S at timing
Lighting is performed with a lighting width corresponding to TB7. In this case, if the correction data is “127” (= “01111111”),
At the timing of b0 to b6 (= T0 to T6) when the bit is set, the lighting is performed with the lighting width corresponding to each strobe pulse STB0 to STB6. For example, if the correction data is “1”
29 "(=" 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 a bit is set. The 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 (see “LED array writing type color electrophotographic printer”, p.205).
To 206, see Journal of the Electrographic Society of Japan, Vol. 24, No. 3 (1995)), and the correction data for changing the dot diameter of the one-dot binary expression of the present embodiment can be easily applied as it is.

Under such a premise, the number of dots P and the LED
Under the condition that the number of elements N is set to be 2P = N,
A process of acquiring light quantity correction data when it is desired to always obtain a desired dot diameter (spot diameter) D for P dots for all N LED elements 3 will be described with reference to the 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). 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. When the prescribed dot diameter D is set by the measurement condition setting unit 44 (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 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 C _y (y = 1) is set (Y in S2), n = 1 and p = 1 are set to target the dot 1 (the LED element 3 of No. 1 and No. 2) ( S3). Next, correction data M _ny (meaning correction data for the n-th LED element 3 under the measurement condition C _y ), M _{n + 1y} (meaning correction data for the n + 1-th LED element 3 under the measurement condition C _y ) ) Is temporarily set to "128" (= "10000000") (S4). However, there is no meaning limited to the numerical value “128”, and “1” to
Any numerical value within the range of "255" is arbitrary, but as in the present embodiment, it is set to an intermediate value "128" to facilitate increase / decrease adjustment, or a desired dot diameter based on existing experimental data and the like. It is preferable to use a value expected to be closest to D. The correction data M _ny and M _{n + 1y} are set in the correction data setting unit 45 and provided to the multi-value conversion unit 33.

Next, the dot p, here, dot 1 (N
o. The LED array driving unit 16
(S5). The lighting timing at this time is shown in FIG. The dot diameter (spot diameter) Dd of the dot p at this time is measured by the dot diameter measuring device 43 (S6), and the measurement result is sent to the controller 42. The controller 42 having received the measurement result obtains the dot diameter Dd
Is substantially equal to the specified dot diameter D (S7). If they are still not substantially equal (N in S7), the correction data M _ny , M
By increasing or decreasing the value of _{n + 1y} (for example, M
_ny , _{Mn + 1y} = “129”, or _Mny , _{Mn + 1y} =
Change it to “127” ... However, the increment / decrement width is not limited to one) (S8), the dot diameter Dd of the dot p 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 to each other. However, the measurement of the number of bits of the correction data _Mny and _{Mn + 1y} and the dot diameter Dd Since it is conceivable that the data may not always be equal due to the relationship of an error or the like, the data is determined to be normal when the data is within an allowable approximation range.
The approximate range is the number of bits of the correction data M _ny and M _{n + 1y} ,
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.
Is substantially equal to (Y in S7), the measurement condition C
_The correction data M _ny and M _{n + 1y} for the dot p in _y (y = 1) are stored in the data storage device 46 (S
9). The correction data M _ny and M _{n + 1y} at this time are the numerical values set in the correction data setting unit 45 at that time. Thereafter, the dot p, here, dot 1 (L of No. 1 and No. 2)
The ED element 3) is turned off (S10), and n is incremented by +2 and p is incremented by +1 to target the next dot p, here, dot 2 (the LED elements 3 of Nos. 3 and 4) (S11). ). At this time, it is checked whether or not the new dot p exceeds the total number of dots P (S12). If not, the processes of steps S4 to S11 are repeated for the dot p. Thus, the correction data M _ny for all dot p (p = 1~P) the dot diameter Dd provisions dot diameter D for the measurement condition C _y, is M n _{+ 1y} stored in the data storage device 46 You.

When this process is completed, the other measurement conditions C _y
It is checked whether or not there is (S13), and if there is, those measurement conditions are changed to _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 _Mny and _{Mn + 1y} is repeated for each measurement condition.

[0033] 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 , correction data M _ny and M _{n + 1y} for each dot are stored in pairs with each measurement condition _Cy as an address. The correction data M _ny and M _{n + 1y} stored in the data storage device 46 are written into the correction data storage unit 35 in the optical writing device 31 using a ROM writer or the like.
Provided for practical use.

The correction data M _ny ,
When optical writing is actually performed by the optical writing device 31 using the correction data storage unit 35 in which M _{n + 1y} is written,
An image forming condition is set by the image writing condition setting unit 36. This condition corresponds with the measurement conditions, for example, by setting the image forming conditions corresponding to the measurement condition C _y, the correction data M _ny which is from the correction data storage unit 35 is identified by the corresponding measurement condition C _y, M _{n + 1y} is read out and the multi-value conversion unit 3
3 is output. For example, in the case of the measurement condition _{C 2, M 12, M 22} , M 32, ..., the correction data as M _N2 is read. Now, as an example, M ₁₂ = M ₂₂ = “48”
(= “00110000”), M ₃₂ = M ₄₂ = “49”
(= “00110001”), M ₅₂ , M 5 ₆₂ = “51”
(= “00110011”), the lighting drive timing at this time is as shown in FIG.

That is, 1-dot binary image data for P dots is input to the FIFO memory 21 for one line, and the FIFO memory 21 outputs an 8-divided synchronizing signal / HSYNC.
The image data is repeatedly output at the timing shown in FIG. If 2P = N, the data for one dot is output twice consecutively at the timing of the eight-division synchronization signal / HSYNC. On the other hand, from the correction data storage unit 35, the 8-bit correction data for each dot (two adjacent LED elements 3) is stored in the same manner as the image data by the eight-segment synchronization signal /
It is repeatedly output at the timing of HSYNC. And
The multi-value converter 33 performs an AND operation on the image data and the correction data, and sends the result to the selector 34 as 8-bit data (b0 to b7). In the selector 34, the least significant bit b0 at the timing T0, the bit b1,.
At timing T7, the most significant bit b7 is output. On the other hand, the timing T
Strobe pulses ST having different pulse widths from 0 to T7
B0 to STB7 are sent to the selector 32. Selector 3
In ST2, STB0 at timing T0, S at timing T1
, STB7 is output at timing T7, and lights up at the timing when AND is taken with 8-bit data.
In the case of dot 1, the light is turned on at timings T4 and T5 according to the strobe pulses STB4 and STB5. , The timings T0, T1,
Strobe pulses STB0, STB1, S at T4, T5
Lighting is performed according to TB4 and STB5, and as a result, lighting control is performed so that the dot diameter (spot diameter) is uniformed at D in one line.

Therefore, according to the present embodiment, under the condition that one dot is formed by two adjacent LED elements 3, various photoconductors are considered as the measurement condition C _y (therefore, image forming condition). Since the light amount correction data for setting the dot diameter for each of the various image forming conditions to D, which is assumed in consideration of the conditions that can be changed in actual image formation, is stored in the correction data storage unit 35, Even if the image forming conditions are changed to match the body characteristics, the corresponding correction data M _ny , M _{n + 1y} is read from the correction data storage unit 35 in accordance with the image forming conditions, and the correction data M _ny , M
_Since the lighting operation of each LED element 3 can be controlled using _{n + 1y} , optical writing with a desired spot diameter D is ensured. As a result, for example, as shown in FIG. 1, 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. Also, the work of setting the correction data does not need to set the LED array 12 and the photoconductor as a pair, and can be performed by each LED array head 11 alone, so that the versatility of the setting work or the setting state can be secured.

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

Here, the acquisition of the correction data written and stored in advance 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 Light amount correction data is obtained when it is desired to obtain various dot diameters (spot diameters) D _x (x = 1 to X: X is arbitrary) for all N LED elements 3 for P dots in a relationship of 2P = N. The processing 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 specified dot diameter _Dx is set by the measurement condition setting unit 44 (Y in S1 '), it is checked whether the measurement condition _Cy (y = 1) is set (S2). Measurement conditions C _y (y =
When 1) is set (Y in S2), dot 1 (No.
In order to target 1, 2 LED elements 3), n = 1,
p = 1 is set (S3). Next, the correction data M
_NXY (dot diameter D _x, the n-th in the measurement condition C _y L
Correction data for ED element 3), correction data M
_{n + 1xy} (dot diameter D _x, refers to the correction data for the (n + 1) -th LED elements 3 in the measurement condition C _y) and if "128" (= "10000000") set to (S
4 '). The correction data M _nxy and M _{n + 1xy} are set in the correction data setting unit 45 and provided to the multi-value conversion unit 33.

Next, the dot p, here, dot 1 (N
o. The LED array driving unit 16
(S5). The dot diameter (spot diameter) Dd of the dot p at this time is measured by the dot diameter measuring device 43 (S6), and the measurement result is sent to the controller 42. Measurement results In the controller 42 has received its dot diameter Dd checks almost equal or not to the provision dot diameter D _x (S7 '). If it is still not almost equal (S
7 ', N), the correction data M
_NXY, by reducing or or increase the value of _{M n +} 1xy (e.g., change in _{M nxy = M n + 1xy =} "129", or change the _{M nxy = M n + 1xy =} "127" Do ...
However, varying width is not limited to one by 1) (S8 '), the correction re-measure the dot diameter Dd of dots p to be lighted in accordance with the data (S6), which almost equals the dot diameter Dd is defined dot diameter D _x Repeat until

The measured dot diameter Dd is equal to the specified dot diameter D.
when it becomes approximately equal to _x (Y in S7 '), defined dot diameter D _{x (x} = 1), the correction data M _NXY for dots p in the measurement condition _{C y (y = 1),} M n + 1xy data storage It is stored in the device 46 (S9 '). The correction data M _nxy and M _{n + 1xy} at this time are the numerical values set in the correction data setting unit 45 at that time. Thereafter, the dot p, here, the dot 1 (the LED elements 3 of Nos. 1 and 2) is turned off (S10), and the next dot p, here, the dot 2 (N
o. In order to target the 3 and 4 LED elements 3), n is incremented by +2 and p is incremented by +1 (S11). At this time, it is checked whether or not the new dot p exceeds the total number of dots P (S12), and if not, the processes of steps S4 'to S11 are repeated for the dot p. Accordingly, all dots p in the measurement condition C _y (p = 1~P) the correction data M _NXY for the dot diameter Dd the prescribed dot diameter D _x, M
_{n + 1xy} is stored in the data storage device 46.

When this process is completed, the other measurement conditions C _y
Is checked (S13), and if so, the measurement conditions C _y (y = 2), C _y (y = 3),.
_{y (y} = _Y) set in the order as (S2), the correction data M _NXY described above for each measurement condition, acquisition and storing processing of the M n _{+ 1x y} is repeated.

[0042] Further, after the processing has been completed for some defined dot diameter D _x, checks whether another specified dot diameter D _x exists (S14), of which if specified dot diameter D
_x (x = 2), D _x (x = 3),..., D _x (x = X) are set in this order (S1 ′), and the correction data M described above is set for each specified dot diameter and for each measurement condition. _{Acquisition of nxy} and M _{n + 1xy}
The storing 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 _NXY as correction data M _NXY for each dot in the form of an address for each defined dot diameter D _x and the measurement condition C _y, M
_That is, _{n + 1xy} is stored in pairs. The correction data M _nxy , stored in such a data storage device 46,
M _{n + 1xy} 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 section 35 in which the correction data M _nxy and M _{n + 1xy for} each of the various conditions are written, an image A desired dot diameter and image forming conditions are set by the printing condition setting unit 36. Setting the desired dot size and image forming conditions, the correction data M _NXY that from the correction data storage unit 35 is identified by the corresponding dot diameter to D _x and measurement conditions C _y, is read out _M n ₊ 1xy multilevel Converter 3
3 is output. For example, dot diameter D ₂ , measurement condition C ₂
, M ₁₂₂ , M ₂₂₂ , M ₃₂₂ ,..., M _N22
The correction data is read as shown in FIG. Thus, even dot diameter both within one line (spot diameter) is controlled to light as uniform in any and desired dot diameter D _x.

Therefore, according to the present embodiment, in addition to the above embodiment, the correction data M for each spot diameter D _x
NXY, since _M n ₊ 1xy also stored in the correction data storage unit 35, the LED elements 3 so as to be uniform in also the spot diameter D _x if desired spot diameter D _x is changed Lighting operation can be performed.

In the second and third embodiments, the light amount correction for equalizing the spot diameter of each dot is performed by controlling the light emission time. The current may be varied according to the correction data. In these embodiments, two adjacent LED elements 3 are used in accordance with the above-described embodiment.
Is used to form one dot, but the same can be applied to a case where one dot is formed by three or more LED elements 3. As further, with respect to the two pairs of LED elements 3 forming one dot in the present embodiment, the same correction data _{(M ny = M n + 1y} , M nxy = M n + 1xy) was a, made different (M _ny ≠ M _{n + 1y} ,
M _nxy ≠ M _{n + 1xy} ).

[0047]

According to the first aspect of the present invention, a plurality of continuous LED elements in an LED array are grouped into one group, and an image is formed using this group as a minimum unit of image information. Even if only one LED element is unstable, the peak light quantity can be increased by adding the light quantities of the LED elements forming a group and broadening the light quantity distribution in the main scanning direction. Occurrence is reduced and dots can be formed stably.

According to the second aspect of the invention, in the image forming apparatus according to the first aspect, two adjacent LED elements are grouped into one group, so that the resolution is reduced as much as possible. The effect of can be ensured.

According to the third aspect of the present invention, in the image forming apparatus according to the first or second aspect, one dot is formed by the LED elements forming each group in the LED array. A storage unit for storing correction data for obtaining a desired spot diameter preset for each of various image forming conditions for the LED element, a specifying unit for specifying a desired image forming condition, and a specified image forming condition Correction data reading means for reading out the corresponding correction data for each LED element from the storage section in accordance with the above, and each L of the LED array using the read out correction data.
By providing a drive control means for controlling the lighting operation of the ED element, even if the image forming condition is changed when a desired spot diameter is determined for dots formed by a plurality of LED elements, The correction data reading means reads the corresponding correction data from the storage unit according to the condition, and the drive control means uses the correction data to read the LE data.
Since the lighting operation of the D element is controlled, optical writing with a desired spot diameter can be secured, and
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 ensured.

According to a fourth aspect of the present invention, in the image forming apparatus of the first or second aspect, one dot is formed by the LED elements forming each group in the LED array. A storage unit for storing correction data for setting each spot diameter for each image forming condition and each spot diameter for the LED element, and a specifying unit for specifying a desired image forming condition and a spot diameter; Correction data reading means for reading, from the storage unit, correction data corresponding to each LED element according to the image forming conditions and the spot diameter, and lighting operation of each LED element of the LED array using the read correction data. The image forming apparatus is basically the same as the image forming apparatus according to the third aspect of the present invention by including a drive control unit for controlling the image forming apparatus. Since the correction data for each spot diameter is also stored in the storage unit, even when the desired spot diameter is changed, each LED element can be turned on so that the spot diameter becomes uniform. .

According to the fifth aspect of the present invention, the first aspect is provided.
In the image forming apparatus described in 2, 3, or 4, the minimum unit of image information is controlled to emit light by one-dot binary image data. It is sufficient to form one dot, which is the minimum unit of image information, based on a certain threshold level, and the formed image can be stabilized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an LED array, a light emission distribution, and dots formed according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a schematic structure of a writing unit of the LED array printer together with a control system block.

FIG. 3 is a block diagram illustrating a configuration of an LED array driving unit.

FIG. 4 is a block diagram illustrating a configuration of an LED array control unit.

FIG. 5 is a time chart showing the drive timing.

FIG. 6 is a block diagram of an optical writing device according to a second embodiment of the present invention.

FIG. 7 is a time chart showing the basic LED array driving timing.

FIG. 8 is a block diagram showing an optical writing device and a dot diameter data measuring device.

FIG. 9 is a time chart showing a light amount control method based on variable light emission time.

FIG. 10 is a flowchart illustrating a process for acquiring correction data.

FIG. 11 is a time chart showing an example of lighting timing of each dot according to correction data.

FIG. 12 is a flowchart illustrating a process for acquiring correction data according to the third embodiment of the present invention.

FIG. 13 is an explanatory view showing a conventional LED array, a light emission distribution, and dots to be formed.

[Explanation of symbols]

 3 LED element 12 LED array 35 Storage unit 36 Designating means

Claims (5)

[Claims] 1. An image forming apparatus for forming an image by electrophotography using an LED array in which a large number of LED elements whose light emission is controlled in accordance with image data is arranged in an array, wherein the continuous An image forming apparatus, wherein a plurality of LED elements to be formed are grouped into one group, and the group is used as a minimum unit of image information to form an image. 2. The image forming apparatus according to claim 1, wherein two adjacent LED elements are grouped into one group. 3. One dot is formed by the LED elements forming each group in the LED array, and the LED element for each dot has a desired spot diameter preset in accordance with various image forming conditions. A storage unit storing the correction data of the above, a designation unit for designating a desired image forming condition, and a correction data readout for reading out the correction data corresponding to each LED element from the storage unit according to the designated image formation condition. 3. The image forming apparatus according to claim 1, further comprising: a driving unit configured to control a lighting operation of each of the LED elements of the LED array using the read correction data. 4. One dot is formed by the LED elements forming each group in the LED array, and each LED element in the LED array is used for each dot LED element.
A storage unit that stores correction data for setting each spot diameter for each image forming condition and each spot diameter for the ED element; a specifying unit for specifying a desired image forming condition and a spot diameter; LEs depending on the image forming conditions 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: 5. The image forming apparatus according to claim 1, wherein a minimum unit of the image information is controlled to emit light by one dot binary image data.