JP2586482B2 - Optical writing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing device that irradiates a photoreceptor with light for exposure.

[Related Art] In recent years, with the remarkable progress of office automation, demand for high-quality, high-speed, low-cost non-impact printers has been increasing. Also in the medical field, the appearance of high-quality video printers and photo printers used for medical equipment is desired.

In these areas, to meet such demands,
Although laser printers are most widely used, they do not meet the requirements of small size, high speed, high image quality, high reliability, and low price to a high level, and do not satisfy both of them.

Well, as a driving method of such an optical writing device, LED
A so-called light modulation element array in which light-emitting parts are arranged in rows, such as a (light-emitting diode) array printer, a laser diode array printer, an EL (electroluminescence) array printer, a liquid crystal light shutter printer, and a fluorescent display tube printer. Electrophotographic printers and photo printers that use the printer are receiving attention because of their high reliability and high-speed suitability.

These printers, like laser printers, emit light to form an electrostatic latent image, develop it, and record it by a so-called electrophotographic method, by selectively emitting light from the light-emitting elements. I have a picture. Alternatively, it is also possible to irradiate a silver salt film with light using this light modulation element array, expose the light, and obtain a negative film similar to that of a normal photograph for printing.

However, these methods have not been able to sufficiently satisfy the demand for high image quality. In particular, in an electrophotographic printer using an LED array, variations in light emission intensity between light emitting elements occur due to manufacturing variations, which leads to deterioration in image quality and makes it impossible to make use of its excellent high-speed suitability. Conventionally, various proposals have been made to correct the variation in the light emission intensity of each light emitting element of such an optical writing device (Japanese Patent Application Laid-Open No. 58-78).
476, 60-5387, 60-6471, 60-6472, 60-647
3, JP 61-47556, JP 60-67870).

That is, an LED array used in a general optical writing device is configured by incorporating a control circuit as shown in FIG.

In this circuit, a large number of LEDs 1 are arranged in a line, and the blinking data stored in the shift register 2 is
It is configured to be supplied via a latch circuit 3, an AND gate 4, and a driver 5.

In this circuit, when one line of blinking data 2a is input to the shift register 2 in synchronization with the transfer clock 2b, a latch signal 3a is input to the latch 3 circuit,
The blinking data is retained. Next, when the lighting signal 4a is supplied to the AND gate 4 for a certain period of time, if the blinking data held in the latch circuit 3 has the content of lighting the corresponding LED1, the time during which the LED1 is supplied with the lighting signal Only lights up.

By the way, in this case, all the LEDs are lit for the same constant lighting time. Therefore, LED array 1
Each light emitting element is turned on a plurality of times within the light writing time for the main scanning, and correction is performed with a difference in the total lighting time.

More specifically, as shown in FIG.
Tr is divided into, for example, three temporal sections, and a lighting time t having a certain width is selected. On the other hand, for each light-emitting element, an appropriate total lighting time according to the light-emitting intensity is determined in advance. In this example, three types of lighting times, t, 2t, and 3t, can be selected as the total lighting time of each light emitting element. Of course, if no exposure is required, the lighting time is zero. Here, a light emitting element whose luminous intensity is close to the average value has a total lighting time of 2t, a device whose luminous intensity is close to 50% of the average value is 3t, and a device whose luminous intensity is close to 150% of the average value. The total lighting time t is set. Thus, the light-emitting element to be turned on during the time Tr irradiates the photoconductor with substantially uniform light energy.

According to the circuit of FIG. 8, first, the first blink data 2a is input to the shift register 2 in synchronization with the transfer clock 2b. Thereafter, the latch signal 3a is supplied to the latch circuit 3, and the blinking data is held in the latch circuit 3. When the blink data and the lighting signal 4a are supplied to the AND gate 4, only the light emitting element whose blink data is "1" is turned on. This operation is repeated three times, and the blinking data in the shift register 2 is replaced each time. If all three blinking data are "1", the total lighting time of the light emitting element is 3t. If two times are "1" and the other one is "0", the total lighting time is 2t.

As described above, the variation in the light emission intensity of each light emitting element is corrected.

[Problems to be Solved by the Invention] By the way, in the above-described apparatus, the light emission time is corrected by dividing the time for performing the exposure for one main scan into a plurality of time sections. In order to increase the accuracy of the, the number of divisions must be increased. For example, if the accuracy of the correction is to be twice as high as that of the example of FIG. 9, as shown in FIG. Lighting must be repeated. As a result, in the case of FIG. 10, six types of total lighting time can be selected.

Here, in FIG. 9, the time for exposing the blinking data for one main scan is Tr (hereinafter, referred to as one main scanning write time), and the frequency of the transfer clock 2b of the blinking data 2a is f.
_Assuming that _CLK is _CLK , the total number of blinking data stored in the shift register 2 is Nd, and the number of temporal sections is Ni, the following relationship must be established between them.

Ni ≦ Tr / {(1 / _fCLK ) × Nd} (1) Here, {(1 / _fCLK ) × Nd} corresponds to the transfer time of the blink signal for one line.

Thus, since the number of divisions Ni has a certain upper limit,
The correction accuracy cannot be improved to some extent.

 Note that the correction error Ec can be expressed by the following equation.

Ec = 1 / Ni ≧ gNd / addition _{(f CLK × Tr) ...... (} 2), 1 main examination writing time Tr is determined by the dot density ds and process speed Up of the auxiliary scanning direction which is required in the recorded image.

Tr = 1 / (Up × ds) (3) By substituting equation (1) into equation (2), the following equation is obtained.

Ec = Nd × ds × Up / f _CLK, that is, high speed (Up → large) high image quality (ds
→ large and Ec → small) to increase the number of serial signal lines for transferring blinking data to the shift register and perform parallel transfer, and perform one serial data transfer
It is necessary to reduce Nd or use a shift register 1 or a latch 2 capable of high-speed data transfer and increase the data transfer frequency _fCLK . However, increasing the number of serial signal lines is not preferable because it increases the cost of the device and decreases the reliability. In addition, the use of a high-speed element increases the cost per se, and measures against high-frequency noise are expensive, which is not preferable.

The present invention has been made to solve the above points,
An object of the present invention is to provide an optical writing device capable of realizing high speed and high image quality at high cost.

"Means for Solving the Problems" The optical writing apparatus of the present invention comprises (a) a photoreceptor and (b)
A light modulation element array in which a plurality of light modulation elements are arranged in a row; (c) M (M is a positive integer) lighting times T; and N lighting times T / 2 ^K (K = 0, 1 ,..., N−1; N is an integer of 2 or more), and a total of N + M lighting times or non-use are necessary for generating a recorded image having the same intensity on the photoreceptor with the same sum of the lighting times used. Time
Correction information storage means for storing correction information, which is information specified for each of the plurality of light modulation elements constituting the light modulation element array; and (d) image storage means for storing image signals for one main scan. , (E) for each of the N + M lighting times, based on the image signal stored in the image signal storage means and the correction information stored in the correction information storage means, The light modulation element array is illuminated for the corresponding lighting time with a signal in which the correction information on the lighting time that is specified for non-use stipulates non-use, thereby producing an image signal for one main scan. And an exposure unit for exposing a corresponding recorded image onto a photoreceptor.

[Operation] In the present invention, first, before assembling the light modulation element array into the optical writing device, the light emission intensity of each element of the light modulation element array is measured using an automatic multi-point light quantity measuring device or the like. Then, based on the measured light emission intensity data, the time required to generate a recorded image of the same intensity on the photoreceptor is calculated for each element, and the M (M is a positive integer) lighting time T And N lighting times T / 2 ^K (K = 0,
From the total of N + M lighting times of 1,..., N−1; N is an integer of 2 or more, find a combination of lighting times that makes the sum of the lighting times closer to the most calculated time, and finds the combination (each lighting time). Is stored in the optical writing device as correction information.

Then, based on the correction information and the image signal to be exposed, N + M image signals whose contents have been corrected in accordance with the correction information are created, and the light modulation element array is formed using the N + M image signals. Are turned on for the corresponding lighting times, thereby exposing one scan.

"Example" (Automatic multi-point light quantity measuring device) The light modulation element array used in the optical writing device of the present invention is prepared in advance by an automatic multi-point light quantity measuring apparatus as shown in FIG. The emission intensity is measured.

In this device, an optical sensor 10 is mounted so as to be movable in the direction of arrow A, and an LED array unit 15 is installed below the optical sensor. The optical sensor 10 is supported by two pins 13 and 13 ′ that extend over bearings 12 erected at both ends of a fixed base 11. One of the two pins 13, 13 '
An external thread is cut on the outer periphery of 13 so that it can be rotated by the drive motor 14. As the drive motor 14, a five-phase stepping motor was used. Optical sensor 10
A female screw that fits into the male screw of the pin 13 is attached to the upper part of the optical sensor 10, and the optical sensor 10 moves in the direction of arrow A when the pin 13 is rotated by the drive motor 14.

On the other hand, the LED array unit 15 on the fixed base 11 includes an LED array 16, a light converging rod lens array 15a, and a bracket 15b.
It is composed of

On the other hand, the control device 17 for controlling the operation of this device comprises a microprocessor (not shown), a memory element storing a program for the operation thereof, a recording device for temporarily storing signals, and the like. The control device 17 uses a command for moving the optical sensor 10 in the direction of arrow A for positioning and a command corresponding to LED address information indicating which light emitting element of the LED array 16 is turned on as a drive device control signal 17a. Drive unit 18
Circuit to send to The drive device 18 is a circuit that interprets these commands, creates an LED lighting control signal 18a and an optical sensor fine movement signal 18b, and applies them to the LED array 16 and the optical sensor fine movement motor 14, respectively. As the drive unit 18, a digital output board for a so-called personal computer including a decoder and a driver is used.

The optical power meter 19 is a circuit that converts a signal output from the optical sensor 10 from analog to digital (A / D), obtains a digital light emission intensity signal 19a, and outputs the signal to the control device 17. The optical power meter 19 is composed of an A / D conversion circuit and the like, and GPIB (compliant with IEEE488) is used as an interface with the control device 17.

 The above automatic multi-point light quantity measuring device operates as follows.

First, when the driving device 18 outputs the lighting control signal 18a and the optical sensor fine movement signal 18b based on the command 17a output from the control device 17, each light emitting element of the LED array 16 measures the light intensity one by one from the left. Turn on for a sufficient time. The optical sensor 10 is an optical element (LED) that is lit each time.
, And receives the light to perform photoelectric conversion.

The output signal of the optical sensor 10 is
Thus, a digital light emission intensity signal 19a is input to the control device 17. Control device 17 temporarily stores the signal in a built-in storage device. This procedure is executed for all the light emitting elements constituting the LED array 16, and the light emission intensity signals corresponding to all the light emitting elements are stored in the storage device.

In this embodiment, a variation correction signal 17b corresponding to all the light-emitting elements is created based on the emission intensity signal temporarily stored in the storage device, and the variation correction signal 17b is transmitted through the ROM writer 20 to the EPROM 21 (Electrically Programmable Read / Write). (Only memory). The EPROM 21 is incorporated in an electrophotographic printer, which will be described later, together with the LED array unit 15, and is used to correct a variation in light emission intensity of each light emitting element of the LED array 16.

(Electrophotographic Printer) FIG. 3 shows a block diagram of an electrophotographic printer suitable for implementing the present invention.

This device has an LED array 16
, A light converging lens array 15a, and a circuit for controlling lighting of the LED array 16. This circuit includes a two-line buffer memory 24, a counter circuit 25, a memory control circuit 26, an AND gate 27, and a lighting signal generation circuit.

The two-line buffer memory 24 has two shift registers.
24a and 24b, one of which is an image signal 30 for one line.
And the other is provided for outputting the already stored image signal 24d, and a changeover switch 24c for connecting the two terminals to the input / output terminal is added to both ends of these.

The counter circuit 25 receives the input reference clock 31 and the line synchronization signal 32, and inputs the reference clock 25a for inputting the image signal, the transfer clock 25b for outputting the image signal, and the transfer clock 25b for switching to the two-line buffer 24. This is a circuit for supplying a switching pulse 25c. This circuit includes a counter and a frequency divider (not shown). Further, this circuit supplies an address signal 25d for memory reading to a memory control circuit 26, and also supplies a line synchronizing signal 25e for generating the control signal to a lighting signal generation circuit 28 to a transfer clock 25b. To supply. Further, a shift clock 25f for blinking data and a latch signal 25g are supplied to the LED array 16.

This is an arithmetic circuit in which the EPROM 21 in which the variation correction signal created previously for the LED array 16 is stored in the memory control circuit 26. This circuit includes a variation correction signal 26a corresponding to the address signal 25d input from the counter circuit 25.
Is output to the AND gate 27.

The lighting signal generation circuit 28 is a circuit that repeatedly outputs a lighting signal 28a having a preset width to the LED array 16 in a predetermined order. This circuit is reset by a line synchronization signal 25e input from the counter circuit 25, and includes a counter 28b that counts the transfer clock 25b, and a decoder 28c that receives the count value of the counter 28b and outputs a high-level or low-level lighting signal. It is composed of

(Operation of Electrophotographic Printer) The electrophotographic printer configured as described above receives an image signal 30, a reference clock 31, and a line synchronization signal 32 from an image output device (not shown) and exposes an electrostatic latent image corresponding to the image. Formed on body 23. Between the image output device and the electrophotographic printer, there are process control commands for controlling each known electrophotographic process such as paper feeding, charging, development, transfer, cleaning, fixing, and the like, and whether a paper jam or a fixing device temperature is appropriate. The exchange of a ready status notifying a ready / not ready indicating whether or not is performed is omitted, but the description is omitted because it is not related to the present invention.

The image signal 30 is input to the two-line buffer 24, stored in one of the shift registers 24a and 24b, and then read out alternately. A reference clock 31 given as a pulse synchronized with the image signal 30 is input to the counter circuit 25. The counter circuit 25 is composed of the above two-line buffer.
A switching pulse 25c is output to 24 and a 2-line buffer 2
The connection of the switch 24c in 4 is alternately switched, so that reading / writing proceeds simultaneously. This technique is a well-known technique.

At the same time, the counter circuit 25 sends an address signal 25d for reading the variation correction signal to the memory control circuit 26.
Output to Each variation correction signal is a 2-line buffer
It corresponds to the image signal 24d output from 24. The memory control circuit 26 outputs a variation correction signal 26a based on the address signal 25d. The AND gate 27 generates the blinking data 27a by taking the logical product of the image signal 24d and the variation correction signal 26a, and outputs the blinking data 27a to the LED array 16.

FIG. 1 is a time chart showing the transfer of the blinking data 27a to the LED array 16 and the lighting signal.

Note that the LED array 16 incorporates circuits such as the shift register 2 shown in FIG. Here, the first
In the figure, blinking data 27a is input to the shift register 2 of the LED array 16 (FIG. 1a). The transfer of the blinking data 27a is performed in synchronization with the shift clock 25f. When the transfer of the blinking data 27a is completed, a latch signal 25g is input from the counter circuit 25, and the blinking data 27a is
Is held.

For example, in this embodiment, the time Tr for one main scan is divided into four time sections N1 to N4. Also, during the one main scanning write time Tr in which the same image signal 30 is stored in the two-line buffer 24 (FIG. 3), the image signal is repeatedly read out four times. Therefore, both the transfer clock 25b and the shift clock 25f have four times the frequency of the reference clock 31.

When the transfer of the blinking data 27a in the first section N1 is completed, the lighting signal 28a for the lighting time T1 is supplied from the lighting signal generation circuit 28 (FIG. 3) to the LED array 16. Next, the blinking data 27a of the second section N2 is transferred. Second
For the second section N2, the lighting signal 28a of the lighting time T2 is supplied. Similarly, the lighting signals for the lighting times T3 and T4 are supplied until the fourth section N4, and the exposure for one main scan is completed. Thereafter, in the two-line buffer 24, the switch 24c is switched for outputting the next image signal.

As described above, focusing on one light emitting element of the LED array 16, one light emitting element is turned on for T1 + T2 + T3 + T4 hours during one main scanning writing time Tr, and is turned on for a certain light emitting element T1 + T4 hours. That is, the lighting time of each light emitting element is selected by combining the lighting signals of these four widths. In the embodiment of FIG. 1, T1: T2: T3: T4 is set to 8: 4: 2: 1. In this manner, the light emitting element having a low light emission intensity is turned on for a long time, and the light emitting element having a high light emission intensity is turned on for a short time.

(Example 1 of Variation Correction Signal) In which section each light-emitting element is lit is determined by the content of the variation correction signal 26a (FIG. 3).

Table 1 shows the variation correction signals for the embodiment of FIG.
26a shows an example of the content of 26a.

Table 1 shows a case where there are 16 kinds of variation correction signals (including a case where no lighting is performed at all).
One of these variation correction signals is prepared for each light emitting element, and stored in the EPROM 21 in the memory control circuit 26. In this table, d _j is called duty, which is
It represents the total lighting time of each light emitting element with respect to one main scanning writing time Tu. For example, in FIG. 1, when a certain light emitting element is turned on for T1 + T3 time, its duty _dj is (T1 + T3) / Tr.

T1: T2: T3: T4 is 8: 4: 2: 1 so the minimum total lighting time is T4,
The duty at that time is T4 / Tr. Also, since the maximum total lighting time is T1 + T2 + T3 + T4, the maximum duty is (T1
+ T2 + T3 + T4) / Tr.

In Table _{1, σ 1j, σ 2j ... σ} 4j , respectively the sections N1,
This is data indicating whether or not the light emitting element is turned on at N2, N3, and N4. Here, j indicates the number of the light emitting element. If σ _1j is “1”, it indicates that the lighting is performed during the lighting time T1 in the section N1, and if “0”, it indicates that the lighting is not performed in the section N1. When σ _1j (i = 1 to 4) are all “0”,
After means that the light-emitting element is not at all illuminated, it can be provided to exclude the step s ₁ ~s ₁₅ to 15 kinds of total lighting time this.

If the duty is expressed by a general expression, the following expression is obtained.

i: Section number (in the above equation, the number of sections is Ni) j: Light emitting element number Tr: Main scanning write time σ _1j = 1: Light emission j in section Ni σ _1j = 0: Light emission j in section Ni Ti: width of lighting signal in section i. That is, the time for performing exposure for one main scan is divided into a plurality of temporal sections Ni, and the lighting time in each section Ni is defined as Ti (i
.., Ni, the unit lighting time is T, and an arbitrary integer from 1 to N is ni (i = 1, 2, 3,... Ni), and the minimum value of this ni is min (ni). ), The maximum value is max (ni),
For ni, A = {ni | i = 1, 2, 3,... Ni} and for an integer x, B = {X | min (ni) ≦ x ≦ max (ni)}, A = Select ni that has a relationship of B or A⊃B,
The lighting time Ti is set to satisfy Ti = 2 ^niT .

 Referring to FIG. 1, Ti is as follows.

T1 = 2 ³ T4 T2 = 2 ² T4 T3 = 2 ¹ T4 In this example, Tr / 40 was selected as T4.

When d _j is obtained in this manner, the first table shown above is obtained.

(Example 2 of Variation Correction Signal) FIG. 4 shows an example in which the time for one main scan is divided into five sections N1 to N5. In this example, T1: T2: T3: T4: T5 is 8:
8: 4: 2: 1 was selected. The maximum total lighting time in this case is T1
+ T2 + T3 + T4 + T5. Table 2 shows the variation correction signal in this embodiment.

Table 2 shows a case where the number of types of variation correction signals is 16 (not including the case where no light is emitted at all).

In this example, since T1: T2: T3: T4: T5 is 8: 8: 4: 2: 1, the minimum total lighting time is T5, and the duty at that time is T5 / Tr.

Since the maximum total lighting time is T1 + T2 + T3 + T4 + T5, the maximum duty is (T1 + T2 + T3 + T4 + T5) / Tr.

 The lighting time Ti of each section is as follows.

T1 = T2 = 2 ³ T5 T3 = 2 ² T5 T4 = 2 ¹ T5 In this example, Tr / 50 is selected as T5.

In Table 1, σ _1j is all set to “1” because the variation in the luminous intensity of the light emitting element is generally about ± 5% of the average value in a small number of devices, and the average value is large in a large number of devices. It is about ± 40%. The range of duty required for correction is about 2.4 times when the ratio of the maximum value to the minimum value is obtained. Therefore, in this case, it is not necessary to control σ _1j , and it is sufficient if σ _1j is always 1. Further, by providing two or more sections with the maximum lighting time, the maximum value of the duty can be increased, and hence the amount of light after correction is increased, and further, high-speed optical writing is required.

By controlling σ _ij (i = 1, 2, 3, 4, 5) for each element as described above, in this embodiment,
2 ⁴ = 16 different duties can be obtained.

(Correction of Variation) As described above, the exposure amount P _wj (corresponding to the total lighting time) by the i-th light emitting element of the LED array 16 is expressed by the following equation.

P _wj = d _j Trp _j p _j : light intensity before correction By selecting d _j (combination of σ _ij ) in Table 1 or 2 according to this p _j , the light amount variation (variation in p _j ) Correction can be made. Further, when the image output device outputs a multi-valued image, that is, when the image signal is multi-valued instead of binary, the exposure amount can be positively multi-valued. Also in this case, variation correction can be performed in a similar manner.

In the present embodiment, σ _{ij is calculated} as follows with respect to the uncorrected light amount p _j .
Was determined and its variation was corrected.

First, a minimum value pmin of p _j is obtained. If the maximum duty _dj is applied to the element having the minimum light emission intensity, the light amount after the variation correction of the entire LED array can be maximized. Therefore, the maximum step number shown in Table 1 with respect to pmin
to apply the s _15.

FIG. 5 is a correction diagram in which the horizontal axis indicates the light emission intensity of each light emitting element before correction, and the vertical axis indicates the total light emission energy after correction, that is, the exposure amount. The light intensity before correction of each element varies between pmin and pmax due to manufacturing variations and the like.
As described above, since the maximum duty is applied to the element of pmin, the exposure amount Pmin after the correction is obtained by the following equation.

Pmin = d ₁₅ Tr pmin This d ₁₅ is a step number s ₁₅ k duty. First
According to the table, since d ₁₅ = 15/40 = 3/8, the following equation is obtained by substituting d ₁₅ = 15/40 = 3/8.

If the exposure amounts of the other elements are made to match this reference exposure amount, the exposure amounts of all the elements can be made uniform.

When this reference exposure amount is set to the lower limit threshold value and the graph of FIG. 5 is viewed from left to right, first, the duty of step s _j = 15 in Table 1 is used for correction. If the previous light emission intensity exceeds px between pmin and px, the corrected value becomes closer to the reference exposure amount Pmin when using the duty of step s _j = 14. In this way, selection of a more appropriate duty is repeated, and correction of the maximum pmax of the emission intensity before correction can be performed with the duty of step s _j = 8. As a result, the corrected voltage amount is suppressed in the range from Pmin to Pmax.

When pa is the average value of the light emission intensities of the respective elements before correction, if there is a variation of about pmin / pa ≒ 0.7 pmax / pa ≒ 1.3, the exposure amount after correction is Pmin by the method of this embodiment. It is improved to /pa≒0.946 Pmax / pa 改善 1.054. That is, the light amount variation of ± 30% before the correction can be reduced to ± 5.4% after the correction.

In practice, the measurement error of p _j as measured by the automatic multi-point light amount measurement apparatus, somewhat increase the variation of the corrected P _wj.
In the case of the above embodiment, when the corrected _Pwj was measured for each element, the variation was ± 5.9%.

 FIG. 6 shows a correction diagram for the embodiment shown in Table 2.

Also in this case, the exposure amount Pmin after the correction is obtained by the following equation.

Pmin = d ₁₅ Tr pmin From Table 2, d ₁₅ = 0.46, so the following equation can be obtained by substituting d ₁₅ .

Pmin = 0.46 Tr pmin By adjusting the exposure amount of other elements to the reference exposure amount, the exposure amount of all elements can be made uniform.

When this reference exposure amount is set to the lower limit threshold and the graph of FIG. 6 is viewed from left to right, first, the duty of step s _j = 15 in Table 1 is used before correction. If the light emission intensity exceeds px between pmin and pxm, the corrected value becomes closer to the reference exposure amount Pmin when the duty of step s _j = 14 is used. In this way, selection of a more appropriate duty is repeated, and in step s _j = 3, the light emission intensity before correction can be corrected to the maximum pmax. As a result, the exposure amount after the correction is suppressed to a range from Pmin to Pmax.

When it is assumed that there is a variation of about pmin / pa ≒ 0.6 pmax / pa ≒ 1.4 when pa is the average value of the light intensity of each element before correction, the exposure amount after correction is Pmin / It is improved to pa ≒ 0.945 Pmax / pa ≒ 1.055. That is, the light amount variation of ± 40% before the correction can be reduced to ± 5.5% after the correction.

Actually, a measurement error of _Pwj measured by the automatic multi-point measuring device causes the variation of _Pwj after correction to be somewhat large. In the case of the above embodiment, when the corrected _Pwj was measured for each element, the variation was ± 5.9%.

(Specific Signal Processing) Referring back to FIG. 3, a more specific circuit operation using the above-described variation correction signal will be described with reference to the time charts of FIGS.

First, the image signal 30 is input to the two-line buffer memory 24 in synchronization with the reference clock 31 (FIGS. 7A and 7C). In this case, the counter circuit 25 supplies the reference clock signal 25a to the two-line buffer memory 24 to adjust the input timing. In addition, in order to synchronize the starting end of the image signal 25a for one line, the line synchronizing signal 32 is also input to the counter circuit (FIG. 7B).

The switching signal 25c is input from the counter circuit 25 to the two-line buffer memory 24, and the switch 24c switches between the input shift register 24a and the output shift register 24b (FIG. 7d).

On the other hand, the image signal transfer clock 25b is output to the output shift register 24b (FIG. 7E).

Assuming that the apparatus of this embodiment operates to divide one main scanning write time into four time sections as shown in FIG. 1, the image signal transfer clock 25b has a frequency four times as high as the reference clock. While the same image signal for one line is stored in the output shift register 24b,
The reading is performed repeatedly.

On the other hand, the counter circuit 25 supplies an address signal 25d to the memory control circuit 26. This address signal 25d
Are output at the same timing as the output of the image signal 24d from the two-line buffer memory 24, whereby the variation control signal 26a is output from the memory control circuit 26 (FIG. 7i). The address signal 25d is reset in the counter circuit 25 to input a line synchronization signal (FIG. 7h).

Image signal 24 output from two-line buffer memory 24
When d and the variation correction signal 26a output from the memory control circuit 26 are input to the AND gate 27 at the same time, the logical sum is obtained to obtain blinking data 27a, and the LED array 16
Supplied to.

As for the latch signal 25g, the blinking data 27a for one line is LED
It is output once each time it enters the array (FIG. 7f).

The content of the image signal 24d is always "1" for the light emitting element to be turned on.

On the other hand, the variation correction signal 27a is “0” for each section.
Alternatively, any value of "1" is selected and output in the manner shown in Table 1. That is, since σ _1j is output in the section N1 shown in FIG. 1 and σ _2j is output in the order of N2, blinking according to the emission intensity of the light emitting element can be performed by taking the logical product of the two. . Subsequent operations are the first
This is as described with reference to the drawings.

When printing was performed using the above-described electrophotographic printer, a high-quality printed image with little unevenness was obtained not only for characters and figures but also for halftone images. Although a slight one-dimensional noise remained on the screen in the halftone image, it was confirmed that this was not due to the variation in the amount of light but corresponded to the poor alignment accuracy of the light emitting elements of the LED array. The electrophotographic printer uses an As-Se type photoreceptor, the process speed (photoreceptor moving speed) is 140mm / sec, the LED array uses a GaAsP type light emitting element, the emission wavelength is about 680nm at the peak wavelength,
Dot density (LED array density) 240SPi (spot per inch (1
Inch is 2.54cm)), LED forward current is 5mA / dot constant current drive, and the aperture angle is 20 as Selfoc lens array.
S SLA-20 manufactured by Nippon Sheet Glass was used.

In the above-described embodiment, the lighting time is allocated and supplied in ascending order within the one main scanning writing time. However, this order may be, of course, any order.

Further, the emission intensity data of each light emitting element measured by the automatic multi-point light intensity measuring device may be transferred to an electrophotographic printer, and a variation correction signal may be generated on the electrophotographic printer side based on the data. In this case, the electrophotographic printer is provided with a so-called non-volatile random access memory (RAM) that stores the variation correction signal and is backed up by a battery. For example, lithium battery and CMO
With a combination of low power consumption RAM, a design life of 6 years can be achieved.

Further, a silver halide film or the like may be used as the photoreceptor.

[Effects of the Invention] According to the optical writing apparatus of the present invention described above, it is possible to correct variations in light emission intensity of each light emitting element at high speed and with high accuracy, so that the efficiency of optical writing is increased and high-quality recording is performed. Can be. In addition, maintenance is easy at low cost, and there is no problem of generation of high frequency noise.

[Brief description of the drawings]

FIG. 1 is a time chart for explaining the operation procedure of the optical writing apparatus of the present invention, FIG. 2 is a block diagram of an automatic multi-point light quantity measuring apparatus suitable for measuring the light emission intensity of the light modulation element array, and FIG. FIG. 4 is a block diagram of an electrophotographic printer to which the present invention is applied, FIG. 4 is a time chart for explaining an operation procedure of the optical writing device when five kinds of lighting times are set, and FIG. FIG. 6 is a graph showing the effect of another embodiment of the variation correction,
FIG. 7 is a time chart for explaining an actual variation correction operation by the electrophotographic printer, FIG. 8 is an explanatory diagram of a driving circuit of an LED array used in a general optical writing device,
FIG. 9 and FIG. 10 are time charts showing a driving method of the conventional optical writing device. 16 ... Light modulation element array, 23 ... Photoconductor, 25g ... Latch signal, 27a ... Flashing signal, N1 to N5 ... Time section, Tr ... Time for one main scan, T1 to T5 ... Lighting time.

Continuation of the front page (56) References JP-A-58-78476 (JP, A) JP-A-63-87078 (JP, A) Jikai Sho 62-71642 (JP, U)

Claims (1)

(57) [Claims] 1. A photoreceptor, a light modulation element array in which a plurality of light modulation elements are arranged in a row, M light-up times T (M is a positive integer), and N light-up times
A total of N + M lighting times T / 2 ^K (K = 0, 1,..., N−1; N is an integer of 2 or more) are used or not used. Correction information storage means in which correction information, which is information defined for each of a plurality of light modulation elements constituting the light modulation element array, is stored so that a time required for generating the light modulation element on the photoconductor is obtained. Image signal storage means for storing image signals for one main scan; and image signals stored in the image signal storage means and stored in the correction information storage means for each of the N + M lighting times. Based on the correction information that has been, the light modulation element array with a signal that has been changed to non-display pixels that correction information about the target lighting time of the image signal has been defined as non-use, Corresponding lighting time minutes By optical writing apparatus characterized by comprising an exposure means for exposing the recording image corresponding to the image signal of the one main scanning on the photosensitive body.