JPS63272570A - Driving method for optical writing device - Google Patents

Abstract

PURPOSE:To correct total lighting time uniformly, by constituting lighting signals except that having longest lighting time of a plurality of lighting pulse signals obtained through uniform splitting of that lighting signal, then distributing the lighting pulse signals uniformly to a region having predetermined width in a time section. CONSTITUTION:In a fluctuation correcting circuit, lighting signals except that having maximum width are splitted into many uniform pulses and distributed in respective time sections. In all time sections, time TLIM for feeding lighting signals is expanded/shrunk corresponding to other correction factors. Expansion/ shrinkage of the lighting signal is carried out by opening/closing a gate inserted in a lighting signal feeding circuit by means of a correction signal. A lighting- signal cut signal 25k is fed from a counter circuit 25 to every time section. A specific correction signal 25h is inputted from the correction circuit to the counter circuit 25 in order to time the output from the lighting-signal cut signal 25k.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of driving an optical writing device that exposes a photoreceptor by irradiating it with light.

``Conventional technology'' With the remarkable progress in office automation in recent years, the demand for high-quality, high-speed, low-cost non-impact printers is increasing. Furthermore, in the medical field, there is a desire for high-quality video printers and photo printers to be used in medical equipment.

Laser printers are the most widely used in these fields to meet these demands, but the more they meet the demands of small size, high speed, high image quality, high reliability, and low price, the more This has not yet been achieved.

Now, as a driving method for such an optical writing device, an LED is used.
A so-called light modulation element array in which light emitting parts are arranged in rows, such as (light emitting diode) array printers, laser diode array printers, EL (electroluminescence) array printers, liquid crystal light shutter printers, fluorescent display tube printers, etc. Electrophotographic printers and photo printers using this type of technology are attracting attention because of their high reliability and high-speed suitability.

By selectively emitting light from light-emitting elements, these printers, like laser printers, irradiate light onto a photoreceptor to form an electrostatic latent image, which is then developed and recorded using a so-called electrophotographic method. I'm getting the image. Alternatively, it is also possible to use this light modulation element array to irradiate light onto a silver salt film and expose it to obtain a negative film similar to ordinary photography, which can then be printed.

However, these conventional methods have not been able to fully satisfy the demand for high image quality. In particular, in electrophotographic printers using LED arrays, manufacturing variations cause variations in luminous intensity between the light emitting elements, which causes a decline in image quality and makes it impossible to take advantage of its excellent high-speed suitability. In the past, various proposals have been made to correct variations in the light emission intensity of each light emitting element of such an optical writing device (Japanese Patent Application Laid-Open No. 1983-1989).
78476, 60-5387, 60-1471, 60-6472, 60-6473, 61-4755
6, Publication No. 60-64870).

That is, an LED array used in a general optical writing device is configured with a control circuit as shown in FIG. 10 incorporated therein.

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

In this circuit, when one line of blinking data 2a is transferred to the shift register 2 and input to the lock 2b at the same timing, a latch signal 3a is input to the latch 3 circuit and the blinking data is held. Next, when the lighting signal 4a is supplied to the AND gate 4 for a certain period of time, the latch circuit 3
If the blinking data held in is such that the corresponding LED 1 is turned on, that LED 1 is turned on for the duration of time when the lighting signal is supplied.

By the way, this means that all the LEDs are lit for the same constant lighting time. Therefore, each light emitting element is turned on multiple times within the optical writing time for one main scan of the LED array, and the total lighting time is adjusted by making a difference.

Specifically, as shown in FIG. 11, the time Tr for one main scan is divided into, for example, three time intervals, and a lighting time t of a constant width is selected for each time interval. On the other hand, an appropriate total lighting time is determined in advance for each light emitting element according to its emission intensity. In this example, the total lighting time of each light emitting element is t, 2t.

You can select from three types of lighting time: 3t.

Of course, if no exposure is required, the lighting time is 0. Here, the total lighting time is 2t for light emitting elements whose emission intensity is close to the average value, the total lighting time is 3t for those whose emission intensity is close to 50% of the average value, and the total lighting time is 3t for those whose emission intensity is close to 150% of the average value. The total lighting time is set to t. Now the time TrO
The photoreceptor is irradiated with substantially uniform light energy from the light emitting elements that are to be turned on during this period.

According to the circuit shown in FIG. 10, first, the first blinking data 2a
is transferred to the shift register 2 in synchronization with the lock 2b. Thereafter, the latch signal 3a is supplied to the latch circuit 3, and the blinking data is held in the latch circuit 3. Then, by supplying this blinking data and the lighting signal 4a to the AND gate 4, only the light emitting element whose blinking data is "1" lights up. This operation is repeated three times, and the blinking data in the shift register 2 is replaced each time. If the blinking data for three times are all "1", the total lighting time of the light emitting element is 3t. If two times are "1" and the remaining time is "0", the total lighting time will be 2t.

As described above, the variation in the light emission intensity of each light emitting element was 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 exposure time for one main scan into multiple time intervals. In order to increase the accuracy of the calculation, the number of divisions must be increased.

For example, if we try to double the correction accuracy as in the example shown in Figure 11, as shown in Figure 12, the blinking data will be transferred twice, or six times, within the exposure time for one main scan. You have to repeat the process of turning on the light. As a result, in the case of FIG. 12, six types of total lighting time can be selected.

Here, in FIG. 11, the time for exposing blinking data for one main scan is Tr (hereinafter referred to as one main scanning write time), and the frequency of the transfer lock 2b of the blinking data 2a is f. L, the total number of blinking data stored in the shift register 2 is Nd, and the number of temporal intervals is Ni, then the following relationship must hold between these.

Ni≦Tr/ ((1/ fcLx )XNd)...
(1) Here, ((1/fCLK) x Nd) corresponds to the transfer time of one line of blinking signals.

In this way, since the number of divisions Ni has a certain upper limit,
Correction accuracy cannot be improved beyond a certain level.

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

Ec=1/Ni≧Nd/ (f'ccg XT r
)...(2) Also, one main scanning writing time Tr is determined by the dot density ds in the sub-scanning direction required for a recorded image and the process speed Up.
It depends.

Tr=1/(UpXds)=(3)(1)
By substituting the formula into formula (2), the following formula is obtained.

Ec=NdxdsxUp/rCL, that is, high speed (Up-large) high image quality (d
s - + large and Ec → small), increase the number of serial signal lines for transferring blinking data to the shift register, perform parallel transfer, and reduce the number of serial data transfers Nd for one time. , it is necessary to increase the data transfer frequency fCLI+ by using a shift register 1 or latch 2 that is capable of high-speed data transfer. but,
Increasing the number of serial signal lines increases equipment costs;
This is undesirable because it reduces reliability. In addition, using high-speed elements increases costs, and
High-frequency noise countermeasures are expensive, which is also not desirable.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for driving an optical writing device that can achieve high speed and high image quality at low cost.

"Means for Solving the Problems" The method of the present invention involves arranging a light modulation element array in which a plurality of light modulation elements are arranged in a row to face a photoreceptor, selectively causing the light modulation elements to emit light, The photoreceptor is exposed for one scan, then the photoreceptor and the light modulation element are moved relative to each other in the sub-scanning direction, and the photoreceptor is exposed again for one main scan. do. Here, the time for performing exposure for one main scan is divided into a plurality of time sections, and a lighting signal is created by selecting different predetermined lighting times for at least two or more sections. At this time, at least the lighting signal other than the lighting signal with the maximum lighting time is composed of a plurality of pulsed lighting signals obtained by equally dividing the lighting signal, and this pulsed lighting signal is divided into a plurality of pulsed lighting signals in a predetermined time interval. Distribute evenly over the width area. Then, for each light modulation element, a combination of sections to be lit is selected so that an appropriate total lighting time can be obtained according to the light emission intensity, and the light modulation element is lit only in the selected section.
Exposure for main scanning is performed.

In addition, if the width of the region where the pulsed lighting signal is dispersed is made equal to the width of the lighting signal with the maximum lighting time, and the width of that region and the width of the lighting signal with the maximum lighting time are expanded or contracted at the same ratio. , the total lighting time can be corrected without changing the ratio of each total lighting time that has been corrected for variation.

"Operation" In the present invention, first, before incorporating the light modulation element array into an optical writing device, the light emission intensity of each element of the light modulation element array is measured using an automatic multi-point light amount measuring device or the like. Then, a variation correction signal for each element obtained by arithmetic processing of these emission intensity data is written into a storage element or the like provided in the light modulation element array drive device.

The light modulation element array driving device has l main scanning writing time T.
r is divided into Ni temporal intervals, and lighting signals of various preselected widths are supplied to each interval. For example, when N1=4, the lighting time of each section is 8:4:2:
Select 1.

The variation correction signal indicates the selection of any combination of these lighting times having different widths.

If you combine these lighting times with different widths, “1”
You can select from 15 types of total lighting time from "15" to "15".

This total lighting time T1 may be determined based on the conditions described above. In this way, one main scanning writing time can be divided into a relatively small number of parts to realize various total lighting times.

Also, the maximum value of the lighting time, in this example, the lighting time is “8”.
” lighting signal can be supplied twice within one main scanning write time Tr, for example, 8:8:4:2.
:1 lighting time may be selected. Thereby, it is possible to increase the ratio (duty) of the total lighting time to one main scanning write time Tr, and improve both efficiency and accuracy.

Furthermore, in the present invention, the lighting signals excluding at least the lighting signal with the maximum width are divided into a large number of equal pulses and distributed in each time interval.

In this way, the total lighting time after variation correction can be directly corrected to a negative rate based on conditions caused by other factors of the device.

"Example" (Automatic multi-point light intensity measurement device) In carrying out the method of the present invention, the emission intensity of each light modulation element constituting the light modulation element array is measured in advance.

FIG. 2 shows a block diagram of an automatic multi-point light amount measuring device suitable for this task.

In this device, an optical sensor 10 is attached movably in the direction of arrow A, and an LED array unit 15 is installed below it. The optical sensor 10 is mounted on a fixed base 11
It is supported by two pins 13 and 13' extending between bearings 12 erected at both ends. 2 pins 13.13
The outer periphery of one of the pins 13 is male threaded, and is rotated by a drive motor 14. A five-phase stepping motor was used as the drive motor 14. A female thread that fits into the male thread of the pin 13 is attached to the upper part of the optical sensor 10, and the optical sensor 10 is configured to move 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 is
It is composed of an ED array 16, a light converging rod lens array 15a, and a bracket 15b.

On the other hand, a control device 17 that controls the operation of this device is composed of a microprocessor (not shown), a memory element storing a program for its operation, a recording device for temporarily storing signals, and the like. This control device 17 sends commands to move and position the optical sensor 10 in six directions of arrows, and commands to move and position the optical sensor 10 in the six directions of arrows.
This circuit sends LED address information indicating which light emitting element of 6 is to be turned on and a desired command to the driving device 18 as a driving device control signal 17a. 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. This drive device 18 uses a so-called digital output board for a personal computer, which includes a decoder, a driver, and the like.

The optical power meter 19 is a circuit that performs analog-to-digital (A/D) conversion on the signal output from the optical sensor IO to obtain a digital light emission intensity signal 19a, and outputs this to the control device 17. This optical power meter 19 is
It consisted of an A/D conversion circuit, etc., and GP IB (IEEE488 compliant) was used as an interface with the control device 17.

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

First, when the drive device 18 outputs the lighting control signal 18a and the optical sensor micro-motion 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. light for a sufficient period of time. Then, the optical sensor 10 moves directly above the optical element (LED) that is turned on each time, receives the light, and photoelectrically converts the light.

The output signal of this sensor 10 is transmitted to the optical power meter 1.
At step 9, it becomes a digital light emission intensity signal 19a and is inputted to the control device 17. The 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 symbol 17b corresponding to all the light emitting elements is created based on the light emission intensity signal temporarily stored in this storage device, and is stored in the EPROM 21 (electrically programmable read only) through the ROM-like 20.・Write to memory). This EP
The ROM 21 is incorporated into an electrophotographic printer to be described later together with an LED array unit 15, and the LED array 16
is used to correct variations in the emission intensity of each light emitting element.

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

This device includes an LED array 1 arranged opposite to a photoreceptor 23.
6, a light converging lens array 15a, and a circuit for controlling lighting of this 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 2-line buffer memory 24 consists of two shift registers 24a and 24b, one of which stores the image signal 30 for one line, and the other which stores the already stored image signal 2.
4d, and a changeover switch 24c is added at both ends of the switch 24c to connect both terminals to an input/output terminal.

The counter circuit 25 receives a manually generated reference clock 31 and a line synchronization signal 32, and outputs a two-line buffer 24.
This circuit supplies a reference clock 25a for inputting an image signal, a transfer lock 25b for outputting an image signal, and a switching pulse 25c for switching a switch. This circuit is composed of a counter and a frequency dividing circuit (not shown). Also,
This circuit supplies an address signal 25d for memory reading to the memory control circuit 26, and also transfers a line synchronization signal 25e for generating a control signal to the lighting signal generation circuit 28, and transfers it to the lock 25b. supply Furthermore, a shift clock 25f for blinking data and a latch signal 25g are supplied to the LED array 16.

The memory control circuit 26 includes an EPROM 2 in which a variation correction signal previously created for the LED array 16 is stored.
This is an arithmetic circuit equipped with 1. This circuit is a circuit that outputs a variation correction signal 26a corresponding to the address signal 25d inputted from the counter circuit 25 to the AND gate 27.

The lighting signal generation circuit 28 repeatedly generates a lighting signal 28a having a preset width in a fixed order.
This is a circuit that outputs to 6.

This circuit is reset by the line synchronization signal 25e input from the counter circuit 25, and the transfer register 25''
A counter 28b that counts b, and this counter 28
It is composed of a decoder 28c which receives the count 1 shift of count 1 and outputs a high level or low level lighting signal.

(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 generates an electrostatic latent image corresponding to the image. is formed on the photoreceptor 23. Between the image output device and this electrophotographic printer, there are process control commands that control each known electrophotographic process such as paper feeding, charging, development, transfer, cleaning, fixing, etc. Printer status is exchanged to notify whether the printer is ready or not ready, but since it is not relevant to the present invention, a description thereof will be omitted.

Now, the image signal 30 is input to the two-line buffer 24, stored in either one of the shift registers 24a, 24b, and then read out alternately. A reference clock 31 provided as a pulse synchronized with the image signal 30 is input to the counter circuit 25 . The counter circuit 25 outputs a switching pulse 25c to the two-line buffer 24, and alternately switches the connection of the switch 24C in the two-line buffer 24, so that reading and writing can proceed simultaneously. This method is well known.

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

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

Note that this LED array 16 incorporates circuits such as the shift register 2 shown in FIG. 10. here,
In FIG. 1, the blinking data 27a corresponds to the LED array 16.
(Figure 1a). This blinking data 27a is transferred in synchronization with the shift clock 25f.

When the transfer of the blinking data 27a is completed, the counter circuit 2
A latch signal 25g is input from 5, and this blinking data 27
a is held in the latch circuit 3.

For example, in this embodiment, the time Tr for one main scan is divided into four temporal sections N1 to N4.

Further, during one main scanning write time TrO during which the same image signal 30 is stored in the two-line buffer 24 (FIG. 3), that image signal is repeatedly read out four times. Therefore, both the transfer lock 25b and the shift clock 25f have a frequency four times that of the reference clock 31.

Then, when the transfer of the blinking data 27a of the first section N1 is completed, a lighting signal 28a of lighting time T1 is supplied to the LED array 16 from the lighting signal generation circuit 28 (FIG. 3). Next, the blinking data 27a of N2 for the second section is transferred. For the second section N2, lighting time T
Two lighting signals 28a are supplied. Similarly, lighting signals of lighting times T3 and T4 are supplied until the fourth section N4, and exposure for one main scan is completed. Thereafter, in the 2-line buffer 24, the switch 24c is changed over to output the next image signal.

In this way, when focusing on one light emitting element of the LED array 16, a certain light emitting element has one main scanning writing time Tr.
During this period, the light is lit for T1+T2〒T3-'T4 hours, and a certain light emitting element is lit for T1+T4 hours. That is, the lighting time of each light emitting element is selected by combining the lighting signals with these four types of widths. In the embodiment of FIG. 1, Tl :T2 :T3
:T4 was set to 8+4:2:1. In this way, the light emitting elements with low emission intensity are turned on for a long time, and the light emitting elements with high emission intensity are turned on for a short time, so that the total light energy irradiated to the photoreceptor 23 within one main scanning writing time is adjusted to be equal.

(Structure of Lighting Signal) Here, in the present invention, as shown in FIG. 1, the lighting signal of lighting times T2, T3, and T4 is divided into a large number of pulses of equal width.

A partially enlarged view is shown in FIG.

A detailed explanation will be given later, but in FIG. 8, the lighting signal for the lighting time T2 is, for example, T2 as shown in a in FIG.
/K (K is a constant) pulses having a width T2' are arranged at equal intervals. Similarly, the lighting signal for the lighting time T3 has a configuration as shown in FIG. 2, and the lighting signal for the lighting time T4 has a configuration as shown in FIG. The width ratio of each pulse is T2:T3:T4=T2':T3':T4
'. Note that in this example, K=512
And so.

Hereinafter, the contents of the variation correction signal and its specific processing will be explained, assuming that this lighting signal is a continuous signal that is not divided, and then the effect when the lighting signal is divided will be explained.

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

Table 1 shows the variation correction signal 2 for the embodiment shown in FIG.
6a shows an example of the contents.

(Margin below) Table 1 This table 1 lists 16 types of variation correction signals (
(including cases where the light does not turn on at all) are shown. 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, dj is called duty,
This represents the total lighting time of each light emitting element for one main scanning write time Tu. For example, in FIG. 1, when a certain light emitting element is lit for TI+T3 hours, its duty d'' becomes (TI+73)/T'r.

Since Tl:T2:'l'3:T4 is 8:4:2:l, the minimum edge lighting time is T4, and the duty at that time is T4/Tr. In addition, the maximum total lighting time is T I +
Since 72+T3+T4, the maximum duty is (Tl+T
2+T3+T4)/Tr.

In Table 1, σIJ%σ2''...σ and j are data indicating whether or not the light emitting element is lit in each section N1, N2, N3, and N4, respectively. Here, j indicates the number of the light emitting element. σ1. If is “1”, the interval N
A value of 1 indicates that the light is lit for the lighting time T1, and a value of "0" indicates that the light is not lit during the period N1. σz(i=1
~4) are all "0", which means that the light emitting element does not light up at all, so if this is excluded, Step S
, to 515, 15 types of total lighting time can be prepared.

Note that if the duty is expressed as a general formula, it will be as shown in the following formula.

1: Section number (in the above formula, the number of sections is Ni) J: Light emitting element number Tr: 1 main scanning writing time σ + J = 1: σIJ to light the light emitting element J in the section Ni
=O: Not allowed Tl: Width of the lighting signal in section l, that is, the time to perform exposure for one main scan is divided into a plurality of temporal sections Ni, and the lighting time in each section N1 is set as Ti.
(i=1.2.3,...N1), unit lighting time T
, ni any integer from 1 to N (i=1.2.
3, -N i ), and the minimum value of nl is m1n(n
l), the maximum value is max(ni), the set A-(nili=1.2.3,...N1) of nl, and the integer X
Set B = (xlmin (ni)≦X≦max(ni))
When defining , select ni in the relationship AmB or Am)B, and set the lighting time T1 to T1-2""
Rub T on both feet.

Referring to FIG. 1, T1 is as follows.

TI=23 T4 T2=2” T4 T3=2' T4 Note that in this example, Tr/40 was selected as T4.

When d is determined in this way, Table 1 shown above is obtained.

(Example 2 of variation correction signal) In Fig. 4, the time for l main scanning is divided into five sections N1 to N5.
An example of dividing into two is shown. In this example, Tl:T2:
T3:T4:T5 was selected as 8:8:4:2:1. In this case, the maximum total lighting time is T1+T2+T3+T
4+T5. The variation correction signal in this example is shown in Table 2.

(Margin below) Table 2 This table 2 lists 16 types of variation correction signals (
(excluding cases where the light does not turn on at all) is shown.

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

Since the maximum total lighting time is T 1 +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' T5 T3=22 T5 T4=2' T5 Note that in this example, Tr150 is selected as T5.

In Table 1, all σ1j are set to "1" because the variation in the luminous intensity of the light emitting elements is about ±5% of the average value in devices with a small amount of -15), and even in devices with a large variation in luminescence intensity. The difference is about ±40%. The duty range required for correction may be about 2.4 times the ratio of the maximum value to the minimum value. Therefore, in this case, there is no need to control σIJ, and it is sufficient that it is always 1. In addition, by providing two or more divisions with the maximum lighting time, the maximum duty value can be increased.
As a result, the amount of light after correction is increased, and furthermore, high-speed optical writing becomes possible.

By controlling σ1J (i=2.3.4.5) for each element as described above, 2'
=16 different duties can be obtained.

(Correction of Variation) Now, as described above, the exposure amounts P and J (corresponding to the total lighting time) by the third light emitting element of the LED array 16 are expressed by the following formula.

PWJ = di T r I); p,: Light intensity before correction d, (
σ. By selecting a combination of (combinations of), it is possible to correct variations in light amount (variations in pt).

Furthermore, when the image output device outputs a multivalued image, that is, when the image signal is not binary but multivalued,
It is also possible to actively increase the exposure amount to multiple values. In this case as well, variation correction can be performed in the same manner.

In this embodiment, σ is calculated as follows for the light amount pj before correction.
IJ was determined and its variation was corrected.

First, find the minimum value pmin of p. If the maximum duty dj is applied to the element with the minimum emission intensity, LE
Since it is possible to maximize the amount of light after correcting the variations in the entire D array, the maximum step number srs shown in Table 1 is applied to pmin.

In Figure 5, the horizontal axis shows the luminescence intensity of each light emitting element before correction,
There is a correction diagram in which the vertical axis represents the total luminous energy after correction, that is, the exposure amount. The light intensity of each element before correction 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 corrected exposure amount Pm1n is determined by the following equation.

Pm1n=d, s Tr pmin This aSS has a step number s and a duty of 5 k. From Table 1 d
Since 15=15/40=3/8, by substituting this, the following formula is obtained.

Pm1n=-Tr pmin By matching the exposure amount of other elements to this reference exposure amount, it is possible to equalize the exposure amount of all the elements.

Setting this standard exposure amount as the lower limit threshold and looking at the graph in Figure 5 from left to right, first, the duty of step 5j = 15 in Table 1 is used before correction. If the light emission intensity exceeds px between pmin and px, the value after correction will be closer to the reference exposure amount P m 'in if the duty of step 5i=14 is used. In this way, selection of a more appropriate duty is repeated, and at the duty of step 5J=8, it becomes possible to correct pmax, which has the maximum emission intensity before correction. As a result, the amount of lightning after correction is suppressed within the range from Pm1n to Pmax.

When pa is the average value of the emission intensity of each element before correction, if there is a variation of about pmin/pa#0.7 pmax/pai1.3, the exposure amount after correction can be calculated using the method of this example. is improved as follows: Pm1n/Pa=0.946 Pm1n/Pa=0.054. That is, the variation in light amount which was ±30% before correction can be reduced to ±5.4% after correction.

In reality, measurement errors in p measured by an automatic multi-point light amount measuring device, etc., somewhat increase the variation in Pwj after correction. In the case of the above example, when the corrected P w i was actually measured for each element, the variation was ±5.9%.

A correction diagram for the embodiments shown in Table 2 is shown in FIG.

In this case as well, the corrected exposure amount Pm1n can be obtained by the following formula.

Pm1n=d,s Tr pmin From Table 2, d1s=0.46, so by substituting this, the following equation is obtained.

Pm1n=Q, 45 Tr pmin By matching the exposure amount of other elements to this reference exposure amount, it is possible to equalize the exposure amount of all the elements.

Setting this standard exposure amount as the lower limit threshold and looking at the graph in Figure 6 from left to right, first, the duty of step S* = 15 in Table 1 is used before correction. When the emission intensity exceeds px between pmin and px, the value after correction becomes closer to the reference exposure amount Pm1n when the duty of step s and -14 is used. thus,
Selection of a more appropriate duty is repeated, and in step S, =3, correction becomes possible until the emission intensity before correction reaches pmax, which is the maximum. As a result, the exposure amount after correction is Pm1n
to Pmax.

If pa is the average value of the light intensity of each element before correction, and there is a variation of about pmin/pa#o, 6 pmax/pa#1.4, the method of this example can be used to calculate the exposure after correction. The amount is Pm1n/Pa#0.945 pmax/Pa'=1. It will be improved to CL55. In other words, the variation in light amount which was ±40% before correction can be reduced to ±5.5% after correction.

In reality, measurement errors in Pwj measured by an automatic multi-point measuring device, etc., somewhat increase the variation in PIIJ after correction. In the case of the above example, when the corrected P wj was actually measured for each element, the variation was ±5.9%.

(Specific Signal Processing) Returning again to FIG. 3, a more specific circuit operation using the above-mentioned variation correction signal will be explained using the time charts of FIGS. 3 and 7.

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 uses the reference clock signal 25
A is supplied to the 2-line buffer memory 24 to achieve manual timing. Further, in order to synchronize the starting end of the image signal 25H for one line, a line synchronization signal 32 is also input to the counter circuit (FIG. 7b).

A switching signal 25C is input from the counter circuit 25 to the 2-line buffer memory 24, and a switch 24c causes the manual shift register 24a and the output shift register 24 to
(FIG. 7d).

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

If the apparatus of this embodiment operates so as to divide one main scanning write time into four time periods as shown in FIG. 1, the frequency of the image signal transfer lock 25b will be four times that of the reference clock. And a shift register 24b for output
While one line of the same image signal is stored in
The readout is repeated four times.

On the other hand, the counter circuit 25 supplies an address signal 25d to the memory control circuit 26.

This address signal 25d is output at the same timing as the output of the image signal 24d from the two-line buffer 24, and thereby the variation correction signal 26a is output from the memory control circuit 26 (FIG. 71). This address signal 25d is reset within the counter circuit 25 each time a line synchronization signal is input (FIG. 7h).

Image signal 2 output from the 2-line buffer memory 24
4d and the variation correction signal 26a outputted from the memory control circuit 26 are simultaneously input to the AND gate 27, the logical sum is taken and blinking data 27a is obtained.
It is supplied towards the LED array 16.

The latch signal 25g is output once every time one line of blinking data 27a is input to the LED array (FIG. 7f).

The content of the image signal 24d is always 1'' for a light emitting element to be lit.

On the other hand, the variation correction signal 27a is "0" for each section.
” or “1” are selected and output in the manner shown in Table 1. In other words, in section N1 shown in Figure 1, σ1, JSN2, σ□, etc. are output in this order. Therefore, by taking the logical product of the two, it is possible to cause the light emitting element to blink in accordance with the light emission intensity.The subsequent operation is as described using FIG.

When printed using the electrophotographic printer described above, high-quality printed images with less unevenness were obtained not only for characters and figures but also for halftone images. A slight one-dimensional noise remained on the screen in the halftone image, but it was confirmed that this was not due to variations in the amount of light, but was due to poor alignment accuracy of the light emitting elements of the LED array. The electrophotographic printer uses an As-3e photoreceptor, the process speed (photoreceptor movement speed) is 140 mm/sec, and the LED
The array uses GaASP-based light emitting elements, the peak wavelength of light emission is approximately 680 nm, and the dot density (LED arrangement density) is 240 SPi (spots per 1 inch (1 inch is 2.5 nm).
4 cm)), the LED forward current was driven at a constant current of 5 mA/dat, and 5LA-20 manufactured by Nippon Sheet Glass Co., Ltd. with an aperture angle of 20° was used as the SELFOC lens array.

In the above embodiment, the lighting signals are allocated and supplied in order from the longest one within one main scanning write time, but this order may of course be any arbitrary order.

Alternatively, the emission intensity data of each light emitting element measured by the automatic multi-point light intensity measuring device may be transferred to the electrophotographic printer, and the variation correction signal may be generated on the electrophotographic printer side based on this data.

In this case, the electrophotographic printer is provided with a so-called nonvolatile random access memory (RAM) backed up by a battery that stores this variation correction signal. For example, a design life of 6 years can be achieved by combining a lithium battery and CMO5 low power consumption RAM.

Furthermore, a silver salt film or the like may be used as the photoreceptor.

(Effect when the lighting signal is divided) As explained above, according to the method of the present invention, the lighting can individually correct variations in the light emission intensity of each light modulation element constituting the light modulation element array with high precision. It is possible to supply signals.

On the other hand, in optical writing devices, there are various other factors that cause changes in the image quality of recorded images, such as environmental changes, changes over time, and changes in the concentration of a developer such as toner used to develop a photoreceptor.

Various stabilization control devices are provided to prevent fluctuations in image quality due to these factors and to stabilize image quality.

Here, if the density of the recorded image as a whole becomes too dark, the exposure time by the light modulation element should be extended; conversely, if the density of the recorded image as a whole becomes too light, the exposure time by the light modulation element should be extended. You can shorten it.

This is, for example, the lighting signal Tl obtained in the previous embodiment.
, T2, T3, T4, and T5 at the same rate.

However, incorporating circuits corresponding to other correction factors into the circuit for processing the variation correction signal undesirably complicates the circuit unnecessarily.

Therefore, in the present invention, in this variation correction circuit, the lighting signals excluding at least the lighting signal with the maximum width are
As shown in the figure, the pulses were divided into a large number of equal pulses and distributed within each time segment.

Then, for example, in all time intervals, as shown in FIG. 8, the time TL□ for supplying the lighting signal is expanded or contracted at a constant rate in accordance with other correction factors.

In this way, each lighting signal can be expanded or contracted at the same ratio for each temporal section in which the lighting signal width substantially differs.

The lighting signal supply time T L I X is expanded or contracted, for example, by opening and closing a gate inserted in the lighting signal supply circuit using a correction signal. Or maybe the third
The counter circuit 25 shown in the figure supplies a signal 25k for lighting signal capturing in each time interval. A predetermined correction signal 25h is inputted to the counter circuit 25 from a correction circuit (not shown) in order to adjust the output timing of the lighting signal cut signal 25.

Note that this correction signal may be supplied from a circuit that performs process control of the entire optical writing device, or may be manually input by an operator operating a predetermined key on a console panel.

FIG. 9 shows another embodiment of the present invention, in which the lighting signal is
In the case of division as shown in the figure, the pulse width after division is all set to a constant width.

In this case, as shown in the figure, the ratio of the width of the lighting signal is T2:T
3: When T4 is set to 4:2:1, the ratio of the number of divided pulses is set to 4: and 2:1. For example, in FIG. 9a, if we look at the range of one unit of time T2' when T2/T2'=N (N is an integer), we can see that the lighting signal is T2'.
The one with T3 has 4 pulses (a), and the one with T3 has 2 pulses (
(b) in the same figure, T4 is composed of one pulse (C
).

T2':T3':T4'=T2:T3:
Needless to say, it is T4. In this case, each pulse is not necessarily arranged at equal intervals, but as long as it is divided into a large number of pulses, uniform correction is possible.

Of course, it does not matter if they are all equally spaced.

In any of the above cases, it is possible to correct the expansion and contraction of the lighting signal as a whole while preventing the configurations of the counter circuit and the lighting signal generation circuit shown in FIG. 3 from becoming complicated.

"Effects of the Invention" According to the method for driving an optical writing device of the present invention described above, it is possible to correct variations in the light emission intensity of each light emitting element at high speed and with high precision, thereby increasing the efficiency of optical writing and recording high-quality images. It can be performed.

Furthermore, it is low cost and easy to maintain, and there is no problem of high frequency noise generation.

[Brief explanation of the drawing]

FIG. 1 is a time chart showing an embodiment of the method for driving an optical writing device of the present invention, FIG. 2 is a block diagram of an automatic multi-point light amount measuring device suitable for implementing the method of the present invention, and FIG. A block diagram of an electrophotographic printer used to implement the method, FIG. 4 is a time chart showing another embodiment of the method of the present invention, FIG. 5 is a graph showing the effect of the variation correction, and FIG. 6 is the variation correction. FIG. 7 is a time chart illustrating the actual variation correction operation by an electrophotographic printer, and FIGS. 8 and 9 are graphs showing the effect of another embodiment of the present invention. An explanatory diagram, FIG. 10 is an explanatory diagram of a driving circuit for an LED array used in a general optical writing device, and FIGS. 11 and 12 are time charts showing a driving method of a conventional optical writing device. 16...Light modulation element array, 23...Photoconductor, 25g...False signal, 27a...Flashing signal, N1-N5... ...Temporal interval, Tr...Time for one main scan, T1-T5...Lighting time. Applicant: Fuji Xerox Co., Ltd. Agent

Claims (1)

[Scope of Claims] 1. A light modulation element array in which a plurality of light modulation elements are arranged in a row is opposed to a photoreceptor, and the light modulation elements are selectively emitted to expose one main scan; In an optical writing device, the photoreceptor is exposed to light corresponding to a recorded image by repeating an operation of relatively moving the photoreceptor and the light modulation element in a sub-scanning direction and exposing the photoreceptor for one main scan again. ,
Divide the time for exposure for one main scan into a plurality of time intervals, select different predetermined lighting times for at least two or more intervals to create a lighting signal, and create a lighting signal with the maximum lighting time at least. For other lighting signals, the lighting signal is composed of a plurality of pulsed lighting signals obtained by equally dividing the lighting signal, and the pulsed lighting signals are averagely distributed over an area of a predetermined width within the time interval, and the For each light modulation element, a combination of sections to be lit is selected so that an appropriate total lighting time can be obtained according to the light emission intensity, and the light modulation element is lit only in the selected section for one main scan. 1. A method of driving an optical writing device, the method comprising: performing exposure. 2. The width of the region in which the pulsed lighting signal is dispersed is equal to the width of the lighting signal with the maximum lighting time, and the width of the region and the width of the lighting signal with the maximum lighting time are in the same ratio. 2. The method of driving an optical writing device according to claim 1, wherein the total lighting time is corrected by expanding and contracting.