KR0146662B1 - Exposing device - Google Patents

Abstract

The present invention mainly provides an exposure apparatus capable of changing the dot exposure cycle without disturbing the edge correction function or the gradation variable setting function in the laser printer.

The exposure apparatus of the present invention has a surface divided into a plurality of exposure areas in the scanning direction, a photosensitive drum 30 for holding an image formed by exposure of this surface, and a laser light source 18, 19 for irradiating a laser beam. ), A polygon mirror (PM) rotating at a constant speed to scan the surface of the photosensitive drum 30 in the scanning direction by the laser beam output from the laser light source, and the number of emission data for one dot for each exposure area. A light source control circuit (11, 12, 13) for changing the light emission data for one line and supplying the light emission data to the laser light sources (18, 19) in synchronization with a clock pulse. In order to obtain a predetermined function from the light emission data for dots, the reference value of the number of data whose value should be corrected is multiplied by a coefficient corresponding to one exposure area to which this light emission data for one dot is allocated, and as a result, is obtained. And a light source data creation unit 11 for modifying the light emission of the number of binary data.

Description

Exposure device

1 is a view showing an exposure portion of a laser printer according to the prior art.

2 is a view for explaining a technique for correcting the fe error according to the angle of the polygon mirror (polygon mirror) shown in FIG.

3a and 3b are views for explaining the edge correction function of the laser printer according to the prior art.

4A and 4B are diagrams for explaining a gradation variable setting function of a laser printer according to the prior art.

5 is a block diagram schematically showing the circuit configuration of the laser printer according to the first embodiment of the present invention.

6 is a block diagram showing the exposure control circuit configuration of the laser printer shown in FIG.

FIG. 7 is a view for explaining an exposure area on the photosensitive drum shown in FIG.

FIG. 8 is a flowchart showing light emission data creation processing of the exposure control circuit shown in FIG.

9A and 9B are views for explaining the edge correction function of the exposure control circuit shown in FIG.

10 is a block diagram showing the exposure control circuit configuration of the laser printer according to the second embodiment of the present invention.

FIG. 11 is a view for explaining an exposure area on a photosensitive drum exposed by a laser beam output from the laser diode shown in FIG.

FIG. 12 is a flowchart showing light emission data creation processing of the exposure control circuit shown in FIG.

13A and 13B are views for explaining the gray scale variable setting function of the exposure control circuit shown in FIG.

* Explanation of symbols for the main parts of the drawings

11: CPU 12: ROM

13: RAM 14: I / O Port

15: blackout charge 16: warrior charge

17: high voltage source 18: laser diode

19: laser diode driver 21: motor driver

23: heater driver 25: sensor signal input circuit

26: communication interface 27: host computer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a laser printer having a fe error correction function, and more particularly, to an exposure apparatus of a laser printer capable of performing fe error correction without using a fe lens.

1 shows an exposure portion of a laser printer according to the prior art. In this laser printer, the laser diode 1 is driven in accordance with the image information and irradiates a polygon mirror 3 which rotates the laser beam at a constant speed. The polygon mirror 3 reflects the laser beam output from the laser diode 1 according to the mirror angle fe, and scans the surface of the photosensitive drum 2 in the main scanning direction shown in FIG. 1 by the laser beam. By selectively exposing this, an image for one line is formed on the surface of the photosensitive drum 2 as an electrostatic latent image. A dot is formed by continuously driving the laser diode 1 in a dot exposure period, and a space is formed by continuously stopping driving of the laser diode 1 in a dot exposure period. The photosensitive drum 2 is rotated by a predetermined amount every scan of one line. The image of the plurality of lines thus obtained is developed as a toner image in which toner adheres to the dot portion, and is transferred to a sheet and printed.

The scanning speed in the main scanning direction changes in accordance with the mirror angle fe of the polygon mirror 3, which causes non-uniform gradation of dots constituting the image formed on the surface of the photosensitive drum 2. For example, when the surface of the photosensitive drum 2 is divided into four exposure regions A, B, C, and D sequentially scanned by a laser beam in a quarter scan interval, each dot width is shown in FIG. It is relatively long in the exposure areas A and D at both ends, and relatively short in the exposure areas B and C at the center.

The fe error due to the mirror angle (fe) is determined by the polygon mirror (3) and the photosensitive drum (2) to refract the laser beam from the pulley mirror (3) according to the mirror angle (fe) so that the longitudinal scanning speed is constant. Correction is provided by providing a fe lens (not shown) in between. However, this fe error correction technique increases the total number of parts and requires space for installing the fe lens, which makes it difficult to miniaturize and reduce the price of a laser printer.

As another fe and correction technique, instead of using a fe lens, there is a correction technique for controlling the dot exposure period for each of the above-described exposure regions A, B, C, and D in scanning in the main scanning direction. In this correction technique, the dot exposure period is set such that the scanning of the exposure areas A and D at both ends is shorter than the scanning of the central exposure areas B and C. As shown in FIG. 2, the dot exposure period is set equal to the three-signal clock pulse in the scan of the exposure areas A and D, and the four-signal clock pulse in the scan of the exposure areas B and C, for example. Is set equal to As a result, the dot width becomes almost uniform in the exposure areas A, B, C, and D. Further, if the number of exposure areas is increased and the dot exposure period is set for each exposure area, fe error correction can be made more accurate.

By the way, any of the conventional laser printers has an edge correction function. This laser printer is a character. In order to smooth the outline of the image to be coded, the laser beam is partially irradiated to the space of one dot adjacent to the terminal dot in the scanning in each scanning direction. When the dot dot G, F, E forms the slope H outline as shown in FIG. 3A such that the dot exposure period is equal to the four-signal clock pulse, the laser diode 1 is connected to the terminal G, It is determined according to the slope H of this contour in the space adjacent to F, E). For example, it is additionally driven by three sign clock pulses, two guard clock pulses, and one sign clock pulse intervals. The slope H of the contour is inclined in accordance with the decrease in the pulse between the end dots.

Moreover, any of the laser printers according to the prior art has a gradation variable setting function. The laser printer variably sets the gray level of the dots instead of continuously irradiating the laser beam in the same dot exposure period as the predetermined number of code clock pulses. Stop the drive. When the dot exposure period is the same as the four code clock pulse, the irradiation of the laser beam is stopped in at least one pulse section selected from the first to fourth code clock pulses in accordance with the gray level of the dot to be set. For example, when the driving of the laser diode 1 is stopped in the second pulse section shown in FIG. 4A, the gray level of the dot becomes thinner than when the laser diode 1 is driven over the first to fourth pulse light bulbs. .

However, the fe error correction technique for controlling the dot exposure period is difficult to apply to a laser printer having the edge correction function or the gradation variable setting function as described above.

In a laser printer having an edge correction function, a normal edge correction function is obtained by controlling the laser dot exposure period. For example, the dot exposure period is set equal to the 4-signal clock pulse in the terminal exposure areas A and D shown in FIG. 1, and set to the same as the 8-signal clock pulse in the central exposure areas B and C. In the case where the above-described additional driving of the laser diode 1 is executed, the outline becomes the inclination H in the exposure areas A and D, and in the exposure areas B and C, as shown in FIG. 3B. It becomes the slope I. That is, edge correction for contours of the same slope cannot be performed in the same form between exposure areas.

In addition, in a laser printer having a gradation variable setting function, the normal gradation variable setting function is not obtained by controlling the dot exposure period. For example, the dot exposure period is set equal to the four-signal clock pulse in the exposure areas A and D shown in FIG. 1 and equal to the eight-signal clock pulse in the exposure areas B and C. When the irradiation is stopped in the second pulse section, the portion where the laser beam is not irradiated becomes narrower than the exposure regions A and D, as shown in FIG. 4B. That is, the gradation setting which obtains the same gradation cannot be performed in the same way between the exposure areas.

Accordingly, it is an object of the present invention to provide an exposure apparatus capable of changing a dot exposure cycle without disturbing functions such as an edge correction function or a gradation variable setting function.

In order to achieve the above object, according to the present invention, a photosensitive member having a surface divided into a plurality of exposure areas in the scanning direction, and holding an image formed by the exposure of the surface, a laser light source for irradiating a laser beam, and A polygon mirror is rotated at a constant speed to scan the surface of the photoconductor in the scanning direction by the laser beam output from the laser light source, and the number of emission data for one dot is changed for each exposure area to create one line of emission data. And a light source control unit for supplying the light emission data to a laser light source in synchronization with a clock pulse, wherein the light source control unit has a reference value of the number of data whose contents should be modified in order to obtain a predetermined function from one dot of light emission data. Is multiplied by a coefficient corresponding to one exposure region to which the light emission data for one dot is assigned, and the result is obtained. There is provided an exposure apparatus including a light emitting data creating unit for correcting light emitting data of the light emitting device.

According to such an exposure apparatus, the light emission data generating unit has one light exposure area in which light emission data for one dot is allocated to a reference value of the number of data whose contents must be corrected in order to obtain an edge correction function or a gradation correction function for light emission data for one dot. Multiply the corresponding coefficients in and correct the resulting number of luminescence data. For this reason, even if the dot exposure period changes for each exposure area, the edge correction function or the gradation variable setting function is normally performed.

Hereinafter, a laser printer according to a first embodiment of the present invention will be described with reference to the drawings.

5 shows a circuit configuration of the laser printer according to the present invention. This laser printer temporarily stores the CPU (central processing unit) 11 constituting the control unit body, the ROM 12 storing fixed data such as a control program of the CPU 11, and the input / output data of the CPU 11. It consists of a RAM 13, I / O port (14). The RAM 13 includes an image data memory area for storing image data in dot-matrix format and a light emission data memory area for storing light emission data for one line.

The CPU 11, ROM 12, RAM 13 and I / O port 14 are connected to each other via a bus line 29 composed of an address bus, a data bus, a control bus and the like.

The I / O port 14 is connected to the high voltage source 17, the laser diode driver 19, the motor driver 21, the heater driver 23, the sensor signal input circuit 25, and the communication interface 26. The high voltage source 17 is connected to the electrostatic charge 15 and the transfer charge 16, the laser diode driver 19 is connected to the laser diode 18, and the motor driver 21. ) Is connected to the motor group 20, the heater driver 23 is connected to the fixed heater 22, the sensor signal input circuit 25 is connected to the sensor group 24, the interface 26 is a communication cable This is connected to the host computer 27, respectively. The motor group 20 is connected to a polygon mirror PM, a photosensitive drum 30, a yongjin conveying roller (not shown) and the like.

The CPU 11 controls each of these elements by executing a control program stored in the ROM 12. In this control operation, the electrostatic charge 15 electrostatics the surface of the photosensitive drum 30 in the same form with the high voltage from the high voltage source 17. The laser diode driver 19 selectively drives the laser diode 18 based on the luminescence data supplied in synchronization with the sign clock pulse to irradiate the laser beam from the laser diode 18. As shown in FIG. 5, the polygon mirror PM rotates at a constant speed, reflects the laser beam output from the laser diode 18 according to the mirror angle fe, and causes the photosensitive drum ( 30) Scan the surface along the axis of the photosensitive drum in the main scanning direction and selectively expose it. Therefore, an image for one line is latent on the surface of the photosensitive drum 2 by electrostatic discharge. The photosensitive drum 30 is rotated by a predetermined amount every scan of one line. The images of the plurality of lines obtained in this manner are developed as a toner image in which toner adheres to the dot portion. The transfer charge 16 electrostatics the paper to the high voltage from the high voltage source circuit 17 and transfers the toner image on the photosensitive drum 30 onto the paper. This sheet is supplied from the paper cassette to the transfer charger 16 at a predetermined time by the conveying roller. The heater driver 23 controls the current flow of the fixed heater 22, and fixes the transferred toner image on the paper.

The sensor group 24 includes a paper sensor for detecting the presence or absence of paper, a laser beam sensor for detecting a laser beam irradiated from the pulley mirror PM and directed to a scanning start position adjacent to the end of the photosensitive drum 30; The sensor signal input circuit 25, which includes other sensors, supplies the detection signals from these sensors to the CPU 11 through the I / O port. The interface 26 receives character / code data including the exposure area information from the host computer 27 and also transmits various processing data to the host computer 27.

As shown in Fig. 7, the surface of the photosensitive drum 30 is divided into a plurality of exposure areas A1 to An in the main scanning direction. The ROM 12 has a memory area constituting a pulse number data table 32, a smoothing data table 35, and a coefficient data table 33. The pulse number data table 32 stores pulse number data set corresponding to each of the plurality of exposure areas on the photosensitive drum 30, and each pulse number data has the same number of coded clock pulses as the number of emission data for one dot (N). ). The flat data table 35 stores smoothing data set corresponding to various inclinations of the contour, and each smoothing data is added to a part of a space having a width of one dot adjacent to the terminal dot constituting the contour. The reference value of the number of sign clock pulses (number of emission data 1 (= ON)) of the section to be irradiated normally is shown. The coefficient data table 33 stores coefficient data corresponding to a plurality of exposure areas, and each coefficient data represents a coefficient D multiplied by the value of the smoothing data.

The code clock pulse number N (dot exposure period) is set so as to be larger in the exposure area of the center part scanned at a slower speed than the exposure area of the terminal part on the sensitizing drum 30. This is for uniform fe error correction of the gradation of dots formed in each exposure area on the photosensitive drum 30 irrespective of the mirror angle of the polygon mirror PM. The accuracy of this fe error correction is improved by increasing the number n of exposure areas.

The coefficient D is set to be large in proportion to the number of code clock pulses N in order to adjust the value of the smoothing data for each exposure area. This is to make the width of the portion to which the laser beam is additionally irradiated in the edge correction uniform in the exposure area.

6 shows an exposure control circuit of a laser printer.

The CPU 11 shown in FIG. 5 performs exposure control in accordance with a control program stored in the ROM 12. As shown in FIG. In this control operation, the CPU 11 functions as the exposure area detection unit 31 and the light emission data generating unit 34 shown in FIG. The CPU 11 detects which area of the exposure areas A1, A2,..., Received from the host computer 27 belongs to, and converts the character.-code data into image data in dot matrix format. To the RAM 13.

In the RAM 13, each image data is stored in a part of the image data memory corresponding to the detection exposure area. Thereafter, as shown in FIG. 8, the CPU 11 executes light emission data creation processing for creating light emission data for one line.

Referring to FIG. 8, in this light emission data creation process, the CPU 11 reads one dot of image data from the RAM 13 in step ST1, and the image data is read into the exposure area A1. Check if it belongs.

When it is detected that it belongs to the exposure area A1, at step ST2, the pulse number data N1 corresponding to this exposure area A1 is read out from the pulse number data table 32, and this is the number of emission data for one dot. Set as. In addition, when the image data for one dot represents a space adjacent to the dot to be subjected to the edge correction, the CPU 11 in step ST3 calculates the coefficient data D1 and the contour corresponding to this exposure area A1. The smoothing data Nadl according to the slope of is read out from the coefficient data table 33 and the smoothing data table 35, respectively. However, in the case of indicating a space or dot which is not related to edge correction, nothing is performed in step ST3.

In step ST4, the CPU 11 creates the light emitting data as many as set in step ST2 in accordance with the image data and stores it in the light emitting data memory of the RAM 13. These light emission data are all set to 1 when the image data represents a dot, and all to 0 when the image data represents a space. When the image data is read, the smoothing data Nad1 is multiplied by the coefficient D1, and the multiplication result (smooth data Nad1 x coefficient data D1) is performed on the emission data side of the terminal dot to be subjected to edge correction. The same number of luminescence data as) is corrected to 1 (= ON).

Next, in step ST5, it is determined whether or not light-emitting data creation for one line has finished. If the generation of light emission data for one line has not been completed, the process returns to step ST1 and is repeatedly executed.

If it is detected in step ST1 that the image data does not belong to the exposure area A1, it is determined in step ST6 whether the image data belongs to the exposure area A2. When it is detected that this image data belongs to the exposure area A2, at step ST7, the pulse number data N2 corresponding to this exposure area A2 is read out from the pulse number data table 32, and this dot is 1 dot. It is set as the light emission data number of minutes. In addition, when one dot of image data indicates a space adjacent to a dot to be subjected to edge correction, the CPU 11 determines that the coefficient data D2 and the contour corresponding to this exposure area A2 are deformed in step ST8. Smoothing data Nad2 according to the slope is read out from the coefficient data table 33 and the smoothing data table 35, respectively. However, in the case of indicating a space or dot which is not related to edge correction, neither is performed in step ST8.

In step ST9, the CPU 11 creates the light emission data corresponding to the image data by the number set in step ST7, and stores it in the light emission data memory of the RAM 13. These light emission data are set to mode 1 when the image data represents a dot, and are all set to 0 when the image data represents a space. If the image data represents a space and the smoothing data Nad2 and the coefficient data D2 are read, the smoothing data nad2 is multiplied by the coefficient data D2, and light emission of the terminal dots targeted for edge correction is performed. The same number of luminescence data as the multiplication result (smooth data (Nad2) x coefficient data (D2)) on the data side are corrected to 1 (= ON).

Next, in step ST5, it is determined whether or not light-emitting data creation for one line has finished. If the generation of light emission data for one line has not been completed, the process returns to step ST1 and is repeatedly executed.

If the image data does not belong to any of the exposure areas A1 and A2, the remaining exposure areas A3 to An are also checked and processed as described above. In this process, the light emission data creation process ends after the light emission data for one line is obtained.

Light emission data for one line is sequentially read from the light emission data memory in synchronization with a sign clock pulse and supplied to the laser diode driver 19. The laser diode driver 19 supplies a driving current to the laser diode 18 when light emission data 1 is supplied, and stops supplying the driving current when light emission data 0 is supplied.

The luminescence data creation process is repeated to perform all line scans. In the process in which the photosensitive drum 30 prints one page in one rotation, a light emission data memory for storing one page of light emission data generated in units of one line is prepared, and the light exposure data is generated after one line of light emission data is generated. You can also start

Here, edge correction when the photosensitive drum 30 is divided into four exposure areas A1 to An in the main scanning direction will be described. The code clock pulse number N of the dot exposure period is set to 4 in the terminal exposure areas A1 and A4, and is set to 8 in the center exposure areas A2 and A3, for example. Is set to 1 in the terminal exposure areas A1 and A4, and is set to 2 in the center exposure areas A2 and A3. Therefore, edge correction in the terminal exposure areas A1 and A4 is performed by multiplying the coefficient data D (= 1) by the smoothing data Nad and correcting the same number of luminescence data as the number of results. Further, in the central exposure areas A2 and A3, edge correction is performed by the coefficient data D (= 2) being multiplied by the smoothing data Nad, and correcting the same number of luminescence data as the number of results. Further, in the central exposure areas A2 and A3, edge correction is performed by the coefficient data D (= 2) being multiplied by the smoothing data Nad, and correcting the same number of luminescence data as the number of results. When edge correction is performed on the basis of the same smoothing data Nad, the inclination of the outline indicated by the arrow j in FIG. 9A is obtained in the terminal exposure areas A1 and A4, and the outline indicated by the arrow k in FIG. 9B. The slope of is obtained in the central exposure areas A2 and A3. That is, the inclination of these contours becomes uniform in each exposure area.

In this embodiment, even if fe error correction is performed by changing the number of code clock pulses of the dot exposure period for each exposure area, edge correction is performed based on the coefficient data set for each exposure area, so that the slope of the outline is changed in the exposure area. It does not depend on. Therefore, the accuracy of edge correction can be made uniform in all exposure areas.

In addition, since the fe error correction is performed without using the fe lens, the printer itself can be miniaturized and low in price.

Next, a laser printer according to a second embodiment of the present invention will be described with reference to the drawings.

Since the basic circuit configuration of the laser printer of the present invention is almost the same as that shown in FIG. 10 shows the exposure control circuit configuration of the laser printer of the present invention. This exposure control circuit differs from that shown in FIG. 6 in that it has a gradation variable setting function instead of an edge correction function.

As shown in Fig. 11, the surface of the photosensitive drum 30 is divided into a plurality of exposure areas B1 to Bn in the main scanning direction. The ROM 12 has a memory area consisting of a pulse number data table 42, a tone data table 45, and a coefficient data table 43. As shown in FIG. The pulse number data table 42 stores pulse number data set corresponding to each of the plurality of exposure areas on the photosensitive drum 30, and each pulse number data is the number of coded clock pulses equal to the number of emission data for one dot (M). ). The gradation data table 45 stores the gradation data set corresponding to each of the various gradations, and each gradation data represents a reference value of the number of sign clock pulses (number of emission data 0 (= OFF)) of the section selected for gradation setting. . The coefficient data table 43 stores coefficient data corresponding to the plurality of exposure areas, and each coefficient data represents a coefficient E which is multiplied by the gradation data value. The number of sign clock pulses M (dot exposure period) is set to be larger in the exposure area at the center portion scanned on the photosensitive drum 30 at a slower speed than the exposure area at the end portion. This is to perform the fe error correction which makes the gray level of the dot formed in each exposure area on the photosensitive drum 30 uniform, irrespective of the mirror angle of the polygon mirror PM. The accuracy of this fe error correction is improved by increasing the number n of exposure areas.

The coefficient E is set to be large in proportion to the code clock pulse number M in order to adjust the value of the gray scale data for each exposure area. This is to make the width of the portion not exposed for gradation setting uniform in each exposure area.

The CPU 11 shown in FIG. 10 performs exposure control in accordance with a control program stored in the ROM 12. As shown in FIG. In this control process, the CPU 41 functions as the exposure area detection unit 41 and the light emission data generating unit 44 shown in FIG. The CPU 11 detects to which exposure areas B1, B2 ... the character / code data received from the host computer 27 belongs, and converts the character / code data into dot matrix format image data. Stored in the RAM 13. In the RAM 13, each image data is stored in a part of the image data memory corresponding to the detection exposure area. Next, as shown in FIG. 12, the CPU 11 performs light emission data generation processing for generating light emission data for one line.

In this light emission data creation process, the CPU 11 reads out one dot of image data from the RAM 13 in step ST11, and determines whether the image data belongs to the exposure area B1. When it is detected that it belongs to the exposure area B1, in step ST12, the pulse number data M1 corresponding to the exposure area B1 is read out from the pulse number data table 42, and this data is emitted for one dot. Set as a number. In addition, when one dot of image data represents a dot, the CPU 11 in step ST13 counts data E1 corresponding to the exposure area B1 and gradation data Mad1 corresponding to the gradation of the dot. Are read from the coefficient data table 43 and the gradation data table 45, respectively. However, if the image data represents a space, nothing is performed in step ST13.

In step ST14, the CPU 11 creates the light emission data corresponding to the image data by the number set in step ST12 and stores it in the light emission data memory of the RAM 13. These light emission data are all set to 1 when the image data represents a dot, and are all set to 0 when the image data represents a space. If the image data represents a dot and the gradation data Mad1 and the coefficient data E1 are read, the position determined by multiplying the gradation data Mad1 by the coefficient data E1 and corresponding to the gradation of the surrounding dots Based on the above, the same number of light emission data as the multiplication result (gradation data (Mad1) x coefficient data (E1)) are corrected to 0 (= OFF).

Next, in step ST15, it is determined whether or not the generation of light emission data for one line has been completed. If the light emission for one line has not been completed, the process returns to step ST11 to be repeatedly failed.

If the image data does not belong to the exposure area B1 at step ST11, it is determined at step ST16 whether the image data belongs to the exposure area B2. When the image data belongs to the exposure area B2, in step ST17, the pulse number data M2 corresponding to the exposure area B2 is read out from the pulse number data table 42, and this is equal to one dot. It is set as the number of emission data. In addition, when the image data for one dot represents a dot, the CPU 11, at step ST18, the coefficient data E2 corresponding to the exposure area B2 and the gradation data Mad2 corresponding to the gradation of the dot. The data is read from the coefficient data table 43 and the gradation data table 45, respectively. However, if the image data represents a space, nothing is executed in step ST18.

In step ST19, the CPU 11 creates the light emission data corresponding to the image data by the number set in step ST17, and stores it in the light emission data memory of the RAM 13. These emission data are all set to zero when the image data represents a space. If the image data represents a dot and the gradation data Mad2 and the coefficient data E2 are read, the gradation data Mad2 is multiplied by the coefficient data E2 and centered on the position determined according to the gradation of the surrounding dots. As a result, the same number of luminescence data as the multiplication result (gradation data (Mad2) x coefficient data (E2)) are corrected to 0 (= OFF).

Next, in step ST15, it is determined whether or not light-emitting data creation for one line has finished. If the light emission data for one line has not been completed, the process returns to step ST11 to be repeated again.

If the image data does not belong to any of the exposure areas B1 and B2, the remaining exposure areas B3 to Bn are also checked and processed as described above. The light emission data creation process ends after the light emission data for one line is obtained.

Light emission data for one line is sequentially read from the light emission data memory in synchronization with a sign clock pulse and supplied to the laser diode driver 19. The laser diode driver 19 supplies the driving current to the laser diode 18 when light emission data 1 is supplied, and stops supplying the driving current when light emission data 0 is supplied.

The luminescence data creation process is repeated to perform this scan of all lines. In the process in which the photosensitive drum 30 performs printing for one page in one rotation, a light emitting data memory for storing one page of light emitting data created in units of one line is prepared, and then after one page of light emitting data is created. You may start exposure.

Here, the tone setting when the photosensitive drum 30 is divided into four exposure areas B1 to B4 in the main scanning direction will be described. The number of sign clock pulses M in the dot exposure period is set to 4 in the terminal exposure areas B1 and B4, and is set to 8 in the center exposure areas B2 and B3, for example. Is set to 1 in the terminal exposure areas B1 and B4, and is set to 2 in the central exposure areas B2 and B3. Therefore, the gradation setting in the terminal exposure areas B1 and B4 is performed by multiplying the coefficient data E (= 1) by the gradation data Mad and correcting the number of luminescence data equal to the number of the results. Further, the gradation setting in the central exposure areas B2 and B3 is performed by multiplying the gradation data Mad by the coefficient data E (= 2) and correcting the same number of luminescence data as the number of results. When gradation setting is performed based on the same gradation data Mad, as shown in FIG. 13A, the second code clock pulses are selected in the terminal exposure areas B1 and B4, and as shown in FIG. 13B. As described above, the third and fourth coded clock pulses are selected in the central exposure areas B2 and B3. That is, the width of the selected portion is made uniform in each exposure area.

In this embodiment, even when fe error correction is performed by changing the number of code clock pulses of the dot exposure period for each exposure area, gradation setting is performed based on the coefficient data set for each exposure area, so that the width of the selected portion is changed in the exposure area. It does not depend on. Therefore, the gradation can be made uniform in all exposure areas.

In addition, since the fe error correction is performed without using the fe lens, the printer itself can be miniaturized and low in price.

According to the present invention, the dot exposure period can be changed without disturbing functions such as an edge correction function or a gradation variable setting function.

Claims (3)

A photosensitive member 30 having a surface divided by a plurality of exposure areas in the scanning direction, and holding an image formed by the exposure of this surface, laser light sources 18 and 19 for irradiating a laser beam, and from the laser light source A polygon mirror (PM) rotated at a constant speed to scan the surface of the photoconductor in the scanning direction by the output laser beam, and the number of emission data for one dot is changed for each exposure area to create one line of emission data. And light source controllers 11, 12, and 13 for supplying the light emission data to the laser light sources 18, 19 in synchronization with a clock pulse, wherein the light source controller is configured to obtain a predetermined function from one dot of light emission data. , Multiplying the reference value of the number of data values whose value is to be corrected by a coefficient corresponding to one exposure area to which the one-dot light emission data is allocated, and correcting the resulting number of light emission data. And light emitting data generating means (11). 2. The light source control unit according to claim 1, wherein the light source control unit has a clock pulse number corresponding to a section in which a laser beam is additionally irradiated to a part of a space having a width of one dot adjacent to a terminal dot constituting an outline. The smoothing data indicating the reference value is calculated by the smoothing data table 35 generated according to the slope specified in the outline and the coefficient data indicating coefficients multiplied by the reference value indicated by the smoothing data read out from the smoothing data table 35. And a coefficient data table (33) generated according to the exposure area to which the space belongs. The gradation data generated in response to the gradation according to claim 1, wherein the light source control unit generates gradation data indicating a reference value of the number of clock pulses corresponding to a section in which driving of the laser light source is stopped in order to set the gradation to a dot. Coefficient data representing coefficients multiplied by a reference value appearing in accordance with the table 45 and the gray scale data read out from the gray scale data table 45 is further added to the coefficient deta table 43 generated in accordance with the exposure area to which the dot belongs. Exposure apparatus comprising a.