JP3292482B2 - Laser exposure image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to a laser exposure image forming apparatus for detecting jitter (image distortion caused by an instantaneous error in synchronization of a scanning mechanism) to reduce the influence of the jitter on a formed image. Related to the device.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus for obtaining an image by attaching toner to an electrostatic latent image, changes in the environment of the photosensitive member and changes with time, and changes in the characteristics of a developer used for development. Due to the change or the characteristic of the development itself, the state of the finally obtained image becomes unstable. In such a situation, in order to continuously obtain a stable image, process control has been conventionally performed. In the conventional method, a pattern for process control is formed on a photoreceptor, irradiated with light using an LED as a light source, and the reflected light is detected by a photo sensor. As such a device, for example, there is a device disclosed in JP-A-1-206368.

The conventional method is also used in an image forming apparatus in which an image is formed by an analog optical system, and detects an average density of a pattern having a certain width. Being able to obtain an averaged density is a reasonable detection means when controlling the toner density or the like based on the density information, because the user wants to know the overall density state rather than the detailed reproduction state.

[0004]

However, when more information is to be obtained from the pattern on the photoreceptor, it cannot be said that the desired information can be sufficiently obtained by the conventional method. In the case of an image forming apparatus that forms an image using a digital optical system, reproduction in small dot units is a problem, and the reproduction state of details is smaller than that of a conventional analog image forming apparatus. Reflected directly in the reproduction state. Therefore, it is necessary to know more detailed image information, and the conventional method is insufficient.

In the case of an electrophotographic image forming apparatus,
A latent electrostatic image is formed by writing on a pre-charged photoconductor, but fluctuations in the rotation of the photoconductor at the time of this writing cause uneven writing in the sub-scanning direction, resulting in jitter. In particular, in the case of a digital image forming apparatus that writes a latent image with a digital optical system, the writing unit is small, for example,
In the case of 400 dpi, since one unit is as small as 62.5 μm, a small amount of speed fluctuation causes shading as a large dot overlap, and this jitter is very noticeable. In order to solve this problem, a method has been adopted in which the writing beam in the sub-scanning direction is set large so that jitter is not noticeable even if the resolution in the sub-scanning direction is sacrificed. When the beam diameter is determined as in this method, the rotation speed fluctuation is determined based on the worst condition, so that the device is normally used at a level equal to or lower than the capability of the device, and in the sub-scanning direction. This is a big minus in obtaining high resolution.

The present invention solves the above problems by forming a periodic toner image for jitter detection in the sub-scanning direction on a photoreceptor and measuring the reflection density to accurately detect the amount of jitter. By adjusting the writing beam diameter of the laser according to the value, it is possible to always obtain a beautiful image in which the influence of jitter on the image quality is reduced without sacrificing the resolution in the sub-scanning direction. And

[0007]

A laser exposure image forming apparatus according to the present invention forms a latent image by irradiating a laser beam corresponding to an original image onto a photoreceptor (3) uniformly charged in advance. In an electrostatic transfer type image forming apparatus that develops a latent image with a developing device (14) to visualize the image, and then transfers the visualized image to transfer paper to form an image, a plurality of dots for jitter detection are used. Pattern forming means (10, 13, 14, 36) for forming on the photoreceptor (3) a pattern in which are arranged in the sub-scanning direction, and a slit (24) having a slit width equal to or less than the width of the dot in the sub-scanning direction. Density detecting means (20, 31) for detecting the density of the pattern for jitter detection through the slit, and the density detecting means (2
(0, 31), if the variation between the dots at the rising edge, the falling edge, or the center between them is large, the laser
Control means (32, 33, 36) for controlling the laser light output so as to widen the light beam diameter .

The symbols in parentheses are the corresponding elements in the embodiments described later.

[0009]

According to this, the pattern forming means (10, 13, 14, 3
The concentration of the pattern 6) is formed on the photosensitive member (3), detected by the concentration detection means (20, 31), the rise of the detected concentration, the fall or the center between them, the variation between the dots Big
The control means (32, 33, 36) controls the laser light output such that the beam diameter of the laser light is widened when the time is short. Therefore, it is possible to prevent image deterioration due to jitter.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0011]

FIG. 1 is a schematic perspective view of a writing optical system of a copying apparatus using a semiconductor laser according to an embodiment of the present invention.
FIG. 2 shows a schematic configuration of the copying apparatus. First, referring to FIG. 1, the optical system 10 includes a semiconductor laser 34, a condenser lens 5, a cylindrical lens 6, a polygon mirror 2, a polygon mirror driving motor 1, an fθ lens 4, a mirror 7, a synchronization detector 8, a laser It is composed of an aperture 9 for adjusting the beam diameter. The data subjected to image processing such as gamma conversion and halftone reproduction processing in the control unit 35 (shown in FIG. 4) of the image processing circuit 30 is transmitted to the driver 35.
, And a dot output is generated from the semiconductor laser 34. The beam emitted from the semiconductor laser 34 becomes a parallel beam in the condenser lens 5, passes through the aperture 9, and is irradiated on the polygon mirror 2 by the cylindrical lens 6. Further, the parallel beam is reflected by the polygon mirror 2, passes through the fθ lens 4, is reflected by the mirror 7, and forms an image on the photoconductor 3. The beam irradiated to the polygon mirror 12 changes its reflection angle by the rotation of the polygon mirror 2, and scans the photosensitive member 3. The polygon mirror 2 is configured to rotate at a constant speed by the motor 1 so that a laser beam is incident on the synchronization detector 8 every scanning of one run.

Referring next to FIG. 2, the optical system 10 has a sealed structure with a case 11, and the beam formed by the optical system 10 is irradiated onto the photoreceptor 3 via a dustproof glass 17. The photoconductor 3 is uniformly charged in advance by the charger 13, and the charged portion is irradiated with laser light from the optical system 10. A latent image is formed on the photoreceptor 3 by the irradiation of the laser beam, and the latent image is visualized by toner in the developing device 14 and further transferred to the transferred transfer paper 15. The transfer paper 15 is discharged out of the apparatus through a fixing process. Photoconductor 3
Is cleaned by the cleaning unit 16 after the visible image is transferred to the transfer paper 5. The photoconductor 3
Of the micro-density detecting device 2 immediately downstream of the developing device 14
0, the density of the formed predetermined pattern is read to detect jitter.

FIG. 3 shows a schematic configuration of the micro concentration detection device 20. In FIG. 3, reference numeral 3 denotes an object to be measured, which indicates a photoconductor. 21 is a lighting device, 22 is a condenser lens, 2
4 is a slit and 25 is a photo sensor. DUT 3
Is illuminated by the illumination device 2, and the reflected light enters from the entrance 23. The incident light is converted into parallel light by the condenser lens 22, passes through the slit 24, and passes through the photosensor 25.
The intensity is measured.

FIG. 4 shows a schematic configuration of an image processing circuit 30 for controlling the output of the semiconductor laser 34. The micro-concentration measuring unit 31 includes a measuring optical system, a driver circuit, and a memory for temporarily storing measurement data. The micro-concentration measuring unit 31 samples the micro-concentration data at regular time intervals according to a clock from the control unit 36 and stores the data on the memory. ing.
The sampling interval (time) X at this time is F / K ≧
V × X> E. In this equation, F is the dot diameter in the sub-scanning direction of the pattern for jitter detection, K is the sampling number within one dot, V is the rotation speed of the photoconductor 3, and E is the slit width in the sub-scanning direction at the time of measurement. Express. In the jitter detecting section 32, the micro concentration measuring section 3
1. Data is sequentially called from the memory in 1 and jitter is detected. The density data is also sent to the feedback determination unit 33. The feedback determination unit 33 determines feedback based on the density data and a signal indicating the degree of jitter from the jitter detection unit 32.

In this embodiment, the measurement for the micro density and the detection of the jitter are performed before the dot generation based on the image data of the original. This will be described below. First, a predetermined jitter detection pattern signal is sent to the laser driver 35. As a result, before the original image data is written on the photoconductor 3, a pattern for jitter detection is written on the photoconductor 3. The electrostatic latent image of the jitter detection pattern on the photoconductor 3 is visualized by the toner in the developing device 14. The toner image formed on the photoconductor 3 moves with the rotation of the photoconductor 3 and passes through the micro density detection device 20. In the micro concentration detecting device 20, the reflected light amount illuminated by the
The micro-density is measured while the toner image passes through the photo sensor 25 through 4, and the result is sent to the image processing circuit 30.

FIG. 5 shows an example of a jitter detection pattern. This pattern has a shape in which a plurality of dots are arranged in a line in the sub-scanning direction, and one dot has a width of 65 in the main scanning direction.
μm, the sub-scanning direction is 70 μm, and writing is performed every other dot. In order to detect the reproduction state of such a pattern, it is necessary to detect the density in fine units.
In particular, in order to detect the amount of pattern change in the sub-scanning direction and to detect jitter, it is necessary to set the detection unit in the sub-scanning direction small. The width of the detection unit depends on the width of the slit used for measurement, and therefore, the slit width is determined by the state of the jitter detection pattern. In the case of the pattern shown in FIG. 5, since the width in the sub-scanning direction is 70 μm, the slit width in the sub-scanning direction needs to be at least 70 μm or less, preferably 20 μm or less. FIG. 6 shows slits used for micro-concentration measurement when measuring this pattern.

The jitter detection process of the image processing circuit 30 will be described below. FIG. 7 shows an example of the density data obtained from the micro density measuring unit 31. The vertical axis indicates the density, and the horizontal axis indicates the amount of displacement in the sub-scanning direction. FIG. 8 is a diagram showing a value obtained by differentiating the density data shown in FIG. 7 with respect to the displacement on the vertical axis and the displacement amount on the horizontal axis. In FIG. 8, Thr2 and Thr3 are thresholds for judging the rise and fall of the density data waveform, respectively, and a differentiated result is compared with the threshold to identify a rising portion and a falling portion. Since the absolute value of the differential value shown in FIG. 8 changes depending on the absolute value of the density value shown in FIG.
hr2 and Thr3 are determined by the highest concentration in FIG. In the present embodiment, the amount of jitter is detected from the variation in the interval between the rising portions and the variation in the interval between the falling portions detected using Thr2 and Thr3.

FIG. 9 shows the contents of the jitter detection control of the image processing circuit 30. As shown in FIG. 11, D0 to Dm are stored in the memory in the microconcentration measuring unit 31 until addresses 0 to m.
Is stored. Five data are sequentially read from this memory (Step 1: hereinafter, the word "step" is omitted in parentheses), a first-order differentiation process is performed (2), and an edge portion is determined (3, 4). Thr
2 and Thr3, the address of the data determined to be the rising edge is stored in Pj (j is a variable and the initial value = 1) (6), and the value of j is updated (8). Further, the address of the data determined to be the falling edge is stored in Qi (i is a variable and initial value = 1) (5), and the value of i is updated (7). Thereafter, the value of N is updated (9), and if the value of N is smaller than the address smaller than the maximum address m by four, the process returns to step 1 again (1).
0).

FIG. 10 shows a flowchart of the laser output control. P (j + 1) and P detected in the process shown in FIG.
The amount of variation in the interval between j, Q (i + 1) and Qi is calculated (20, 21) and compared with the allowable value T of each variation (22). If the value exceeds the allowable value, feedback is made to the optical system to widen the writing beam diameter in the sub-scanning direction (24). If it is less than the allowable value, no feedback is performed (23).

As described above, in the present embodiment, a predetermined pattern for detecting jitter is formed on the photosensitive member, and the amount of jitter is detected based on the density data of the pattern. The output of the semiconductor laser 34 is controlled based on the amount of jitter.

By the way, in the above example, the data detected by the density detection is subjected to the differentiation process to perform the jitter detection. However, the laser output control may be performed by performing the jitter detection control without performing the differentiation. The processing in this case will be described below with reference to FIG. 12, FIG. 13 and FIG.

FIG. 12 shows density data obtained from the micro density detection device 20. The vertical axis indicates the density, and the horizontal axis indicates the amount of displacement in the sub-scanning direction. Thr1 is a threshold value for determining an image portion, and when it is larger than this value, it is determined that the portion is an image portion.

FIG. 1 is a flowchart of the jitter detection control.
3 will be described. First, initialization is performed (31). Here, the values of variables A and B are 0, and the initial value of variable n is -1.
And the address Qi (i = 1) is set to 00 and the address Pj
(J = 1) is set to FF. Next, the value of n is incremented by 1 (32), density data Dn is input from the memory in the micro density controller (33), and it is determined whether or not the image is an image portion by comparing it with Thr1 (34). If it is determined that the data is not an image portion, 1 is added to B and 0 is substituted for A (40, 41). Since 0 is assigned to each of A and B in the initial state, the value of B is "1" and the value of A is "0" in this state. When it is determined that the data is an image portion, 1 is added to A and 0 is substituted for B (35, 37). By this processing, the value of A is 1 when the data changes from the non-image portion to the image portion, and the value of B is 1 when the data changes from the image portion to the non-image portion. As long as image or non-image data continues, A,
Since the value of B is added, each of them becomes "1" only when data changes from the non-image part to the image part and from the image part to the non-image part. The address at that time is stored, and the center address of each dot of the image part is obtained from both (38, 39, 43 to 47). The above processing is performed on all data (48).

FIG. 14 shows a flow chart of the feedback control processing of the feedback determination section. The variation in the interval between the center addresses detected by the jitter detection control (FIG. 13) is calculated as an amount representing jitter (51). The jitter amount is compared with the jitter allowable value Ts (52), and Ts
If it is larger, feedback (53) is performed so as to widen the beam diameter in the sub-scanning direction, and if Ts or less, no feedback is performed (54).

As described above, the output of the semiconductor laser 34 can be controlled by detecting the density of the image portion of the original image, detecting the amount of jitter from the interval between the center addresses of each dot of the image portion.

[0026]

As described above, according to the present invention, the density of the pattern formed on the photoreceptor (3) by the pattern forming means (10, 13, 14, 36) is determined by the density detecting means (20, 31). If the variation between the dots at the rising and falling of the detected pattern density or at the center between them is large, the laser light beam
The control means (32, 33, 36) controls the laser light output so as to increase the beam diameter . Therefore, it is possible to prevent image deterioration due to jitter.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a writing optical system of a copying apparatus using a semiconductor laser embodying the present invention as an example.

FIG. 2 is a side view illustrating a schematic configuration of a copying apparatus that implements the present invention as an example.

FIG. 3 is a block diagram showing a schematic configuration of a micro concentration detection device 20.

FIG. 4 is a block diagram illustrating a schematic configuration of an image processing circuit 30.

FIG. 5 is a plan view showing an example of a jitter detection pattern.

FIG. 6 is a plan view schematically showing a slit 24.

FIG. 7 is a waveform chart showing an example of density data obtained by the micro density detection device 20.

8 is a waveform diagram in which a value obtained by differentiating the density data shown in FIG. 7 with respect to a displacement is shown on a vertical axis, and a horizontal axis also shows a displacement amount.

FIG. 9 is a flowchart illustrating a jitter detection control operation of the image processing circuit 30.

FIG. 10 is a flowchart showing an operation of laser output control of the image processing circuit 30.

FIG. 11 is a memory map showing a memory configuration of a micro concentration measurement unit 31.

FIG. 12 is a waveform diagram showing density data obtained from the micro density detection device 20 and a predetermined level Thr1.

FIG. 13 shows a case where the data obtained by detecting the concentration is not differentiated.
5 is a flowchart illustrating a jitter detection control operation of the image processing circuit 30.

FIG. 14 shows a case where the data obtained by detecting the concentration is not differentiated.
4 is a flowchart illustrating an operation of laser output control of the image processing circuit 30.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 drive motor 2 polygon mirror 3 photoreceptor 4 fθ lens 5 condenser lens 6 cylindrical lens 7 mirror 8 synchronization detector 9 beam aperture 10 optical system 11 case 13 charger 14 developer 15 transfer paper 16 cleaning unit 17 dust-proof glass 20 micro Density detecting device 21 Illuminating device 22 Condensing lens 24 Slit (slit) 25 Photosensor 30 Image processing circuit 31 Micro density measuring unit (20, 31: density detecting means) 32 Jitter detecting unit 33 Feedback determining unit 35 Laser driver 36 Control unit (32, 36: jitter detection means) (33, 36: control means) (10, 13, 14, 36: pattern formation means)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/04-1/207 H04N 1/23-1/29

Claims (1)

(57) [Claims] 1. A latent image is formed by irradiating a laser beam corresponding to an original image onto a photoreceptor uniformly charged in advance, and the latent image is developed by a developing device to be visualized. Forming means for forming a pattern in which a plurality of dots for jitter detection are arranged in a sub-scanning direction on a photoreceptor in an electrostatic transfer type laser exposure image forming apparatus for forming an image by transferring a formed image to transfer paper A slit having a slit width equal to or less than the width of the dot in the sub-scanning direction; density detecting means for detecting the density of the pattern for jitter detection through the slit; rising of the density detected by the density detecting means , If the variation between the dots at the falling edge or at the center between them is large
Control means for controlling a laser light output so as to widen a beam diameter of the laser light, wherein: