JPH10104896A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adequately adjust the focusing position of an exposing device for an electrophotographic device which is changed by the influence of environment, etc. SOLUTION: This device is provided with a focus variable means 31 varying the focusing position of the exposing device 7, and a test pattern 38 on which many dots are arrayed at a specified area is formed by successively changing the focusing position. Each printing density is individually detected by a density detecting means 36, a coincident focusing position is detected on the surface of a photoreceptor 15 from the printing density, and the focusing position is set on the means 31. The most adequate focusing position of the exposing device 7 is detected from the printing density of the test pattern 38. Thus, the focusing position of the exposing device 7 can be adequately adjusted without requiring a complicated device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art At present, an electrophotographic image forming apparatus is put to practical use as a laser printer or an electrostatic copying machine. A general image forming apparatus has a photoconductor, and such a photoconductor is formed as a rotatable drum or a circulating belt. On the surface of such a photoreceptor,
A charging device, an exposure device, a developing device, a transfer device, and the like are arranged in this order, and a conveyance path of the printing paper is located in a gap between the photoconductor and the transfer device. The exposure device is formed, for example, in a structure in which a reflection surface of a rotatable polygon mirror is positioned on the optical axis of a laser light source, and an imaging optical system such as an fθ lens is arranged on a scanning optical path.

When an image is formed by such an image forming apparatus, the surface of a photosensitive body which moves sequentially is charged by discharging of a charger, and the charged surface is optically scanned by an exposure device to form an electrostatic latent image. To form The electrostatic latent image is developed with toner supplied from a developing device, and the toner image is sequentially transferred to the surface of the printing paper by the potential of the transfer device. In an actual image forming apparatus, the printing paper to which the toner has been transferred is pressed and heated by a fixing device to fix the toner on the printing paper.

[0004]

The image forming apparatus as described above can form an image on printing paper with toner by electrophotography.

At present, there is a demand for such an image forming apparatus to have a high resolution and a high definition color, and in order to realize this, it is necessary that the focal position of the exposure device exactly coincides with the surface of the photosensitive member. But this is actually difficult. For example, in recent image forming apparatuses, an imaging lens and the like are often made of resin for reasons of productivity and the like, but the focal position of an imaging lens made of resin fluctuates due to a change in environmental temperature. In particular, when the image forming spot is narrowed down to increase the resolution or the like, the change in the spot diameter with respect to the change in the focal position is large.

[0006]

According to the first aspect of the present invention, a movable surface of a photoreceptor is charged by discharge of a charger, and is then optically scanned by an exposure device to form an electrostatic latent image. In an electrophotographic image forming apparatus that forms and develops the electrostatic latent image with toner supplied from a developing device to form an image, a plurality of focus changing means for changing a focal position of the exposing device are provided. Pattern storage means for storing a test pattern in which dots are arranged in a predetermined area is provided, and pattern forming means for forming an electrostatic latent image of a plurality of test patterns having sequentially changed focal positions on the exposure device is provided.
Providing density detecting means for individually detecting print densities of a plurality of developed test patterns, and providing focus detecting means for detecting a focal position coinciding with the surface of the photoconductor based on the detected print density. A focus adjusting means for setting the focus position to the focus variable means. Therefore, when adjusting the focus position of the exposure device, the pattern forming means controls the operation of the exposure device in accordance with the test pattern stored in the pattern storage means, and the focus position of the exposure device is sequentially varied by the focus variable means. On the surface of the photoreceptor, electrostatic latent images of a plurality of test patterns whose focal positions are sequentially changed are formed. The plurality of test patterns are developed with toner supplied from a developing device, and their print densities are individually detected by density detecting means. A coincident focus position is detected. Since the detected focus position is set in the focus variable means by the focus adjustment means, the focus position of the exposure device is adjusted so as to exactly coincide with the surface of the photoconductor. The focal position in the present invention means the position of the focal point in the optical axis direction of the light beam with respect to the surface of the photoconductor, and does not mean the position where the light beam enters the surface of the photoconductor.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pattern storage means stores a test pattern in which a large number of dots are arranged at positions where they do not overlap with each other. The detecting means detects a focus position when the print density slightly decreases between the two peak values. Therefore, when the light intensity at the spot center of the exposure device is higher than the saturation intensity of the photosensitive characteristic of the photoconductor, the printing density of the dot is higher than the state where the focal position of the exposure device is exactly on the surface of the photoconductor. It is the highest when it is slightly displaced.
Since the test pattern is set in the pattern storage means so that such dots do not overlap with each other, the print density reflects the print density of the dots satisfactorily.
The print density of such a test pattern is highest when the focal position of the exposure device is slightly displaced than when the focal position of the exposure device exactly matches the surface of the photoreceptor. And when it drops slightly. Since the focus position in such a state is detected by the focus detection means, a state in which the focus position of the exposure device exactly matches the surface of the photoconductor is detected.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the pattern storage means stores a test pattern in which a large number of dots are arranged at a high density, and the focus detection means includes: , The focus position when the print density is at the peak value is detected. Therefore, when the light intensity at the spot center of the exposure device is lower than the saturation intensity of the photosensitive characteristic of the photoconductor,
The print density of the dot becomes highest when the focal position of the exposure device exactly matches the surface of the photoconductor. Since a test pattern in which such dots are arranged at a high density is set in the pattern storage means, the print density reflects the accuracy of the focal position of the exposure device satisfactorily. Since the focus position at the time of (1) is detected by the focus detection means, a state where the focus position of the exposure device exactly matches the surface of the photoconductor is detected.

According to a fourth aspect of the present invention, in the image forming apparatus of the second aspect, at least the light intensity at the spot center at the time of forming the test pattern is higher than the saturation intensity of the photosensitive characteristic of the photosensitive member. . Therefore, the printing density of the dots by the exposure device having such a light intensity becomes highest when the focal position of the exposure device is slightly displaced from the state where the focal position of the exposure device exactly matches the surface of the photoconductor. Since the test patterns are set in the pattern storage means so that they do not overlap with each other, the print density will reflect the print density of the dots well, and this print density will drop slightly between the two peak values. The focus position at this time is detected by the focus detection means, so that a state where the focus position of the exposure device exactly matches the surface of the photoconductor is detected.

According to a fifth aspect of the present invention, in the image forming apparatus of the third aspect, the exposure device has a light intensity at least at the spot center at the time of forming the test pattern lower than the saturation intensity of the photosensitive characteristic of the photosensitive member. . Therefore, the print density of dots by the exposure device having such light intensity becomes the highest when the focal position of the exposure device exactly matches the surface of the photoconductor. Since a test pattern in which such dots are arranged at a high density is set in the pattern storage means, the print density reflects the accuracy of the focal position of the exposure device satisfactorily. Since the focus position at the time of (1) is detected by the focus detection means, a state where the focus position of the exposure device exactly matches the surface of the photoconductor is detected.

[0011] The invention according to claim 6 is the invention according to claims 1 to 5.
The image forming apparatus according to any one of the preceding claims, further comprising an intensity varying means for varying the light intensity of the exposure device, and changing the light intensity of the exposure device to a test pattern so that a change in print density with respect to a change in a focal position is maximized. There is provided a strength adjusting means for adjusting at the time of forming. Therefore, since the light intensity of the exposure device is changed by the intensity changing device, the light intensity of the exposure device is adjusted by the intensity adjusting device so that the change in the print density with respect to the change in the focal position when the test pattern is formed is maximized. A state where the focal position of the exposure device exactly matches the surface of the photoconductor is detected satisfactorily.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 2, a color copying machine 1 as an image forming apparatus according to the present embodiment has an image reading block 2, an image processing circuit 3, an image printing block 4, and the like as main parts.

The image reading block 2 has a contact glass 5 and a sensor unit 6 as main parts, and the sensor unit 6 is movable in the sub-scanning direction by a unit support mechanism (not shown). Supported. The sensor unit 6 has three contact-type line sensors (not shown), and these line sensors individually read image data of RGB (Red, Green, Blue) components from a read document. .

The image processing circuit 3 accepts input of RGB component image data read and scanned by the image reading block 2 and converts this image data to KMYC (Black, Mag).
(enta, Yellow, Cyanide) components, and then output to the image print block 4.

The image printing block 4 has one scanner unit 7, four printing stations 8, one paper transport mechanism 9, one fixing device 10, and the like. The paper transport mechanism 7 has a paper feed cassette 11, a paper discharge tray (not shown), a belt transport mechanism 12, and the like. The belt transport mechanism 12 has an endless paper transport belt 13 that can freely circulate. It has a structure of being horizontally stretched by a pair of guide rollers 14. At the position where the paper transport belt 13 is stretched linearly, the four printing stations 8 are sequentially arranged, and the fixing device 10 is provided between the paper transport belt 13 and the paper discharge tray. Is located.

The printing station 8 has a rotatable photosensitive drum 15 as a photosensitive member, and a toner cleaner 16 and a discharging lamp 1 are provided on the surface of the photosensitive drum 15.
7, the charger 18, the light transmitting window 1 of the scanner unit 7
9, a developing device 20, a transfer device 21, and the like are arranged in order to face each other. The photosensitive drum 15 is in contact with the surface of the paper transport belt 13, and the transfer device 21 faces the photosensitive drum 15 via the paper transport belt 13.

The scanner unit 7 is formed so as to emit four scanning lights from the four light-transmitting windows 19 to the printing station 8, and corresponds to a structure in which four exposing units are integrated. The scanner unit 7 has one scanner motor 22, and two polygon mirrors 23 are mounted on the scanner motor 22.
As shown in FIG. 1, four laser light sources 24 are arranged opposite to each other on these two polygon mirrors 23, and as shown in FIG. An image forming optical system 25 and a deflecting optical system 26 are individually arranged on a scanning optical path deflected by the polygon mirror 23.

The deflection optical system 26 includes a plurality of reflection mirrors 2.
7, the final mirror 28 facing the photosensitive drum 15 of the printing station 8 through the light transmitting window 19.
Are rotatably supported by a servomotor 29. As shown in FIG. 1, a motor driving circuit 30 is connected to the servo motor 29, and the servo motor 29 is connected to the final mirror 28 by the motor driving circuit 30.
Is rotated, the position where the light beam enters the photosensitive drum 15 changes.

In this case, the focal length of the image forming optical system 25 does not change, but the optical path length to the photosensitive drum 15 changes, so that the focal position of the light beam with respect to the surface of the photosensitive drum 15 in the optical axis direction changes. In this case, a focus changing device 31 which is a focus changing means for changing the focus position of the scanner unit 7 is formed. That is, the focal position referred to here means the position of the focal point in the optical axis direction of the light beam with respect to the surface of the photosensitive drum 15, but does not mean the incident position of the light beam on the surface of the photosensitive drum 15. .

An LED (Light Emitting Diode) is provided on the surface of the paper transport belt 13 at a position below the linearly stretched belt.
ode) 32 are arranged opposite to each other, and a photodiode 34 is arranged opposite to the rear surface via an aperture 33. Since a density detecting circuit 35 is connected to the photodiode 34, a density detecting device 36 which is a density detecting means for detecting a print density on the surface of the paper transport belt 13 is formed here.

The laser light source 24 of the scanner unit 7
Is connected to an operation control circuit 37. The operation control circuit 37 controls the operation of the image printing block 4 in a different system from the image processing circuit 3. That is, the operation control circuit 37 has a microcomputer, and the microcomputer executes various control operations according to programs stored in the memory. More specifically,
The color copying machine 1 according to the present embodiment is set to execute the adjustment operation of the focal position of the scanner unit 7 at a predetermined timing, and the operation control circuit 37 is provided to integrally control the adjustment operation. I have.

In the memory of the operation control circuit 37, a storage area as a pattern storage means is secured, and a test pattern 3 in which a large number of dots are arranged in a predetermined area is provided.
8 are stored. The operation control circuit 3
When the focus position adjusting operation is performed, the scanner unit 7 forms the electrostatic latent images of the plurality of test patterns 38 whose focus positions are sequentially changed, and thus functions as a pattern forming unit at this time.

A plurality of test patterns 38 whose image forming positions at the time of exposure are sequentially changed are formed on the surface of the paper transport belt 13 by each of KMYC toner, and the print density of the test patterns 38 is detected by the density detection. The devices 36 detect individually. The print density of the test pattern 38 detected in this way is fed back to the operation control circuit 37, and the operation control circuit 37 matches the surface of the photosensitive drum 15 of the scanner unit 7 based on the detected print density. Since the focus position is detected, it functions as a focus detection unit at this time.

More specifically, in the color copying machine 1 of the present embodiment, the scanner unit 7 determines that the light intensity at the center of the spot formed on the surface of the photosensitive drum 15 is different from the photosensitive characteristic of the photosensitive drum 15. Higher than saturation intensity. Corresponding to this, the test pattern 38 is formed by arranging a large number of dots formed by imaging spots on the surface of the photosensitive drum 15 at positions that do not overlap each other, as shown in FIGS. I have.

When the operation control circuit 37 detects the optimum focus position of the scanner unit 7 based on the print density of the test pattern 38, the print density is determined as described later with reference to FIG. Is detected as optimum when the focus position slightly decreases between the two peak values. The operation control circuit 37 sets the optimum focus position detected as described above in the focus variable device 31, and thus functions as a focus adjustment unit at this time.

However, if the optical path of the scanner unit 7 is deflected in the sub-scanning direction in order to change the predetermined position with respect to the surface of the photosensitive drum 15, an electrostatic latent image is formed on the photosensitive drum 15. Since the timing also changes, the operation control circuit 37 also corrects this timing in accordance with the setting of the focus variable device 31.

With such a configuration, the color copying machine 1 of the present embodiment can execute various processing operations corresponding to various switchable operation modes. Mode and focus adjustment mode are provided.

The original copy mode is normally set at all times, and an image of a read original can be copied in full color on printing paper. In this case, the image reading block 2 reads and scans the RGB image data from the read document, and the image processing circuit 3 converts the image data from RGB to KMYC.
The image data of KMYC is printed out on printing paper by the image printing block 4.

At this time, in this image printing block 4,
In the four printing stations 8, the surface of the rotating photosensitive drum 15 is charged by corona discharge of the charger 18, and an electrostatic latent image is formed on the charged surface of the photosensitive drum 15 by optical scanning of the scanner unit 7. . At this time, the scanner unit 7 optically scans the surfaces of the four photosensitive drums 15 corresponding to the respective KMYC image data, and the electrostatic latent images of the four photosensitive drums 15 are supplied from the developing device 20. Each image is formed individually by the KMYC toner.

Since the paper transport mechanism 9 sequentially transports the printing paper by the circulating paper transport belt 13 in synchronization with the above-described operation, four potentials are generated on the surface of the printing paper by the potential difference generated by the transfer unit 21. From the photosensitive drum 15 to KMYC
Are sequentially transferred. The printing paper on which the full-color toner image is formed is heated and pressed by the fixing device 10, so that the printing paper on which the full-color image is formed is discharged to the paper discharge tray.

The color copying machine 1 of the present embodiment can copy a color image on a printing sheet as described above, but in order to perform such color copying with high quality, the image of each color must be copied. The formation must be performed with high resolution and high definition. In order to realize this, the focal position of the scanner unit 7 needs to exactly coincide with the surface of the photosensitive drum 15, but the focal position of the scanner unit 7 actually fluctuates even if the environmental temperature changes. I do.

To cope with this, in the color copying machine 1 of the present embodiment, the focus adjustment mode is automatically activated at a predetermined timing such as between image copying, and the scanner unit 7
Is provided so as to be automatically adjusted.
More specifically, when the focus position of the scanner unit 7 is adjusted in the focus adjustment mode, each unit of the image printing block 4 is driven as in the case of the above-described image copying, but the printing paper is not fed.

At this time, the operation control circuit 37 reads out the image data of the test pattern 38 and causes the scanner unit 7 to optically scan the image data, and sequentially changes the focal position of the scanner unit 7 by the focus changing device 31. On the surface of No. 15, electrostatic latent images of a plurality of test patterns 38 whose focal positions are sequentially changed are formed for each color. The plurality of test patterns 38 are developed into respective colors by the toner supplied from the developing device 20, and the toner images of the test patterns 38 are transferred to the surface of the paper transport belt 13.

When the test pattern 38 transferred to the surface of the paper transport belt 13 moves to the position of the density detecting device 36, the density detecting device 36
The toner image of No. 8 is illuminated by the LED 32, and its print density is detected by the photodiode 34 from the opening of the aperture 33. Since the print density detected in this way is input to the operation control circuit 37, the operation control circuit 37
The optimum focus position of the scanner unit 7 is detected from the print densities of the plurality of test patterns 38 having different focus positions at the time of exposure. Since the optimum focus position detected in this way is set in the focus variable device 31, the focus variable device 31 thereafter executes the image copying operation at the set focus position.

In the color copying machine 1 of the present embodiment, since the focal position of the scanner unit 7 is adjusted as described above, a color image copying operation can always be performed well. In particular, the test pattern 38 is set according to the light intensity of the scanner unit 7, and the test pattern 3
Since the method of detecting the optimum focus position of the scanner unit 7 from the print density of 8 is devised, the optimum focus position of the scanner unit 7 can be detected satisfactorily without requiring a complicated device.

This will be sequentially described below. First, as shown in FIGS. 3 and 4, the density detecting device 36 detects the print density of the test pattern 38 from the opening of the aperture 33, so that the detection of the print density is performed for a two-dimensional predetermined area. Will be. That is, it is difficult to detect the print density of the image print block 4 from zero-dimensional dots or one-dimensional line segments, and it is necessary to detect the print density from the two-dimensional test pattern 38 as described above.

However, in the case of such a test pattern 38, the focal position of the scanner unit 7 and the print density may not correspond one-to-one. That is, as shown in FIG. 5, when the light intensity at the center of the spot of the scanner unit 7 corresponds to the saturation intensity of the photosensitive characteristic of the photosensitive drum 15,
Since the print density is highest when the focal position is optimal, it is possible to detect the optimal focal length from the maximum print density without particularly devising the test pattern 38.

However, as shown in FIG. 6, when the light intensity at the center of the spot of the scanner unit 7 is higher than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15, the printing density of the dot becomes as shown in FIG. The maximum is obtained when the unit 7 is slightly displaced from the state where the focal position of the unit 7 exactly matches the surface of the photosensitive drum 15. In the case where the dots are formed with a large diameter and a high density in this manner, if the dots are arranged in the test pattern 38 at a high density, the scanner unit 7
It can be assumed that the print density of the test pattern 38 does not change even if the focal position is changed. However, in the color printer 1 of the present embodiment, the test pattern 38 is formed so that many dots do not overlap with each other.
The print density satisfactorily reflects the print density of the dots.

Since the density detecting device 36 detects the print density of the test pattern 38 from the opening of the aperture 33, the detected print density corresponds to the circulation of the paper transport belt 13 as shown in FIG. Stabilizes at a predetermined timing. However, as described above, when the light intensity at the center of the spot of the scanner unit 7 is higher than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15, the detection voltage of the photodiode 34, which is the detection density of the density detection device 36, also changes as shown in FIG. As shown in FIG. 7B, from the voltage V ₀ in a state where the focal position of the scanner unit 7 exactly matches the surface of the photosensitive drum 15, FIG.
As shown in, the higher in voltage V _n in a state of slight displacement.

That is, when a plurality of test patterns 38 whose focal positions are sequentially changed are formed by the scanner unit 7 having the light intensity as described above and the print density is detected, the focal positions are accurately positioned on the surface of the photosensitive drum 15. Since the state is slightly displaced from the state corresponding to the above, the optimum focus position is when the print density is slightly lowered between the two peak values.

Then, in the color copying machine 1 of the present embodiment, as shown in FIG. 8, the focus position when the print density detected by the density detecting device 36 slightly decreases between the two peak values is: Since the operation control circuit 37 detects the state as optimum, the state where the focal position of the scanner unit 7 exactly matches the surface of the photosensitive drum 15 is detected. The detection of such an optimum focus position is realized by, for example, detecting the dip value in the process of reaching the next peak value, starting from the time when the sequentially changing print density reaches the peak value.

That is, the color copying machine 1 of the present embodiment
Detects the optimum focus position of the scanner unit 7 from the print density of the toner, so that no complicated device is required for this detection, and the print density is determined by the two-dimensional test pattern 38.
, The print density can be detected satisfactorily. Further, since the test pattern 38 is arranged so that a large number of dots do not overlap each other, the light intensity at the spot center of the scanner unit 7 is
, The change in the focal position of the scanner unit 7 can be satisfactorily reflected on the change in the print density of the test pattern 38.

When the light intensity at the center of the spot of the scanner unit 7 is higher than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15, the detection result of the print density of the test pattern 38 and the focal position of the scanner unit 7 correspond one to one. However, since the dip value between the two peak values of the print density is detected, the optimum focus position of the scanner unit 7 can be detected satisfactorily.

The present invention is not limited to the above-described embodiment, but allows various modifications. For example, in the present embodiment, the color copying machine 1 is exemplified as the image forming apparatus. However, the image forming apparatus of the present invention may be any apparatus that forms an image by an electrophotographic method.
The present invention can also be applied to a monochrome copying machine, a monochrome printer, and the like.

Further, in this embodiment, the focus changing device 31 as the focus changing means adjusts the focus position of the scanner unit 7 by the displacement of the optical path due to the rotation of the final mirror 28 of the deflecting optical system 26. However, for example, it is also possible to realize this by displacing the optical components of the imaging optical system 25 in the optical axis direction. In other words, the present invention only needs to be able to change the focal position of the exposure device with respect to the photoreceptor in the optical axis direction. To achieve this, at least one of the optical path length and the focal length may be changed.

Further, in the present embodiment, an example has been described in which the developed test pattern 38 is transferred to the surface of the paper transport belt 13 to detect the print density, but, for example, the test pattern 38 is transferred to printing paper. The print density can be detected, and the print density of the test pattern 38 can be detected on the surface of the photosensitive drum 15.

In the present embodiment, it is assumed that the light intensity at the center of the spot of the scanner unit 7 is higher than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15, but as shown in FIG. Even when the light intensity at the center is lower than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15,
The present invention can be used.

In the scanner unit 7 having such a light intensity, as shown in FIG. 10, when the focus position is optimum, the print density of the test pattern 38 is the highest. The optimum focus position is simply detected from the highest state. However, since the dots printed by the scanner unit 7 having the light intensity as described above have a low density as a whole, as shown in FIGS. 11 and 12, the test pattern 38 is set in a form in which the dots are densely arranged. Is preferred. In this case, as shown in FIG. 13, since the print density of the dots is favorably reflected on the print density of the test pattern 38, the optimum focus position of the scanner unit 7 can be detected from the print density.

Further, up to this point, it is exemplified that the test pattern 38 is appropriately set corresponding to the case where the light intensity at the spot center of the scanner unit 7 is higher or lower than the saturation intensity of the photosensitive characteristic of the photosensitive drum 15. did. But,
It is also possible to set one of the two types of test patterns 38 as described above as desired, and adjust the light intensity of the scanner unit 7 when forming the test patterns accordingly.

In this case, an intensity varying means for varying the light intensity of the scanner unit 7 is provided by utilizing a driver circuit or the like of the laser light source 24, so that the change in the print density with respect to the change in the focal position is maximized. The drive control circuit 37 and the like are provided with intensity adjusting means for adjusting the light intensity of the test pattern when forming the test pattern. In this case, since the print density of the test pattern greatly changes with the change of the focal position of the scanner unit 7, the optimal focal position of the scanner unit 7 can be detected from the print density of the test pattern.

[0051]

According to the first aspect of the present invention, there is provided an image forming apparatus comprising:
A focus changing means for changing a focus position of the exposure device; a pattern storage means for storing a test pattern in which a large number of dots are arranged in a predetermined area; and an electrostatic latent of a plurality of test patterns in which the focus positions are sequentially changed. Pattern forming means for forming an image on an exposure device; density detecting means for individually detecting print densities of a plurality of developed test patterns; a focal point corresponding to the surface of the photoconductor based on the detected print density; By providing focus detection means for detecting the position and providing focus adjustment means for setting the detected focus position to the focus variable means, the exposure device in which the optimum focus position is set as described above can be statically operated at the highest resolution. Since an electrostatic latent image can be formed, an image can be formed with high resolution even if the focal length of the exposure device fluctuates due to environmental changes or the like, and a large number of test patterns can be formed. The optimal focus position of the exposure unit is detected from the print density of this test pattern, so that the optimal focus position of the exposure unit can be detected without the need for complicated equipment. Can be
It is possible to provide an image forming apparatus that can maintain good image quality with a simple structure.

According to a second aspect of the present invention, the pattern storage means stores a test pattern in which a large number of dots are arranged at positions not overlapping with each other, and the focus detection means has a print density of two peak values. By detecting the focal position when the position is slightly lowered in the middle, for example, even if the light intensity at the spot center of the exposure device is higher than the saturation intensity of the photosensitive characteristic of the photoconductor, the change in the focal position of the exposure device can be detected by a test pattern. And the optimum focus position of the exposure device can be satisfactorily detected from the print density.

According to a third aspect of the present invention, the pattern storage means stores a test pattern in which a large number of dots are arranged at a high density, and the focus detection means determines a focus position when the print density is a peak value. By detecting, for example, even when the light intensity at the spot center of the exposure device is lower than the saturation intensity of the photosensitive characteristic of the photoreceptor, the change in the focal position of the exposure device can be reflected well in the print density of the test pattern. The optimum focus position of the exposure device can be detected satisfactorily from the print density.

According to a fourth aspect of the present invention, the exposure device is formed by such an exposure device because at least the light intensity at the center of the spot at the time of forming the test pattern is higher than the saturation intensity of the photosensitive characteristic of the photosensitive member. Even though the dots have a large diameter and a high density, the test pattern is set so that such dots do not overlap each other, so that the change in the focus position of the exposure device can be reflected in the print density satisfactorily.
From this print density, the optimum focus position of the exposure device can be detected satisfactorily.

According to a fifth aspect of the present invention, the exposure device is formed by such an exposure device because at least the light intensity at the spot center at the time of forming the test pattern is lower than the saturation intensity of the photosensitive characteristic of the photosensitive member. Although the dots have low density as a whole, the test pattern is set so that such dots are arranged at high density, so that the change in the focus position of the exposure unit can be reflected well in the print density. Thus, the optimum focus position of the exposure device can be satisfactorily detected from the print density.

According to a sixth aspect of the present invention, there is provided an intensity varying means for varying the light intensity of the exposure device, and the light intensity of the exposure device is adjusted at the time of forming a test pattern so that the change in print density with respect to the change in the focal position is maximized. By providing the intensity adjusting means for adjusting, the print density of the test pattern changes greatly with the change of the focus position of the exposure device, so that the optimum focus position of the exposure device can be favorably detected from the print density of the test pattern. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a main part of a color copying machine as an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view schematically showing the entire structure of the color copying machine.

FIG. 3 is a schematic diagram illustrating a state in which a test pattern when a focus position is appropriate is read by a density detection device serving as density detection means.

FIG. 4 is a schematic diagram showing a state in which a density detection device reads a test pattern when a focus position is inappropriate.

FIG. 5 shows the relationship between the light intensity of the scanner unit and the printing state of dots when the light intensity at the center of the spot of the scanner unit, which is an exposure device, corresponds to the saturation intensity of the photosensitive characteristic of the photoconductor and the focal position is appropriate. FIG.

FIG. 6 shows the relationship between the light intensity of the scanner unit and the printing state of dots when the light intensity at the center of the spot of the scanner unit is higher than the saturation intensity of the photosensitive characteristic of the photoconductor;
(A) is a schematic diagram when the focal position is appropriate, and (b) is a schematic diagram when the focal position is inappropriate.

FIGS. 7A and 7B show print densities detected by a density detecting device from a test pattern that moves sequentially. FIG. 7A is a characteristic diagram when a focus position is appropriate, and FIG. 7B is a characteristic diagram when a focus position is inappropriate. .

FIG. 8 is a schematic diagram illustrating a relationship between a change in a focal position of a scanner unit and a change in print density.

FIG. 9 shows a relationship between the light intensity of the scanner unit and the printing state of dots when the light intensity at the center of the spot of the scanner unit is lower than the saturation intensity of the photosensitive characteristic of the photoconductor;
(A) is a schematic diagram when the focal position is appropriate, and (b) is a schematic diagram when the focal position is inappropriate.

FIG. 10 is a schematic diagram illustrating a relationship between a change in a focal position of a scanner unit and a change in print density.

FIG. 11 is a schematic diagram showing a state where a test pattern when a focus position is appropriate is read by a density detecting device as a density detecting unit.

FIG. 12 is a schematic diagram illustrating a state in which a density detection device reads a test pattern when a focus position is inappropriate.

13A and 13B show print densities detected by a density detection device from a test pattern that moves sequentially, wherein FIG. 13A is a characteristic diagram when the focal position is appropriate, and FIG. 13B is a characteristic diagram when the focal position is inappropriate. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Photoreceptor 7 Exposure device 18 Charger 20 Developing device 31 Focus changing means 36 Density detecting means 38 Test pattern

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Shinohara 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Yutaka Shio 10-3 Kitamura, Tottori City, Tottori Prefecture Ricoh Microelectronics Co., Ltd. (72) Inventor Tomonori Yabuta 10-3 Kitamura, Tottori City, Tottori Prefecture Ricoh Microelectronics Co., Ltd.

Claims (6)

[Claims] An electrostatic latent image is formed by charging a movable surface of a photoreceptor by discharging of a charger, and then performing optical scanning with an exposure device, and using the electrostatic latent image as a toner supplied from a developing device. An image forming apparatus of an electrophotographic type for forming an image by developing by using a focus variable means for changing a focal position of the exposure device, and a pattern storage means for storing a test pattern in which a number of dots are arranged in a predetermined area Provided, pattern forming means for forming an electrostatic latent image of a plurality of test patterns in which the focal position is sequentially changed in the exposure device,
Providing density detecting means for individually detecting print densities of a plurality of developed test patterns, and providing focus detecting means for detecting a focal position coinciding with the surface of the photoconductor based on the detected print density. An image forming apparatus provided with a focus adjusting means for setting the focus position to the focus changing means. 2. The pattern storage means stores a test pattern in which a large number of dots are arranged at positions where they do not overlap with each other, and the focus detection means determines that the print density has slightly decreased between two peak values. 2. The image forming apparatus according to claim 1, wherein a focus position at the time is detected. 3. The pattern storage means stores a test pattern in which a large number of dots are arranged at a high density, and the focus detection means detects a focus position when the print density is at a peak value. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 2, wherein the exposure device has a light intensity at a spot center at least at the time of forming the test pattern higher than a saturation intensity of a photosensitive characteristic of the photosensitive member. 5. The image forming apparatus according to claim 3, wherein the exposure device has a light intensity at a spot center at least at the time of forming the test pattern, which is lower than a saturation intensity of a photosensitive characteristic of the photosensitive member. 6. Intensity adjusting means for varying the light intensity of the exposure device, wherein the light intensity of the exposure device is adjusted at the time of forming a test pattern so that the change in print density with respect to the change in the focal position is maximized. The image forming apparatus according to claim 1, further comprising: