JP2001030537A - Optical scanning apparatus and image-recording apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a positional deviation of recording dots as a result of a scanning speed change by setting a rotary polygon mirror for rotating and scanning a light from a light-emitting element, an optical system for scanning the scanned light at a uniform velocity on a body to be scanned, and a photodetection means for detecting that the light passes through a light scanning area. SOLUTION: A light emitted from a semiconductor laser 2 irradiates a rotary polygon mirror 5 rotating at high speed of a uniform rotation angular velocity, and scanned. A scanned light 6 is turned to a uniform velocity scanning light by an fθ lens 8 and exposed to a photosensitive body or the like object to be irradiated with the light. In this case, a moving mirror 10 is arranged behind the fθ lens 8, so that the scanning light 6 can be switched to a vertical direction as an exposure direction of the photosensitive body and a horizontal direction as an exposure position detecting direction. A plurality of photodetection means 11 are set in a light scanning are in the horizontal direction, so that a pass timing of the scanned light can be detected. Scanned image information is changed on the basis of a detect signal 13, whereby the exposure is executed to a correct position on the photosensitive body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus using an electrophotographic process used in a printer, a facsimile, a copying machine, and the like. Optical scanning device for performing

[0002]

2. Description of the Related Art In an image recording apparatus using an electrophotographic process, a photosensitive member uniformly charged by a charger is exposed by an exposure device in accordance with image information, so that an electrostatic latent image is formed on the photosensitive member. A visible image is formed by forming an image and developing and visualizing it with a developing machine. Image recording on a final recording medium such as paper is performed by transferring a visible image formed on a photoreceptor and heating and fixing it with a fixing machine.

As an exposure apparatus for forming an electrostatic latent image in an electrophotographic process, there are a laser scanning exposure apparatus and an array type exposure apparatus using an LED array or a liquid crystal array (see, for example, JP-A-5-241092, JP-A-10-297022, JP-A-9-127613, etc.). The laser scanning device is
Since the exposure apparatus uses a single light source, the exposure apparatus has features such as easy stabilization of the amount of exposure light over the entire scanning range and variable resolution in the scanning direction. In the array method, it is essential to stabilize the variation in the amount of light between individual dots, and to increase the resolution in the scanning direction, the pitch of each exposure dot must be narrowed. It is difficult to achieve high resolution. For this reason,
At present, a laser exposure apparatus is often used as an exposure apparatus for an electrophotographic process.

[0004] A laser exposure apparatus irradiates a rotating polygon mirror with light emitted by a laser light source such as a semiconductor laser to perform optical scanning. The scanned light is scanned at a constant speed on an irradiation target plane such as a photoconductor, and an optical system is configured using an fθ lens or the like so as to be focused.

[0005] Emission or stoppage of laser light in accordance with image information is performed by modulation of a laser light source. In order to stabilize the exposure position of each dot in the scanning area, a laser light detecting means called a beam detector is arranged at the start end side of the scanning range of the light scanned by the rotating polygon mirror, and the laser light detecting means Based on the timing at which the exposure beam passes, in synchronization with the reference clock corresponding to each dot interval in the main scanning direction,
Laser modulation according to the image information of each scanning line is performed sequentially.

[0006]

In the above-mentioned laser exposure apparatus, each of the laser exposure signals is synchronized with a reference clock corresponding to each dot interval in the main scanning direction on the basis of a beam detector signal arranged at the start end of an optical scanning area. Laser modulation is performed sequentially according to the image information of the scanning line. In this case, when the scanning light is completely scanned at a constant speed on the irradiation target plane such as the photosensitive member, the intervals and positions of the dots in the main scanning direction are stabilized. In the above laser exposure apparatus, the light scanned by the rotating polygon mirror is converted by using an fθ lens or the like so that the scanning at a constant rotation angular speed is performed so that the scanning speed on the surface to be exposed is a constant speed scanning. However, the scanning speed of the converted scanning light slightly varies due to optical components such as an fθ lens and a mirror. The fθ lens is also deformed due to the expansion and contraction of the material due to a change over time or a change in the temperature of the surrounding environment, and causes a change in scanning speed. The fθ lens includes a lens using plastic such as acrylic or polycarbonate and a lens using glass. The plastic fθ lens is liable to be deformed due to the expansion and contraction of the material due to aging or temperature change of the surrounding environment. The scanning speed fluctuation amount of the plastic lens has a scanning speed fluctuation of about 0.7 to 1%. Approximately 0.2-0.5% for glass lenses
A slight variation in scanning speed occurs. Although glass lenses have slightly higher accuracy, plastic lenses are generally more often used because they are considerably more expensive than plastic lenses. Further, it is difficult to completely remove these fluctuations due to the material properties and the like.

[0007] These fluctuations are not so problematic in a monochrome image forming apparatus. However, a multicolor image forming layer value in which images of a plurality of colors are superimposed causes a shift in the superposition position between the respective color images, which is a serious problem in image quality. In particular, in a so-called tandem-type multicolor image forming apparatus in which a plurality of exposure devices are juxtaposed to form each color image, fluctuations in the scanning speed of each exposure system cause a serious problem in the accuracy of overlapping each color image. A speed variation of 0.7 to 1% due to the plastic fθ lens causes a scanning width of A4 width of 210 mm.
In this case, a dot position error of 0.5 to 2 mm may be obtained as the dot position. 0.2 with glassy fθ lens
Even a speed fluctuation of 0.5% can cause a scanning speed error of about several 100 μm. The dot position error increases as the scanning width increases. For example, in A3, the scanning width is about 3
Since it is 00 mm, a dot position error of about 1.5 times the A4 width may occur. Current color printers have a resolution of 600 dpi (dots / inch) or more, and have a size of about 40 μm per dot. Since the exposure position deviation of several hundreds μ corresponds to several lines, such an exposure position deviation is not allowed in a color printer. For this reason, in a color image forming apparatus using a plurality of exposure apparatuses, it is the actual situation that an expensive lens having a small scanning speed fluctuation is selected and applied to an optical system or an array type exposure apparatus is applied.

[0008] Such absolute displacement of the exposure dots can be a problem not only in a color image forming apparatus but also in a monochromatic image forming apparatus, such as a drafting image recording apparatus that requires accurate image dimensions.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical scanning device which suppresses a shift of a recording dot position due to a change in scanning speed. Another object of the present invention is to provide an inexpensive and high-precision exposure apparatus and provide a monochrome or color image recording apparatus capable of high-quality recording.

[0010]

In order to achieve the above object, the present invention provides a rotating polygon mirror having at least one mirror surface by rotating and scanning light emitted by a light emitting element, and a rotating polygon mirror having at least one mirror surface. A configuration having an optical system for scanning the light to be scanned on the object to be scanned at a constant speed, and light detecting means for detecting that the light has passed at least one position in the light scanning region; did. With this configuration, it is possible to provide an inexpensive and high-precision optical scanning device that does not cause displacement of recording dots.

An exposure unit for optically scanning a photosensitive member based on image information, a developing machine for forming a visible image on the exposed member, and at least one unit for detecting a position of the visible image in the optical scanning direction. And a scanning light information control unit that changes the image information based on the position information from the image recording position detection unit. According to this configuration, it is possible to provide an image recording apparatus capable of performing high-quality recording without a displacement of recording dots.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a view for explaining an embodiment of the optical scanning device of the present invention. Light emitted from the semiconductor laser 2 is applied to a rotating polygon mirror 5 that rotates at a high speed at a constant rotation angular velocity and is scanned. The scanned light 6 is applied to an fθ lens 8
With this, the scanning light is converted into the uniform scanning light, and the light irradiation target such as the photoconductor is exposed. After the fθ lens 8, the movable mirror 1
0 is arranged, and the scanning light 6 is configured to be switched between a vertical direction which is a photosensitive member exposure direction and a horizontal direction which is an exposure position detection direction. A plurality of light detecting means 11 are provided in the light scanning area in the horizontal direction. Each light detecting means is accurately arranged at a specified position, and detects the passage timing of light to be scanned. The image information to be scanned is changed on the basis of the detection signal 13 of the light detection device 11 so that an accurate position is exposed on the photoconductor.

Next, a method of changing image information based on the detection signal of the optical sensor will be described with reference to FIG. The figure shows a pixel clock corresponding to each dot in the main scanning direction and output signals of a plurality of photodetectors. The pixel clock is given a number from n−4 to n + 4 to indicate the number of the dot pixel from the end of the main scanning image.
Originally, when there is no error in the pixel position, the optical sensor is arranged such that the rising timing or the falling timing of the output signal of the light detecting means coincides with the n-th pixel clock. The signal of the light detecting means of the present embodiment shown in the drawing is based on the rising position. In the case of the detection signal of the light detection means as shown in FIG. 2A, since the clock of the nth pixel and the signal detection timing of the light detection means match,
There is no need to change the exposure image information. However, FIG.
When the detection signal of the light detecting means as shown in FIG. 2B or FIG. 2C is detected, it is necessary to change the image data because the exposure position is shifted by one dot or more. In the case of FIG. 2B, it indicates that the scanning speed is low, and the shift of one dot can be corrected by making the (n-1) th or the nth data continuous. FIG. 2B shows that the n-th data is used twice. In the case of FIG. 2C, it indicates that the scanning speed is high, and the shift of one dot can be corrected by omitting the (n-1) th data. FIG. 2C shows that the (n-1) -th data is omitted. Such a correction is less preferred because it indicates that the (n-1) th data will be lost. Therefore, it is preferable to set the rotation speed of the rotary polygon mirror and the pixel clock frequency indicating each dot exposure timing in the main scanning direction so that the scanning speed is shifted to the proper or faster side.

As described above, the image information is changed by adding or omitting pixels for correcting the exposure position shift. In order to detect the deviation of the exposure position, it is difficult to perform the exposure at the same time as the image recording because the exposure is required in the entire search range. Before printing a printed image, information on addition or deletion of a pixel to be subjected to exposure position shift correction is detected, pixel information to be exposed is changed according to the information, and optical scanning for actual image printing is performed. Since the displacement of the exposure position does not change suddenly, the sequence for detecting the displacement of the exposure position is as follows.
By performing the operation when the image recording apparatus is started, when the specified number of recordings are recorded, when the specified time elapses, or when the surrounding environment changes, a sufficient exposure position deviation correction effect can be achieved.

If an image which emits light in the vicinity of the area passing through the light detecting means in the actual recorded image is detected and the exposure position deviation is controlled at the same time, the detection sequence of the exposure position deviation can be particularly improved. No need to use. But,
In this case, it is necessary to separate and guide the scanning light to the light position detecting means simultaneously with the exposure of the photosensitive member. FIG. 3 is a diagram for explaining an example of the configuration of the exposure apparatus for that purpose. The light that has passed through the fθ lens 8 is split not in a movable mirror but in two directions by a beam splitter 15, one of which exposes the photoconductor 16, and one of which is guided to the light position detecting means 12 side. In this method, it is not necessary to operate the mirror, and the light passage timing of the exposure position can be detected with high accuracy with a simpler configuration. However, since a part of the scanning light is always guided in the direction of the light detecting means 11, the light amount for scanning the photosensitive member is reduced. .

A method using a half mirror, a hologram, or the like can be applied as long as it is a means for separating a light beam other than the beam splitter.

The light detecting means arranged in the optical scanning apparatus of the present invention shown in FIG. 1 is arranged at such an interval that an exposure position shift of one dot or more does not occur due to a change in scanning speed. It is necessary. If the exposure position shifts within one dot, the exposure position can be corrected by duplicating the exposure data twice or deleting one. Data omission is necessary, which is not preferable in terms of image quality. If such position correction of two or more dots is inevitable,
Instead of duplicating the dot data to three or four,
Image quality deterioration is reduced by correcting by overlapping two or more different dot position data. As described above, it is not preferable to omit the dot information. However, when it is necessary to omit a plurality of dot information, omission of the dot information as discrete as possible reduces information loss and image quality deterioration. Specified number of dots m at intervals of arrangement of light detection means
Assuming that the number of dots r to be omitted is integer (m /
r) Omitting dots at dot intervals is simple and effective.

In such addition or omission of pixel data, 1
An exposure position shift below a dot and data loss occur. For more accurate exposure position control, it is necessary to adjust the pixel clock so that exposure is performed at an accurate exposure position. Using the specified distance between the light detecting means and the specified number of dots between them, one dot scanning time can be calculated from the detection time interval between the light detecting means. By adjusting the pixel clock to this calculated frequency, extremely accurate exposure position control can be performed. However, in order to adjust the pixel clock frequency with a high precision of 1 dot or less, the circuit tends to be complicated. For this reason, in this embodiment, a simple method of adding or omitting dot information is applied.

Next, another embodiment of exposure data correction will be described with reference to FIG. The illustrated image recording apparatus is an image forming apparatus using an electrophotographic process to which the present invention is applied. In the method shown in FIG. 4, instead of providing a light detecting means in the scanning area of the scanning light, the CCD 20 is placed on the photoreceptor after development.
Is disposed. In this apparatus, a vertical line (light emission of only the prescribed dots in the main scanning direction) is exposed at a dot position corresponding to a reference position by an exposure unit, and is developed into a visible image. Is detected, and the exposure image information is corrected in the same manner as the correction of the exposure image data according to the amount of deviation from the specified position. In the embodiment of FIG. 4, the exposure position deviation is detected using the image after development, but it can also be realized by arranging an electrostatic latent image detection unit capable of detecting the electrostatic latent image before development with high accuracy. it can.

However, in this method, toner and the like necessary for the charging operation and development of the photosensitive member are required. However, there is no need to make a major change to the exposure apparatus, and there is no light loss due to light detection. Any method may be applied as needed.

In a tandem-type multicolor image forming apparatus and the like, in which a plurality of exposure apparatuses and a plurality of printing systems are juxtaposed to form a plurality of color images and a color image is formed by superimposing them, In order to superimpose the images of the exposure system and printing system with high precision, CC
In many cases, an image detecting means such as D is provided (for example, JP-A-11-41473). In the case of a multicolor image forming apparatus having such a configuration, the exposure position shift correction technique of the present optical scanning device is applied by substituting a detection unit for detecting an image position shift between each exposure device and each printing device. Is also effective. In this case, it is not necessary to dispose a light detection unit or the like in the exposure apparatus.

[0023]

As described above, according to the present invention, the position of each dot exposed can be controlled with high accuracy. Further, it is possible to realize high-precision superposition of the respective color images, and to provide a high-quality image recording apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an optical scanning exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an image data correction method of the optical scanning device according to the present invention.

FIG. 3 is a view for explaining another embodiment of the optical scanning exposure apparatus of the present invention.

FIG. 4 is a diagram illustrating an embodiment of an image forming apparatus to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Printed image information, 2 ... Laser light emitting element, 3 ... Image data sent to laser, 4 ... Laser emission control means, 5 ... Rotating polygon mirror, 6 ... Scanning light, 7 ... Beam detector (exposure starting point detection signal) Reference numeral 8: fθ lens (constant-speed scanning conversion lens), 9: photoconductor-side scanning light emission port, 10: movable mirror (for scanning light direction conversion), 11: light detection element, 12: light scanning position-timing detection unit Reference numeral 13 denotes a light scanning position detection signal, 14 denotes means for correcting image information based on the light position detection signal, 15 denotes a beam splitter, 16 denotes a photoconductor, 17
... optical scanning exposure device, 18 developing device, 19 image position detecting means (control section), 20 CCD (image detecting means), 2
DESCRIPTION OF SYMBOLS 1 ... Pick roller (paper feed roller), 22 ... Paper feed cassette, 23 ... Registration roller (transfer conveyance timing control means), 24 ... Transfer roller (image transfer means), 25 ... Auxiliary peeling means, 26 ... Photoconductor Residual charge removing means, 27: paper discharge tray, 28: fixing means, 29: cleaner (photoconductor residual toner collecting means), 30: charger.

Continued on the front page F-term (reference) 2C362 AA03 BA04 BA50 BA52 BA69 BB03 BB30 BB32 CA22 CA39 2H045 AA01 CA03 CA23 CA63 CA82 CA88 CA98 CA99 2H076 AB12 AB16 AB31 AB76

Claims (3)

[Claims] 1. A rotating polygonal mirror having at least one mirror surface, wherein light emitted by a light emitting element is rotated and scanned, and light scanned by the rotating polygonal mirror is scanned at a constant speed on an object to be scanned. Scanning apparatus for detecting the passage of light to at least one position in a light scanning area. 2. The optical scanning device according to claim 1, further comprising: a scanning light information control unit that changes emission stop timing of scanning light, exposure light amount information, and the like based on the light passage information detected by the light detection unit. Optical scanning device. 3. An exposure section for performing optical scanning on a photoconductor based on image information; a developing machine for forming a visible image on the exposure body; and at least one for detecting a position of the visible image in the optical scanning direction. An image recording apparatus comprising: one image recording position detecting unit; and a scanning light information control unit that changes the image information based on position information obtained by the image recording position detecting unit.