JPH112766A - Beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a beam scanner suppressing deterioration in a reproduced image even while using a resin lens. SOLUTION: Black, yellow image writing laser beams LK, LY and cyan magenta image writing laser beams LC, LM reflected by a mirror surface of a polygon mirror 4 respectively pass through scan lenses 5a, 5b, and are optical path revised by turning mirrors, and pass through cylindrical lenses 9C-9K to exposure scan respectively photoreceptor drum bodies 44C-44K surfaces. A copying machine integrated with this beam scanner is provided with a write-in position corrective function correcting write-in positions of images of respective colors based on a black image, and glass lenses are used for the scan lens 5a and the cylindrical lens 9K, etc., passing the laser beam LK through, and the all resin lenses are used for lens systems of other colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam scanning device used for a multicolor copying machine, a laser printer, and the like.

[0002]

2. Description of the Related Art In a multicolor image forming apparatus, for example, a tandem type full-color copying machine, four (4) colors corresponding to cyan (C), magenta (M), yellow (Y), and black (K) are provided. Photosensitive drums are arranged in line along the transfer surface of the transfer belt, and four laser beams are scanned by a beam scanning device to form an electrostatic latent image of each color on the peripheral surface of each photosensitive drum, and the corresponding color is The image is visualized with toner, and the image is sequentially transferred onto a recording sheet conveyed by a transfer belt to form a full-color image.

A beam scanning device used in such a full-color copying machine includes four laser diodes provided corresponding to respective colors of C, M, Y, and K, and a laser beam emitted from the laser diodes. And an optical system that deflects and exposes and scans the surface of the photosensitive drum. The optical system includes optical elements such as a polygon mirror, a scanning lens, and a return mirror.

Each laser diode is driven by input image data and emits a laser beam. After being reflected and deflected by the mirror surface of the rotating polygon mirror, the laser beam is exposed and scanned on the surface of the corresponding photosensitive drum via a lens system such as a scanning lens or a cylindrical lens. . By the way, recently, a resin lens made of a resin such as plastic is often used as a lens system of such a beam scanning device. Such a resin lens can be formed into a complicated shape by an injection molding technique, has a high degree of freedom in design, and has a low cost of raw materials, so that it is more cost-effective than a conventional glass lens. In particular, as described above, in a beam scanning apparatus in which the number of laser beams is large and the number of lenses to be used is large, the use of the resin lens can greatly reduce the cost.

[0005]

However, the resin lens has a problem that the change in physical properties with respect to the temperature change is larger than that of a glass lens. In particular, since the copying machine is configured to thermally fix the toner, the heat of the heater of the fixing unit results in an unnecessary increase in the environmental temperature inside the copying machine.

Generally, resin has a higher coefficient of thermal expansion than glass.
As the environmental temperature rises, the resin lens expands and deforms, and a scan line of a laser beam passing through the resin lens is disturbed and curved, or left and right asymmetry occurs.
As a result, not only does the linearity of the reproduced image deteriorate, but also in the above-described tandem-type full-color copying machine, the distortion of the scanning line for each color varies, which causes color misregistration.

Such a problem is not limited to a tandem type copying machine having a plurality of photosensitive drums, but is another type of image forming apparatus having a configuration for forming a multicolor image using a plurality of beams. This is a problem that can also occur in the beam scanning device described above. The present invention has been made in view of the above problems, and in a beam scanning apparatus for forming a multicolor image using a plurality of scanning beams, a resin lens having a relatively large change in physical properties with respect to a temperature change. It is an object of the present invention to minimize the deterioration of a reproduced image while enjoying the advantage of cost reduction by using an inexpensive lens.

[0008]

In order to achieve the above object, the present invention provides a lens system provided with a plurality of beams for writing images of a plurality of colors including black on a photoreceptor, respectively. Or a beam scanning device that scans through a lens system provided in common for some of the plurality of beams, at least a lens system through which a beam for forming the black image passes. One of the lenses is characterized in that a change in physical properties with respect to a change in temperature is smaller than that of a lens of another lens system.

Further, according to the present invention, a plurality of beams for writing images of a plurality of colors including yellow on a photoreceptor, respectively, are provided by a lens system provided for each scanning beam, or any of the plurality of scanning beams. A beam scanning device that scans a photosensitive member via a lens system commonly provided for each book, wherein at least one lens of a lens system through which the yellow image forming beam passes is provided. It is characterized in that a change in physical properties with respect to a change in temperature is larger than that of a lens of another lens system.

Further, the present invention comprises an image writing position correcting means for correcting the writing position of an image on a photosensitive member of another color based on the writing position of an image on a photosensitive member of a specific color. A beam scanning device used as image writing means of an image forming apparatus, wherein the beam scanning device outputs a plurality of beams for writing an image of each color to a lens system provided for each beam, or the plurality of beams. Among the lens systems through which a beam for image formation of at least the specific color passes is configured to scan each of the photoconductors via a lens system provided in common for some of the plurality of the photoconductors. One lens is characterized in that a change in physical properties with respect to a change in temperature is smaller than a lens of another lens system.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a beam scanning apparatus according to the present invention will be described below in the case where it is used in a tandem type full-color digital copying machine (hereinafter simply referred to as "copying machine"). FIG. 1 is a schematic diagram showing the overall configuration of the copying machine 100. As shown in FIG.
Is composed of an image reader unit 10 for reading a document image, and a printer unit 20 for printing the read image on a recording sheet S and reproducing it.

The image reader section 10 is a publicly known one that reads an image of a document placed on a document glass plate (not shown) by moving a scanner. The document image is composed of red (R) and green (G). ), Blue (B), and separated into three colors, and a CCD image sensor (not shown)
), Thereby obtaining R, G, B image data of the document.

The image data for each color component obtained by the image reader unit 10 is transmitted to a control unit 30 in the printer unit 20.
Undergoes various data processing, and further receives cyan (C),
The image data is converted into image data of each reproduction color of magenta (M), yellow (Y), and black (K) (hereinafter, each reproduction color of cyan, magenta, yellow, and black is converted into C, M, Y, K
And the number of the component related to each reproduction color is C,
M, Y, and K are added as subscripts). This image data is stored in the image memory in the control unit 30 for each reproduced color.

The printer unit 20 forms an image by a known electrophotographic method, and forms an image by forming a toner image on a photosensitive drum by scanning a laser beam.
And a sheet feeding unit 50 for supplying the recording sheet S, a sheet conveying unit 60 for conveying the supplied recording sheet S to a transfer position for each color, and a fixing unit 70 for fixing the recording sheet S to which the toner has been transferred. Etc.

Image data of each reproduced color is read out from the image memory in the control unit 30 for each scanning line and output to the printer head 41 of the image forming unit 40, and the internal laser diode is driven. Four laser beams corresponding to each color are emitted. Each laser beam light is changed in optical path while being adjusted by the folding mirror group 45 so that the optical path length becomes equal, and the peripheral surfaces of the corresponding photosensitive drums 44C to 44K are exposed and scanned in the main scanning direction to form an electrostatic latent image. To form Each of the electrostatic latent images is
The C, M, Y, and K toners are supplied from 2C to 42K and are visualized as toner images.

On the other hand, when the recording sheet S is
Sheets are fed one by one, and are conveyed by the sheet conveying unit 60 to a transfer position immediately below each of the photoconductors. This sheet transport section 60
Transfer belt 64 with drive roller 61 and support roller 62
To give the necessary tension with the tension roller 63,
By driving the driving roller 61 to rotate, the recording sheet S at a predetermined conveyance speed is synchronized with the image forming operation for each color.
Is configured to be transported.

Transfer chargers 43C to 43K are disposed directly below the transfer belt 64 at the transfer positions of the respective colors, and the toner images on the surfaces of the photosensitive drums 44C to 44K are sequentially transferred onto the recording sheet S by these electrostatic forces. Is done. At this time, the image forming operation of each color is performed with a timing shifted from the upstream side to the downstream side in the conveying direction so that the toner image is transferred to the same position of the conveyed recording sheet S in a superimposed manner. Is done.

Recording sheet S on which toner images of each color have been transferred
Is transported to the fixing unit 70 where the toner is pressed at a high temperature, and the toner on the surface of the recording sheet S is melted and adhered to the sheet surface to be fixed.
FIG. 2 is a perspective view of the image forming unit 40 and the sheet conveying unit 60 of FIG. 1 as viewed from the front left side of the figure. For simplification, a developing unit and a charging charger around the photosensitive drum are not shown. I have.

The printer head 41 has four laser diodes 1C to 1C centered on a polygon mirror 4 which rotates at a constant speed by being driven by a polygon motor (not shown).
K and lenses such as the scanning lenses 5a and 5b are arranged at symmetrical positions with respect to a plane passing through the rotation axis of the polygon mirror 4 and orthogonal to the sheet conveying direction.

The laser beams LC to LK emitted from the respective laser diodes 1C to 1M pass through cylindrical collimator lenses 2C to 2K, respectively, and are converted into parallel rays.
Thereafter, the laser beam LK is reflected by the reflection mirror 21, becomes a light beam that is vertically parallel to the laser beam LY, passes through the same first cylindrical lens 3a, and is converged only in the rotation axis direction of the polygon mirror 4. Then, the light is reflected and deflected by the mirror surface.

Usually, the polygon mirror is directly attached to the rotation axis of the polygon motor.
In order to obtain a smooth rotation operation, a minute gap is inevitably interposed between the rotating shaft and the bearing, which may cause the rotating shaft to be inclined even though it is minute. As a result, the mirror surface of the polygon mirror is also inclined with respect to the rotation axis direction, so-called "surface tilt" occurs, and the scanning beam may swing in an unnecessary direction and the scanning line may shift in the sub-scanning direction. Therefore, as described above, the laser beam is converged in the axial direction in advance and made incident on the mirror surface of the polygon mirror to minimize the error due to the surface tilt.

After the deflected laser beams LK and LY pass through a scanning lens 5a composed of a toroidal lens and an fθ lens, the lower laser beam LK has its optical path changed by a turning mirror 6K, and the second cylindrical lens 9K Is converged in the sub-scanning direction through the
K is exposed and scanned, and the one upper laser beam LY is reflected by folding mirrors 6Y, 7Y and 8Y and converged in the sub-scanning direction via the second cylindrical lens 9Y to expose and scan the photosensitive drum 44Y. .

Similarly, the laser beam LC is reflected by the reflection mirror 22 and becomes light beams that are vertically parallel to the laser beam LM, passes through the first cylindrical lens 3b, and converges in the axial direction of the polygon mirror 4. The light is deflected by the polygon mirror 4. At this time, the laser beam L
Since C and LM are incident on the polygon mirror 4 from the direction opposite to the laser beams LY and LK, they are reflected in the opposite directions, and the movement directions on the respective scanning lines are also reversed.

After the deflected laser beams LC and LM have passed through the common scanning lens 5b, the lower laser beam LC has its optical path changed by the return mirror 6C, and
Photoreceptor drum 44C through cylindrical lens 9C
And the upper laser beam LM is reflected by the return mirrors 6M, 7M and 8M to expose and scan the photosensitive drum 44M via the second cylindrical lens 9M.

According to the configuration of such a beam scanning device, the number of polygon motors may be one, so that a rotation control system can be easily configured and two laser beams can be scanned by one set of scanning lenses. Therefore, the number of necessary lenses can be reduced and cost can be reduced. Further, as described later, a collimator lens 2 through which a black laser beam LK serving as a reference for image writing position correction passes.
K, the first cylindrical lens 3a, the scanning lens 5a, and the second cylindrical lens 9K are glass lenses, but the other lenses are made of less expensive resin lenses, which further reduces the cost. It is planned.

Reference numerals 31a and 31b denote SOS (Start Of Scan) sensors each composed of a photodiode, which receive the reflected light of the laser beam incident on the mirrors 32a and 32b, and emit an SOS signal.
The control unit 30 determines the timing (horizontal synchronization) of writing an image in the main scanning direction for each color based on the SOS signal. This SOS sensor is provided only at a position corresponding to the laser beams LK and LC. As described above, the laser beam LY is parallel to the laser beam LK, and the laser beam LM is vertically parallel to the laser beam and LC. This is because, as a set, the light is reflected and scanned by the same mirror surface of the polygon mirror 4, so that horizontal synchronization can be achieved using the SOS signal of the other one of the laser beams.

The X marks formed on the transfer belt 64 are registration marks transferred from the photosensitive drum of each color, and the registration marks 65C to 65K formed for each color are reflected by a photoelectric sensor of a reflection type. 33, 34,
35, the C, M, and Y image writing positions are corrected based on the K registration mark 65K (hereinafter, referred to as “registration correction”).

That is, the control section 30 stores the image data of the registration marks of each color. Based on the image data, the photosensitive drums 44C to 44K are exposed to form toner images. Is transferred onto the transfer belt 64. Then, based on the detection signals from the photoelectric sensors 33, 34, and 35, the control unit 30 controls the relative positions of the C, M, and Y registration marks in the sub-scanning direction and the main scanning direction with respect to the K registration mark. The shift amount is calculated, the storage position of the image data of each color is corrected so that the position shift amount becomes “0”, the write timing is adjusted,
Alternatively, the position and direction of the return mirror are controlled. Such a method of resist correction is already known (for example, JP-A-2-50176, JP-A-2-1-1).
07463, JP-A-6-18796), and the detailed description is omitted here.

As described above, in the present apparatus, a glass lens whose physical properties hardly change with respect to a temperature change is used for a lens system through which a black laser beam LK serving as a reference for registration correction passes. Even if the ambient temperature changes, the scan line is hardly disturbed, and another color registration correction is performed in accordance with this black registration mark. In addition, the reproduced image does not deteriorate. Since resin lenses are inexpensive, costs can be reduced accordingly.

As described above, according to this embodiment, the laser beams LK and LY and the laser beams LM and LC
Are scanned in directions opposite to the main scanning direction, the control unit 30 controls the order of reading image data from the image memory in the main scanning line direction to be reversed. It is needless to say that the present invention is not limited to the above embodiment, and the following modified examples can be considered.

(1) In the above embodiment, the first cylindrical lens 3a, the scanning lens 5a, the second cylindrical lens 9K, and the like through which the black laser beam LK passes are all glass lenses. Even if the lens is a glass lens, the effect that the distortion of the scanning line is smaller than that of the other beams can be obtained. (2) The scanning lenses 5a and 5b in FIG. 2 are commonly used by two laser beams, respectively. However, as shown in FIG.
5K may be provided. In this case, the laser beam LK
In addition to the collimator lens 2K, the first cylindrical lens 3a, and the scanning lens 5K shaded,
The second cylindrical lens 9K is a glass lens.

(3) In the above embodiment, a glass lens is used for the lens system of the black beam as a reference of the registration correction. However, when the registration correction is performed based on another color, for example, a cyan image. , A glass lens is used for a lens system through which the cyan laser beam LC passes. In addition, a glass lens may be used for a lens system of a plurality of colors including a color used as a reference for resist correction. If at least one lens of the other lens system is a resin lens, the cost can be reduced as compared with the related art. Can be obtained to some extent.

(4) The present invention is also applicable to an image forming apparatus having no registration correction function. In a full-color image, in general, the distortion of a black image is most noticeable, and therefore, as in the case of FIG. By using glass lenses as the lenses, it is possible to obtain an image with less noticeable distortion as compared with a case where all of the lenses are resin lenses.

On the other hand, since yellow is the most difficult to stand out, this yellow laser beam LY is used as shown in FIG.
In addition to the collimator lens 2Y and the first cylindrical lens 3a (not shown) through which only the light passes, the scanning lens 5Y and the second cylindrical lens 9Y may be resin lenses, and at least one of these lenses is a resin lens. Or just As a result, it is possible to obtain an effect that the cost can be reduced even a little while maintaining the image quality.

(5) Further, in the above-described embodiment, the glass lens is used for the resin lens because the physical property change with respect to the temperature change is small. However, the same resin lens or the same glass lens may be used. In general, it is considered that the smaller the change in physical properties is, the higher the cost is. Therefore, even in this case, the same cost reduction effect as described above can be obtained.

(6) In the above embodiment, the case where the present invention is applied to a full-color tandem-type copying machine has been described. However, the present invention relates to a single photosensitive drum such as a two-color copying machine. The present invention can be applied to a case where the periphery of the object is scanned by two laser beams. In addition, the present invention can be applied not only to a copying machine but also to all image forming apparatuses having a device for scanning a plurality of light beams as image writing means, such as a color laser printer.

[0037]

As described above, according to the present invention, there is provided a beam scanning apparatus for scanning a plurality of beams for writing a plurality of color images including black on a photosensitive member, wherein at least a black image is formed. Since one of the lens systems through which the beam for forming the light passes has a smaller change in physical properties with respect to temperature change than the lens of the other lens system, the most noticeable distortion of the black image While pressing to improve the impression of the reproduced image, other lenses can be configured with inexpensive lenses with large changes in physical properties,
The cost can be reduced accordingly.

According to the present invention, there is provided a beam scanning device for scanning a plurality of beams for writing images of a plurality of colors including yellow on a photosensitive member, wherein a scanning beam for forming an inconspicuous yellow image passes therethrough. Since at least one of the lens systems used has a larger change in physical properties with respect to temperature change than the lenses of the other lens systems, even if the yellow image is distorted due to the temperature change, This makes it possible to use an inexpensive lens that is hardly noticeable and has a large change in physical properties while maintaining image quality, thereby reducing costs.

Further, the present invention comprises an image writing position correcting means for correcting the writing position of the image on the photosensitive member of another color based on the writing position of the image on the photosensitive member of a specific color. A beam scanning device used as an image writing unit of an image forming apparatus, wherein at least one lens of a lens system through which the image forming beam of the specific color passes has a temperature higher than that of another lens system. Since a change in physical properties with respect to the change is used, even if a temperature change occurs, a scan line of the specific color image is unlikely to be distorted, and the writing position of an image of another color is corrected based on the distortion. Accordingly, it is possible to form an excellent reproduced image while significantly reducing costs by using an inexpensive lens having a large change in physical properties for another lens system.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of a tandem-type copying machine according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of an image forming unit and a sheet conveying unit in the copying machine.

FIG. 3 is a side view illustrating a configuration of a lens system in an image forming unit.

FIG. 4 is a diagram illustrating another example of a lens system in an image forming unit.

FIG. 5 is a diagram showing still another example of the lens system in the image forming unit.

[Explanation of symbols]

 1C, 1M, 1Y, 1K Laser diode 2C, 2M, 2Y, 2K Collimator lens 3a, 3b First cylindrical lens 4 Polygon mirror 5a, 5b Scanning lens 9C, 9M, 9Y, 9K Second cylindrical lens 10 Image reader unit 20 Printer Unit 30 Control Unit 40 Image Forming Unit 41 Printer Heads 44C, 44M, 44Y, 44K Photoconductor Drum 50 Paper Feeding Unit 60 Sheet Conveying Unit

Claims (3)

[Claims] A plurality of beams for writing images of a plurality of colors including black on a photoreceptor, respectively, are shared by a lens system provided for each of the beams or by several of the plurality of beams. A beam scanning device that scans through a lens system provided, wherein at least one lens of a lens system through which a beam for forming a black color image passes passes through a lens of another lens system. A beam scanning device characterized in that a change in physical properties with respect to a temperature change is small. 2. A method according to claim 1, wherein a plurality of beams for writing images of a plurality of colors including yellow on a photosensitive member are respectively applied to a lens system provided for each scanning beam, or a plurality of scanning beams. A beam scanning device that scans a photosensitive member via a commonly provided lens system, wherein at least one lens of the lens system through which the yellow image forming beam passes is another lens. A beam scanning apparatus characterized in that a physical property change with respect to a temperature change is larger than a system lens. 3. An image forming apparatus comprising an image writing position correction unit for correcting a writing position of an image on a photosensitive member of another color based on a writing position of an image on a photosensitive member of a specific color. A beam scanning device used as an image writing unit, wherein the beam scanning device outputs a plurality of beams for writing an image of each color to a lens system provided for each beam, or a number of beams out of the plurality of beams. One of a lens system configured to scan each of the photoconductors via a lens system provided in common for each of the plurality of lenses and through which at least the beam for forming an image of the specific color passes Is a beam scanning apparatus characterized in that a change in physical properties with respect to a change in temperature is smaller than that of a lens of another lens system.