JP4400743B2 - Scanning lens, optical scanning device, image forming apparatus, and scanning lens manufacturing method - Google Patents

Description

  The present invention relates to a scanning lens, a scanning optical system, an optical scanning device, and an image forming apparatus that can be applied to laser printers, digital copying machines, fax machines, and the like.

  An image forming method in an image forming apparatus such as a laser printer or a digital copying machine generally uses an electrophotographic process, and an optical scanning device is used as an apparatus for executing an exposure process in the electrophotographic process. FIG. 5 schematically shows an example of an optical scanning device. In FIG. 5, a light source unit 1 includes a semiconductor laser as a light source and a coupling for converting a laser light beam emitted from the semiconductor laser into a parallel light beam, a gentle diffused light, or a convergent light in order to cooperate with a subsequent optical system. It has a lens and also has a cylindrical lens 1a that converges the laser beam only in the sub-scanning direction. On the path of the light beam L1 emitted from the light source unit 1, a rotating polygon mirror 2 as an optical deflector is disposed. In the rotary polygon mirror 2, a plurality of deflection reflection surfaces are formed at equal intervals in the circumferential direction on the peripheral surface of a rotating body that is rotationally driven by a motor. By the cylindrical lens 1a, a long line image in the main scanning direction by the laser beam is formed near the deflection reflection surface.

  When the rotary polygon mirror 2 is driven to rotate, the laser beam is deflected and reflected at an equal angular velocity by each deflecting reflecting surface. A scanning optical system is disposed on the path of the light beam deflected and reflected. In the example shown in FIG. 5, a scanning optical system is configured by two scanning lenses 3 and 4. The scanning lens 2 on the rotary polygon mirror 2 side is a spherical lens, and the other scanning lens 4 is a toric lens. The scanning optical system comprising these two lenses 3 and 4 condenses the laser beam as a light spot on the surface to be scanned, and scans the light spot on the surface to be scanned at a constant speed by the deflection reflection. have. In the example shown in FIG. 5, a mirror 7 for guiding the light beam transmitted through the scanning optical system to the surface to be scanned is disposed. Each of the optical elements described above is attached to a flat housing 5 so that the light beam reflected by the mirror 7 is guided from the window 6 of the housing 5 to the surface of the photosensitive drum, for example, as the surface to be scanned. ing.

  The scanning lens 4 made of a toric lens has upper and lower surfaces serving as reference surfaces, and a lower reference surface is brought into contact with a predetermined position of the housing 5 and is positioned by an integrally formed positioning pin 8. Are fixed by appropriate means. The scanning lens 4 is a plastic lens, and integrally includes a protrusion 4a at the center in the length direction and a dowel 4b at a position away from the protrusion 4a on one side in the length direction. An interference pin 9 is integrally formed on the bottom of the housing 5 adjacent to the mounting position of the scanning lens 4. The dowel 4b and the interference pin 9 are for making the orientation of the scanning lens 4 correct. When the scanning lens 4 is to be assembled upside down, the dowel 4b interferes with the interference pin 9, and the scanning lens 4 It is comprised so that 4 cannot be assembled | attached.

  In recent years, in an image forming apparatus such as a laser printer or a digital copying apparatus, an image to be formed has been improved in image quality and density, and accordingly, the shape of a scanning lens used in an optical scanning device in the image forming apparatus is not good. A scanning lens that has become spherical and has an asymmetric shape in the main scanning direction with respect to the optical axis has been proposed. However, it is difficult to recognize that a scanning lens with an asymmetric shape in the main scanning direction with respect to the optical axis is asymmetrical in terms of optical design, but it is difficult to recognize that it is asymmetrical in appearance. It has become. The conventional example shown in FIG. 5 is one proposal for solving the above-described problem. The scanning lens is provided with a dowel for preventing the reverse direction, and an interference pin that interferes with the dowel in the reverse direction is provided on the housing side. (For example, refer to Patent Document 1).

JP-A-9-90255

  However, in the scanning lens positioning structure described in Patent Document 1, not only is the shape asymmetrical in the sub-scanning direction of the scanning lens, but the amount of resin is different between the one side and the other side in the sub-scanning direction. The flow of the resin at the time becomes asymmetric, and the cooling time after molding differs between the one side and the other side in the sub-scanning direction, the internal structure is distorted, and it is difficult to ensure the accuracy of the lens surface.

The present invention has been made in view of the above-described problems of the prior art, and has an asymmetric shape in the main scanning direction with respect to the optical axis without providing projections for preventing reverse mounting on both the scanning lens and the housing. It is possible to provide a scanning lens , an optical scanning device , an image forming apparatus, and a manufacturing method of the scanning lens that can prevent the scanning lens from being reversed and can ensure the surface accuracy of the scanning lens surface. Objective.

The present invention, a light beam is deflected by the light deflector to a scanning lens constituting the scanning optical system of the optical scanning device for converging the scanned surface, said scanning lens comprises at least one, the scanning lens , together are formed asymmetrically in the main scanning direction is made of resin, the main positioning reference scanning direction is provided a pair in the sub-scanning direction across the optical axis, the shape of the positioning reference Ri is Do different width and length, respectively The most important feature is that the projected areas of the pair of positioning references are substantially equal so that the amount of resin in the sub-scanning direction of the scanning lens becomes substantially equal .
The present invention is characterized by an optical scanning device using the scanning lens and an image forming apparatus using the optical scanning device.

The scanning lens according to the present invention has an asymmetric shape in the longitudinal direction (main scanning direction) with respect to the optical axis, and even if this cannot be visually recognized, the scanning lens according to the present invention is mounted on the housing. When mounting, a correct orientation in the main scanning direction can be identified by a positioning reference that is provided in a pair in the sub-scanning direction across the optical axis and has different widths and lengths, thereby preventing reverse attachment. I can . Also, by approximately the area of both positioning reference paired same, since the asymmetrical shape by the sub-scanning direction of the scanning lens can be eliminated as much as possible, the flow and resin of the resin during molding is symmetrical, It is possible to prevent internal distortion due to asymmetric resin flow and resin amount, and deterioration of the accuracy of the lens surface due to a difference in cooling time.
According to the optical scanning device and the image forming apparatus according to the present invention, it is possible to use a scanning lens with high surface accuracy by eliminating asymmetry of the scanning lens shape, and an optical scanning device capable of outputting a high-quality image. An image forming apparatus using this can be provided.

Embodiments of a scanning lens , an optical scanning device, an image forming apparatus, and a scanning lens manufacturing method according to the present invention will be described below with reference to the drawings. The optical scanning device according to the present invention is characterized by the components corresponding to the scanning lens 3 or the scanning lens 4 constituting the scanning optical system in the conventional optical scanning device shown in FIG. The optical scanning device will be described with reference to FIG.

  1 to 3 show an embodiment of a scanning lens according to the present invention. 1 to 3, the scanning lens 10 has an asymmetric shape in the longitudinal direction (main scanning direction) with respect to the optical axis, and the optical axis is sandwiched between the central portions in the longitudinal direction (main scanning direction). A pair of positioning references 12 and 14 are provided on both sides in the short direction (sub-scanning direction), that is, vertically. The scanning lens 10 is a lens integrally formed of resin, and the positioning references 12 and 14 are integrally formed protrusions. The positioning references 12 and 14 are for positioning the scanning lens 10 in the longitudinal direction, and are formed in the vicinity of the optical axis by being formed at the above positions. As shown in FIGS. 2 and 3, the pair of reference pins 12 and 13 both protrude from the scanning lens body in parallel with the optical axis, and have a width (L) and a length, that is, a protruding length as viewed from the optical axis direction. Both (H) are different. More specifically, the width of the upper positioning reference 12 is narrower than the width of the lower positioning reference 14, and the length of the upper positioning reference 12 is longer than the length of the lower positioning reference 14.

  By configuring the scanning lens 10 in this way, it is possible to prevent reverse mounting when the scanning lens 10 is attached to the housing. That is, if the positioning reference 12 having a narrow width and a long length is attached to the housing so as to be on the upper side, even if the correct orientation of the scanning lens 10 in the main scanning direction cannot be identified by visual observation, a pair of positioning references 12 The correct orientation can be easily identified from the vertical positional relationship of 12,14.

  In the embodiment shown in FIGS. 1 to 3, the areas of the pair of positioning references 12 and 14 viewed from the top, that is, L × H are substantially the same. More specifically, when the area of the upper positioning reference 12 is L × H = 5 mm × 3 mm, the area of the lower positioning reference 14 can be 3 mm × 5 mm. Thus, by making the area of the pair of positioning references 12 and 14 substantially the same, asymmetry in the shape of the scanning lens 10 in the sub-scanning direction can be eliminated as much as possible. Therefore, when manufacturing the scanning lens by resin molding, The resin flow is almost symmetrical, and internal distortion due to the resin flow becoming asymmetric can be prevented. In addition, since the amount of resin in the sub-scanning direction can be made substantially uniform, the cooling time after resin molding on both sides in the sub-scanning direction is almost the same, and the accuracy of the lens surface is deteriorated due to the difference in cooling time. It can also be prevented. In this way, a highly accurate scanning lens can be obtained.

  The areas (L × H) of the positioning references 12 and 14 do not need to be completely matched, and there is no problem even if there is a difference to the extent that there is no problem in internal distortion and lens surface accuracy. In the embodiment shown in FIGS. 1 to 3, the positioning references 12 and 14 have a shape protruding in the optical axis direction. However, the positioning references 12 and 14 may have a concave shape. Even if it is a shape, the same effect can be acquired. The positioning references 12 and 14 may be provided on the incident surface side or the exit surface side of the scanning lens 10, and one positioning reference is provided on the entrance surface side, and the other positioning reference is provided on the exit surface side. May be. However, the pair of positioning references 12 and 14 are provided on one side of the entrance surface and the exit surface of the scan lens 10 because of the symmetry of the resin flow when the scan lens 10 is resin-molded and the balance of the resin amount. desirable.

  The scanning lens 10 described above is used as a lens constituting the scanning optical system of the optical scanning device. The scanning optical system of the optical scanning lens has a function of condensing the light beam deflected by the optical deflector on the surface to be scanned, and is composed of one scanning lens or a plurality of scanning lenses. As at least one scanning lens constituting this scanning optical system, the scanning lens 10 described with reference to FIGS. 1 to 3 is used.

  If the optical scanning device has the optical arrangement shown in FIG. 5, the scanning lens 10 shown in FIGS. 1 to 3 is arranged as the lens 3 or the lens 4 in FIG. 5. The light beam radiated from the light source unit and deflected and reflected by the optical deflector is condensed as a light spot on the surface to be scanned by passing through the scanning optical system that includes only the scanning lens 10 or includes the scanning lens 10. In the optical deflector, the light beam is deflected and reflected at a constant angular velocity, whereas the light beam is scanned at a constant velocity on the surface to be scanned by the fθ function of the scanning optical system.

  The surface to be scanned is used as the surface of an image carrier such as a photosensitive drum, and an image forming apparatus can be configured by disposing each device or unit for performing an electrophotographic process around the image carrier. That is, a charging device that uniformly charges the surface of the image carrier around the image carrier, an exposure device that exposes the charged image carrier surface to write an image based on an electrostatic latent image, and the electrostatic latent image with toner. A developing device for visualizing, a transfer device for transferring the toner image on the surface of the image carrier to the transfer paper, a cleaning device for removing residual toner on the surface of the image carrier, a fixing device for fixing the toner image transferred to the transfer paper, etc. To do. The above-described optical scanning device is used as the exposure device. A predetermined image based on an electrostatic latent image can be written on the surface of the image carrier by modulating a semiconductor laser, which is a light source, with an image signal in synchronization with optical scanning by rotation of the optical deflector.

  By forming the scanning optical system with the scanning lens according to the present invention capable of obtaining the above-described effects and applying the scanning optical system to the optical scanning device, high-precision and high-density optical scanning can be performed. it can. Also, by applying this optical scanning device to an image forming apparatus, it is possible to form a high-quality and high-density image.

  When mounting the scanning lens according to the present invention on the housing of the optical scanning device, unless the main scanning direction of the scanning lens is in the correct direction, the scanning lens positioning reference is applied to the projection on the housing side, the bottom surface of the housing, etc. It is further preferable that the scanning lens is configured so as not to be in contact therewith.

  FIG. 4 shows an embodiment of an optical scanning device provided with a scanning lens and a scanning optical system according to the present invention. The embodiment shown in FIG. 4 is an example of an optical scanning device that can constitute a so-called four-drum tandem image forming apparatus. A total of four light source units, two scanning optical systems, and a photosensitive drum as a surface to be scanned are arranged on both sides of the rotary polygon mirror 2 as an optical deflector. Reference numerals 1-1 to 1-4 are light source units, 1a-1 to 1a-4 are cylindrical lenses, 3-1 to 3-4 are one type of scanning lenses constituting the scanning optical system, and 4-1 to 4-4. Denotes another type of scanning lens constituting the scanning optical system, and 15-1 to 15-4 denote photosensitive drums each having a surface to be scanned.

  The rotary polygon mirror 2 has a rotary reflection surface in which a plurality of deflection reflection surfaces are formed at equal intervals in the periphery in two stages in the vertical direction, and the upper reflection surface has light source units 1-2 and 1-3. The light beam from the light source units 1-1 and 1-4 is deflected and reflected on the lower reflecting surface. One type of scanning lenses 3-2 and 3-1 constituting the scanning optical system is arranged on one side of the rotary polygon mirror 2 so as to be superposed vertically, and the same type of scanning lenses 3-3 and 3-4 as this scanning lens. Are arranged vertically on the other side of the rotary polygon mirror 2. The other types of scanning lenses 4-2 and 4-1 constituting the scanning optical system are also arranged so as to overlap one side of the rotary polygon mirror 2 on the developed view shown in FIG. As shown in FIG. 4B, when the optical scanning device is incorporated in the housing, the optical path is appropriately bent by a mirror to reduce the size and thickness of the device. Thus, the scanning lenses 4-2 and 4-1 are arranged at different positions. Similarly, scanning lenses 4-3 and 4-4 of the same type as the scanning lenses 4-2 and 4-1 are also superimposed on the other side of the rotary polygon mirror 2 on the development view shown in FIG. However, in the state mounted as an optical scanning device, as shown in FIG. 4B, they are arranged at the same height and shifted in position. Each light beam that has passed through each scanning optical system is guided to the surfaces of the photosensitive drums 15-1 to 15-4 that are different scanning surfaces corresponding to the respective scanning optical systems. Each light beam is converged as a light spot by each scanning optical system on each surface to be scanned, and the surface to be scanned is scanned by the rotary polygon mirror 2 by rotational driving.

  As is apparent from the above description, the optical scanning device having the configuration shown in FIG. 4 uses a plurality of scanning optical systems to divide a plurality of light beams deflected by the rotary polygon mirror 2 as an optical deflector having a common rotation axis. A plurality of light beams directed to the rotating polygonal mirror 2 have an opening angle in the deflection rotation surface of the rotating polygonal mirror 2 and are guided to different scanning surfaces. It is configured. The plurality of scanning optical systems corresponding to different scanning surfaces include scanning lenses configured in the same manner as the scanning lenses described with reference to FIGS. 1 to 3, and these scanning lenses are 180 degrees with respect to the optical axis. Inverted arrangement. More specifically, for example, if the above-mentioned positioning reference is provided for one kind of scanning lenses 3-1 to 3-4 shown in FIG. The scanning lenses 3-2 and 3-1 are arranged so as to be reversed 180 degrees around the optical axis. Similarly, the scanning lenses 3-3 and 3-4 arranged on the other side of the rotary polygon mirror 2 are also arranged so as to be reversed by 180 degrees around the optical axis.

In the above description, the above-mentioned positioning reference is provided for one type of scanning lens 3-1 to 3-4, and they are inverted by 180 degrees around the optical axis. 1 to 4-4 can be similarly configured. As shown in FIG. 4B, the other types of scanning lenses 4-1 to 4-4 are not necessarily arranged one above the other in terms of mounting, but one side and the other side sandwiching the rotary polygon mirror 2. It is preferable to arrange them so that they are reversed 180 degrees around the optical axis.
In an optical scanning device having a plurality of scanning optical systems and having different scanning surfaces corresponding to the scanning optical systems, as described above, at least one type of scanning lens constituting the scanning optical system is positioned. The scanning lens can be prevented from being reversed by using a lens with a reference and disposing the lenses by inverting each other by 180 degrees with respect to the optical axis.

It is a perspective view which shows the Example of the scanning lens concerning this invention. It is a top view of an Example same as the above. It is a front view of an Example same as the above. (A) which shows the Example of the optical scanning device concerning this invention is a plane expanded view, (b) is a side view. It is a top view which shows the prior art example of an optical scanning device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source unit 2 Rotary polygon mirror as optical deflector 10 Scan lens 12 Positioning reference 14 Positioning reference

Claims (6)

A scanning lens constituting a scanning optical system of an optical scanning device for condensing a light beam deflected by an optical deflector on a surface to be scanned,
The scanning lens consists of at least one lens,
The scanning lens is made of resin and formed asymmetrically in the main scanning direction, and a pair of positioning references in the main scanning direction is provided in the sub-scanning direction across the optical axis.
The shape of the positioning reference are Ri is Do different width and length, respectively, and the projected area of the positioning reference pair so that the amount of resin in the sub-scanning direction is substantially equal to the scanning lens is characterized by substantially equal Scanning lens.   3. The scanning lens according to claim 1, wherein the pair of positioning references is provided on one side of the incident surface or the exit surface of the scanning lens. 2. An optical scanning device of an optical scanning device for condensing a light beam deflected by an optical deflector on a surface to be scanned, wherein the scanning optical system is configured to condense the light beam on the surface to be scanned and scan the surface to be scanned. An optical scanning device having the scanning lens according to 2 . It has a plurality of scanning optical systems that guide a plurality of light beams deflected by an optical deflector having a common rotation axis onto different scanned surfaces, and the plurality of light beams directed to the optical deflector have an opening angle in the deflection rotation surface. And an optical scanning device that is guided to different scanned surfaces,
Different said plurality of scanning optical systems corresponding to the surface to be scanned, claim includes scanning lens according to 1 or 2, the scanning lens is an optical scanning device disposed mutually inverted 180 degrees with respect to the optical axis . An image forming apparatus for forming an image by executing an electrophotographic process, wherein the image forming apparatus uses the optical scanning device according to claim 3 as an exposure process execution means in the electrophotographic process. A method of manufacturing a resin-made scanning lens that constitutes a scanning optical system of an optical scanning device that condenses a light beam deflected by an optical deflector on a surface to be scanned,
A step of forming the shape in the main scanning direction asymmetrically and providing a pair of positioning reference in the main scanning direction of the scanning lens in the sub scanning direction across the optical axis;
The positioning reference shapes have different widths and lengths, and the projected areas of the pair of positioning references are substantially equal so that the amount of resin in the sub-scanning direction of the scanning lens is substantially equal. A manufacturing method of a scanning lens.

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