JP5031485B2 - Plastic lens, optical scanning device, and image forming apparatus - Google Patents

Description

  The present invention relates to a plastic lens, an optical scanning device, and an image forming apparatus, and more particularly to a highly accurate and minute plastic lens and a technique for bonding the plastic lens to a housing with high accuracy.

  In an optical scanning optical system in a laser-type image device such as a digital copying machine or a printer, the density of an image has been increased, and accordingly, a demand for reducing the diameter of a beam spot on a photoconductor is increasing. In the optical scanning optical system, a lens having a laser beam imaging and various correction functions is used. One of the factors that influence the reduction of the beam spot diameter is the characteristic of the lens. In a generally used glass lens, there is a limit to the shape that can be processed, and the shape of the lens surface is generally spherical. For this reason, the lens performance is insufficient, and the beam spot cannot be reduced in diameter.

  In view of this, an effort has been made to reduce the diameter of the beam spot by plasticizing the lenses constituting the optical scanning optical system. That is, if a metal mold constituting a lens surface of a mold used for molding plastic is processed into a desired shape, for example, an aspherical shape, a desired lens can be obtained by using a manufacturing technique such as an injection molding method. This is because a plastic lens having a surface shape can be obtained. In addition, since the injection molding method can be mass-produced, a high-performance plastic lens can be obtained at a lower cost than a glass lens.

  However, on the other hand, since plastic has a large linear expansion coefficient, the curvature and dimensional variation due to temperature change are large compared to glass lenses. Also, the refractive index variation due to temperature change is larger than that of the glass lens. When the above-described variations in curvature, size, and refractive index occur in the plastic lens, the focus position varies, and the beam spot diameter increases. As a result, the quality of the image equipment is degraded.

  Further, when the temperature changes, the wavelength of the semiconductor laser as the light source also changes. As the temperature rises, the wavelength of the semiconductor laser becomes longer. This variation in wavelength also causes a variation in focus position, which increases the beam spot diameter and causes a deterioration in quality of the image equipment.

Here, as a conventional example using a plastic lens in the optical scanning optical system, a conventional example in Patent Document 1 will be described below.
FIG. 7 is a plan view showing a conventional example when a plastic lens is used in the optical scanning optical system. The optical scanning optical system 100 shown in FIG. 1 includes a light source 101 using a semiconductor laser, a coupling lens 102, an aperture 103, an anamorphic lens 104, a polygon mirror 105, a deflector side scanning lens 106, an image plane side scanning lens 107, and a dustproof glass 108. The image plane 109 is included. In the optical scanning optical system 100 having such a configuration, the light beam emitted from the light source 101 which is a semiconductor laser becomes weakly divergent light by the coupling lens 102, passes through the aperture 103, and by the anamorphic lens 104 constituting the first optical system. The main scanning direction is parallel light, and the sub-scanning direction is a light beam condensed near the polygon mirror 105. Further, the light is deflected by the polygon mirror 105, and formed on the image surface 109 through the dust-proof glass 108 by the deflector side scanning lens 106 and the image surface side scanning lens 107. In such a conventional example, detailed optical system data is omitted, but the focus position with respect to the image plane position is calculated taking into account variations in the light source wavelength, refractive index, lens surface shape, and lens thickness due to temperature. Then, the result of FIG. 8 was obtained. From this result, it is understood that when the environmental temperature is changed from 25 ° C. to 45 ° C., the focus position is greatly changed by 11.6 mm in the main scanning direction and 3.3 mm in the sub scanning direction.

Therefore, in order to solve such a problem, as shown in FIG. 9, an optical scanning optical system 200 using a diffractive optical surface as a lens surface is proposed in Patent Document 1. The lenses shown in FIG. 9 are all made of plastic, and diffractive optical surfaces are used for the lens surface on the light source side of the coupling lens 201 and the image surface side lens surface of the anamorphic lens 202. The diffractive optical surface has a refraction angle change direction opposite to that of a normal refracting surface due to a wavelength change. If this characteristic is used, a focus position shift due to a temperature change can be canceled by the diffractive optical surface. As a result, the beam spot can be reduced in diameter without causing a focus position shift. In such Patent Document 1, detailed optical system data is omitted, but the focus position with respect to the image plane position is determined taking into account variations in the light source wavelength, refractive index, lens surface shape, and lens thickness due to temperature. When calculated, the result of FIG. 10 was obtained. From this result, it is understood that when the environmental temperature is changed from 25 ° C. to 45 ° C., the focus position is hardly changed to −0.2 mm in the main scanning direction and 0.0 mm in the sub scanning direction.
JP 2005-258392 A

  However, the value of the focus position with respect to the image plane position described above is a value in optical design, and problems in production technology have occurred in manufacturing a coupling lens having a diffractive optical surface. One of the problems is internal distortion in the vicinity of the gate of the plastic lens. Coupling lenses and anamorphic lenses are very minute lenses because of the demand for compact image equipment and a compact optical scanning optical system. The coupling lens has a round shape with an outer dimension of about 4 mm in diameter, and the anamorphic lens has a square shape with an outer dimension of about 4 mm × 8 mm. In particular, a coupling lens having a round shape is a minute lens. Such a plastic lens is generally obtained by an injection molding method which is suitable for mass production and has a low manufacturing cost. The injection molding method is a mold cavity (lens-shaped cavity) maintained at a constant temperature by temperature control means such as heating by a heater or circulating oil in a heated plastic material. ) Is injected into the inside, cooled and solidified, and then taken out from the mold to obtain a lens. However, when a minute lens is molded using the injection molding method, the internal distortion becomes large in the vicinity of the gate of the plastic lens, which is an entrance for filling the molten plastic material into the cavity of the mold. In order to prevent the occurrence of sink marks (dents) in the lens, a holding pressure, which is a pressure applied to the plastic material in the mold by the screw of the injection molding machine, is applied for a predetermined time. It will solidify and thermal stress will not be relieved and internal strain will increase. FIG. 11 shows the internal distortion of the plastic lens. Due to the large internal distortion of the plastic lens, birefringence increases as an optical characteristic. Since the birefringence phenomenon is a phenomenon in which the refractive index varies depending on the vibration direction of light, the laser beam of the optical scanning optical system becomes thick and cannot be reduced in diameter.

  Another problem is internal distortion generated around the ejector bin of the plastic lens. The plastic lens is generally obtained by using an injection molding method which is suitable for mass production and has a low manufacturing cost. In the injection molding method, the plastic material heated and melted is injected and filled into a cavity of a mold maintained at a constant temperature by temperature control means such as a method of heating by heating or circulating oil. In this method, after cooling and solidifying, the lens is taken out from the mold. When removing this plastic lens from the mold, open the two molds, that is, the molds on the mold fixed side and the mold movable side, and then remove the plastic lens remaining on the mold movable side mold. In general, the desired plastic lens is taken out by ejecting with an ejector pin. However, internal distortion tends to occur in the vicinity of the ejector pin, and the shape of the lens surface tends to deteriorate. Internal distortion is likely to occur because a clearance of about 10 to 20 μm is always provided between the ejector pin and the entrance frame constituting the periphery to ensure the slidability of the ejector pin. However, it is because a molten plastic material enters and is rapidly cooled. Further, the deterioration of the lens surface shape is due to mold release deformation in the vicinity of the ejector pin when the plastic lens remaining on the mold movable side is projected by the ejector pin.

  Another problem is that the plastic lens collapses when it is bonded to the optical scanning optical system housing. When a plastic lens is obtained by an injection molding method, as shown in FIG. 12, it is common to provide a draft angle in order to release the lens from the mold without resistance. Generally, the draft angle applied to the plastic lens is about 3 ° to 5 °. If there is no draft angle, the resistance when releasing the lens from the mold will increase, and the lens surface shape will be deformed, making it impossible to obtain a plastic lens with a highly accurate lens surface shape. End up. By the way, as a method of fixing the plastic lens to the optical scanning optical system housing, there is an adhesion by an ultraviolet curable resin. Bonding with UV curable resin means fixing a plastic lens in place with a jig, applying a liquid UV curable resin between the lens and the housing, and then irradiating with UV to cure the UV curable resin. This is a method of bonding. At that time, when the ultraviolet curable resin is irradiated with ultraviolet rays, the ultraviolet curable resin undergoes curing shrinkage. Therefore, when a plastic lens with a draft is to be bonded to the housing with an ultraviolet curable resin, as shown in FIG. 13A, the cure shrinkage of the ultraviolet curable resin varies depending on the location with the draft. As a result, as shown in FIG. 13B, the plastic lens falls down and the optical axis shifts. For example, if the thickness of the plastic lens is 3 mm, the draft is 3 °, and the curing shrinkage of the UV curable resin is 7%, then it will fall after bonding θ = about 0.21 ° (decrease by 11 μm at the height of the lens apex) ) Occurs. As a result, the laser beam of the optical scanning optical system is not directed in a predetermined direction, so that the focus position is shifted and the diameter cannot be reduced.

  The present invention is intended to solve these problems. The internal distortion is small, the lens surface shape is highly accurate, and the optical scanning optical system housing is made of a UV curable resin so that it does not fall down. It is an object of the present invention to provide a plastic lens, an optical scanning optical device, and an image forming apparatus that can be bonded accurately.

In order to solve the above problems, one lens surface is a diffractive surface, a plastic lens having a height formed in a resin and extending in the optical axis direction, which corresponds to a cylindrical side surface the rectangular edge portions extending in a direction orthogonal to the optical axis direction from a point that is provided, the side surface of the flange portion has a draft angle with respect to the optical axis direction to release from the mold during injection molding, co Bas At least part of the part is a plastic lens directly connected to the gate for injecting a molten resin material at the time of injection molding. It is characterized in that a bonding surface to the bonding target member parallel to the axial direction is provided . Therefore, it is possible to prevent a collapse when the member to be bonded, for example, the optical scanning optical system housing is bonded using the ultraviolet curable resin .

  Furthermore, since the edge portion is provided at a position corresponding to the ejector pin arranged for releasing from the mold at the time of injection molding, the mold release deformation in the vicinity of the ejector pin does not reach the light transmission region. It is also possible to prevent deformation of the lens surface shape.

  Furthermore, an optical scanning device as another invention includes a light source composed of a semiconductor laser, a coupling optical system for coupling a light beam from the light source, and a light beam from the coupling optical system as parallel light in the main scanning direction. The optical system for condensing the polarizer in the sub-scanning direction, the polarizer for polarizing the light beam from the optical system in the main scanning direction, and the scanning optical system for condensing the light beam polarized by the polarizer. To do. In the optical scanning device of the present invention, the lens constituting the coupling optical system, the optical system, and the scanning optical system is the above-described plastic lens, and each of the plastic lenses is made of ultraviolet curable resin in the housing of the bonding target member. It is characterized by bonding. Therefore, it is possible to provide an optical scanning device capable of reducing the beam spot diameter without causing a focus position shift due to a temperature change.

  An image forming apparatus as another invention is characterized in that the above optical scanning device is mounted. Therefore, an image forming apparatus equipped with an optical scanning device capable of reducing the beam spot diameter without causing a focus position shift due to a temperature change can form a very good image.

In the plastic lens of the present invention, one lens surface is a diffractive surface, is formed of resin, and has a cylindrical shape having a height extending in the optical axis direction. A rectangular parallelepiped edge portion extending in a direction perpendicular to the optical axis direction from a portion corresponding to the cylindrical side surface is provided, and the side surface of the edge portion has a draft angle with respect to the optical axis direction for releasing from the mold during injection molding. have. At least a part of the edge portion is directly connected to a gate for injecting a molten resin material at the time of injection molding. The plastic lens of the present invention is provided with an adhesive surface to a member to be bonded parallel to the optical axis direction at a portion corresponding to a cylindrical side surface that is not provided with an edge and has no draft angle. There is a feature. Therefore, it is possible to prevent a collapse when the member to be bonded, for example, the optical scanning optical system housing is bonded using the ultraviolet curable resin .

  FIG. 1 is a schematic view showing the configuration of a plastic lens according to the first embodiment of the present invention. (A) of the figure is a front view, (b) of the figure is a plan view, and (c) of the figure is a side view. The plastic lens 10 of the present embodiment is a plastic diffractive lens having a diffractive surface on one side, and the outer shape of a light transmitting region through which light passes is substantially cylindrical. Then, as shown in FIG. 5B, the portion other than the portion without the draft angle has the edge portion 11 protruding in the region where the light beam does not transmit, and the surface of the edge portion 11 has an optical axis. They are not parallel, that is, they have a draft angle to facilitate release from the mold during injection molding. An ejector pin is disposed on the edge portion 11 having the draft angle. Further, as shown in (c) of the figure, only a part (two places) of the cylindrical side surface in the outer shape of the light transmission region is parallel to the optical axis, that is, has no draft. The surface of the portion without the draft is an adhesive surface that adheres to the housing described later. The plastic lens 10 according to the present embodiment is a plastic diffractive lens having a diffractive surface on one side, but need not be limited to this and can be applied to various types of plastic lenses.

  When such a plastic lens 10 according to the present embodiment is obtained by injection molding, the lens is removed from the mold with a small resistance by having a draft angle in a region excluding a part of the region other than the light transmission region. The mold can be released and the lens surface shape is not deformed. Therefore, a plastic lens having a highly accurate lens surface shape can be obtained.

  Further, when the edge portion 11 is provided like the plastic lens 10 of the present embodiment and the gate of the plastic lens 10 is provided in the vicinity of the edge portion 11, the internal distortion is increased in the vicinity of the gate. The area does not reach the light transmission area. As a result, the birefringence as an optical characteristic does not increase and the laser beam of the optical scanning optical system does not become fat.

  Further, by disposing the ejector pin in the molding die region corresponding to the edge portion 11 like the plastic lens 10 of the present embodiment, the light beam does not pass through the region where the internal distortion of the plastic lens 10 is large. Degradation of optical characteristics can be prevented. Further, since the light transmitting area of the molding die ejector pin and the plastic lens 10 is separated, when the plastic lens 10 remaining on the movable side of the mold is released with the ejector pin, it is separated in the vicinity of the ejector pin. Since the mold deformation does not reach the light transmission region, it is possible to prevent the lens surface shape from being deformed.

  Further, as shown in FIG. 2, the surface of the plastic lens 10 that is parallel to the optical axis, that is, the surface of the portion that has no draft angle is used as an adhesive surface that adheres to the housing, so that it is adhered to the housing with an ultraviolet curable resin. However, the amount of cure shrinkage of the ultraviolet curable resin does not vary depending on the location. Therefore, the plastic lens 10 does not fall down. As a result, the laser beam of the optical scanning optical system is directed in a predetermined direction, and the diameter of the beam spot can be reduced without causing a focus position shift.

  FIG. 3 is a schematic view showing a configuration of a plastic diffractive lens according to the second embodiment of the present invention. (A) of the figure is a front view, (b) of the figure is a plan view, and (c) of the figure is a side view. The plastic diffractive lens 20 according to the present embodiment is a plastic diffractive lens having a diffractive surface on one side, and the outer shape of a region through which light passes is a cylinder. And as shown to (a), (b) of the figure, the edge part 21 which protruded to the area | region which the light ray of the plastic lens 20 does not permeate | transmits is a rectangular parallelepiped shape from two places of the cylindrical side surface in the external shape of a light transmissive area | region. It protrudes. The rectangular parallelepiped edge portion 21 does not have a side surface parallel to the optical axis, that is, has a draft angle. Further, as shown in FIG. 5C, all of the cylindrical side surfaces in the outer shape of the light transmission region are parallel to the optical axis, that is, have no draft. The surface of the portion without the draft is an adhesive surface that adheres to the housing described later. The plastic lens 20 of the present embodiment is a plastic diffractive lens having a diffractive surface on one side, but need not be limited to this and can be applied to various types of plastic lenses.

  When such a plastic lens 20 of the present embodiment is obtained by an injection molding method, the draft is attached to a region excluding a part of the region other than the light transmission region, so that the lens can be removed from the mold with less resistance. The mold can be released and the lens surface shape is not deformed. Therefore, a plastic lens having a highly accurate lens surface shape can be obtained.

  Further, when the edge portion 21 is provided like the plastic lens 20 of the present embodiment and the gate of the plastic lens 20 is provided in the vicinity of the edge portion 21, the internal distortion is increased in the vicinity of the gate. The area does not reach the light transmission area. As in this embodiment, this effect is very effective when the distance from the gate directly connected to a part of the edge portion 21 of the plastic lens 20 to the light transmission region is long, for example, 1 mm or more. . As a result, the birefringence as an optical characteristic does not increase and the laser beam of the optical scanning optical system does not become fat.

  Further, by disposing an ejector pin in a region corresponding to the edge 21 of the molding die as in the plastic lens 20 of the present embodiment, the light beam does not pass through a region where the internal distortion of the plastic lens 20 is large. Degradation of optical characteristics can be prevented. Further, since the light transmitting area of the molding die ejector pin and the plastic lens 20 is separated, when the plastic lens 20 remaining on the movable side of the mold is released with the ejector pin, the separation in the vicinity of the ejector pin is performed. Since the mold deformation does not reach the light transmission region, it is possible to prevent the lens surface shape from being deformed. As in the present embodiment, this effect is very effective when the distance from the position of the ejector pin to the portion corresponding to the region through which the light beam of the plastic lens passes is long, for example, 1 mm or more.

  Further, as shown in FIG. 2, even if the surface of the plastic lens 20 parallel to the optical axis, that is, the surface of the portion having no draft is attached to the housing with the ultraviolet curable resin, the amount of cure shrinkage of the ultraviolet curable resin is not reduced. There is no difference depending on the location. Therefore, the plastic lens 20 does not fall down. As a result, the laser beam of the optical scanning optical system is directed in a predetermined direction, and the diameter of the beam spot can be reduced without causing a focus position shift.

  FIG. 4 is a schematic view showing the configuration of a plastic diffractive lens according to the third embodiment of the present invention. (A) of the figure is a front view, (b) of the figure is a plan view, and (c) of the figure is a side view. The plastic lens 30 of the present embodiment is a plastic diffractive lens having a diffractive surface on one side, and the outer shape of a region through which light passes is a cylinder. And as shown to (a), (b) of the figure, a part of cylindrical side surface in the external shape of the light transmissive area | region of the plastic lens 30 is not parallel to an optical axis, ie, a draft is attached. Yes. Further, the edge portion 31 protruding into the region where the light beam of the plastic lens 30 does not transmit protrudes in a rectangular parallelepiped shape from two portions of the cylindrical side surface in the outer shape of the light transmission region. The rectangular parallelepiped edge 31 is not parallel to the optical axis, that is, has a draft. Further, as shown in FIG. 5C, all of the cylindrical side surfaces in the outer shape of the light transmitting region are parallel to the optical axis. Further, the surface of the portion without the draft becomes an adhesive surface that adheres to the housing described later. Although the plastic lens 30 of the present embodiment is a plastic diffractive lens having a diffractive surface on one side, it is needless to say that the plastic lens 30 is not limited to this and can be applied to various plastic lenses.

  When such a plastic lens 30 according to the present embodiment is obtained by injection molding, the lens is removed from the mold with less resistance because a draft is attached to a region excluding a part of the region other than the light transmission region. The mold can be released and the lens surface shape is not deformed. Therefore, a plastic lens having a highly accurate lens surface shape can be obtained.

  Further, when the edge portion 31 is provided like the plastic lens 30 of the present embodiment and the gate of the plastic lens 30 is provided in the vicinity of the edge portion 31, the internal distortion is increased in the vicinity of the gate. The area does not reach the light transmission area. As a result, the birefringence as an optical characteristic does not increase and the laser beam of the optical scanning optical system does not become fat.

  Further, by disposing the ejector pin in the region corresponding to the edge 31 of the molding die like the plastic lens 30 of the present embodiment, the light beam does not pass through the region where the internal distortion of the plastic lens 30 is large. Degradation of optical characteristics can be prevented. Further, since the light transmitting area of the molding die ejector pin and the plastic lens 30 is separated, when the plastic lens 30 remaining on the mold movable side is released with the ejector pin, the mold release in the vicinity of the ejector pin is performed. Since the deformation does not reach the light transmission region, it is possible to prevent the lens surface shape from being deformed.

  In addition, as shown in FIG. 2, even if the surface of the plastic lens 30 parallel to the optical axis, that is, the surface of the portion having no draft is adhered to the housing with the ultraviolet curable resin, the amount of curing shrinkage of the ultraviolet curable resin is not reduced. There is no difference depending on the location. Therefore, the plastic lens 30 does not fall down. As a result, the laser beam of the optical scanning optical system is directed in a predetermined direction, and the diameter of the beam spot can be reduced without causing a focus position shift.

  FIG. 5 is a schematic view showing the internal distortion of the plastic lens of the second embodiment. (A) of the figure is a front view, (b) of the figure is a plan view, and (c) of the figure is a side view. In the light transmission region of the plastic lens 20, the internal distortion is small, and the birefringence is also small as an optical characteristic. Since the birefringence phenomenon does not occur, the laser beam of the optical scanning optical system can be narrowed to reduce the diameter.

  FIG. 6 is a schematic diagram showing the configuration of an image forming apparatus equipped with the optical scanning device of the present invention. In the image forming apparatus 40 of the present invention shown in the figure, a photoconductive photoconductor 41 is formed in a drum shape and rotates at a constant speed in a clockwise direction. The peripheral surface of the photoconductor 41 is uniformly charged by a charging roller 42 as a charging means, and a book having an optical scanning device comprising an optical scanning optical system on which the plastic lens of the present invention described above is mounted as shown in FIG. The scanning device 43 performs optical scanning, and an electrostatic latent image is written. The electrostatic latent image (negative latent image) is reversely developed by the developing device 44 and visualized as a toner image. The obtained toner image is transferred onto the sheet-like recording medium S by the transfer unit 45 and is fixed by the fixing device 46. It is fixed and discharged out of the device. After the toner image is transferred, the photoconductor 41 is cleaned by a cleaning device 47 to remove residual toner and paper dust. By using the writing device 43 having the optical scanning device of the present invention, a good image can be formed.

  In addition, this invention is not limited to the said embodiment, It cannot be overemphasized that various deformation | transformation and substitution are possible if it is description in a claim.

It is the schematic which shows the structure of the plastic lens which concerns on the 1st Embodiment of this invention. It is a schematic sectional drawing which shows a mode that the plastic lens of this invention was adhere | attached on the housing. It is the schematic which shows the structure of the plastic lens which concerns on the 2nd Embodiment of this invention. It is the schematic which shows the structure of the plastic lens which concerns on the 3rd Embodiment of this invention. It is the schematic which shows the mode of the internal distortion of the plastic lens of 2nd Embodiment. 1 is a schematic diagram illustrating a configuration of an image forming apparatus equipped with an optical scanning device of the present invention. It is a top view which shows the prior art example at the time of using a plastic lens for an optical scanning optical system. It is a figure which shows the focus position calculation result with respect to the image plane position in the prior art example of FIG. It is a top view which shows the prior art example of the optical scanning optical system which used the diffractive optical surface for the lens surface. It is a figure which shows the focus position calculation result with respect to the image plane position in the prior art example of FIG. It is the schematic which shows the mode of the internal distortion of a plastic lens. It is a schematic sectional drawing which shows the draft angle of the plastic lens released from the metal mold | die. It is a schematic sectional drawing which shows a mode that the plastic lens with a draft angle was adhere | attached on the housing.

Explanation of symbols

10, 20, 30; plastic lens,
11, 21, 31; edge portion, 40; image forming apparatus.

Claims (4)

One of the lens surfaces is a diffractive surface, and is a plastic lens having a cylindrical shape that is molded from a resin and has a height extending in the optical axis direction, from a portion corresponding to the side surface of the cylindrical shape to the optical axis direction. A rectangular parallelepiped edge portion extending in a direction orthogonal to each other, the side surface of the edge portion has a draft angle with respect to the optical axis direction for releasing from the mold during injection molding, and at least a part of the edge portion is injection molded. In the plastic lens directly connected to the gate for injecting the molten resin material,
Plastic, wherein the edge portion is not provided, and the portion corresponding to the side surface of the draft is not the cylindrical, provided with adhesive surface in the optical axis direction parallel to the contact bonding target member lens. 2. The plastic lens according to claim 1, wherein the edge portion is provided at a position corresponding to an ejector pin that is arranged to release from the mold during injection molding . A light source comprising a semi-conductor laser, a coupling optical system for coupling a light beam from the light source, the main scanning direction the light beam from the coupling optics is parallel light, the sub-scanning direction is condensed on the polarizer In an optical scanning device comprising: an optical system; a polarizer that polarizes a light beam from the optical system in the main scanning direction; and a scanning optical system that condenses the light beam polarized by the polarizer.
The lens constituting the coupling optical system, the optical system, and the scanning optical system is the plastic lens according to claim 1 , and each of the plastic lenses is bonded to a housing of a member to be bonded using an ultraviolet curable resin. An optical scanning device. An image forming apparatus comprising the optical scanning device according to claim 3 .

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