JPH09265052A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly prevent scattered light, stray light and ghost light by providing a shield plate which pass a light beam through only when a scan light beam exists on a prescribed area of a surface to be scanned in the vicinity of an image forming point of an optical path from a first rotary reflection surface to a second rotary reflection surface. SOLUTION: The light beam polarized by the first reflection is made incident on a first transmission lens 31 of a transmission optical system, and becomes a convergent beam to be image formed on the image forming point P. The light beam image formed once on the image forming point P becomes a divergent beam next, and changes the direction by a first turning mirror 41 to be incident on a second transmission lens 32. An afocal optical system is used for a transmission optical system from the first reflection surface to the second reflection surface, and the shield plates 71, 72 are placed in the vicinity of the image forming point P between the first transmission lens 31 and the second transmission lens 32. The device is constituted so that the light beam passes through the shield plates 71, 72 only when the beam exists in the range to be scanned, from a reference position detector 81 to a terminal end of an effective scan area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in a laser beam printer or the like, and more particularly to an optical system in which a light beam is incident twice on a reflecting surface of a rotary polygon mirror.

[0002]

2. Description of the Related Art A rotary polygon mirror has been widely used as a deflector for deflecting and scanning a light beam in an image recording device such as a laser beam printer and an optical scanning device used for various image reading and measuring devices.

In these devices, an optical scanning device is used to repeatedly scan a light beam so as to draw a straight line or a curved line on the surface to be scanned. This scanning is called "main scanning", and a surface including the optical axis of the optical system of the optical scanning device and parallel to the main scanning direction is called "main scanning surface".

Further, the medium to be scanned located on the surface to be scanned is relatively moved in a direction substantially orthogonal to the main scanning direction.
Perform a dimensional scan. This relative movement is called "sub-scan",
A surface including the optical axis of the optical system of the optical scanning device and parallel to the sub-scanning direction is defined as a "sub-scanning surface". In a laser beam printer, a cylindrical photosensitive member is positioned on the surface to be scanned, and main scanning is performed with a light beam along its generatrix,
By performing sub-scanning that rotates the photoconductor around its axis,
A two-dimensional latent image is sequentially formed on the surface of the photoconductor.

In recent years, a higher-speed optical scanning device has been demanded in the above-mentioned devices in order to improve resolution and processing speed. In an optical scanning device that uses a rotary polygon mirror for deflecting a light beam, in order to increase the scanning speed (scanning frequency), the number of rotations of the rotary polygon mirror is increased or the number of surfaces of the rotary polygon mirror is increased. A method can be considered.

[0006] In order to increase the rotation speed of the rotary polygon mirror, a bearing capable of high-speed rotation is required. However, the most frequently used ball bearing at present has an upper limit of about 20,000 rotations per minute. 3000 per minute with air bearing
Although it can be used at a rotation speed of 0 rotation or more, usable devices are limited because the bearing is expensive. In particular, it is difficult to use for an inexpensive laser beam printer for general consumers.

On the other hand, if the number of reflecting surfaces is increased while keeping the size of the rotary polygon mirror, the rotation angle per one reflecting surface becomes smaller, and the scanning angle of the light beam decreases, resulting in a focal length of the scanning optical system. Will increase. Therefore, the size of the entire optical scanning device becomes large. At the same time, the size of the reflecting surface is also reduced. Therefore, when it is attempted to secure the size of each reflecting surface necessary for forming an image of the light beam, the diameter of the rotary polygon mirror becomes large this time. As the size of the rotary polygon mirror increases, the load on the motor to be driven increases, which not only increases the driving power, but also requires the number of rotations to be reduced in some cases.

As described above, since the number of surfaces and the number of rotations of the rotary polygon mirror have upper limits, various scanning devices have been devised in order to obtain a scanning speed exceeding them.

Among them, in Japanese Patent Laid-Open No. 51-32340, a light beam emitted from a light source is incident on a rotary polygon mirror with a very small diameter in the main scanning direction, and a deflected light beam is emitted. A method is disclosed in which the light is incident on the rotary polygon mirror again via the transmission optical system. That is, the light beam is made to enter the rotating polygon mirror twice.

This method will be described below with reference to FIG.
The diameter of the beam in the main scanning direction when the light beam emitted from the light source 110 first enters the rotating polygon mirror 120 is 2
The transmission optical system 130 is made smaller than the case of the second incidence, and the light beam incident on the rotating polygon mirror 120 the second time follows the center point of the rotating reflecting surface in the scanning direction.
Is composed. The light beam that is incident on the reflecting surface for the second time and is deflected is imaged on the surface to be scanned 160 by the scanning optical system 150.

With such a configuration, when the light beam first enters the polygon mirror, the diameter of the light beam can be extremely reduced, so that scanning can be performed up to the full division angle of the rotary polygon mirror. When the light beam deflected by the first reflection enters the rotary polygon mirror through the transmission optical system for the second time, the diameter of the light beam is large enough to obtain a predetermined spot on the surface to be scanned. However, since it follows the rotation of the reflecting surface, the size of the light beam can be set to the full size of the reflecting surface of the rotating polygon mirror.

Further, the light beam deflected by the first reflection by the transmission optical system is given a deflection angle θ2 with respect to the optical axis when the light beam is incident on the rotary polygon mirror at the second time, so that the second time is obtained. The deflection angle of the light beam deflected by reflection can be made larger than the deflection angle by the first reflection.

Due to these effects, it is possible to make the diameter relatively small while increasing the number of reflecting surfaces of the rotary polygon mirror.

In general, in an optical scanning device, a light beam is turned on outside the effective scanning area and before the scanning area, and the light beam is guided to a photodetector to generate a signal serving as a scanning reference. Done. Also in this conventional technique, the light beam before reaching the effective scanning area is reflected by the reference position detecting mirror 181, and the reference position detector 182 is used.
Leading to.

[0015]

However, in order to surely detect the light beam with the above-mentioned reference position detector 182,
With respect to the time required for the light beam to reach the reference position detector 182, the time required for stabilization of the intensity of the light beam, the shape error of each reflecting surface of the rotating polygon mirror, and the margin for rotation fluctuation are taken into consideration, and a certain time before It is necessary to forcibly turn on the light beam.

However, the number of reflecting surfaces can be remarkably increased in the method of making the light incident on the rotary polygon mirror twice as described above, as compared with the conventional method.
After all, it is desirable that the diameter can be reduced. Therefore, the size of the reflecting surface cannot secure a large margin with respect to the beam diameter or the rotation angle of the rotary polygon mirror.

Further, when the operation of controlling the light quantity of the light source to a constant value is performed during the forced lighting period, a longer time is required. In particular, as the speed of the optical scanning device increases, the scanning cycle becomes shorter, but the time required for controlling the light amount for control does not become so short. Therefore, the ratio of the forced lighting time in one scanning cycle is increased. It is necessary to let

For this reason, if there is no room in the size of the reflecting surface as described above, the light beam is emitted from the adjacent reflecting surface immediately before and across the original reflecting surface. That is, the light beam is turned on from the downstream side of the effective scanning region of the previous scan, and the light beam is continuously emitted to the reference signal detection position of the next scan.

FIG. 9 shows how the incident beam straddles the two reflecting surfaces during the first reflection. At this time, the incident light beam is divided into a light beam L101 reflected by the reflecting surface 121 and a light beam L102 reflected by the reflecting surface 122.

The light beam L101 and the light beam L102 reach the first transfer lens 131, but partly scatter or go in another direction because they reach the first transfer lens 131. After that, the light beam L101 and the light beam L102 are emitted from the first folding mirror 1
41, the 2nd transmission lens 132, the 2nd folding mirror 14
As it passes through 2, scattering may occur as well. After passing through these optical elements, the two light beams respectively enter the reflecting surfaces 123 and 124 of the rotating polygon mirror.
Due to the function of the transmission optical system, the light is deflected so as to follow the center of each reflecting surface, so that there is no protrusion in principle. Further, although these two light beams reach the scanning optical system, they are applied to both ends of the scanning lens, so that they may be scattered here.

As described above, since the light beam during the forced lighting period is directed to the outside of the effective scanning area, it is irradiated to various places in the optical system and radiates scattered light in all directions. Some of these scattered lights reach the scanned surface after passing through various paths. Therefore, for example, when a photoconductor is optically scanned in a laser beam printer or the like, the surface potential is lowered, and “fog” that is printed at a very low density occurs on a portion where nothing is originally printed. Problems such as deterioration of quality occur.

Further, when these scattered lights enter the transmission optical system or the scanning optical system again, there is a possibility that they form an image on the surface to be scanned, that is, a ghost image is generated. Obviously, the generation of such a ghost image also significantly impairs the function of the scanning device.

With respect to such a problem, Japanese Patent Laid-Open No. 4-26
In the technique disclosed in Japanese Patent No. 4874, a shielding plate is provided on the downstream side of the effective scanning area of the surface to be scanned ("photosensitive drum" in the same publication) to prevent exposure of the surface to be scanned.
However, since the scattered light and the ghost image as described above are also generated in the effective scanning area on the surface to be scanned, only a partial effect can be exhibited. Further, if there is no member to be attached near the surface to be scanned, it is impossible to attach the shield plate near the surface to be scanned in this way.

Further, in this method, although measures for the downstream side of the effective scanning area on the surface to be scanned are disclosed, the upstream side of the position detector of the light beam does not move to the surface to be scanned. There is no disclosure of how to block the exposure. However, when the light beam is turned on until the next reference position is detected after the scanning of the effective scanning area, the light beam does not reach the surface to be scanned directly in the middle of the period, but the optical component on the optical path There is a possibility that the peripheral portion, the mounting portion, and other members will be irradiated with the light beam, and will reach the surface to be scanned along an unexpected path as stray light or ghost light.

In particular, in the scanning optical system in which the light is incident on the rotary polygon mirror twice as compared with the normal scanning optical system, the transmission optical system exists, so that unnecessary reflection and scattering paths of the light beam on the way are complicated. Therefore, it is very difficult to deal with the above-mentioned obstacles.

[0026]

In order to solve the above-mentioned problems, an optical scanning device of the present invention comprises a light source, a first rotary reflecting surface for deflecting a light beam emitted from the light source, and the first rotary reflecting surface. The light beam deflected by the rotary reflecting surface of the
And a second rotary reflecting surface that deflects the light beam that has passed through the transfer optical system. The scanning light beam deflected by the second rotary reflecting surface is used. In an optical scanning device that repeatedly scans the surface to be scanned, if the surface formed by deflecting and sweeping the light beam by the first reflecting surface is the main scanning surface, the light beam is reflected by the first rotary reflection surface on the main scanning surface. An image is formed at an image forming point at least once in the optical path from the surface to the second rotary reflecting surface, and the scanning light beam is located in the vicinity of the image forming point and is in a predetermined area of the surface to be scanned. It is characterized in that it has a shield plate which is arranged so as to allow the light beam to pass therethrough and shield the light beam when it is outside a predetermined region.

Further, the predetermined area includes a position at which the scanning light beam is incident on a reference position detector for obtaining a reference signal for starting scanning of the scanning light beam.

Further, it is characterized in that the first rotary reflecting surface and the second rotary reflecting surface are provided on the same rotary polygon mirror.

Further, the transmission optical system is an afocal optical system in which a parallel light beam is incident and a parallel light beam is emitted.

Alternatively, the afocal optical system is composed of two groups of lenses, a front group and a rear group, and the imaging point is located between the front group and the rear group on the optical axis of the afocal optical system. It is located at.

Then, the focused light beam is incident on the first rotary reflecting surface, and between the first lens of the transfer optical system and the first rotary reflecting surface on the optical axis of the transfer optical system. The image forming point is located.

Next, the shielding plate is adjustable in a direction orthogonal to the optical axis of the transmission optical system.

Further, the present invention is characterized in that it has a base member for supporting an optical component constituting the transmission optical system or the optical scanning device, and the shielding plate is formed integrally with the base member.

Finally, the shielding plate has an angle different from a right angle with respect to a surface formed by sweeping the light beam deflected by the light beam deflected by the first rotary reflecting surface in the transmission optical system. It is characterized by being provided.

[0035]

FIG. 1 shows a plan configuration of a first embodiment of an optical scanning device according to the present invention. 2 is an enlarged view of the transmission optical system shown in FIG. Light source 10
The light beam emitted from is converted into a parallel light beam by the collimator lens 11. Any light source may be used as the light source 10, but a semiconductor laser is preferable from the viewpoint of directivity, coherency and the like. The parallel light beam is incident on the rotary reflecting surface and is deflected for the first time. In this embodiment, the rotary reflecting surface is a polygonal prism-shaped reflecting surface provided around the rotary polygon mirror 20.

The light beam deflected by the first reflection enters the first transfer lens 31 of the transfer optical system 30, becomes a focused beam, and forms an image at the image forming point P. The light beam once imaged at point P becomes a divergent beam, changes its direction by the first folding mirror 41, enters the second transfer lens 32, and is converted into a parallel light beam again by the second transfer lens 32. It

The ratio of the diameter d1 of the light beam when it enters the first transfer lens 31 and the diameter d2 of the light beam that exits the second transfer lens 32 is determined by the focal length f1 of the first transfer lens and the second transfer lens. The ratio of the focal length f2 is 32. That is, the first transfer lens 31 and the second transfer lens 32 constitute an afocal optical system.

The light beam converted to parallel by the second transmission lens 32 is again incident on the rotary reflecting surface on the rotary polygon mirror 20 via the second folding mirror 42 and is deflected for the second time. The light beam that has been deflected the second time is scanned by the scanning optical system 5.
An image is formed as a spot of a required size on the surface 60 to be scanned by 0.

By the way, FIGS. 1 and 2 show the optical characteristics in the plane formed by the movement of the light beam deflected or scanned by the rotary polygon mirror 20, that is, in the main scanning plane.
In the plane including the optical axis and orthogonal to the main scanning plane, that is, in the sub-scanning plane, the configuration and characteristics of the optical system may be different from those in the main scanning plane described above. For example, the image formation point of the light beam when viewed in the sub-scanning plane does not necessarily have to coincide with point P described above.

In the present invention, the diameter of the light beam is
For example, when a laser is used as the light source 10 and the intensity distribution of the cross section of the light beam becomes a Gaussian beam, it is defined as a point having an intensity of 1 / e ² with respect to the peak intensity.
Further, when a Gaussian beam is not obtained, it is also defined as a diameter of a cross section having a predetermined intensity or more. However, the size of the effective area of each lens or reflecting surface is determined with a margin with respect to the diameter thus defined.

The light beam which has passed through the scanning optical system 50 has a reference position detecting mirror 8 prior to the exposure of the effective scanning area.
1 is guided to the reference position detector 82. When the light beam passes, the reference position detector 82 generates a pulse signal that serves as a reference for scanning the light beam. Based on this pulse signal generated for each scanning, writing, inputting, or reading with a light beam is performed at accurate timing.

First transfer lens 31 and second transfer lens 32
Shielding plates 71 and 72 are placed outside the moving range of the light beam in the vicinity of the image forming point P between. The operation will be described later in detail.

Next, how the beam is deflected as the rotary polygon mirror 20 rotates will be described with reference to FIG. FIG. 3 shows a cross section including a surface from which the light beam of the optical system is deflected from the first reflection surface to the second reflection surface of the first example of the exemplary embodiment of the present invention shown in FIG. The folding of the optical path by the folding mirror is expanded and displayed. Now, when the rotary polygon mirror 20 rotates by θ1, the first reflecting surface 21
The light beam is deflected by 2.θ1. When the deflected light beam enters the reflecting surface 23 for the second time through the first transfer lens 31 and the second transfer lens 32, it has a deflection angle θ2 with respect to the optical axis.

When the light beam is incident on the reflecting surface 23 for the second time, the deflection angle of the deflected light beam is inclined by θ2 with respect to the optical axis, but the rotary polygon mirror 20 is rotated by θ1. Therefore, it is inclined by θ1 + θ2 with respect to the second reflection surface 23. In this way, by making the light beam enter the rotary polygon mirror 20 twice, the scanning angle of the light beam deflected by the reflection surface 23 for the second time becomes 2 · θ1 + θ2, which has the effect of amplifying the scanning angle by θ2. .

When the deflected light beam is incident on the reflecting surface for the second time, the incident point of the light beam is displaced from the optical axis by δ according to the rotation angle θ1 of the rotary polygon mirror 20. Since this displacement amount δ is set to be substantially equal to the movement amount of the reflecting surface due to the rotation of the rotary polygon mirror 20,
As a result, regardless of the rotation angle θ1 of the rotary polygon mirror 20,
The deflected light beam almost follows the second movement of the reflecting surface. Therefore, the transmission optical system 30 enlarges the diameter d.
A light beam of 2 can utilize the size of the second reflecting surface to the limit.

On the other hand, on the first reflection surface, the incident light beam is fixed, and since the reflection surface moves with respect to the light beam, the diameter d1 of the incident light beam allowed by the amount of the movement. Becomes smaller.

Next, FIG. 4 shows the positional relationship of the incident beams on the first reflecting surface of the rotary polygon mirror 20. However, for convenience of explanation, the rotary polygon mirror is fixed and the angular position of the incident beam is changed. Now, let us say that the radius of the inscribed circle is R, and the diameter of the light beam incident on the reflecting surface for the first time is d1. The rotation angle θc per one reflecting surface cannot be assigned to the angle θs for scanning the effective scanning area. As described above, the reference position detector 82 for optically detecting the reference point of the start of scanning is placed in front of the effective scanning area.
Since the light beam is on at the time of detection, there is a certain margin θh so that the light beam does not enter the effective scanning area.
Must be placed with.

From the detection position to the rear end of the effective scanning area, all the incident light beam must be reflected on the first reflection surface. Therefore, by further setting the angle θu on both sides, the value obtained by adding the length corresponding to the diameter d1 of the incident beam to the relative movement amount of the incident beam in the period from the detection position to the rear end of the effective scanning area becomes Is smaller than the effective width of.

After all, it is understood that it is necessary to satisfy at least the relationship of θs + θh + 2 · θu ≦ θc for each angle described above.

As described in the section of the problem to be solved by the invention, in order to absorb the error in the shape accuracy and the rotation accuracy of the reflecting surface of the polygon mirror, the light beam is made slightly before entering the reference position detector 82. Need to be lit. Further, considering the time for stabilizing the output of the light beam and the time for controlling when the light amount control for each scanning is performed at the time of detecting the reference position, it is necessary to turn on the light further from the front side. Become. Therefore, when .theta.u is taken at a minimum angle, the incident light beam is emitted from the reflection surface immediately before.

Of course, it is possible to set θu to a sufficiently large value so that even if the light beam is turned on before the reference position detector 82, it does not stick out from the reflecting surface. However, for that purpose, it is necessary to reduce the rotation angle θs of the rotary polygon mirror 20 used for scanning the effective scanning region or increase the inscribed circle radius R of the rotary polygon mirror. When θs is made small, there arise problems that the focal length of the scanning optical system becomes long, the optical system becomes large, the optical magnification from the light source to the surface to be scanned increases, and the adjustment accuracy of the optical system becomes strict. Further, increasing R causes a problem that the load on the motor that drives the rotary polygon mirror 20 increases.

In particular, in the present invention, the purpose of allowing the light beam to enter the rotating polygon mirror twice is to focus on increasing the number of reflecting surfaces of the polygon mirror without increasing the diameter thereof.
Providing a margin for θu as described above is incompatible with the premise of the present invention.

FIG. 5 shows a case in which the incident light beam is irradiated over the two reflecting surfaces in this way. The incident light beam has two reflecting surfaces 21 as the first reflecting surface,
It is incident on 22 and is split into two light beams L1 and L2. The two divided light beams L1 and L2 are incident on the first transfer lens 31, but since the first transfer lens 31 is set to be sufficiently large, it becomes a deflected light beam having a very large deflection angle. On the other hand, it can be made to completely enter the lens.

The two deflected light beams incident on the first transmission lens 31 are imaged at points P'and P ". However, the shielding plates 71 and 72 are placed at these positions, and the two light beams On the other hand, since the position of the light beam in the effective scanning area or the light beam detection position is within the range of the opening formed by the two shield plates 71, 71, it passes through without any problem.

As described above, the image formation point of the light beam is moved by the deflection, and the light beam is incident on the reference position detector 82 immediately after it is disengaged from the shield plate 71 and is shielded immediately after the scanning of the effective scanning area is completed. The ideal arrangement is to position the two shields so that they rest on the plate 72. The expression "immediately after" does not mean "simultaneously", but the rotation fluctuation of the rotary polygon mirror, the shape error of the reflecting surface of the rotary polygon mirror, the reference position detector 82, each lens, and the folding mirror. ,
This means securing a minimum margin in consideration of the position error of the shielding plate.

Further, if the shielding plates 71, 72 are structured so that they can be adjusted in the direction perpendicular to the optical axis, the above-mentioned margin can be further reduced, so that the deflection range through which the light beam passes. Can be set more accurately, and it is possible to more strictly prevent an unnecessary light beam from reaching the surface to be scanned.

For example, the diameter d1 of the light beam on the first reflecting surface is 1 mm, and the focal length f of the first transmission lens is f.
1 = 50 mm and the light source 10 is a semiconductor laser having a wavelength of 780 nm, the diameter of the light beam is 50 μm or less at the points P ′ and P ″. Thus, at the points P ′ and P ″, the light beam is deflected. Since the diameter of the light beam in the image formation state is very small with respect to the amount of movement, it is possible to shield the light beam very sharply. Of course, the shield plates 71, 72
It is desirable to perform a surface treatment on the surface of so as to prevent unnecessary reflection of the light beam.

On the other hand, the shield plates are replaced with the shield plates 171, 17 in FIG.
When it is arranged at a position as shown in FIG. 2, the diameter of the light beam at this position is about 1 to several mm, which is considerably larger than the amount of movement of the light beam. It is impossible, and the amount of light gradually decreases or increases as the rotary polygon mirror rotates. Therefore, if the shielding plate is placed at a position that shields all unnecessary light beams, some of the light beams in the effective scanning area are also shielded by the shielding plate 17.
The light quantity is reduced by being blocked by 1, 172. On the other hand, if the interval between the shield plates 171 and 172 is widened so that all the light beams in the effective scanning area are transmitted, some unnecessary light beams also pass through without being blocked.

As described above, since only the light beam within the effective scanning area from the reference detection position can pass through the shielding plates 71 and 72, the first folding mirror 41, the It is guaranteed that the light beam will pass through the second transmission lens 32, the second folding mirror 42, and the scanning lens 50 only within the range of each effective area. Therefore, since no countermeasures such as ghost and reflection prevention are required for these lenses and mirrors, the device can be downsized, and there is no need to consider ghost or reflection in the structure of the lens or mirror mounting part. The shape can be optimized according to each mounting function.

Furthermore, as described in the section of the prior art, it is not necessary to place a shield plate located near the surface to be scanned, and the shield plate can be easily attached to the base that supports the optical components of the optical scanning device. Therefore, it is very simple in structure and can be manufactured at low cost. In particular, when the base is injection-molded with plastic or the like, the shielding member can be formed integrally with the base, so that there is no difficulty in manufacturing at the same time and the size and position of the shielding plate can be accurately made.

If the shield plate is formed at an angle other than the surface formed by deflecting the light beam, that is, the main scanning surface, the reflected light when the surface of the shield plate is irradiated with the light beam is main-scanned. It moves away from the surface in a different direction. The reflected light reflected by the shield plate moves away from the shield plate,
Although the distance from the optical axis increases, other lenses and mirrors around the shield plate are below a certain height (in the sub-scanning direction) from the optical axis, so the reflected light from the shield plate should hit. There is no. Therefore, it is not necessary to carry out an antireflection treatment on the surface of the shielding plate, and the manufacturing cost can be reduced.

In the first example of the embodiment of the present invention described above, the afocal optical system is used as the transmission optical system from the first reflection surface to the second reflection surface, and the first transmission is performed. By placing the shielding plates 71 and 72 in the vicinity of the image forming point P between the lens 31 and the second transfer lens 32, the light beam is in a range of scanning from the reference position detector 81 to the end of the effective scanning area. It is possible to only pass through the shield.

Next, as a second example of the embodiment of the present invention, the case of using the transmission optical system as previously filed by the applicant of the present application in Japanese Patent Application No. 7-306197, the plane of FIG. This will be described with reference to the configuration diagram and FIG. 7, which is an enlarged view of the transmission optical system thereof.

In FIG. 6, the light beam emitted from the light source 10 is converted into a focused light beam by the beam shaping lens 12. The light beam deflected by the first reflection is
An image is once formed at an image forming point S in front of the transfer lens 33, and then enters the transfer lens as a divergent beam. Transmission lens 33
The light beam that has passed through becomes a parallel light beam, enters the rotary polygon mirror 20 again via the first folding mirror 41 and the second folding mirror 42, and is deflected for the second time. The light beam subjected to the second deflection is imaged by the scanning lens 51 on the surface 60 to be scanned as a spot having a required size. A correction lens 52 that corrects the tilt of the reflecting surface of the rotary polygon mirror 20 is placed between the surface to be scanned and the scanning lens 51.

As in the first example of the embodiment of the present invention, the light beam that has passed through the scanning lens 51 is
Prior to the exposure of the effective scanning area, it is guided to the reference position detector 82 by the reference position detection mirror 81.

Shielding plates 73 and 74 are placed on both sides of the image forming point S to pass only the deflected light beam from the reference detection position to the end of the effective scanning area, as in the first embodiment.
Light beams before and after that range are blocked. Unlike the first embodiment, in this embodiment, since the shield plates 73 and 74 are provided immediately after the first reflecting surface, the light beam is not irradiated to the portion other than the effective area of the transmission lens 33,
The size of the transmission lens 33 may be set to the minimum necessary size for the beam to pass from the light beam detection position to the rear end of the effective scanning area, and the ends and mounting portions of the lenses on both sides thereof may be set. Since no light beam is emitted onto the lens, the structure for mounting the lens can be simplified.

As described above, as compared with the first embodiment, the effect of the present invention is enhanced because all the optical systems after the first reflecting surface are released from unnecessary irradiation of the light beam.

Further, the structure of the transmission optical system is not limited to the above-mentioned first and second embodiments, but a light beam is formed between the first and second reflecting surfaces. If the format has an image point, it has the same effect.

In the above-mentioned two embodiments, the light beam is guided to the reference signal generator prior to scanning the effective scanning area. However, the scanning reference signal need not be an optical method, but may be, for example, a rotating polygon mirror. It may be a method of electromagnetically generating inside the motor for driving. In that case, the positions and intervals of the shielding plates may be set so that only the light beam scanning the effective scanning region can pass through the region sandwiched by the pair of shielding plates.

In the first and second embodiments, the first and second reflecting surfaces are the reflecting surfaces of the same rotary polygon mirror, and the light beam is incident twice to deflect the light. As described above, the same effect is exhibited even when the first and second reflecting surfaces are in two different rotating polygon mirrors that rotate in synchronization with each other. Further, even if a galvanometer mirror is used as the deflector instead of the rotary polygon mirror, the same effect can be obtained without changing the essence of the present invention.

[0071]

As described above, according to the optical scanning device of the present invention, by placing the shielding plate in the vicinity of the image forming point of the light beam in the optical path of the transmission optical system, it is possible to rearward the image forming point on the optical axis. The optical element such as the lens and the reflection mirror in Fig. 2 can be made to irradiate only the light beam in the deflection position from the reference detection position to the rear end of the effective scanning area, and it is possible to prevent unnecessary reflection and ghost. Eliminates the need for processing and additional components. That is, it is possible to completely prevent scattering of the light beam, stray light, and ghost light, regardless of the location of the deflected light beam, by only placing a shield plate at one place.

Particularly, in the present invention, the rotating polygon mirror is provided with two light beams.
Although it has a transmission optical system for making it incident once, this transmission optical system is inevitably arranged around the rotary polygon mirror in terms of function. Therefore, if unwanted reflection or scattering of the light beam occurs in the transmission optical system, there is a high risk that the light beam will enter the rotating polygonal mirror, and eventually it may reach the surface to be scanned and cause an obstacle.

However, according to the present invention, since the light beam always passes through the effective range of each lens of the transmission optical system and the reflection mirror, unnecessary reflection and scattering do not occur at all. Therefore, the size of each lens and the reflection mirror can be minimized, and at the same time, the structure and shape of the mounting portion can be functionally optimized without any consideration of receiving the light beam irradiation. The optical scanning device not only has a simple design but also has a simple structure and is inexpensive.

In particular, as in the second embodiment of the present invention, the focused light beam is made incident on the first reflection surface and the light beam is once imaged between the first reflection surface and the transmission optical system. By arranging the shield plate in the vicinity, this effect is further enhanced because the entire transmission optical system is never exposed to unnecessary light beam irradiation.

Further, by adopting a structure in which the shield plate is adjustable in a direction perpendicular to the optical axis of the transmission optical system, the effective scanning area or the reference signal of the reference signal is passed through the shield plate within the deflection range of the light beam. The range that reaches the detection position can be set more accurately, the scattering of the light beam, etc. can be prevented more strictly, and at the same time, without increasing the shape accuracy and mounting accuracy of the lens, the folding mirror, and the rotary reflecting mirror, It can be effective.

Alternatively, by forming the shield plate integrally with the base member supporting the components of the optical scanning device, it is possible to improve the positional accuracy of the shield plate and at the same time reduce the component cost.

Further, the light beam reflected by the surface of the shield plate can be deflected from other lenses, rotary polygon mirrors, and folding mirrors by forming an angle with respect to the surface of the shield plate that is formed by deflecting the light beam. it can. Therefore, there is no need to perform an antireflection treatment on the surface of the shield plate, and there is an effect that the shield plate can be manufactured more easily.

[Brief description of drawings]

FIG. 1 is a plan configuration diagram of a first embodiment of an optical scanning device according to the present invention.

FIG. 2 is a detailed view of a transmission optical system in the first embodiment of the optical scanning device according to the present invention.

FIG. 3 is a development cross-sectional view of a transmission optical system in a deflecting surface in the first embodiment of the optical scanning device according to the present invention.

FIG. 4 is a diagram showing a movement of an incident light beam on a first reflecting surface in the first embodiment of the optical scanning device according to the present invention.

FIG. 5 is a diagram showing an incident light beam straddling two reflecting surfaces in the first reflecting surface in the first embodiment of the optical scanning device according to the present invention.

FIG. 6 is a plan configuration diagram of a second embodiment of the optical scanning device according to the present invention.

FIG. 7 is a detailed view of a transmission optical system in a second embodiment of the optical scanning device according to the present invention.

FIG. 8 is a plan configuration diagram of a conventional optical scanning device.

FIG. 9 is a detailed view of a transmission optical system of an optical scanning device in the related art.

[Explanation of symbols]

10 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Light source 20 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Rotating polygon mirror 30 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Transmission optical system 31 , 32, 33 ··· Transfer lens 41, 42 ···· Folding mirror 50 ····· Scanning optical system 60 ···・ ・ ・ ・ ・ ・ Surfaces to be scanned 71, 72, 73, 74 ・ ・ ・ Shielding plate 81 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Reference position detection mirror 82 ・ ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ Reference position detector

Front Page Continuation (72) Inventor Kata Takada 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (9)

[Claims] 1. A light source, a first rotary reflecting surface for deflecting a light beam emitted from the light source, and a light beam deflected by the first rotary reflecting surface to a second rotary reflecting surface described later. It has a transfer optical system for making it enter and a second rotary reflecting surface for deflecting the light beam that has passed through the transfer optical system, and scans the surface to be scanned by using the scanning light beam deflected by the second rotary reflecting surface. In an optical scanning device that repeatedly scans, when a surface formed by deflecting and sweeping the light beam by the first reflecting surface is a main scanning surface, the light beam is moved from the first rotary reflecting surface to the first scanning surface in the main scanning surface. When the scanning light beam is located near the image forming point and the scanning light beam is in a predetermined area on the surface to be scanned, the light is imaged at least once in the optical path leading to the two rotary reflecting surfaces. Allow the beam to pass, and The optical scanning device, the optical scanning device further comprises a shield plate arranged to shield the light beam. 2. The position in which the scanning light beam is incident on a reference position detector for obtaining a reference signal for starting scanning of the scanning light beam is included in the predetermined region. Item 2. The optical scanning device according to item 1. 3. The optical scanning device according to claim 1, wherein the first rotary reflecting surface and the second rotary reflecting surface are provided on the same rotary polygon mirror. 4. The optical scanning device according to claim 1, wherein the transmission optical system is an afocal optical system in which a parallel light beam enters and emits a parallel light beam. 5. The afocal optical system is composed of two groups of lenses, a front group and a rear group, and the imaging point is located between the front group and the rear group on the optical axis of the afocal optical system. 5. The optical scanning device according to claim 4, wherein the optical scanning device is located at. 6. A focused light beam is incident on the first rotary reflecting surface, and is between the first lens of the transfer optical system and the first rotary reflecting surface on the optical axis of the transfer optical system. The optical scanning device according to claim 1, wherein the image forming point is located. 7. The optical scanning device according to claim 1, wherein the shield plate is adjustable in a direction orthogonal to the optical axis of the transmission optical system. 8. A base member that supports an optical component that constitutes the transmission optical system or the optical scanning device, and the shielding plate is formed integrally with the base member. The optical scanning device described. 9. The shield plate is provided at an angle different from a right angle with respect to a surface formed by sweeping a light beam deflected by the light beam deflected by the first rotary reflecting surface in the transmission optical system. The optical scanning device according to claim 1, wherein the optical scanning device is provided.