JPH06317758A - Optical scanning device and manufacturing method therefor - Google Patents

Abstract

PURPOSE:To provide an optical scanning device without the irregularity of scanning pitch and the deviation of a scanning position by positioning plural optical elements so as to be symmetric about the rotary shaft. CONSTITUTION:Projections 141 for positioning in the direction of the rotary shaft at three places and projections 142 for positioning in the radial direction at two places are provided on the bottom surface of a lens mirror 14 and the plural lens mirrors 14 are positioned so as to be symmetric about the rotary shaft 131. Namely, in order to fix the lens mirrors in such a positioning direction, they are pushed against the directions of a positioning surface 134 in the direction of rotary shaft and a positioning surface 135 in the radial direction. The foot part of a fixing spring is engaged with the notch 136 for mounting the fixing spring of a supporting plate 132 and the lens mirrors 14 are pushed against the positioning surface 134 in the direction of rotary shaft by means of an arm part. The lens mirrors 14 are exerted by centrifugal force as a motor 130 rotates and, by being automatically pushed against the positioning surface 135 in the radial direction, they are fixed while being positioned.

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 laser printers, facsimiles and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A rotary polygon mirror used in a conventional optical scanning device such as a laser beam printer usually has a parallelism error of each surface caused in the manufacturing process of the polygon mirror, and the polygon mirror needs to be attached to a rotary shaft. There is an error caused by this, and the traveling direction of the reflected light beam changes in a plane perpendicular to the deflection surface, resulting in uneven scanning pitch. Therefore, in order to reduce such errors so that pitch unevenness cannot be observed on the image, it takes a long time for the manufacturing process such as processing of the polygon mirror,
It becomes extremely expensive due to deterioration of manufacturing yield. Therefore, conventionally, various ideas have been made to correct this.

JP-A-48-49315 and JP-A-56-
The conjugate tilt correction method disclosed in Japanese Patent No. 36622 uses an anamorphic scanning optical system in which the powers of a deflecting surface (hereinafter referred to as a main scanning surface) and a surface perpendicular to the deflecting surface (hereinafter referred to as a sub-scanning surface) are different. On the sub-scanning surface, a light beam is imaged on the reflecting surface of the rotary polygon mirror so that the reflecting surface and the photoconductor surface are optically conjugate.

Further, in the relaxation type tilt correction system disclosed in JP-A-52-153456 and JP-A-58-134618, a long cylindrical lens is arranged in the vicinity of the surface of the photosensitive member, and a sub-scanning surface due to surface tilt occurs. The change in the deflection direction of is reduced.

Further, the polygon index correction method disclosed in Japanese Patent Laid-Open No. 3-100620 uses a two-sided polygon mirror having a surface tilt error, and the fact that it is two surfaces allows the amount of relative surface tilt of each surface to be corrected. The rotary polygon mirror mounting position is set so that is almost zero.

[0006]

However, in the above-mentioned conjugate type, a toroidal lens that requires a special manufacturing method must be used as compared with a spherical lens, and if a cylindrical lens is used, a large number of lenses are required. Inevitably it became expensive, and it also led to an increase in the size of the device. Further, in the case of the relaxation type described above, there is a problem that it is expensive because it requires a long cylindrical lens, and the tilt correction magnification is low. Furthermore, in the polygon indexing method, the optical system itself has nothing special. Although it does not require such a thing, it requires a step for adjusting so as to eliminate a relative tilt error between the two reflecting surfaces, resulting in a high cost.

Further, the image forming apparatus such as a laser printer using the above-mentioned optical scanning device is inevitably large in size and high in price, and the downsizing flow of OA equipment such as personal computers in recent years and the flow toward personal use. It was an obstacle.

The present invention has been made to solve the above-mentioned problems, and provides an optical scanning device which simultaneously realizes miniaturization, cost reduction and high performance.

[0009]

That is, the present invention provides an optical scanning device for achieving the above-mentioned problems, wherein a part of means for supporting a plurality of optical elements around a rotation axis is provided with the plurality of optical elements. Is provided with a portion for positioning so as to be symmetrical with respect to the rotation axis, and as a method for manufacturing this device, means for positioning and supporting a plurality of optical elements so as to be symmetrical with respect to the rotation axis, First, it is fixed to the rotary shaft, and then the positioning portion on the supporting means is processed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The basic configuration of the optical scanning device of the present invention is such that a plurality of optical elements are rotated around one rotation axis by a driving device such as a motor, and a light beam is output each time the light beam passes through one optical element. The deflection scanning is performed by the scanning amount. Therefore, by arranging a plurality of optical elements, a plurality of scans can be performed with one rotation. Here, the optical element may be composed of only a reflecting surface such as a plane mirror or a curved mirror, or may be an element that transmits light like a prism. Japanese Patent Application by application 4-16
A combination of a lens and a reflecting mirror as disclosed in No. 6042 may be used. When a plurality of these optical elements are arranged, the scanning line pitch unevenness occurs due to the arrangement accuracy and shape accuracy of the individual optical elements as in the case of the rotary polygon mirror described above. It was designed so that it could be easily removed by paying attention to the characteristics of the arrangement.

The basic idea of the tilt error removal of the deflecting device of the present invention is devised so that the positions and angles of the respective elements are not absolutely precise, but relatively accurate. It is a thing. The relative positional relationship in which the scanning line pitch unevenness does not occur even if the absolute accuracy is not high will be described with reference to FIG. Each element M as shown in FIG.
1 and M2 move around the axis Z while drawing a rotation locus. When the element M1 rotates, the element M1 passes through the position that existed before the element M2 rotated, but at that time, if the element M1 is at the same position as the element M2 and has the same posture, it is incident. Since the position and direction of the luminous flux are constant, the outgoing luminous flux passes through exactly the same path. Since each element rotates on the same axis, in such a state, the elements M1 and M2 always pass on the same rotation locus, and the scanning line pitch unevenness does not occur. Now, the conditions for drawing the same rotation trajectory in this way will be clarified. First, as shown in FIG. 2, a coordinate system O-X, Y, Z fixed to the rotation axis and a coordinate system Oi-x, y, z fixed to each element are defined. The position of the origin Oi of the coordinate system fixed to each element is converted into a cylindrical coordinate system display defined by X = r · cos θ Y = r · sin θ Z = z (r, θ, z)
Express. In addition, the degree of freedom of the posture of the coordinate system Oi fixed to each element is the rotation angle (α, β, γ) around the coordinate axes x, y, and z.
It is represented by. However, when r, θ, z, α, β, and γ are all 0, Oi-x, y, and z take α, β, and γ so as to match O-X, Y, and Z. Here, the coordinate system O of each element
If the coordinate systems can be made to coincide with each other when i is rotated about the rotation axis, that is, θ of the position and orientation (r, θ, z, α, β, γ) of the coordinate system Oi of each element The same locus can be drawn if positioning can be performed so as to take the same value except for. In the description of the present invention, such a case is defined as being arranged symmetrically with respect to the rotation axis.

By the way, in the case of the rotary polygon mirror described in the conventional example, the tilt error only appears in the scanning line pitch unevenness because it is a plane mirror. However, in the present invention, not only the plane mirror but also an element having various refractive powers as an optical element. In this case, an error in the mounting position or the like generally causes not only uneven scanning pitch but also deviation of the spot position in the main scanning direction for each scanning line. This also does not occur if the above-mentioned rotational axis symmetry is satisfied. The deviation of the spot position and the unevenness of the scanning pitch are collectively called a scanning position deviation. Further, even if the optical parameters such as the shape and the refractive index of each optical element are not the same other than the mounting position of each optical element, the scanning position shift occurs.

An image forming apparatus equipped with the optical scanning device according to the present invention will be described below.

3a and 3b are a front view and a side view of this apparatus. A light beam emitted from a semiconductor laser 11 is collimated by a collimator lens 12 and then deflected by a deflecting device 13.
Then, after being deflected in the main scanning direction and passing through the imaging lens 15 and the folding mirror 16, a spot is formed on a photosensitive drum (not shown). The semiconductor laser is modulated in accordance with the recorded information, and while the intensity-modulated light spot is raster-scanned in the main scanning direction on the photosensitive drum, the photosensitive drum rotates and is sub-scanned to cause a latent image on the photosensitive drum. An image is formed. Further, the horizontal synchronization sensor 17 is provided outside the image area of the scanning range in order to align the scanning line start positions in the main scanning direction. In order to simplify the device and prevent malfunction due to noise, the horizontal synchronization sensor 17 is installed near the semiconductor laser 11, and the sensor mirror 1
The luminous flux is guided by 8. Semiconductor laser 11,
Collimator lens 12, deflection device 13, imaging lens 1
5, the folding mirror 16, the horizontal synchronization sensor 17, and the sensor mirror 18 are fixed and housed in the optical case 10 so that the positional relationship between them is easy to obtain and are not easily affected by dust and the like.

FIG. 4 shows the deflecting device 13. The deflecting device 13 described later is a shaft 131 of a motor 130.
The lens mirror 14 is mounted on the support base 132 fixed to the. The deflecting device 13 is one in which the reflecting surfaces R of the two lens mirrors 14 and 14 are arranged so as to face each other back to back, as disclosed in Japanese Patent Application No. 4-258406 by the present applicant. As described in detail in Japanese Patent Application No. 4-166042 disclosed by a person, the entrance surface S1 and the exit surface S2 of the lens mirror 14 are shaped so as to perform predetermined aberration correction, and are extremely small. It is configured as a low-cost scanning optical system. Because
In order to correct the field curvature aberration, astigmatism, and distortion that are required in the case of ordinary laser beam printers,
In an optical system that uses an inexpensive axisymmetric shape,
If a sufficient scanning angle is taken for downsizing, two or more imaging lenses are required. According to this lens mirror 14, the degree of freedom for aberration removal is equal to that.
In addition, the lens action and the function of the deflecting mirror are performed by one component so that the number of expensive optical components is not increased.

The material of the lens mirror 14 is preferably an optical plastic such as polymethylmethacrylate (PMMA) or polycarbonate, or an optical glass. In this embodiment, it is manufactured by injection molding using PMMA, and aluminum is evaporated on the reflecting surface. is doing.

Next, the optical design values of this embodiment are shown below according to the method of describing the parameters in FIG. All lens surfaces are spherical.

Surface number Radius of curvature Surface spacing Refractive index (mm) (mm) # 1 R1 = −13.32 d1 = 10 n1 = 1.480 # 2 Plane d2 = 10 n2 = 1.480 # 3 R3 = −19 .81 d3 = 12 n3 = 1.000 # 4 R4 = 162.79 d4 = 3 n4 = 1.511 # 5 R5 = −199.72 d5 = 175 n5 = 1.000 The scanning width is 210 mm by the above optical system. The field curvature is ± 2 in both meridional and sagittal directions.
High-resolution scanning characteristics within 5 mm and fθ characteristics within 1.4% are obtained.

Next, regarding the structure for attaching the optical element to the motor, a perspective view of FIG. 4 and a front view of FIGS.
This will be described with reference to a side sectional view. The support base 132 is provided with a rotational axis direction positioning surface 134, a radial direction positioning surface 135, and a fixed spring mounting notch 136. The rotation axis direction positioning surface 134 has sufficient verticality with respect to the rotation axis and flatness of the surface so that fluctuations of the respective portions of the positioning surface 134 in the rotation axis direction are negligible when rotated about the rotation axis. It is formed so that it can be secured.
The radial positioning surface 135 is formed so as to ensure sufficient cylindricity with respect to the rotation axis so that the variation of the distance of each part of the positioning surface 135 from the rotation axis becomes small when rotated about the rotation axis. ing. This can be done by fixing the support base 132 to the motor shaft 131 and then cutting or grinding the rotary shaft direction positioning surface 134 and the radial direction positioning surface 135 while rotating the motor shaft 131, as described later.

On the other hand, the lens mirror 14 is provided with three rotation axis direction positioning projections 141 and two radial direction positioning projections 142 on the bottom surface. The rotational axis direction positioning protrusion 141 contacts the rotational axis direction positioning surface 132 at all three points at the apex. As a result, the lens mirror 14
Will be constrained on a plane perpendicular to the axis of rotation. In addition, the radial positioning projections 142 contact the radial positioning surface at all two points on the side surface. This makes the lens mirror 1
The movement of 4 is restricted except for the rotation around the rotation axis. This will be described with reference to the coordinate system of FIG.
By positioning the points, the coordinate system Oi-x, y,
z is allowed to move only in the XY plane of the coordinate system O-X, Y, Z fixed to the rotation axis, that is, three of z, α, and β among the six degrees of freedom representing the position and orientation. The degrees of freedom are deprived, and the degrees of freedom of r, θ, and γ are left. Furthermore, by positioning in the radial direction, that is, by positioning at two points on a cylindrical surface with a constant r,
The two degrees of freedom of r and γ are deprived, and the degree of freedom of only θ remains (however, when the coordinate axes Z and z substantially match as shown in FIG. 7, the rotations of γ and θ also match, so γ It seems that the degree of freedom is also left). This is a condition of the rotational axis symmetry described above, and each element draws the same locus as the motor 130 rotates.

The fluctuation of the rotation θ around the rotation axis does not affect the scanning position shift as described above and causes a change in the image writing timing on each scanning line, but the horizontal synchronizing sensor 17 causes the image writing position. Are aligned so they have no effect on the image.

Next, a method of fixing the lens mirror 14 to the support base 132 will be described with reference to the perspective view of FIG. In order to fix the lens mirror 14 in the above-mentioned positioning direction, the rotation axis direction positioning surface 134 and the radial direction positioning surface 1
Press in the direction of 35. The foot 145 of the fixed spring 144 has a notch 1 for mounting the fixed spring of the support base 132.
The lens mirror 14 is pressed against the positioning surface 134 in the rotation axis direction by the arm portion 146 by engaging with 36. Further, as the motor 130 rotates, the lens mirror 14 receives a centrifugal force and is automatically pressed against the radial positioning surface 135 so that the lens mirror 14 is positioned and fixed.
By thus supporting the lens mirror 14 in the direction in which the radial direction positioning surface 135 receives the centrifugal force, stable positioning can be performed even when the apparatus is operating.

Here, the conditions for stable positioning will be described with reference to the three views of FIGS. 8 and 9. First, since the positioning in the rotation axis direction can be stably performed in a stationary state, that is, since the three projections 141 for the rotation axis direction positioning are surely pressed against the rotation axis direction positioning surface 134, the pressing by the fixed spring is performed. It suffices for the force action line to pass through the area inside the triangle formed by the three points, which is shown by the diagonal lines in the figure. This is because all three points can be balanced with the resultant force of the reaction force having a positive value. Further, even when centrifugal force is applied during rotation, the radial positioning can be stably performed, that is, the radial positioning protrusion 142 is 2
In order to ensure that both points are pressed against the radial positioning surface 135, the line of action of centrifugal force may pass through the line segment connecting the two points in the plane perpendicular to the rotation axis. In other words,
When an extension line of a straight line connecting the center of gravity G of the lens mirror 14 and the rotation axis Z perpendicularly and a line segment connecting the support positions of the two optical elements are projected on a plane perpendicular to the rotation axis, the two straight lines intersect each other. That's good.

Further generalizing the method for stable positioning, it will be understood that all the forces acting on the five support points may take positive values. There are various cases depending on the relationship of the position of the positioning point and the position and direction of applying the fixing force, but in any case, it can be obtained from the relationship of the balance of 3 degrees of freedom of position and 2 degrees of freedom of rotation. it can.

By the way, as described above, the lens mirror 1
Although 4 is made of an optical plastic, the optical plastic generally has low rigidity and photoelasticity characteristics, so that excessive stress causes deformation and distribution of the refractive index to deteriorate the optical performance. Generally, it is desirable that the force applied by the fixed spring 144 to the lens mirror 14 is about 2 kg or less, and the reaction force from the support base 132 applied to the positioning portion is also about 2 kg or less.

Now, after the support base 132 is attached to the motor shaft 131, the positioning portion of the support base 132 is machined so that the axial positioning surface 13 with respect to the rotary shaft is formed.
A method for making the verticality of No. 4 and the cylindricity of the radial direction positioning surface 135 highly accurate will be described. As a method, the support base 13
2 is fixed to the rotary shaft by a method such as press-fitting, the rotary shaft is chucked coaxially with a shaft of a lathe or a grinding machine, and is cut or ground while rotating around the rotary shaft, and the motor shaft 131 is supported. The motor that the platform 132 is integrated is
There is a method in which the motor 130 is rotated and then cut or ground after being attached to the unit 30 and manufactured until it can be rotated. At that time, a feed component force of cutting or grinding resistance, that is, a drag component perpendicular to the processing surface is added, so that the member is processed in a bent state, and as a result,
It should be noted that flatness cannot be ensured in the case of flat surface processing and cylindricity cannot be ensured in the case of cylindrical processing. For example, in the case of cutting, the rigidity of the support member and the rotary shaft,
This can be avoided by appropriately setting conditions such as the rigidity of the bearing that supports the rotating shaft, the free cutting property of the material, the cutting depth, the cutting speed, and the cutting temperature. The precision of the support base 132 processed in this way can be finished so that the amount of deviation from the ideal position is about 1 μ. For example, the radius of the circumscribed circle of the triangle formed by the three points for axial positioning is 10
If it is mm, the angle error of the reflecting surface of the lens mirror 14 is about 20 seconds, and the scanning pitch unevenness can be made sufficiently small. Comparing this with the case of machining a rotary polygon mirror, in the case of mirror grinding of a commonly used rotary polygon mirror, the work piece or tool is moved when processing one surface to another. It is very difficult to do so with high accuracy as described above. Furthermore, in the case of mirror surface processing, the processing speed is slow and the processing cost is high by preventing multiple polygon mirrors from being processed at the same time, and therefore processing must be performed separately from the rotary shaft. It is difficult to avoid errors due to mounting. As described above, the manufacturing method of the present invention can make use of the accuracy that can be achieved by cutting or grinding by uniaxial rotation as it is, so that high accuracy can be easily achieved.

However, if the precision of the shape and the precision of the refractive index of each optical element are not secured, even if the precision of the support base 132 is secured by the above-described processing method, the scanning position shift will occur. This can also be solved by the method of the present invention, for example, by forming a lens mirror by injection molding using optical plastic. The method is described below. Note that it is not necessary to ensure absolute accuracy in terms of shape accuracy and refractive index accuracy, and it is sufficient if each element is relatively aligned. Regarding the shape accuracy, the cause of the error may be due to the mold transfer property at the time of molding or the shape accuracy of the mold. With respect to the former, various methods have already been realized for forming with extremely high precision. For example, there are a method for accurately controlling the mold temperature in ordinary injection molding, an injection compression method for narrowing the cavity volume after filling by allowing for shrinkage of the resin during molding, and a gate sealing method for cooling the gate after injection by blocking. . Whichever method is used, it is possible to make the shape repeatability 1 μm or less. However, with regard to the latter, it is extremely difficult to bring the precision of a die manufactured by machining such as cutting and grinding to a submicron level. Here, focusing on increasing the relative accuracy, which is the basic idea of the present invention, and the repeatability of the molding process, if only those molded from the same mold are always collected and used, it will be There is almost no error in relative accuracy due to this, and scanning position shift due to element shape accuracy does not occur. When molding a large number of dies in order to improve productivity, each cavity may be marked so as to distinguish the cavities, and only the elements having the same marking may be collected and used.

Also, the optical characteristics change due to the difference in the refractive index of each element, and the scanning position shift occurs. This is because the optical plastic material is slightly different depending on the manufacturing lot and the molding conditions are slightly different. Occurs. Therefore, this problem can be solved by using the elements of the same lot and molding the elements as close to each other as possible.

Although the configuration of the optical scanning device in which the scanning position deviation does not occur has been described above, the meaning that the scanning pitch unevenness does not occur is naturally suppressed to a value equal to or lower than a value at which sufficient image quality can be determined. That is exactly 0
It doesn't mean that. According to a study made by the present inventors, the scanning line pitch unevenness is 10 to 20 μm or less with respect to the reference scanning line position and the spot position deviation in the main scanning direction is 20 to 40 μm or less regardless of the image recording density. Almost invisible. How much the mounting accuracy of each optical element should be set in this embodiment to satisfy this condition is shown in FIG. This value naturally varies depending on the optical system, but in general, the scanning position deviation is not largely deviated from the above-mentioned reference as long as it is within the value of the following formula.

R <20 μm z <100 μm α <20 seconds β <20 seconds γ: No strict precision is required. As described above, the present invention has an effect that the scanning pitch unevenness can be corrected with a simple structure. Furthermore, it has been discovered that the present embodiment also has the effect that the optical performance does not deteriorate due to the movement of the deflection point that deflects the light beam by the rotating mirror. This is because, as shown in FIG. 7, in the case of the rotating polygon mirror, the center of rotation is not on the reflecting surface, so when comparing the center portion and the end portion of the polygon mirror surface, the end portion produces a light beam on the outer peripheral side of the rotation circle. Will be reflected. This means that the entrance pupil position fluctuates asymmetrically due to changes in the angle of view, and field curvature aberration and distortion aberration appear due to it. In particular, when the image forming spot is made smaller so that high density recording is performed, for example, when the spot size is 50 μm or less, it has a great influence. On the other hand, if the rotating mirror of the present invention is used, the center of rotation can be set on the reflecting surface, and the fluctuation of the entrance pupil position is eliminated. Therefore, a scanning optical system with high recording density can be realized.

Next, an embodiment in which the present invention is applied to an image forming apparatus will be described with reference to the side sectional view of FIG. In this embodiment, a compact high resolution laser printer is constructed by using the embodiment of the optical scanning device described above.

In the image forming process, while the photosensitive drum 2, which is an electrostatic latent image carrier having an organic photoconductor (OPC) formed on a conductive substrate, rotates, an elastic conductive material having a predetermined charging bias potential applied thereto. Process for uniformly charging the photosensitive drum 2 by the contact charging device 3 which is an electrostatic roller, an image exposure process for forming an electrostatic latent image on the photosensitive drum 2 by the exposure unit 1 which is the optical scanning device described above, and a predetermined development Development process for developing an electrostatic latent image on a photosensitive drum 2 into a toner image by a non-magnetic one-component pressure contact developing device 4 which is an elastic conductive roller to which a bias potential is applied and whose surface is coated with toner in a thin layer. , A transfer process for transferring a toner image on the photosensitive drum 2 onto a recording material by a roller transfer device 5 which is an elastic conductive roller to which a predetermined transfer bias is applied, a heater 6 Heating roller 61 which is heated by the
A fixing device 6 including an elastic pressure roller 62 heats and presses the recording material 8 so that the toner image on the recording material 8 is melted and solidified and fixed, and is not transferred onto the photosensitive drum 2. The cleaning process is performed in which the toner remaining on the toner is collected by the blade 7. As the charging method, corona charging, brush charging, etc., as the developing method, a two-component developing method, a magnetic one-component developing method,
It is also possible to use a corona transfer method as a transfer method such as a non-contact developing method. However, the present invention has an effect that it is possible to realize an image forming apparatus that is small in size, low in cost, and high in resolution at the same time, and in order to make use of the effect further, the configuration of the above embodiment Is desirable.

Further, in the apparatus of this embodiment, the toner circulation mechanism disclosed in Japanese Patent Application No. 4-315348 filed by the applicant of the present invention, that is, toner not shown in the toner path 21 which circulates the developing device and the cleaner endlessly is shown. Since a mechanism for providing a replenishing container is used, a waste toner container is not necessary, and the toner replenishing container can be arranged relatively freely, which is more suitable for downsizing of the apparatus.

The printer of this embodiment has a resolution of 600 dots / inch, a printing speed of 3 sheets / minute, and an apparatus size of about 10 liters or less in volume, and has a high resolution and an extremely small size. Here, the volume of the exposure unit occupying therein is about 0.4 liters or less, which is 1/2 to ⅕ of the volume of the exposure unit used in the conventional laser printer and medium resolution 300 DPI. Has become. Further, since the cost of the exposure apparatus is lower than that of the conventional one, the cost of the entire apparatus is reduced. This is because the optical scanning device of the present invention can be configured with a simple optical system that does not require a tilt correction optical system as compared with the conventional optical scanning device, and further, the adjustment process is unnecessary and the manufacturing cost is low,
Further, since the optical system using the solid lens mirror in the present embodiment can be used, it is possible to reduce the size and cost of the scanning optical system. As described above, it can be seen that by constructing the image forming apparatus with the optical scanning apparatus of the present invention, remarkable progress can be achieved as compared with the conventional image forming apparatus.

Several other embodiments of the present invention will be described below.

First, the second embodiment shown in the exploded perspective view of FIG. 12 for explaining three embodiments in which elements other than lens mirrors are used as optical elements is the one having the same optical function as the rotary polygon mirror. It is an optical scanning device constituted by the method of the invention.
The difference from the above-described first embodiment is that four mirror elements 204 each having a plane mirror surface are installed on the support base instead of the lens mirrors. The mirror element 204 is manufactured by injection molding of resin such as polycarbonate, and a vapor deposition film of aluminum is formed on the reflection surface of the surface. Also in this embodiment, by forming the mirror element 204 from the same mold and using the same support base structure as in the previous embodiment, the tilt correction optical system becomes unnecessary and a simple scanning optical system is sufficient. by the way,
Conventionally, the rotary polygon mirror was manufactured by mirror grinding of aluminum, but recently, technological development for manufacturing by injection molding of plastic has been actively performed to reduce the manufacturing cost. The most difficult problem in that case is that the scanning position in the main scanning direction shifts for each scanning line and the image quality deteriorates even if the flatness of each of the reflecting surfaces of the polygon mirror slightly shifts. Therefore, it is necessary to select a polygonal mirror in which all surfaces can be manufactured with high precision, and the manufacturing yield is very low. However, according to the present invention, since the reflecting surface of each element is formed by transferring the surface of the same mold, the surface shapes are highly uniform and the scanning position is hardly displaced. Further, even if an element having a poor shape accuracy appears, only the element needs to be replaced, so that the yield is remarkably high as compared with the case where the entire surface of the polygon mirror requires a good product. As described above, it is extremely easy to reduce the cost by using plastic as compared with the conventional polygon mirror.

The third embodiment shown in the exploded perspective view of FIG. 13 is one in which the present invention is applied to an optical system using a curved rotary polygon mirror as disclosed in, for example, Japanese Patent Laid-Open No. 1-116516. The curved rotary polygon mirror has some of the functions of the scanning optical system.
By making the reflecting surface of the rotating polygonal mirror a curved surface, the reflecting surface is provided, and the scanning optical system is simplified. The deflecting device of this embodiment is the same as that of the second embodiment except that the reflecting surface of the curved mirror element 304 is a curved surface. When the curved polygonal mirror is manufactured by grinding, the manufacturing cost is higher than that of the flat surface, so that the demand for plasticization is greater than in the second embodiment. Also in the present embodiment, the present invention can eliminate the obstacles when plasticizing the polygonal mirror as described above, so that the combination with the curved polygonal mirror is highly effective.

In the case of this embodiment, in order to secure the symmetry with respect to the optical axis in the main scanning direction, it is necessary to enter the light beam from the front side in the main scanning direction, and therefore a predetermined angle is set in the sub scanning direction. It will be configured to be incident.

In the fourth embodiment shown in the exploded perspective view of FIG. 14, instead of the lens mirror 14 of the first embodiment, a lens mirror 404 having an entrance surface and an exit surface on the same surface, and a reflecting surface having a curvature. Is used. In the case of the present embodiment, as in the case of the first embodiment, the surface of the lens mirror that performs the lens function is
Since there is a surface and the degree of freedom of optical parameters is large, a high-resolution and small-sized optical system can be obtained. Moreover, since the number of optical elements can be made larger than that of the lens mirror 14 of the first embodiment, it is possible to cope with high speed. Also in the case of this embodiment, front incidence in the main scanning direction is required as in the case of the third embodiment.

Next, three examples of the supporting structure of the optical element will be described.

In the fifth embodiment shown in the front view and the sectional view of FIG. 15, a flange portion 241 is provided on the optical element 14, and the flange portion 241 is utilized to attach the flange portion 241 to the support base 132. The optical characteristics of the optical element 14 are the same as those of the lens mirror 214 of the first embodiment. The flange portion 241 is provided on the bottom surface of the lens mirror 214, and
The strength of No. 4 and the handling at the time of assembly can be improved.
The positioning protrusion is provided on the flange portion 241.
As a result, it is possible to prevent a reaction force from being applied to the lens mirror 214 due to the centrifugal force at the time of rotation so that the lens mirror 214 is slightly deformed or the optical characteristics are deteriorated due to the change in the refractive index due to the distortion.

In the sixth embodiment shown in the front view and the sectional view of FIG. 16, the radial positioning surface 135 of the support base 332 is a cylindrical outer surface, and the radial positioning projection 3 of the lens mirror 314 is used.
Positioning is performed by urging 42 from the outside toward the inside. In this case, since the support base 332 can be configured to be smaller than the size of the lens mirror 314, the moment of inertia of rotation can be reduced and the time required for activation can be shortened. In this embodiment, the lens mirror 314 is fixed to the support base 332 by adhesion. In the case of bonding, in order to prevent a large amount of adhesive from flowing between the support and the positioning protrusions to cause a positioning error, bonding is performed under pressure contact. As the adhesive, epoxy resin, polyester resin or the like is desirable.

The seventh embodiment shown in the sectional view of FIG. 17 is one in which a positioning portion is provided on the rotor of the motor without preparing any part as a support base. The motor 437 of this embodiment is a DC brushless motor, and the rotor 432 is provided with permanent magnets provided with appropriate magnetic poles. The motor shaft 431 is fixed, and the rotor 432 is rotatably attached to the motor shaft 431 via a bearing 433. The rotating shaft in this case is also the same as the motor shaft 431. In the case of the present embodiment, it is not necessary to prepare a special part as a support base, and thus cost reduction can be achieved.

The eighth embodiment shown in the perspective view of FIG. 18 is a fixed spring so that the urging force for fixing the optical element to the support is applied in the direction of pressing both the rotational axis direction positioning surface and the radial direction positioning surface. The projection 543 for receiving is attached to the lens mirror 51.
4 is provided. Biasing projection 5 of fixed spring 544
Reference numeral 45 urges the lens mirror 514 in the direction of the arrow in the figure by the leaf spring action of the arm portion 546. In this case, in the first embodiment, as described with reference to FIG. 9, the radial-direction positioning projection 1 does not need to be affected by the centrifugal force generated by the rotation.
42 is pressed against the radial positioning surface 135 of the support base 132 for stable positioning. Further, in the configuration of this embodiment, the lens spring 51 is fixed by the fixed spring 544.
Since the point where a load is applied to 4 is away from the optical path in the lens mirror 514, it is possible to prevent the deformation caused by the excessive stress as described above and the deterioration of the optical performance due to the distribution of the refractive index.

Next, a ninth embodiment in the case where there is some variation in the optical element will be described.

In the first embodiment, it has been explained that if precision injection molding is performed for the optical elements using the same mold, a relative error between the elements hardly occurs. However, when higher precision is required, As described below, the optical element is actually passed a light beam to measure the scanning position, and the optical element is classified by the number of divisions so that the error falls within the allowable range and combined with the same classification. Relative errors due to variations will not occur.

FIG. 19 shows the measuring method. An optical element 614 is installed on a measuring table 632 having the same shape as a supporting table used in an optical scanning device to be incorporated, and a light beam emitted from a semiconductor laser 611 and made into parallel light by a collimator lens (not shown) is optically reflected. Imaging lens 61 used in an optical scanning device to be incident on the element and incorporated therein
After passing 5, the two-division optical sensor or line CC capable of detecting the spot position in the sub-scanning direction near the image formation position
An image forming position sensor 617 such as a D sensor is arranged to detect the image forming position, and the control device 620 reads the scanning position deviation amount. At this time, the support base 632 is slightly rotated so that the spot surely enters the imaging position sensor 617. The scanning pitch unevenness can be suppressed by classifying the elements by about 10 μm according to the value of the imaging position and combining the elements classified into the same.

Next, instead of actually measuring the image forming position through the light beam as in the ninth embodiment, an embodiment will be described in which the shape accuracy of the reflecting surface, which is most sensitive to the scanning pitch unevenness, is directly measured as described above. . Also in this embodiment, similarly to the ninth embodiment, the lens mirror 614 is installed on a measuring table having the same shape as the supporting table used in the optical scanning device in which the lens mirror 614 is to be incorporated, and the inclination of the reflecting surface is tilted by the shape measuring instrument. To measure. As the measuring device, a contact-type measuring device, a non-contact-type measuring device such as a laser scanning micrometer, an interferometer for measuring by using interference fringes of incident light and reflected light, or the like can be used. The scanning pitch unevenness can be suppressed by classifying the elements every 20 seconds according to the measured inclination value of the reflecting surface and combining the elements classified into the same class.

By the way, in the above-mentioned embodiments, the description has been given assuming that all the positioning surfaces in the rotation axis direction are one plane perpendicular to the rotation axis, but the invention is not limited to this, and a shape capable of restraining the movement in the axial direction. If it is good. Eg 2
A step may be provided on one surface to be used as a positioning surface.
Further, although the radial positioning surfaces of the above-described embodiments are all described as cylindrical surfaces, the present invention is not limited to this and may be any shape that can restrain radial movement. For example, a conical surface or the like can be used.

Further, in the above-described embodiment, the example in which the image forming apparatus is applied to the laser printer has been described, but it can be widely applied to the facsimile, the digital copying machine and the like. Further, although it has been described that the optical scanning device of the present invention exerts a remarkable effect by being applied to an image forming device, other than that, it is widely applied to an image reading device, a bar code scanner, a laser display and the like. it can.

[0051]

As described above, according to the present invention, an optical scanning device which deflects and scans a light beam by rotating a plurality of optical elements about a rotation axis is arranged so that the plurality of optical elements are symmetrical with respect to the rotation axis. Since it is positioned so that the tilt correction function is unnecessary, the device can be simplified.
Moreover, it is possible to realize an optical scanning device that does not have scanning pitch irregularities or scanning position deviations without using expensive and highly accurate parts such as a rotary polygon mirror.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating the principle of the present invention.

FIG. 2 is a diagram showing a coordinate system for explaining the principle of the present invention.

FIG. 3 is a front view (a) and a side view (b) for explaining an optical scanning device according to an embodiment of the invention.

FIG. 4 is an exploded perspective view illustrating a deflecting device according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining optical parameters of the optical system of the present invention.

FIG. 6 is a front view (a) and a side view (b) for explaining a deflecting device according to an embodiment of the present invention.

FIG. 7 is a diagram showing a coordinate system for explaining the positioning principle of the embodiment of the present invention.

FIG. 8 is a trihedral view showing a positioning condition according to the embodiment of the invention.

FIG. 9 is a trihedral view showing a positioning condition according to the embodiment of the invention.

FIG. 10 is a diagram for explaining movement of a reflection point that occurs in a conventional rotary polygon mirror.

FIG. 11 is a side view showing an embodiment in which the present invention is applied to a laser printer.

FIG. 12 is an exploded perspective view showing a second embodiment of the present invention.

FIG. 13 is an exploded perspective view showing a third embodiment of the present invention.

FIG. 14 is an exploded perspective view showing a fourth embodiment of the present invention.

FIG. 15 is an exploded perspective view showing a fifth embodiment of the present invention.

FIG. 16 is a front view (a) and a side view (b) showing a sixth embodiment of the present invention.

FIG. 17 is a side view showing a seventh embodiment of the present invention.

FIG. 18 is an exploded perspective view showing an eighth embodiment of the present invention.

FIG. 19 is a perspective view showing a ninth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 semiconductor laser 12 collimator lens 13 deflector 14 lens mirror 15 imaging lens 131 rotation axis 132 support stand 134 rotation axis direction positioning surface 135 radial direction positioning surface 141 rotation axis direction positioning projection 142 radial direction positioning projection

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kata Takada 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (16)

[Claims] 1. A part for supporting a plurality of optical elements around a rotation axis is provided with a part for positioning the plurality of optical elements so as to be symmetrical with respect to the rotation axis. Optical scanning device. 2. The optical scanning device according to claim 1, wherein the supporting means is provided with a surface perpendicular to the rotation axis for positioning the optical element in the axial direction. 3. The support means is provided with a portion for positioning the optical element in a radial direction.
Or the optical scanning device according to 2. 4. The optical scanning device according to claim 1, wherein the supporting means is provided with a cylindrical surface portion around the rotation axis for positioning the optical element in the radial direction. 5. The optical scanning device according to claim 1, wherein there are three axial positioning positions of the optical element. 6. The optical scanning device according to claim 1, wherein there are two radial positioning positions of the optical element. 7. The optical scanning device according to claim 1, wherein the supporting means is provided with means for pressing the plurality of optical elements in the axial direction and / or the radial direction. 8. The pressing means is arranged so that a straight line drawn in a pressing direction from a point of pressing the optical element passes through the inside of a triangle formed by the three axial positioning points. The optical scanning device according to claim 1 or 7, wherein a directional positioning portion is set. 9. When an extension line of a straight line orthogonal to the rotation axis and passing through the center of gravity of the optical element and a line segment connecting the two radial positioning points are projected on a plane perpendicular to the rotation axis, 7. The optical scanning device according to claim 1, wherein the radial position is set so that two straight lines intersect. 10. The optical scanning device according to claim 1, wherein the plurality of optical elements have the same shape. 11. The optical element according to claim 1, wherein the plurality of optical elements are molded by the same mold.
The optical scanning device described. 12. The optical scanning device according to claim 1, wherein a plurality of the optical elements are combined and arranged on the supporting means based on a characteristic value representing a variation of the optical elements. 13. The characteristic value is a measured value of a scanning line position of the optical element.
The optical scanning device described. 14. The optical scanning device according to claim 1, wherein the characteristic value is a shape measurement value of the optical element. 15. The optical scanning device according to claim 1, wherein the optical element includes a reflecting surface, and an entrance surface and an exit surface whose shapes are determined so as to correct a predetermined aberration. 16. A means for positioning and supporting a plurality of optical elements so as to be symmetrical with respect to a rotation axis is first fixed to the rotation axis, and then a positioning portion on the support means is processed. And a method for manufacturing an optical scanning device.