JP2650529B2 - Optical printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deflection scanning device used in an optical system for exposure such as a laser beam printer or the like, and comprises a protective cover for covering a rotating mirror rotating at a high speed to deflect a light beam with a protective cover. It relates to a scanning device.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic configuration of a conventional laser beam printer using a deflection scanning device. The laser diode 1 emits a laser beam pulse-controlled by the laser drive circuit 2. The laser beam is shaped into a parallel beam by the collimator lens 3,
The beam is deflected by the rotating polygon mirror 5, narrowed down by the Fθ lens 6, and forms an image on the surface of the photoconductive photosensitive drum 7 to form a minute beam spot. The beam spot is scanned by the rotation of the rotary polygon mirror 5. In an electrophotographic recording type laser beam printer, a charger 9, a developing device 10,
The transfer device 11 and the like are arranged. The surface of the photosensitive drum 7, which is rotated in the direction of the arrow by a driving source (not shown), is uniformly charged by a charger 9, and is then scanned and exposed to a laser beam by the optical system to form an electrostatic latent image. It is formed. The developing device 10 is a one-component developer using magnetic fine powder toner or a two-component developer obtained by mixing a magnetic carrier and fine powder toner.
The electrostatic latent image is developed by rubbing the surface of the photosensitive drum 7 with a magnetic brush in which the component developer is attracted to a magnetic roll, and a toner image is formed on the surface of the photosensitive drum. On the other hand, the recording paper 12 conveyed by a paper feeding mechanism (not shown)
, And a transfer charge is given by the transfer device 11, and the toner image on the surface of the photosensitive drum is transferred to the recording paper 12.

A laser beam printer records predetermined information on a recording paper 12 by such an electrophotographic process. To realize these functions, a reflecting mirror 13 and a photodetector 14 for obtaining a synchronizing signal for synchronizing the modulation signal are provided.
And a synchronizing signal generating circuit 15, a printing signal control circuit 16, and a control circuit 17 for a rotary polygon mirror driving motor.

The rotary polygon mirror 5 in the optical system for exposure of the laser beam printer described above will be described.

The rotary polygon mirror 5 rotates at a constant speed to deflect the laser beam at each reflection plane. The shape, size, rotation speed, and the like are determined by the functions required of the optical system. The relationship will be described with reference to FIGS.

FIGS. 3A and 3B show the optical system of the laser beam printer shown in FIG. 2 extracted and projected on an xy plane and a yz plane according to the xyz coordinate axes defined in FIG. The peripheral speed V of the photosensitive drum 7 is determined by the printing speed of the printer, the light sensitivity characteristics of the photosensitive drum 7, and the output of the laser diode 1. That is, in order to perform high-speed printing, it is necessary to increase the peripheral speed V of the photosensitive drum. As the photosensitive drum 7 has higher light sensitivity and the laser diode 1 has higher output, higher-speed printing can be performed.

On the other hand, the number of reflecting surfaces of the rotary polygon mirror 5 is determined by the scanning width W of the optical system and the focal length fθ of the Fθ lens 6. That is, the Fθ lens 6 is designed so that the scanning position x on the surface of the photosensitive drum 7 becomes fθ × θm with respect to the deflection angle θm of the laser beam deflected by the rotary polygon mirror 5, and W and fθ are given. Then, the deflection angle is determined by the relational expression of 2θm = W / fθ, whereby the number of reflection surfaces Nm of the rotary polygon mirror 5 is determined by the geometrical relational expression of Nm = 2π / θm.

The rotational speed N of the rotary polygon mirror 5 is determined by the scanning line density in the sub-scanning direction (photosensitive drum rotation direction), the photosensitive drum peripheral speed V, and the number of reflection surfaces Nm of the rotary polygon mirror 5. That is, as the scanning line density is increased to achieve high-resolution printing and the number of reflecting surfaces of the rotating polygon mirror 5 is reduced, the rotating polygon mirror 5 is required to rotate at a high speed. In recent years, laser beam printers have tended to perform high-speed printing, high-resolution printing, miniaturization of the apparatus, and cost reduction. However, as is apparent from the above, the requirements of the rotary polygon mirror 5 are as follows.
That is, the result is that high-speed rotation is required with a large deflection angle.

In order to realize high-resolution image recording, the laser beam must be accurately deflected and scanned. On the other hand, the rotating polygon mirror 5 requires that the angle between the normal of each reflecting surface and the axis of rotation be changed. The beam spot has a non-uniform surface tilt, which causes the scanning position of the beam spot to shift in the rotation direction of the photosensitive drum 7 to cause uneven scanning line pitch.
FIG. 3B shows this relationship. For example, when the rotary polygon mirror 5 has a tilt angle of φ / 2, the deflected scanning beam tilts at an angle φ with respect to the optical axis. In other words, the scanning line pitch unevenness of δ is generated on the surface of the photosensitive drum 7 with respect to the rotation direction of the drum.

In order to reduce the scanning line pitch unevenness, it is necessary to manufacture the rotary polygon mirror 5 with high precision to minimize surface tilt. For example, the distance between the rotating polygon mirror 5 and the surface of the photosensitive drum 7 is 500 (mm), the scanning line pitch unevenness allowable on the surface is ± 0.01 (mm), and the correction effect due to the power of the Fθ lens 6 is ignored. when the allowable surface inclining angle of the rotary polygonal mirror 5 becomes ± (1/2 × 0.01 / 500) = ± 1 × 1/10 5 ( radian) (Equation 1) = ± 2 (s) . Even considering the power of the Fθ lens 6, this value is
Usually, it is about ± 3 seconds, and this allowable angle is close to the limit of the processing accuracy of the rotary polygon mirror 5, and the obtained rotary polygon mirror 5 becomes extremely expensive. In order to realize a high-definition deflection scanning device, it is necessary to reduce the tilt of the rotary polygon mirror 5 or to correct it with an optical system, and various proposals have been made. One example is disclosed in
Japanese Patent Application Publication No. 153456 proposes that a cylindrical lens is used for correcting surface tilt, and the cross-sectional shape of a laser beam incident on the Fθ lens 6 is rectangular in a scanning direction.

FIG. 4 is a perspective view showing an example in which the surface tilt correcting means proposed in JP-A-52-153456 is applied to the conventional optical system shown in FIG.

A cylindrical lens 8 is arranged between the Fθ lens 6 and the surface of the photosensitive drum 7, and a collimator lens 3
2 in that a beam shaper 4 composed of two prisms is disposed between the polygon mirror 5 and the rotary polygon mirror 5. That is, the cylindrical lens 8 optically corrects the deviation of the scanning position of the laser beam due to the tilt of the rotary polygon mirror 5, and the tilt correcting action will be described with reference to FIG.

In FIG. 5, the tilt angle φ /
The deviation amount of the deflection scanning position corresponding to 2 is approximately δc / δ = fΨy / (fθ · φy) where δ represents the case where the cylindrical lens 8 is not used and δc the case where the cylindrical lens 8 is used. fθ: focal length of the Fθ lens 6 f: focal length of the cylindrical lens 8 Therefore, if the focal length of the cylindrical lens 8 is sufficiently short with respect to the focal length of the Fθ lens 6, a considerable amount of surface tilt correction can be performed.

Next, the process of forming a beam spot in the optical system with a surface tilt correction function and the function of the beam shaper 4 using a prism will be described with reference to FIGS. FIG. 6 is a yz-plane view (a), an xz-plane view (b), and an xy cross-sectional view (c) of the laser beam optical path of the optical system shown in FIG. The radiation angle of the laser beam emitted from the laser diode 1 usually shows different values in the x direction and the y direction. Here, the case where the radiation angle is wide in the x direction will be described. In this case, the sectional dimensions dx ₁ and dy _{1 of the} laser beam emitted from the collimator lens 3
Is dx ₁ > dy ₁ . Then, d is placed on the surface of the photosensitive drum 7.
When forming a laser beam spot of x ₃ and dy ₃ , x
On the y-plane, dx ₂ = (4 · λ · fθ) / (π · dx ₃ ) (Equation 3) where fθ: focal length of the Fθ lens 6 λ: wavelength of the laser beam, and dx ₃ = 0.07 ( In order to obtain a small laser beam spot of (mm), λ = 0.78 × 1/10 ³ (m
m), fθ = 250 (mm), dx ₂ = 3.6 (m
m). Furthermore, on the yz plane, dy ₂ is Fθ
The size is set to such an extent that almost a parallel light beam can be maintained even after passing through the lens 6. That is, the light convergence of the Fθ lens 6 is set to a degree that balances the light divergence due to the diffraction phenomenon.
For this purpose, dy ₂ is selected so as to satisfy (dy ₂ ) ² = (4 · λ · fθ) / π (Equation 4). λ = 0.78 × 1/1
Assuming that 0 ³ (mm) and fθ = 250 (mm), dy ₃ = 0.
5 (mm). In order to set dy ₃ = 0.07 (mm), the focal length f of the cylindrical lens 8 becomes f = (dy ₃ · π · dy ₂ ) / 4λ (Equation 5). f = 35.1 (mm).
Thus, the surface of the photosensitive drum 7 has dx ₃ = dy ₃
= 0.07 (mm) circular laser beam spot is obtained. The beam shaper 4 is used to obtain a required beam diameter dy ₂ , and is configured by combining two prisms so as to have a refractive power only in the yz plane. Here, a characteristic point of the optical system with the surface tilt correction function described above is that the laser beam incident on the rotary polygon mirror 5 has a thin and long cross section in the scanning direction (for example, 0.5 mm × 3.6 mm). It is worth noting that.

Next, a prior art will be described with respect to a deflection scanning device including a rotary polygon mirror 5 used in such an optical system.
FIGS. 7A and 7B are views showing the configuration of a conventional general deflection scanning device. The deflection scanning device includes a rotating polygon mirror 5.
And a scanner motor 18 for driving the same and a protective cover 19, and the protective cover 19 is formed with an entrance / exit window 20 for a laser beam. As described above, the rotating polygon mirror 5 rotates at a very high speed in order to realize high-resolution and high-speed printing. The rotating polygon mirror 5 is provided on the protective cover 19.
A function is required to prevent fragments from being scattered when the device is broken and to prevent intrusion of dust from the outside. However, in the configuration of FIG. 7, the above-described function is satisfied because the laser beam entrance / exit window 20 is open. Not only is it impossible to perform the scanning, but also generates high-frequency wind noise (noise) as the rotating polygon mirror 5 rotates at a high speed and induces vibration of the rotating polygon mirror 5 to amplify the above-mentioned surface tilt and scan. This results in reduced accuracy.

FIG. 8 shows an example of the laser beam entrance / exit window 20 of the protective cover 19 in order to prevent scattering of debris, dust and sound.
Glass plates 21 and 22 are provided to cover the windows, and the Fθ lens 6 is used in place of the exit window side glass plate 22 in the example of FIG.

However, even if these means are used, since the rotating polygon mirror 5 has a polygonal shape, generation of turbulence due to high-speed rotation cannot be avoided.

Hereinafter, the influence of the turbulence will be described with reference to FIGS. 10 (a) and 10 (b). FIG. 10 schematically shows an airflow generated around the rotating polygon mirror 5 as the rotating polygon mirror 5 rotates. When the rotary polygon mirror 5 rotates at a high speed in the direction of the arrow shown in the figure, the surrounding air flow becomes a turbulent air flow that rapidly changes near the ridge line of the rotary polygon mirror 5 as shown in FIG. Tend to be. As a proof of this, when dust is floating around the rotary polygon mirror 5, a phenomenon in which the dust adheres to the reflecting surface with a distribution as shown in the drawing can be mentioned. Naturally, these turbulences affect the rotational movement of the rotary polygon mirror 5 and increase noise, vibration, rotational unevenness, dynamic surface tilt, and lower the scanning accuracy.

The vibration, uneven rotation, and dynamic surface tilt of the rotary polygon mirror 5 are caused by imbalance of mass distribution in addition to the above-mentioned factors. This imbalance is caused by forming a reflection plane in a polygonal shape on the outer periphery of a disk-shaped or columnar basic structure.

In addition, recent laser beam printers
High-speed printing, high resolution, small size of apparatus, and low cost are required, and the deflection scanning apparatus rotates a rotating polygon mirror having a small number of reflection surfaces at high speed in a small protective cover. Therefore, there is only a small gap between the rotating polygon mirror and the inner wall of the protective cover, and there is a step formed on the inner wall to form a laser beam input / output window. Interfering with the turbulence generated with this, the above-mentioned noise generation and the cause of the decrease in scanning accuracy are increased, and even if the tilting correction optical system is used, these problems still remain as problems to be overcome. Remains.

[0021]

SUMMARY OF THE INVENTION As described above, a deflection scanning apparatus using a rotating mirror in a laser beam printer or the like is required to rotate at a high speed, be quiet, and have a small scanning error. Is to meet these requirements.

[0022]

The present invention is based on image information.
A light source that is driven in accordance with
A first lens system for conversion, and a plurality of
A rotating mirror provided with a reflecting plane, and the rotating mirror in a protective cover
A window formed on the protective cover by turning the parallel light
Scan that emits light deflected by passing through another window through another window
Inspection device and the deflection light emitted from the deflection scanning device.
In an optical printer that irradiates a photoreceptor via a system,
The outer peripheral part of the rotating base is made thinner with respect to a central part,
The central part and the outer peripheral part of the rotating body are connected by a conical part, and the mirror part
The thickness is 1.5 to 2.5 mm, and the optical system is an Fθ lens system.
Tilt correction made up of cylindrical lenses in addition to
It is characterized by having an optical system with a function .

[0023]

The outer peripheral portion which disturbs the surrounding airflow and causes imbalance in mass is thinned to a thickness of about 1/4 of the conventional thickness, so that the occurrence of turbulence and imbalance in mass is reduced. Noise, vibration, uneven rotation, and dynamic fall are reduced.

[0024]

1 (a) and 1 (b) are a partial cross-sectional plan view and a partial side view of a deflection scanning device according to the present invention. The rotary polygon mirror 23 rotatably installed in the protective cover 19 in which the entrance / exit opening (window) 20 is formed is roughly divided into a basic structural body 23a having a cylindrical outer shape and an outer periphery thereof. It comprises a reflecting flat portion 23b and a concavely curved conical portion 23c connecting the reflecting flat portions 23b. That is, the bases of the basic structure 23a and the conical portion 23c are rotated at a high speed.
By applying a predetermined rotational inertia force to the rotary polygon mirror, it has a basic function of suppressing dynamic fluctuation during rotation and maintaining the strength and accuracy of the rotary polygon mirror. In addition, since this portion has a cylindrical shape, that is, a rotationally symmetric shape with respect to the center of the rotation axis, it goes without saying that the air resistance, the turbulence generation factor, and the dynamic imbalance during rotation are extremely small.

On the other hand, a reflection plane portion 23b having a reflection plane
Is very thin in the direction of the rotation axis with respect to the basic structure 23a, so that air resistance and turbulence during rotation are extremely reduced, and the step of the entrance / exit opening 20 of the protective cover 19 opposed with a small gap. Noise, vibration,
Rotation unevenness and the like are reduced. Further, the imbalance of the mass inevitably generated in the vicinity of the reflection plane portion is also effectively reduced, and the vibration due to the imbalance is reduced so that it is not necessary to consider the dynamic imbalance.

Conventionally, a lightweight member such as aluminum has been used to reduce unbalance, or a balance work has been mechanically performed. These restrictions are relaxed, the degree of freedom in material selection is expanded, and the manufacturing process is not complicated.

Next, an embodiment of a deflection scanning apparatus employing an optical system with a surface tilt correction function will be described with reference to FIG. In the case of the optical system with the surface tilt correction function, the cross-sectional shape of the laser beam incident on the rotary polygon mirror 23 is a rectangular shape elongated in the scanning direction, and in the example described with reference to FIG.
It is a 3.6 mm rectangle. Accordingly, the dimension ym in the rotation axis direction of the reflection plane formed on the reflection plane portion 23b shown in FIG.
It should be at most 1.5mm. On the other hand, in the case of an optical system that does not perform surface tilt correction, the beam is usually a circular or elliptical beam of 4 to 6 mm, and the required dimension ym is 6 to 10 mm.
Even if it is 6 mm, the rotating polygon mirror 23 can reduce the thickness of the reflection flat portion 23b to a quarter of the size by using an optical system with surface tilt correction.

Next, an example of a rotary polygon mirror devised so as to further reduce the generation of air resistance and turbulence at high speed rotation will be described with reference to FIG. The rotating polygon mirror 23 is
It is composed of a cylindrical basic structural body 23a, a reflecting plane 23b and a conical section 23c connecting them, and a ridge 23 between two adjacent reflecting planes of the reflecting plane 23b.
d is chamfered. The ridge portion 23d between the adjacent reflection planes in the rotary polygon mirror 23 is a portion where the airflow changes abruptly due to a change in shape, as described with reference to FIG. In this embodiment, the ridge 23d is chamfered with an arc slightly smaller than a circumscribed circle in order to reduce the change.
If it is performed by a lathe or the like in the material cutting process of 3, the increase in the number of manufacturing steps can be reduced.

Such a rotary polygon mirror 23 has an air resistance,
It is possible to provide a small-sized deflection scanning device which simultaneously realizes generation of turbulence and further reduction of mass imbalance.

In this embodiment, the ridge 23d between the reflection planes is chamfered by an arc concentric with the rotation axis.
If the processing is not difficult, it is also possible to perform the processing with other arcs or straight lines. The columnar basic structural body does not need to be vertically symmetrical about the reflection plane portion 23b, and may be only one side or may have a shape that is different vertically.

Further, in the optical system with a surface tilt correcting function to which the rotary polygon mirror 23 is applied, the sectional shape of the laser beam incident on the rotary polygon mirror 23 is changed to a beam shape other than a rectangular shape elongated in the scanning direction, for example, A similar effect can be obtained by using a focusing optical system in which the reflection plane of the rotary polygon mirror 23 is made confocal before and after the rotary polygon mirror 23.

[0032]

As described above, according to the present invention, a rotating mirror provided with a plurality of reflection planes on the outer periphery of a rotating base is rotated in a protective cover, and a light beam deflected by the rotating mirror is formed on the protective cover. In the deflection scanning device which enters and exits through the window, the outer peripheral portion of the rotating base is made thinner with respect to the central portion, so that the airflow generated around the rotating mirror at high speed rotation and the steps of the protective cover window and the like are reduced. Dynamic fluctuation factors such as noise, vibration, and rotational unevenness due to interference with parts and imbalance of mass can be reduced, and a small, quiet, and highly accurate deflection scanning device can be realized. In addition, it is possible to prevent the manufacturing of the rotary polygon mirror from becoming complicated, and to obtain a secondary effect such as an increase in the degree of freedom of material selection.

[Brief description of the drawings]

FIG. 1 is a partially cross-sectional plan view and a partially longitudinal side view of a deflection scanning device according to the present invention.

FIG. 2 is a perspective view showing a schematic configuration of a conventional laser beam printer.

FIG. 3 is an xy, yz plane projection view of an optical system in the laser beam printer shown in FIG. 2;

FIG. 4 is a perspective view showing a schematic configuration of a laser beam printer employing a surface tilt correction optical system.

FIG. 5 is a yz-plane projection diagram for explaining a surface tilt correcting operation in the optical system of the laser beam printer shown in FIG. 4;

FIG. 6 is a development view of a yz plane, an xz plane, and an xy plane in the optical system of the laser beam printer shown in FIG.

FIG. 7 is a partial cross-sectional plan view and a partial vertical sectional side view of a conventional deflection scanning device.

FIG. 8 is a partial cross-sectional plan view of the improved deflection scanning device.

FIG. 9 is a partial cross-sectional plan view of the improved deflection scanning device.

FIG. 10 is a partial cross-sectional plan view and a partial vertical cross-sectional side view showing an airflow generation state in a conventional deflection scanning device.

FIG. 11 is a partially cross-sectional plan view and a partially longitudinal side view showing an operation state of the rotary polygon mirror in the deflection scanning device according to the present invention.

FIG. 12 is a plan view and a side view showing a modification of the rotary polygon mirror in the deflection scanning device according to the present invention.

[Explanation of symbols]

19 ... Protective cover, 20 ... Incoming / outgoing opening (window), 23 ...
Rotating polygon mirror, 23a: basic structure, 23b: reflection plane, 23c: cone, 23d: ridge.

Claims (1)

(57) [Claims] A light source driven based on image information;
A first lens system for converting light from the light source into parallel light,
A rotating mirror provided with a plurality of reflection planes on the outer periphery of the rotating base,
Rotate the rotating mirror in the protective cover to move the parallel light forward.
The light incident and deflected through the window formed in the protective cover
A deflection scanning device for emitting light from another window, and the deflection scanning device
Irradiates the deflected light from the photoreceptor via the optical system
In the optical printer, the outer peripheral portion of the rotating base is made thin with respect to the central portion.
Then, the central portion and the outer peripheral portion of the rotating body are connected by a conical portion,
The thickness of the mirror surface portion is set to 1.5 to 2.5 mm, and
The ridge between the reflection planes is chamfered, and the optical system is
Consisting of a cylindrical lens in addition to the θ lens system
An optical system characterized by an optical system with a surface tilt correction function.
Linta.