JPH08111749A - Optical scanner and image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device provided with an optical scanner without using f-θ lens. CONSTITUTION: Beams from a semiconductor laser 10 are changed to nearly parallel rays by a collimator lens 31, and become approximate non-diffracted light beams by an axial condenser 40. The approximate non-diffracted light beams are reflected on a rotary polygonal mirror 45, and scan a photosensitive material 201. The approximate non-diffracted light beams are propagated to the photosensitive material 201 scarcely changing a beam diameter. The center intensity of light beams can be corrected from the correction coefficient of center intensity of the light beams at a center image forming part for a light scanning position decided in advance by a light intensity calculation circuit 454, and also, such control so as to increase the center intensity almost proportionally to the scanning speed of the light beams is applied. In this way, the optical scanner and the image forming device simple in constitution, low in cost and capable of easily adjusting an optical axis can be provided.

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 for scanning light and an image forming apparatus such as a printer or a copying machine using the optical scanning device.

[0002]

2. Description of the Related Art An image forming apparatus (for example, a printer or a copying machine) that scans light to form an image on a photoconductor is widely used. In such a device, scanning of light and focusing on a photoconductor are realized by a rotating polygon mirror and an f-θ lens. For such technology, for example,
“Basics and Applications of Electrophotographic Technology” (Electrophotographic Society, 19
1988). Further, the optical scanning device is disclosed in, for example, Japanese Patent Laid-Open No. 4-217079. The publication describes that the depth of focus is expanded by disposing an optical element such as an axicon in the optical path between the laser light source and the scanning mirror.

[0003]

In the above-mentioned conventional image forming apparatus, it is necessary to dispose the f-θ lens between the rotary polygon mirror and the photoconductor, and the optical system is complicated. Moreover, since the f-θ lens needs to be processed to be long and highly accurate, it is costly. Further, since the angle of light incident on the f-θ lens cannot be increased, it is necessary to increase the distance between the rotating polyhedron and the photoconductor in order to scan a fixed width such as A4 size width. This has been an obstacle to the miniaturization of the optical system.

Furthermore, in order to position the focal point of the converging beam on the photoconductor, the f-θ lens and the like must be adjusted with high precision, which is troublesome. Therefore, there has been a demand for an optical system that does not require such highly accurate adjustment.
As an optical scanning device with an increased depth of focus, there is, for example, a technology relating to a bar code scanner disclosed in Japanese Patent Laid-Open No. 4-217079. In this technique, the width of each bar and space is detected from the reflectance. Even if the light intensity changes gently within the range of scanning the bar code, there is no problem in reading the bar code. However, in the technique described in this publication, when the distance from the optical element for expanding the depth of focus changes, the light intensity at the beam center changes. Therefore, the technique cannot be applied to the image forming apparatus.

An object of the present invention is to provide an optical scanning device and an image forming apparatus using a simple and low cost optical system which does not use an f-θ lens.

Another object of the present invention is to provide an optical scanning device and an image forming apparatus in which adjustment of an optical system is easy.

[0007]

The present invention has been made to achieve the above object, and a first aspect thereof is as follows.
In an image forming apparatus that forms a pixel image by irradiating light on a light scanning medium and forms an image as a set of the pixel images, when a light source and light irradiation are received, a predetermined change is made in the irradiated position. An optical scanning medium that is generated, an optical scanning unit that scans the light emitted from the light source on the optical scanning medium, and a light from the light source that is arranged on an optical path of the light emitted from the light source to the optical scanning unit. Approximate non-diffractive beam converting means for converting the light into an approximate non-diffractive beam, control means for controlling the light emitting state of the light source according to image data input separately, and for obtaining the pixel image of a certain density. An image forming apparatus is provided, which comprises: a light amount changing unit that changes the amount of light applied to the optical scanning medium according to the position of the light in the scanning direction on the optical scanning medium.

The control means may also serve as the light amount changing means. In this case, the control means outputs the signal (hereinafter referred to as "intensity signal") determined corresponding to the scanning position of the light on the optical scanning medium, and the intensity output means based on the image information. It is preferable to include a modulation signal generation means for generating and outputting a modulation signal and a light source driving means for changing the emission intensity of the light source based on the modulation signal and the intensity signal.

The light amount changing means includes an optical filter installed between the light scanning means and the light scanning medium, and the optical filter is at least responsive to the position of the light in the scanning direction. They may have different light transmittances.

The approximate non-diffractive beam is different from a beam in which the beam diameter increases with the propagation distance due to ordinary diffraction, but the beam diameter in the bright portion of the central portion remains almost constant for a certain distance. This is a beam that propagates. This approximate non-diffractive beam can collect light up to the wavelength. The approximate non-diffractive beam converting means may include an axicon or a Fresnel lens composed of grooves at equal intervals.

As the image forming apparatus of the present invention, it is desirable to use an image forming apparatus using an electrophotographic process.
In this case, the optical scanning medium may be a photoconductor in which the amount of electrification of a portion irradiated with light changes. An electrical image is formed on the photoconductor by the scanned light.

A lens having a condensing characteristic only in the light scanning direction may be provided between the light scanning means and the photoconductor.

According to a second aspect of the present invention, in a light quantity control method of an image forming apparatus for irradiating light on an optical scanning medium to form a pixel image and forming an image as a set of the pixel images, a certain density is provided. Controlling the amount of light to be applied to the optical scanning medium to obtain the pixel image according to the scanning position of the light on the optical scanning medium. A method is provided.

According to a third aspect of the present invention, in an optical scanning device which operates in response to a separately input image signal, a light source, an optical scanning means for scanning the light emitted from the light source,
The approximate non-diffractive beam converting means for converting the light from the light source into the approximate non-diffracting beam, which is arranged on the optical path of the light emitted from the light source to the optical scanning means, and the optical scanning means. Also provided is an optical scanning device characterized in that the optical scanning device is also arranged on the rear stage side, and is configured to include an optical filter having a different light transmittance depending on at least the position in the light scanning direction.

According to a fourth aspect of the present invention, in a printer which forms a pixel image by irradiating light on a photosensitive member and forms an image as a set of the pixel images, the printer receives a light source and light irradiation. And a photoconductor whose charge amount at the irradiated position changes, an optical scanning unit for scanning the light emitted from the light source on the photoconductor, and an optical path arranged from the light source to the optical scanning unit. Based on the approximate non-diffractive beam converting means for converting the light from the light source into the approximate non-diffractive beam, the interface for receiving the image data input from the outside, and the image data received by the interface. Control circuit for forming an electric pixel image on the photoconductor by controlling the light emission state of the light source, and developing for attaching toner to an area on the photoconductor where the electric image is formed. Means and Transfer means for transferring the toner attached on the photoconductor to a recording medium supplied separately, and the control means further provides the photoconductor for obtaining the electric pixel image of a certain density. There is provided a printer, characterized in that the amount of light radiated to the printer is changed according to the scanning position of the light on the photoconductor.

[0016]

The first to fourth aspects of the present invention will be collectively described.

The control means (control circuit) controls the light emitting state of the light source based on the image data received by the interface. Then, the approximate non-diffractive beam converting means converts the light emitted from the light source into the approximate non-diffractive beam. The optical scanning unit scans the approximate non-diffracted beam on an optical scanning medium (for example, a photoconductor that generates an electric charge in a portion irradiated with light).

Since the approximate non-diffractive beam can be propagated without substantially changing the beam diameter, an optical system which does not use an f-θ lens becomes possible. Therefore, it is possible to directly irradiate the photoconductor with the light from the optical scanning means. However, the intensity of this approximate non-diffracted beam changes depending on the distance from the approximate non-diffracted beam to the optical scanning medium. Moreover, when the f-θ lens is not used, the scanning speed changes depending on the scanning position. Therefore, if the light emission intensity of the light source is simply kept constant, the density of the pixel image will differ depending on the position. Therefore, the light amount changing means changes the amount of light applied to the optical scanning medium in order to obtain a pixel image of a certain density according to the position of the light in the scanning direction on the optical scanning medium.

When the light quantity changing means also serves as the control means, the control means may be constituted by, for example, an intensity output means, a modulation signal generating means, and a light source driving means. The light source driving means adjusts the light emission intensity of the light source by taking into consideration not only the modulation signal but also the intensity signal determined according to the scanning position, so that a pixel image is formed when forming a pixel image of a certain density. The density can be kept constant regardless of the scanning position (scanning position).

When the light amount changing means is realized by an optical filter, the light transmittance is made different at least in accordance with the position of the light in the scanning direction so that the density of the pixel image is also kept constant. be able to.

If a lens having a condensing characteristic only in the light scanning direction is arranged between the light scanning means and the photoconductor, the light quantity adjustment by the light quantity changing means does not include the change in the scanning speed. Is also good. It suffices to adjust the fluctuation amount of the light intensity due to the change in the distance between the optical scanning medium and the approximate non-diffractive beam converting means.

When a photoconductor which changes its charge amount when receiving light is used as the optical scanning medium, an electric pixel image is formed on the photoconductor at the portion irradiated with light. ing. The developing means attaches toner to the electric pixel image. The transfer unit transfers the toner attached to the photoconductor to a recording medium (e.g., paper) supplied separately.

[0023]

Embodiments of the present invention will be described below.

The optical scanning device of the present embodiment is characterized by adopting an approximate non-diffracting beam and solving the various problems that accompany the adoption of the approximate non-diffracting beam.

First, an outline of an optical system (optical scanning device) used in the image forming apparatus of this embodiment will be described with reference to FIG.

The semiconductor laser 10, which is a light source, generates a pulsed laser beam. Collimating lens 31
Makes this laser beam substantially parallel light and makes it incident on an axicon 40 which is an approximate non-diffractive beam converting means. The axicon 40 is a conical prism. This axicon 4
0 makes the incident beam an approximate non-diffracted beam. The rotating polygon mirror 45 reflects the approximate non-diffracted beam and scans the photoconductor 201.

Next, the approximate non-diffracting beam which is a feature of the present embodiment and the structure related thereto (for example, the beam diameter of the approximate non-diffracting beam, the specifications of the axicon 40, and the light intensity control).
Will be described in detail.

First, the inclination angle α of the axicon 40 will be described.

As shown in FIG. 3, the collimated light incident on the axicon 40 is refracted at the conical portion, and the refracted beams are superposed on the inclined surfaces on both sides of the apex. In general, this overlapping portion becomes an approximate non-diffractive beam. Assuming that the inclination angle of the axicon 40 is α, the radius of the beam incident on the axicon 40 is R, and the refractive index of the axicon is n, the range L in which the non-diffracted beam is generated is expressed by the following formula 1. .

[0030]

[Equation 1]

The distance r in the direction perpendicular to the optical axis of the non-diffracted beam
The intensity distribution I in is approximately represented by the following mathematical expression 2.

[0032]

[Equation 2] I∝ | J ₀ (ar) | ² where J ₀ is the 0th-order Bessel function, and a is defined by the following Equation 3.

[0033]

(Equation 3)

If the diameter when the equation 2 first becomes 0 is defined as the beam diameter φ of the approximate non-diffracted beam, the beam diameter φ is given by the following equation 4.

[0035]

[Equation 4]

Currently, the resolution of the image forming apparatus is 200d.
It is from pi to 1000 dpi. To address this,
The beam diameter φ needs to be 30 μm to 130 μm, and more preferably 30 to 50 μm. The tilt angle α of the axicon 40 depends on the required beam diameter, n, and
It can be obtained by substituting λ and Mathematical Expression 3. As typical conditions, n = 1.5 (refractive index of glass), λ = 780 nm
Substituting (a wavelength of a general semiconductor laser) into the equation 3, when the beam diameter φ is 30 μm to 130 μm, the range of the inclination angle α is 2.3 ° to 0.52 °. When the beam diameter φ is 30 μm to 50 μm, the range of the inclination angle α is 2.3 ° to 1.3 °. In this way, the inclination angle α can be determined from the condition of the beam diameter φ by using the equation (3).

Next, the beam diameter R incident on the axicon 40 will be described.

This beam diameter R (see FIG. 3) is determined by the photoconductor 2
01 so that the approximate non-diffracted beam hits. That is, from the axicon 40 to the photoconductor 201
The beam diameter R incident on the axicon 40 is determined so that the optical path length up to is not more than L of the equation 1. In this case, it goes without saying that the axicon 40 having the above-mentioned value (2.3 ° to 0.52 °, or 2.3 ° to 1.3 °) as the inclination angle α is assumed.

The detailed intensity distribution of the approximate undiffracted beam can be calculated using Fresnel's theory of diffraction. FIG.
When the axicon 40 is used, the intensity distribution I (z, r) at the coordinates (z, r) is expressed by the following mathematical expression 5.

[0040]

(Equation 5)

[Alpha] = 1.3 ° and R = 5.2 mm are given by
FIG. 5 shows the relationship between the relative value of the central intensity and the distance from the axicon, which was obtained by substituting in. When the distance from the axicon is small, the central intensity fluctuates with a small period. As the distance increases, the period and the peak value increase. After the center strength reaches its maximum, as the distance is further increased, the center strength approaches zero. Thus, the central intensity of the approximate undiffracted beam changes with the distance from the axicon.

Since the approximate non-diffracted beam is scanned on the photoconductor, the distance between the axicon 40 and the position on the photoconductor 201 where the beam is irradiated (beam center) (hereinafter simply referred to as ""Optical path length" is the photoconductor 2
01 depends on the irradiation position of the beam. The shortest distance is when the photosensitive member 201 is vertically irradiated, and the longest distance is when the end portion 201 of the photosensitive member is irradiated.

In order to effectively use the light, it is desirable to arrange the optical system so that the distance (position) at which the central intensity of the beam becomes maximum falls within the range of this optical path length. In this embodiment, the effective range of the photoconductor 201 is the lateral width of A4 size. Further, the rotary polygon mirror 45 is installed at a position 50 mm from the photoconductor 201. in this case,
The distance from the rotary polygon mirror 45 to the beam on the photoconductor 201 varies between 50 and 116 mm. Therefore, the axicon 40 is arranged so that the range of the optical path length substantially matches the range shown as "laser scanning range" in FIG. In this way, by setting the laser scanning range so as to include the distance (position) where the beam center intensity becomes maximum, the output control of the laser 10 described later becomes easy. If the distance between the photoconductor 201 and the rotary polygon mirror 45 is increased, the change in the distance between the beam on the photoconductor 201 and the rotary polygon mirror 45 is reduced. This leads to the suppression of the variation width of the light intensity, and the output control of the laser 10 described later becomes easy.

Next, the control of the exposure amount will be described.

Since the output of the laser 10 is simply kept constant in this embodiment by using the axicon 40, the exposure amount (irradiation energy amount per unit area) on the photoconductor 201 becomes non-uniform. . There are two causes of non-uniform exposure.

Cause: Variation in optical path length The optical path length from the axicon 40 to the position on the photoconductor 201 where the beam is irradiated (beam center position) is:
It changes as shown in FIG. 6A with the scanning. In the figure, the horizontal axis is the position on the photoconductor 201 where the beam is irradiated (in the figure, simply referred to as "beam position"). The vertical axis is the optical path length. As shown in FIG. 1, when the scanning angle by the rotary polygon mirror 45 is θ and the distance from the rotary polygon mirror 45 to the photoconductor 201 is m, the beam position x on the photoconductor 201 is expressed by the following formula 6. To be done. The beam position = 0 corresponds to the scanning angle θ = 0.

[0047]

X = m · tan θ Here, when the distance from the axicon 40 to the rotary polygon mirror 45 is m ₀ , the optical path length M changes according to the following expression 7.

[0048]

## EQU7 ## M = m ₀ + m / cos θ As described above, the central intensity of the approximate non-diffracted beam varies depending on the magnitude of the optical path length M (see FIG. 5). Even if the laser 10 which is the light source emits light of the same energy,
The exposure amount per unit area varies depending on the position on the photoconductor 201.

Cause: Fluctuation of scanning speed The scanning speed of the beam on the photosensitive member 201 depends on the photosensitive member 201.
It changes like FIG.6 (b) according to the position above.
The beam scanning speed v is expressed by the following equation 8. Since the rotary polygon mirror rotates at a constant angular velocity of 45, dθ / dt is constant in Expression 8.

[0050]

## EQU00008 ## v = (m / cos ² .theta.). Multidot. (D.theta./dt) As can be seen from the equation 8, the scanning speed changes according to the scanning angle .theta. Even if the photoconductor 201 is irradiated with light of the same intensity, if the scanning speed v is changed,
The exposure amount per unit area varies depending on the place.

From the above-mentioned causes, simply replacing the f-θ lens of the conventional device with the axicon 40
The amount of exposure will vary depending on the location. Then, such non-uniformity of the exposure amount causes density unevenness of the image. In order to eliminate the density unevenness of the image, it is necessary to make the exposure amount constant regardless of the place. In the present embodiment, this uniforming of the exposure amount is realized by controlling the output of the laser 10.

The contents of control of the output of the laser 10 will be described.

In this embodiment, the photoconductor 20 obtained from the equation 5 is used.
Considering the beam center intensity I (z, 0) on 1 and the equation (8), the output P of the laser 10 is changed according to the following equation (9).

[0054]

[Equation 9] P ∝ v / I (z, 0) ∝ 1 / I (z, 0) cos ² θ When the light amount control is performed based on Equation 9 and when not performed (the output of the laser 10 is constant) And the photoconductor 20
FIG. 7 shows the difference in the central intensity of the beam irradiated on the beam No. 1. FIG. 7A shows the output of the laser 10 when the light amount control is not performed, and FIG. 7B shows the photoconductor 2 in that case.
01 is the central intensity of the beam irradiated. Figure 7
FIG. 7C shows the output of the laser 10 when the light amount control according to the above equation 9 is performed, and FIG. 7D shows the central intensity of the beam applied to the photoconductor 201 in that case.

As can be seen from FIG. 7D, when the laser output control is being performed, the beam on the photoconductor 201 is
The beam center intensity is proportional to the beam scanning speed v (Note:
The scanning speed increases as the beam position moves away from zero. 6B), the exposure amount is almost constant regardless of the place.

Up to this point, the output control mainly for solving the uneven density has been described. However, the above-described cause (fluctuation of scanning speed) also causes a problem of varying the pixel length in the scanning direction. That is, if the scanning speed changes, even if the laser 10 is made to emit light for each pixel for the same time (Note: the light emission intensity is not always the same), the pixel length in the scanning direction will change. Therefore, control for solving the problem that the pixel length varies will be described next.

In order to solve this problem, in this embodiment, the clock frequency for modulating and driving the laser 10 is made 4 to 20 times higher than the maximum frequency determined by the pixel pitch. Then, control is performed to adjust the number of clocks in each pixel so that the length of each pixel becomes substantially the same according to the scanning speed. For example, in a portion where the scanning speed is high, the number of clocks is set small, and the number of pulses of a beam emitted per pixel is reduced. On the contrary, in the part where the scanning speed is slow, the number of clocks is increased to increase the number of pulses of the beam emitted per pixel.

Next, an image forming apparatus having a specific structure for realizing the control of the exposure amount and the like described above and its operation will be described with reference to FIG.

The detector 70 detects the beam scanned on the photoconductor 201 at a position (photoconductor 201) immediately before the start of scanning.
(Horizontal position of)). The detector 70 outputs the detection signal to the synchronization signal generation circuit 4 through the preamplifier 462.
It outputs to 60 as a pulse. Sync signal generation circuit 460
Is this pulse (that is, the timing of optical scanning start)
A synchronization signal synchronized with is generated every optical scanning.

The light intensity calculation circuit 454 sequentially finds the position where the light is being scanned at that time based on the elapsed time after the synchronization signal is generated. Further, the light intensity at the position is sequentially obtained, and the data of the obtained light intensity is sent to the laser drive circuit 452. The light intensity table 456 stores in advance the relationship between the light scanning position and the light intensity (the output P of the laser 10) (this is determined from the above-mentioned equation 9). . The light intensity calculation circuit 454 reads out necessary data from the light intensity table 456 to obtain the light intensity necessary to create a pixel image having a certain fixed density.

On the other hand, the microcomputer 450 processes the input image signal and sends it to the laser drive circuit 452 as a modulation signal.

The laser driving circuit 452 is the semiconductor laser 1
0 is being driven. In this case, on / off of light and intensity modulation of light for expressing gradation are performed based on the modulation signal sent from the microcomputer 450. Further, based on the light intensity data from the light intensity calculation circuit 454, the light intensity is corrected according to the optical scanning position.

The rotary polygon mirror drive circuit 458 is the microcomputer 4
Based on the clock from 50, the rotary polygon mirror 45 is controlled to rotate at a predetermined rotation speed.

In addition, the microcomputer 450 detects a change in the output power of the semiconductor laser 10 due to the influence of the environment (for example, temperature), and corrects the drive current so as to obtain a predetermined power. It should be noted that the variation of the emission power is caused by the preamplifier
The determination is made based on the magnitude of the signal from 2.

In this embodiment, the light intensity calculation circuit 454 and the light intensity table 456 are realized by a microprocessor, a memory, and programs and data stored and executed by these. However, the specific configuration is not limited to this.

In the claims, "light source,"
Corresponds to the semiconductor laser 10 in the example of FIG. The “optical scanning medium” corresponds to the photoconductor 201. The “light scanning means” is configured to include the rotary polygon mirror 45, the rotary polygon mirror drive circuit 458, and the like. The “approximate non-diffractive beam converting means” is an axicon 40
Alternatively, it corresponds to a Fresnel lens 41 or the like described later. The “control means” includes the detector 70 and the preamplifier 4
62, a synchronization signal generation circuit 460, a microcomputer 450, a laser drive circuit 452 and the like. The "intensity output means" in the mode in which the control means also serves as the light quantity changing means is the light intensity calculation circuit 454, the light intensity table 456, etc., and the "modulation signal generating means" is the microcomputer 45.
The “light source driving means” corresponds to the laser driving circuit 452. The “intensity signal” corresponds to the signal output from the light intensity calculation circuit 454. The "modulation signal" is sent from the microcomputer 450 to the laser drive circuit 45.
This is equivalent to the signal output to 2. The “optical filter” corresponds to the filter 36 described later.

FIG. 8 shows the result of measuring the light intensity distribution of the beam irradiated to the center position (scanning angle θ = 0) of the photoconductor 201. The tilt angle of the axicon 40 is 1.3.
The wavelength of the beam light is 780 nm. The beam diameter is about 50 μm. Even if the beam was scanned, the beam diameter on the photoconductor 201 was hardly changed.

Still another problem in the case of using the approximated diffracted light is that the width of the image in the sub-scanning direction becomes wide when the sensitivity of the photoconductor 201 depends gently on the exposure amount. This is because the approximate non-diffractive beam 100 has a large light intensity in the ring zone, as can be seen from FIG.
This is because the exposure width in the vertical direction (sub-scanning direction) with respect to the optical scanning direction becomes wider.

To solve this problem, the influence of the ring zone should be reduced. This can be achieved, for example, by providing the slit 35 between the rotary polygon mirror 45 and the photoconductor 201 as shown in FIG. The width of the slit 35 is preferably about the diameter of the center peak of the intensity distribution 102 (in FIG. 9, the portion with high light intensity is drawn in black). This slit 35 can suppress the spread of the exposure width in the direction perpendicular to the light scanning direction. Such a problem does not occur when a photosensitive member whose sensitivity is steep with respect to the intensity of light is used, and therefore it is not necessary to use the slit 35.

The spread in the optical scanning direction can be suppressed by changing the clock frequency for modulating the laser and shortening the light irradiation time, as in the above-mentioned problem.

As described above, in the optical scanning device using the approximate non-diffractive beam of this embodiment, the light quantity is controlled according to the irradiation position of the light, so that the performance applicable to the image forming apparatus can be obtained. It was realized. In addition, the object to be irradiated (photosensitive member 201 in the above embodiment) without using the f-θ lens.
Since the focused beam can be scanned over the entire surface of the device, the cost of the device can be reduced.

In the conventional optical scanning device, it was necessary to adjust the positions of the f-θ lens and the photosensitive member with high accuracy. On the other hand, in the optical scanning device of the present embodiment, the beam diameter hardly changes within the range where an approximate non-diffractive beam can be obtained. Therefore, optical adjustment is very easy.

In the optical scanning device of this embodiment, the rotary polygon mirror 4
The distance between the optical scanning unit such as 5 and the optical scanning medium such as the photoconductor 201 can be narrowed, and the device can be downsized. In order to bring the rotary polygon mirror 45 and the photoconductor 201 closer to each other to reduce the size of the optical system, it is preferable that the rotary polygon mirror 45 has a small number of surfaces (see FIGS. 1 and 2). Desirably, it is 2 to 4 sides. Since the number of surfaces is small, there is also an effect that it is easy to adjust the tilt. The optical system can be further downsized by reducing the number of surfaces.

When the distance between the rotary polygon mirror 45 and the photoconductor 201 is narrowed, the optical path length is shortened, so that the beam center intensity vibrates according to the position on the photoconductor 201 (see FIG. 5). . However, the rotary polygon mirror 45 and the photoconductor 201
When the position of is determined, the center intensity of the beam on the photoconductor 201 is also determined. Therefore, the light intensity table 456 (see FIG. 1) may be set in advance so as to correct this central intensity.

As the optical scanning means, an acousto-optic element or a galvano mirror may be used in addition to the rotary polygon mirror.

In order to secure the f-θ property, the rotary polygon mirror 4
5 and the photoconductor 201 may be provided with an f-θ lens having no light-condensing property in the sub-axis direction. At this time, since the beam scanning speed is constant, it is not necessary to correct the light amount with respect to the scanning speed.

In this embodiment, the approximate non-diffracted beam is formed by the axicon 40. However, the approximate non-diffracted beam can be realized by using a Fresnel lens or a hologram in addition to the axicon. Also, with an annular slit,
It can also be realized by using a lens installed apart from the slit by a focal length. Further, it can be realized by a laser which constitutes a resonator using an annular reflecting mirror. The effect of the present invention (particularly, facilitating adjustment of the optical system) occurs because the beam diameter of the approximate non-diffracted beam hardly changes within a predetermined range. Therefore, this effect can be obtained by using any of these methods. As an example, a case where the Fresnel lens 41 is used instead of the axicon will be described with reference to FIG.

As the Fresnel lens 41, one having concentric grooves at equal intervals is adopted. When the groove period is λp, the intensity distribution I at the distance r in the direction perpendicular to the optical axis is expressed by the following formula 10.

[0079]

## EQU10 ## I = | J ₀ (2πr / λp) | ^{2 In} this case, the range L in which the approximate non-diffraction beam is generated is the range shown by the following formula 11.

[0080]

[Equation 11]

Further, the beam diameter φ of the approximate non-diffractive beam
Is expressed by the following Expression 12.

[0082]

(Equation 12)

Similar to the case of using the axicon, first, the groove period λp is determined from the condition of the beam diameter, and then the beam diameter R incident on the Fresnel lens 41 is determined. The beam diameter is also determined from the viewpoint that the approximate non-diffractive beam hits the photoconductor, as in the above embodiment. That is, the optical path length M from the Fresnel lens 41 to the photoconductor is set to be equal to or less than L of the equation 1. The groove is preferably blazed so that the diffraction angle and the refraction angle match as shown in the figure.

In this embodiment, the exposure amount is made uniform by controlling the output of the laser 10. However, the exposure dose may be made uniform by other methods. For example, as shown in FIG. 10, a filter 36 for adjusting the amount of light may be arranged between the rotary polygon mirror 45 and the photoconductor 201. As the filter 36, its transmittance changes according to the incident position of the beam as shown in FIG. 11 so that the center intensity of the beam after passing through the filter 36 is proportional to the scanning speed of light. Use one. The filter 36 can be formed by forming a metal film of silver or the like on a transparent substrate with a different thickness.
In this case, the emission intensity of the laser 10 may be constant.

In this embodiment, the density of the point image (pixel image) corresponding to each pixel is changed by changing the intensity of the light that strikes the photosensitive member. However, it is also possible to perform substantial gradation expression (density expression when viewed visually) by changing the time of light irradiation and the number of pulses. In such a case, the above-mentioned "intensity signal" indicates the number of the pulses or the irradiation time of light.

The second embodiment of the present invention will be described with reference to FIG.

The second embodiment is a laser beam printer equipped with the optical scanning device of the first embodiment.

The charger 210 charges the photoconductor 201 in advance. The optical system 91 irradiates this with an intensity-modulated approximate non-diffractive beam to form a latent image. In this embodiment, the configuration of FIG. 2 is adopted as the optical system 91 (FIG. 10).
It is also possible to adopt the configuration of). In FIG. 12, the configuration from the light source to the axicon is omitted as the optical system 91. As in the case of FIG. 2, a beam that has been converted into an approximately non-diffracted beam is reflected by the rotating polygon mirror 45, reflected by the mirror 42, and then applied to the rotating photosensitive member 201.

The developing device 211 develops the latent image drawn on the photoconductor 201 using a toner as an image forming medium. On the other hand, in parallel with this, the carrier rolls 230, 232
Conveys the paper 150 from the paper feed cassette 290. The transfer device 212 transfers the developed toner to the conveyed paper 150. The fixing device 240 fixes the transferred toner. After that, the transport roll 231 changes the paper 1
Carry out 50. Finally, the cleaner 213 removes the toner remaining on the photoconductor 201 after the transfer.

The control of the beam when the latent image is formed on the photosensitive member 201 is performed by the control circuit 421 in accordance with the image signal input through the interface 420. That is, the functions of the microcomputer 450, the light intensity table 456, the light intensity calculation circuit 454, etc. in the first embodiment are realized by this control circuit 421. Control circuit 421
In addition to this, the control of the supply of the paper 150, the supply of the toner, etc. is also performed.

The laser driving circuit 452, the rotary polygon mirror driving circuit 458, the synchronizing signal generating circuit 460 and the like are not shown.

As described above, in this embodiment, by adopting the optical scanning system which can be miniaturized and reduced in cost, the laser beam printer as a whole can be miniaturized and reduced in cost.

As the image formed body, a plastic film or the like can be used other than paper.

The optical scanning device and the image forming apparatus using the same according to the present invention can of course be used in an image forming unit such as a copying machine or a facsimile. When used in a facsimile, the image forming apparatus according to the above-described embodiment includes at least a document reading unit, an image signal communication input / output unit,
It is necessary to provide a communication control means.

The image forming process to which the constitution of the present invention is applicable is not limited to the electrophotographic process shown in the above embodiment. As long as it is a process of scanning light to form an image, it can be applied to other image forming processes. For example, it is also applicable to a photothermal transfer process in which light is scanned on a thermal transfer ink ribbon and the ink is melted by the light energy to form an image.

[0096]

As described above, according to the present invention, f-
It has become possible to provide an optical scanning device and an image forming apparatus equipped with a simple and low-cost optical system that does not use a θ lens.

Furthermore, it is possible to provide an optical scanning device and an image forming apparatus in which the optical system can be easily adjusted.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of an image forming apparatus that is a first embodiment of the present invention.

FIG. 2 is a perspective view showing an arrangement state of components of the optical scanning device used in FIG.

FIG. 3 is a diagram showing how an axicon 40 transforms parallel light into an approximate non-diffractive beam.

FIG. 4 is a diagram showing how the equally-spaced Fresnel lens 41 transforms parallel light into an approximate non-diffractive beam.

FIG. 5 shows the distance from the axicon and the beam center strength,
It is a graph which shows the relationship of.

FIG. 6A shows a beam scanning position on the photoconductor 201 and a distance from the axicon to the position.
It is a graph which shows the relationship of. FIG. 6B shows the photoconductor 20.
3 is a graph showing the relationship between the beam scanning position on the first position and the optical scanning speed at the position.

FIG. 7 is a diagram showing a correspondence relationship between the presence or absence of light intensity control of the present invention, the output of the laser 10 and the central intensity of the beam actually irradiated on the photosensitive member 201.

FIG. 8 is a graph showing an intensity distribution of an approximate non-diffractive beam.

FIG. 9 is an enlarged view of the vicinity of the photoconductor of the optical scanning device.

FIG. 10 is a conceptual diagram of an image forming apparatus that is a second embodiment of the present invention.

11 is a filter 36 used in the image forming apparatus of FIG.
5 is a graph showing the relationship between the position in the scanning direction and the light transmittance at that position for.

FIG. 12 is a schematic diagram showing an internal structure of a printer which is a third embodiment of the present invention.

[Explanation of symbols]

10 ... Semiconductor laser, 31 ... Collimating lens, 3
2 ... f-theta lens, 35 ... slit, 36 ... filter, 40 ... axicon, 41 ... Fresnel lens,
42 ... Mira, 45 ... Rotating polyhedron, 70 ... Sensor,
91 ... Optical system, 100 ... Beam, 102 ... Intensity distribution,
150 ... paper, 201 ... photoreceptor, 210 ... charger,
211 ... Developing device, 212 ... Transfer device, 213 ... Cleaner, 230 ... Conveying roll, 231 ... Conveying roll
232 ... Paper feeding roll, 240 ... Fixing roll,
290 ... Paper feed cassette, 301 ... Rays, 420 ... Interface, 421 ... Control circuit, 450 ... Microcomputer, 452 ... Laser drive circuit, 454 ... Light intensity calculation circuit, 456 ... Light intensity table, 458 ... Rotating polygon mirror drive circuit, 460 ... Synchronous signal generation circuit, 462
… Preamp

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location H04N 1/23 103 Z 1/40 H04N 1/40 A

Claims (10)

[Claims] 1. An image forming apparatus for forming a pixel image by irradiating light on an optical scanning medium and forming an image as a set of the pixel images, wherein the light source and the irradiated object receive the light irradiation. An optical scanning medium that causes a predetermined change in position, an optical scanning unit that scans the light emitted from the light source on the optical scanning medium, and a light emitted from the light source is disposed on an optical path leading to the optical scanning unit. Approximate non-diffractive beam converting means for converting light from the light source into approximate non-diffractive beam, control means for controlling the light emitting state of the light source according to image data input separately, and the pixel having a certain density An image forming apparatus comprising: a light amount changing unit that changes an amount of light applied to the optical scanning medium to obtain an image according to a position in the scanning direction of the light on the optical scanning medium. 2. The image forming apparatus according to claim 1, wherein the control unit also serves as the light amount changing unit. 3. The image forming apparatus according to claim 2, wherein the control means outputs a signal (hereinafter referred to as “intensity signal”) determined corresponding to a scanning position of the light on the optical scanning medium. Intensity output means, modulation signal generation means for generating and outputting a modulation signal based on the image information, and light source driving means for changing the emission intensity of the light source based on the modulation signal and the intensity signal. An image forming apparatus comprising: 4. The image forming apparatus according to claim 1, wherein the light quantity changing unit includes an optical filter installed between the optical scanning unit and the optical scanning medium, and the optical filter includes: An image forming apparatus, wherein the light transmittance is different at least according to the position of the light in the scanning direction. 5. The image forming apparatus according to claim 1, wherein the approximate non-diffractive beam converting means includes an axicon or a Fresnel lens having grooves at equal intervals. Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the optical scanning medium is a photoconductor in which a charge amount of a portion irradiated with light changes. 7. The image forming apparatus according to claim 1, further comprising a lens disposed between the optical scanning unit and the photoconductor, the lens having a condensing characteristic only in a light scanning direction. Image forming apparatus. 8. A light quantity control method for an image forming apparatus, wherein a pixel image is formed by irradiating light on an optical scanning medium, and an image is formed as a set of the pixel images, in order to obtain the pixel image having a certain density. A light quantity control method for an image forming apparatus, comprising: changing an amount of light to be applied to the optical scanning medium according to a scanning position of the light on the optical scanning medium. 9. An optical scanning device which operates according to an image signal separately input, a light source, an optical scanning means for scanning the light emitted from the light source, and light emitted from the light source to the optical scanning means. An approximate non-diffractive beam converting means arranged on the optical path for converting the light from the light source into an approximate non-diffracting beam, and arranged at a stage subsequent to the optical scanning means, at least in the scanning direction of the light. An optical scanning device comprising: an optical filter having a different light transmittance depending on the position of. 10. A printer for forming a pixel image by irradiating light on a photoconductor and forming an image as a set of the pixel images, wherein a light source and charging of the irradiated position when the light is irradiated. A photosensitive member of which the amount changes, an optical scanning means for scanning the light emitted from the light source on the photosensitive body, and a light from the light source arranged on the optical path from the light source to the optical scanning means are approximate to each other. Approximate non-diffractive beam converting means for converting to a diffracted beam, an interface for receiving image data input from the outside, and control of the light emission state of the light source based on the image data received by the interface. By doing so, a control circuit that forms an electric pixel image on the photoconductor, a developing unit that attaches toner to a region of the photoconductor where the electric image is formed, and Adhesion Transfer means for transferring the toner thus obtained to a separately supplied recording medium, and the control means further controls the amount of light with which the photoconductor is irradiated to obtain the electric pixel image of a certain density. A printer which changes according to a scanning position of the light on the photoconductor.