JPH06208068A - Optical scanning device - Google Patents

Abstract

PURPOSE:To adjust beam intervals and beam diameters independently of each other when plural scanning beams are used. CONSTITUTION:This optical scanning device is equipped with a laser diode array 1 which emits two laser beams, a collimator lens 2 which collimates the beams from the laser diode array 1 into parallel luminous flux, a rotary polygon mirror 3 which deflects the beams passed through the collimator lens 2, an image forming lens 4 which forms; images of the deflected beams nearby a photosensitive body 5, a cylinder lens 8 for correcting the surface tilt of the rotary polygon mirror 3, a beam interval varying optical system 7 which can vary subscanning-directional beam intervals on the photosensitive body 5, and a slit width varying device 6 which can vary beam diameters on the photosensitive body 5; and the slit width varying device 6 corrects variation in beam diameter due to the variation in beam interval by the beam interval variable optical system 7.

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 an image forming apparatus such as a copying machine or a laser printer, and more particularly, it uses a light source section for emitting a plurality of independent laser beams and is used on a surface to be scanned. Simultaneously scan multiple scan lines,
It relates to an optical scanning device for recording information.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer, a method has been proposed in which a surface to be scanned is simultaneously scanned with a plurality of laser beams in order to achieve high speed or high resolution. As an optical scanning device for realizing this method, for example, one disclosed in Japanese Patent Publication No. 1-45065 is known.

FIG. 8 is an explanatory view showing a schematic structure of the optical scanning device disclosed in the above publication. In this device, the laser beams emitted from the two light emitting sources 51a and 51b are
After the objective lens 52, a deflector 53 composed of a rotating polygon mirror
The image is formed on the photosensitive medium surface of the rotating cylindrical body 55 which is deflected by the scanning lens 54 and rotates at a constant speed, and the surface of the photosensitive medium is scanned. In the figure, L ₁ and L ₂ indicate scanning lines scanned by the laser beams emitted from the light emitting sources 51a and 51b, respectively.

In such an apparatus, it is necessary to set the interval between the scanning lines L ₁ and L ₂ on the surface to be scanned with high accuracy, but this interval can be set to a desired value without adjustment. Since it is very difficult, various beam spacing changing methods have been proposed. Among them, as shown in Japanese Patent Laid-Open No. 57-54914, only between the objective lens 52 and the deflector 53 in FIG. 8 in a plane perpendicular to the deflection plane of the beam deflected by the deflector 53. There is a method of providing an optical means capable of changing the imaging magnification. This optical means is, for example, an afocal beam expander. The afocal beam expander refers to an optical system in which paraxial rays that are incident parallel to the optical axis are emitted parallel to the optical axis. Parallel paraxial rays incident on the afocal beam expander are parallel to each other even after passing through the afocal beam expander, but the angles formed by the rays with the optical axis on the object side and the image side are generally equal. I won't. The ratio of the angle formed by the emitted light ray with the optical axis to the angle formed by the incident light ray with the optical axis is called angular magnification.

FIG. 9 is an explanatory view showing an example of an afocal beam expander disclosed in Japanese Patent Laid-Open No. 57-54914. This afocal beam expander is composed of three groups of lens systems, and the angular magnification can be changed by changing the lens arrangement. In the example of FIG. 9, when two beams are emitted from the afocal beam expander, one of which is along the optical axis and the other is at an angle θ with respect to the optical axis and enters the afocal beam expander, The angle θ ′ formed by the emitted light of
In the lens arrangement of (a), θ ′ = θ / 3, in the lens arrangement of (b), θ ′ = θ / 6, and in the lens arrangement of (c), θ ′ =
θ / 9.

In the afocal beam expander shown in FIG. 9, the larger the angular magnification, the smaller the beam diameter of the outgoing beam. Further, due to the characteristics of the Gaussian beam, the beam diameter on the surface of the photosensitive medium after passing through the scanning lens changes depending on the beam diameter before passing through the scanning lens. Therefore, the beam diameter on the surface of the photosensitive medium changes depending on the angular magnification of the afocal beam expander, that is, the exit angle of the beam from the afocal beam expander. Therefore, in the optical scanning device that changes the beam interval using the afocal beam expander, the beam interval and the beam diameter are changed at the same time when the resolution is switched.

[0007]

However, the adjustment of the beam interval is not necessary only when the beam interval is changed as in the case of switching the resolution, but when the beam interval is changed by disturbance. Will also be needed. In this case, even if you change the beam spacing, you want to maintain the current beam diameter, but in the configuration using the afocal beam expander described above, changing the beam spacing will always change the beam diameter accordingly. There was a problem that it would end up.

Further, when the resolution is switched, the beam interval is proportional to the resolution, but it is not always preferable that the beam diameter is proportional to the resolution, and there is a case where it is desired to finely adjust the beam diameter independently of the beam interval. is there. However, with the above-described configuration, the beam interval and the beam diameter cannot be adjusted independently, so that the demand cannot be met.

Therefore, an object of the present invention is to provide an optical scanning device capable of adjusting the beam interval and the beam diameter independently of each other when scanning a plurality of light beams.

[0010]

According to another aspect of the present invention, there is provided an optical scanning device including a light source section for generating a plurality of independent light beams, and a light source section for deflecting the respective light beams from the light source section. Is provided between the light source section and the deflector, and a light beam in the sub-scanning direction is provided between the light source section and the deflector. A variable beam spacing optical system capable of varying the beam spacing and a beam diameter varying means capable of varying the beam diameter of each light beam on the surface to be scanned are provided separately from the variable beam spacing optical system. It is a thing.

In this optical scanning device, a plurality of light beams from the light source section are deflected by the deflector and focused on the surface to be scanned by the imaging optical system to scan the surface to be scanned. In addition, the variable beam-spacing optical system can adjust the distance between the light beams in the sub-scanning direction on the surface to be scanned, and the beam diameter changing means can also adjust the beam diameter of each light beam on the surface to be scanned.

An optical scanning device according to a second aspect of the present invention is the optical scanning device according to the first aspect, further comprising a beam diameter changing means for changing the beam diameter due to the change in the beam distance by the variable beam distance optical system. A beam diameter correcting means for correcting is provided.

In this optical scanning device, when the beam spacing is changed by the variable beam spacing optical system, the beam diameter also changes accordingly, but this change in beam diameter is corrected by the beam diameter correcting means.

The optical scanning device according to a third aspect of the present invention is the optical scanning device according to the second aspect, further comprising: a change in the intensity of the light beam on the surface to be scanned due to the correction of the change in the beam diameter by the beam diameter changing means. The light intensity correction means for correction is provided.

In this optical scanning device, when the change of the beam diameter is corrected by the beam diameter changing means, the intensity of the light beam on the surface to be scanned also changes accordingly. The change of the intensity of the light beam is corrected by the light intensity correction. Corrected by means.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 relate to an embodiment of the present invention.

FIG. 1 is an explanatory diagram showing the overall structure of the optical scanning device of this embodiment, and FIG. 2 is an explanatory diagram showing the state of the beam from the light source to the deflector of the optical scanning device of FIG. As shown in these figures, the optical scanning device of the present embodiment is provided with a plurality of laser diode arrays 1, here two independent laser beams, and a divergent laser beam generated by the laser diode array 1. Collimator lens 2 for converting the light beam into a parallel light beam, and a photoconductor 5 that rotates the laser beam after passing through the collimator lens 2 and rotates at a constant speed.
A rotary polygonal mirror 3 as a deflector for scanning above, and an imaging lens 5 for correcting the scanning speed of the laser beam deflected by the rotary polygonal mirror 3 and for focusing the laser beam in the vicinity of the photoconductor 5. And a cylinder lens 8 that is provided between the collimator lens 2 and the rotary polygon mirror 3 and forms a part of an optical system that corrects the surface tilt of the rotary polygon mirror 3. As shown in FIG. 2, the laser diode array 1 emits two laser beams at a predetermined interval along a direction perpendicular to the scanning direction, and these two laser beams are shown in FIG. As shown, two scanning lines L ₁ and L ₂ are formed on the photoconductor 5.

The optical scanning device is further provided between the collimator lens 2 and the cylinder lens 8 and includes a photoconductor 5
It is provided between the beam interval variable optical system 7 capable of changing the laser beam interval in the sub-scanning direction above, and the collimator lens 2 and the beam interval variable optical system 7, and determines the beam diameter of the laser beam on the photoconductor 5. A slit width changing device 6 as a beam diameter changing means that can be changed, and a photoconductor 5.
Two scanning lines L on the photoconductor 5 provided near the
₁ and a beam interval detector 9 for detecting an interval of L ₂ .

In the image forming apparatus having the optical scanning device, the photoconductor drum 5 is uniformly charged according to the usual xerographic process, and the photoconductor drum 5 is exposed by the two laser beams modulated in accordance with the image information. An electrostatic latent image is formed on the body 5, and toner is attached to the electrostatic latent image by a developing device to form a visible toner image.
The transfer device transfers the toner image onto the sheet.

The variable beam-spacing optical system 7 is, for example, an afocal beam expander composed of a plurality of lenses as shown in FIG. 9, and the arrangement of the lenses is changed by a lens moving device (not shown). The distance between the laser beams in the sub-scanning direction, that is, the distance between the two scanning lines L ₁ and L ₂ can be changed.

FIG. 3 is a perspective view showing an example of the slit width changing device 6. The slit width changing device 6 is provided with a slit plate 6b having a slit 6a in the center and a shaft portion 6c for rotating the slit plate 6b. The shaft portion 6c is arranged along an axis A perpendicular to the traveling direction of the laser beam, and as shown in FIG. 2, two laser beams pass through the slit 6a. And
By rotating the slit plate 6b around the axis A by a driving means such as a motor (not shown), as shown in FIG. The opening width is changed so that the beam width of the laser beam after passing through the slit 6a is adjusted.

FIG. 5 is a perspective view showing another example of the slit width changing device 6. The slit width changing device 6 includes two movable plates 1 arranged along a direction corresponding to the sub-scanning direction.
0a and 10b, and a holder 11 that holds the movable plates 10a and 10b so as to be movable in a direction corresponding to the sub-scanning direction. The two movable plates 10a, 10b are moved by a driving means such as an actuator (not shown) along the direction corresponding to the sub-scanning direction and symmetrically with respect to the traveling direction of the laser beam. 10b
The opening width of the slit 10c formed between them is changed so that the beam width of the laser beam after passing through the slit 10c is adjusted.

FIG. 6 is a block diagram showing a configuration for controlling the lens position of the variable beam spacing optical system 7, the slit width of the slit width changing device 6 and the laser power of the laser diode array 1 in this embodiment. As shown in this figure, in the present embodiment, an arithmetic unit 20 for performing the later-described arithmetic operation based on the output of the beam interval detector 9, and the beam interval variable optical system 7 based on the output of this arithmetic unit 20.
Lens position control circuit 24 that controls the lens moving device 28 that moves the lens of FIG. First to do
Laser power control circuit 26, a second laser power control circuit 27 for setting the laser power based on the output of the arithmetic unit 20, and the first laser power control circuit 2
An adder 29 for adding the setting value of 6 and the setting value of the second laser power control circuit 27 and supplying the result to the laser diode array 1 is provided. In addition, each setting value of the beam interval, the slit width, and the laser power is input to the arithmetic unit 20 from the control circuit 30 of the image forming apparatus.

The arithmetic unit 20 is composed of, for example, a microcomputer, and realizes the functions of the lens position determining unit 21, the slit width determining unit 22, and the laser power determining unit 23 by executing the program. .

The lens position determining means 21 determines the optimum lens position in the variable beam spacing optical system 7 from the difference between the beam spacing detected by the beam spacing detector 9 and the set value of the beam spacing from the control circuit 30. Then, the required movement amount of the lens is sent to the lens position control circuit 24. The slit width determining means 22 calculates the difference between the angular magnifications of the optical system at the current lens position and the optical system at the adjusted lens position, and further calculates the beam diameter change to optimize the slit width changing device 6. The slit width is determined, and the required amount of change in slit width is sent to the slit width control circuit 25. The laser power determining means 23 determines the photosensitive member 5 based on the change amount of the slit width.
The amount of change in the laser power reaching the top is calculated, the optimum laser power value is determined, and the value is sent to the second laser power control circuit 27.

Next, referring to the flowchart of FIG.
The operation relating to the control of the beam interval, the beam diameter and the laser power in this embodiment will be described. As shown in FIG. 7, first, after powering on the image forming apparatus, in step (hereinafter referred to as S) 101, the control circuit 30 instructs the arithmetic unit 20 to move the lens position of the variable beam spacing optical system 7, The initial value of the slit width of the slit width changing device 6 is set.

Next, in step S102, the beam interval detector 9 detects the beam interval. Next, in step S103, the lens position determining means 21 of the arithmetic unit 20 determines the difference in the beam distance detected by the beam distance detector 9 and the set value of the beam distance from the control circuit 30 in the variable beam distance optical system 7. The optimum lens position, that is, the lens position where the beam interval becomes a set value is determined, and the required lens movement amount is sent to the lens position control circuit 24. In accordance with this lens movement amount, the lens position control circuit 24 controls the lens position of the variable beam distance optical system 7 via the lens movement device 28 to control the beam distance.

When the beam spacing is changed by the beam spacing variable optical system 7, the beam diameter also changes accordingly. Therefore, in S104, the change in the beam diameter is corrected. That is,
Based on the lens position determined by the lens position determination unit 21, the slit width determination unit 22 calculates the difference between the angular magnifications of the optical system at the current lens position and the optical system at the adjusted lens position, and The beam diameter variation is calculated to determine the optimum slit width in the slit width changing device 6, and the necessary variation in slit width is sent to the slit width control circuit 25. Then, the slit width of the slit width changing device 6 is controlled by the slit width control circuit 25 according to the change amount of the slit width, and the beam diameter on the photoconductor 5 is corrected. From the characteristics of the laser beam which is a Gaussian beam, when the slit width is increased, the beam diameter on the photoconductor 5 after passing through the imaging lens 4 is reduced, and when the slit width is decreased, the beam diameter on the photoconductor 5 is increased. .

When the slit width is changed by the slit width changing device 6, the light amount of the laser beam passing through the slit changes, and the laser power on the photosensitive member 5 changes.
Therefore, in S105, the change in laser power is corrected. That is, the amount of change in the laser power reaching the photoconductor 5 is calculated from the amount of change in the slit width obtained by the slit width determining means 22, the optimum laser power value is determined, and the second laser power control circuit Send to 27. Then, the laser power output from the laser diode array 1 is controlled by the second laser power control circuit 27, and the change in the laser power on the photoconductor 5 is corrected.

Next, in S106, it is judged whether or not the control of the beam interval, the beam diameter and the laser power is ended. If the control is ended ("Y"), the operation is ended, but if the control is not ended ("N"). ") Returns to S102.

FIG. 7 shows the operation in the case of correcting the change of the beam diameter due to the change of the beam interval and further correcting the change of the laser power due to the change of the beam diameter.
The beam interval, the beam diameter, and the laser power can be controlled independently. That is, when changing the beam interval, the set value of the lens position is changed. Further, when changing the beam diameter, the set value of the slit width is changed, and the laser power on the photoconductor 5 changes due to the change of the slit width, so the laser power is also changed if necessary. Further, when changing the laser power, the set value of the laser power is changed.

As described above, in this embodiment, since the beam interval, the beam diameter, and the laser power can be controlled independently of each other, when the resolution is switched, etc.
It is possible to change both the beam interval and the beam diameter, or to change only the beam interval without changing the beam diameter. Further, even if the beam diameter is changed, it is possible to keep the laser power on the photoconductor 5 constant or to change only the laser power independently. Further, when the beam interval changes due to disturbance or the like, it is possible to adjust the beam interval without changing the beam diameter.

The present invention is not limited to the above embodiment,
For example, when adjusting the beam interval only within a range where the change in laser power due to the slit width change can be ignored,
The laser power determining means 23 and the second laser power control circuit 27 in FIG. 6 are not always necessary.

If the variation of the beam spacing is not taken into consideration, it is possible to move the lens of the variable beam spacing optical system 7 based only on the set value of the beam spacing. In this case, the beam spacing detector 9 is used. Is not always necessary.

[0035]

As described above, according to the first aspect of the invention, in the optical scanning device for scanning a plurality of light beams, the variable beam spacing optical system and the beam spacing variable optical system are separate beams. Since the diameter changing means is provided, there is an effect that the intervals between the plurality of light beams and the beam diameter of each light beam can be independently controlled.

Further, according to the second aspect of the invention, since it is possible to correct the change in the beam diameter due to the change in the beam interval by the variable beam interval optical system, in addition to the above effect, the beam interval changes, Even when this is adjusted, there is an effect that the beam diameter can be kept constant and the image quality can be kept in a good state.

According to the third aspect of the invention, it is possible to correct the change in the intensity of the light beam on the surface to be scanned due to the correction of the change in the beam diameter by the beam diameter changing means. In addition to the effects of the invention described in 2,
Even if the beam interval fluctuates and is adjusted, both the beam diameter and the light beam intensity can be kept constant, and the image quality can be kept in a better state.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of a beam from a light source to a deflector of the optical scanning device of FIG.

FIG. 3 is a perspective view showing an example of a slit width changing device in FIG.

FIG. 4 is an explanatory diagram showing an operation of the slit width changing device of FIG.

5 is a perspective view showing another example of the slit width changing device in FIG. 1. FIG.

FIG. 6 is a block diagram showing a configuration for controlling a lens position of a variable beam spacing optical system, a slit width of a slit width changing device, and a laser power of a laser diode array in one embodiment.

FIG. 7 is a flowchart showing an operation regarding control of a beam interval, a beam diameter, and a laser power in one embodiment.

FIG. 8 is an explanatory diagram showing a schematic configuration of a conventional optical scanning device.

FIG. 9 is an explanatory diagram showing an example of an afocal beam expander.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser diode array, 3 ... Rotating polygonal mirror, 4 ... Imaging lens, 5 ... Photoconductor, 6 ... Slit width changing device, 7 ...
Beam spacing variable optical system, 9 ... Beam spacing detector

Claims (3)

[Claims] 1. A light source section for generating a plurality of independent light beams, a deflector for deflecting each light beam from the light source section to scan a surface to be scanned, and each light beam from the light source section. An imaging optical system that focuses on the surface to be scanned, and a beam interval variable optical system that is provided between the light source unit and the deflector and is capable of changing the interval between the light beams in the sub-scanning direction on the surface to be scanned. And an optical scanning device provided separately from the variable beam spacing optical system and capable of changing the beam diameter of each light beam on the surface to be scanned. 2. A beam diameter correcting means for correcting the change of the beam diameter due to the change of the beam spacing by the variable beam spacing optical system using the beam diameter changing means. Optical scanning device. 3. The light intensity correcting device according to claim 2, further comprising a light intensity correcting device that corrects a change in the intensity of the light beam on the surface to be scanned due to the correction of the change in the beam diameter by the beam diameter correcting device. Optical scanning device.