JP2001108930A - Scanning optical device and its controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning optical device and its controlling method capable of printing a high-quality image by correcting the condensing position of light beams in addition to changing the spot diameter of the light beam with switching of printing density in a multi-beam scanning system. SOLUTION: This optical device image-forms and scans laser beams LBa and LBb emitted from laser diodes 10a and 10b at prescribed intervals corresponding to printing density in the sub-scanning direction on a photoreceptor surface 50. A beam spot diameter on the surface 50 is adjusted by changing a slit through which the beams LBa and LBb pass by driving an opening regulating plate 14. A beam interval in the sub-scanning direction is adjusted by controlling the tilt angle of a prism 11 and a condensing position is adjusted by controlling the lens interval of collimator lenses or that of cylinder lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical apparatus and a control method therefor, and more particularly, to a scanning optical apparatus for simultaneously scanning a plurality of light beams at a predetermined interval in a sub-scanning direction on a surface to be scanned at the same speed, and a scanning optical apparatus. It relates to a control method.

[0002]

2. Description of the Related Art Conventionally, there have been provided various multi-beam scanning optical devices for simultaneously scanning a photosensitive member surface with a plurality of light beams in order to record an image on the photosensitive member. In this type of scanning optical device, as a method of switching the optical resolution (print density), the interval between the light emitting points of each light beam in the sub-scanning direction is changed according to a print density switching instruction.
It is known that a plurality of light source units in which the intervals of the light emitting points of each light beam in the sub-scanning direction are different are provided in accordance with the printing density and are selectively driven.

In switching the printing density, the optical system corresponds to the density in the sub-scanning direction, and the density in the main scanning direction corresponds to a method such as controlling the light emission timing of a light source.

[0004]

By the way, in addition to the above-mentioned change of the beam interval in the sub-scanning direction, the spot diameter of the light beam on the photosensitive member surface is changed along with the switching of the print density. It is preferable to correct the light position (autofocus). However, the conventional multi-beam scanning method does not include an autofocus mechanism, and cannot adjust the spot diameter to an optimum spot diameter according to the printing density.

Further, the intervals in the sub-scanning direction of a plurality of light beams and the condensing position (beam spot diameter on the photosensitive member surface) are
Since it fluctuates due to environmental conditions such as temperature, it is necessary to fine-tune and correct them. Even if the autofocus mechanism is incorporated in the multi-beam scanning method, there is a problem in how to correct the beam interval and the condensing position when switching the print density.

Accordingly, an object of the present invention is to provide a multi-beam scanning system which not only changes the spot diameter of a light beam in accordance with switching of printing density but also corrects the light beam condensing position, thereby achieving high-quality scanning. An object of the present invention is to provide a scanning optical device capable of obtaining a printed image and a control method thereof.

Another object of the present invention is to provide, in addition to the above objects,
It is an object of the present invention to provide a scanning optical device and a control method therefor that can prevent the occurrence of an adjustment error (improper image printing) such as a beam spot diameter when switching the printing density.

[0008]

To achieve the above object, a scanning optical apparatus according to the present invention comprises a light beam generating means for emitting a plurality of light beams and a plurality of light beams emitted from the generating means. Optical means for forming an image at a predetermined interval in the sub-scanning direction according to the print density on the scanned surface, and spot diameter changing means for changing the spot diameter of the light beam on the scanned surface according to the print density Focusing position detecting means for detecting the focusing position of the light beam; and focusing position correction for correcting the focusing position of the light beam by converting the optical magnification of the optical means based on the detection result of the detecting means. Means, when changing the spot diameter of the light beam by the spot diameter changing means,
There is provided control means for operating the light condensing position detecting means and the light condensing position correcting means.

In the present invention, when the print density is switched, the distance between the light beams in the sub-scanning direction is changed and the spot diameter of the light beam is changed. That is, if switching to a high density, change the spot diameter in the direction of decreasing,
If switching to a low density, change the spot diameter in the direction to increase. Then, the focus position is corrected together with the change in the spot diameter. As a result, the light beam is set at the interval and spot diameter in the sub-scanning direction corresponding to the printing density on the surface to be scanned, and further, the focusing position is corrected so that an image is formed correctly on the surface to be scanned. A quality printed image can be obtained.

In particular, in the scanning optical apparatus according to the present invention, when the spot diameter of the light beam is changed in a direction of decreasing the spot diameter (from a low printing density to a high printing density), the focusing position detecting means and the focusing position correction are used. Preferably, the means is operated to correct the focus position. The deterioration of the image when scanning by the multi-beam method is more remarkable at a high printing density than at a low printing density. Therefore, if the focus position is corrected at the time of switching to a high printing density, image deterioration can be made inconspicuous.

Further, in the scanning optical apparatus according to the present invention, an interval detecting means for detecting an interval in the sub-scanning direction of the plurality of light beams on the surface to be scanned, and based on a detection result of the detecting means. Interval correction means for correcting the interval of the light beam in the sub-scanning direction. This makes it possible to control the beam interval that fluctuates due to a temperature change or the like to an accurate value, and to obtain a higher quality printed image.

In particular, when the spot diameter of the light beam is changed in a direction of decreasing the spot diameter (from a low printing density to a high printing density), the interval detecting means and the interval correcting means are operated to reduce the interval of the light beam in the sub-scanning direction. It is preferable to correct. At a high printing density, the magnification in the sub-scanning direction tends to be low, and the error in the interval between light beams tends to be noticeable as image deterioration. By correcting the beam interval at the time of switching to a high printing density, it is possible to prevent image deterioration before it occurs.

Further, when the spot diameter of the light beam is changed in a direction of decreasing the spot diameter (from a low printing density to a high printing density),
It is preferable to correct the focusing position and then correct the beam interval. For example, if the beam interval is corrected before correcting the focal position, the light beam is not narrowed down to a predetermined spot diameter at the time of correcting the interval.
, The rising of the detection signal is unclear, and the detection accuracy deteriorates. Also, when correcting the focal position with a change in optical magnification, if the focal position correction is performed after the beam interval correction, the corrected beam interval will change due to the correction of the focal position, and it will be re-corrected. Is required. By correcting the beam interval after the correction of the focusing position, the accuracy of detecting the beam interval can be increased, and waste such as re-correction can be eliminated.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a scanning optical device and a control method thereof according to the present invention will be described with reference to the accompanying drawings.

1 and 2, a scanning optical apparatus according to an embodiment of the present invention generally includes two laser diodes 10a and 10b, a prism 11, a beam splitter 12, a collimator lens 13, an aperture control. Plate 14,
Cylinder lens 15, polygon mirror 20, fθ lens 25, beam interval detector 30, focus detector 40
It is composed of

The light beams LBa and LBb emitted from the laser diodes 10a and 10b in directions orthogonal to each other are combined by a beam splitter 12 and a collimator lens 13
Is converted into parallel light (or convergent light). The beam splitter 12 is a well-known type in which two prisms are joined via a semi-permeable membrane.
Bb is reflected 90 °.

Combined by a beam splitter 12 and
Light beams LBa and LB transmitted through collimator lens 13
b reaches the polygon mirror 20 via the aperture regulating plate 14 and the cylinder lens 15. The polygon mirror 20 is driven to rotate at a constant angular velocity in the direction of arrow A, and the light beam LB
a and LBb are deflected at equal angular velocities by the respective reflection surfaces of the polygon mirror 20 based on this rotation, form an image on the photoreceptor surface 50 via the fθ lens 25 and a folding mirror (not shown), and scan in the main scanning direction X. I do. That is, in this optical device, two lines are simultaneously written on the photoreceptor surface 50 by one scanning.

Lens 25 is a well-known one, and has a function of correcting the main scanning speed on the image plane at a constant speed, a function of correcting the curvature of field, or a troublesome operation of the polygon mirror 20 in cooperation with the cylinder lens 15. It has a function to correct the error.

The photoreceptor surface 50 is usually formed as a drum type, is driven to rotate at a constant speed, and is two-dimensionally formed on the photoreceptor surface 50 by this rotation (sub scanning) and main scanning of the light beams LBa and LBb (in the direction of arrow X). An image (electrostatic latent image) is written.

The distance between the light beams LBa and LBb in the sub-scanning direction on the photoreceptor surface 50 is adjusted by changing the inclination angle of the prism 11 so as to be a predetermined distance corresponding to the printing density. For example, when the print density is 400 dpi, the interval on the image plane is 63.5 μm, and when the print density is 600 dpi, it is 42.3 μm. The intervals in the main scanning direction accompanying the switching of the printing density are the same as those of the laser diodes 10a and 10b.
It is adjusted by controlling the light emission timing.

The beam interval in the sub-scanning direction also varies depending on environmental conditions such as temperature. In such a case, correction can be made by finely adjusting the inclination angle of the prism 11.

The light beams LBa,
The change of the spot diameter of the LBb on the photoreceptor surface 50 is shown in FIG.
As shown in FIG.
This is performed by selectively moving a and b with respect to the optical axis. Therefore, the opening regulating plate 14 is configured to be driven by the actuator 16. In the present embodiment, the print density is switched between two types, low dpi and high dpi. Therefore, the opening regulating plate 14 having two types of slits 14a and 14b is used.

The spot diameter can be changed by moving the collimator lens 13 on the optical axis to change the optical magnification.

On the other hand, the light beam L accompanying the switching of the printing density
Adjustment of the light condensing positions (focal points) of Ba and LBb is performed by changing the interval between two collimator lenses 13 or cylinder lenses 15. FIG. 4 shows an embodiment in which one of the two cylinder lenses 15 is driven by the actuator 17.

Although the light condensing position varies depending on environmental conditions such as temperature, the collimator lens 1 is also used in such a case.
Correction can be made by finely adjusting the distance between 3 and the cylinder lens 15.

In order to perform the above-mentioned beam interval correction and light-condensing position correction, the detectors 30 and 40 are provided at optically equivalent positions to the photosensitive member surface 50 and at the start side in the main scanning direction.

As shown in FIG. 5, the beam interval detector 30 has the triangular detection surfaces 31 and 32 with the respective oblique sides positioned upstream in the main scanning direction X and along the main scanning direction X. They are juxtaposed. In FIG. 5, a is the light beam LB
The scanning trajectory a and the scanning trajectory b of the light beam LBb.

Here, the amount of deviation of the interval Y _{1 from} a predetermined value is detected. First, the light beams LB are output from the optical sensors 31 and 32.
A time difference t1 at which a is detected and a time difference t2 at which the light beam LBb is detected are measured. And the time difference t1, t2
A deviation t3 of, compares the reference value of deviation t3, the light beams LBa, and calculates the shift amount of spacing Y ₁ of LBb. This calculation is performed by the control unit 51 to which detection signals from the optical sensors 31 and 32 are input.

Further, in order to determine the scanning position in the sub-scanning direction, another optical sensor 33 is provided on the scanning locus a.
It detects that the light beam LBa is scanned at a predetermined position.

The controller 51 calculates correction data according to the calculated shift amount, and finely adjusts the inclination angle of the prism 11 based on the correction data.

The focus detector 40 detects at least one of the light beams LBa and LBb with an optical sensor such as a CCD or a PD, and detects the light condensing state. It is well known in the field of scanning optics. The detection signal from the focus detector 40 is also transmitted to the control unit 5.
1, the defocus amount is calculated, and the correction data corresponding to the defocus amount is calculated. The interval between the collimator lens 13 and the cylinder lens 15 is finely adjusted based on the correction data.

Next, a control procedure of the scanning optical device will be described. The light beams LBa and LBb emitted from the laser diodes 10a and 10b are kept on the photoreceptor surface 50 at intervals in the sub-scanning direction corresponding to the respective print densities (dpi) based on the inclination angle of the prism 11. Adjusted. The light beams LBa, LBb pass through one of the slits 14a, 14b of the aperture regulating plate 14, and are adjusted to have a predetermined spot diameter on the photoreceptor surface 50. During printing for each page or for each job, the detector 30 and 40 are used to detect the beam interval and the condensing position using the detectors 30 and 40, and to determine the beam interval and the condensing position due to a rise in temperature inside the printer. Correct the misalignment.

On the other hand, when the print density (dpi) switching is instructed, the angle of the prism 11 and the collimator lens 13 or the cylinder lens 15 are adjusted so that the beam interval and the beam spot diameter correspond to the instructed print density. Adjust the lens spacing. Then, in the present embodiment, at the time of switching the print density from low dpi to high dpi, at least the detection of the focus position and the correction thereof are executed. Preferably,
It also detects the beam interval and corrects it. In the latter case, it is desirable to perform detection / correction of the beam interval after correcting the condensing position to a normal state.

The reason why at least the light condensing position is corrected at the time of switching from low dpi to high dpi is as follows.

FIG. 6 shows a state in which the light beam condensing position (beam waist) is normally located on the surface of the photosensitive member. In this case, the writing spot diameter is high dpi and low dpi.
Both i are within the range of the allowable spot diameter. FIG. 7 shows a state where the beam waist is shifted from the photoconductor surface. Since the spot diameter of the beam is different between the high dpi and the low dpi, the depth width indicating the allowable range of the spot diameter is different, and the depth width at the high dpi is narrower than the low dpi.

For example, in the case where the light beams LBa and LBb are shifted in the condensing position due to a rise in the temperature inside the printer, as shown in FIG. 7, since the depth width is wide in the printing state at low dpi, as shown in FIG. The writing spot diameter is determined to be within the allowable range. If printing is performed by switching to a high dpi in this state, the spot diameter falls outside the allowable range because the depth width is narrow at a high dpi even at the same shift of the focusing position, and the image quality is degraded. Also, when detecting the light condensing position, low d
The pi light beam has a problem that the diameter change near the beam waist is gentle, and the detection sensitivity of the condensing position is low. Therefore, it is preferable to perform detection / correction of the condensing position when the scanning optical device is switched to a high dpi.

In the present embodiment, when switching to a high dpi, the beam interval is always detected and corrected so that the beam interval becomes an appropriate value. At a high dpi, the magnification in the sub-scanning direction tends to be low, and the error in the beam interval degrades the image (especially, the size of the print line interval in the sub-scanning direction is alternately displayed, resulting in uneven density of the stripe pattern). Tend to stand out. In the present embodiment, such an image deterioration can be prevented by always correcting the beam interval when switching to high dpi.

Further, in this embodiment, when switching to a high dpi, after correcting the condensing position, the angle of the prism 11 is adjusted to change the optical axis of the light beam LBa to correct the beam interval. For example, if the beam interval is corrected with a change in the optical magnification after the light-collecting position is corrected, the corrected light-collecting position will be misaligned, so that re-correction is required. In the present embodiment, since the correction of the beam interval does not involve a change in the optical magnification, the correction of the beam interval does not change the focusing position.

In order to achieve the same object, the distance between the light emitting points of the light beams LBa and LBb may be changed, that is, the distance between the object points may be changed.

If the beam interval is corrected before correcting the focusing position, the rise of the detection signal of the detector 30 is unclear because the light beam is not narrowed to a predetermined spot diameter at the time of correcting the interval. Detection accuracy deteriorates. If detection / correction of the beam interval is performed after correcting the focusing position, such a decrease in detection accuracy can be avoided.

Further, in this embodiment, since the beam interval is changed at the time of switching of the printing density and the beam interval is corrected by a single member such as the prism 11 in order to cope with the fluctuation of the optical magnification, the beam interval correcting mechanism is used. Can be made compact at low cost.

Here, an example of a control procedure at the time of switching from low dpi to high dpi will be described with reference to FIG.

When the instruction to switch to the high dpi is confirmed in step S1, the aperture regulating plate 14 is driven in step S2 to switch the slits 14a and 14b. Next, the light beams LBa and LBb are scanned, and the focus position is detected in step S3. Next, in step S4, it is determined whether or not the light condensing position is within an allowable range. If not, the collimator lens 13 or the cylinder lens 15 is driven to adjust the lens interval in step S5, and in step S6, The focus position is detected again. Next, in step S7, it is determined whether or not the light condensing position is within the allowable range. If not, steps S5 and S6 are repeated.

If the focusing position falls within the allowable range (YES in steps S4 and S7), the beam interval is detected in step S8, and it is determined in step S9 whether the beam interval is within the allowable range. If not, the prism 11 is driven in step S10, and the beam interval is detected again in step S11. Next, in step S12, it is determined whether or not the beam interval is within an allowable range. If not, steps S10 and S11 are repeated. If the beam interval falls within the allowable range (YES in steps S9 and S12), this subroutine ends.

It should be noted that the scanning optical device and the control method thereof according to the present invention are not limited to the above embodiment, but can be variously modified within the scope of the invention.

In particular, various methods can be employed for the means for detecting / correcting the intervals of the plurality of light beams in the sub-scanning direction and the means for detecting / correcting the condensing position. Further, a multi-beam system of not only two beams but also three beams or more may be used, and the printing density may be switched to three or more types. Further, the types and arrangement of the various optical elements constituting the optical path are arbitrary.

[Brief description of the drawings]

FIG. 1 is a schematic plan view illustrating a scanning optical device according to an embodiment of the invention.

FIG. 2 is a configuration diagram of the scanning optical device as viewed from a sub-scanning direction, showing a portion from a laser diode to a polygon mirror.

FIG. 3 is a perspective view showing a driving mechanism of an opening regulating plate.

FIG. 4 is a perspective view showing a driving mechanism of a cylinder lens.

FIG. 5 is an explanatory diagram showing a method of detecting a beam interval.

FIG. 6 is an explanatory diagram showing a light beam condensing state (in a normal case).

FIG. 7 is an explanatory diagram showing a light beam condensing state (when the light beam is shifted).

FIG. 8 is a flowchart illustrating a control unit when the print density is switched.

[Explanation of symbols]

 10a, 10b laser diode 11 prism 12 beam splitter 13 collimator lens 14 aperture control plate 15 cylinder lens 16, 17 actuator 20 polygon mirror 25 fθ lens 30 beam interval detector 40 focus detection Unit 50: Photoconductor surface 51: Control unit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenji Takeshita 2-13-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. (reference) 2C362 AA21 AA22 AA34 AA47 BA58 BA61 BA67 BA71 BA85 BA86 CB03 CB08 CB14 2H045 AA01 BA21 CA82 CA92 CA98 CB24 CB32 DA22 DA24

Claims (10)

[Claims] 1. A light beam generating means for emitting a plurality of light beams, and a plurality of light beams emitted from the light beam generating means are separated on a surface to be scanned in a sub-scanning direction at a predetermined interval according to a printing density. Optical means for forming an image by focusing; spot diameter changing means for changing the spot diameter of the light beam on the surface to be scanned in accordance with the printing density; light-condensing position detecting means for detecting the light-condensing position of the light beam; Focusing position correcting means for converting the optical magnification of the optical means based on the detection result of the focusing position detecting means to correct the focusing position of the light beam, and changing the spot diameter of the light beam by the spot diameter changing means And a control means for operating the focus position detecting means and the focus position correcting means. 2. The apparatus according to claim 1, wherein the control means operates the light condensing position detecting means and the light condensing position correcting means when changing the light beam spot diameter to a smaller direction. Scanning optics. 3. An interval detecting means for detecting an interval in the sub-scanning direction of the plurality of light beams on the surface to be scanned, and correcting the interval of the light beams in the sub-scanning direction based on a detection result of the interval detecting means. The scanning optical device according to claim 1, further comprising: an interval correction unit. 4. The scanning optical apparatus according to claim 3, wherein the control unit operates the interval detecting unit and the interval correcting unit when changing the spot diameter of the light beam to a smaller direction. 5. The controller according to claim 1, wherein the controller is configured to operate the converging position detecting unit and the converging position correcting unit when changing the spot diameter of the light beam to a smaller direction. 4. The scanning optical device according to claim 3, wherein 6. A control method for a scanning optical apparatus for scanning a plurality of light beams emitted from a light beam generating means on a surface to be scanned at predetermined intervals in a sub-scanning direction, comprising the steps of: A step of changing the spot diameter of the light beam in step (a), and a step of detecting the light beam condensing position and correcting the light beam condensing position based on the detection result. Method. 7. The control method according to claim 6, wherein a step of detecting / correcting a condensing position of the light beam is performed when the light beam spot diameter is changed in a direction of decreasing the spot diameter. 8. The method according to claim 1, further comprising the step of detecting intervals in the sub-scanning direction of the plurality of light beams on the surface to be scanned, and correcting the intervals of the light beams in the sub-scanning direction based on the detection result. The control method according to claim 6, wherein 9. When changing the spot diameter of the light beam in a direction to reduce the spot diameter, the distance between the light beams in the sub-scanning direction is detected /
The control method according to claim 8, wherein a correcting step is performed. 10. The method according to claim 8, wherein when changing the diameter of the light beam to a smaller direction, the light beam condensing position is detected / corrected, and then the interval between the light beams is detected / corrected. The control method described.