JP4197806B2 - Scanning optical system and focus position adjusting method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device applicable to an image writing optical system such as a digital electrophotographic copying machine and a laser printer, and can be applied to an image forming apparatus, a measuring instrument, an inspection apparatus, and the like.
[0002]
[Prior art]
In recent years, the density of formed images has been increasing in digital copying machines, laser printers, and the like, and accordingly, it is desired to reduce the beam spot diameter on the surface of the photoconductor that is the surface to be scanned. However, when the beam spot diameter is reduced to about 30 μm, the depth of focus can be only about 1 mm, so that component accuracy and assembly accuracy are strictly required. Accordingly, various methods for adjusting the focal position by detecting the imaging state of the light beam have been proposed.
[0003]
An example of this is an optical scanning device proposed in Japanese Patent No. 2761723 and Japanese Patent Laid-Open No. 10-20225. The detection means for detecting the imaging state of the light beam is optically connected to the surface to be scanned outside the image area. They are arranged on a substantially equivalent surface.
[0004]
[Problems to be solved by the invention]
However, in an actual scanning optical system, the curvature of field often deteriorates outside the image area, and the focal position often deviates from a position that is optically substantially equivalent to the surface to be scanned. Also, even if the amount of field curvature at the detection means position is kept small by design, the field curvature deteriorates due to accumulation of component tolerances and component assembly tolerances in actual use, and the focal position within the image area And the detection means position may cause the focal position to deviate. Therefore, even if the focus position is adjusted to the detection means position, the optimum focus position in the image region is not always obtained.
[0005]
In addition, the focal positions in the main scanning direction and the sub-scanning direction are not always the same both inside and outside the image area. Even if the focus position is optimized in the main scanning direction, the focus position in the sub-scanning direction is not always optimal, and even if the focus position is optimized in the sub-scanning direction, the focus position in the main scanning direction is optimal. There are problems such as not always.
[0006]
The present invention has been made to solve the above-described problems of the prior art, and a detecting means for detecting the imaging state of the light beam scanned by the scanning optical system is adapted to the actual curvature of field. It is an object of the present invention to provide a scanning optical system that can adjust the focal position in an image region to an optimal position by arranging them.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present application includes a light source that emits a light beam, a scanning optical system that deflects the light beam from the light source and focuses it on the surface to be scanned, and In an optical scanning apparatus including a detection unit that detects an imaging state of a light beam scanned by a scanning optical system and an adjustment unit that adjusts a focal position of the light beam on a surface to be scanned, the detection unit includes an image It is located on the locus of the beam waist position in a state where it is located outside the region and is shifted in the optical axis direction from a position optically substantially equivalent to the surface to be scanned to suppress curvature of field in the image region to a small extent, The adjusting means adjusts the focal position of the light beam to the detection means position based on the detection result of the detection means .
[0008]
According to a second aspect of the present invention, there is provided a light source that emits a light beam, a scanning optical system that deflects the light beam from the light source and focuses the light beam on a surface to be scanned, and a light beam that is scanned by the scanning optical system. In an optical scanning apparatus including a detecting unit that detects an imaging state and an adjusting unit that adjusts a focal position of a light beam on a scanned surface, the detecting unit is located outside an image area and is It is arranged on the locus of the beam waist position in a state in which the curvature of field in the image area is suppressed to be small by shifting from the optically equivalent position to the optical axis direction and the scanning direction. On the basis of this detection result, adjustment is made so that the focal position of the light beam is adjusted to the detection means position .
[0009]
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the detection means is also used as the synchronization detection means.
According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, the image writing timing in the scanning direction is corrected in accordance with the amount of movement of the detecting means.
[0010]
According to a fifth aspect of the invention, in the optical scanning apparatus according to claim 2, wherein the adjustment means, the main scanning direction, you characterized in that the focal position adjustable independently in at least one direction in the sub-scanning direction.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a light source that emits a light beam, which is composed of a coupling lens 2, a correction lens 3, a correction lens 4, and a polygon mirror in order in the traveling direction of the light beam emitted from the light source 1. A deflector 5 is arranged. The light beam from the light source 1 is deflected by the reflection surface by the rotational drive of the deflector, and the imaging element 6 is disposed on the path of the deflected light, and on the path of the light beam transmitted through the imaging element 6. The surface of the photosensitive drum 7 as the surface to be scanned is located. The deflector 5 and the imaging element 6 constitute a scanning optical system that deflects the light beam from the light source 1 and focuses it on the surface to be scanned.
[0012]
The correction lens 3 is an optical element that has power only in the main scanning direction and adjusts the focal position in the main scanning direction. The correction lens 4 is an optical element that has power only in the sub-scanning direction and adjusts the focal position in the sub-scanning direction. For example, a cylindrical lens can be used as the correction lenses 3 and 4. Reference numerals 11 and 12 denote moving mechanisms for moving the correction lenses 3 and 4 in the optical axis direction, respectively. These moving mechanisms 11 and 12 are controlled by the control unit 13. Reference numeral 10 denotes a means for detecting the imaging state of the light beam scanned by the scanning optical system, and is disposed on the side of the photosensitive drum 7, that is, outside the image area of the scanned surface. The control unit 13 has a calculation unit that calculates the amount by which the correction lenses 3 and 4 are moved in the optical axis direction based on the detection signal from the detection means 10, and controls the moving mechanisms 11 and 12 based on the calculation result. To do. As the moving mechanisms 11 and 12, an appropriate mechanism can be adopted. For example, a feed screw mechanism or a cam mechanism is used, and the amount of rotation of the feed screw or the rotation angle of the cam is controlled to move the correction lenses 3 and 4. The amount can be adjusted.
[0013]
Next, the invention according to claim 1 will be described with reference to FIGS. 2, 3, and 4. In the conventional optical scanning apparatus proposed in the above-mentioned Japanese Patent No. 276723 and Japanese Patent Laid-Open No. 10-20225, the detecting means for detecting the image formation state of the light beam is optically connected to the surface to be scanned outside the image area. Is disposed at a position substantially equivalent to. That is, as shown in FIG. 2, the light receiving surface of the detection means 10 is disposed on the side of the surface to be scanned on the surface that is an extension of the surface to be scanned. However, as described above, in the actual scanning optical system, the curvature of field often deteriorates outside the image area, and therefore the focal position deviates from a position optically equivalent to the surface to be scanned. In addition, even if the amount of field curvature at the detection means position is kept small by design, the field curvature deteriorates due to the accumulation of component tolerances and assembly tolerances in actual use, and the focal position in the image area, The focus position at the detection means position may be shifted. Therefore, as shown in FIG. 3, when the focus position is adjusted to the detection means position, the optimum focus position does not always come within the image area of the surface to be scanned.
[0014]
Therefore, as shown in FIG. 4, the detection means 10 is shifted in the optical axis direction, and the position of the detection means 10 is adjusted to the actual curvature of field, so that the focus position is adjusted to the detection means position, so that the optimum in the image region. The focus position was set. The invention according to claim 1 is based on this technical idea. As shown in FIG. 4, if the position of the detection means 10 is matched to the actual curvature of field, the optimum focus position can be adjusted even on the surface to be scanned.
[0015]
In the first aspect of the invention, the detection means 10 is shifted only in the optical axis direction. However, in addition to shifting in the optical axis direction as in the embodiment shown in FIG. Good. The invention described in claim 2 corresponds to this embodiment. According to this embodiment, the same effect as that of the embodiment shown in FIG. 4 corresponding to the first aspect of the invention can be obtained.
[0016]
Next, an embodiment corresponding to the third aspect of the present invention will be described. In this embodiment, the detection means 10 is also used as a synchronization detection means, and a signal from the detection means 10 is also used as a synchronization detection signal for determining the write start timing. Here, the detection means 10 may be a line CCD or a PD (position detection diode) provided with a slit mask.
[0017]
Next, an embodiment corresponding to the invention of claim 4 will be described with reference to FIG. As described in the first aspect of the present invention, the detection means 10 is shifted by an amount indicated by d in the optical axis direction so as to match the actual curvature of field, thereby adjusting the focal position to the arrangement position of the detection means, and the image area. In this case, when the focus position is optimal, the angle of view of the light beam incident on the detection means 10 and the detection means 10 when the detection means 10 is optically substantially equivalent to the surface to be scanned are detected. There is a deviation from the angle of view of the incident light beam by an angle Δθ shown in FIG. For this reason, when the detection unit 10 is also used as a synchronization detection unit, a so-called registration shift that causes a shift in the writing position on the surface to be scanned occurs. Therefore, if the image writing timing in the scanning direction is corrected according to the amount of movement d of the detecting means 10 in the optical axis direction, the occurrence of registration deviation can be avoided. This is the technical idea according to the invention of claim 4.
[0018]
As described in the embodiment of FIG. 6 corresponding to the invention described in claim 2, if the detection means 10 is shifted in the scanning direction in addition to shifting in the optical axis direction, the following advantages are obtained. . That is, by shifting the detection means 10 in the optical axis direction and also in the scanning direction, the angle of view of the light beam incident on the detection means 10 at this arrangement position can be determined by using the detection means 10 and the surface to be scanned. Therefore, when they are arranged at substantially equivalent positions, the angle of view of the light beam incident on the detection means 10 can be made the same, thereby avoiding the occurrence of resist misalignment.
[0019]
Next, an embodiment corresponding to the fifth aspect of the present invention will be described. In FIG. 2 to FIG. 6, for the sake of simplicity, the field curvature is shown without being divided into the main scanning direction and the sub-scanning direction. However, actually, as shown in FIG. Field curvature also occurs in the sub-scanning direction. Further, the amount of field curvature that varies due to environmental fluctuations such as temperature fluctuations is often different between the main scanning direction and the sub-scanning direction. Accordingly, an embodiment corresponding to the invention according to claim 5 is configured such that the field curvature in each of the main scanning direction and the sub-scanning direction can be corrected by independently moving the correction lenses 3 and 4. It is. Correction of the curvature of field in the main scanning direction is performed by the correction lens 3, and correction of the curvature of field in the sub-scanning direction is performed by the correction lens 4.
[0020]
7, the main scanning direction and the sub-scanning direction each curvature They become optimal state within the image area, shifted by the optical axis direction e combined detection means 10 in field curvature in the main scanning direction Shows the case. In this state, when the focal position in the sub-scanning direction is adjusted, the field curvature in the sub-scanning direction outside the image area is shifted in the opposite direction to the field curvature in the main scanning direction, as shown in FIG. The focal position in the sub-scanning direction is shifted in the image area. Therefore, the main scanning at the position where the detecting means 10 is arranged in advance when the field curvature (focal position) in each of the main and sub-scanning directions and the sub-scanning direction is optimal in the image area (for example, when the unit is assembled). The focal position deviation amount L between the direction and the sub-scanning direction is measured, and the deviation amount L is stored in the control unit 13. Then, at the time of adjusting the focal position, the main scanning direction and the sub scanning direction are adjusted independently in consideration of the stored focal position shift amount L in the main scanning direction and the sub scanning direction. By doing so, the curvature of field (focus position) in each of the main scanning direction and the sub-scanning direction can be optimized in the image region.
[0021]
【The invention's effect】
According to the first aspect of the present invention, the detection means for detecting the imaging state of the light beam scanned by the scanning optical system is shifted in the optical axis direction from a position optically substantially equivalent to the surface to be scanned. Since the detection means is arranged in accordance with the actual curvature of field, if the optimum focus position is adjusted on the detection means, the optimum focus position can be adjusted on the scanned surface.
[0022]
According to the second aspect of the invention, the detecting means for detecting the imaging state of the light beam scanned by the scanning optical system is shifted in the optical axis direction from a position optically substantially equivalent to the surface to be scanned and also in the scanning direction. Even if shifted, the same effect as that of the first aspect of the invention can be obtained.
[0023]
According to the third aspect of the present invention, since the detection means for detecting the imaging state of the light beam scanned by the scanning optical system is also used as the synchronization detection means, the cost can be reduced.
[0024]
According to the fourth aspect of the invention, since the image writing timing in the scanning direction is corrected according to the amount of movement of the detecting means in the optical axis direction, it is possible to avoid the occurrence of registration deviation.
[0025]
The amount of curvature of field that varies due to environmental variations such as temperature variations is often different between the main scanning direction and the sub-scanning direction. According to the invention of claim 5, the focal position of the light beam on the surface to be scanned Since the adjustment means for adjusting the focus position can be adjusted independently in at least one of the main scanning direction and the sub-scanning direction, the adjustment means is moved independently to thereby adjust the main scanning direction and the sub-scanning direction. Each field curvature can be independently corrected.
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of an optical scanning device according to the present invention.
FIG. 2 is a plan view showing an example of the arrangement of detection means for detecting the imaging state of a light beam in a conventional optical scanning device, together with a field curvature line.
FIG. 3 is a plan view for explaining a problem due to the arrangement example of the conventional detection means.
FIG. 4 is a plan view showing an arrangement example of detection means for detecting the imaging state of a light beam in the optical scanning device according to the present invention, together with a field curvature line.
FIG. 5 is a plan view for explaining a shift in the angle of view of an incident b on the detection means in the arrangement example of the detection means.
FIG. 6 is a plan view showing another arrangement example of the detecting means for detecting the imaging state of the light beam in the optical scanning device according to the present invention, together with the field curvature line.
FIG. 7 is a plan view showing an example of field curvature in each of the main scanning direction and the sub-scanning direction on the surface to be scanned in the optical scanning device.
FIG. 8 is a plan view for explaining a problem that occurs when the focal position is aligned with one of the curvature of field in each of the main scanning direction and the sub-scanning direction.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Coupling lens 3 Correction lens 4 Correction lens 5 Deflector 6 Imaging element 10 Detection means 11 Adjustment means 12 Adjustment means 13 Control part

Claims (6)

A light source that emits a light beam, a scanning optical system that deflects the light beam from the light source and focuses it on the surface to be scanned, and a detection means that detects the imaging state of the light beam scanned by the scanning optical system And an adjustment unit that adjusts the focal position of the light beam on the surface to be scanned.
The detecting means is located outside the image area and shifted in the optical axis direction from a position optically substantially equivalent to the surface to be scanned, and the locus of the beam waist position in a state in which the curvature of field in the image area is suppressed to be small. Placed on top
The optical scanning device according to claim 1, wherein the adjusting unit adjusts the focal position of the light beam to a detection unit position based on a detection result of the detection unit. A light source that emits a light beam, a scanning optical system that deflects the light beam from the light source and focuses it on the surface to be scanned, and a detection means that detects the imaging state of the light beam scanned by the scanning optical system And an adjustment unit that adjusts the focal position of the light beam on the surface to be scanned.
The detecting means is positioned outside the image area and shifted from the optically equivalent position to the surface to be scanned in the optical axis direction and the scanning direction to suppress the curvature of field in the image area to a small extent. Placed on the locus of the position,
The optical scanning device according to claim 1 , wherein the adjusting unit adjusts the focal position of the light beam to a detection unit position based on a detection result of the detection unit .   3. The optical scanning device according to claim 1, wherein the detection unit also serves as a synchronization detection unit.   4. The optical scanning device according to claim 3, wherein the image writing timing in the scanning direction is corrected in accordance with the amount of movement of the detection means.   5. The optical scanning device according to claim 1, wherein the adjusting unit independently adjusts the focal position in at least one of the main scanning direction and the sub-scanning direction. A light source that emits a light beam, a scanning optical system that deflects the light beam from the light source and focuses it on the surface to be scanned, and a detection means that detects the imaging state of the light beam scanned by the scanning optical system And adjusting means for adjusting the focal position of the light beam on the surface to be scanned,
  The detection means is a focal position adjustment method for an optical scanning device that is located outside the image region and is shifted in the optical axis direction from a position that is optically substantially equivalent to the surface to be scanned.
Arranging the detection means on the locus of the beam waist position in a state in which the curvature of field in the image region is suppressed to a small extent;
And a step of adjusting the focal position of the light beam at the position of the detection means using the adjustment means based on the detection result of the detection means.

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