JP2005283606A - Scanning optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce expansion/contraction due to the variation in temperature or humidity in the vicinity of the starting point of scanning of an imaging optical element in a scanning optical system equipped with the imaging optical element which focuses a light beam on a surface to be scanned which is scanned from a prescribed starting point to an ending point. <P>SOLUTION: The imaging optical element 13 is fixed by abutting the end part 13a on the side of the starting point of scanning to the abutting face 20a of a fixing member 20, and the end face 20c on the side of the ending point of scanning with the imaging optical element 13 is pressurized with a leaf spring 21c toward the starting point of scanning. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a scanning optical system including an imaging optical element that forms an image on a surface to be scanned with light beams scanned from a predetermined scanning start point to a scanning end point on the surface to be scanned. The present invention relates to a position where the imaging optical element is fixed.

  Conventionally, beam light such as laser light traveling in a certain direction is deflected within a predetermined angle range using a deflector such as a rotating polygon mirror, and the deflected beam light is applied to an imaging optical element such as an fθ lens. There has been proposed a scanning optical system in which an image is formed on a surface to be scanned and repeatedly scanned in a certain direction.

  The scanning optical system as described above, for example, scans a recording medium on which an image is recorded with a laser beam having a certain intensity, and reflects reflected light, fluorescence, stimulated emission light, etc. emitted from the recording medium by the scanning. It is used in an image reading device that reads photoelectrically. When an image is read by the image reading apparatus as described above, first, the scanning start of the beam light imaged by the scanning optical system is detected by an optical sensor or the like, and after that detection, the scanning is performed together with the beam light scanning. Thus, the electrical signal read photoelectrically is sampled at regular time intervals to obtain image data for each pixel.

  Further, in the image reading apparatus as described above, shading correction is performed in order to avoid deterioration in image quality due to variation in transmittance in the imaging optical element of the scanning optical system. Specifically, for example, Patent Document 1 proposes a method of reading an image having a uniform density in advance and correcting the read image signal based on this image signal.

  Here, the imaging optical element of the scanning optical system used in the image reading apparatus as described above has recently been made into a plastic in terms of weight reduction and cost reduction, and examples of the material include acrylic and polycarbonate. ZEONEX (registered trademark) is used.

Japanese Patent Publication No. 7-87532 JP-A-10-268221

However, compared with optical glass, the above materials have optical properties that are relatively close to those of optical glass, as shown in the table below. However, hygroscopicity and temperature characteristics are poor, and expansion and contraction occur due to changes in humidity and temperature. Resulting in.

  Therefore, for example, when the imaging optical element expands, if the imaging optical element is fixed at the center of the imaging optical element as in the scanning optical system described in Patent Document 2, the imaging optical element scans from the center. Since it expands toward both sides of the start point side and the scan end point side, on the surface to be scanned, as shown in FIG. An image spreading toward both sides on the point side is formed.

  However, when the scanning optical system as described above is used in the image reading apparatus, the sampling timing in the image reading apparatus does not change with respect to the change in the scanning position as described above. Therefore, as shown in FIG. There is a difference between the sampling timing and the pixel position that is actually read (note that the Roman numerals in FIG. 3B indicate the sampling timing of each pixel). Therefore, for example, as shown in FIG. 3B, in the shading correction data acquired in advance, even when the tenth pixel is a pixel to be corrected, the shading correction data and the actually read image data are corrected. The position of the power pixel is shifted, and appropriate shading correction cannot be performed.

  In view of the above circumstances, the present invention provides a scanning optical system capable of performing appropriate shading correction in the image reading apparatus as described above without being affected by changes in temperature and humidity. It is intended to provide.

  The scanning optical system of the present invention includes an imaging optical element that forms an image of a beam light scanned from a predetermined scanning start point on the scanned surface to a scanning end point on the scanned surface, and a center of the imaging optical element. In a scanning optical system including a fixing member that fixes an imaging optical element so as to be positioned between a scanning start point and a scanning end point, the imaging optical element is fixed in the vicinity of the scanning start point of the imaging optical element. It is fixed to the member.

  In the scanning optical system of the present invention, the end of the imaging optical element on the scanning start point side can be fixed to the fixing member.

  The scanning optical system of the present invention may include a pressing member that presses the end surface on the scanning end point side of the imaging optical element toward the scanning start point side.

  Here, the “scanning start point of the imaging optical element” means a point where the beam light passes through the imaging optical element when the scanning start point on the surface to be scanned is scanned by the beam light. means.

  The “end of the imaging optical element on the scanning start point side” means an end closer to the scanning start point of the imaging optical element.

  The “scanning end point of the imaging optical element” means a point where the beam light passes through the imaging optical element when the scanning end point on the scanning surface is scanned by the beam light. The “end surface on the scanning end point side of the imaging optical element” means an end surface closer to the scanning end point of the imaging optical element.

  According to the scanning optical system of the present invention, since the imaging optical element is fixed to the fixing member in the vicinity of the scanning start point of the imaging optical element, the scanning start point of the imaging optical element due to a change in temperature or humidity The expansion / contraction of the vicinity can be reduced, and the deviation between the sampling timing and the pixel position actually read as shown in FIG. 3B can be reduced. Appropriate shading correction can be applied.

  In the scanning optical system of the present invention, when the end of the imaging optical element on the scanning start point side is fixed to the fixed member, the imaging optical element can be fixed to the fixed member with a simpler configuration. it can.

  In the scanning optical system of the present invention, when the end surface on the scanning end point side of the imaging optical element is pressed toward the scanning start point side by the pressing member, the imaging optical element of the imaging optical element due to changes in temperature or humidity Since expansion / contraction near the scanning start point can be further reduced, more appropriate shading correction can be performed.

  Hereinafter, an embodiment of a scanning optical system of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a scanning optical system according to the present embodiment. 2 is a cross-sectional view taken along line 2-2 of FIG.

  As shown in FIG. 1, the scanning optical system according to the present embodiment scans a spot S by deflecting the beam light 11 that emits the beam light and the beam light 11 that rotates in the R direction and emits the beam light. The rotary polygon mirror 12 that scans in the X direction from the scanning start point to the scanning end point of the surface 15 and the beam light deflected by the rotary polygon mirror 12 are incident, and the incident beam light is imaged on the scanned surface 15. The imaging optical element 13 to be fixed, and a fixing member 20 that fixes the imaging optical element 13 so that the center C of the imaging optical element 13 is located between the scanning start point and the scanning end point.

  As the imaging optical element 13, for example, an fθ lens can be used.

  As shown in FIG. 2, the fixing member 20 is formed so that the installation surface 20a on which the imaging optical element 13 is installed is inclined at an angle θ with respect to the horizontal plane. Due to this inclination, the imaging optical element 13 is caused by its own weight. It moves in the tilt direction, and the end 13a on the scanning start point side of the imaging optical element 13 is fixed in contact with the contact surface 20a. In the present embodiment, as described above, the fθ lens is fixed at the end on the scanning start point side. However, for example, another imaging optical element such as an fθ mirror is arranged in the vicinity of the scanning start point side or It may be fixed at the end on the scanning start point side. In the above embodiment, one fθ lens is fixed to the fixing member 20. However, when an imaging optical system is constituted by a plurality of imaging optical elements, these are also fixed to the fixing member 20. You may do it. In the above case, the imaging optical element other than the fθ lens is also fixed at the end of the imaging optical element near the scanning start point or at the end of the scanning start point side, similarly to the fθ lens. It is desirable to fix to.

  Further, as shown in FIG. 2, the fixing member 20 is provided with a pressing member 21 that presses the end face 20c on the scanning end point side of the imaging optical element 13 toward the scanning start point side. In the scanning optical system of the present embodiment, a V-shaped leaf spring is used as the pressing member 21. However, the present invention is not limited to this, and other members may be used.

  The fixing member 20 is provided with a leaf spring 22 that presses the imaging optical element 13 in the direction of the installation surface 20a.

  In the scanning optical system of the present embodiment, the pressing member 21 and the leaf spring 22 are provided as described above, but these are not necessarily provided.

  In the scanning optical system of the present embodiment, as shown in FIG. 2, the imaging optical element 13 is fixed by bringing the end 13a of the imaging optical element 13 into contact with the contact surface 20b of the fixing member 20. However, the present invention is not limited to this, and any configuration may be adopted as long as it is fixed near the scanning start point of the imaging optical element 13. It is more preferable to fix at the scanning start point of the imaging optical element 13.

  According to the scanning optical system of the above embodiment, the imaging optical element 13 is fixed to the fixing member 20 at the end portion 13a on the scanning start point side of the imaging optical element 13, and therefore due to changes in temperature and humidity. Expansion / contraction near the scanning start point of the imaging optical element 13 can be reduced. Therefore, for example, when the scanning optical system is used in an image reading apparatus, the deviation between the sampling timing and the pixel position that is actually read can be reduced as described above. More appropriate shading correction can be performed.

1 is a schematic configuration diagram of an embodiment of a scanning optical system of the present invention. 2-2 sectional view of the scanning optical system shown in FIG. Diagram for explaining the prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Beam light source 12 Rotating polygon mirror 13 Imaging optical element 14 Scanning start detection sensor 15 Surface to be scanned 20 Fixed member 21, 22 Leaf spring

Claims (3)

An imaging optical element that forms an image of a beam light scanned from a predetermined scanning start point on the scanning surface to a scanning end point on the scanning surface, and the center of the imaging optical element is the scanning start point and the scanning optical point. In a scanning optical system provided with a fixing member that fixes the imaging optical element so as to be positioned between the scanning end point,
The scanning optical system, wherein the imaging optical element is fixed to the fixing member in the vicinity of the scanning start point of the imaging optical element.   The scanning optical system according to claim 1, wherein an end portion on the scanning start point side of the imaging optical element is fixed to the fixing member.   3. The scanning optical system according to claim 1, further comprising a pressing member that presses an end surface of the imaging optical element on the scanning end point side toward the scanning start point side.

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