JP2011227279A - Laser scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser scanning optical device that can keep beam detecting performance for optical performance correction, without extending size of scanning optical element.SOLUTION: A laser scanning optical device comprises: a multi-beam light source 1 which has multiple light emitting points; a polygon mirror 4 which deflects multiple beams emitted from the light source 1 in a main-scanning direction Y; scanning lenses 11, 12 and 13 which image the deflected beams on a photoreceptor 30; beam detecting means 21A and 21B; and half mirrors 22A and 22B which are located between the scanning lens 13 and a photoreceptor 30 and divide the beams which are heading to spread areas C at the starting and ending edges of an effective exposure area A on the photoreceptor 30. After being divided by the half mirrors 22A, 22B, one beam goes to the spread areas C and the other beam goes to the beam detection means 21A, 21B.

Description

  The present invention relates to a laser scanning optical device, and more particularly to a laser scanning optical device mounted as an image writing unit in an image forming apparatus such as an electrophotographic copying machine or printer.

  2. Description of the Related Art In recent years, various types of laser scanning optical devices have been developed that simultaneously scan a photosensitive member with a plurality of beams using a multi-beam light source having a plurality of light emitting points as image formation becomes more precise. In this type of laser scanning optical apparatus, it is necessary to control the relative positions (in particular, the beam interval in the sub-scanning direction) of a plurality of beams scanned simultaneously.

  In Patent Document 1, a beam transmitted through all scanning optical elements (lenses) is detected by a deviation amount detecting means arranged on the start end side and the end end side outside the effective exposure region, and the scanning timing in the main scanning direction and the sub scanning direction are detected. It is disclosed to correct the scanning position. In Patent Document 2, beams transmitted through all scanning optical elements (lenses) are detected by beam detecting means arranged on the start end side and the end end side outside the effective exposure region, and the scanning timing in the main scanning direction is determined and the main scanning is performed. It is disclosed to correct the direction magnification. In Patent Document 3, a beam transmitted through all scanning optical elements (lenses) is detected by light receivers arranged on the start end side and the end end side outside the effective exposure area, and is emitted from a light source and passes through a coupling lens. Among them, it is disclosed that a part of the beam reflected by the reflective optical element is detected by another light receiver, and the output level of the light source is controlled with high accuracy by two light receivers.

  However, in each of the laser scanning optical devices described in Patent Documents 1, 2, and 3, since the beam transmitted outside the effective exposure area is detected, both ends of the scanning optical element are extended outside the effective exposure area. It was necessary to let them. This has a problem that the scanning optical element becomes long, which leads to cost increase and enlargement of the scanning optical device.

Japanese Patent Laid-Open No. 10-177144 JP 2002-122799 A JP 2009-157014 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laser scanning optical device capable of avoiding an increase in the length of a scanning optical element without impairing beam detectability for correcting optical performance.

A laser scanning optical device according to an aspect of the present invention is
A multi-beam light source having a plurality of emission points;
A deflector for deflecting a plurality of beams emitted from the light source in a main scanning direction;
A scanning optical element that forms an image of the beam deflected by the deflector on the photosensitive member;
First beam detection means;
A beam separating unit that is disposed between the scanning optical element and the photosensitive member and separates a beam toward a nobi region located on at least one of a starting end side and a terminal end side of an effective exposure region on the photosensitive member;
With
One beam separated by the beam separating means is directed to the nobi region,
The other beam separated by the beam separating means is directed to the first beam detecting means;
It is characterized by.

  The effective exposure area on the photoconductor is composed of an effective image forming area and a nobi area located on the start side and / or the end side thereof. The nobi region is an area for forming an image such as a register mark and detecting the inclination of the image with respect to the paper and applying feedback to the image formation. In this laser scanning optical device, the beam for exposing the nobi region is separated, and one of the separated beams is directed to the nobi region to form a predetermined image in the nobi region. Then, the other separated beam is detected by the first beam detecting means and used as a beam for correcting the optical performance. Therefore, it is not necessary to lengthen the scanning optical element beyond the effective exposure area. The optical performance correction is, for example, correction of a plurality of beams in the sub-scanning direction and magnification correction in the main scanning direction.

  According to the present invention, it is possible to avoid an increase in the length of the scanning optical element without impairing the detectability of the beam for correcting the optical performance. As a result, the laser scanning optical device can be reduced in cost and size.

It is a top view which shows schematic structure of the laser scanning optical apparatus which is 1st Example of this invention. It is a top view which shows schematic structure of the laser scanning optical apparatus which is 2nd Example of this invention.

  Embodiments of a laser scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings. In each figure, common parts and portions are denoted by the same reference numerals, and redundant description is omitted.

(See the first embodiment, FIG. 1)
As shown in FIG. 1, the laser scanning optical apparatus according to the first embodiment of the present invention is schematically shown as a light source 1, a collimator lens 2, a cylinder lens 3, a polygon mirror 4, scanning lenses 11, 12 and 13, and a dust-proof glass 14. Etc. A mirror (not shown) for bending the optical path is also appropriately arranged. The basic configuration of these optical systems for forming an image (electrostatic latent image) on the photoreceptor 30 is well known.

  The light source 1 is a multi-beam light source (laser diode array) having a plurality of light emission points, and the beam interval in the sub-scanning direction Z can be corrected by rotating the central axis of the plurality of light emission points. The beam emitted from the light source 1 is deflected at a uniform angular velocity in the main scanning direction Y by the polygon mirror 4, and is scanned by scanning lenses 11, 12, and 13 having at least one of a beam shaping function, an fθ function, and an imaging function. Aberrations in the main scanning direction Y are corrected, and scanning / exposure is performed with the image formed on the photoreceptor 30.

  The laser scanning optical device includes beam detection means (photoelectric conversion element) 15 for controlling the image writing position. The beam is scanned in the main scanning direction Y by the polygon mirror 4. The beam detection means 15 detects the beam that is transmitted through the outside of the effective exposure area A on the start end side in the main scanning direction Y and reflected by the mirror 16. A detection signal from the beam detection means 15 is input to a control circuit (not shown), and a synchronization signal (also referred to as an SOS signal) is generated. The beam input to the beam detector 15 is transmitted through the scanning lenses 11 and 12 and does not transmit through the scanning lens 13.

  The laser scanning optical device further includes beam detection means (photoelectric conversion elements) 21A and 21B arranged on both ends in the main scanning direction Y, and both the scanning lens 13 and the photoconductor 30 on both ends in the main scanning direction Y. Beam separating means (specifically, half mirrors 22A and 22B) disposed between them is provided. The half mirrors 22 </ b> A and 22 </ b> B separate beams that are directed to the novi region C located on the start end side and end end side of the effective exposure region A. One of the separated beams is directed to the novi region C, and the other beam is directed to the beam detection means 21A and 21B.

  By the way, the effective exposure area A on the photoconductor 30 is composed of an effective image forming area B and a nobi area C located on the start and end sides thereof. The nobby region C is a region for forming an image such as a registration mark and detecting the inclination of the image with respect to the paper and applying feedback to the image formation. In the laser scanning optical device, the beam for exposing the nobi region C is separated. One of the separated beams is directed to the nobi area C, and a predetermined image is formed in the nobi area C. The other separated beam is detected by the beam detectors 21A and 21B, and the detection signal is input to a control circuit (not shown) to correct the optical performance. The optical performance correction is, for example, correction of a plurality of beams in the sub-scanning direction and magnification correction in the main scanning direction.

  In the conventional laser scanning optical apparatus, the optical performance is corrected using the beam passing outside the effective exposure area A. On the other hand, in the first embodiment, the optical performance is corrected by using a part of the beam that exposes the inside of the effective exposure area A (novi area C). Therefore, it is not necessary to lengthen the scanning lens 13 to the outside of the effective exposure area A. As a result, the cost and size of the laser scanning optical device can be reduced.

  That is, by correcting the optical performance using the beams transmitted through all the scanning lenses 11, 12, and 13, the relative position change of the beam can be detected, and the scanning lenses 11, 12, and 13 are deformed by the temperature change. Even when the relative position of the beam changes, a stable quality image can be obtained by feeding back the detection results of the beam detectors 21A and 21B.

  The half mirrors 22A and 22B function as beam separating means with a simple configuration. The half mirrors 22A and 22B preferably have a transmission / reflection ratio of transmission / reflection> 1. By setting it as such a transmission / reflection ratio, the light quantity for forming an image in the nobby area | region C is securable.

  Further, the beam detectors 21A and 21B may be arranged on either one, but by providing a pair on the start end side and the end end side of the effective exposure area A, the magnification in the main scanning direction Y can be detected with high accuracy. it can.

(See the second embodiment, FIG. 2)
The laser scanning optical apparatus according to the second embodiment of the present invention is one in which two light sources (laser diodes) 1A and 1B are arranged as shown in FIG. The light sources 1A and 1B emit beams having different polarization directions in directions orthogonal to each other, and the beams are combined so as to travel in the same direction by the polarization beam splitter 6 after passing through the collimator lenses 2A and 2B. Further, a quarter wavelength plate 7 is disposed between the polarizing beam splitter 6 and the polygon mirror 4 via the cylindrical lens 3.

  Further, in order to separate the beam from the scanning lens 13 toward the nobi region C, polarization beam splitters 23A and 23B for separating the beam synthesized by the polarization beam splitter 6 are provided, and the scanning lens 13 and the polarization beam splitter 23A, Quarter-wave plates 24A and 24B are provided between 23B and 23B.

  As is well known, the quarter-wave plates 7, 24A and 24B convert linearly polarized light and circularly-polarized light to each other. The quarter-wave plate 7 located in the preceding stage is a beam emitted from the light sources 1A and 1B. Is converted from linearly polarized light to circularly polarized light. Further, the quarter-wave plates 24A and 24B located in the subsequent stage convert the beam toward the nobi region C from circularly polarized light to linearly polarized light.

  Other configurations of the laser scanning optical apparatus are the same as those in the first embodiment. Accordingly, the two beams synthesized by the polarization beam splitter 6 are converted into circularly polarized light by the quarter wave plate 7 and then deflected in the main scanning direction Y by the polygon mirror 4 to be scanned by the scanning lenses 11, 12, 13. , And forms an image on the photoreceptor 30. Then, the two beams directed to the novi region C are converted into linearly polarized light by the quarter-wave plates 24A and 24B, one of the separated / converted beams is directed to the novi region C, and the other beam is a beam detecting means. Head to 21A, 21B.

  The optical performance is corrected based on the detection signals from the beam detectors 21A and 21B, and the operational effects obtained by using the beam toward the novi region C are the same as described in the first embodiment. . In particular, in the second embodiment, since the photosensitive member 30 is exposed with a beam converted into circularly polarized light, the unevenness in image density is reduced because circularly polarized light has little light amount unevenness.

  In the second embodiment, a laser diode array may be used as the light sources 1A and 1B. For example, two light beams may be emitted from the light sources 1A and 1B, and the photoconductor 30 may be scanned with a total of four beams.

(Other examples)
The laser scanning optical apparatus according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

  In particular, the configuration and arrangement of the light source optical system and the scanning optical system are arbitrary. Also, the number of beams scanned simultaneously is arbitrary.

  As described above, the present invention is useful for a laser scanning optical apparatus, and is particularly excellent in that it is possible to avoid an increase in the length of a scanning optical element without impairing beam detectability for correcting optical performance. .

DESCRIPTION OF SYMBOLS 1,1A, 1B ... Light source 4 ... Polygon mirror 6 ... Polarization beam splitter 7 ... 1/4 wavelength plate 11, 12, 13 ... Scan lens 15 ... SOS beam detection means 21A, 21B ... Correction beam detection means 22A, 22B ... half mirrors 23A, 23B ... polarizing beam splitters 24A, 24B ... quarter wave plates 30 ... photoconductor Y ... main scanning direction

Claims (7)

A multi-beam light source having a plurality of emission points;
A deflector for deflecting a plurality of beams emitted from the light source in a main scanning direction;
A scanning optical element that forms an image of the beam deflected by the deflector on the photosensitive member;
First beam detection means;
A beam separating unit that is disposed between the scanning optical element and the photosensitive member and separates a beam toward a nobi region located on at least one of a starting end side and a terminal end side of an effective exposure region on the photosensitive member;
With
One beam separated by the beam separating means is directed to the nobi region,
The other beam separated by the beam separating means is directed to the first beam detecting means;
A laser scanning optical device.   2. The laser scanning optical apparatus according to claim 1, further comprising second beam detecting means for controlling an image writing position in the main scanning direction.   The said beam separation means and said 1st beam detection means are arrange | positioned with respect to the beam which goes to the nobi area | region located in the start end side and the terminal end side of the said effective exposure area | region. Item 3. The laser scanning optical device according to Item 2.   4. The laser scanning optical apparatus according to claim 1, wherein the beam separating means is a half mirror.   The laser scanning optical apparatus according to claim 4, wherein the transmission / reflection ratio of the half mirror is transmission / reflection> 1. A first polarization beam splitter for combining two beams having different polarization directions is disposed between the multi-beam light source and the deflector;
The beam separating means is a second polarizing beam splitter that separates the two beams synthesized by the first polarizing beam splitter;
The laser scanning optical apparatus according to claim 1, wherein A first quarter wave plate is disposed between the first polarizing beam splitter and the deflector;
A second quarter-wave plate is disposed between the scanning optical element and the second polarizing beam splitter;
The laser scanning optical apparatus according to claim 6.

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