JP2008040136A - Optical scanner and color image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain the compactness of the entire scanner, to improve the latitude of design structure, and to reduce the deviation of a writing starting position. <P>SOLUTION: An optical scanner is provided with a plurality of scanning units comprising a light source means, an incident optical system, a deflection means, and an image forming optical system. Among the plurality of scanning units, two or more scanning units use a luminous flux reflected/deflected on different deflection faces of one and the same deflection means. A timing to start writing on a surface to be scanned is determined by detecting a luminous flux from the deflection face of each deflection means with one detecting means for writing starting position and by using a signal therefrom. In the same scanning time, the angle measured along the rotating direction of the deflection means is less than 180°, among the two or more scanning units, from the scanning position on the surface to be scanned by the scanning unit in which the detecting means for writing starting position is installed, to the scanning position on the surface to be scanned by the opposite scanning unit relative to the deflection means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device and a color image forming apparatus using the same, and is suitable for a laser beam printer having an electrophotographic process, a digital copying machine, and a color image forming apparatus for a multifunction printer (multifunction printer).

  Conventionally, in an optical scanning device of a laser beam printer (LBP) or a digital copying machine, an optical deflector (deflecting means) composed of a rotating polygon mirror (polygon mirror) is used to emit a light beam modulated from a light source means according to an image signal. Is deflected periodically. The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  In recent years, in order to form a color image at high speed, a plurality of photoconductors for each color are simultaneously optically scanned, and a color image is formed by superimposing image information on a recording medium (or an intermediate transfer member). Various so-called tandem type optical scanning devices (color image forming devices) have been proposed. (Patent Documents 1 to 6).

  In this tandem type optical scanning apparatus, if the optical deflector is shared by a plurality of scanning units (stations), the entire apparatus can be reduced in size and simplified.

  In such an optical scanning device, light beams emitted from a plurality of light source means are respectively deflected by different deflection surfaces of the same optical deflector (polygon mirror) and scanned on a plurality of photosensitive drum surfaces. In such an optical scanning device, the writing position on the photosensitive drum surface is detected by the following method.

  The first method A includes a plurality of writing position detection means for each surface to be scanned, and determines the writing timing on the photosensitive drum surface based on the detection information obtained by each writing position detection means. Is the method.

  In the other method B, the writing position is detected by one writing position detecting means, and the writing position information on the scanning surface by one deflection surface is used, and the other scanning surface by another deflection surface is used. This is a method for determining the writing position.

  FIG. 7 is a schematic view of the main part of an optical scanning device using the method B for detecting the writing position by one conventional writing position detecting means.

  In the figure, first, in the first scanning unit (station) S1, the light beam modulated and emitted from the light source 71a according to the image information is regulated by the aperture stop 74a. The regulated light beam is converted into a parallel light beam by the collimator lens 72a and is incident on the cylindrical lens 73a. Out of the light beam incident on the cylindrical lens 73a, the light beam is emitted as it is in the main scanning section. In the sub-scan section, the light beam converges to form a line image (a line image elongated in the main scanning direction) on the deflection surface 75a of the deflector 75.

  The light beam deflected by the deflecting surface 75a of the optical deflector 75 is imaged in a spot shape on the photosensitive drum surface 78a by the imaging optical system 85a, and the optical deflector 75 is rotated in the direction of the arrow A to thereby rotate the photosensitive drum. Optical scanning is performed on the surface 78a at a constant speed in the direction of arrow B (main scanning direction). As a result, an image is recorded on the photosensitive drum surface 78a which is a recording medium.

  At this time, the timing of the scanning start position on the photosensitive drum surface 78a is adjusted before optical scanning on the photosensitive drum surface 78a. For this purpose, a part of the light beam reflected and deflected by the deflecting surface 75a of the optical deflector 75 (synchronous detection light beam) is condensed on the surface of the synchronous detection edge portion 81 by the synchronous detection lens 80, and then synchronous detection is performed. Is guided to the sensor 82. Then, the timing of the scanning start position of image recording on the photosensitive drum surface 78a is adjusted by using the writing position detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 82. .

  In the second scanning unit (station) S2, the light beam emitted from the light source 71b enters the deflecting surface 75b of the deflector 75 from the same direction as the incident direction of the first scanning unit S1. Then, the light beam reflected and deflected by the deflection surface 75b is imaged in a spot shape on the photosensitive drum surface 78b by the imaging optical system 85b and optically scanned.

At this time, in the second scanning unit S2, the timing of the scanning start position of image recording on the photosensitive drum surface 78b is obtained using the synchronization detection light beam when the deflection surface 5b is scanning the first scanning unit S1 side. It is adjusted.
JP-A-5-19586 JP-A-4-313776 Japanese Patent Laid-Open No. 10-48548 Japanese Unexamined Patent Publication No. 2000-121983 JP 2004-102276 A Japanese Unexamined Patent Publication No. 2004-219817

  The conventional writing position determination method described above has the following problems.

  First, since the former method A has a plurality of writing position detecting means, an optical element, a light receiving element, and a circuit board are required for each. For this reason, the whole apparatus tends to be complicated. In addition, a device for controlling the rotation of the optical deflector is required, and it is difficult to reduce the size of the entire device.

  Further, when the deflecting surface of the optical deflector is used at a high angle of view, there is a high possibility that the light beam guided to any of the writing position detecting means is greatly distorted and cannot be used practically.

  In the case of the latter method B, by measuring the division error of the optical deflector in advance, other writing is performed by correcting the writing position detection detected on the side having the writing position detection means based on the division error data. The position can be determined. This method is effective for downsizing and simplification of the entire apparatus.

  In Patent Document 4, each element is configured such that the scanning timing is matched between the side having the writing position detection means and the side not having the writing position detection position means, thereby reducing the writing position deviation. However, the configuration of Patent Document 4 has a problem that the degree of freedom in configuration is low.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning apparatus capable of reducing the overall position of the apparatus and improving the degree of freedom of configuration, and further reducing the writing position deviation, and a color image forming apparatus using the same.

The optical scanning device of the invention of claim 1
A scanning unit having a light source means, an incident optical system for guiding the light beam emitted from the light source means to the deflecting means, and an imaging optical system for guiding the light beam deflected by the deflecting means onto the surface to be scanned A plurality of
Among the plurality of scanning units, two or more scanning units use light beams reflected and deflected by different deflection surfaces of the same deflection unit,
The two or more scanning units each have a distance Tc on the optical axis from the deflection point of the deflection surface to the scanned surface, and are closest to the deflection unit in the imaging optical system from the deflection point of the deflection surface. The distance on the optical axis to the incident surface of the imaging optical element is a, and the angle between the principal ray of the light beam incident on the deflection surface of the deflecting means and the optical axis of the imaging optical system in the main scanning section is θ. and when,
a / Tc <0.12
θ> 2π / n (where n is the number of deflection surfaces of the deflection means and n ≧ 5)
And
The writing timing of the light beam on the surface to be scanned of the two or more scanning units is determined by detecting the light beam from the deflecting surface of the deflecting means by one writing position detecting means and outputting a signal from the one writing position detecting means. Is determined using
Among the two or more scanning units in the same scanning time, the scanning unit opposite to the deflecting unit from the scanning position of the light beam on the surface to be scanned by the scanning unit provided with the writing position detecting unit The angle when measured along the rotation direction of the deflecting means to the scanning position of the light beam on the surface to be scanned is less than 180 degrees.

An optical scanning device according to a second aspect of the present invention comprises:
A plurality of light source units, an incident optical system provided for each of the plurality of light source units, one deflecting means for deflecting and reflecting light beams incident from different incident optical systems on different deflection surfaces, and the plurality of light source units An imaging optical system that is provided every time and that guides the light beam deflected by the deflecting surface onto the surface to be scanned,
The writing timing of the light beam on the surface to be scanned is determined by detecting the light beam from the deflection surface of the deflecting means by one writing position detecting means and using a signal from the one writing position detecting means. ,
Of the plurality of incident optical systems, the principal ray of the light beam incident on the deflection surface of the deflecting unit via the first incident optical system and incident on the writing position detecting unit, and the first incident optical system via the first incident optical system The angle formed by the optical axis of the first imaging optical system that guides the light beam deflected by the deflecting surface of the deflecting means to the scanned surface is θ, and the distance on the optical axis from the deflecting surface to the scanned surface Tc, a distance on the optical axis from the deflection point of the deflection surface to the incident surface of the imaging optical element closest to the deflection surface in the imaging optical system is a, and the number of the deflection surfaces is n When
a / Tc <0.12
360 degrees / n <θ degrees,
In the same scanning time, the principal ray via the first imaging optical system and the principal ray via the second imaging optical system disposed on the opposite side of the first imaging optical system with respect to the deflecting means. The angle measured along the direction of rotation of the deflection means with respect to the light beam is less than 180 degrees.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The writing position detecting means determines the writing timing of the light beam on the surface to be scanned using the light beam that has passed through the imaging optical element closest to the deflecting means in the imaging optical system. It is said.

The invention of claim 4 is the invention of any one of claims 1 to 3,
Each of the light source means has a plurality of light emitting sections, and a plurality of light beams emitted from the plurality of light emitting sections are guided to the same surface to be scanned, and the incident optical system and the deflecting means An aperture stop that restricts the plurality of light beams is disposed in the optical path between them.

The color image forming apparatus of the invention of claim 5
Each of the optical scanning devices according to any one of claims 1 to 4 is arranged on a surface to be scanned, and has a plurality of image carriers that form images of different colors.

The invention of claim 6 is the invention of claim 5,
It is characterized by having a printer controller that converts color signals input from an external device into image data of different colors and inputs them to each optical scanning device.

  According to the present invention, it is possible to achieve an optical scanning device that can reduce the size of the entire apparatus and improve the degree of freedom of configuration, and that can reduce the write position deviation, and an image forming apparatus using the same. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view (main scanning sectional view) of a main part in the main scanning direction of Embodiment 1 of the present invention, and FIG. is there.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the optical deflector and the optical axis of the imaging optical system (the direction in which the light beam is reflected and deflected (deflected and scanned) by the optical deflector). The sub-scanning direction is a direction parallel to the rotation axis of the optical deflector. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section is a section perpendicular to the main scanning section.

  The optical scanning apparatus of the present embodiment includes two imaging optical systems (fθ lens systems) 15a and 15b with an optical deflector (polygon mirror) 5 serving as a deflecting unit interposed therebetween. The four light beams are incident and the four light beams are simultaneously reflected and deflected by one optical deflector 5. Then, the four light beams are guided to the corresponding photosensitive drum surfaces 8a, 8b, 8c, and 8d corresponding to the scanned surfaces, and tandem type light that optically scans the photosensitive drum surfaces 8a, 8b, 8c, and 8d. It is a scanning device.

  In the figure, S1 and S2 are first and second scanning units (hereinafter also referred to as “station” or “scanning optical system”).

  Hereinafter, each member of the first and second scanning units S1 and S2 will be described focusing on the first scanning unit S1. Of the members of the second scanning unit S2, the same members as those of the first scanning unit S1 are shown in parentheses.

  The first (second) scanning unit S1 (S2) is a first optical system as a first optical system that converts the state of the light beam from the light source means 1a, 1c (1b, 1d) to the state of another light beam. The optical elements 2a and 2c (2b and 2d) are provided. The light source means 1a and 1c form one light source unit. Furthermore, it has 2nd optical element 3a, 3c (3b, 3d) as a 2nd optical system imaged as a long line image in the main scanning direction. Furthermore, aperture stops 4a and 4c (4b and 4d) for limiting the light flux and an optical deflector 5 as a deflecting means are provided. Further, it has an imaging optical system 15a (15b) for forming a light beam reflected and deflected by the optical deflector 5 on a photosensitive drum surface 8a, 8c (8b, 8d) as a scanned surface.

  In the present embodiment, the first and second scanning units S1, S2 use the same optical deflector 5. The first and second scanning units S1 and S2 are arranged symmetrically with respect to a plane including the rotation axis of the optical deflector 5 and parallel to the sub-scanning direction, and use light beams deflected and reflected by different deflection surfaces. ing.

  In this embodiment, the writing timing to the scanned surfaces 8a, 8c, 8b and 8d of the first and second scanning units S1 and S2 is 1 using the light beam deflected by the deflecting surface 5a of the optical deflector 5. These are detected by two write position detection means (synchronization detection means) 16. Then, using the signal detected by the writing position detecting means 16, the writing timing to the photosensitive drum surfaces 8a, 8c, 8b, 8d is determined.

  In the present embodiment, in the same scanning time, the optical deflector 5 is provided along the rotational direction from the scanning position on the deflecting surface 5a side of the optical deflector 5 provided with the writing position detecting means 16 to the scanning position on the opposite side. The angle δ when measured in this way is configured to be less than 180 degrees.

  In this embodiment, the angle δ is set to 160 degrees.

  In the first and second scanning units S1 and S2, the light source means 1a, 1c, 1b and 1d are each composed of a semiconductor laser.

  The first optical elements 2a, 2c, 2b, and 2d are each composed of a collimator lens, and convert the light beams emitted from the light source means 1a, 1c, 1b, and 1d into parallel light beams (or divergent light beams or convergent light beams). .

  Each of the second optical elements 3a, 3c, 3b, and 3d includes a cylindrical lens, and has a refractive power only in the sub-scanning direction.

  Aperture stops 4a, 4c, 4b, and 4d are disposed on the optical deflector 5 side between the optical deflector 5 and the cylindrical lenses 3a, 3c, 3b, and 3d, respectively, and the cylindrical lenses 3a, 3c, 3b, and 3d are disposed. The beam shape of the passed light beam is shaped.

  The light source means 1a, 1c (1b, 1d), collimator lenses 2a, 2c (2b, 2d), cylindrical lenses 3a, 3c (3b, 3d), and aperture stops 4a, 4c (4b, 4d) It constitutes one element of the incident optical system LA (LB).

  The optical deflector 5 is composed of a rotating polygon mirror (polygon mirror) having six deflection surfaces, and is rotated at a constant speed in the direction of arrow A in the figure by a motor driving means (not shown). In the present embodiment, as described above, the first and second scanning units S1 and S2 use the optical deflector 5 together, and the first and second scanning units S1 and S2 include the optical deflector 5. The light beams reflected and deflected by the different deflecting surfaces 5a and 5b are used.

  Reference numeral 15a (15b) denotes an image forming optical system (fθ lens system) having a condensing function and an fθ characteristic, and includes first and second image forming lenses 6a and 7a (6b and 7b). . The imaging optical system 15a (15b) forms a plurality of light beams reflected and deflected by the optical deflector 5 in a spot shape on the corresponding scanned surfaces 8a and 8c (8b and 8d). In addition, the imaging optical system 15a (15b) is troublesome by providing a conjugate relationship between the deflecting surface 5a (5b) of the optical deflector 5 and the scanned surfaces 8a, 8c (8b, 8d) in the sub-scan section. It has a correction function.

  Reference numerals 20a, 21a, and 22a (20b, 21b, and 22b) are reflection mirrors, respectively, that fold the light beams that have passed through the imaging optical system 15a (15b) toward the corresponding photosensitive drum surfaces 8a and 8c (8b and 8d). .

  Reference numeral 16 denotes a writing position detection means (synchronization detection means), which is provided on the first scanning unit S1 side. The synchronization detection means 16 has a reflection mirror 9 and a synchronization detection lens 10. Further, the synchronization detection means 16 has a linear edge portion 11 and a synchronization detection sensor 12. Based on the synchronization signal detected by the synchronization detection means 16, the timing of writing the scanned surfaces 8a, 8c, 8b and 8d of the first and second scanning units S1 and S2 is determined.

  The synchronization detection means 16 in this embodiment determines the timing of writing to the scanned surfaces 8a, 8c, 8b, and 8d using the light beam that has passed through the first imaging lens 6a closest to the optical deflector 5. .

  The synchronization detection mirror 9 is disposed in the optical path of the synchronization detection means 16, and reflects the light beam that has passed through the first imaging lens 6a toward the synchronization detection sensor 12 side. This synchronization detection mirror 9 contributes to the miniaturization of the entire apparatus.

  The synchronization detection lens 10 forms an image of the synchronization detection light beam (synchronization detection light beam) reflected and deflected by the deflection surface 5 a on the surface of the synchronization detection edge 11. The synchronization detection lens 10 scans on the synchronization detection edge 11 in the main scanning section, and the deflection surface 5a and the synchronization detection edge 11 are conjugate in the sub-scanning section. It has become.

  The synchronization detection edge 11 determines the image writing position. This synchronization detection edge 11 has a knife edge at its end, and determines the position at which the spot imaged by the synchronization detection lens 10 scanned in the main scanning direction is incident on the surface of the synchronization detection sensor 12. It is. As a result, the detection accuracy of synchronization detection is higher when the knife edge of the synchronization detection edge 11 is cut than when the synchronization detection light beam is emitted at the end of the light receiving surface of the synchronization detection sensor 12.

  The synchronization detection sensor 12 includes a sensor in which a plurality of elements are arranged in a one-dimensional direction.

  The synchronization detecting sensor 12 in this embodiment is arranged independently of the light source means 1a, 1c, 1b, 1d, but may be arranged on the same substrate as the light source means 1a, 1c, 1b, 1d. good.

  Further, in the present embodiment, the synchronization detection lens 10 is provided individually. However, the present invention is not limited thereto, and a part of the first imaging lens 6a of the first scanning unit S1 may be used. When a part of the first imaging lens 6a is used, the synchronization detection edge 11 is usually disposed at a position optically equivalent to the photosensitive drum surfaces 8a and 8c.

  Further, in this embodiment, since the synchronization detection light beam is imaged on the surface of the synchronization detection edge 11 in both the main scanning direction and the sub-scanning direction, the spot diameter on the surface of the synchronization detection sensor 12 is equal to the synchronization detection edge 11. It is set to be larger than the diameter on the surface. As a result, in this embodiment, it is difficult to pick up sensitivity variations due to manufacturing errors of the synchronization detection sensor 12 and sensitivity variations due to dust deposits.

  In the present embodiment, first, in the first scanning unit S1, two light beams emitted after being light-modulated from the light source means 1a and 1c according to image information are converted into parallel or convergent light beams by the collimator lenses 2a and 2c. Then, the light enters the cylindrical lenses 3a and 3c. Among the light beams incident on the cylindrical lenses 3a and 3c, the light beams exit as they are in the main scanning section and pass through the aperture stops 4a and 4c (partly shielded). In the sub-scan section, the light beams converge and pass through the aperture stops 4a and 4c (partially shielded) and are incident (obliquely incident) on the deflecting surface 5a of the optical deflector 5 at different angles. The image is formed as a longitudinal line image in the scanning direction.

  The two light beams reflected and deflected by the deflecting surface 5a of the optical deflector 5 are spot-formed on the photosensitive drum surfaces 8a and 8c by the imaging optical system 15a via the corresponding reflecting mirrors 20a, 21a and 22a. Is done. Then, by rotating the optical deflector 5 in the direction of arrow A, optical scanning is performed on the photosensitive drum surfaces 8a and 8c in the direction of arrow B (main scanning direction) at a constant speed. Thus, image recording is performed on the photosensitive drum surfaces 8a and 8c which are recording media.

  At this time, the timing of the scanning start position on the photosensitive drum surfaces 8a and 8c is adjusted before optically scanning the photosensitive drum surfaces 8a and 8c. For this purpose, a part of the light beam reflected and deflected by the deflecting surface 5 a of the optical deflector 5 (synchronous detection light beam) is condensed on the synchronous detection edge 11 surface by the synchronous detection lens 10. Thereafter, the light beam condensed on the surface of the synchronization detection edge 11 is guided to the synchronization detection sensor 12. Then, the timing of the scanning start position of image recording on the photosensitive drum surfaces 8a and 8c is adjusted by using the write position detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 12. ing.

  In the second scanning unit S2, the two light beams emitted from the light source means 1b and 1d are incident on the deflecting surface 5b of the optical deflector 5 at different angles from the same direction as the incident direction of the first scanning unit S1. To do. Then, the two light beams reflected and deflected by the deflection surface 5b are imaged in a spot shape on the photosensitive drum surfaces 8b and 8d via the corresponding reflection mirrors 20b, 21b and 22b by the imaging optical system 15b, and optically scanned. The

  At this time, the timing of the scanning start position on the photosensitive drum surfaces 8b and 8d is adjusted before optically scanning the photosensitive drum surfaces 8b and 8d. For the adjustment at this time, a signal obtained by detecting a part of the light beam reflected and deflected by the deflection surface 5a used for scanning of the first scanning unit S1 (synchronization detection light beam) by the synchronization detection sensor 12 is used.

  In other words, a pseudo write position detection signal (pseudo-pseudo) obtained by correcting the division error of the optical deflector by a method described later on the write position detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 12. Synchronization detection signal). The timing of the scanning start position of image recording on the photosensitive drum surfaces 8b and 8d is adjusted based on the pseudo writing position detection signal.

  Thus, in this embodiment, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, and 8d, and image recording is performed.

In this embodiment, on the optical axis from the deflection point 5a1 (5b1) where the light beam of the optical deflector 5 is reflected and deflected to the first surface (incident surface) 6a1 (6b1) of the first imaging lens 6a (6b). Is a. Further, the distance on the optical axis from the deflection point 5a1 (5b1) to the scanned surfaces 8a and 8c (8b and 8d) is Tc. At this time,
a / Tc <0.12 (1)
Is set to satisfy the following conditions.

  Conditional expression (1) defines the ratio between the distance a and the distance Tc. If the conditional expression (1) is not satisfied, the first of the first and second imaging lenses 6a and 7a (6b and 7b) constituting the imaging optical system 15a (15b) that is closest to the optical deflector 5 will be described. This is not good because it is difficult to reduce the size of the imaging lens 6a (6b).

In this embodiment, a / Tc = 0.1
And satisfies the conditional expression (1). This reduces the size of the first imaging lenses 6a and 6b.

  Furthermore, it is preferable to set the conditional expression (1) as follows.

0.08 <a / Tc <0.12 (1a)
If the lower limit of the above conditional expression is not reached, the first imaging lens becomes too close to the optical deflector, which increases the influence of the heat generated by the drive motor of the optical deflector, causing focus shift and overall magnification change due to temperature rise. Is not good because it grows.

In this embodiment, when the angle formed by the optical axis of the incident optical system LA and the optical axis L of the imaging optical system 15a in the main scanning section is θ,
θ> 2π / n (2) (where n is the number of deflection surfaces of the optical deflector and n ≧ 5)
Is set to satisfy the following conditions.

  Conditional expression (2) defines an angle θ formed by the optical axis of the incident optical system LA and the optical axis L of the imaging optical system 15a.

  In other words, the angle θ between the principal ray of the light beam incident on the deflecting surface 5a of the optical deflector 5 and the optical axis L of the imaging optical system 15a is defined in the main scanning section.

If the conditional expression (2) is not satisfied, it will be difficult to reduce the size of the first imaging lens 6a (6b) while avoiding interference between the incident light beam and the first imaging lens 6a (6b). Not good.

  Moreover, the optical scanning device of the present embodiment satisfies the following conditions.

360 degrees / n <θ degrees (3) (where n is the number of deflection surfaces of the optical deflector and n ≧ 5)
In this embodiment, θ = 70 °
And satisfies the conditional expression (2). As a result, the first imaging lens 6a (6b) can be reduced in size while avoiding interference between the incident light beam and the first imaging lens 6a (6b).

  In this embodiment, the aperture stops 4a and 4c (4b and 4d) are arranged between the optical deflector 5 and the cylindrical lenses 3a and 3c (3b and 3d) by satisfying the conditional expressions (1) and (2). Easy to do.

  As a result, even when the light source means 1a, 1c, 1b, and 1d are constituted by a multi-beam light source having a plurality of light-emitting portions (light-emitting points), it is possible to effectively reduce jitter (field curvature) at the time of multi-beam. .

  When the light source means 1a, 1c, 1b, 1d are each composed of a plurality of light emitting units, a plurality of light beams emitted from the plurality of light emitting units are guided to the same surface to be scanned.

  In this embodiment, the case where the number of deflecting surfaces of the optical deflector (polygon mirror) 5 is six has been described. However, the present invention is not limited to this, and is effective when five or more optical deflectors are used. It is.

  In this embodiment, as described above, the writing timing to the scanned surfaces 8a, 8c, 8b and 8d is detected by the single synchronization detecting means 16 for the light beams from the different deflecting surfaces of the optical deflector 5, and the synchronization is detected. This is determined based on the detection signal from the detection means 16.

  In the present embodiment, the angle θ formed by the optical axis of the incident optical system LA and the optical axis L of the imaging optical system 15a is set to 70 degrees as described above in the main scanning section. A difference occurs in the scanning timing of the second scanning units S1 and S2.

  Therefore, in this embodiment, the writing timing of the second scanning unit S2 having no synchronization detection means is determined based on the following determination method.

  First, on the photosensitive surface (scanned surface), before the start of image formation, the deflection surface of the optical deflector 5 is specified and the division error between the deflection surfaces is measured. The identification of the deflection surface and the division error of the optical deflector can be calculated by a known method.

  The six deflection surfaces of the optical deflector 5 are A, B, C, D, E, and F surfaces.

As shown in FIG. 3, detection signals obtained by the synchronous detection means when the optical deflector 5 starts to rotate, as shown in FIG. The time of each section of the D plane (TC-D) is measured. Furthermore, the time of each section of D plane-E plane (TD-E), E plane-F plane (TE-F), and F plane-A plane (TF-A) is measured. The average scanning time T of one scan is calculated from the measured time between the A surface and the A surface: (time between A surface and A surface / 6), and the difference (division error) from the time between each surface measured previously. : Δt is calculated. For example, if the A plane and the B plane, Δt = T− (TA−B)
It is.

  It should be noted that the surfaces are specified together when measuring the time between the previous surfaces (at this time, if the average scanning time is calculated from the calculated value, an error occurs due to the rotational jitter of the motor. ).

  When the division error Δt is Δt> 0, the writing of the second scanning unit S2 is delayed by Δt in the direction of delaying the writing with respect to the writing position signal detected by the first scanning unit S1 having the synchronization detecting means. A position signal may be used.

  On the other hand, when the division error Δt is Δt <0, the write position signal of the second scanning unit S2 may be obtained by delaying Δt in the direction to advance writing.

  As shown in FIG. 1, in the present embodiment, the first and second scanning units S1 and S2 have a phase difference of 20 degrees in scanning timing. Therefore, in practice, the phase difference is further delayed by a phase difference (corresponding to 20 ° in scanning angle of view in this embodiment) with respect to the signal whose division error is corrected. The delayed signal becomes the pseudo write position signal (pseudo synchronization detection signal) of the second scanning unit S2.

  Based on this pseudo-synchronization detection signal, the writing timing to the scanned surfaces 8b and 8d of the second scanning unit S2 is controlled. FIG. 4 is a time chart showing each signal at this time.

In the first scanning units S1 in FIG. 4, when the S1 synchronization detection signal by detecting a light beam from one deflecting surface 5a is detected, writes images based to S1 image signal after a certain time t ₀ .

  On the other hand, the second scanning unit S2 detects the light flux from one deflection surface 5a. When a synchronization detection signal is detected, a signal (a phase difference between the first scanning unit S1 and the second scanning unit S2 and a division error of a plurality of deflection surfaces corrected from the S1 synchronization detection signal at this time ( S2 synchronization detection signal determined from (time) is determined. Then, an image is written based on the S2 image signal after a specific time from the S2 synchronization detection signal.

As described above, in the optical scanning device of this embodiment,
A plurality of light source units, an incident optical system provided for each of the plurality of light source units, and one deflecting unit having a plurality of deflection surfaces are provided. The light beams from a plurality of light source units are incident on different deflecting surfaces of the deflecting means via the incident optical system, and the light beams deflected by the deflecting surfaces are respectively formed on different scanned surfaces by the imaging optical system. It is guided to. One writing position detection for detecting a light beam from one light source unit out of a plurality of light source units and deflected by the deflection surface, and obtaining a synchronization signal for writing by the light beam to the scanned surface Means are provided.

  At this time, through the second imaging optical system 15b disposed on the opposite side of the first imaging optical system 15a with respect to the principal ray and the deflecting means 5 via the first imaging optical system 15a in the same scanning time. The angle measured along the rotation direction of the deflecting means 5 with respect to the principal ray is configured to be less than 180 degrees.

  That is, in the present embodiment, the writing synchronization signal for writing on each scanned surface by the light beams from the plurality of light source units is detected by the writing position detecting means 16 with the light beam deflected by one deflection surface of the deflecting means 5. The decision is based on the signal that is sometimes obtained.

  Since the error increases as the phase difference in scanning timing increases, the phase difference in scanning timing is desirably 90 ° or less.

  As described above, in this embodiment, as described above, even when the writing position does not match between the scanning units (stations) facing each other with the optical deflector interposed therebetween, writing of the scanning unit having the synchronization detecting means always precedes. ing. As a result, the writing position of the opposing scanning unit can effectively suppress the influence of the change in the rotational speed of the optical deflector.

In the present embodiment, as described above, even in the case of a multi-beam light source in which the number of light emitting portions of the plurality of light source means is plural, the conditional expressions (1) and (2) are satisfied and the first imaging lens 6a ( The light beam that has passed 6b) is configured to be guided to the synchronization detecting means 16. As a result, it is possible to easily dispose an aperture stop between the optical deflector and the cylindrical lens, and jitter at the time of multi-beam can be reduced.
[Comparative example]
FIG. 5 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the optical scanning device of the comparative example for explaining the effect of the present invention. In the figure, the same elements as those shown in FIG.

  This comparative example is different from the first embodiment in that the rotation direction of the optical deflector 5 is reversed, and the synchronization detection light beam is guided to the synchronization detection means without passing through the imaging optical element 6a.

  When the configuration as in this comparative example is adopted, the writing timing is determined for the first scanning unit S1 based on the detection signal detected by the synchronization detecting means on the first scanning unit S1 side. In the second scanning unit S2, the image writing precedes.

  Accordingly, the second scanning unit S2 is simulated based on the write position detection signal (synchronization detection signal) detected by the light beam deflected by the deflecting surface 5c that is one surface before the deflecting surface 5a currently scanned by the first scanning unit S1. A write position signal (pseudo synchronization detection signal) is generated. Therefore, the jitter for one surface is deteriorated.

  Therefore, in the present embodiment, as described above, even when the writing position does not match between the scanning units (stations) facing each other with the optical deflector interposed therebetween, writing of the scanning unit having the synchronization detecting means always precedes. . As a result, the writing position of the opposing scanning unit can effectively suppress the influence of a change in the rotational speed of the optical deflector.

  In this embodiment, two light source means are used as the light source means of the first and second scanning units S1 and S2. However, the present invention is not limited to this, and each light source means may be composed of one light source means.

[Color image forming apparatus]
FIG. 6 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which one optical scanning device is arranged in parallel and image information is recorded on the surface of a photosensitive drum as an image carrier. In FIG. 6, 60 is a color image forming apparatus, 61 is an optical scanning device having the structure shown in the first embodiment, 21, 22, 23, and 24 are photosensitive drums as image carriers, 31, 32, 33, and 34, respectively. Are developing units, and 51 is a conveyor belt.

  In FIG. 6, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from the external device 52 of the personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are input to the optical scanning device 61. The optical scanning device 61 emits light beams 41, 42, 43, and 44 that are modulated in accordance with each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are mainly formed by these light beams. Scanned in the scanning direction.

  In the color image forming apparatus according to this embodiment, one single optical scanning device 61 including a plurality of scanning units is arranged. Each luminous flux corresponds to each color of C (cyan), M (magenta), Y (yellow), and B (black), and in parallel, image signals (images) on the surfaces of the photosensitive drums 21, 22, 23, and 24, respectively. Information) and color images are printed at high speed.

  As described above, the color image forming apparatus according to the present embodiment uses the light beam based on each image data by the single light scanning device 61 composed of a plurality of scanning units, and the corresponding photosensitive drums 21, respectively. It is formed on the 22, 23, and 24 surfaces. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the optical scanning device according to the first embodiment of the present invention. The figure explaining correction | amendment of the division | segmentation error of Example 1 of this invention. Timing chart of embodiment 1 of the present invention Main scanning sectional view of optical scanning device of comparative example Sectional drawing of the principal part of the color image forming apparatus of this invention Main scanning sectional view of a conventional optical scanning device

Explanation of symbols

1a, 1b, 1c, 1d Light source means 2a, 2b, 2c, 2d Condensing lens (collimator lens)
3a, 3b, 3c, 3d Cylindrical lenses 4a, 4b, 4c, 4d Aperture stop 5 Deflection means (polygon mirror)
15a, 15b Imaging optical system (fθ lens system)
6a, 6b First imaging lens (fθ lens)
7a, 7b Second imaging lens (fθ lens)
8a, 8b, 8c, 8d Scanned surface (photosensitive drum surface)
DESCRIPTION OF SYMBOLS 9 Sync detection mirror 10 Sync detection lens 11 Sync detection edge 12 Sync detection sensor 61 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller 60 Color image forming apparatus

Claims (6)

A scanning unit having a light source means, an incident optical system for guiding the light beam emitted from the light source means to the deflecting means, and an imaging optical system for guiding the light beam deflected by the deflecting means onto the surface to be scanned A plurality of
Among the plurality of scanning units, two or more scanning units use light beams reflected and deflected by different deflection surfaces of the same deflection unit,
The two or more scanning units each have a distance Tc on the optical axis from the deflection point of the deflection surface to the scanned surface, and are closest to the deflection unit in the imaging optical system from the deflection point of the deflection surface. The distance on the optical axis to the incident surface of the imaging optical element is a, and the angle between the principal ray of the light beam incident on the deflection surface of the deflecting means and the optical axis of the imaging optical system in the main scanning section is θ. and when,
a / Tc <0.12
θ> 2π / n (where n is the number of deflection surfaces of the deflection means and n ≧ 5)
And
The writing timing of the light beam on the surface to be scanned of the two or more scanning units is determined by detecting the light beam from the deflecting surface of the deflecting means by one writing position detecting means and outputting a signal from the one writing position detecting means. Is determined using
Among the two or more scanning units in the same scanning time, the scanning unit opposite to the deflecting unit from the scanning position of the light beam on the surface to be scanned by the scanning unit provided with the writing position detecting unit An optical scanning device characterized in that the angle when measured along the rotational direction of the deflecting means to the scanning position of the light beam on the surface to be scanned is less than 180 degrees. A plurality of light source units, an incident optical system provided for each of the plurality of light source units, one deflecting means for deflecting and reflecting light beams incident from different incident optical systems on different deflection surfaces, and the plurality of light source units An imaging optical system that is provided every time and that guides the light beam deflected by the deflecting surface onto the surface to be scanned,
The writing timing of the light beam on the surface to be scanned is determined by detecting the light beam from the deflection surface of the deflecting means by one writing position detecting means and using a signal from the one writing position detecting means. ,
Of the plurality of incident optical systems, the principal ray of the light beam incident on the deflection surface of the deflecting unit via the first incident optical system and incident on the writing position detecting unit, and the first incident optical system via the first incident optical system The angle formed by the optical axis of the first imaging optical system that guides the light beam deflected by the deflecting surface of the deflecting means to the scanned surface is θ, and the distance on the optical axis from the deflecting surface to the scanned surface Tc, a distance on the optical axis from the deflection point of the deflection surface to the incident surface of the imaging optical element closest to the deflection surface in the imaging optical system is a, and the number of the deflection surfaces is n When
a / Tc <0.12
360 degrees / n <θ degrees,
In the same scanning time, the principal ray via the first imaging optical system and the principal ray via the second imaging optical system disposed on the opposite side of the first imaging optical system with respect to the deflecting means. An optical scanning device characterized in that an angle measured along the rotation direction of the deflecting means with respect to a light beam is less than 180 degrees.   The writing position detecting means determines the writing timing of the light beam to the scanned surface using the light beam that has passed through the imaging optical element closest to the deflecting means in the imaging optical system. The optical scanning device according to claim 1 or 2.   Each of the light source means has a plurality of light emitting sections, and a plurality of light beams emitted from the plurality of light emitting sections are guided to the same scanned surface, and the incident optical system and the deflecting means 4. The optical scanning device according to claim 1, wherein an aperture stop that restricts the plurality of light beams is disposed in an optical path between the optical paths.   5. A color image, comprising: a plurality of image carriers that are arranged on a surface to be scanned of the optical scanning device according to claim 1 and that form images of different colors. Forming equipment.   6. The color image forming apparatus according to claim 5, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the image data to each optical scanning device.