JP2006215483A - Optical scanner, method of detecting of reference luminous flux, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner capable of reducing the positional displacement of dots between a plurality of light beams (luminous fluxes). <P>SOLUTION: In the case of an optical system in which the luminous flux made incident on a scanning optical system 15 is "a divergent luminous flux" in a main scanning cross section, the light spot distance e(-') between two light spots can be increased by dislocating a synchronization detection sensor 18 from a position optically equivalent to a face to be scanned 16 in the direction where the sensor 18 moves away from a polygon mirror 14. Namely, the relation e(-')>e1>e(-) is established. Further, the positional relation of the two light spots approaches the relation ¾e1-e(-')¾≈¾e2-e(-')¾, (where e1-e(-)'<0 and e2-e(-)'>0), and "the overall bad impression of a picture" of an outputted picture on a recording medium is reduced by the coincidence of centers of the optical scanning widths of the two laser beams. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device that performs optical scanning, a method for detecting a reference light beam using the optical scanning device, and an image forming apparatus such as a copying machine, a printer, a facsimile, and a plotter having the optical scanning device.

In an optical scanning device that optically scans a light beam having divergence or convergence from the light source side using an optical deflector such as a rotary polygon mirror, the distances from the rotation axes of the reflecting surfaces of the optical deflector are mutually different. If they are different (there is a shape error), so-called “vertical line fluctuation” occurs due to the reflection point position variation due to the shape error.
In order to reduce image quality deterioration due to this, Japanese Patent No. 3466370 discloses a one-beam scanning device characterized in that the light receiving surface of the synchronization detection sensor is shifted from the imaging position.

Japanese Patent No. 3466370

[Regarding the two-beam scanning device]
Optical scanning devices are widely known in connection with optical printers and the like. Since the light source of the optical scanning device is generally a semiconductor laser and emits a divergent light beam, a coupling lens is used to make this light beam easily compatible with the subsequent optical system.
Conventionally known as such a coupling lens is a collimating lens that converts a divergent light beam from a semiconductor laser into a parallel light beam.
In recent years, in order to increase the speed and density of optical scanning, the “multi-beam scanning method” in which the number of light sources (that is, the number of light beams to be scanned) is plural has become common.
As a method for achieving multi-beam scanning, (1) a method using a multi-beam semiconductor laser having a plurality of light emitting points, and (2) a beam combining means such as a beam combining prism for light beams emitted from a plurality of semiconductor lasers. Conventionally, methods for synthesizing these have been proposed.
As a modification of (2), a system in which two light beams are directly incident on the optical deflector with a certain opening angle without using beam combining means has been put into practical use.

Further, it is intended to use a coupling lens that converts a divergent light beam from a semiconductor laser into a divergent or convergent light beam. With such a coupling lens, for example, when a light beam coupled to a convergent light beam is used for optical scanning, the power of a conventional scanning imaging lens known as an fθ lens can be reduced and the thickness can be reduced. This is advantageous when the lens is molded with plastic.
As an optical deflector for deflecting a light beam from the light source side, there is a wide variety of optical deflectors that reflect the light beam from the light source side by a deflecting reflection surface and deflect the reflected light beam at a constant angular velocity by rotating the deflection reflection surface at a constant speed. It is used.
When two light beams having different opening angles in the main scanning section, that is, non-parallel to each other, are incident on such an optical deflector, the reflection point of the two light beams on the deflecting reflection surface is the optical deflector. It moves with the rotation.
In the case of an optical scanning device that uses a light beam coupled to a “divergent or convergent light beam” by a coupling lens, the two scanning points in the optical scanning are caused by the positional deviation of the reflection points of the two light beams as described above. A deviation between the writing position of the light beam and the writing end position occurs.

[Regarding Tandem Color Image Forming Apparatus]
In recent years, plastic materials are often used for optical elements of scanning optical systems. In the scanning optical system, there are many optical elements that are long in the main scanning direction, and depending on the holding method, the scanning position shifts in the sub-scanning corresponding direction such as scanning line inclination and scanning line bending. Further, the mounting error of the optical element to the housing is also a shift in the scanning position in the sub-scanning corresponding direction on the scanning surface, and often has a size that cannot be ignored.
Further, in an image forming apparatus having a plurality of scanning means, scanning in the sub-scanning corresponding direction such as scanning line inclination and scanning line bending for each scanning means due to temperature deviation between housings holding and fixing the scanning means. The amount of displacement is different.
On the other hand, in a system in which a plurality of light beams are incident on a single deflector to scan and optical elements are superposed in the sub-scanning direction (a system in which all scanning means are held in the same optical housing) Due to the shape error, mounting error of the scanning optical system, and temperature distribution within the same housing, the amount of scan position deviation in the sub-scanning corresponding direction such as scan line tilt and scan line bending on each photoconductor differs. End up.

In the tandem type full-color image forming apparatus, four photosensitive drums corresponding to each of cyan (C), magenta (M), yellow (Y), and black (K) are arranged along the transfer belt conveyance surface. The beam scanning device scans the beam provided corresponding to each photosensitive drum, and forms an electrostatic latent image on the peripheral surface of the photosensitive drum and visualizes it with toner of the corresponding color. Are sequentially transferred onto a sheet conveyed by a transfer belt to form a multicolor image.
For this reason, if the scanning position shift in the sub-scanning corresponding direction is different for each color, the image quality is deteriorated and the color shift is caused.
As one means for suppressing such output image quality degradation, there is a method of correcting the scanning line inclination with the temperature change over time, and for that purpose, the degree of the scanning line inclination (absolute value or station) It is necessary to grasp the relative value). Various detection sensors have been proposed as means for detecting the scanning line inclination. Many of such detection sensors employ a configuration in which the time during which the light beam scans (crosses) the light receiving surface is detected and measured, and the detection result is converted to “length”.

As described above, in the case of an optical scanning device that uses a light beam coupled to a “divergent or convergent light beam” by a coupling lens, the positional deviation between the writing position and the writing end position of the two light beams in the optical scanning, That is, a dot position shift between the two light beams occurs.
The quality of an output image from an image forming apparatus using such an optical scanning device as an exposure unit is likely to deteriorate.
In addition, as described above, a detection sensor is often provided in the optical scanning device in order to detect a scanning line inclination accompanying a temperature change with time. However, the detection sensor does not detect the scanning line tilt amount (i.e., the scanning position or the light beam position) itself, but measures the time when the light beam scans (crosses) the light receiving surface of the detection sensor. It is converted into “length”.
Therefore, when the arrangement of the detection sensors is inappropriate, there is a possibility that the scanning distance (that is, the position of the light beam) cannot be obtained accurately even if the scanning time can be measured with high accuracy.

  The present invention provides an optical scanning device capable of reducing dot position deviation between a plurality of light beams (light beams), and an optical scanning device capable of detecting a scanning position (that is, a scanning line inclination) of the light beam with high accuracy. Provision of an image forming apparatus capable of high-quality image output, provision of a reference light beam detection method capable of detecting a dot position shift between a plurality of light beams and a scanning position of a light beam with high accuracy , Its main purpose.

  In order to achieve the above object, according to the first aspect of the present invention, an optical deflector having a deflection reflection surface for deflecting a plurality of light beams emitted from a light source, and a light beam deflected by the optical deflector are scanned. A scanning imaging element for condensing the surface to be scanned as a light spot on the surface and optically scanning the surface to be scanned; reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam; and at least in the direction corresponding to the main scanning A reference beam optical element that has power and guides the reference beam to the reference beam detection means, and the reference beam detection means and the reference beam optical element are at least one of the start side and the end side of the optical scanning. In accordance with the optical characteristics of the plurality of light beams incident on the optical deflector, the position of the reference light beam detecting means is adjusted so that the centers of the light scanning widths of these light beams coincide with each other. Stagger It is characterized in.

  According to the second aspect of the present invention, an optical deflector having a deflecting / reflecting surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is collected as a light spot on the surface to be scanned. A scanning imaging element for optically scanning the surface to be scanned, a reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam, and a power having at least a direction corresponding to the main scanning, A reference beam optical element that leads to the reference beam detection means, and the reference beam detection means and the reference beam optical element are optical scanning devices arranged on at least one of the start side and the end side of the optical scanning. And at least two of the plurality of light beams emitted from the light source are incident on the optical deflector in a convergent state, and the principal rays of the at least two light beams overlap each other in the deflection scanning plane. In the optical scanning device in which the optical deflector is incident on the optical deflector from the scanning start side, the reference light beam detecting means arranged on the optical scanning start side among the reference light beam detecting means has a light receiving surface as a reference light beam. The reference light beam detecting means arranged so as to be closer to the optical deflector than the imaging position in the main scanning corresponding direction and arranged on the end side of the optical scanning has a light receiving surface in the main scanning corresponding direction of the reference light beam. It is characterized by being arranged so as to be away from the optical deflector in a direction away from the optical deflector.

  According to a third aspect of the present invention, an optical deflector having a deflection reflection surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is collected as a light spot on the surface to be scanned. A scanning imaging element for optically scanning the surface to be scanned, a reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam, and a power having at least a direction corresponding to the main scanning, A reference beam optical element that leads to the reference beam detection means, and the reference beam detection means and the reference beam optical element are optical scanning devices arranged on at least one of the start side and the end side of the optical scanning. And at least two of the plurality of light beams emitted from the light source are incident on the optical deflector in a convergent state, and the principal rays of the at least two light beams overlap each other in the deflection scanning plane. In the optical scanning device that is incident on the optical deflector from the scanning end side in a state in which the reference beam is detected, the reference beam detection unit disposed on the optical scanning start side among the reference beam detection units has a light receiving surface as a reference beam. The reference light beam detecting means disposed at a position farther from the optical deflector than the imaging position in the main scanning corresponding direction and disposed on the end side of the optical scanning has a light receiving surface in the main scanning corresponding direction of the reference light beam. It is characterized by being arranged so as to be closer to the optical deflector than the imaging position.

  According to a fourth aspect of the present invention, an optical deflector having a deflection reflection surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is collected as a light spot on the surface to be scanned. A scanning imaging element for optically scanning the surface to be scanned, a reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam, and a power having at least a direction corresponding to the main scanning, A reference beam optical element that leads to the reference beam detection means, and the reference beam detection means and the reference beam optical element are optical scanning devices arranged on at least one of the start side and the end side of the optical scanning. And at least two of the plurality of light beams emitted from the light source enter the optical deflector in a divergent state, and the principal rays of the at least two light beams overlap each other in the deflection scanning plane. In the optical scanning device in which the optical deflector is incident on the optical deflector from the scanning start side, the reference light beam detecting means arranged on the optical scanning start side among the reference light beam detecting means has a light receiving surface as a reference light beam. The reference light beam detecting means disposed at a position farther from the optical deflector than the imaging position in the main scanning corresponding direction and disposed on the end side of the optical scanning has a light receiving surface in the main scanning corresponding direction of the reference light beam. It is characterized by being arranged so as to be closer to the optical deflector than the imaging position.

  According to the fifth aspect of the present invention, an optical deflector having a deflection reflection surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is collected as a light spot on the surface to be scanned. A scanning imaging element for optically scanning the surface to be scanned, a reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam, and a power having at least a direction corresponding to the main scanning, A reference beam optical element that leads to the reference beam detection means, and the reference beam detection means and the reference beam optical element are optical scanning devices arranged on at least one of the start side and the end side of the optical scanning. And at least two of the plurality of light beams emitted from the light source enter the optical deflector in a divergent state, and the principal rays of the at least two light beams overlap each other in the deflection scanning plane. In the optical scanning device that is incident on the optical deflector from the scanning end side in a state in which the reference beam is detected, the reference beam detection unit disposed on the optical scanning start side among the reference beam detection units has a light receiving surface as a reference beam. The reference light beam detecting means arranged so as to be closer to the optical deflector than the imaging position in the main scanning corresponding direction and arranged on the end side of the optical scanning has a light receiving surface in the main scanning corresponding direction of the reference light beam. It is characterized by being arranged so as to be away from the optical deflector in a direction away from the optical deflector.

  According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, of the scanning start timing and the optical scanning end timing of the optical scanning according to the output signal from the reference light beam detecting means. At least one is determined.

  According to a seventh aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, the reference light beam detecting means calculates at least one of a light spot position and a light spot interval on the surface to be scanned. It has the function to detect.

  According to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect, the reference beam detection unit detects a time during which the reference beam scans at least a part of a light receiving surface of the reference beam detection unit. Thus, at least one of the light spot position and the light spot interval on the surface to be scanned is calculated.

  According to a ninth aspect of the present invention, in the optical scanning device according to any one of the second to fifth aspects, the reference beam detecting means and the reference beam optical element are arranged on the start side and the end side of the optical scanning. Based on detection signals from the reference light beam detecting means arranged on the start side and the end side of the optical scanning so as to correct the difference in the optical scanning width on the scanned surface of the at least two light beams, The modulation frequency is adjusted.

  According to a tenth aspect of the present invention, in the optical scanning device according to the eighth aspect, the reference beam detecting means includes a plurality of laser beam detectors including two light receiving elements, and at least one of the two light receiving elements. The system has two light receiving regions formed non-parallel to each other in the region through which the laser beam passes, and the two light receiving elements are arranged adjacent to each other in the main scanning direction so that adjacent edges are parallel to each other. It is characterized by.

According to an eleventh aspect of the present invention, in the optical scanning device according to the ninth aspect, the angular velocity (or rotational speed) of the optical deflector is ω / 2 [rad / s] (or N [rpm]),
V [mm / s], the speed at which the light spot scans the surface to be scanned,
The time (detection time) that the light spot scans at least a part of the light receiving portion of the reference light beam detecting means is τ [s], the scanning distance is x [mm],
When
The scanning speed V is approximately proportional to the angular speed ω / 2 with the relationship V = K × ω,
When the scanning distance x is arranged by shifting the light receiving surface of the reference beam detecting means in a direction away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction,
x = (π / 15) × (K + ΔK1) × N × τ; ΔK1> 0,
When the light receiving surface of the reference light beam detecting means is shifted from the imaging position in the main scanning corresponding direction of the reference light beam in a direction closer to the optical deflector,
x = (π / 15) × (K−ΔK2) × N × τ; ΔK2> 0,
It is calculated by.

  According to a twelfth aspect of the present invention, in the optical scanning device according to any one of the second to fifth aspects, the principal rays of the at least two light beams are deflected in a state in which they are not parallel to each other within a deflection scanning plane. It is the structure which injects into a container, It is characterized by the above-mentioned.

According to a thirteenth aspect of the present invention, an optical deflector having a deflecting / reflecting surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is collected as a light spot on the surface to be scanned. A scanning imaging element for optically scanning the surface to be scanned, a reference beam detecting means for detecting the beam deflected by the optical deflector as a reference beam, and a power having at least a direction corresponding to the main scanning, A reference beam optical element that leads to the reference beam detection means, and the reference beam detection means and the reference beam optical element are optical scanning devices arranged on at least one of the start side and the end side of the optical scanning. And at least two of the plurality of light beams emitted from the light source enter the optical deflector in a convergent or divergent state, and the principal rays of the at least two light beams are within the deflection scanning plane. In the optical scanning device that is incident on the optical deflector without overlapping, the optical scanning start position on one scanned surface of the at least two light beams is Ya (START), and the optical scanning end position is Ya (END). ),
The optical scanning start position on the other scanned surface is Yb (START), the optical scanning end position is Yb (END),
When
{Ya (START) −Yb (START)} × {Ya (END) −Yb (END)} ≦ 0
Is established.

  According to a fourteenth aspect of the present invention, an image forming apparatus includes the optical scanning device according to any one of the first to thirteenth aspects.

  According to a fifteenth aspect of the present invention, in the reference light beam detection method, the optical scanning device according to any one of the first to thirteenth aspects is used.

According to the sixteenth aspect of the present invention, an optical deflector having a deflecting / reflecting surface for deflecting a plurality of light beams emitted from the light source, and the light beam deflected by the optical deflector is condensed on the surface to be scanned as a light spot. A scanning imaging element for optically scanning the surface to be scanned, and a reference light beam detecting means for detecting the light beam deflected by the optical deflector as a reference light beam. A reference beam optical element guided to the beam detection means, and the reference beam detection means and the reference beam optical element are arranged on at least one of a start side and an end side of the optical scanning. At least two of the plurality of light beams emitted from the light source are incident on the optical deflector in a convergent or divergent state, and the principal rays of the at least two light beams are mutually in the deflection scanning plane. The optical scanning device is incident on the optical deflector at non-overlapping state as the exposure apparatus, the toner image is transferred onto the recording medium, an image forming apparatus that forms an image by fixing,
The dot position at the optical scanning start end corresponding to one of the at least two light beams is Da (START), the dot position at the optical scanning end is Da (END),
The dot position at the optical scanning start end corresponding to the other is Db (START), the dot position at the optical scanning end is Db (END),
When
{Da (START) −Db (START)} × {Da (END) −Db (END)} ≦ 0
Is established.

According to the first aspect of the present invention, the positional deviation in the main scanning direction between the two laser beams due to the optical characteristics of the light beam incident on the optical deflector (or the scanning optical system) can be reduced, and the deterioration of the image quality can be prevented. can do.
According to the invention of claim 2 or 3, by moving the position in the optical axis direction of the reference light beam detecting means (synchronous detection sensor) installed on the optical scanning start side and the optical scanning end side in a predetermined direction, Reduces the positional deviation in the main scanning direction between the two laser beams (deviation between the optical scanning start end and the optical scanning end end) that occurs when the light beam incident on the optical deflector (or scanning optical system) is a “convergent light beam” And deterioration of image quality can be prevented.

  According to the invention of claim 4 or 5, by moving the position in the optical axis direction of the reference light beam detecting means (synchronous detection sensor) installed on the optical scanning start side and the optical scanning end side in a predetermined direction, Reduces the positional deviation in the main scanning direction between the two laser beams (deviation between the optical scanning start end and the optical scanning end end) that occurs when the light beam incident on the optical deflector (or scanning optical system) is a “divergent light beam”. And deterioration of image quality can be prevented.

According to the sixth aspect of the invention, since the optical scanning start timing can be determined by the synchronization signal from the reference light beam detecting means (synchronous detection sensor), the optical scanning start position between the two laser beams is electrically controlled. Thus, the scanning control can be facilitated.
According to the seventh aspect of the invention, by detecting the light spot position and the light spot interval using a line CCD, a two-dimensional CCD, etc., the position and inclination of the scanning line are corrected based on the detection result. Correction data can be obtained.

According to the eighth aspect of the present invention, it is possible to detect the light spot position and the light spot interval with a relatively low cost detection sensor.
According to the ninth aspect of the present invention, since the reference light beam detecting means (synchronous detection sensor) is arranged on both sides of the optical scanning start side and the optical scanning end side, it is possible to detect the deviation of the scanning speeds of the two laser beams. It is possible to match the optical scanning widths (optical scanning regions) of both laser beams by adjusting the modulation frequency according to the image information of both laser beams based on the detection result.

According to the tenth aspect of the present invention, since the reference light beam detecting means (synchronous detection sensor) is configured by using two non-parallel sensors each having a light receiving surface divided into two, the shape of the laser beam in the light receiving portion is good. Even if it is not (image is not formed at the light receiving portion), the reference light beam can be detected with high accuracy.
According to the eleventh aspect of the present invention, in the ninth aspect, the “scanning distance (scanning width)” is derived from the product of the “scanning speed” and the “scanning time (detection result by the detecting means)” on the light receiving surface. However, when the position of the reference light beam detection means (synchronization detection sensor) is shifted, the scanning speed is different from that when the position is not shifted. An accurate scanning speed can be calculated by appropriately changing the proportional constant in calculating the scanning speed.

According to the twelfth aspect of the present invention, the principal rays of the two laser beams incident on the polygon mirror are made non-parallel in the deflection scanning surface, so that the distance between the two light spots on the surface to be scanned is changed in the main scanning direction. Thus, both light spots can be detected independently by one detection sensor.

According to the thirteenth aspect of the present invention, the conditions for including the entire optical scanning width of the other laser beam within the optical scanning width of the one laser beam are defined. ) Light spot position deviation in the main scanning direction can be reduced.
According to the fourteenth aspect of the present invention, since the optical scanning device according to any one of the first to thirteenth aspects is used as an exposure apparatus for an electrophotographic process in an image forming apparatus, a high-quality output image can be obtained. Can do.
According to the fifteenth aspect of the present invention, since the reference light beam is detected by the optical scanning device according to any one of the first to thirteenth aspects, the dot position deviation between the two light beams or the light beam It becomes possible to detect the scanning position or both of them with high accuracy.

  According to the sixteenth aspect of the present invention, on the recording medium, as in the thirteenth aspect, the toner image region corresponding to one laser beam and the toner image region corresponding to the other laser beam are all included. Therefore, the “bad impression of the image as a whole” of the output image on the recording medium can be reduced.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Usually, “main scanning direction or main scanning corresponding direction” and “sub scanning direction or sub scanning corresponding direction” mean a direction in which a light spot is scanned on a surface to be scanned and a direction orthogonal thereto, The directions corresponding to the main scanning direction and the sub-scanning direction of the surface to be scanned are called “main scanning direction or main scanning corresponding direction” and “sub-scanning direction or sub-scanning corresponding direction”, respectively, in a broad sense at each location on the optical path. Shall.

First, before describing the present invention, an outline of a conventional optical scanning device as a comparative example of the present invention will be described.
FIG. 19 is an example of an optical arrangement in an optical scanning device used in an exposure apparatus of an image forming apparatus. Usually, these optical elements are housed inside a housing (not shown).
In this optical scanning device, laser beams emitted from two semiconductor lasers (single beam semiconductor lasers) 11a and 11b as light sources and coupled by two coupling lenses 12a and 12b according to the characteristics of the optical system thereafter. The beams 17a and 17b are imaged in the sub-scanning direction on the deflection reflection surface of the polygon mirror 14 as an optical deflector by the action of the cylindrical lens 13 having power in the sub-scanning direction, and are formed as a long line image in the main scanning direction. Image.

  Here, a configuration is adopted in which the chief rays of the two laser beams 17a and 17b cross each other in the vicinity of the deflection reflection surface of the polygon mirror 14 within the deflection scanning surface (that is, the optical paths projected onto the main scanning section). Yes. In this way, the configuration in which the chief rays of the two laser beams 17a and 17b intersect each other ensures a sufficient interval between the two light spots on the surface to be scanned (and a synchronization detection sensor described later). The synchronization signal can be detected independently.

The two laser beams 17a and 17b deflected and scanned by the deflecting / reflecting surface of the polygon mirror 14 are used as a light spot on the photosensitive drum 16 as the surface to be scanned by the action of the scanning optical system 15 as a scanning imaging element. Fast scan.
Further, a synchronization detection sensor 18 as a reference light beam detecting means for obtaining a so-called synchronization signal for setting the timing of starting optical scanning on each surface of the polygon mirror 14 is rotated by a rotation direction of the polygon mirror 14 (in this figure). (Synchronous direction) is provided on the scanning start side at a position optically equivalent to the surface to be scanned (photosensitive drum 16), and constitutes a synchronous optical system 19 as an optical element for a reference beam. ing.
The synchronization optical system 19 in FIG. 19 is included in the scanning optical system 15 that guides the laser beam to the surface 16 to be scanned, but may be composed of another optical element having power in at least the main scanning direction.
The “optically equivalent position” means that the image plane position (image forming position) is not changed when the optical path of the laser beam is bent by a folding mirror (not shown).

[A: When the laser beam incident on the scanning optical system is a parallel light beam in the main scanning section]
Consider a case in which laser beams emitted from two semiconductor lasers (single beam semiconductor lasers) 11a and 11b are coupled into parallel light beams by two coupling lenses 12a and 12b, respectively.
The two laser beams (parallel light beams) 17a and 17b emitted from the two coupling lenses 11a and 11b are polygon mirrors in a state of parallel light beams in the main scanning direction because the cylindrical lens 13 has no power in the main scanning direction. After being incident on the deflecting reflecting surface 14 and deflected and reflected, the scanning optical system 15 scans the surface to be scanned 16 at a constant speed as light spots BSa and BSb.
Assuming that the rotation direction of the polygon mirror 14 is clockwise, the two light spots BSa and BSb scan the surface to be scanned 16 from above (light scanning start end) to below (light scanning end end). become. The target value (design median value) of the scanning width is 300 [mm].

Similarly, the laser beams 17a and 17b deflected and reflected by the polygon mirror 14 enter the synchronous optical system 19 in the state of a parallel light beam, and are then guided to the synchronous detection sensor 18.
20 to 22 schematically show the movement of the reflection points (reflection positions) of the two laser beams 17a and 17b on the deflecting / reflecting surface as the polygon mirror 14 rotates.
(# A-1: When two laser beams reach the central image height (H = 0))
FIG. 21 shows the case where the two laser beams 17a and 17b reflected by the polygon mirror 14 reach the vicinity of the center of the surface to be scanned 16 (in this description, the light spot position of the laser beam 17a on the surface to be scanned 16 is FIG. 6 is a schematic diagram of the center of a surface to be scanned 16 (when the image height is H = 0).
The principal rays of the two laser beams 17a and 17b reflected by the polygon mirror 14 are indicated by solid lines (reference numerals 17a ′ and 17b ′). In FIG. 21, in order not to complicate the explanatory diagram, the two laser beams 17a and 17b intersect each other at the position on the rotation center side of the polygon mirror 14 from the deflection reflection surface. May be on the deflecting / reflecting surface or on the light source side of the deflecting / reflecting surface.

Now, the angle at which these laser beams intersect each other (within the main scanning section) will be referred to as “intersection angle: 2φ”.
In the case of the arrangement of the polygon mirror 14 shown in FIG. 21, the light spot BSa of the laser beam 17a reaches the image height H = 0 on the surface to be scanned 16 as described above, but the laser beam 17b that scans backward is scanned. The light spot BSb is located closer to the optical scanning start end [(−) image height side]. Note that the scanning optical system 15 maintains constant speed scanning, and the angle of view θ of the chief ray of the laser beam (the normal of the scanned surface 16 and the chief ray of the laser beam reflected by the deflecting reflecting surface). Angle) and the light spot position H,
H = F × θ (F is the focal length of the scanning optical system 15)
If the relationship is satisfied, the light spot BSb is
H = −F × 2φ (a negative sign means closer to the optical scanning start side, that is, (−) image height side)
Will be located.

The principal ray of the laser beam 17b when the polygon mirror 14 is rotated clockwise by an angle φ is indicated by a broken line (reference numeral 17b ″). Strictly speaking, since the polygon mirror 14 is rotated by an angle φ, the reflection point of the laser beam 17b slightly moves. However, since the essence of this description is not affected, the reflection point is illustrated as the same position. As shown in the figure, the principal ray 17b '' of the laser beam 17b indicated by a broken line and the principal ray 17a 'of the laser beam 17a indicated by a solid line are parallel to each other.
In the case of the scanning optical system 15 described in this comparative example, the two laser beams 17a and 17b having principal rays parallel to each other are the same on the scanned surface 16 because they have a function of forming an image of a parallel light beam on the scanned surface. The position (image height H = 0 [mm] in FIG. 21) is reached.

(# A-2: When two laser beams reach the vicinity of the optical scanning start end (H = −150 [mm]))
20 shows a case where the two laser beams 17a and 17b reach the vicinity of the outermost periphery of the scanning surface 16 on the optical scanning start side (in this description, the light spot position BSa of the laser beam 17a on the scanning surface 16 is the image height. H = −150 [mm]). The principal rays of both laser beams reflected by the polygon mirror 14 are indicated by solid lines (reference numerals 17a ′ and 17b ′).
As in the case of FIG. 21, the principal ray of the laser beam 17b when the polygon mirror 14 is rotated clockwise by an angle φ is indicated by a broken line (reference numeral 17b ″). The chief ray (17b '') of the laser beam 17b indicated by a broken line and the chief ray (17a ') of the laser beam 17a indicated by a solid line are parallel to each other. That is, both laser beams reach the same position (image height H = −150 [mm]) on the scanning surface 16.

(# A-3: When two laser beams reach the vicinity of the optical scanning end (H = + 150 [mm]))
22 shows the case where the two laser beams 17a and 17b reach the vicinity of the outermost periphery of the scanning surface 16 on the optical scanning end side (in this description, the light spot position of the laser beam 17a on the scanning surface 16 is the image height H = + 150 [mm]), and the principal rays of both laser beams reflected by the polygon mirror 14 are indicated by solid lines (reference numerals 17a ′ and 17b ′).
As in the case of FIGS. 20 and 21, the principal ray of the laser beam 17b when the polygon mirror 14 is rotated clockwise by an angle φ is indicated by a broken line (reference numeral 17b ″). In addition, the principal ray (17b ″) of the laser beam 17b indicated by a broken line and the principal ray (17a ′) of the laser beam 17a indicated by a solid line are parallel to each other.
That is, both laser beams reach the same position (image height H = + 150 [mm]) on the surface to be scanned 16.

(# A-4: When two laser beams reach the vicinity of the light receiving portion (synchronous image height) of the synchronous detection sensor 18)
When the light receiving portion of the synchronization detection sensor 18 is disposed at a position optically equivalent to the scanned surface 16, it is considered that the light receiving portion of the synchronization detection sensor 18 is disposed on an extension line of the scanned surface 16. Can do.
The light receiving surface is assumed to be parallel to the scanned surface 16 (that is, the same surface), and the image height corresponding to this is referred to as “synchronous image height”.
The “synchronous image height” located outside the optical scanning start image height (H <−150 [mm]) also has the same situation as in the case of (# A-2).

As described above with reference to FIGS. 20 to 22, the two laser beams 17 a and 17 b incident on the scanning optical system 15 having a function of forming an image of a parallel light beam on the surface to be scanned have an arrangement angle of the polygon mirror 14. When they are the same (that is, at the same time), always (synchronous optical system-light scanning start end-light scanning end end), the light spot BSb is compared to the light spot BSa.
Spacing ΔY = F × 2φ
It can be seen that only the scanning is carried out behind.
That is, in the case of such an optical scanning device, the synchronization detection sensor 18 is disposed at a position equivalent to the scanned surface 16 and the optical scanning start timing is set based on the “synchronization signal” by the synchronization detection sensor 18. Thus, the light spots BSa and BSb of the laser beam 17a and 17b on the scanned surface 16 can always reach the same position for the same angle of view θ (while being shifted by the interval ΔY).

[B: When the laser beam incident on the scanning optical system is a divergent light beam in the main scanning section (1)]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Note that the same parts as those in the comparative example are denoted by the same reference numerals, and the structural and functional descriptions already described will be omitted unless otherwise necessary, and only the main parts will be described (the same applies to other embodiments below).
First, before explaining the gist of the present embodiment, when the laser beam incident on the scanning optical system is “divergent” in the main scanning section, optical scanning of a plurality (here, two) light spots is performed. The principle of deviation in width will be described.
When the laser beam incident on the scanning optical system is a divergent light beam (within the main scanning section), the situation is completely different from the case of the parallel light beam described in the comparative example. This will be described with reference to FIGS.

To make the laser beam incident on the scanning optical system a divergent beam (within the main scanning section)
(1) The laser light emitted from the semiconductor laser 11 is converted into a “divergent light beam” by the coupling lens 12, passes through the cylindrical lens 13 having power only in the sub-scanning direction, and is then deflected and reflected by the polygon mirror 14. A structure to be incident on the
(2) The laser beam emitted from the semiconductor laser 11 is converted into a “parallel beam” by the coupling lens 12 and then deflected by the polygon mirror 14 through at least an optical element having “weak power” in the main scanning direction. A structure that makes the light incident on the reflecting surface;
Any configuration may be adopted.
The behavior of the laser beams 17a and 17b when the scanning optical system 15 has a function of forming a divergent light beam on the scanned surface 16 (within the main scanning section) will be described below with reference to FIGS. explain.
In FIG. 5, the scanning optical system 15 is indicated by a vertical “double arrow” at a position corresponding to the principal point. Further, the focal point of the scanning optical system 15 is indicated by “one-dot chain line”.

(# B-1: When two laser beams reach the vicinity of the optical scanning start end (H = −150 [mm]))
As shown in FIGS. 4 and 5, the laser beam 17a incident on the polygon mirror 14 is reflected by the polygon mirror 14 (the principal ray is indicated by reference numeral 17a1), and then passed through the scanning optical system 15 to be covered. It reaches the optical scanning start end (image height H = −150 [mm]) on the scanning surface 16.
The principal ray of the reflected beam of the laser beam 17b incident on the polygon mirror 14 with the same angle of arrangement of the polygon mirror 14 as described above (solid line indicated by reference numeral 17b1 ′) passes through the scanning optical system 15 on the scanned surface 16. It reaches the outside of the scanning start end [corresponding to the position of image height H = − (150 + K × 2φ)] (following the light spot BSa by K × 2φ). The definition of K will be described later.

Next, the principal ray of the reflected beam (indicated by reference numeral 17b1) of the laser beam 17b incident on the polygon mirror 14 when the polygon mirror 14 is rotated clockwise by an angle φ from this state is represented by a broken line. Since the angle 2φ formed by the laser beams 17a and 17b incident on the polygon mirror 14 is the same, the laser beams 17a1 and 17b1 are parallel to each other.
Unlike the “parallel light beam”, the scanning optical system 15 shown in FIG. 5 has a function of forming a divergent light beam on the surface to be scanned 16 in the main scanning section. The principal rays of the two laser beams 17a1 and 17b1 incident on the scanning optical system 15 are not on the surface to be scanned 16 but at positions close to the polygon mirror 14 (focal position of the scanning optical system 15; indicated by a one-dot chain line). Will intersect.
That is, on the surface 16 to be scanned, the light spot BSa of the laser beam 17a1 precedes the light spot BSb of the laser beam 17b1 (positioned more (+) on the image height side).
The interval between the two light spots in the main scanning direction is indicated by e1 in FIG.

(# B-2: When two laser beams reach the vicinity of the optical scanning end (H = + 150 [mm]))
In FIG. 5, the principal ray reaching the optical scanning end (image height H = + 150 [mm]) of the laser beam 17a deflected and reflected by the polygon mirror 14 is denoted by reference numeral 17a2. On the other hand, from this state, the polygon mirror 14 The principal ray of the reflected beam (indicated by reference numeral 17b2) of the laser beam 17b incident on the polygon mirror 14 while being rotated clockwise by an angle φ is represented by a broken line.
Similarly to the optical scanning start side, both laser beams 17a2 and 17b2 enter the scanning optical system 15 in a state of being parallel to each other, and then approach the polygon mirror 14 from the scanned surface 16 (the focal point of the scanning optical system 15). Crossing each other at a position (indicated by a one-dot chain line) to reach the scanned surface 16. In this case, the distance between the two light spots in the main scanning direction is indicated by e2.

On the other hand, the distance between two parallel laser beams (between 17a1-17b1 and 17a2-17b2) incident on the scanning optical system 15 will be compared at the optical scanning start end and the optical scanning end end. Since the angle formed between the incident beam and the reflected beam at the deflecting / reflecting surface of the polygon mirror 14 is larger at the optical scanning end than at the optical scanning start end, two parallel laser beams 17a2 incident on the scanning optical system 15 are present. The distance between -17b2 also increases.
Therefore, when the distances e1 and e2 between the two light spots are compared,
e1 <e2
The relationship is established.
Similarly, in the entire region (width: 300 [mm]) from the optical scanning start end to the end end, the distance between both light spots at the image heights H1 and H2 (H1 <H2) of the light spot BSa of the laser beam 17a is represented by e01. And e02,
e01 <e02
The relationship is established.
Therefore, as can be seen from FIG. 5, the optical scanning width of the laser beam 17b (BSb) is shortened by “e2-e1” with respect to the optical scanning width 300 [mm] of the laser beam 17a (BSa).

(# B-3: When two laser beams reach the vicinity of the synchronous detection sensor)
Similarly, laser beams reaching the light receiving surface of the synchronization detection sensor 18 are denoted by reference numerals 17a (−) and 17b (−).
If the interval between the light spots of the laser beams 17a (−) and 17b (−) in the main scanning direction on the surface to be scanned 16 is e (−), it is the same as described in (B-1) and (B-2). For reasons, as shown in FIG.
e (-) <e1 <e2
The relationship is established.

As described above in (# B-1) to (# B-3), when two laser beams are incident on the scanning optical system 15 having a function of forming an image of a “divergent light beam” on the surface to be scanned However, the optical scanning widths of the laser beams 17a and 17b on the scanned surface 16 are different. That is, the optical scanning width of the laser beam 17a becomes wider.
Furthermore, as will be described below, the optical scanning start positions of the two laser beams 17a and 17b become inappropriate, and this causes a deterioration in output image quality.
Based on FIGS. 5 and 6, the difference between the optical scanning start ends of the two light spots when the synchronization detection sensor 18 (the light receiving surface thereof) is arranged at a position equivalent to the scanned surface 16 will be described.
As described in (B-1) to (B-3), the synchronous image height, the optical scanning start end, and the two parallel laser beams 17a and 17b reflected from the deflecting reflection surface of the polygon mirror 14; The intervals between the light spots at the end of the optical scanning are assumed to be e (−), e1, and e2, respectively (FIG. 5).

On the other hand, the constant speed scanning property of the light spot on the scanned surface 16 with respect to the angle of view θ is ensured.
Light spot position: Y = K × θ (K is a proportional constant)
Light spot scanning speed: VY = dY / dt = K × (dθ / dt) = K × ω
(Ω is the time derivative of the angle of view = angular velocity)
Therefore, the time from when the laser beam 17a (light spot BSa) enters the synchronization detection sensor 18 until the laser beam 17b (light spot BSb) enters the synchronization detection sensor 18 is t0, and the scanning speed is VY. Then
e (−) = VY × t0 = K × ω × t0
It becomes. That is,
t0 = e (−) / (K × ω)
It is represented by
The relative positions (displacements from the optical scanning start end and the optical scanning end) of the laser beam 17b after time t0 after the laser beam 17a reaches the optical scanning start end and the optical scanning end end are respectively indicated by E1. And E2,
E1 = | e1-e (−) |
E2 = | e2-e (−) |
e (-) <e1 <e2
(FIG. 6). The displacements E1 and E2 correspond to the light spot position deviation in the main scanning direction on the scanned surface 16.

The angle of view θ (−) of the chief ray of the laser beam reaching the synchronous image height and the angle of view θ1 of the chief ray of the laser beam reaching the optical scanning start end (image height H = −150 [mm]) Compared with the angle of view θ2 of the principal ray of the laser beam reaching the end (image height H = + 150 [mm]), it is substantially equal [e1≈e (−)], so that the light spot position shift on the optical scanning start side The amount E1 is small [E1 = e1-e (−) ≈0], while the light spot position deviation amount E2 on the optical scanning end side is large.
When such an optical scanning device is used as an exposure unit of an image forming apparatus, the image quality varies (differs) between areas in the output image corresponding to the optical scanning start side and the optical scanning end side. In particular, in the case of an output image in which density unevenness such as “halftone” is likely to appear remarkably, the overall image impression is deteriorated.

When the light beam incident on the scanning optical system 15 is not a “parallel light beam” such as a “divergent light beam” in the main scanning section, if the synchronization detection sensor 18 is disposed at a position optically equivalent to the scanning surface 16, As described above, in principle, a deviation occurs between the optical scanning start end and the optical scanning end end between the two laser beams, resulting in a deviation in the optical scanning width. When such an optical scanning device is applied to the exposure unit of the image forming apparatus, the output image is deteriorated due to this.
In order to suppress this problem, it is only necessary to reduce variations in image quality between regions in the output image corresponding to the optical scanning start side and the optical scanning end side. For this purpose, the relationship between E1 and E2 defined above is set to “E1 = E2” at the time of design, that is, the centers of the optical scanning widths of the two laser beams 17a and 17b (light spots BSa and BSb) are matched. Thus, the “bad impression of the image as a whole” can be reduced.

As a method for optically achieving this, the synchronization detection sensor 18 may be shifted from the position optically equivalent to the scanned surface 16 in the optical axis direction. This positional shift is performed according to the light characteristic (form) of the light beam.
For example, in the case of an optical system in which the light beam incident on the scanning optical system 15 is a “divergent light beam” in the main scanning section, the synchronization detection sensor 18 is optically equivalent to the scanned surface 16 as shown in FIG. By shifting the position away from the polygon mirror 14 from the position, the distance between the two light spots e (−) ′ can be made larger than e (−) in FIG. That is,
e (-) '>e1> e (-)
The relationship is established. Therefore, in the case of the configuration of FIG.
| E1-e (−) | <| e2-e (−) |
Here, e1-e (-)> 0
e2-e (-)> 0
However, by adopting the configuration of FIG. 1, the distance e (−) ′ between the two light spots can be enlarged, so the relationship between the two light spot positions is
| E1-e (−) ′ | ≈ | e2-e (−) ′ |
Here, e1-e (−) ′ <0
e2-e (-) '> 0
It becomes possible to approximate the relationship.
In terms of design, the synchronization detection sensor 18 is
e (−) ′ = (e2 + e1) / 2
By moving to a position where, i.e., a distance Δ indicated by an arrow in FIG.
E1 = | e1-e (−) ′ |
E2 = | e2-e (−) ′ |
However, as shown in FIG. 2, “E1 = E2” can be satisfied.

However, if the shift amount of the position of the synchronization detection sensor 18 from the position optically equivalent to the surface to be scanned 16 is set too large, E1 becomes too larger than E2, and the light spot position shift on the optical scanning start side becomes too large. The amount will increase. In addition, since the laser beam does not form an image on the light receiving surface of the synchronous detection sensor 18 (the beam waist is not formed), the detection accuracy may be deteriorated depending on the type of sensor.
Therefore, the shift amount of the synchronization detection sensor 18 is
e1 <e (−) <e2 (Formula 1-1)
It is desirable to be within a range where the above relationship is established.

When this relational expression (Formula 1-1) and (Formula 1-2) described later are expressed by another relational expression, in FIG. 3, the optical scanning start position of the light spot BSa (laser beam 17a) is represented by Ya (START). ), The optical scanning end position is Ya (END), the optical scanning start position of the light spot BSb (laser beam 17b) is Yb (START), and the optical scanning end position is Yb (END).
Ya (START) -Yb (START) = e1
Ya (END) -Yb (END) = e2
far. The fact that the entire optical scanning width of the light spot BSb is included in the optical scanning width of the optical spot BSa.
e1 × e2 ≦ 0
Because it means
{Ya (START) −Yb (START)} × {Ya (END) −Yb (END)} ≦ 0 (Formula 1-3)
If is established, relational expressions (Equation 1-1) and (Equation 1-2) are established.

Similarly, in an image forming apparatus in which the optical scanning apparatus of the present invention is applied as an exposure apparatus for an electrophotographic process, the “light spot” position in the optical scanning apparatus corresponds to the “toner image” position fixed on the recording medium. To do. Accordingly, as described above, the dot position of the optical scanning start end corresponding to the light spot BSa is Da (START), the dot position of the optical scanning end end is Da (END), and the optical scanning start end corresponding to the light spot BSb is When the dot position is Db (START) and the dot position at the end of optical scanning is Db (END),
{Da (START) −Db (START)} × {Da (END) −Db (END)} ≦ 0
In order to obtain a high-quality output image, it is desirable to move the light receiving surface of the synchronous detection sensor to a range where the above is established.

In the present embodiment, when the time (light scanning start timing) from when the “synchronization signal” is obtained from the synchronization detection sensor 18 until the start of optical scanning is the same in the two laser beams 17a and 17b, A method for optically achieving the subject has been described.
On the other hand, in order to achieve this electrically, it is possible to individually determine the optical scanning start ends by individually setting the optical scanning start timings of the two laser beams. However, in this case, it is not possible to correct a scanning position shift in the main scanning direction, that is, a so-called “vertical line fluctuation” due to a shape error of the polygon mirror.
As another effect of shifting the position of the synchronization detection sensor 18 in this way, it is caused by a polygon mirror shape error (variation in distance from the rotation axis to each deflection reflection surface) as proposed in Patent Document 1. In other words, the so-called “vertical line fluctuation” can be reduced.

In the present embodiment, the principal rays of the laser beams 17a and 17b emitted from the two semiconductor lasers 11a and 11b and coupled by the two coupling lenses 12a and 12b are deflected and reflected by the polygon mirror 14. By adopting the configuration of “crossing each other in the deflection scanning plane in the vicinity of the surface”, the configuration “enters the optical deflector (polygon mirror) without overlapping each other in the deflection scanning plane” is adopted.
As a result, it is possible to maintain the interval between the light spots on the surface to be scanned in the main scanning direction, and it is possible to independently detect both light spots with one synchronization detection sensor.

When the focal length of the scanning optical system is F and the angle at which the two laser beams (principal rays) intersect is 2φ, the interval PY between the light beams in the main scanning direction on the surface to be scanned is expressed by “PY = F × 2φ”. Therefore, PY can be adjusted by appropriately setting φ.
The semiconductor lasers 11a and 11b may be single beam semiconductor lasers having a single light emitting point or multibeam semiconductor lasers having a plurality of light emitting points.

As another configuration, for example, the configurations illustrated in FIGS. 7 and 8 may be used.
In the configuration shown in FIG. 7, laser beams 17 a and 17 b emitted from two semiconductor lasers 11 a and 11 b and coupled by two coupling lenses 11 a and 11 b are combined by a beam combining unit (beam combining prism) 23. Then, the light enters the polygon mirror 14. By combining the two laser beams 17a and 17b by the beam combining means 23, the angle at which the two laser beams intersect can be reduced, and the deviation of the optical characteristics of the two laser beams on the surface to be scanned can be suppressed. It becomes possible.
The configuration shown in FIG. 8 is a configuration in which a semiconductor laser (for example, a semiconductor laser array) 11 having a plurality of light emitting points is used as a light source and is coupled by one coupling lens 12. The arrangement of the light emitting points of a semiconductor laser having such a monolithically formed light emitting point hardly fluctuates due to temperature changes or the passage of time, so the light spot interval on the surface to be scanned must be maintained with high accuracy. Is possible.

[C: When the laser beam incident on the scanning optical system is a divergent light beam in the main scanning section (2)]
(# C-1: When the synchronization detection sensor is arranged outside the optical scanning end)
A second embodiment will be described with reference to FIG.
The synchronization detection sensor can also be arranged outside the optical scanning end.
In this case, as shown in FIG. 9, the light spot interval in the synchronous detection sensor 18 ′ as the reference beam optical element of the two parallel laser beams 17a and 17b incident on the scanning optical system 15 is represented by e (+). Then, the time t0 from when the light spot of the laser beam 17a is incident until the light spot of the laser beam 17b is incident is the same as in the case of the first embodiment.
t0 = e (+) / (K × θ)
It is represented by
The relative positions (displacements from the optical scanning start end and the optical scanning end) of the laser beam 17b after time t0 after the laser beam 17a reaches the optical scanning start end and the optical scanning end end are respectively indicated by E1. And E2,
E1 = | e1-e (+) |
E2 = | e2-e (+) |
The displacements E1 and E2 correspond to the light spot position deviation in the main scanning direction on the scanned surface 16.

The chief ray angle θ (+) of the laser beam reaching the synchronous image height and the chief ray angle θ2 of the laser beam reaching the optical scanning end (image height H = + 150 [mm]) Compared with the field angle θ1 of the chief ray of the laser beam up to the image height H = −150 [mm]), it is almost equal [e2≈e (+)], so the light spot position shift amount on the optical scanning end side E2 is small, while the light spot position shift amount E1 on the optical scanning start side is large.
By making the light spot position deviation amounts E1 and E2 close to “E1 = E2”, it is possible to reduce the maximum value of the light spot position deviation amount that occurs in the entire region of the optical scanning width. For this purpose, in contrast to the case of the first embodiment, the synchronization detection sensor 18 ′ may be shifted in a direction approaching the polygon mirror 14 from a position optically equivalent to the surface to be scanned.

Accordingly, the distance between the two light spots e (+) ′ can be made smaller than e (+) in FIG.
| E1-e (+) ′ | ≈ | e2-e (+) ′ |
It becomes possible to approach. Also in this case, if the shift amount of the synchronization detection sensor 18 ′ is too large, | e1−e (+) ′ | becomes too larger than | e2−e (+) ′ | The amount of displacement becomes large. Further, since the laser beam does not form an image on the light receiving surface of the synchronization detection sensor 18 ′ (the beam waist position is shifted), the detection accuracy may be deteriorated depending on the type of the sensor.
Therefore, the shift amount of the synchronization detection sensor 18 ′ is
e2 <e (+) <e1 (Formula 1-2)
It is desirable that the range satisfy this relationship.
The light receiving surface is divided into two in the main scanning direction in order to prevent the detection accuracy from deteriorating due to the fact that the synchronization detecting sensors are shifted, that is, the laser beam is no longer imaged on the light receiving surface of the synchronization detecting sensor. Alternatively, a “two-divided light receiving element” can be used. Thereby, it is possible to obtain a highly accurate detection signal by generating the detection signal when the light amounts of the two light receiving portions in the two-divided light receiving element become the same.

(# C-2: When the synchronization detection sensor is arranged outside both the optical scanning start end and the optical scanning end end)
A third embodiment will be described with reference to FIG.
As shown in FIG. 10, when the rotation direction of the polygon mirror 14 is clockwise, the distance between the synchronization detection sensors 18 and 18 ′ is “outside the optical scanning start end” and “outside the optical scanning end end”. Can be arranged.
At that time, as described in (# C-1), the synchronization detection sensor may be arranged so as to be shifted from a position equivalent to the surface to be scanned.
By adopting such a configuration, the above-described “the deviation of the optical scanning width between two light spots caused by the divergent light beam that is incident on the scanning optical system” is generated in principle. It becomes possible to suppress.
Now, a time (one scanning time) when the light spots BSa and BSb of the two laser beams 17a and 17b pass through the synchronization detection sensors 18 and 18 'arranged on both outer sides of the optical scanning region is shown. Let ta and tb respectively. Normally, since the rotation angle of the polygon mirror 14 in one scan is the same between BSa and BSb, the optical scan width of BSa is larger than the scan width of BSb as described above.
That is, the relationship “ta <tb” is established. The modulation frequency of the light source corresponding to the image information so as to correct such “deviation of one scanning time between two light spots” or “deviation from an ideal (single) scanning time”. Can be adjusted. Such adjustment is generally called “clock adjustment”.

[D: When the laser beam incident on the scanning optical system is a divergent light beam in the main scanning section (3)]
A fourth embodiment will be described with reference to FIG.
In each of the above embodiments, the configuration in which the laser beam from the light source is incident on the optical deflector (polygon mirror) from the optical scanning start side has been described.
On the other hand, as another configuration, a configuration in which the laser beam from the light source is incident on the optical deflector (polygon mirror) from the optical scanning end side may be adopted. That is, FIG.
As shown in the figure, it is possible to adopt a configuration in which the rotation direction of the polygon mirror 14 is the counterclockwise direction.
As can be inferred from the above-described contents, it goes without saying that the optical layout, such as the arrangement of the synchronization detection sensors 18 and 18 ′, may be the same in FIGS. 10 and 11 regardless of the rotation direction of the polygon mirror 14. .
Further, only one of the synchronization detection sensors 18 and 18 ′ may be arranged, or both may be arranged in the same manner as the above-described configuration.

[E: When the laser beam incident on the scanning optical system is a convergent beam within the main scanning section (1)]
Next, a fifth embodiment will be described based on FIG.
Unlike the case where the laser beam incident on the scanning optical system 15 is “divergent”, the case where it is “convergent” will be considered.
This will be described in comparison with FIG. 1 in which the laser beam incident on the scanning optical system 15 is “divergent”.
In the case of the scanning optical system 15 shown in FIG. 12, since it has a function of forming a “convergent” light beam (laser beam) on the surface to be scanned 16, it is in a state parallel to each other (that is, the arrangement angle of the polygon mirror 14). The principal rays of the two laser beams 17a and 17b incident on the scanning optical system 15 in a state where they are shifted by φ intersect each other not at the scanned surface 16 but at a position away from the polygon mirror 14.
As a result, a light spot interval of e1 at the optical scanning start end on the scanned surface 16, e2 at the optical scanning end end, and e (−) on the synchronization detection sensor 18 is generated.
At this time,
e (-) <e1 <e2
It is.

When the optical scanning is started after a predetermined time has elapsed after the synchronization signal is acquired by the synchronization detection sensor 18, unlike the example shown in FIG. 1, the laser beam 17a is scanned with the laser beam BSa. The light spot BSb of the beam 17b scans the scanned surface 16 in advance.
The time from when the laser beam 17a enters the synchronization detection sensor 18 until the laser beam 17b enters the synchronization detection sensor 18 is t0, and after the laser beam 17a reaches the optical scanning start end and the optical scanning end end. If the relative positions of the light spot of the laser beam 17b after time t0 (displacement amounts from the optical scanning start end and the optical scanning end end) are E1 and E2, respectively.
e (−) = K × t0 × ω
K: proportionality constant, ω: time derivative of angle of view E1 = | e1-e (−) |
E2 = | e2-e (−) |
It is. The displacements E1 and E2 correspond to the light spot position deviation in the main scanning direction on the scanned surface 16.

The chief ray angle θ (−) of the laser beam reaching the synchronous image height and the chief ray angle θ1 of the laser beam reaching the optical scanning start end (image height H = −150 [mm]) Compared with the field angle θ2 of the chief ray of the laser beam reaching the end (image height H = + 150 [mm]), “e1≈e (−)”, which is substantially equal, the light spot position shift on the optical scanning start side The amount E1 is small, while the light spot position deviation amount E2 on the optical scanning end side is large.
In order to bring the relationship between the light spot position deviation amounts E1 and E2 (E1 <E2) closer to the ideal state of “E1 = E2”, e (−) may be increased.
In contrast to the case of FIG. 1, the synchronization detection sensor 18 may be moved from the position optically equivalent to the scanned surface 16 in a direction approaching the polygon mirror 14. If the distance between the two light spots at this time is e (-) ', e (-)' can be made larger than e (-) in FIG.

That is, by adopting the configuration of FIG. 12, e (−) can be made larger, so the relationship between the two light spot positions is the relationship before improvement:
| E1-e (−) | <| e2-e (−) |
Here, e1-e (-)> 0
e2-e (-)> 0
From
| E1-e (−) ′ | ≈ | e2-e (−) ′ |
Here, e1-e (−) ′ <0
e2-e (-) '> 0
It becomes possible to approximate the relationship.

Side effects when the amount of movement of the synchronization detection sensor 18 from the optically equivalent position to the scanned surface 16 toward the polygon mirror 14 is too large are the same as in the first embodiment.
Further, when another synchronization detection sensor 18 ′ is arranged outside the optical scanning end side, the synchronization detection sensor 18 ′ is moved in the opposite direction to the second embodiment (direction approaching the polygon mirror 14). Needless to say, what should be done.
Similarly, it is desirable that the shift amount of the synchronization detection sensor 18 is within a range in which the relationship “e1 <e (−) <e2” is satisfied.
That is, the laser beam incident on the scanning optical system 15 is “convergent” and the laser beam from the light source is incident on the optical deflector (polygon mirror) from the optical scanning start side (the polygon mirror is rotated clockwise). In order to rotate in the direction, a layout as shown in FIG. 13 (an example in which synchronization detection sensors are arranged on both outer sides of the optical scanning start side and the end side) may be used.

[F: When the laser beam incident on the scanning optical system is a convergent beam within the main scanning section (2)]
A sixth embodiment (another configuration in the case of “convergence”) will be described with reference to FIG.
In the fifth embodiment, the configuration in which the laser beam from the light source is incident on the optical deflector (polygon mirror) from the optical scanning start side has been described.
As another configuration, a configuration in which the laser beam from the light source is incident on the optical deflector (polygon mirror) from the optical scanning end side may be adopted. That is, as shown in FIG. 14, a configuration in which the rotation direction of the polygon mirror 14 is counterclockwise can be employed.
Even in such a configuration, as can be inferred from the above-described contents, the optical layout such as the arrangement of the synchronization detection sensors 18 and 18 ′ is not shown in FIGS. 13 and 14 regardless of the rotation direction of the polygon mirror 14. Needless to say, it should be the same.
Similarly, it is desirable that the shift amount of the synchronization detection sensor 18 ′ is within a range where the relationship “e2 <e (+) <e1” is satisfied.
Further, only one of the synchronization detection sensors 18 and 18 'may be arranged, or both may be arranged as in the configurations of the first embodiment and the second embodiment. .

[G: Correction of scan line tilt]
(# G-1: Outline of tandem color image forming apparatus)
As described above, when an optical scanning device is used as an exposure device of a tandem color image forming apparatus, the inclination of the scanning line may fluctuate between stations corresponding to each color over time or with a temperature change. is there.
In the tandem type color image forming apparatus, after forming an electrostatic latent image on the peripheral surface of the photosensitive drum corresponding to each color, the image is visualized with the toner of the corresponding color, and the sheet is conveyed by, for example, a transfer belt ( A multicolor image is formed by sequentially transferring onto a recording medium.
Therefore, when “scanning line inclination” occurs at each station in the optical scanning device, a scanning position shift in the sub-scanning corresponding direction occurs, resulting in degradation of output image quality such as color shift.

  As one means for suppressing such output image quality deterioration, there is a method of correcting the scanning line inclination with the temperature change over time. For this purpose, the degree of the scanning line inclination (absolute value or station) is used. It is necessary to grasp the relative value). Conventionally, various detection sensors have been proposed as means for detecting the scanning line inclination. Many of such detection sensors employ a configuration in which the time during which the light beam scans (crosses) the light receiving surface is detected or measured, and the detection result is converted to “length”.

(# G-2: Scanning line tilt detection method (1))
Next, a seventh embodiment will be described.
As shown in the layouts shown in FIGS. 10, 11, 13, and 14, the configuration in which the synchronization detection sensor as the reference light beam detection unit is arranged on both outer sides of the optical scanning start side and the end side is shown. In the case of an optical scanning apparatus having such a reference beam detection means, not only the optical scanning width of the two laser beams is corrected, but also the “scan line tilt amount” is detected using the reference beam detection means. It is also possible.
For example, a “line CCD” in which pixels are arranged in a row or a “two-dimensional CCD” in which the pixels are arranged two-dimensionally can be employed as the reference light beam detecting means.
From the detection results of the two reference beam detecting means provided on both the outer side of the optical scanning start side and the end side, the positions of both ends of the scanning line (optical scanning start end and end end) or their displacement amounts are derived. .
Based on the derived result, a conventionally known scanning line inclination correcting unit provided in the optical scanning device may be controlled and driven.
As the scanning line inclination correcting means, for example, (1) a type that displaces a folding mirror disposed in an optical path from a polygon mirror to a surface to be scanned (photosensitive drum surface), and (2) a lens constituting a scanning optical system Any method, such as a type of displacing, may be adopted.

(# G-3: Scanning line tilt detection method (2))
The eighth embodiment will be described with reference to FIGS. 15 and 16.
In the seventh embodiment, a configuration using a relatively expensive “line CCD” or “two-dimensional CCD” is proposed as an example of the reference light beam detecting means for detecting the scanning line inclination amount.
An example of the reference beam detecting means for detecting the scanning line inclination amount that can be realized at a lower cost will be described below.
First, an outline of the configuration of the tandem-compatible optical scanning device 105 in this embodiment will be described with reference to FIG.
In the figure, reference numeral 110 denotes a light source that emits a laser beam, 111 denotes a window arranged in a housing (not shown), 112 denotes a polygon mirror as deflection scanning means (optical deflector), and 114 denotes a first lens constituting an fθ lens group. 115, a liquid crystal deflecting element 115 for correcting the scanning line, 116 a mirror, 117 a second lens constituting the fθ lens group, 119 a half mirror (semi-transparent mirror), 120 a photoconductor, and 121 An intermediate transfer belt, 122 to 124 are detection units as color misregistration detection means, P1 is a scanning upstream laser beam detector as reference light beam detection means, and P2 is a scanning downstream laser beam detector as reference light beam detection means. Show.
A color imaging machine has a scanning imaging optical system for four colors of yellow, magenta, cyan, and black (hereinafter abbreviated as Y, M, C, and K), and a laser beam corresponding to each color is focused on the photosensitive member. Is shown.

The light source 110 shown in the figure has four sets of “light source devices” composed of a semiconductor laser, a coupling lens, and a cylindrical lens. The light beam emitted from each semiconductor laser is converted into a light beam form (parallel light beam or weak divergent or convergent light beam) suitable for the subsequent optical system by the coupling lens, and converged in the sub-scanning direction by the cylindrical lens. A line image that is long in the main scanning direction is formed in the vicinity of the deflection reflection surface of the polygon mirror 112 serving as the deflection scanning means.
Each of the four semiconductor lasers in the light source emits a light beam for writing each color component image of Y, M, C, and K.

The deflected light beams for four colors deflected in the same direction by the rotation of the polygon mirror 112 are transmitted through the first lens 114 constituting the fθ lens group which is a part of the scanning imaging optical means. The luminous flux (for example, the position of the upper end of the lens) for writing the K (black) component image is reflected by the mirror 116K, passes through the second lens 117K constituting the fθ lens group, and is branched by the half mirror 119K. The transmitted light beam is condensed as a light spot on the drum-shaped photoconductive photosensitive member 120K that forms the actual state of the surface to be scanned, and optically scans the photosensitive member 120K in the direction of the arrow.
The other reflected light beam forms an image on a scanning upstream laser beam detector P1K and a scanning downstream laser beam detector P2K that detect the laser beam, and scans the light receiving portion. The laser beam detector is mounted and fixed on the fixing substrates B1 and B2, respectively. The fθ lens group, the mirror 116, and the half mirror 119 are collectively referred to as scanning imaging optical means.

The material of the first lens 114 and the second lens 117K of the fθ lens group is an aspherical shape made of a plastic material that is easy and low in cost, and specifically, polycarbonate and polycarbonate having low water absorption, high transmittance, and excellent moldability. A synthetic resin containing as a main component is preferred.
Similarly to the above, the light beams for writing the respective color component images of Y (yellow), M (magenta), and C (cyan) are reflected by the mirror, transmitted through the lens, transmitted through the half mirror, and reflected to form a drum shape. An image is formed as a light spot on the photoconductive photoreceptor, and each color is scanned in the same arrow direction. By this optical scanning, an electrostatic latent image of a color component image corresponding to each photoconductor is formed. In the same figure, optical elements corresponding to each color other than K are not labeled, but components with “K”, which is an abbreviation of black, are optically attached to Y, M, and C. It is arranged at the same position.

These electrostatic latent images are visualized with a corresponding color toner by a developing device (not shown) and transferred onto the intermediate transfer belt 121. At the time of transfer, the color toner images are superimposed on each other to form a color image.
This color image is transferred onto a sheet-like recording medium and fixed. The intermediate transfer belt 121 after the color image transfer is cleaned by a cleaning device (not shown).
As described above, the optical scanning device shown in FIG. 15 causes each light beam emitted from a plurality of light source devices corresponding to two or more color component images constituting a color image to be directed in the same direction by the polygon mirror 112 of the deflection scanning means. The scanning lens corresponding to each color component image is scanned by the first lens 114 that transmits each deflected light beam to each color in the scanning imaging optical system and the lens 117 provided in each scanning imaging means. The optical scanning device has four scanning image forming means corresponding to the respective color components by individually condensing light toward the surface 120 and performing optical scanning.

Immediately after the first lens 114, a liquid crystal deflecting element 115 is disposed as an optical element having a function of correcting the scanning line. The liquid crystal deflecting element 115 is an element that can be finely adjusted by electrically controlling the emission direction of the laser beam locally arbitrarily. The deflection angle is arbitrarily variable depending on the peak value of the drive voltage waveform or the pulse width Duty, and the deflection angle is set as follows.
First, when the image output start signal is input, the scanning position of the laser beam that has passed through the scanning beam reference color portion (for example, black) 115K is detected by P1K and P2K. If the liquid crystal deflecting elements corresponding to the other colors are not driven, and if they are more than that, the liquid crystal deflecting elements are driven to deflect by a predetermined amount to correct the scanning position.
The correction means for feeding back the result obtained from the laser beam detector can correct the scanning position and sub-scanning interval by appropriately correcting and controlling the attitude of the optical element (scanning lens, mirror) in addition to the liquid crystal deflecting element. .

Reference numerals 122, 123, and 124 denote detection units that constitute “color misregistration detection means” on the intermediate transfer belt. The detection units 122, 123, and 124 collect a light beam from another semiconductor laser with a condensing lens, irradiate a fixed position of the intermediate transfer belt 121, and form an image of reflected light on the light receiving element by the lens. It has become. When color misregistration detection is performed, detection patterns are written in three portions at both ends and the center in one scan by each light flux, visualized for development, and transferred to the intermediate transfer belt 121.
At this time, the detection patterns for the respective colors are formed on the intermediate transfer belt 121 at equal intervals in the sub-scanning direction. These pattern images for detection are detected by each detection unit of the color misregistration detection means, and based on the result, the scanning line bending of each scanning beam (including the scanning line tilt and the positional deviation between the scanning lines) is determined. . The detection of the laser beam and the toner pattern on the intermediate transfer belt in the scanning imaging optical system for each color described above are performed, and the corrector described later is operated appropriately based on the two detection results. High image quality can be achieved.

  Next, the laser beam detector will be described in detail. As described above, the scanning beam incident on the laser beam detector is transmitted through and reflected by the same optical lens, reflecting mirror, and half mirror as the laser beam that scans the image area of the photosensitive member, and reaches the laser beam detector. Image. Since no dedicated optical lens or reflection mirror leading to the laser beam detector is used, the scanning optical characteristics are the same as those in the image area. Therefore, there is no difference in optical characteristics due to temperature changes that are likely to occur in a dedicated optical lens or reflecting mirror, and it is possible to perform highly accurate laser beam detection without affecting the detection accuracy of the laser beam detector. The laser beam detector is arranged in the same configuration in the other scanning image forming means.

FIG. 16 is a diagram for explaining the configuration of the laser beam detector and detection signals. FIG. 4A shows the configuration of the detector, and FIG. 4B shows the output waveform.
In the figure, reference numeral 219 is a detector, PD1 is a light receiving element of the first system, PD2 is a light receiving element of the second system, D is a maximum element width (full width), H is an effective detection height, and θ is a light receiving element inclined side. Angle, AMP indicates an amplifier, and CMP indicates a comparator.
There are a plurality of laser beams corresponding to each color, and they are separated from each other at a predetermined interval in the main scanning direction and the sub-scanning direction, and scan on the surface of the photoreceptor through the optical system. In the figure, there are two examples (L1 and L2), and scanning is performed at predetermined intervals in both the main and sub directions. The main scanning direction is set wider than at least the interval of D (detailed below, several mm level), and the sub-scanning direction is appropriately set according to the recording density of the image (in the case of 1200 dpi, about 21 μm). On the other hand, the main scanning interval is much wider (all of the above are when scanned by the laser beam detector).

The light receiving element PD1 of the first system and the light receiving element PD2 of the second system are arranged adjacent to each other in the main scanning direction, and both are divided into two light receiving areas formed non-parallel to each other in the area where the laser beam passes. The respective regions are arranged adjacent to each other with the light receiving elements PD1 and PD2, and the adjacent edge portions are linearly formed in parallel with each other.
The angle between the two light receiving regions of each light receiving element is arranged with an angle θ (0 <θ <90). The angle θ is preferably 30 ° to 60 °. In the figure, an example of 45 ° is disclosed, which is the most preferable example.
This is because if the angle is smaller than 30 °, the difference between T1 and T2 with respect to the laser beam to be scanned is reduced and the detection sensitivity is deteriorated. In order to secure the necessary effective detection height H, the entire width D of the light receiving surface is increased in order to secure the necessary effective detection height H, and the problem of the light receiving surface entering the image region or the effective region of the scanning optical system is reduced. There is a problem that the scanning lens needs to be set wide and the scanning lens becomes long. It is preferable that the height H in the sub-scanning direction and the total width D of the light receiving surface are set to H = 1 to 3 mm and D = 5 mm or less, respectively, without causing the above problem. Note that 45 ° is most preferable because the above problem can be distributed and allowed in a balanced manner.
There is no particular limitation on the interval between the adjacent portions of the two systems of light receiving elements, but in order to make the configuration as small as possible, it is better not to be larger than the spot size of the passing beam.
It is preferable to form one of the two light receiving regions perpendicular to the scanning direction of the laser beam because the sensor output timing does not change even when the laser beam is shifted in the sub scanning direction.
Reference numeral 219 in FIG. 16A is a detector shown in the light receiving surface shape and circuit block diagram of the laser beam detector P1K (or P2K) shown in FIG. A laser beam detector having this function is mounted and fixed on the substrate B1 or B2.

After the output signals of the light receiving elements PD1 and PD2 are subjected to current-voltage conversion and voltage amplification by the amplifiers AMP1 and AMP2, respectively, voltage comparison is performed by the comparator CMP, and the output signal level of the AMP2 becomes lower than the output signal level of the AMP1. Sometimes outputs a signal.
FIG. 16B is a timing chart of output signals of the laser beam detector when two laser beams pass through the light receiving elements PD1 and PD2. Two pulses are output by passing one laser beam. The time interval (T1 or T2) between the two pulses depends on the sub-scanning position where the laser beam is scanned. When the time interval between the two laser beams is T1 and T2, the sub-scan interval ΔP of the laser beam can be obtained from the following equation.
ΔP = v × (T2−T1) / tan θ
Here, v represents the speed of the scanned laser beam.

Since v and θ are substantially constant during image formation and when a laser beam is detected, (T2−T1) is performed in actual calculation, and the sub-scanning interval is corrected using the result.
When the scanning beam characteristics in the image area and the both end positions have different characteristics due to temperature changes, a laser beam detector is provided at an optically equivalent position in the image area in addition to both ends. By detecting at a high level, information such as the actual state of the scanning beam and the bending and tilting of the scanning beam can be obtained, and correction based on the results corrects the bending and tilting of the scanning beam with high accuracy. It becomes possible.

By providing such a reference light beam detecting means capable of detecting the position of two light spots or the interval between them on both outer sides of the optical scanning start side and the end side, the above-mentioned “line CCD” and “two-dimensional CCD” As in the case of using, the amount of inclination of the scanning line can be detected, and the scanning line inclination can be corrected by controlling and driving the scanning line inclination correcting means based on the result.
It should be noted that the scanning start / end timing of the optical scanning may be determined by the output signal from the reference light beam detecting means including “line CCD” and “two-dimensional CCD”.

(# G-4: Problem of scanning line tilt detection method (2))
The reference light beam detecting means described in (# G-3) converts the result of detecting the time for scanning (crossing) the light receiving portion into a “length” and uses a line CCD or the like as a light spot. This method is greatly different from the method of detecting the position (or interval) of.
The length x of scanning (crossing) the light receiving surface is obtained by the product of “scanning speed VY on the light receiving surface” and “scanning time τ for scanning the light receiving surface”.

(# G-4-1: parallel light flux)
Here, the case where the laser beam incident on the scanning optical system 15 described in the comparative example with reference to FIG.
As shown in (# A-1), the position H in the main scanning direction of the light spot on the scanning surface 15 is “the focal length F of the scanning optical system 15” and “the laser deflected and reflected by the polygon mirror 14”. Angle of view of chief ray of beam θ ”
Product with
H = F × θ
It is represented by Therefore, the scanning speed VY is
VY = dH / dt = F.times. (D.theta./dt) = F.times..omega. (.Omega. Is the time derivative of the angle of view = angular velocity [rad / s])
It becomes. Here, when the rotation speed of the polygon mirror 14 is N [rpm], the time differential ω [rad / s] of the angle of view is
ω = 2 × N × (2π / 60) = (π / 15) × N
So the scanning speed VY is
VY = (π / 15) × F × N (Formula 2-1)
It is represented by

Now, in FIG.
The interval between the sub-scanning methods of the light spots BSa and BSb
The time difference in the main scanning direction is Δτ = τ2−τ1.
The arrangement angle of the light receiving part is θs.
Then,
p = (π / 15) × F × N × Δτ / tan θs
It is represented by

(In the case of # G-4-2: divergent beam or convergent beam)
Next, a ninth embodiment will be described.
In the case of “divergent light beam” or “convergent light beam”, the situation is different from the above. As described in the first embodiment, the light spot on the surface to be scanned 16 has constant speed scanning, and the scanning speed VY of the light spot on the surface to be scanned is
VY = dY / dt = K × (dθ / dt) = K × ω (K is a proportional constant indicating constant speed scanning)
Is established. However, in the case of “divergent light flux”, as shown in FIG. 10 or FIG. 11, on the optical scanning start side or the optical scanning end side, The “reference beam detecting means” is arranged in a direction away from the polygon mirror 14 and shifted from a position optically equivalent to the scanned surface 16. Therefore, the scanning speed on the light receiving surface of the reference light beam detecting means arranged in this way becomes faster than (Equation 2-1).

(Equation 2-1) is used to obtain the scanning speed, and the scanning position (or scanning line interval, etc.) is derived from the result, and for example, it is grasped whether or not the scanning position variation accompanying the temperature change has occurred. Is possible.
However, in order to grasp the absolute value of the fluctuation amount, it is necessary to accurately derive VY.
Accordingly, the scanning speed VY ′ in this case needs to be rewritten as shown in (Equation 2-2).
VY ′ = (π / 15) × (K + ΔK1) × N (Formula 2-2)
ΔK1> 0
The length x of scanning (crossing) the light receiving surface is obtained by the product of “scanning speed VY ′ on the light receiving surface” and “scanning time τ for scanning the light receiving surface”. 3)
As on the light receiving surface,
x = (π / 15) × (K + ΔK1) × N × τ (Expression 2—By calculating the scanning distance x, the scanning distance x can be derived with higher accuracy.

On the other hand, on the optical scanning start side or the optical scanning end side, the “synchronization detection sensor” installed on the side opposite to the side where the light source is arranged, that is, the “reference light beam detection means” is in the direction approaching the polygon mirror, The position is shifted from a position optically equivalent to the surface to be scanned. Therefore, the scanning speed on the light receiving surface of the reference light beam detecting means arranged in this way is slower than (Equation 2-1).
Therefore, in such a case,
x = (π / 15) × (K−ΔK2) × N × τ (Formula 2-4)
ΔK2> 0
The scanning distance x on the light receiving surface may be calculated as follows.
Similarly, in the case of the “convergent light beam”, when the “reference light beam detecting means” is arranged in a direction away from the polygon mirror and shifted from the position equivalent to the surface to be scanned (Equation 2-3), When the “reference light beam detecting means” is arranged so as to be shifted from the position equivalent to the surface to be scanned in the approaching direction, it may be derived by (Equation 2-4).

FIG. 18 is a diagram showing a color image forming apparatus equipped with any one of the optical scanning devices in the above embodiments.
In the figure, reference numeral 102 denotes a belt roller, 105 denotes an optical scanning device, 106 denotes a developing device, 125 denotes an image forming device, 127 denotes a paper feed cassette, and 126 denotes a fixing device.
An optical scanning device 105 in which a plurality of scanning imaging means of the optical scanning device shown in FIG. 1 and the like are accommodated in a single housing is disposed in a color image forming device 125. The optical scanning device 105 is disposed above an image forming unit in which four photoconductors 120Y, 120M, 120C, and 120K in the image forming apparatus 125 are arranged in parallel.
This is a tandem type color image forming apparatus in which a plurality of photoconductors 120Y, 120M, 120C, and 120K are arranged in parallel. An optical scanning device 105, a developing device 106, a photoconductor 120, an intermediate transfer belt 121, a fixing device 126, and a paper feed cassette 127 are laid out in order from the top of the apparatus.

On the intermediate transfer belt 121, photoconductors 120Y, 120M, 120C, and 120K corresponding to the respective colors are arranged in parallel at equal intervals. The photoreceptors 120Y, 120M, 120C, and 120K are formed to have the same diameter, and members are sequentially arranged around the photoreceptors according to an electrophotographic process.
Taking the photoconductor 120Y as an example, a charging charger (not shown), a laser beam LY based on an image signal emitted from the optical scanning device 105, a developing device 106Y, a transfer charger (not shown), a cleaning device (not shown), and the like. Are arranged in order. The same applies to the other photoconductors 120M, 120C, and 120K.
That is, in this embodiment, the photoconductors 120Y, 120M, 120C, and 120K are to be scanned surfaces set for each color, and the laser beams LY, LM, LC, and LK are emitted from the optical scanning device 105 for each color. Are provided to correspond to each.

The corresponding laser beam 120Y is irradiated with the laser beam LY in which the bending or distortion in the main scanning direction is corrected by the laser beam detector.
The photoconductor 120Y uniformly charged by the charging charger rotates in the direction of arrow A, thereby sub-scanning the laser beam LY, and an electrostatic latent image is formed on the photoconductor 120Y. Further, a developing device 106Y that supplies toner to the photoconductor 120Y is disposed downstream of the irradiation position of the laser beam LY by the optical scanning device 105 in the rotation direction of the photoconductor, and yellow toner is supplied.
The toner supplied from the developing device 106Y adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, M, C, and K monochromatic toner images are formed on the photoreceptors 120M, 120C, and 120K, respectively.

An intermediate transfer belt 121 is disposed further downstream in the rotational direction than the position at which the developing device 106 of each photoconductor 120 is disposed. The intermediate transfer belt 121 is wound around a plurality of rollers 102a, 102b, and 102c, and is moved and conveyed in the direction of arrow B by driving a motor (not shown).
By this conveyance, the intermediate transfer belt 121 is sequentially moved to the photosensitive members 120Y, 120M, 120C, and 120K. The intermediate transfer belt 121 sequentially superimposes and transfers the single color images developed by the photoconductors 120Y, 120M, 120C, and 120K, thereby forming a color image on the intermediate transfer belt 121.
Thereafter, the transfer paper is conveyed from the paper feed tray 127 in the direction of arrow C, and the color image is transferred. The transfer paper on which the color image is formed is discharged as a full-color image after fixing processing by the fixing device 126.

It is a figure which shows the scanning characteristic by the optical scanning device in the 1st Embodiment of this invention. It is a figure which shows the state which shifted the position of the reference | standard light beam detection means so that the center of optical scanning width might correspond. It is a figure which shows the imaging characteristic of the scanning start side in the case of a divergent light beam, and an end side. It is a figure which shows the imaging characteristic of the scanning start side in the case of a divergent light beam. FIG. 6 is a diagram showing a difference in light spot at the scanning start end when the reference light flux detecting means is arranged at a position equivalent to the scanned surface on the scanning start side in the divergent light flux. FIG. 6 is a diagram showing a difference in light spot at the scanning start end when the reference light flux detecting means is arranged at a position equivalent to the scanned surface on the scanning start end side in the divergent light flux. It is a figure which shows the modification of the structure which guides the light beam radiate | emitted from a light source to an optical deflector. It is a figure which shows another modification of the structure which guides the light beam radiate | emitted from a light source to an optical deflector. In the divergent light beam, it is a diagram showing the difference in the light spot at the scanning start end when the reference light beam detecting means is arranged at the position equivalent to the surface to be scanned on the scanning end side, and is an explanatory diagram of the second embodiment. It is a figure which shows the reference | standard light beam detection means arrangement layout in 3rd Embodiment (divergent light beam). It is a figure which shows the reference | standard light beam detection means arrangement layout in 4th Embodiment (divergent light beam). In the convergent light beam, it is a diagram showing the difference in the light spot at the scanning start end when the reference light beam detecting means is arranged at the position equivalent to the scanned surface on the scanning end side, and is an explanatory diagram of the fifth embodiment. It is a figure which shows the reference | standard light beam detection means arrangement layout in 5th Embodiment (convergent light beam). It is a figure which shows the reference | standard light beam detection means arrangement layout in 6th Embodiment (convergent light beam). FIG. 10 is a perspective view of an optical scanning device according to an eighth embodiment. It is a figure which shows the structure and characteristic of the reference light beam detection means in 8th Embodiment. It is a figure which shows the structure and characteristic of the reference light beam detection means in 8th Embodiment. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. It is a figure which shows the arrangement layout of the reference light beam detection means in the case of a parallel light beam. It is a figure which shows the scanning characteristic in the scanning start side in the case of a parallel light beam. It is a figure which shows the scanning characteristic in the scanning center in the case of a parallel light beam. It is a figure which shows the scanning characteristic in the scanning end side in the case of a parallel light beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor laser as light source 14 Polygon mirror as optical deflector 15 Scanning optical system as scanning imaging element 16 Scanned surface 17a, 17b Light beam 18, 18 'Synchronous detection sensor as reference light beam detecting means

Claims (16)

An optical deflector having a deflecting / reflecting surface for deflecting a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned to optically scan the surface to be scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, wherein the reference light beam detecting means and the reference light beam optical element are disposed on at least one of the start side and the end side of the light scanning,
An optical scanning device characterized by shifting the position of the reference light beam detecting means in accordance with the optical characteristics of the plurality of light beams incident on the optical deflector so that the centers of the optical scanning widths of these light beams are matched. . An optical deflector having a deflecting and reflecting surface that deflects a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the surface to be scanned is optically scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, and the reference light beam detecting means and the reference light beam optical element are arranged on at least one of a start side and an end side of the optical scanning, and are emitted from the light source. At least two of the plurality of light beams are incident on the optical deflector in a convergent state, and the optical deflector is in a state where the principal rays of the at least two light beams do not overlap each other in the deflection scanning plane. In the optical scanning device is incident from the scanning start side against,
Among the above-mentioned reference beam detection means, the reference beam detection means arranged on the light scanning start side is arranged by shifting the light receiving surface in a direction closer to the optical deflector than the imaging position of the reference beam in the main scanning corresponding direction. The reference beam detecting means arranged on the end side of the optical scanning is characterized in that the light receiving surface is arranged so as to be shifted away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. Optical scanning device. An optical deflector having a deflecting and reflecting surface that deflects a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the surface to be scanned is optically scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, and the reference light beam detecting means and the reference light beam optical element are arranged on at least one of a start side and an end side of the optical scanning, and are emitted from the light source. At least two of the plurality of light beams are incident on the optical deflector in a convergent state, and the optical deflector is in a state where the principal rays of the at least two light beams do not overlap each other in the deflection scanning plane. In the optical scanning device is incident from the scanning end side against,
Of the reference beam detection means, the reference beam detection means arranged on the light scanning start side is arranged by shifting the light receiving surface away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. The reference beam detecting means arranged on the end side of the optical scanning is characterized in that the light receiving surface is arranged so as to be shifted in a direction approaching the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. Optical scanning device. An optical deflector having a deflecting and reflecting surface that deflects a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the surface to be scanned is optically scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, and the reference light beam detecting means and the reference light beam optical element are arranged on at least one of a start side and an end side of the optical scanning, and are emitted from the light source. At least two of the plurality of light fluxes are incident on the optical deflector in a divergent state, and the optical deflector is in a state where the principal rays of the at least two light fluxes do not overlap each other in the deflection scanning plane. In the optical scanning device is incident from the scanning start side against,
Of the reference beam detection means, the reference beam detection means arranged on the light scanning start side is arranged by shifting the light receiving surface away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. The reference beam detecting means arranged on the end side of the optical scanning is characterized in that the light receiving surface is arranged so as to be shifted in a direction approaching the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. Optical scanning device. An optical deflector having a deflecting and reflecting surface that deflects a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the surface to be scanned is optically scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, and the reference light beam detecting means and the reference light beam optical element are arranged on at least one of a start side and an end side of the optical scanning, and are emitted from the light source. At least two of the plurality of light fluxes are incident on the optical deflector in a divergent state, and the optical deflector is in a state where the principal rays of the at least two light fluxes do not overlap each other in the deflection scanning plane. In the optical scanning device is incident from the scanning end side against,
Among the above-mentioned reference beam detection means, the reference beam detection means arranged on the light scanning start side is arranged by shifting the light receiving surface in a direction closer to the optical deflector than the imaging position of the reference beam in the main scanning corresponding direction. The reference beam detecting means arranged on the end side of the optical scanning is characterized in that the light receiving surface is arranged so as to be shifted away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction. Optical scanning device. The optical scanning device according to any one of claims 1 to 5,
An optical scanning apparatus characterized in that at least one of a scanning start timing and an optical scanning end timing of optical scanning is determined by an output signal from the reference light beam detecting means. The optical scanning device according to any one of claims 1 to 5,
The reference light beam detecting means has a function of detecting at least one of a light spot position and a light spot interval on the surface to be scanned. The optical scanning device according to claim 7.
The reference light beam detecting means detects at least one of a light spot position and a light spot interval on the surface to be scanned by detecting a time during which the reference light beam scans at least a part of the light receiving surface of the reference light beam detection means. An optical scanning device characterized by calculating The optical scanning device according to any one of claims 2 to 5,
The reference beam detecting means and the reference beam optical element are arranged on the start side and the end side of optical scanning, and the optical scanning is performed so as to correct the difference in the optical scanning width on the scanned surface of the at least two light beams. An optical scanning device characterized in that the modulation frequency of the light source is adjusted based on detection signals from reference light beam detecting means arranged on the start side and the end side of the light source. The optical scanning device according to claim 8.
The reference beam detecting means has a plurality of laser beam detectors composed of two light receiving elements, and at least one of the two light receiving elements has two non-parallel ones formed in a region through which the laser beam passes. An optical scanning device having a light receiving region, wherein the two light receiving elements are adjacent to each other in the main scanning direction so that adjacent edges are parallel to each other. The optical scanning device according to claim 9.
The angular velocity (or rotational speed) of the optical deflector is ω / 2 [rad / s] (or N [rpm]),
V [mm / s], the speed at which the light spot scans the surface to be scanned,
The time (detection time) that the light spot scans at least a part of the light receiving portion of the reference light beam detecting means is τ [s], the scanning distance is x [mm],
When
The scanning speed V is approximately proportional to the angular speed ω / 2 with the relationship V = K × ω,
When the scanning distance x is arranged by shifting the light receiving surface of the reference beam detecting means in a direction away from the optical deflector from the imaging position of the reference beam in the main scanning corresponding direction,
x = (π / 15) × (K + ΔK1) × N × τ; ΔK1> 0,
When the light receiving surface of the reference light beam detecting means is shifted from the imaging position in the main scanning corresponding direction of the reference light beam in a direction closer to the optical deflector,
x = (π / 15) × (K−ΔK2) × N × τ; ΔK2> 0,
An optical scanning device characterized by the above calculation. The optical scanning device according to any one of claims 2 to 5,
An optical scanning device characterized in that the principal rays of the at least two light beams are incident on the deflector in a non-parallel state within the deflection scanning plane. An optical deflector having a deflecting and reflecting surface that deflects a plurality of light beams emitted from a light source, and the light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the surface to be scanned is optically scanned. A scanning imaging element to be detected, a reference light beam detecting means for detecting a light beam deflected by the optical deflector as a reference light beam, and a reference having power in at least a main scanning corresponding direction and guiding the reference light beam to the reference light beam detecting means A light beam optical element, and the reference light beam detecting means and the reference light beam optical element are arranged on at least one of a start side and an end side of the optical scanning, and are emitted from the light source. At least two of the plurality of luminous fluxes are incident on the optical deflector in a convergent or divergent state, and the principal rays of the at least two luminous fluxes are not overlapped with each other in the deflection scanning plane. In the optical scanning device is incident on the optical deflector,
The optical scanning start position on one scanned surface of the at least two light beams is Ya (START), the optical scanning end position is Ya (END),
The optical scanning start position on the other scanned surface is Yb (START), the optical scanning end position is Yb (END),
When
{Ya (START) −Yb (START)} × {Ya (END) −Yb (END)} ≦ 0
An optical scanning device characterized in that   An image forming apparatus comprising the optical scanning device according to claim 1.   14. A method for detecting a reference light beam, wherein the optical scanning device according to claim 1 is used. An optical deflector having a deflecting reflecting surface for deflecting a plurality of light beams emitted from a light source;
The light beam deflected by the optical deflector is condensed as a light spot on the surface to be scanned, and the scanning imaging element for optically scanning the surface to be scanned, and the light beam deflected by the optical deflector is detected as a reference light beam. A reference beam optical element that has power in at least a direction corresponding to the main scanning and guides the reference beam to the reference beam detection unit, and the reference beam detection unit and the reference beam optical element are An optical scanning device disposed on at least one of a start side and an end side of optical scanning, wherein at least two of a plurality of light beams emitted from the light source are converged or divergent to the optical deflector. An optical scanning device that is incident on the optical deflector in a state where the principal rays of the at least two light beams do not overlap each other in the deflection scanning plane is an exposure device, and a toner image is transferred to a recording medium. An image forming apparatus for forming an image by wearing,
The dot position at the optical scanning start end corresponding to one of the at least two light beams is Da (START), the dot position at the optical scanning end is Da (END),
The dot position at the optical scanning start end corresponding to the other is Db (START), the dot position at the optical scanning end is Db (END),
When
{Da (START) −Db (START)} × {Da (END) −Db (END)} ≦ 0
An image forming apparatus characterized in that

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