JP2005164997A - Optical scanner and method of detecting synchronization used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which has simple structure and readily detects the synchronization of a plurality of light beams, and to provide a method of detecting the synchronization used for the optical scanner. <P>SOLUTION: In a laser scanning unit 1, laser beams 30a and 30b, and laser beams 30c and 30d, emitted from multibeam light sources 2A and 2B, respectively, are made incident on the mirror face of a polygon mirror 8 at different incident angles in a deflection direction. Further, the luminous flux on the beginning side of scanning is folded between the polygon mirror 8 and an optical path separation optical element 24 by a folding mirror 21, made incident on a synchronization sensor unit 22, and the synchronization detection of four beams are performed by a single synchronization sensor unit 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device. In particular, the present invention relates to an optical scanning device suitable for a device that scans a plurality of scanned media after deflecting a plurality of light beams by one light deflecting unit, for example, a tandem color image forming system.

2. Description of the Related Art Conventionally, in a color image forming system or the like, an optical scanning device is used that scans a plurality of scanned media by separating a light path after deflecting a plurality of light beams by a single light deflecting unit. As a light source for forming a plurality of light beams, a semiconductor laser array (LD array) element in which a plurality of light emitting units are integrated to emit a multi-beam is known. However, for example, in a color image forming system, at least four light beams are required, and such an element for four beams is very expensive.
In view of this, various apparatuses have been proposed in which a plurality of light source units are constituted by a single beam LD or a two-beam LD array, and light beams emitted from the light source units are incident on the light deflecting means.
For example, in Patent Document 1, in order to form a latent image corresponding to an image separated into four colors for a full-color image, a cylindrical lens is disposed in front of each of four laser light sources that emit a single beam. A laser beam scanning device is described in which a laser beam is incident on a polygon mirror at a different incident angle in the deflection direction, an fθ scanning characteristic is imparted by an fθ lens, and then guided to four exposure positions by a beam splitter or the like. Has been. In this apparatus, a laser beam is separated by a beam splitter by a combination of a wavelength and a polarization direction.
In addition, it is described that an index sensor that can receive one of the laser beams by a wavelength filter and a polarization filter is provided between the polygon mirror and the fθ lens, thereby performing synchronization detection.
In Patent Document 2, four laser beams emitted from a multi-beam generator are received by a photodetector, and each laser beam is controlled to be turned on / off so that the laser beams approach in the scanning direction. However, there is described a multi-beam optical recording apparatus capable of generating a scanning start signal for each laser beam.
JP-A-6-160743 (page 4-5, FIG. 1) JP 2003-237127 A (page 2-3, FIGS. 1 and 7)

However, the conventional optical scanning apparatus and the synchronization detection method used therefor have the following problems.
In the technique described in Patent Document 1, since the laser beam emitted from the light source is incident on the polygon mirror at different incident angles in the deflection direction, the laser beam deflection directions are different. Therefore, there is a problem that accurate writing control cannot be performed only by detecting the arrival of one laser beam by the index sensor.
In general, it is conceivable to adjust the delay time based on one laser beam reference and adjust the writing position while measuring the color shift of the image, or to provide a plurality of synchronization detection sensors for each laser beam. In the former case, since the incident angles are different, there is a problem that a difference in delay time becomes large and adjustment is required. In the latter case, the number of synchronization detection sensors increases, so that there is a problem that the arrangement space is increased, the apparatus is increased in size, and the component cost is increased.
In the technique described in Patent Document 2, although a laser beam close to the scanning direction using a semiconductor laser array element can be received by a photodetector, a synchronization detection signal can be generated for each laser beam. When the laser beam is very close to the scanning direction, for example, deviating by about the spot diameter or less, the laser beam is turned off within a short period of time when the amount of received laser beam is small. Therefore, there is a problem that a signal with high accuracy cannot be obtained.

  The present invention has been made in view of the above problems, and provides an optical scanning device capable of easily performing synchronization detection of a plurality of light beams with a simple configuration and a synchronization detection method used therefor. With the goal.

In order to solve the above-mentioned problem, in the invention described in claim 1, a plurality of light sources, a light deflecting means for deflecting a plurality of light beams emitted from the light sources, and a plurality of light deflected by the light deflecting means are provided. An optical path separating means for separating the optical paths of the light beams, a plurality of scanning optical systems for imaging and scanning the light beams separated by the optical path separating means on different scanning planes, the light deflecting means and the optical path An optical path changing unit that bends a part of the optical path to and from the separating unit; a synchronization detecting unit that detects the plurality of light beams along the optical path bent by the optical path changing unit at a predetermined position and generates a synchronization signal; It is set as the structure provided with.
According to the present invention, the plurality of light beams deflected by the light deflecting means are bent between the light deflecting means and the optical path separating means by the optical path changing means and guided to the synchronization detecting means. Even a plurality of light beams to be scanned can be detected by one synchronization detection means without using individual synchronization detection means.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the plurality of light beams have different incident angles in a plane along a deflection direction with respect to a deflection reflection surface of the light deflection unit. The configuration is as described above.
According to the present invention, since the plurality of light beams are incident on the light deflecting means so as to have different incident angles in the plane along the deflection direction with respect to the deflection reflection surface, the optical axes of the plurality of light sources are along the deflection direction. They can be placed in-plane and spaced apart from each other. The light beam can be incident on the light deflecting means without using a member for synthesizing the optical paths.

According to a third aspect of the present invention, in the optical scanning device according to the second aspect, the plurality of light beams having different incident angles are each formed by a multi-beam light source including a plurality of light-emitting portions, and the multi-beam light source The scanning line pitch in the sub-scanning direction can be changed by adjusting the rotation of each.
According to the present invention, since light beams emitted from a plurality of multi-beam light sources are incident on the light deflecting means at different incident angles, a relatively large number of scans can be performed with a relatively small number of light sources.
Since the scanning line pitch in the sub-scanning direction can be changed by rotating and adjusting each multi-beam light source, the light-emitting pitch accuracy of the light-emitting units in the multi-beam light source can be relaxed. In particular, if the multi-beam light source is a two-beam light source, the scanning line pitch can be adjusted by adjusting the rotation even if the emission pitches of the two beams are different.

According to a fourth aspect of the present invention, there is provided a synchronization detection method used in the optical scanning device according to the third aspect, wherein in one of the multi-beam light sources, the first reference beam is emitted by one of the plurality of light emitting units. In addition to the multi-beam light source, one of the plurality of light emitting units is selectively lit, and light beams corresponding to the number of the multi-beam light sources are incident on the synchronization detection unit, A difference in detection time between the first reference beam and a light beam selectively turned on in addition to the multi-beam light source is measured by the synchronization detecting means, and the light is selectively turned on in addition to the multi-beam light source. In a first step of sequentially switching light beams and performing the same measurement, and in one of the multi-beam light sources, light beams other than the first reference beam are selectively turned on, and the multi-beam light In the other one, the second reference beam emitted from one of the plurality of light emitting units is turned on, and the two beams are incident on the synchronization detecting means, and selected by one of the multi-beam light sources. The detection time difference by the synchronization detection means between the light beam that is turned on and the second reference beam is measured, and the light beam that is selectively turned on is sequentially switched in one of the multi-beam light sources. In-light source detection between one light beam and the other light beam in each multi-beam light source from the second step of performing the same measurement and the detection time differences measured in the first and second steps. A third step of calculating a time difference, and performing the first to third steps before the start of the synchronization control, and generating a reference synchronization detection signal by the incidence of the first reference beam on the synchronization detection means during the synchronization control Thereby, the respective horizontal synchronizing signal for emission control of each scanning line of each multi-beam light source, a method of forming on the basis of the detected time difference and the light source in the detection time difference from the reference synchronization detection signal.
According to the present invention, in the first step performed before the start of the synchronous control, each detection time difference between the first reference beam and the light beam emitted from the other of the multi-beam light source is measured. Each detection time difference between the second reference beam and the light beam emitted from one of the multi-beam light sources is measured. In these processes, since one light beam is turned on for each multi-beam light source, each light beam has a relatively large detection time difference according to the incident angle. Therefore, even when the light emitting units in the multi-beam light source are close enough to be difficult to separate in the scanning direction, the detection time difference can be accurately measured. In the third step, the in-light source detection time difference between one light beam in each multi-beam light source and the other light beam is calculated.
At the time of synchronization control, the horizontal synchronization signal of each light beam can be formed by delaying the reference synchronization detection signal based on the first reference beam based on each detection time difference and in-light source detection time difference measured before the start of the synchronization control. .

According to the optical scanning device of the present invention, even a plurality of light beams respectively scanning on different scanning planes can be detected by one synchronization detection unit without installing a synchronization detection unit for each light beam. As a result, it is possible to easily detect the synchronization of a plurality of light beams with a simple configuration.
Further, according to the synchronization detection method used for one optical scanning device of the present invention, the detection by the synchronization detection means is performed by lighting one light beam between the multi-beam light sources having different incident angles in the plane along the deflection direction. Since the time difference is measured and the detection time difference in the light source between each light beam is calculated, a horizontal synchronization signal can be easily formed with a simple configuration even if the light emission pitch in the scanning direction in the multi-beam light source is very close. There is an effect that can be done.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and redundant description is omitted.
An optical scanning device according to an embodiment of the present invention will be described.
FIG. 1 is a plan view explanatory diagram for explaining a schematic configuration of an optical scanning device according to an embodiment of the present invention. FIG. 2 is also an explanatory view of the front view. FIG. 3 is a schematic explanatory view of the light source of the optical scanning device according to the embodiment of the present invention as viewed in the optical axis direction.

In this specification, in order to show the relative directions in a concise manner, the sub-scanning direction and the main-scanning direction are used in a broad sense by common usage when there is no possibility of misunderstanding.
In other words, the sub-scanning direction means a direction orthogonal to the scanning line on the surface to be scanned (recording medium), and scanning when one of the directions orthogonal to the optical path direction reaches the scanning line along the optical path. Sometimes it means the direction perpendicular to the line.
The main scanning direction means the direction of the scanning line, the direction perpendicular to the optical path direction, the direction perpendicular to the sub-scanning direction, and the light of the optical system in the plane where the light beam is deflected. A direction orthogonal to the axis may be referred to as a main scanning direction.

The laser scanning unit 1 (optical scanning device) of this embodiment forms a plurality of laser beams on a different scanning line and forms an appropriate spot diameter, and repeatedly scans in a fixed direction. For example, it can be suitably used in an image forming system such as a laser printer, a digital copying machine, a laser fax machine, and a plate making machine. In particular, it can be suitably used in an image forming system such as a full-color printer that forms images separated into four colors on four recording media.
The schematic configuration of the laser scanning unit 1 includes multi-beam light sources 2A and 2B, collimating lenses 3A and 3B, apertures 4A and 4B, cylindrical lenses (imaging members) 5A and 5B, a polygon mirror 8 ( Optical deflection means), optical path separation optical system 24 (optical path separation means), fθ lenses (scanning optical systems) 19a, 19b, 19c, 19d, folding mirror 21 (optical path changing means), and synchronization sensor unit 22 (synchronization detection means). Become.
Hereinafter, in the description of the reference numerals, for example, when alphabetic subscripts for the same number continue in alphabetical order such as “19a, 19b, 19c, 19d”, they may be simply abbreviated as 19a to 19d.

  1 and 2, reference numerals 23a, 23b, 23c, and 23d form electrostatic latent images for development with toners of yellow, magenta, cyan, and black (black), respectively, in a full-color image forming system (not shown). 1 shows a photosensitive drum (recording medium). The photoconductive drums 23a to 23d are arranged in parallel with a distance d between the drums.

As shown in FIGS. 1 and 2, the schematic configuration of the multi-beam light sources 2A and 2B includes an LD array 2c, a base 2a (holding member), and an LD drive circuit board 2b, respectively.
As shown in FIG. 3, the LD array 2c is a two-beam LD array element having two light emitting portions 20a and 20b separated by a distance Y. Then, it is attached to the base 2a made of an appropriate metal plate having high thermal conductivity in order to promote heat dissipation and make the temperature uniform.
In this way, heat dissipation is promoted by the base 2a, so that there is an advantage that the life of the LD array element can be extended. In addition, since the temperature is made uniform, even if the light emission amount differs between the LD array elements, a shift in the wavelength change amount due to the temperature characteristic occurs, and a magnification shift due to chromatic aberration in which the scanning region for each laser beam fluctuates. In addition, there is an advantage that image quality deterioration when used in an image forming system can be prevented.

Since the distance Y varies due to manufacturing errors of the LD array 2c, the distance Y is enlarged by an optical system which will be described later, and the position of the scanning line is displaced in the sub-scanning direction. Therefore, as shown in FIG. 3, for example, the mounting position of the base 2a with respect to the housing 20 can be rotated around an axis that is parallel to the optical axis direction and passes between the light emitting units 20a and 20b. Then, when the apparatus is assembled, the rotation is adjusted so that the scanning pitch between the scanning lines in the sub-scanning direction becomes a predetermined value. Any known mechanism and method may be used as the rotation adjustment mechanism and rotation adjustment method.
As described above, in this embodiment, since the rotation can be adjusted, the pitch of the light emitting units 20a and 20b can be varied within the range of the distance Y or less. Therefore, the LD array 2c is also suitable for an element having a large variation in the light emitting point pitch accuracy. There is an advantage that can be adopted. In addition, since the distance Y can be made larger than the distance corresponding to the desired scanning line pitch, there is an advantage that an element having a large light emission pitch that hardly causes crosstalk or the like can be employed.

The LD drive circuit board 2b is fixed to the base 2a, is electrically connected to the LD array 2c, and a drive circuit is formed for modulation driving based on a modulation signal input from the outside to the light emitting units 20a and 20b. It is a substrate.
The light beam modulated by the LD drive circuit board 2b is emitted from the light emitting portions 20a and 20b of the multi-beam light source 2A, and the two laser beams (light beams) 30a and 30b are emitted from the light emitting portions 20a and 20b of the multi-beam light source 2B. The laser beams (light beams) 30c and 30d are emitted in the parallel direction as divergent light.

The collimating lens 3A (3B) is disposed on the front side of the light emitting portion of the LD array 2A (2B), and is a lens that makes the laser beams 30a, 30b (30c, 30d) emitted from the LD array 2A (2B) parallel beams. It is a lens group.
The aperture 4A (4B) is a light regulating member for shaping the collimated light beam emitted from the collimating lens 3A (3B) into a predetermined light beam diameter. In this embodiment, it consists of a metal plate having a substantially elliptical opening whose major axis is extended in the main scanning direction.

  The multi-beam light sources 2A and 2B, the collimating lenses 3A and 3B, and the apertures 4A and 4B may be directly fixed to the casing 20, but a light source unit fixed integrally with the base 2a is formed, and the casing It is preferable to detachably attach to the body 20. Further, it is preferable to divide the base 2a into a portion where the LD array 2c is fixed and a portion where the base 2a is fixed to the housing 20, and fix the positions of the LD array 2c in a state where the rotation is adjusted. If it does so, it can attach or detach to the housing | casing 20, hold | maintaining the adjustment state of angle (theta).

  The cylindrical lenses 5A and 5B have power only in the sub-scanning direction, form images of the laser beams 30a to 30d emitted from the multi-beam light source 2 in the sub-scanning direction, and extend substantially in the main scanning direction. It is an optical element.

  The polygon mirror 8 is for deflecting the laser beams 30a to 30d in the main scanning direction in the vicinity of the imaging position. In the present embodiment, in a plane orthogonal to the sub-scanning direction, that is, in a plane along the deflection direction (hereinafter also referred to as a beam scanning surface), for example, a regular hexagon is formed, and a mirror surface (deflection reflection surface) is provided on each side. 1 is rotated at a constant angular velocity in the direction of the arrow in FIG. 1 by a motor (not shown) that rotates at a predetermined speed in response to a drive signal external to the laser scanning unit 1.

The optical path separation optical system 24 is an optical system for separating the optical paths of the laser beams 30a to 30d deflected by the polygon mirror 8 so that the scanning lines are finally scanned in parallel at a pitch d between the drums. .
As shown in FIGS. 1 and 2, each of the reflection mirrors 9 to 18 is composed of a surface reflection mirror that is extended to an appropriate length in the main scanning direction and has an inclination angle with respect to the sub-scanning direction. The

As shown in FIG. 2, the separation / reflection mirror 9 folds the laser beam 30 d substantially in the sub-scanning direction and guides the laser beam 30 d to the separation / reflection mirror 10 disposed substantially parallel to the separation / reflection mirror 9. The separation / reflection mirror 10 is arranged such that the laser beam 30d is scanned in a plane orthogonal to the sub-scanning direction.
The separating / reflecting mirror 11 folds the laser beam 30c substantially in the sub-scanning direction and guides the optical path to the separating / reflecting mirrors 12 and 13 arranged so as to be folded in a substantially triangular shape in the sub-scanning direction. It arrange | positions so that the beam 30c may be scanned in the plane parallel to the laser beam 30d.
The separating / reflecting mirror 14 folds the laser beam 30b substantially in the sub-scanning direction, and guides the optical path to the separating / reflecting mirrors 15 and 16 arranged so as to be folded in a substantially triangular shape in the sub-scanning direction. It arrange | positions so that the beam 30b may be scanned in the plane parallel to the laser beam 30d.
The separation / reflection mirror 17 folds the laser beam 30a in the substantially sub-scanning direction and guides the laser beam 30a to the separation / reflection mirror 18 disposed substantially parallel to the separation / reflection mirror 17. The separation reflection mirror 18 is arranged so that the laser beam 30a is scanned in a plane parallel to the laser beam 30d.

  The separating / reflecting mirrors 9, 11, 14, and 17 are arranged with their positions appropriately shifted in the optical axis direction and the sub-scanning direction so that they can be separated without leaving the optical path of the laser beams 30a to 30d emitted simultaneously. When the laser beams 30a to 30d are too close to each other in the sub-scanning direction and cannot be separated, the LD array 2c is rotated and adjusted to obtain a predetermined pitch.

The fθ lenses 19a to 19d connect the laser beams 30a to 30d scanned in the plane parallel to each other by the optical path separation optical system 24 so that the light beam diameters become appropriate at the scanning line positions on the photosensitive drums 23a to 23d, respectively. A lens or a lens group having an image with an fθ characteristic for making the scanning speed in the main scanning direction substantially constant.
In the sub-scanning direction, the imaging positions of the fθ lenses 19a to 19d and the imaging positions of the cylindrical lenses 5A and 5B are optically conjugate. Accordingly, a surface tilt correction optical system is configured in which the deviation of the scanning line in the sub-scanning direction due to the surface tilt of the polygon mirror 8 is remarkably reduced.

The folding mirror 21 is an optical element for bending the light beam on the scanning start side of the non-image area in the direction intersecting the optical axis among the laser beams 30 a to 30 d deflected by the polygon mirror 8 and guiding it to the synchronous sensor unit 22. is there.
The synchronous sensor unit 22 is a means for detecting the arrival of the light beam folded by the folding mirror 21 and controlling image writing.
The schematic configuration of the synchronization sensor unit 22 is to collect and shape the light flux into an appropriate shape to improve the S / N ratio of light detection, and to pass through the synchronization sensor lens 22a and be condensed. And a horizontal synchronization sensor 22b for detecting the reflected light flux. The horizontal synchronization sensor 22b is composed of a high-speed responsive photodetection sensor such as a PIN photodiode. Although not shown, the horizontal synchronization sensor 22b is connected to an appropriate electric circuit that signals the generation timing of the light detection output, and is configured to output a horizontal synchronization signal to the outside of the laser scanning unit 1. Such an electric circuit may be integrated into an IC and integrally formed in the vicinity of the horizontal synchronization sensor 22b.

Next, the operation of the optical scanning device according to the embodiment of the present invention will be described together with the synchronization detection method.
In the synchronization detection method of the optical scanning device according to the embodiment of the present invention, when a drive signal for rotationally driving the polygon mirror 8 is input from the outside of the laser scanning unit 1 and the polygon mirror 8 rotates at a constant speed, the image signal corresponds to the image signal. Prior to the exposure scanning step of scanning the modulated laser beam, a pre-synchronization control step consisting of three steps is performed.
FIG. 4 is a schematic timing chart for explaining the synchronization detection method of the optical scanning device according to the embodiment of the present invention. The horizontal axis indicates the time axis t, and the signals S ₁ , S ₂ , and S ₃ indicate output signals of the horizontal synchronization sensor 22b. The signal L _sa indicates one of the horizontal synchronization signals.

In the first step before the synchronous control, one of the multi-beam light sources 2A and 2B is DC-lit. For example, in the multi-beam light sources 2A and 2B, the respective light emitting units 20a are turned on, and the light emitting units 20b are turned off to turn on the laser beams 30a and 30c.
The laser beam 30a (30c) is emitted from the LD array 2c as divergent light, and then passes through the collimating lens 3A (3B) and the aperture 4A (4B) to be a parallel light beam having a predetermined light beam diameter.
Then, the light is condensed in the sub-scanning direction by the cylindrical lens 5A (5B), imaged in the sub-scanning direction in the vicinity of the reflection surface of the polygon mirror 8, and a substantially linear light beam extending in the main scanning direction. Then, it is deflected in the main scanning direction by the polygon mirror 8.

  The deflected laser beam 30a is incident on the fθ lens 19a after the optical path is folded by the separation reflection mirrors 17 and 18. When incident on the fθ lens 19a, an image is formed on the scanning line of the photosensitive drum 23a by the image forming action. The deflection angle increases at a constant speed, and scanning is performed at a constant speed on the scanning line in the direction of the vertical arrow in FIG. 1 due to the fθ characteristic of the fθ lens 19a.

Similarly, the deflected laser beam 30c is folded on the optical path by the separation reflecting mirrors 11, 12, and 13 and is incident on the fθ lens 19c, and is imaged on the scanning line of the photosensitive drum 23c. Thus, scanning is performed at a constant speed in the direction of the vertical arrow in FIG.
Since the laser beam 30c has a shallower incident angle with respect to the mirror surface of the polygon mirror 8 than the laser beam 30a, the deflection angle with respect to the tilt of the mirror surface is shifted to the scanning direction side where the incident angle is deviated. . That is, on the scanning surface, scanning is performed with a shift of the distance ΔH ₁ shown in FIG.

On the other hand, on the scanning start side, the laser beam 30 a (30 c) is folded by the folding mirror 21 and enters the synchronous sensor unit 22. When the laser beam 30a (30c) reaches a predetermined position, the synchronization sensor unit 22 outputs a horizontal synchronization signal and is turned off once.
Signal _{S 2} shows the output signal of the horizontal synchronization sensor 22b in the first step. That is, at time t ₀ when the laser beam 30a is incident, will signal S ₂ from high to low, so when it is turned off to high. At time t _2, the by laser beam 30c enters the horizontal synchronization sensor 22b, made from high to low, after turning off the laser beam 30c, goes high.
A time difference ΔT ₁ (detection time difference) between times t ₂ and t _{0 is} a time difference due to a difference in deflection angles of the laser beams 30a and 30c, and corresponds to a distance ΔH ₁ (see FIG. 1) on the scanning plane. That is, when a delay time of ΔT ₁ is given to the laser beam 30a, the laser beams 30a and 30c can be aligned in the scanning direction on the scanning surface.

Next, the laser beam 30d is turned on by DC while the laser beam 30c is turned off. Then, the laser beam 30a of the multi-beam light source 2A as the first reference beam, the laser beam 30d emitted from the light emitting portion 20b of the multi-beam light source 2B detects the detection time difference [Delta] T ₂ to be detected.
As shown in FIG. 3, when the laser beam 30d is inclined at an angle θ in the sub-scanning direction between the light emitting units 20a and 20b, the laser beam 30d is separated by a distance Δh (= Ysin θ) in the main scanning direction. Therefore, the detection timing is shifted.
Shows the signals S ₁ in this case is shown in FIG. 3. From the detection time t ₀ a laser beam 30a, the detection time difference [Delta] T ₂ only passed time t _3, the signal level to detect the laser beam 30d goes low.
In this way, the detection time differences ΔT ₁ and ΔT _{2 of} the multi-beam light source 2B with the first reference beam as a reference are measured.

In the second step before the synchronous control, instead of the first reference beam, one light beam of the multi-beam light source 2B is used as the second reference beam (for example, the laser beam 30c), and the multi-beam light source 2A with respect to the second reference beam is used. measuring a detection time difference [Delta] T ₃ for the laser beam 30b (the reference signal _{S 3} in FIG. 4).

In the third step before the synchronous control, it was measured in the first and second steps. From ΔT ₁ , ΔT ₂ , and ΔT ₃ , the in-light source detection time differences Δt _A and Δt _B between the light beams in the multi-beam light sources 2 _A and 2 _B are calculated as follows:
Δt _A = ΔT ₁ −ΔT ₃ (1)
Δt _B = ΔT ₂ −ΔT ₁ (2)
These detection time difference and in-light source detection time difference are stored in, for example, a memory, and are called appropriately so that the reference synchronization detection signal generated by the first reference beam can be delayed to form a horizontal synchronization signal for each light beam. deep.

  Such a pre-synchronization control process is always performed when the laser scanning unit 1 that adjusts the rotation of the multi-beam light sources 2A and 2B is assembled or when the multi-beam light sources 2A and 2B are replaced. In order to maintain the scanning start position with high accuracy, it is preferable to perform the scanning first after the laser scanning unit 1 is turned on. More preferably, it is performed every time the polygon mirror 8 is activated.

When the pre-synchronization control process is completed, the delay time with respect to the reference synchronization detection signal of the horizontal synchronization signal of each light beam necessary for aligning the writing position in the scanning direction is obtained as a detection time difference, a detection time difference within the light source, and their sum. Therefore, it is possible to align the writing positions of all the light beams in the scanning direction.
Therefore, when the laser beam 30a is incident on the horizontal synchronization sensor 22b and a reference synchronization detection signal is generated, the modulation signal is synchronized with the light emitting unit 20a after a delay time _Td corresponding to a desired image writing position on the photosensitive drum 23a. A horizontal synchronization signal L _sa (see FIG. 4) is formed. Therefore, the modulation of the LD array 2c of the multi-beam light source 2A is started from a predetermined image writing position, and the lighting of the laser beam 30a is controlled.

On the other hand, for the laser beam 30b, a horizontal synchronization signal L _sb (not shown) is formed after a delay time (T _d + Δt _A ).
Similarly, horizontal synchronization signals L _sc and L _sd (not shown) relating to the laser beams 30c and 30d are formed after delay times (T _d + ΔT ₁ ) and (T _d + ΔT ₁ + Δt _A ), respectively.
The laser beams 30b to 30d are controlled to be turned on in synchronization with the writing position of the laser beam 30a.
In this way, the pre-synchronization control process ends.

In this way, each laser beam is synchronously controlled by synchronizing the writing position, and scans the modulated laser beam onto the image area on the scanning line.
When the deflection scanning by one reflecting surface of the polygon mirror 8 is completed, the same scanning is performed on the next reflecting surface, and the laser beams 30a to 30d modulated according to the image signal are repeatedly scanned on the scanning line. . On the other hand, the photosensitive drums 23a to 23d are rotated at a constant linear velocity in one direction. Therefore, each laser beam is raster-scanned on each photosensitive drum, and latent images are formed on the photosensitive drums 23a to 23d.

  As described above, according to the laser scanning unit 1, four scanning beams can be formed by using two two-beam LD array elements which are cheaper than those for four beams. On the other hand, they are incident at different incident angles in the beam scanning plane. Therefore, for example, the multi-beam light sources 2A and 2B can be easily arranged in parallel in the beam scanning plane without using optical path combining means such as a half mirror or a beam splitter prism. Therefore, there is an advantage that the number of parts can be reduced. Further, there is an advantage that light loss due to the optical path combining means can be reduced.

  In addition, since the multi-beam can be generated by combining the two-beam LD array elements as described above, the degree of freedom in changing the scanning line pitch in the sub-scanning direction can be increased. For example, in an LD array element with three or more beams, the pitch error of the light emitting section on the same element cannot be individually adjusted. However, according to the combination of two beam LD array elements, the scanning pitch between each light beam is predetermined. It can be adjusted freely within the range. Therefore, there is an advantage that the light beam can be easily separated by the optical path separating means.

  Further, since the optical path is bent between the polygon mirror 8 and the optical path separation optical system 24 by the folding mirror 21, and guided to the synchronous sensor unit 22, the four light beams before being separated in the sub-scanning direction are received. The synchronous sensor unit 22 can be shared by one. Therefore, there is an advantage that the number of parts can be reduced.

  Further, according to the synchronization detection method of the optical scanning device according to the present embodiment, the detection time difference in the light source is calculated by measuring the detection time difference between the light beams having different incident angles in the pre-synchronization control process. When sequentially incident on the horizontal synchronization sensor 22b, there is an advantage that a horizontal synchronization signal can be easily and accurately formed even with light beams that are close enough to be separated.

  In the above description, in order to describe a synchronization detection method that can be used in one of the optical scanning devices according to the present invention, a plurality of light sources has been described as an example using a multi-beam light source. Needless to say, for example, four 1-beam LDs may be used only to reduce the number of parts.

  In the above description, the example used in the full-color image forming system has been described. However, the present invention is not limited to this, and may be used in a full-color image system that performs multi-beam scanning of each color. For example, two beams of each color may be scanned using eight light sources.

  In the above description, the number of multi-beam light sources is described as two examples. However, even when three or more multi-beam light sources are incident at three or more different incident angles, a horizontal synchronization signal is obtained in the same manner. Needless to say.

  In the above description, the third step of the pre-synchronization control step is described as an example performed after the first and second steps. However, the third step is measured by the first step after the first step. A step of calculating an in-light source detection time difference in addition to the multi-beam light source from the detection time difference, and after the second step, an in-light source detection time difference in one of the multi-beam light sources is calculated from each detection time difference measured in the second step. The process may be divided into steps.

1 is a plan view explanatory diagram for explaining a schematic configuration of an optical scanning device according to an embodiment of the present invention. It is the front view explanatory drawing similarly. It is a schematic explanatory drawing of the optical axis view of the light source of the optical scanning device which concerns on embodiment of this invention. 5 is a schematic timing chart for explaining a synchronization detection method of the optical scanning device according to the embodiment of the present invention.

Explanation of symbols

1 Laser scanning unit (optical scanning device)
2c LD array 2A, 2B Multi-beam light source 8 Polygon mirror (light deflecting means)
19a, 19b, 19c, 19d fθ lens (scanning optical system)
20a, 20b Light emitting part 21 Folding mirror (optical path changing means)
22 Synchronous sensor unit (synchronous detection means)
23a, 23b, 23c, 23d Photosensitive drum (recording medium)
24 Optical path separation optical system (optical path separation means)
30a, 30b, 30c, 30d Laser beam (light beam)

Claims (4)

Multiple light sources;
Light deflecting means for deflecting a plurality of light beams emitted from the plurality of light sources;
Optical path separating means for separating optical paths of a plurality of light beams deflected by the light deflecting means;
A plurality of scanning optical systems for imaging and scanning the light beams separated by the optical path separating means on different scanning planes;
An optical path changing means for bending a part of the optical path between the light deflecting means and the light separating means;
An optical scanning device comprising: synchronization detecting means for detecting the plurality of light beams along the optical path bent by the optical path changing means at a predetermined position and generating a synchronization signal.   2. The optical scanning device according to claim 1, wherein the plurality of light beams have different incident angles in a plane along a deflection direction with respect to a deflection reflection surface of the light deflection unit. A plurality of light beams having different incident angles are formed by a multi-beam light source including a plurality of light emitting units,
3. The optical scanning device according to claim 2, wherein the scanning line pitch in the sub-scanning direction can be changed by rotating and adjusting each of the multi-beam light sources. A synchronization detection method used in the optical scanning device according to claim 3,
In one of the multi-beam light sources, the first reference beam is turned on by one of the plurality of light-emitting units, and one of the plurality of light-emitting units is selectively turned on in addition to the multi-beam light source. Then, the number of light beams corresponding to the number of the multi-beam light sources is incident on the synchronization detection means, and the synchronization between the first reference beam and the light beam selectively turned on in addition to the multi-beam light source is performed. A first step of measuring a detection time difference by a detecting means, and performing the same measurement by sequentially switching the light beam to be selectively turned on in addition to the multi-beam light source;
In one of the multi-beam light sources, a light beam other than the first reference beam is selectively turned on, and in the other one of the multi-beam light sources, a second light emitted from one of the light emitting units. The reference beam is turned on, the two beams are incident on the synchronization detection means, and the synchronization detection between the light beam selectively turned on in one of the multi-beam light sources and the second reference beam is performed. A second step of measuring the detection time difference by the means, and performing the same measurement by sequentially switching the light beam selectively lit in one of the multi-beam light sources,
A third step of calculating an in-light source detection time difference between one light beam and the other light beam in each multi-beam light source from each detection time difference measured in the first and second steps. ,
Before starting synchronous control, perform the first to third steps,
During synchronization control, a reference synchronization detection signal is generated by incidence of the first reference beam on the synchronization detection means, and each horizontal synchronization signal for performing light emission control for each scanning line of each multi-beam light source is detected by the reference synchronization detection. A synchronization detection method used for an optical scanning device, wherein the synchronization detection method is formed from a signal based on the detection time difference and the detection time difference in the light source.

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