JP2005091570A - Optical scanner, image forming apparatus and beam interval correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which corrects the variation of a beam pitch interval (scanning position) on a surface to be scanned, and also to provide an image forming apparatus and a beam interval correction method. <P>SOLUTION: A pitch detecting sensor 19 detects N times a plurality of beam intervals emitted in the direction of a surface 16 to be scanned. A controller 22 estimates, on the basis of the beam intervals so detected, the true value of the beam intervals and, on the basis of the estimated value and target value of these intervals, determines their correction value. Wedge-shaped prisms 28a, 28b correct the beam intervals on the basis of the determined correction value. The optical scanner 18 sequentially repeats the operations for detection, estimation, correction value determination and correction of the beam intervals and performs the correction process, while at least one operation among the detection, estimation and correction value determination is carried out simultaneously with the correction operation of the beam intervals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device, an image forming apparatus, and a beam interval correction method, and more particularly, to an optical scanning device, an image forming apparatus, and a beam interval correction method that adjust the traveling direction of laser light emitted from a light source.

In an optical scanning device used in a writing system for forming an image with a laser beam on an image carrier such as a photosensitive drum, there has been a method for increasing the rotational speed of a polygon mirror as a deflecting means as a means for improving the recording speed. .
However, this method has problems such as motor durability, noise, vibration, laser modulation speed, and the like. Therefore, a conventional technique has been proposed in which a plurality of light beams are scanned at a time to record a plurality of lines simultaneously.

  As a method of a multi-beam light source device that emits a plurality of laser beams, for example, there is a method using a multi-beam semiconductor laser (for example, a semiconductor laser array) having a plurality of light emitting points (light emitting channels) in one package. It is now an expensive light source means because it is difficult to increase the number of upper channels, it is difficult to eliminate the influence of thermal / electrical crosstalk, and it is difficult to shorten the wavelength.

  On the other hand, single beam semiconductor lasers are still widely used in various industrial fields because they are still relatively easy to shorten the wavelength and can be manufactured at low cost. Many proposals have been made on a light source device and a multiple beam scanning device that use this single beam semiconductor laser (or the above-mentioned multi-beam semiconductor laser) as a light source and synthesize a plurality of laser beams using beam combining means.

  As described above, the method of synthesizing a plurality of laser beams using the beam synthesizing means has many advantages in terms of shortening the wavelength and reducing the cost. Furthermore, even when adjusting (setting) the beam spot interval (beam pitch; scan line interval) in the sub-scanning direction on the surface to be scanned, this can be easily achieved by slightly deflecting the emission direction of each laser beam. There is a merit that can be done.

However, in comparison with a method using a semiconductor laser array as a light source means, in the case of a method of combining a plurality of laser beams using a beam combining means, the emission direction of each laser beam depends on the influence of environmental changes / aging, etc. It is easy to change, and the problem that the beam spot interval on the surface to be scanned fluctuates easily occurs.
Therefore, it has been conventionally performed to detect the beam spot interval and perform feedback correction based on the detection result. A typical example of the prior art is shown below.

  In the laser printer device and the scanning method disclosed in Patent Document 1, a deviation from a predetermined value of the laser beam is detected during the non-scanning time, and a signal based on the deviation is held in the next scanning time.

Further, in the image forming apparatus disclosed in Patent Document 2, in the image forming apparatus provided with the multiple beam scanning device, correction characteristics determined based on the scanning position deviation amount between the multiple beams detected before the start of the sub-scanning are obtained. The amount of deviation of the scanning position is corrected as fixed during one image recording.
Japanese Patent Publication No. 6-94215 Japanese Patent Laid-Open No. 7-248458

  As described above, many conventional techniques related to feedback correction for detecting the deviation amount of the beam pitch (scanning line position) and correcting based on the result have been proposed. However, the prior art has the following problems.

For example, the prior art disclosed in Patent Document 1 detects the beam pitch deviation / data processing (derivation of correction values) during the scanning time, drives the beam pitch correction means, and then performs the correction at the next scanning time. The value was retained.
However, it is difficult to perform the above-described processing (deviation detection → correction value derivation → correction means driving) during the scanning time.

In addition, the conventional technique disclosed in Patent Document 2 corrects the scanning position deviation amount by fixing a correction characteristic determined based on the scanning position deviation amount between a plurality of beams detected before the start of sub-scanning during one image recording. It was something to do.
However, since the correction value determined before the start of sub-scanning is fixed during the recording of one image, there is a possibility that the scanning position shift will occur again due to a rise in the internal temperature when printing a large number of tens of sheets or more. It was.

  The present invention has been made in view of the above problems, and an optical scanning device that corrects fluctuations in the interval (scanning position) of the beam pitch on the surface to be scanned, which is mainly caused by an increase in the internal temperature during mass printing, An object is to provide an image forming apparatus and a beam interval correction method.

  In order to achieve this object, the present invention provides a uniformly charged surface to be scanned in a scanning medium that moves in the sub-scanning direction by periodically deflecting laser beams emitted from a plurality of laser light sources by a deflector. An optical scanning device that scans the top in the main scanning direction orthogonal to the sub-scanning direction to form an electrostatic latent image on the surface to be scanned. A pitch detecting means for detecting; a first calculating means for estimating a true value of the plurality of beam intervals based on the plurality of beam intervals detected by the pitch detecting means; and an estimated value of the plurality of beam intervals by the first calculating means; A second calculating means for calculating a correction value for the plurality of beam intervals based on the target value for the plurality of beam intervals, and a pitch for correcting the plurality of beam intervals based on the correction value calculated by the second calculating means. Correction hand Multiple beam interval detection operation by the pitch detection means, multiple beam interval estimation operation by the first calculation means, multiple beam interval correction value calculation operation by the second calculation means, multiple by the pitch correction means The beam interval correction operation is sequentially repeated, and at least one of the multiple beam interval detection operation, the multiple beam interval estimation operation, and the multiple beam interval correction value calculation operation is executed simultaneously with the multiple beam interval correction operation. It is characterized by being.

  Further, according to the present invention, the laser beam emitted from each of the plurality of laser light sources is periodically deflected by the deflector, and the uniformly charged scanning surface in the scanning medium moving in the sub-scanning direction is An optical scanning device that scans in the main scanning direction orthogonal to the sub-scanning direction to form an electrostatic latent image on the surface to be scanned, and detects a plurality of beam intervals irradiated in the direction of the surface to be scanned N times A first calculating unit that estimates a true value of the plurality of beam intervals based on the plurality of beam intervals detected by the pitch detecting unit; an estimated value of the plurality of beam intervals by the first calculating unit; and a plurality of beams A second computing means for calculating a correction value for a plurality of beam intervals based on the target value of the spacing; a pitch correcting means for correcting the plurality of beam intervals based on the correction value calculated by the second computing means; And Multi-beam interval detection operation by the first detection unit, multi-beam interval estimation operation by the first calculation unit, multi-beam interval correction value calculation operation by the second calculation unit, multi-beam interval correction operation by the pitch correction unit Are repeated in order, and when the deviation between the estimated value and the target value is smaller than a predetermined value, the multiple beam interval detection operation is executed after the multiple beam interval correction operation is completed.

  Further, according to the optical scanning device of the present invention, the pitch correction means is characterized in that a signal indicating a correction value is always input from the second calculation means when executing a correction operation for a plurality of beam intervals.

  According to the optical scanning device of the present invention, the pitch correction means is an optical element that is rotated or displaced by a piezoelectric element that is deformed by an electric signal.

  Further, according to the optical scanning device of the present invention, the pitch correction means is a liquid crystal element driven by an electric signal.

  Further, according to the optical scanning device of the present invention, the pitch correction means is an acousto-optic element driven by an electric signal.

  Further, according to the optical scanning device of the present invention, the pitch correction means is an electro-optical element driven by an electric signal.

  Further, according to the optical scanning device of the present invention, the first calculation means is configured to detect the plurality of beam intervals based on the interval between the plurality of beams deflected by a specific reflecting surface in the polarizer detected by the pitch detection unit. The true value of is estimated.

  According to the present invention, there is also provided an image forming apparatus for transferring a latent image formed on a surface to be scanned to a medium for recording an image and printing it out. It is characterized by that.

  In addition, according to the image forming apparatus of the present invention, the detection operation of a plurality of beam intervals is started after the power supply to the apparatus is turned on.

  In addition, according to the image forming apparatus of the present invention, the detection operation of the multiple beam intervals, the estimation operation of the multiple beam intervals, the calculation operation of the correction value of the multiple beam intervals, and the correction operation of the multiple beam intervals are one of the print output operations. It is executed immediately before the first output image in the job is formed.

  Further, according to the present invention, the laser beam emitted from each of the plurality of laser light sources is periodically deflected by the deflector, and the uniformly charged scanning surface in the scanning medium moving in the sub-scanning direction is A beam interval correction method using an optical scanning device that scans in a main scanning direction orthogonal to the sub-scanning direction and forms an electrostatic latent image on a surface to be scanned, and a pitch detection unit that detects laser light, A pitch detection step for detecting a plurality of beam intervals irradiated in the scanning surface direction N times, and a first calculation means for executing a calculation process are configured to perform a plurality of beam intervals based on the plurality of beam intervals detected in the pitch detection step. A first calculation step for estimating the true value of the second calculation means, and a second calculation means for executing the calculation process, the estimated value of the plurality of beam intervals calculated in the first calculation step, and the target value of the plurality of beam intervals. On the basis of, A second calculation step for calculating a correction value for several beam intervals, and a correction unit for correcting the traveling direction of the laser beam, based on the correction value calculated by the second calculation step, a pitch for correcting a plurality of beam intervals. A pitch detection step, a first calculation step, a second calculation step, and a pitch correction step are repeated in order, and the pitch detection step, the first calculation step, and the second calculation step are At least one process is performed simultaneously with the pitch correction process.

  Further, according to the present invention, the laser beam emitted from each of the plurality of laser light sources is periodically deflected by the deflector, and the uniformly charged scanning surface in the scanning medium moving in the sub-scanning direction is A beam interval correction method using an optical scanning device that scans in a main scanning direction orthogonal to the sub-scanning direction and forms an electrostatic latent image on a surface to be scanned, and a pitch detection unit that detects laser light, A pitch detection step for detecting a plurality of beam intervals irradiated in the scanning surface direction N times, and a first calculation means for executing a calculation process are configured to perform a plurality of beam intervals based on the plurality of beam intervals detected in the pitch detection step. A first calculation step for estimating the true value of the second calculation means, and a second calculation means for executing the calculation process, the estimated value of the plurality of beam intervals calculated in the first calculation step, and the target value of the plurality of beam intervals. On the basis of, A second calculation step for calculating a correction value for several beam intervals, and a correction unit for correcting the traveling direction of the laser beam, based on the correction value calculated by the second calculation step, a pitch for correcting a plurality of beam intervals. The pitch detection step, the first calculation step, the second calculation step, the pitch correction step is repeated in order, and the deviation between the estimated value and the target value is smaller than a predetermined value, A pitch detection step is performed after the pitch correction step.

  According to the invention, the pitch correction step is characterized in that the correction means corrects the plural beam intervals based on a signal indicating a correction value that is always input from the second calculation means.

  According to the invention, in the pitch correction step, the optical element that is rotated or displaced by the piezoelectric element that is deformed by the electrical signal as the correction means adjusts the traveling direction of the laser light to correct the plural beam intervals. It is characterized by that.

  According to the invention, the pitch correction step is characterized in that as a correction means, a liquid crystal element driven by an electric signal adjusts the traveling direction of the laser light to correct the plural beam intervals.

  According to the invention, the pitch correction step is characterized in that the acousto-optic device driven by an electrical signal adjusts the traveling direction of the laser light to correct a plurality of beam intervals as a correction means. .

  According to the invention, the pitch correction step is characterized in that the electro-optic element driven by the electric signal adjusts the plural beam intervals by adjusting the traveling direction of the laser light as the correction means. .

  Further, according to the present invention, the first calculation step is based on the interval between the plurality of beams deflected by a specific reflecting surface in the polarizer, which is detected in the pitch detection step. It is characterized in that a true value of a plurality of beam intervals is estimated.

  Further, according to the present invention, the pitch detecting step is an image forming apparatus for transferring a latent image formed on the surface to be scanned to a medium for recording an image and printing out the optical scanning device. A plurality of beam intervals are detected after power is turned on.

  According to the present invention, in the pitch detection step, the first calculation step, the second calculation step, and the pitch correction step, the first output image in one job of the print output operation by the image forming apparatus is formed. It is performed immediately before.

  According to the present invention, it is possible to complete the beam pitch correction processing for suppressing the beam pitch deviation during the multiple beam scanning in a short time.

  An optical scanning device according to an embodiment of the present invention is an optical writing unit of a laser writing optical system, for example, and is mounted on an image forming apparatus such as a laser printer, a digital copying machine, or a laser facsimile.

The optical scanning device according to the present embodiment periodically deflects laser beams emitted from a plurality of laser light sources by a deflector, and uniformly scans a surface to be scanned in a scanning medium moving in the sub-scanning direction. The optical scanning device scans in a main scanning direction orthogonal to the sub-scanning direction and forms an electrostatic latent image on the surface to be scanned.
The optical scanning device according to the present embodiment includes a pitch detection sensor that detects a plurality of beam intervals irradiated in the scanning surface direction N times, and the plurality of beams based on the plurality of beam intervals detected by the pitch detection sensor. A controller that estimates a true value of the interval, calculates a correction value of the multiple beam interval based on the estimated value of the multiple beam interval, and a target value of the multiple beam interval, and based on the calculated correction value And a wedge-shaped prism for correcting a plurality of beam intervals.
The optical scanning device repeats the above-described multi-beam interval detection operation, multi-beam interval estimation operation, multi-beam interval correction value calculation operation, and multi-beam interval correction operation in order, thereby performing multi-laser interval correction processing. Execute.
In the present embodiment, at least one of a detection operation of a plurality of beam intervals, an estimation operation of a plurality of beam intervals, and a calculation operation of a correction value of a plurality of beam intervals is performed simultaneously with the correction operation of the plurality of beam intervals. Yes.

(Outline of optical scanning device)
FIG. 1 is a diagram showing a configuration of an optical scanning device (two-beam scanning device) 18 in Embodiment 1 of the present invention. FIG. 2 is a simplified plan view showing the configuration of the optical scanning device (two-beam scanning device) 18 according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of the light source unit 41 according to the first embodiment of the present invention.
Hereinafter, the configuration and operation of the optical scanning device 18 in this embodiment will be described with reference to FIGS. 1 to 3.

  As shown in FIG. 1, the optical scanning device 18 includes a cylindrical lens 13, a polygon mirror (deflector) 14, a scanning optical system (scanning means) 15, a photosensitive drum (scanned surface) 16, and a pitch. A detection sensor (pitch detection means) 19, a control unit 22, a rotation adjustment unit 23, wedge-shaped prisms 28 a and 28 b, and a light source unit 41 are configured.

As shown in FIG. 1 and FIG. 2, the laser beams 21a and 21b emitted from the light source unit 41 are (in the main scanning direction) due to the action of the cylindrical lens 17 incident through the wedge-shaped prisms 28a and 28b. After being reflected in the sub-scanning direction on the deflecting / reflecting surface of the polygon mirror 14 (as a long line image) and reflected, it reaches the surface of the photosensitive drum 16 that becomes the scanned surface via the scanning optical system 15.
That is, the optical scanning device 18 in the present embodiment is a two-beam scanning device capable of simultaneously scanning the two laser beams 21a and 21b by one scanning with the polygon mirror 14 surface.

The control unit 22 includes an arithmetic device such as a CPU and a storage device (storage medium) that stores a program for executing the arithmetic processing.
Further, the rotation adjusting means 23 adjusts the traveling direction of the laser beams 21a and 21b by rotating the wedge-shaped prisms 28a and 28b.

When a signal indicating the beam pitch between the laser beams 21 a and 21 b is input from the pitch detection sensor 19, the control unit 22 performs a calculation process based on the input signal and outputs a signal for driving the rotation adjusting unit 23. Output.
The rotation adjusting means 23 rotates the wedge-shaped prisms 28a and 28b based on the drive signal.

As shown in FIG. 3, the light source unit 41 includes a pair of semiconductor lasers 11a and 11b and coupling lenses 12a and 12b for coupling laser beams emitted from the semiconductor lasers 11a and 11b, respectively. And semiconductor lasers 11a and 11b and a base member 43a for holding the coupling lenses 12a and 12b. The semiconductor lasers 11a and 11b are fixed to the base member 43a by press fitting.
The number of laser beams emitted from the light source unit 41 may be other numbers as long as it is two or more.

Further, as shown in FIG. 3, the coupling lenses 12a and 12b have the characteristics of the emitted laser beam (collimating property and the direction of the emitted optical axis) depending on the characteristics of the optical system and the semiconductor lasers 11a and 11b. After the relative positional relationship is adjusted, it is fixed by UV bonding.
The method for fixing the semiconductor lasers 11a and 11b and the coupling lenses 12a and 12b is not limited to the above method, and any known method may be adopted. Each semiconductor laser may be a single beam semiconductor laser having one light emitting point or a multi-beam semiconductor laser having a plurality of light emitting points.

(Description of pitch detection process A1 and first calculation process A2)
As shown in FIG. 1, the optical scanning device 18 includes a pitch detection sensor (pitch detection means) 19 for detecting a beam pitch (scanning line interval) between the two beams 21a and 21b. 16 is provided at a position optically equivalent to 16.
The pitch detection sensor 19 can detect the beam pitch at a rate of once per scan as the polygon mirror 14 rotates.
In order to detect the beam pitch with high accuracy, the measurement error due to the displacement of the scanning position caused by the influence of the unevenness of the pitch due to the surface tilt of the polygon mirror 14 or the vibration of the machine, or the measurement variation of the pitch detection sensor 19. Is desired to be removed. For this purpose, it is only necessary to provide arithmetic processing means (control unit 22) such as acquiring signal data a plurality of times (for N scans) and processing the average value thereof.

In the present embodiment, the above-described processing for detecting the beam pitch between the two beams 21a and 21b a plurality of times (N times) (a processing for acquiring a plurality of times (N times) of data signals) is referred to as “pitch detection processing A1”. Means for obtaining the data signal is referred to as pitch detection means.
Further, the arithmetic processing for predicting the true value from the plurality of (N) data signals (for example, calculating the average value of the N beam pitch values) is referred to as “first arithmetic processing A2”, and the true value is The calculation means to be predicted is referred to as “first calculation means (control unit 22)”.

(Explanation of second calculation process A3 and pitch correction process A4)
Further, the optical scanning device 18 calculates correction data to be input to the “pitch correction means” described below based on the “predicted beam pitch value” and the “correction target value” derived by the first arithmetic processing A2. A “second calculation means (control unit 22)” is provided (calculating), and such calculation processing is referred to as “second calculation processing A3”.
The “correction target value” may be stored in advance in the second calculation means.

  The optical scanning device 18 is provided with “pitch correction means (wedge-shaped prisms 28a and 28b in the first embodiment)” that is driven to receive the correction data and correct the beam pitch. Such a process for correcting the beam pitch is referred to as a pitch correction process A4.

(Beam pitch correction means: configuration / operation of wedge-shaped prism)
As described above, wedge-shaped prisms 28a and 28b having a wedge-shaped cross section are disposed in the optical paths of the two laser beams 21a and 21b between the light source unit 41 and the cylindrical lens 13, respectively. Therefore, beam pitch correction processing can be performed. The configuration / operation of the wedge-shaped prism will be described in detail below.

The wedge-shaped prisms 28a and 28b are transmission-type prisms having two non-parallel planes as an entrance surface and an exit surface, and have a function of deflecting the optical path of the laser beam by a minute angle.
The wedge-shaped prisms 28a and 28b do not have to be disposed in the optical path of the two laser beams 21a and 21b, and may be disposed in only one of the optical paths.

  4A is a schematic diagram of optical path deflection by the wedge-shaped prisms 28a and 28b in the main scanning section in the first embodiment of the present invention, and FIG. 4B is a wedge shape in a plane parallel to the scanned surface. It is a schematic diagram of the optical path deflection | deviation by the prisms 28a and 28b.

As shown in FIG. 4A, when the laser beams 21a and 21b are incident on the wedge-shaped prisms 28a and 28b having the apex angle α, the laser beams 21a and 21b are incident on the wedge-shaped prisms 28a and 28b. Refracted and the optical path is deflected by φ = (n−1) α (in the range where α is relatively small).
That is, it is possible to easily achieve a desired deflection angle φ by appropriately designing the apex angle α of the wedge-shaped prisms 28a and 28b (according to the characteristics of the combined optical system).
At this time, by rotating the wedge-shaped prisms 28a and 28b around a rotation axis substantially parallel to the optical axes of the laser beams 21a and 21b (referred to as γ rotation), the emission direction of the laser beams 21a and 21b is a circle having a radius φ. It can be varied along the circumference.

Now, the state in which the wedge-shaped prisms 28a and 28b are arranged so that the entrance and exit surfaces of the wedge-shaped prisms 28a and 28b are perpendicular to the deflection surface is set as an initial state, and the wedge-shaped prisms 28a and 28b are changed from this state. γ can be rotated.
As a result, as shown in FIG. 4B, only the sub-scanning direction component can be effectively varied without largely changing the main scanning direction of the outgoing beams 21a and 21b.

(Adjustment of scanning line interval by γ rotation of wedge-shaped prism)
More precise adjustment of the scanning line interval can be achieved by γ rotation of the wedge-shaped prisms 28a and 28b (by rotating the wedge-shaped prisms 28a and 28b around a rotation axis substantially parallel to the optical axis). .
By rotating wedge-shaped prisms 28a and 28b as shown in FIG. 4 around the optical axis, the deflection angle can be varied by a maximum φ by refraction.
When the apex angle of the wedge-shaped prisms 28a and 28b is α and the refractive index of the wedge-shaped prisms 28a and 28b is n, the maximum deflection angle φ is expressed by the following formula 1.
φ = (n−1) × α (Formula 1)

Further, when the focal length of the coupling lens is fcol, the sub-scanning lateral magnification of the entire optical system is m, and the adjustment angle around the rotation axis of the wedge-shaped prism is Δγ, the beam spot position (sub-scanning on the surface to be scanned) (Direction) correction amount Δz is expressed by the following equation.
Δz = m × fcol × tan (φ × sin Δγ) (Formula 2)

(Example of γ rotation mechanism of wedge-shaped prism using stepping motor)
FIG. 5 is a diagram illustrating an example of an adjustment mechanism that rotates the wedge-shaped prisms 28a and 28b around the rotation axis according to the first embodiment of the present invention.
As shown in FIG. 5, the rotation adjusting means of the wedge-shaped prisms 28a and 28b is a lead screw type actuator using a stepping motor as a drive source.
The wedge-shaped prisms 28a and 28b are inserted into a prism cell 55 having a pressing portion (pressed by a nut portion of a stepping motor) extended from the cylindrical portion.

  6 and 7 are diagrams showing another example of an adjusting mechanism for rotating the wedge-shaped prisms 28a and 28b around the rotation axis in the first embodiment of the present invention. FIG. 6 is a diagram of another example adjustment mechanism viewed from the optical axis direction, and FIG. 7 is a diagram of another example adjustment mechanism viewed from the sub-scanning direction.

  FIG. 5 shows a configuration in which the prism cell 55 is brought into contact with a “V-shaped groove” provided in the holding member. On the other hand, FIG. 6 and FIG. 7 show an example of a configuration in which the prism cell 55 is inserted into the insertion hole provided in the holding member and is held by rotation.

  5, 6, and 7, the stepping motor that outputs rotational displacement and the lead screw are combined. However, a stepping motor that incorporates the lead screw and can output linear displacement is used. You can use it. Further, as the driving means, not only a stepping motor but also a method using a piezoelectric element or a method using an ultrasonic motor may be adopted.

The amount of movement Δz in the sub-scanning direction of the beam spot on the surface to be scanned when the wedge-shaped prism is rotationally driven by an actuator combining such a stepping motor and a lead screw uses the following specifications. (Equation 3).
fcol: focal length of collimating lens mz: sub scanning magnification of entire system (from light source to scanned surface) α: apex angle of wedge-shaped prism n: refractive index of wedge-shaped prism β0: deflection angle at wedge-shaped prism = ( n-1) × α
N: Input pulse (number of steps)
Δγ: rotation angle of triangular prism per N pulses = tan ⁻¹ ((ω / 360 °) × P × N / R)
ω: Step angle of stepping motor (per pulse)
P: lead screw pitch R: wedge-shaped prism cell span length (rotating radius)
fcyl: focal length of cylindrical lens m1: sub-scan magnification of pre-polygon optical system = fcyl / fcol
m2: Sub-scan magnification of the post-polygon optical system Δz = mz × fcol × tan (β0 × sin Δγ)
= Mz × fcol × tan ({(n−1) α} × sin [tan ⁻¹ {(ω / 360 °) × P × N / R}])) (Formula 3)
Δγ = tan ⁻¹ [(ω / 360 °) × P × N / R] (Formula 4)

  According to Equation 3, the sub-scanning beam spot position (that is, the scanning line interval: sub-scanning beam pitch) can be adjusted with respect to the number of input pulses. Further, by appropriately setting the apex angle α of the wedge-shaped prisms 28a and 28b (designed in accordance with the combined scanning optical system 15), the sensitivity of the adjustment (sub-scanning beam spot position fluctuation amount with respect to the number of input steps) is optimized. Can be achieved.

For example, mz = 3 times, fcol = 15 [mm], n = 1.514, α = 1.5 [°], ω = 18 [°], P = 0.25 [mm], N = 1, R = 30 [mm]
Δz = mz × fcol × tan ({(n−1) α} × sin [tan ⁻¹ {(ω / 360 °) × P × N / R}])) (Formula 3)
= 3 × 15 × tan ({(1.514-1) · 1.5 °} × sin [tan ⁻¹ {(18 ° / 360 °) × 0.25 × 1/30}])
= 0.3 × 10 ⁻³ [mm] = 0.3 [μm]
Thus, the beam spot can be varied at 0.3 [μm] per pulse input to the stepping motor: 1 pulse.

On the other hand, if the amount of deviation of the current scanning line interval from the target value is Δz = 30 [μm], the number N of input steps for correcting this becomes N = 120 steps from Equation 3.
If the pulse speed of the input pulse is 200 [pps], the response time Tr = 120/200 = 0.6 [s].

(Pitch detection to pitch correction flow)
FIG. 8 is a diagram showing a series of correction processing by the optical scanning device in Embodiment 1 of the present invention. Hereinafter, a series of correction processing [executed in the order of A1 (i) → A2 (i) → A3 (i) → A4 (i)] will be described below with reference to FIG.
Pitch detection processing A1: Beam pitch detection is repeated (N times).
First arithmetic processing A2: The true value of the beam pitch is predicted from the beam pitch detection result (N pieces of data).
Second calculation process A3: A beam pitch correction amount (correction data) is calculated from the predicted value and the correction target value.
Pitch correction processing A4: According to the correction data, the actuator is driven to correct the beam pitch.
Subscript i in (): Indicates an i-th series of processing operations.

  When the above-described wedge-shaped prisms 28a and 28b are used as pitch correction means, the behavior of the beam spot position correction amount Δz with respect to the number of input steps N varies depending on errors such as apex angle α and refractive index n of the wedge-shaped prisms 28a and 28b. May differ from the design value. In such a case, the target value may not be reached by performing a series of processing operations (from the pitch detection process A1 to the pitch correction process A4) only once. Therefore, by performing the above-described series of processing operations a plurality of times, the target value is gradually approached.

(Comparative example of beam pitch correction processing)
FIG. 9A is a diagram showing a comparative example (conventional beam pitch correction processing) with respect to the beam pitch correction processing by the optical scanning device in Embodiment 1 of the present invention.
Hereinafter, the beam pitch correction processing in the prior art will be described with reference to FIG. 8 and FIG.

In the conventional beam pitch correction, as shown in FIG. 9A, after the first correction process [A1 (1) → A2 (1) → A3 (1) → A4 (1)], The second correction process [A1 (2) → A2 (2) → A3 (2) → A4 (2)] is performed, and further, the third and subsequent correction processes need to be performed as necessary.
At this time, the processing times of A1 (i), A2 (i), and A3 (i) are constant regardless of the i-th time. On the other hand, the processing time of A4 (i) becomes shorter as i increases because the beam pitch approaches the target value.
For example, when the rotational speed of the polygon mirror 14 (polygon scanner) is 30,000 [rpm] = 500 [Hz], the time required for one scan is 0.002 [seconds], so the data signal in the processing operation A1 If the number of acquisitions (number of data) N = 100, processing time T1 = 0.002 × 100 = 0.2 [seconds] is required.

On the other hand, in the case of the above numerical example described with reference to FIG. 5 and Expression 3, the time of the processing operation A4 required to correct the initial value: 30 μm is T4 = 0.6 [seconds].
Note that the times T2 and T3 required for the processing operations A2 and A3 are negligibly small compared to the above T1 and T4.

However, if an error occurs in the apex angles of the wedge-shaped prisms 28a and 28b and αerror = 0.75 ° (= αdesign / 2) with respect to the design value αdesign = 1.5 °, the first correction processing is performed. Then, only 30 μm / 2 = 15 μm can be corrected, and therefore an adjustment residual of 15 μm (initial value 30 μm−correction amount 15 μm) is generated. Therefore, it is necessary to continue the second and subsequent correction processes.
A plurality of correction processes are performed, and such a correction process may be terminated when the deviation between the beam pitch detection result and the target value falls below a certain set value.

(Beam pitch correction processing in this embodiment)
FIG. 9B is a diagram showing the beam pitch correction process in the first embodiment of the present invention.
Hereinafter, the beam pitch correction processing by the optical scanning device in the present embodiment will be described with reference to FIGS. 8 and 9B.

  The present embodiment is characterized in that the second correction process is started before the first correction process is completed.

FIG. 9B shows an example in which the (i + 1) th processing operation A1 (i + 1) is started before the i-th processing operation A4 (i) is completed. In the present embodiment, the second pitch detection processing A1 (2) is started before the first processing operation A4 (1) is completed.
Further, when there is an error in the apex angle α of the wedge-shaped prisms 28a and 28b, the “correction data” derived by A1 (2) and A2 (2) is less accurate than in the case of [Comparative Example]. Tend to be. However, since “pitch detection processing A4 (i)” and “pitch correction processing A1 (i + 1)” having a long processing time can be performed at the same time, the beam pitch can be targeted in a shorter time than in the case of [Comparative Example]. It becomes possible to approach the value.

  FIG. 9B shows an example in which A1 (i + 1) is performed during execution of A4 (i). However, A2 (i + 1) and A3 (i + 1) may be further performed during execution of A4 (i). A part of the data acquired in A1 (i) may be used as data used for the arithmetic processing of A2 (i + 1).

If the deviation between the “predicted value by the first calculation means” and the “correction target value” becomes smaller than a predetermined value by repeating the correction processing, the processing operation from the processing operation A4 (1) is performed. The processing operations A1 (i + 1) to A3 (i + 1) may be performed after the period repeated up to A4 (i).
As a result, the frequency of beam pitch correction processing is reduced, and unnecessary arithmetic processing can be deleted.

In addition, when all of the plurality of data detected in the processing operation A1 are fetched for each scanning and the arithmetic processing is performed in the processing operation A2, the processing operation is caused by the influence of the scanning position deviation caused by the surface of the polygon mirror 14 reflecting surface. There is a risk that the accuracy of the correction data derived in A3 may be reduced. In such a case, only signal data corresponding to a specific reflection surface out of the plurality of reflection surfaces of the polygon mirror 14 may be derived as correction data.
For example, when the number of polygon mirror surfaces is 6,
・ Detect signal data at a rate of once every 6 scans and calculate correction data.
-All the signal data for each scan is taken in, and every 6 of these are taken out to calculate correction data.
Or the like.

(Correction process execution timing)
When the ambient temperature of the image forming apparatus is different, for example, when the power is turned on in the early morning of winter and when the power is turned on during the summer, the beam pitch at the time of turning on the power may be different. In order to reduce this influence and shorten the correction processing time when the actual print image is output, the above-described beam pitch correction processing may be performed after the power is turned on.

  In addition, a series of beam pitch correction processes are performed immediately before the first output image is formed in one job (from the print image output command to the end of the final print image output), so that the beam from the first output image can be changed. A high-quality output image without pitch deviation can be obtained.

(Summary of Example 1)
As yet another configuration of the pitch correction means for maintaining the correction value (deflection angle of the outgoing beam) in a state where a voltage is always applied, that is, in a state where a drive signal is continuously applied, each is driven by an electric signal.
-Liquid crystal elements-Acousto-optic elements-Electro-optic elements

  In this embodiment, the pitch correction processing is performed by rotating the wedge-shaped prisms 28a and 28b. However, as another configuration, the cylindrical lens 13 is shifted / rotated, the coupling lenses 28a and 28b, and the semiconductor laser. You may employ | adopt the structure etc. which shift the relative position with 11a, 11b.

  In this embodiment, an example in which two laser beams are emitted from the light source unit 41 has been described. However, when three or more laser beams are emitted, the above-described beam pitch correction processing is performed based on each beam pitch. By executing, the same effect as in the present embodiment can be obtained.

As described above, in the multiple beam scanning apparatus that corrects the beam pitch using the beam pitch correction processing method described in the present embodiment, it is possible to realize multiple beam scanning with suppressed beam pitch deviation.
In addition, in the image forming apparatus provided with the above-described multiple beam scanning device, a high-quality output image without beam pitch deviation can be obtained.

  Further, according to the present embodiment, the beam pitch correction process can be completed in a shorter time than the conventional method by performing the pitch detection process and the correction data derivation process during the pitch correction process.

  Further, according to the present embodiment, since beam deflection is performed using a liquid crystal element, an acousto-optic element, or an electro-optic element, beam pitch correction can be performed with a small size / light weight, low power consumption, and no noise.

  In addition, according to the present embodiment, it is possible to eliminate the influence of the scanning position shift caused by the tilting of the polygon mirror reflecting surface and perform highly accurate beam pitch correction.

  In addition, according to the present embodiment, since the beam pitch correction processing is performed after the power is turned on, the influence of the installation environment / aging change of the apparatus is reduced, and the beam pitch correction processing time at the time of printing the first sheet after the power is turned on is reduced. It becomes possible to shorten.

  Further, according to the present embodiment, since the beam pitch correction process is performed before the image formation, it is possible to ensure the quality of the first print output image when outputting a plurality of prints.

  Hereinafter, Example 2 of the present invention will be described. The configuration and operation of this example are the same as those of Example 1 unless otherwise specified.

In the first embodiment, the configuration in which the wedge-shaped prisms 28a and 28b are driven by the stepping motor as the pitch correction unit has been described above.
When the lead screw type stepping motor shown in FIG. 5 is used as an actuator, it is not always necessary to keep a signal input state in order to maintain the adjustment value, and it is sufficient to input a signal only during the pitch correction process A4.

  In the present embodiment, a piezoelectric element is used as an actuator for driving the wedge-shaped prisms 28a and 28b. The wedge-shaped prisms 28a and 28b can be rotated using the displacement of the piezoelectric element.

  As is well known, piezoelectric elements are classified into a laminated type, a bimorph type, and the like, but any type can obtain a large generated force with a low driving voltage. In addition, a minute displacement of several tenths to several tens of μm can be achieved with high resolution by the configuration of the piezoelectric element.

On the other hand, the piezoelectric element has a problem in that the linearity of displacement with respect to voltage is poor (hysteresis or the like) due to its characteristics, and even if the applied voltage is fixed, creep occurs and the amount of displacement changes.
However, when the beam pitch correction process shown in FIG. 9B is performed, the correction value is maintained in a state where a voltage is constantly applied, that is, in a state where a drive signal is continuously applied (wedge-shaped prisms 28a, 28b). Therefore, even if the above hysteresis and creep occur, there is no problem in practical use.

As described above, according to the present embodiment, the optical scanning device realizes a multiple beam scanning with suppressed beam pitch deviation even when the optical scanning device has a piezoelectric element as an actuator for driving the wedge-shaped prisms 28a and 28b. can do.
In addition, in the image forming apparatus provided with the above-described multiple beam scanning device, a high-quality output image without beam pitch deviation can be obtained.

  Further, according to the present embodiment, there is no demerit when performing continuous feedback correction.

  Further, according to the present embodiment, since the optical element is driven using the piezoelectric element, it is possible to easily correct the beam pitch with high resolution.

  Hereinafter, Example 3 of the present invention will be described. The configuration and operation in this example are the same as those in Example 1 or Example 2 unless otherwise specified.

FIG. 10 is a diagram showing a configuration of an image forming apparatus (4-drum tandem type image forming apparatus) in Embodiment 3 of the present invention.
As shown in FIG. 10, the image forming apparatus includes a cylindrical lens 13, a polygon mirror (deflector) 14, a scanning optical system (scanning means) 15, and photosensitive drums (scanned surfaces) 16K, 16Y, and 16C. 16M, a pitch detection sensor (pitch detection means) 19, wedge-shaped prisms 40b to 40d, light source portions 22a to 22d, a transfer belt 31, and a color misregistration detection sensor 32.

In the image forming apparatus according to the present exemplary embodiment, for example, four photosensitive drums are arranged in the conveyance direction of the recording paper, and a plurality of light source units 22a and 22b respectively corresponding to the photosensitive drums 16K, 16Y, 16C, and 16M. , 22c, and 22d are simultaneously exposed to light to form latent images on the photosensitive drums 16K, 16Y, 16C, and 16M. These latent images are yellow (Y), magenta (M), cyan (C), Visible images are formed by developing units using developers of different colors such as black (K), and these visible images are sequentially superimposed and transferred onto the same recording paper to obtain a color image.
Further, the image forming apparatus in this embodiment may be a color image forming apparatus (for example, a 4-drum tandem system) such as a digital copying machine or a laser printer.
The 4-drum tandem system is advantageous for high-speed printing because it can output color and monochrome at the same speed as the 1-drum system.

  When writing is performed simultaneously on each of the photosensitive drums 16K, 16C, 16M, and 16Y with multiple beams, the rotation of the polygon mirror 14 and the feed speed of the photosensitive drums 16K, 16C, 16M, and 16Y are generally asynchronous, so the principle Therefore, the scanning position deviation for one scanning at maximum occurs in the sub scanning direction. This is one cause of color misregistration between the photosensitive drums 16K, 16C, 16M, and 16Y.

  According to the present invention, in an optical scanning device that scans laser beams (total of 8 beams) emitted from four light source units by a deflecting unit (polygon mirror) 14 and exposes a plurality of photosensitive drums 16, the light source unit In the optical path from 22a to 22d to the deflecting means 14, at least one wedge-shaped prism 40 (three in this embodiment, wedge-shaped prisms 40b to 40d) is provided, and each wedge-shaped prism is rotated about the optical axis. It is characterized by having a writing start position correcting means for making the beam spot position in the sub-scanning direction variable by adjusting.

The principle of correcting the sub-scanning beam spot position by the wedge-shaped prisms 40b to 40d is the same as that of the wedge-shaped prisms 28a and 28b of the first embodiment.
That is, by rotating the wedge-shaped prisms 40b to 40d about the optical axis, the incident beam can be deflected in the sub-scan section, and as a result, the scanned surface (photosensitive drums 16K, 16C,. 16M, 16Y) the sub-scanning beam spot position can be varied.

Further, three color misregistration detection toner images 33 are formed on the transfer belt 31. Each color misregistration detection toner image 33 is a toner image (YMCK) formed by each irradiation light from the light source units 22a to 22d.
The color misregistration detection sensor 32 detects each position of the color misregistration detection toner image 33 formed on the transfer belt 31.
The wedge-shaped prisms 40b to 40d are driven based on the detection result of the color misregistration detection sensor 32, and perform a series of beam pitch correction processes shown in FIG.
As a result, it is possible to reduce color misregistration when transferring toner images developed on the photosensitive drums 16Y, 16C, and 16M.

  As described above, according to the present embodiment, it is possible to provide a multiple beam scanning apparatus capable of optical scanning without a beam pitch deviation.

  Further, according to the present embodiment, it is possible to provide an image forming apparatus capable of obtaining a print output image with no beam pitch deviation.

  The above arithmetic processing is executed by a computer program included in the image forming apparatus. The above program is recorded on a recording medium such as an optical recording medium, a magnetic recording medium, a magneto-optical recording medium, or a semiconductor, and The recording medium may be loaded from a recording medium, or may be loaded from an external device connected via a predetermined network.

  The above-described embodiment is an example of a preferred embodiment of the present invention. The embodiment of the present invention is not limited to this embodiment, and various modifications may be made without departing from the scope of the present invention. Is possible.

It is a figure which shows the structure of the optical scanning device in Example 1 of this invention. It is the simplified top view which shows the structure of the optical scanning device in Example 1 of this invention. It is a figure which shows the structure of the light source part in Example 1 of this invention. (A) is a schematic diagram of optical path deflection by a wedge-shaped prism in the main scanning section in Embodiment 1 of the present invention, and (b) is a schematic diagram of optical path deflection by a wedge-shaped prism in a plane parallel to the scanned surface. FIG. It is a figure which shows an example of the adjustment mechanism which rotates the wedge-shaped prism in Example 1 of this invention around a rotating shaft. It is a figure which shows the other example of the adjustment mechanism which rotates the wedge-shaped prism in Example 1 of this invention around a rotating shaft, Comprising: It is the figure which looked at the adjustment mechanism of the other example from the optical axis direction. It is a figure which shows the other example of the adjustment mechanism which rotates the wedge-shaped prism in Example 1 of this invention around a rotating shaft, Comprising: It is the figure which looked at the adjustment mechanism of the other example from the subscanning direction. It is a figure which shows a series of correction | amendment processes by the optical scanning device in Example 1 of this invention. (A) is a figure which shows the comparative example with respect to the beam pitch correction process by the optical scanning device in Example 1 of this invention, (b) is a figure which shows the beam pitch correction process in Example 1 of this invention. . It is a figure which shows the structure of the image forming apparatus in Example 3 of this invention.

Explanation of symbols

11a, 11b Semiconductor laser 12a, 12b Coupling lens 13 Cylindrical lens 14 Polygon mirror 15 Scanning optical system 16, 16K, 16C, 16M, 16Y Photosensitive drum 18 Optical scanning device 19 Pitch detection sensor 21a, 21b Laser beams 22a-22d, 41 Light source unit 28a, 28b, 40, 40b to 40d Wedge shaped prism 31 Transfer belt 32 Sensor for color misregistration detection 33 Toner image for color misregistration detection 43 Base member 55 Prism cell

Claims (21)

A laser beam emitted from each of a plurality of laser light sources is periodically deflected by a deflector, and a uniformly charged surface to be scanned in a scanned medium that moves in the sub-scanning direction is orthogonal to the sub-scanning direction. An optical scanning device that scans in a scanning direction and forms an electrostatic latent image on the surface to be scanned,
Pitch detection means for detecting a plurality of beam intervals irradiated in the scan surface direction N times;
First computing means for estimating a true value of the plurality of beam intervals based on the plurality of beam intervals detected by the pitch detection means;
Second calculation means for calculating a correction value of the plurality of beam intervals based on an estimated value of the plurality of beam intervals by the first calculation means and a target value of the plurality of beam intervals;
Pitch correction means for correcting the plurality of beam intervals based on the correction value calculated by the second calculation means;
Multiple beam interval detection operation by the pitch detection means, multiple beam interval estimation operation by the first calculation means, multiple beam interval correction value calculation operation by the second calculation means, multiple beams by the pitch correction means The interval correction operation is repeated in order,
At least one of the multiple beam interval detection operation, the multiple beam interval estimation operation, and the multiple beam interval correction value calculation operation is performed simultaneously with the multiple beam interval correction operation. Optical scanning device. A laser beam emitted from each of a plurality of laser light sources is periodically deflected by a deflector, and a uniformly charged surface to be scanned in a scanned medium that moves in the sub-scanning direction is orthogonal to the sub-scanning direction. An optical scanning device that scans in a scanning direction and forms an electrostatic latent image on the surface to be scanned,
Pitch detection means for detecting a plurality of beam intervals irradiated in the scan surface direction N times;
First computing means for estimating a true value of the plurality of beam intervals based on the plurality of beam intervals detected by the pitch detection means;
Second calculation means for calculating a correction value of the plurality of beam intervals based on an estimated value of the plurality of beam intervals by the first calculation means and a target value of the plurality of beam intervals;
Pitch correction means for correcting the plurality of beam intervals based on the correction value calculated by the second calculation means;
Multiple beam interval detection operation by the pitch detection means, multiple beam interval estimation operation by the first calculation means, multiple beam interval correction value calculation operation by the second calculation means, multiple beams by the pitch correction means The interval correction operation is repeated in order,
The optical scanning device according to claim 1, wherein when the deviation between the estimated value and the target value is smaller than a predetermined value, the multiple beam interval detection operation is executed after the multiple beam interval correction operation is completed. The pitch correction means is
3. The optical scanning device according to claim 1, wherein a signal indicating the correction value is constantly input from the second calculation unit when the correction operation of the plurality of beam intervals is performed. The pitch correction means includes
4. The optical scanning device according to claim 3, wherein the optical scanning device is an optical element that is rotated or displaced by a piezoelectric element that is deformed by an electric signal. The pitch correction means includes
4. The optical scanning device according to claim 3, wherein the optical scanning device is a liquid crystal element driven by an electric signal. The pitch correction means includes
4. The optical scanning device according to claim 3, wherein the optical scanning device is an acousto-optic element driven by an electrical signal. The pitch correction means includes
4. The optical scanning device according to claim 3, wherein the optical scanning device is an electro-optical element driven by an electric signal. The first calculation means includes
3. The true value of the plurality of beam intervals is estimated based on the interval between the plurality of beams deflected by a specific reflecting surface in the polarizer, which is detected by the pitch detection unit. The optical scanning device described. An image forming apparatus that transfers a latent image formed on the surface to be scanned to a medium for recording an image, and prints it out.
An image forming apparatus comprising the optical scanning device according to claim 1.   The image forming apparatus according to claim 9, wherein the detecting operation of the plurality of beam intervals is started after power is supplied to the apparatus.   The detection operation of the plurality of beam intervals, the estimation operation of the plurality of beam intervals, the calculation operation of the correction value of the plurality of beam intervals, and the correction operation of the plurality of beam intervals are the first output in one job of the print output operation The image forming apparatus according to claim 9, wherein the image forming apparatus is executed immediately before an image is formed. A laser beam emitted from each of a plurality of laser light sources is periodically deflected by a deflector, and a uniformly charged surface to be scanned in a scanned medium that moves in the sub-scanning direction is orthogonal to the sub-scanning direction. A beam interval correction method using an optical scanning device that scans in a scanning direction and forms an electrostatic latent image on the surface to be scanned,
A pitch detection step in which the pitch detection means for detecting the laser beam detects a plurality of beam intervals irradiated in the scanning surface direction N times;
A first calculation step of calculating a first value of the plurality of beam intervals based on the plurality of beam intervals detected in the pitch detection step;
A second calculation means for executing calculation processing calculates the correction value for the plurality of beam intervals based on the estimated value for the plurality of beam intervals calculated in the first calculation step and the target value for the plurality of beam intervals. A second computing step to perform,
A correction unit that corrects the traveling direction of the laser beam has a pitch correction step of correcting the plurality of beam intervals based on the correction value calculated by the second calculation step;
The pitch detection step, the first calculation step, the second calculation step, and the pitch correction step are repeated in order,
A beam interval correction method, wherein at least one of the pitch detection step, the first calculation step, and the second calculation step is performed simultaneously with the pitch correction step. A laser beam emitted from each of a plurality of laser light sources is periodically deflected by a deflector, and a uniformly charged surface to be scanned in a scanned medium that moves in the sub-scanning direction is orthogonal to the sub-scanning direction. A beam interval correction method using an optical scanning device that scans in a scanning direction and forms an electrostatic latent image on the surface to be scanned,
A pitch detection step in which the pitch detection means for detecting the laser beam detects a plurality of beam intervals irradiated in the scanning surface direction N times;
A first calculation step of calculating a first value of the plurality of beam intervals based on the plurality of beam intervals detected in the pitch detection step;
A second calculation means for executing calculation processing calculates the correction value for the plurality of beam intervals based on the estimated value for the plurality of beam intervals calculated in the first calculation step and the target value for the plurality of beam intervals. A second computing step to perform,
A correction unit that corrects the traveling direction of the laser beam has a pitch correction step of correcting the plurality of beam intervals based on the correction value calculated by the second calculation step;
The pitch detection step, the first calculation step, the second calculation step, and the pitch correction step are repeated in order,
When the deviation between the estimated value and the target value is smaller than a predetermined value, the pitch detection step is executed after the pitch correction step is completed. The pitch correction step includes
14. The beam interval correction method according to claim 12, wherein the correction unit corrects the plurality of beam intervals based on a signal indicating the correction value that is constantly input from the second calculation unit. The pitch correction step includes
15. The correction unit according to claim 14, wherein an optical element that is rotated or displaced by a piezoelectric element that is deformed by an electric signal adjusts the traveling direction of the laser light to correct the plurality of beam intervals. Beam spacing correction method. The pitch correction step includes
The beam interval correction method according to claim 14, wherein a liquid crystal element driven by an electric signal adjusts the traveling direction of the laser light to correct the plurality of beam intervals as the correction unit. The pitch correction step includes
The beam interval correction method according to claim 14, wherein an acousto-optic element driven by an electric signal adjusts the traveling direction of the laser light as the correction unit to correct the plurality of beam intervals. The pitch correction step includes
15. The beam interval correction method according to claim 14, wherein as the correction means, an electro-optical element driven by an electric signal adjusts the traveling direction of the laser light to correct the plurality of beam intervals. The first calculation step includes
The first calculation step estimates the true value of the plurality of beam intervals based on the intervals of the plurality of beams deflected by a specific reflecting surface in the polarizer detected in the pitch detection step. The beam interval correction method according to claim 12 or 13, characterized in that: The pitch detection step includes
A latent image formed on the surface to be scanned, on which the optical scanning device is installed, is transferred to a medium for recording an image, and after turning on the power to the image forming device for printing out, the plurality of beam intervals are set. The beam interval correction method according to claim 1, wherein detection is performed.   The pitch detection step, the first calculation step, the second calculation step, and the pitch correction step are performed immediately before the first output image is formed in one job of the print output operation by the image forming apparatus. 21. The beam interval correction method according to claim 1, wherein the beam interval correction method is performed.

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