JP2004212485A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner and an image forming apparatus capable of adjusting beam positions on a surface to be scanned without having effect on various optical characteristics, in a multi-beam scanner for adjusting the beam positions on the surface to be scanned using liquid crystal elements and an image forming apparatus using the same. <P>SOLUTION: The optical scanner for scanning the surface to be scanned with N pieces (N≥2) of light beams emitted from a light source; the scanner is provided with a plurality of means for adjusting the scanning line positions of a plurality of the light beams 21a, 21b, and at least one of the plurality of means is liquid crystal elements 40a, 40b driven by an electric signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device (multi-beam scanning device) that simultaneously scans a surface to be scanned with a plurality of light beams emitted from a light source, a laser printer using the optical scanning device in an optical writing system, and digital copying. And an image forming apparatus such as a laser facsimile, a laser plotter, and the like.
[0002]
[Prior art]
In an optical scanning device used in an optical writing system of an image forming apparatus, as a means for improving a recording speed, there is a method for increasing a rotation speed of a polygon mirror serving as a deflecting unit. However, this method has limitations due to problems such as motor durability, noise, vibration, and laser modulation speed. Therefore, there has been proposed an optical scanning device (multi-beam scanning device) for simultaneously recording a plurality of lines by scanning a plurality of light beams at a time (for example, see Patent Documents 1, 2, and 3).
As a method of a multi-beam light source device which is used as a light source means of this optical scanning device (multi-beam scanning device) and emits a plurality of light beams, for example, a multi-beam semiconductor having a plurality of light-emitting points (light-emitting channels) in one package Although there is a method using a laser (for example, a semiconductor laser array), it is difficult to increase the number of channels due to a manufacturing process of the semiconductor laser array, and it is difficult to eliminate the influence of thermal / electrical crosstalk. It is currently recognized as an expensive light source because it is difficult and it is difficult to shorten the wavelength.
[0003]
On the other hand, single-beam semiconductor lasers are still relatively easy to reduce the wavelength even at present, can be manufactured at low cost, and are widely used in various industrial fields. Many proposals have been made on a multi-beam scanning apparatus that combines a single beam semiconductor laser or the above-described multi-beam semiconductor laser as a light source and combines a plurality of light beams using a beam combining unit.
However, in comparison with the method using a semiconductor laser array as the light source means, the method of combining a plurality of light beams using the beam combining means has a problem in that the beam on the surface to be scanned is affected by environmental fluctuation / time-dependent fluctuation. The problem that the spot arrangement (beam pitch; scanning line interval) fluctuates easily occurs.
Therefore, a liquid crystal element driven by an electric signal is disposed at or immediately after the light source section, and the light beam is deflected by a very small angle (several minutes to several tens of minutes) according to the electric signal, thereby performing scanning. A method of correcting a beam spot arrangement on a surface has been proposed (for example, see Patent Documents 4 and 5).
[0004]
Here, the liquid crystal element will be described.
A liquid crystal element used as an optical path deflecting element has a structure in which a nematic liquid crystal layer having a homogeneous molecular arrangement is sandwiched between two glass substrates, and a metal oxide transparent electrode is formed inside the glass substrate. Normally, a uniform electrode for forming an electric ground plane is formed over the entire surface on one side, for example, the lower surface of the glass substrate, and an electrode for giving a necessary electric field distribution to the liquid crystal layer is formed on the other (upper surface). A pattern is formed. When a driving AC voltage (for example, a rectangular wave of several kilohertz) is applied, nematic liquid crystal molecules having a birefringence (difference between the major axis and the minor axis of the molecule) tilt along the electric field. That is, for monochromatic light having linearly polarized light parallel to the liquid crystal molecules (the direction of the long axis), the liquid crystal layer becomes equivalent to a medium having a locally different refractive index distribution according to the electric field distribution. Therefore, the wavefront of the light transmitted through the liquid crystal is subjected to spatial wavefront modulation or phase modulation according to the in-plane distribution of the voltage applied to the liquid crystal.
[0005]
The shape of the electro-optical characteristics is determined from the elastic constant of the liquid crystal used, the dielectric anisotropy, and the initial orientation angle of the liquid crystal molecules when no voltage is applied. A liquid crystal element having a small initial alignment angle (5 degrees or less) shows a sharp fall (threshold) in a low voltage region of the electro-optical characteristics, but shows a nearly linear response as the voltage increases, It shows characteristics that saturate to a constant value. On the other hand, in a liquid crystal element having a large initial alignment angle, the threshold value disappears, and a characteristic in which a curve in a low voltage region can be approximated by a square curve.
As an electrode pattern on the upper surface, there has been proposed an electrode design in which a large number of strip-shaped elongated electrodes are arranged and a predetermined voltage is applied to each of the electrodes. This structure has features that can realize high-speed response, high spatial resolution, and freedom of wavefront modulation (arbitrarily complicated wavefront modulation as well as beam deflection and lens functions).
[0006]
When an optical path deflecting element is configured by a liquid crystal element, the liquid crystal element uses a ladder-type electrode structure using a linear characteristic region of the electro-optical characteristics of the liquid crystal. Stripe-shaped elongated transparent electrodes are formed in the beam irradiation area of the liquid crystal element with a line width and an interval determined by the resolution (about 1 μm) of the current exposure technology. Both ends of this striped electrode are connected to two laterally extending inclined potential electrodes outside the irradiation area, so that a ladder-type electrode is arranged as a whole. The number (width) of the bundled elongated electrodes is determined by the maximum beam deflection angle required in that area.
When two different voltages selected from the linear region of the electro-optical characteristics are applied to both ends of the inclined potential electrode extending in the horizontal direction, a blazed phase profile is obtained, which is equivalent to a microprism array. By changing the blaze angle by controlling the applied voltage, it is possible to control the direction of the light beam that is perpendicularly incident on the liquid crystal layer.
[0007]
[Patent Document 1]
JP 2000-227563 A
[Patent Document 2]
JP-A-10-215351
[Patent Document 3]
JP-A-9-189873
[Patent Document 4]
JP 2000-3110A
[Patent Document 5]
JP 2000-47214 A
[0008]
[Problems to be solved by the invention]
When a liquid crystal element is used as an optical path deflecting element, it is necessary to give a necessary electric field distribution to the liquid crystal layer and form a linear refractive index distribution (refractive index gradient) as described above. On the other hand, when it is desired to increase the beam deflection angle (maximum deflection angle), it is necessary to increase the thickness of the liquid crystal layer. For example, when securing a liquid crystal layer thickness of more than 10 μm, the versatility of a spherical spacer member (typically about 5 μm in a liquid crystal monitor or the like) dispersed in the liquid crystal layer is poor, and the degree of variation in diameter is small. That is, it is necessary to use a spacer member having a low grade. As a result, it is difficult to ensure a uniform thickness of the liquid crystal layer, and it is difficult to maintain the linearity of the refractive index distribution in the liquid crystal layer.
[0009]
The present invention has been made in order to solve the problems of the conventional technology as described above, and is directed to a multi-beam scanning apparatus that adjusts a beam position on a surface to be scanned using a liquid crystal element and an image forming apparatus using the same. It is another object of the present invention to provide an optical scanning device and an image forming apparatus which can adjust a beam position on a surface to be scanned without affecting various optical characteristics.
[0010]
[Means for Solving the Problems]
The invention according to claim 1 is an optical scanning device that scans a surface to be scanned with N (N ≧ 2) light beams emitted from a light source, wherein the plurality of light beams adjust a scanning line position of the plurality of light beams. Means, wherein at least one of the plurality of means is a liquid crystal element driven by an electric signal.
[0011]
According to a second aspect of the present invention, in the first aspect, a memory means for storing an electric signal for driving the liquid crystal element is further provided.
[0012]
According to a third aspect of the present invention, in the second aspect of the present invention, the initial adjustment of the scanning line position is performed by an electric signal stored in the memory means.
[0013]
According to a fourth aspect of the present invention, in the first aspect of the present invention, the liquid crystal element corrects a change in the position of the light beam due to the influence of disturbance.
[0014]
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the liquid crystal element has a function of deflecting the optical path of the light beam by a small angle.
[0015]
According to a sixth aspect of the present invention, in the first aspect of the present invention, the liquid crystal element is disposed in an optical path of at least “N−1” light beams among the N light beams. It is characterized by having.
[0016]
According to a seventh aspect of the present invention, when the maximum value of the optical path deflection angle by the liquid crystal element is θ, θ is within ± 4.0 (minutes).
[0017]
The invention according to claim 8 is the invention according to claim 7, wherein the liquid crystal element is disposed in the optical path of the N light beams, and θ is within ± 2.0 (minutes).
[0018]
According to a ninth aspect of the present invention, there is provided an apparatus for performing optical writing on a scanned surface from an optical scanning device having a liquid crystal element for adjusting a scanning line position, and forming an electrostatic latent image on the scanned surface by an electrophotographic process. Wherein the optical scanning device is the optical scanning device according to any one of claims 1 to 8.
[0019]
According to a tenth aspect of the present invention, in the ninth aspect, the liquid crystal element is capable of converting a pixel density in the sub-scanning direction.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described with reference to the drawings.
[0021]
FIG. 1 is a diagram showing an embodiment of an optical scanning device according to the present invention, and is a perspective view showing an optical arrangement.
The optical scanning device 20 is a device that scans a light beam (laser beam) emitted from a light source on a surface to be scanned as a light spot, and includes a light source unit 22 having a light source, a cylindrical lens 13, and a polygon serving as a deflector. It has a mirror 14, a scanning optical system 15 composed of two plastic scanning lenses and one folding mirror 18, and a photosensitive drum 16 whose surface is the surface to be scanned.
Although FIG. 1 shows an example of a two-beam optical scanning device that simultaneously scans two light beams, the optical scanning device according to the present invention is a multi-beam optical scanning device that scans a larger number of light beams. It can be deployed in a scanning device.
[0022]
FIG. 2 is an explanatory diagram illustrating the configuration of the light source unit 22. The light source unit 22 includes semiconductor lasers 11a and 11b, which are light sources fixed to a common base member 43, and corresponding coupling lenses 12a and 12b. The semiconductor lasers 11a and 11b are fixed to the base member 43 by press fitting. On the other hand, the coupling lenses 12a and 12b are fixed to the base member 43 by bonding. At this time, the coupling lenses 12a and 12b are coupled in accordance with the characteristics of the light beam emitted from the coupling lens, that is, the collimating property and the direction of the emitted optical axis. The fixed position of the ring lens is adjusted.
[0023]
In FIG. 2, a configuration is adopted in which the two light beams 21a and 21b intersect each other near the deflection reflection surface of the polygon mirror 14 in the main scanning cross section. By adopting such a configuration, it is possible to suppress the deviation of the optical characteristics between the two light beams due to the difference between the reflection points on the polygon mirror 14, that is, the occurrence of an imaging position, a magnification, and the like. Become. Here, a direction in which the beam spot is scanned on the surface to be scanned is defined as a main scanning direction, and a direction orthogonal to the main scanning direction is defined as a sub-scanning direction.
[0024]
Light beams emitted from the semiconductor lasers 11a and 11b are coupled by coupling lenses 12a and 12b, respectively, to become light beams 21a and 21b. The two light beams 21a and 21b are converged only in the sub-scanning direction on the deflecting and reflecting surface of the polygon mirror 14 by the action of the cylindrical lens 13 to form an image as a long linear image in the main scanning direction. The surface of the photosensitive drum 16, that is, the surface to be scanned is scanned as a beam spot by the lens 15.
[0025]
In an optical scanning device (multi-beam scanning device), the “light beam position” is used for the initial adjustment of the scanning line position (light beam position) and the beam spot interval of the light beam on the surface to be scanned, and the correction of environmental / temporal variations. Correction means "are often provided. Here, a configuration example of a mechanical “light beam position correcting unit” will be described.
[0026]
FIG. 3 is an optical arrangement diagram showing a schematic configuration of the optical scanning device 20 housed in the optical housing 53 and developed in a plane parallel to the deflection rotation surface. FIG. FIG. 4 is an explanatory diagram showing a method of attaching the light source unit 22. As shown in FIG. 4, the light source unit 22 is fixed by being screwed into insertion holes 55 provided in a side wall 54 of the optical housing 53 by a pair of screws 45. At this time, by rotating the circular protruding portion 22a of the light source unit 22 in the circular mounting hole 54a formed in the side wall 54, in the γ direction indicated by the arrow in FIG. The rotation (hereinafter, this rotation is referred to as “γ rotation”) is adjusted. Since the two light beams 21a and 21b are non-parallel to each other as described above, by rotating the light source unit 22 by γ, the relative optical axis direction in the sub-scanning direction between the two beams can be changed. . As a result, it becomes possible to correct the light beam position and the beam spot interval on the surface to be scanned.
[0027]
However, when the light source unit 22 is fixed to the side wall 54 of the optical housing 53 with the screws 45 after the γ rotation, the adjustment amount of the γ rotation is deviated due to a rotation torque by a fastening tool such as a screw driver when the screw is fixed. It often happens. For this reason, conventionally, it is necessary to repeat the process of “adjustment → screw fastening” a plurality of times by trial and error, and a desired adjustment value may not be obtained within the finally required adjustment time. there were.
[0028]
Therefore, in the optical scanning device according to the present invention, the light beam position, that is, the scanning position is corrected by using the liquid crystal element 40 driven by an electric signal, separately from the mechanical “light beam position correcting unit”. did. That is, if the liquid crystal element 40 having the function of deflecting the exit direction of the incident light beam by a small angle (about several mrads) is used, the distance between the coupling lenses 12a and 12b and the cylindrical lens 13 shown in FIG. Since the liquid crystal element 40 can be disposed at an arbitrary position, the degree of freedom of mechanical layout design in the optical housing 53 can be increased.
[0029]
here,
Set the focal length of the coupling lens to Fcol [mm].
The sub-scanning magnification of the entire optical system of the optical scanning device is m [times]
The optical path deflection angle (in the sub-scan section) of the liquid crystal element is θ [rad].
The amount of beam position variation (adjustment) on the non-scanning surface is z [mm]
Then
z = m × Fcol × θ
There is a relationship. Therefore, for example, in the case of an optical scanning device (optical system) with Fcol = 15 [mm] and m = 10 [times], to adjust with a resolution of Δz = 0.001 [mm] = 1 [μm]
Δθ = z / Fcol × m
= 0.001 / 15 × 10
= 6.7 × 10 ^-6 [Rad] = 6.7 [μrad]
Only the light path may be deflected by the liquid crystal element 40.
[0030]
As described above, the liquid crystal element can drive a rectangular AC voltage of about several kilohertz as a drive signal, but by changing its effective voltage with respect to a reference input signal pulse, the emission direction of the light beam incident on the liquid crystal element can be changed. It is possible to deflect, that is, to deflect the optical path. FIG. 8A is an explanatory diagram illustrating beam deflection due to modulation of an input signal pulse, and FIG. 8B is an explanatory diagram illustrating an example of a reference input signal pulse.
Here, as a general method of changing the effective voltage, a method of changing the pulse width (duty) (W → W ′) as shown in FIG. 8C and a method of changing the pulse width (duty) as shown in FIG. And a method of changing the pulse height (A → A ′). As described above, by changing the effective value of the applied voltage, the refractive index gradient in the liquid crystal layer, that is, the optical path deflection angle can be controlled.
[0031]
For example, when the effective value is changed by changing the pulse height of the applied voltage, a liquid crystal element that can obtain an optical path deflection angle of 3.0 [mrad] at an effective voltage of 2.0 volts has 10 bits (= 1024 floors). By modulating the pulse height by the converter of (g.), 2.0 [V] / 1024 gradation = 1.95 [mV / gradation] and 3.0 [rad] / 1024 gradation = 2.93. An optical path deflection of [μrad] (0.44 [μm] in terms of the beam position on the surface to be scanned of the optical system described above) can be easily achieved.
[0032]
Therefore, the adjustment of the light beam position (beam spot interval) by the mechanical γ rotation of the light source unit 22 described above is applied as a coarse adjustment, and the adjustment by the liquid crystal element is used as the fine adjustment. Can be achieved reliably. Therefore, a memory means for storing an electric signal for driving the liquid crystal element is provided in the optical scanning device, and a drive voltage (effective value), which is an electric signal used for the fine adjustment, is stored in this memory means. According to this configuration, the desired light beam position can be reproduced by calling the main drive voltage from the memory unit at the time of use at the user after shipment from the factory, for example, at the time of initial setting. The frequency of position adjustment can be reduced.
[0033]
In the case of the light source unit 22, the two sets of semiconductor lasers 11a and 11b and the coupling lenses 12a and 12b are fixed to a common base member 43, but the coupling lenses 12a and 12b are made of an adhesive (with a thickness of several tens of (Several hundred μm), the relative positional relationship between the semiconductor laser and the coupling lens may fluctuate, for example, due to disturbance after factory shipment. Here, the “disturbance” refers to an influence on the position of the light beam on the surface to be scanned, such as a change with time after assembly adjustment, vibration during machine transport / installation, or a change in temperature / humidity during use at the user's site. Refers to the effect (cause).
If the relative positional relationship between the semiconductor laser and the coupling lens, especially the relative positional relationship in the sub-scan section, changes, the light beam position on the surface to be scanned changes, and the distance between the two beams, that is, the scanning line interval May fluctuate to cause deterioration of the output image.
Thus, by applying the above-described liquid crystal element, it is possible to correct the fluctuation of the light beam position (scanning line interval) on the surface to be scanned due to the influence of disturbance, and to maintain the light beam position with high accuracy.
[0034]
In the embodiment described above, a liquid crystal element is disposed in the optical path of each light beam, that is, the number of liquid crystal elements is set to N for the number of beams N. A liquid crystal element may be provided in an optical path other than the light beam, that is, the number of liquid crystal elements may be N−1 for the number of beams N, and the alignment with the reference light beam may be performed. By doing so, the number of liquid crystal elements can be reduced.
[0035]
In order to determine the correction amount of the light beam position, a light beam position detection sensor may be provided in the optical scanning device or the image forming device, or if it can be derived by design / experiment, A correction table storing the data of the correction amount may be prepared, and the correction amount may be determined based on this data.
[0036]
FIG. 5 is an exploded perspective view of a light source device that emits four beams. In this light source device, a first light source unit 41 and a second light source unit 42 having the same configuration as the light source unit 22 shown in FIG. 2 and two beams emitted from the light source units 41 and 42 are combined adjacently. And a holding member (flange) 44 for integrally holding the light source units 41 and 42 and the beam combining prism 17. In the light source device having such a configuration, the relative posture of the first light source unit 41 and the second light source unit 42 changes in the sub-scanning cross section, and as a result, the two beams emitted from the light source unit 41 There is a possibility that the relative positional relationship between the two beams emitted from the light source unit 42 and the light source unit 42 may fluctuate significantly due to a change over time or a change in temperature / environment.
In the case of a light source device having such a configuration, as shown in FIG. 6A, a configuration in which a liquid crystal element 40 is added to the conventional light source device shown in FIG. FIG. 6 (b) shows only the main optical elements of FIG. 6 (a).
[0037]
FIG. 7 is an explanatory diagram illustrating a configuration example (six examples) of the liquid crystal element 40 illustrated in FIG. FIGS. 7A and 7C are examples in which a liquid crystal element or an effective area is provided for four light beams, and the remaining four examples are liquid crystal elements for at least three light beams. This is an example in which elements or effective areas are provided. That is, this is an example in the case where the number of light beams N = 4. Here, the effective area is each divided part obtained by dividing the light transmitting part of the liquid crystal element, and each effective area is independently driven and controlled.
[0038]
The respective configurations of FIGS. 7A to 7F are as follows.
(A): One liquid crystal element 40 having four effective areas (a1) to (a4) is provided corresponding to four light beams.
(B): One liquid crystal element 40 having three effective areas (b2) to (b4) corresponding to three light beams is provided (one is a reference beam).
(C): Four liquid crystal elements 40a to 40d are fixedly provided on the common holding member 23 in correspondence with the four light beams.
(D): Three liquid crystal elements 40b to 40d are fixed to the common holding member 23 and arranged corresponding to the three light beams (one is a reference beam).
(E): A liquid crystal element having two or two effective areas (e1) and (e2) so that both beams can be independently deflected in correspondence with two beams emitted from the first light source unit 41. Is arranged. Note that no liquid crystal element is provided for the two beams emitted from the second light source unit 42.
(F): One liquid crystal element is provided so as to correspond to two beams emitted from the first light source unit 41 and to be able to deflect both beams at the same deflection angle. Note that no liquid crystal element is provided for the two beams emitted from the second light source unit 42.
[0039]
By using the liquid crystal element having the configuration shown in FIG. 7, the above-described positional fluctuation of the light beam can be corrected.
[0040]
Here, in the multi-beam scanning apparatus using the four-beam light source device shown in FIG. 6A, the "maximum deflection angle" required for the liquid crystal element, that is, the maximum value of the optical path deflection angle in the liquid crystal element will be described. .
For example, in the case of the configuration of the four-beam light source device shown in FIG. 6, the relative optical axis deviation between the two beams emitted from the first light source unit 41 and the two beams emitted from the second light source unit 42, That is, the sub-scanning component of the optical axis fluctuates due to a temporal change or a temperature / environmental change. The relative optical axis deviation between the two beams is called “relative optical axis deviation”. For the base members 43a and 43b and the flange 44, a metal material such as iron, aluminum or zinc, or a resin material having excellent moldability is used industrially, but when a component is processed with such a material, It has been empirically found that a relative optical axis deviation of about ± 2.0 [min] occurs at the maximum.
[0041]
Further, as described with reference to FIG. 2, the present light source device has a configuration in which the coupling lenses 12a and 12b are fixed to the holding member via an adhesive layer having a layer thickness of about several tens μm to several hundreds μm. For this reason, the thickness of the adhesive layer changes due to the influence of thermal expansion or the like based on a change in temperature and humidity, and as a result, the relative optical axis deviation between light beams may fluctuate. Therefore, the liquid crystal element is required to have a maximum deflection angle that at least corrects the relative optical axis shift.
[0042]
On the other hand, as described in the above-mentioned [Problems to be Solved by the Invention], generally, as the "maximum deflection angle" of the liquid crystal element increases, the thickness of the liquid crystal layer needs to be increased. At present, a spacer member for securing a liquid crystal layer thickness of about 10 μm or more is not versatile. If a spacer member having a high grade, that is, a small diameter variation is used, an increase in cost cannot be avoided. Also, as a side effect of increasing the thickness of the liquid crystal layer, variations in the thickness of the liquid crystal layer, the transparent electrode (ITO) film, the alignment film, and the like are caused.
(A) Degradation of linearity of refractive index distribution
(B) Occurrence of transmittance fluctuation due to multiple interference
(C) Deterioration of wavefront aberration
And the like may occur. Therefore, in consideration of cost, performance, yield, and the like in manufacturing a liquid crystal element, it is practically practical to set the maximum deflection angle to about ± 4.0 [minutes].
[0043]
In the case where the liquid crystal element is arranged in the optical path of at least N-1 light beams as shown in FIGS. 7B, 7D, and 7F, the above-mentioned relative optical axis deviation: ± 2.0 [ Minutes] needs to be corrected. Further, in consideration of the adjustment amount at the time of assembly at the factory, the maximum deflection angle of the liquid crystal element is required to be ± 2.5 [min] or less, preferably ± 4.0 [min] or less.
[0044]
On the other hand, when a liquid crystal element is provided in the optical path of N light beams as shown in FIG. 7E, the relative light between the light beams emitted from the first light source unit and the second light source unit Axis deviation: ± 2.0 [minutes] can be corrected in the two effective areas (1) and (2). Therefore, the required maximum deflection angle may be about の of the case shown in FIGS. 7B, 7D, and 7F. That is, the maximum deflection angle of the liquid crystal element is required to be ± 1.5 [min] or less, preferably ± 2.0 [min] or less, by adding the adjustment amount at the time of assembly. Of course, also in the cases shown in FIGS. 7A and 7C, the maximum deflection angle specification can be relaxed similarly to FIG. 7E.
[0045]
By arranging the liquid crystal elements in the optical path of the N light beams in this manner, the number of necessary liquid crystal elements can be increased. However, the required maximum deflection angle can be reduced. It is possible to maintain performance and reduce parts costs.
[0046]
According to the embodiment described above, by limiting the maximum deflection angle of the liquid crystal element to ± 4.0 [min] or less, the beam position adjustment range on the surface to be scanned can be obtained without affecting the optical characteristics. Can be secured.
[0047]
Next, an image forming apparatus according to the present invention will be described.
The image forming apparatus includes an optical scanning device, a charger, a developing device, a transfer device, a fixing device, a photoconductor, and a cleaning unit. An electrostatic latent image is formed on the photoconductor by a photographic method. The principle of image formation by an image forming apparatus is well known, and the photoreceptor is uniformly charged by a charger, and the potential decreases in accordance with the exposure distribution formed by the optical scanning device. An electrostatic latent image is formed, and toner is adhered by a developing device. The toner adhering to the photoreceptor is transferred to a sheet by a transfer unit and then fused and fixed to the sheet by a fixing unit. The cleaning unit removes residual toner on the photoconductor.
[0048]
Here, by applying the optical scanning device according to the present invention described so far as the optical scanning device, the above-described effect, that is, the position of the light beam (beam spot) on the photosensitive member can be changed as necessary. Therefore, a high-quality output image can be obtained. In the case of a multiple beam scanning device that scans multiple beams simultaneously, it is possible to increase the printing speed / density.
[0049]
When the image forming apparatus was used as an actual machine such as a printer or a digital copier, the adjustment was performed in an adjustment process before shipment due to vibration during transportation of the product after shipment from the factory or restrictions on an installation location at a user. The beam spot interval, mainly the interval in the sub-scanning direction, that is, the scanning line interval may vary. In addition, there is a possibility that the scanning line interval may change due to a temporal change during use at the user's site, a temperature environment at the installation location / internal temperature rise during continuous printing, and the like.
In such a case, the image forming apparatus is provided with a detection system for detecting the scanning line interval, thereby detecting the scanning line interval generated due to the above-described cause, and driving the liquid crystal element based on the result to set the scanning line interval. It becomes possible to correct.
[0050]
Note that the liquid crystal element can change the pixel density in the sub-scanning direction. That is, for example, when the image forming apparatus is applied to a multifunction peripheral having both functions of a printer and a copier (copier), a printer mode, that is, a state in which the multifunction peripheral is used as a printer, and a copy mode, that is, the multifunction peripheral is copied. There is a case where the pixel density is switched depending on the state used as a device. For example, the pixel density may be switched to “600 dpi in the printer mode, 400 dpi in the copy mode”. According to the present invention, it is possible to realize a pixel density suitable for each mode.
[0051]
In addition, an operator issues a command for switching pixel density from an operation panel or the like provided in the image forming apparatus, so that “high image quality (1200 dpi) ← → high speed (multiple output sheets) ) (600 dpi) ". In such a case, the pixel density can be easily switched by driving / controlling the optical path deflecting element provided in the image forming apparatus.
[0052]
【The invention's effect】
According to the present invention, it is possible to adjust the beam position on the surface to be scanned without affecting various optical characteristics.
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment of an optical scanning device according to the present invention, and is a perspective view showing an optical arrangement.
FIG. 2 is an exploded perspective view illustrating a configuration of a light source unit included in the optical scanning device.
FIG. 3 is an optical arrangement diagram showing a schematic configuration of the optical scanning device housed in an optical housing, which is developed in a plane parallel to a deflection rotation surface.
FIG. 4 is an exploded perspective view showing a method of attaching a light source unit included in the optical scanning device to a side wall of the optical housing.
FIG. 5 is an exploded perspective view of a light source device that emits four beams, which is an example of a conventional light source device.
6A is an exploded perspective view of a light source device configured by adding a liquid crystal element to the light source device illustrated in FIG. 5, and FIG. 6B is a perspective view illustrating a configuration of only main optical elements.
7 is a perspective view showing various examples of a liquid crystal element added to the light source device shown in FIG.
FIGS. 8A and 8B are diagrams illustrating optical path deflection of a light beam incident on a liquid crystal element, wherein FIG. 8A is an explanatory view illustrating optical path deflection, and FIGS. 8B, 8C, and 8D are electric signals (D) for driving the liquid crystal element. FIG. 6 is a waveform chart showing a change in an effective voltage.
[Explanation of symbols]
11a, 11b Semiconductor laser
12a, 12b coupling lens
13 Cylindrical lens
14 Polygon mirror
15 Scanning optical system
16 Photoconductor drum
17 Beam combining prism
18 Folding mirror
19 Synchronous sensor
20 Optical scanning device
21a, 21b Light beam
22 Light source
23 Holding member
40a, 40b liquid crystal element
41, 42 light source unit
43 Base member
44 Flange
53 Optical housing
54 Side wall

Claims (10)

An optical scanning device that scans a surface to be scanned with N (N ≧ 2) light beams emitted from a light source,
Comprising a plurality of means for adjusting the scanning line position of the plurality of light beams,
An optical scanning device, wherein at least one of the plurality of units is a liquid crystal element driven by an electric signal. 2. The optical scanning device according to claim 1, further comprising memory means for storing an electric signal for driving the liquid crystal element. 3. The optical scanning device according to claim 2, wherein the initial adjustment of the scanning line position is performed by an electric signal stored in the memory means. The optical scanning device according to claim 1, wherein the liquid crystal element corrects a change in a light beam position due to an influence of a disturbance. 5. The optical scanning device according to claim 1, wherein the liquid crystal element has a function of deflecting the optical path of the light beam by a small angle. The optical scanning device according to claim 1, wherein the liquid crystal element is disposed in an optical path of at least “N−1” light beams of the N light beams. When the maximum value of the optical path deflection angle by the liquid crystal element is θ,
θ = ± 4.0 (min)
The optical scanning device according to claim 6, wherein The liquid crystal element is disposed in an optical path of N light beams,
The optical scanning device according to claim 7, wherein θ is within ± 2.0 (minutes). An apparatus for performing optical writing on a scanned surface from an optical scanning device having a liquid crystal element for adjusting a scanning line position, and forming an electrostatic latent image on the scanned surface by an electrophotographic process,
An image forming apparatus, wherein the optical scanning device is the optical scanning device according to any one of claims 1 to 8. The image forming apparatus according to claim 9, wherein the liquid crystal element is capable of changing a pixel density in a sub-scanning direction.

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