JP5233236B2 - Optical scanning device - Google Patents

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device including a liquid lens.

  FIG. 12 is a top view of the optical scanning device 110 provided with a liquid lens. In FIG. 12, the y-axis indicates the main scanning direction, and the z-axis indicates the sub-scanning direction. The z axis also coincides with the vertical direction.

  An optical scanning device 110 illustrated in FIG. 12 is used in, for example, an image forming apparatus, and includes a laser diode 112, a collimator lens 113, a cylindrical lens 118, a polygon mirror 120, and scanning lenses 122 and 124.

  The laser diode 112 emits light. The light emitted from the laser diode 112 is diffused light. The collimator lens 113 collects the light emitted from the laser diode 112 and converts it into substantially parallel light. The cylindrical lens 118 condenses the light that has passed through the collimator lens 113 in the z-axis direction in the vicinity of the mirror surface of the polygon mirror 120.

  The polygon mirror 120 is rotated in the direction of the arrow by a motor (not shown), and deflects the light passing through the cylindrical lens 118 at a constant angular velocity in the y-axis direction. The scanning lenses 122 and 124 scan the light deflected by the polygon mirror 120 at a constant speed in the y-axis direction and form an image of the light on the photosensitive drum 132. The photosensitive drum 132 is driven to rotate at a predetermined speed. As a result, a two-dimensional electrostatic latent image is formed by main scanning with light and sub-scanning with rotation of the photosensitive drum 132.

  However, the optical scanning device 110 has a problem that field curvature occurs on the photosensitive drum 132 due to manufacturing errors of the scanning lenses 122 and 124. Such curvature of field occurs over the entire y-axis direction of the photosensitive drum 132.

  In this field, for example, in Patent Documents 1 to 3, it is proposed to apply a liquid lens capable of changing a focal length to an optical scanning device. In such an optical scanning device, light is detected by a beam detecting means, and the focal length of the liquid lens is changed based on the detection result.

However, in the optical scanning devices described in Patent Documents 1 to 3, the curvature of field cannot be eliminated. More specifically, the field curvature occurs over the entire y-axis direction of the photosensitive drum 132. Therefore, in order to eliminate the curvature of field, it is necessary to detect light over the entire y-axis direction of the photosensitive drum 132 and control the focal length of the liquid lens based on the detection result. However, beam detecting means cannot be arranged on the photosensitive drum 132.
JP 2006-251343 A JP 2006-251513 A JP 2006-258838 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical scanning device that can suppress curvature of field caused by manufacturing errors such as scanning lens manufacturing errors and mounting errors.

The present invention provides an optical scanning device that scans light on a photosensitive member, a light source, an optical element that collects the light emitted from the light source and can change a focal length, and light that has passed through the optical element. Deflection means for deflecting the light, an imaging element for imaging the light deflected by the deflection means on the photosensitive member, and a predetermined pattern in a period during which the light is scanned on the photosensitive member. and a control means for changing the focal length, and wherein the predetermined pattern, the progress of the light and the position of the condensing positions of the light the photosensitive member when the constant focal length of the optical element by detecting the causes by condensing positions move the light receiving element in the traveling direction of light in a plurality of locations in the main scanning direction misalignment in the direction, the image with respect to the condensing position of the light when the focal length of the optical element constant Detect surface curvature And, it is defined so as to cancel the image surface curvature, and wherein.

  The curvature of field caused by the manufacturing error occurs in a constant pattern on the photoreceptor. Therefore, the control means cancels the curvature of field by changing the focal length of the optical element with a predetermined pattern during the period in which the photoconductor is scanned with light. As a result, the optical scanning device can suppress curvature of field caused by a manufacturing error without providing a beam detection unit in the vicinity of the photosensitive member.

  In the present invention, the optical element may include a liquid, and a focal length of the optical element may be changed by changing a shape of an interface of the liquid due to an electrowetting phenomenon.

  In the present invention, it may further comprise storage means for storing control information relating to the predetermined pattern, and the control means may change the focal length of the optical element based on the control information.

  In the present invention, the optical element may be a collimator lens, and the curvature of field may occur in the main scanning direction in the photoconductor.

  In the present invention, βt / βs> 2 may be satisfied, where βt is the magnification in the main scanning direction of the entire optical system and βs is the magnification in the sub-scanning direction of the entire optical system.

  In the present invention, the optical element may be a cylindrical lens, and the curvature of field may occur in the sub-scanning direction on the photoconductor.

  In the present invention, the control means may start controlling the focal length of the optical element triggered by an SOS signal.

(First embodiment)
(About the configuration of the optical scanning device)
The configuration of the optical scanning device according to the first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a top view of the optical scanning device 10. FIG. 2 is a side view of the optical scanning device 10. 1 and 2, the y axis indicates the main scanning direction, and the z axis indicates the sub scanning direction. The z axis also coincides with the vertical direction.

  As shown in FIGS. 1 and 2, the optical scanning device 10 includes a laser diode 12, a liquid lens 14, a mirror 16, a cylindrical lens 18, a polygon mirror 20, scanning lenses 22, 24, a mirror 26, a light receiving element 28, and a housing. 29, a control unit 30 and a storage unit 31 are provided.

  The laser diode 12 serves as a light source that emits light. The light emitted from the laser diode 12 is diffused light. Therefore, the liquid lens 14 serves as a collimator lens that condenses the light emitted from the laser diode 12 and has a function of changing the focal length thereof. Details of the liquid lens 14 will be described later.

  The mirror 16 reflects the light that has passed through the liquid lens 14 toward the polygon mirror 20. The cylindrical lens 18 condenses the light reflected by the mirror 16 in the z-axis direction in the vicinity of the mirror surface of the polygon mirror 20.

  The polygon mirror 20 is rotated in the direction of an arrow by a motor (not shown), and serves as a deflecting unit that deflects light that has passed through the cylindrical lens 18 at a constant angular velocity in the y-axis direction. The scanning lenses 22 and 24 scan the light deflected by the polygon mirror 20 at a constant speed and form an image of the light on the photosensitive drum 32. The photosensitive drum 32 is rotationally driven at a predetermined speed. As a result, a two-dimensional electrostatic latent image is formed by main scanning with light and sub-scanning with rotation of the photosensitive drum 32.

  The mirror 26 plays a role of reflecting the light deflected by the polygon mirror 20 and passed through the scanning lenses 22 and 24 toward the light receiving element 28. The light receiving element 28 receives the light reflected by the mirror 26 and generates a SOS (Start Of Scan) signal which means that scanning of the light onto the photosensitive drum 32 is started.

  As shown in FIG. 1, the housing 29 houses the laser diode 12, the liquid lens 14, the mirror 16, the cylindrical lens 18, the polygon mirror 20, the scanning lenses 22 and 24, the mirror 26, and the light receiving element 28.

  The control unit 30 is configured by a CPU, for example, and serves as a control unit that controls the focal length of the liquid lens 14 with a predetermined pattern during a period in which light is scanned on the photosensitive drum 32 by one line. Fulfill. In addition, the storage unit 31 is configured by, for example, a hard disk, and serves as a storage unit that stores control information related to a predetermined pattern, which is control information for the control unit 30 to control the operation of the liquid lens 14. Fulfill.

  Next, the configuration of the liquid lens 14 will be described with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional structure diagram of a surface including the optical axis of the liquid lens 14. 3A is a cross-sectional structure diagram of the liquid lens 14 in a state where a voltage is applied, and FIG. 3B is a cross-sectional structure diagram of the liquid lens 14 in a state where no voltage is applied. FIG. 4 is an enlarged view of a portion C of the liquid lens 14 in FIG. In FIGS. 3 and 4, the liquid lens 14 shown in FIG. 2 is vertically inverted in the z-axis direction for easy understanding.

  As shown in FIG. 3, the liquid lens 14 includes a conductive liquid 40, an insulating liquid 42, transparent plates 44 and 46, a first electrode 48, an insulating film 50, and a second electrode 52. The liquid lens 14 can change the focal length by changing the shape of the interface S between the conductive liquid 40 and the insulating liquid 42 by an electrowetting phenomenon. Specifically, when a voltage is applied, the interface S changes from the state shown in FIG. 3B to the state shown in FIG.

  The transparent plates 44 and 46 are made of transparent resin or glass, and are arranged in parallel with each other leaving a predetermined gap. In this gap, the conductive liquid 40 and the insulating liquid 42 are sealed.

  The conductive liquid 40 is an inorganic salt aqueous solution, an organic liquid, or the like that has its own conductivity, or a liquid that is made conductive by adding an ionic component. The insulating liquid 42 has a refractive index different from that of the conductive liquid 40 and is not mixed with the conductive liquid 40 such as silicone oil or paraffin oil. Therefore, the conductive liquid 40 and the insulating liquid 42 are separated from each other, and form the interface S. Thus, the conductive liquid 40 and the insulating liquid 42 constitute a lens. Note that the refractive index of the conductive liquid 40 is preferably smaller than the refractive index of the insulating liquid 42.

  The first electrode 48 is provided on the transparent plate 44 so as to be in contact with the conductive liquid 40. The second electrode 52 is provided between the transparent plate 46 and the first electrode 48. The insulating film 50 is formed so as to cover the second electrode 52. Specifically, the insulating film 50 is formed between the first electrode 48 and the second electrode 52 to insulate the first electrode 48 and the second electrode 52, and The second electrode 52 is formed on the inner peripheral surface of 52 so that the conductive liquid 40 and the insulating liquid 42 do not come into contact with each other. A voltage is applied between the first electrode 48 and the second electrode 52 when the liquid lens 14 is driven.

  The operation principle of the liquid lens 14 configured as described above will be described below with reference to FIG. FIG. 4 is an enlarged view of a portion C of the liquid lens 14 in FIG. FIG. 4A is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 3B) in a state where no voltage is applied, and FIG. 4B is a diagram in which voltage is applied. FIG. 4 is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 3A) in a state.

  First, the interfacial tension between the conductive liquid 40 and the insulating liquid 42 is set to an interfacial tension γ12, the interfacial tension between the insulating film 50 and the conductive liquid 40 is set to an interfacial tension γ31, and the insulating liquid 42 and the insulating film are set. The interfacial tension between 50 and 50 is defined as interfacial tension γ23. As shown in FIG. 4A, when no voltage is applied between the first electrode 48 and the second electrode 52, the interfacial tension γ12, the interfacial tension γ23, and the interfacial tension γ31 The interface S and the insulating film 50 form an angle θ1. At this time, the relationship of the formula (1) is established by the Young's equation among the angle θ1, the interfacial tension γ12, the interfacial tension γ23, and the interfacial tension γ31.

  Here, when a voltage is applied to the first electrode 48 and the second electrode 52, for example, as shown in FIG. 4B, a positive charge is applied to the boundary between the insulating film 50 and the conductive liquid 40. Appears. On the other hand, negative charges appear at the boundary between the insulating film 50 and the second electrode 52. As a result, a pressure drop due to the charge is generated between the insulating liquid 42 and the insulating film 50 in the same direction as the interfacial tension γ23. This pressure Π is expressed as in equation (2).

  Here, ε is the dielectric constant of the insulating film 50, ε0 is the vacuum dielectric constant, e is the thickness of the insulating film 50, and V is between the first electrode 48 and the second electrode 52. Voltage.

  Due to the occurrence of the pressure drop, the interface S and the insulating film 50 form an angle θ2 larger than the angle θ1. At this time, the interface S of the liquid lens 14 is curved as shown in FIG. This angle θ2 is expressed as in Expression (3).

  As described above, it can be seen that the angle formed between the interface S and the insulating film 50 is changed by changing the voltage applied between the first electrode 48 and the second electrode 52. Then, as the angle between the interface S and the insulating film 50 changes, the interface S is curved and the focal length is relatively short as shown in FIG. 3A when a voltage is applied. Become. In the state where no voltage is applied, as shown in FIG. 3B, the interface S becomes flat and the focal length becomes relatively long. The control unit 30 shown in FIG. 1 controls the focal length of the liquid lens 14 by controlling the magnitude of this voltage.

(Operation of optical scanning device)
The operation of the optical scanning device 10 will be described below with reference to the drawings. FIG. 5 is a graph showing the correction amount of the condensing position due to the deviation of the condensing position caused by the curvature of field in the main scanning direction and the change in the focal length of the liquid lens 14. The horizontal axis indicates the position in the y-axis direction on the photosensitive drum 32 shown in FIG. The vertical axis indicates the light collection position when the light traveling direction (x-axis direction) is positive. On the vertical axis, the peripheral surface of the photosensitive drum 32 is the reference (0 mm).

  Here, the curvature of field in the main scanning direction means that, as shown in FIG. 6, a deviation occurs in the condensing position of the condensed light in the xy plane, and the main scanning direction on the photosensitive drum 32 in the main scanning direction. A state in which the amount of deviation of the light collection position differs depending on the position.

  The optical scanning device has a problem that curvature of field occurs on the photosensitive drum due to a manufacturing error of the scanning lens. Such curvature of field cannot be detected by the beam detection means in Patent Document 1 and Patent Document 2.

  Therefore, in the optical scanning device 10, the deviation of the condensing position is measured by the method described below. Specifically, when the assembly of the optical scanning device 10 is completed, the light receiving elements are arranged at a position equivalent to the photosensitive drum 32, and the optical scanning device 10 is driven to irradiate the light receiving elements with light. At this time, the light collection position is detected by moving the light receiving element in the x-axis direction and measuring the light. By repeating this operation as many times as necessary in the y-axis direction, field curvature is detected. As a result, a field curvature curve as shown in FIG. 5 is obtained. The curve is obtained, for example, by approximating each point of the detected condensing position with a polynomial.

  Next, as shown in FIG. 5, a curve of the correction amount of the condensing position generated by the change in the focal length of the liquid lens 14 is generated. The curve of the correction amount of the condensing position caused by the change in the focal length of the liquid lens 14 is determined so as to cancel the curvature of field caused by the manufacturing error of the optical scanning device 10. Specifically, the correction amount curve is determined so that the condensing position is substantially zero over the entire region in the main scanning direction.

  Further, control information for controlling the focal length of the liquid lens 14 is generated based on the obtained curve of the focal length correction amount by the liquid lens 14. This control information is information relating to the voltage to be applied to the liquid lens 14 at each timing during light scanning, and is stored in the storage unit 31. This control information may be stored, for example, as an analog signal waveform, or may be stored in the form of a table. Thereafter, the optical scanning device 10 is mounted on the image forming apparatus.

  Next, the operation of the optical scanning device 10 will be described with reference to the drawings. FIG. 7 is a diagram illustrating a waveform diagram of a drive signal of the optical scanning device 10. FIG. 7A is a waveform diagram of the control signal Sig2 of the laser diode 12 output from the control unit 30. FIG. FIG. 7B is a waveform diagram of the control signal Sig1 of the liquid lens 14 output from the control unit 30. FIG. 7C is a diagram showing a change in the focal length of the liquid lens 14.

  First, in response to the input of image data, the control unit 30 generates a high-level control signal Sig2 shown in FIG. 7A to emit light to the laser diode 12, and rotates a motor (not shown). The polygon mirror 20 is rotated.

  Next, the light emitted from the laser diode 12 is reflected by the mirror 26 and enters the light receiving element 28. When light is incident, the light receiving element 28 outputs an SOS signal to the control unit 30. As a result of the SOS signal, as shown in FIG. 7A, the control signal Sig2 is switched from the high level to the low level, and the laser diode 12 is turned off.

  After a predetermined clock from when the control signal Sig2 is switched to the low level, the control unit 30 switches the control signal Sig2 from the low level to the high level (SOI (Start Of Image) in FIG. 7). Accordingly, the optical scanning device 10 scans the photosensitive drum 32 with light. Further, the control unit 30 applies the control signal Sig1 shown in FIG. 7B to the liquid lens 14 based on the control information stored in the storage unit 31. That is, the control unit 30 starts controlling the focal length of the liquid lens 14 triggered by the output of the SOS signal. Thereby, as shown in FIG. 7C, the focal length of the liquid lens 14 changes according to the change of the control signal Sig1. Next, when the scanning of the light on the photosensitive drum 32 is completed, the control unit 30 switches the control signal Sig2 from the high level to the low level (EOI (End Of Image) in FIG. 7). Further, the control unit 30 ends the control of the focal length of the liquid lens 14. With the above operation, scanning of light for one line is performed on the photosensitive drum 32. Thereafter, by repeating this operation, an electrostatic latent image is formed on the photosensitive drum 32.

(About effect)
According to the optical scanning device 10, the control unit 30 is a liquid lens that functions as a collimator lens with a predetermined pattern during a period in which light is scanned on the photosensitive drum 32 (period from SOI to EOI in FIG. 7). The focal length of 14 is changed. The predetermined pattern is determined so as to cancel the field curvature in the main scanning direction due to the manufacturing error of the optical scanning device 10. Therefore, the optical scanning device 10 can suppress the curvature of field in the main scanning direction caused by a manufacturing error without providing a beam detecting unit in the vicinity of the photosensitive drum 32.

  Note that the magnification in the main scanning direction of all the optical systems (laser diode 12, liquid lens 14, mirror 16, cylindrical lens 18, polygon mirror 20 and scanning lenses 22, 24) of the optical scanning device 10 is βt, When the magnification in the sub-scanning direction is βs, it is preferable that βt / βs> 2. The reason will be described below.

  In the optical scanning device 10, the liquid lens 14 functions as a collimator lens. Since the collimator lens is a rotationally symmetric lens, when the focal length of the liquid lens 14 changes, it changes not only to the light condensing position in the main scanning direction but also to the light condensing position in the sub-scanning direction. Therefore, it is necessary to configure the optical scanning device 10 so that the light condensing position in the sub-scanning direction does not change much while the light condensing position in the main scanning direction is changed.

Here, the ratio of the moving amount of the condensing position in the main scanning direction in the light traveling direction to the moving amount of the laser diode 12 in the light traveling direction is βt ² . Similarly, the ratio of the moving amount of the condensing position in the sub-scanning direction in the light traveling direction to the moving amount of the laser diode 12 in the light traveling direction is βs ² . Thus, the light condensing position moves with the sensitivity of the square of the magnification.

Therefore, as described above, by setting βt / βs> 2, βt ² / βs ² > 4. Thus, in the light traveling direction, the light condensing position in the sub-scanning direction moves only ¼ of the light condensing position in the main scanning direction. As a result, even if the focal length of the liquid lens 14 is changed, the light condensing position in the main scanning direction changes, and the light condensing position in the sub-scanning direction hardly changes.

  The liquid lens 14 includes a conductive liquid 40 having a relatively high specific gravity and an insulating liquid 42 having a relatively low specific gravity. Therefore, as shown in FIG. 8, when the optical axis is oriented in the horizontal direction, an asymmetric deformation occurs in the optical axis in the cross section including the optical axis and the vertical direction as shown by the interface S ′ due to the influence of gravity. . More specifically, the conductive liquid 40 sinks below the insulating liquid 42, and the interface S is deformed into an S shape as indicated by the interface S ′. Therefore, in the optical scanning device 10, the liquid lens 14 is disposed so that the optical axis of the liquid lens 14 and the z-axis (vertical direction) are substantially parallel. As a result, although deformation symmetric with respect to the optical axis occurs at the interface S of the liquid lens 14, deformation asymmetric with respect to the optical axis does not occur. As a result, a high-definition electrostatic latent image can be formed by the photosensitive drum 32. Note that the optical axis and the z-axis need only be approximately parallel, and an error of manufacturing variation is allowed. This error is preferably within ± 10 degrees, for example.

  Furthermore, the specific gravity of the conductive liquid 40 is greater than the specific gravity of the insulating liquid 42, and the conductive liquid 40 is disposed below the insulating liquid 42 in the vertical direction as shown in FIG. 2. . Therefore, it is also possible to effectively suppress deformation at the interface S that is symmetric with respect to the optical axis due to the influence of gravity.

  Furthermore, since the conductive liquid 40 having a large specific gravity is disposed on the lower side in the vertical direction, the conductive liquid 40 having a large specific gravity is symmetrical to the optical axis due to the influence of gravity as in the case where the conductive liquid 40 having a large specific gravity is disposed on the upper side in the vertical direction. In order to suppress the occurrence of strong deformation at the interface S, it is not necessary to reduce the specific gravity difference between the conductive liquid 40 and the insulating liquid 42 as much as possible. Thereby, the freedom degree of selection of the liquid used for the electroconductive liquid 40 and the insulating liquid 42 spreads.

(Second Embodiment)
Hereinafter, an optical scanning device 10 according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a top view of the optical scanning device 10.

  In the optical scanning device 10 according to the first embodiment, the light emitted from the laser diode 12 travels in the xy plane after traveling in the z-axis direction. For example, as shown in FIG. It may proceed only in the xy plane. In this case, the laser diode 12, the liquid lens 14, the cylindrical lens 18 and the polygon mirror 20 are arranged so as to be aligned.

(Third embodiment)
The optical scanning device 10 according to the third embodiment of the present invention will be described below with reference to the drawings. FIG. 10 is a top view of the optical scanning device 10.

  In the optical scanning device 10 according to the first embodiment, the liquid lens 14 is used as a collimator lens in order to cancel the curvature of field in the main scanning direction. On the other hand, in the optical scanning device 10 according to the present embodiment, the liquid lens 14 ′ is used as a cylindrical lens in order to cancel the curvature of field in the sub-scanning direction (the rotation direction of the photosensitive drum 32). The remaining configuration of the optical scanning device according to the present embodiment is the same as that of the optical scanning device 10 according to the first embodiment, and a description thereof will be omitted. As shown in FIG. 11, the curvature of field in the sub-scanning direction causes a deviation in the condensing position in the xz plane, and the amount of deviation in the condensing position depends on the position in the main scanning direction on the photosensitive drum 32. A state that is different.

  According to the optical scanning device 10 according to the present embodiment, the control unit 30 determines the focal length of the liquid lens 14 that functions as a cylindrical lens in a predetermined pattern during a period in which the photosensitive drum 32 is scanned with light. It is changing. The predetermined pattern is determined so as to cancel the field curvature in the sub-scanning direction due to the manufacturing error of the optical scanning device 10. Therefore, the optical scanning device 10 can suppress the curvature of field in the sub-scanning direction, which is caused by a manufacturing error, without providing a beam detection unit in the vicinity of the photosensitive drum 32.

(Other embodiments)
In the optical scanning device 10, the specific gravity of the conductive liquid 40 is greater than the specific gravity of the insulating liquid 42. However, the specific gravity of the conductive liquid 40 prevents the specific gravity of the conductive liquid 40 from being lower than the specific gravity of the insulating liquid 42. is not.

  The light deflected by the polygon mirror 20 passes through the scanning lenses 22 and 24 and then directly irradiates the photosensitive drum 32. However, the light is sensitized after the traveling direction is changed by the mirror. The body drum 32 may be irradiated.

  Moreover, although the external shape in the top view and side view of the housing | casing 29 shown in FIG.1, FIG.2, FIG.9 and FIG. 10 is a square shape, the external shape of this housing | casing 29 is not restricted to this.

  Further, the liquid lenses 14 and 14 ′ may be used for both the collimator lens and the cylindrical lens.

  Further, in the liquid lenses 14 and 14 ', two types of liquid are sealed, but for example, one type of liquid may be sealed. Further, the liquid lens 14 may contain three or more kinds of liquids.

It is a top view of the optical scanning device concerning a 1st embodiment. It is a side view of the optical scanning device. It is a cross-sectional structure figure in the surface containing the optical axis of a liquid lens. FIG. 4 is an enlarged view of a portion C of the liquid lens in FIG. 3. It is the graph which showed the correction amount of the condensing position by the shift | offset | difference of the condensing position which generate | occur | produces by the curvature of field in a main scanning direction, and the focal distance of a liquid lens. FIG. 6 is an enlarged view when the vicinity of the photosensitive drum is viewed from the z-axis direction. It is the figure which showed the wave form diagram of the drive signal of an optical scanning device. It is a cross-sectional structure figure in the surface containing the optical axis of a liquid lens. FIG. 5 is a top view of the optical scanning device according to a second embodiment. It is a top view of the optical scanning device concerning a 3rd embodiment. FIG. 6 is an enlarged view when the vicinity of the photosensitive drum is viewed from the y-axis direction. It is a top view of a general optical scanning device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical scanning device 12 Laser diode 14,14 'Liquid lens 16 Mirror 18 Cylindrical lens 20 Polygon mirror 22, 24 Scan lens 28 Light receiving element 30 Control part 31 Memory | storage part 32 Photosensitive drum 40 Conductive liquid 42 Insulating liquid

Claims (7)

In an optical scanning device that scans light on a photoconductor,
A light source;
An optical element capable of condensing the light emitted from the light source and changing a focal length;
Deflection means for deflecting light that has passed through the optical element;
An imaging element for imaging the light deflected by the deflecting means on the photosensitive member;
Control means for changing a focal length of the optical element in a predetermined pattern during a period in which the photoconductor is scanned with light;
With
In the predetermined pattern, the light receiving elements at a plurality of positions in the main scanning direction are shifted in the light traveling direction between the light condensing position and the position of the photosensitive member when the focal length of the optical element is constant. By detecting the condensing position by moving the light in the traveling direction, the curvature of field with respect to the condensing position of the light when the focal length of the optical element is fixed is detected, and the curvature of field is canceled out. To be determined,
An optical scanning device characterized by the above. The optical element includes a liquid;
The focal length of the optical element is changed by the shape of the interface of the liquid being deformed by an electrowetting phenomenon;
The optical scanning device according to claim 1. Storage means for storing control information related to the predetermined pattern,
In addition,
The control means changes a focal length of the optical element based on the control information;
The optical scanning device according to claim 1, wherein: The optical element is a collimator lens,
The curvature of field occurs in the main scanning direction in the photoconductor;
The optical scanning device according to claim 1, wherein: Βt / βs> 2 where βt is the magnification in the main scanning direction of the entire optical system and βs is the magnification in the sub-scanning direction of the entire optical system,
The optical scanning device according to claim 4 . The optical element is a cylindrical lens,
The curvature of field occurs in the sub-scanning direction in the photoconductor;
The optical scanning device according to claim 1, wherein: The control means starts the control of the focal length of the optical element triggered by the SOS signal;
The optical scanning device according to any one of claims 1 to 6, characterized in.

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