JP2009098401A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner comprising a detecting means for detecting a light diameter, and a liquid lens dispensing with feedback control. <P>SOLUTION: The liquid lens 14 including a conductive liquid 40 constituting a negative lens, and an insulating liquid 42 constituting a positive lens, can convert light emitted from a laser diode 12, into substantially parallel light and change a focal length. A polygon mirror 20 deflects light that passed through the liquid lens 14. Scanning lenses 22, 24 image light deflected by the polygon mirror 20, on a photoreceptor drum 32. The shape of an interface between the conductive liquid 40 and insulating liquid 42 is deformed by an electro-wetting phenomenon to change the focal length of the liquid lens 14. A value of a ratio of a refractive index change to the temperature change of the conductive liquid 40 is smaller than a value of a ratio of a refractive index change to the temperature change of the insulating liquid 42. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Liquid lenses that can deform the interface shape of two kinds of liquids by an electrowetting phenomenon and deform the focal length thereof have been put into practical use. Patent Documents 1 to 3 propose applying such a liquid lens to an optical scanning device. In the optical scanning device to which the liquid lens is applied, the beam condensing state detection means detects the diameter of the light collected by the liquid lens (referred to as the light diameter), and the control unit detects the focal length of the liquid lens. Feedback control is based on the results. Thereby, even if the temperature in the optical scanning device rises and the focal length of the liquid lens fluctuates, it is possible to accurately collect light on the photosensitive drum.

However, in the optical scanning device, it is necessary to provide a beam condensing state detecting means for detecting the light diameter or to perform feedback control, and there is a problem that the manufacturing cost increases. Patent Document 2 describes an objective lens system that selects a physical property value of a liquid lens and a physical property value of a solid lens to guarantee performance due to a temperature change. However, Patent Document 2 does not describe selecting the physical property value of the liquid lens and the physical property value of the solid lens in the optical scanning device.
JP 2006-251513 A JP-A-9-101456

  Accordingly, an object of the present invention is to provide an optical scanning device including a beam condensing state detecting unit for detecting a light diameter and a liquid lens that does not require feedback control.

  The present invention includes a light source, an optical element having a first liquid and a second liquid having a refractive index smaller than that of the first liquid, and a light source that converts light emitted from the light source into substantially parallel light. An optical system, and deflecting means for deflecting light that has passed through the light source optical system, and the shape of the interface between the first liquid and the second liquid is deformed by an electrowetting phenomenon, The focal length of the optical element changes, and the value of the ratio of the refractive index change with respect to the temperature rise of the first liquid is smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the second liquid. And

  According to the present invention, the value of the ratio of the refractive index change with respect to the temperature rise of the first liquid is smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the second liquid. As a result, the light source and the deflecting means are driven, so that the light emitted from the light source is condensed on the peripheral surface of the photosensitive member even when the temperature in the optical scanning device rises. This will be described below.

  When the temperature in the optical scanning device rises, each part of the optical scanning device thermally expands, and the distance between the light source and the optical element becomes longer than the design value. In this case, the light condensed by the optical element does not become parallel light but is slightly condensed.

  Therefore, in the present invention, the value of the ratio of the refractive index change with respect to the temperature rise of the first liquid is made smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the second liquid. Since the refractive index of the substance decreases with an increase in temperature, the value of the ratio of the refractive index change with respect to the increase in temperature of the first liquid and the second liquid becomes a negative value. Therefore, when the temperature in the optical scanning device rises, the reduction width of the refractive index of the first liquid is larger than the reduction width of the refractive index of the second liquid. The difference in the refractive index of the second liquid is reduced. Thereby, the length of the focal length of the optical element becomes longer than before the temperature rise. As a result, even if the temperature in the optical scanning device rises, it is possible to prevent the focal position of the optical element from deviating from the light source. That is, according to the present invention, it is not necessary to provide a beam condensing state detection unit or perform feedback control in order to suppress a shift of the light condensing position of the light onto the photosensitive member due to a temperature change.

  In the present invention, the value of the ratio of the refractive index change with respect to the wavelength extension of the first liquid may be smaller than the value of the ratio of the refractive index change with respect to the wavelength extension of the second liquid.

  In the present invention, the optical element further includes a holding member holding the light source and the optical element, and the optical element further includes a main body containing the first liquid and the second liquid, The holding member may hold the surface of the main body facing the deflecting unit.

  In this invention, the linear expansion coefficient of the material which comprises the said main body may be larger than the linear expansion coefficient of the material which comprises the said holding member.

  In the present invention, the first liquid is disposed closer to the light source than the second liquid, and the optical element includes a main body containing the first liquid and the second liquid; A tank connected to the main body and containing a part of the first liquid, wherein the part of the first liquid moves from the main body to the tank as the temperature rises. May be.

  In the present invention, the focal length of the optical element is changed in a predetermined pattern during a period in which the light deflected by the deflecting means forms an image on the photosensitive member and the light is scanned on the photosensitive member. And a control means for making it possible.

  In the present invention, the first liquid may constitute a positive lens, and the second liquid may constitute a negative lens.

(About the configuration of the optical scanning device)
The configuration of an optical scanning device according to an 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. In FIG. 1, 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 FIG. 1, the optical scanning device 10 includes a laser diode 12, a holding member 15, a light source optical system 19, a polygon mirror 20, scanning lenses 22 and 24, a mirror 26, a light receiving element 28, a housing 29, and a control unit 30. And a storage unit 31.

  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 light source optical system 19 condenses the light emitted from the laser diode 12 and condenses it into substantially parallel light, and includes a liquid lens 14 and a cylindrical lens 18. The liquid lens 14 includes a conductive liquid 40, an insulating liquid 42, and a main body 43 that accommodates them, and collects light emitted from the laser diode 12 in a plane perpendicular to the z-axis to generate substantially parallel light. It plays a role as a collimator lens for converting to, and has a function of changing the focal length. Details of the liquid lens 14 will be described later.

  The holding member 15 holds the laser diode 12 and the liquid lens 14. Specifically, the holding member 15 holds the laser diode 12 and the liquid lens 14 so that the light emitting surface of the laser diode 12 is positioned at the focal point of the liquid lens 14. At this time, the holding member 15 holds the surface of the main body 43 facing the polygon mirror 20.

  The cylindrical lens 18 condenses the light that has passed through the liquid lens 14 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 are resin or glass lenses, and scan the light deflected by the polygon mirror 20 at a constant speed to 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 holding member 15, 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. 2 and 3. FIG. 2 is a cross-sectional structure diagram of a surface including the optical axis of the liquid lens 14. 2A is a cross-sectional structure diagram of the liquid lens 14 in a state where a voltage is applied, and FIG. 2B is a cross-sectional structure diagram of the liquid lens 14 in a state where no voltage is applied. FIG. 3 is an enlarged view of a portion C of the liquid lens 14 in FIG.

  As shown in FIG. 2, 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, a second electrode 52, and a side surface 53. 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. 2B 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 side surface 53 is made of resin or the like and is formed so as to surround the conductive liquid 40 and the insulating liquid 42. Thereby, the conductive liquid 40 and the insulating liquid 42 are sealed in the transparent plates 44 and 46 and the side surface 53. The transparent plates 44 and 46 and the side surface 53 constitute a main body 43. The linear expansion coefficient of the material forming the main body 43 is larger than the linear expansion coefficient of the material forming the holding member 15.

  The conductive liquid 40 is a liquid that has conductivity by itself or is made conductive by adding an ionic component, and constitutes a negative lens. The insulating liquid 42 has a refractive index different from that of the conductive liquid 40 and does not mix with the conductive liquid 40 and constitutes a positive lens. Therefore, the conductive liquid 40 and the insulating liquid 42 are separated from each other, and form the interface S. As a result, the conductive liquid 40 and the insulating liquid 42 constitute a single lens by combining the negative lens and the positive lens. Note that the refractive index of the conductive liquid 40 is smaller than the refractive index of the insulating liquid 42.

  Further, the value of the ratio of the refractive index change with respect to the temperature rise of the insulating liquid 42 is smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the conductive liquid 40. As a result, the laser diode 12 and the motor of the polygon mirror 20 are driven, so that the light emitted from the laser diode 12 is collected on the circumferential surface of the photosensitive drum 32 even when the temperature in the optical scanning device 10 rises. Come to be lighted.

  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. 3 is an enlarged view of a portion C of the liquid lens 14 in FIG. 3A is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 2B) in a state where no voltage is applied, and FIG. 3B is a diagram in which voltage is applied. FIG. 3 is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 2A) 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. 3A, 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. 3B, 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. 2A when a voltage is applied. Become. Further, in the state where no voltage is applied, the interface S becomes flat as shown in FIG. 2B, 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. 4 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 focal length change by 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 where the light traveling direction (x-axis direction) is positive, and 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. 5, a deviation occurs in the light condensing position in the xy plane, and the light is condensed depending on the position in the main scanning direction on the photosensitive drum 32. A state in which the amount of displacement is different.

  When the scanning lens is composed of a spherical lens that is easy to manufacture or a toric surface, it is difficult to eliminate the deviation of the condensing position at all positions in the main scanning direction on the photosensitive drum, and field curvature occurs. There is a problem of doing. Such curvature of field cannot be detected by the beam condensing state detecting means in Patent Document 1.

  Therefore, in the optical scanning device 10, the deviation of the condensing position is measured by the method described below. Note that the field curvature caused by the scanning lens is determined at the design stage of the scanning lens, and therefore the following measurement is not necessary if the deviation of the condensing position due to the field curvature is known in advance. First, the light receiving elements are arranged at positions 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 curve of the deviation of the condensing position in the main scanning direction caused by the scanning lens as shown in FIG. 5 is obtained. The curve is obtained by approximating each point with a polynomial, for example.

  Next, a curve of the focal length correction amount by the liquid lens 14 as shown in FIG. 4 is generated. The curve of the correction amount of the focal length by the liquid lens 14 is determined so as to cancel the field curvature caused by the scanning lenses 22 and 24. Specifically, the condensing position generated by the field curvature in the main scanning direction. The deviation curve is determined so that the condensing position is approximately 0 mm 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. 6 is a diagram illustrating a waveform diagram of a drive signal of the optical scanning device 10. FIG. 6A is a waveform diagram of the control signal Sig2 of the laser diode 12 output from the control unit 30. FIG. FIG. 6B is a waveform diagram of the control signal Sig1 of the liquid lens 14 output from the control unit 30. FIG. 6C 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. 6A 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. 6A, 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. 6). As a result, the optical scanning device 10 scans the photosensitive drum 32 with light. Furthermore, the control unit 30 applies the control signal Sig1 shown in FIG. 6B 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. 6C, 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. 6). 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 value of the ratio of the refractive index change with respect to the temperature rise of the insulating liquid 42 is smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the conductive liquid 40. As a result, the laser diode 12 and the motor of the polygon mirror 20 are driven, so that the light emitted from the laser diode 12 is collected on the circumferential surface of the photosensitive drum 32 even when the temperature in the optical scanning device 10 rises. Come to be lighted. This will be described below.

  When the temperature in the optical scanning device 10 rises, the holding member 15 is thermally expanded, and the distance between the laser diode 12 and the liquid lens 14 becomes longer than the design value. In this case, as shown in the cross-sectional structure diagram of the laser diode 12, the liquid lens 14, and the holding member 15 shown in FIG. 7, the focal point of the liquid lens 14 is downstream of the light emitting surface of the laser diode 12 in the light traveling direction. Will be located. As a result, the light condensed by the liquid lens 14 does not become parallel light but is slightly condensed.

  Therefore, in the optical scanning device 10, the value of the ratio of the refractive index change with respect to the temperature rise of the insulating liquid 42 is made smaller than the value of the ratio of the refractive index change with respect to the temperature rise of the conductive liquid 40. Since the refractive index of the substance decreases with a rise in temperature, the value of the ratio of the refractive index change with respect to the rise in temperature of the insulating liquid 42 and the conductive liquid 40 becomes a negative value. Therefore, when the temperature in the optical scanning device 10 rises, the reduction width of the refractive index of the insulating liquid 42 becomes larger than the reduction width of the refractive index of the conductive liquid 40, and the refractive index of the conductive liquid 40. The difference in refractive index between the insulating liquid 42 and the insulating liquid 42 becomes small. Thereby, the length of the focal length of the liquid lens 14 becomes longer than before the temperature rises. As a result, even if the temperature in the optical scanning device 10 rises, the position of the focus of the liquid lens 14 and the light emitting surface of the laser diode 12 are suppressed from shifting. That is, according to the optical scanning device 10, in order to suppress the shift of the light condensing position of the light onto the photosensitive drum 32 due to the temperature change, no beam condensing state detecting means is provided or feedback control is not performed. Also good.

  Furthermore, according to the optical scanning device 10, the control unit 30 functions as a collimator lens with a predetermined pattern during the period in which the photosensitive drum 32 is scanned with light (the period from SOI to EOI in FIG. 6). The focal length of the liquid lens 14 is changed. The predetermined pattern is determined so as to cancel the field curvature in the main scanning direction caused by the scanning lenses 22 and 24. Therefore, the optical scanning device 10 can suppress the curvature of field in the main scanning direction caused by the scanning lenses 22 and 24 without providing the beam condensing state detecting means.

  As described above, according to the optical scanning device 10, the deviation of the light condensing position on the photosensitive drum 32 due to the temperature rise and the scanning can be performed without providing the beam condensing state detecting means or performing the feedback control. Both curvature of field in the main scanning direction caused by the lens can be suppressed.

  Further, according to the optical scanning device 10, since the linear expansion coefficient of the main body 43 is larger than the linear expansion coefficient of the holding member 15, even if the temperature in the optical scanning device 10 rises and the holding member 15 thermally expands. The distance between the laser diode 12 and the liquid lens 14 can be prevented from changing. This will be described below with reference to FIG. FIG. 8 is a cross-sectional structure diagram of the laser diode 12, the liquid lens 14, and the holding member 15. More specifically, the upper half of FIG. 8 is a cross-sectional structural view of the laser diode 12, the liquid lens 14, and the holding member 15 in a state where the temperature in the optical scanning device 10 is not increased, and the lower half of FIG. FIG. 3 is a cross-sectional structure diagram of the laser diode 12, the liquid lens 14, and the holding member 15 in a state where the temperature in the optical scanning device 10 is rising.

  As shown in FIG. 8, when the temperature in the optical scanning device 10 rises, the main body 43 and the holding member 15 are thermally expanded. Here, since the holding member 15 is attached to the transparent plate 44 of the liquid lens 14, the transparent plate 44 is displaced to the polygon mirror 20 side.

  However, since the transparent plate 44 of the liquid lens 14 is fixed, the transparent plate 46 is displaced so as to return to the laser diode 12 side when the main body 43 is thermally expanded. As a result, even if the main body 43 and the holding member 15 are thermally expanded, fluctuations in the distance between the laser diode 12 and the liquid lens 14 are suppressed. The amount of the transparent plate 46 returning to the laser diode 12 side can be increased by making the linear expansion coefficient of the material constituting the main body 43 larger than the linear expansion coefficient of the material constituting the holding member 15. As a result, fluctuations in the distance between the laser diode 12 and the liquid lens 14 can be more effectively suppressed.

  When the temperature in the optical scanning device 10 rises, the scanning lenses 22 and 24 also thermally expand. In the case where the scanning lenses 22 and 24 are glass lenses, the problem of deviation of the light condensing position of light on the peripheral surface of the photosensitive drum 32 due to the thermal expansion is negligible. , 24 are resin lenses, there is a possibility that the light condensing position shift of about several mm on the peripheral surface of the photosensitive drum 32 may occur. However, since this deviation occurs substantially uniformly in the main scanning direction of the photosensitive drum 32, it can be corrected by selecting the material of the holding member 15 or selecting the material of the liquid lens 14. Further, the deviation of the light condensing position caused by the thermal expansion of the holding member 15 occurs so as to cancel the deviation of the light condensing position caused by the thermal expansion of the scanning lenses 22 and 24. Therefore, it is possible to correct the condensing position shift generated by the scanning lenses 22 and 24 in the holding member 15.

(Other embodiments)
Note that the value of the ratio of the refractive index change with respect to the wavelength extension of the insulating liquid 42 is preferably smaller than the value of the ratio of the refractive index change with respect to the wavelength extension of the conductive liquid 40. This will be described below.

  The wavelength of the light emitted from the laser diode 12 becomes longer as the temperature in the optical scanning device 10 increases, and the refractive index of the conductive liquid 40 and the insulating liquid 42 becomes smaller as the wavelength of the light becomes longer. That is, the value of the ratio of the refractive index change with respect to the wavelength extension of the insulating liquid 42 and the conductive liquid 40 is a negative value. Therefore, the value of the ratio of the refractive index change with respect to the wavelength extension of the insulating liquid 42 is made smaller than the value of the ratio of the refractive index change with respect to the wavelength extension of the conductive liquid 40. Therefore, when the temperature in the optical scanning device 10 rises, the reduction width of the refractive index of the insulating liquid 42 becomes larger than the reduction width of the refractive index of the conductive liquid 40, and the refractive index of the conductive liquid 40. And the refractive index of the insulating liquid 42 are reduced. Thereby, the length of the focal length of the liquid lens 14 becomes longer than before the temperature rises. As a result, even if the temperature in the optical scanning device 10 rises, the position of the focus of the liquid lens 14 and the light emitting surface of the laser diode 12 are suppressed from shifting. That is, according to the optical scanning device 10, in order to suppress the shift of the light condensing position of the light onto the photosensitive drum 32 due to the temperature change, no beam condensing state detecting means is provided or feedback control is not performed. Also good.

  9, the liquid lens 14 ′ is connected to the main body 43 and includes a tank 54 that stores a part of the conductive liquid 40. Also good. The conductive liquid 40 and the insulating liquid 42 are thermally expanded as the temperature rises, and a part of the conductive liquid 40 moves from the main body 43 to the tank 54. Thereby, when the temperature in the optical scanning device 10 rises, the interface S moves to the laser diode 12 side. As a result, the focal position of the liquid lens 14 can be moved to the laser diode 12 side, and the focal position of the liquid lens 14 deviates from the light emitting surface of the laser diode 12 even if the temperature in the optical scanning device 10 rises. It is suppressed.

  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.

  The collimator lens may be configured by a combination of the liquid lens 14 and a glass or resin lens.

It is a top view of an optical scanning device. 2A is a cross-sectional structure diagram of the liquid lens in a state where a voltage is applied, and FIG. 2B is a cross-sectional structure diagram of the liquid lens in a state where no voltage is applied. FIG. 3 is an enlarged view of a portion C of the liquid lens in FIG. 2. It is the graph which showed the correction | amendment amount of the condensing position by the shift | offset | difference of the condensing position in the main scanning direction resulting from a scanning lens, and the focal distance change by a liquid lens. 3 is an enlarged view of a photosensitive drum 32. FIG. FIG. 6A is a waveform diagram of the control signal Sig2 of the laser diode output from the control unit. FIG. 6B is a waveform diagram of the control signal Sig1 of the liquid lens output from the control unit. FIG. 6C shows a change in the focal length of the liquid lens. It is a cross-section figure of a laser diode, a liquid lens, and a holding member. It is a cross-section figure of a laser diode, a liquid lens, and a holding member. It is a cross-section figure of liquid lens 14 'concerning a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical scanning device 12 Laser diode 14,14 'Liquid lens 15 Holding member 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 43 Main body 53 Side 54 Tank

Claims (7)

A light source;
A light source optical system including an optical element having a first liquid and a second liquid having a refractive index smaller than that of the first liquid, and converting light emitted from the light source into substantially parallel light;
Deflecting means for deflecting light that has passed through the light source optical system;
With
By changing the shape of the interface between the first liquid and the second liquid due to the electrowetting phenomenon, the focal length of the optical element changes,
The ratio of the refractive index change to the temperature rise of the first liquid is smaller than the value of the refractive index change ratio to the temperature rise of the second liquid;
An optical scanning device characterized by the above. The ratio of the refractive index change to the wavelength extension of the first liquid is smaller than the ratio of the refractive index change to the wavelength extension of the second liquid;
The optical scanning device according to claim 1. A holding member holding the light source and the optical element;
In addition,
The optical element is
A main body containing the first liquid and the second liquid;
In addition,
The holding member holds the surface of the main body facing the deflecting means;
The optical scanning device according to claim 1, wherein: The linear expansion coefficient of the material constituting the main body is larger than the linear expansion coefficient of the material constituting the holding member;
The optical scanning device according to claim 3. The first liquid is disposed closer to the light source than the second liquid;
The optical element is
A main body containing the first liquid and the second liquid;
A tank connected to the body and containing a portion of the first liquid;
Further including
A part of the first liquid moves from the main body to the tank as the temperature rises;
The optical scanning device according to claim 1, wherein: An imaging element for imaging the light deflected by the deflecting means on a photosensitive member;
Control means for changing the focal length of the optical element in a predetermined pattern during a period in which the photoconductor is scanned with light;
Providing
The optical scanning device according to claim 1, wherein: The first liquid constitutes a positive lens, and the second liquid constitutes a negative lens;
The optical scanning device according to claim 1, wherein:

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