JP2007216469A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To arrange in order diameters of spots formed on a latent image carrying body in the main scanning direction in an image forming apparatus which focuses optical beams into a spot-like beam on the latent image carrying body to form an image while the optical beam is scanned in the main scanning direction by a vibrating deflecting mirror face. <P>SOLUTION: While a movable member 656 is vibrated, a vibration driving part synchronizes the angle of vibration of the deflecting mirror face 651 and adjusts a driving force given to first and second vibrators to shift in parallel the movable member 656 vibrating in the normal line direction Z as the whole. A position of the deflecting face is changed by this parallel shift, and a position of incidence of a shape adjusting optical beam in the sub-scanning direction Y is changed. The length in the main scanning direction of the optical beam reflected by the deflecting mirror face 651 among the shape adjusting optical beams Li is changed. As a result, on every angle of vibration of the deflecting mirror face 651, the spot diameter on a photo-conductor surface of the optical beam reflected by the deflecting mirror face 651 is corrected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus which forms an image by deflecting a light beam by a vibrating deflection mirror surface and scanning the light beam on a latent image carrier in a main scanning direction.

  Examples of this type of image forming apparatus include image forming apparatuses such as laser printers, copiers, and facsimile machines. In this image forming apparatus, an image signal such as a gradation reproduction process is added to image data related to a toner image to be formed on the surface of a latent image carrier such as a photoconductive drum to form an image signal. In this image forming apparatus, an exposure unit is provided, and the exposure unit forms a latent image corresponding to the image data on the latent image carrier. For example, in an exposure unit equipped in an image forming apparatus described in Patent Document 1, a semiconductor laser is used as a light source, and a light beam from the light source is modulated based on the image signal, and the modulated light beam is transmitted from a deflector. The light beam is scanned in the main scanning direction by being deflected by a reflection mirror (corresponding to the “deflection mirror surface” of the present invention). The scanning light beam is applied to the surface of the photosensitive drum (latent image carrier) in the form of a spot to form a spot latent image. The spot latent image formed in this way is developed by the developing unit, dots are formed at the spot latent image position, and a toner image corresponding to the image data is formed.

JP-A-1-302317 (FIG. 3)

  However, in the above-described exposure unit, the light beam deflected by the oscillating reflecting mirror is imaged on the photosensitive drum via the optical system, so that the following problem may occur. That is, for example, a lens system having an arc-sin characteristic or an fθ lens system is used as the optical system. When the deflected light beam is irradiated onto the surface of the photosensitive drum by the optical system, the incident angle of the light beam with respect to the surface of the photosensitive drum. Depends on the position in the main scanning direction. As a result, the spot diameter of the light beam irradiated on the surface of the photosensitive drum changes according to the position in the main scanning direction. More specifically, as shown in FIGS. 12A and 15A described later, the swing angle of the reflecting mirror surface is almost zero in the vicinity of the optical axis in the scanning position in the main scanning direction. ), The spot diameter formed on the photosensitive drum is the smallest, the spot diameter gradually increases as the distance from the optical axis in the main scanning direction, and becomes the maximum at the effective scanning end. In this way, the variation of the spot diameter according to the main scanning position (the swing angle of the reflecting mirror surface) has been one of the main causes of image quality degradation.

  The present invention has been made in view of the above problems, and forms an image by forming a light beam in a spot shape on a latent image carrier while scanning the light beam in the main scanning direction by a vibrating deflection mirror surface. An object of the image forming apparatus is to improve the image quality by aligning the diameters of spots formed on the latent image carrier in the main scanning direction.

  In order to achieve the above object, the present invention shapes the latent image carrier moving in the scanning direction and the light beam from the light source into a beam shape extending in the main scanning direction substantially orthogonal to the sub scanning direction, and in the sub scanning direction. The shaped light beam is obliquely incident on the deflecting mirror surface formed on the surface of the movable member that vibrates around the drive axis parallel to the sub-scanning direction including the sub-scanning direction and is scanned in the main scanning direction. An exposure unit that forms a latent image by forming a scanning light beam in a spot shape on the surface of the latent image carrier using an optical system so that the width of the deflection mirror surface in the main scanning direction changes in the sub-scanning direction. The deflection mirror surface is formed, and the exposure unit oscillates the movable member and shifts the oscillating movable member in parallel to the normal direction of the deflection mirror surface in synchronization with the swing angle of the deflection mirror surface. It is characterized by varying the length in the main scanning direction of the light beam reflected by the deflection mirror surface by changing the incident position of the shaped light beam in the sub-scanning direction by.

  In the invention configured as described above, the light beam from the light source is shaped into a beam shape extending in the main scanning direction, and is incident obliquely on the deflection mirror surface in the sub-scan section, so-called oblique incidence. For this reason, when the movable member is displaced in the normal direction and the position of the deflection mirror surface in the normal direction (deflection surface position) varies, the incident position of the shaped light beam in the sub-scanning direction changes according to the variation. In the present invention, the deflection mirror surface is formed such that the width of the deflection mirror surface in the main scanning direction changes in the sub-scanning direction. Therefore, as the incident position of the shaped light beam changes as described above, the length of the light beam reflected by the deflection mirror surface in the shaped light beam varies in the main scanning direction. For this reason, the spot diameter obtained by imaging the light beam reflected by the deflecting mirror surface on the latent image carrier also varies. Thus, in the present invention, the spot diameter on the latent image carrier can be changed by the parallel shift of the movable member, and the change is performed in synchronization with the swing angle of the deflection mirror surface. Therefore, the spot diameter on the latent image carrier can be corrected according to the swing angle of the deflection mirror surface, and a good image can be formed.

  Here, as the shape of the deflection mirror surface, it is desirable to adopt a shape in which the width of the deflection mirror surface in the main scanning direction continuously changes in the sub-scanning direction. For example, a deflecting mirror surface having a trapezoidal shape in front view from the normal direction can be employed. When the trapezoidal shape is adopted as described above, the amount of change with respect to the width of the deflection mirror surface can be set large, and the range of fluctuation of the spot diameter can be widened.

  Further, as the shape of the deflection mirror surface, for example, a shape in which the width of the central portion is the shortest in the sub-scanning direction and becomes longer from the central portion in the sub-scanning direction may be adopted. This is because the spot diameter on the latent image carrier is the smallest at the scanning center in the conventional apparatus that does not correct the spot diameter, as shown in FIGS. 12A and 15A, and proceeds to the scanning end. This corresponds to the characteristic of gradually increasing. This point will be described in detail later with reference to FIG.

  In addition, the exposure unit is provided with a base portion having first and second support portions provided at a predetermined interval, and an outer end portion is fixed to the first support portion, while an inner end portion is a free end. A first vibrator having two first arm portions, and two second arm portions whose outer end portions are fixed to the second support portion and whose inner end portions are free ends. The second vibrator and a movable member arranged so that the drive shaft is located between the first arm portion and the second arm portion are connected to the first arm portion on the first vibrator side with respect to the drive shaft. The first torsion spring part, the second torsion spring part connecting the movable member to the second arm part on the second vibrator side with respect to the drive shaft, and the first and second vibrators The movable member is vibrated by applying a driving force independently and reciprocating each arm in the normal direction of the deflection mirror surface. The vibration drive unit adjusts the driving force applied to the first and second vibrators in synchronization with the swing angle of the deflecting mirror surface while vibrating the movable member, and the movable member in vibration May be configured to be shifted in parallel in the normal direction as a whole.

  Further, the vibration drive unit includes two first piezoelectric actuators interposed between the base unit and each first arm unit, and two units interposed between the base unit and each second arm unit. The second piezoelectric actuator can be used. Then, one end of each piezoelectric actuator is connected to the base portion, the other end is connected to the arm portion, and a mirror drive signal having a phase opposite to each other is applied to the first piezoelectric actuator and the second piezoelectric actuator, thereby moving the movable member. Can be vibrated. When such a vibration drive unit is adopted, the movable member is entirely arranged by giving each of the four piezoelectric actuators a signal obtained by adding an offset voltage corresponding to the swing angle of the deflection mirror surface to the mirror drive signal. Can be shifted parallel to the normal direction. By using the piezoelectric actuator in this way, the overall parallel shift amount of the movable member can be accurately controlled with excellent responsiveness.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is a so-called four-cycle color printer. That is, in this image forming apparatus, when an image forming command is given from an external device such as a host computer to the main controller 11 having a CPU, a memory and the like in response to a user's image forming request, an image corresponding to the image forming command is displayed. Signals, control signals, and the like are given from the main controller 11 to the engine controller 10 and the engine unit EG. Then, the CPU of the engine controller 10 controls each part of the engine unit EG to form an image corresponding to the image formation command on the sheet S such as copy paper, transfer paper, paper, and OHP transparent sheet.

  In the engine unit EG, the photosensitive member 2 is provided so as to be rotatable in the arrow direction (sub-scanning direction) in FIG. Further, a charging unit 3, a rotary developing unit 4, and a cleaning unit (not shown) are arranged around the photoconductor 2 along the rotation direction. A predetermined charging bias is applied to the charging unit 3 from the engine controller 10. By applying this bias, the outer peripheral surface of the photoreceptor 2 is uniformly charged to a predetermined surface potential. Further, the photosensitive member 2, the charging unit 3, and the cleaning unit integrally constitute a photosensitive member cartridge, and the photosensitive member cartridge is integrally detachable from the apparatus main body 5.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 2 charged by the charging unit 3. As a result, an electrostatic latent image corresponding to the image data included in the image formation command is formed on the photoreceptor 2. Thus, the exposure unit 6 is a so-called optical scanning device, and the configuration and operation thereof will be described in detail later.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided around the axis, and a cartridge that is detachable with respect to the support frame 40, and for yellow that contains toner of each color. A developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4K are provided. Then, based on a control command from the developing device controller 104 of the engine controller 10, the developing unit 4 is driven to rotate, and the developing devices 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 2. Alternatively, when positioned at a predetermined developing position facing each other with a predetermined gap, toner is applied to the surface of the photoreceptor 2 from a developing roller 44 provided in the developing unit and carrying toner of a selected color. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 that is stretched over a plurality of rollers 72, 73, and the like, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction by rotationally driving the roller 73. It has. A transfer belt cleaner (not shown) is disposed in the vicinity of the roller 72.

  When transferring a color image to a sheet, each color toner image formed on the photoreceptor 2 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet conveyed along the conveyance path F to the secondary transfer region TR2.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet, the timing of feeding the sheet to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. Are sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet on which the color image is formed in this way is conveyed to the discharge tray portion 51 provided on the upper surface portion of the apparatus main body 5 via the fixing unit 9 and the discharge roller 82. When images are formed on both sides of the sheet, the sheet on which the image is formed on one side as described above is switched back by the discharge roller 82. As a result, the sheet is conveyed along the reverse conveyance path FR. Then, it is put again on the transport path F before the gate roller 81. At this time, the image is transferred to the surface of the sheet that is in contact with the intermediate transfer belt 71 and transfers the image in the secondary transfer region TR2. The surface is the opposite of the surface. In this way, images can be formed on both sides of the sheet.

  FIG. 3 is a main scanning sectional view showing the structure of the exposure unit provided in the image forming apparatus of FIG. FIG. 4 is a sub-scan sectional view of the exposure unit. FIG. 5 is a diagram showing an exposure unit of the image forming apparatus of FIG. 1 and an exposure control unit for controlling the exposure unit. 6 to 8 are views showing a deflector which is one component of the exposure unit. 9 and 10 are main scanning sectional views showing the operation of the deflector. Hereinafter, the configuration and operation of the exposure unit 6 will be described in detail with reference to these drawings.

  As shown in FIG. 3, the exposure unit 6 has an exposure housing 61. A single laser light source 62 is fixed to the exposure housing 61, and a light beam can be emitted from the laser light source 62. The laser light source 62 is ON / OFF controlled based on the image signal Sv from the main controller 11, and a light beam modulated in accordance with the image signal Sv is emitted forward from the laser light source 62. That is, in this embodiment, the video clock generator 111 is provided in the main controller 11 and outputs a video clock signal VC having a reference frequency, for example, 68 MHz. Then, the image output unit 112 creates an image signal Sv corresponding to the image data included in the image formation command given to the main controller 11 with the video clock signal VC as a reference. The image signal Sv is output to the laser light source 62 of the exposure unit 6, the light beam is modulated according to the image signal Sv, and the modulated light beam is emitted forward from the laser light source 62.

  Further, in the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a mirror 64, and a deflector 65 are used to scan and expose the light beam from the laser light source 62 onto the surface (not shown) of the photoreceptor 2. A scanning lens 66 and a mirror 68 are provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651 of the deflector 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that focuses the light beam from the laser light source 62 in the sub-scanning direction Y. Then, the light beam from the laser light source 62 is shaped into a beam shape extending in the main scanning direction X by the beam shaping system 63, and this shaped light beam Li is inclined with respect to the deflection mirror surface 651 as shown in FIG. Incident. That is, in this embodiment, a mirror 64 is provided between the beam shaping system 63 and the deflecting mirror surface 651 of the deflector 65 to constitute a so-called oblique incident structure. More specifically, the shaped light beam Li has an acute angle γ with respect to the reference plane SS orthogonal to the swing axis (corresponding to the “drive axis” of the present invention) AX of the deflecting mirror surface 651 of the deflector 65. Incident on the deflecting mirror surface 651.

  The deflector 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique. The deflector 65 reflects the light beam reflected by the deflection mirror surface 651 in the main scanning direction X. Deflection is possible. More specifically, the deflector 65 is configured as follows. As shown in FIGS. 6 and 7, the deflector 65 includes a base portion 652 having first and second support portions 652a and 652b that are provided at a predetermined interval. The first and second vibrators 653a and 653b are attached to the first and second support portions 652a and 652b, respectively. That is, with respect to the first (left) vibrator 653a, the two left first arm portions 654a and 654a whose left outer end is fixed to the first (left) support portion 652a and whose inner end is a free end. It has become. The second (right) vibrator 653b has two left arm portions 654b and 654b whose left outer end is fixed to the second (right) support portion 652b and whose inner end is a free end. It has become.

  Further, a rectangular flat plate shape is formed so that the swing axis AX passing through the center of gravity position 655 is substantially parallel to each arm portion 654a, 654b at an intermediate position between the first arm portions 654a, 654a and the second arm portions 654b, 654b. The movable member 656 is disposed. In the movable member 656, one side (left side) portion of the gravity center position 655 is connected to the first arm portions 654a and 654a by the first torsion spring portions 657a and 657a, and the other side (right side) of the gravity center position 655. The site | part is connected with 2nd arm part 654b, 654b by 2nd torsion spring part 657b, 657b. That is, in the deflector 65, the first (left) vibrator 653a and the second (right) vibrator 653b face each other to form an outer frame portion, and the first and second vibrators 653a and 653b The first and second torsion spring portions 657a, 657a, 657b, and 657b are integrally connected to the movable member 656.

  In this embodiment, in order to make it possible to adjust the spot diameter of the beam spot formed on the photosensitive member (latent image carrier) 2 as described later, the movable member 656 is finished in a trapezoidal shape when viewed from the front. An aluminum film or the like is formed as a deflection mirror surface 651 on the surface of the movable member 656. Accordingly, as shown in FIG. 8, the deflection mirror surface 651 is formed such that the width W of the deflection mirror surface 651 in the main scanning direction X continuously changes in the sub-scanning direction Y.

  In addition, a vibration drive unit 658 is provided in the deflector 65 in order to vibrate the movable member 656 around the swing axis AX. The vibration driving unit 658 includes first laminated piezoelectric actuator portions 659a and 659a disposed on one side (left side) with respect to the swing axis AX, and a second stacked piezoelectric element disposed on the other side (right side) with respect to the swing axis AX. Actuators 659b and 659b are provided. That is, the first laminated piezoelectric actuator portions 659a and 659a are disposed between the upper left and lower ends 652c and 652c of the base portion 652 and the free ends of the two arm portions 654a and 654a of the first vibrator 653a. The upper and lower end surfaces are fixed to the base portion 652 and the first arm portions 654a and 654a, respectively. The second laminated piezoelectric actuator portions 659b and 659b are disposed between the upper right and lower lower end portions 652d and 652d of the base portion 652 and the free end portions of the two arm portions 654b and 654b of the second vibrator 653b. The upper and lower end surfaces thereof are fixed to the base portion 652 and the second arm portions 654b and 654b, respectively. The first and second laminated piezoelectric actuator sections 659a and 659b are periodically applied with voltages having opposite phases from the mirror driving section 121 of the exposure control unit 12.

  Each of the stacked piezoelectric actuator portions 659a and 659b is a piezoelectric actuator in which a plurality of piezoelectric elements are stacked in a predetermined direction Z, and expands and contracts in the stacking direction Z according to a signal given from the outside. Then, when a signal whose drive voltage periodically changes is applied to each of the laminated piezoelectric actuator portions 659a and 659b from the mirror drive portion 121, the laminated piezoelectric actuator portion expands and contracts according to the signal. For this reason, when a voltage having an opposite phase is applied to the first and second laminated piezoelectric actuator portions 659a and 659b, the movable member 656 swings about the swing axis AX passing through the center of gravity position 655. When a voltage is applied only to the first laminated piezoelectric actuator portion 659a, for example, as shown in FIG. 9, the arm portion 654a of the first vibrator 653a moves in the normal direction (upward direction) Z. Then, the movement of the arm portion 653a is transmitted to the movable member 656 via the first torsion spring portion 657a, and this becomes rotational torque, and the movable member 656 is clockwise about the swing axis AX passing through the center of gravity position 655. Rocks. Further, when a voltage is applied only to the second laminated piezoelectric actuator portion 659b, the arm portion 654b of the second vibrator 653b moves in the normal direction (upward direction in the figure) Z, and the above is applied to the movable member 656. A reverse rotational torque is applied, and as a result, the movable member 656 swings counterclockwise about the swing axis AX. Here, the “normal direction” means the normal direction of the deflection mirror surface 651 in a state where the movable member 656 is stationary.

  Then, as described above, the deflector 65 swings the movable member 656, deflects the light beam from the light source 62 by the deflection mirror surface 651, and scans in the main scanning direction X. This scanning light beam forms an image on the photosensitive member 2 via the scanning lens 66 and the folding mirror 67, and a light beam spot is formed on the photosensitive member surface 21. In this embodiment, the scanning lens 66 is composed of a single lens, and the scanning lens 66 corresponds to the “optical system” of the present invention. Note that the number and arrangement of the lenses are not limited to this, and a scanning lens employed in an exposure unit equipped with a deflection mirror surface can be used.

  Here, the apparatus employing the deflector 65 having the above configuration has the following characteristics. That is, in this deflector 65, the movable member 656 can be displaced in the normal direction Z by adjusting the voltage of the mirror drive signal applied to the first and second laminated piezoelectric actuator portions 659a and 659b. For example, as shown in FIG. 10, when the same offset voltage is applied to the mirror drive signals applied to both laminated piezoelectric actuator portions 659a and 659b with the deflection angle of the deflecting mirror surface 651 being zero, the volume variation in the normal direction (+ Z) The amount is the same, and the movable member 656 is displaced in the normal direction (+ Z) by an amount corresponding to the offset voltage. Of course, the displacement of the movable member 656 according to the offset voltage is not a phenomenon peculiar when the swing angle is zero, and the movable member 656 is adjusted as a whole by adjusting the offset voltage at any swing angle. A parallel shift in the line direction Z can be performed. In other words, in this embodiment, the mirror driving signal is supplied from the mirror driving unit 121 to the vibration driving unit 658 to vibrate the movable member 656, and the movable member 656 is adjusted by adjusting the offset voltage for each swing angle of the deflecting mirror surface 651. It is possible to shift in parallel in the normal direction Z as a whole.

  When the movable member 656 is thus shifted in parallel in the normal direction Z, the position of the deflection mirror surface 651 in the normal direction Z (hereinafter referred to as “deflection surface position”) fluctuates. As a result, the scanning lens 66 and the folding mirror are changed. The diameter of the spot imaged on the photosensitive member 2 via 67 changes in the main scanning direction X. This point will be described with reference to FIG.

  FIG. 11 is a diagram schematically showing the relationship between the deflection surface position and the spot shape. In the figure, the leftmost column shows the position of the deflection surface, and the position of the deflection mirror surface 651 can be controlled by setting an offset voltage. Here, three typical deflection surface positions will be described.

(A) Standard position: set the offset voltage to zero When the offset voltage is set to zero, only the mirror drive signal is given from the mirror drive unit 121 to the vibration drive unit 658, and the movable member 656 vibrates. For this reason, the deflection mirror surface 651 has zero parallel shift amount due to the application of the offset voltage, and the deflection surface position becomes the standard position. At this standard position, the shaped light beam Li is incident at the upper end side of the deflecting mirror surface 651, that is, when the width W of the deflecting mirror surface 651 in the main scanning direction is narrow, and the so-called overfill state is established. Only the portion of the shaped light beam Li corresponding to the length DWa in the main scanning direction is reflected by the deflecting mirror surface 651 and deflected toward the photoreceptor 2. As the offset voltage is gradually increased, the deflection surface position gradually moves in the normal direction Z, and the length of the light beam reflected by the deflection mirror surface 651 increases in the main scanning direction.

(B) Intermediate position: the offset voltage is set to the intermediate value Vb (<Vmax),
When the offset voltage reaches the intermediate value Vb, the shaped light beam Li is incident on the center of the deflecting mirror surface 651 in the sub-scanning direction Y, and the portion corresponding to the main scanning direction length DWb (> DWa) of the shaped light beam Li. Is reflected by the deflecting mirror surface 651 and deflected toward the photosensitive member 2.

(C) Maximum position: Set the offset voltage to the maximum value Vmax When the offset voltage reaches the maximum value Vc, the lower end side of the deflection mirror surface 651 in the sub-scanning direction Y, that is, the main scanning direction width W of the deflection mirror surface 651 is the largest. The shaped light beam Li is incident on the wide side, and the portion corresponding to the length DWc (>DWb> DWa) in the main scanning direction of the shaped light beam Li is reflected by the deflecting mirror surface 651 and deflected toward the photosensitive member 2. The

  As described above, when the deflection surface position fluctuates, the incident position of the shaped light beam in the sub-scanning direction Y changes according to the parallel shift amount SD from the standard position and is reflected by the deflection mirror surface 651 of the shaped light beam Li. The length of the light beam in the main scanning direction varies. As a result, the spot diameter on the photoreceptor 2 also varies. That is, in the main scanning direction X, the beam waist diameter decreases and the spot diameter decreases as the width of the scanning light beam increases. Therefore, the spot diameter in the main scanning direction X on the photosensitive member surface 21 is corrected by adjusting the offset voltage for each swing angle of the deflecting mirror surface 651 and shifting the movable member 656 in parallel in the normal direction Z as a whole. can do. That is, in this embodiment, the spot diameter can be dynamically controlled according to the position in the main scanning direction while scanning the light beam in the main scanning direction X. In addition, the effect by this dynamic control is explained in full detail later.

  Further, the light beam thus scanned in the main scanning direction X is guided to the light detection sensor 60 by the folding mirror 69. In addition, a signal Hsync output by the sensor 60 detecting and outputting a light beam is given to the writing timing adjusting unit 102 of the engine controller 10. The write timing adjusting unit 102 is supplied with a clock signal for timing from the count clock generating unit 103 of the engine controller 10, and based on this clock signal for timing, the write timing adjusting unit 102 has elapsed from the detection signal Hsync. Time is measured, and video request (write request) signals Vreq are sequentially output to the image output unit 112 at an appropriate timing. Upon receiving the video request signal Vreq, the image output unit 112 outputs the image signal Sv with reference to the video clock signal VC. In this way, the writing timing adjusting unit 102 adjusts the output timing of the video request signal Vreq, thereby adjusting the latent image writing position in the main scanning direction X. In this embodiment, the frequency of the clock signal for timing is set to a value larger than that of the video clock signal VC, for example, four times the frequency of the video clock signal VC. As a result, the video request signal Vreq can be controlled with high resolution, and the writing start position of the latent image can be accurately controlled.

  The detection signal Hsync of the scanning light beam from the light detection sensor 60 is also transmitted to the measurement unit 123 of the exposure control unit 12, and the measurement unit 123 calculates drive information related to the scanning time of the light beam and the drive cycle. The The actual measurement information calculated by the measuring unit 123 is transmitted to the mirror driving unit 121, and the mirror driving unit 121 adjusts the mirror driving signal as necessary. Further, the mirror drive unit 121 corrects the spot diameter by giving the vibration drive unit 658 a signal in which an offset voltage corresponding to the swing angle of the deflecting mirror surface 651 is superimposed on the mirror drive signal.

  FIG. 12 is a graph showing the spot diameter correcting operation. FIG. 13 is a diagram showing a signal given to the vibration drive unit for performing the correction of FIG. Also in this embodiment, a mirror driving signal (thick broken line in FIG. 13) indicating a reverse phase voltage is applied to the first and second laminated piezoelectric actuator portions 659a and 659b to cause the deflecting mirror surface 651 to sine vibrate. When the light beam is scanned, the diameter of the beam spot BS formed on the photosensitive member surface 21 varies in the main scanning direction X as in the conventional apparatus (FIG. 12A). Therefore, in this embodiment, the spot diameter is dynamically controlled according to the position in the main scanning direction while scanning the light beam in the main scanning direction X. More specifically, in order to change the offset voltage in accordance with the swing angle of the deflecting mirror surface 651, a correction signal (thin broken line in FIG. 13) indicating the change in the offset voltage is superimposed on the mirror drive signal and the combined signal. (Solid line in FIG. 13) is created, and a composite signal is given to the first and second laminated piezoelectric actuator portions 659a and 659b. As a result, the deflection surface position becomes the standard position near the optical axis OA (scanning center) as shown in FIG. 12B, that is, the deflection surface position = 0 mm, whereas the absolute value of the swing angle increases. Therefore, the amount of parallel shift SD is increased, and the spot diameter is reduced. As a result, the tendency that the spot diameter gradually increases as it goes to the scanning end (FIG. 12A) and the effect of adjusting the parallel shift amount SD are canceled each other, and the spot diameter becomes uniform over the entire scanning range. (FIG. (C)).

  As described above, according to this embodiment, the movable member 656 is shifted in parallel according to the swing angle of the deflecting mirror surface 651 to correct the spot diameter on the photosensitive member surface 21. The image quality can be improved by aligning the diameters formed on the photoreceptor surface 21.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the deflection mirror surface 651 is finished in a substantially trapezoidal shape when viewed from the front, but the shape of the deflection mirror surface 651 is not limited to this. The deflection mirror surface 651 can be formed such that the width W of the deflection mirror surface 651 in the main scanning direction X changes in the sub-scanning direction Y. For example, as shown in FIG. 14, the deflection mirror surface 651 may be formed so that the width of the central portion is the shortest in the sub-scanning direction Y and becomes longer as the distance from the central portion increases in the sub-scanning direction Y.

  In this case, it is necessary to make the adjustment of the deflection surface position different from that of the above-described embodiment in accordance with the shape of the deflection mirror surface 651. More specifically, in the apparatus using the deflection mirror surface 651 having the shape shown in FIG. 14, the above-described implementation is performed by dynamically controlling the spot diameter by adjusting the deflection surface position as shown in FIGS. 15 and 16. The same effect as the form can be obtained. That is, also in this embodiment, the mirror driving signal (thick broken line in FIG. 16) indicating the reverse phase voltage is applied to the first and second laminated piezoelectric actuator portions 659a and 659b to make the deflection mirror surface 651 sinusoidal. When the light beam is scanned by being oscillated, the diameter of the beam spot BS formed on the photosensitive member surface 21 varies in the main scanning direction X as in the conventional apparatus (FIG. 15A). Therefore, in this embodiment, in order to change the offset voltage according to the swing angle of the deflecting mirror surface 651, a correction signal (a thin broken line in FIG. 16) indicating the change in the offset voltage is superimposed on the mirror drive signal and synthesized. A signal (solid line in FIG. 16) is created, and a composite signal is given to the first and second laminated piezoelectric actuator portions 659a and 659b. As a result, the deflection surface position is the maximum position at one end of the effective scanning range as shown in FIG. 15B, and the deflection surface position approaches the standard position toward the other end side, and the optical axis OA Near (scanning center) is an intermediate position, and the other end is a standard position. For this reason, as in the embodiment shown in FIGS. 12 and 13, there is a tendency that the spot diameter gradually increases from the scanning center to the scanning end (FIG. 15A) and the effect of adjusting the parallel shift amount SD. Are canceled each other and the spot diameter becomes uniform over the entire scanning range ((c) in the figure).

  Further, in the above embodiment, as shown in FIG. 11, for example, the shaping light beam Li is incident on the deflection mirror surface 651 in an overfill state at any deflection surface position. However, maintaining the overfill state is not an essential component requirement, and the overfill state may not be satisfied at a specific deflection surface position. For example, in FIG. 11, the entire shaped light beam Li may be reflected by the deflection mirror surface 651 when the deflection surface position reaches the maximum position.

  In the above-described embodiment, the present invention is applied to a four-cycle color image forming apparatus. However, the application target of the present invention is not limited to this, and a so-called tandem color image forming apparatus or a single color image forming apparatus. The present invention can be applied to a monochrome image forming apparatus that forms an image.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. 2 is a main scanning sectional view of an exposure unit provided in the image forming apparatus of FIG. FIG. 2 is a sub-scan sectional view of an exposure unit provided in the image forming apparatus of FIG. 1. FIG. 2 is a view showing an exposure control unit for controlling the exposure unit and the exposure unit of the image forming apparatus of FIG. 1. The figure which shows the deflector which is one component of an exposure unit. The figure which shows the deflector which is one component of an exposure unit. The figure which shows the deflector which is one component of an exposure unit. The main scanning sectional view showing operation of a deflector. The main scanning sectional view showing operation of a deflector. The figure which shows typically the relationship between a deflection surface position and spot shape. The graph which shows correction | amendment operation | movement of a spot diameter. The figure which shows the signal given to a vibration drive part in order to perform correction | amendment of FIG. The figure which shows other embodiment. The graph which shows the correction | amendment operation | movement of the spot diameter in other embodiment. The figure which shows the signal given to a vibration drive part in order to perform correction | amendment of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Photoconductor (latent image carrier), 6 ... Exposure unit, 21 ... Photoconductor surface, 62 ... Laser light source, 65 ... Deflector, 66 ... Scanning lens (optical system), 651 ... Deflection mirror surface, 652 ... Base , 652a ... first support, 652b ... second support, 653a ... first vibrator, 653b ... first vibrator, 654a ... first arm, 654b ... second arm, 655 ... center of gravity, 656 ... movable member, 657a ... first torsion spring part, 657b ... second torsion spring part, 658 ... vibration drive part, 659a, 659b ... laminated piezoelectric actuator part (vibration drive part), AX ... swing axis ( Drive axis), DWa, DWb, DWc ... length in the main scanning direction, L ... light beam, Li ... shaped light beam, X ... main scanning direction, Y ... sub-scanning direction, Z ... normal direction

Claims (6)

A latent image carrier that moves in the sub-scanning direction;
A deflecting mirror surface formed on the surface of a movable member that shapes a light beam from a light source into a beam shape extending in a main scanning direction substantially orthogonal to the sub-scanning direction and vibrates around a drive axis parallel to the sub-scanning direction In contrast, the shaped light beam is incident obliquely on the sub-scan section including the sub-scan direction and scanned in the main scan direction, and the scanning light beam is spot-shaped on the surface of the latent image carrier by the optical system. An exposure unit that forms a latent image by forming an image on
The deflection mirror surface is formed such that the width of the deflection mirror surface in the main scanning direction changes in the sub-scanning direction,
The exposure unit oscillates the movable member and shifts the vibrating movable member as a whole in parallel to the normal direction of the deflection mirror surface in synchronization with a swing angle of the deflection mirror surface. An image forming apparatus, wherein a length of a light beam reflected by the deflection mirror surface is changed in a main scanning direction by changing an incident position of the shaped light beam in a scanning direction.   The image forming apparatus according to claim 1, wherein the deflection mirror surface is formed such that a width of the deflection mirror surface in the main scanning direction continuously changes in the sub-scanning direction.   The image forming apparatus according to claim 2, wherein the deflecting mirror surface has a trapezoidal shape when viewed from the normal direction.   The image forming apparatus according to claim 2, wherein the deflection mirror surface is formed such that the width of the central portion is the shortest in the sub-scanning direction and becomes longer as the distance from the central portion increases in the sub-scanning direction. The exposure unit includes
A base portion having first and second support portions spaced apart by a predetermined interval;
A first vibrator having two first arm portions whose outer end portions are fixed to the first support portion and whose inner end portions are free ends;
A second vibrator having two second arm portions whose outer end portions are fixed to the second support portion and whose inner end portions are free ends;
The movable member arranged so that the drive shaft is positioned between the first arm portion and the second arm portion, and the first arm portion on the first vibrator side with respect to the drive shaft. A first torsion spring portion to be coupled;
A second torsion spring portion connecting the movable member to the second arm portion on the second vibrator side with respect to the drive shaft;
A vibration drive unit that vibrates the movable member by applying a driving force to the first and second vibrators independently and reciprocally moving each arm unit in the normal direction of the deflection mirror surface; And
While vibrating the movable member, the vibration driving unit adjusts the driving force applied to the first and second vibrators in synchronization with the swing angle of the deflecting mirror surface, so that the moving movable member as a whole is adjusted. The image forming apparatus according to claim 1, wherein the image forming apparatus is shifted in parallel to the normal line direction. The vibration drive unit includes two first piezoelectric actuators interposed between the base unit and each first arm unit, and 2 interposed between the base unit and each second arm unit. Second piezoelectric actuators, one end of each piezoelectric actuator is connected to the base portion, and the other end is connected to the arm portion, and the first piezoelectric actuator and the second piezoelectric actuator are connected to each other. The image forming apparatus according to claim 5, wherein the movable member is vibrated by receiving mirror drive signals having opposite phases to each other.
Each of the four piezoelectric actuators is given a signal obtained by adding an offset voltage corresponding to the swing angle of the deflecting mirror surface to the mirror drive signal, and the movable member is totally shifted in parallel to the normal direction. Image forming apparatus.

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