JP2013014044A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct distances between light-emitting elements and image locations, that change depending on changes of temperatures of the light-emitting elements of an exposure device.SOLUTION: An image forming apparatus 100 which forms an image on a recording medium includes: an image carrier 6; the exposure device 23 having a plurality of light-emitting elements 5a which are arranged side by side in a longitudinal direction orthogonal to a rotation direction of the image carrier and which emit light in accordance with image information to expose a surface of the image carrier, and image forming elements 4 which form, on the surface of the image carrier, images of the lights from the plurality of the light-emitting elements; an optical member 1 which is arranged movably on a light path between the plurality of light-emitting elements and the image carrier so as to correct the distances between the plurality of light-emitting elements and the image locations on the image carrier of the lights from the plurality of light-emitting elements wherein that distances change depending on changes of the temperatures of the plurality of light-emitting elements; and a drive unit 12 which moves the optical member so as to correct the distances between the plurality of light-emitting elements and the image locations in accordance with information related to the temperatures of the plurality of light-emitting elements.

Description

  The present invention relates to an image forming apparatus having an exposure device.

  Conventionally, image forming apparatuses such as copying machines and printers, particularly electrophotographic image forming apparatuses, use a laser scanning method or an LED exposure method described below as an image writing method (exposure method).

  The LED exposure method is a method using an LED (light emitting diode) array as a light source for exposure and a rod lens array as an imaging element. An LED exposure type image forming apparatus forms an image of light output from an LED array on the surface of a photosensitive drum (image carrier) via a rod lens array (imaging element), and the surface of the photosensitive drum. An electrostatic latent image is formed thereon.

  The LED array has a plurality of LEDs (light emitting elements) arranged side by side in a longitudinal direction orthogonal to the rotation direction of the photosensitive drum. A plurality of LEDs are selectively emitted while rotating the photosensitive drum. Light from the plurality of LEDs forms an image on the surface of the photosensitive drum via the rod lens array, and an electrostatic latent image is formed on the surface of the photosensitive drum. Hereinafter, the combination of the LED array and the rod lens array is referred to as an LED head (exposure device).

  The LED exposure method has an advantage that the image forming apparatus can be greatly downsized as compared with the laser scanning method. In a so-called tandem color image forming apparatus having a plurality of image forming units, the effect of downsizing the apparatus is particularly great.

  The conjugate length (imaging position or focal length: TC) of the rod lens array is about 10 millimeters (mm), and the focal depth is about ± 0.05 mm. While the focal depth of the laser scanning method is about ± 2 mm, the focal depth of the LED exposure method is extremely shallow. Therefore, an optical system using a rod lens array is extremely sensitive to defocusing. When the parallel position or the position in the optical axis direction of the photosensitive drum, the LED array, and the rod lens array is shifted, it is likely to cause a focus shift. When defocusing occurs, the image quality is significantly reduced.

  In order to solve such a problem, the invention described in Patent Document 1 measures the density distribution of the toner image formed on the photosensitive drum with a density sensor, and based on the measurement result, the LED head is mounted. Move in the optical axis direction to adjust the focus.

JP 2004-151543 A

However, the imaging position may shift due to the temperature rise of the exposure apparatus.
In the light emitting element used in the exposure apparatus, the temperature of the light emitting element rises due to the continuous lighting operation. The wavelength of light of the light emitting element has temperature dependency. As the temperature of the light emitting element increases, the wavelength of light of the light emitting element increases.

  The conjugate length of the imaging element used in the exposure apparatus has wavelength dependency. The conjugate length of the imaging element extends in proportion to the increase in wavelength. For this reason, as the temperature of the light emitting element rises, the conjugate length of the imaging element increases.

  That is, even when the image forming position of the exposure apparatus is accurately adjusted on the surface of the image carrier during assembly, the conjugate length of the image forming element changes due to the temperature change of the light emitting element. Arise.

  In view of such a conventional problem, the present invention can correct the distance between the light emitting element and the imaging position, which changes due to the temperature change of the light emitting element of the exposure apparatus, according to the information about the temperature of the light emitting element. An object is to provide an image forming apparatus.

  In order to achieve the above object, an image forming apparatus for forming an image on a recording medium according to the present invention is provided with an image carrier and the image carrier arranged side by side in a longitudinal direction perpendicular to the rotation direction of the image carrier. An exposure apparatus comprising: a plurality of light emitting elements that emit light according to image information to expose the surface of the image; and an imaging element that forms an image of light from the plurality of light emitting elements on the surface of the image carrier; In order to correct the distance between the plurality of light emitting elements and the imaging position on the image carrier of the light from the plurality of light emitting elements, which changes according to the temperature change of the plurality of light emitting elements. An optical member movably disposed on an optical path between the plurality of light emitting elements and the image carrier, and the information regarding the temperature of the plurality of light emitting elements. Correct the distance to the imaging position And having a drive unit for moving the optical member in order.

  According to the present invention, it is possible to correct the distance between the light emitting element and the imaging position, which is changed by the temperature change of the light emitting element of the exposure apparatus, according to the information regarding the temperature of the light emitting element.

1 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention. The figure which shows a LED head. The figure which shows the change of the conjugate length of the rod lens array with respect to the temperature change of LED. The figure which shows the refraction | bending of the light ray by the movement of a wedge-shaped optical member, and the movement of an optical path. The figure which shows the wedge-shaped optical member arrange | positioned in the optical path between LED array and a photoreceptor drum. The figure which shows the support member which supports a wedge-shaped optical member. Sectional drawing of an optical member. The block diagram of the control apparatus which drives a motor according to the information regarding the temperature of LED. 6 is a flowchart illustrating adjustment of an imaging position according to the first embodiment. 10 is a flowchart illustrating adjustment of an imaging position according to the second embodiment. 10 is a flowchart illustrating adjustment of an imaging position according to the third embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific descriptions unless otherwise specified. It is just an example.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to Embodiment 1 of the present invention. The image forming apparatus 100 includes an image forming unit 80 and a feeding unit 90 that feeds a sheet (recording medium) S to the image forming unit 80.
The image forming unit 80 includes four image forming stations 81 (81Y, 81C, 81M, 81K) arranged in tandem, an intermediate transfer belt (intermediate transfer member) 26, and a fixing device 28. Each of the image forming stations 81 includes a photosensitive drum (image carrier) 6 (6Y, 6C, 6M, 6K). The photosensitive drum 6 rotates in the direction indicated by the arrow R. Around the photosensitive drum 6, a charging device 22, an LED head (exposure device) 23, a developing device 24, a primary transfer member 25, and a cleaning device 21 are provided.
The charging device 22 (22Y, 22C, 22M, 22K) uniformly charges the surface of the photosensitive drum 6 (6Y, 6C, 6M, 6K). The LED head 23 (23Y, 23C, 23M, 23K) exposes the uniformly charged surface of the photosensitive drum 6 according to image information, and forms an electrostatic latent image on the surface of the photosensitive drum 6. The developing device 24 (24Y, 24C, 24M, 24K) develops the electrostatic latent image on the surface of the photosensitive drum 6 with a developer (toner) to form a toner image.
The developing device 24Y has a yellow developer (yellow toner). The developing device 24Y forms a yellow toner image on the surface of the photosensitive drum 6Y. The developing device 24C has a cyan developer (cyan toner). The developing device 24C forms a cyan toner image on the surface of the photosensitive drum 6C. The developing device 24M includes a magenta developer (magenta toner). The developing device 24M forms a magenta toner image on the surface of the photosensitive drum 6M. The developing device 24K has a black developer (black toner). The developing device 24K forms a black toner image on the surface of the photosensitive drum 6K.
The intermediate transfer belt 26 contacts the photosensitive drum 6 and rotates in the direction indicated by the arrow E.
The primary transfer member 25 (25Y, 25C, 25M, 25K) transfers the toner image on the surface of the photosensitive drum 6 onto the intermediate transfer belt 26. The cyan toner image is superimposed on the yellow toner image on the intermediate transfer belt 26. The magenta toner image is superimposed on the cyan toner image. The black toner image is superimposed on the magenta toner image.
The four toner images sequentially superimposed on the intermediate transfer belt 26 are transferred onto the sheet S fed from the feeding unit 90 by the secondary transfer roller 27.
The toner image on the sheet S is fixed on the sheet by the fixing device 28 and an image is formed on the sheet S. The sheet S on which the image is formed is discharged onto the discharge tray 30 by the discharge roller 29.

Next, the LED head 23 used in the image forming apparatus 100 according to the first embodiment will be described in detail with reference to FIG.
FIG. 2 is a diagram showing the LED head 23. FIG. 2A is a perspective view showing the LED head 23. As shown in FIG. 2A, the photosensitive drum 6 rotates about the axis X in the direction indicated by the arrow R.
The LED head 23 has an elongated shape extending in the longitudinal direction parallel to the axis X of the photosensitive drum 6. The LED head 23 includes an LED array (light emitting element array) 5 and a rod lens array (imaging element array) 4.
The LED array 5 includes a plurality of LEDs (light emitting elements) 5 a arranged side by side along the axis X of the photosensitive drum 6. In the first embodiment, the plurality of LEDs 5a are arranged linearly. That is, the LED heads 23 are provided side by side in a longitudinal direction (axial direction) orthogonal to the rotation direction R of the photosensitive drum 6, and a plurality of LEDs 5 a that emit light according to image information to expose the surface of the photosensitive drum 6. Have
The plurality of LEDs 5a are driven by the LED drive circuit 18 (FIG. 8), and are made to emit light according to the image information. The plurality of LEDs 5a and the LED drive circuit 18 are disposed on a substrate (not shown).
The rod lens array 4 has a plurality of rod lenses (imaging elements) 4 a arranged along the axis X of the photosensitive drum 6. FIG. 2B is a partial cross-sectional perspective view of the rod lens array 4. The rod lens array 4 has a plurality of rod lenses 4a arranged linearly in two rows between two plates 4b. Reference numeral 4a denotes an erecting equal-magnification imaging lens. In the present embodiment, the diameter of the rod lens 4a is about 0.6 mm. The rod lens 4a collects the light emitted from the plurality of LEDs 5a and forms an image on the surface of the photosensitive drum 6 at an equal magnification. In the first embodiment, the LED array 5 and the rod lens array 4 are integrated to form an LED head 23 as an exposure light source.
A two-dimensional electrostatic latent image is formed on the surface of the photosensitive drum 6 by selectively causing the plurality of LEDs 5a of the LED array 5 to emit light while rotating the photosensitive drum 6 in the direction indicated by the arrow R.

  The focal depth of the rod lens array 4 is extremely shallow, about ± 0.05 mm. Due to the lighting operation of the LED 5a, the LED 5a is self-heated and the emission center wavelength (hereinafter referred to as wavelength) λ is extended. The conjugate length TC (FIG. 5) of the rod lens array 4 extends in proportion to the extension of the wavelength λ. The conjugate length TC is the distance between the LED 5a and the imaging position. For this reason, even when the imaging position can be accurately adjusted on the surface of the photosensitive drum 6 during assembly, the conjugate length TC is extended by the heat generated by the LED 5a, so that the distance between the LED 5a and the imaging position is increased. Extend. For this reason, the imaging position deviates from the surface of the photosensitive drum 6.

  FIG. 3 is a diagram showing a change in the conjugate length TC of the rod lens array 4 with respect to the temperature change of the LED 5a. Fig.3 (a) is a figure which shows the change of wavelength (lambda) of the light of LED5a with respect to the temperature rise of LED5a. The LED 5a generates heat according to usage conditions such as a continuous lighting operation. The wavelength λ of the light of the LED 5a has temperature dependence. As can be seen from FIG. 3A, when the temperature of the LED 5a rises once, the wavelength λ extends by about 0.3 nanometer (nm).

  The conjugate length TC of the rod lens array 4 has wavelength dependency. FIG. 3B is a diagram showing a change in the conjugate length TC of the rod lens array 4 with respect to a change in the wavelength λ of light. The rod lens array 4 has a nominal conjugate length TC0 of 9.1 mm for light of wavelength λ of 570 nm. As can be seen from FIG. 3B, the conjugate length TC extends in proportion to the increase in the wavelength λ.

For this reason, the conjugate length TC of the rod lens array 4 extends as the temperature of the LED 5a increases. FIG. 3C is a diagram showing a change in the conjugate length TC of the rod lens array 4 with respect to the temperature rise of the LED 5a. As can be seen from FIG. 3C, when the temperature of the LED 5a is increased by about 26.3 ° C., the conjugate length TC of the rod lens array 4 is extended by about 0.05 mm. The extension of the conjugate length TC of 0.05 mm corresponds to the focal depth of ± 0.05 mm of the LED head 23. That is, when the temperature of the LED 5a rises by 26.3 ° C. or more, focus shift occurs.
In general, it is known that the temperature increase Δt due to continuous light emission of the LED 5a reaches about 60 to 70 ° C. If the temperature rise Δt is 60 ° C., the change ΔTC in the conjugate length TC is about 0.11 mm. Accordingly, the imaging position is deviated from the surface of the photosensitive drum 6.
In the first embodiment, the optical distance between the LED 5a and the surface of the photosensitive drum 6 is corrected by inserting the wedge-shaped optical member 1 into the optical path between the LED 5a and the surface of the photosensitive drum 6. That is, the optical distance between the LED 5a and the surface of the photosensitive drum 6 is changed by changing the insertion amount of the wedge-shaped optical member 1 into the optical path by the change amount ΔTC of the conjugate length TC of the rod lens array 4. By correcting the optical distance between the LED 5 a and the surface of the photosensitive drum 6, the actual distance between the LED 5 a and the imaging position is corrected so that the imaging position matches the surface of the photosensitive drum 6. .

Next, the wedge-shaped optical member (optical member) 1 of Example 1 will be described.
The wedge-shaped optical member 1 is made of a material having excellent light transmittance and a refractive index different from that of air. In consideration of moldability, the wedge-shaped optical member 1 is preferably formed of, for example, a resin such as acrylic or styrene.

  FIG. 4 is a diagram showing the refraction of the light beam 3 and the movement of the optical path due to the movement of the wedge-shaped optical member 1. The wedge-shaped optical member 1 has an incident surface 1a on which light rays (exposure light) 3 from a plurality of LEDs 5a are incident, and an emission surface 1b that emits light rays 3. The entrance surface 1a is not parallel to the exit surface 1b. In Embodiment 1, the wedge-shaped optical member 1 has a triangular cross-sectional shape. The cross-sectional shape of the wedge-shaped optical member 1 is not limited to a triangle but may be a trapezoid. Other shapes may be used as long as the optical conditions described later are satisfied. The wedge-shaped optical member 1 has a length comparable to the length in the longitudinal direction of the LED array 5 and the rod lens array 4 (FIG. 6A).

仮にθ＝１０°、ｎ＝１．４９の楔形光学部材１を用いた場合、α＝５．０°と算出することができる。 Since the entrance surface 1 a and the exit surface 1 b of the wedge-shaped optical member 1 are not parallel to each other, the light beam 3 is refracted by the wedge-shaped optical member 1 due to the difference between the refractive index of air and the refractive index of the wedge-shaped optical member 1.
As shown in FIG. 4, the angle formed by the entrance surface 1a and the exit surface 1b of the wedge-shaped optical member 1 is defined as θ. An angle formed by the light beam 3 incident on the incident surface 1a with respect to the perpendicular P1 of the exit surface 1b is defined as α. Let n be the refractive index of the material of the wedge-shaped optical member 1 with respect to air.
When the light beam 3 is emitted in a direction (perpendicular direction) perpendicular to the exit surface 1b of the wedge-shaped optical member 1, an angle α formed by the light beam 3 with respect to the normal line P1 of the exit surface 1b is calculated by the following equation (1). Is done.

If the wedge-shaped optical member 1 with θ = 10 ° and n = 1.49 is used, α = 5.0 ° can be calculated.

As shown in FIG. 4, when the wedge-shaped optical member 1 is moved in a direction B perpendicular to the longitudinal direction of the photosensitive drum 6 in a plane parallel to the exit surface 1b, refraction derived from the shape of the wedge-shaped optical member 1 is generated. For this reason, the irradiation position on the photosensitive drum 6 is shifted. The irradiation position is shifted in a direction B orthogonal to the longitudinal direction of the photosensitive drum 6.
In the first embodiment, the LED drive circuit (light emission timing adjusting means) 18 (FIG. 8) corrects the deviation of the irradiation position by adjusting the light emission timing of the LED 5a according to the movement amount of the wedge-shaped optical member 1.

上記と同様に、θ＝１０°、ｎ＝１．４９の楔形光学部材１を用いた場合、光線３のＢ方向への移動量Δｄと、光線３が楔形光学部材１の中を通過する実空間上の距離の変化量Δｌは、以下のように算出される。
Δｄ＝０．０１５６ΔＸ
Δｌ＝０．１７９ΔＸ As shown in FIG. 4, the movement amount of the wedge-shaped optical member 1 in the direction B perpendicular to the longitudinal direction of the photosensitive drum 6 in a plane parallel to the exit surface 1b is Δx. Let Δd be the amount of movement of the light beam 3 emitted from the exit surface 1b in the B direction. Let Δl be the amount of change in the distance in real space through which the light beam 3 passes through the wedge-shaped optical member 1. The movement amount Δd and the change amount Δl are calculated by the equations (2) and (3), respectively.

Similarly to the above, when the wedge-shaped optical member 1 with θ = 10 ° and n = 1.49 is used, the amount of movement Δd of the light beam 3 in the B direction and the actual amount of the light beam 3 passing through the wedge-shaped optical member 1. The amount of change Δl in the space is calculated as follows.
Δd = 0.156ΔX
Δl = 0.179ΔX

From FIG. 3C, when the temperature rise Δt of the LED 5a is 60 ° C., the change amount ΔTC of the conjugate length TC of the rod lens array 4 is 0.11 mm.
In order to correct the variation ΔTC of 0.11 mm, the distance variation Δl is calculated as follows.
(N-1) Δl = 0.11
Since the refractive index n is 1.49, the distance change Δl is 0.2245 mm.
The movement amount Δx of the wedge-shaped optical member 1 for obtaining the change amount Δl of 0.2245 mm is calculated as 1.25 mm from the above formula.
By moving the wedge-shaped optical member 1 by 1.25 mm in a direction B orthogonal to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the exit surface 1b, a plurality of components that change according to changes in the temperature of the plurality of LEDs 5a. The distance between the LED 5a and the imaging position can be corrected.
The movement amount Δd of the light beam 3 in the B direction at this time is calculated as 0.020 mm from the above formula. The movement amount Δd can be corrected by adjusting the light emission timing of the LED 5a by the LED drive circuit 18 (FIG. 8).

FIG. 5 is a view showing the wedge-shaped optical member 1 disposed in the optical path between the LED array 5 (a plurality of LEDs 5 a) and the photosensitive drum 6.
FIG. 5A is a view showing the wedge-shaped optical member 1 disposed in the optical path between the LED array 5 and the rod lens array 4. The rod lens array 4 is arranged so that the optical axis OA1 of the rod lens array 4 is parallel to the normal P2 of the surface of the photosensitive drum 6 at the target irradiation position TP. The wedge-shaped optical member 1 is arranged so that the perpendicular P1 of the exit surface 1b of the wedge-shaped optical member 1 is parallel to the optical axis OA1 of the rod lens array 4.
Since the light beam 3 from the LED array 5 is refracted by the wedge-shaped optical member 1, the optical axis OA <b> 2 of the LED array 5 is perpendicular to the perpendicular line P <b> 1 of the exit surface 1 b of the wedge-shaped optical member 1, that is, the rod lens array 4. It arrange | positions so that it may incline with respect to optical axis OA1. That is, the emission direction of the light beam 3 of the LED array 5 is arranged to be inclined with respect to the normal line P <b> 2 of the surface of the photosensitive drum 6.
In FIG. 5A, the inclination angle of the optical axis OA2 of the LED array 5 with respect to the optical axis OA1 of the rod lens array 4 is set to α.
As described above, when a light beam is incident perpendicularly to the surface of the photosensitive drum 6 at the target irradiation position TP, the light beam incident on the wedge-shaped optical member 1 is previously applied to the normal line P2 of the surface of the photosensitive drum 6. Tilt.

FIG. 5B is a view showing the wedge-shaped optical member 1 disposed in the optical path between the rod lens array 4 and the photosensitive drum 6. The wedge-shaped optical member 1 is arranged so that the perpendicular P1 of the exit surface 1b of the wedge-shaped optical member 1 is parallel to the normal P2 of the surface of the photosensitive drum 6 at the target irradiation position TP.
Since the light beam 3 from the LED array 5 is refracted by the wedge-shaped optical member 1, the LED array 5 is arranged so that the optical axis OA2 of the LED array 5 is inclined with respect to the perpendicular P1 of the exit surface 1b of the wedge-shaped optical member 1. Have been placed. That is, the emission direction of the light beam 3 of the LED array 5 is arranged to be inclined with respect to the normal line P <b> 2 of the surface of the photosensitive drum 6.
The rod lens array 4 is arranged so that the optical axis OA1 of the rod lens array 4 is parallel to the optical axis OA2 of the LED array 5. That is, the rod lens array 4 is arranged so that the optical axis OA1 of the rod lens array 4 is inclined with respect to the perpendicular P1 of the exit surface 1b of the wedge-shaped optical member 1.
5B, the inclination angle of the optical axis OA1 of the rod lens array 4 with respect to the perpendicular P1 of the exit surface 1b of the wedge-shaped optical member 1 is set to α.
In FIG. 5B, the LED array 5 and the rod lens array 4 are arranged so that the light beam emitted from the rod lens array 4 and refracted by the wedge-shaped optical member 1 is parallel to the normal line P2 of the surface of the photosensitive drum 6. It is arranged to be inclined with respect to the normal line P2.
In the first embodiment, the wedge-shaped optical member 1 may be disposed in the optical path between the LED array 5 (the plurality of LEDs 5a) and the surface of the photosensitive drum 6 as shown in FIG.

FIG. 5 also shows a shift of the imaging position (focus shift) due to a temperature rise of the LED 5a.
In FIG. 5, the light beam path before the temperature of the LED 5a rises is indicated by a solid line. The imaging position is on the surface of the photosensitive drum 6.
The light beam path after the temperature of the LED 5a is increased is indicated by a dotted line. The conjugate length TC of the rod lens array 4 extends by a change amount ΔTC. The imaging position is shifted from the surface of the photosensitive drum 6 by a change amount ΔTC.
The light beam path after adjusting the optical distance by moving the wedge-shaped optical member 1 in a direction B perpendicular to the longitudinal direction of the photosensitive drum 6 in a plane parallel to the exit surface 1b is indicated by a broken line. The imaging position is adjusted on the surface of the photosensitive drum 6.
When the conjugate length TC of the rod lens array 4 is extended due to the temperature rise of the LED 5a, the wedge-shaped optical member 1 is moved in a direction B perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the emission surface 1b. As a result, the imaging position can be adjusted.

Below, the support member 7 which supports the position of the wedge-shaped optical member 1 so that adjustment is possible is demonstrated.
FIG. 6 is a view showing the support member 7 that supports the wedge-shaped optical member 1. FIG. 6A is a plan view of the support member 7. FIG. 6B is a cross-sectional view of the support member 7 taken along line VIB-VIB in FIG.
The wedge-shaped optical member 1 is supported by a support member 7. The support member 7 has seat surfaces 7a and 7b. The exit surface 1b of the wedge-shaped optical member 1 is in contact with the seating surfaces 7a and 7b. The wedge-shaped optical member 1 can slide on the seating surfaces 7a and 7b. The support member 7 has an opening 10 through which the light beam 3 passes.
Leaf springs (elastic members) 11 for holding the wedge-shaped optical member 1 are provided at both ends of the support member 7 in the longitudinal direction. Both ends in the longitudinal direction of the wedge-shaped optical member 1 are urged and held by the leaf spring 11 toward the seating surfaces 7a and 7b of the support member 7.
Elastic members 9 are provided at both ends of one side 7c of the support member 7, respectively. At both ends of the wedge-shaped optical member 1, the sharp tip 1 d of the wedge-shaped optical member 1 is in contact with each of the elastic members 9. The elastic member 9 biases the wedge-shaped optical member 1 in a direction orthogonal to the longitudinal direction of the support member 7. The elastic member 9 is, for example, a leaf spring, a coil spring, a rubber member, or the like.
Set screws (adjustment members) 8 are provided at both ends of the other side 7d of the support member 7, respectively. The set screw 8 is disposed to face the elastic member 9. The set screw 8 abuts on the side surface 1c on the side opposite to the tip 1d of the wedge-shaped optical member 1.
By rotating the set screw 8 clockwise, the set screw 8 moves the end portion of the wedge-shaped optical member 1 toward one side 7c of the support member 7 indicated by the arrow A1 against the urging force of the elastic member 9. Let By rotating the set screw 8 counterclockwise, the elastic member 9 moves the end portion of the wedge-shaped optical member 1 toward one side 7d of the support member 7 indicated by the arrow A2.
By rotating the two set screws 8 by the same rotation amount, the wedge-shaped optical member 1 can be translated in a direction perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the exit surface 1b.
Further, by rotating the two set screws 8 by different rotation amounts, the wedge-shaped optical member 1 can be swung in the directions indicated by the arrows A3 and A4 in a plane parallel to the emission surface 1b.
When the LED head 23 is assembled, the wedge-shaped optical member 1 is placed on the surface of the photosensitive drum 6 with respect to the support member 7 in a plane parallel to the exit surface 1b so that the imaging position is aligned with the surface of the photosensitive drum 6. 6 is moved in a direction perpendicular to the longitudinal direction. If necessary, the wedge-shaped optical member 1 is swung with respect to the support member 7 in a plane parallel to the exit surface 1 b so that the imaging position is aligned with the surface of the photosensitive drum 6.
With the above configuration, the optical distance of the light beam 3 from the LED 5a through the wedge-shaped optical member 1 to the surface of the photosensitive drum 6 can be changed, and an image can be formed on the surface of the photosensitive drum 6 with high accuracy. . When the LED array 5, the rod lens array 4, and the photosensitive drum 6 are assembled, the position of the wedge-shaped optical member 1 is adjusted by the support member 7 even when the parallel relationship and positional accuracy of these members are not high. Thus, the imaging position can be adjusted.
By using the support member 7, it is not necessary to provide a special focus adjustment mechanism for assembling the LED array 5, the rod lens array 4, and the photosensitive drum 6 with a high degree of parallelism and positional accuracy.

Nut members 19 and 20 are provided at both ends of the support member 7, respectively. Screw members 14 and 15 extending in a direction indicated by an arrow B orthogonal to the longitudinal direction of the support member 7 are screwed onto the nut members 19 and 20. A motor (drive device) 12 is connected to one end of each of the screw members 14 and 15. When the screw members 14 and 15 are rotated by the motor 12, the support member 7 is in the longitudinal direction of the photosensitive drum 6 in a plane parallel to the emission surface 1b by screwing the screw members 14 and 15 and the nut members 19 and 20. Move in the B direction orthogonal to the direction.
When the image forming apparatus 100 is in operation, the distance between the LED 5a and the imaging position can be corrected by driving the wedge-shaped optical member 1 by adjusting the rotation amount of the motor 12 according to the temperature rise of the LED 5a.

  As described above, the support member 7 supports the wedge-shaped optical member 1 in a swingable manner in a plane substantially perpendicular to the optical axis. By swinging the wedge-shaped optical member 1, the optical path length of the light beam passing through the wedge-shaped optical member 1 can be changed for each image height. For example, even when the parallel relationship among the LED array 5, the rod lens array 4, and the photosensitive drum 6 at the time of assembly is not accurately adjusted, the optical path length is changed by the swinging of the wedge-shaped optical member 1. Thus, the exposure light can be suitably imaged on the surface of the photosensitive drum 6. That is, even when the distances in the real space in the optical axis direction of the LED array 5, the rod lens array 4, and the photosensitive drum 6 are different for each image height, the photosensitive drum 6 can be moved by swinging the wedge-shaped optical member 1. It is possible to focus so that a light beam is imaged on the surface of the lens.

  Since the support member 7 that supports the wedge-shaped optical member 1 moves in a direction substantially perpendicular to the optical axis, the optical path length of the light beam that passes through the wedge-shaped optical member 1 can be changed regardless of the image height. Thus, when a focus shift due to the temperature rise of the LED 5a occurs, the wedge-shaped optical member 1 is changed by changing the movement amount Δx of the support member 7 in a direction substantially perpendicular to the optical axis according to the focus shift amount. The optical path length of the light beam passing through can be changed. Therefore, by adjusting the movement amount Δx of the wedge-shaped optical member 1, the light beam from the LED 5a can be imaged on the surface of the photosensitive drum.

  The motor 12 can move the support member 7 that supports the wedge-shaped optical member 1 in a direction substantially perpendicular to the optical axis. As a result, it is possible to correct the focus shift caused by the heat generated by the LED 5a during operation of the image forming apparatus while the image forming apparatus is operating.

In the first embodiment, the wedge-shaped optical member 1 is disposed alone in the optical path between the LED 5 a and the photosensitive drum 6. However, as shown in FIG. 7, a plurality of wedge-shaped optical members may be provided.
FIG. 7 is a cross-sectional view of the optical member 41. The optical member 41 includes a wedge-shaped optical member (optical element) 1 (hereinafter referred to as a first wedge-shaped optical member in the embodiment shown in FIG. 7) and a second wedge-shaped optical member (optical element) 2.
The optical member 41 cancels (cancels) the deviation of the irradiation position on the photosensitive drum 6 due to the refraction of the light beam 3 that has passed through the first wedge-shaped optical member 1 without controlling the light emission timing of the LED array 5.
The optical member 41 has a second wedge-shaped optical member 2 in addition to the first wedge-shaped optical member 1. The first wedge-shaped optical member 1 has a flat entrance surface (one surface) 1a and an exit surface (the other surface) 1b. The entrance surface 1a of the first wedge-shaped optical member 1 is inclined at an angle θ with respect to the exit surface 1b. The second wedge-shaped optical member 2 has a flat incident surface (the other surface) 2a and an exit surface (one surface) 2b. The exit surface 2b of the second wedge-shaped optical member 2 is inclined at an angle θ with respect to the entrance surface 2a.
The first wedge-shaped optical member 1 and the second wedge-shaped optical member 2 are arranged so that the incident surface 2a and the exit surface 1b of the optical member 41 are parallel to each other. 1 is brought into contact with the incident surface 1a. The second wedge-shaped optical member 2 is disposed on the light incident side of the first wedge-shaped optical member 1 and is parallel to the incident surface 2 a substantially orthogonal to the light beam 3 from the LED array 5 and the incident surface 1 a of the first wedge-shaped optical member 1. It has the injection | emission surface 2b which opposes. Since the incident surface 2a of the second wedge-shaped optical member 2 and the exit surface 1b of the first wedge-shaped optical member 1 are parallel, the light beam 3 is not refracted.
The optical member 41 is disposed in the optical path between the LED array 5 and the photosensitive drum 6. Similar to the single wedge-shaped optical member 1 described above, the optical member 41 is disposed in the optical path between the LED array 5 and the rod lens array 4 or in the optical path between the rod lens array 4 and the photosensitive drum 6. Is done.
The first wedge-shaped optical member 1 and the second wedge-shaped optical member 2 are arranged such that the longitudinal direction of the photosensitive drum 6 is in a state where the incident surface 1b of the first wedge-shaped optical member 1 and the exit surface 2b of the second wedge-shaped optical member 2 are in contact with each other. It is relatively movable in the B direction orthogonal to the direction.
However, a space may be provided between the exit surface 2 b of the second wedge-shaped optical member 2 and the entrance surface 1 a of the first wedge-shaped optical member 1. In this case, the first wedge-shaped optical member 1 and the second wedge-shaped optical member 2 maintain a constant distance between the incident surface 1b of the first wedge-shaped optical member 1 and the exit surface 2b of the second wedge-shaped optical member 2. In this state, it may be configured to be relatively movable in the B direction orthogonal to the longitudinal direction of the photosensitive drum 6. Although the light beam 3 from the LED array 5 is refracted in the optical member 41, the light beam 3 incident on the incident surface 2a and the light beam 3 emitted from the exit surface 1b become parallel.
Due to the relative movement of the first wedge-shaped optical member 1 and the second wedge-shaped optical member 2 in the B direction, the optical path length of the light beam 3 passing through the optical member 41 changes. As a result, the optical distance between the LED array 5 and the surface of the photosensitive drum 6 changes. Therefore, the distance between the LED array 5 and the imaging position is corrected, and the light beam from the LED array 5 is transferred to the photosensitive member. An image can be formed on the surface of the drum 6. In this case, since the optical path of the light beam 3 does not move in the B direction due to the relative movement of the first wedge-shaped optical member 1 and the second wedge-shaped optical member 2 in the B direction, it is necessary to control the light emission timing of the LED array 5. Disappears.
It is not necessary to incline the optical axis OA2 of the LED array 5 with respect to the normal P2 of the surface of the photosensitive drum 6 at the target irradiation position TP. The LED array 5 is arranged so that the optical axis OA2 of the LED array 5 is parallel to the optical axis OA1 of the rod lens array 4 and the normal line P2 of the surface of the photosensitive drum 6.
As described above, by arranging a plurality of optical members on the optical path of the exposure light, the image height or the optical path length is adjusted without tilting the incident angle when the exposure light is incident on the plurality of optical members. It becomes possible.

FIG. 8 is a block diagram of a control device that drives the motor 12 in accordance with information about the temperature of the LED 5a.
FIG. 8A is a block diagram of a control device that drives the motor 12 according to the information about the temperature of the LED 5a according to the first embodiment. The driving amount of the motor 12 is changed according to the temperature change of the LED 5a, and the position of the wedge-shaped optical member 1 supported by the support member 7 is changed.

The LED array 5 is provided with an LED temperature measurement unit (temperature information acquisition unit) 17a that obtains temperature information corresponding to the temperature of the LED 5a. The LED temperature measurement unit 17a is a thermocouple that measures the temperature of the LED 5a, or a device that acquires temperature information (current value or voltage value) corresponding to the temperature of the LED 5a or a temperature change.
The LED temperature measurement unit 17 a is electrically connected to the CPU 13. The CPU 13 is electrically connected to the motor drive control device 16 and the LED drive circuit 18. The motor drive control device 16 controls the motor 12.
The CPU 13 stores a lookup table of the driving amount of the motor 12 with respect to the temperature threshold value Tm of the LED 5a. The look-up table is obtained by measuring in advance. CPU13 determines the drive amount of the motor 12 from the temperature information of LED5a according to a look-up table. The CPU 13 instructs the motor drive control device 16 on the determined drive amount of the motor 12. The motor drive control device 16 drives the motor 12 according to the instructed drive amount of the motor 12. The motor 12 moves the support member 7 of the wedge-shaped optical member 1 in a direction perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the emission surface 1 b of the wedge-shaped optical member 1.

Further, from the expression (2), the movement of the light beam 3 emitted from the exit surface 1b in the B direction according to the movement amount Δx when the wedge-shaped optical member 1 is moved in the direction indicated by the arrow B in FIG. Amount (irradiation position shift on the surface of the photosensitive drum 6) Δd occurs. In order to correct this irradiation position shift, the CPU 13 calculates the LED light emission timing delay time according to the determined drive amount of the motor 12, and instructs the LED drive circuit 18 of the LED light emission timing delay time. The LED drive circuit 18 causes the LED 5a to emit light with a delay by the instructed LED light emission timing delay time.

FIG. 9 is a flowchart illustrating adjustment of the imaging position according to the first embodiment.
The CPU 13 sets the number of times of measuring the temperature of the LED 5a in advance, the number-of-measurements threshold j, and the temperature threshold Tm (T ₁ , T ₂ , T ₃ ,..., Tn) of the LED 5a set in advance. Is remembered. Further, the CPU 13 stores a lookup table of the drive amount of the motor 12 with respect to the temperature threshold value Tm (T ₁ , T ₂ , T ₃ ,..., Tn) of the LED 5a.

  In step S1, the CPU 13 initializes m representing the stage of the temperature threshold Tm and i representing the number of measurements. The CPU 13 sets the stage m of the temperature threshold Tm to m + 1 (step S2), and sets the number of measurements i to i + 1 (step S3). After the above setting, the CPU 13 obtains temperature information T corresponding to the temperature of the LED 5a by the LED temperature measuring unit 17a in step S4.

CPU13 at step S5, comparing the temperature information T of LED5a the temperature threshold value _{T m.} If T ≦ Tm (NO in step S5), the measurement number i is compared with the measurement number threshold value j in step S6. If i ≦ j (NO in step S6), the process returns to step S3, and the temperature measurement of the LED 5a (step S4) is repeated until T> Tm in step S5. Each time the temperature of the LED 5a is measured, the number of measurements i is set to i + 1 in step S3.

In step S5, when the temperature information T of the LED 5a exceeds the temperature threshold value Tm (YES in step S5), the CPU 13 performs the movement of the wedge-shaped optical member 1 and the light emission timing delay of the LED simultaneously in parallel. Adjust the imaging position (focus).
Specifically, in step S7, the CPU 13 follows the motor 12 drive amount lookup table with respect to the temperature threshold value Tm (T ₁ , T ₂ , T ₃ ,..., Tn) of the LED 5a. Determine the driving amount. In step S <b> 8, the CPU 13 instructs the motor drive control device 16 on the drive amount of the motor 12.
The motor drive control device 16 drives the motor 12 according to the drive amount of the motor 12. By driving the motor 12, the wedge-shaped optical member 1 together with the support member 7 is moved in a direction perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the emission surface 1 b of the wedge-shaped optical member 1. As a result, the optical distance between the LED 5a and the photosensitive drum 6 is corrected, so that the distance between the LED 5a and the imaging position is corrected.
The CPU 13 also controls the delay of the LED light emission timing in parallel with the driving of the motor 12. That is, in step S9, the CPU 13 calculates the light emission timing delay time of the LED 5a corresponding to the driving amount of the motor 12. In step S10, the CPU 13 instructs the LED drive circuit 18 on the light emission timing delay time of the LED 5a.
The LED drive circuit 18 delays the light emission timing of the LED 5a according to the light emission timing delay time of the instructed LED 5a. By delaying the light emission timing of the LED 5a, the movement amount of the light beam 3 (irradiation position deviation on the surface of the photosensitive drum 6) Δd according to the movement amount Δx of the wedge-shaped optical member 1 is corrected.
Due to the driving of the motor 12 and the delay of the light emission timing of the LED 5 a, the light from the LED 5 a is imaged at a desired position on the surface of the photosensitive drum 6.
After the movement of the wedge-shaped optical member 1 and the light emission timing of the LED 5a are delayed and the adjustment of the imaging position (focus) is completed, the process returns to step S2. In step S2, the CPU 13 sets the stage m of the temperature threshold Tm to m + 1, and initializes the number of measurements i to 0. Thereby, the temperature threshold value is rewritten from Tm to Tm + 1, and the temperature measurement of the LED 5a is repeated (step S4).

When the temperature measurement of the LED 5a is repeated and the measurement count i of the LED 5a exceeds the preset measurement count threshold j in step S6 (YES in step S6), the temperature of the LED 5a converges to a certain value. Judge. Since the temperature of the LED 5a has converged to a certain value, it is determined that the fluctuation of the imaging position (focus) has also been settled, and the adjustment of the imaging position is completed.
Each parameter of n, Tm (T1, T2, T3,..., Tn) is arbitrarily determined according to the characteristics of the image forming apparatus 100.
According to the first embodiment, by driving the wedge-shaped optical member 1 according to the information regarding the temperature of the LED 5a, the distance between the LED 5a and the imaging position is corrected, and an appropriate imaging position (focus) is ensured. Can do.

Next, Example 2 will be described.
The image forming apparatus according to the second embodiment is substantially the same as the image forming apparatus according to the first embodiment. In the second embodiment, instead of the LED temperature measuring section 17a of the first embodiment, an output number measuring section 17b that obtains output number information corresponding to the number of output sheets of the recording medium on which an image is formed by the image forming apparatus is used. Other structures of the second embodiment are the same as those of the first embodiment. In the second embodiment, the same structure as that of the first embodiment is denoted by the same reference numeral, and the description thereof is omitted.
The number of output sheets is the number of sheets discharged when an image is formed on a sheet (recording medium) S such as paper in the image forming apparatus 100, and the sheet after image formation is discharged to a discharge tray 30 outside the apparatus. Indicates the number of output images.

FIG. 8B is a block diagram of a control device that drives the motor 12 according to the information related to the temperature of the LED 5a according to the second embodiment. In the second embodiment, the information regarding the temperature of the LED 5 a is output sheet number information corresponding to the output sheet number of the recording medium S on which an image is formed by the image forming apparatus 100.
As the number of output sheets of the recording medium S on which an image is formed by the image forming apparatus 100 increases, the temperature of the LED 5a increases. Therefore, in the second embodiment, the drive amount of the motor 12 is changed according to the output sheet number information, and the position of the wedge-shaped optical member 1 supported by the support member 7 is changed.
The image forming apparatus 100 is provided with an output number measurement unit (temperature information acquisition unit) 17b that obtains output number information corresponding to the number of output sheets of the recording medium S on which an image is formed by the image forming apparatus 100.
The output sheet number measurement unit 17b is electrically connected to the CPU 13.

The CPU 13 stores a lookup table of the driving amount of the motor 12 corresponding to the output sheet number threshold Nm of the recording medium. The look-up table is obtained by measuring in advance. The CPU 13 determines the drive amount of the motor 12 according to the look-up table from the output number information of the output number measurement unit 17b.
The CPU 13 instructs the motor drive control device 16 on the determined drive amount of the motor 12. The motor drive control device 16 drives the motor 12 according to the instructed drive amount of the motor 12. The motor 12 moves the support member 7 of the wedge-shaped optical member 1 in a direction perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the emission surface 1 b of the wedge-shaped optical member 1.

  Similar to the first embodiment, the movement of the wedge-shaped optical member 1 causes an irradiation position shift. In order to correct this irradiation position shift, the CPU 13 calculates the LED light emission timing delay time according to the determined motor drive amount, and instructs the LED drive circuit 18 of the LED light emission timing delay time. The LED drive circuit 18 emits the LED 5a with a delay by the instructed LED light emission timing delay time.

FIG. 10 is a flowchart illustrating adjustment of the imaging position according to the second embodiment.
The flowchart shown in FIG. 10 differs from the flowchart shown in FIG. 9 in which the determination process is performed using the temperature of the LED 5a as a parameter in that the number of output sheets of the recording medium is used as a parameter. The other steps of the second embodiment shown in FIG. 10 are the same as the steps of the first embodiment shown in FIG. In the following description, the flowchart of FIG. 10 will be described focusing on the differences.

The CPU 13 sets a measurement count threshold j that presets the number of output counts of the recording medium on which an image has been formed by the image forming apparatus 100, and a preset output count threshold Nm (N ₁ , N ₂ , N _3). ,..., Nn). Further, the CPU 13 stores a lookup table of the driving amount of the motor 12 with respect to the output sheet number threshold value Nm (N ₁ , N ₂ , N ₃ ,..., Nn).

In step S14, the CPU 13 obtains output sheet number information N corresponding to the output sheet number of the recording medium S on which the image is formed by the image forming apparatus 100, by the output sheet number measuring unit 17b.
In step S15, the CPU 13 compares the output number information N with the output number threshold Nm. When N ≦ Nm (NO in step S15), the measurement number i is compared with the measurement number threshold value j in step S16. If i ≦ j (NO in step S16), the process returns to step S3, and the measurement of the output sheet number information N (step S14) is repeated until N> Nm in step S15. Each time the output sheet number information N is measured, the measurement number i is set to i + 1 in step S3.

In step S15, when the output sheet number information N exceeds the output sheet number threshold Nm (YES in step S15), the CPU 13 simultaneously performs the movement of the wedge-shaped optical member 1 and the light emission timing delay of the LED in parallel. Adjust the imaging position (focus).
Specifically, in step S17, the CPU 13 drives the motor 12 in accordance with a look-up table of the driving amount of the motor 12 with respect to the output sheet number threshold value Nm (N ₁ , N ₂ , N ₃ ,..., Nn). Determine the amount.
In step S <b> 8, the CPU 13 instructs the motor drive control device 16 on the drive amount of the motor 12. In step S9, the CPU 13 calculates the light emission timing delay time of the LED 5a corresponding to the driving amount of the motor 12. In step S10, the CPU 13 instructs the LED drive circuit 18 on the light emission timing delay time of the LED 5a.
After the adjustment of the imaging position (focus) is completed, the process returns to step S2. In step S2, the CPU 13 sets the stage m of the output number threshold Nm to m + 1 and initializes the number of measurements i to 0. Thereby, the output sheet number threshold value is rewritten from Nm to Nm + 1, and the output sheet number measurement of the recording medium S on which the image is formed is repeated (step S14).

When the number of output sheets is repeatedly measured and the number of times i of the number of output sheets of the recording medium S exceeds the preset number of times of measurement threshold j in step S16 (YES in step S16), the number of output sheets of the recording medium S is Judged to have converged to a certain value. Since the number of output sheets of the recording medium S has converged to a certain value, it is determined that the fluctuation of the imaging position (focus) has been settled, and the adjustment of the imaging position is ended.
Each parameter of n and Nm (N ₁ , N ₂ , N ₃ ,..., Nn) is arbitrarily determined according to the characteristics of the image forming apparatus 100.
According to the second embodiment, the wedge-shaped optical member 1 is driven in accordance with the output sheet number information as the information about the temperature of the LED 5a, thereby correcting the distance between the LED 5a and the image forming position, and an appropriate image forming position (focusing position). ) Can be secured.

Next, Example 3 will be described.
The image forming apparatus according to the third embodiment is substantially the same as the image forming apparatus according to the first embodiment. In the third embodiment, an operation time measurement unit 17c that obtains operation time information corresponding to the operation time of the image forming apparatus 100 is used instead of the LED temperature measurement unit 17a of the first embodiment. Other structures of the third embodiment are the same as those of the first embodiment. In the third embodiment, the same structure as that of the first embodiment is denoted by the same reference numeral, and the description thereof is omitted.

FIG. 8C is a block diagram of a control device that drives the motor 12 according to the information regarding the temperature of the LED 5a according to the third embodiment. In the third embodiment, the information regarding the temperature of the LED 5 a is operating time information corresponding to the operating time of the image forming apparatus 100.
As the operating time of the image forming apparatus 100 increases, the temperature of the LED 5a increases. Therefore, in the third embodiment, the driving amount of the motor 12 is changed according to the operating time information, and the position of the wedge-shaped optical member 1 supported by the support member 7 is changed.
The image forming apparatus 100 is provided with an operating time measurement unit (temperature information acquisition unit) 17c that obtains operating time information corresponding to the operating time of the image forming apparatus 100.
The operating time measuring unit 17 c is electrically connected to the CPU 13.
The CPU 13 stores a lookup table of the driving amount of the motor 12 corresponding to the operating time threshold value tm of the image forming apparatus 100. The look-up table is obtained by measuring in advance. The CPU 13 determines the driving amount of the motor 12 according to the lookup table from the operating time information of the operating time measuring unit 17c.
The CPU 13 instructs the motor drive control device 16 on the determined drive amount of the motor 12. The motor drive control device 16 drives the motor 12 according to the instructed drive amount of the motor 12. The motor 12 moves the support member 7 of the wedge-shaped optical member 1 in a direction perpendicular to the longitudinal direction of the photosensitive drum 6 within a plane parallel to the emission surface 1 b of the wedge-shaped optical member 1.

Similar to the first embodiment, the movement of the wedge-shaped optical member 1 causes an irradiation position shift. In order to correct this irradiation position shift, the CPU 13 calculates the LED light emission timing delay time according to the determined motor drive amount, and instructs the LED drive circuit 18 of the LED light emission timing delay time. The LED drive circuit 18 emits the LED 5a with a delay by the instructed LED light emission timing delay time.

FIG. 11 is a flowchart illustrating adjustment of the imaging position according to the third embodiment.
The flowchart shown in FIG. 11 is different from the flowchart shown in FIG. 9 in which the determination process is performed using the temperature of the LED 5a as a parameter, in that the operation time of the image forming apparatus 100 is a parameter. The other steps of the third embodiment shown in FIG. 11 are the same as the steps of the first embodiment shown in FIG. In the following description, the flowchart of FIG. 11 will be described focusing on the differences.
The CPU 13 sets a measurement count threshold j in which the number of measurements of the operation time of the image forming apparatus 100 is set in advance, and an operation time threshold tm (t ₁ , t ₂ , t ₃ ,. ) Is remembered. Further, the CPU 13 stores a lookup table of the drive amount of the motor 12 with respect to the operating time threshold value tm (t ₁ , t ₂ , t ₃ ,..., Tn).

In step S24, the CPU 13 obtains operating time information t corresponding to the operating time of the image forming apparatus 100 by the operating time measuring unit 17c.
In step S25, the CPU 13 compares the operating time information t with the operating time threshold value tm. If t ≦ tm (NO in step S25), the measurement number i is compared with the measurement number threshold value j in step S26. If i ≦ j (NO in step S26), the process returns to step S3, and the measurement of the operation time information t (step S24) is repeated until t> tm in step S25. Every time the operating time information t is measured, the number of measurements i is set to i + 1 in step S3.

In step S25, when the operation time information t exceeds the operation time threshold value tm (YES in step S25), the CPU 13 simultaneously performs the movement of the wedge-shaped optical member 1 and the light emission timing delay of the LED in parallel. Adjust the imaging position (focus).
Specifically, in step S27, the CPU 13 drives the motor 12 according to a look-up table of the driving amount of the motor 12 with respect to the operating time threshold value tm (t ₁ , t ₂ , t ₃ ,..., Tn). Determine the amount.
In step S <b> 8, the CPU 13 instructs the motor drive control device 16 on the drive amount of the motor 12. In step S9, the CPU 13 calculates the light emission timing delay time of the LED 5a corresponding to the driving amount of the motor 12. In step S10, the CPU 13 instructs the LED drive circuit 18 on the light emission timing delay time of the LED 5a.
After the adjustment of the imaging position (focus) is completed, the process returns to step S2. In step S2, the CPU 13 sets the stage m of the operating time threshold tm to m + 1, and initializes the number of measurements i to 0. As a result, the operating time threshold value is rewritten from Nm to Nm + 1, and the operating time measurement of the image forming apparatus 100 is repeated (step S24).

When the operation time measurement is repeated and the measurement number i of the operation time of the image forming apparatus 100 exceeds the preset measurement frequency threshold j in step S26 (YES in step S26), the operation time of the image forming apparatus 100 is determined. Is converged to a certain value. Since the operation time of the image forming apparatus 100 has converged to a certain value, it is determined that the fluctuation of the imaging position (focus) has also been settled, and the adjustment of the imaging position is ended.
The parameters n, tm (t ₁ , t ₂ , t ₃ ,..., tn) are arbitrarily determined according to the characteristics of the image forming apparatus 100.
According to the third embodiment, the wedge-shaped optical member 1 is driven in accordance with the operation time information as the information about the temperature of the LED 5a, thereby correcting the distance between the LED 5a and the imaging position, and the appropriate imaging position (focusing point). ) Can be secured.
According to the embodiment described above, the distance between the light emitting element and the imaging position can be adjusted in a short time with a simple configuration without moving the LED or the rod lens array in the optical axis direction.
In the above embodiments, the present invention has been described using the photosensitive drum as the image carrier. However, the present invention is not limited to this, and a photosensitive belt may be used as the image carrier.

1 wedge-shaped optical member (optical member)
2 Second wedge-shaped optical member (optical member)
4 Rod lens array (imaging element)
5a LED (light emitting element)
6 Photosensitive drum (image carrier)
12 Motor (drive device)
23 LED head (exposure device)
41 Optical member 100 Image forming apparatus S Recording medium

Claims (16)

An image forming apparatus for forming an image on a recording medium,
An image carrier;
A plurality of light emitting elements that are arranged in a longitudinal direction orthogonal to the rotation direction of the image carrier and emit light according to image information in order to expose the surface of the image carrier, and light from the plurality of light emitting elements An exposure apparatus having an imaging element that forms an image on the surface of the image carrier;
In order to correct the distance between the plurality of light emitting elements and the imaging position on the image carrier of the light from the plurality of light emitting elements, which changes according to the temperature change of the plurality of light emitting elements. And an optical member movably disposed on an optical path between the plurality of light emitting elements and the image carrier,
A driving device configured to move the optical member to correct the distance between the plurality of light emitting elements and the imaging position in accordance with information about the temperature of the plurality of light emitting elements. Image forming apparatus. A temperature measuring unit for obtaining temperature information corresponding to the temperature of the plurality of light emitting elements;
The image forming apparatus according to claim 1, wherein the information on the temperature of the plurality of light emitting elements is the temperature information obtained by the temperature measurement unit. An output number measurement unit for obtaining output number information corresponding to the number of output sheets of the recording medium on which the image is formed by the image forming apparatus;
The image forming apparatus according to claim 1, wherein the information regarding the temperature of the plurality of light emitting elements is the output number information obtained by the output number measurement unit. An operating time measuring unit for obtaining operating time information corresponding to the operating time of the image forming apparatus;
The image forming apparatus according to claim 1, wherein the information on the temperature of the plurality of light emitting elements is the operating time information obtained by the operating time measuring unit.   5. The optical member according to claim 1, wherein the optical member has a flat entrance surface and a flat exit surface, and the entrance surface is inclined with respect to the exit surface. The image forming apparatus described.   The image forming apparatus according to claim 5, wherein the optical member is moved by the driving device in a direction orthogonal to the longitudinal direction within a plane parallel to the emission surface.   The image forming apparatus according to claim 5, further comprising: a light emission timing adjusting unit that adjusts a light emission timing of the plurality of light emitting elements according to a driving amount of the optical member by the driving device. The optical member has two optical elements,
Each of the two optical elements has two flat surfaces,
One of the two flat surfaces is inclined with respect to the other surface;
The other surface of one optical element forms an incident surface of the optical member;
The other surface of the other optical element forms the exit surface of the optical member;
The one surface of the one optical element and the one surface of the other optical element are brought into contact with each other so that the incident surface and the exit surface of the optical member are parallel to each other. The image forming apparatus according to claim 1, wherein an element is superimposed on the other optical element.   The image forming apparatus according to claim 8, wherein the one optical element is moved by the driving device in a direction perpendicular to the longitudinal direction with respect to the other optical element.   10. The image forming apparatus according to claim 5, further comprising a support member that supports the optical member in a swingable manner in a plane parallel to the emission surface of the optical member.   The image forming apparatus according to claim 1, wherein the optical member is disposed between the plurality of light emitting elements and the imaging element.   The image forming apparatus according to claim 1, wherein the optical member is disposed between the imaging element and the image carrier. The optical member is disposed between the plurality of light emitting elements and the imaging element,
The image forming apparatus according to claim 5, wherein optical axes of the plurality of light emitting elements are inclined with respect to an optical axis of the imaging element. The optical member is disposed between the imaging element and the image carrier,
The image forming apparatus according to claim 5, wherein an optical axis of the imaging element is tilted with respect to a normal to the exit surface of the optical member.   The image forming apparatus according to claim 1, wherein the optical member is formed of a resin. The imaging element is a rod lens array;
The image forming apparatus according to claim 1, wherein the distance between the plurality of light emitting elements and the imaging position is a conjugate length of the rod lens array.

Images