JP6547965B2 - Optical scanning device and image forming apparatus provided with the optical scanning device - Google Patents

Description

  The present invention relates to a light scanning device and an image forming apparatus provided with the light scanning device.

  2. Description of the Related Art Conventionally, there has been known an optical scanning device which is mounted in an electrophotographic image forming apparatus and irradiates the surface of a photosensitive drum with a light beam corresponding to image data to scan in the main scanning direction.

  The light scanning device includes a light source, a rotary polygon mirror that reflects, deflects and scans a light beam emitted from the light source, and an imaging lens that forms an image of the light beam reflected by the rotary polygon mirror on a surface to be scanned And have.

  In the above-described optical scanning device, in order to increase the degree of freedom of the optical path layout, a folding mirror may be provided in the optical path from the rotary polygon mirror to the surface to be scanned (see, for example, Patent Document 1).

  The folding mirror is in the form of a rectangular column elongated in the main scanning direction. The turning mirror is supported from the surface side (reflection surface side) by four support pins. The folding mirror is pressed against the four support pins by a pressing spring. The four support pins abut on the four corners of the surface of the turning mirror.

  When the rotary polygon mirror is rotated with the operation of the light scanning device, vibration from the rotary polygon mirror is transmitted to the turning mirror. As a result, bending vibration and rotational vibration occur in the folding mirror.

  The bending vibration is a vibration in which a central portion in the main scanning direction of the folding mirror reciprocates in the thickness direction of the mirror with respect to both ends. When deflection vibration occurs, uneven density in the central portion of the image in the main scanning direction is significantly generated.

  On the other hand, rotational vibration is vibration in which the mirror is alternately displaced in the clockwise direction and counterclockwise direction when the turning mirror is viewed from the main scanning direction. The center of rotation of the turning mirror is determined by the support position of the turning mirror by the plurality of support pins. When the rotational vibration of the turnback mirror occurs, uneven density occurs notably over the entire area of the print image in the main scanning direction.

  Here, the bending vibration is more likely to occur as the dimension in the longitudinal direction (main scanning direction) of the folding mirror is longer. Therefore, as the length of the folding mirror in the main scanning direction becomes shorter with the recent miniaturization of the optical scanning device, the above-mentioned bending vibration becomes difficult to occur. On the other hand, rotational vibration is affected more by the support position of the folding mirror by the support pins than in the main scanning direction of the folding mirror, so it is difficult to suppress even if the size in the main scanning direction of the folding mirror decreases. Therefore, it is important to suppress the rotational vibration of the folding mirror in order to improve the image quality while realizing the downsizing of the optical scanning device.

  Therefore, in the optical scanning device shown in Patent Document 1, the rotational vibration of the folding mirror is prevented by bringing the rotation preventing member into contact with the folding mirror.

Japanese Patent Application Laid-Open No. 09-015523

  However, in the optical scanning device disclosed in Patent Document 1, when the position of the rotation preventing member with respect to the folding mirror (optical element) is not appropriate, the rotational vibration of the folding mirror (optical element) is amplified instead and jitter is generated in the printed image. Image defects such as are significantly generated. Therefore, it is difficult to completely suppress the rotational vibration of the turning mirror.

  The present invention has been made in view of such a point, and it is an object of the present invention to minimize positional deviation of the light beam in the sub-scanning direction on the image forming plane even if rotational vibration occurs in the return mirror. And to.

  The optical scanning device according to the present invention is provided so as to extend in the main scanning direction, provided with a light source, a rotary polygon mirror that reflects the light beam emitted from the light source and deflects and scans it, and is reflected by the rotary polygon mirror. And a plurality of support pins for supporting the return mirror from one side in the thickness direction.

The folding mirror is configured such that one side in the sub scanning direction is the incident side of the light beam and the other side is the emission side of the light beam when viewed from the direction perpendicular to the reflection surface, and the folding mirror The reflection position of the light beam at the point is separated at one side in the sub-scanning direction with respect to the rotation axis at the time of rotational vibration of the turning mirror determined by the support position of the turning mirror by the plurality of support pins . Let L be the distance between the reflection position of the light beam on the reflection surface and the image forming surface, let θ be the incident angle of the light beam to the reflection surface of the turning mirror, and sub-scan the reflection position of the light beam and the rotation axis When the separation amount in the direction is d, the relationship of d = L / sin θ is satisfied .

  According to the present invention, even if rotational vibration occurs in the folding mirror, it is possible to minimize positional deviation of the light beam in the sub-scanning direction on the imaging surface. As a result, it is possible to suppress the occurrence of image defects such as jitter in the print image.

FIG. 1 is an image forming apparatus provided with the light scanning device according to the first embodiment. FIG. 2 is a perspective view showing the light scanning device. FIG. 3 is a schematic view showing a scanning optical system in the light scanning device as viewed from the rotation axis direction of a polygon mirror. FIG. 4 is a perspective view showing an outline of a support structure of a turning mirror by a plurality of support pins. FIG. 5 is a plan view of the support structure of FIG. 4 as viewed from the side of the reflection surface of the turning mirror. FIG. 6 is a geometrical view seen from the main scanning direction showing the relationship between the incident angle and the reflection angle when the light beam is reflected by the reflection surface of the folding mirror. FIG. 7 is an image corresponding to FIG. 6 showing Comparative Example 1. FIG. 8 is a view corresponding to FIG. FIG. 9 is a view corresponding to FIG. 6 showing a modification of the first embodiment. FIG. 10 is a view corresponding to FIG. 4 showing the second embodiment. FIG. 11 is a view on arrow XI in FIG.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The present invention is not limited to the following embodiments.
Embodiment 1

  FIG. 1 is a cross-sectional view showing a schematic configuration of a laser printer 1 as an image forming apparatus in the present embodiment.

  As shown in FIG. 1, the laser printer 1 includes a box-shaped printer main body 2, a manual paper feed unit 6, a cassette paper feed unit 7, an image forming unit 8, a fixing unit 9, and a paper discharge unit 10. Is equipped. Then, the laser printer 1 is configured to form an image on a sheet based on image data transmitted from a terminal (not shown) or the like while conveying the sheet along the transport path T in the printer main body 2 ing.

  The manual sheet feeding section 6 has a manual sheet feeding tray 4 provided on one side of the printer main body 2 so as to be openable and closable, and a manual sheet feeding roller 5 rotatably provided inside the printer main body 2. ing.

  The cassette sheet feeding unit 7 is provided at the bottom of the printer body 2. The cassette feeding unit 7 separates the fed sheets one by one from a sheet feeding cassette 11 for storing a plurality of sheets stacked one another, a pick roller 12 for taking out sheets in the sheet feeding cassette 11 one by one, and A feed roller 13 and a retard roller 14 for feeding the sheet to the transport path T are provided.

  The image forming unit 8 is provided above the cassette feeding unit 7 in the printer body 2. The image forming unit 8 includes a photosensitive drum 16, a charger 17, a developing unit 18, a transfer roller 19, a cleaning unit 20, a toner hopper 21, and an optical scanning device 30. The image forming unit 8 forms a toner image on the sheet supplied from the manual sheet feeding unit 6 or the cassette sheet feeding unit 7.

  The transport path T is provided with a pair of registration rollers 15 which supply the sheet having been fed out to the image forming section 8 at a predetermined timing after temporarily waiting.

  The fixing unit 9 is disposed to the side of the image forming unit 8. The fixing unit 9 includes a fixing roller 22 and a pressure roller 23 which are pressed against each other to rotate. The fixing unit 9 fixes the toner image transferred onto the sheet by the image forming unit 8 to the sheet.

  The paper discharge unit 10 is provided above the fixing unit 9. The paper discharge unit 10 includes a paper discharge tray 3, a paper discharge roller pair 24 for conveying the paper to the paper discharge tray 3, and a plurality of conveyance guide ribs 25 for guiding the paper to the paper discharge roller pair 24. . The discharge tray 3 is formed in a concave shape in the upper portion of the printer body 2.

  When the laser printer 1 receives the image data, the photosensitive drum 16 is rotationally driven in the image forming unit 8, and the charger 17 charges the drum surface 16a.

  Then, based on the image data, a light beam is emitted from the light scanning device 30 to the photosensitive drum 16. An electrostatic latent image is formed on the drum surface 16a by being irradiated with a light beam. The electrostatic latent image is developed as a toner image by developing with the toner charged in the developing unit 18.

  Thereafter, the sheet supplied from the sheet feeding cassette 11 passes between the transfer roller 19 and the photosensitive drum 16. At that time, the toner image carried on the drum surface 16 a moves to the printing surface of the sheet under the electrostatic attraction from the transfer roller 19. As a result, the toner image on the photosensitive drum 16 is transferred to the sheet. The sheet on which the toner image has been transferred is heated and pressed by the fixing roller 22 and the pressure roller 23 in the fixing unit 9. As a result, the toner image is fixed to the sheet.

  Next, the details of the light scanning device 30 will be described with reference to FIGS. 2 and 3. The optical scanning device 30 is deflected and scanned by a housing 31 (shown only in FIG. 2), a polygon mirror 35 housed inside the housing 31 for deflecting and scanning a light beam from the light source 32, and a polygon mirror 35 An imaging lens 36 for imaging a light beam, a folding mirror 38 for reflecting the light beam passed through the imaging lens 36 and guiding the light beam to the drum surface 16a, and a lid member (not shown) attached to the housing 31 Have.

  The polygon mirror 35 is provided at the bottom of the housing 31 via the polygon motor 40. The polygon mirror 35 is a rotary polygon mirror and is rotationally driven by the polygon motor 40.

  The light source 32 is disposed on the side wall portion of the housing 31 as shown in FIG. The light source 32 is, for example, a laser light source having a laser diode. The light source 32 emits a laser beam (light beam) toward the polygon mirror 35. A collimator lens 33 (see FIG. 3) and a cylindrical lens 34 are disposed between the light source 32 and the polygon mirror 35.

  The imaging lens 36 is installed at the bottom of the housing 31 on the side of the polygon mirror 35, as shown in FIG. The imaging lens 36 extends in the main scanning direction along the bottom of the housing 31.

  A folding mirror 38 is disposed inside the housing 31 on the opposite side of the imaging lens 36 to the polygon mirror 35 side. The folding mirror 38 is in the form of a rectangular column elongated in the main scanning direction.

  A synchronization detection sensor 50 (see FIG. 3) is disposed at a position opposite to one end of the side wall portion of the housing 31 in the main scanning direction of the folding mirror 38. A synchronization detection mirror 53 is provided near the other end of the folding mirror 38 in the main scanning direction. The synchronization detection mirror 53 reflects a light beam which is deflected by the polygon mirror 35 and travels the optical path out of the effective scanning range (the range where the image data is actually written) and causes the light to enter the synchronization detection sensor 50.

  The synchronization detection sensor 50 is configured of, for example, a photodiode, a phototransistor, a photo IC, and the like. When detecting the light beam, the synchronization detection sensor 50 outputs a detection signal indicating that to the control unit 100.

  The control unit 100 is, for example, a microcomputer having a CPU, a ROM, a RAM and the like, and starts emission of a light beam corresponding to image data by the light source 32 after a predetermined time elapses from the reception of the synchronization detection signal.

  The laser light emitted from the light source 32 is collimated by the collimator lens 33 and then condensed on the reflection surface of the polygon mirror 35 by the cylindrical lens 34. The light collected on the polygon mirror 35 is reflected by the reflection surface of the polygon mirror 35 and enters the imaging lens 36 as scanning light. The scanning light having passed through the imaging lens 36 is reflected by the return mirror 38 toward the photosensitive drum 16 outside the housing 31 through the opening 39. Thus, the scanning light forms an image on the drum surface (corresponding to the surface to be scanned) 16a. The scanning light formed on the drum surface 16a scans the drum surface 16a in the main scanning direction by the rotation of the polygon mirror 35, scans in the sub scanning direction by the rotation of the photosensitive drum 16, and electrostatic latent latent on the drum surface 16a. Form an image.

  As shown in FIG. 4, the reflecting mirror 38 has a reflecting surface 38a for reflecting the light beam and a back surface 38b facing the reflecting surface 38a. The folding mirror 38 is configured to reflect the light beam incident from one side in the sub-scanning direction and to emit it to the other side, as viewed in the direction perpendicular to the reflecting surface 38 a. The folding mirror 38 is supported from the side of the reflecting surface 38 a by the first support pin 41, the second support pin 42, and the third support pin 43. In the first embodiment and the following modified examples and the second embodiment, the dimension in the sub-scanning direction of the folding mirror 38 is, for example, 10 mm or more and 20 mm or less, and the dimension in the main scanning direction is, for example, 200 mm or more and 350 mm or less .

  The tips of the support pins 41 to 43 are spherical and point-contact with both ends in the main scanning direction of the reflection surface 38 a of the return mirror 38. Leaf springs 49 are respectively provided at both ends in the main scanning direction on the back surface 38 b of the turning mirror 38. The folding mirror 38 is pressed against the tip end portions of the support pins 41 to 43 by the pair of leaf springs 49.

  As shown in FIG. 5, the first support pin 41 supports one end of the reflection surface 38 a of the folding mirror 38 in the main scanning direction. The second support pin 42 and the third support pin 43 support the other end of the reflection surface 38 a of the folding mirror 38 in the main scanning direction. The positions of the second support pin 42 and the third support pin 43 in the main scanning direction are the same. The second support pin 42 and the third support pin 43 are spaced in the sub-scanning direction.

  Here, at the time of operation of the optical scanning device 30, the rotational vibration of the polygon mirror 35 is transmitted to the folding mirror 38, whereby the folding mirror 38 is alternately displaced clockwise and counterclockwise as viewed from the main scanning direction. Vibration may occur. The rotational axis Lr at the time of rotational vibration of the folding mirror 38 is determined by the support position of the folding mirror 38 by the support pins 41 to 43. That is, when a middle point between the support position of the return mirror 38 and the support position of the return mirror 38 by the third support pin 43 is M, the return mirror by the middle point M and the first support pin 41 A straight line passing through the support position 38 is the rotation axis Lr at the time of rotational vibration of the folding mirror 38. The rotation axis Lr is a straight line extending in the main scanning direction, passing through the center of a triangle formed by connecting the supporting positions of the folding mirror 38 by the support pins 41 to 43 when the folding mirror 38 is viewed in the thickness direction. In the present embodiment, the rotation axis Lr coincides with a center line passing through the center position in the sub scanning direction when the turning mirror 38 is viewed from the reflecting surface 38 a side.

  When the folding mirror 38 rotationally vibrates around the rotation axis Lr, as indicated by the broken line in FIG. 6, the scanning position of the light beam on the drum surface (the imaging surface of the light beam, hereinafter referred to as drum surface) 16a is rotated. It deviates by ΔZb in the sub-scanning direction as compared with before the occurrence of vibration. As a result, image defects such as jitter may occur in the printed image.

  In order to solve this problem, in this embodiment, the reflection position Rp of the light beam on the reflection surface 38a of the reflection mirror 38 is one side in the sub scanning direction with respect to the rotation axis Lr of the reflection mirror 38, that is, the incident side of the light beam. And is separated from the drum surface 16a by a predetermined distance (see FIGS. 5 and 6). As a result, even if rotational vibration occurs in the folding mirror 38, it is possible to minimize the vibration of the light beam on the drum surface 16a.

  Next, the reason why the vibration of the light beam is suppressed at the drum surface 16a will be described with reference to FIGS. FIG. 7 is a schematic view seen from the main scanning direction showing how a light beam is reflected by the reflecting surface 38a of the folding mirror 38 in the light scanning device 30 of this embodiment, and FIG. 8 is a view at the reflecting surface 38a. 6 equivalent view showing a comparative example 1 in which the reflection position Rp of the light beam coincides with the rotation axis Lr of the folding mirror 38. FIG. 9 shows the rotation of the reflection mirror 38 at the reflection position Rp of the light beam on the reflection surface 38a. FIG. 7 is a view corresponding to FIG. 6 showing Comparative Example 2 separated on the other side in the sub scanning direction with respect to the axis Lr (the opposite side to the present embodiment and the light beam emission side).

  The solid line in each figure shows a reference state in which no rotational vibration occurs in the folding mirror 38, and θ shows the incident angle and the reflection angle of the light beam in the reference state. The broken line in the figure shows a state in which the folding mirror 38 is rotated clockwise with respect to the reference state due to rotational vibration, and θ ′ indicates the incident angle and reflection angle of the light beam in the rotational state. . .DELTA.Za, .DELTA.Zb, .DELTA.Zc represent the positional deviation amount of the light beam on the drum surface 16a in the sub scanning direction, and .DELTA.Xb, .DELTA.Xc represent the change amount of the optical path length of the light beam incident on the reflection surface 38a of the folding mirror 38. There is.

  According to FIGS. 7 to 9, it is found that the positional deviation amount of the light beam on the drum surface 16a is ΔZb <ΔZa <ΔZc. That is, in the light scanning device 30 of the present embodiment, the positional deviation amount ΔZb of the light beam on the drum surface 16a is reduced compared to the positional deviation amounts ΔZa and ΔZc of the light beam in Comparative Example 1 and Comparative Example 2. Therefore, it is possible to suppress the occurrence of image defects such as jitter in the printed image due to the positional deviation of the light beam on the drum surface (imaging surface) 16a.

  Referring to FIG. 6, the optical path length from the reflection surface of polygon mirror 35 to reflection surface 38a of reflection mirror 38 changes by ΔXb when reflection mirror 38 is rotated. Is smaller than the positional deviation amount .DELTA.Za of the light beam on the drum surface 16a, and therefore, falls within the order of several micrometers. Therefore, in the light scanning device 30 of the present embodiment in which the depth of focus is on the order of several millimeters, the influence of the change amount ΔXb of the optical path length on the optical characteristics is minor.

<< Modification >>
FIG. 9 shows a modification of the first embodiment, in which the displacement amount of the light beam in the sub-scanning direction on the drum surface 16a in the state in which the rotational vibration occurs in the return mirror 38 and in the state before the rotational vibration occurs. An example is shown that becomes almost zero. In this example, if the change amount Δxb of the optical path length of the light beam is sufficiently small with respect to the distance L between the reflection position Rp of the light beam on the reflection surface 38a of the folding mirror 38 and the imaging position of the light beam, The dimension Xc in the figure is substantially equal to the distance L even if the incident angle θ changes, and the distance d between the reflection position Rp of the light beam on the reflection surface 38a of the return mirror 38 and the rotation axis Lr of the return mirror 38 is L /. It becomes approximately equal to sin θ. Conversely, by setting the optical system to satisfy the distance d = L / sin θ, it is possible to minimize the amount of positional deviation of the light beam on the drum surface 16 a in the sub scanning direction. In order to satisfy the relationship of distance d = L / sin θ, the distance L between the reflection position Rp of the light beam at the folding mirror 38 and the drum surface 16a is close to the length in the sub scanning direction of the folding mirror 38 As a premise, therefore, the distance L is preferably 50 mm or less.

<< Embodiment 2 >>
10 and 11 show a second embodiment. This embodiment differs from the first embodiment in that the foldback mirror 38 is not supported directly by the support pins 41 to 43 but indirectly through the pair of holding plates 46.

  The pair of holding plates 46 have a rectangular plate shape extending in the sub scanning direction, and are arranged at intervals in the main scanning direction. Each holding plate 46 is provided at both ends in the main scanning direction of the reflecting surface 38 a of the folding mirror 38. The folding mirror 38 is sandwiched between the holding plate 46 and the opposing plate 47 opposed to the holding plate 46 and is fixed by the fixing bolt 48. The fixing bolt 48 penetrates the holding plate 46 and the folding mirror 38 and is screwed into the screw hole of the opposing plate 47.

  The base end of one holding plate 46 is supported by the first support pin 41. The proximal end portion of the other holding plate 46 is supported by the second support pin 42 and the third support pin 43. Each holding plate 46 is pressed against the support pins 41 to 43 by a plate spring 49.

  When the middle point M between the supporting position of the folding mirror 38 by the second support pin 42 and the supporting position of the folding mirror 38 by the third support pin 43 as viewed from the thickness direction of the folding mirror 38, the middle point M A straight line passing through the first support pin 41 and the support position of the turning mirror 38 is the rotation axis Lr of the turning mirror 38.

  According to this configuration, by using the holding plate 46, the degree of freedom in adjusting the reflection position Rp with respect to the rotation axis Lr of the folding mirror 38 can be enhanced.

Other Embodiments
In the above embodiments, the folding mirror 38 is supported by the three support pins 41 to 43, but the number of support pins is not limited to three, and may be two or less. There may be four or more. For example, when there are four support pins, both ends in the main scanning direction of the folding mirror 38 may be supported by two support pins. In this case, the middle point of the support position by the two support pins provided at one end of the folding mirror 38 in the main scanning direction and the middle point of the support position by the two support pins provided at the other end in the main scanning direction. And a straight line connecting them together is the rotation axis Lr.

  In the above embodiment, an example in which the image forming apparatus is the laser printer 1 has been described. However, the present invention is not limited to this, and the image forming apparatus may be a copier, a multifunction peripheral, or an MFP.

  Furthermore, the present invention includes any combination of the above-described embodiments and modifications.

  As described above, the present invention is useful for an optical scanning device and an image forming apparatus provided with the optical scanning device.

L distance Lr rotation axis Rp reflection position d distance (distance)
1 Laser printer (image forming device)
30 light scanning device 32 light source 35 polygon mirror (rotation polygon mirror)
38 Folded mirror 38a Reflective surface 41 First support pin 42 Second support pin 43 Third support pin

Claims (2)

A light source, a rotary polygon mirror for reflecting, deflecting and scanning a light beam emitted from the light source, and extending in the main scanning direction are provided, and the light beam reflected by the rotary polygon mirror is reflected to form an image What is claimed is: 1. An optical scanning device comprising: a folding mirror leading to a surface; and a plurality of support pins supporting the folding mirror from one side in the thickness direction,
The folding mirror is configured such that one side in the sub scanning direction is the light beam incident side and the other side is the light beam emission side, as viewed from the direction perpendicular to the reflection surface.
The reflection position of the light beam in the turning mirror is spaced apart to one side in the sub scanning direction with respect to the rotation axis at the time of rotational vibration of the turning mirror determined by the support position of the turning mirror by the plurality of support pins .
Let L be the distance between the reflecting position of the light beam on the reflecting surface of the turning mirror and the image forming surface, let θ be the incident angle of the light beam on the reflecting surface of the turning mirror, and An optical scanning device satisfying a relation of d = L / sin θ, where d is a separation amount of an axis in the sub scanning direction . An image forming apparatus comprising the light scanning device according to claim 1 .

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