JP2007136780A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve the formation of a high picture quality by the ensuring of a sufficient dot clock while making the correspondence of an image forming device wider in the image forming device A equipped with an exposing means U having light sources 70R, 70G and 70B, a polygon mirror 78, an fθ lens 79, and a carrying means 9 which carries a photo-sensitive material P at a specified carrying speed. <P>SOLUTION: The number n of surfaces of the polygon mirror 78 is set to be 8 surfaces or lower, and the relationship between a resolution X in the main scanning direction and a resolution Y in the subsidiary scanning direction of the exposing means U is set to be Y=2X. The carrying speed v of the photo-sensitive material P is set to be v≥5.1×10<SP>-6</SP>×N<SP>2</SP>f(mm/sec) (in this case, N is the rotation number(rps) of the polygon mirror, and f is the focal distance(mm) of the fθ lens). Thus, the dot clock T which is the irradiation time per 1 dot on the photo-sensitive material P is set to be 100×10<SP>-9</SP>sec or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a latent image on a photosensitive material by scanning and irradiating a photosensitive material such as photographic paper with a light beam.

  In recent years, based on image data of frame images formed on developed negative films and image data stored in various storage media, red, blue, and green monochromatic light is irradiated on each pixel, for example, on photographic paper Thus, digital exposure for performing printing exposure is performed.

As one configuration for performing such digital exposure, for example, Patent Document 1 discloses an image forming apparatus equipped with a laser exposure type engine that scans and exposes photographic paper while modulating laser light in accordance with image data. ing. This image forming apparatus includes a light source that generates laser light of each color of red, blue, and green. The laser light of each color is modulated based on digital image data, and the modulated laser light is mainly processed by a polygon mirror. It is deflected in the scanning direction. The deflected laser light is irradiated onto the photographic paper transported in the sub-scanning direction via the fθ lens, whereby a two-dimensional color image is printed on the photographic paper.
JP-A-10-325983

  By the way, there is a demand for such an image recording apparatus to be able to cope with a wide photographic paper in the main scanning direction.

  In that case, it is conceivable to increase the deflection angle θ of the polygon mirror. However, the curvature of the field, lateral chromatic aberration, and shading become problems due to the characteristics of the fθ lens. For example, a highly accurate and expensive fθ lens is required. This is disadvantageous in terms of cost. Even if a highly accurate and expensive fθ lens is used, if the deflection angle θ is large, it is difficult to completely eliminate curvature of field, lateral chromatic aberration, and shading.

  Therefore, it is conceivable to increase the focal length f of the fθ lens and thereby increase the maximum effective width C. In this case, since it is not necessary to increase the deflection angle θ, a high-precision and expensive fθ lens is not necessary, and it is relatively easy to eliminate field curvature, lateral chromatic aberration, and shading.

  On the other hand, when the focal distance f is increased, the deflection angle θ of the polygon mirror is decreased, so that the time required for one scan is shortened, and the dot clock corresponding to the irradiation time per dot is relatively shortened.

  However, it has been found that if the dot clock becomes too short, the desired Dmax (maximum density) cannot be obtained even if the output of the laser beam is increased. That is, if the image forming apparatus is configured to be wide, the image quality is degraded.

  The present invention has been made in view of this point, and an object of the present invention is to achieve high image quality by securing a sufficient dot clock while making the image forming apparatus wide.

  As a result of intensive studies by the inventors of the present invention to achieve the above object, it has been found that the dot clock in the image forming apparatus needs to be set to 100 nsec or more in order to obtain a desired Dmax. This will be described with reference to FIG.

  FIG. 15 shows the output of the light beam when the photosensitive material is irradiated with the light beam (R (red) laser light, cyan color) under the conditions in which the dot clock is set to 98, 59, and 50 nsec. The density value is shown. Here, QSS-31 type (manufactured by Noritz Steel Co., Ltd.) was used as the image forming apparatus, and PORTRA III (manufactured by Kodak Co., Ltd.) was used as the photosensitive material. The horizontal axis in FIG. 15 is a logarithmic value of the maximum-minimum output of the light beam in the QSS-31 type image forming apparatus expressed in 12-bit gradation (for example, the numerical value “3” on the horizontal axis is 3000). It corresponds to the gradation (log3000 = 3)).

  The concentration is measured with an X-Rite densitometer (manufactured by X-Rite), and the vertical axis in FIG. 15 is the concentration value of the X-Rite densitometer.

  According to the result of FIG. 15, when the dot clock is 59 nsec and 50 nsec, the density value does not exceed 2.0 even if the output of the light beam is increased. On the other hand, when the dot clock was 98 nsec, the density value could exceed 2.0.

  Here, when the image forming apparatus is an apparatus that performs photographic printing, a density value of 2.0 or more is required (Dmax is 2.0). Therefore, it is necessary to set the dot clock in the image forming apparatus to at least 98 nsec, preferably 100 nsec or more.

  FIG. 15 shows the measurement result in cyan. However, cyan is the most difficult to obtain Dmax, and for other colors (magenta, yellow) as long as Dmax is obtained for cyan. Dmax is obtained.

  The present invention has been made based on this fact. Specifically, the apparatus of the present invention includes a light source that emits a light beam, a polygon mirror that deflects the light beam from the light source in a main scanning direction, and a light beam deflected by the polygon mirror is converged on a photosensitive material. an exposure unit having an fθ lens; and a transport unit that transports the photosensitive material in the sub-scanning direction at a predetermined transport speed, and the exposure unit is transported in the sub-scanning direction by the transport unit. The image forming apparatus forms a latent image on the photosensitive material by scanning the photosensitive material with a light beam in the main scanning direction.

In this image forming apparatus, the number n of surfaces of the polygon mirror is 8 or less, and the relationship between the resolution X (dpi) in the main scanning direction and the resolution Y (dpi) in the sub-scanning direction is Y = 2X,
The conveyance speed v of the photosensitive material is
v ≧ 5.1 × 10 ⁻⁶ × N ² f (mm / sec) (where N is the rotation speed of the polygon mirror (rps), f is the focal length of the fθ lens (mm))
By
The dot clock T, which is the irradiation time per dot on the photosensitive material, is set to 100 × 10 ⁻⁹ (sec) or more.

That is, the light beam scanning system of the exposure means having the polygon mirror and the fθ lens is configured as shown in FIG. In this configuration, the dot clock T (sec) is
T = (time required for one scanning) / (number of dots in the main scanning direction)
Therefore, the dot clock T (sec) is

となる。

It becomes.

  Here, n: number of surfaces of the polygon mirror 78, N: rotation speed (rps) of the polygon mirror 78, C: maximum effective width (mm), α: effective scanning period rate, θ: deflection angle (rad), X: The resolution (dpi) in the main scanning direction.

  The effective scanning period rate α is expressed by α = θ / (2π / n), and the maximum effective width C is expressed by C = 2fθ (mm) where the focal length of the fθ lens 79 is f (mm). Therefore, the effective scanning period rate α is

となる。

It becomes.

  Therefore, the dot clock T (sec) is obtained from the equations (1) and (2).

で表される。

It is represented by

  Here, in the image forming apparatus, it is desirable to have a relationship of Y = X × 2 between the resolution X in the main scanning direction and the resolution Y in the sub scanning direction from the viewpoint of performing interlace correction. Further, the resolution Y in the sub-scanning direction can be obtained by assuming that the photosensitive material transport speed is v (mm / sec).

で表されるため、主走査方向の解像度Ｘは、

Therefore, the resolution X in the main scanning direction is

で表される。

It is represented by

  Here, the number n of surfaces of the polygon mirror 78 is preferably eight or less from the viewpoint of versatility. This reduces the cost.

  Based on this condition, the condition of the resolution X in the main scanning direction is

となり、ドットクロックＴの条件は、式（３），（７）より、

Thus, the condition of the dot clock T is as follows from the equations (3) and (7):

となる。

It becomes.

  Therefore, the conveyance speed v (mm / sec) of the photosensitive material is obtained from the equation (8).

に設定すれば、ドットクロックＴをＴ≧１００×１０^-9（sec）以上に設定することができる。

If set to, the dot clock T can be set to T ≧ 100 × 10 ⁻⁹ (sec) or more.

  In this manner, the dot clock T can be sufficiently secured by setting the photosensitive material transport speed v to a predetermined speed in accordance with the focal length f of the fθ lens and the rotational speed N of the polygon mirror. In other words, the desired Dmax can be obtained while the focal length f of the fθ lens is relatively long to make the image forming apparatus compatible with a wide range, and the image forming apparatus can be improved in image quality.

  Here, from equations (3) and (4), the dot clock T is

で表され、ドットクロックＴを１００×１０^-9sec以上に設定する場合、ポリゴンミラーの面数ｎ、搬送速度ｖ、焦点距離ｆ及び解像度Ｘ，Ｙの間には、

When the dot clock T is set to 100 × 10 ⁻⁹ sec or more, the number of polygon mirror surfaces n, the conveyance speed v, the focal length f, and the resolutions X and Y are

の関係がある。

There is a relationship.

  As described above, in the wide image forming apparatus, the focal length f of the fθ lens has to be increased. However, if the number n of polygon mirrors and the resolutions X and Y are not changed, the focal length f is increased. In addition, the transport speed v must be lowered (see formula (11)).

  However, there is a correlation between the conveyance speed v and the rotation speed N of the polygon mirror, and the rotation speed N of the polygon mirror must be decreased in response to the decrease in the conveyance speed v.

  Here, in an image forming apparatus, an air bearing is generally employed as a bearing for a polygon mirror from the viewpoint of rotational stability and durability. However, since the air bearing type polygon mirror has a lower stability when the rotational speed is lowered, it must be set to a predetermined rotational speed or higher (for example, 10,000 rpm or higher). For this reason, when it is necessary to reduce the rotation speed of the polygon mirror, it is difficult to employ an air bearing.

  Therefore, it is conceivable that the bearing of the polygon mirror is a rolling bearing that can be used at a low rotational speed.

  However, the problem with the use of rolling bearings is their durability. That is, in the image forming apparatus, the optical system parts including the polygon mirror are accommodated in the case, but it is difficult to replace the bearings of the polygon mirror from the viewpoint of dust prevention. Therefore, it is necessary to design the life of the bearing as the product life of the image forming apparatus.

  The inventor of the present application has found through a durability test and the like that when a rolling bearing is adopted as a bearing of a polygon mirror in an image forming apparatus, it is desirable to set the maximum rotational speed to 5000 rpm (80 rps). That is, the rotational speed N of the polygon mirror is preferably set to 80 rps or less.

The dot clock T is preferably set to 150 × 10 ⁻⁹ sec or less. This is because when the dot clock T is too large, the processing capability of the image forming apparatus is reduced.

  As described above, according to the image forming apparatus of the present invention, a sufficient dot clock can be ensured, so that the image quality can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

<Overall configuration of photo processing system>
FIG. 1 is a partial cross-sectional view showing a configuration of a photographic processing system including an image forming apparatus A according to the present invention. The photographic processing system shown in FIG. 1 has a function of acquiring image data, printing an image on the emulsion surface of paper (printing paper) based on the image data, and creating a photographic print. This photographic processing system scans frame images formed on developed photographic film and uses it for film scanners (not shown) for acquiring image data, storage media for digital cameras, and other recording media. A media reading unit (not shown) for reading stored image data is provided.

  The paper magazines 3 and 3 shown in FIG. 1 respectively accommodate long papers having different paper widths as rolls R wound in a roll shape. The paper magazines 3 and 3 are image forming apparatuses. A is detachably attached to the main body. Of the two paper magazines 3 and 3 attached to the main body of the image forming apparatus A, one paper magazine 3 is selected according to the print size and the like, and is drawn out from the selected paper magazine 3. The paper P is transported along a predetermined transport path. That is, the direction of the paper drawn out from the paper magazine 3 is changed by the advance roller unit 4 and cut into a predetermined print size by the paper cutter 5. Then, the cut paper P is transported by the transport unit 6 to the exposure engine 7 located on the downstream side. The image forming apparatus A is configured to be wide, and one of the two paper magazines 3 and 3 contains a wide paper having a width of, for example, 350 mm or more.

  The exposure engine 7 includes an exposure unit U disposed above the transport path, and an upstream exposure transport roller 9a and a downstream exposure transport roller 9b disposed on the transport path. Between these exposure transport rollers 9a and 9b, an exposure position for exposing the paper P by the laser light emitted from the exposure unit U is set. A paper detection sensor 10 is provided on the upstream side of the exposure conveyance roller 9. When the paper P is fed in, the front end (front end) portion is detected and a signal is output. The paper detection sensor 10 includes a light emitting element that outputs infrared light and a light receiving element that receives the light. By detecting the position of the paper P by the paper detection sensor 10, the exposure start timing at the exposure position can be determined.

  The exposure unit U has a known structure, which will be described later in detail. The exposure unit U modulates laser light output from a laser light source (laser diode or the like) based on image data, and the light modulated laser light. Is exposed to the paper P to perform image exposure. When performing image exposure, the paper P is transported at a predetermined speed (constant speed) while being sandwiched between the exposure transport rollers 9a and 9b. Since the laser beam is scanned in the main scanning direction orthogonal to the transport direction (sub-scanning direction) of the paper P, an image (latent image) is printed and exposed on the paper P for each line.

  Then, while the image exposure as described above is performed, the paper P is sent to the downstream side of the exposure position by the downstream exposure transport roller 9b. A first transport unit 11 is provided on the downstream side of the exposure engine 7. As will be described in detail later, the first transport unit 11 is provided so as to be rotatable around a predetermined rotation axis, and the second transport unit 12 further receives the paper P delivered by the downstream exposure transport roller 9b. It has a function to pass to. The second transport unit 12 includes a plurality of nipping and transporting roller pairs 12a arranged along the transport path, and a guide plate 12b for forming the transport path, and the transport roller pair 12a is not shown. It is configured to be driven by a mechanism.

  An accommodation space S for temporarily accommodating the paper P is provided on the downstream side of the exposure engine 7 (left side of the exposure engine 7 in FIG. 1). That is, if the length of the paper P is longer than the distance from the exposure position to the development processing unit, the paper P enters the development processing unit during exposure, and the vibration generated by the processing in the development processing unit Since it is transmitted to the exposed portion of P and causes uneven exposure, the paper P is accommodated in the accommodating space S so that the occurrence of uneven exposure is reliably prevented.

  In addition, as will be described in detail later, the method of storing the paper P in the storage space S differs depending on the length of the paper P in the transport direction. In the following embodiment, a case where the length in the transport direction of the paper P is a predetermined value (for example, 594.1 mm) or more will be described.

  In the accommodation space S, a winding drum 20 for winding the paper P and a pressure roller 21 for pressing and holding the paper P on the outer peripheral surface of the winding drum 20 are arranged. As will be described in detail later, the take-up drum 20 and the pressure roller 21 sandwich the front end side in the transport direction of the paper P and also function as the take-up mechanism 8.

  A sag detection sensor 22 for detecting the sag of the paper P accommodated in the accommodation space S is provided below the winding drum 20 in the accommodation space S. The sag detection sensor 22 includes a light emitting element 22a and a light receiving element 22b. When light irradiated from the light emitting element 22a is blocked by the paper P, it is determined that the sag amount is greater than a predetermined amount. The Here, the line connecting the light emitting element 22a and the light receiving element 22b is set to be inclined with respect to the horizontal line as shown in FIG.

<Constitution of accommodation space>
Next, the structure in the accommodation space part S in FIG. 1 is demonstrated based on FIG. The first transport unit 11 is disposed further downstream of the downstream exposure transport roller 9b, and includes a sandwiching transport roller pair 11a and a guide plate 11b. The position in the height direction of the pair of nipping and conveying rollers 11a is set to be the same height position as that of the exposure and conveying roller 9, and an opening 11c is formed at the upstream end of the guide plate 11b. Therefore, the paper P can be easily received.

  The first transport unit 11 is configured to be able to rotate 90 ° around a predetermined rotation axis (see FIG. 12), and in the state rotated 90 °, the paper P can be delivered to the second transport unit 12. It can be done. The second transport unit 12 includes a plurality of transport roller pairs 12a and a guide plate 12b, and plays a role of feeding the paper P received from the first transport unit 11 to a development processing unit (not shown).

  The take-up drum 20 is configured to be rotatable around the rotation axis 20a. Before the winding of the paper P by the winding drum 20 is started, the outer peripheral surface of the winding drum 20 and the surface of the pressure roller 21 are separated from each other and a gap is formed. Thereby, the conveyed paper P can be easily inserted into the gap between the winding drum 20 and the pressure roller 21.

  The receiving height of the paper P by the winding drum 20 is set to be the same as the height of the conveyance surface by the exposure conveyance roller 9 and the conveyance surface before the rotation of the first conveyance unit 11. Yes. Thereby, the paper P sent out by the exposure transport roller 9 can be smoothly received on the winding drum 20 side. In the state shown in FIG. 2, the shaft core of the pressure roller 21 is located just above the shaft core of the winding drum 20.

  Furthermore, a winding movement mechanism 13 for moving the winding mechanism 8 in the vertical direction is provided in the accommodation space S, and the entire winding mechanism 8 is located above the exposure position of the exposure engine 7. It is possible to move from the first position (position in FIG. 2) to the lower second position (position in FIG. 9) that is far from the exposure position. Specifically, the take-up moving mechanism 13 includes a guide member 13a extending in the vertical direction and a timing belt 13b for moving the take-up mechanism 8 along the guide member 13a. A support 15 for supporting the take-up mechanism 8 is fixed, and the take-up mechanism 8 can be moved up and down by driving the timing belt 13b by a motor (not shown). . The support 15 is mounted with drum driving means (motor, speed reduction mechanism, etc.) for rotationally driving the take-up drum 20.

  Here, the storage space S is adjacent to the development processing unit and is partitioned by the wall surface 14. However, when the paper P is moved up and down on the winding drum 20, the paper P is It is preferable not to rub the wall surface 14. On the other hand, if the accommodating space S is made larger, the rubbing between the wall surface 14 and the paper P can be eliminated, but there is a problem that the entire apparatus becomes larger. Therefore, the take-up moving mechanism 13 is configured such that the take-up mechanism 8 moves obliquely downward as shown in FIG. Specifically, the winding movement mechanism 13 is configured to move in a direction away from the wall surface 14 as the winding mechanism 8 is lowered downward. Thereby, the winding mechanism 8 can move downward in the accommodation space S without the paper P rubbing the wall surface 14.

  In addition, although mentioned later in detail, after the said winding mechanism 8 is moved below by the winding movement mechanism 13, when the paper P has more than a predetermined sag, the paper P is removed by the winding mechanism 8. I'm trying to wind it up. In this way, by providing a certain degree of slack, the paper P can be taken up without transmitting large vibrations or load fluctuations to the exposed portion of the paper P, thereby preventing uneven exposure. can do.

  By providing the accommodation space S and the winding mechanism 8 configured as described above, the following effects can be obtained. Image exposure by the exposure engine 7 is performed while the paper P is conveyed at a predetermined speed by the exposure conveyance roller 9. When this scanning exposure is performed, for example, development processing or the like is performed on the front side in the conveyance direction. If done, large vibrations and load fluctuations will occur in the paper P, or the latent image progression time cannot be secured sufficiently, and the image quality of the image formed on the paper P will deteriorate. On the other hand, as described above, the paper P sent out by the exposure transport roller 9b is temporarily accommodated in the accommodation space S until the exposure is completed, so that the paper P does not undergo large vibration or load fluctuation. And sufficient time for the latent image to travel.

  Moreover, when a long paper having a long length in the transport direction is to be stored in the storage space portion S, a large storage space is required. However, the winding mechanism 8 as described above is provided to wind the paper P. As a result, the space of the accommodation space portion S can be reduced, and an increase in the size of the entire apparatus can be prevented.

<Configuration of winding mechanism>
Next, a detailed configuration of the winding drum 20 and the pressure roller 21 constituting the winding mechanism 8 will be described with reference to FIG. FIG. 4 shows a cam mechanism (corresponding to a roller interval changing means) for moving the pressure roller 21 in the pressure direction.

  The take-up drum 20 is configured to be rotatable around a fixed shaft 200. The winding drum 20 is made of resin, and the paper P is wound on the outer peripheral surface thereof. Both ends in the axial direction of the take-up drum 20 are provided with circumferential grooves 202 for engaging the coil springs 24 for urging the press roller 21 in the press-fit direction. Among them, a connecting gear 201 for rotating the winding drum 20 is provided on the end side of the circumferential groove 202 at one end.

  The pressure roller 21 includes a roller support shaft 210 disposed substantially parallel to the axis of the take-up drum 20, and a resin product provided in a plurality in the axial direction so as to cover the outer peripheral surface of the roller support shaft 210. .., And crimping members 212, 212,... Described later attached to the surfaces of the respective spindles 211. The roller support shaft 210 is fitted with an E-ring 213 for preventing the support shafts 211, 211,... From moving in the axial direction with respect to the roller support shaft 210.

  Grooves 214 and 214 for engaging the coil spring 24 are formed at both ends of the roller support shaft 210 in the axial direction. Further, cam connecting shafts 215 and 215 are provided at both axial ends of the roller support shaft 210 and inside the groove portions 214 and 214, respectively. The cam connecting shafts 215 are cam mechanisms which will be described later. By moving up and down according to the shape of the cam surface 203a, the pressure roller 21 can be moved in the pressure bonding direction or the non-pressure bonding direction. According to the mechanism shown in FIG. 3, when the take-up drum 20 rotates, the pressure roller 21 also rotates and moves along the outer peripheral direction of the take-up drum 20 (rotates around the fixed shaft 200) in conjunction with the rotation. Can do. The pressure roller 21 itself is pivotally supported so as to be freely rotatable about the roller support shaft 210 as a rotation center.

  Next, a cam mechanism for moving the pressure roller 21 in the pressure bonding direction will be described with reference to FIG. FIG. 4 shows a cross-sectional view of the winding mechanism 8 shown in FIG. 3 cut along a plane perpendicular to the fixed shaft 200 at a portion where a cam is formed. As shown in FIG. 4, the cam member 203 is coupled to the fixed shaft 200 via the clutch member 204. The cam member 203 has a cam surface 203a, and the tip 215a of the cam coupling shaft 215 is always in contact with the cam surface 203a by the biasing force of the coil spring 24 described above.

  As shown in FIG. 4, the cam surface 203 a is formed in a range of θ = 210 ° on the outer peripheral surface of the cam member 203, so that the cam connecting shaft 215 (the pressure roller 21) is in contact with the cam member 203. The range that can be rotated is also 210 °. A first wall surface 203b and a second wall surface 203c are formed at both circumferential ends of the cam surface 203a. When the cam connecting shaft 215 moves relative to the cam surface 203a, the cam connecting shaft 215 Are positioned in contact with the wall surfaces 203b and 203c.

  4A is a diagram showing an initial state in which a gap is formed between the pressure roller 21 and the take-up drum 20, and FIG. 4B shows a state where the pressure roller 21 rotates 210 ° and the pressure roller 21 is rotated. It is a figure which shows the state by which the paper P was crimped | bonded by. Thus, when the take-up drum 20 is rotated 210 °, the state shown in FIG. 4B is obtained, but when the take-up drum 20 is further rotated, the cam coupling shaft 215 comes into contact with the second wall surface 203c, The cam member 203 is forcibly rotated around the fixed shaft 200 together. At this time, the frictional slip is generated in the clutch member 204. That is, by providing the clutch member 204, the pressure roller 21 can be rotated beyond a range (210 °) regulated by the cam member 203.

<Crimping member>
Next, the material of the crimping member 212 which is one of the characteristic portions of the present invention will be described in detail below. That is, the crimping member 212 is formed of an elastic foamed member (for example, foamed urethane) such as a sponge, and can be easily used when the paper P is sandwiched between the outer peripheral surface of the winding drum 20. Elastic deformation is generated. Thereby, when the paper P is sandwiched between the take-up drum 20 and the pressure roller 21, it is possible to prevent the paper P from being subjected to large vibrations and load fluctuations. Accordingly, even when the leading end side in the transport direction of the paper P is sandwiched between the winding drum 20 and the pressure roller 21 during the exposure process, a large vibration or load fluctuation acts on the paper P to cause exposure unevenness. Can be prevented.

  Here, as described above, the pressure roller 21 is pressure-bonded to the take-up drum 20 by the coil springs 24 hung on both ends in the axial direction. The pressure roller 21 is in a floating state without receiving a force, and the pressure roller 21 is deformed in a bow shape. On the other hand, if the pressure roller 21 is made of a foamed member as described above, both end portions in the axial direction of the pressure roller 21 are largely elastically deformed and do not float at the central portion in the axial direction. P can be held between the winding drum 20 and the pressure roller 21. As a result, when the paper P is sandwiched between the winding drum 20 and the pressure roller 21, it is possible to prevent the paper P from being wrinkled or subjected to load fluctuations, and to ensure that uneven exposure is generated. Can be prevented.

  In the above-described case, the distribution of the pressure-bonding force between the winding drum 20 and the pressure roller 21 is different in the axial direction, but in this embodiment, the paper is between the winding drum 20 and the pressure roller 21. The paper P is merely sandwiched, and the paper P is not transported by the take-up drum 20 and the pressure roller 21. Therefore, there is no problem such that the paper P meanders due to imbalance of the pressure.

  The crimp member 212 is not limited to a foam member, and any material that elastically deforms so as not to give vibration or load fluctuation to the paper P when the paper P is sandwiched, such as a rubber material, for example. It may be anything.

  The outer peripheral surface of the crimping member 212 is preferably in a low friction state in order to reduce resistance when the paper P is sandwiched between the winding drum 20 and the outer peripheral surface. By doing so, when the paper P is sandwiched between the take-up drum 20 and the pressure roller 21, the frictional resistance between the pressure roller 21 and the paper P is reduced. Variation can be effectively reduced.

  Here, the low friction state means that the friction coefficient with respect to the paper P is 0.5 or less. The value of this friction coefficient is the maximum frictional force and vertical drag when a rectangular parallelepiped member made of the same material as that of the crimping member 212 is slid in a substantially horizontal direction on the paper in the atmosphere of 25 ° C. It is required from the relationship. Specifically, each maximum frictional force when the vertical drag was changed was measured, and the friction coefficients calculated from those values were averaged.

<Control block diagram>
Next, the control block configuration of the image forming apparatus A will be described with reference to FIG. In FIG. 5, the paper leading edge detection means 30 detects the leading edge (front edge) of the paper P by the output signal from the paper detection sensor 10 and detects the arrival of the paper P. Further, it is also possible to recognize at which position the paper P is present on the downstream side based on the timing at which the leading edge of the paper P is detected. The roller driving unit 31 is configured by a driving mechanism, a driving circuit, and the like for driving the exposure conveyance roller 9. Further, the transport amount detection unit 32 is configured to detect the transport amount of the paper P by detecting the rotation amount of the exposure transport roller 9. That is, since the exposure transport roller 9 is controlled to rotate at a constant speed, the transport amount can be monitored by an encoder or the like.

  The paper position detection unit 33 is configured to detect various positions of the paper P based on the front end position of the paper P detected by the paper front end detection unit 30 and the transport amount of the paper P detected by the transport amount detection unit 32. It has the function which calculates | requires and calculates | requires. Specifically, the paper position detection unit 33 includes an exposure start timing detection unit 33a, a paper rear end escape detection unit 33b, and an insertion detection unit 33c (insertion determination unit).

  The exposure start timing detection means 33a is configured to detect the exposure start timing by the laser beam based on the leading edge position of the paper P detected by the paper leading edge detection means 30. That is, since the position of the paper detection sensor 10 and the exposure position by the laser beam are determined by design, if the leading end position of the paper P is known, the exposure start timing detection means 33a calculates the exposure start timing at the exposure position. Can do. The paper trailing edge escape detecting means 33b is for detecting that the trailing edge of the paper P on which image printing exposure has been completed has escaped from the printing exposure position. The insertion detection means 33c is for detecting that the front end of the paper P is inserted into the gap between the winding drum 20 and the pressure roller 21. The amount of insertion into this gap is usually about 20 mm, but this amount of insertion can be set as appropriate.

  The exposure control unit 34 is configured to start image exposure with laser light based on the calculation result of the exposure timing by the exposure start timing detection unit 33a. Thus, the latent image can be formed by scanning the emulsion surface of the paper P with the laser beam light-modulated by the image data.

  The first transport unit driving unit 35 has a mechanism for driving the first transport unit 11. Specifically, the first transport unit driving unit 35 rotates the entire first transport unit 11 by 90 ° with the crimp driving means 35a for switching the transport roller pair 11a between the crimping state and the non-crimping state. Unit rotation means 35b for switching between the horizontal state and the vertical state, and roller drive means 35c for rotationally driving the conveyance roller pair 11a are provided. Here, when the exposure engine 7 is performing image exposure, the pressure-bonding driving unit 35a places the transport roller pair 11a in a non-pressure-bonded state so that no load is applied to the paper P.

  The second transport unit driving unit 36 has a mechanism for driving the second transport unit 12, and includes a roller driving unit 36a that rotationally drives the transport roller pair 12a.

  The transport unit drive control means 37 is configured to perform drive control of the first transport unit 11 and the second transport unit 12. For example, when the paper position detection unit 33 detects that the rear end of the paper P has escaped from the printing exposure position, the transport roller pair 11a is switched to the press-bonded state.

  In the print size setting means 40, print size data of the paper P subjected to image exposure is set and stored. Then, based on the print size data stored in the print size setting means 40, the winding movement mechanism 13 and the winding drum 20 are controlled. For example, when the length of the paper P is shorter than a predetermined length (430.1 mm in this embodiment), the paper P is not crimped by the winding mechanism 8.

  The sag amount detecting means 41 is configured to detect whether the sag amount is equal to or larger than a predetermined amount based on an output signal from the sag detection sensor 22. The drum driving unit 42 includes a mechanism for driving the winding drum 20 to rotate. The rotation amount detection means 43 is configured to detect the rotation amount of the winding drum 20. For example, the amount of rotation can be monitored by an encoder that rotates in conjunction with the winding drum 20.

  The drum rotation control means 44 has a function of performing rotation drive control of the winding drum 20. The drum rotation control unit 44 detects the leading end of the paper P by the insertion detection unit 33c, and print size data stored and set in the print size setting unit 40. Perform stop control.

  The winding control means 45 performs drive control of the winding movement mechanism 13. For example, when the rotation amount detecting means 43 detects that the pressure bonding operation by the pressure roller 21 is completed (θ = 210 ° rotation), the winding drum 20 is controlled to move from the first position to the second position. In the case of the paper P having a short length, since the winding operation by the winding mechanism 8 is not performed, the winding drum 20 is allowed to escape to the lowermost second position. In the case of the paper P having an intermediate length, the paper P is crimped by the winding mechanism 8 but the amount of sag is not detected by the sag detection sensor 22, so that the winding drum 20 is set to the first position. Control is performed to move to an intermediate position (third position) of the second position. Thus, the winding control means 45 is configured to change the control of the winding moving mechanism 13 in accordance with the length of the paper P in the transport direction. Information on the length dimension of the paper P can be obtained from the print size setting means 40.

  Here, the control block shown in FIG. 5 can be constructed by the function of computer software or hardware. Which function is realized by software and which function is realized by hardware can be appropriately determined according to the paper processing capability and the like.

<Operation of winding mechanism>
Next, the operation from the image exposure to the paper P until it is sent to the development processing unit will be described with reference to the flowcharts of FIGS. 6A and 6B and FIGS. 2 and 7 to 12. It is assumed that the print size setting means 40 is set with a print size having a length that requires the winding mechanism 8 to be lowered to the second position.

  First, the leading edge of the paper P cut to a predetermined print size is detected by the paper detection sensor 10 and the paper leading edge detection means 30 (step ST1). A predetermined timing elapses after the leading edge of the paper P is detected, and the exposure start timing detection means 33a detects that the exposure start timing is reached, and then the exposure control unit 34 applies laser to the emulsion surface of the paper P. The light is scanned and exposed to form an image (step ST2).

  While performing scanning exposure with laser light in this way, the paper P is transported toward the downstream side by the exposure transport roller 9, and the leading end of the paper P passes through the guide plate 11 b of the first transport unit 11. At this time, since the pair of transport rollers 11a of the first transport unit 11 is in a state where the pressure bonding is released, the paper P passes through the position of the first transport unit 11 without applying a large load to the paper P. Can do.

  Since the take-up drum 20 is set in the first position as shown in FIG. 2 in advance, the paper P that has passed through the first transport unit 11 as described above is directly between the take-up drum 20 and the pressure roller 21. It is conveyed toward the gap between them. The leading end position of the paper P is calculated by the paper position detection unit 33 based on the detection result by the paper detection sensor 10 and the transport amount of the paper P, and the leading end of the paper P is wound by the insertion detection unit 33c from the calculation result. It is determined whether or not it has been inserted into the gap between the take-up drum 20 and the pressure roller 21 (step ST3). In the present embodiment, the front end of the paper P is detected by the paper detection sensor 10 provided before the exposure position, and the front end position of the paper P is determined based on the detection result and the transport amount of the paper P. By calculating, it is detected that the leading end of the paper P is inserted between the winding drum 20 and the pressure roller 21, but this is not restrictive, and the winding drum 20, pressure roller 21, A sensor or the like may be provided so that the amount of insertion between the two can be directly detected.

  When it is detected by the insertion detection means 33c that the leading end of the paper P is inserted into the gap between the winding drum 20 and the pressure roller 21 (YES in step ST3), the rotation of the winding drum 20 Is started (step ST4). FIG. 2 shows a state immediately after the leading end of the paper P is inserted into the gap. Then, the take-up drum 20 rotates counterclockwise in FIG. 2, and the pressure roller 21 similarly rotates around the rotation axis 20a. Thereafter, the gap between the pressure roller 21 and the take-up drum 20 is gradually narrowed by the cam mechanism described above, and the pressure roller 21 moves in the pressure direction.

  At this time, scanning exposure with laser light is performed on the rear side in the transport direction of the paper P. That is, the leading end side in the transport direction of the paper P being exposed is sandwiched between the winding drum 20 and the pressure roller 21. In this way, even during exposure, by sandwiching the front side of the long paper P in the conveyance direction, the conveyance direction of the paper P can be easily changed or wound around the take-up drum 20 even in a narrow space. Therefore, it is possible to secure a post-exposure buffer that can sufficiently prevent the occurrence of uneven exposure without increasing the accommodation space S according to the length of the paper P. Accordingly, it is possible to perform long printing while preventing an increase in the size of the entire apparatus.

  Then, it is determined whether or not the winding drum 20 has rotated a predetermined amount (210 ° in the example in the figure) (step ST5). If it is determined that the winding drum 20 has rotated by a predetermined amount (YES in step ST5), the winding drum 20 is wound. The rotation of the take-up drum 20 is stopped (step ST6). The rotation amount is detected by the rotation amount detection means 43. FIG. 7 is a view showing a state immediately after the rotation of the winding drum 20 is stopped. Here, the rotational speed of the take-up drum 20 is set so that the peripheral speed thereof is substantially the same as the feeding speed of the paper P by the exposure transport roller 9. By setting the rotation speed of the take-up drum 20 in this way, the paper P can be taken up at a speed as fast as possible without large load fluctuations acting on the paper P. Note that if the rotation of the take-up drum 20 is made slightly slower than the feed speed of the paper P, the take-up can be performed with a slight slack. Can be prevented.

  After the rotation of the take-up drum 20 is stopped in step ST6, the take-up movement mechanism 13 is driven by the take-up control means 45 to lower the take-up mechanism 8 from the first position to the second position (step ST7). ). Steps ST6 and ST7 may be performed almost simultaneously. For example, the downward movement of the winding mechanism 8 may be started immediately before the winding drum 20 stops.

  Here, it is preferable that the downward movement of the winding mechanism 8 as described above is set to be slower than the speed at which the paper P is fed into the accommodation space S. Thereby, it is not necessary to give a large load fluctuation to the paper P. FIG. 8 shows a state in which the take-up drum 20 has moved to an intermediate position (third position) between the first position and the second position. In FIG. 8, since the lowering speed of the take-up drum 20 is slow, sagging begins to occur in the paper P portion between the take-up drum 20 and the first transport unit 11. FIG. 9 shows a state where the take-up drum 20 has been lowered to the second position.

  Even after the rotation of the take-up drum 20 is stopped and the take-up drum 20 is moved to the second position as described above, the paper P is fed into the accommodation space S by the exposure transport roller 9. At this time, it is determined by the paper trailing edge escape detection means 33b whether or not the trailing edge of the paper P has reached the first transport unit 11 (step ST8). If it is determined that the trailing edge of the paper P has arrived (YES in step ST8), the process proceeds to step ST15. On the other hand, if it is determined in step ST8 that the rear end has not reached (in the case of NO), since the paper P is fed in, the sag gradually increases. As shown in FIG. The light is blocked by the slack of the paper P (step ST9). At this time, even if the sagging increases, the winding drum 20 moves obliquely downward in a direction away from the wall surface 14, so that the paper P sags without rubbing the wall surface 14.

  Here, the state in which the rear end of the paper P reaches the first transport unit 11 is defined as a state in which the rear end of the paper P slightly protrudes upstream from the nipping and transporting roller pair 11a. About this protrusion amount, it can set suitably.

  In the state shown in FIG. 10, the sag amount detecting means 41 determines that a sag of a predetermined amount or more has occurred (in the case of YES at step ST9), and the winding drum 20 is rotated again (step ST10). The winding drum 20 is rotated at a higher speed than the rotational driving in the previous step ST4. This is for eliminating the sag that has become too large at an early stage. When it is determined that the light blocking state of the light emitting element 22a is eliminated by the rotation of the winding drum 20 and the amount of sag is less than a predetermined amount (YES in step ST11), the winding drum 20 is stopped again. (Step ST12). Thereafter, the process returns to step ST8, and it is determined whether or not the rear end of the paper P has reached the first transport unit 11.

  If the amount of sag is not less than the predetermined amount (NO in step ST11), the process proceeds to step ST13 and the same determination as in step ST8 is performed. If the trailing edge of the paper has not reached the first transport unit 11 (NO in step ST13), the process returns to step ST11 and the sag amount is monitored again. On the other hand, if the trailing edge of the paper has reached the first transport unit 11 (YES in step ST13), the rotation of the take-up drum 20 is stopped (step ST14). FIG. 11 shows a state in which the take-up drum 20 is further rotated from the state of FIG. 10, but the pressure roller 21 has been rotated by 210 ° or more, and therefore the clutch member 204 is slipping.

  Control of rotation and stop of the take-up drum 20 as described above is performed based on the function of the drum rotation control means 44. Then, by detecting the amount of sag by the sag detection sensor 22 and performing rotation control of the winding drum 20 based on the amount of sag, the winding drum 20 is subjected to intermittent drive control that repeats rotation and stop. Become. The number of times this rotation and stop are repeated depends on the print size.

  When the rear end of the paper P reaches the first conveyance unit 11 and the rotation of the take-up drum 20 stops, the clamping conveyance roller pair 11a of the first conveyance unit 11 is brought into a pressure-bonded state from a non-pressure-bonded state by the pressure-bonding driving means 35a. (Step ST15). Then, as shown in FIG. 12, the first transport unit 11 is rotated 90 ° by the unit rotating means 35b to assume a vertical posture (step ST16). At this time, the transport surface of the first transport unit 11 and the transport surface of the second transport unit 12 are in a line. Next, the conveyance roller pair 11a is rotationally driven to convey the paper P toward the second conveyance unit 12, and deliver it (step ST17). At this time, the take-up drum 20 is rotated in the reverse direction (clockwise).

  As a result, the paper P sandwiched by the second transport unit 12 is transported upward, sent to a development processing section (not shown), and subjected to development processing. That is, the paper P is transported in a state where the front end side and the rear end side in the transport direction are switched between before the paper P is wound by the winding mechanism 8 and when it is transported by the second transport unit 12. Will be.

  When the delivery of the paper P to the second transport unit 12 as described above is completed, the paper P is set to an initial state to receive the next paper P. That is, the take-up drum mechanism 8 is raised from the second position to the first position, and the pressure roller 21 is also returned to the initial position so that the next paper P can be received. Further, the first transport unit 11 is also returned to the horizontal state, and the transport roller pair 11a is set in a non-pressing state.

  Here, in the above description, the transport method in the case where the length of the paper P in the transport direction is a print size equal to or larger than a predetermined value (for example, 594.1 mm, the first length) has been described. Is less than the predetermined value, the following two operations are performed according to the length.

  That is, when the transport direction length of the paper P is shorter than a predetermined length as in the service size (for example, when the length is shorter than 430.1 mm, the second length), the paper P is wound up by the winding drum 20. Since there is no need, the winding mechanism 8 is moved from the beginning to the second position. As a result, the paper P subjected to image exposure by the exposure engine 7 is immediately changed in direction by the first transport unit 11 and transferred to the second transport unit 12. As a result, the load applied to the paper P can be reduced more reliably.

  On the other hand, when the length of the paper P is a third length intermediate between the first length and the second length (430.1 to 594.1 mm in the example of the present embodiment), the winding mechanism 8 Only the winding operation by, and the movement of the winding mechanism 8 to the intermediate position (third position) between the first position and the second position are performed. That is, in step ST7 of FIG. 6A, the winding drum 20 is lowered to the intermediate position. At this time, in the case of the paper P of the third length, since there is no need to detect sag by the sag detection sensor 22, sag detection is not performed. Therefore, in FIG. 6A and FIG. 6B, the operation | movement except the step regarding a sagging detection is performed.

<Configuration of exposure unit>
Next, the configuration in the exposure unit U will be described with reference to FIG. The exposure unit U scans the laser beam in the main scanning direction (vertical direction on the paper surface in FIG. 13) perpendicular to the sub-scanning direction (direction orthogonal to the paper surface in FIG. 13) which is the transport direction of the paper P. It is configured in a laser exposure type for exposing and forming an image.

  The exposure unit U includes three laser light sources 70R, 70G, and 70B for the three primary colors that are arranged at appropriate positions in the unit case 71 that are disposed at a position above the conveyance path. The laser light source 70R is configured by, for example, a semiconductor laser (Laser Diode: LD) that emits R (red) laser light having a wavelength of 680 nm. The laser light source 70G includes a semiconductor laser and a second harmonic generator (SHG) that converts laser light emitted from the semiconductor laser into G (green) laser light having a wavelength of 532 nm, for example. The The laser light source 70B includes a semiconductor laser and a second harmonic generator (SHG) that converts laser light emitted from the semiconductor laser into B (blue) laser light having a wavelength of 473 nm, for example.

  On the output side of the laser light sources 70R, 70G, and 70B, acousto-optic modulators (AOM) 72R, 72G, and 72B for adjusting (modulating) the intensity of the laser light are disposed correspondingly. , Mirrors 74R, 74G and 74B, a reflection mirror 76 for reflecting the laser light from each mirror 74R, 74G and 74B, and a polygon mirror for deflecting the laser light from the reflection mirror 76 in the main scanning direction within a predetermined deflection angle range. 78 are arranged in order.

  The AOMs 72R, 72G, and 72B respectively adjust the laser beams with a certain intensity supplied from the laser light sources 70R, 70G, and 70B in the range of 0 to 100%.

  The mirror 74R is a total reflection mirror, and the mirrors 74G and 74B are half mirrors. The laser light emitted from the AOM 72R is totally reflected by the mirror 74R, combined with the laser light emitted from the AOM 72G by the mirror 74G, and further combined with the laser light emitted from the AOM 72B by the mirror 74B. Thus, three colors of laser light are synthesized. The synthesized laser beam is reflected by the reflection mirror 76 and enters the polygon mirror 78.

  The polygon mirror 78 has n reflecting surfaces (eight in the example of FIG. 13 and six in the example of FIG. 14), and is supported by a rolling bearing so as to be rotatable around a predetermined rotation axis. The bearing of the polygon mirror 78 may be an air bearing, an oil bearing, or the like. However, in the image forming apparatus A, the conveyance speed of the paper P is set to be relatively low, and the rotation speed of the polygon mirror 78 is accordingly increased. Since the rotation is relatively low (this will be described later), a rolling bearing is preferable from the viewpoint of rotational stability. The polygon mirror 78 scans the paper P in the main scanning direction with respect to the paper P by rotating in the arrow Z direction at a constant angular velocity.

  In addition, between the polygon mirror 78 and the paper P, one or more cylindrical lenses for keeping the moving speed (scanning speed) of the laser light scanned by the rotation of the polygon mirror 78 on the paper P constant. Is disposed. The laser light that has passed through the fθ lens 79 is irradiated downward from the unit case 71 in which the exposure unit U is accommodated (see the one-dot chain line in FIG. 1).

  The configuration for modulating the intensity of the laser light may employ, for example, an electro-optic modulation element (EOM) or a magneto-optic modulation element (MOM) without using the AOMs 72R, 72G, and 72B. Moreover, you may employ | adopt the structure which can modulate directly the output itself of laser light source 70R, 70G, and 70B.

  The configuration of the optical system that guides the laser light from each AOM 72R, 72G, and 72B to the polygon mirror 78 is not limited to the above-described configuration, and various configurations can be employed.

  Then, the exposure control unit 34 controls the rotation of the polygon mirror 78 according to the image data input to the image forming apparatus A based on the clock signal (dot clock) corresponding to one dot width on the paper P, The laser light sources 70R, 70G, and 70B and the AOMs 72R, 72G, and 72B are controlled. As a result, the exposure unit U applies light-modulated laser light to the emulsion surface of the paper P that is transported at a predetermined transport speed in the sub-scanning direction by the exposure transport roller 9 in accordance with the rotational speed of the polygon mirror 78. Scanning is performed at the scanning speed in the main scanning direction, and a latent image having a predetermined resolution in each of the main scanning direction and the sub-scanning direction is formed on the paper P.

  Then, the exposure unit U in the present embodiment sets the number n of the polygon mirror 78 to a predetermined number, the relationship between the resolutions X and Y in the main scanning direction and the sub-scanning direction to a predetermined relationship, and the conveyance of the paper P. The dot clock T is configured to be equal to or higher than a predetermined value by setting the speed v to a predetermined speed (see FIG. 14).

  Specifically, the number n of surfaces of the polygon mirror 78 is set to 8 or less. This is in consideration of versatility, and the cost can be reduced by making the number of faces of the polygon mirror 78 eight or less. In consideration of versatility, the number n of polygon mirrors 78 is preferably 6 or more.

  In an apparatus that performs photographic printing such as the image forming apparatus A, a sufficient resolution can be ensured if the maximum resolution in the main scanning direction is 300 dpi. The maximum resolution in the main scanning direction may be 300 dpi or more. Further, it is desirable that the resolution in the sub-scanning direction is Y = X × 2 in order to perform interlace correction. For this reason, in the image forming apparatus A, the maximum resolution in the sub-scanning direction may be 600 dpi. Note that the maximum resolution in the sub-scanning direction may be 600 dpi or more. In consideration of the image quality of photographic prints, in this image forming apparatus A, the minimum resolution in the main scanning direction may be 150 dpi and the minimum resolution in the sub-scanning direction may be 300 dpi.

  Here, interlace correction means that the dots of each color on the paper P shift in the sub-scanning direction due to the shift of RGB laser light caused by the arrangement accuracy of the mirrors 74R, 74G and 74B. This is a technique of reducing by using double writing of dots. The double writing of dots is a technique of shifting and forming two dots corresponding to one dot of the image on the paper P, and this double writing of dots is a sub-scan of the dots formed on the paper. This is done to eliminate directional gaps and connect these dots smoothly. On the other hand, when writing dots twice, each dot is formed by shifting in the sub-scanning direction in units of 0.5 dots, and the center of the image is canceled by two dots shifted by 0.5 dots. It becomes the midpoint of the distance. For this reason, if the amount of color misregistration between two different colors is 0.25 dots or more, each of the two dots forming an image of one color is shifted by 0.5 dots in the sub-scanning direction. The amount of color misregistration between two colors can be suppressed to within 0.25 dots (for example, when the amount of color misregistration between two colors is 0.7 dots, an image of either color is 0.5 dots Therefore, the amount of color misregistration between two colors is 0.2 dots.

Under the above conditions, the conveyance speed v (mm / sec) of the paper P is set to v ≧ 5.1 × 10 ⁻⁶ × N ² f (mm / sec). f is the focal length (mm) of the fθ lens 79, and N is the rotational speed of the polygon mirror 78.

  That is, the roller driving means 31 and the number n of the surface of the polygon mirror 78, the rotation speed N of the polygon mirror 78, the resolutions X and Y in the main and sub-scanning directions, and the focal length f of the fθ lens 79 are determined. The minimum value of the conveyance speed v of the paper P by driving the exposure conveyance roller 9 is set.

As a result, the dot clock T can be set to 100 × 10 ⁻⁹ sec or more, which makes it possible to obtain a desired Dmax while widening the image forming apparatus, thereby improving the quality of photographic prints. Can be achieved.

  The present image forming apparatus A is wide, and the width of the paper P accommodated in the paper magazine 3 is larger than that of the conventional image forming apparatus. Therefore, the inertia of the roll R is larger than that of the conventional one, and it is difficult to cut the paper P into a predetermined print size by the paper cutter 5 unless the conveyance speed v of the paper P is lower than that of the conventional image forming apparatus. become. If the conveyance speed v is to be increased, it is necessary to increase the size of each conveyance motor or to increase the size of the advance roller unit in order to increase the pressure-bonding force of the advance roller unit 4. Will lead to a change.

  Further, in the present image forming apparatus A, the focal length f of the fθ lens 79 is large (for example, about 750 mm) to increase the width, and the number n of surfaces of the polygon mirror 78 is increased or the resolutions X and Y are decreased. Since it is difficult from the viewpoint of cost and image quality, the conveyance speed v must be lowered from this.

  In this image forming apparatus A, the rotation speed N of the polygon mirror 78 is set to a relatively low speed as the conveyance speed v is set to a low speed. It is preferable to employ a rolling bearing that is highly stable even in rotation.

  Here, the rotational speed N of the polygon mirror 78 is set to 80 rps or less. This is in consideration of the durability of the rolling bearing and, in turn, the product life of the image forming apparatus A.

Note that the dot clock T is preferably set to 150 × 10 ⁻⁹ sec or less, so that a decrease in processing capability of the image forming apparatus A is suppressed.

  As described above, the image forming apparatus according to the present invention is useful for an image forming apparatus such as a photographic processing system because a sufficient dot clock can be secured to improve image quality.

It is a fragmentary sectional view which shows the structure of the photographic processing system provided with the image forming apparatus. It is a figure which shows the structure of a storage space part. It is a detailed perspective view which shows the structure of a winding mechanism. It is sectional drawing which shows the cam mechanism which moves a pressurizing roller. FIG. 3 is a diagram illustrating a control block configuration of the image forming apparatus. 3 is a flowchart (first half) showing an operation of the image forming apparatus. 6 is a flowchart (second half) illustrating the operation of the image forming apparatus. FIG. 6 is a diagram illustrating an operation (part 1) of the image forming apparatus. FIG. 10 is a diagram illustrating an operation (No. 2) of the image forming apparatus. FIG. 10 is a diagram illustrating an operation (part 3) of the image forming apparatus. FIG. 10 is a diagram illustrating an operation (part 4) of the image forming apparatus. FIG. 10 is a diagram illustrating an operation (No. 5) of the image forming apparatus. FIG. 10 is a diagram illustrating an operation (No. 6) of the image forming apparatus. It is a block diagram which shows the structure of an exposure unit. It is explanatory drawing which shows the structure of a light beam scanning system. It is the measurement result which measured the density value with respect to the output of a light beam, changing a dot clock.

Explanation of symbols

70R Laser light source (light source)
70G Laser light source (light source)
70B Laser light source (light source)
78 Polygon mirror 79 fθ lens 9 Exposure conveyance roller (conveyance means)
A Image forming device P Paper (photosensitive material)
U Exposure unit (exposure means)

Claims (3)

An exposure unit comprising: a light source that emits a light beam; a polygon mirror that deflects the light beam from the light source in a main scanning direction; and an fθ lens that converges the light beam deflected by the polygon mirror on a photosensitive material; ,
Transport means for transporting the photosensitive material at a predetermined transport speed in the sub-scanning direction,
An image forming apparatus that forms a latent image on the photosensitive material by scanning the light beam in the main scanning direction with respect to the photosensitive material conveyed in the sub-scanning direction by the exposure unit. Because
The number n of surfaces of the polygon mirror is 8 or less, and the relationship between the resolution X (dpi) in the main scanning direction and the resolution Y (dpi) in the sub-scanning direction is Y = 2X,
The conveyance speed v of the photosensitive material is
v ≧ 5.1 × 10 ⁻⁶ × N ² f (mm / sec)
(Where N is the rotational speed of the polygon mirror (rps), f is the focal length of the fθ lens (mm))
By
An image forming apparatus in which a dot clock T which is an irradiation time per dot on the photosensitive material is set to 100 × 10 ⁻⁹ sec or more. The image forming apparatus according to claim 1.
The rotation speed N of the polygon mirror is set to 80 rps or less. The image forming apparatus according to claim 1, wherein
2. The image forming apparatus according to claim 1, wherein the dot clock T is set to 150 × 10 ⁻⁹ sec or less.

Images