JP2007153549A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device having a pixel forming means capable of forming a pixel in a line shape in the main scanning direction and a carrying mechanism carrying a recording medium in the sub-scanning direction crossing with the main scanning direction, and having the carrying mechanism having roller pairs capable of sandwiching and carrying the recording medium and a driving belt transmitting a rotational driving force of a driving motor to the roller pairs, that is, the image forming device without causing a stripe-shaped defect on an outputting image even if the free length part of the driving belt vibrates the image forming device in a frequency approximate to a natural frequency of a casing. <P>SOLUTION: A tension pulley 70 for increasing the tension of the driving belt 61 is arranged so that a position can be adjusted in the direction crossing with the free length part H1, by pressing the free length part H1 of the driving belt 61 in the direction crossing with the longitudinal direction of the free length part H1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes pixel forming means capable of forming pixels in a line along the main scanning direction, and a transport mechanism for transporting the recording medium in the sub-scanning direction, and the transport mechanism can sandwich and transport the recording medium The present invention relates to an image forming apparatus having a pair of rollers and a drive belt that transmits a rotational driving force of a drive motor to the pair of rollers.

  As this type of image forming apparatus, there is Patent Document 1 shown below as prior art document information related to the present invention. The image forming apparatus described in Patent Document 1 is emitted from an exposure engine (pixel forming unit) to a photosensitive surface of a photographic paper (recording medium) conveyed in the sub-scanning direction by a conveying mechanism including a roller pair. By performing linear exposure in the main scanning direction with a laser beam, a two-dimensional image can be formed on the photographic paper. The rotational driving force of the drive motor is wound between a first pulley having a small diameter fixed to the rotation shaft of the drive motor and a second pulley having a large diameter spaced from the first pulley in the radial direction. The first drive belt, a small third pulley that rotates integrally with the second pulley, and a large fourth pulley that is spaced radially from the third pulley are wound around the first drive belt. The second drive belt is decelerated and transmitted to a pair of rollers that can rotate integrally with the fourth pulley. By using a stepping motor type drive motor as the drive motor, it becomes possible to transport the recording medium sandwiched between the roller pair at a constant speed, and as a result, the image data input to the exposure engine is accurate and accurate. An image can be formed.

Japanese Patent Laying-Open No. 2005-239330 (paragraph number 0017, FIGS. 2 and 3)

  However, in the image forming apparatus described in Patent Document 1, the free length portion of the first drive belt that is rotationally driven at a relatively high speed vibrates at a specific frequency. When the natural frequency is matched, the vibration is amplified and transmitted to the roller pair, and as a result, a streak-like defect may occur in a photographic image obtained as a product by development processing. The first and second drive belts may be reduced by using metal drive belts instead of rubber drive belts. In this case, however, the parts cost is extremely high. Become.

  Therefore, in view of the above-mentioned drawbacks of the image forming apparatus according to the prior art exemplified above, the object of the present invention is to output even when the free length of the drive belt vibrates at a frequency approximate to the natural frequency of the housing. It is an object of the present invention to provide an image forming apparatus that is less likely to cause a streak-like defect in a printed image with a configuration that is as inexpensive as possible.

A first characteristic configuration of the present invention includes a pixel forming unit capable of forming pixels in a line shape along a main scanning direction, and a transport mechanism that transports a recording medium in a sub-scanning direction. An image forming apparatus having a pair of rollers capable of sandwiching and conveying a recording medium, and a drive belt for transmitting a rotational driving force of a drive motor to the pair of rollers,
A tension pulley that increases the tension of the drive belt by pressing the free length portion of the drive belt in a direction that intersects the longitudinal direction of the free length portion can be adjusted along the direction that intersects the free length portion. It is in the point provided.

  Therefore, in the image forming apparatus according to the first characteristic configuration of the present invention, since the tension of the drive belt is increased by the tension pulley, the frequency of the free length portion of the drive belt during the rotation drive is increased. Even if the output image is affected in the form of density unevenness (unevenness) in the sub-scanning direction, high frequency inconspicuous unevenness (unevenness), or the frequency of the drive belt moves away from the natural frequency of the housing, Since the phenomenon in which the vibration is amplified and transmitted to the roller pair is suppressed, an effect is obtained that it becomes difficult for the output image to have unevenness such as streaks. Alternatively, when the tension of the drive belt is increased by the tension pulley, it becomes difficult for the free length portion of the drive belt to be displaced particularly along the rotation surface of the drive belt, and the vibration of the free length portion of the drive belt during the rotational drive is caused. In some cases, the effect of suppressing the occurrence of streaky spots (unevenness) in the output image is suppressed. Furthermore, since the tension pulley is provided so that its position can be adjusted along the direction intersecting the free length part, even if the tension applied by the tension pulley fluctuates due to the elasticity of the drive belt and the change over time, the tension pulley By appropriately changing the position of the pulley, the tension of the drive belt can be corrected to an appropriate value.

  In another feature of the present invention, the tension pulley is supported so as to be displaceable in a direction intersecting with the free length portion of the drive belt, and biasing means that elastically presses the tension pulley against the free length portion. It is in the point provided.

  In this configuration, the tension pulley can be displaced in the direction intersecting the free length portion of the drive belt according to the amplitude condition of the oscillating drive belt, so that the tension pulley is generally in the direction intersecting the free length portion. By always following the displacement of the drive belt having the maximum amplitude, the vibration of the drive belt can be effectively damped.

  Another feature of the present invention is that an auxiliary pulley that elastically presses the free length portion of the drive belt against the tension pulley is provided.

  With this configuration, the free length portion of the drive belt is elastically pressed against the first tension pulley by the auxiliary pulley, so that the possibility of the drive belt being separated from the first tension pulley is further reduced, and the vibration of the drive belt is reduced. Is attenuated more effectively.

  Another characteristic configuration of the present invention is that a tension pulley having a fixed shaft core and an auxiliary pulley that elastically presses a free length portion of the drive belt against the tension pulley are provided.

  In this configuration, since the free length portion of the drive belt is elastically pressed by the auxiliary pulley against the tension pulley having the shaft core fixed, the amplitude of the free length portion of the drive belt is effectively suppressed, and the drive belt Vibration is damped more effectively.

  According to another characteristic configuration of the present invention, the tension pulley includes a first tension pulley and a second tension pulley that are spaced apart from each other on a support member, and the first tension pulley is disposed on an outer surface side of the drive belt. There is an urging means for urging the support member so as to press and press the second tension pulley against the inner surface side of the drive belt.

  With this configuration, both the two free length portions formed on the drive belt wound around the output pulley near the drive motor and the input pulley near the roller are vibrated by a single biasing means. Therefore, the vibration of the drive belt is more effectively damped. In particular, the first tension pulley is pressed from the outer surface side for the free length portion that is the loose side during rotation, and the second tension pulley is pressed from the inner surface side for the free length portion that is the tension side during rotation. The vibration of the free length part is effectively prevented.

  In another aspect of the present invention, the diameter of the first driven pulley rotated by the drive pulley through the drive belt by the drive pulley that rotates integrally with the output shaft of the drive motor is b, and the second that rotates integrally with the first driven pulley. The diameter of the driven pulley is c, the diameter of the third driven pulley that is rotated by the second driven pulley via the second drive belt is d, and the diameter of the roller of the roller pair that rotates integrally with the third driven pulley. e, V = (0.34 × b · d) / (c · e) where V (mm) is the repetition pitch of the irregularities formed on the inner surface side of the drive belt along the length direction of the drive belt. ) Is set so as to hold the relationship.

  If the relationship of this configuration is established, the unevenness on the inner side of the drive belt will destabilize the conveyance speed of the recording medium and affect the output image in the form of density unevenness (unevenness) in the sub-scanning direction. However, the density unevenness in the sub-scanning direction is 0.34 mm or less, which is considered to be negligibly negligible from the relationship with the resolution per pulse of the drive motor, and the quality of the output image is kept moderate. Be drunk.

The best mode for carrying out the present invention will be described below with reference to the drawings.
The photographic printing apparatus shown in FIG. 1 has an exposure block Ex that exposes a silver salt photographic paper P (an example of a recording medium, hereinafter referred to as a photographic paper P) as a photosensitive material, and is thus exposed. The housing 10 is provided with a development block De for developing the photographic paper P and a drying block Dr for drying the photographic paper P after the development processing. Further, outside the housing 10, a stacking device that feeds the photographic paper P that is fed out from the upper part of the housing 10 in the horizontal direction after processing to the sorter (not shown) from the transport belt 11, and sorts and stacks them in order units. Is provided. This photographic printing apparatus is generally called a digital minilab, and transmits image information captured by photoelectrically converting a frame image of a photographic film by a film scanner or image information taken by a digital camera to the photographic printing apparatus. Thus, in the exposure block Ex, the image information can be exposed and printed on the photographic paper P.

  The exposure block Ex cuts the roll-shaped photographic paper P stored in one of the two photographic paper magazines M, M into a print size by the supply unit U1 and conveys the photographic paper P from the supply unit U1. In the exposure unit U2, the image information is exposed while transporting the transport path in the vertical posture from below to above, and the transport direction of the photographic paper P sent upward from the exposure unit U2 is set to the horizontal direction in the front roller unit U3. After the conversion, it is configured so as to be sent in the horizontal direction by the sorting unit U4 and then transferred from the rear roller unit U5 to the developing block De.

The supply unit U1 includes a plurality of pressure rollers 13 that convey the photographic paper P from the photographic paper magazine M, a cutter 14 that cuts the photographic paper P into a print size, and a chuck mechanism that sandwiches the photographic paper P and moves upward. 15. The exposure unit U2 (an example of an image forming apparatus) is a laser scanning type that forms pixels on the photographic paper P in a line along the main scanning direction while conveying the photographic paper P from below to above by the conveying means. Exposure engine 17 (an example of a pixel forming unit) and an exposure transport unit TU (an example of a transport mechanism) that transports in a sub-scanning direction extending perpendicular to the main scanning direction. The front roller unit U3 includes a plurality of conveying rollers 18 arranged to be switched between a crimping state (crimping position) and an open state (opening position) in a curved conveyance path. The sorting unit U4 includes two chuckers CH that pinch the photographic paper P and distribute it to two rows of distribution paths. The rear roller unit U5 includes a plurality of pressure rollers 19 that convey the photographic paper P sorted by the sorting unit U4 along two rows of sorting paths.
The development block De includes a plurality of development processing tanks 20 including a color development tank, a bleach-fixing tank, and a stabilization tank, and a transport having a number of pressure rollers so as to supply the photographic paper P to each of the development processing tanks. A unit 21 is provided. The drying block Dr forms a conveyance path for supplying dry air from the blower 22 to the photographic paper.

  As shown in FIG. 2, the transport unit U2 is supported by a main frame F1 formed entirely of a metal material such as aluminum, and is separably supported with respect to the main frame F1, and is formed entirely of a metal material such as aluminum. The movable frame F2 is provided, and a conveyance path for conveying the printing paper P in the vertical direction (sub-scanning direction) is formed at the boundary position between the main frame F1 and the movable frame F2. Further, a conveying means for conveying the photographic paper P in the sub-scanning direction with respect to this conveying path is provided, and a laser beam from the exposure engine 17 is applied to the photosensitive surface of the photographic paper P sent to the exposure position X by the conveying means. Line exposure is performed in the main scanning direction by LB. Incidentally, the exposure engine 17 uses an acousto-optic modulation means to convert the laser beam LB from the laser light sources of the three primary colors R (red), G (green), and B (blue) housed in the casing. A structure in which the light is adjusted and sent to the exposure position X while being scanned in the main scanning direction by being reflected by the mirror surface of a polygon mirror that rotates about the vertical axis is used. As the exposure head, that is, the pixel forming means, in addition to the laser scanning type, a fluorescent beam method, a liquid crystal shutter method, a DMD method, or the like can be used.

  The main frame F1 includes a reference plate 25 that is formed flat so as to contact and guide the substrate side of the photographic paper P on the conveyance path side of the photographic paper P, and a movable member at a position facing the reference plate 25. A guide body G for guiding the photosensitive surface side of the photographic paper P is disposed at F2. The movable frame F2 is fixed by a holding mechanism (not shown) such as a buckle in such a manner that the connecting shaft 26 formed at the lower end is engaged with the recess 27 on the main frame side, and the upper end is pulled toward the main frame F1. Thus, the reference plate 25 and the guide body G are configured to be held in a predetermined positional relationship facing each other.

  The guide body G includes a front guide body 31 disposed upstream of the exposure position in the conveyance direction of the photographic paper P, and a rear guide body 33 disposed downstream of the exposure position X. The distance between the front guide body 31 and the reference plate 25 is set to about 0.8 mm, and the distance between the rear guide body 33 and the reference plate 25 is set to about 0.4 mm. The thickness of the photographic paper P is assumed to be about 0.2 mm.

At the lower position of the main frame F1, there is provided a press-fit introduction roller R0 that receives the photographic paper P from the chuck mechanism 15. This introduction roller R0 includes a front drive roller 35 that rotates and rotates, and a front pressure roller 36 that can be switched to a pressure-bonding position that is crimped to the front drive roller 35 and an open position that is separated from the front drive roller 35. The driving force of the stepping motor type introduction motor 37 is transmitted to the partial drive roller 35 via the speed reduction mechanism 38.
The front drive roller 35 has a structure in which a roller portion 35B made of metal such as aluminum is externally fixed to the shaft portion 35A. The pressure roller 36 that is pressure-bonded to the shaft portion 35A is made of rubber or flexible to the shaft body 36A. The pressure roller 36 has a structure in which a roller portion 36B made of resin is formed. The pressure roller 36 is pivotally supported by a swing end of an arm 39 that swings around a support shaft 39A. 2 (shown by a solid line in FIG. 2).

  The exposure transport device TU includes a first pressure-conveying roller R1 disposed upstream of the exposure position X so as to send the photographic paper P from the introduction roller R0 to the exposure position X, and a print from the first pressure-conveying roller R1. It is composed of a second pressure-conveying and conveying roller R2 disposed downstream of the exposure position so as to feed the paper upward. The first pressure-conveying roller R1 is composed of a driving roller 41 and a pressure-bonding roller 42 that rotates by being pressure-bonded to the driving roller 41. The second pressure-conveying and conveying roller R2 is composed of a driving roller 51 and the driving roller 51. It comprises a pressure roller 52 that rotates by pressure bonding.

  Each of the drive rollers 41 and 51 has a structure in which a plurality of roller portions 41B and 51B are fitted and fixed to shaft portions 41A and 51A made of stainless steel. The roller portions 41B and 51B are made of a metal material such as aluminum. The outer peripheral surface is coated with ceramic fine particles by a technique such as thermal spraying, and the shaft portions 41A and 51A are pivotally supported with respect to the main frame F1. An opening for accommodating the roller portions 41B and 51B is formed in the reference plate 25, and the outer peripheral portions of the roller portions 41B and 51B are slightly opened from the guide surface 25S of the reference plate 25 to the transport path side through the openings. Drive rollers 41 and 51 are pivotally supported so as to have a protruding positional relationship.

  A stepping motor type drive motor 60 is provided on the main frame F1 side. The driving force from the drive motor 60 includes a small-diameter first pulley L1 fixed to the output shaft of the drive motor 60, and a large-diameter second pulley L2 having an axis arranged in parallel with the output shaft. A first endless belt 61 wound between the second pulley L2 and a small-diameter third pulley L3 that rotates integrally with the second pulley L2, and a medium-diameter shaft having an axial core disposed in parallel with the third pulley L3. A transmission system is formed which is transmitted to the drive rollers 41 and 51 via a reduction transmission system composed of a second endless belt 62 wound between the two fourth pulleys L4. The fourth pulley L4 is connected to the drive rollers 41 and 51 so as to rotate integrally. The double pulley in which the large-diameter second pulley L2 and the small-diameter third pulley L3 are integrated is supported on the main frame F1 so as to be slightly displaceable in the axial direction. In order to eliminate rattling that may affect the movement of the main frame F1, it is pressed against the vertical wall surface of the main frame F1 by an urging means such as a compression spring (not shown).

  The drive shaft of the introduction motor 37 and the drive shaft of the drive motor 60 are provided with a rotary damper RD having no temperature dependency. This rotary damper RD functions to absorb rotation unevenness by fixing a metal ring on the outer periphery of a flexible resin, and is not affected by the temperature of the environment by using a non-temperature-dependent one. Smooth rotation power can be taken out.

As described above, when the shaft portions 41A and 51A of the drive rollers 41 and 51 are formed of stainless steel or the like, and the diameter values of the shaft portions 41A and 51A are set to values to be described later, the photographic paper P is pressed. It is comprised so that the bending of shaft part 41A, 51A in may be suppressed.
Each of the pressure-bonding rollers 42 and 52 has a structure in which a plurality of roller portions 42B and 52B are formed in a direction along the axis with respect to the shaft bodies 42A and 52A. The plurality of roller portions 42B and 52B are driven. It arrange | positions in the position facing the some roller parts 41B and 51B of the rollers 41 and 51. FIG. Further, the shaft bodies 42A and 52A are made of rod-like titanium material, and the roller portions 42B and 52B are made of foamed rubber having a hardness of about 30 degrees to reduce the weight.

  A pair of operation shafts 43 and 53 in a posture parallel to the shaft bodies 42A and 52A of the pressure-bonding rollers 42 and 52 are rotatably supported with respect to the movable frame F2, and are also swung integrally with the operation shafts 43 and 53. The shaft bodies 42A and 52A of the pressure-bonding rollers 42 and 52 are pivotally supported on the swinging ends of the moving arms 44 and 54, and from this structure, the operation shafts 43 and 53 are crimped by rotating around the axis. It is configured to be switchable between a crimping position where the rollers 42, 52 are crimped to the driving rollers 41, 51 and an open position separated from the driving rollers 41, 51. Further, although not shown in the drawing, an urging means (not shown) such as a spring for urging the respective pressure rollers 42 and 52 to the pressure bonding position is provided.

  As shown in FIG. 3, roller-type cam followers 46 and 56 are pivotally supported on the swinging ends of crank members 45 and 55 fixed to the ends of the operation shafts 43 and 53, respectively. Rotating cams 47 and 57 that contact 56 are supported by the main frame F1, and the driving force from stepping motor type cam motors 48 and 58 is transmitted to the respective rotating cams 47 and 57 by belt transmission mechanisms 49 and 59. A cam operation system is formed. The cam followers 46 and 56 are arranged on the shaft centers of the pressure-bonding rollers 42 and 52. When the movable frame F2 is separated from the main frame F1, the cam followers 46 and 56 and the rotating cams 47 and 57 are connected to each other. It becomes a form to separate.

  Although a detailed description of the control system is omitted, the exposure unit U2 transports the photographic paper P according to the following control. That is, as shown in FIG. 5, when receiving the photographic paper P sandwiched by the chuck mechanism 15 of the supply unit U1, the front pressure roller 36 of the introduction roller R0 is set to the open position, and the chuck mechanism 15 The leading end portion of the photographic paper P sandwiched between the chuck members 15a and 15a is allowed to be inserted (a). Next, by setting the front pressure roller 36 to the pressure bonding position, the front drive roller 35 and the front pressure roller 36 are used to pressure-bond the photographic paper P, and then the chuck members 15a and 15a of the chuck mechanism 15 are used. The nipping is released, and after the nipping is released, the introduction roller R0 is driven to start conveyance (b). By continuing this conveyance, the photographic paper P is guided while its base side contacts the reference plate 25, and at the same time, its photosensitive surface side is guided by the front guide body 31, thus. The photographic paper P is fed to the first pressure roller R1 side while being guided by the reference plate 25 and the front guide body 31.

  The driving rollers 41 and 51 of the first and second pressure rollers R1 and R2 are basically in a driving state regardless of the presence or absence of the photographic paper P, and after the conveyance of the photographic paper P is started by the introduction roller R0, Before the leading end of the photographic paper P reaches the site of the first pressure roller R1, the pressure roller 42 of the first pressure roller R1 is set to the open position (c). When the leading end of the photographic paper P reaches a position where it can be conveyed by the first pressure roller R1, the pressure roller 42 is set at the pressure position, so that the driving roller 41 and pressure roller 42 of the first pressure roller R1 are set. After the photographic paper P is pressed and conveyed, the conveyance by the first pressure roller R1 is started in this way, and then the front pressure roller 36 of the introduction roller R0 is set to the open position, thereby photographic paper. No external force is applied to P from the introduction roller R0 side (d).

Next, before the leading edge of the photographic paper P on which the exposure to the photographic paper P is started is sent, the pressure roller 52 of the second pressure roller R2 is set to the open position (e), and the second pressure roller R2 is placed at the position of the second pressure roller R2. By setting the pressure roller 52 to the pressure bonding position when the leading edge of the photographic paper P reaches, the driving roller 51 and the pressure roller 52 of the second pressure roller R2 are pressure-bonded to start conveyance, After the conveyance of the photographic paper P by the second pressure roller R2 is started in this way, the pressure roller 42 of the first pressure roller R1 is switched to the open position at an appropriate timing, so that the first pressure roller R1 side can be opened. The photographic paper P is transported only by the transport force of the second pressure roller R2 in the state where no external force is applied (f).
These operations are performed by controlling the actuator 39 of the front pressure roller 36 that constitutes the introduction roller R0, the control of the introduction motor 37 that drives the front drive roller 35, and the pressure pressure that constitutes the first and second pressure rollers R1 and R2. This is realized by controlling the cam motors 48 and 58 that rotate the rotating cams 47 and 57 that determine the postures of the rollers 42 and 52.

  In the exposure transport apparatus TU according to the present invention, the diameters of the roller portions 41B and 51B in the drive rollers 41 and 51 of the first and second pressure-bonding transport rollers R1 and R2 are 30 mm, but as shown in FIG. By setting the diameters D1 and D2 (D1 = D2) of 51A to 24 mm, the bending amount when the photographic paper P is pressed is configured to be less than 0.005 mm. Further, the diameter of the roller portion 35B of the front drive roller 35 of the introduction roller R0 is about 24 mm. However, by setting the diameter D0 of the shaft body 35A to 14 mm, the amount of bending when the photographic paper P is pressure-bonded is 0. It is configured to be less than 0.005 mm. That is, when the photographic paper P is pressure-bonded by the first and second pressure-conveying rollers R1 and R2, a force of about 19.6 N is applied, and when the photographic paper P is pressure-bonded by the introduction roller R0, 9.8 N is applied. The crimping force by the crimping rollers 42, 52, and 36 is set so as to apply a certain amount of force, and the deflection of the central position in the length direction of the shaft portions 41A and 51A when such a force is applied. The amount is less than 0.005 mm, and the amount of deflection at the center position in the length direction of the shaft body 35A is less than 0.005 mm. This configuration suppresses banding.

  As described above, in the exposure transport device TU, the diameter d of the shaft portions 41A and 51A in the drive rollers 41 and 51 of the first and second pressure transport rollers R1 and R2 is set to 24 mm, and the front drive roller of the introduction roller R0. By setting the diameter D0 of the shaft body 35A at 35 to 14 mm, it is possible to maintain the respective deflection amounts at the time of pressure bonding of the photographic paper P to less than 0.005 mm. By reducing the amount of bending in this manner, the disturbance of the conveyance speed when the photographic paper P is crimped and conveyed is suppressed, and the vibration that acts on the photographic paper P when the crimped state is released is suppressed. It is intended to obtain a print with good image quality. In particular, increasing the diameter of the shaft portions 41A and 51A increases the dynamic inertia of the first and second pressurizing and transporting rollers R1 and R2. Therefore, when the photographic paper P is also crimped by this, the crimping is released. In this case, the first and second pressurizing and conveying rollers R1 and R2 are stably rotated to obtain a print with good image quality.

  Furthermore, in the exposure transport apparatus TU according to the present invention, a first pulley L1 having a small diameter fixed to the output shaft of the drive motor 60 and a second pulley L2 having a large diameter having an axial center arranged in parallel with the output shaft. A tension mechanism is provided for increasing the tension of the first endless belt 61 wound between them. As shown in FIG. 7, the tension mechanism includes a tension pulley 70 that presses the free length portion H <b> 1 on the slack side of the first endless belt 61. A bracket 71 that rotatably supports the tension pulley 70 is placed on a support plate 72 fixed to the main frame F1 by screws 73, perpendicular to the longitudinal direction of the free length portion H1 on the loose side of the first endless belt 61. The first endless belt 61 is supported by a compression spring 74 provided on the support plate 72 so that the outer peripheral surface of the first endless belt 61 is moved in the first direction. The endless belt 61 is biased so as to be pressed along the moving direction Q toward the center in the rotation surface. In addition, the moving direction Q of the bracket 71 does not necessarily need to intersect the longitudinal direction of the free length portion H1 at right angles, and may be a direction that intersects the longitudinal direction of the free length portion H1.

Since the tension of the first endless belt 61 is increased by the action of the tension mechanism, the frequency of the free length portion of the first endless belt 61 during the rotational driving is increased so as to exceed a critical value 172 Hz described later. As a result, even if the output image is affected in the form of density spots (unevenness) in the sub-scanning direction, high-frequency spots are not noticeable, or the frequency of the first endless belt 61 is the main. Since the phenomenon that the vibration is amplified and transmitted to the roller pair 51 is suppressed away from the natural frequency of the frame F1 or the like, streaks (unevenness) such as streaks are less likely to occur in the output image. Alternatively, when the tension is increased by the tension pulley 70, the free length portion of the first endless belt 61 becomes difficult to be displaced particularly along the rotation surface of the first endless belt 61, and the vibration of the free length portion during the rotational drive is caused. In some cases, the effect of suppressing the occurrence of streaky spots (unevenness) in the output image is suppressed.
Incidentally, the photographic paper transport speed by the exposure transport apparatus TU according to the present invention is 58.42 mm / second, and as will be described later, the generation period T of density unevenness (unevenness) in the sub-scanning direction in the finished photograph is 0.34 mm or less. Therefore, if the vibration of the free length of the first endless belt 61 is a factor of density unevenness (unevenness), the critical value of the frequency is 58. 42 / 0.34 = 171.8 Hz. That is, by adjusting the frequency of the free length portion of the first endless belt 61 to exceed 172 Hz, the quality of the photograph can be within an allowable range.

Further, since the tension pulley 70 is elastically pressed against the free length portion by the compression spring 73, the tension pulley 70 itself can freely move the first endless belt 61 according to the amplitude of the vibrating first endless belt 61. Because the first endless belt 61 can be displaced in the direction intersecting the long part within the rotation plane of the first endless belt 61, the tension pulley 70 generally always follows the displacement of the first endless belt 61 having the maximum amplitude in the direction intersecting the free length part. By doing so, the vibration of the first endless belt 61 can be effectively damped.
Further, since the support plate 72 is fixed to the main frame F1 with screws 73 through a pair of long holes 72a formed in the support plate 72, one of the first endless belts 61 is loosened once by loosening the screws 73. The position can be adjusted along the moving direction Q that intersects the longitudinal direction of the free length portion H1 at a right angle. Therefore, even when the tension applied by the tension pulley 70 fluctuates due to changes in the elasticity and length of the first endless belt 61, the tension of the first endless belt 61 is changed by appropriately changing the position of the tension pulley 70. It is possible to correct to an appropriate value.

Regarding a method of setting an appropriate tension applied by the tension pulley 70, that is, how to determine the fixing position of the support plate 72 in the above-described embodiment, the rotational speed of the roller is changed by a rotary encoder or the like while changing the position of the support plate 72. What is necessary is just to take the method of finding the position with the least vibration by measuring.
Incidentally, the first endless belt 61 is a flat belt having a rectangular cross section made of polyurethane as a main material, and includes a wire cord made of glass fiber or Kevlar (trade name) as a core wire. By the way, in the molded product of the polyurethane belt, the thickness is not necessarily uniform along the length direction. If it is used as it is, the conveyance speed of the photographic paper P becomes unstable, so that the thickness is made uniform. In addition, it is necessary to polish the contact surface with the pulley with an abrasive or the like. However, since the base material is polyurethane, as schematically illustrated in FIG. 6, fine unevenness still exists after the polishing is completed, and this unevenness also makes the conveyance speed of the photographic paper P unstable, As an element different from the vibration of the free end portion of the one endless belt 61, there is a possibility that streaky spots are formed on the image.

  Therefore, when polishing the first endless belt 61, it is necessary to provide a quality control standard, but here, the generation period T of density unevenness (unevenness) in the sub-scanning direction is a level that can be ignored with the naked eye. The allowable value for quality control of the first endless belt 61 is defined as 0.34 mm or less. Specifically, in order to rotate the first endless belt 61, the diameter of the drive pulley that rotates integrally with the output shaft of the drive motor 60 is a, the diameter of the driven pulley that is rotated by the drive belt is b, and the second pulley The diameter of the small third pulley L3 that rotates integrally with L2 is c, the diameter of the two fourth pulleys L4 that rotate integrally with the drive rollers 41 and 51 is d, the diameter of the rollers of the roller pair is e, and the inner surface side of the drive belt When the repetition pitch of the unevenness formed along the length direction of the drive belt is V, the necessary and sufficient condition for satisfying the allowable value that the generation period T is 0.34 mm or less is V ≦ (0.34). Xb · d) / (c · e). This relationship is derived from the following calculation formula.

a: Diameter of the first pulley L1 having a small diameter fixed to the output shaft of the drive motor 60 b: Diameter of the second pulley L2 having a large diameter c: Diameter of the third pulley L3 having a small diameter rotating integrally with the second pulley L2 d : Diameter of the two fourth pulleys L4 that rotate integrally with the drive rollers 41 and 51. e: Diameter of the roller parts 41B and 51B. The operating conditions of the drive motor 60, the step angle of the two-phase half step: θ, and the photographic paper transport speed. Assuming 58.42 mm / second,
The resolution S per pulse of the drive motor 60 is obtained from Equation 1 below.
S = (a / b) · (c / d) × 30π × (θ / 360)
= (A ・ c ・ π ・ θ × 30) / (b ・ d × 360) ―――― (Equation 1)
Further, the number of steps for conveying the photographic paper by 0.34 mm = 0.34 / S.
Therefore, the feed length x of the first endless belt 61 corresponding to the number of steps = 0.34 / S can be obtained from Equation 2 below.
x = (0.34 / S) × (θ / 360) × a × π ---- (Equation 2)
Given the value of S according to equation 1 to equation 2, the following equation 3 is obtained.
x = (0.34 × b · d) / (c · e) (Equation 3)
Accordingly, the necessary and sufficient condition for making the density unevenness (unevenness) generation period T in the sub-scanning direction at a level that can be ignored with the naked eye is the repetition pitch V of the unevenness of the first endless belt 61. Obtained from.
V ≦ (0.34 × b · d) / (c · e) ―――― (Equation 4)
Incidentally, in this embodiment, since b = 118.27 mm, c = 14.17 mm, d = 30.585 mm, and e = 30.00 mm, Equation 4 is substantially V ≦ 2.9 mm.

[Another embodiment]
<1> As a tension mechanism, a pair of brackets 75 formed on the bracket 75 is provided with a bracket 75 that rotatably supports the tension pulley 70 without providing an urging unit that presses the tension pulley 70, as illustrated in FIG. It may be fixed to the main frame F1 with a screw 73 through the long hole 75a. Even in this configuration, the position of the tension pulley 70 can be adjusted along the moving direction Q perpendicular to the longitudinal direction of one free length portion H1 of the first endless belt 61 by once loosening the screw 73.

<2> As illustrated in FIG. 9, an auxiliary pulley 80 that elastically presses the inner peripheral surface of the free length portion of the first endless belt 61 against the tension pulley 70 similar to that of the first embodiment may be provided. Here, the bracket 71 that rotatably supports the tension pulley 70 is arranged on the support plate 72 that is fixed to the main frame F1 by screws 73, in the longitudinal direction of one free length portion H1 of the first endless belt 61. A compression spring 74 provided on the support plate 72 is supported on the outer peripheral surface of the first endless belt 61 in a moving direction. We are energizing along Q. A bracket 81 that rotatably supports the auxiliary pulley 80 is perpendicular to the longitudinal direction of one free length portion H1 of the first endless belt 61 on a support plate 82 fixed to the main frame F1 by screws 83. Is supported so as to be displaceable within the rotation surface of the first endless belt 61 along a moving direction Q that intersects with the compression spring 84, and a compression spring 84 provided on the support plate 82 moves on the inner peripheral surface of the first endless belt 61. It is energized along the direction Q. The auxiliary pulley 80 is disposed opposite to the tension pulley 70 with the first endless belt 61 interposed therebetween. The urging force of the compression spring 84 is set to be smaller than the urging force of the compression spring 74.
Furthermore, since the support plate 82 is fixed to the main frame F1 with screws 83 through a pair of long holes 82a formed in the support plate 82, like the support plate 72, by loosening the screws 83 once, The position of the first endless belt 61 can be adjusted along a moving direction Q that intersects the longitudinal direction of one free length portion H1 at a right angle. Therefore, it is possible to change and set the urging force for pressing the free length portion H1 of the first endless belt 61 against the tension pulley 70 by the auxiliary pulley 80.

<3> As illustrated in FIG. 10, similar to the embodiment of FIG. 8, the tension pulley 70 with the fixed shaft core and the free length portion of the first endless belt 61 are elastically pressed against the tension pulley 70. A configuration in which an auxiliary pulley 80 is provided is also possible. A bracket 81 that rotatably supports the auxiliary pulley 80 intersects the longitudinal direction of one free length portion H1 of the first endless belt 61 on a support plate 82 fixed to the main frame F1 by screws 83. A compression spring 84 provided on the support plate 82 is supported on the inner peripheral surface of the first endless belt 61 in the movement direction Q. Is elastically pressed against the tension pulley 70. The auxiliary pulley 80 is disposed opposite to the tension pulley 70 with the first endless belt 61 interposed therebetween.

<4> As illustrated in FIG. 11, two tension pulleys spaced apart from each other, that is, the first tension pulley 70 a and the second tension pulley 70 b supported on the long bracket 76 can be rotated. It may be provided. Here, the bracket 76 is disposed on a support plate 77 fixed to the main frame F1 by screws 78 along a moving direction Q that intersects the longitudinal directions of the two free length portions H1 and H2 of the first endless belt 61 at a right angle. The first endless belt 61 is supported so as to be displaceable in the rotation surface, and a compression spring 79 provided on the support plate 77 is a free length portion that allows the first tension pulley 70a to be loosened during rotation of the drive belt. The second tension pulley is pressed against the outer surface side of H1 and elastically pressed against the inner surface side of the free length portion H2 that becomes the tension side during rotation of the drive belt. With such a configuration, vibration prevention of both free length parts is effectively performed by a simple tension mechanism using two tension pulleys and a single compression spring.
Further, since the support plate 77 is fixed to the main frame F1 with a screw 78 through a pair of long holes 77a formed in the support plate 77, the first endless belt 61 is freed by loosening the screw 78 once. The position can be adjusted along a moving direction Q that intersects the longitudinal direction of the long portions H1 and H2 at a right angle.

  As a modification of the embodiment of FIG. 7, as illustrated in FIG. 12, the tension pulley 70 is pivotally supported in the vicinity of the free end of the swing plate 85 that is rotatably supported around the fixed axis 85 a. A part of the swing plate 85 may be elastically pressed against the free length portion H1 of the first endless belt 61 by a coil spring 86 or the like.

1 is a longitudinal side view of a photographic printing apparatus provided with an image forming apparatus according to the present invention. 1 is a longitudinal side view showing a main part of an image forming apparatus according to the present invention. 1 is a schematic perspective view showing a main part of an image forming apparatus according to the present invention. Sectional drawing which shows the dimensional relationship of the shaft member of the drive roller and driven roller of an image forming apparatus Schematic diagram showing the transport sequence of photographic paper with respect to the transport path of the exposure unit Schematic diagram showing a cross section of a drive belt used in an image forming apparatus Side view of image forming apparatus and tension pulley viewed from the opposite side of FIG. Side view showing another embodiment of the tension mechanism Side view showing still another embodiment of a tension mechanism Side view showing another embodiment of the tension mechanism Side view showing still another embodiment of a tension mechanism Side view showing another embodiment of the tension mechanism

Explanation of symbols

P photographic paper Ex exposure block M photographic paper magazine U1 supply unit U2 exposure unit U3 front roller unit U4 sorting unit U5 rear roller unit F1 main frame F2 movable frame TU exposure transport device (transport mechanism)
G guide body R0 introduction roller R1 first pressure conveying roller R2 second pressure conveying roller L1 first pulley L2 second pulley L3 third pulley L4 fourth pulley H1 loose side free length part H2 tension side free length part 10 Body 17 Exposure engine (pixel forming means)
25 Reference plate 31 Front guide body 33 Rear guide body 41 Drive roller 42 Pressure roller 51 Drive roller 52 Pressure roller 60 Drive motor 61 First endless belt 62 Second endless belt 70 Tension pulley 71 Bracket 72 Support plate 73 Screw 74 Compression spring

Claims (6)

A pixel forming unit capable of forming pixels in a line shape along the main scanning direction; and a transport mechanism for transporting the recording medium in the sub-scanning direction, wherein the transport mechanism includes a pair of rollers capable of sandwiching and transporting the recording medium. An image forming apparatus having a driving belt for transmitting a rotational driving force of a driving motor to the roller pair,
A tension pulley that increases the tension of the drive belt by pressing the free length portion of the drive belt in a direction that intersects the longitudinal direction of the free length portion can be adjusted along the direction that intersects the free length portion. An image forming apparatus provided.   The image forming apparatus according to claim 1, further comprising an urging unit that elastically presses the tension pulley against a free length portion of the drive belt.   The image forming apparatus according to claim 2, wherein an auxiliary pulley that elastically presses a free length portion of the drive belt against the tension pulley is provided.   The image forming apparatus according to claim 1, further comprising: a tension pulley having a fixed shaft core; and an auxiliary pulley that elastically presses a free length portion of the drive belt against the tension pulley.   The tension pulley includes a first tension pulley and a second tension pulley that are spaced apart from each other on a support member, and presses the first tension pulley against the outer surface side of the drive belt, and the second tension pulley The image forming apparatus according to claim 1, further comprising: an urging unit that urges the support member so as to press against the inner surface side of the drive belt.   The diameter of the first driven pulley that is rotationally driven through the drive belt by the drive pulley that rotates integrally with the output shaft of the drive motor is b, the diameter of the second driven pulley that rotates integrally with the first driven pulley is c, and the first 2) The diameter of the third driven pulley that is rotationally driven by the driven pulley via the second drive belt is d, the diameter of the roller of the roller pair that rotates integrally with the third driven pulley is e, and the inner surface side of the drive belt It is set so that a relationship of V ≦ (0.34 × b · d) / (c · e) is established, where V is a repetition pitch of the unevenness formed along the length direction of the drive belt. Item 6. The image forming apparatus according to any one of Items 1 to 5.

Images