Patent Publication Number: US-6336404-B1

Title: Printing apparatus, and a processing device in the printing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing apparatus for recording images on printing plates mounted peripherally of plate cylinders, feeding processing solutions from processing solution feed rollers to the plates to develop image areas of the plates having the images recorded thereon, and thereafter printing the images by feeding ink to the plates. The invention relates also to a processing device for use in the printing apparatus. 
     2. Description of the Related Art 
     In an ordinary conventional printing apparatus, a prepress process is carried out first to make a plate by exposing the plate placed in contact with a film having a binarized black and white image recorded thereon. Then, the plate is loaded into the printing apparatus to carry out a printing process. 
     Recently, printing apparatus commonly called digital printers have been proposed, one such printer being capable of performing both the prepress process and printing process. The digital printers employ a “computer-to-plate” system for forming images on plates by directly scanning and exposing the plates with laser beams or the like modulated with image signals. 
     A processing device for use in such a printing apparatus is described, for example, in Japanese Patent Publication (Unexamined) H11-105235 (1999). This processing device places a developer feed roller in contact with a printing plate to feed a developer to an image area thereof, and then places a fixer feed roller in contact with the plate to feed a fixer to the image area, thereby developing and fixing the image area having an image recorded thereon. 
     In the processing device described in the above publication, processing solutions such as the developer and fixer are fed to the image area of the printing plate from the developer feed roller and fixer feed roller placed in contact with the image area. Thus, the image area is rubbed by the developer feed roller and fixer feed roller. This could result in a processing unevenness due to vibration of the developer feed roller and fixer feed roller. 
     In the developing process for processing the image area of the plate with the developer, silver is continually deposited around cores provided by silver deposits formed from the developer initially contacting the image area. In the construction where the developer feed roller is placed in contact with the image area to feed the developer to the image area, the silver deposits formed immediately after the developer is fed are rubbed by the developer feed roller. This could result in an imperfect deposition of silver. In such a case, the plate has reduced durability after the developing process. 
     Further, it is desirable that, in such a printing apparatus, the processing device is easily movable to a position for maintenance services. 
     SUMMARY OF THE INVENTION 
     An object of the present invention, therefore, is to provide a processing device in a printing apparatus which is free from a processing unevenness due to vibration of a developer feed roller and a fixer feed roller, and which can prevent reduced durability due to an insufficient deposition of silver. 
     The above object is fulfilled, according to the present invention, by a processing device in a printing apparatus for recording an image on a plate mounted peripherally of a plate cylinder, developing an image area of the plate with the image recorded thereon by feeding a processing solution from a processing solution feed roller to the plate, and printing the image by feeding ink to the plate, wherein the processing device comprises a processing solution tank for storing the processing solution for processing the plate; the processing solution feed roller having a portion thereof immersed in the processing solution stored in the processing solution tank; a drive mechanism for rotating the processing solution feed roller; and a positioning mechanism for positioning the processing solution feed roller such that a surface of the processing solution feed roller is slightly spaced from a surface of the plate; whereby the processing solution feed roller feeds the processing solution to the image area without contacting the image area. 
     With the above processing device, the processing solution may be applied to the image area of the plate in a noncontact mode. This construction effectively avoids a processing unevenness due to vibration of a developer feed roller or fixer feed roller, and reduced durability due to an insufficient deposition of silver. 
     In one preferred embodiment, the positioning mechanism includes positioning members having a larger outside diameter than the processing solution feed roller, and mounted coaxially on opposite end portions of the processing solution feed roller. 
     Preferably, the positioning members are arranged to contact the plate between side edges of the plate and side edges of the image area. 
     The positioning members may be arranged to contact the plate cylinder in regions thereof outwardly of opposite sides of the plate. 
     In another preferred embodiment, the drive mechanism is operable to rotate the processing solution feed roller with the surface thereof slightly spaced from the surface of the plate to form an accumulation of the processing solution between the surface of the plate and the surface of the processing solution feed roller before applying the processing solution to and processing the image area of the plate. 
     Preferably, the drive mechanism is operable to rotate the processing solution feed roller with the surface thereof slightly spaced from the surface of the plate, in a position opposed to a region between a forward end of the plate and a forward end of the image area. 
     In another aspect of the invention, a printing apparatus is provided, which comprises a plate cylinder for supporting a plate mounted peripherally thereof; an image recorder for recording an image on the plate mounted peripherally of the plate cylinder; a processing device for feeding a processing solution to and processing an image area of the plate where the image is recorded, the processing device including a processing solution feed roller slightly spaced from the image area to feed the processing solution to the image area in a substantially non-contact mode, and a drive mechanism for rotating the processing solution feed roller; an ink feed mechanism for feeding ink to the plate; and a transfer mechanism for transferring the ink from the plate to printing paper. 
     In a further aspect of the invention, a printing apparatus comprises a plate cylinder for supporting a plate mounted peripherally thereof; an image recorder for recording an image on the plate mounted peripherally of the plate cylinder; a processing device for feeding a processing solution to and processing an image area of the plate where the image is recorded, the processing device including a processing solution feed roller for feeding the processing solution to the image area, and a roller moving mechanism for moving the processing solution feed roller between a processing position adjacent the plate mounted peripherally of the plate cylinder and a retracted position away from the plate; a moving mechanism for moving the processing device in a substantially horizontal direction perpendicular to an axis of the plate cylinder; an ink feed mechanism for feeding ink to the plate; an impression cylinder rotatable with printing paper mounted peripherally thereof; a blanket cylinder for transferring the ink from the plate to the printing paper mounted peripherally of the impression cylinder; a printing paper feed mechanism for feeding the printing paper to the impression cylinder; and a printing paper discharge mechanism for discharging the printing paper having been printed from the impression cylinder. 
     With these printing apparatus, the processing device may easily be moved to a position for maintenance services. 
     Other features and advantages of the present invention will be apparent from the following detailed description of the embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown. 
     FIG. 1 is a schematic side view of a printing apparatus according to the present invention; 
     FIG. 2 is a schematic side view of a plate cylinder; 
     FIG. 3 is a side view of a plate grip mechanism; 
     FIG. 4 is a front view of the plate grip mechanism; 
     FIG. 5 is an explanatory view schematically showing pawls gripping a forward end of a printing plate; 
     FIG. 6 is a block diagram showing a principal electrical structure of the printing apparatus; 
     FIG. 7 is a flow chart showing prepress and printing operations of the printing apparatus; 
     FIG. 8 is a schematic side view of a processing device; 
     FIG. 9 is a perspective view showing a relationship between a developer feed roller (or fixer feed roller) and a printing plate mounted peripherally of the plate cylinder; 
     FIG. 10 is a front view showing the relationship between the developer feed roller (or fixer feed roller) and the printing plate mounted peripherally of the plate cylinder; 
     FIG. 11 is a front view showing a relationship between a developer feed roller (or fixer feed roller) and a printing plate mounted peripherally of the plate cylinder in another embodiment; 
     FIG. 12 is a schematic view of roller moving mechanisms; 
     FIG. 13 is another schematic view of the roller moving mechanisms; 
     FIG. 14 is a side view showing an outline of a roller rotating mechanism; 
     FIG. 15 is a side view showing various gears included in the roller rotating mechanism; 
     FIG. 16 is a plan view showing the various gears included in the roller rotating mechanism; 
     FIG. 17 is a perspective view of a double gear mechanism; 
     FIG. 18 is a side view of a lift mechanism and a moving mechanism; 
     FIG. 19 is another side view of the lift mechanism and moving mechanism; 
     FIG. 20 is a further side view of the lift mechanism and moving mechanism; 
     FIG. 21 is a plan view of a principal portion of the lift mechanism; 
     FIG. 22 is an enlarged view of a portion of the lift mechanism seen from the direction of arrow A in FIG. 21; 
     FIG. 23 is an explanatory view showing a developing operation: 
     FIG. 24 is another explanatory view showing the developing operation; and 
     FIG. 25 is a further explanatory view showing the developing operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter with reference to the drawings. FIG. 1 is a schematic side view of a printing apparatus according to the present invention. 
     This printing apparatus makes plates by recording and developing images on blank plates mounted on plate cylinders  11 , feeds inks to the plates having the images recorded thereon, and transfers the inks from the plates through blanket cylinders  12  to printing paper held on impression cylinders  19 , thereby printing the images on the printing paper. 
     The printing apparatus includes a first printing unit  1  and a second printing unit  2  each for printing with two color inks, a paper feeder  3  for feeding printing paper to the first printing unit  1 , an intermediate transport section  4  for transporting the printing paper from the first printing unit  1  to the second printing unit  2 , a paper discharger  5  for discharging the printing paper from the second printing unit  2 , and a printing driver  6  for synchronously rotating the plate cylinders  11 , blanket cylinders  12 , impression cylinders  19  and intermediate transport section  4 . 
     The construction of the first printing unit  1  and second printing unit  2  will be described first. 
     The first printing unit  1  includes the plate cylinder  11  constructed to hold two plates mounted peripherally thereof, the blanket cylinder  12  equal in diameter to the plate cylinder  11 , the impression cylinder  19  having half the diameter of the plate cylinder  11  and blanket cylinder  12 , a plate feed and remove mechanism  13  for feeding and removing plates to/from the plate cylinder  11 , an image recorder  14  for recording images on the two plates mounted peripherally of plate cylinder  11 , a processing device  16  for developing and fixing the plates with the images recorded thereon, two dampening water feed mechanisms  17  for feeding dampening water to the two respective plates after the developing process, two ink feed mechanisms  15  for feeding inks to the two respective plates after the dampening water is fed thereto, and a blanket cleaning mechanism  18  for cleaning the surface of blanket cylinder  12  after a printing operation is completed. 
     The plate cylinder  11  is used to perform a prepress process of the two plates mounted peripherally thereof and a printing process using these plates. As shown in FIG. 2, the plate cylinder  11  has a pair of cylinder grooves  21 . Each groove  21  houses a plate grip mechanism  22  for gripping the forward end of one plate  7  and the rear end of the other plate  7 . 
     FIG. 3 is a side view of the plate grip mechanism  22  disposed in each cylinder groove  21  of plate cylinder  11 . FIG. 4 is a front view of the plate grip mechanism  22 . 
     The plate grip mechanism  22  includes a plate gripper  23  for gripping the rear end of one plate  7 , and a plate gripper  24  for gripping the forward end of the other plate  7 . 
     The plate gripper  23  for gripping the rear end of one plate  7  has a seat  25  defining an upper receiving surface  26 , and pawls  27  pivotable about a support axis  30 . Each pawl  27  is pivotable between a pinch position shown in a solid line in FIG.  3  and an open position shown in a two-dot chain line. The pawl  27  is biased to the open position by a spring not shown. Four such pawls  27  are arranged axially of plate cylinder  11 . 
     A cam shaft  28  is disposed between the rear ends of pawls  27  and the seat  25 . The cam shaft  28  is operable to move each pawl  27  to the pinch position shown in the solid line in FIG.  3 . When the pawl  27  is in the pinch position, the rear end of plate  7  is pinched between a lower surface at the forward end thereof and the receiving surface  26 . When the cam shaft  28  is rotated to a position shown in a two-dot chain line in FIG. 3, the rear end of each pawl  27  moves into contact with a cutout formed in the cam shaft  28 , whereupon the pawl  27  is moved to the open position by the action of the spring not shown. 
     On the other hand, the plate gripper  24  for gripping the forward end of the other plate  7  has a seat  32  defining an upper receiving surface  31 , and pawls  34  pivotable about a support axis  33 . Each pawl  34  is pivotable between a pinch position shown in a solid line in FIG.  3  and an open position shown in a two-dot chain line. The pawl  34  is biased to the open position by a spring not shown. Four such pawls  34  are arranged axially of plate cylinder  11 . 
     A cam shaft  35  is disposed between the rear ends of pawls  34  and the seat  32 . The cam shaft  35  is operable to move each pawl  34  to the pinch position shown in the solid line in FIG.  3 . When the pawl  34  is in the pinch position, the forward end of plate  7  is pinched between a lower surface at the forward end thereof and the receiving surface  31 . When the cam shaft  35  is rotated to a position shown in a two-dot chain line in FIG. 3, the rear end of each pawl  34  moves into contact with a cutout formed in the cam shaft  35 , whereupon the pawl  34  is moved to the open position by the action of the spring not shown. 
     The grip mechanism  22  includes a base  36  with a plurality of rails  37  arranged thereon, the plate grippers  23  and  24  being slidable along the rails  37 . The seats  25  and  32  of plate grippers  23  and  24  have projections  38  and  39 , respectively. These projections  38  and  39  are pressed at upper surfaces thereof by rails  41 . Thus, the grippers  23  and  24  are reciprocable right and left in FIG. 3 (perpendicular to the plane of FIG.  4 ). 
     A stationary block  42  is disposed centrally of base  36 . A spring  43  is disposed between the stationary block  42  and seat  25 , while a spring  44  is disposed between the stationary block  42  and seat  32 . A cam shaft  46  with a cutout  45  is disposed between side walls of seat  25  and cylinder groove  21 . A cam shaft  48  with a cutout  47  is disposed between side walls of seat  32  and cylinder groove  21 . 
     The cam shafts  46  and  48  may be rotated from the positions shown in FIG. 3, with the plate gripper  23  gripping the rear end of one plate  7 , and the plate gripper  24  gripping the forward end of the other plate  7 . Then, the plate grippers  23  and  24  move toward each other. Consequently, the plates  7  are extended over the peripheral surface of plate cylinder  11 . 
     FIG. 5 is an explanatory view schematically showing the pawls  34  of plate gripper  24  gripping the forward end of plate  7 . 
     In this figure, numeral  8  denotes an image area (region where an image is recorded) formed on the plate  7 . The pawls  34  of plate gripper  24  are constructed to pinch the plate  7  by a marginal area (region indicated by arrow a in FIG. 5) between the forward end of plate  7  and the forward end of image area  8 . Though not shown in this figure, the pawls  27  of plate gripper  23  are constructed to pinch the plate  7  by a marginal area between the rear end of plate  7  and the rear end of image area  8 . 
     Referring again to FIG. 1, each blanket cylinder  12  has the same diameter as the above plate cylinder  11 . The blanket cylinder  12  has a blanket mounted peripherally thereof for transferring ink images on the plates  7 . The blanket cylinder  12  is rotatable synchronously with the plate cylinder  11  through engagement between a gear disposed laterally of plate cylinder  11  and a gear disposed laterally of blanket cylinder  12 . 
     The impression cylinder  19  is rotatable with printing paper mounted peripherally thereof, and has half the diameter of plate cylinder  11  and blanket cylinder  12 . The impression cylinder  19  has a gripper, not shown, mounted peripherally thereof for gripping the forward end of printing paper. The impression cylinder  19 , with every two rotations, receives new printing paper from a paper feed cylinder  10 , and with every two rotations, discharges printed paper to a paper discharge cylinder  20 . 
     The plate feed and remove mechanism  13  feeds blank plates  7  to the plate cylinder  11 , and removes plates  7  used in printing from the plate cylinder  11 . The plate feed and remove mechanism  13  includes a plate feeding cassette not shown, a plate removing cassette not shown, and a plate transport mechanism, not shown, for transferring the plates  7  between the plate feeding cassette/plate removing cassette and plate cylinder  11 . 
     The image recorder  14  records images on the two plates  7  mounted peripherally of plate cylinder  11 . The image recorder  14  includes numerous LEDs for emitting light beams to the plates  7  on the plate cylinder  11 . 
     The processing device  16  performs developing and fixing processes of the plates  7  after the images are recorded thereon by the image recorder  14 . The processing device  16  will be described in detail hereinafter. 
     The two dampening water feed mechanisms  17  feed dampening water to the two plates  7  mounted peripherally of plate cylinder  11 , respectively. Each dampening water feed mechanism  17  includes a storage tank for storing the dampening water, and dampening water feed rollers for feeding the dampening water stored in the storage tank to one of the plates  7  on the plate cylinder  11 . 
     The two ink feed mechanisms  15  feed different color inks to the two respective plates to which the dampening water has been fed by the dampening water feed mechanisms  17 . Each ink feed mechanism  15  includes an ink storage for storing an ink, and numerous ink rollers for feeding the ink stored in the ink storage to one of the plates  7  on the plate cylinder  11 . 
     The blanket cleaning mechanism  18  is operable to clean the inked surface of blanket cylinder  12  after a printing operation is completed. The blanket cleaning mechanism  18  includes a cleaning cloth for contacting the blanket on the surface of blanket cylinder  12  to clean the blanket, a cleaning solution supply nozzle for supplying the cleaning cloth with a cleaning solution. 
     In the first printing unit  1 , the plates  7  fed from the plate feed and remove mechanism  13  and mounted peripherally of plate cylinder  11  undergo an image recording process by the image recorder  14  and developing and fixing process by the processing device  16 . The plates  7  emerging from a prepress operation, which includes image recording, developing and fixing processes, are fed with the dampening water from the dampening water feed mechanisms  17  and the inks from the ink feed mechanisms  15 . The ink images on the plates  7  are transferred through the blanket cylinder  12  to the printing paper mounted peripherally of impression cylinder  19 . 
     The first printing unit  1  and second printing unit  2  are similar in construction. Thus, like reference numerals are used to identify like parts, and the second printing unit  2  will not particularly be described. 
     However, in the first printing unit  1 , the plate cylinder  11  is used to hold a plate for printing a K (black) image on the printing paper, and a plate for printing a C (cyan) image on the printing paper. In the second printing unit  2 , the plate cylinder  11  is used to hold a plate for printing an M (magenta) image on the printing paper, and a plate for printing a Y (yellow) image on the printing paper. 
     The components of this printing apparatus other than the first printing unit  1  and second printing unit  2  will be described next. 
     The paper feeder  3  includes a paper feed tray  51  for stacking numerous sheets of printing paper, and a paper feed mechanism  52  for separating each sheet of printing paper from the rest stacked on the paper feed tray  51  and transporting it to the paper feed cylinder  10 . One paper separating and transporting operation of the paper feeder  3  is executed for every two rotations of the paper feed cylinder  10 . 
     The intermediate transport section  4  includes transfer cylinders  53 ,  54  and  55  for transferring the printing paper between the paper discharge cylinder  20  of first printing unit  1  and the paper feed cylinder  10  of second printing unit  2 . Each of these transfer cylinders  53 ,  54  and  55  has twice the diameter of the impression cylinder  19  (i.e. the same diameter as the plate cylinder  11  and blanket cylinder  12 ). Each of these transfer cylinders  53 ,  54  and  55  has grippers arranged in angular positions 180 degrees apart from each other for gripping the forward ends of sheets of printing paper, respectively. 
     The paper discharger  5  is operable to receive printed sheets of printing paper from the paper discharge cylinder  20  of second printing unit  2  and discharge the sheets to a paper discharge tray  56 . The paper discharger  5  includes an endless chain  57 , and a plurality of grippers, not shown, arranged on the chain  57  to be movable while gripping the forward ends of the sheets of printing paper. 
     The printing driver  6  includes a motor  58  for synchronously rotating the various cylinders in the printing apparatus. The drive of this motor  58  is transmitted by a belt  59  to a pulley  61 , and then to the paper feed cylinder  10  of the first printing unit  1  through a gear  62  fixed coaxially to the pulley  61 . 
     FIG. 6 is a block diagram showing a principal electrical structure of the printing apparatus. 
     This printing apparatus includes a control unit  140  having a ROM  141  for storing operating programs necessary for controlling the apparatus, a RAM  142  for temporarily storing data and the like during a control operation, and a CPU  143  for performing logic operations. The control unit  140  has a driving circuit  145  connected thereto through an interface  144 , for generating driving signals for application to the various driving devices of the apparatus. The printing apparatus is controlled by the control unit  140  to execute prepress and printing operations including the developing and fixing processes described hereinafter. 
     The control unit  140  acts also as a control device for causing roller rotating mechanisms to rotate developer feed rollers  66  with surfaces thereof slightly spaced from the surfaces of plates  7 . This measure is taken in order to form an accumulation of the developer between the surface of each plate  7  and the surface of each developer feed roller  66  as described hereinafter. 
     Prepress and printing operations of the printing apparatus will be described next. FIG. 7 is a flow chart showing the prepress and printing operations of the printing apparatus. 
     First, plates  7  are fed to the peripheries of each of the plate cylinders  11  in the first printing unit  1  and second printing unit  2  (step S 1 ). This plate feeding operation is carried out by the plate feed and remove mechanisms  13 . 
     Next, images are recorded on the plates  7  mounted peripherally of each plate cylinder  11  (step S 2 ). The image recording operation is carried out by irradiating the plates  7  mounted peripherally of the plate cylinder  11  with laser beams emitted from the LEDs of each image recorder  14 . 
     Next, the plates  7  having the images recorded thereon are put to the developing and fixing processes (step S 3 ). The developing and fixing processes are executed by the processing device  16  according to the present invention. The developing and fixing processes will be described in detail hereinafter. 
     The prepress operation for the plates  7  mounted peripherally of each plate cylinder  11  is completed with the image recording and processing operations noted above. Then, a printing operation is carried out (step S 4 ). Specifically, the plates  7  on each plate cylinder  11  are fed with dampening water from the dampening water feed mechanisms  17 , and inks from the ink feed mechanisms  15 . The ink images on the plates  7  are transferred through the blanket cylinder  12  to the printing paper mounted peripherally of the impression cylinder  19 . 
     Desired prints are made by continuing the above printing operation for a required time. Then, the plates  7  used are removed from each plate cylinder  11  (step S 5 ) to complete the entire operation. 
     The construction of processing device  16  which characterizes the present invention will be described next. FIG. 8 is a schematic side view of the processing device  16 . 
     The processing device  16  includes a developing unit  61  for applying a developer to and developing the plates  7  mounted peripherally of each plate cylinder  11 , a fixing unit  62  for applying a fixer to and fixing the images to the plates  7 , a squeezing unit  63  for removing the developer and fixer from the plates  7 , and a watering unit  64  for applying water to the surface of plate cylinder  11 . 
     The developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  are all movable by a lift mechanism and a moving mechanism, described hereinafter, between a processing position (shown in solid lines in FIG.  1 ), a lowered position and a withdrawn position (both shown in phantom lines in FIG.  1 ). 
     In this embodiment, lithographic plates using the diffusion transfer process (DTR process) are used as plates  7 . The developer acts as an activator, and the fixer as a stabilizer. In this specification, a developing process and a fixing process are collectively called the developing process as necessary. 
     As shown in FIG. 8, the developing unit  61  includes a developer tank  65  for storing the developer, and a developer feed roller  66  with a lower portion thereof immersed in the developer stored in the developer tank  65 . The fixing unit  62  includes a fixer tank  67  for storing the fixer, a fixer feed roller  68  with a lower portion thereof immersed in the fixer stored in the fixer tank  67 , and a shower nozzle  69  for jetting the fixer to the fixer feed roller  68 . The squeezing unit  63  includes a squeeze roller  71 , and a brush roller  72  with peripheries thereof contacting the squeeze roller  71 . The watering unit  64  includes a water feed roller  74  with a lower portion thereof immersed in the water stored in a water tank  73 . 
     The developer feed roller  66  feeds the developer to the plates  7  mounted peripherally of the plate cylinder  11 . The fixer feed roller  68  feeds the fixer to the plates  7  on the plate cylinder  11 . The squeeze roller  71  removes the developer and fixer from the plates  7 . The brush roller  72  cleans the squeeze roller  71  with a cleaning solution, such as a fixing solution. 
     Further, the water feed roller  74 , though not playing an active role in the developing process, supplies water to the surface of plate cylinder  11  before the plates  7  are placed thereon in order to enhance contact of the plates  7  with the cylinder  11 . 
     The developer feed roller  66  and fixer feed roller  68  are distributed to opposite positions across the lower end of plate cylinder  11 , with the upper ends of the two rollers  66  and  68  located above the lower end of plate cylinder  11 . This is an optimal arrangement for the plates  7  mounted peripherally of the plate cylinder  11  to be contactable by the developer feed roller  66  for feeding the developer from the developer tank  65  and by the fixer feed roller  68  for feeding the fixer from the fixer tank  67 . 
     Each of the developer feed roller  66 , fixer feed roller  68  and water feed roller  74  is movable by a roller moving mechanism, described hereinafter, between a processing position adjacent the plates  7  mounted on the plate cylinder  11 , and a retracted position away from the plates  7 . Further, the developer feed roller  66 , fixer feed roller  68  and water feed roller  74  are rotatable synchronously with one another by a roller rotating mechanism described hereinafter. 
     FIG. 9 is a perspective view showing a relationship between the developer feed roller  66  (or fixer feed roller  68 ) and a plate  7  mounted peripherally of the plate cylinder  11 . FIG. 10 is a front view showing this relationship. The developer feed roller  66  and fixer feed roller  88  have the same construction. Thus, the following description will be made only in relation to the developer feed roller  66 . The plate cylinder  11  is omitted from FIG.  9 . 
     The developer feed roller  66  includes a main roller body  75  and a shaft  76 . The main roller body  75  has a pair of positioning elements  77  mounted on opposite end portions thereof to act as a positioning mechanism. The positioning elements  77  are in the form of cylindrical members having a larger outside diameter than the main roller body  75  and coaxially mounted thereon. 
     Consequently, when the developer feed roller  66  contacts the plate  7  mounted peripherally of the plate cylinder  11 , the surface of main roller body  75  of developer feed roller  66  is spaced from the surface of plate  7  by a slight distance Y. That is, a gap Y as shown in FIG. 9 exists between the surface of main roller body  75  of developer feed roller  66  and the surface of plate  7 . 
     The above positioning elements  77  are arranged to contact the surface of plate  7  in regions (indicated by arrows b in FIG. 5) between the side edges of plate  7  and the side edges of image area  8 . 
     With the developer feed roller  66  having the above construction, the main roller body  75  and image area  8  are spaced from each other by distance Y. The outside diameter of positioning elements  77  is set so that this distance Y has a very small value. Thus, the developer picked up from the developer tank  65  by the developer feed roller  66  may be applied to the surface of plate  7  by capillary action. 
     At this time, the main roller body  75  of developer feed roller  66  and the image area  8  of plate  7  are not in direct contact with each other. Consequently, the image area  8  is free from the rubbing action of developer feed roller  66  which could result in a processing unevenness due to vibration of developer feed roller  66 . It is also possible effectively to avoid an imperfect deposition of silver which could occur when silver deposits formed immediately after the developer is fed are rubbed by the developer feed roller  66 . 
     It is desirable that the above slight distance Y is in the order of 0.1 mm to 1.0 mm, and preferably 0.3 mm to 0.6 mm. 
     FIG. 11 is a front view showing a relationship between the developer feed roller  66  (or fixer feed roller  68 ) and a plate  7  mounted peripherally of the plate cylinder  11  in another embodiment. 
     In the embodiment shown in FIGS. 9 and 10, the positioning elements  77  contact the surface of plate  7  in the regions between the side edges of plate  7  and the side edges of the image area  8 . In the embodiment shown in FIG. 11, on the other hand, the positioning elements  77  contact regions of the plate cylinder  11  outwardly of the opposite sides of plate  7 . The embodiment shown in FIG. 11 is, as is the embodiment shown in FIGS. 9 and 10, effective to avoid a deterioration in quality of the developing process resulting from the image area  8  contacting the positioning elements  77 . 
     The constructions of the roller moving mechanisms will be described next. These roller moving mechanisms move the developer feed roller  66 , fixer feed roller  68  and water feed roller  74  between the processing position adjacent the plates  7  mounted on the plate cylinder  11 , and the retracted position away from the plates  7 , respectively. FIGS. 12 and 13 are schematic views of the roller moving mechanisms. 
     The developer feed roller  66  is rotatably supported by arms  82  pivotable about an axis  81  disposed on a main body of the printing apparatus. One of the arms  82  has an arm  84  fixed thereto, with a cam follower  83  attached to a distal end of arm  84 . The main body of the printing apparatus supports an air cylinder  85  with a cylinder rod  86  extendible to cause a distal end  87  thereof to press the cam follower  83 . The arms  82  are biased, by a spring not shown, in a direction to move the developer feed roller  66  toward the plate cylinder Thus, when the cylinder rod  86  of air cylinder  85  is retracted to move the distal end  87  away from the cam follower  83 , as shown in FIG. 12, the developer feed roller  66  is moved to the processing position where the surface of roller  66  (or, strictly speaking, the surfaces of positioning elements  77  mounted on the developer feed roller  66 ) contacts the plate cylinder  11 . When the cylinder rod  86  of air cylinder  85  is extended to cause the distal end  87  to press the cam follower  83 , as shown in FIG. 13, the developer feed roller  66  is moved to the retracted position where the surface of roller  66  (or, strictly speaking, the surfaces of positioning elements  77  mounted on the developer feed roller  66 ) is separated from the plate cylinder  11 . 
     Similarly, the fixer feed roller  68  is rotatably supported by arms  92  pivotable about an axis  91  disposed on the main body of the printing apparatus. One of the arms  92  has an arm  94  fixed thereto, with a cam follower  93  attached to a distal end of arm  94 . The main body of the printing apparatus supports an air cylinder  95  with a cylinder rod  96  extendible to cause a distal end  97  thereof to press the cam follower  93 . The arms  92  are biased, by a spring not shown, in a direction to move the fixer feed roller  68  toward the plate cylinder  11 . 
     Thus, when the cylinder rod  96  of air cylinder  95  is retracted to move the distal end  97  away from the cam follower  93 , as shown in FIG. 12, the fixer feed roller  68  is moved to the processing position where the surface of roller  68  (or, strictly speaking, the surfaces of positioning elements  77  mounted on the fixer feed roller  68 ) contacts the plate cylinder  11 . When the cylinder rod  96  of air cylinder  95  is extended to cause the distal end  97  to press the cam follower  93 , as shown in FIG. 13, the fixer feed roller  68  is moved to the retracted position where the surface of roller  68  (or, strictly speaking, the surfaces of positioning elements  77  mounted on the fixer feed roller  68 ) is separated from the plate cylinder  11 . 
     The water feed roller  74  is rotatably supported by arms  102  pivotable about an axis  101  disposed on the main body of the printing apparatus. One of the arms  102  has an arm  104  fixed thereto, with a cam follower  103  attached to a distal end of arm  104 . The main body of the printing apparatus supports an air cylinder  105  with a cylinder rod  106  extendible to cause a distal end  107  thereof to press the cam follower  103 . The arms  102  are biased, by a spring not shown, in a direction to move the water feed roller  74  toward the plate cylinder  11 . 
     Thus, when the cylinder rod  106  of air cylinder  105  is retracted to move the distal end  107  away from the cam follower  103 , as shown in FIG. 12, the water feed roller  74  is moved to the processing position where the surface of roller  74  contacts the plate cylinder  11 . When the cylinder rod  106  of air cylinder  105  is extended to cause the distal end  107  to press the cam follower  103 , as shown in FIG. 13, the water feed roller  74  is moved to the retracted position where the surface of roller  74  is separated from the plate cylinder  11 . 
     The construction of the roller rotating mechanism will be described next. This roller rotating mechanism synchronously rotates the developer feed roller  66 , fixer feed roller  68  and water feed roller  74 . 
     FIG. 14 is a side view showing an outline of the roller rotating mechanism. FIG. 15 is a side view showing various gears  111 ,  112 ,  113 ,  114 ,  115 ,  121 ,  122  and  123  included in the roller rotating mechanism. FIG. 16 is a plan view of these gears. FIGS. 14 and 15 show the opposite side of what is shown in FIGS. 1 and 12. 
     This roller rotating mechanism includes a roller gear  121  disposed coaxially with the developer feed roller  66 , a roller gear  123  disposed coaxially with the fixer feed roller  68 , a roller gear  122  disposed coaxially with the water feed roller  74 , a drive gear  115  connected through a chain  117  to a gear  116  mounted on a drive shaft of a motor  118 , three double gear mechanisms  111 ,  112  and  113 , and a plurality of drive transmission gears  114 . 
     As shown in FIG. 17, the double gear mechanism  111  includes a first gear  124 , a second gear  125 , and three connecting members  126  extending between eccentric positions of the first gear  124  and second gear  125  to interconnect these gears  124  and  125  to be coaxial with each other. The double gear mechanism  112  and double gear mechanism  113  have the same construction as the double gear mechanism  111 . 
     The first gear  124  of double gear mechanism  111  is connected through one drive transmission gears  114  to the roller gear  121  disposed coaxially with the developer feed roller  66 . The second gear  125  of double gear mechanism  111  is connected through another drive transmission gear  114  to the second gear  125  of double gear mechanism  112 . 
     The first gear  124  of double gear mechanism  112  is connected through one drive transmission gear  114  to the roller gear  122  disposed coaxially with the water feed roller  74 . The second gear  125  of double gear mechanism  112  is connected through three drive transmission gears  114  to the second gear  125  of double gear mechanism  113 . 
     The first gear  124  of double gear mechanism  113  is connected with through one drive transmission gear  114  to the roller gear  123  disposed coaxially with the fixer feed roller  6 . 
     Further, the drive transmission gears  114  connecting the double gear mechanism  112  to the double gear mechanism  113  are connected to the drive gear  115  through other drive transmission gears  114 . 
     In the roller rotating mechanism having the above construction, the drive of drive gear  115  connected through the chain  117  to the gear  116  mounted on the drive shaft of motor  118  is transmitted to the roller gears  121 ,  122  and  123  through the plurality of drive transmission gears  114  and three double gear mechanisms  111 ,  112  and  113 . As a result, the developer feed roller  66 , fixer feed roller  68 , and water feed roller  74  rotate synchronously with one another. 
     As noted above, each of the double gear mechanisms  111 ,  112  and  113  has the first gear  124 , second gear  125 , and three connecting members  126  extending between eccentric positions of the first gear  124  and second gear  125  to interconnect these gears  124  and  125  to be coaxial with each other. A liquid such as the developer, fixer or water adhering to the first gear  124  of each double gear mechanism  111 ,  112  or  113  will be scattered therefrom under centrifugal force since the first gear  124  and second gear  125  are not interconnected in their axial regions. Thus, the liquid is not transferred to the second gear  125  via the connecting members  126 . 
     Consequently, even when a liquid such as the developer, fixer or water adheres to the first gear  124 , the liquid is effectively prevented from reaching the other gears by way of the second gear  125 . If the fixer should pass from the fixer feed roller  68  through the plurality of gears and developer feed roller  66  into the developer, the developer would deteriorate to become unable to process the plates. The above construction is effective to avoid such an inconvenience. 
     In the above embodiment, the roller rotating mechanism synchronously rotates the developer feed roller  66  and fixer feed roller  68 . However, this roller rotating mechanism is dispensable. Where no such mechanism is provided, the rotation of plate cylinder  11  may be transmitted to the developer feed roller  66  and fixer feed roller  68  through the positioning elements  77 , thereby rotating the developer feed roller  66  and fixer feed roller  68  synchronously with the plate cylinder  11 . 
     The constructions of the lift mechanism and moving mechanism will be described next. These lift mechanism and moving mechanism move the processing device  16  including the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64 , between the processing position, lowered position and withdrawn position. FIGS. 18 through 20 are side views showing the lift mechanism and moving mechanism. 
     FIG. 18 shows the processing device  16  in the processing position. FIG. 19 shows the processing device  16  in the lowered position. FIG. 20 shows the processing device  16  in the withdrawn position. 
     As shown in FIGS. 18 through 20, the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  are supported by a single support deck  131 . The support deck  131  has four nuts  132  (see FIG. 22 to be described hereinafter). The nuts  132  are meshed with vertical drive screws  133  of the lift mechanism, respectively. 
     FIG. 21 is a plan view of a principal portion of the lift mechanism. FIG. 22 is an enlarged view of a portion of the lift mechanism seen from the direction of arrow A in FIG.  21 . 
     The vertical drive screws  133  of the lift mechanism are supported by a pair of right and left support plates  134 . Each drive screw  133  has a worm wheel  136  fixed to a proximal end thereof. A pair of rotary shafts  137  are arranged between the right and left support plates  134 . Each rotary shaft  137  has a pair of worms  138  mounted on opposite end portions thereof and meshed with the worm wheels  136 . 
     Each rotary shaft  137  further includes a pulley  139  attached to a forward end thereof. The pulleys  139  are connected through a belt  152  to a pulley  155  attached to a rotary shaft of a motor  151 . Thus, the pair of rotary shafts  136  are synchronously rotatable by the drive of motor  151 . With the rotation of rotary shafts  136 , the four vertical drive screws  133  rotate synchronously with one another. 
     As noted above, the vertical drive screws  133  are meshed with the nuts  132  of the support deck  131  supporting the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64 . Thus, as the vertical drive screws  133  are  20  rotated by the drive of motor  151 , the support deck  131  is moved up and down, along with the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64 , between the processing position shown in FIG.  18  and the lowered position shown in FIG.  19 . 
     As shown in FIGS. 18 through 22, each of the right and left support plates  134  has three bearings  153  projecting therefrom. On the other hand, as shown in FIGS. 18 through 20, guide grooves  154  are formed in a pair of right and left side plates  135  of the main body of the printing apparatus for supporting the plate cylinder  11 . The bearings  153  are fitted in the guide grooves  154  to run therealong. 
     With the above construction, the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  are reciprocable, along with the right and left support plates  134 , between the lowered position shown in FIG.  19  and the withdrawn position shown in FIG.  20 . The bearings  153  and guide grooves  154  constitute the moving mechanism for moving the processing device  16  between the lowered position and the withdrawn position. 
     For moving the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  from the processing position shown in FIG. 18 to the withdrawn position shown in FIG. 20, these units  61 - 64  are first moved by the drive of motor  151  to the lowered position shown in FIG.  19 . Subsequently, the operator, by pulling a handle  156 , moves the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  from the lowered position shown in FIG. 19 to the withdrawn shown in FIG.  20 . 
     The developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  are moved in two stages as described above. This is necessary because the developer feed roller  66  and fixer feed roller  68  are arranged in opposite positions across the lower end of plate cylinder  11 , with the upper ends of the two rollers  66  and  68  located above the lower end of plate cylinder  11 . 
     Next, a processing operation of the processing device  16  having the above construction will be described next. The following operation is performed under control of the control unit  140 . 
     In time of starting a developing operation immediately following completion of an operation of the image recorder  14  to record an image on one of the plates  7  mounted peripherally of plate cylinder  11 , the processing device  16  including the developing unit  61 , fixing unit  62 , squeezing unit  63  and watering unit  64  lies in the lowered position shown in FIG.  19 . 
     In this state, the plate cylinder  11  is first rotated at low speed for processing of one of the plates  7  mounted thereon. The plate cylinder  11  is stopped in a position where the forward end of plate  7  mounted thereon may be opposed to the developer feed roller  66 . Subsequently, the motor  151  of the lift mechanism is operated to raise the processing device  16  to the processing position. The air cylinder  85  of the roller moving mechanism also is operated to move the developer feed roller  66  from the retracted position to the processing position. The developer feed roller  66  and other components now assume the position shown in FIG.  23 . 
     In this state, the main roller body  75  of developer feed roller  66  shown in FIG. 9 is opposed to the marginal area (region indicated by arrow a in FIG. 5) between the forward end of plate  7  and the forward end of image area  8 , or, strictly speaking, the marginal area between the pawls  34  of plate gripper  24  and the forward end of image area  8 . In this state, as noted hereinbefore, the surface of main roller body  75  of developer feed roller  66  is spaced from the surface of plate  7  by the slight distance Y. 
     In this state, the roller rotating mechanism, under control of the control unit  140 , rotates the developer feed roller  66  at high speed for a predetermined time. As a result, the developer accumulates in a sufficient quantity between the surface of the main roller body  75  of developer feed roller  66  and the surface of plate  7 . 
     The time for rotating the developer feed roller  66  at high speed, preferably, is 2 to 3 seconds where, for example, the gap Y between the surface of main roller body  75  of developer feed roller  66  and the surface of plate  7  shown in FIG. 9 is approximately 0.3 mm, and 4 to 5 seconds where the gap Y is approximately 0.5 mm. 
     The rotating speed of developer feed roller  66  at this time, preferably, is 4 to 5 rps where, for example, the rotating speed of developer feed roller  66  in time of the developing process is 1 to 2 rps. 
     Next, the developer feed roller  66  is decelerated to a normal rotating speed. The motor  58  of printing driver  6  is operated to rotate the plate cylinder  11  at low speed clockwise from the position shown in FIG.  23 . With the rotation of plate cylinder  11 , the developer is applied over the surface of plate  7  mounted peripherally of plate cylinder  11 , thereby developing the image area  8 . 
     At this time, the main roller body  75  of developer feed roller  66  is not in direct contact with the image area  8  of plate  7 . Consequently, the image area  8  is free from the rubbing action of developer feed roller  66  which could result in a processing unevenness due to vibration of developer feed roller  66 . It is also possible effectively to avoid an imperfect deposition of silver which could occur when silver deposits formed immediately after the developer is fed are rubbed by the developer feed roller  66 . 
     The image area  8  of plate  7  where the developer has been applied by the developer feed roller  66  then comes into contact with the squeeze roller  71 . The developer applied to the surface of plate  7  is squeezed off by the squeeze roller  71  rotated through contact with the plate  7 . At this time, the squeeze roller  71  may be cleaned by the brush roller  72 . In parallel with this process, the fixer starts being jetted from the shower nozzle  69  to the fixer feed roller  68  in the fixing unit  62 . 
     With a further rotation of plate cylinder  11 , the forward end of plate  7  mounted peripherally of plate cylinder  11  reaches a position opposed to the fixer feed roller  68  as shown in FIG.  24 . In this state, as noted hereinbefore, the surface of main roller body  75  of fixer feed roller  68  is spaced from the surface of plate  7  by the slight distance Y. However, a sufficient accumulation of the fixer has been formed between the surface of main roller body  75  of fixer feed roller  68  and the surface of plate  7  as a result of the fixer being jetted thereto from the shower nozzle  69 . 
     With a continued rotation of plate cylinder  11 , the fixer is applied over the surface of plate  7  mounted peripherally of plate cylinder  11 , thereby fixing the image area  8 . 
     At this time, the main roller body  75  of fixer feed roller  68  is not in direct contact with the image area  8  of plate  7 . Consequently, the image area  8  is free from the rubbing action of fixer feed roller  68 , thereby effectively avoiding a processing unevenness due to vibration of fixer feed roller  68 . 
     The developing and fixing operation for the first plate  7  is completed with the fixation of the image area  8  on this plate  7 . The other plate  7  mounted peripherally of plate cylinder  11  is processed by repeating the same operation. 
     In this embodiment, the fixer is not removed from the plate surface by the squeeze roller  71  since the fixer remaining on the plate surface will not affect printing. However, the fixer may be removed by the squeeze roller  71  after the fixing process. 
     As shown in FIG. 25, when the cylinder groove  21  housing the plate grip mechanism  22  is opposed to the shower nozzle  69  in the fixing unit  62 , with the fixer feed roller  68  moved to the retracted position, the fixer may be jetted from the shower nozzle  69  directly to the squeeze roller  71  to clean the squeeze roller  71  with the fixer. 
     Further, the fixer may be dripped to the fixer feed roller  68  instead of being jetted from the shower nozzle  69  to a location between the surface of plate  7  and the surface of main roller body  75  of fixer feed roller  68 . 
     In the foregoing embodiments, the positioning elements  77  mounted coaxially on opposite end portions of developer feed roller  66  and fixer feed roller  68  are employed as the positioning mechanism for positioning the surfaces of developer feed roller  66  and fixer feed roller  68  at the slight distance from the surface of plate  7 . It is possible to employ a positioning mechanism, for example, in the form of stoppers or the like for limiting the swing angle of the arms  82  and  92  of the roller moving mechanisms shown in FIGS. 12 and 13. This alternative construction can also position the surfaces of developer feed roller  66  and fixer feed roller  68  at the slight distance from the surface of plate  7 . 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention. 
     The present application claims priority benefit under 35 U.S.C. Section 119 of Japanese Patent Application No. 11-24235 filed in the Japanese Patent Office on Feb. 1, 1999 and No. 11-255724 filed in the Japanese Patent Office on Sep. 9, 1999, the entire disclosure of which is incorporated herein by reference.