US3904188A

US3904188A - Printing plate transfer and support apparatus

Info

Publication number: US3904188A
Application number: US447600A
Authority: US
Inventors: Henry N Fairbanks; James T Mccutcheon
Original assignee: Itek Corp
Current assignee: AB Dick Co
Priority date: 1972-10-26
Filing date: 1974-03-04
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

Apparatus for transporting a printing plate to and from an imaging station and for supporting the plate at the imaging station during the exposure thereof. The apparatus includes a perforated belt movable in a forward direction to carry a plate supported thereon into the imaging station and movable in a reverse direction to withdraw the plate from the imaging station following exposure while, at the same time, to substantially self-correct any tracking errors in the belt movement. The plate is held against the belt by suction drawn through the perforations in the belt. More particularly, the belt is provided with both a perforated area and a solid area positioned such that there will not be large numbers of perforations on the belt that are uncovered by the plate through which air may be drawn to reduce the suction acting on the plate.

Description

United States Patent Fairbanks et a1.

Sept. 9, 1975 PRINTING PLATE TRANSFER AND SUPPORT APPARATUS [75] Inventors: Henry N. Fairbanks; James T.

MeCutcheon, both of Rochester, NY.

[73] Assignee: Itek Corporation, Lexington. Mass.

[22] Filed: Mar. 4, 1974 [21] Appl. No.: 447,600

Related U.S. Application Data [63] Continuation of Ser. No. 301,031, Oct. 26, 1972.

abandoned.

[52] U.S. Cl. 271/3; 271/276; 271/197; 27l/D1G. 9 [51] Int. C1. B65H 5/02; B65H 29/24 [58] Field of Search 271/D1G. 9, 3, 197, 196, 271/194, 276, 4, 5, 6, 7, 264, 266, 267, 184, 225, 94

[56] References Cited UNITED STATES PATENTS 3,556,511 1/1971 Howard ct a1. 271/4 3,599,967 8/1971 Rapparlic ct a1. 271/94 X 3,641,931 2/1972 Hickox ct a1. 271/3 X 3,698,706 10/1972 Mihojevich ct a1. 271/197 X Primary ExaminerRichard A. Schacher Assistant Examt'nerBruce H. Stoner, Jr. Attorney, Agent, or FirmHomer 0. Blair; Robert L.

Nathans; Gerald H. Glanzman [57] ABSTRACT Apparatus for transporting a printing plate to and from an imaging station and for supporting the plate at the imaging station during the exposure thereof. The apparatus includes a perforated belt movable in a forward direction to carry a plate supported thereon into the imaging station and movable in a reverse direction to withdraw the plate from the imaging station following exposure while, at the same time, to substantially self-correct any tracking errors in the belt movement. The plate is held against the belt by suction drawn through the perforations in the belt. More particularly, the belt is provided with both a perforated area and a solid area positioned such that there will not be large numbers of perforations on the belt that are uncovered by the plate through which air may be drawn to reduce the suction acting on the plate.

5 Claims, 2 Drawing Figures DRIVE MOTOR "1 Va I I6 2.9 l0 l5 F3] TEBRIVE MOTOR PATENTED SEP 91975 PRINTING PLATE TRANSFER AND SUPPORT APPARATUS This is a continuation of application Ser. No. 301,031, filed Oct. 26, 1972, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to printing plate making apparatus. More specifically, the present invention relates to apparatus for transporting a printing plate to and from an imaging station and for supporting the plate at said imaging station during the exposure thereof.

2. Description of the Prior Art In electrostatic plate making apparatus, it is known to employ an endless belt for the purpose of carrying electrostatically charged photosensitive printing plates to an imaging station and for supporting the plates thereat during exposure. In such systems also, it is known to provide a vacuum platen or the like for maintaining the plate in the focal plane of the optical imaging system during exposure by suction drawn through openings in the belt.

In practice, however, it has been found that there are several inadequacies with this known structure. For example, one particularly significant problem concerns the tracking of the belt. Since the belt is endless and is always moved in the same direction. any tracking errors in the belt movement tend to be cumulative and cause the belt to shift around significantly on its supporting rollers and rub against the edges of the rollers or against other surfaces on the machine. This rubbing has the effect of rapidly weakening the belt making frequent replacement necessary, and, also, often causes the belt to break during use.

In order to reduce these tracking errors, one practice has been to utilize crowned rollers to support the belt. With such structure, however, belt replacement and maintenance becomes a complicated operation requiring excessive time and a substantial degree of skill. Also, with crowned rollers, the belts must be made somewhat elastic, and as a result, it becomes more difficult to maintain the belt perfectly flat and ripple free during use which is necessary to ensure proper alignment of the plate in the focal plane of the imaging system.

A further difficulty that arises in the prior art machines relates to the fact that the belts are perforated substantially throughout their length. Thus, when a plate is only partially positioned on the belt, for example, a substantial number of the perforations are uncovered. During this period, the fan or other source of suction is drawing air through these uncovered perforations which reduces the amount of suction acting on the plate itself. Accordingly, to retain the plate accurately on the belt, during these periods, a relatively large fan or pump capable of maintaining a strong suction must be utilized. This necessitates greater power to run the machine and, generally makes it more expensive as well.

SUMMARY OF A PREFERRED EMBODIMENT OF THE INVENTION In accordance with a preferred embodiment of the present invention, some of the above described inadequacies have been obviated by employing a belt that is adapted to be wound back and forth between supply and takeup spools for carrying a charged printing plate to the imaging station for exposure and back out for subsequent development. More specifically, the belt employed is not an endless belt that always moves in the same direction, but instead is mounted on spools to be moved forwardly from a first plate loading position to a second imaging position and then moved back to the first position for unloading during each imaging operation.

Several advantages are provided by this structure. For one thing any tracking errors in the forward move ment of the belt will be substantially self-corrected during the reverse movement of the belt. Tracking errors will thus not be cumulative as when an endless belt moving in only one direction is utilized. This has the effect of extending belt life and also makes it unnecessary to utilize crowned rollers with their attendant maintenance and replacement problems.

A further important feature of the present invention relates to the construction of the belt itself. Specifically, only a portion of the belt is perforated rather than the entire belt and the movement of the belt is synchro nized with the feeding of the printing plate onto it such that the perforated area on the belt will come adjacent to the vacuum platen at substantially the same time as the plate. This means that there will not be a large number of uncovered perforations through which air will be drawn to reduce the suction acting on the plate and, accordingly, much less power is needed to provide the necessary suction to hold the plate on the belt. This improved holding ability also makes it unnecessary to provide wire guides or other supporting structure to ensure that the plate is kept firmly on the belt at all times.

Also, with the present invention, the belt need not be particularly elastic and a flat, ripple-free belt is easier to maintain and generally lesser amounts of tension must be applied to the belt to keep it smooth.

In general, the present invention provides an effective system for handling electrostatically charged printing plates in a plate making machine. The invention obviates some of the inadequacies of the prior art and its incorporation into the machine provides a compact and efficient system. Yet further features of the invention will be set forth in detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates, in schematic form, the imaging station of a plate making system employing the plate transfer and support structure in accordance with a preferred embodiment of the present invention.

FIG. 2 illustrates the construction of the transfer belt in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I schematically illustrates an imaging station, generally designated by reference number 10, for employment in an electrostatic plate making machine. More specifically, a photoconductive printing plate 11 which has had an electrostatic charge placed thereon in any conventional manner is adapted to be fed into the imaging station 10 and aligned in the focal plane 15 of an optical imaging system, illustrated schematically by lens 12, for the purpose of exposing it to a desired image.

In order to support the plate and to transfer it to and from the imaging station 10, a belt 13 is provided. This belt, which is preferably made of Mylar" plastic material but could also be made of a fabric, foil, or other material if desired, is attached at its ends to a supply spool 14 and a take-up spool 16 as shown.

Spools

14 and 16 are adapted to be driven in rotation by a reversible drive motor 18 through an appropriate mechanical connection 17 for the purpose of moving belt 13 back and forth across the focal or imaging plane of the optical imaging system 12 for the purpose of carrying the printing plate 11 thereto. More specifically, belt 13 is adapted to be supported around

rollers

19 and 21 for movement across the imaging plane 15. One or more tension rollers 22 or their equivalent may also be provided, if desired, for'the purpose of maintaining the proper tension on the belt and ensuring that it is kept flat and ripple free.

Positioned in alignment with the optical imaging system 12 is a vacuum platen which, in the embodiment illustrated, consists of a vacuum chamber 23 having a perforated base 24 and suitable structure illustrated as a fan 26 or a pump for reducing the air pressure in chamber 23. Base plate 24 is perforated substantially over its surface such that fan 26, by reducing the pressure in chamber 23, will also draw air upwardly through the perforations creating a suction therethrough as will be explained in greater detail hereinafter. Belt 13 as shown, extends across base plate 24 and is also provided with perforations as will also be explained hereinafter.

Exposure of a charged printing plate is accomplished in the following manner. Initially, a charged plate, shown at 11a for illustrative purposes, is fed from a charging station (not shown) to the imaging station 10. The plate is fed in at an inclined angle of, for example, 30" with respect to focal plane 15. A suitable guide 27 may be provided to ensure proper alignment, if desired. Specifically, the plate is fed between roller 19 and a cooperating roller 28 into Contact with the lower surface of belt 13 which is wrapped around roller 19. The speed of the incoming plate and of the belt are substantially synchronized to ensure proper cooperation.

As the plate comes adjacent the vacuum chamber 23, preferably immediately after it passes between the rollers l9 and 28, the suction drawn through the perforations in the base plate 24 and the perforations in the belt 13 will suck up the belt and the plate carried thereby against base plate 24 and hold it in the focal plane 15 of the optical imaging system 12. The belt 13 will continue to move from spool 14 to spool 16 carrying the plate with it until the plate is accurately aligned with the imaging system 12. At this time, the leading edge of the plate 11 will actuate a suitable switch 29 which is coupled to the drive motor 18 by a suitable electrical connection 31 to shut off the drive motor and stop further movement of the belt. At this position the printing plate 11 will be accurately aligned in the focal plane 15 of optical system 12 and, further, will be held firmly in that position by the suction drawn through the perforations in base plate 24 and the belt 11. The plate may then be exposed to the desired image through optical imaging system 12 in a conventional manner.

After being exposed, the plate is then ready to be withdrawn from the imaging station and transported to other succeeding stages of the plate making machine for development and further treatment. This is accomplished as follows. After completion of the exposure, the drive motor 18 is automatically actuated by a suitable switch, not shown, and reversed to drive the belt 13 in the reverse direction back to its original position. This will cause the belt 13 to unwind from spool 16 and rewind on to spool 14 carrying the plate 11 with it back through

rollers

19 and 28. Upon exiting from between the rollers, the plate (illustrated as 11b) will fall by gravity against a suitable support frame 32 inclined downwardly at an angle of about 30 relative to the focal plane 15 to be carried to the next stage of the machine (not shown). After the plate has fully exited from the imaging station, the belt will be fully rewound on spool 14 and again be in its initial position to receive the next plate coming from the charging station. The drive motor will also be shut off to await receipt of the next plate.

The present invention thus avoids many of the inadequacies of the prior art by providing a belt that is movable from a first position to a second position and back to the first position to transfer a printing plate to the imaging station for exposure and back out after exposure. Since the belt is moved in two different directions for each imaging operation, tracking errors are minimized thus extending the life of the belt and providing a more economical system. Furthermore, with the present invention it is not necessary to employ crowned rollers for the purpose of minimizing tracking errors. This makes maintenance of the system substantially easier than in the prior art and in addition makes it unnecessary to employ elastic belts which are needed when crowned rollers are used. When elastic belts are employed, the tendency for them to ripple increases significantly and substantial tension must be applied to the belt to maintain it smooth and flat. With the present in vention, the belt does not have to be elastic and, therefore, less tension must be maintained on it. This also ex tends the belt life.

Finally, by feeding the plates in and out of the imaging station on the same side, a more compact system may be provided. Greater compactness is also achieved by avoiding the need for endless belts.

FIGS. 2 illustrate a further important feature of the present invention. More particularly, FIG. 2 illustrates a section of the belt 13 employed in the system of FIG. 1. As shown, this belt is provided with a perforated area 36 and an unperforated or solid area 37. Solid area 37 is located in advance of the perforated area 36 when the belt is moved from supply spool 14 to take-up spool 16 as illustrated by the arrow. More specifically, when the belt is in its initial position awaiting receipt of the printing plate 11, essentially the entire belt surface beneath the vacuum chamber 23 will be unperforated or solid. Upon feeding of the printing plate 1 1 into the imaging station, however, the motion of the belt is synchronized with the feeding of the plate 11 such that the leading edge of the plate will come adjacent the base plate 24 of the vacuum chamber 23 at substantially the same time as the first row of perforations 38 of the perforated area 36. This provides several important advantages.

Primarily, when the plate 11 and the first row 38 of perforations 39 comes adjacent the vacuum chamber 23, the remainder of the belt beneath the vacuum chamber will be unperforated. Thus, essentially all the suction forces produced by the vacuum chamber will act upon the printing plate. There will be no uncovered perforations in the belt through which air may be drawn to weaken the suction. This means that a less powerful suction is needed to firmly hold the plate on the belt. As more and more of the plate is moved beneath the vacuum chamber, the perforated area thereat is also increased to firmly hold the plate over its entire length. Put another way, with the present invention, the belt is perforated substantially only where the printing plate will be supported and, therefore, there is no significant waste of energy as would be the case when air is also being drawn through uncovered perforations. This permits a reduction in the size of the fan needed to produce the suction with the attendant savings in cost and energy requirements. In the prior art, wherein an endless belt, perforated throughout its length is provided, air is drawn not only through perforations adjacent the printing plate but also through uncovered perforations which means much larger fans are needed to produce the much stronger suction required to hold the plate on the belt. Any type of conventional sensing or timing means may be utilized to ensure alignment of the incoming plate with the first row of perforations 38.

Preferably also, the perforations 39 in the belt are of elongated form as illustrated in FIG. 2 and are adapted to cooperate with generally circular perforations 41 in the base plate 24 of the vacuum chamber. This will insure that suction is maintained at all times during belt movement and that there are no periods during which the perforations in the belt are not aligned with the perforations in the plate. Obviously the perforation shapes could be varied or reversed if desired. Preferably also, the perforations are aligned on the belt in a staggered relationship, preferably in a plurality of rows of perforations with the alternating rows being in staggered relationship as shown in FIG. 2. This also ensures that the printing plate is held firmly and uniformly at all times.

Thus, in conclusion, the present invention provides a plate making apparatus that is inexpensive in construction, yet capable of operating for extended periods of time without maintenance or repair. When maintenance is required it may be accomplished rapidly with a minimum of skill. The invention also provides a highly compact system that may be readily incorporated into plate making equipment of all types.

It should also be appreciated that the term printing plate" as employed herein is intended to include any type of photosensitive medium such as Electrofax" paper and the like and should not be limited to lithographic printing plates as described in the preferred embodiment. in this regard also, it should be understood that the above-described embodiment is, in general, meant to be only a preferred embodiment and that the invention may take many other forms as recognized by those skilled in the art. For this reason, it should be understood that the present invention should be limited only as required by the scope of the following claims.

We claim:

1. Platemaking apparatus comprising:

a. an imaging station including an optical imaging system having an image plane; and

b. means for transferring a printing plate to said imaging station and for supporting it in the image plane of said optical system for exposure thereat,

said transferring and supporting means comprising:

1. a belt movable between a first position and a second position, said belt having first and second opposed surfaces and including a perforated area having a plurality of openings extending therethrough from said first surface to said second surface and a substantially solid area, said solid area being located in advance of said perforated area during movement of said belt from said first position to said second position, said perforated area being at least substantially as large as said printing plate;

2. means for positioning said plate adjacent said first surface of said belt;

3. a vacuum source positioned adjacent the second surface of said belt for drawing and holding said plate against said first surface thereof by suction drawn through said openings in said perforated area of said belt; and,

4. drive means for moving said belt between said first and second positions, said drive means in cluding means for moving said belt in a forward direction from said first position to said second position for transferring said plate held thereon to said imaging station to be held in the image plane of said imaging system for exposure, and for moving said belt in a reverse direction from said second position back to said first position for withdrawing said plate held thereon from said imaging station following exposure.

2. Apparatus as recited in claim 1 wherein said vacuum source comprises a vacuum chamber of reduced pressure extending across said imaging station, said vacuum chamber including a base having a plurality of openings therein, and wherein said apparatus further includes means for supporting said belt for movement adjacent said base, said reduced pressure in said vacuum chamber holding said plate against the first surface of said belt as said drive means moves said belt across said base by suction drawn through the openings in said base and in said belt.

3. Apparatus as recited in claim 1 wherein said plate positioning means includes:

a. first and second rollers, said belt being supported for movement between said rollers; and

b. means for directing said plate between said first and second rollers into contact with said first surface of said belt.

4. Apparatus as recited in claim 3 wherein said directing means includes means for directing said plate between said first and second rollers at a first inclined angle relative to said belt.

5. Apparatus as recited in claim 4 and further including means for withdrawing said plate from said belt following exposure, said plate withdrawal means including means for directing said plate away from between said rollers at a second inclined angle relative to the belt different from said first inclined angle.

Claims

1. Platemaking apparatus comprising: a. an imaging station including an optical imaging system having an image plane; and b. means for transferring a printing plate to said imaging station and for supporting it in the image plane of said optical system for exposure thereat, said transferring and supporting means comprising: 1. a belt movable between a first position and a second position, said belt having first and second opposed surfaces and including a perforated area having a plurality of openings extending therethrough from said first surface to said second surface and a substantially solid area, said solid area being located in advance of said perforated area during movement of said belt from said first position to said second position, said perforated area being at least substantially as large as said printing plate; 2. means for positioning said plate adjacent said first surface of said belt; 3. a vacuum source positioned adjacent the second surface of said belt for drawing and holding said plate against said first surface thereof by suction drawn through said openings in said perforated area of said belt; and, 4. drive means for moving said belt between said first and second positions, said drive means including means for moving said belt in a forward direction from said first position to said second position for transferring said plate held thereon to said imaging station to be held in the image plane of said imaging system for exposure, and for moving said belt in a reverse direction from said second position back to said first position for withdrawing said plate held thereon from said imaging station following exposure.

2. means for positioning said plate adjacent said first surface of said belt;

3. Apparatus as recited in claim 1 wherein said plate positioning means includes: a. first and second rollers, said belt being supported for movement between said rollers; and b. means for directing said plate between said first and second rollers into contact with said first surface of said belt.

4. drive means for moving said belt between said first and second positions, said drive means including means for moving said belt in a forward direction from said first position to said second position for transferring said plate held thereon to said imaging station to be held in the image plane of said imaging system for exposure, and for moving said belt in a reverse direction from said second position back to said first position for withdrawing said plate held thereon from said imaging station following exposure.