Method and apparatus for magnetically clamping printing plates

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to printing apparatus. It relates more particularly to a calamping mechanism for securing a printing plate to a plate cylinder.

2. Description of the Related Art

In offset lithography, an image is present on a printing plate as a pattern of ink-accepting and ink-repellant surface areas. In a typical sheet-fed offset press, the imaged plate is mounted to a plate cylinder where it is inked and then brought into contact with the compliant surface of a blanket cylinder. The blanket cylinder, in turn, applies the image to paper sheets which are brought into contact with the blanket cylinder by an impression cylinder.

It should be understood at the outset that nowadays a “printing plate” may actually be a thin, flexible plastic film or sheet.

Plates can be imaged on-press or, more traditionally on an off-press platesetter. A digitally operated platesetter includes an imaging cylinder to which the plate is initially mounted and which carries the plate past the head of the imaging device. That device transfers the image to the plate. The imaged plate is then removed from the platesetter and transferred to the plate cylinder of the printing press. When mounting an imaged plate to a plate cylinder for a press mount or when mounting a plate to an imaging cylinder for imaging, it is essential that the leading and trailing edges of the plate be secured firmly to the cylinder and that the plate be wrapped tightly around the cylinder. This ensures that there will be no relative movement between the plate and the cylinder when the cylinder is rotated.

A plate cylinder typically includes two plate clamps mounted to the cylinder that extend along its surface. To load a plate onto the cylinder, the leading edge of the plate is secured to the cylinder by one clamp and the plate is wrapped around the surface of the cylinder. The trailing edge of the plate is then secured to the cylinder with the other clamp.

Some printing processes require that two superimposed plates or sheets be mounted independently to the cylinder. For example, in color proofing apparatus, a receptor plate or sheet is secured to the cylinder by a first pair of clamps and successive donor plates or sheets representing color separations are secured to the cylinder over the receptor sheet by a second pair of clamps. After the donor sheet representing each color component has been imaged, that sheet is unclamped from the cylinder and replaced by the donor sheet corresponding to the next color component which must be wrapped around the cylinder and clamped. This process must be repeated three or four times for three or four color printing.

Various devices including hydraulic clamps, vacuum clamps, mechanical and electromechanical clamps have been developed over the years for holding a plate or sheet to a plate cylinder. However, for the most part, these prior devices have tended to be relatively complex. Also, in requiring heavy metal plates as clamps, they take up a relatively large amount of space on the plate cylinder creating a substantial “void” segment on the cylinder which is the space on the cylinder occupied by the clamps and the space immediately between them. Furthermore, the ancillary mechanisms for operating such clamps, such as air/hydraulic cylinders and lines thereto, take up additional space in the printing apparatus.

The above problems are exacerbated in the case of color proofing apparatus where four such clamps are required to secure the donor and receptor sheets to the cylinder.

The prior clamping devices are also disadvantaged in that the clamping mechanisms are fixed to the plate cylinders such that the mechanisms can only secure to the cylinder a plate or sheet having a specific length. Since the plates are often precut to fit the specific plate cylinder of the printing press, this inability to accommodate different length plates substantially increases the cost of operating and running printing and proofing apparatus.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a speedy and efficient clamping mechanism for clamping a printing plate to a plate cylinder or other support surface.

Another object of the invention is to provide a clamping device for clamping a plate or sheet to a cylinder which takes up a minimum amount of space on the cylinder.

A further object of the invention is to provide a clamping device which allows the associated cylinder to accept plates or sheets of different lengths.

Yet another object is to provide a clamping mechanism which minimizes void space on the cylinder.

Still another object of the invention is to provide a clamping mechanism which does not require bulky ancillary pumps or other apparatus to actuate the plate clamps.

An additional object of the invention is to provide a clamping mechanism of this type which is relatively simple and takes up a minimum amount of space in the imaging, proofing or printing apparatus in which it is installed.

Other objects will, in part, be obvious and will, in part, appear hereinafter. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.

Briefly, our clamping mechanism comprises at least one pair of similar clamping devices for clamping the leading and trailing edges of a plate or sheet preferably wrapped around a rotary cylinder. As alluded to above, in those applications requiring that a second plate or sheet be secured to the cylinder independently of the first, a second similar pair of clamping devices may be required. We will describe the invention as applied to a plate cylinder in an otherwise more or less conventional printing or proofing apparatus. It should be understood however that the invention is useful in other applications in which a thin plate or sheet has to be releasably clamped to a flat or curved surface of one kind or another.

In accordance with the invention, each clamping device is a long thin blade clamp and the cylinder (in whole or in part) and each blade clamp are made of ferromagnetic materials and at least one of the cylinder and clamps is magnetized so that the blade clamp is magnetically attracted to the cylinder with sufficient force to securely clamp the leading or trailing edge of the underlying plate or sheet to the cylinder.

In one embodiment of the invention, each blade clamp is laid down on and retrieved from the cylinder by a separate dispensing mechanism. More particularly, each blade clamp is wound up on a spool which may shuttle along a track extending parallel to the cylinder. The spool is movable along the track between a home position located just beyond one end of the cylinder and an extended position located just beyond the opposite end of the cylinder. The leading end of the blade clamp extending from the spool is terminated by a hook. When the spool is moved from its home position and passes by the adjacent confronting end of the cylinder, the hook engages that end of the cylinder. Resultantly, as the spool travels along the track, the blade clamp is paid out from the spool much like the steel tape of a tape measure, such that the blade clamp is laid down onto the surface of the cylinder (or more specifically onto the printing plate thereon) parallel to the cylinder axis.

When the spool reaches its extended position beyond the opposite end of the cylinder, the trailing end of the blade clamp is released from the spool so that the blade clamp is free to rotate with the cylinder, while the now empty spool remains at its extended position until it is time to unclamp the plate from the cylinder.

In order to unclamp the plate from the cylinder, the rotation of the cylinder is stopped and the cylinder is oriented to position the blade clamp on the cylinder so that its trailing end is aligned with the spool still reposing at its extended position on the track. Then, the spool is moved back along the track toward its home position. As will be described in more detail later, the trailing end of the blade is picked up by the spool and as the spool moves along the track towards home, the blade clamp is rewound onto the spool. This winding up of the blade clamp on the spool peels, rather than pulls, the blade clamp away from the cylinder. Therefore, the motion of the spool along the track is sufficient to overcome the strong magnetic attraction of the blade clamp to the cylinder. By the time the spool reaches the end of the cylinder adjacent to the home position of the spool, substantially the entire length of the blade clamp has been wound up on the spool. Then, as the spool travels the remaining distance to its home position, the hook at the leading end of the blade is released from the end of the cylinder so that the cylinder is again free to rotate independently of the clamping mechanism.

In a second embodiment of our invention, a single blade dispenser or applicator applies all of the blade clamps to, and removes them from, the plate cylinder. As such it is particularly suitable for use in proofing apparatus in which substantially superimposed donor and receptor sheets, drawn from a single roll of sheet material, are clamped to the proofer's imaging or plate cylinder. In other words, a first pair of blade clamps clamp the leading and trailing ends of the receptor sheet to the plate cylinder and, a second pair of blade clamps clamp the overlying donor sheet to that cylinder.

In this case, the blade dispenser comprises an elongated rotary applicator bar which extends parallel to the cylinder at a clamping station located adjacent to the cylinder. The bar has a polygonal cross-section in that it has a plurality of facets, the number of facets being at least equal to the number blade clamps to be dispensed, i.e. four in this case. In accordance with the invention, a magnet, which may be an electromagnet or a permanent magnet, is present at each facet of the applicator bar which, when operative, is sufficiently strong to attract and hold a blade clamp to the corresponding facet of the applicator bar. As will be described in detail later, the applicator bar may be rotated to selectively position each magnet, and any blade clamp magnetically adhered thereto, opposite the cylindrical surface of the plate cylinder. Also, the dispenser as a whole is movable toward and away from the plate cylinder between an extended position which locates the confronting magnet close to the cylinder surface and a retracted position in which that magnet is spaced away from the cylinder surface. All of the active components of the dispenser, along with the movement of the print cylinder, are controlled by a controller which may also control the other elements of the proofing apparatus.

Since the material for both the donor sheet and the receptor sheet are drawn from a single roll of sheet material, provision is made for separating the donor and receptor sheets from the roll supply after each sheet is wrapped around the plate cylinder and clamped. The dispenser includes a cutting device located at a cutting station adjacent to is the plate cylinder which can be brought into contact with the sheet material on the plate cylinder under the control of the controller at the appropriate times in the blade dispensing cycle as will be described in detail later.

To apply the donor and receptor sheets to the plate cylinder, with the dispenser in its retracted position, four blade clamps are releasably adhered to the applicator bar by the four magnets on that bar, the bar being oriented so that one blade clamp faces the plate cylinder. Then, proofing material from the supply roll is fed to the plate cylinder so that the material is draped over the cylinder with the leading edge of that material positioned between the plate cylinder and the confronting blade clamp on the applicator bar. Next, the dispenser is moved to its extended position so that the operative blade clamp is moved toward the plate cylinder whereby that blade clamp becomes magnetically attracted to the plate cylinder by a force that is stronger than the force holding that blade clamp to the applicator bar (or the electromagnet is deenergized). Then, the dispenser is retracted leaving the blade clamp clamping the proofing material to the plate cylinder.

Next, the controller controls the feeding of additional proofing material from the supply roll and rotates the plate cylinder so that the additional proofing material from the supply roll becomes wrapped around the plate cylinder, while at the same time the controller rotates the applicator bar to position a second blade clamp thereon opposite the plate cylinder. After the plate cylinder has rotated through a selected angle less than 360°, the plate cylinder is stopped and the dispenser is again moved to its extended position so that the second blade clamp is moved to the proofing material on the plate cylinder and becomes magnetically attracted to the cylinder. The magnet holding the second blade clamp to the applicator bar then releases the blade clamp to the cylinder and the dispenser is retracted leaving the second blade clamp clamping the proofing material to the plate cylinder.

At this point, the controller activates the cutting device which cuts the proofing material just behind the second blade clamp thereby separating the material on the cylinder from the roll supply. That segment of sheet material wrapped around and clamped to the plate cylinder constitutes a receptor sheet for the proofing apparatus and there is a gap between the leading and trailing edges of that sheet, i.e., between the first and second blade clamps.

Similar steps are repeated to apply a donor sheet to the plate cylinder over the receptor sheet. That is, with the dispenser in its retracted position, the applicator bar is rotated to position the third blade clamp adhered thereto opposite the plate cylinder and the plate cylinder is rotated to position the void space thereof opposite the third blade clamp. Also, proofing material is fed from the supply roll so that the leading edge thereof is introduced into the space between the plate cylinder and the third blade clamp. Next, the dispenser is moved to its extended position thereby moving third or operative blade clamp to the void space on the plate cylinder, the third blade clamp being magnetically attracted to that cylinder and released by the applicator bar. The dispenser is then moved to its retracted position and the applicator bar is rotated to position the fourth blade clamp opposite the plate cylinder. At the same time, the plate cylinder is rotated while additional proofing material is fed from the supply roll to the plate cylinder so that additional material overlies the just-applied receptor sheet.

Rotation of the plate cylinder is stopped when the void space thereon is disposed opposite the fourth blade clamp at which point the dispenser is again moved to its extended position so that the fourth blade clamp is released from the applicator bar to the plate cylinder thereby clamping the sheet material to the plate cylinder. Following retraction of the dispenser, the cutting device is activated to sever the sheet material just behind the fourth blade clamp thereby separating the outer layer of sheet material wrapped around the plate cylinder, which constitutes a donor sheet, from the supply roll which roll may then be rotated in the opposite direction to remove the leading edge of the roll supply from the vicinity of the plate cylinder.

With the donor and receptor sheets firmly clamped to the plate cylinder, the proofing apparatus can now be operated to process the sheets in a manner known in the art.

After the proofing operation is completed, the blade dispenser may be operated to remove the blade clamps, in reverse order, from the plate cylinder so as to release only the donor sheet or both sheets from the cylinder. That is, with the dispenser in its retracted position and with one of the magnets on the applicator bar facing the plate cylinder, the plate cylinder is rotated to position the fourth blade clamp opposite the applicator bar and the dispenser is moved to its extended position. If the magnets on the applicator bar are electromagnets, the operative magnet is energized and produces a magnetic field that is stronger than that of the magnetized plate cylinder. Resultantly, the fourth blade clamp becomes attracted to that magnet so that when the dispenser is retracted, the fourth blade clamp is pulled away from the plate cylinder thereby releasing the trailing end of the outer donor sheet. The plate cylinder is then rotated to position the third blade clamp opposite the applicator bar and the applicator bar is rotated to orient a second electromagnet opposite the plate cylinder. Then, the dispenser is extended again and that electromagnet is energized to pick up the third blade clamp from the plate cylinder thereby releasing the leading end of the donor sheet.

If the magnets on the applicator bar are permanent magnets, a stripper mechanism to be described later is inserted under one end of the blade clamp being removed from the cylinder and is moved along under the blade clamp. Resultantly, the blade clamp is progressively moved away from the cylinder a distance such that it has a stronger attraction for the confronting magnet on the applicator bar than for the cylinder. Thus, after the stripper mechanism moves to the opposite end of the blade clamp, the entire blade clamp will have been released by the cylinder to the applicator bar.

Once the clamps holding the donor sheet have been removed as aforesaid, the donor sheet must be removed from the cylinder and replaced by another donor sheet representing another color component which new sheet may then be clamped to the cylinder as described above.

Alternatively, the above procedures may be repeated to remove the second and then the first blade clamp from the plate cylinder thereby unclamping the inner receptor sheet so that both the donor sheet and receptor sheet can be removed from the plate cylinder at the end of a proofing operation.

It should be appreciated from the foregoing that the blade clamp component of our clamping mechanism can be quite thin and only wide enough to provide the necessary magnetic attraction to effectively clamp the leading or trailing edge of the underlying plate to the cylinder. The blade clamp can be laid down anywhere around the circumference of the cylinder simply by properly orienting the cylinder and activating the clamping mechanisms at the proper times.

As will become apparent, the clamping mechanisms utilized to lay down and pick up each blade clamp are relatively simple and occupy a minimum amount of space. Furthermore, they are quite fast and efficient and are relatively easily incorporated into otherwise conventional printing and proofing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention, references should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1

is a fragmentary perspective view of a pair of clamping mechanisms for clamping the leading and trailing ends of a printing plate to a support surface, to wit: a plate cylinder;

FIG. 2

is a plan view taken along line

22

of

FIG. 1

, on a larger scale and with parts broken away, showing in greater detail the blade clamp dispenser of the

FIG. 1

clamping mechanism reposing at its home position;

FIG. 3

is a sectional view taken along line

33

of

FIG. 2

;

FIG. 4

is a view similar to

FIG. 3

showing the blade clamp dispenser in its extended position;

FIG. 5

is a fragmentary perspective view on a still larger scale showing a blade clamp embodiment in greater detail;

FIG. 6

is a front elevational view with parts broken away showing proofing apparatus incorporating a second embodiment of our magnetic clamping mechanism;

FIG. 7

is an end view thereof,

FIGS. 8A

,

8

B are alternative views similar to

FIG. 7

illustrating the operation of the

FIG. 6

mechanism; and

FIG. 9

is a diagrammatic view showing the placements of the blade clamps on the plate cylinder of the

FIG. 6

apparatus.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Refer to

FIG. 1

of the drawings which show a rotary cylinder

10

whose shaft

11

may be rotated by a motor

12

under the control of a programmable controller

14

having a keyboard

14

a

for entering instructions into the controller. The controller receives signals from a shaft encoder

16

or the equivalent which enables the controller to monitor the angular position of cylinder

10

and to set cylinder

10

at selected angular positions about its axis. Cylinder

10

may be part of an imaging; printing or proofing apparatus and is arranged to support a flexible sheet such as a printing plate P which may be wrapped around cylinder

10

when the cylinder is stationary.

For reasons that will become apparent, arcuate slots

16

a

,

16

b

. . .

16

x

are formed in one end

10

a

of cylinder

10

. Also, a lengthwise series of small spaced-apart magnets

18

are inserted into the cylindrical surface of cylinder

10

in alignment with each slot

16

a

,

16

b

. . .

16

x

. Alternatively, the cylinder surface itself may be magnetized.

In order to clamp the leading edge P

L

of the plate P to the cylinder, a first clamping mechanism shown generally at

22

is provided adjacent to cylinder

10

. A second clamping mechanism

24

is located adjacent to the cylinder in order to clamp the trailing edge P

T

of the plate to the cylinder. For ease of illustration, mechanisms

22

and

24

are shown spaced about 120° around the axis of cylinder

10

. In actuality, they may be spaced much further apart to maximize the length of the plate P that can be clamped to cylinder

10

and to minimize the amount of void space on the cylinder. Aside from their angular positions relative to cylinder

10

, the clamping mechanisms

22

and

24

are substantially identical. Therefore, we will only describe mechanism

22

in detail.

Mechanism

22

comprises a blade dispenser

26

arranged to travel back and forth on a stationary track

28

extending parallel to cylinder

10

between a home position H located just beyond a first end

10

a

of cylinder

10

and an extended position E located just beyond the opposite end

10

b

of the cylinder. In

FIG. 1

, the blade dispenser

26

of mechanism

22

is shown at its home position H, while the dispenser

26

of mechanism

24

is illustrated at its extended position E.

As best seen in

FIGS. 2 and 3

, dispenser

26

of mechanism

22

comprises a pair of mirror-image, generally rectangular side walls

32

a

and

32

b

which are held in spaced relation by posts

34

adjacent to the four corners of the side walls. The posts are retained by threaded fasteners

36

which extend through the side walls and are turned down into threaded holes

38

(

FIG. 2

) in the ends of the posts.

Positioned between side walls

32

a

and

32

b

is a spool

42

having stub shafts

44

a

and

44

b

journalled in the dispenser side walls

32

a

and

32

b

so that spool

42

can be rotated about an axis relative to the dispenser walls. In the illustrated embodiment, spool

42

is rotated by a reversible step motor

48

mounted to side wall

32

a

and whose shaft

48

a

is rotatably coupled to stub shaft

44

a

. Preferably, motor

48

is a step motor which is energized by signals from the controller

14

shown in FIG.

1

.

Referring now to

FIGS. 1

to

3

, track

28

includes longitudinal slides

28

a

formed in the opposite sides of the track which slides are slidably engaged by slides

52

present at the tops of housing walls

32

a

and

32

b

, respectively. As shown in

FIG. 3

, dispenser

26

is moved along track

28

by a pinion

54

at the end of a shaft

55

rotatably mounted to housing walls

32

a

and

32

b

and arranged to mesh with a rack

56

formed at the underside of track

28

. Shaft

55

is rotated by a reversible step motor

48

mounted to housing wall

32

a

above motor

48

. The motor

48

is also controlled by controller

14

. In other words, when motor

54

is rotated in one direction or the other by controller

14

, dispenser

26

is caused to move in one direction or the other along track

28

.

As best seen in

FIGS. 2 and 3

, spool

42

is arranged to support the coiled length of a thin, flexible blade clamp

62

. The clamp has a leading end

62

a

to which is attached a hook

64

and a trailing end

62

b

(

FIG. 3

) arranged to engage in a slot

66

extending along a chord of spool

42

. Preferably, slot

66

has a relatively wide mouth or entrance

66

a

at the periphery of spool

42

to facilitate the entry of the blade end

62

b

into slot

66

as will be described later.

When the trailing end

62

b

of blade clamp

62

is captured in slot

66

and spool

42

is rotated clockwise as viewed in

FIG. 3

, the clamp

62

is wound up on spool

42

. As we shall see, this occurs when dispenser

26

moves from left to right in

FIG. 1

, i.e., from its extended position E to its home position H. Preferably, spool

42

is provided with side flanges

42

a

and

42

b

as shown in

FIG. 2

in order to center the blade on the spool. Desirably also, an endless band

72

of flexible material is looped around posts

34

between housing side walls

32

a

and

32

b

such that an inner stretch of the band conforms to the perimeter of the spool and no material extends between the two posts

34

closest to cylinder

10

as shown in FIG.

1

. Thus, when spool

42

is rotated clockwise, the blade

62

may be drawn into the dispenser

26

between those lower posts

34

with the inner stretch of band

72

causing the blade clamp

62

to wind up tightly on the spool.

Preferably, the blade clamp

62

has a slight crown as shown in

FIG. 5

so that it can only be rolled up in one direction, i.e., like the metal tape of a tape measure.

Of course, when spool

42

is rotated counterclockwise as viewed in

FIG. 3

, which occurs when dispenser

26

moves from right to left in

FIG. 1

, i.e., from home position H to the extended position E, the blade clamp

62

is unwound from spool

42

and paid out from dispenser

26

. dispenser side walls

32

a

and

32

b

just above the point where the blade clamp

62

enters and leaves the dispenser

26

. Actuator

82

includes a shaft

84

whose lower end supports a magnet

86

facing blade clamp

62

. The shaft and magnet are biased away from the blade clamp

62

by a coil spring

88

encircling shaft

84

between the actuator body and a cap

84

a

at the upper end of the shaft. Normally, the magnet

86

is biased away from the blade clamp

62

by spring

88

as shown in FIG.

3

. However, when the actuator

82

is energized by signals from controller

14

, the shaft is extended to bring the magnet

86

into contact with the blade clamp

62

as shown in phantom in

FIG. 4

for reasons that will become apparent.

The dispenser

26

of clamping mechanism

24

shown at its extended position E in

FIG. 1

, has the same components as mechanism

22

and operates in the same way as described above under the control of controller

14

.

Usually when cylinder

10

is not being used, the dispenser

26

of both clamping mechanisms

22

and

24

are located at their respective home positions H just beyond the cylinder end

10

a

with each blade being wound up on its respective spool

42

. Preferably, when each dispensers is so parked, a nose

64

a

on hook

64

engages a ramp

92

projecting from actuator

82

to retain the leading end

62

a

of each blade clamp

62

.

When the apparatus with which cylinder

10

is associated is to be used, a plate P is wrapped around the cylinder as shown in

FIG. 1

so that the leading end P

L

of the plate is located opposite the cylinder slot

16

a

. Then, the cylinder is rotated by motor

12

under the control of controller

14

from information put in via its keyboard

14

a

to position the cylinder slot

16

a

opposite the blade hook

64

of clamping mechanism

22

. As soon as the cylinder

10

is correctly positioned, controller

14

may activate the motor

57

of that mechanism's dispenser

26

causing the dispenser to move along its track

28

away from its home position H. When the dispenser passes over the cylinder end

10

a

, the hook

64

at the leading end of the blade clamp

62

engages in the slot

16

a

in the cylinder end

10

a

thereby securing the leading end of the blade clamp to the cylinder. At the same time, controller

14

activates the spool motor

48

of mechanism

22

so that the spool

42

in the dispenser rotates counterclockwise whereupon the blade clamp is paid out from the dispenser as the dispenser moves along the cylinder. Since the radius of the spooled blade clamp in the dispenser decreases as the dispenser moves along its track, the speed of each spool motor

48

is increased by controller

14

to compensate for that fact.

In accordance with the invention, the blade clamp

62

is of a ferromagnetic material and is attracted to the magnets

18

embedded in cylinder

10

(or to the surface of the cylinder) under the plate leading edge P

L

thereby firmly clamping that leading edge to the cylinder surface.

After the dispenser

26

of mechanism

22

has passed the cylinder end

10

b

and approaches its extended position E, the dispenser will have traveled a distance greater than the length of the blade clamp

62

. Resultantly, the trailing end

62

b

of the blade clamp

62

pulls out of its slot

66

in dispenser spool

42

and overhangs cylinder end

10

b

as best seen in FIG.

4

. Thus, the blade clamp is separated from its dispenser and is free to rotate with cylinder

10

.

When the dispenser

26

reaches its extended position E shown in

FIG. 4

, a limit switch there (not shown) sends a signal to controller

14

whereupon the controller deactivates motors

48

and

57

of mechanism

22

. Dispenser

26

remains in position E until it is time to retrieve the blade clamp

62

from cylinder

10

.

After the leading end P

L

of plate P has been clamped to cylinder

10

as aforesaid, the controller

14

rotates the cylinder clockwise as viewed in

FIG. 1

to position the slot in the cylinder end

10

a

that underlies the trailing end P

T

of the plate, i.e., slot

16

b

in

FIG. 1

, so that that slot is opposite the clamping mechanism

24

and more particularly opposite the blade hook

64

of that mechanism which, as noted above, is in its home position H.

Next, controller

14

activates the motor

57

(and motor

48

) of mechanism

24

causing that mechanism to move away from its home position H toward the cylinder end

10

a

. When the dispenser passes end

10

a

, the hook

64

engages in slot

16

b

and, as a result, that mechanism's blade clamp

62

is paid out from the dispenser and laid down over the trailing end P

T

of the plate as shown in FIG.

1

. As the dispenser

26

of mechanism

24

approaches its extended position E as shown in

FIG. 1

, the trailing end

62

b

of the corresponding blade clamp

62

is released from the dispenser so that it overhangs the cylinder end

10

b

as shown in that figure. When the dispenser does reach its position E, it trips a limit switch (not shown) causing controller

14

to turn off the motor

57

(and motor

48

) of mechanism

24

. Now both dispensers repose in their extended positions so that both blade clamps

62

are free to rotate with cylinder

10

as a scanning or imaging operation is performed on plate P by the associated imaging or printing apparatus.

After the plate P has been processed and the cylinder

10

is brought to a stop, controller

14

may be programmed to rotate the cylinder to position the blade clamp

62

at the leading end P

L

of the plate opposite the dispenser

26

of clamping mechanism

22

which dispenser is still at its extended position E. When cylinder

10

is properly oriented, the overhanging trailing end

62

b

of that blade clamp is located directly under that mechanism's magnet

86

and ramp

92

as shown in FIG.

4

. At this point, controller

14

energizes the actuator

82

of dispenser

26

momentarily causing the actuator

82

to move magnet

86

into contact with the blade end

62

b

as shown in dotted lines in FIG.

4

. Resultantly, the blade end is attracted to the magnet so that when the magnet is retracted by spring

88

, the blade end is pulled up by the magnet thereby aligning the bitter end of the clamp with the mouth

66

a

of slot

66

in spool

42

.

Controller

14

now activates motor

57

of dispenser

26

causing the motor pinion

54

to rotate in a direction that moves dispenser

26

away from position E toward cylinder

10

. The magnetic attraction of the blade end

62

b

to magnet

86

and the magnet/blade frictional forces are such that the magnet can slide along the top of the blade clamp while keeping the blade end aligned with the mouth

66

a

of slot

66

. As dispenser

26

passes over blade end

62

b

, the blade end is inserted into slot

66

. At this point, the controller

14

activates motor

48

(

FIG. 1

) of dispenser

26

so that the motor rotates spool

42

clockwise as viewed in

FIG. 4

thereby rolling up the blade clamp

62

, trailing end first, on spool

42

. As the blade clamp is rolled up, it is incrementally peeled, rather than pulled, from plate P. Therefore, the winding action of the traveling spool

42

suffices to overcome the magnetic attraction of the blade clamp to the cylinder as the dispenser

26

progresses along track

28

toward its home position H in FIG.

1

.

As the dispenser

26

passes the cylinder end

10

a

, just before it reaches its home position H, the hook

64

of the now almost wound up blade clamp

62

is disengaged from its slot

16

a

in cylinder

10

so that by the time the dispenser reaches its home position H, the blade clamp has been wound up on spool

42

sufficiently to park the nose

64

a

of hook

64

on that dispenser's ramp

92

.

With the plate leading end P

L

having been released from the cylinder

10

, controller

14

rotates the cylinder to position the blade clamp

62

at the trailing end P

T

of the plate opposite the clamping mechanism

24

. The dispenser

26

of mechanism

24

can then be moved under the control of controller

14

to its home position in the same fashion just described to peel away the blade clamp

62

from the trailing end P

T

of the plate P thereby enabling the plate to be removed from the cylinder

10

.

In some applications, the trailing end segment of each blade clamp

62

may be bent upwardly as shown in

FIG. 5

so that when the blade clamp is magnetically adhered to cylinder

10

, the trailing end

62

b

is in alignment with the mouth

66

a

of the spool slot

66

. In that event, the actuator

82

and magnet

86

of dispenser

26

may not be needed.

It will be appreciated from the foregoing that our magnetic blade clamp may be laid down and removed quite quickly thereby minimizing the time required to clamp a sheet or plate to a cylinder or other support surface. The clamping mechanism is quite compact and therefore easy to incorporate into more or less conventional printing apparatus. Furthermore, the blade clamp itself is quite small thereby minimizing void space on the cylinder around which the plate is wrapped. Finally, the clamping mechanism is able to clamp to the cylinder plates a sheet or plate having a wide variety of different lengths. This simply involves programming the controller to orient cylinder

10

so that the appropriate slot

16

b

,

16

c

, etc. is aligned with the mechanism

24

that lays down and removes the blade clamp at the trailing end P

T

of the plate.

It should also be appreciated that if the cylinder

10

will only handle plates P of a fixed length, controller

14

can be programmed to position two cylinder slots, e.g.,

16

a

and

16

b

, opposite clamping mechanisms

22

and

24

, respectively, and to operate both mechanisms simultaneously so that both clamps can be laid down and picked up at the same time.

Refer now to

FIGS. 6 and 7

which illustrate proofing apparatus incorporating magnetic blade clamps for clamping superimposed donor and receptor sheets to the plate cylinder of that apparatus and a single blade dispenser or applicator for applying all the blade clamps to, and removing them from, the plate cylinder of that apparatus. As shown there, the proofing apparatus comprises a driven rotary plate cylinder

110

which is similar to cylinder

10

described above in that it is controllably rotated by a controller

112

having a keyboard

112

a

. Also, the cylindrical surface of the cylinder is magnetically attractive due to the rows of small cylindrical magnets

114

recessed into that surface of the cylinder, which rows, as with cylinder

10

, may extend around substantially the entire circumference of the cylinder. Alternatively, the entire surface of the cylinder may be of a magnetized material.

Cylinder

110

is adapted to support printing material P drawn from a supply roll

116

and fed to the surface of the cylinder via a roll couple consisting of a pinch roller

118

and a feed roller

122

rotated by a motor

124

under the control of controller

112

.

Referring for a moment to

FIG. 9

, the material P drawn from roll

116

(

FIG. 7

) is adapted to be wrapped around cylinder

110

to provide a receptor sheet R thereon. After the leading and trailing edges of the receptor sheet are clamped to the cylinder by blade clamps

126

L

and

126

T

, respectively, the receptor sheet R is separated from the roll supply. Then, additional material P, drawn from roll

116

, is wrapped around the cylinder to provide a donor sheet D which overlies the receptor sheet R. The leading and trailing edges of the donor sheet are also clamped to cylinder

110

by a second pair of blade clamps

128

L

and

128

T

, respectively. The donor sheet is then separated from the roll supply, leaving superimposed donor and receptor sheets wrapped around cylinder

110

, which sheets may then be processed in a known way by the associated proofing apparatus. For ease of illustration the donor and receptor sheets are shown as occupying only a small sector of cylinder

110

. In actuality, they would be wrapped around almost the entire circumference of the cylinder leaving a minimum amount of void space on the cylinder.

For reasons that will be described later the blade clamps

126

,

128

may have ends

126

′ and

128

′, respectively, which overhang an end of cylinder

110

as shown in dashed lines in FIG.

9

.

Referring again to

FIGS. 6 and 7

, the applicator or dispenser for applying the blade clamps

126

,

128

to, and removing them from, cylinder

110

is shown generally at

132

. The applicator comprises an elongated applicator bar

134

rotatably supported via shafts

135

at its opposite ends by a pair of standards

136

which extend down to a carriage

138

. The applicator bar and carriage extend the entire length of cylinder

110

. The carriage is slidably mounted to a fixed base

142

so that the carriage

138

can slide on base

142

toward and away from cylinder

110

between an extended position shown in the dotted lines in

FIG. 8A

which positions the applicator bar

134

close to the surface of the cylinder and a retracted position shown in solid lines in

FIG. 8A

wherein the applicator bar is spaced an appreciable distance away from the cylinder. The carriage is moved between its two positions by a linear actuator

144

mounted to base

142

and having and arm

144

a

connected to carriage

138

. The operation of the actuator

144

is also controlled by controller

112

.

The applicator bar

134

has a polygonal cross-section. That is, it has a plurality, herein six, of facets or faces

134

a

. Furthermore, magnets, which may be electromagnets controlled by controller

112

, are mounted to selected ones of those faces. In accordance with the invention, there is a magnet corresponding to each blade clamp

126

,

128

to be applied to cylinder

110

. Thus in the illustrated apparatus, magnets are mounted to four of the applicator bar faces

134

a

, the magnets being identified as

146

RL

,

146

RT

,

146

DL

and

146

DT

.

Further in accordance with the invention, means are provided for rotating the applicator bar

134

to selectively position the magnets

146

so as to face cylinder

110

. In the illustrated apparatus, the bar

134

is rotated in the direction indicated by the arrow by a step motor

148

supported by a standard

152

extending up from carriage

138

. The motor shaft carries a pulley

154

connected by an endless belt

156

to a pulley

158

fixed to the end of applicator bar shaft

135

. Motor

148

is also controlled by controller

112

.

Still referring to

FIGS. 6 and 7

, the subject proofing apparatus also includes a cutting assembly shown generally

162

for severing the proofing material P to separate the receptor and donor sheets R and D shown in

FIGS. 8A and 9

from the roll supply of proofing material P. As evident from

FIG. 9

, the cutting assembly

162

cuts the sheet material P just behind the clamps

126

T

,

128

T

which clamp the trailing ends of the receptor and donor sheets to the cylinder

110

.

Assembly

162

comprises a carriage

164

which is moved along a pair of guide rods

166

extending parallel to cylinder

110

by a lead screw

186

extending between the guide rods and threaded through the carriage. The opposite ends of the lead screw are rotatably mounted to the machine frame and the lead screw

186

is rotated under the control of controller

112

by a motor

187

(

FIG. 6

) mounted to the machine frame. The upper surface of carriage

164

forms slides

164

a

for a slider

188

so that the slider

188

can be moved relative to carriage

164

toward and away from cylinder

110

.

Slider

188

includes a branch

188

a

which extends toward cylinder

110

and carries an electric motor

192

having a shaft

192

a

which rotates a circular cutting blade

194

under the control of controller

112

. Slider

188

may be moved between an extended position shown in dotted lines in

FIG. 8A

wherein the edge of the cutting blade

194

contacts the surface of cylinder

110

and a retracted position shown in solid lines in

FIG. 8A

wherein the cutting blade

194

is spaced away from cylinder

110

. The slider is moved between these two positions by a linear actuator

196

mounted to carriage

164

and whose armature

196

a

is connected to slider

188

. Actuator

196

is also controlled by controller

112

.

Before applying the receptor and donor sheets to cylinder

110

, the proofing apparatus is initialized. For this, controller

112

causes actuator

144

to retract carriage

138

. The controller also energizes the electromagnets so that the blade clamps

126

,

128

can be magnetically adhered to the faces of the applicator bar as shown in FIG.

7

. The controller

112

also controls the step motor

148

so that the blade clamp

126

L

faces cylinder

110

as shown in FIG.

7

. Finally, the controller controls motor

187

to position the cutter carriage

164

adjacent to one end of cylinder

110

. Upon receiving a START command via keyboard

112

a

controller

112

causes motor

124

to rotate feed roller

122

so that proofing material P is drawn from roll

116

until the leading edge of that material is located between cylinder

110

and applicator bar

134

as shown in FIG.

7

. Next, the controller energizes actuator

144

causing the actuator to move carriage

138

to its extended position shown in dotted lines in

FIG. 8A

so that the blade clamp

126

L

facing cylinder

110

move sufficiently close to the cylinder magnets

114

underlying the leading edge of material P such that the blade clamp becomes attracted to those magnets. At this point, controller

112

de-energizes the magnet

146

RL

holding the blade clamp

126

L

to the applicator bar thereby releasing that blade clamp to cylinder

110

so as to clamp the leading edge of material P to the cylinder surface.

Following the application of the first blade clamp

126

L

to the cylinder, controller

112

retracts carriage

138

to its solid line position in FIG.

8

A and rotates the applicator bar

134

to position the blade clamp

126

T

opposite cylinder

110

. At the same time, the controller controls the motor rotating the cylinder

110

under the influence of the timing signals from the cylinder shaft encoder (

FIG. 1

) to rotate cylinder

110

clockwise as viewed in

FIG. 7 through a

selected angle less than 360°, while controlling the rotation of feed roller

122

so that proofing material P is wrapped around the cylinder. Then, the controller causes the actuator

144

to move carriage

138

to it extended position so that the second blade clamp

126

T

is magnetically engaged to cylinder

110

following which the controller de-energizes the magnet

146

RT

holding that blade clamp to the applicator bar and retracts carriage

138

.

Next, the controller causes the cylinder motor to rotate cylinder

110

in the direction of the arrow in

FIG. 7

to position the blade clamp

126

T

just applied to the cylinder slightly beyond or below the cutting blade

194

as viewed in FIG.

7

. The controller then activates the blade motor

192

causing the cutting blade to rotate. The controller also energizes actuator

196

to move slider

188

to its extended position shown in dotted lines in

FIG. 8

which places the edge of the cutting blade against the proofing material P on cylinder

110

. Finally, the controller activates motor

187

which rotates lead screw

186

causing carriage

164

and the cutting blade

194

supported thereby to move along the entire length of the cylinder thereby severing the proofing material P just behind the blade clam

126

T

so as to separate the proofing material wrapped around cylinder

110

from the material supply from roll

116

. That wrap constitutes the receptor sheet R illustrated in

FIGS. 8

and

9

whose leading end trailing edges are clamped to the cylinder

110

by blade clamps

126

L

and

126

T

, respectively.

Preferably the blade clamps

126

L

and

126

T

holding the leading and trailing edges of the receptor sheet R to the cylinder are spaced apart leaving a gap or void space on cylinder

110

between those clamps. As we shall see, this space will be used to receive the blade clamps

128

L

and

128

T

which clamp the leading and trailing edges of the donor sheet D to the cylinder as shown in FIG.

9

.

At this point, controller

112

again retracts carriage

138

and rotates the applicator bar

134

to position the third blade clamp

128

L

opposite cylinder

110

. The controller also retracts slider

188

and maintains the slider at one extreme position on the guide rods

166

. The controller is also programmed to rotate motor

124

in the opposite or nonfeed direction to withdraw proofing material P back toward supply roll

116

until the leading edge of that material is located opposite the now operative blade clamp

128

L

. Then, the controller rotates cylinder

110

to a position that places the already-applied blade clamp

126

L

just above the blade clamp

128

L

on the applicator bar

134

that faces the cylinder.

Next, the controller causes the actuator

144

to extend carriage

138

so that the blade clamp

128

L

is moved to the leading edge of the proofing material from roll

116

whereupon that blade clamp is magnetically attracted to the cylinder thereby clamping the proofing material to the cylinder. Following the deenergizing of the electromagnet

146

DL holding that blade clamp to the applicator bar

134

, the controller retracts carriage

138

and controls step motor

148

to rotate the applicator bar to position the fourth blade clamp

128

T

opposite cylinder

110

. At the same time, the controller rotates cylinder

110

and activates motor

124

causing additional proofing material P to be fed from roll

116

onto the cylinder to provide a second wrap which overlies the receptor sheet R present on that cylinder. The cylinder continues to rotate until the blade clamp

126

T

magnetically clamped thereto is located just beyond or below the blade clamp

128

T

still magnetically adhered to the applicator

134

bar. Thereupon, the controller extends carriage

138

and deenergizes the magnet

146

DT

holding that blade clamp to the applicator bar so that the blade clamp

128

T becomes magnetically attracted to cylinder

110

by the magnets

114

thereon.

At this point, the controller

112

retracts carriage

138

and rotates cylinder

110

and feed roller

122

until the blade clamp

128

L

is positioned just below the cutting blade

194

. Then, the controller activates the cutting mechanism

162

as before so that the rotating cutting blade

194

severs the proofing material P just behind the blade clamp

128

T

thereby separating the donor sheet D (

FIG. 9

) from the roll supply. Finally, the controller retracts and deactivates the cutting assembly

162

and rotates the feed roll

122

in the opposite direction to withdraw the new leading edge of the material from roll

116

away from surface of cylinder

110

. The donor and receptor sheets D and R clamped to cylinder

110

as shown in

FIG. 9

are now ready to be processed in the usual way by the associated proofing apparatus.

Controller

112

may be programmed to rotate cylinder

110

by different amounts between the application of the blade clamps to the leading and trailing edges of the receptor and donor sheets. This will change the lengths of those sheets applied to the plate cylinder. The only requirement is that the void space on the cylinder left after application of the receptor sheet must be sufficiently wide to accommodate the blade clamps for the donor sheet.

After the proofing operation is completed and it is time to remove the donor and receptor sheets from the plate cylinder, the applicator

132

is operated in more or less the same way to remove the blade clamps

128

,

126

from cylinder

110

and thereby release the donor and receptor sheets from the cylinder. More particularly, the controller rotates cylinder

110

to position the blade clamp

128

T

opposite applicator bar

134

which is now is devoid of blade clamps and the controller extends carriage

138

while energizing the magnet

146

that is opposite the cylinder. The field produced by that magnet

146

is stronger than the field produced by the magnets

114

in the cylinder. Therefore, the blade clamp

128

T

is disengaged from the cylinder and magnetically adhered to the applicator bar

134

. Then, the controller retracts the carriage

138

, rotates applicator bar

134

to position a second electromagnet

146

opposite cylinder

110

and energizes that magnet.

After the controller has rotated cylinder

110

to position the blade clamp

128

L thereon opposite the applicator bar, the controller extends carriage

138

so that the operative magnet

146

attracts and removes that blade clamp

128

L

from the cylinder. This releases the donor sheet D from the cylinder so that it can be replaced by another one.

If the receptor sheet R is also to be removed, the controller again retracts carriage

138

and rotates applicator bar

134

to position the next empty magnet

146

thereon opposite cylinder

110

while at the same time rotating the cylinder

110

to position the blade clamp

126

T

opposite the applicator bar. Thereupon, the controller again extends carriage

138

and energizes that electromagnet so that the applicator bar picks up the blade clamp

126

T

from the cylinder. One more cycle of the blade applicator

132

removes the final blade clamp

126

T

from the cylinder thereby releasing the receptor sheet R from the cylinder.

Referring to

FIG. 8B

, as noted above, the magnets

146

, instead of being electromagnets, may be permanent magnets. In this event, a stripper mechanism shown in dotted lines at

202

in

FIG. 8B

may be used to strip the blade clamps

126

,

128

from cylinder

110

. Stripper mechanism

202

comprises a slider

204

which may be slidably mounted on carriage

138

and moved along the carriage by suitable motive means

206

under the control of controller

112

. For example, the motive means may comprise a driven endless belt or a motorized lead screw. Extending up from slider

204

is a curved finger or stripper member

208

which passes up and over applicator bar

134

and down into the gap between the retracted applicator bar

134

and cylinder

110

.

When it is time to strip each blade clamp

126

,

128

from the cylinder

110

, the stripper mechanism may be activated by controller

112

to engage stripper member

208

under the overhanging end

126

′,

128

′ (

FIG. 9

) of each blade clamp. When the slider

204

is moved along the carriage

138

, the stripper member

208

progressively lifts the blade clamp away from the cylinder and toward the confronting magnet

146

on applicator bar

134

with sufficient force to overcome the magnetic attraction of the blade clamp to the cylinder. Resultantly, the blade clamp adheres to the magnet

146

. Thus, by the time slider

204

reaches the end of its travel along carriage

138

, the entire blade clamp will have been removed from the cylinder

110

and magnetically adhered to the operative confronting magnet

146

on the applicator bar

134

.

The

FIGS. 6

to

9

invention embodiment has all of the attributes of the one shown in FIG.

1

. It is further advantaged in that all of the blade clamps may be handled by a single blade applicator or dispenser. Therefore, it requires less room in the associated proofing, imaging or printing apparatus.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained. Also, certain changes may be made in carrying out the above method and in constructions set forth without departing from the scope of the invention. For example, the travelling cutting blade

194

may be substituted by a hot wire movable toward and away from cylinder

110

. Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein.

Number	Name	Date	Kind
3581257	Priessnetz	May 1971	A
3670646	Welch, Jr.	Jun 1972	A
4138102	Palmer	Feb 1979	A
4528906	Hasegawa	Jul 1985	A

Method and apparatus for magnetically clamping printing plates

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

US Referenced Citations (4)