Patent Application
20100101386
The present invention relates generally to printing presses, and more particularly to web printing presses with web-conversion machines.
U.S. Pat. No. 5,692,440 discloses a cutting device used to accomplish the transverse cutting of running webs into products of variable lengths and is usable particularly in a folding apparatus that is situated downstream of a rotary printing press. The cutting device has a cutting cylinder support that carries two diametrically opposed cutting cylinders which rotate with, as well as with respect to, the cutting cylinder support. Each cutting cylinder carries a plurality of cutting blades with these blades being engageable with cutting strips located on the surface of a counter cutting and collection cylinder. The cutting cylinder support is rotatable at a first speed and the cutting cylinders supported by it are rotatable at a second speed.
U.S. Pat. No. 7,338,425 discloses a variable length cutting device includes a cutting cylinder and a transfer cylinder. The transfer cylinder cooperates with the cutting cylinder for cutting a ribbon into signatures having a desired cutoff length. An adjustable diameter portion of the transfer cylinder can be moved in a direction toward and away from the central axis of the transfer cylinder for adjusting the desired cutoff length of the signatures.
A variable cutoff web cutting apparatus is provided including a first knife cylinder having a first segmented knife blade. The first knife cylinder rotates about a first cylinder axis in a direction corresponding to a web travel direction and the first segmented knife blade rotates about a first knife axis in a direction opposite the web travel direction. The cutting apparatus also includes a first counterpart cylinder and the first segmented knife blade contacts the first counterpart cylinder to perforate a web. The cutting apparatus also includes a second knife cylinder having a second knife blade. The second knife cylinder rotates about a second cylinder axis in the direction corresponding to the web travel direction and the second knife blade rotates about a second knife axis in the direction opposite the web travel direction. The cutting apparatus also includes a second counterpart cylinder and the second knife blade contacts the second counterpart cylinder and cuts the web adjacent to where the first segmented knife blade perforated the web, so as to sever the web and create a signature.
A knife cylinder is also provided including a cylinder body rotating about a cylinder axis and a knife shaft rotating about a knife axis. The knife shaft is rotably connected to the cylinder body. The knife cylinder also includes a knife blade rotably connected to the knife shaft and a rocker arm connecting the knife shaft to the cylinder body such that a radial distance between the cylinder axis and the knife axis may be adjusted by adjusting the position of the rocker arm.
A method of varying a length of signatures using a web cutting apparatus is also provided. The method includes the steps of rotating a knife blade about an axis of a knife cylinder body in one direction; rotating the knife blade about an axis of a knife shaft in a second direction; and adjusting a first distance between the axis of the knife cylinder body and the axis of the knife shaft and adjusting a second distance between the axis of the knife shaft and a tip of the knife blade. The knife blade cuts a web and creates signatures.
The present invention is described below by reference to the following drawings, in which:
In the web offset printing process, a continuous web of paper is transported through a printing press. Near the beginning of the press, one or more printing units apply ink to the web to repeatedly create a pattern, or impression, of text and images. At the end of the press, a web conversion machine, such as a folder, is typically used to cut and fold the web into signatures.
There are many known ways to convert a web into signatures. The web is commonly slit into ribbons, which can be stacked on top of each other and then former folded. Some folders, such as pinless former folders, cut the ribbons or web and deliver one or more streams of signatures. Other folders, such as combination folders, commonly introduce additional folds, such as half-folds and quarter-folds. The ribbons or web are typically cut with a knife cylinder having a knife blade.
Signature length is the distance between successive cuts. Signature length may be varied by changing the knife cylinder diameter, or by accelerating and decelerating the knife cylinder between cut events. To avoid damage to the signature during cutting, it is desirable to match the velocity of the knife blade with the velocity of the web or ribbons being cut.
Signatures may be created in web offset printing presses when a rotating knife, mounted on a knife cylinder, engages a rotating anvil, mounted on an opposing anvil cylinder, and cuts a web, or alternatively ribbons. The knife cylinder and anvil cylinder may be directly geared to each other and therefore are phase locked. In such instances, the knife cylinder is sized so that a diameter of the knife cylinder matches a diameter of a print cylinder, which prints images on the web, and the rotational frequency of the knife cylinder is equal to the print unit rotational frequency. A knife tip, or a point that pierces the web to create signatures, extends outside a theoretical pitch diameter of the knife cylinder. The knife tip sweeps an arc through the web, through some angle. The knife is fixed to the knife cylinder and therefore can travel at a velocity that is greater than the velocity of the web. During cutting, there often is a short interval of time when there is a slight velocity differential between the knife tip and the web. A urethane body running parallel to the knife and extending about an inch on both sides of the knife may be employed to pinch the web help minimize an affect of the velocity differential. The pinch is localized, yet wide enough to tension the web about the knife tip and enable a clean cut. Some velocity differential, or knife tip gain, may be preferred, but excessive knife tip gain is not.
Successive cutting cylinder pairs may employed, with first and second cylinder pairs performing a portion of each cut. The second cutting cylinder pair may be over sped in order to accommodate a small range of product length variation. After the second cutting cylinder pair makes a cut the resulting signature is accelerated to move the signature away from the rotating knife so the knife tip does not damage a tail edge of the signature. A velocity-matched knife tip may be employed to cut the web because velocity differentials between the knife tip and the web can damage the product. A first partial cut, completed by the first cutting cylinder pair, only perforates the web, so an over sped knife will elongate the perforation in a direction of the web travel.
Creating signatures of a different length can require changing the rotational frequency of the cutting cylinder pairs relative to the rotational frequency of the associated printing cylinder, which can cause a velocity mismatch between the knife tip and the web. A velocity mismatch can cause tearing of the signature, instead of a clean cut. To prevent such tearing, the knife tip may be driven so that the velocity of the knife tip in the direction of the web travel equals the web velocity or have some minor gain above a nominal web velocity. Drive motors can be fashioned to alter the rotational velocity within a single cycle to vary the position of the knife. The cutting cylinder pair can be accelerated so that the cutting cylinder pair is in a proper position to cut the web, then decelerated back to match the web velocity at a moment when the knife engages the associated anvil. This method of accelerating and decelerating may be limited, however; because the amount of torque required to accelerate and decelerate the knife and anvil cylinders can increase beyond the capability of the drive motors, beyond a certain rotational velocity.
Knife blades 26, 28 convert a web 30 into signatures 32. While web 30 travels past knife cylinder 18 at a velocity V3, knife blade 26 partially cuts web 30 in a cross-web direction. The partial cut may be a series of slits, for example. Web 30 then approaches cylinders 20, 24 and knife blade 28 cuts web 30 at positions where knife blade 26 did not cut web 30, in a manner finishing the cut started by cylinder pair 12, creating signatures 32. Cylinders 22, 24 may be geared together and thus phase locked. Transport tapes 16 may be provided between cylinder pairs 12, 14 to prevent snap back caused by a cutting event.
Motors 201, 203 may rotate cylinder bodies 19, 21 counterclockwise, respectively, which in a preferred embodiment may, via gearing, rotate knife blades 26, 28 clockwise, respectively. Motors 205, 206 may rotate counterpart cylinders 22, 24 clockwise, respectively. Motors 201, 203, 205, 206 may be controlled by a controller 200.
Web cutting apparatus 10 may create signatures having different cut lengths by rotating cylinder bodies 19, 21 at various rotational frequencies for different signature lengths, while maintaining a constant velocity of knife tip 84 (
In an alternative embodiment a single cylinder pair cuts web 30 into signatures 32, operating in a manner similar to each cylinder pair 12, 14, but equipped with a knife blade having a continuous trim edge.
Gears 50, 52, 54 may be are centered about center axes CA1, CA2, and CA3, respectively. In this embodiment, gear 52 is a compound gear. Rocker arm 56 is connected to knife shaft 48 on one end and screw rod 58 on the other end and includes a pivot point at compound gear 52. A radial position of knife shaft 48, and thus a radial distance R1 between center axes CA1, CA2, may be adjusted by pivoting a section of rocker arm 56 between center axes CA3, CA2, about center axis CA3 using screw rod 58. This may be accomplished by rocker arm 56 swinging knife shaft 48 about compound gear 52. Screw thread 60 is fixed to cylinder body 21 and supports screw rod 58, such that screw rod 58 may be translated within screw thread 60.
In a preferred embodiment, gear 50 is stationary and compound gear 52 is rotated about gear 50 via rotation of cylinder body 21. As compound gear 52 rotates, compound gear 52 rotates gear 54, which is coupled to knife shaft 48. The gearing ratios between gears 50, 52, 54 may be fixed so that knife blade 28 is properly phased and is traveling at the desired velocity as knife 28 contacts web 30. Gear 50 may be provided with a phasing mechanism for initial set-up to correct the phasing of knife blade 29 with respect to web 30 to accommodate signature length adjustments. In an alternative embodiment, cylinder body 21 and knife blade 28 may each be rotated by a separate motor.
Knife blade 28 is oriented on knife shaft 48 so that knife blade 28 extends radially away from center axis CA1 when center axis CA2 is located below CA1. As knife shaft 48 rotates about center axis CA2, a tip 84 of knife blade 28 travels a cycloidal path, relative to a stationary reference. As knife blade 28 cuts web 30, knife blade 28 is preferably a straight line that is perpendicular to web 30.
For clarity, knife blade 28 is shown directly above and below center axis CA1 in
Counterpart cylinder 24 rotates about a center axis CA4 with a surface velocity V2 equal to a web velocity V3. In a preferred embodiment, counterpart cylinder 24 can include a rotating anvil 44, which provides a backstop for knife blade 28 as knife blade 28 cuts web 30. Anvil 44 rotates about CA4 as knife blade 28 rotates about center axis CA1. Anvil 44 can be configured and geared in relation to cylinder 24 as knife blade 46 is configured and geared in relation to cylinder 20. Anvil 44 can be eccentrically mounted on a rotating anvil shaft and rotated about the rotating shaft to change a radial distance of anvil 44, in relation to CA4, to match radial distance R1. Accelerator tapes 16 may grips signatures 32 as signatures 32 are formed. In another embodiment, accelerator tapes may be present between knife cylinder pairs 12, 14 to prevent snap back which may be caused by a break in web 30 or by a cutting event.
In another embodiment counterpart cylinder 24 can include a continuous blanket of high density urethane to provide a continuous cutting rubber for knife blade 28. The continuous blanket may be a changeable blanket sleeve that is replaced with a blanket sleeve having a different circumference with each change in signature length. When changeable blanket sleeve are employed center axis CA4 may be translated to accept sleeves of different circumferences.
Cylinder pair 12 (
In
In one embodiment, counterpart cylinder 24 is covered with a high density urethane to provide a continuous cutting rubber. A drawback to such a design is that knife blade 28 may engage counterpart cylinder 24 at a different circumferential location with each revolution of counterpart cylinder 24. Alternately, counterpart cylinder 24 could have a changeable outer sleeve, and a new sleeve could be installed whenever signature length L is changed so that knife blade 28 engages the sleeve at the same location with each sleeve revolution.
A preferred embodiment has a counterpart cylinder 24 designed like knife cylinder 20 with a cutting rubber in place of knife blade 28, and the cutting rubber being engaged by knife blade 28 with each knife cylinder 20 revolution. The cutting rubber could be mounted eccentrically to facilitate changing the cutting rubber height.
Knife blade 28 is essentially driven by two independent drive inputs. During operation of knife cylinder 20, a motor connected to drive gear 74 rotates knife cylinder 20 about center axis CA1 at an angular velocity W1. As knife cylinder 20 rotates, center axis CA2 of knife shaft 48 rotates along with knife cylinder 20 about center axis CA1 at angular velocity W1. At the same time, gears 50, 52, 54 are driven so that knife shaft 48 rotates about CA2 at an angular velocity W2, where W2=−W1. Knife shaft 48 thus rotates in a direction opposite the rotational direction of knife cylinder 20, and in this embodiment knife shaft 48 performs one full revolution about center axis CA2 for each revolution of cylinder body 21 about center axis CA1.
Because knife blade 28 is being rotated in two opposite directions simultaneously, the net velocity of knife blade 46 in the direction that web 30 is traveling substantially equals the velocity of web 30, as knife blade 46 cuts web 30. Thus, knife blade 28 must be rotated fast enough about center axis CA2 to compensate for a velocity component opposite the direction web 30 is traveling, which is a product of rotation of knife blade 28 about center axis CA1, as knife blade 28 cuts web 30.
A length of signatures 32 is controlled by angular velocity W1 of knife cylinder 20. For a given web velocity V3, signature length L is increased by reducing angular velocity W1 and decreased by increasing angular velocity W1. Unlike conventional methods, adjusting signature length L advantageously does not require changing angular velocity W1 between cuts by accelerating and decelerating cylinder body 21 or changing knife cylinder pitch radius R3. Signature length L is infinitely variable within the operating window of knife cylinder 20.
Knife shaft 48 runs at an angular velocity W2 about center axis CA2 at radial distance R2 necessary for the velocity of knife blade 28 to equal the velocity of web 30. Angular velocity W2 and radial distance R2 are also adjusted so knife blade 28 is in a proper position to cut web 30 as knife shaft 48 approaches nip 100.
A tangential velocity, in relation to web 30, at which knife blade 28 cuts web 30 is dependent upon radial distance R1, radial distance R2, angular velocity W1 or angular velocity W2. For a set pitch radial distance R3, radial distance R1 is varied in proportion to radial distance R2 to achieve a desired tangential velocity of knife blade 28 at which knife blade 28 cuts web 30. Radial distance R2 may be varied by adjusting a length of knife blade 28, replacing knife blade 28 with a blade of a different length or adjusting how knife blade 28 is attached to knife shaft 48. As angular velocity W1 is adjusted to change a cutoff length of signatures produced by web cutting apparatus 10, angular velocity W2 is varied accordingly so that knife blade 28 is in proper position to cut web 30. Thus, radial distance R1, radial distance R2, angular velocity W1 and angular velocity W2 may be adjusted to satisfied desired tangential velocity and cutoff length values.
When knife blade 28 is in the position along line 92, at the bottom of the guillotine cutting motion, knife blade 28 is still being rotated about central axes CA1, CA2 at angular velocities W1, W2, respectively. Along line 92, tip 84 of knife blade 28 has a tangential velocity V4, in a direction opposite of web 30 travel, due to rotation of knife blade 28 about central axis CA1 and a tangential velocity V5, in the direction of web 30 travel, due to rotation of cylinder body 21 about central axis CA2. Because velocity V4 is greater than velocity V5, tip 84 is traveling at a net velocity Vn in the direction of web 30 travel (Vn=V4−V5).
By adjusting radial distance R1 with rocker arm 56 (
While radial distance R1 is adjusted to achieve the desired tangential net velocity Vn, radial distance R2 may also be adjusted so that the sum of radial distances R1 and R2 exceeds pitch radius R3 by a desired amount. In one embodiment, knife blade 28 is eccentrically mounted on knife shaft 48 for adjustment of radial distance R2.
The guillotine motion of knife blade 28 reduces an angle Y of contact, in related to center axis CA1 (
Each scenario 100, 102, 104, 106, 108 has a different desired signature length L. For a constant web velocity V3, to decrease signature length L, angular velocity W1 of cylinder body 21 about center axis CA1 is increased. As angular velocity W1 of cylinder body 21 about center axis CA1 is increased, angular velocity W2 of knife shaft 48 is proportionately increased. To ensure that a tangential net velocity Vn of knife blade 28, in the direction of web 30 travel, equals a velocity V3 of web 30, a radial distance R1 between center axis CA1 and center axis CA2 is decreased as angular velocity W2 is increased. The distance from center axis CA2 to knife tip 84 (
As shown, to change signature length L from 11 to 5.5 inches, while maintaining a knife tangential net velocity Vn equal to web velocity V3, requires a reduction in radial distance R1 from 2.6261 inches to 2.1324 inches.
As an additional embodiment, cylinder body 21 and knife shaft 48 can be embedded into a rotating sleeve. A degree of freedom exists between the cylinder body 21 and the sleeve where the rotational frequency can be different between the two elements. Since the drum is embedded in a sleeve with a surface velocity matched to the web, there is no undue strain or change in tension to the web at the cut event.
The sleeve would have a series of rings spaced in the axial direction with openings between rings in accordance with a profile of knife blade 28. Knife blade 28 extends beyond cylinder body only through these openings as it penetrates anvil 44. The rings are constructed with urethane to eliminate snap back during the cut event. The rings may be connected at various locations that do not interfere with the rotation of knife blade 28. The sleeve has to be velocity matched to web 30 for this purpose and is only needed if tension of web 30 is sufficient to cause snap back. The sleeve would be removed in a signature creation scheme that isolated the snap back or minimized web tension.
A further embodiment incorporates two knife blades on opposite sides of knife cylinder 20. The second knife would help balance knife cylinder 20 and would advantageously reduce angular velocity W1 of cylinder body 21 about center axis CA2 by a factor of two.
As an additional embodiment, the signature creation could be generated by a single knife cylinder using a cut on cylinder approach, rather than the two knife cylinders 18 and 20 shown in
A further embodiment is a knife cylinder pair without a fixed theoretical pitch radius. For longer signatures, the two cylinders in the knife cylinder pair can pivot about a respective gear to increase the center to center distance. The knife shaft radius relative to the cylinder body would still move, but movements would be over a smaller range. A smaller knife adjustment range would be required.
In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.
