SELECTABLE PHASE CROSS-WEB PERFORATOR

Abstract: A perforation assembly (55) has a backup roller (56) placed on one side of a web (W) and a perf knife (65) rotatably held on the opposite side. The backup roller (56) runs at a constant surface speed substantially matched to that of the web (W) which is tensioned around the roller (56) and supported thereon. A servo motor (5) rotates the perf knife into engagement with the web (W) and with the backup roller (56), which then carries the knife (65) past a nip, perforating the web (W) without loss of speed during the perforation impact. The perf knife (65) rotates out of engagement with the web (W) and continues to accelerate up to a sensor (68) which triggers application of a braking torque by the servo motor (5), bringing it to rest at a home position. The backup roller (56) thus serves as an energy-storage mechanism which engages and maintains the perf knife (65) at the web speed once the perf knife (65) has been moved to the engagement point adjacent the nip region. Because the perf knife (65) is passively synchronized by contact with the backup roller (56), the backup roller (56) and perf knife (65) may rotate on different circumferential diameters without the high inertia of a mechanically coupled gear train. The inertia of the perf knife (65) holder is significantly reduced, allowing a simple servo (5) to quickly move the perf blade (65) to engage with a short response time, to recycle to home position with a relatively quick recovery time, and to be actuated in arbitrary phase relation to the rotation of the backup roller (56) at arbitrarily selected times as the web (W) passes adjacent thereto. A preferred system is an electrographic print system, wherein electronic printer drive signals provide timing synchronization for actuating the knife (65) to form perforations in the printed web (W). Position sensors (68, 69) synchronize the motor braking and locking power cycles, allowing fast response and high accuracy perforation of webs moving at one hundred feet per minute or more.

Description: SELECTABLE PHASE CROSS-WEB PERFORATOR Technical Field The present invention relates to perforators as used in continuous web printers, and more particularly to perforators that form a line of perforations which extend across the direction of movement of the web. Such perforators are used as sub-assemblies in web printing systems, for example to form a line of perforations for a tear-off section of a business form, a manually removable coupon in an advertising print, or other such applications wherein printed matter is required to have a portion or sub-part which is to be cleanly separable from another portion or sub-part. Most printing processes, particularly those requiring multiple colors, require precise justification of the printed graphics with the dimensions of the printed sheet. In the case of a continuous web printer this entails precise positioning of the various print stations and synchronization of the image areas of the print rollers or other image- applying mechanisms. This also necessitates similar registration, justification or synchronization with the related punching, perforating, and cutting mechanisms in the print line which apply perforations and reduce the web to sheets of a final size. As currently practiced, web printers involve a large roll of web material such as plastic, newsprint or paper which, in general, successively passes through one or more print stations and is then punched or perforated following the printing but before being cut into final sheet form. The continuous print web allows tension to be maintained on the print surface at all times, typically by using idler rollers and the like, and this in turn leads to a well defined print geometry and stable spacing between the various printing and cutting stations of the assembly. In printers of the prior art, one approach to perforation of the printed work is to run the web between a pair of opposed rollers, one of which is a hard steel backing roller, and the other of which, called a perf roller, carries a narrow-bladed knife positioned so that it rotates into contact with the paper and perforates the paper at a nip formed with the backing roller. Both the backing roller and the perf roller are coupled, by fixed mechanical gearing or otherwise, such that they rotate in opposite senses but with an identical peripheral speed, which is set equal to the web speed. The provision of a gear coupling between the two rollers assures that their speeds are identical, so they contact the web at a stationary nip, thus eliminating the possibility of shear or ripping of the paper as the knife rotates into the tangentially moving web in the nip area. However, a pair of rollers coupled in this manner constitutes a cumbersome mechanical assembly of relatively high mechanical inertia, and is limited in flexibility as to the timing and spacing of its engagement with the paper. This assembly is therefore most useful for forming relatively fixed or repetitive patterns of perforation, or for performing perforations at a small set of predetermined locations, and is thus a system of limited potential. It would therefore be desirable to provide a more flexible perforation assembly for printing systems. Summary of the Invention This is accomplished in accordance with an embodiment of the present invention by providing a perforation assembly wherein a backup roller is placed on one side of a web, and a perf knife is rotatably held on the opposite side at a home position out of contact with the roller. The backup roller runs at a constant surface speed which is substantially matched to that of the web; the web, in turn, is tensioned around the backup roller and supported thereon. To make a perforation line, a servo motor propels the perf knife up into a position to engage the web at the backup roller, and the knife is driven by engagement with the backup roller so that it continues to rotate in engagement with the backup roller, past the nip position, perforating the web. The perf knife then continues to rotate further, out of engagement with the web, until it reaches a sensor which triggers a reversal of servo motor current to apply braking torque to the knife. The knife then comes to rest at a home position, ready to commence another cycle of operation. The backup roller thus serves as an energy-storage mechanism which engages and maintains the perf knife at speed once the perf knife has been moved to the engagement point adjacent the nip region. The servo motor which drives the perf knife need only apply a sufficiently large torque impulse to bring the knife quickly intc engagement at an adequate speed which approximates the web speed, and thereafter apply reverse braking torque between the brake point and home position. Preferably the servo also continues to accelerate the knife after it passes the nip and until it reaches the brake point, thereby reducing the overall recycling period. Significantly, because the perf knife is passively synchronized by contact with the backing roller rather than by gears, the backing roller may rotate on a different, preferably larger, circumferential diameter than the perf knife, and the inertia of the perf knife holder may therefore be significantly reduced. In particular, when the perf blade is clamped in a roller or other holder, the holder need only have sufficient bending rigidity to maintain the perforation force along the width of the web, and need have neither a large diameter, a solid body, nor the high inertia of a mechanically coupled gear train. This allows the perf blade to engage with a quick response time, to recycle to home position with a relatively quick recovery time, and to be actuated in arbitrary phase relation to the rotation of the backup roller, and at arbitrarily selected instants as the web passes adjacent thereto. A preferred system employing the invention is an electrographic print system, wherein images are generated by electrically controlled latent imaging or direct printing, for example, using a multi-electrode printing cartridge driven by an imagewise series of generally multiplexed electrical drive signals. A number of common printers have this construction such as "ionographic or charge transfer" printers, laser printers and more generally, electrographic printers. In this embodiment, line synchronization signals available from the imaging portion of the printer provide, with appropriate offset, the control signal for initiating perf knife actuation. Brief Description of the Drawings These and other features of the invention will be understood by reference to the description herein taken together with the drawings of a representative embodiment of the invention, wherein: Figure 1 shows a print system of the prior art; Figure 2 shows a prior art perforation assembly such as used in the system of Figure 1; Figure 3 illustrates one embodiment of the perforation assembly of the present invention; Figure 4 illustrates rotational velocity in a representative cycle of the perforation assembly of Figure 3; and Figures 5, 5 A and 5B illustrate a perf blade holder adapted to the assembly of Figure 3. Detailed Description The structure and advantages of the present invention will be best understood after a consideration of prior art printing and perforation systems as illustrated in Figures 1 and 2. The prior art system 1 shown in Figure 1 involves a generally extensive mechanical assembly in which a large supply roll WR of web material, such as newsprint or other paper, provides a web W of continuous print substrate which extends through the assembly 1 past one or more printing stations, 10, 20... at which graphics or text images are applied to the web, and proceeds through a perforator 50 which perforates, punches, or otherwise carries out mechanical operations on the web short of physically separating the web into sheets. The web then passes into a cutter/handling assembly 60 which may cut the web into sheets of a standard size, e.g. book, booklet, or newspaper size sheets, and may also stack, fold, sort, bind, or otherwise handle tie final output of the printer. In general, perforations are commonly applied across the web, or parallel to the direction of travel, or both. Cross-web perforations are commonly used where a section of a paper or form is to be manually torn off and used as a separate document, such as an entry blank, a ticket, or a return form. Perforations running in the direction of travel may serve a similar function, and may be used together with cross-web perforations to define rectangular tear-out sections such as small coupons, graphic windows, or other bounded generally rectangular segments. Figure 2 illustrates a representative prior art perforation assembly for placing cross-web perforations in the moving web. In such a device, a perforation knife 2, which is essentially a sharp comb is secured in a first roller A and a second or backup roller B is mounted in a rigid frame opposite to the rol er A. The rollers are driven at the web speed, and a pair of drive gears, Gl , G2, attached to the respective rollers couple the rollers so that they always move synchronously, i.e. at the same speed as the web and in counterclockwise and clockwise directions such that the nip between the two rollers defines a substantially stationary contact region. As noted above, such an arrangement is characterized by high inertia, and because the perf blade is fixed in a synchronously operated roller, has limited flexibility as regards timing and spacing of perforations. Figure 3 shows a cross-web perforation assembly 55 in accordance with the present invention. Assembly 55 includes a backup roller 56 around which the web is positioned to wrap by idler rollers 57a, 57b, and a perf knife assembly 58 opposed to the backup roller. The perf knife assembly 58 includes a fixed mounting 60 such as a frame with a pair of pillow blocks for securing shaft bearings at a defined position across from roller 56, and a pivoting knife holder 62 which holds and adjustably positions a perf knife 65 so that it can rotate up against the web and perforate it as the web passes over the backup roller 56. The rotating holder 62 provides a support of high bending stiffness to hold the perf knife straight. It may be a shaft such as a steel shaft of diameter approximately one inch having a groove therein in which the perf blade and a plurality of adjusting clamp screws and adjusting jacks are fitted. The details of mounting the perf blade in such a roller are well known, and are similar to constructions as employed, for example, to hold planer blades in molding planes or wood jointing machines, and need not be described in detail here. It suffices to note that in general the perf knife is mounted so as to contact the backing roller 56 uniformly, and is a somewhat flexible blade made of thin spring steel sheet, which is adjusted to have a preload of approximately one to ten mils against the backup roller, thus assuring that the knife dependably presses with sufficient force to perforate the thin web across the full width of the knife blade. As further indicated in Figure 3, a source of motive power is provided to the backup roller 56 to maintain it rotating in direction R at a constant speed substantially equal to the web speed. The rotatable knife holder 62, however, is not coupled to roller 56 but instead lies in a resting state with the perf blade 65 contacting neither the web nor the backup roller. Perf blade 65 extends outward from the pivot point (not numbered) by a distance greater than the separation of that pivot point from the surface of roller 56, and lies generally at a home position that is close to, but not contacting, the web W. In the preferred embodiment, a servo motor S indicated in phantom is connected to the rotatable blade-holder 62, and is electrically actuated to rotate the blade upward into engagement. The blade itself is made of spring steel which may for example have a thickness of approximately .65 millimeters, and height of approximately 2.3 centimeters, and in a representative embodiment extends for a length of approximately 26 centimeters, slightly more than the width of the web W. This blade is a flexible saw-like or comb toothed blade set in a bearing-mounted shaft which in one prototype embodiment had a maximal outer diameter of approximately thirty-six millimeters, less than half the diameter of the backup roller 56. Thus the backup roller 56 had a mass over four times as great as the blade holder 62, with an even higher disparity in rotational inertia. This disparity in size allows the backup roller to couple energy into the pivoting holder 62 without slowing substantially when the perf blade 65 engages the web, and to carry the perf blade along substantially synchronously with the web despite the absence of direct drive coupling between the rollers. Furthermore, the perf blade is of thin spring steel, and may flex and bend as it engages the roller 56 thus assuring that it maintains a high degree of pressure along the entire perforation line through the web without having so high a degree of rigidity as to rip the delicate web as it travels. Operation of the perf blade proceeds as follows. When a web position which is to be perforated approaches the nip of the perforator assembly 55, the servo motor S is actuated to rotate shaft 62 up from the home position and quickly bring the perf blade 65 up to approximately the rotational speed of backup roller 56. The blade engages the web and the backup roller 56 and is carried along by motion of the web, undergoing additional angular acceleration so that it moves synchronously into and past the c ontact nip and out of engagement with the web. As the knife continues rotating, it passes a first sensor 68 located in the housing 58 and this triggers a control circuit which reverses the current applied to the servo motor S. The servo motor S therefore brakes the shaft rotation, progressively slowing it down. When the knife 65 reaches a second position a second sensor 69 detects its presence and an electromagnetic lock is applied to the servo motor to lock the holder 62, securing the knife in position at or just beyond the sensor 69. This stopping position, referred to as the home position, is approximately π/6 radians below the point at which the perf blade would engage the web, a location sufficiently close to the web that the blade may be quickly accelerated into an operative position. In the prototype embodiment, the complete cycle from servo motor advance, through perforation to braking and return to home position can be effected in approximately 90 milliseconds, allowing perforation to be effected up to about 10 times per second as the web moves therepast. By locking the device in the home positi an, the blade is maintained ready at a fixed location to be propelled into engagement with the backup roller, and the servo motor may be repeatedly driven to effectively bring the blade into engagement with the web at a precise instant in time, with an accuracy on the order of a millisecond or less. This has proven to be sufficiently accurate to place perforations within the tolerance band for perforations which is currently accepted in the industry today. Figure 4 shows the movement of the perf blade holder during a representative cycle. The abscissa plots velocity, while the ordinate plots time or rotational position, with angle of the blade, starting at a home position of zero degrees, indicated at selected points. The origin is 31° before the web contact portion. As shown, the blade holder starts off resting at the home position and is accelerated by the servo S until it rotates 31 °, at which time the perf blade engages the web. The web is carried synchronously with or by the backup roller, which in this prototype was a 2.940 inch diameter hardened steel roller moving at 178 RPM, i.e., a surface speed of 27.5 inches/second. Thus, as the blade contacted the web at the 31 ° position, it engaged the backup roller and despite the energetic impulse of perforation impact was then smoothly carried along at the web speed for approximately 5°, while the idler rolls maintained the web closely in contact with the backup roll, so that no ripping would occur. Drive acceleration thereafter continued up to the brake cell, located at 300°. Upon reaching the brake position at 300° , the stepper drive current was reversed bringing the blade back to a low velocity at the home position where the servo armature was locked to keep the blade stationary. As shown, the initial drive impulse successfully brings the blade up to an adequate speed and thereafter blade travel is such that ripping of the web cannot occur. The entire cycle occupies approximately 90 milliseconds, and the lead time between actuation and perforation represents approximately one-half that interval. This time interval was constant for a fixed servo drive current, varying by no more than about one millisecond. Thus perforation can be laid down at an interval of as little as three and one-half inches at this web speed, with a registration that is within existing industry tolerances. With this construction, the perf holder can complete a cycle before the backup roller has undergone a complete revolution, and may be actuated to perform several perforations on a single page, or to perforate different pages at different locations, allowing much greater flexibility in arranging the print process line or producing final prints, as regards areas such as layout of two-sided copy, design of forms, and other aspects of creating prints. In Figure 4, it should be observed that, except for the constant plateau in angular velocity during engagement with the heavier backup roller at the nip region, the servo actively accelerates or retards the perf holder. The servo may be continuously powered between the zero degree home position and the brake sensor position, at which time the drive current is reversed. While the Figure shows substantially linear velocity profiles, it will be understood that in fact the regions on both sides of the plateau, where the perf holder is driven by the servo, will in general be slightly curved due to the characteristic energy output of the servo and the velocity-dependent rotational energy of the perf blade holder. Figure 5 illustrates the construction of the perf blade holder in the system measured in Figure 4. As shown in Figure 5, the rotary holder 62 is a generally solid cylindrical roller shaft which extends across the width of the web and into which a broad flat face 63 has been formed, for example by milling, to support the perf blade 6.5. A plurality of holes 63a extend along the length of face 63 perpendicular to its surface, which are tapped for receiving threaded hold-down bolts, while a second plurality of holes 65a oriented perpendicularly thereto extend through the shaft and are threaded for at least part of their length to accommodate jack screws. The jack screw holes lie in the plane of face 63, centered under the blade position, which is indicated by B in the cross- sectioned view, Figure 5A. As shown in that Figure, the shaft is also milled flat on the side opposite the blade, forming the face F into which the jack screw holes are drilled. Additional material is removed along an edge 68, further reducing the overall inertial mass of the perf holder assembly 62. Figure 5B shows a cross-sectional view of the assembly 6 together with the perf blade 65 and a clamp bar 62a, in a system with a backup roller 56 and guide rollers 57a, 57b. The clamp bar is a solid prism of substantially triangular cross section extending the length of face 63 with deep set holes on a spacing matching that of holes 63a for clamping the blade against the face. This provides a rigid support for the perf blade 65, and enhances balance by its approximate symmetry with face 68. It also enhances clearance from the printed face of the web and contributes to the low weight of the assembly. As is shown in Figure 5B, the perf roller 62 and backup roller 56 lie on parallel axes in a plane P at a separation such that the perf blade contacts the web just as i t rotates through the plane and contacts roller 56. Thus, the blade remains in contact with the web only when the web is essentially tensioned flat against roller 56, and it remains in contact for only a short arcuate distance 8 subtending 2-5° of arc, as it is engaged and accelerated by contact. The assembly then brakes, and returns to the home position which is shown in Figure 5B. Figures 5-5B show a prototype system which is assembled by machining and customizing commonly available elements of metal stock. However, it will be realized that the invention may desirably be practiced with machine elements that are fabricated with less costly manufacturing steps, or with materials specifically selected to enhance the performance of the perforator. Thus, for example, a several fold reduction of mass and corresponding reduction in cycle time may be obtained by substituting a low weight, e.g., cast magnesium, blade holder for the steel shaft of Figure 5. Furthermore, synchronization of the perf actuation with the imaging areas of the web, although discussed only briefly, will be understood to be effected by any conventional web-or process- synchronization or registration technique. These may include, for example synchronization with electrical print line signals, synchronization by laying down and detection of registration marks on the web itself, or other techniques. The invention being thus disclosed and described, further variations and modifications will occur to those skilled in the art. All such variations and modifications are considered to lie within the scope of the invention as set forth in the claims appended hereto.

Claims: What is claimed is: A perforation assembly comprising a backup roller having an inertial mass and rotating at a substantially constant speed means for tensioning a web over a contact region of the backup roller a perforation blade suspended opposite the backup roller in a position to rotatably engage the backup roller with an interference fit through the web means for selectively rotating the perforation blade into contact with the web such that it engages the backup roller to perforate the web at said contact region v/hereby said perforation blade is moved in synchrony with the web by said engagement tc perforate the web cleanly without tearing. 2. A perforation assembly according to claim 1, further comprising means for bringing the perforation blade to rest at a home position out of engagement with said web. 3. A perforation assembly according to claim 2, wherein the means for rotating the perforation blade includes an electrically actuable servo motor. 4. A perforation assembly according to claim 3, wherein the perforation blade is mounted in a rotatable assembly having an inertial mass substantially less than the inertial mass of the backup roller. 5. A perforation assembly according to claim 4, wherein the servo motor is actuated with an energy to drive the rotatable assembly from a stationary state at the home position to approximately said constant speed when it rotates into engagement. 6. A perforation assembly according to claim 4 wherein the servo motor accelerates the perforation blade prior to engagement and decelerates the perforation blade after the engagement to bring the blade to rest between successive perforations, while the backup roller moves continuously at a substantially constant rotational speed. 7. A perforation assembly according to claim 1, wherein said means for selectively rotating includes an electrically powered motor actuated to accelerate the blade into contact, and to further accelerate the blade after contact, thereby reducing return time between successive perforations. 8. A perforation system comprising energy-storing means for storing rotational energy means suspending a web for motion with said energy-storing means a perforation blade adjacent said energy storing means, and means for moving the perforation blade into contact with the web to initiate a perforation cycle wherein the energy-storing means rotates the perforation blade through a perforating position synchronously with the web so as to perforate the web without ripping, said perforation blade being otherwise mechanically decoupled from said energy storing means and independently advanced into said contact to effect perforations. 9. A perforation .system comprising energy-storing means for storing rotational energy means suspending a web for motion contacting said energy-storing means at a nip a perforation blade mounted adjacent said nip, and means independent of said energy-storing means for moving the perforation blade into contact with the web such that the energy-storing means engages the perforation blade to carry it through the nip at a substantially constant velocity synchronously with the web to complete a perforation. 10. A perforation system according to claim 9, further comprising a printer for printing on a web, and electronic control means, coupled to said printer and to said means for moving the perforation blade, for synchronizing perforation of the web in relation to features printed on the web by said printer. 1 1. A perforation system according to claim 10, wherein said energy storing means is a backup roller having a rotational inertia greater than rotational inertia of said perforation blade. 12. A perforation system according to claim 11, wherein said backup roller rotates at a constant speed, and said perforation blade accelerates and decelerates between successive perforations. 13. A perforation system according to claim 12, wherein said constant speed is greater than twenty-five surface feet per minute. 14. A perforation system according to claim 9, wherein said means for moving moves said perforation blade to effect plural lines of perforation on a single page. 15. A perforation system according to claim 9, wherein said means for moving moves said perforation blade at times effective to effect perforations at different positions on different pages. 16. A method of placing cross perforations in a moving web, such method comprising the steps of providing a backup roller having an inertial mass and rotating at a substantially constant speed in contact with a web extending along a web path suspending a rotatable perforation blade assembly opposite the backup roller and positioned for rotation into an interference contact with said backup roller at a nip, and actively driving the perforation blade assembly to a contact position in the web path such that the blade is then driven by contact without geared coupling to the backup roller and is passively carried along past the nip synchronously with the v/eb whereby the perforation blade assembly rotates with selectable phase and enhanced speed to effect cross-web perforations. 17. The method of claim 16, wherein the inertial mass of the backup roller is at least four times as great as that of the perforation blade assembly. 18. The method of claim 16, wherein the step of actively driving includes actively decelerating said blade to a surface speed faster than said constant speed during a blade return cycle. 19. The method of claim 16, wherein the step of driving further includes actively accelerating said blade during a blade return cycle. 20. The method of claim 19, wherein the step of driving further includes actively decelerating said blade during said blade return cycle.

Inventors: SHRAMEK JAMES F, SHRAMEK, JAMES, F.
Applicants: DELPHAX SYSTEMS, SHRAMEK JAMES F, SHRAMEK, JAMES, F.
Application year: 1997
Main classification: B26F1
IPC codes: B26D1, B26D5, B26D7, B26F1, B65H35