WO2002016244A2

WO2002016244A2 - Rotary cutter with automatic knife offset

Info

Publication number: WO2002016244A2
Application number: PCT/US2001/023206
Authority: WO
Inventors: Roger A. Jacques
Original assignee: Moore North America, Inc.
Priority date: 2000-08-23
Filing date: 2001-07-24
Publication date: 2002-02-28
Also published as: WO2002016244A3; AU2001282950A1

Abstract

A scissor-action rotary cutter for high speed sheeting from a continuous web is described. Conventionally, the rotary knife is offeset to provide a square cut for, e.g., a constant knife velocity following web speed, and making one revolution per cut length, so that the sheet length equals the knife circumference. A knife offset compesensation is necessary to achieve a perpendicular transverse cut for a selected cut length that differs from that for which the knife offset is predetermined. The invention provides a cutter section that is automatically positioned for the offeset adjustment, if any, required when the sheet length is entered. Positioning is preferably accomplished by a gear motor, encoder, coupling and lead screw connected between the cutter and the web feed section. The knife offset compensation is determined as a function of the knife offset and the difference between sheet length and knife circumference.

Description

ROTARY CUTTER WITH AUTOMATIC KNIFE OFFSET

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to rotary cutters and, more specifically, to a rotary cutter for use in transversely severing a web of material to produce sheets having predetermined dimensions.

For a constant velocity rotary knife wherein one knife revolution occurs per cut sheet length, the knife must be angularly offset to achieve a square transverse cut for a selected cut length. For a constant knife velocity following web speed and making one revolution per cut length, a square cut occurs only for a sheet length equal to the knife circumference.

With reference to FIGURE 1 , line A-B corresponds to the desired cut line. Line A-C illustrates the knife offset and the distance B to C is the cut offset. In this example, L is the cut sheet length and W is the web width. If the web is not moving when a rotary knife having an A-C offset makes the cut, then the cut edge will not be square to the sides by length B to C. When the length to which the web is to be cut is changed for different jobs, it is common for the operator to not bother to or to forget to, perform a mechanical offset adjustment to ensure a square cut. This can lead to problems during subsequent processing such as cross folding. Also, even when an adjustment is contemplated, the relationship of the offset is usually linked to speed differences between the knife cutter and the web rather than to the selected cut length, which is the more practical parameter for the operator.

It is an object of the invention to provide an assembly for automatically compensating the offset of the knife to ensure an orthogonal scissor cut. According to the presently preferred embodiment, knife offset is correlated to cut length. As a result, it is possible for the invention to provide for automatic compensation every time a new cut length is entered into the operator panel.

DESCRIPTION OF THE DRAWINGS

These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view showing the relationship of knife offset to web feed;

FIGURE 2 is a schematic plan view showing a rotary cutter with automatic knife offset according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As is evident from the discussion above with reference to FIGURE

1 , to achieve a scissor cut of the moving web material, the knife is conventionally offset with respect to a transverse direction of the web. Thus, if the web is not moving when the rotary knife makes the cut, the cut edge will not be square to the sides by the length B to C. When the web is moving, for a constant knife velocity following web speed and making one revolution per cut length, a square cut is achieved for sheet length equal to knife circumference. If the sheet length is changed, the knife offset must be adjusted.

With reference to FIGURE 2, a rotary cutter system for sheeting a web is schematically illustrated in plan view. In the illustrated embodiment, the web 10 is fed, from the right in the illustrated configuration, with the aid of web feed tractors 12. From the web feed tractors, the web is fed to margin slitters 14 which sever the perforated edges of the web. In systems where the web is not edge perforated, and a feed mechanism other than the web feed tractors, such as feed rollers or the like, are provided, the margin slitters may be omitted.

Downstream of the margin slitters, web pull rolls 16 are provided for positively feeding the web 10 toward the rotary cutter. A rotary cutter assembly for sheeting the web to sheets of predetermined length is schematically shown at 18. In the illustrated embodiment, the rotary cutter component is a cutting cylinder 20 that is disposed vertically above the web for periodically effecting a transverse cut as the cutting cylinder is rotated about its longitudinal axis. As illustrated, a knife element 22 extends along the outer periphery of the cylinder 20 in a generally part helical path to define the knife offset (Ko ). An anvil 24 is provided below the web for countering the rotary knife action to effect a clean severance of the web. In the illustrated embodiment, the rotary cutter and anvil are provided as a unit that is mounted for pivotal movement together about pivot mount 26, so that clean severance can be achieved irrespective of a knife offset adjustment, as described in greater detail below.

The severed sheets 28 are received downstream of the rotary cutter assembly by overspeed transport belts 30 and are aligned with the aid of a ball rail edge aligner 32 or the like. The sheets are then stacked and/or transported for further processing.

In accordance with the invention, a knife offset adjustment assembly 34 is provided for selectively pivoting the rotary cutter assembly 18 about pivot mount 26 to adjust the knife offset according to sheet length. In the illustrated embodiment, the angular position of at least the rotary cutter component is controlled with a gear motor and encoder assembly on instruction from a control unit 36 in response to entry of a desired sheet length by the operator. More specifically, as illustrated in FIGURE 2, a threaded lead screw or adjustment shaft 38 is connected via a coupling 40 to a helical gear reduction unit 42 and a reversible drive motor 44. The motor and gear reduction unit are typically available as a gear motor unit. DC power is supplied to the drive motor to selectively drive the motor 44 in a clockwise or counterclockwise manner. Further, a conventional shaft encoder 46 is connected to the rear shaft end of the motor to provide output signals indicating the angular displacement of the motor. The shaft encoder output is shown as the conductor(s) identified by reference numeral 48.

The gear motor 44 rotates the lead screw 38 to displace the longitudinal axis of the rotary cutter component with respect to the web. By way of example, for the case where the system is initially set to knife velocity following web speed and making one revolution per cut length, the longitudinal axis of the cutting cylinder is initially disposed generally transverse to the longitudinal axis of the web and the knife is defined as a part helix on the outer circumference of the cutting cylinder so as to define the knife offset. When sheet length is changed, the web feed speed to knife speed ratio is increased or decreased, and the knife offset must be adjusted. This can be achieved by displacing the longitudinal axis of the rotary cutter with respect to its initial position transverse (perpendicular) to the longitudinal axis of the web. In accordance with the invention, this adjustment is achieved automatically with the adjustment assembly described above. More specifically, according to an input sheet length, the gear motor selectively rotates the lead screw clockwise or counterclockwise to determine an inclination of the longitudinal axis of the rotary cutter with respect to a perpendicular orientation across the web, to ensure a square cut according to the web sheet length.

By ascertaining the angular displacement of the motor and knowing the ratio of reduction of the gear reduction unit, the angular displacement of the cutting cylinder or other rotary cutter can be accurately determined. By utilizing an overall gear reduction in excess of e.g. 1000:1 , very accurate and stable angular positioning of the rotary cutter can be achieved.

In the embodiment illustrated in FIGURE 2, the web feed, rotary cutter and cut sheet take-up assemblies are provided as separate sections mounted on a common support or stand with a small space therebetween. The rotary cutter assembly is securely held in place but able to rotate about pivot mount 26 as described above. A small amount of movement plus or minus from the centered position of the cutter assembly is equal to the knife offset compensation for the selected cut length. The cutter section is automatically positioned by the gear motor for the offset required when the sheet length is entered into the control unit. In the illustrated embodiment the gear motor, encoder, coupling and lead screw are connected between the cutter and web feed assemblies to move the cutter assembly with respect to the web feed assembly to achieve the desired offset compensation. However, this adjustment assembly could be connected between the cutter assembly and the cut sheet take-up assembly between the cutter assembly and another fixed support structure.

The kriife offset compensation, Koc, is a function of the knife offset, Ko, and the difference in sheet length, L, from the knife circumference, CK as follows.

Referring again to FIGURE 1 , the axis of the rotary knife is initially generally perpendicular to the web as shown at A-B. The knife on the rotary cutter is offset from one side of the web to the other by the distance B to C Thus, as the web is being fed, the knife ideally cuts starting at point A and terminating point C with the knife surface moving from B to C along the web path.

If the knife surface speed and the web speed are equal, then the knife will move from point A to point C as the web moves from point B to point C and the cut will be straight, that is perpendicular to the sides of the web. If the knife speed is unequal to the web speed, then there will

be a cut error Δc. The error Δc is the difference in distance traveled by

the web and the knife, dw and d«.

Δc = d|< - dw-

distance equals velocity times time, d« = VK X t.Ac and d_w = V x t_AC. Accordingly, Δc = dK - w = VK x t_Ac - Vw x tAc. where tAc = the time for the knife to

travel from A to C, the distance from B to C = Ko

m lrev C

Δc = (V_κ -V_w)t_AC, V_κ = V_w — x— - x κi^xn C

= ^ V, w sec L in sec

where L = the cut length and CK = the knife circumference. Substituting, we get:

where t AC

Substituting, we get:

Rearranging, we get:

Δc = K_r 1 - — , where K_or = -Δc equation (1)

In the case where the length to be cut equals CK, the

circumference of the knife, then Δc = 0. Thus, the knife is inclined at the outset so as to achieve a perpendicular cut when the knife circumference is equal to the cut length.

L < CK, VK > Vw, Δc = +, Δc is in the direction of web travel, Koc is

in the direction towards the infeed, the maximum + Δc = Ko.

L > CK, VK< VW, ΔC = -, Δc is in the direction opposite to the web

traveland Koc is in the direction towards the outfeed, for L = 2 CK, ΔC = -

Ko.

EXAMPLE

For a typical example, Ko equals .05 inches, B to C in FIGURE 1.

CK = 8.5 inches, knife diameter = 8.5/π = 2.705 inches.

Koc = -05 (1 - L/8.5)

The gear motor contains control means or has control means provided such as the encoder 46 or an incremental counter or transmitter for electronic control of the rotary speed, the rotary phase and the motor brake with respect to both opposing directions of rotation of the shaft. These controls (encoder) are effected by the control unit shown schematically at 36 via a signal lead 48. As an example, the control unit receives input data such as a sheet cut length via an input device 50, which may be, for example, a keyboard or touch screen, and determines the knife offset compensation. A knife offset compensation map may be provided with a predetermination of offset for a given sheet length, knife offset, and knife circumference, or the appropriate offset can be calculated using equation 1 , based on input and/or stored parameters such as knife circumference and the like, and the web sheet length. The processor generates a suitable output signal to motor 44 to control encoder 46 to adjust the rotary cutter from the current position to one appropriate to the newly input cut length. Concurrently the processor adjusts web feed velocity and/or knife velocity to achieve the desired knife to web speed ratio for the input cut length.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A rotary cutter system for transversely severing a web of material to produce sheets having predetermined dimensions comprising: a rotary cutter assembly including a rotary cutter component mounted for rotation about a longitudinal axis thereof and having a knife element mounted thereon that extends along a generally part helical path with respect to said longitudinal axis, said so that when said longitudinal axis is disposed transverse to a longitudinal direction of feed of said web material and said web is fed at a predetermined^* speed with respect to a rotary speed of said rotary cutter, said knife element of said rotary cutter component severs said web so as to achieve a square transverse cut; at least said rotary cutter component being pivotally mounted so as to be selectively pivotable to be oriented at an angle relative to a position transverse to said web feed direction; a web feed assembly disposed upstream of said rotary cutter assembly for feeding web material from a source of web material towards said rotary cutter assembly; a cut sheet take-up assembly for receiving cut sheets downstream of said rotary cutter assembly; a knife offset adjustment assembly operatively coupled to said rotary cutter component for selectively angularly offsetting said rotary cutter component with respect to said transverse position; and a control unit for selectively actuating said knife offset adjustment assembly to adjust a position of said rotary cutter component according to a cut sheet length.

2. A rotary cutter system as in claim 1 , wherein said rotary cutter component is mounted in opposed facing relation to an anvil for engaging said knife component.

3. A rotary cutter system as in claim 2, wherein said anvil is mounted to pivot with said rotary cutter component.

4. A rotary cutter system as in claim 1 , wherein said knife offset adjustment assembly is coupled to said web feed assembly to selectively displace said rotary cutter component with respect to said web feed assembly, thereby to angularly offset the same with respect to said transverse position.

5. A rotary cutter system as in claim 1 , wherein said knife offset adjustment assembly comprises a gear motor, an encoder, and a driven shaft, said driven shaft being threadably engaged with a fixed support structure for selectively displacing said rotary cutter component with respect to said fixed support structure.

6. A rotary cutter system as in claim 1 , wherein said control unit includes an input device for inputting a cut sheet length.

7. A rotary cutter system as in claim 6, wherein the knife offset adjustment amount is calculated according to the following equation:

where K₀= knife offset, Cκ= rotary cutter circumference, L=cut

sheet length, K₀c = knife offset adjustment, and where Koc- -Δc.

8. A rotary cutter system as in claim 1 , wherein said web feed assembly comprises feed rolls mounted so as to be disposed at spaced locations across the web material.

9. An apparatus for transversely cutting a web of material to form blanks of equal length, the apparatus comprising a rotary cutter and an infeed assembly for feeding the web to the rotary cutter, the rotary cutter comprising a cutting cylinder having at least one knife blade thereon, a counter-blade extending below the cutting cylinder, and a frame supporting the cutting cylinder so that said cutting cylinder is rotatable about a longitudinal axis thereof and so that said cutting cylinder is pivotable from a position transverse to a direction of web feed to any one of a plurality of knife offset positions angularly offset therefrom, and an automatic adjustment assembly for automatically positioning said cutting cylinder to one of said plurality of knife offset positions according to a sheet length to be cut.

10. An apparatus as in claim 9, wherein said automatic adjustment assembly comprises a control unit for selectively actuating a knife offset adjustment assembly to adjust a position of said cutting cylinder according to a cut sheet length.

11. An apparatus as in claim 10, wherein said knife offset adjustment assembly comprises a gear motor, an encoder, and a driven shaft, said driven shaft being threadably engaged with a fixed support structure for selectively displacing said cutting cylinder with respect to said fixed support structure.

12. A rotary cutter system as in claim 10, wherein said control unit includes an input device for inputting a cut sheet length.

13. A rotary cutter system as in claim 12, wherein the knife offset adjustment amount is calculated according to the following equation:

where Ko= knife offset, Cκ= rotary cutter circumference, L=cut

sheet length, where Koc= knife offset adjustment, and where Koc= -Δc.

14. An apparatus as in claim 10, wherein said knife offset adjustment assembly comprises a gear motor, an encoder, and a driven shaft, said driven shaft being threadably engaged with a threaded receiver provided on said infeed assembly for selectively displacing said cutting cylinder with respect to said infeed assembly.