Apparatus For Transverse Cutting Or Perforating A Continuously Advancing Web

Abstract

In an apparatus for repetitively cutting or perforating, in a transverse direction, a continuously advancing web by means of a rotating blade that cooperates with a stationary counterblade having a cutting edge that lies in the plane of motion of the web; the counterblade being inclined with respect to the axis of rotation of the rotating blade by an angle of approximately 2.degree. maximum, the angular orientation of the apparatus with respect to the direction of motion of the paper can be varied precisely by micrometric means in order to compensate for intentional differences between the tangential speed of the rotating blade and the translational speed of the web.

Description

BACKGROUND OF THE INVENTION

The invention concerns an apparatus permitting the severing or the making of detachable perforations on a continuously advancing web or strip. It is also to be understood that the invention contemplates the cutting and piercing of stacks of material. In the specification, the word "cut" will have the meaning "cut or detachable perforations."

DESCRIPTION OF PRIOR ART

Progressive sheet cutters are well known in this connection, see the U.S. Pat. No. 3,401,585, Schmermund, the cutting as disclosed in this patent being achieved by a device which has one rotatable straight edged blade arranged to turn on an axis and cooperate with another straight fixed blade, the two blades being adapted to cross each other at all of their surface points during each revolution of rotating blade. In a construction, such as that disclosed by Schmermund, the blade and the counterblade are both inclined at equal angles but in opposite sense with reference to the axis of rotation at the moment where they cross at their midpoints. Furthermore, the tangential speed of the rotating blade is equal to the speed of advance of the web.

SUMMARY OF THE INVENTION

Now, on the one hand, it has been found, that these speeds can be very different, i.e., that the tangential speed of the rotating blade can be as much as 10 times the linear speed of advance of the web or can be as little as one half that speed without reducing the sharpness of the cut or of the perforation.

Furthermore, the elasticity of the steel blade permits the application of certain elastic deformations by stress at the moment of the shearing, without causing inconvenience. The permissible limits of such deformations are, of course, very small near the points of fixation or attachment points, and attain their maximum value at the midpoint between two successive attachment points. It is clear that the deformations of the two blades are additive when these blades cross each other forcibly. Moreover, the very structure of the frame supporting the rotating blade is susceptible of elastic deformations and, further still, the rotational axis of such rotating blade is mounted in its bearings with necessary and non-negligible mechanical tolerances.

All these tolerances are additive and one may say that the blades are pushing progressively against one another and repulse each other and each assumes an arc-shape. This is the same as saying that a given point of the edge of the lower blade might be situated at a distance from the axis of rotation which is smaller than the radius of the rotating blade; this difference at its maximum being equal to the sum of the admissible flexures for the blade at this point of their crossing. In order to avoid a damaging shock to the blades and to the entire machine, it is necessary that the two blades begin their engagement at the first point of crossing by gliding without stress; the stress increasing progressively beginning at this null value. By the same token, it is preferable that the stress be essentially zero at the moment when the rotating blade leaves the fixed blade, that is to say, at that end of this fixed blade which is opposite the last point of engagement. Since these considerations have been duly verified by a large number of tests, it is possible to construct a rotating cutting apparatus of simpler form, whose particular construction permits the solution of problems in format changes, that is to say, in the variation of the spacing of the cut.

One of the objects of the present invention is, therefore, to specify a rotating cutting apparatus with straight, inclined blades and in which the rotating blade is parallel to its axis of rotation so that its edge describes around that axis a cylinder of revolution which is effectively tangent to the moving plane of the web, while the counterblade which is obliquely positioned with reference to said axis of rotation has a slightly offset edge with reference to the plane of motion of the web, the two ends of said counterblade being situated on the surface of the imaginary cylinder described by the edge of the rotating blade. Preferably, the counterblade is mounted as rigidly as possible at its ends, whereas the adjustment screws 15 which are placed along its entire length, form stops to limit its flexing to a predetermined value which is a function of the angle of inclination of said blade with reference to the axis of rotation and also of the dimensional characteristics of the machine.

It is of advantage to mount the counterblade on the frame of the cage of the moving blade and the entire assembly is mounted so that it may be pivoted with respect to the direction of motion of the web in such a way as to permit adjustment of the angle which the cutting line makes with respect to that direction.

The invention will be better understood by the following description which makes reference to the attached drawing in which:

FIG. 1 is a perspective schematic view of the device according to the invention;

FIG. 2 shows the determination of the maximum flexure of the blade without respect to the angular scale;

FIG. 3 shows the web as seen from above at the time of the cut; the angles being considerably enlarged.

TURNING NOW TO THE DRAWINGS

In FIG. 1 a device for progressive cutting is placed on a conveyor table on which a continuous web 1 having marginal perforations is fed in the direction of arrow F1. For greater clarity, the only elements of the table which are shown are a roller 2 and two pin conveyors 3a and 3b which engage the perforations in the margins of the web. It is to be understood, however, that additional conveyors are spaced transversely of those identified as 3a and 3b, the driving pins thereof being visible in the drawings of FIG. 1. The cutting device is placed on a support 4 which is a part of the frame of the table between the two pairs of conveyors 3a and 3b as will be understood from the drawing.

This device comprises a frame or cage of which only the rectangular brackets 5a and 5b are represented, but it should be noted that those brackets are, in fact, rigidly connected with one another. One of them, 5a, slides freely on the support 4, and the other, 5b, carries a pivot 6 which is free to rotate in a seat provided in the support 4. By means not shown, any lifting of the frame 5a, 5b with reference to support 4 is prevented.

A shaft 7, parallel to the plane of the transport table, rotates in bearings within brackets, 5a, 5b, and extends through bracket 5b. A toothed wheel 8 is keyed to the end of shaft 7. This wheel 8 is intended to be driven in rotation in the direction of arrow F2 by means of a toothed belt, which is not shown, and by the same motor which also drives the conveyors 3a and 3b. The driving pulleys (not shown) of these conveyors and that of the belt are preferably arranged respectively on the two "takeoffs" of a gear box 16.

The shaft 7 carries two flanges 9a and 9b between which blade 10 extends parallel thereto. Hence, this blade is rotated around shaft 7, and its edge generates the lateral surface of an imaginary cylinder of revolution of radius R. The shaft 7 is placed at a distance R from the plane of motion of the web so that the edge of the mobile blade 10 brushes said plane at each revolution.

A fixed counterblade 11 is mounted transversely between the brackets 5a, 5b of the device within an opening extending transversely of the transport table with its ends being mounted as rigidly as possible on the base plates of said brackets 5a and 5b. This counterblade includes an edge portion that extends the entire length of the spacing between the two flanges 9a and 9b. The end 11b of said edge is located within the plane of motion of web 1 and also lies on the line representing the geometrical projection of the axis of rotation of the mobile blade 10 onto the plane of motion. The blade 11 and this projection of the axis of rotation form a small angle whose maximum value will be evaluated hereinafter and the other end of the edge 11a is then slightly raised with reference to the plane of motion in such a way as to bring it back, as exactly as possible, to a distance R from the axis of rotation. In the example shown, the end 11a is displaced in the direction of arrow F1 relative to the end 11b.

It is believed that it will now be clear that in each revolution of shaft 7, the end 10b of the mobile blade comes into shockless contact with the end 11b of the counterblade. Since the blades are angularly displaced, they cross one another and glide over one another in a shearing movement which determines the angle of the cut of web 1. During the course of this gliding motion, the edge of the counterblade 11 represents a secant to the cylinder generated by the edge of blade 10; the two blades press against each other and flex lightly, these flexures attaining their maximum values when the blades cross each other midway of their length and then the flexure thereof decreases uniformly until it becomes null, this being achieved when the cooperation of the blades corresponds to the contact of extremities 10a and 11a, which are both situated at a distance R from the axis of rotation. An instant after attaining this position, the blades are no longer in contact until the following rotation.

In order to obtain a clean and regular cut, it is necessary that the blades 10 and 11 be sufficiently rigid so as not to vibrate. In order to accommodate these contradictory demands, rigidity and applied flexure, it is necessary that the angular displacement of these blades be small.

Referring now to FIG. 2, there is shown a geometric construction which permits the calculation of the maximum value of this displacement (for greater clarity, the angular scale has been considerably enlarged). In this drawing, O represents an end view of the axis of rotation, P is the plane of motion of the web, C represents the cylinder of radius R which is generated by the edge of the rotating blade, Oa represents the projection of axis O onto the plane of motion. In the plane of that figure the extremity 11b of the counterblade lies in Oa. The other extremity (11a) of the counterblade is first displaced in the direction of arrow F1 and arrives at 11a' and then is brought to a distance R from O, at point 11a. For a better understanding of this, one could let .theta. be the angle between O Oa and O 11a and let d be the distance Oa 11a'. If .alpha. is the angle which the counterblade 11 makes with the axis O, and L is the length of the blades:

d = L tan .alpha. = R tan .theta.

where the sagitta f of the arc Oa 11a is given by:

f = 2R Sin.sup.2 (.theta./4)

This sagitta corresponds to the sum of the maximum flexures of the two blades as they cross medially of their length. Since all these angles are small, one may, as a first approximation, equate their value in radians to those of their sines or their tangents, which results in:

.theta. = L/R .alpha.

and

f = L.sup.2 .alpha..sup.2 /8R (.alpha. in radians)

Experience shows that f may have a maximum value of 7 .times. 10.sup. .sup.-4 L, which corresponds to a maximum value of .alpha. such that:

.alpha..sup.2 = 56 .times. 10.sup. .sup.-4 .times. R/L

or

.alpha. = 10.sup..sup.-2 .sqroot.56 R/L

R is limited mechanically and L depends on the width of the webs (less than 80 cm). The ratio R/L may be as high as one-fourth. In that case, .alpha. can be at most 0.0374 radians, or .alpha. < 2.degree.10'.

It is obvious that in order to obtain a cut in the strip or webs which is perpendicular to the direction F1 of the motion thereof, the mobile blade 10 can be perpendicular to F1 only if its tangential speed is equal to the speed of motion thereof. This is possible if the apparatus is intended to make cuts of predetermined format. But, to make use of the aforementioned fact that the speeds can be made quite different, and in order to effect changes in the spacing of the cuts by varying the ratio of said speeds, particularly by means of a gear box with two take-offs, (as has already been mentioned before), the mobile blade 10 is inclined by an angle .beta. with respect to the perpendicular to F1.

The view of FIG. 3 shows the web 1 resting on the counterblade 11 and the projection of the mobile blade 10 on said web at the moment where the two blades cross at A at the starting edge of the web. As in FIG. 2, the angles are greatly exaggerated for greater clarity. Let .gamma. be the angle of inclination of the counterblade with respect to the straight line P which is perpendicular to F1. As the mobile blade moves, the web 1 is cut progressively beginning at A until the blade 10 crossses the counterblade 11 at C. During this time the web has travelled in the direction of F1 and the point A of the web has arrived at A', the line of cut is therefore A'C. The ratio of the tangential speed of the blade 10 to the lateral speed of motion of the web is therefore given by .rho. = BC/AA'.

In order that the cutting line be perpendicular to F1, i.e. parallel to P, which is generally desired, it is sufficient that AA' = a tan .gamma. (a is the width of the web) and since

BC = a (tan .beta. + tan .gamma. )

P = tan .beta. + tan .gamma./tan .gamma.

Since these angles are small, it is possible to set with sufficient accuracy .rho. = .beta. + .gamma./.gamma. = .alpha./.gamma.

(.alpha. equals the angle between the two blades which is constant by construction).

If .beta. = 0, then .rho. = 1; the two speeds are equal and the length of the cut equals 2.pi. R if the device carries a single moving blade. Starting with this format one can, therefore, obtain a format which is n times smaller by multiplying the tangential speed of the blade by n without changing the speed of lateral motion of the web; this can be done, for example, with the aid of a gear box with the two take-offs mentioned above. The ratio of speeds is, therefore, equal to n and in order that the cut be parallel to P, it is necessary that n = .beta./.gamma. or .gamma. = .alpha./n. To achieve that, it is sufficient to pivot the entire device around pivot 6 on support 4 (FIG. 1). In order to permit a precise regulation, pivoting is achieved with the aid of a micrometric screw 12 connected to the frame of the device and travelling in a nut 13 which is part of support 4.

If it is required to cut thick stacks of sheets having, for example, six sheets and five carbons, it is necessary that the shearing angle .alpha. be at least 1.degree. so that by approaching the limiting angle of 2.degree. 10' calculated beforehand and beginning with a format 2.pi. R with .beta. = 0 and .gamma. = .alpha. = 2.degree., it is easy to obtain a format which is 5 times smaller, for example, all this while maintaining the perpendicularity of the cutting line, by taking .gamma. = 2.degree./5 = 24' (.beta. = 1.degree. 36') and by multiplying the tangential speed of the mobile blade by a factor of 5.

In practice, the usual formats vary between 3 inches and 12 inches, i.e. a ratio of 1:4.

Since .rho. = .beta. + .gamma./.gamma., it would also be possible to vary .rho. by varying .gamma. without varying .beta., i.e. by a different mechanical construction, namely that of leaving the frame of the mobile blade fixed with respect to the table and by making only the counterblade pivot around one of its extremities, the other extremity held by suitable means at a point within a portion of the surface of the cylinder described by the edge of the rotating blade. In this case, of course, angle .alpha. must vary. It is clear that the variation of .gamma. alone allows less flexibility for adjustment since .gamma. appears in both the numerator and the denominator of the ratio .rho., (for example, if at the outset .beta. = .gamma. = 1.degree. then to obtain .alpha. < 2.degree. 10' one has .rho. = 2, but in order to obtain .rho. = 8, one must put .gamma. .apprxeq. 8' and the total angle .alpha. is 1.degree. 8', which is insufficient for thick stacks. This arrangement is, therefore, only possible with very small angles and, therefore, only for single sheets or very thin stacks.

One could also vary only .beta., which would entail the same inconveniences; in this case, the counterblade would remain fixed and the frame of the mobile blade would pivot as described before.

If it is necessary to cut (or to perforate) only webs which are not very thick, the shearing angle can be very small and, therefore, it is possible to do without the control of the inclination of the device on its support in order to reduce the cost.

Further, by looking at FIG. 3, one sees that if the speed of rotation of blade 10 increases from the value which makes the trace of the cut A'C perpendicular to F1, then the point A of the web relocates to A'1 which lies between A and A'. If .rho. diminishes, A'1 passes beyond A' with respect to A. In any case, this displacement equals A.sub.1 ' A' = AA' - AA.sub.1 ' and A.sub.1 'A' = a[.gamma. - .alpha.1.rho.] , where .gamma. and .alpha. are in radians and the displacement is positive if A.sub.1 ' is between A and A' and it is negative if A.sub.1 ' is to the right of A' in FIG. 3.

Since .rho. should vary within the ratio 1:4, for example, by passing through the values between 0.5 and 2, or 1 and 4, or 1.5 and 6, or 2 and 8, without ever exceeding the value 10, it is easy to make a table or a graph which gives the various absolute values of the coefficient .gamma./.beta. - 1/.rho., and one finds that the best possible combination consists in taking .gamma. = .alpha./3 while .rho. varies between 2 and 8 in order that the maximum value of this coefficient be as small as possible, and this maximum value is then 5/24.

For example, if .alpha. equals 6 minutes of arc, i.e. 18 .times. 10.sup..sup.-4 radians, then the maximum displacement is: a .times. 18 .times. 10.sup..sup.-4 .times. 5/24 or a .times. 3.75 .times. 10.sup..sup.-4 and for a strip width of 400 mm, for example, this maximum displacement will be 0.15 mm, which is quite acceptable for commercial printing material, even if it is intended for an optical reader. (As a matter of fact, any type of reader may be used.)

One should note that when detachable perforations are desired, one of the blades is provided with teeth which are generally of the order of 4 mm long and whose spacing is of the order of one millimeter (almost always equal to 1.2 mm). Since the edges of the blades have a width of at least approximately 0.3 mm, the flat blade will always bear against at least two teeth of the toothed blade as long as the angle .alpha. is less than the limit for which tan .alpha. = 0.3/1.2 = 1/4, that is to say, as long as .alpha. is less than 14.degree.. The values of .alpha. encountered in all the preceding examples are very much smaller than this limit and there is no fear that the crossing of the blades will take place between two teeth which would, of course, be unacceptable since the flexure could not be maintained and a lateral shock on each tooth would result.

Naturally, numerous modifications could be made to the aforementioned construction of the device, either in the mode of transport of the web or their disposition, or in the arrangement of the cutting device. Thus, for example, it could be advantageous to reverse the elements previously described and place the mobile blade in the lower position beneath the traveling web while the counterblade would be in the superior or upper position. It is also contemplated that where it is desirable to have a double cut in the web, i.e., the blade would include an edge which gives two cutting lines, with one each of the cutting lines straddling the line of folding, such an arrangement would permit the faster removal of the narrow strips as they fall down.

It could be useful in certain cases, in order to facilitate the motion of the paper, that the pairs of conveyors such as 3a and 3b (FIG. 1) be replaced by one single conveyor extending across the cut, or at least one of the conveyors 3b may be in frictional engagement with the paper above it. In order to achieve this, it is necessary only that the marginal zones of strip 1 not be cut, that is to say, one makes a cut between the edges by limiting the length of the edge of at least that blade which is located underneath the web, so as to perform a cut of predetermined length across the web.

Claims

What is claimed is:

1. An apparatus for performing periodic, sequential penetrations in a continuously advancing material web, comprising:

a. a supporting frame including first drive means for the material web;

b. a transversely extending assembly pivotally mounted on said supporting frame and including:

1. laterally associated bracket members;

2.

2. a straight shaft extending between and associated with the bracket members, said shaft being positioned parallel to the plane of the material web and further having an axis of rotation and provided with second drive means;

3. a straight-edged rotatable cutter blade having a cutting edge and mounted on and rotatable about said shaft in parallelism to said axis of rotation so that, when rotated, the cutting edge generates a rectangular cylinder of revolution; and

4. a flexible straight-edged counterblade having a cutting edge including terminal end points and being held in its operative position solely by attachment of said end points to said bracket members and at an angle with respect to said axis of rotation and in such a position that at least said two end points of the cutting edge of the counterblade always lie on the surface of said cylinder of revolution, that portion of said counterblade between said end points being free of support; whereby during operation of the apparatus, the cutting edge of the counterblade cooperates with the cutting edge of the rotatable blade to perform the periodic, sequential penetrations of the material web and the flexibility of the counterblade alone permits the passage of the rotating blade beyond the counterblade.

An apparatus as claimed in claim 1, wherein at least one of the cooperating cutter means has a longitudinal extent of lesser length than the width of the material to be severed to thereby retain parallel uncut areas on oppositely disposed edges of the material to thereby sustain continuous, uninterrupted travel thereof.

3. An apparatus as claimed in claim 1, wherein movement of the counterblade means relative to its longitudinal extent is limited by adjustable means.

4. An apparatus as claimed in claim 3, wherein the adjustable means limits the degree of local bending of said counterblade means to a predetermined value, said adjustable means including plural elements.

5. An apparatus as claimed in claim 1, wherein the rotatable cutter means has a tangential speed relative to the speed of travel of the advancing material which may vary from 0.5 to 10 and preferably from 2 to 8.

6. An apparatus as claimed in claim 1, wherein the rotatable cutter means and the counterblade means from an angle which has a value in radians at most equal to (10.sup..sup.-2 .sqroot.56R/L), R being the radius of rotation of the rotary cutter and L being said longitudinal extent of the counterblade means.

7. An apparatus as claimed in claim 6, wherein the angle between the counterblade and the line perpendicular to the direction of motion of the continuously advancing material is effectively equal to .alpha./3 and is approximately equal to 0.003 radians.

8. An apparatus as claimed in claim 1, wherein at least one of the bracket members is mounted adjustably relative to the direction of motion of the continuously traveling material by a micrometric means to thereby control the angle of cut with respect to the travel of the material, with the angle .alpha. formed by the rotary blade and the counterblade remaining constant.