US3836089A

US3836089A - Web splicing, unwinding and forwarding apparatus

Info

Publication number: US3836089A
Application number: US00342556A
Authority: US
Inventors: C Riemersma
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1973-03-19
Filing date: 1973-03-19
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: CA1012522A; DE2412435A1; FR2222294B1; NL7403573A; FR2222294A1; GB1457583A; JPS5025968A; BE812444A; CH575875A5; IT1007473B

Abstract

An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension. The improvements include: means for maintaining a low level of tension in the web except during splicing transients and the like during which transients web tension is caused to increase whereby the periods of such transients are reduced; and, means for sensing the rate of increasing the length of web looped through the apparatus and means responsive to such rate means for preventing the length of such loop from exceeding the capacity of the apparatus. The latter improvement functions to prevent the loop of web from becoming slack.

Description

United States Patent [1 1 Riemersma Sept. 17,1974

[ WEB SPLICING, UNWINDING AND FORWARDING APPARATUS [75] Inventor: Coenraad E. Riemersma, Cincinnati,

Ohio

[73] Assignee: The Procter & Gamble Company, Cincinnati, Ohio [22] Filed: Mar. 19, 1973 [21] Appl. No.: 342,556

[52] US. Cl 242/58.1, 226/189, 242/75.4 [51] Int. Cl B65h 19/18, B65h 51/20 [58] Field of Search 242/58.1, 75.4, 75.43,

[56] References Cited UNITED STATES PATENTS 3,024,157 3/1962 Beerli 242/58.l X 3,305,189 2/1967 Butler 242/58.1 3,414,208 12/1968 Butler 242/58.1 3,645,463 2/1972 Helm 242/58.l 3,669,375 6/1973 Bruton 242/58.1

Primary Examiner-John W. Huckert Assistant Examiner-Edward J. McCarthy Attorney, Agent, or Firm-Thomas J. Slone; John V. Gorman; Richard C. Witte [5 7 ABSTRACT An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension. The improvements include: means for maintaining a low level of tension in the web except during splicing transients and the like during which transients web tension is caused to increase whereby the periods of such transients are reduced; and, means for sensing the rate of increasing the length of web looped through the apparatus and means responsive to such rate means for preventing the length of such loop from exceeding the capacity of the apparatus. The latter improvement functions to prevent the loop of web from becoming slack.

7 Claims, 9 Drawing Figures Pmmm SEP 1 1 m4 SHEET 2 OF 6 PAIENIEBSEPIYW I 3386.089

SHEET 3 [IF 6 Fig. 8

PAIENIEusEPmsu 3.886.089

SHEEI 5 [IF 6 ELECTRIC POWER DANCER ELEVATION, INCHES ABOVE DOWN STOP Pmmmsim 5.856089 SHEET 6 OF 6 Fig.9

DANCER LOAD, POUNDS 5 IO I5 '20 25 3O 40 I I I I l WEB TENSION, POUNDS WEB SPLICING, UNWINDING AND FORWARDING APPARATUS FIELD OF THE INVENTION This invention relates generally to providing apparatus for continuously forwarding web material such as one mill polyethylene into a web consuming apparatus such as a converter for manufacturing disposable diapers. Continuous forwarding is enabled through successively splicing the leading edge of a new roll of web to the trailing edge of a just depleted roll of web. Such an apparatus, commonly called an unwind stand, normally includes some means for controlling web tension during steady state operation and, to a degree, during splicing transients and the like. The present invention relates to providing a low tension unwind stand having improved means for causing and controlling increased tension in the web during splicing and other major transients whereby the equipment can be re-stabilized quickly.

BACKGROUND OF THE INVENTION In order to continuously supply a web consuming apparatus with web from a succession of rolls of web material each new roll must be spliced to the preceding roll. Desirably, this is done without diminishing the rate of forwarding web to the web consuming apparatus. Such splicing is commonly accomplished by stopping the trailing edge of the just depleted roll while the leading edge of the succeeding roll is spliced to it.

Accumulator means defining a variable length looped path for the web are provided between the splicing means and the web forwarding means to store and pay out the web required by the web consuming apparatus during the splicing interval. That is, while the trailing edge of a just depleted roll of web is stopped to perform a splice, web is forwarded to the web consuming apparatus from the accumulator whereby the length of web stored therein is diminished. After the splice is completed, tension in the web acts tangentially on the new roll of web whereby the new roll of web is caused to accelerate.

The length of web which must be provided by the accumulator during a splicing operation is dependent on the time required to perform the splice and on the time required for tension in the web to accelerate the new roll to line velocity.

Certain web converting processes require that web materials such as distensible thermoplastic films be forwarded under very low tension although the web material is capable of withstanding relatively high tension loads without breaking. An example of such converting operations is the combining of polyethylene film with cellulose pads to make absorbent disposable diapers having a substantially impervious covering. If the plastic film is cut to length while distended, and is joined with a cellulose pad before it returns to'its unstressed length, the film will cause the pad to become distorted.

The prior art discloses a variety of approaches for controlling web tension in unwind stands incorporating web accumulators. Representative prior art U.S. Patents include U.S. Pat. No. 1,637,892 issued Aug. 2, 1927 to Winthrop W. Benner et al., U.S. Pat. No. 2,062,008 issued Nov. 24, 1936 to Arthur P. Lewis et al., U.S. Pat. No. 2,242,751 issued May 20, 1941 to Owen D. McFarland, U.S. Pat. No. 2,494,402 issued Jan. 10, 1950 to William H. Mursch, U.S. Pat. No. 2,631,847 issued Mar. 17, 1953 to Clarence L. Hornberger, and U.S. Pat. No. 3,414,208 issued Dec. 3,1968 to Richard A. Butler, Jr. et a1. However, none of these approaches has solved the problems associated with low tension unwind stands in the manner nor to the degree of the present invention.

SUMMARY OF THE INVENTION The nature and substance of the invention will be more readily appreciated after giving consideration to its major aims and purposes. The principle objects of the invention are recited in the insuing paragraphs in order to provide a better appreciation of its important aspects prior to describing the details of a preferred embodiment in later portions of this description.

A major object of the invention is providing an improved, low tension, web splicing, unwinding and forwarding apparatus wherein a low level of steady state web tension can be maintained and in which web tension is increased during splicing transients in order to shorten such splicing induced transient intervals.

Another major object of the present invention is providing an improved web splicing and forwarding apparatus comprising an accumulator having an underslung, web supported dancer and means responsive to dancer rate-of-descent for preventing slack in the web looped through the accumulator.

Yet another major object of the invention is providing an improved web splicing, unwinding and forwarding apparatus comprising an underslung, web supported dancer which apparatus comprises means for normally maintaining a low level of tension in the web and means for increasing web tension during splicing transients, and comprises means responsive to the rate of dancer descent for preventing slack in the web looped through the accumulator.

These and other objects are achieved by providing an improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension. The improved apparatus includes a frame, splicing means, web forwarding means, web unwinding means including means for revolvingly mounting a plurality of rolls of web for unwinding them and braking means for applying a controllable braking force to retard such unwinding. The apparatus further includes a web accumulator means intermediate the web forwarding means and the splicing means. The accumulator means includes a vertically movable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for the web, the length of the looped path being inversely related to the displacement of the dancer assembly above the lower end of its range of travel. Means are provided for normally controlling the unwind braking force as a dependent function of dancer elevation to maintain a substantially constant low level of web tension. The improved apparatus may comprise means for maintaining substantially constant dancer loading only throughout a lower range of dancer elevations and means for increasing dancer loading in a predetermined manner with respect to dancer elevations above said lower range. Alternatively or conjunctively, the improved apparatus may comprise means for increasing, in a predetermined manner, unwind brake loading above its normal dancer-elevation-dependent value during periods when the dancer is decending at a rate equal to or greater than a predetermined rate.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a diagramic fragmentary side elevational view of a web splicing, unwinding and forwarding apparatus embodying the present invention.

FIG. 2 is an enlarged scale diagramatic side elevational view of the accumulator portion of the apparatus shown in FIG. 1 having the dancer disposed against the DOWN stop.

FIG. 3 is en enlarged scale diagramatic side elevational view of the accumulator of the apparatus of FIG. 1 having the dancer disposed against the UP stop.

FIG. 4 is a fragmentary front elevational view of the dancer assembly of the apparatus shown in FIG. 1 taken along line 44 thereof.

FIG. 5 is a diagramatic pictorial schematic of the tension control system for the apparatus shown in FIG. 1.

FIG. 6 is an enlarged scale view of the dancer operated cam and air pressure regulator shown in FIG. 5 which are used to control unwind braking as a function of dancer elevation in the apparatus shown in FIG. 1.

FIG. 7 is a graph showing the dependent relation of regulated brake pressure to dancer displacement from the DOWN stop of the dancer assembly.

FIG. 8 is an enlarged fragmentary view of the dancer rate-of-descent sensing mechanism embodied in the tension control system shown in FIG. 5.

FIG. 9 is a composite graph showing dancer loading versus dancer elevation, and showing brake-induced web tension versus dancer elevation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to FIGS. 1, 2 and 3, there is shown an improved web splicing, unwinding and forwarding apparatus 20 (alternatively referred to as unwind stand 20) which is a preferred embodiment of the present invention comprising frame 21, web forwarding means 22, roll support means 23, unwind braking means 24, web splicing means 25, web accumulator 26, transient dancer loading means 27, and dancer rate-of-descent responsive means 28.

The ensuing description of the preferred embodiment unwind stand 20 is of such an unwind stand which is configured and adjusted to unwind and forward web from 21 inch diameter rolls of one mill polyethylene, 16 inches wide, at line velocities of up to about 750 feet per minute. Such rolls weigh about 140 pounds and commonly have 3% inch diameter spools. However, it is not intended to thereby limit the scope of the present invention to such sizes and velocity.

For convenience also, the present invention is described as improving the performance of unwind stand during splicing induced transients. Although improved performance during splicing induced transients is believed to be a primary benefit of the present invention, the present invention generally improves the overall operation of unwind stand 20.

Briefly, web forwarding means 22 acts to unwind rolls 31 of web material 30 while braking means 24 provides torque to retard such unwinding in order to establish and maintain desired tension in web 30. Web splicing means 25 is provided to splice a new roll of web to a just depleted roll of web so that web can continuously be forwarded by web forwarding means 22 at a substantially constant velocity to downstream apparatus even during splicing transients and the like. Transient dancer loading means 27 enables maintaining a low level of web tension during normal, steady state op eration while providing increased web tension during splicing and other major transients. Such increased tension is provided to quickly accelerate a new roll of web whereby the length of web stored in accumulator 26 can be small as compared to the length that would be required if tension were not increased during such transients. Dancer rate-of-descent responsive means 28 is provided to increase unwind braking torque in a predetermined manner whenever the rate-of-descent of the dancer equals or exceeds a predetermined value. The predetermined manner of increasing braking torque and the predetermined rate-of-descent are selected to prevent the dancer from reaching the DOWN stop which would otherwise precipitate slack in the web..

In order to accomplish such a splice, the trailing edge of a just depleted roll of web is substantially slowed while the leading edge of a new roll of web is secured to it. During a splicing interval, web forwarding means 22 withdraws web stored in web accumulator 26. Following the splicing operation, web forwarding means 22 applies tension through the web which, acting tangentially on the new roll, causes the new roll of web to accelerate until its peripheral velocity equals and then exceeds the forwarding velocity of web 30 passing through web forwarding means 22. The fact that the roll must have a peripheral velocity greater than the forwarding velocity in order to reload the accumulator, necessitates reducing the peripheral velocity of the roll to equal the forwarding velocity before the dancer reaches the DOWN position. The dancer rate-ofdescent responsive means 28 enables doing this as will be described more fully after completing the description of the preferred embodiment of the present invention.

Web forwarding means 22, FIG. 1, comprises nip

rollers

35, 36 which are so disposed and so configured to form a nip 37 therebetween for engaging web material 30 whereby web can be forwarded to downstream apparatus.

Rollers

35 and 36 are driven by means not shown in FIG. 1 to provide the desired web forwarding velocity.

Upper and lower roll support means 23, FIG. 1, are provided

formounting rolls

31a, 31b of web material 30 so that they are freely rotatable in the unwind direction except when such rotation is retarded by braking means 24.

Braking means 24, alternatively referred to as brakes 24, comprises pneumatically actuated brakes which are secured to frame 21 so that they can act, through means not shown, to apply torque to retard unwinding rolls 31a and 31b in the direction indicated. As will later be described in more detail, the braking torque provided by brakes 24 is controllable by controlling the pressure of air supplied to them.

Web splicing means 25, as shown in FIG. 1, is provided with

idler rollers

40, 41 and 42 for guiding web 30 from roll 31a between

splicing rollers

43 and 44. Splicing means is further provided with

idler rollers

45, 46 and 47 for guiding a web from roll 31b to between

splicing rollers

43 and 44. Briefly, the splicer is prepared to perform a splice by applying pressure sensitive splicing tape 50 to the transversely extending leading edge of the new roll of web and to secure tape 50 to transversely extending support 51 so that the leading edge 53 of splicing tape 50 extends between

splicing rollers

43 and 44. The

splicing rollers

43 and 44 are mounted on eccentric axes so that when they are simultaneously rotated, they will press splicing tape 50 against the trailing edge of web 30 from a just depleted roll of web.

Because it is believed that the splicing operation and means therefore are not critical with respect to the present invention, the means for synchronizing the rotation of

splicing rollers

43 and 44 to perform the splice as described is not shown. Suffice it to say that it is believed to be within the range of skill or persons having ordinary skill in the art to provide means for synchronizing the rotation of the splicing rollers. Such means might comprise, for instance, a photo electric detector.

After a splice is completed, a new roll of web is installed on roll support means 23 to replace the just depleted roll. Then the newest roll of web would be prepared for splicing its leading edge to the trailing edge of roll 31b upon depletion of roll 31b. Thus, rolls of web 31 are alternately forwarded from the upper and lower roll support means 23 to enable web forwarding means 22 to uninterruptedly forward web 30 to downstream apparatus at substantially constant velocity.

Accumulator means 26, FIG. 1, is provided intermediate web forwarding means 22 and web splicing means 25 for the purpose of storing a loop of web of sufficient length to permit web forwarding means 22 to uninterruptedly forward web 30 to downstream apparatus even during splicing operations when infeed into the accumulator is momentarily stopped and until the new roll of web is accelerated to line velocity. Another function of the accumulator is to provide means for establishing and maintaining a low level of the tension in web 30 during steady state operation.

The web accumulator 26, FIGS. 1, 2 and 3, comprises frame supported, rotatably mounted

idler rollers

55, 56 and 57, a vertically movable, underslung dancer assembly 58, and vertically extending guides 65, FIG. 4, secured at their ends to frame 21. The accumulator also comprises two loops of chain 66, two upper sprockets 67, two lower sprockets 68,

shafts

69, 70, DOWN stop 61, and UP stop 62.

The dancer assembly 58, only one end of which is shown in enlarged scale in FIG. 4, comprises hollow aluminum dancer

idler rollers

59, 60 to reduce the inertia of the dancer.

Rollers

59, 60 are rotatably supported at both ends of guide blocks 64. Each guide block 64 is provided with bushing means not shown for telescoping a guide 65 through it. Tie bar 63, disposed within dancer idler roller 59, is non-rotatably secured to guide blocks 64 to increase the structural integrity of dancer assembly 58. Because guides 65 extend vertically,

dancer assembly 58 has a vertically extending range of travel. As also indicated in FIG. 4, means is provided for securing a chain to each end of dancer assembly 58 which chain is looped about upper sprockets 67 and lower sprockets 68, FIGS. 2 and 3, mounted on shafts 69, respectively.

Shafts

69, 70 are rotatably secured to frame 21. The lower sprockets 68 are non-rotatably secured to shaft 70. By thus coupling the dancer assembly 58 to the loops of chain 66, vertical movement of dancer assembly 58 is translated into rotational movement of shaft 70 and linear motion of a yoke 72. The purpose of yoke 72 will be described in conjunction with describing transient dancer loading means 27, and the functions associated with rotating shaft 70 will be described in conjunction with describing the control of unwind braking means 24 and in describing dancer rate-of-descent responsive means 28.

A storage loop of web 30 comprising two nested Vs is formed by threading web 30 through accumulator 26 as shown in FIG. 1. The dancer assembly is operable between a DOWN stop 61 and an UP stop 62 which stops are secured to frame 21 and are provided with suitable cushioning means not shown. In the preferred embodiment of unwind stand 20, DOWN and UP stops 61 and 62 respectively are spaced to provide a vertical range of travel for dancer assembly 68 of about forty inches for use with 21 inch diameter rolls of polyethylene as described hereinbefore.

One side of two substantially identical sides of the transient dancer loading means 27 which is incorporated in the preferred embodiment of the improved unwind stand 20 is shown in FIGS. 2 and 3. Each side of means 27 comprises a tension spring 73 intermediate frame 21 and the smaller end of a headed rod 74 so that spring 73 and rod 74 depend from frame 21. Yoke 72 is provided with a clearance aperture through which rod 74 will freely pass except for its headed end. As shown in FIG. 2, when the dancer is against DOWN stop 61, a length L of rod 74 extends below yoke 72. Thus, referring to only one side of means 27, upon upward movement of dancer assembly 58, yoke 72 passes over the length L of rod 74. Upon continued upward movement of dancer assembly 58, yoke 72 engages the headed end of rod 74 whereupon spring 73 will be elongated. Referring to FIG. 3 in which the dancer assembly is shown against UP stop 62, it will be observed that spring 73 has been extended by the action of yoke 72 through rod 74 as described. Length L in the preferred embodiment apparatus is about 12 inches.

From the foregoing description of the transient dancer loading means 27, it will be obvious that the dancer imparted load on the web, hereinafter the dancer load, on web 30 will essentially be the weight of dancer assembly 58 through stroke L and will be the sum of the weight of dancer assembly 58 and tension in springs 73 through the remainder of the dancers range of travel.

The means for controlling braking torque applied by brakes 24 to retard unwinding the

rolls

31a, 31b of web 30 is shown in the diagrammatic schematic FIG. 5. Pressurized air is received from a suitable source therefore to pressurize tubing 79 to a pressure of about pounds. Cam 80, secured on shaft 70a is driven by shaft 70 through a suitable gearbox for synchronized rotation therewith. Cam 80 operates air pressure regulator 81 through a follower mechanism as better illustrated in enlarged scale in FIG. 6.

In the preferred embodiment of the unwind stand 20, cam 80 is ground and indexed with dancer elevation to provide the regulated pressure for the unwind brakes 24 versus the dancer elevation as graphed in FIG. 7. As is evident from examining FIG. 7, maximum pressure is applied to brakes 24 through tubing 82 between the zero and three inch levels of dancer elevation as measured from DOWN stop 61. The pressure is rapidly reduced between the 3 and 7 inch levels to a value of 8 p.s.i. Between the 7 and 12 inch levels of dancer elevation, pressure is gradually reduced from 8 p.s.i. to O p.s.i. O p.s.i. air is applied to tubing 82 through regulator 81 while the dancer is between the l2 and 40 inch levels.

Dancer rate-of-descent responsive means 28 is shown, FIG. 5, to comprise winching sheave 85, cable 86, bracket 87, air cylinder 88, tension springs 89, 90, tubing 91, adjustable bleed orifice 92, pressure operated switch 93, solenoid valve 94, and electric wires 95, 96 and 97. Also, the discharge port of solenoid valve 94 is connected to tubing 82 through an adjustable orifice 98 and tubing 99.

Referring now to FIG. 8, cylinder 88 is shown in enlarged scale with its piston rod connected by cable 86 to winching sheave 85 so that upward travel of the dancer assembly 58 will extend the piston rod and, upon downward movement of the dancer assembly, springs 89 and 90 will act through bracket 87 to retract the piston of the air cylinder. Thus, air is drawn into tubing 91 through bleed orifice 92 during upward movement of the dancer assembly which air is pressurized within cylinder 88 upon downward movement of the dancer assembly 58. The pressure developed by cylinder 88 is a function of the dancer rate-of-descent and the adjustment of bleed orifice 92. Because switch 93 is only operated to its closed position by a higher than ambient pressure, it is closed only when the dancer rate-of-descent equals or exceeds a predetermined value. Bleed orifice 92 is used to adjust the predetermined rate.

Upon closing of switch 93, electric power is applied from a suitable source to solenoid valve 94 which then ports unregulated pressurized air from tubing 79 to tubing 82 through tubing 99 and orifice 98 and thence to brakes 24 whereby increased braking is effected whenever the dancer rateof-descent equals or exceeds the predetermined value. Switch 93 will open when the dancers rate-of-descent decreases to below the predetermined rate and the pressure in tubing 91 bleeds down through bleed orifice 92.

Air pressure regulator 81 is a continuous bleed type regulator which acts to bleed its discharge line to ambient whenever the pressure in the discharge line exceeds the pressure which the regulator is positioned for. Thus, upon the opening of switch 93 causing solenoid valve 94 to be degenerized, valve 94 closes. Then, with no air applied to tubing 82 through valve 94, the pressurized air in tubing 82 will bleed through regulator 81 whereby brakes 24 are depressurized to whatever pressure regulator 81 is positioned for by cam 80 (i.e., the elevation of dancer assembly 58).

The operation of the improved unwind stand embodying the present invention can be understood best by describing the sequence of events which occur during an interval from just after stand 20 has stabilized after a splicing event until steady state operation is achieved again after the next splicing event. The following description describes splicing roll 31b, FIG. 1, to roll 31a with the understanding that rolls disposed in the upper and lower roll supports will be spliced alternately.

Referring to FIG. 9, curves 100, 101, and 102 show web tension versus dancer elevation for 21, 10, and 3% inch diameter rolls respectively which curves reflect the effect of regulating brake pressure as a function of dancer elevation, FIG. 7. Referring again to FIG. 9, dancer load curve 103 reflects the fact that the dancer load consists only of the dancer weight between the 0 and 12 inch levels of the dancer travel and is increased above the 12 inch level due to the elongation of springs 73 as described hereinbefore.

The intersection between

curves

100 and 103, FIG. 9, indicates that dancer 58 of unwind stand 20 is balanced with the dancer at about the 7 inch level because web tension is then equal to dancer load. The intersections between curve 103 and

curves

101 and 102 further indicate that as a roll of web is depleted and its diameter decreases to the 3%. inch spool diameter, the dancer will rise to about the eleven inch level in order to reduce regulated braking pressure to maintain a substantially constant low level of tension in the web of about 2 /2 pounds.

When a splice is initiated, the stopping of the trailing edge of the just depleted roll 31a of web 30 causes dancer assembly 58 to move upwardly towards UP stop 62, FIG. 3. As the dancer moves upwardly, the dancer load on the web causes the web tension to increase as indicated by the dancer load curve 103, FIG. 9. Thus, after the splice is completed, an increased level of tension is applied through web 30, FIG. 1, to the newly spliced roll 31b of web 30 which will cause the new roll 31b of web to accelerate. The dancer assembly 58 will continue to rise, as will web tension, until the peripheral velocity of the newly spliced roll of web equals the velocity of web being forwarded through nip 37. Because the dancer assembly will have risen above the 12 inch level by the time the splice is completed, the new roll of web is accelerated without being retarded by brakes 24.

Therefore, at the time the peripheral velocity of the newly spliced roll of web equals the velocity of web being forwarded through nip 37, a large torque is still being applied to roll 31b through web 30 to continue to accelerate the newly spliced roll. This causes the peripheral velocity of roll 31b to exceed the velocity of web 30 through nip 37 whereupon the dancer assembly 58 will begin to travel downwardly to reload the storage loop in accumulator 26. It is at this time when no retarding brake force is being demanded by virtue of the dancer elevation that the dancer rate-of-descent responsive means 28 acts to apply braking torque to the overspeeding roll to prevent the dancer from descending to the DOWN stop 61 which would cause web 30 to go slack.

As the dancer moves downwardly past the twelve inch level, normal braking force as a function of dancer elevation is applied to brakes 24 whereupon the dancer will again stabilize at about the 7 inch level. The response of the system can be adjusted through bleed orifice 92 to achieve rapid stabilization.

Referring again to FIG. 9, the high levels of web tension that are induced by brakes 24 when the dancer is in the 0 to 7 inch range of travel are provided primarily to quickly stop high inertia rolls of web in the event nip

rollers

35, 36 are quickly slowed or stopped. However, this range of dancer travel is operative during start-up and will become operative if the dancer moves to below the 7 inch level during transients such as post-splice stabilization. However, the brake control system functions substantially the same during such events as during a-quick stop by applying increased regulated air pressure to brakes 24 as a function of dancer elevation.

While the preferred embodiment of the improved unwind stand has been described for use in unwinding rolls of polyethylene having an initial diameter of 21 inches, a terminal diameter of 3 /2 inches, a width of 16 inches, and a weight of 140 pounds, at a velocity of up to about 750 feet per minute, it is not intended to limit the scope of the present invention to such material, the size of the roll described, or to such range of velocity. It is believed that it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention and it is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

What is claimed is:

1. An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant ve locity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for maintaining substantially constant dancer loading only throughout a lower range of dancer elevation and means for increasing dancer loading in a predetermined manner with respect to dancer elevations above said lower range.

2. An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for maintaining substantially constant dancer loading only throughout a lower range of dancer elevation and means for increasing dancer loading in a predetermined manner with respect to dancer elevations above said lower range, said means for increasing said dancer loading comprising a spring, and spring engaging means for adding spring force to said dancer loading as a direct function of dancer displacement above said lower range.

3. The improved web splicing, unwinding and forwarding apparatus of Claim 2 wherein said spring is a tension spring having one end secured to said frame, and said spring engaging means comprises a rod and yoke assembly intermediate the other end of said spring and said dancer.

4. An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for increasing, in a predetermined manner, brake loading above its normal dancer-elevation-dependent value during periods said dancer is descending at a rate equal to or greater than a predetermined rate, said apparatus further comprising means for maintaining substantially constant dancer loading only throughout a lower portion of said range of dancer elevations, and means for increasing dancer loading in a predetermined manner as a function of dancer elevation above said lower portion of said range of dancer elevations.

5. An improved web splicing, unwinding and, forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for increasing, in a predetermined manner, brake loading above its normal dancer-elevation-dependent value during periods said dancer is descending at a rate equal to or greater than a predetermined rate, said means for increasing brake loading comprising rate sensing and signaling means for sensing whenever said rate equals or exceeds said predetermined value and for providing an output signal during such periods, and means responsive to said signal for increasing said braking.

6. The improved web splicing, unwinding and forwarding apparatus of claim wherein said braking ment above said lower range.

Claims

1. An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for maintaining substantially constant dancer loading only throughout a lower range of dancer elevation and means for increasing dancer loading in a predetermined manner with respect to dancer elevations above said lower range.

5. An improved web splicing, unwinding and forwarding apparatus for unwinding web from a succession of supply rolls and forwarding web uninterruptedly to downstream apparatus at substantially constant velocity under substantially constant tension, said apparatus including a frame, splicing means, web forwarding means, unwinding means including means for revolvingly mounting a plurality of said rolls for unwinding them and braking means for applying a controllable braking force to retard said unwinding, web accumulator means intermediate said forwarding means and said splicing means, said accumulator means including a vertically moveable underslung web loading dancer assembly and a plurality of idler rollers defining a looped path of variable length for said web, the length of said path being inversely related to the displacement of said dancer assembly above the lower end of its range of travel, and means for normally controlling said braking force as a dependent function of dancer elevation to maintain substantially constant web tension, the improvement comprising means for increasing, in a predetermined manner, brake loading above its normal dancer-elevation-dependent value during periods said dancer is descending at a rate equal to or greater than a predetermined rate, said means for increasing brake loaDing comprising rate sensing and signaling means for sensing whenever said rate equals or exceeds said predetermined value and for providing an output signal during such periods, and means responsive to said signal for increasing said braking.

6. The improved web splicing, unwinding and forwarding apparatus of claim 5 wherein said braking means are pneumatically operated and said means for increasing said braking force comprises an electrically operated valve and means for operating it to bypass the normal source of dancer-position-dependent regulated pressure supplied to said braking means.

7. The improved web splicing, unwinding and forwarding apparatus of claim 4 wherein said means for increasing said dancer loading comprises a spring, and spring engaging means for adding spring force to said dancer loading as a direct function of dancer displacement above said lower range.