CA1301448C - Precision positioning system for a coater - Google Patents

Abstract

PRECISION POSITIONING SYSTEM FOR A COATER

Abstract of the Disclosure A die, preferably one with internal metering pumps for applying an extremely uniform coating to a traveling web, is mounted over a pair of very rigid side plates. Horizontal surfaces of the plates support linear slides which in turn support the die through uprights. The slides have preloaded bearings to allow a linear movement of each upright with no lost motion. Pneumatic cylinders move each upright along its slide independently of the other upright. Adjustable stops set the die-to-web spacing when the cylinders draw the uprights, and therefore the die, toward the web. Other air/hydraulic cylinders drive the uprights away fro- the web, against the action of the main cylinders, to jump splices in the web. The system preferably-includes an outrigger arm extending from each upright to a pair of auxiliary linear slides mounted on the side face of each side plate to relieve side loading on the main linear slides. In the preferred form, the stops are positioned and the actuators are controlled by a servo loop to provide, in combination with the independently movable uprights, continuous automatic control of the cross web coating dimensions in response to a coating thickness sensor. The servo system preferably also controls adjustment screws across the die to provide a continuous automatic control of the web coating profile.

Description

13(~1~413 1 Backqround of the Invention Thls lnventlon relate6 ln general to ~echanlcal positioning system6. More 6peclfically, lt relate~ to a preclslon positioning system for a web coater whlch controls the coating profile acros6 a one to fifteen foot web to withln a tenth of a thousandth of an inch despite varlatlon in the web thlcknes6 or other operatlng para~eter6, For many applications lt is necessary to apply a coating material to a wide, traveling web. A typical appllcation is lo coating a thln layer of a hot melt adhes$ve onto a web of a paper, plastlc or metal foil havinq a width of one to fifteen feet and a thlcknes~ of 4 mils, and with a varlation ln that thickness of ~5%. Ideally the coating thic~nes~ should be controlled to within tenths of a ~il despitc variations ln the web thickness, its width, or the type of naterial being coated. Known coaters are not able to meet these requirements.
A flrst difficulty has been the die itself. ~t i~ very difficult to create a die which reliably and repeatably produces a coating of uniform thickness across the die, particularly when there are changes in the ~aterial being coated or the flow rate of coating ~aterial through the die.
The Park coater, described in U.S. Patent No. 3,854,441, is an improvement over prior slot dies. It utilizes a fixed die and a movable backing roll that carries the web. Thi~
coater extrudes all of the coating material fed into lt using a variable rate pump external to the die. There i8 no 1 3~

1 po6itlv~ control of the coating thlcknes6~ the only control 16 the indirect one provlded by ~n ad~u6tment of the flow rate vla an ad~ustment ln the pump speed. ~hus whlle Park coater ls a ~lgnlflcant lmprovement over earller coatlng apparatus, lt ha~ not provlded the aforement~oned preclslon control over the coatlng thlckne6s, nor has lt proven to be useful for a wide range of coatlng mater~alc. It has been useful with hot-melt materials, but less than optimal with water and 601vent ba6ed materlals.
A conventlonal extru~lon die for coating ls the ~coat hanger~ dle whlch use~ a contoured cavity precl~lon ground into the dle to dlstribute the materlal acros~ the web. This type of dle i~ c06tly to manufacture, i6 sensltive to the mater~al belng coated and the coatlng flow rate, and usua11y produces a heavier coatlng near the center of the web. More recently the assignee of the present application lntroduced a gear-in-die ~GID~) coater which has a set of drivcn gears acting as a pump located within the die to ~eter the flow.
Thi6 die has proven to be substantially lnsensitlve to the materlal belng coated and therefore it is an lmprovement over the Park coater and extrusion-type dies. However, the present positloning system for this GID coater has several slqnificant drawback6.
The GID coater has a pair of massive pivoting arms which ~upport the die between them at an upper end and are pivotally mounted to a frame at the lower end. A tor~lon bae, and the die ltself, couple the arm~. She arms mount a ~3~ 8 1 motor and a chaln drlve for the geDr pump ln the dle. Thls mountlng system thus posltlon~ a die welghlng approxlmately 1,000 to 1,200 pound~ on the ends of two plvoted arm~. Two large, maln pneumatlc cyllnder~ are coupled to th- arm~ to plvot the die toward and away from the web carrled around a fixed backlng roll.
This posltlonlng sy6ten 16 characterized by less than optimal rigidity in the ar~s and a large angular momentum which re61st6 rapid movement requlred to ~u~p~ a 6pllce, and in qeneral has proven to be difflcult to potltlon and move with the desired precision. In particular, the force of an operator leanlng on the dle to make adjustment6 on the dle has been 6ufficient to di6tort the dle po6itlon and re6ult ln non-uniform coatings.
Varlous mechanical positionlng systems are known from the machine tool arts, but the conventional slide an~ gib arrangement typlcally produces a posltioning accurate to withln only a mll. Usinq preloaded ball bearing and sophisticated lubrication systems, machine tools can overcome 6tatic frlctlon and 106t motion problems to approach the degree of posltioning control envisioned for the present coater applicatlonc, but only with difficulty. Also, in machlne tool design a movable platform is typically slide mounted on a palr of ways with the platform rigidly coupled between them. In other words, it ls undesirable to have parallel sllde paths where lndependent mot~on ls posslble along each path. In the coater art, this rigldity interfere6 ~ 3~ 8 l wlth an accommodatlon to ClOS6 web thlcknessec 80 that the . .
coatlng is of uniform thlckness even lf the underlying web ls not.
one special order coater has attempted to posltlon a die with respect to a backing roll with the die sounted for linear, horlzontal movement. The mount, however, involved a cumbersome mechanical llnkage to move the die. The frlctlon and lost motion problem6 allowed only a coarse posltioning.
It ls therefore a prlnclpal ob~ect of the pre6ent lnventlon to provlde a precislon posltioninq system for a coater that controls the cross-web orlentation of the die and lts spacing from a backlng roll, and a web carrled on the backlng roll, to within a tenth of a mil.
Another principal ob~ect of this invention ls to providc a positioning system wlth the foregoing advantage which reliably positions and re-positions the die to a precisely known and adjustable position.
A further ob~ect of this invention is to provide a positioning system with the foregoing advantages that can also ~ump splices in the web.
Another significant advantage of the invention ls to provide a system that is readily adapted to full servo control to provide fully automatic and continuous control of the cross-web coating profile.
Stlll another object is to provide a positloning system that applles a coating of closely-controlled, uniform thickne~s despite cross-web variatlons in the thic~nes6 of s :13(~4~

1 the web.
_ Another ob~ect 1~ to provlde a posltloning system or a gear-ln-dle extru610n dle where the gears are drlven dlrectly.
A 6till further ob~ect is to provide a positionlng sy6te~ wlth all of the foregoing advantages ~hich ha~ a favorable cost of manufacture as compared to comparable systems for GID coater6.

Summary of the Invention A die ls mounted at its ends ln a palr of uprlght supports mounted on linear sllde6 that ln turn are 6ecured on very rigid slde platcb. The slldes allow the die to uove horlzontally toward and away from a fixed backlng roll, preferably also mounted between the side plate6. A maln actuator, preferably an air cylinder, ls co~pled to each upright and drives one end of the die through the associated upright along a horlzontal, linear path determined by the sllde. Each actuator and the associated die end mo~nt operates independently. The uprlghts are each mounted so that they can pivot about a pin mounted on a carriage of each sllde to accommodate this independence of movement of the two 61ides. The bearings of the linear slides are preloaded, and preferably ad~u6tably preloaded, to avoid lost motion which would degrade the positioning of the die with respect to the backing roll with a repeatable precision within a tenth of a ~11 .

13(11~4~

1 Ad~ustable ~top8 as60ciated with each uprlght ~et the web-to-dle 6pacing when the maln cyllnder~ draw th- dl-toward the backlng roll. ~n a preferred for- the stops are each formed by a flxed abutment 8ecured on one of the ~lde plates and a matlng ad~ustable abutment ln thc for4 of a rod mounted ln one of the uprights and threaded at one end to advance longltudlnally when it ls rotated, preferably by a stepper or servo motor acting through a reduc~ng worm gear.
To reduce slde loading on the linear slides carrying the lo uptlghtg, each uprlght mounts an ~outrigger~ arm that extend~
downwardly along the 61de face of the 6ide plate, termlnatlng at an auxiliary llnear slide orlented perpendlcular to the maln linear slide. To provide the capability to ~ump a spllce ln the web, a palr of hlgh force, short travel actuator~ are coupled between the 6ide plates and the uprlghts. These high force actuators act agalnst the main cyllnders a6 they draw the die agalnst the fixed abutments to momentarlly lncrease the web-to-die spacing to allow a spllce to pass freely through the spacing.
Also ln the preferred form the die has an internal gear pump and the cross-web profile of the coating i6 ad~usted by a set of ad~ustment screw6 actlng on a member which determines the outlet opening area of the die in the area of the ad~ustment. This dle is driven directly, not through a chaln drive or tlmlng belt, by a motor mounted on one of the uprlght6. The die as a whole ~s plvotally mounted ln the uprlghts wlth lt~ orlentatlon secured by a set of screws ~ 3~

1 threaded lnto the uprlghts. Wlth thls arrangement, ~nd wlth .
the plvotal mountlng of the uprlght6 on the sllde~, the degrees of freedom of movement of the dlc a~e separated to facllltate ad~ustments o the d~e posltlon.
A coatlng thlckness sensor scans across the moving, coated web to produce a slgnal $ndicative of the coatlng th~ckness across the web. Thls slgnal is an lnput to a mlcrocomputer controller, along wlth other operating parameters such as web tension, splice detectlon, web ~peed, coating temperature, and coating material supply. The controller generates output control signals that operate the ~otors whlch set the two stops, control the coater ad~ustment screws, and operate the main and splice-jump actuators. Thls servo-control loop allows a continuous auto~atic operatlon of the coater wh~le achieving a precisely controlled coating thickness, even where the web thickness varies.
These and other features and ob~ects of the present lnventlon will be more fully understood fro~ the followlng detailed descrlptlon which should be read in light of the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a top plan view of a coater utilizing a preclsion posltioning system of the present invention to locate a GID die with respect to a flxed bac~ing roll;
Fig. 2 ls a view in slde elevation of the coater shown in Fig. 1~

~3U144~

Fig. 3 ls a detalled vlew in slde elevatlon, wlth portlons broken away and the die hopper omltted, of the po~itlon system according to the present lnventlon;
rig. 4 ls a view ln side elevatlon opposlte the view shown in Fig. 2~
Fig. S is ~ detailed vlew in front ele~atlon, and partially in vertical ~ection, of the dle mounting and gear drlve assembly shown in Fig. 4;
Fiq. 6 is a detailed top plan view, with portions broken lo away, of the die mounting arrangement shown in Figs. 2 and 3 Fig. 7 18 a view in side elevation of one 61ide and uprlght which shows a worm gear ad~ustment for the angular position of the die~
Fig. 8 is a top plan view corresponding to Fig. 7;
Fig. 9 i~ a detail view in vertical section of one of the linear slide~ ghown in rigs. 1-8;
Fig. 10 i~ a detail view of the crossed roller bearings that support the carriage of the llnear slide; and Fig. 11 i~ a schematic drawing showing a servo control system for automatic control of coater shown in Figs. 1-10.

Detailed Description of the Preferred Embodi~ent5 Figs. 1-10 show a coater 10 that applies a thin layer of a coating material such as a hot melt adhesive to a moving web 12 of paper, plastic or metal foil. The web typically has a width of 2 to lS feet and a thickness of 4 mils with varlations in the thickne6s of ~5%. ~hickness variations ~3Vl~

occur whlch are generally unlform across the web co that one slde of the web ls thlcl~er than the other. The coater utillzes a die 14 which extrudes the coating materlal lnltlally held in a supply hopper 16 through an lnternal supply channel, lnclud~ng a set of meterlng gear pumps lnternal to the dle, to a llp rod 20 at the outlet of the dle. The web wraps around a flxed backing roll 22. ~he spacing 2q between the web on the backing oll 22 and the lip 20 of the dle determines the thickness of the coatinq applled lo to the web by the dle (other factors such as web speed, coat$ng feed rate, etc. belng ln the correct relatlon6hlp).
A preclslon posltlonlng system 26 whlch locates the die ln an extremely well-deflned and well-controlled spaced relatlonship with respect to the backing roll includes a pair of main llnear slides 28, uprlqht die supports 30 secured on the slldes through a mounting plate 27, and an ad~ustable stop 32 that utillzes a flxed abutment 32a and a longltud~nally ad~ustable abutment rod 32b. The llnear slldes are mounted on horlzontal surfaces 3~a of a palr of slde frames 34 that are preferably formed froo 1 1/2 to 2 lnch thick steel plate which has been machined, ground and stress relieved to be very rigid. Hereinafter the side frames will also be referred to as side plates. Ihe llnear 611des are preferably llnear roller ways with ad~ustably 25 preloaded roller bearings 28c (Fig. 10) so that movement of the slide carrlage 28a on the sllde ra~l 28b ls with no detectable lost motlon despite the substantial statlc 13~4E~

1 feictlon whlch 16 generated by the welght of tho dle and other assemblles supported by the slldet. The ~lldes are preferably those sold by IK0 Internatlonal, Inc. of Plne ~rook, New Jersey under thelr catalog No. 5~16. Each rall 28b is bolted to the plate surface 34a and each uprlght 30a is secured to the mountlng plate 27 by bolts 29 which ln turn is secured to the carriages 28a. ~he bolts 29 capture belleville sprlngs 29a under the head of each bolt. It i8 significant that each upright can plvot about a pln 29b whlch lo locates a low friction bushing 29c in a mating recess of the upright with substantially a zero clearance. Because the ~lides are linear and the surfaces 34a are borizontal, the uprights 30,30 and the die they mount move in a llnear horizontal path toward and away from the bac~lng roll as indicated by atrow 36. The pivot pin 29b and the resllient clamping force generated by the springs 29a allow the uprights to pivot to accommodate non-equal ~ovements of the two slides and their uprights.
~he dle 14 has a main mountlng shaft 14a which is pivotally mounted in the vertical plates 30a,30a of the uprights. A circular flange 38 with closed circular slots 38a is secured on the ends of the shaft 14a and abut the outer surface of the uprights. Bolts 40 located in the openings and threaded in the side plates provide a convenient arrangement for adjusting and then securing the angular relationship of the die 14 to the web 12. As shown in detail in Figs. 7 and 8, thi~ ad~ustment is made using a worm 41 ~ 3~

1 which engage~ a seml-clrcular gear 43 6ecured to the 6haft 14a by bolt~ 45 threaded ln a seml-clrcular clamplng plece 43~. The worm has a shaft 4ia which 18 rotated to nake the angular ad~ust~ent when thc bolt6 qO are loosened. Thl~ wor-arrangement prevents the die from turnlng under lt~ own weight when the bolts are loosened. It ls al80 slgn~flcant that this ad~ustment of anqular position about thls axl6 of the shaft 14a can be made independently of the adjustment of the dle position alonq any other axis, due In part to the aforementloned plvot pin mountlng of the uprights.
The fixed stop abutment 32a is secured on an edge 34b of each side plate 34. The ad~u~table stop ls preferably a rod mounted in the upright plate 30a and having an abut~ent surface 32c at the end ad~acent the fixed abutment 32a and a threaded port~on 32d at it~ opposite end which couples w~th a worm gear reducer 42 driven by a stepping or servo ~otor 44 mounted on a plate 30b mounted on the upright 30a. The rod is ~upported in the upright plate 30a in a Thomson torque-resistant ball bu6hinq bearing 46. Actuation of the motor 44 rotates the thread rod 32b which causcs it to advance or withdraw from the fi~ed abutment 32a thereby ad~usting the die-to-web spac~ng which is set when the abutment surfaces 32a and 32c contact one another.
A pair of main actuators 48,48 such as air, air/hydraulic, or hydraulic cylinders a mount~ng brac~et 34c and a pin 30c secured to each die support 30. The nain actuator draws the uprights and the die 14 mounted between 13¢1448 1 the uprlght6 toward the web untll the a~utments 32a ~nd 32c engage to set the operatlng spacing 24 whlch determlnes the thlckness of the coatlng belng applled to the web (other parameter6 belng ln the correct relationshlp). The main actuator drives the dle ln the opposite dircctlon to dlscontlnue coating, for ~ervicing, or between runs. A pair of smaller actuators 50,50, preferably air/hydraullc intenslfiers with the hydraulics provlding a 30:1 power increase, provlde a h~gh force, short travel drlve mechanl6m whlch can momentarlly push the dle and lts ount away from the web a small distance, agalnst the drawing force of the main actuator, to allow the coater to ~ump over~ a splice ln the web. The actuators 50,50 are each mounted on a bracket 34d secured to the full fra~e 34 and act on a stop on the vertical plate 3Oa of the upriqht.
To relieve side loading on the main linear slides 28,28, an ~outr~gger~ plate 52 is secured to each upright assembly so that it extends downwardly along the slde plate in a qenerally parallel spaced relatlonship. The lower end of the plate 52 ls mounted on a carriage 54a of an a~xlllary linear slide 54 which has its rail 54b mounted on the outer face of the ride plate 34 so that it is oriented perpendlcular to the associated main slide 28. ~he plate 52 preferably has a stiffening flange 56. This auxlliary slide arrangement resl~ts moments which would tend to cause the maln slide to twlst about lts longitudinal axls and produce sllde loading that can generate unacceptablc levels of statlc frlction in 13~)144~

1 the maln linear sllde.
~6 ls be~t seen ln rig. 5, one die 6upport 30 ~ount~ a variablc speed D.C. motor 58 which drlve~ the gear pump of dle 14 directly via a gear box S9 -- as oppored to chaln drlves of the prior art. The die 14, as 1~ be~t seen in Fig.
1, has a 6et of ad~ustment screws 60 arrayed across lt~
outlet at uniform intervals. ~hese adjustment screw~, a5 1~
best ~een ln Flg. 3, have a tapered cam surface at their tlp which acts on a wedge 62 that can deform slightly ln response lo to the screw setting to ad~ust the sized slot opening for the coating materlal in the reglon around any one of the ad~ustinq screw6. These screw~ 60 control tbe coating thlckness proflle acros~ the web (for a given settlng of the sald uprlght dle support~ 30,30 along the direction 36).
Whlle the screws 60 are shown as being manually ad~ustable, they can be controlled by stepping or servo ~otor~ 61, as shown schematic~lly in phantom in rig. 3, to provide an automatlc ad~ustment as will be described below given the precl6ion of the positloning system of thi~ invention.
In operatlon an uncoated web 12 travels over roll~ 64, 66 and 6~, with an optional loop around a preheat roll 70.
Rolls 64 and 66 are idlers and roll 68 is a nip roll which directs the web to a nip between itself and the backinq roll 22. The web then passes around a tension sensing roll 72 and a bowed roll 74 before moving upwardly to the spacing 24 where the die 14 applies the coating. As shown in Fig. 11, a sensor 76 such a~ a conventional nuclear gauging device scan~

B

l the coating thlckness applied to the web and generates a 61gnal lndicative of the sensed thickness. Thi6 6ignal i6 processed by gauqe electronics 78 and then applied as an input to a microcomputer controller 80 such a6 a ~MAC-6000 sold by Analoq Devices of Norwood, Massachu6ett6. The controller 80 al60 monitors other rele~ant operating parameters such as the tension in the web, whether there is a splice in the web, whether a web is present, web speed, the temperature of the coating material in the die 14, the level of coating material held ln the supply hopper 16 and a set point ad~ustment. In response to these inputs, the controller 80 produces output control signals, whlch will usually be amplified or act though relays or other conventional interface devices, to control mechanis~s such as the motors 44,58, the main actuators 48,48 (~SLIDE ADJ~ in Fig. 11) and the splice-~ump actuators 50,50, and the 6ervo motors 61 acting on the die lip rod 20 ~ROD ADJ~ in Fig.
11) .
While the system shown in Fig. 11 i~ the preferred arrangement to control the web-to-die spacing, it will be understood that other arrangements can be used. For example, the coater can be operated without a feedbac~ loop and the web-to- die spacing can be measured with conventional mechanisms such as mechanical dial indicators or linear variable differential transformers (LVDT's).
It is significant that the mounts for both ends of the die 14 are independent of one another, having separate drlve * Trac9e Mark 15 -`A `

13~1448 1 mechanisms, 11near sl1de6, and mounts. Thls allows thc posltlonlng 6ystem 26 to set the posltlon of the onds o th-dles independently to apply uniform coatlngs even when the web ltself has a cross-web variation ln lts thickness. ~The plates 52 and auxiliary llnear slldes 54, as well as the maln l~near slldes themselves, assist to reslst slde loadlng when the die is ln such a skewed orlentatlon wlth respect to the web.) It ls also significant that the positioning system moves only in a horizontal plane over two main linear slides lo wlth direct llnear drive mechanisms. This arrangement avoids the signiflcant rlgidity and angular momentu- problems lnherent ln the predecessor design.
There has been described a positioning system which can reliably position and re-positlon, a die in a closely spaced relationship with respect to a fixed backing roll and a web carried by that roll with a high degree of precislon, typically to withln one ten-thousandth of an lnch. The preclslon posltloning system of the present inventlon al50 provides ad~ustment ln the cross-web orientation of the die, has a splice-jump capability, ls rigid, provides a self-contalned drive for a gear pump in the die, and readily adapts to servo control in response to a down-stream sensed coating thickness to continuously and automatically vary operating parameters such as the position of the die with respect to the web, the cross-web coating thickness profile, and the operating speeds of the web transport and gear pump systems to yield a coating characterized by a unlformlty that 1 3~ 1 4~ ~

1 ha6 heretofore been unattalnable ln a commerclal coatet, partlcularly a coater that can apply coatlngs of a wlde range of materials. The present lnventlon not only posltlons the die precl~ely, but it does so with a decrease ln the amount of drive force required. ~he drive system is therefore smaller and less costly. The compactness and design simplificatlons of the present inventlon also provide additional competltive costs of manufacturing advantages.
While the invent$on has been described with respect to lts preferred embodiments, lt will be under~tood that various alteratlon8 and modiflcations will occur to those 6~111ed ln the art. ~he ad~ustable ~top can be provlded in a variety of alternative ways such as a fixed stop abutment secured on each upright strlking a wedge-shaped abutment member that i6 mounted on a side frame and is movable vertically to vary the web-to-dle spaclng. Also, while the invention has been de~crlbed with reference to cylinders which draw the die aqalnst ad~ustable stops, it is possible to use precicion ground lead 6crews (single or twinJ drlven by approprlate motor~, actlng ln cooperatlon wlth known encoding devices to provide a measure of the position of the die. One dlsadvantage of this arrangement is that it does not readily provide a splice-jump capability. Further, while the linear slldes have been described as mounted on horizontal surfaces of a pair of side plate5, the horizontal surfaces do not necessarily need to be formed on the slde plates. Therefore in this applicatlon horizontal mounting surfaces on the 6ide 13~48 1 plate6 6hould be interpreted a6 includlng equivalent 6urface~
formed on other member6 or member Still further, whlle the invention ha6 been de6cribed w1th referencc to the application of a thin, well-controlled coating to a web, it may al60 be u6ed ln a laminatlng applicatlon where two or more web6 are secured together with a thin adheslve coatlng, or it may be used to produce thin film materials using the equlpment descrlbed herein to extrude the film onto the backing roll and then remove and pcoces6 it using standard technique6. These and other variations and modification6 are intended to fall within the scope of the appended claim6.

Claims (17)

1. Precision positioning means that repeatably locates and adjustably aligns a die with respect to a backing roll, comprising:
a die;
a pair of rigid side plates having a generally vertical orientation and located at the ends of said die, each of said side plate having a horizontal mounting surface, linear slides secured on said mounting surfaces, said slides being preloaded so that they move along a first direction with substantially no lost motion, means for mounting said die at its ends, said mounting means being in turn mounted on said linear slides to allow movement of both sides of said die independently of one another, and means operatively coupled to said mounting means to drive said mounting means and said die mounted thereon along said first direction on said linear slides, and means operating in cooperation with said drive means for controlling the position of said die with respect to said backing roll.

2. The precision system of claim 1 wherein said position controlling means comprises stop means operatively coupled to said mounting means which adjustably sets the spacing between the die and the backing roll, wherein said driving movement toward said stop means sets said spacing as determined by said adjustable stop means.

3. The precision positioning means of claim 1 further comprising second means for driving said mounting means and said die away from said backing roll against the force of said drive means, said second driving means being characterized by a high force and short travel to provide a web splice jump capability.

4. The precision positioning system of claims 1, 2, or 3 further comprising means for controlling side loading on said linear slides.

5. The precision mounting system of claim 4 wherein said side loading controlling means comprises a second linear slide mounted on said side plate and a side arm extending between said mounting means and said second linear slide that transmits side loading forces at said linear slide to said second linear slide.

6. The precision positioning system of claim 1 wherein said mounting means includes a pair of upright members each mounted on one of said linear slides.

7. The precision positioning system of claim 6 wherein said die is mounted in said upright members and said mounting is pivotally adjustable about a horizontal axis extending between said uprights.

8. The precision positioning system according to claim 2 wherein said stop means includes a shaft secured in said mounting means and a fixed abutment surface spaced from one end of said shaft.

9. The precision positioning system of claim 8 wherein said shaft is threaded so that its rotation adjusts its longitudinal position with respect to said fixed abutment.

10. The precision positioning system of claim 9 wherein said stop means further comprises a motor and gear means operatively coupled between said motor and said rod threads whereby activation of said motor adjusts said spacing through a rotation of said shaft.

11. The precision positioning system according to claim 1 wherein said die includes an internal gear pump to meter and distribute said coating material.

12. The precision positioning system according to claim 11 further comprising drive means for said gear pump mounted on one of said upright members.

13. The precision positioning system of claim 11 further comprising adjustment means for setting the coating thickness profile across the web.

14. The precision positioning system of claims 1, 10 or 13 further comprising means for continuously sensing the thickness of said coating on said web and generating an output signal proportional to the sensed thickness and means for generating control signals in response to said output signals to adjust said coating thickness.

15. The precision positioning system of claim 14 wherein said control signal controls the operation of said stop means by motor to continuously adjust the web-to-die spacing.

16. The precision positioning system of claim 14 wherein said control signal controls the operation of said adjustment means to control the cross-web profile of the coating automatically.

17. The precision positioning system of claim 16 wherein said adjustment means includes motors secured to each of a set of adjustment screws arrayed across the die.