CA2213238A1 - Stretching system for flexible planar materials - Google Patents

Abstract

A frame (10) is disclosed for stretching a printing screen (12) quickly and with uniform application of tension to the screen (12). The frame (10) includes a base portion (14) that defines a stretching plane in which the work piece is stretched. A swingable portion (30) of the frame (10) pivots relative to the base (14) and moves from a relaxed position in which the swingable portion (30) defines a plane that intersects the stretching plane, to a stretching position in which the swingable portion (30) is fixed in the stretching plate. A retainer (90) secures the edges of the screen (12) to the frame (10) such that the screen mesh is uniformly stretched as the swingable portion (30) is pushed into the stretching plane. A tension cable (140) extends through the frame (10) over a series of pulleys (142, 144, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166) spaced at several locations through each leg of the frame. Increased tension on the cables (140) pulls the swingable portion (30) of the frame (10) into the stretching plane.

Description

W O 96/25239 P ~ AUS9~a2127 ~l~ULl~l~G SYSTEM FOR FTT~XT~TT~ PLANAR MAl~DTAT,.S
BACKGROUND OFINVENTION
The present h~ ion concerns methods and , r ' for ;,L~ g planar w~, and more i li~ an i-u~-uv~d system for Dl ~,t~ g a printing ~reen.
In many ~ , it is i~Gll~t to be able to quickly stretch~ a sheet of planar material to a desired tension or desired c' ~ . For , '- screen printing requires tbat S a rnesh screen of metal or fabric be ~ir..~.y stretched under very high tel~sion while ink is applied through the mesh of the screen. Uniform tension on all parts of the screen is critical to ensure uniform ~' ' of ink through the screen and to produce a ~high qualiq image.
To achieve uniform tension on the ~reen, prior devices have applied clamps to the edges of a ~reen at di~rete spaced l~-~ The clamps are then pulled outwardly to e~ert tension on 10 the screen in all dhwlionD until the screen is taut.
Very high tensile forces must be applied through the clamps to the ~reen to achieve tension of a ~ rr.~ in such devices. Rapid ~h~.t~,L;,,g of the ~reen by the clamps can, however, e~ceed the tensile strength of a screen and damage the integrity of the mesh. Hence, prior screen printing p.vc~s have required that the ~reen be sl.~ ~ ' -' very~5 slowly,often over many hours. This delay in ~reen Dhc;l~l~g impairs printing ~ and the cost of ~reen printing p,~.
Several frames are known for holding mesh ~reens used in screen printing p.. U.S. Patent No. 2,903,967;U.S. Patent No. 3,863,368;U.S. Patetlt No. 3,477,574;
U.S. Patent No. 3,762,080,U.S. Patent No. 4,452,138;and U.S. Patent No. 4,702,783-li- tr,~
20 planar frames that e~cert tension in the plane of the frame to stretch a ~reon taut. U.S. Patent No. 4,144,660and U.S. Patent No. 4,190,974also di~lose planar frames for Dt,~.t~l~g a w~ , such as an artist's canvas. U.S. Patent No. 2,752,63~h-~ ~ ;1~-~ a star-shaped, planar "' forDl-~l~g i ),' "- films. Finally,U.S.Patent No.2,042,874;U.S.Patent No.

2,455,640;and U.S. Patent No. 2,604,7~ r~ planar frames for sl..' ' ' I curtains.
Such devices have many uses. But, all such devices have dra~backs which limit their . ~ ' - for p~_;D;U~ work, such as sl-~' ' ~ 7 mesh ~reens for use in printing. In ~i ' , rnany of the prior devices require a highly trained worker to - , ' the ~ 'l " over a long period of time. With prior ~reen printing _, , t, for e , '~, it typically takes hours to gradually tension a ~reen. And, even skilled work~-rs are prone to 30 damage printing ~reens. Other of the devices are too il,.~;~ to be useFul.
Acco.d~sly, it is an object of this .,..~lliu.. to provide an iu,~.u.~ frame forquickly and ~ Dt.~.t~;L;..g a planar w~ lc, --~ such as a mesh ~reen.
It is another object of the ...~. to provide such an i~ ,.u._d frame that ~ ~r ly applies tension to the w~
Also, it is an object of the i--~. to provide a s~ .L;.. g system that requires oDly minirnal training to use.

W 096/25239 PCTrUS95102127 A further object is to provide rnodular w- '~, ,c , I li,~.l ,1~ printing screens, that can be .cir "~, instal1ed and removed from a frame.
More ~ifirnlly~ it is an object to provide w~ ~~P-S that can be ~I;r ~ ~lY
installed at the same position and tension.
The~se and other objects of the in.,~ willbe ~ more clearly by .ef~,.... to the followingdetailed d~ and .1~ SUMMARY OF TB INVENTION
The r~ g oyects are achieved by providing a frame for ~ ' ~ g a planar w~ ~, ~ such as a printing screen. The frame includes a base portion that defines a 10 ;,h~ ' ~ _ plane in which the ~ is stretched. A ~ ~ _ ' '~ portion of the frame pivots relative to the base and moves from a rela~ced position in which the ~..- ' 1e portion defines a pbne that ~ the sl._t~,Ling plane at an angle, to a ~ ' ~ g position in which the _. _ ' '- portion is fi~ed in the ,h~h;.,g plane. A retainer secures the edges of the screen to the frame such that the rnesh is ~ ~r 1~ as the _ _ ''- portion is pushed into the 15 sh~- ' - plane.
In p. r~..~ . - the frarne is ,~ , ' , and the base and ~ _ ' '-portions are each a right angle shaped frame member. Each frame member has a first leg and a second leg joined at a fi~ced mitered comer. The first legs of the frame member have distal ends that are pivotdly joined by a hinge at a common rnitered rnating junction. The distal 20 ends of the second legs are similarly joined pivotally by a hinge at a common rnitered mating - Each hinge includes a pivot ' ~ between the hinge and one of the legs such that the _.. _ ' '- portion of the frame is free to rotate about an a~cis of one of the legs as the .. ' '- portion rnoves out of the :.h~1 ' ~ g plane.
The frarne further includes a lock that sel~live;ly retains the ~ portion in25 the ..I.,J~ ' ~ lg pbne. The loclc is p.~ , a tension rnember that pulls the ~..- ' '- portion towu~ the ~h~ ' ~ e pl~ne- In ~-r-';~~ P~f~ ' the lock iS a tension cable reeved over a series of pulleys spaced at several 1 ~- - through each leg of the fr~me.
T ~ - ~d tension on the cable pulls the _.. _ ' '- portion of the frame into the sh~ ' ~ Ig pbne and holds the frame in place to rnaintain tension on the ~
A w~ to the i .......... includes a retainer that holds the screen to a frarne. The retainer includes four; ' _ ~ C,~ each having a w~ b, ~~ retaining portion and a frame; _ g portion. The ~ retaining portion i6 an e' 1, ~ planar rnember to which a ~ p?- ' border of the ~ 'r, ~ can be adhered. The frune _ ~
portion is p.~ an L-shaped member that e~ctends over the outside face of each leg of the 35 frame and into a slot on the outside face of the leg. The w~ p~ a fourffided sheet having edges that, when not i ~ d, are arcuate and curved so that the width and length of the sheet are less at the center of the screen tban at the corners. This _ CA 022l3238 l997-08-l5 shape ensures that the greatest arnount of outward force is applied to &e center portion of the sc , which rlught, - . i~ tend to sag, when the frarne is in its stretching ~-BRIEF DESCRI~TION OF THE DRAWINGS
FIG. 1 is a top, p ~ ;v.; view of the frame of the present ...~- shown in S its rel~ced position, the :,he' ' g position of the ~..- _ ' '- portion of the frame being shown in I ' FIG. 2 is a ' c, top view of a rela~ed screen before it is attached to ._ ~ the I ' ~ lines showing the .~ " of the sc to the retainers after the p~ ~.' ' borders of the screen are adhered and the screen is I ~ ~ on a frame.
FIG. 3 is a top, plan view of the frarne with the retainers in place on it, the folding a~cis of the frame being il' ~ by a dashed line.
FIG. 4 is an enlarged, r C~ sectional viewtaken alorg line 4 1 of FIG. 3 showing the sc secured to a retsiner, which is in turn hooked to the firame. Internal detail of the frame - ' ~ is omitted.
FIG. 5 is sn enlarged, top, plan view of a comer of the firame showing spacers for ~ ~ ~- ~-- - .. ~ of the .~_' . retracted p~ A~ of the spacers being shown in FIG. 6 is an enlarged, bottom, oblique view of a hinged comer of the frame shown in FIG. 1.
FIG. 7 is an end, ~ ,. ' view of the hinged face of a ~ leg of the fiame shown in FIG. 6.
FIG. 8 is an end, el~ . -' view of the end face of a ~- .~ leg of the firarne shown in FIG. 6.
FIG. 9 is a reduced, ! ' ' ~ C, sectional view taken along line 9-9 of FIG. 4, 25 showing a l ~ ~ g device inside the firame.
FIG. 10 is sn; ' ,, d, ~ _ .r, sectional view taken alc~ng line 9-9 of FIG. 4, showing ~1 ' ~ for the ~ ~ ~ g device.
FIG. 11 is a f _ .~, sectional view taken along line 11- 11 of FIG. 10.
FIG. 12 is a top, plan view of an ~ . ' ~ ' ~ of the ~.. frame, 30 portions of the screen being broken away.
FIG. 13 is an enlarged, bottom, oblique view of one of the hinged c - .,~ of the frame of FIG. 12.
FIG. 14 is u side, eL..J1 ~ ' view of the firame shown in FIG. 12.
FIG. 15 is a partial, sectianal view tsken slong line 15-15 of FIG. 14.
DETAILED DESCRIPTION
A ..J frame 10 is shown in FIG. 1 for ~l.et~ ..g a iour-sided plansr w~ - . such as primting screen 12 (FIG. 2) having edges 12a, 12b, 12c, 12d and comers 13a, 13b, 13c, 13d.

The ~ ' 1 ' frame 10 includes a right angle shaped base or: ~
portion 14 tbat includes first and second legs 16,18 F~ , joined at a mitered corner 20 and I ~ g in first and second distal ends 22,24. Each leg 16, 18 has an upper face 25 (FIGS. 1 and 4), inner face 26, bottom face 27, and outer face 28. Upper faces 25 of legs 16, 18 of base portion 14 define a :.h.,t.,L;.. g plane P F~llel to which screen 12is:,L~ '-' Frame 10 also includes a right angle shaped ~ portion 30 having first and second legs 32,34 joined at a common mitered corner 36 and ~ ~ in first and second distal ends 38,40. Each leg 32,34 has an upper face 41 and inner face 42 (FIG. 1), and bottom fsce 43 and an outer face 44 (FIGS. 6 and 8). S.. g ''- portion 30 pivots relative to 10 base portion 14 and moves from a rela~ed or retracted position (shown in solid lines in FIG. 1) to a ~h. ~ g position (shown in phantom in FIG. 1). In a fillly rela~ed position, the upper fsces 41 of L..- _ ~- portion 30 define a plane that ~ ;~ the sl-c;~l~& plane at an angle of sbout 90to lSOdegrees. In the ~h. ' Hg position, however, the upper faces 41 of L..- _ ~-~- portion 30 define a plane that is ' l1y co-planar with the upper faces 25 of 15 base portion 14 and that e~tends parallel to the ~ ;tcl~ihg plane P.
S~ ~ _ ' '- portion 30 phots about a pair of aligned hinged . - between the _.. _ ' '- portion 30 and base portion 14. A first hinge c ~c~ 48 connects the first ends 22,38 of the base portion 14 and ~ portion 30 along a mitered junction 50.
When the ~ portion 30 is in the sh~,t~,h; g position, the pin of hinge 48 e~tends in the 20 plsne of faces 25. Hinge 48 further includes a pivot ~- ' ~ that allows the first leg 32 of the L..~ ~ portion to rotate as the leg 32 moves up out of the ~h~;L;ng position.
Hinge . l - 48is sbown in greater detail in FIGS. 6-8 to include a tubular binge barrel 50 that is formed by ~ ~ ~ nuclcles of a pair of hinge leaves. ~ne ~nuclcle of the barrel is secured to an end face 52 of leg 32 by a ~ hinge leaf plate 54.
25 The plste 54 is fised to fsce 52 by screws 56,58. The other leaf 60 of hinge 48 is ~ pivot leaf plste that is .~ secured to an end face 59 of leg 16 by a pivot screw 62 which has a ' a~is ' n,~ through the leg 16. Because the leaf 60 snd leg 32 csm rotate aboutthe 1 _ ' ' alcis of the screw 62, the leg 32 swings out of its position pardlel to the ~t.~ ' ~ g pl~ne P ss the leg 32 moves into a rela~ced position. A dowel pin 64 p.~
30 ~t h _ ~ from the end fsce of first leg 32 to serve as a guide member. The pin 64is -' to fit into a ~,yl ' ~ ' or sr~-tirS~I guide soclcet 66 in the end face of first leg 16 for guiding legs 16,32 into proper -'i"
A second hinge - ~ 80 (I;IG. 1) connects the second ends 24,40 of the bsse ~nd _ .. ~ _ ' '- portions 14,30. When the _ .. ~ _ ' ' - portion 30 is in the ~hJ ' ~ ~e 35 position, the pin of hinge ~ ~ - 80 e~tends in the plane of faces 25 dong a mitered junction 82 between ends 24,40. The hinge . ~ ~ 80 further includes ~ pivot r (not ~ihown) to the second end 24 of the base portion 14. The pivot ' allows the leg 34 of the _.. _ ' '~ portion 30 to rohte about an a~is of the pivot ' Hinge -W 096125239 PCTflUS95~2~27 - 80 is similar to hinge ~ 48 and pivot leaves 54, 60 that ~Ire shown and d~ ~ in c ~ ~ with FIGS. 6-8.
Each leg includes a device to engage the w~ 'c, - - e In ~ I ' , an . '~ , linear slot 84 (FIGS. 1 and 4) is provided through the outer face 28 or 44 of each leg 16, 18 32,34 of the frame and e~tends partially along the length of each leg. Each slot 84 has flat p~llel top and bottom surfaces 86, 87 that are 1~ ~ 'ly parallel to th~ top face 25 or 41 of the leg in which the slot is placed. In the ~ of FIG. 1, esch slot through the outside fsce t ~ ~ near each rnitered corner at a position slightly short of the rnitered Slot 84 in leg 16, for , '- I ~ - adjacent mitered comer 20 at a wdl 88 10 (FIGS. 1 and 5), and slot 84 in leg 18 l ~ ~ adjace~nt comer 20 at a ~vall 89 (FIG. 5).
Four elongate retainers 90, 92, 94, 96 are provided to hold a screen on the frame.
The retsiners are attached to the screen along the ~ ~ of a ~. t' ;~' figure, most e'~ , a figure that is generally in the shape of a ,. _ - When the ~-- ~ ~ screen is DL~he~i on the frame, the figure has a l~ngi~- ' ' . ' - Cl that e~lends parallel to and 15 is ~, ~ ~- ~ from the retainers 92, 94 and a latersl ~ ' - C2 that e~tends parsllel to ~md is ~ . ~ ' ~ ~ from retainers 90, 96.
Each retainer secures an edge of the ill ' screen to the frame by hooking into one of the slots. In the e ~ of FIG. 1, the slots 84 are longer thsn the retainers such that, after ~ ~ ~1 of a screen is _ , ' ~ there is a gap between each end of each~0 retainer and the ends of the slot which contains that retainer. Although tlhe ret~iners would be , self ~' ~ g if the ret~iners were the same length as the slots, this i8 not ,f~,...,d. It would be difficult or: . ~- '- to install the retsiners in the slots if there were no leeway.
Each retsiner, as ill ~ ~ I by retainer 90 in FIG. 4, is a J-shaped mernber 25 h~ving a first planar screen .~ ~ ~ g member or flange 98 for securing ar~ edge of the screen to the retainer, and a spaced second plansr member or flange 100 that fils into one of the slots 84 in the outer faces of the frame. The first and second planar ~ 98, 100 are - ' by a spacer or web 102 that is ~ 1 ~- ' to ' 98, l~D0 and is ~ rr; ~
high to allow rnember 98 to rest on the top face of the frame, yet allow n~ernber 100 to insert 30 into the slot 84. Hence, the distance between ~ 98, 100 is about ~he ssme as the distance between the plane of the top face 25 and the slot 84. The member 100 and spacer 102 together , ~ an L-shaped hook.
For ~.. lc, ~ ItO be reused or ~ ~ d, sn ~'i, device is provided so that ~ a~ can be mounted at a p-. ~- ~ ' '- location on a given frsme.
In the e ' - ' ~ of FIG. 1, four spacers 110, 112, 114, 116 are each rnounted on pivot pins 118, 120, 122, 124, .~ , to position the retainers andl to inhibit the retainers from I ~- ' '1~/ sliding in slots 84. Spacers are mounted on opposite sides of each fi~ced corner that does not have a hinge, wch as mitered corn* 20 that joins legs 16, 19 (FIGS.

W 096/25239 PCTrUS95/02127 1 and 5). Each spacer is a flat member having a straight edge 128 that abuts against the terminal edge of an adjacent retainer.
The edges 128 of spacers 110, 112, ~ , abut edges 113a, l l5a of the screen ,:d ~ ~ g member of the retainers 90, 92 when the screen is irlstalled and I
S The spacers 110, 112 also have a straight edge 130 that is L ' ' " 'Iy aligned with, or parallel to, the outer edge of the frame when the spacers are in the spacing position shown in solid lines in FIG. S. Stops (not shown) can be provided to limit the arc through which the spacers 110, 112 can swing.
Each spacer ~Iso has an end portion with arcuate edges 132 that form a portion 10 of acircle. Thearcuate edges 132allowadjacent spacers 110,112to~vewithout ~ . r ~ as the spacers are rotated around pivot pios 118, 120 from the active position shown in solid lines in FIG. S to a retracted position shown in p~ ~ In the retracted position of the spacers, straight edges 130 al~st abut against one another to act s a stop agairlst further ~ .. The length of each spacer 110, 112 is s r~ ' that it prevents ._ of retainers 90, 92 toward mitered edge 20, and properly p ~ ~ terminal edges113a, l l5a of the retainers with respect to the frame. In the . ' - ' of FIG. 1, those edges sre spaced d- ~ c2 from the ends 88, 89 of slots 84. And, the ends 113b, l lSb of retsiners 90, 92 at the opposite ends of the slots are spaced d ~ ~ q Yl, Y2 from the end walls of the slots. In a ~.~,f~ d e_L- ' all the d - ~c and all the ~' y are equal.
20 But, it is possible to allow different d - at each end of each retainer.
Another p~ur of spacers 114,116 is mounted on opposite sides of mitered corner 36 thst joins legs 32, 34. Each spacer 114, 116 is identical to spacers 110, 112 and is r ' '1~ long to space each retainer 94, 96 ~" ~ ~"~4 (not shown) from the of slots 84 adjacent corner 36. The retainers 94, 96, when installed with the 25 screen l ~ d are also thus spaced ~' - y3, y4 (not shown) from the ~ ~ - of slots 84 nearest the hinge ~ ' - 48, 80. Thus, in the; ' ' ~ ill ~ ~ in FIG. 1, the length of each slot 84 is equal to the length of the retainer in the slot plus the distance ~c and the distance y ut the ends of the retainer.
ly, the slots 84 could e~tend (not shown) all the way to the ends and 30 corners 20, 22, 24, 36, 38, 40. And, grooves (not shown) could be provided iostead of the slots 84.
The w~ (e.g.,screen) held by the retainers willbe ~ ~ ~ -~
on the frame, at its optimsl location, when all the spacers 90-96 are in the ~ ' d ~
(shown in solid lines in FIG. 1) and are abutting adjacent .. R. ~ 90, 96, for 35 , ' ~, secure opposite edges of the ~.. 1c~ ~ The retainers 90, 96 will not be inclined to move away from sp~acers 110, 116 because tension from the screen 12 urges the retainers toward the spscers. Screen tension similarly urges the retainers 92, 94 toward the spacers 112, 114. Even though w~ r thus tend to be self aligning, the installer can confirm proper W 096125239 P ~ AUS95~a2I27 9~i~, ' sirnply by ~ ig whether a retainer abuts each edge 128 during ~ 'I of a w~ e Frsme 10 is also ~,~,.. ~ with a lock ' (FIGS. 9-11) that the ~.... ~ portion 30 of frame 10 in the st,~ position. The lock _ ' is shown in S FIGS. 9-11 to be a cable 140 that e~tends through the frame. A series of pulley wheels 142, 144, 146, 148, 150, 152, 154, 155, 156, 158, 160, 162, 164 and 166 are rnounted the top face of frarne 10 on shafts (s~uch as shaft 163 in FIG. 11) that e~tend between the top and bottom faces of the frame and allow wheels 142-1661,o rotate freely. The wheels ure held against the top faces of the frame by an annular collar (such as collar 165 in 10 FIG. 11) fi~ed around each shaft (such as shaft 163). Cab1e 140 is fi~ed at each end to pulleys 142, 166 (FIG. 11) such that rotation of pulleys 142,166 winds cable 140 around pulleys 142, 16ti and ~ tension on the cable.
Each wheel is a sheave with a groove in which cable 140 rides. Pulley 142 is mounted in corner 20 1 ' ' the mitered junction of top faces 25 where legs 16, 18 join.
15 Wheels 144, 146 re rnounted in leg 16 with wheel 146 nea~r a ~i of leg 16 and wheel 144 between wheels 142, 146. Wheel 144 ~ ~ -rlly abuts against outer face 28 of leg 16, while wheel 146 abuts against inner face 26. Wheels 148, 150 are ~ ; ' in corner 22 on either side of the rnitered junction of legs 16, 32, with outer faces 28, 44 .~ butting '1~, agaiDst wheels 148, 150. Wheel 152 is p~ -~l beneath top face 41 at a ~j of leg 32 i ,, 'ly to inner face 42, and wheel 154 is located ~lear the mitered junction 36 abutting against the outer face 44 of leg 32. Wheel 155 is loca~ted within leg 34, near the mitered junction 36, i ' to the outer face 44. Wheel 156 is F ~ ~ d at a 1~ of leg 34 against inner face 42, while wheels 158, 160 are at a mitered corner 82 on either side of hinge ~ J 80 and abutting agaiost outer face~s 28, 44. Wheel 162 is near a ~ of leg 18 adjacent inner face 26, while wheel 166 is adjacent comer 20 and wheel 164 is between wheels 162, 164 in leg 18. Cable 140 is reeved around the gro~ve in wheels 144-164 by -' E the cable around sides of the wheels such that the cable is between each of the wheels and the wall of the leg that abuts I _ -~y against the wheel. Hence the walls help hold the cable in place on the wheel.
The i ,,' ~ - ' for the wheel is a worm gea~ 170 shown in grester detsil in FIGS. 10 nd 11 at the junction of legs 16, 18. The worm gea~r sits in a housing 171 that 1~ ,~ comer 20 and includes a plastic grealse retention member 171a pl-;~ ~; into leg 16dong the path of cable 140toward wheel 144,and another plastic ,grease l~Jt member 171b pl.j g into leg 18 along the path of cable 140 toward wheel 164. Each of 35 wheels 14Z, 166 is a gesr wheel with ~' ~ ' arcuate teeth that engage a helical groove 172 on a barrel of the worm gea~r ' such that rotation of the barrel rot~s wheel 142 in the direction of arrow 174 and wheel 166 in the direction of ar ow 176. A l~ey ring 178 is ~ _ r ~ ly secured against an outer face of the ba~rel and forms a Icey slot 180. The slot W 096/25239 PCTrUS95102127 180 mates with a pair of key pins 182, 184 (FIG. 1) that e~ctend .,ut~ _ dly in opposite from a tip 186 of a shaft 188 of a ~ tool 190 that has a handle 192. Shaft 188 i6 _ ,1 1 at a right angle to handle 192 by a socket 194 that rotates shaft 186 when hsndle 192 is moved through an arc.
FIG. 2 il' ~ the ~ 5_ of certsin w~ ' g to the present . .~ ~- Shown is a rela~ed printing screen 12 (solid lines in FIG. 2) that is 8 - .. ., ~ ' mesh printing screen having four edges ~ ' ' _ two lateral edges 12a, 12d and two I e ~ edges 12b, 12c, and four corners 13a, 13b, 13c, 13d. Each of the edges is arcuate such that the length and width of the screen tapers toward the center of the 10 screen. Hence, ~ ..~ r of the corners, the width w of the rela~ced screen 12 is less than the width W that the screen would have if it were truly .~ ~ ' . Similarly, ~ ~.. ~ of the comers, the length I of the rela~ced screen is less than the length L tbat the screen would have if it were truly .~,~ ' . Or, in other words, due to the arcuate shape of the edges, the width and length of the ~ e are less at the _ ~ ' - of the w~ 1~ ~ . e than at the 15 outlying~ regions of the wl ~ ~ r e e The arcuate shapes of the edges are chosen such that when r _ ' ' and lateral tensile forces are applied to the edges while the edges are held straight, the w~ ~, - e is ~ , 1 ~ ' For the purpose of this ~' ~~' ~, ~l if ~y t ~ '~ means that, when _ I - -' ... '~- ~e isheld ~ ~ 'Iy and multiple tension (N/cm)~0 are t~en at different points tL. g! the ~ _ region of the w~ 'c, - - e the re r~l~ ~ 'ly equ~l. In the r t; ' case of printing screens, such ~r ~~r of tension applies to that region where ink is I ~ through a screen.
To ~chieve ~ r~' ~ b;'i~y and ~~ , of screens, sclreen ~ ' ' must behave 1~ r. Thus, for each screen, the distance between the inner surfaces of spacers 25 102 of opposed retsiners must be csrefully selected so that each screen D~ ~ I on a given frame willhave the desired unifomm tension across the entire ~ r '-~~ region of the screen.
The ~ ' ~ c' ~ 1, w can be ~1 t ~ ~ by using a ratio X. By g the ~' ~ L, W by the ratio X, one can ~' ~ ~ the ~' ~ 1, w for various sizes of the s_me fabric. The ratio X will vary sv~ ' ~ ' , on the type of 30 material used for the ... b, ~c e, the fle~ibilityof the frame on which it will be DL. ' d, and possibly other factors. The best ~' ~ ~ ~ for a ~'; ' type of ~ e csrn be ~' ~ -' by e_r ~ ~ '- Direction for the e . ~ ~ comes from the ratios ' ' ' - ' p.~ , for other types of fabric and from ~ ' ~- from fabric ~ _.D
on optirnal tension. ~ ' L r ~ ' ~-~ can require some tirne, it only need be 35 ~ ~ ' once for a l L~ l~ type of w~ b, - Tl- ~r~., 9' ' ' w~ ;7~1 pie es of fabric c~n be quiclcly pre-cut prior to being att~ched to .~ -In a p.~,f~.~,d; ' - ' t, a printing screen is made of 230 rnesh PECAP
pol.~ fabric. The fsbric is cut to the ~- ~ ~ L = 20 inches and W = 16 inches. The W 096125239 PC~fUS9S/02I27 g rstio X for this . ~ ~ ' is 0.96, i eful~, the ~ ' - d - are cut to I =
19.3 inches _nd w = 15.4inches. The fabric is thus bL-- ' - d by sbout four percent dong its ~- during t g. The pe , of lateral and 1 _ " -' SLI_' ' ' g, 9s ~d along lines that e~ctend parallel to &e center lines, d~l v p.u6.~h,~ from the S . " - to the fabric edges due to the ~ ~ shape of the edges. Tile 0.96 ratio is A ' ' for a screen to be ~1 - ' ' on a frame, as il' ' in FIG. 1, c ' of 1-1/4 inch squsre 9' stock having a wall i' ' of 1/8 inch. Th~ retainers sre - i, parallel to the frame legs, at a spacing such that the I - ' fabric has ~1~, straight edges with the ~' - I = 20.0inches and w = 16.0inches and has a tension of 20 to 30 N/cm ( ; -/d~ n~ distance) across the entire c, ~_ region ofthe screen.
Multiiple uniiform w~ 'c, can be obtained by cutting fabriic to si~ using a pattem shaped as shown by the solid lines in FIG. 2. To insure proper ~' the fabric should first be ironed, if- ~ to remove ~. ' ' . The rela~ced fabnc can then be cut to the desired, pl~l ~ ~ size.
The ~ L, W are obtained by ~ g a flat, rela~ced ~ , ~ -3 from comer to comer. The ~ l, w are taken along I -' c. ' - Cl snd latersl ' ~ C2 which are located midway between the comers. Most ~ r ~ each edge of the fabric is a miinor arc of a circle.
Another method of 9'' ~ ~ g &bric to ~~ ~ though not p.ef~.-~l due to the ~ - ~ it will produce in the CJ~ ~_ region of the ~ , e, is to start with an u._,;,~d piece of fabric and then stretch it to a desired tension pattem, using an u._.,,i~d frame, the fra ne being of the type now .- ~ , used in the screen priinting art. A ~. _'-in the desired ~' -- ~ of a l d ~ , ~ , is then drawn on the u._,~i~d, I - - ' 25 fabric. The fabric is then removed from the c_.~ d frame and cut along the edges of the . l _'- that was drawn thereon. The result is a ~ , sc L:~d piece of fabric wiith u _' center pOIi , since at least the central ~' of the fab/ic reduce when tension is released. C~ .. ~ 1~" the rela~ced, w~ 1c, ~ ~;._d piece of fs,bric is trsced to rnalce a pattem. The pattem is then used for cutting r~ '~ . S ~1 pieces of 30 f bric from bolts of rela~ed fabric of the same _ , Although use of a prior I g device is a slow step, it cmly needs to be ~ r ~ d once for a ~ t; ' type of &bric.
T~ r ~ t~e s' ' ' w~ 1~ ~e ' pieces of fabric are cut quickly,without i the fabric, by using the pattern.
Another ~.~ ' method for ' ~ _ fabric to ~. though again not 3!i p.ef~,..~, slso involves ~ ' e an u._.:,;~d piece of fabriic on an u._.;,;._d frame. In this method, four retainers are ~unted on a jig (not shown) which holds the!m in the 1.: _ ' ~'i,, of r~3tainers for a fully ;,ll,~l ~ 3r1 w~ ~ ~ .3 . e on a ~.~ l~g ~7P~ f~ame. While held by the jig, the retainers _re glued or ~ .;~ attached to the fabric while it is stretched on the W 096/25239 PCTnUS95/02127 1 frame. Once tension applied by the oversi~d frame is released, e~cess fabric is trimmed from around the - , ~. . . the resulting w~ ~ e is ready for ~ ; e on a ~ g sized frame. Although not pl~,f.,..~d, multiple screens could be r ' ~1~ ' u 1~, by using a very large piece of fabric and ,l.~ ,. it on a very large frame so 5 that multiple sets of retainers could be attached to the fabric at once. Then, after the tension is released, the fabric is trimmed to provide multiple . . '~ ~ with the retainers in place. It is possible to attach the retainers without using a jig, e.g.,by simply ~ g to position the .~ ~ . but such is less c<",~_ ~
In the . ' ' of FIG. 1, the p~ .' ' borders of screen 12 were glued to 10 the screen .e~ ~ ~ g member 98 of each retainer. Edge 12a was glued to retainer 90, edge 12b to retainer 92, edge 12c to retainer 94 and edge 12d to retainer 96. Each screen border edge was adhered in a straight line l ~- '~y parallel to the l~ _ ' ' free edge of the retainer with a ,. ~ __' area of overlap between the screen and retainer. The retainer 90, for e . '-, has parallel front and back top edges 9&, 98b (FIGS. 2 and 4). Edge 12a of the 15 screen was glued to the top surface of retainer plate 98, parallel to edges 98a, 98b and closer to edge 98b than 9&, such that a l~ -' _ ' r - i~ '-Al margin of the screen overlaps the retainer. Edges 12b, 12c and 12d were similarly adhered to retainers 92, 94, 9o with similar l. ~ ' margins ~,.. ~, ~ ~g the .~ ~ If desired, the edges of the scroen can further be ~ '~ d around the retainers and glued to the spaces 102 (not shown) to increase the area 20 of contact between the screen and the .J ~ It is helpful for the retainers to be made of a materid which is generally rigid, but '-- ~ ly fle~cible that a retainer can be bent to the same arc as the edge of the fabric during gluing.
Adhering the curved edges of the screen 12 parallel to the edges of the retainers is an 1~ _ way to obtain uniform tension when the screen is ~ ' ' ' on the frame.
25 Because the frame supports the retainers in straight and parallel ~ - , the screen is ~ ' - d the greatest amount along the c ~ ' where the d ~ - are the smsllest when the screen is rela~ed.
The edges of the screen are ~ 1y adhered to the ._"~L~_ ret~iners by a c~ ~' adhesive. U.S. Patent No. 4,702,783,which is h.cc, ~- ~ ' herein 30 by ,~f~ - o, ~ ~ e one such adhesive that has been used to attach fabric to a fi~ced frame.
Other ~ nethods can be used. For , 'e, fabric could be heat bonded to the ,~, ~ or a binding strip (not shown) could be used to attach the fabric ~ ~ 'ly, e.g., to 1~. ;,~ a ~, ' region of the fabric between ~ secured with rivets or other r In the ill t~ - the length of each retainer is less than the length of the edge of the escreen that is su}~l~urt~,d by the retainer. Retainer 94 (FIG. 2), for ~ ,~'R, is adhered to edge 12c such that end ll5a of the retainer is a distance dl from corner 13c and end l l5b is a distance d2 from corner 13d. OpF ~ .5 retainer 92 is plsced co~ l.y on -edge 12b with its ends a distance d3 and d4 from ~ corners 13a, 13b. Retuiner 90 is adhered to edge 12a with its end 113a spaced a distance d5 from corner 13c and end 113b a distance d6 from corner 13a. Retuner 96 is cc, ,c, ' ~ adhered to edge 12d with its ends a distance d7 from corner 13b and a distance d8 from corner 13d. For w.~ , the S ~ - dl-d8 can all be equal; or all opposed pairs Of .~ (dl and d4, d2 and d3, d5 and d7, ~nd d6 ~nd d8) can ,c_~ be equal. By using such ~ , a w~ lc, - ~ e c~n be installed on a frame in either of two ~~ ~ Unequal spacings can be used, but such is less c~,,~. ~
Once each edge of the screen is adhered to a retainer, the r,~tainers ue placed 10 on the frame 10 while portion 30 is in its rela~ed position shown in FIG. l and the spacers are in the .~ ' position shown in ~ in FIG. 3. Retainer 90 is placed in the slot in outer face 28 of leg 16 by inserting a hook member 100 into the slot 84. Retainer 92 is ;r 1~, inserted into the slot 84 through the outer face of leg 18, retainer 94 is inserted into the slot on leg 32, and retuner 96 is inserted into the slot on leg 34. Spaeers 110, 112, 114 and 15 116 are then rotated from their retracted p~- - ;, ~ ~c to the active F ~ ti shown in solid lines in FIG. 5. After the screen is held in place by the retuners on frame 10, the tip of conner 13a fits between sp~lcers 110, 112,and the tip of corner 13d fits between spacers 114, 116.
As shown in FIGS. 2 and 3, conner regions of the w~ e may be folded back or cut off ~' g~ 'ly, e.g. aiong lines 194a, 194b, 194c, 194d. For the - - ~ . . ;l d 20 in this ~' --' .;, ~' between conners are _d between the conners that would have e~isted had conner regions not been folded back or cut off. I.e.,comer to comer ~ ~re taken from the points where the arcuate edges would intersect if ' ' Once the retuners are in position abutting the spacers, ~.. ' '- portion 30 of the frame is ~ved into the Dtl~ ~ g position. This can most rapidly be ~ ~ , ' ' - ' by 25 resting the base portion 14 on a surface, as shown in FIG. 1, while manually pushing ~lv..,.. ~ on the ~ portion 30 at a location near the conner 36. The fr~ne is locked in the Dll~ ~ ~ g position by inserting shaft 188 of tool 190 into collar 178 w-ith pins 182 aligned with slot 180 (FIGS. 1 and 11). Shaft 188 is then rotated by ~ving handle 192 through an arc to e~ert ~I torque on the shaft. Rotary .. ~ of shaft 188 turns collar 178 snd the barrel 30 of worm gear 170. As the barrel rotates, helical groove 172 moves gear wheels 142, 166 in the di.. of arrows 174, 176. Cable 140 is thereby wound around wheels 142, 166 to tighten cable 142 and lock the ~ portion 30 in the Dt~J ~ ' g position. ~ I.y, the tool 190 can be used to crsDk the _ ' '- portion 30 from a rela~ed position into the ~L.''' g position. Using this rnethod, the screen is locked as soon as the _ 'e portion 30 reaches 35 the DL~
As the _.. _ ' '~ portion 30 ~l~o~P~ s, tension is e~erted, vi~ the .~ ~ on the screen 12 to stretch it. A screen printing process c~n then be ~ ~ ' with the ~ ' - ' screen locked in position.

W 096/25239 PCTrUS95/02127 When the screen printing process is ~ , ' d, handle 192 is rnoved through Yn arc in a direction opposite the direction that was used to tighten the cable. The barrel of worm gear 170 then rotates in sn opposite ~ as do gear wheels 142, 166. Tension on cable 140 is rela~ced, dlowing the _.. ,, ' '~ portion 30 to be ~ved out of the Dtl~ g 5 position. As the ~ portion is ~ved out of the DLG- ' g position, the screen ~.. 'c, ~ ~ is relu~ed and can then be re~ved from the frame by sliding the retainers 9~96 out of the slots 84.
r ~
An ' ~ " of the frame is shown in FIGS. 12-14. The frame 200 10 is simil~r to the frame 10 shown in FIGS. 1-11, e~cept for the ~ ,. of the hinged :~- between the ~vable and ~ parts of the frame, and the ~ of the retainers to the frame.
Frame 200 is a .~ ~ ' , frame having a ~ .~ portion 202 and a ~vable portion 204. The ~ portion 202 includes legs 206,208 that are made from a body of a 15 rnaterial such as wood and are fi~ed to one another along a common mitered junction 210.
Legs 206, 208 have a top surface member that defines a c~ top face. The top face is p~f ~ provided by an L-shaped plastic surface member 213 (FIG. 14) that is adhered to the top faces of ~ g legs 206,208. The plastic surface member I ~ ~ along a slanted edge 214 at a distal end of leg 206 and a slanted edge 216 at a distal end of leg 208.
20 The inner border of the retainer sits flush against a top surfa.e of legs 206, 208, but the top surface of the legs is recessed du. .,~ _ ~ along the outer border 218 of &e frarne such that there is a slot 220 between the retainer 213 and the I ' l~, g leg, such as leg 208 in FIG. 15.
Movable portion 204 of the frame 200 is sirnilar to t: .~ portion 202, and includes legs 230, 232 that are fi~ced to one another along a mitered junction 234. An L-shaped 25 surface rnember (such as surface mernber 213 in FIG. 14) e~ctends ~ over the top surf~ce of legs 230, 232 to provide a flat top face 236. The surface rnember I ~ dong inclined edges 238,240adjacent hinged _ :- between - ~ and movable portic~ns 202, 204 of frame 200. The outer border of legs 230,232 is recessed to provide a .' ~ ' slot between the surface member and the I ' 1~ frame.
Four retainers 250, 252,254 and 256 are similar to the ret"iners 90, 92, 94 and 96 . ;l d in c - ~l- with FlGS. l and 4. Each retainer is similar to retainer 252 shown in FIG. 14, and includes a flat upper plate 260 adhered to a screen 212, a I ._.~ spacer plate 262, and an ~ . ~ ~--; e ~ - hook plate 264 that e~tends into the slot 220 between the surf~ce rnember and frame to hook the retainer to the frame.
The distd ends of legs 206,230 are joined along a hinged junction 280, that is shown in greater detail in FIG. 13. The hinged junction p-~ r J~ includes u pair of met~ll plates 282,284 that are fi~ed .~ to the end faces of legs 208,206 by bolts 286, 288.
Plate 282 contains a socl~et 288 and notch 290 for ,~:ti~ ~;vi. g a dowel pin 292 and W 096125239PCT~US95/02127 latch pin 294 that project ~.~ uul~ dly from the outer surface of plate 284. A
.~~;},.~ ' latch 296 moves in the d;.. ,' - of arrow 298 in a recess 300 behind plate 282 to ~ve a lock in and out of; , _ with latch pin 294 when pin 294 is in place witbin notch 290 after plates 282, 284 are brought into I ' by closing frsme 200. A slot 302 e~ctends behind platls 284 such tbat a hook 304 that e~tends from the edge of platls 282 can hook over plate 284 and into notch 302 to help retain plates 282, 284 in ~ vhen the frame is in its sl.. ' ~ g ~ ~ Finally, the opposite ends of a csble 306 are attac~hed to the wooden f~une by screws 308,310. Cable 306 e~tends across junction 280 between terrninal edges 214, 238 of the plastic ' This cable 306 helps rnaint~in legs 206, 230 in ~
10 s li,when the hinged junction is in the I ~ ' ' c ~ shown in FIG. 13.
Legs 208, 232 are similarly joined at a hinged c~ 31' 2 tbat is similar to the hinge ~ 280 A~ ~ ;1.~ above.
In ~n~ a printing screen is attached to r~stainers 250, 252, 254 and 256, as.;1~ in . with the ~ r ~- of frame 10 above. The hooking plates (such as lS plate 264 in FIG. 14) of the retainers are then inserted into the slots of the rela~ced fr~ne between the surface member and ~ ,~ wooden leg. Indicia 314 or 318 on the screenare digned with indicia 316 or 320 on the frame to insure proper F- ~ g of the screen ~ ~ 1~,.
Movable portion 204 of the frsme is then pushed down tow~ard the surface on 20 which -~ base portion 202 is resting, to bring the opposed rnetal plates at hinged :- 280,312 into ~ ~ with one another. The dowel pin 292 fits into soclcet 288, while latch pin 294 fits into socket 290 (FIG. 13). Hook 304 engages ove~r the edge of plate 284, to further align plates 282, 284, and latch 296 is rnoved over the enlarged he~d of latch pin 294 in notch 290 to lock the legs ~r '- ~ to one another in the c ~ - shown in FIG.
2S 12. Screen printing can then proceed as ~ '-;1~1 in c with tho previous e When it is desired to change screens, latch 296 can be pulled away from latch pin 294 to free legs 206, 208 from one another and allow rnovable portion 2()4 to swing up away from the surface on which ~ portion 202 rests. Once movable p~rtion 204 is moved30 into the rela~ed F ~ . the retainers can be removed from the frame, ~md the screen stored for ' , use. A new screen csn then be placed on the frame, and the p~u~
;l ,d above repeated to lock the screen taut on the frame for use.
Having " d and ~ 1 the . ~ , - of the ~. in two ~.~,f~,o~
~ ~- it should be apparent to those skilled in the art that the ~ .~tion can be ~- ~ d in ~ and detail without ~ r '- g from such J ~ . l~ I claim dl - ~- coming within the spirit and scope of the following claims.

W 096125239 PCTrUS9S/02127 For , ~a, although the locking . ' ~ above are unique, there are other ~ ' ~ s, such as lc~ '~ pins or screws joining hinged legs, that would work in certain ~
In the i~ ' c ' ~ uniform tension is achieved by using a ~.. ~c, ---5 that is u.._d near the centers of its edges and pulled to a ' ~ - -'ly uniform tension and 8 ' ' ' '- 'Iy r~ - ' shape. A . ;~' ' Iy less c~ . ~ way to achieve uniform tension would be to start with a truly ~~J ~ .. 'f~ e and stretch it on a frame with the edges of the w~ 'c, -~le bowed uul~. ~lly at their centers (not shown) so as to stretch the ~. . b, ~- . e a greater amount between the centers of two w~ ,e edges than between two 10 adjacent corners of each edge. It is not ~ that the w~ b, ~-c be even generslly ,~ _ ' or have edges c~n~ ~ g to the n ~ ~ ~ . The ~ _ of this e system willbe obtained so long as a greater amount of w~ ~, ~ sl,~ ' g occurs along the c ' of the w~ ~f, -ce than along lines that are located outwardly of and that e~tend parallel to the ~
1~ Also, although spacers 90-96 and indicia 314-320are .l:~ ~ d above, other -~, ~ ' ~ can be used to achieve ~r ' ~ ~~ W~ ~ ~~ p~ ~' ~ ' g.
It should also be, ' ~d that the ~ e can be ' g other than a printing screen. The systems d~ d above can be used ~.' ._. it is -- ~ to tightly stretch a sheet of msterid. Some signs, for ~ are printed on fle~cible plastic ~ ' - e.
20 Such sign shèeting can ~ , be ~ - ~ -d~ mounted and/or D~ ' -' on a fra~ne ~r. c .' g to the present ~ ~.

Claims

1. A frame for stretching a planar workpiece, the frame comprising:
a base portion defining a first plane in which the workpiece is stretched;
a swingable portion that pivots relative to the base portion and moves from a relaxed position in which the swingable portion defines a plane that intersects the first plane at an angle, to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane; and a device to secure a flexible planar workpiece to both portions of the frame.
2. The frame of claim 1 wherein the workpiece is a screen.
3. The frame of claim 1 wherein the frame is quadrilateral, the base and swingable portions each comprising an angled, two-legged member, each two-legged member having first legs joined by a hinge at common mating ends of the first legs and second legs joined by a hinge at common mating ends of the second legs.
4. The frame of claim 3 wherein each hinge is mounted to rotate about an axis that extends through one of the angled members.
5. The frame of claim 4 further comprising at a common mating end of the frame, a guide member on one of the two-legged members and a guide socket in the other two-legged member into which the guide member fits.
6. The frame of claim 1 further comprising a lock that maintains the swingable portion in the stretching position relative to the base portion.
7. The frame of claim 6 wherein the lock comprises a mechanism capable of pulling the swingable portion toward the first plane.
8. The frame of claim 7 wherein the lock comprises a cable extending through the frame and crossing at least one of the hinges.
9. The frame of claim 8 wherein the lock further comprises:
a plurality of pulleys spaced around the frame with the cable riding on the pulleys; and a tightener that selectively increases the tension on the cable.
10. The frame of claim 9 wherein the tightener comprises a worm gear.
11. The frame of claim 1 wherein the device comprises a plurality of elongated retainers each having a workpiece retaining portion and a frame engaging portion.
12. The frame of claim 11 wherein:
each portion of the frame has an outside face that defines an elongated slot;
each workpiece retaining portion has a planar surface to which an edge of the workpiece can be adhered; and each frame engaging portion comprises an L-shaped hook that fits over one of the outside faces and into a slot of that face.

13. The frame of claim 12 wherein the workpiece is secured to the retainingmember by an adhesive.
14. The frame of claim 12 further comprising a spacer that selectively fitsagainst one of the retainers to inhibit longitudinal movement of that retainer toward the spacer.
15. The frame of claim 1 further comprising a four-cornered, four-sided workpiece having arcuate edges that curve such that the width and length of the workpiece are reduced toward the center of the workpiece.
16. The frame of claim 15 wherein:
each retainer has a longitudinal free edge that extends parallel to a leg of the frame when the retainer is installed on the frame; and the workpiece is a printing screen adhered to the retainers with the arcuate edges conforming to the longitudinal free edges.
17. A rectangular frame for stretching a quadrilateral printing screen, comprising:
a right angle-shaped base portion defining a first plane;
a right angle-shaped swingable portion that pivots relative to the base portion and moves from a related position in which the swingable portion defines a plane that intersects the first plane at an angle, to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane;
the base portion comprising first and second legs, joined at a common mitered corner and terminating in first and second distal ends, the swingable portion comprising first and second legs joined at a common mitered corner and terminating in first and second distal ends;
a first hinge between the first ends of the base and swingable portions, the hinge extending in the plane along a mitered junction between the first ends, and further including a pivot attachment to the first end of the swingable portion that allows the first leg of the swingable portion to rotate about a longitudinal axis of the first leg of the swingable portion;
a second hinge between the second ends of the base and swingable portions, the hinge extending in the plane along a mitered junction between the second ends, and further including a pivot attachment to the second end of the swingable portion that allows the second leg of the swingable portion to rotate about a longitudinal axis of the second leg of the swingable portion;
an elongated slot in an outer face of each leg of the frame;
four retainers for securing the screen to the frame, each retainer comprising a J-shaped member having a first planar flange for adhesively securing an edge of the screen to the retainer, and a spaced second planar flange that fits into one of the slots;
a spacer that selectively fits against each retainer to inhibit movement of the retainer in the slot toward the spacer;

a plurality of pulleys spaced around the interior of the frame, and a cable extending through the frame across the first and second hinges, the cable riding on the pulleys; and a tightener that selectively increases the tension on the cable.
18. The frame of claim 17 further comprising a quadrilateral screen having four edges, in which at least a portion of each of the four edges is adhered to the first planar flange of one of the retainers with a rectangular area of the screen overlapping the retainer, each of the four edges arcuately curving so that the length and width of the screen is reduced toward the center of the screen when the screen is not mounted on the frame.
19. A method of stretching a planar workpiece, comprising:
providing a frame comprising a base portion defining a first plane, and a swingable portion that pivots relative to the base portion and moves from a relaxed position in which the swingable portion defines a plane that intersects the first plane at an angle, to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane;
securing edges of a workpiece to the frame with the swingable portion in the relaxed portion; and then moving the swingable portion from the relaxed to the stretching position tostretch the workpiece.
20. The method of claim 19 further comprising the step of providing a screen as a workpiece.
21. The method of claim 20 further comprising the step of performing screen printing with the screen while the swingable portion is in the stretching position.
22. The method of claim 20 wherein:
the frame further comprising a cable crossing at least one hinge; and the method further comprising increasing tension on the cable to maintain the swingable portion in the stretching position.
23. The method of claim 20 wherein:
the step of providing the screen as a workpiece comprises providing a quadrilateral screen having four arcuate edges that curve such that the width and length of the screen is toward the center of the screen;
the step of providing a frame comprises providing a quadrilateral frame comprising four legs, each leg having a top face in the first plane when the swingable arm is in the stretching position and an outwardly facing side face that is perpendicular to the top face and defines an elongated slot; and the step of securing the edges of the screen to the frame comprises providing multiple retainers each of which includes first and second spaced planar flanges, and adhering each of the four edges of the screen to the first planar flange of one of the retainers, then inserting the second planar flange of each retainer into one of the slots.
24. The method of claim 20 wherein:

the step of providing the screen as a workpiece providing a quadrilateral screen having four arcuate edges that curve such that the width and length of the screen is reduced toward the center of the screen;
the step of providing a frame comprises providing a quadrilateral frame comprising four legs; and the step of securing the edges of the screen to the frame comprises adhering peripheral margins of the screen to a plurality of retainers such that the arcuate edges of the screen are substantially linear when the screen is tensioned on the frame.
25. A method for providing a stretched planar workpiece, the method comprising:
providing a frame;
providing a workpiece that is generally rectangular, but that has arcuate edges such that the width and length of the workpiece are less at the centerlines of the workpiece than at outlying regions of the workpiece; and securing the edges of the workpiece to the frame in such a manner that the edges lie in a rectangle and such that the frame applies both lateral and longitudinal tensile forces to the workpiece.
26. A printing screen that is generally in the shape of a rectangle having two longitudinal edges, two lateral edges, a longitudinal centerline and a lateral centerline, the edges being arcs such that, when the screen is not tensioned, the width and length of the screen are less when measured along the centerlines than when measured at locations outwardly of the centerlines.
27. The printing screen of claim 26 wherein the arcs are shaped such that when longitudinal and lateral tensile forces are applied to the edges with the edges held straight, the screen is uniformly tensioned.
28. The printing screen of claim 26 further comprising four elongate retainers attached to the screen, one retainer extending along and conforming to each edge.
29. The printing screen of claim 26 wherein each edge is a minor arc of a circle.
30. A workpiece comprising:
a piece of screen printing fabric; and multiple retainers that are attached to the fabric along the perimeter of a geometric figure and that are adapted to be releasably held by and to receive opposed outwardly directed forces from a stretching frame.
31. The workpiece of claim 30 wherein the retainers are permanently attached to the fabric by a cyanoacrylate adhesive.
32. A planar workpiece system comprising:

a workpiece that includes a sheet of planar material and four elongate retainers that are attached to the sheet and are arranged generally in the shape of a rectangle, the workpiece having a longitudinal centerline that extends parallel to and is equidistant from two of the retainers, and a lateral centerline that extends parallel to and is equidistant from the other two of the retainers; and a frame adapted to engage and exert an outward force on each of the retainers, the workpiece and frame being shaped and constructed such that the workpiece canrepeatedly be released from and reattached to the frame at a set location and such that the frame stretches the sheet a greater amount along the centerlines of the sheet than along other lines that extend parallel to the centerlines.
33. The system of claim 32 comprising multiple, interchangeable workpieces.
34. A method of supporting a planar workpiece on a frame having movable leg portions, the method comprising:
attaching a sheet of planar material, along the perimeter of a figure generally in the shape of a rectangle having a longitudinal centerline and a lateral centerline, to the leg portions of a generally rectangular frame having movable leg portions; and moving the leg portions to positions wherein the frame applies predetermined tensile forces to the sheet and stretches the sheet a greater amount along the centerlines than along other lines that extend parallel to the centerlines.
35. A frame for stretching a planar workpiece, the frame having four bars arranged substantially as a rectangle and comprising:
a base portion defining a first plane in which the workpiece is stretched;
a swingable portion that pivots about a fold axis which extends diagonally with respect to the bars and that thus moves, relative to the base portion, from a relaxed position in which the swingable portion defines a plane that is not co-planar with the first plane, to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane;
a hinge assembly joining the base portion and swingable portion; and a device to secure four edge portions of a flexible planar workpiece along each bar respectively.
36. The frame of claim 35 wherein the workpiece is a screen.
37. The frame of claim 35 wherein:
the frame is quadrilateral;
the base and swingable portions each comprise an angled, two-legged member;
each two-legged member has a first and a second leg; and the frame further comprises a hinge joining the first legs and a hinge joining the second legs.

38. The frame of claim 37 wherein each hinge is mounted to rotate about an axis that extends through one of the angled members.
39. The frame of claim 38 further comprising, at a common mating end of the frame, a guide member of one of the two-legged members and a guide socket in the other of the two-legged members into which the guide member fits.
40. The frame of claim 35 further comprising a lock that maintains the swingable portion in the stretching position relative to the base portion.
41. The frame of claim 40 wherein the lock comprises a tensioning mechanism which is connected to the base portion and to the swingable portion and which, in use, pulls the swingable portion toward the first plane.
42. The frame of claim 41 wherein the lock comprises a cable extending through the frame and crossing at least one of the hinges.
43. The frame of claim 42 wherein the lock further a plurality of pulleys spaced around the frame with the cable riding on the pulleys;
and a tightener that selectively increases the tension on the cable.
44. The frame of claim 43 wherein the tightener comprises a worm gear.
45. The frame of claim 35 wherein the device comprises a plurality of elongated retainers each having a workpiece retaining portion and a frame engaging portion.
46. The frame of claim 45 wherein:
each portion of the frame has an outside face that defines an elongated slot;
each workpiece retaining portion has a planar surface to which an edge of the workpiece can be adhered; and each frame engaging portion comprises an L-shaped hook that fits over one of theoutside faces and into a slot of that face.
47. The frame of claim 46 further comprising a body of adhesive securing the workpiece to the retaining member.
48. The frame of claim 46 further comprising a spacer that selectively fits against one of the retainers to inhibit longitudinal of that retainer toward the spacer.
49. The frame of claim 45 wherein:
each retainer has a long longitudinal free edge that extends parallel to a leg of the frame when the retainer is installed on the frame; and the workpiece is a printing screen adhered to the retainers with the arcuate edges conforming to the longitudinal free edges.
50. The frame of claim 35 further comprising a four-cornered, four-sided workpiece having arcuate edges that curve such that the width and length of the workpiece are reduced toward the center of the workpiece.

51. The frame of claim 35 wherein the bars are 1-1/4 inch square aluminum stock having a wall thickness of 1/8 inch.
52. A rectangular frame for stretching a quadrilateral printing screen, comprising:
a right angle-shaped base portion defining a first plane;
a right angle-shaped swingable portion that pivots relative to the base portion and moves from a relaxed position in which the swingable portion defines a plane that intersects the first plane at an angle, to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane, the base portion comprising first and second legs having first and second distal ends respectively, the swingable portion comprising first and second legs having first and second distal ends respectively;
a first hinge between the first ends of the base and swingable portions, including a pivot attachment to the first end of the swingable portion that allows the first leg of the swingable portion to rotate about an axis that extends through the first leg of the swingable portion;
a second hinge between the second ends of the base and swingable portions, including a pivot attachment to the second end of the swingable portion that allows the second leg of the swingable portion to rotate about an axis that extends through the second leg of the swingable portion;
an elongated slot in an outer face of each leg of the frame;
four retainers for securing the screen to the frame, each retainer comprising a J-shaped member having a first planar flange for adhesively securing an edge of the screen to the retainer, and a spaced second planar flange that fits into one of the slots;
a spacer that selectively fits against each retainer to inhibit movement of the retainer in the slot toward the spacer;
a plurality of pulleys spaced around the interior of the frame, and a cable extending through the frame across the first and second hinges, the cable riding on the pulleys; and a tightener that selectively increases the tension on the cable.
53. The frame of claim 52 further comprising a quadrilateral screen having four edges, in which at least a portion of each of the four edges is adhered to the first planar flange of one of the retainers with a rectangular area of the screen overlapping the retainer, each of the four edges arcuately curving so that the length and width of the screen is reduced toward the center of the screen when the screen is not mounted on the frame.
54. A method of stretching a planar workpiece, comprising:
providing a frame comprising four bars arranged substantially as a rectangle, the frame having a base portion defining a first plane, a swingable portion that pivots relative to the base portion and moves from a relaxed position in which the swingable portion defines a plane that is not co-planar with the first plane to a stretching position in which the swingable portion defines a plane that is substantially co-planar with the first plane, and a hinge assembly that joins the base portion and swingable portion and that defines a fold axis which extends diagonally with respect to the bars;
respectively securing four edge portions of a workpiece along the four bars while the swingable portion is in the relaxed position; and then moving the swingable portion from the relaxed to the stretching position tostretch the workpiece.
55. The method of claim 54 further comprising the step of providing a screen as a workpiece.
56. The method of claim 55 further comprising the step of performing screen printing with the screen while the swingable portion is in the stretching position.
57. The method of claim 55 wherein:
the frame further comprises a cable crossing at least one hinge; and the method further comprises increasing tension on the cable to maintain the swingable portion in the stretching position.
58. The method of claim 55 wherein:
the step of providing the screen as a workpiece providing a quadrilateral screen having four arcuate edges that curve such that the width and length of the screen is narrowed toward the center of the screen;
the step of providing a frame comprises providing a quadrilateral frame comprising four legs, each leg having a top face in the first plane when the swingable arm is in the stretching position and an outwardly facing side face that is perpendicular to the top face and defines an elongated slot; and the step of securing the edges of the screen to the frame comprises providing multiple retainers each of which includes first and second spaced planar flanges, and adhering each of the four edges of the screen to the first planar flange of one of the retainers, then inserting the second planar flange of each retainer into one of the slots.
59. The method of claim 55 wherein:
the step of providing the screen as a workpiece comprises providing a quadrilateral screen having four arcuate edges that curve such that the width and length of the screen is reduced toward the center of the screen;
the step of providing a frame comprises providing a quadrilateral frame comprising four legs; and the step of securing the edges of the screen to the frame comprises adhering peripheral margins of the screen to a plurality of retainers such that the arcuate edges of the screen are substantially linear when the screen is secured to the frame and the swingable portion is in the stretching position.
60. A method for providing a stretched planar workpiece, the method comprising:

providing a planar workpiece that is generally rectangular, but that, when the workpiece is not tensioned, has arcuate edges such that the width and length of the workpiece are less at the centerlines of the workpiece than at outlying regions of the workpiece;
providing a frame having surfaces that are adapted to engage the edges of the workpiece and that are movable to predetermined positions in a plane to exert outward forces on the workpiece at each of the edges;
securing the arcuate edges of the workpiece to the surfaces; and moving the surfaces to the predetermined in the plane in such a manner that the frame applies predetermined lateral and longitudinal tensile forces to the workpiece to stretch the workpiece to a predetermined tensioned configuration wherein (a) the edges are no longer arcuate, but instead have been straightened, and (b) opposite edges have been moved apart, so that the edges lie in a rectangle of predetermined dimensions.
61. The method of claim 60 further comprising the step of providing a screen as the workpiece.
62. The method of claim 60 wherein the step of securing the edges of the workpiece to the surfaces comprises:
providing a plurality of retainers, each retainer having a longitudinal edge;
adhering the workpiece to the retainers with the edges of the workpiece conforming to the edges of the retainers; and securing the retainers to the surfaces.
63. A printing screen that is generally in the shape of a rectangle and that is adapted for mounting on a rectangular frame, the screen:
having two longitudinal edges, two lateral edges, a longitudinal centerline (C1), and a lateral centerline (C2) that is perpendicular to the longitudinal centerline (C1);
having, between the lateral edges, a length (1) measured along lines parallel to a centerline (C1), the length (1) being progressively greater as distance away from the centerline (C1) increases, the measurements being made when the sheet lies flat and nontensioned;
having, between the longitudinal edges, a width (w) measured along lines parallel to a centerline (C2), the width (w) being progressively greater as distance away from the centerline (C2) increases, the measurements being made when the sheet lies flat and nontensioned; and being of a predetermined size and shape such that, when the screen is uniformly tensioned on a frame, the edges lie in a rectangle of predetermined dimensions.
64. The printing screen of claim 63 further comprising four elongate retainers attached to the screen, one retainer extending along and conforming to each edge.
65. The printing screen of claim 63 wherein each edge is a minor arc of a circle.
66. A printing screen that is generally in the shape of a rectangle having two longitudinal edges, two lateral edges, a longitudinal centerline and a lateral centerline, the edges being arcs shaped such that, when the screen is not tensioned, the width and length of the screen are less when measured along the centerlines than when measured at locations outwardly of the centerlines and such that, when sufficient longitudinal and lateral tensile forces are applied by a frame to hold the edges straight, the screen is uniformly tensioned.

67. A planar workpiece system comprising:
a workpiece that includes a sheet of planar material and four elongated retainers that are separately and permanently attached to the sheet and are arranged in a predetermined pattern generally in the shape of a rectangle, of predetermined dimensions, the workpiece having a longitudinal centerline that extends parallel to and is equidistant from two of the retainers, and a lateral centerline that extends parallel to and is equidistant from the other two of the retainers;
and a frame having four surfaces that are adapted to releasably engage the four retainers respectively and that are movable to predetermined positions in a plane to exert an outward force on each of the retainers, the relative spacings of opposed retainers and surfaces being such that the length (L) of the frame measured between the surfaces that engage opposed retainers of the workpiece along a centerline (C1) is greater than the length (1) of the workpiece measured between the retainers along the corresponding centerline (C1) of the workpiece when the workpiece lies flat and relaxed, the difference between the lengths (L) and (1) being greatest along the centerlines (C1) and being progressively less, as measured along lines parallel to the centerlines (C1), as distance away from the centerlines (C1) increases.
68. The system of claim 67 comprising multiple, interchangeable workpieces.69. A method of supporting a planar workpiece on a frame having movable legportions, the method comprising:
providing a non-tensioned sheet of planar material on which is indicated a geometric figure of predetermined dimensions generally in the shape of a rectangle having four edges, a longitudinal centerline and a lateral centerline;
providing a separate frame having movable leg portions which are adapted to moveto a predefined position wherein the frame is generally rectangular, each leg portion having an edge, at least one of (a) the geometric figure and (b) the frame having edges that are not straight but instead are shaped such that the length (L) between opposite edges of the frame measured along a centerline (C1) is greater than the length (1) between opposite edges of the geometric figure measured along the corresponding centerline (C1) of the sheet, the difference between the lengths (L) and (1) being greatest along the centerlines (C1) and being progressively less, as measured along lines parallel to the centerlines (C1), as distance away from the centerlines (C1) increases, the measurements being made when the sheet lies flat and non-tensioned and the leg portions are in the predefined position wherein the frame is generally rectangular;

attaching the non-tensioned sheet to the frame with the four edges of the geometric figure respectively aligned with the edges of the frame; and moving the leg portions to predetermined in a plane: wherein the edges of the frame are arranged generally in a rectangle and the frame applies predetermined tensile forces to the sheet and stretches the sheet to a tensioned configuration where the edges of the geometric figure conform to the corresponding edges of the frame.
70. A planar workpiece system comprising:
a piece of screen printing fabric;
four elongated retainers that are attached to the fabric along the perimeter of a geometric figure generally in the shape of a rectangle; and a frame having four frame surfaces that are adapted to releasably receive each of the retainers respectively and that are movable between (a) first positions wherein the frame surfaces do not exert outward force on the retainers so that the retainers can be mounted on or removed from the frame surfaces and (b) second positions which are predetermined in a common plane and wherein the frame surfaces exert an outward force on each of the retainers to tension the fabric;
the frame surfaces being shaped to allow longitudinal movement of the retainers such that the retainers can slide longitudinally along the frame surfaces when the frame surfaces are in the first positions and the retainers are mounted such that the retainers abut the frame wherein at least one of (a) the geometric figure and (b) the frame surfaces haveedges that are not straight but instead are shaped such that the length (L) of the frame between the frame surfaces along a centerline (C1) is greater than the length (1) of the geometric figure measured along the corresponding centerline (C1) of the fabric, the difference between the lengths (L) and (1) being greatest along the centerlines (C1) and being progressively less, as measured along lines parallel to the centerlines (C1), as distance away from the centerlines (C1) increases, the measurements being made (a) before the retainers are attached to the fabric, (b) while the fabric lies flat and non-tensioned, and (c) while the surfaces are in the second position.
71. A method of forming a planar workpiece to be stretched on a frame that has four rails of predetermined dimensions, the method comprising:
stretching a sheet of planar material, having greater dimensions than the workpiece to be formed, to a predetermined tension;
after the sheet is stretched, fastening four bars to the sheet in the pattern that corresponds to the pattern of the rails of the frame.
72. The method of claim 71 for forming a planar workpiece to be stretched on the rails of a frame that has movable rails, the method further comprising:
positioning the bars on the sheet so the bars are spaced apart at a distance that corresponds to the maximum dimensions of the frame when the rails are fully extended;

providing bars that are adapted to be secured on the rails of the frame; and detensioning the sheet after the bars are attached.