US2637269A

US2637269A - Stencil printing apparatus

Info

Publication number: US2637269A
Application number: US221794A
Authority: US
Inventors: John B Thomas
Original assignee: ROTO MATIC SERCEN PRINTER Ltd
Current assignee: ROTO MATIC SERCEN PRINTER Ltd; ROTO-MATIC SERCEN PRINTER Ltd
Priority date: 1951-04-19
Filing date: 1951-04-19
Publication date: 1953-05-05
Anticipated expiration: 1970-05-05

Description

May 5, 1953 Filed April 19 1951 J. B. THOMAS STENCIL PRINTING APPARATUS fT III-1.

4 Sheets-Sheet l INVENTOR.

JOHN B. THOMAS ATTORNEY May 5, 1953 J. B. THOMAS 2,637,269

STENCIL PRINTING APPARATUS Filed April 19, 1951 4 Sheets-Sheet 2 SOLENOID 827 I :11 BRAKE '44 1% 5 e 1 I I2. E

IN VEN TOR.

JOHN B. THOMAS ATTORNEY May 5, 1953 J. B. THOMAS 2,637,269

STENCIL PRINTING APPARATUS Filed April 19, 1951 4 Sheets-Sheet 5 GTIT A. 7.7. v.

INVENTOR.

JOHN B. THOMAS F1115. @WWL ATTORNEY May 5, 1953 J. B. THOMAS STENCIL PRINTING APPARATUS Filed April 19', 1951 4 Sheets-Sheet 4 INVEN TOR. JOHN B. THOMAS Patentecl May 5, 1953 37,26 STENGEJ mtns rING "APPARATUS :Joh B- lh mas, Wat rwwn, Conn assignor t o B tsan s t?- K s s? creen Printer, 1nd,; Nevv York, fof New Yer-l;

Application April lii, 1951, 'S erialiNo. 221;794

claim .1

This invention relates :to an apparatus ifpr printing sheets, such as textile fabric webshplasic films and paper, with the aid vof 3a stencil. Roisimplicity, such apparatus will be referred vt hereinafter simply as a silk screen printin ma,- chine, it being" understood that this term ,merc 1y is a trade designation for a stencil .prinjging machine and. does not indicate that the =,st;enc il necessarily is of silk.

It is an object of the invention :to provide a power driven silkscreen printing machine in which a scraper rapidly moving back and forth across the screen reverses and .stODS smoothly and quietly,

More specifically, it is anobjectyof the .in lenr tion to providea machine of the character de scribed in which the scraper issloyvedldown pr or to reversal .or stopping joy the vprovision of a variable speed transmission in the 1liinen atic drive tier the scraper and i rsha plr' cre sing the speed redu tion ju t z bsit le th is i' r.= "'r verses 01' stops.

.Iti an her objec of 11 inv nt on is mr ie n apparatu o th ichsra te Qessrb din iwh qh ad u t ent ih A ssih-si tmls ef ill 'sq er can be made easily and rapidly.

lit another object of the invention ;to provise smas 9 th finan ier 'i escr. .fed wa employs far ewer par son the t top than -:a

r s n d newe .QIAYER s k se pr n in i is s o e pbi s o th nven ion t rovide and apparatus of the character qescigibe d in which eith r the P n 9 s q sins Q? a s sa s :th sc ap ca b ad usted at w ll qe s m t a Web .o an W- posit n.

v; is an ther ob ec e t nven n 1 9 pmi a p ra us o the haracte i d sc i ed which i q ash s n trus s tha th 9 r v is aut atica l c t out a an :P i X 9 scr en t ave i u ama in the a paratus,-

i th l t r onn t pn i is a no; object of the invention to provide an a p H o .t r ha ast r e cribed in whi h the so ans er d ve sautsmst al y ut pu i il, s9??? we is raisedso iha thereis no dan er pf hav ng-313s screen torn.

:I is anoth o ec .9 th inven io 4 movies an ap aratu o the chara te .sis q ibsd -WhiQh is of ruseeq ans durab qon t q i nt er Qbi t th n ent qn i l impa be ob u and vm p r w l he oin ed .q j new mafter.

[The invention accordingly cons; ts in the jeatures 0f construction, Combinatio of elements and arrangements of parts which vvill be x'inbiisdin e machine herein s s be n o which i11 co .of appli ion w ll b ndic t d n th ppende c imsin t e sqwmp ny ns draw gs, in whic s shown ens o the v r-1 1 s p ss b mbodiments o 1th inven on,

z s- 1161 a t p plan i o a p wer driven si k sc een printin mach ne constructed in a corglance with the present invention and having 1 many :dfitails thatare-shown elsewhere o nitteid i s ider to pre ent ontu ion;

Fig. 2 is an enlarged fragmentary view taken substantially along the line of ;2?2 of Fig. ane s il ustr t p -th in mati d i e o the Fig. 2a is a schematic gliag-rarn of a hydraulic tra smission unitin i -k nsmati d vs; l

s- 3 1 a sect o a iew taken su sta tial y lon th 1 1? 3-173 Fi A Fist i s an -.en re d v asm i y y sw tak along the line 4-.-.-& of Fig. 1 and-is illustrative of e mechanisms :iQ stamina and starting the scraper upon rise and fall of the stencil screen; Fig. .-5 i a se tiona .view taken al n th 'rl n O :5 of :Fi Fig. 6 is a sectional view taken substantially a on t n *,6' i F Br n 7 -;is a wiring .vdiagrarn of the circuit for the-scraper controlmechanism.

in general, the various objects ,of the present invention are achieved by providing a sill; screen printing gnachine in which thescrape'r is actu' ategl from an electric motor throng ha hydraulic t a smissi n- A emb i i c ud d w i h duplicat s in m n tu e sh move ent .o e scraper and avloich ,fn nc tions as a ,control f or ieysrs ns s pin the ele t m to Th hydraulic ltra smi'ssion enabl s the sc e to be rapiqlr a ce er te and cs e t mmed ately beiorc and after reve sa 1 opp e crime scrape hus ther i p'rovid.ed Iar we r v for t e scrane which i bothefi c en an quie and which can be adjusted rapidly and with ease. Referr n n w in detafl t t drawi s, the refer-s i nu a memes k screen b riti g m hinsem dy n the i v ntion a comprising a suitable printing table 1.2 to either side io'f which a'si ppl y or a take-i 1 reel .(not show disp0se iheip in i bl nins zdes an st apronQM and a reaiiapron l6 s itahly interconnected by struts (not shown).

A ached t t rea a r n a e .a p ir o spscedfcs iriss J (sesFissand 12 "i a i wall vof e a chof which aligned horizontal axles 20 are journaled. Each of said axles has a-ffixed to it a sprocket 22 about which a chain 24 is trained. Moreover, each axle 22 turns a second sprocket 26 about which a chain 28 is trained. The two chains 28 engage sprockets 30 which are secured to aligned horizontal axles 32 journaled in the casings above the axles 22. Turning with each axle 32 is another sprocket 34. Each sprocket 35 engages a different chain 36 having an upper flight 38 and a lower flight 39. Said flights extend forwardly through openings 42, M in the front wall of each casing l8. A pair of hollow

tubular rails

46, 48 are attached to the front wall of each casingin line with the

openings

42, 44, said rails serving to enclose the flights of the chains 36. At the forward end of each said pair of rails there is fixed a housing 50 in which there is contained an idler sprocket (not shown) about which the associated chain 36 is trained. The housings 56 are connected by a cross bar 52 which serves to tie together the scraper supporting frame elements on opposite sides of the machine.

The machine H3 includes a scraper 54 of suitable construction designed to ride back and forth across a stencil screen and to clear the pool of ink at both ends of its travel. One satisfactory form of scraper is that shown in the co-pending application of John B. Thomas and Courtney E. Moorhouse, Serial No. 726,504

for Stencil Printing Apparatus, filed February 9 5,1947; another acceptable form of scraper is the one shown in co-pending application Serial No. 221,793 for Stencil Printing Apparatus filed simultaneously with the present application, both said applications being assigned to the assignee of the present application.

Essentially, the scraper includes a blade 55 whose opposite ends are mounted on carriages 58 having

wheels

60, 62 located between and riding on the

rails

46, 48 at opposite sides of the machine. Each carriage is secured by a fitting 6 3 to the upper flight 38 of its associated chain 36 so that as the chains move back and forth the scraper will be moved in like fashion. The fitting 6 3 rides in a slot 66 at the bottom of the upper rail 56. The machine I0 includes a conventional stencil screen 68 secured to a rectangular screen frame 70. The frame is supported between a front bar 72 and a rear bar 74, the mechanisms used to connect the frame and bars being of any suitable construction and desirably being such as shown, described and claimed in co-pending' application Serial No. 726,504 for permitting fine adjustments of the position of the frame. Heretofore, only the front support for a stencil screen frame customarily has been adjustable to accommodate frames of difierent lengths in a direction from front to back of the machine. However, in accordance with the present invention, both

bars

12, 14 are adjustable for movement toward and away from the front and back of the machine. Thus, the bar M carries at itsopposite ends a pair of brackets 76 including clamp portions which are adapted to grip the lower rails 48 on opposite sides of the scraper. The clamp portions are operated by nuts 78 so that the rear bar 12 can be adjustably set at any point along the lower rails. The front bar 72 is similarly equipped with clamp portions so that it too can have its position varied as desired. 7

To supply the power for reciprocating the scraper, each chain 24 is trained about a sprocket .80 fixed to acountershaft 82 located at the 1 the pump, thereby forming a closed rear of the machine beneath the table. Said countershaft spans the distance between the two sets of

rails

46, 48 and carries two sprockets 80, one for driving each set of chains 24. Secured to the countershaft 82 is a sprocket 84 which is engaged by a chain 86 that is turned by a sprocket 88. Y

In accordance with a principal feature of the instant invention, the sprocket 88 is mounted on the output shaft 90 of a hydraulic transmission unit 92, i. e. a hydraulic unit capable of effecting speed conversion. Said unit includes in its output section a fluid motor M (Fig. 2a) of any conventional type, such far example, as that shown in Lesson 47 of the manual entitled the Hydraulics, published by the Henry Ford Trade School of Dearborn, Michigan, bearing copyright 1941 and reprinted This type of motor consists of two gears similar to an ordinary gear pump. But, unlike an ordinary gear pump, the body of the motor has a pair of passageways leading from the exhaust port to ports diametrically opposite the exhaust port. The body also has another pair of passageways leading from the inlet port to ports diametrically opposite to the inlet port.

This type of fluid .motor will deliver rotaryv power in either direction of rotation at all speeds within its rated limits. The motor is capable of extremely rapid acceleration and deceleration, and can be started, stopped, and even stalled repeatedly without damage.

The input section of the unit 92 constitutes a variable delivery pump P, such for example, that shown at Lesson 15 of said manual, the same being a piston type pump with a stroke which is varied by a change in inclination of a wobble plate. Said pump, when turned at a uniform speed, is capable of varying its delivery I in accordance with the position of a controlmember which regulates the inclination of said plate. The delivery of the pump is connected to the intake of the fluid motor, and the outlet of the fluid motor is connected to the inlet of hydraulic circuit (see Fig. 2a).

The pump is driven by a sheave 94 on the input shaft 96 of the hydraulic transmission unit, and the delivery of the pump is regulated by a control member 98 secured to a shaft Hi0, whose angular position determines the inclination of the wobble plate and thereby the rate of delivery of the pump.

The control member is biased in a counterclockwise direction, as viewed in Fig. 2, by a tension spring I02. When this member is in its extreme counter-clockwise position, as viewed in said figure, the wobble plate is positioned to obtain a maximum piston stroke and, hence, maximum delivery of the hydraulic fluid. Moving the control member against the spring I02 in a clockwise direction, as viewed in Fig. 2, lessens the delivery of the pump and consequently reduces the speed of rotation of the hydraulic motor M. Due to the extremely rapid response of this type of motor to fluctuations in the rate of delivery of hydraulic fluid to it," the output speed of the hydraulic transmission unit follows substantially instantaneously any variation in position of the control member 98.

A belt I04 trained around the sheave 94 is driven by a pulley I06. Said pulley is turned by an electric motor I08 through a fluid clutch H0 of any suitable type that will permit the motor 103 to be reversed rapidly, or to assume rapidly a -.load. wi hout stalli burnin out the motor, rimnosine an 11 15111 5 h h sur o current inwth im t supnl A m r yclutch is suitable for this purpose.

The countershaft 82 fixedly carries a rnale threaded sleeve H2 which meshes with a tapped collar I-I I, so that said collar will duplicatein mini-aturethemotion of the scraper. It will be observed that, murder for the movement of the collar tohe a faithful reproduction. of the scraper movement, the kinematic train between the counter-shaft .82 and thecppositeends of the scrapershouldentirely constitute positive (nonslipping) motion-transmitting mechanismasuch, forexamplaas thechains and sprockets as, 243, 22,125.23, 3.0, 34,3cheretofore described. Moreover,=in orderthat the scraper be capable of as rapid anacceleration,deceleration and reversal as the .hydraulic motor M, a positive motion transmitting mechanism, such as the chain 89 and-sprockets 84,188,,is employedto connect the output of the hydraulic transmission'unitto the countershaft. Since slight variations in theirate at which the hydraulic pump P is driven will not noticeably affect the operation of the machine, the drive from the clutch IIU to the hy draulic transmission unit can be effected by sheaves and a belt. This latter connection, moreovenhas the advantage of easing the load on themotor and power; supply at times 0f reversal :and sudden acceleration.

The collar IIAis secured to a yoke lit having a pair of depending arms H8, I so located on opposite sides of the regulating shaft Hill. The arm I'lt supports astud iii-2 extending in a direction parallel to the shaft 82 and having its h ad facing the opposite arm I23. The is'threadedly received in the arm M8 to permit adjustment thereof and it is held in any adrusted position by a lock nut I-Z l. horizontally aligned with a roller i oarriedby an erect ear I26 on thecontrol member 98.

The otherarm 26 mounts a stud I28 similar tothe-stud I22, but havingits head facing in theopposite direction. The stud liil cooperates with a roller I39 horizontally aligned therewith andmounted on a pendant ear I on the control member 98.

.lfrom the foregoing, it willbe apparent that, when either stud contacts its associated roller, the control member 93 will be rotatedina clockwise direction, as viewed in Fig. 2, t0 decelerate thcoutput' shaft 98 of the hydraulic transmission unit. @Moreover, as soon as either stud disene a esit-s associated roller, the control member will be turned a counterclockwise direction, as viewed in Fig. 2, by the tension spring I532. Movement of the control member in the latter direction is limited by abutment of said member against :a vertically adjustable stop M2. The position of said stop is-set inaccordance with the speed at which the scraper is desired to traverse the screen 68 during the 'major por tiQILof its travel.

Theyoke us also carries an extension its on which there are mounted a "pair of hori zontal threaded studs I35, I 38. These studs, like thestuds I22, I28, are adjustably supported on the yoke. -The studs I36, I38 face inopposite directions and may be disaligned, although they preferably are parallel. The upper stud Ito is horizontally.alignedwith an actuating element I40 of a momentary electric switch I42. This switchis of the twopole single throw type having one normally Open and one normally closed pair of contacts whioh late-rwill be described'in Said stud is detail. Th lower t d I 8 5 orizontally a igned with e ac uat ng ment I44 of another mo mentary electric switch I46 that likewise of the two pole single throw type having one normally open and one normally closed pair of contacts. The switch I42 is the one which is actuated by the stud I38 at the time that the scraper is to be brought to a stop at-the rear of the machine, and hence, this switch will be referred to hereinafter as the stop switch. Thev switch 14s is engaged by the stud I38 when the scraper is to be reversed at the front of the machine and hence, said switch will be referred to hereinafter as the reverse switch.

The stop and reverse switches are mounted on a stationary panel I48 and are connected by suitable wiring in a control circuit soon tobe described for the electric motor I88.

The yoke H6 is prevented from rotating by a guide spindle hill secured to the stationary base iliI of the hydraulic transmission unit. Said spindle is slidable in a bore I52 near the tip of the yoke arm I20.

The axles 26 extend from the casings I8 in which they are journaled and secured in brackets I54 located alongside said casings. Hence, the scraper support, consituting the casings I8, the two pairs of upper and lower rails 46, .48,the housings Eli, and the crossbar 52, pivots about the aligned axles 26 at the rear of the machine, Pivotal movement of the scrapersupport will raise or lower the scraper with respect the printing table it, and, since the stencil screen also is carried by the same frame through the medium of the

bars

72, 14, will raise and lower the stencil. Thus, the instant machine eliminates the dual supports heretofore independently employed for mounting the scraper and the stencil.

The lower side of the crossbar 52 is engaged by a follower I56 (see Figs. 4 and 5) consisting of a roller E53 horizontally journalled on a shaft Hill carried between the arms of a yoke I62. Said yoke is secured on the upper end of a shaftJM slidably mounted for vertical movement in -,a bushing I66 fixed to the front apron I4. The bushing carries a guide bolt I68 having a dog tip I18 slidable in an axial slot Il2 in the shaft I64 to prevent rotation thereof.

The lower end of the shaft fixedlysupports a block I14 having a pin ITS. A similar pin 11.8 is carried by the bushing I65, said pins having stretched between them a tension spring 180 that biases the shaft I54 upwardly.

One side edge of the block I74 is fashioned into a face cam 82 designed to engage a roller actuating element (not shown) of a momentary electric safety stop switch I84 that is carricdby a post I 85 depending from the front apron I4, said switch being of the single throw, double pole type, including two pairs of normally closed contacts. The cam I 82 actuates the switch I84 when the crossbar 52 is raised from its printing position shown in Figs. 4 and 5.

The post i86 also mounts a momentary elec-v trio starting switch 583, this being of the single throw, single pole type, but including a pair of normally open contacts. The switch I88 has a roller actuating element I99 which, in'Fig. 4, conceals the roller actuating element for the switch I84. The element I98 is operated by a lever Hi2 pivotally mounted by a post I94 on the block I'M. The lever is ecoentrically disposed with respect to the post It l so that the opera.- tive short end of the lever is biased in a counterclockwise direction, as viewed in Fig. 4. A stop wardly by the roller i964 as the shaft moves up; However, when until said tip clears the roller. the shaft i6 moves downwardly from its uppermost position, the operative tip of the lever cannot cam past the roller 599 inasmuch as rotation of the lever is prevented by the pin I95 so that upon-such downward movement, the lever I62 forces the 'ro1ler'I9B toward the switch I68 and closes the normally open contacts thereof.

A suitable electric circuit is provided for operating the motor I68, said circuit being illustrated in Fig. '7. The motor derives electric power from three-phase cusses I96, I98, 206, only one phase i36-l98 of which is employed for the purpose of controlling the motor.

Normally, the machine is idle, that is, the scraper is at rest at the rear of the machine with the upper switching stud I36 engaging the actuating element Hit) in the position of the collar II 15 corresponding to said position of the scraper.

The machine is started by lowering the scraper mount. This causes the shaft I64 to be depressed and the lever I92 to actuate the starting switch I88. Actuation of said switch is designed to energize the solenoid 262 of a forward operating motor relay 264 which controls four normally open sets of contacts 266, I66, 2H], 2I2. The energizing circuit for the solenoid 262 extends from the bus I96 to the bus I68 running through a wire 2H4, the momentarily closed but normally open pair of contacts 256 of the starting switch I68, a wire 2 8, a pair of normally open contacts 226 of the stop switch 142 which, however, now are closed because the scraper is at the rear of the machine and the collar H4, accordingly, is in engagement with the actuating element I 46 of said switch, a wire 222, the solenoid 202, a wire 224, a pair of normally closed contacts 226 f the reverse switch I46, a wire 228, a pair of normally closed contacts 229 of the safety stop switch I84, a wire 236, a pair of normally closed contacts 233 of an emergency momentary stop switch 232 (see also Fig. l) and a wire 233. As soon as the solenoid 262 is energized, it draws up and closes all the contacts of the relay 264.

Closing the pair of contacts 266 completes a holding or stick circuit for the forward operating relay 26: 3 as follows: from the bus I96 through a wire 23 5, the pair of closed contacts 266, a wire 236, the Wire 222, the solenoid 262, the wire 224, the pair of closed contacts 226, the wire 228, the pair of closed contacts 229, the wire 238, the pair of closed contacts 23!, and the wire 233 to bus 198, so that when the switch I42 is released, the relay 26 5 will remain energized.

Closing the contacts 263, 21c, 2|2 connects the bus I96 to a motor terminal 238 through the wire 234, the pair of closed contacts 268 and a wire 246; the bus I 9-8 to a motor terminal 242 through a wire 244, the pair of closed contacts 212. and a. wire 246; and the bus 266 to third motor terminal 246 through a wire 256, the pair of closed contacts 2H3 and a wire 252. The connections are such as to turn the motor over in a proper direction to drive the variable delivery fluid pump P in the correct sense to rotate the fluid motor M in such fashion that the scraper isdrivjen toward the front of the machine The field 254 of the motor is energized throughout working hours, the conventional con-' nections therefor being omitted to simplify the drawings.

It thus will beseen that as soon as the scraper support is lowered the starting switch I88 will be closed and the motor I68 will start to move the scraper from the rear to the front of the machine, the scraper continuing to move even after the actuating tip of the lever I92 haspassed the roller I and permitted the switch I88 to reopen.

At the time the scraper starts, the roller I36 on the control member 98 is engaged by the lower speed control stud I28. Accordingly, the scraper starts up slowly. But as soon as the scraper has moved a short distance and the colla-r II4 has experienced a corresponding movement, the stud I28 is backed off and the con-- trol member shifted by the spring I62 into abutment with the stop I32. As this occurs, the scraper speeds up rapidly, it being observed that the roller I30 is quite close to the shaft I 00' which the control member turns so that after a very short movement of the scraper the hydraulic transmission unit is set at its top adjusted speed.

When the scraper nears the front of the machine, the upper speed control stud I 22 will contact the roller I26 to slow down the rate of delivery of the fluid pump P, and thus the rate ofspeed of the hydraulic'motor M, so that very shortly before the scraper reaches the forward limit of its travel, it is rapidly decelerated. This deceleration does not require absorption of the momentum of the scraper and its affiliated parts by buffers, brakes, or the like mechanical power absorption mechanisms which create noise and shock. In the present construction the momentum is absorbed by the hydraulic transmission unit, the same being transmitted from the scraper to said unit in a positive fashion by the divers chains and sprockets.

Very shortly after the upper speed control stud I22 has caused the scraper to be slowed down, the lower switching stud I33 engages the actuating element I44 of the reverse switch I46. As this occurs, the pair of contacts 226 of said switch I46 open, deenergizing the holding circuit for relay 264 and thereupon terminating rotation of the electric motor I66 in the direction which causes the scraper to move forwardly.

At the same time, the normally open pair of contacts 256 of the reverse switch close, thereupon completing a circuit from the bus I96 through a wire 256, said pair of closed contacts 256, a wire 266, a wire 262, a solenoid 264 of a reverse operating motor relay 266, a pair of normally closed contacts 266 of the stop switch I42, a wire 276, the wire 228, the pair of normally closed contacts 226 of the safety stop switch I84, the wire 236, the normally closed contacts 23I of the emergency stop switch 232, and the wire 233 to the bus I96 so as to energize the relay 266.

The reverse operating relay 266 controls four pair of normally

open contacts

272, 274, 276,

278. The first pair of contacts 272 functions as the holding means for the reverse relay. When these contacts 272 are closed, a stick circuit is energized for the solenoid 26d. Said circuit extends from the bus I 98 through the wire 233, the closed pair of contacts 23I, the wire 236, the closed pair of contacts 229, the wire 228, the wire 270, the closed pair of contacts 268, the solenoid 264, the wire 262, the wire 260, the closed pair of contacts 272, a wire 280, and the wire'256 to the'bus I96.'-

aeamce Closing the contacts .214, 218-1andr218 reverses one phase of: the power supply" to. the threephasemotor Hi8; That'is to say, the bus. 200 still? will be connected: to motor: terminal 248, althoughthroughthe.contacts 216 of the reverse operatingsmotor relay, ratherithan' through contactsiZ-IO Of the forward operating motor relay: However, the 'bus. I96, instead of being connected to' motor terminal. 238, now. will be connected-to motor terminal 24 2 through contacts" 2" of the: reverse operating motor-"relay; and the bus- I98, instead of being connected: to. motor. terminal 242', now'will be connected toxmotor terminal 2'38 througlr contacts 218 of .thereverseoperab in'g' motor: relay. As soon as the direction of travel of. the motorisreversed, thescraperwill startzto moveback toward the'rear. of the ma-- chine; and, iniso. doing, first willcause the speed ofttheihydraulic' motor, and hence the scraper, to tie-rapidly accelerated; thisbeing caused by disengagement ofthestud I22: and roller [26.-

When the scraper nears the rear of. the machine, thespeed thereof is. decelerated rapidly upon-engagement of the-studv l28and the roller I304. Very shortly thereafter the stud I36 will engage the actuating element I40 ofstop switch M2: to. thereupon open the pair of contacts Z68 whichdeenergizes-the stock circuit'for the solonoid 264 sothat the-motor IOS isrendered ineffective.

Thus thescrapcr'willistop at the rear of the machine: If it is: desired to have the scraper run-through another cycle; a pair of normally open contacts 281- of a momentary repeating switch 282-.are-closed,.thesecontacts being connccted in shunt with the:contacts 21E so that closure; thereof: will repeat-the cycle hereina-bove described If; at any time; during, a; cycle, the:- rail assemebly.- carrying, the. stencil. frame should bev raised, either accidentally or. otherwise, allmotor control circuits fromthe bus: I98. immediately are opened,.so-that the motor lilais stopped; The scraper also is stopped.

It is desirablefor-the scraper to be brought to a quick stop. so that if thescreenshould beraised rapidly thescraper will nottear. the same To this end I provide a brake 234cm the counter-- shaft 82, saidlbrakebeinga solenoid brake. of any conventional'type,ior'example, one such asshown anddescribedin: detailin application Ser. No. 726,504.. Thebrakehas; a pair of shoes which are. designed toengagea drum mountedtoturn. withthe coimtershaftn A spring biases theshces into engagement. with the drumand. a. solenoid 286 (Big; 7 whenenergizedholds the shoesapart. Thev solenoid is connected. by a lead wire. 288 to. the bus. 299 andby a-lead wire 285i toazpair. of normally closed contacts 2&2.- of the switch I 8.4. Another lead wire 2% runs from said contacts to the. bus L98. Thus as-long. as-theswitch I84: is idle. (the. crossbar 5.2 isdown) thesolenoidwill beenergized' andthecountershaft-fi free. But asisoon. as the, rail assembly carrying the; stencil frame. israised and. the switch. H84 actuated to stop the motonthe solenoid will bedeenergized permitting; the springto brake the rapidly movingscrapen.

It. thus, willbe. seen that there isprovided. a machine which achieves the, several objects: of this. invention and is well adapted to meet the conditionsof practical use.

As-various possible. embodiments-might be made of the. abovev invention, and as various changes might. be made in the embodiment. above. set

10' forth, it is to be understood thatall matter. here: indescribed or shown in the accompanying drawings is to be interpreted as illustrative and not in a limitin sense.

Having thus described the invention, there is claimed as new and desired to be secured by Letter Patent:

1'. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for-movement back and forth across said table; an element, means to mount said element for reciprocation, a positive kinematic train interconnecting said scraper and said element, said train including a motion reducing mechanism whereby said element duplicates in miniature the movement of the scraper, a reversible electric motor, a hydrauiic speed-varying transmission unit driven by the electric motor, a control member regulating the'output speed of. the unit, means to drive the scraper from the unit, a control.circuit'for said electric motor, a starting switch, and switchesfor-governing the operation of said motor, said last named switches and said control member being so disposed for actuation by said element that upon actuation of said starting switch said scraper Willstart at slow speed from the rear of the machine, rapidly accelerate, subsequently rapidly decelerate as it approaches the front of the machine, reverse at the front of the machine, slowly start to the rear of the machine, rapidly accelerate, subsequently rapidly deceler ate as it approaches the rear-of the machine; and finally stop as it reaches the rear of the machine.

2. In a silk screen printing machine having a printing table, a scrapen; a track guiding said scraperfor movementback and forth across said table, an element,.means to mount said element for reci cation, a positive kinematic train intel-connecting said scraper and said element, said train including a: motion reducing mechanism whereby id eieznent duplicates iii-miniature the movement of the scraper, a reversible electric motor: drivingsaid scraper, switches actuated by said element for reversing the motor when the scraper reaches the front of the machine and stoppingthe motor when the scraper reaches the rear of the machine, and a starting switch.

3. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper-for movement back and'forth across said table, .a. reversible electric motor, means governed by theposition of thescraper to reverse the electriciniotorwhenthescraper reaches the front-of the ma'chineand to. stop the electric motorwhen the scraper reaches the rear of the machine, means: to start the scrapertoward the front of the machine from the rear of the machine, a hydraulic:speed-varying transmission unit driven by the electric motor, a control. member regulating the output speed of the unit, means todrivethe scraper'from the unit, means governed by-the position of the scraper and actuating the control member so as to set the unit at a low output speed when the scraper is starting from the Hunter back of the machine, to thereafter rapidly/accelerate the output speed of the unit, and to rapidlyrdecelerate the output speed of the unit asthe' scraper approaches the front or rear of the machine.

l. Ina silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a rotary shaft, means to turn said shaft in opposite directions, means governed. by the position of thescraper to reverse the rotation of the shaft when the scraper reaches the front of the machine and to stop the shaft when the scraper reaches the rear of the machine, means to start the scraper toward the front of the machine from the rear of the machine, a hydraulic speed-varying transmission unit for driving the shaft, a control member regulating the output speed of the unit, means to drive the scraper from the unit, means governed by the position of the scraper and actuating the control member so as to set the unit at a low output speed when the scraper is starting from the front or back of the machine, to thereafter rapidly accelerate the output speed of the unit, and to rapidly decelerate the output speed of the unit as the scraper approaches the front or rear of the machine.

5. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a rotary shaft, means to turn said shaft in opposite directions, means governed by the position of the scraper to reverse the rotation of the shaft when the scraper reaches one end of the machine and to stop the shaft when the scraper reaches the other end of the machine, means to start the scraper toward the first named end of the machine from the other end of the machine, a hydraulic speed-varying transmission unit for driving the shaft, a control member regulating the output speed of the unit, means to drive the scraper from the unit, means governed by the position of the scraper and actuating the control member so as to set the unit at a low output speed when the scraper is starting from either end of the machine, to thereafter rapidly accelerate the output speed of the unit, and to rapidly decelerate the output speed of the unit as the scraper approaches either end of the machine.

6. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across the table, an element, means to mount said element for reciprocation, a positive kinematic train interconnecting said scraper and said element, said train including a motion reducing mechanism whereby said element duplicates in miniature the movement of the scraper, a reversible electric motor driving said scraper, switches actuated by said element for reversing the motor when the scraper reaches the front of the machine and stopping the motor when the scraper reaches the rear of the machine, a starting switch, and means for relatively adjusting the positions of the first named switches and the element in the direction of movement of the scraper.

'7. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, an element, means to mount said element for reciprocation, a positive kinematic train interconnecting said scraper and said element, said train including a motion reducing mechanism whereby said element duplicates in miniature the movement of the scraper, a reversible electric motor, a hydraulic speed-varying transmission unit driven by the electric motor, a control member regulating the output speed of the unit, means to drive the scraper from the unit, a control circuit for said electric motor, a starting switch, switches for governing the operation of said motor, said last named switches and said control member being so disposed for actuation by said element that upon actuation of said starting switch said scraper will start "at slow speed from the rear of the machine, rapidly accelerate, subsequently rapidly decelerate as it approaches the front of the machine, reverse at the front of the machine, slowly start to the rear of the machine, rapidly accelerate, subse-- quently rapidly decelerate as it approaches the rear of the machine, and finally stop as it reaches the rear of the machine, and means for relatively adjusting the positions of the last named switches and the element in the direction of movement of the scraper.

8. In a'silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a reversible electric motor, a positive kinematic train interconnecting said scraper and said motor, an element, means to mount said element for reciprocation, a motion reducing mechanism driven by a member of said train and actuating said element whereby said element duplicates in miniature the movement of the scraper, a control circuit for said electric motor, a starting switch, and switches for governing the direction of rotation of said motor, said last named switches being actuated by said element in such manner that the scraper upon actuation of the starting switch will start from the rear of the machine, reverse at the front of the machine, and stop at the rear of the machine.

9. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a reversible electric motor, a positive kinematic train interconnecting said scraper and said motor, a threaded element, a threaded shaft meshing with said threaded element, means to" actuated by said element in such manner that the scraper upon actuation of the starting switch will start from the rear of the machine, reverse at the front of the machine, and stop at the rear of the machine.

10. In a silk screen machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a rotary shaft, a positive kinematic train interconnecting said shaft and scraper for driving said scraper, and a hydraulic speed-varying transmission unit in said train, said unit including a control member for regulating the output speed of the unit, said control member being disposed for actuation as the scraper approaches the end of its travel to rapidly deceleratethe scraper.

11. In a silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, a rotary shaft, a positive kinematic train interconnecting said shaft and scraper for driving the scraper, an element, means to mount said element for reciprocation, a positive kine-' matic train interconnecting said scraper and said element, said last named train including a motion reducing mechanism whereby said element duplicates in miniature the movement of the scraper, said first named train including a hydraulic speed-varying transmission unit having a control member regulating the output speed of the unit, said member being so disposed for 13 actuation by said element that as the-scraper approaches an: end of the: machine the element will engage: the member: and rapidly accelerate j the output speed of the unit.

12.. In a silk screen printing machine. having a printing table, a scraper, a track guiding-said? scraper for movement each and forth across said table, aneieine'nt, means'to mount said ole ing transmission unit driven by the electric motor, a control member: regulating the" output speed or" the unit, means to drivc= the scraper from the unit, a control circuit for said electric motor, a starting. switch switches for governing the operation of said motor, and means adjustably mounted on. said element for actuating said last named switches and said control member so that upon actuation of said starting switch said scraper will start at slow speed from the rear of the machine, rapidly accelerate, subseduently rapidly decclcrate as it approaches the front of the machine, reverse at the front the machine, slowly start to't'he'rea r of the'niachlne, rapidly accelerate, subsequently" rapidly decelerate as it app-roaches the rear of the machine, and finally stop as it reaches the rear of the machine.

13. In a sill: screen printin machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, an element, means to mount said element for reciprocation, a positive kinematic train interconnecting said scraper and said element, said train includinga motion reducing mechanism whereby said element duplicates in miniature the movement of the scraper, a reversible electric motor, a hydraulic speed-varying transmission unit driven by the electric motor, a control member regulating the output speed of the unit, means to drive the scraper from the unit, a control circuit for said electric motor, a starting switch, switches for governing the operation of said motor, means adjustably mounted on said element for actuating the last named switches so that upon actuation of said starting switch said scraper will be driven from the rear to the front of the machine, reverse, be driven to the rear of the machine and stop, and means adjustably mounted on said element for engaging the con- 1 trol member tof'rapidly accelerate the output speed of the unit as the scraper starts from the front or rear of the machine and to rapidly decelerate the output speed of the unit as the scraper approaches the front 01- rear of the machine.

14. In a silk screen printing machine having a printing table, a scraper, a track guiding said scrap-er for movement forth across said table, an element, means to mount said element for reciprocation, a positive kinematic train interconnecting said scraper and said element, said til) 14 machine" and" at the? rear or the machine:

15.- In a silk screen printing machine havlng'a printing table, a; scraper, a track guiding said scraper for movementba'ck andzfurthacross said table, an: element, means to mount said element for: reclpr ocatio'n;v a positive kinematic train iiitsrcomiecting said scraper and said element,-.sald train including a" motion reducing mechanism whereby said element-duplicates in miniature-the movement of thescraper, a reversible electric motor, a hydraulic: speed-varying transmission unit'drivenby the-electric motor, a control member regulating theoutput speed of: the unit, xneans to drive the scrap'erfrom the unit,ineansto control the' motor soas to startthe scrape'r'from-the rear-of the-machine, reverse it at the front of the machine and: stop it at the rear of the machine; and means adjustably mounted on said elementfor engaging the colitrolmember so as to rapidly accelerate the-output speed ofth'e unit as the scraper starts from the front or rear of the machine: and to rapidlyidecelerate the-output speed or the: unit as the camper approaches the front or rear'o'f the machine.

16; Ina silk-screen printing machine having a: printing. table, a scraper, a pair of tracks at opposite sides'of said scraper and extendingfrom the front to the' rear of the-machine, means supporting the ends of saidscraper and: riding on said traclismeansto pivotally mount said tracks for oscillation about a common horizontal-- axis at the rear of the machine, a pair of elongated flexible members, a rotary member at the front and rear of each track about which the elongated members are trained, means to connect said elongated members to the opposite ends of the scraper supporting means for driving the same, a second rotary member at the rear of each track, said second rotary members being mounted for rotation about said common horizontal axis, means to rotate the first named rear rotary members from the last named rotary members, and means to turn said last named rotary members selectively in one direction or another, said last named means including a countershaft, means operatively connecting said countershaft to said last named pair of rotary members, a threaded member on said shaft, a threaded element meshing with said threaded member so as to duplicate in miniature the movement of the scraper, a hydraulic speed-varyin transmission unit including a fluid motor and a variable delivery fluid pump, an electric motor driving said pump, a control member for said pump, the regulation of which will change the output speed of the unit, switches for controlling the motor, and means movable by said element for operating said switches and said control member.

17. A combination as set forth in claim 16 wherein the switches include a stop switch and a reverse switch, and wherein the element includes a first component adjustable mounted thereon for engaging the stop switch when the scraper reaches a selected point adjacent the rear of the machine and a second component adjustably mounted thereon for engaging the reverse switch when the scraper reaches a selected point adjacent the front of the machine.

18. A combination as set forth in claim 17 wherein the element includes a third component mounted therefor engaging the control member to dccelerate the output speed of the unit when the scraper approaches the selected points adjacent the front or rear of the machine.

19. A combination as set forth in claim 16 wherein the switches include a stop switch and a reverse switch, wherein the element includes a first component adjustably mounted thereon for engaging the stop switch when the scraper reaches a selected point adjacent the rear of the machine and a second component adjustably mounted thereon for engaging the reverse switch when the scraper reaches a selected point adjacent the front of the machine, and wherein the element includes a third component mounted thereon for engaging the control member to decelerate the output speed of the unit when the scraper approaches the selected points adjacent the front or rear of the machine.

20. A combination as set forth in claim 16 wherein the switches include a stop switch and a reverse switch, and wherein the element constitutesa yoke including two arms each of which ,adjustably supports a pair of studs, one of said adjustable studs on one of said arms being disposed to engage the stop switch when the scraper reaches a selected point adjacent the rear of the machine, one of said adjustable studs on the other arm being disposed to engage the reverse switch when the scraper reaches a selected point adjacent the front of the machine, the other adjustable studs on said arms being disposed to engage the control member just before the aforementioned studs engage the stop or reverse switches so as to decelerate the output speed of the unit.

21. Ina silk screen printing machine having a printing table, a scraper, a track guiding said scraper for movement back and forth across said table, said track including two pairs of hollow tubes disposed at opposite ends of the scraper, each pair of tubes including an upper tube and a lower tube, a sprocket rotatably mounted at the rear of each pair of tubes, a sprocket rotatably mounted at the front of each pair of tubes, means to reversibly rotate said rear sprockets, a pair of chains one trained about the sprockets at each end of the scraper, the upper flight of each chain being disposed in an upper tube and the lower flight of each chain being disposed in a lower tube, and means connecting one flight of each chain with the associated end of the scraper.

JOHN B. THOMAS.

References Cited. in the file of this patent UNITED STATES PATENTS Number Name Date 2,039,909 Kern et al May 5, 1936 2,207,818 Perry et a1. July 16, 1940 2,267,596 Montague Dec. 23, 1941 2,355,930 Thorne Aug. 15, 1944 2,571,685 DAutremont Oct. 16, 1951