US3613980A

US3613980A - Sheet advance apparatus

Info

Publication number: US3613980A
Application number: US849780A
Authority: US
Inventors: Frank M Kulig; Lee R Layman
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1969-08-13
Filing date: 1969-08-13
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

Apparatus for intermittently advancing successive equivalent length portions of a generally continuous thermoplastic sheet through upstream article forming and trimming stations. An indexing mechanism in the drive train controls the forward velocity of a carriage on which the sheet is clamped. Fixed stops precisely define the extent of forward movement of the carriage. A resiliently biased plunger in the means for interconnecting the drive train to the carriage absorbs the incremental and variable additional movement of the drive train caused by tolerances therein, after forward movement of the carriage and therefore of the sheet have been positively terminated through contact with the fixed stops.

Description

United States Patent [72] Inventors Frank M. Kulig Bloomfield; Lee R. Layman, Windsor Locks, both of Conn. [21] Appl. No. 849,780 [22] Filed Aug. 13, 1969 [45] Patented Oct. 19, 1971 [73] Assignee Monsanto Company St. Louis, Mo.

[54] SHEET ADVANCE APPARATUS 12 Claims, 5 Drawing Figs.

[52] US. Cl 226/162, 18/ 1 9 P [51] Int. Cl B65h 17/36 [50] Field ofSearch 226/158, 143, 162-466 [5 6] References Cited UNITED STATES PATENTS 2,978,160 4/1961 Bunnell 226/162 X 3,412,995 4/1968 Parups ABSTRACT: Apparatus for intermittently advancing successive equivalent length portions of a generally continuous thermoplastic sheet through upstream article forming and trimming stations. An indexing mechanism in the drive train controls the forward velocity of a carriage on which the sheet is clamped. Fixed stops precisely define the extent of forward movement of the carriage. A resiliently biased plunger in the means for interconnecting the drive train to the carriage absorbs the incremental and variable additional movement of the drive train caused by tolerances therein, after forward movement of the carriage and therefore of the sheet have been positively terminated through contact with the fixed stops.

PAIENIEDUBI 19 I911 SHEET 1 [IF 2 INVUN H )RS FRANK M. KULIG LEE R. LAYMAN ATTORNEY PATENTEUUBT 19 I97| SHE em: 2 v 3,513,980

m 0mm T K Y N .A W

K R W M E E m L HHWJ W ATTORNEY SHEET ADVANCE APPARATUS BACKGROUND OF THE INVENTION This invention relates in general to improvements in equipment for forming articles from plastic sheet, and in particular to improvements in apparatus for advancing the sheet through the article forming and trimming presses.

Several different types of forming operations using heat and pressure are presently carried out on generally continuous plastic sheet to simultaneously form large numbers of articles, for example containers, in a single cycle. One type of operation is by pneumatic pressure differential forcing of segments of a large section of the sheet into female, or over male molds in a forming press, either with or without mechanical assistance, to shape the articles while leaving them peripherally attached to the sheet in order to permit convenient, simultaneous conveying of all of the articles out of the forming press as the sheet section is advanced to a further downstream position. The sheet with the articles still attached therein is then positioned within a trimming press intermediate a series of oppositely aligned punch and die members. The punches are then caused to advance toward the dies or vice versa whereupon a sharp edge on one or the other simultaneously severs each of the articles from the sheet leaving them free to be conveyed to a suitable collection station. The remainder of the sheet section, which now consists of a web made up of the portions of the sheet section intermediate the articles, is then advanced once again, generally to a scrap recovery unit. This type of sheet shaping is known as post trim forming, since the articles are from the sheet downstream of the forming equipment. The apparatus utilized to advance the rather flexible sheet through the forming and trimming presses is generally located downstream of the trim press and operates by pulling on the web section which has had the articles removed therefrom, so as to intermittently advance upstream portions of the sheet through the forming and trimming presses.

Needless to say, it is extremely important that each of the large number of formed articles formed and attached in the sheet during a cycle of the equipment be centered as accurately as possible between the opposed severing members of the trim press. Otherwise, when the movable portion of the press is advanced towards the stationary portion in carrying out the trimming operation, any misaligned articles will be either partially or completely crushed between the cooperating members, or else unevenly trimmed depending on the extent of variation from the desired registration position. Also, it is desirable that the sheet be rapidly advanced through the various stations of the equipment to minimize cycle time, yet as smoothly as possible, since portions of the sheet being pulled are at elevated temperature and can deform under the tension being exerted by the sheet advance equipment. This deformation can produce thickness irregularities in the formed articles and is especially critical when the sheet is preheated prior to entry into the forming press.

Now there has been developed a unique apparatus which provides rapid yet smooth sheet advancement and accurate sheet registration in upstream equipment.

Accordingly, it is a principal object of this invention to provide an improved sheet advance apparatus component for use in an equipment system for forming articles from plastic sheet.

An additional object of this invention is to provide an improved apparatus for intermittently advancing successive equivalent length portions of a generally continuous thermoplastic sheet through upstream article forming and trimming stations which is capable of extremely fine repeatability.

A further object of this invention is to provide apparatus of the aforementioned variety wherein the precision of the extent of sheet travel is generally independent of the tolerances of the means for intermittently moving the sheet.

An additional object of this invention is to provide apparatus of the aforementioned variety wherein the precision of the extent of sheet movement is positively determined by abutments defining the limits of sheet travel.

A further object of this invention is to provide apparatus of the aforementioned variety wherein sheet movement is rapid yet smooth in the sense that it is free of abrupt starts and stops.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

SUMMARY OF THE INVENTION These and other objects are accomplished by providing apparatus for intermittently advancing successive equivalent length portions of a thermoplastic sheet which comprises a frame, a pair of horizontally disposed elongated support members on the frame, a carriage mounted for reciprocative movement on the support members, means on the carriage for gripping the sheet, drive means for intermittently moving the carriage forward including an indexing mechanism for controlling the velocity of the carriage during its forward movement so as to advance the sheet smoothly when engaged by the gripping means, means interconnecting the carriage to the drive means, means for reversing the forward movement of the carriage, and stops for delimiting the reciprocative movement of the carriage.

The means interconnecting the carriage to the drive means preferably comprise three pusher assemblies, each fastened to an endless drive chain at spaced, equidistant intervals about the periphery of the chain and a reciprocatably mounted drive rod on the carriage adapted to consecutively engage each of the three pusher assemblies at the start of the forward movement of the carriage for successive cycles. Each pusher assembly includes a block fastener to the chain and a plunger mounted in the block adapted to engage the drive rod on the carriage to move the carriage forward, the plunger being resiliently biased in the direction of forward movement of the carriage.

Means are provided to decelerate the forward movement of the carriage prior to its engagement with one of the stops, these means including a pivotally mounted latch on the carriage adapted to engage the rear side of the block of the particular pusher assembly then moving the carriage.

BRIEF DESCRIPTION OF THE DRAWINGS In describing the overall invention, reference will be made to the accompanying drawings in which:

FIG. I is a front view of the apparatus of the present invention;

FIG. 2 is a side view of the apparatus of FIG. 1;

FIG. 3 is a plan view of the apparatus of FIG. I with the sheet removed;

FIG. 4 is an exploded perspective view of a portion of the apparatus of FIG. I; and

FIG. 5 is a partial, schematic view with parts broken away of the apparatus portion of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein identical numerals refer to identical parts, there is shown in FIGS. 1-3, apparatus generally indicated as 10 for intermittently advancing successive equivalent length portions of a sheet S of thermoplastic material through known, conventional upstream forming the trimming stations (not shown). Apparatus 10 comprises a frame, generally indicated as 12, for supporting the working components thereof. Frame 12 comprises bedplate 14 to which are fastened four stanchions 16, each extending upwardly from the surface of bedplate 14 in the corners thereof. Stringers 18 connect the upper ends of each pair of stanchions 16 at opposite ends of the frame. Gussets 17 may be used to strengthen the joints between the stanchions l6 and the bedplate l4.

Apparatus 10 further comprises a pair 20 of horizontally disposed, elongated support members cylindrical in cross section and connected at either end to stringers 18 of frame 12. Carriage 22 is mounted for reciprocative movement on members 20 from a rear position situated at the left end of FIG. 1 to a forward position situated at the right end of FIG. 1. Carriage 22 comprises horizontal platform 24 having dual connecting members 26 depending from the under side thereof. Members 26 have cylindrical openings extending therethrough such that platform 24 may be mounted by means of members 26 and ball bushings 27 for extremely low friction transverse movement along support members 20. Carriage 22 further comprises a pair of oppositely aligned yokes 28 fastened to the under side of platform 24 at the outer margins thereof.

Means 30 are provided on carriage 22 for gripping a limited portion of sheet S along its outer margins. Means 30 comprises oppositely aligned support blocks 32 mounted on the outer margin of the upper surface of platform 24, which in turn carry fingers 34 reciprocatably mounted on piston rods 35, which are conventionally operative by suitable fluid pressure introduced to piston housings 36. Fingers 34 may have upturned end portions as depicted in FIG. 1, which serve as a lead in to avoid ripping sheet S as it is being engaged by the fingers.

Drive means, generally indicated as 38, are provided for intermittently moving carriage 22 from a rear position at the left of FIG. 1 to an advance position at the right of FIG. 1. Drive means 38 includes a conventional DC motor 40, having its output shaft coupled to a conventional clutch-brake mechanism 41. The output of mechanism 41 is connected through a stepdown gear reducer 44 to an indexing assembly 42 which controls the velocity of carriage 22 during its forward movement in such a manner as to advance the sheet smoothly when engaged by gripping means 30. Clutch-brake mechanism 41 is of a conventional variety and serves to supply intermittent rotary motion from motor 40 to gear box 44 on demand. Though an AC motor can be used, a DC motor is preferred for flexibility since its shaft speed may be changed primarily by varying the voltage input. Indexing mechanism 42 likewise is of a conventional variety. Commercially available models are obtainable, for example, the Trans-pac II model produced by Ferguson Machine Co. of St. Louis, Missouri. Indexing mechanism 42 has replaceable internal cam components which serve to vary the rotary speed of its output shaft 46 from that of its input shaft. When this varying rotary speed is eventually transmitted to carriage 22, the velocity of the latter and therefore of the sheet held in place thereon will gradually increase. After an adjustable interval along its forward path, mechanism 42, through suitable interconnecting means to be hereafter described, then serves to decelerate the forward movement of carriage 22 and therefore of the gripped sheet, so as to avoid the consequences (for example buckling) of any sudden stop on completion of the intermittent sheet advance cycle. Output shaft 46 of indexing mechanism 42 of drive means 38 has an indexer drive gear 48 thereon which intermeshes with drive car 50 which in turn is conventionally connected to drive shaft 52. Drive gear 50 is sized to rotate 360 for each indexing movement of mechanism 42. Drive shaft 52 is conventionally mounted in pillow blocks 53 on supports 54, which in turn are fastened to plate 56. Drive means 38 further comprises drive sprockets 58 on either end of drive shaft 52, idler sprockets 60 on either end of idler shaft 62 and drive chains 64 interconnecting drive and idler sprockets 58 and 60. Thus it is seen that as DC motor 40 is activated, the rotary motion of its output shaft is transmitted through intermediate means to rotate drive sprockets 58, which in turn rotate chains 64 and therefore idler sprockets 60, and idler shaft 62.

Apparatus 10 further comprises means (FIGS. 4 and 5) for interconnecting carriage 22 to drive means 38. These interconnecting means comprise three pusher assemblies 68 (FIGS. 1, 4 and 5) on each side of the apparatus, fastened to endless drive chains 64 at spaced, equidistant intervals about the periphery of chains 64. These interconnecting means further comprise dual, reciprocatably mounted drive rods 70 on the underside of platform 24 of carriage 22, adapted to consecutively engage one pair of the pusher assemblies at the start of the forward movement of carriage 22. Drive rods 70 are positioned such that end portions 72 (FIG. 5) move in ears 73 and through the U-shaped cavity of yokes 28 (FIG. 2) in response to a suitable conventional control signal applied to fluid operated pistons in housings 74. Each pusher assembly comprises a block 76 (FIGS. 2 and 5) fastened to chain 64 by conventional means. Each block 76 has a plunger 78 mounted therein adapted to engage drive rod 70 to move carriage 22 forward. Plunger 78 has a shank portion 80 and an enlarged end portion 82 having a cutout formed therein, the surface of which engages drive rod 70. Helical compression spring 83 resiliently biases plunger 78 in the direction of forward movement of carriage 22, as generally indicated in FIG. 5, which represents the position of plunger 78 at the completion of the forward movement of the carriage. Each pusher assembly also has dual cam followers 84 mounted outboard of block 76. Elongated cams 86 (FIG. 1) are supported on stanchions 16 on either side of the apparatus and have tracks 88 formed therein adapted to accept followers 84 for travel therein to guide and support chains 64 as they turn.

Means are also provided for reversing the forward movement of carriage 22 to return it to its rearmost position at the left of FIG. 1. These means comprise a flexible member 90 connected at one end to platform 24 of carriage 22 and at its other end to dead weight 92. One or more rotatably mounted pulleys 94 are supported, for example on stringer 18, by means of clip 96 and are adapted to peripherally engage member 90 intermediate its ends, so as to urge carrier 22 under the influence of dead weight 92 in the opposite direction from its forward movement after disengagement of the advanced portion of sheet S.

Stops are provided for delimiting the reciprocative movement of carriage 22. These stops comprise adjustably mounted rear stop 98 at the left end of apparatus 10 and a pair of fixed forward stops 100, conveniently fastened to a suitable support at the forward end of the apparatus, for example to a surface of cam 86. The distance between the carriage contacting portions of

stops

98 and 100 is exactly equivalent to the extent to which it is desired to move the sheet forward during one cycle of the apparatus. Rear stop 98 is threadably connected by means of rod 102 in coupling 104, which in turn is mounted on stringer 18, such that it is manually adjustable in the direction of the path of movement of the carriage, in order to permit varying the starting position of carriage 22 on support members 20, and thereby the overall extent of movement of the sheet. Adjustable stop 98 is vertically positioned so as to obstruct further movement of platform 24 as it is pulled to the rear under the influence of weight 92.

Means are also provided to transmit to carriage 22, the decreased angular velocity of the output shaft of indexing mechanism 42 as it approaches completion of one cycle, thereby decelerating carriage 22 during the latter portion of its forward movement. These means include a pair of latches (FIG. 4) 106, each being pivotally mounted on the outer surface of a yoke 28, and having a stepped end portion 107 adapted to engage the rear side 108 of each block 76 of a pusher assembly during the forward movement of carriage 22. Also provided are means for positioning each latch 106 to the left (FIG. 1) of the rear side 108 of each block 76 of a pusher assembly prior to the start of forward movement of carriage 22, such that it will be in position to later engage side 108 at some point in the forward movement. These means include a cam follower 110 on each latch 106 and a fixed elongated cam 112 for each follower 110 suitably mounted, for example on cam 86, adjacent the rear end of the apparatus. Cam 112 has an upwardly inclined track 114 formedtherein (FIG. 1) so as to elevate pivotally mounted latch 106 above the particular block 76 of a pusher assembly which is to next engage drive rod 70 for the next forward movement of the carriage. Thus as carriage 22 moves toward the forward end of the apparatus, latch 106 will ride along track 114 of earn 112 such that when block 76 is beyond end 116 (FIG. 1) of cam 112, latch 106 has left track 114, and is positioned suchthat stepped end portion 107 may strike against side 108 of block 76, in view of the fact that the forward velocity of block 76 is reducing under the influence of indexing mechanism 42. Latch 106 thereby transmits this reduced velocity to carriage 22 on which it is mounted. A suitable enlargement, e.g. a small boss, may be provided on the outer surface of each yoke 28 on which a latch 106 is mounted to prevent the latch from pivoting too far downwardly after the drive piston 70 and plunger 78 are disengaged at the completion of the forward movement of the carriage, and which would otherwise cause latch 106 to avoid track 114 of cam 112 on the rearward stroke of the carriage.

When it is desired to change the extent of advancement of the sheet for a cycle, in addition to varying the position of adjustable stop 98, drive and idler sprockets 58 and 60 are changed in size and links either removed from or added to chains 64 as necessary to adjust the pitch distance between sprockets. In doing so, tension on each chain 64 is relieved by backing off jackscrews 118 (FIG. 1) toward drive sprockets 58, thereby allowing idler sprocket pillow blocks 120 to be moved laterally toward drive sprockets 58 by loosening suitable bolts holding pillow blocks 120 on support 122, the bolts being situated in laterally extending slots (not shown). After replacement of the sprockets, jackscrew 118 is turned in the opposite direction to develop the necessary tension on chains 64 once more. Pillow blocks 53 supporting drive shaft 52 are constructed similarly to that of pillow blocks 120, except that they are usually held stationary on supports 54. Jackscrews 124 bearing against pillow blocks 53 merely ensure against lateral inward movement of fixedly mounted pillow blocks 53 as chains 64 turn.

As an auxiliary feature of the apparatus, means 126 are provided for clamping sheet S in place when it is a stationary position between intermittent movements. These means help to minimize sagging of the sheet during forming trimming, i.e. at times other than during its advancement. These means 126 comprise dual, oppositely aligned, gripping fingers 128 reciprocatably mounted by means of conventional fluid actuated pistons in housings 130, and are identical to the means for gripping sheet S during its advancement, except that they are fixedly mounted by means of brackets 132 to stringer 18 (FIG. 3) at the rear side of the equipment.

ln operation, DC motor 41 of drive means 38 is continuously energized. At the start of a cycle, carriage 22, as a result of the action of deadweight 92 pulling it under the influence of gravity along support members, is at the rearmost position of the apparatus. On receiving a suitable control signal, fingers 34 reciprocate downwardly to pinch sheet S against support 32 of carriage 22, and cause clutch 41 to engage, thereby transmitting power from motor 40 through gearbox 44 to indexing mechanism 42. indexing mechanism 42, converts the 360 input shaft rotation from gearbox 44 and transmits only an angular portion thereof, e.g. 120 to indexer drive gear 48. This l20 rotation is in turn transmitted through drive gear 50, drive shaft 52 and drive sprockets 58 to chains 64. Sprockets 58 and drive gear 50 are sized for 360 rotation for whatever the amount of angular rotation of the output shaft of the indexing mechanism. Likewise, the distance from one point on a pusher assembly to a corresponding point on one of the other pusher assemblies on a given side of the apparatus is equal to the length of one pitch line circumference of a sprocket 58 times 1r, or in other words is equal to two times the pitch radius of the sprocket times rr. As a result of the number and spacing of the pusher assemblies, one will always be at the rear end of the apparatus after completion of the forward movement portion of a cycle in a position ready to engage drive piston 70 to move carriage 22 forward for the next cycle under the influence of rotating chains 64 of drive means 38. Previous to the start of a cycle each drive piston 70 is caused to reciprocate outwardly through an outer ear 73 of a yoke 28 by means of a suitable control signal, in order to permit engagement therewith in the cutout portion of enlarged section 82 of plunger 78 (FIG. 5) of a pusher assembly. With the plunger and drive piston 70 thus engaged, the motion of the drive means is transmitted to the carriage and-controlled by the changing rate of angular rotation of the output shaft 46 of indexing mechanism 42, in order to advancesheet S as smoothly as possible in as short a time as possible. Output shaft 46 initially builds up to a relatively high angularvelocity in order to correspondingly move carriage 22 at a relatively high rate of speed for the initial portion of the forward stroke. After carriage 22 and therefore sheet S have advanced a percentage of the desired total advancement, e.g. about 50 percent, or just beyond end 116 of cam 112 (FIG. 1) in moving from left to right, output shaft 46 of indexing mechanism 42 commences to slow down or decelerate. At this point, itbecomes necessary to transmit this deceleration to carriage 22, which is being pushed along by plunger 78 and piston 70. This is accomplished by means of stepped portion 107 of latch 106 bearing against rear face 108 of a block 76 of the particular set of pusher assemblies then moving carriage 22 forward. During the initial acceleration portion of the forward stroke of the equipment, latch 106 attached to yoke 28 of carriage 22 rides in track 114 of cam 112 as carriage 22 advances. As is apparent, (FIG. 5) drive piston 70 is being pushed forward by plunger 78 in block 76, which in turn is mounted on chain 64, and is unconfined on its forward side. The decelerated motion resulting from the operation of indexing mechanism 42 otherwise would not be transmitted to carriage 22 except for the contact between latch 106 and block 76. Carriage 22 thus continues to advance until the output shaft of indexing mechanism 42 ceases to rotate, whereupon the brake portion of clutch 41 is automatically engaged by means of a suitable control signal, followed by disengagement of the clutch portion of assembly 41, thereby discontinuing the transmission of power to indexing mechanism 42 from drive motor 40. The internal parts of indexing mechanism 42 are conventionally designed to terminate rotation of its output'shaft 46 substantially at the end of the desired extent of forward advancement of carriage 22. The forward movement of carriage 22, however, is positively terminated as a result of the impingement of the rear surface 134 of latch 106 against forward stops which, as previously mentioned, are fixedly mounted on elongated cam 86. Thus, the extent of the forward movement of the carriage 22 and therefore of sheet S clamped thereon is positively delimited by the position of the fixed forward stop 100. However, indexing mechanism 42, as well as the portions of drive means 38 between output shaft 46 of indexing mechanism 42 and drive pistons 70 have built in angular tolerances which otherwise will affect the accuracy of the extent of advance of a sheet section. Thus, if the forward stroke of carriage 22 were not positively terminated by contact with stop 100, carriage 22 would drift a small but highly significant amount equivalent to the extent of this tolerance, for example on the order of 0.010 to 0.080 inch. As an important part of this invention, resiliently biased plunger 78 absorbs this movement, while permitting the stroke to be delimited by the position of stationary forward stop 100. 'In other words, this tolerance is never transmitted to the carriage and sheet movement. Thus, during forward movement of carriage 22, compression spring 83 is designed such that plunger 78, while engaging drive piston 70, is kept in its foremost, maximum extended position. When surface 134 of latch 106 strikes stop 100 to terminate the forward advance of carriage 22, plunger 78 moves to the rear in opposition to the forward urging of spring 83, an amount equivalent to the extent of the tolerances inherently present in the drive system. Thus, the extent of movement of plunger 78 must at least be equal to and preferably slightly in excess of the maximum amount of tolerances in the drive system in order for the equipment to work properly, otherwise plunger 78 will not be sufficiently compressed at the termination of the forward stroke and mechanical failure of one or more of the parts will occur.

On termination of the forward stroke of carriage 22, stationary clamping means 126 may then be activated to hold sheet S in place during the forming and trimming operations of the upstream equipment. Drive piston 70 is caused to reciprocate inwardly towards the axis of the apparatus, thereby disengaging it from contact with plunger 78 and permitting carriage 22 to reciprocate freely to the rear position of the apparatus on support members under the influence of the gravity pull exerted thereon by deadweight 92. When carriage 22 strikes nose portion 136 on the end of piston 138 adjustable stop 98, its rearward motion is terminated. During rearward movement of carriage 22, latch 106, which is pivotally mounted to yoke 28, of the carriage assembly rides up inclined track 114 of cam 116, and at the termination of the rearward stroke of the carriage is positioned just behind the rear side 108 of the block 76 of the pusher assembly which will carry out the next cycle, thereby leaving it in position to decelerate carriage 22 after commencement of the next forward stroke of the equipment in the manner previously described. The rearmost position of the carriage assembly as a result of the location of adjustable stop 98 will be such that drive pistons 70 are just forward of plungers 78 of the next pusher assemblies to permit engagement of these parts when pistons 70 are caused to reciprocate outwardly and chains 64 begin to turn. After completion of the necessary upstream forming and trimming operations a suitable control signal is transmitted to the clutch 41 of drive means 38 to thus transmit rotation to gearbox 44 from drive motor 40 in order to commence another cycle of the apparatus. Just prior thereto, stationary clamping means 126 must, of course, be disengaged from the sheet.

Though many of the components of the sheet advance apparatus of the invention have been depicted in the drawings and described as existing in duplicate on both sides of the axis of the apparatus, for example, the pusher assemblies, drive chains and sprockets, elongated cams, fixed stops etc. these components may be used singly if suitably designed in terms of mechanical strength to withstand the forces generated during movement of the various parts.

Although the invention has been described in some detail, it is obvious that many variations and modifications may be made thereof without departing from its spirit and scope.

What is claimed is:

1. Apparatus for intermittently advancing successive equivalent length portions of a thermoplastic sheet which comprises:

a. a frame;

b. a pair of horizontally disposed elongated support members on said frame;

c. a carriage mounted for reciprocative movement on said support members;

d. means on the carriage for gripping the sheet;

e. drive means for intermittently moving the carriage forward, said drive means including a rotary indexing mechanism for controlling the velocity of the carriage during its forward movement so as to advance the sheet smoothly when engaged by the gripping means;

f. means interconnecting the carriage to the drive means;

g. means for reversing the forward movement of the carriage; and

h. stops for delimiting the reciprocative movement of the carriage.

2. The apparatus of claim 1 wherein the drive means includes an endless chain mounted on sprockets and the means interconnecting the carriage to the drive means includes (a) a plurality of pusher assemblies fastened to the endless chain at spaced, equidistant intervals about the periphery of the chain and (b) a reciprocally mounted drive rod on the carriage adapted to consecutively engage each of the pusher assemblies at the start of the forward movement of the carriage.

3. The apparatus of claim 2 wherein each pusher assembly comprises a block fastened to said chain, said block having a plunger mounted therein adapted to engage the drive rod on the carriage to move the carriage forward, said plunger being resiliently biased in the direction of forward movement of the carria e.

4. 'fi-ie apparatus of claim 2 including means to decelerate the forward movement of the carriage prior to engagement of the carriage with one of said stops, said decelerating means including a pivotally mounted latch on the carriage adapted to engage the rear side of one of the blocks during forward movement of the carriage.

5. The apparatus of claim 3 wherein the pusher assembly has a cam follower mounted on each block and including an elongated cam on the frame having a track formed therein adapted to accept the follower for travel therein as the chain turns.

6. The apparatus of claim 4 including means for moving the latch to the rear side of the block of each pusher assembly prior to the start of the forward movement of the carriage.

7. The apparatus of claim 6 wherein the means for moving the latch to the rear of each block includes a cam follower on the latch and a fixed cam having an upwardly inclined track formed therein adapted to engage the follower on the latch during the reverse movement of the carriage, so as to elevate the pivotally mounted latch above the block of the pusher assembly which is to engage the drive rod for the next forward movement of the carriage.

8. The apparatus of claim 1 wherein the means for reversing the forward movement of the carriage comprises a flexible member associated at one end with the carriage and at its other end with a weight, and a rotary member on the frame peripherally engageable with said flexible member intermediate said ends, whereby the weight pulls the carriage in the opposite direction from the forward movement after disengagement of the sheet from the gripping means.

9. The apparatus of claim 1 wherein said stops comprise an adjustable stop and a fixed stop, each stop being mounted on the frame, said stops being spaced from each other on the frame a distance equivalent to the extent to which the sheet is moved forward during one intermittent movement by the drive means.

10. The apparatus of claim 1 wherein the means for gripping the sheet comprises oppositely aligned reciprocatably mounted fingers.

11. The apparatus of claim 1 including means for clamping the sheet along the outer margins thereof when in a stationary position between intermittent movements.

12. In apparatus for forming multiple hollow articles such as containers and the like from a sheet of thermoplastic material including means for forcing portions of the sheet into mold cavities to form the containers, means for gripping the sheet while forming the containers, means for removing the containers from the sheet after formation and means downstream of the removing means for intermittently advancing the sheet through the forming removing means, the improvement wherein the means for advancing the sheet comprises:

a. a frame;

b. a pair of horizontally disposed elongated support members on said frame;

c. a carriage mounted for reciprocative movement on said support members;

d. means on the carriage for gripping the sheet;

e. drive means for intermittently moving the carriage forward including an indexing mechanism for controlling the velocity of the carriage during its forward movement so as to advance the sheet smoothly when engaged by the gripping means;

f. means interconnecting the carriage to the drive means;

g. means for reversing the forward movement of the carriage; and

h. stops for delimiting the reciprocative movement of the carriage.

Claims

1. Apparatus for intermittently advancing successive equivalent length portions of a thermoplastic sheet which comprises: a. a frame; b. a pair of horizontally disposed elongated support members on said frame; c. a carriage mounted for reciprocative movement on said support members; d. means on the carriage for gripping the sheet; e. drive means for intermittently moving the carriage forward, said drive means including a rotary indexing mechanism for controlling the velocity of the carriage during its forward movement so as to advance the sheet smoothly when engaged by the gripping means; f. means interconnecting the carriage to the drive means; g. means for reversing the forward movement of the carriage; and h. stops for delimiting the reciprocative movement of the carriage.

3. The apparatus of claim 2 wherein each pusher assembly comprises a block fastened to said chain, said block having a plunger mounted therein adapted to engage the drive rod on the carriage to move the carriage forward, said plunger being resiliently biased in the direction of forward movement of the carriage.

4. The apparatus of claim 2 including means to decelerate the forward movement of the carriage prior to engagement of the carriage with one of said stops, said decelerating means including a pivotally mounted latch on the carriage adapted to engage the rear side of one of the blocks during forward movement of the carriage.

12. In apparatus for forming multiple hollow articles such as containers and the like from a sheet of thermoplastic material including means for forcing portions of the sheet into mold cavities to form the containers, means for gripping the sheet while forming the containers, means for removing the containers from the sheet after formation and means downstream of the removing means for intermittently advancing the sheet through the forming removing means, the improvement wherein the means for advancing the sheet comprises: a. a frame; b. a pair of horizontally disposed elongated support members on said frame; c. a carriage mounted for reciprocative movement on said support members; d. means on the carriage for gripping the sheet; e. drive means for intermittently moving the carriage forward including an indexing mechanism for controlling the velocity of the carriage during its forward movement so as to advance the sheet smoothly when engaged by the gripping means; f. means interconnecting the carriage to the drive means; g. means for reversing the forward movement of the carriage; and h. stops for delimiting the reciprocative movement of the carriage.