US3527166A

US3527166A - Vacuum table system for printing machine

Info

Publication number: US3527166A
Application number: US734991A
Authority: US
Inventors: Matthew L Jaffa; David Jaffa
Original assignee: Matthew L Jaffa; David Jaffa
Current assignee: PRECISION ACQUISITION Inc A DE CORP (NOW KNOWN AS PRECISION SCREEN MACHINES Inc
Priority date: 1968-06-06
Filing date: 1968-06-06
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08

Description

United States Patent [72] Inventors Matthew L. Jalfa 92 Clark St., Rutherford, New Jersey 07070; David Jana, 38-26 Allvvood Place, Fairlawn, New Jersey 07410 [21] Appl. No. 734,991 [22] Filed June 6,1968 [45] Patented Sept. 8, I970 [54] VACUUM TABLE SYSTEM FOR PRINTING MACHINE 9 Claims, 3 Drawing Figs.

[52] U.S.Cl 101/407, 101/126 [51] lnt.Cl B41fl/32, B4lf 15/20 [50] FieldofSearch 101/123, 124,407, l27.l,4l5;271/74, 12,26; 226/95; 248/362, 363; 267/21; 101/126 [56] References Cited UNITED STATES PATENTS 1,288,607 12/1918 Jobke 248/363 SOURCE Morganstern et a1 .laffa et a1.

ABSTRACT: A multiple-suction area vacuum table system for use with a printing machine to hold sheet material to be printed against a porous, endless conveyor belt that carries the sheets from a feed station to a printing station and thence to a collection station. The vacuum levels of the suction areas are independently adjustable and are controlled in accordance with the movements of the belt and the printing head so that when the belt is indexed, the vacuum level along the table length is sufficient to hold the sheets flat against the belt without imposing an excessive suction drag thereon, and dur' ing the printing operation the vacuum level at the printing station is raised to more firmly grip the sheet being printed so as to prevent any rippling thereof by the action of the squeegee associated with the printing head.

Patented Sept. 8, 1970 3,527,166

'1 N VENTOR.

lAtCUlUM TABLE SYSTEM FOR PRINTING MACHINE BACKGROUND AND SUMMARY OF THE INVENTION This invention relates in general to printing machinery which employ vacuum conveyor belts and more particularly to a vacuum table system for holding sheet material against the conveyor belt.

in typical vacuum belt printing machinery installations, the sheet material to be printed is laid upon the belt at a feed station and is carried thereby to a printing station whereat the printing operation is performed, and then the printed sheet is carried by the belt to a collection station to be discharged thereat. Ordinarily an endless belt is used, and the belt moves intermittently such that each time the belt is indexed, a blank sheet at the feed station is brought to the printing station and underneath the printing head, and the sheet that was last printed is advanced from the printing station toward the collection station by an equivalent distance. At the end of each indexing movement, the belt is stopped momentarily and the printing head is brought down toward the belt to print the sheet that has arrived at the printing station. After the printing operation is completed, the printing head is raised and the belt is re-indexed to bring up a new sheet. This sequence of belt indexing and printing head motions is repeated as often as necessary to print the desired number of sheets.

It is important that the sheet at the printing station be held flat and securely to prevent any rippling during the printing operation by the action of the squeegee associated with the printing head. In the prior art, holding of the sheet at the printing station has been accomplished by vacuum forces provided by a vacuum table underlying the belt. Such vacuum table is ordinarily an evacuable chamber that extends lengthwise along the conveyance path for a distance somewhat greater than the sheet length, and extends transversely to the conveyance path for a distance approximately equal to the belt width, and has one or more openings exposed to contact the inner side of the belt. The belt is porous or perforated such that the vacuum table openings establish corresponding suction areas along the outer side ofthe belt sections passing over the openings. Thus, each sheet brought to the printing station will be gripped at these suction areas and will be held flat against the belt so as not to ripple or slip during the printing operation.

The vacuum pressure level required for sheet holding during the printing operation would, if applied to the area of the belt outside the printing station area, such as over that portion of the belt between the feed station and the printing station, have imposed a high suction drag load upon the belt which would give difficulties in indexing it. Consequently, with a vacuum table that could only have a single evacuation pres sure level, which had to be high enough for the printing operation requirements, extension of the table from the printing station area to the feed station so as to provide vacuum gripping of sheets conveyed therebetween was for all practical purposes prohibited.

Since it is also necessary that the sheets conveyed from the feed station to the printing station be held flat and firmly against the belt in order to arrive at the printing station in proper registry with the printing head, it was necessary to provide mechanical grippers or clamps mounted to the belt for movement therewith. Such gripping clamps were normally mounted on both edges of the belt thereby reducing the available Width of sheet that could be handled, and also reducing the width of the pattern which could be printed on the sheets that were handled. Because out. the central width portions of the sheets could be printed. the outer width portions held by the clamps were left blank, and in cases where such blank portions were undesired in the finished product, the printed sheets had to be trimmed.

The invention provides a vacuum table system that dispenses with the need for any mechanical clamps on the belt and instead uses a multiple vacuum zone type vacuum table in which the vacuum gripping forces on sheets being conveyed from the feed station to the printing station can be adjusted without affecting the gripping forces applied to the sheet of the printing station during the printing operation, and vice versa.

In the system of the invention, the vacuum table is positioned for contact with the inner side of the porous belt to support it along the path of conveyance, at least from the beginning of the feed station to the end of the printing station, and the table has partition means defining a plurality of evacuable spaces open to the inner side of the belt to establish corresponding suction areas along the outer side of the belt for gripping the sheet material conveyed thereby. Passage means are provided for communicating selected groups of these spaces with one another so as to allow evacuation of all spaces in each group to a given pressure independently of the pressure to which the spaces of any other group are evacuated. Thus the gripping force exerted on the sheet material conveyed through the suction areas associated with said spaces can be adjusted by correspondingly adjusting the evacuation pressures of individual groups of spaces.

According to a preferred embodiment of the invention there is provided on the table a first group of evacuable spaces establishing suction areas located between the feed station and the beginning of the printing station, and a second group of evacuable spaces establishing suction areas located between the printing station and the collection station and distributed throughout substantially the entire printing area at the printing station.

By controlling the vacuum in the first group of spaces, it is possible to regulate the gripping force on sheets conveyed from the feed station to the printing station so that they are held flat and do not slip out of registry. Likewise by controlling the vacuum in the second group of spaces, the gripping force on the sheet at the printing station can be set to prevent any slippage during the printing operation. Since the vacuum levels of the two groups of spaces can be independently controlled it is possible to hold the two groups of spaces at a reduced vacuum level during the feeding mode of opera tion to reduce the suction drag when indexing the belt, and then during the printing operation, to raise the vacuum level of the second group of spaces and either hold the first group of spaces at the reduced vacuum, or vent them to the atmosphere.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a schematic elevation view, partly in section of a vacuum table system according to a preferred embodiment of the invention and illustrating its use in connection with a typical vacuum belt printing machine.

FIG. 2 is a plan view of the vacuum table used in the vacuum table system of FIG. 1.

FIG. 3 is a sectional elevation view of the vacuum table shown in FIG. 2 as taken along line 3-3 therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION In FIG. 1 there is illustrated a vacuum belt type printing apparatus 10 wherein sheets of paper or other material to be printed are laid upon an endless porous conveyor belt 11 at a feed station 12 and are carried thereby to a printing station 13 where they are contacted by a printing head 14 and printed thereby. After the printing operation is performed on any given sheet, it is carried by belt 11 to a collection station 15 where it is ejected or otherwise removed from the belt 11.

The belt 11 moves intermittently rather than continuously such that the first sheet in a sequence of similar sheets to be printed is laid on the belt 11, and the belt 11 is indexed in the forward direction, as indicated by arrow 16, by the distance required to bring the sheet to printing station 13, under printing head 14 and in registry therewith. Printing head 14 moves up and down with respect to belt 11 and in synchronism with the indexing motion thereof such that printing head 14 is in a raised position when the sheet begins to move from the feed station 12, and remains raised until the sheet arrives in the printing registry position at station 13. This assures that there will not be any interference by the printing head 14 with the movement of the sheets to be printed or that have been just printed. Upon arrival of the sheet at the printing station 13, belt 11 is halted and printing head 14 is lowered into contact with the sheet, as shown in dotted outline form, to perform the printing operation. After the sheet has been printed, the printing head 14 is raised and belt 11 is re-indexed to print the next blank sheet up to printing station 13 and to simultaneously advance the just printed sheet toward collection station 15. The foregoing basic indexing and printing head motions can be repeated as often as necessary to print any selected number of consecutive sheets.

It can therefore be noted that the printing apparatus has two basic states, or modes of operation, one being the indexing mode characterized by the fact that printing head 14 is raised and belt 11 is moving, and the other being the printing mode characterized by the fact that printing head 14 is lowered and belt 11 is halted. These two operating modes are readily detectable by any one ofa variety of monitoring means that can be used in accordance with the invention to control the operation of a vacuum table system associated with printing apparatus 10.

Vacuum table system 20 includes a vacuum table 21 shown in greater detail by FIGS. 2 and 3. The vacuum table 21 is made up of an air tight hollow box 22 subdivided by an air tight barrier 23 into two

plenum chambers

24 and 25 which are covered top and bottom by sealing

panels

26 and 27 respectively. On the top sealing panel 26 is provided a layer of epoxy 19 which acts as a bed for a plate 28. Plate 28 is made up of a plurality of adjoining coplanar grooved or ribbed sections 28A, 28B, arranged in underlying relation to the porous belt 11 and for contact with the inner side thereof to support belt 11 along the path of conveyance from the beginning of feed station 12 up to at least the end of the printing area 29 of printing station 13. Recessed into the upper side of plate 28 are a first set of extended parallel grooves 30A and a second set of longitudinally extending parallel grooves 308. Grooves 30A extend from the beginning of feed station 12 up to approximately the beginning of the printing station 13. and grooves 308 extend from the beginning of printing station 13 up to the end of the printing area 31 associated therewith.

Grooves

30A and 30B are prevented from running into one another by a barrier section 32 of plate 28 extending across the width thereof at the beginning of printing station 13. Grooves 30A are stopped at their feed station 12 end by a barrier section 33 of plate 28, and are spaced apart by intervening barrier sections 34A of plate 28. At the end of the printing area 31, the grooves 30B are stopped by a barrier section 35 of plate 28, and are spaced apart by intervening barrier sections 348 ofplate 28.

Grooves 30A are communicated with plenum chamber 24 and thereby communicated with one another by means of passages 36A drilled through plate 28, epoxy layer 19 and panel 26. Likewise, grooves 303 are communicated with plenum chamber 25, and thereby communicated with one another by means of similar passages 36B drilled through plate 28, epoxy layer 19 and panel 26.

The

plenum chambers

25 and 24 are evacuable independently of each other, and hence the grooves 30A will all have the same evacuation pressure as plenum chamber 24 whereas the grooves 308 will all have the same evacuation pressure as plenum chamber 25.

The

barrier sections

32, 33, 34A, 34B and 35 can be considered as partition means defining a plurality of evacuable spaces, i.e. grooves 30A and 308 open to the inner side of belt 11 and when evacuated establish corresponding suction areas along the outer side of belt 11 for gripping the sheet material conveyed thereby.

To adjust the gripping force on sheets conveyed from feed station 12 to printing station 13 and passing through the suction areas established by grooves 308 it is only necessary to adjust the vacuum pressure within plenum chamber 24, and likewise to adjust the gripping force on sheets conveyed into the printing area 31, the vacuum pressure within plenum chamber 25 is adjusted.

In the operation of printing apparatus 10, it is desirable to hold the grooves 30A and 308 at substantially the same vacuum pressure level during the feeding mode of operation so that sheets conveyed from the feed station 12 to printing station 13 will be held flat against the belt 11 with a vacuum gripping force distributed across the width of belt 11 sufficient to prevent sheet slippage, but not so great as to impose a suction drag upon belt 11 that might overload the motor means (not shown) that effects the belt indexing motion.

During the printing operation, a somewhat higher vacuum gripping force is needed to securely grip the sheet at the printing station 13 against any slippage due to the wiping action of the squeegee (not shown) associated with printing head 14. The vacuum gripping force over the portion of the belt between the feed station 12 and printing station 13 need not be maintained during the printing operation since the belt 11 is stationary.

The regulation of the vacuum pressures of

grooves

30A and 30B is accomplished by means ofa vacuum control regulation circuit 40 in which the inlet of a first solenoid valve 41 is communicated with plenum chamber 24 by a line 42 and the outlet of valve 41 is communicated with one branch of a four-way cross connection fitting 43 by a line 44. Plenum chamber 25 is communicated with another branch of fitting 43 by a line 46, as is the inlet of a second solenoid valve 47 and one side of a bleeder valve 48. The other side of valve 48 and the outlet of valve 47 are both communicated with a vacuum source 49 via a T-fitting 50.

Valve 41 is open during the feeding mode of operation whereas valve 47 is closed so as to establish a vacuum pressure equalizing flow connection between the

plenum chambers

24 and 25 for equalizing the vacuum pressures in both sets of

grooves

30A and 30B. In addition, during the feeding mode,

valves

41 and 47 are in states which establish a flow connection through bleeder valve 48 between the vacuum source 49 and both

plenum chambers

24 and 25. Consequently, both sets of grooves 30A and 308 will be at a uniform pressure level established by bleeder valve 48 during the feeding mode.

During the printing mode of operation, valve 41 is closed and valve 47 opened. This cuts off the vacuum in plenum chamber 24 and establishes a flow connection between plenum chamber 25 and the vacuum source 49 bypassing bleeder valve 48. Thus, in the printing mode, the full vacuum pressure of source 49 will be applied to the grooves 308 whereas vacuum to the grooves 30A will be cutoff. If desired, the valve 41 can be one which when closed will vent plenum chamber 24 and the grooves 30A to the ambient atmosphere.

The operation of

solenoid valves

41 and 47 is coordinated with the operation of the printing apparatus 10 by a monitoring means that is capable of sensing whether the apparatus 10 is in its feeding mode or its printing mode and establishing a corresponding feeding or printing condition indicator signal accordingly. Such monitoring means can be in the form of a switch 60 that senses the position of printing head 14 and either opens or closes to establish a printing condition indicator signal whenever the printing head 14 is in the down position it normally assumes when performing the printing operation. By using a solenoid valve 41 which is normally open when its operating solenoid is de-energized, and a solenoid valve 47 which is normally closed when its operating solenoid is de-energized, the operating solenoids of both valves 4ll and 47 can be conveniently connected together electrically in parallel. For example, with a monitoring switch 60 that is open when printing head 14 is raised, as during the feeding mode, and closed when printing head 14 is lowered, as during the printing mode, switch 60 can be connected in series with an electrical voltage source 61 and the operating solenoids of

valves

41 and 47 to provide at such solenoids a printing condition signal in the form of an electrical voltage approximately equal to that of the source 61 or alternatively a feeding condition signal which is the absence of electrical voltage at the solenoids. Consequently, during the feeding mode,

valves

41 and 47 would be left in their respective normally open and closed states, whereas during the printing mode the signal voltage applied to their solenoids will cause valve 41 to close, thereby cutting off vacuum to plenum chamber 24, and valve 47 to open, thereby applying the full vacuum of source 49 to plenum chamber 25.

The same information as to the operating mode of the printing apparatus llt) can be derived by monitoring the state of motion of the belt ill, since in the apparatus the movements of belt it and printing head 14 are coordinated by suitable means not shown and not forming a part of this invention. To control the operation of

valves

41 and 47 on the basis ofinformation derived from the movement of belt 11, a switch 60A, (shown in phantom) can be substituted for the switch 60 in the same electrical circuit that includes switch 60, voltage source 6i and the operating solenoids of

valves

41 and 47. Switch 60A is connected to or otherwise arranged in relation to belt ll so that when belt 11 is stopped, switch 60A closes, and whenever belt ll is moving, switch 60A is open. In this way,

the same basic types of feeding and printing condition indicator signals will be established for operation of

valves

41 and 47 as in the case ofthe printing head 14 monitoring switch 60.

As can be appreciated by the artisan other vacuum control arrangements can be substituted for those described and illustrated herein provided that the essential objectives of the invention are fulfilled. These objectives are basically to control the vacuum pressure levels of plenum chambers 24 and Z5, and hence the vacuum gripping forces established by their

corresponding grooves

30A and 30B in accordance with the operating mode of the printing apparatus 10 such that during the feeding mode, both the set of grooves 30A in the feed station l2 to printing station 13 belt area, and the set of grooves 30B in the printing area 31 are at a uniform vacuum pressure level that is less than the full vacuum capability of the vacuum source 49, and during the printing mode, the vacuum to the set of grooves EltlA is cut-off while the full vacuum available from source 49 is applied to the set of grooves 308. The uniform vacuum pressure level that is applied to grooves 30A and 308 during the feeding mode can of course be made adjustable simply by choosing a bleeder valve 48 having an adjustable vacuum regulating means, or by substituting another bleeder valve 48 that will give the vacuum pressure level desired.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use ofthe other features.

We claim:

1. ln a printing apparatus wherein sheet material to be printed is conveyed along a given path by a porous belt from a feed station to a printing station and thence to a collection station, with the printing operation being performed at the printing station by a printing head which is moveable relative to the belt, a vacuum table system which comprises a vacuum table positioned for contact with the inner side of said belt to support same along the path of conveyance, said vacuum table having partition means defining a plurality of evacuable spaces open to the inner side of the belt to establish corresponding suction areas along the outer side of the belt for gripping the sheet material conveyed thereby, said plurality of evacuable spaces including a first group of evacuable spaces establishing suction areas located between said feed station and said printing station, and a second group of evacuable spaces establishing suction areas located at said printing station and between said printing station and collection station, and means communicating the spaces of each group with one another to accommodate evacuation of all spaces in one group to a given pressure independently of the pressure to which the spaces of the other group are evacuated, whereby the gripping force exerted on the sheet material conveyed through the suction areas associated with said spaces can be adjusted by correspondingly adjusting the evacuation pressures of said first and second groups of spaces.

2. A vacuum table system according to claim ll including a vacuum source, and control means communicating with said vacuum source and communicating with said first and second groups of evacuable spaces, said control means being operable to selectively communicate said first group of spaces with said vacuum source and establish a predetermined evacuation pressure throughout the suction areas associated with said first group of spaces, and operable to selectively communicate said second group of spaces with said vacuum source and establish a predetermined evacuation pressure throughout the suction areas associated with said second group of spaces.

3. A vacuum table system according to claim 2 wherein said control means includes monitoring means responsive to the condition of said printing apparatus to establish a printing condition indicator signal whenever said apparatus is in a con dition for immediately performing a printing operation upon sheet material at the printing station, and vacuum level regulation means operable to increase the evacuation pressure level of said second group of spaces in response to said indicator signal, whereby during the printing operation the gripping force on the sheet material at the printing station is increased.

4. A vacuum table system according to claim 3 wherein said monitoring means senses the position of said printing head and establishes the printing condition indicator signal whenever the printing head is in the position it normally assumes when performing the printing operation.

5. A vacuum table system according to claim 3 wherein said monitoring means senses the state of motion of said belt and establishes the printing condition indicator signal whenever the belt is in the state of motion it normally assumes during performance of the printing operation.

6. A vacuum table system according to claim 2 wherein said control means includes monitoring means responsive to the operating condition of said printing apparatus to establish a printing condition indicator signal whenever the apparatus is in its printing mode of operation, and to establish a feeding condition indicator signal whenever the apparatus is in its feeding mode of operation, and vacuum level regulation means operable in response to said feeding condition indicator signal to establish a first uniform evacuation pressure level in said first group of spaces and also in said second group of spaces, said vacuum level regulation means being operable in response to said printing condition indicator signal to establish an atmospheric pressure level in said first group of spaces, and a second evacuation pressure level in said second group of spaces, said second evacuation pressure level being higher than said first evacuation pressure level, whereby during the feeding mode of operation a uniform gripping force corresponding to said first evacuation pressure is applied to sheet material conveyed from the feed station to the printing station, and to sheet material conveyed from the printing station toward the collection station, and during the printing mode of operation the gripping force applied to sheet material at the feed station is reduced to approximately zero while the gripping force applied to sheet material at the printing station corresponds to said second evacuation pressure level.

7. A vacuum table system according to claim 6 wherein said control means includes a vacuum source, a bleeder valve, a first control valve and a second control valve both operable in response to said feeding and printing condition indicator signals, said first and second control valves and said bleeder valve being interconnected to define a vacuum level regulation circuit communicating with said first group of spaces, with said second group of spaces, and with said vacuum source, said first and second control valves being responsive to said feeding condition indicator signal to establish in said regulation circuit an evacuation pressure equalizing flow connection between said first and second groups of spaces and to establish a flow connection through said bleeder valve between said vacuum source and both groups of said spaces to maintain a common evacuation pressure therein determined by the bleeder valve, said first and second control valves being responsive to said printing condition indicator signal to establish in said regulation circuit a flow connection between said second group of spaces and said vacuum source.

8. A vacuum table system according to claim 7 wherein one of said first and second control valves is responsive to said printing condition indicator signal to vent said first group of spaces to the ambient atmosphere.

9. A vacuum table system according to claim 1 wherein said vacuum table comprises a plate having a first set of spaced apart grooves defining said first group of evacuable spaces, and having a second set of spaced apart grooves defining said second group of evacuable spaces; a first plenum chamber adjoining said plate in underlying relation to said first set of grooves; a second plenum chamber adjoining said plate in underlying relation to said second set of grooves; passage means extending through said plate to communicate said first set of grooves with said first plenum chamber; and passage means extending through said plate to communicate said second set of grooves with said second plenum chamber, both said first and second plenum chambers being evacuable independently of each other for establishing corresponding evacuation pressures in the spaces defined by their respectively associated sets of grooves.