US3318236A - Electrostatic drum printer - Google Patents

Description

y 9, 1967 R. c. MUELLER ELECTROSTATIC DRUM PRINTER 6 Sheets-Sheet 1 Filed Oct. 24, 1965 INVENTOR. ROBERT C. MUELLER BY 5 4*, W44, Q AM ATTORNEYS y 1967 R. c. MUELLER ELECTROSTATIC DRUM PRINTER 6 Sheets-Sheet 2 Filed Oct. 24, 1965 aw W154, 5mm ill ATTORNEYS y 9, 1967 R. c. MUELLER ELECTROSTATIC DRUM PRINTER 6 Sheets-Sheet 3 Filed Oct. 24, 1965 m G B 4F M 7% p- E w I Q i 4 I 6 H C M 7 m V M M i I a 9 9 4 9 m w w I m B I 5 5 I alml 6 m 4 1 M 5 w R u m I w a? m nw I 2 9 6 9 I 6 f I B E B 3 6 6 m V 1 H M I. 4 3 m w v r H I g/ 8 O 4 m w m m 4 I \W h I M L 4 I mu 6 7 8 O 8 m m m w m m w w m R O T N E V m ROBERT C MUELLER 7 J AiM/F ATTORNEYS y 9, 1967 R. c. MUELLER 3,318,236

ELECTROSTATIC DRUM PRINTER Filed Oct. 24, 1965 6 Sheets-Sheet FlG l2 Foam" INVENTOR. ROBERT C MUELLER ATTORNEYS y 1967 R. c. MUELLER 3,318,236

ELECTROSTATIC DRUM PRINTER Filed Oct. 24, 1965 6 Sheets-Sheet G I90 MVIBZ I I83 :80

I84 [as I87 O D O I 0 :IBI 0 1 l82- Y zos 20/ INVENTOR. ROBERT c MUELLER BY 12%, m, WMw-um.

ATTORNEYS United States Patent 3,318,236 ELECTROSTATIC DRUM PRINTER Robert C. Mueller, Fremont, Calif., assignor to Unimark Corporation, San Ramon, Calif., a corporation of California Filed Oct. 24, 1965, Ser. No. 504,449 11 Claims. (Cl. 101118) This invention relates to electrostatic printing apparatus generally of the type disclosed in copending application Ser. No. 439,720 filed Mar. 15, 1965, by Martin A. Schueler, in which a dry printing powder is conducted through an electrostatic field from a screen onto a material to receive an impression corresponding in outline to that of an open mesh area or areas of said screen, there being an air gap between the screen and the material in which the electrostatic field is established.

One of the objects of the invention is the provision of apparatus of the above general type for selectively electrostatically printing different symbols or patterns at one point along the path of travel of the material to be printed upon, as said material is moved past said point.

Another object of the invention is the provision of an improved method for selectively electrostatically printing different symbols or patterns on material at a single point as the material for receiving said imprint moves past said point.

A still further object of the invention is the provision of apparatus for more efficiently feeding and distributing printing powder on a printing screen for certain types of work, than heretofore.

Another object of the invention is the provision of electrostatic printing apparatus that is more readily serviced than heretofore.

The present invention, in some respects, is particularly suited for printing on sheet material, whether smooth or rough. One example in which the material may be smooth, or relatively rough, is plywood. No modification of the apparatus is required for printing on plywood, or other sheet material, having a relatively rough or a relatively smooth surface, the present apparatus being readily adjustable for different textures and thicknesses of the material.

With respect to plywood, it is customary for the plywood sheets to be carried by a conveyor along a path of travel and to be imprinted with a grade mark, as well as other marks. Heretofore, it has been the practice to stamp symbols such as a trademark, or a grade designation and other marks on the sheets of plywood as they are conveyed along such path. Rubber stamps or the like have heretofore been used with wet ink to imprint the symbols in such ink, with the result that the ink would run or be diffused in the porous surface of the sheets whether the surface were smooth or rough, and also the imprint would, in most instances, be wholly illegible on a rough surface. Furthermore the wear on type due to abrasion or the relatively hard, rough character of the surface engaged thereby would quickly result in defective, if not illegible, imprints, even under the most favorable conditions.

With the present apparatus clear imprints are produced with dry pigment, or printing powder, irrespective of irregularities in the surface receiving the imprint; and there is no detrimental wear on the printer at the printing point due to roughness of said surface.

After plywood sheets are manufactured, they are sorted into grades or classes and are given grade or class designations and at the same time they may be imprinted with other symbols, trademarks, etc. =Heretofore either several printers must be used, one for each grade or class mark, or else the single printer must be stopped and the printing mechanism changed for each mark.

3,318,236 Patented May 9, 1967 With the present invention, a single, conventional conveyor may carry a row of separate plywood sheets in a direction longitudinally of said row past a single printing mechanism in succession. An operator may be positioned to observe each sheet before it passes the printer. The construction of the apparatus is such that the operator may instantly control the printer without stopping the latter or the conveyor, so that a different grade or class mark or symbol may be printed on the sheets at the time they pass the printer, and also other marks may be selectively printed, as desired.

Another object of the invention is the provision in an electrostatic printer adapted to print on a material by electrostatically conducting dry printing powder in a pre determined pattern across an air gap and depositing it on the said material, in which printer the printing powder is contained against escape into the air during printing, and in which printer the supply of powder may be quickly replenished without stopping the printer.

In the present apparatus, surface dry powder pigment is the printing medium, and although certain features of the invention may be used where the powder is provided by abrading it from a cake or stick in which it is lightly bonded together, other features of the invention provide an improved medium for evenly distributing loose powder particles on a screen through which the powder is moved into an electrostatic field for conduction onto the material to receive the imprint.

Other objects and advantages will appear in the description and in the drawings.

In the drawings, FIG. 1 is a simplified side elevational view, partly in section, of the main portion of the apparatus, the near side of the frame being broken away.

FIG. 2 is a top plan view of the apparatus shown in FIG. 1 with portions broken away.

FIG. 3 is an enlarged part sectional, part elevational view of the portion of the printing machine at the printing station.

FIG. 4 is an end elevational view of the printing drum and portions associated therewith, as seen from the right hand side of the machine shown in FIG. 3.

FIG. 5 is an enlarged, fragmentary cross sectional view taken substantially along line 5-5 of FIG. 4.

FIG. 6 is a fragmentary cross sectional view along line 6-6 of FIG. 5.

FIG. 7 is an enlarged fragmentary, cross sectional view showing the printing screen and powder applying roller in printing relation with a piece of plywood.

FIG. 8 is a fragmentary, vertical cross sectional view substantially along line 88 of FIG. 9.

FIG. 9 is a fragmentary, vertical, cross sectional view taken substantially along line 9-9 of FIG. 8, but with certain parts on said line being in elevation.

FIG. 10 is a fragmentary cross sectional view taken generally along line 1010 of FIG. 8.

FIG. 11 is an enlarged fragmentary cross sectional view taken generally along line 11-11 of FIG. 12.

FIG. 12 is a fragmentary cross sectional view taken approximately along line 12-12 of FIG. 11.

FIG. 13 is a schematic view of an electrical circuit in which the printing apparatus is connected.

The apparatus illustrated in FIGS. 1, 2 comprises a horizontally disposed cylindrical drum generally designated 1, which drum has a head 2 (FIGS. 3, 12) at one end thereof rigid therewith. Head 2 has a central hub 3 (FIG. 3) thereon projecting outwardly of said drum, and bearings 4 within said hub rotatably support the drum on a central shaft 5 that, in turn, projects outwardly of the hub 3 and is stationarily held eccentrically within a sleeve 6. Sleeve 6 is supported for rotation within a hearing 7 that is on the lower end of an upwardly extending bracket 8. The upper end of bracket 8 is a-djustably clamped to a horizontally extending overhead frame member 9 by screws 10. The overhead frame member 9, in turn, is rigid on uprights 11 of a supporting frame 12 (FIG. 1) of the machine, and said member9 extends over the drum 1 axially of the latter, whereby said drum may be positioned at different positions longitudinally of said member 9, by loosening screws and moving the bracket 8 longitudinally of the member 9 to different positions, in each of which the screws 10 maybe tightened to hold the drum in the adjusted position.

From the foregoing it is seen that drum 1 is supported at only oneend thereof by shaft 5 and bracket 8. At the ends of member 9 where it is supported on the cross members extending across the upper ends of uprights 11, a recess 13 (FIG. 1) isformed in the side frame members 24, 25. allowing the drum 1 to be removed from the end of member 9 by sliding it outwardly through the opening formed by said cross member, said uprights and recess 13.

Secured to the rearward end of shaft 5 (left hand end as seen in FIG. 3) by a pair of screws 16 (FIGS. 3, 4) is a cap having a generally vertically disposed channel formed therein which is adapted to receive the lower end of a guide arm 14. The upper end of arm 14 is pivotally secured to bracket 8 by a threaded pivot 17.

Secured to eccentric sleeve 6 between said sleeve and the lower end of arm 14 is a drum height adjusting handle 21 which is eccentric of shaft 5 also. Upon rotation of handle 21, sleeve 6 will be rotated to raise and lower shaft 5 within bearing v7 and thereby raise and lower drum 1 with respect to the conveyor over which it may be positioned for printing on material of different thicknesses.

with sleeve 6. The importance of this will be apparent in later description,

Rigid with head 2, and concentric therewith, is a sprocket wheel 18 (FIGS. 2, 3) which sprocket wheel is connected by a chain 19 with a sprocket wheel 20 (FIGS.

1, 2) that is on a shaft 23. Shaft 23 is rotatable in bearings carried by a pair of horizontally extending, vertically disposed, spaced, opposed parallel frame members24, 25 of frame 12 (FIG. 2).. g

Shaft 23 is spaced above a horizontally extending row of rollers 26 of a roller conveyor, which rollers are parallelwith shaft'23, and are rotatably supported at their ends by bearings on frame members 24, 25. Rollers 26'support sheets 27, which in the present instance may be plywood or the like, the sheets being driven from left to right asviewed in FIG. 2 for movement to and past drum' 1.

One or more rollers 28 are secured on shaft 23, and such rollers may be yieldably urged against the sheets 27 in driving relation thereto.

In FIG. 2 the frame 12 is shown as being sufliciently wide to support several drums 1 over the conveyor, if desired, a second drum being indicated at 1 in dot-dash lines.

A second sprocket wheel 29 is on shaft 23 (FIG. 2)

which wheel is connected by a chain 30 with a sprocket wheel 31 driven by a motor 32 for driving rollers 28, and bearings 33' may include springs (not shown) for yieldably'urging the rollers 28 against the plywood, such structure being common. Preferably, one of the rollers 26 is below rollers 28.

, The sprocket wheel 18 is around and concentric with hub 3 that projects rearwardly of head 2 and outwardly relative to drum 1. Concentric with and adjacent to sprocket wheel 18 is a sprocket wheel 34, which wheel is also rigid with head 2 of drum 1.

Sprocket wheel 34 is connected by a sprocket chain 35 (FIGS. 1, 2) with a sprocket wheel 36, the latter being on a shaft 37, and shaft 37, in turn, corresponds to shaft 23 and is similarly supported at its ends for rotation in bearings 38 carried by side frame members The lowerend of arm 14 passing through the channel in cap 15 will prevent shaft 5 from rotating 4 24, 25. Shaft 37 is positioned at the side of drum 1 opposite to shaft 23, and rollers 39 on shaft 37 are adapted to engage sheets 27 in the same manner as rollers 28 for drawing the sheets 27 past the drum 1 after they are driven to said drum by rollers 28.

From the foregoing, it is seen that motor 32 drives drum 1 and rollers 28, 39 for moving the plywood sheets past the drum, and the driving arrangement is such that the surface speeds of the sheets 27 and the outer surface of drum 1 are the same with the lower side of the drum moving in the same direction as the sheets 27.

The head 2 of drum 1 is formed with rearwardly and outwardly projecting lugs 40. Bolts 41 secure the sprocket wheels 18, 34 to said lugs in positions coaxial with shaft 5, and spacers 42 around bolts 41 space the wheels 18, 34 apart.

Shaft 5 includes a flange 45 (FIG. 12) projecting radially outwardly thereof within drum 1, and screws 46 secure said flange to the circular endwall 47 of an inner cylindrical drum generally designated 48.

Drum 48 is coaxial with the cylindrical wall 49 of drum 1, but is spaced within the latter. Sealing rings 50 of yieldable, rubber-like material coaxial with drums 1 and 48 are secured to the inner drum 48 and extend between , drums 1 and 48 in wiping relation to the inner surface of the cylinder49 of drum 1 at positions adjacent to the opposite ends of drum 48 (FIG. 3). These seals preclude ingress of foreign material to the space between the drums as well as egress of material from said space.

Inner drum 48, being rigid on shaft 5, is stationary, and drum 1 rotates about it and about the elements that are carried by drum 48 or by endwall 47.

One or more bayonet connections, such as at 51 (FIG. 3) releasably hold drum 1 to head 2, so that a fractional turn of drum 1 relative to head 2 will release the wall 49 for removal to replace the latter or to service it, or to expose the drum 48. Since drum 1 carries the printing screens, it is apparent that the latter can be quickly replaced.

The front or forward side of the drum 1 is the side thereof that is opposite to head 2, and said forward side is open.

The use herein of the words front, forward, rear, rearwardly, and words of similar meaning are used with reference to the open side of drum 1, which is the front side, while head 2 is the rear side, and shaft 5 projects rearwardly of head 2 while the drum 48 is forwardly of head 2, etc. Thus the drum 1 and the elements within the latter including the inner drum 48 are supported by shaft 5 over the roller conveyor, and which conveyor is generally designated 53 (FIG. 1), and

- is made up of rollers 26. Horizontally elongated guide strips 54 (FIG. 2) are carried by side frame members 24, 25. These guide strips are adapted to engage the edges of sheets 27 when the latter are on conveyor 53 to properlyalign said strips on the conveyor between said side frame members of the apparatus. Hold down strips or members 55 are supported over the conveyor to hold the sheets 27 down on the rollers 26.

Within inner drum 48 is a powder box assembly generally designated 56, and a brush assembly generally designated 57 is below the powder box (FIGS. 1, 3, 4).

The inner drum 48 is alsoopen at its front side, and the box assembly 56 is supported within said inner drum on and between a pair of horizontallyspaced, parallel, opposed rods 58, 59 (FIGS. 8, 11). Rods 58, 59 are secured at one of their ends in a horizontally extending plate 60 (FIGS. 11, 12) which plate, in turn, is secured to endwall 47 of inner drum 48 by bolts 61. The powder box assembly 56 includes a rear wall 63 (FIGS. 8, 9), opposite sidewalls 64, 65 (FIG. 8) and a front wall 66 (FIG. 9). The front and rear walls 66, 63 are connected extensions of the front and rear walls. The upper side of the powder box is open, and divergently upwardly extending walls 69 project upwardly from the upper edges of sidewalls 64, 65 to the upper side of inner cylinder 48, while vertical walls 70 (FIG. 3) extend upwardly from and parallel with the rear and front walls 63, 66. A rubber-like sealing stri 73 (FIGS. 8, 9) is secured to sidewalls 64, 65 and to walls 63, 66 along their upper edges and extends upwardly therefrom into sealing engagement with the lower edges of walls 69, 70. Walls 69, 70 are rigidly secured by screws or by any other suitable means to the inner drum 48.

Rods 58, 59 each have rod-like extensions 74 hingedly secured as -at.75 to the forward ends of said rods. Said extensions 74 are swinga-ble horizontally, from positions extending toward each other at right angles to rods 58, 59, and across the forward side (wall 66) of the powder box (FIG. 4) to dot-dash line positions 76 (FIG. 9), in which positions said extensions are in longitudinal alignment with rods 58, 59. When the extensions 74 are in positions 76, the powder box 56 may be slid out of the forward open side of the inner drum 48 and supported on said extensions outwardly of the drum for charging it with printing powder through its open upper end.

When box 56 is slid back into drum 48, the extensions 74 are swung back to their positions extending across the front side of the box, in which latter positions a generally U-shaped spring clip 77 (FIG. 9) will releasably hold the extensions 74 across the box against yieldably rubberlike pads 78 that are secured to the front side of said box adjacent the connection between said extensions and rods 58, 59 whereby the box will be held in operative position within the drum 48.

The powder box 56 includes a powder distributor or feeder mechanism within its lowered portion, which mechanism comprises a horizontally elongated endless belt 80 (FIG. 8) extending over pulleys 81 at its ends, which pulleys, in turn, are on shafts that are rotatably supported at their ends in bearings 82 (FIG. 9) carried by downward extensions of walls 63, 66.

The upper run of belt 80 extends completely across the lower open end of box 56, and said upper run is slidably supported on a horizontal plate 85 that, in turn, is secured to side plates 86 (FIG. Said plates 86 are secured against the lower marginal portions of walls 63, 66.

Horizontal strips 87 are secured to front and rear walls 63, 66 to extend over and substantially in slidable engagement with the longitudinally extending marginal portions of the upper run of belt 80 (FIG. 9) and a vertically adjustable horizontal strip 88 (FIG. 8) extends transversely across the upper run of belt 80 above the left-hand roller 81 as viewed in FIG. 8 and substantially in engagement with the upper surface of the belt. The upper run of the latter is moved past said strip 88 in a counterclockwise direction and the lower edge of strip 88 is bevelled away from the oncoming surface of the belt when the latter is actuated to act as a metering blade. The amount of pow der carried past blade 88 is varied by adjusting said blade vertically, increasing and decreasing the gap between the lower edge of said blade and the upper run of belt 80.

Belt 80 may have a surface characteristic, such as soft foam-like plastic sheet material that has outwardly opening cells adapted to hold and to carry the dry powder that is deposited thereon, and the combination of the platform 85 and strips 86, 87 provide opposedly inwardly opening parallel grooves in which the longitudinally extending marginal portions of the belt extend to prevent downward passage of powder past the edges of the belt, while strip 88 prevents passage of excess powder over one end of the belt. Thus the powder will be carried past blade 88 to below the belt upon movement of the upper run of the belt from right to left as seen in FIG. 8. The powder will be held in the outwardly opening cells of the belt until rejected therefrom.

Arcuate end walls 89 extend over the pulleys 84 and around the latter and a bottom wall 90 extends below the lower run of the belt 80, these walls being slightly spaced from the belt.

A doctor blade 93 extends transversely across the underside of belt 80 adjacent to the end of the latter nearest to wall 64 of the box, or the left-hand side as seen in FIG. 8, and this blade engages the belt and ejects the powder from the cells so that a steady, uniform curtain of powder will be ejected to fall as the lower run of the belt passes said blade 93. Blade 93 is bevelled away from the oncoming portion of the belt.

Blade 93 is rigidly held at its ends to downwardly extending portions of walls 63, 66 by screws 91 passing through said walls and into threaded engagement with flanges 92 of blades 93 (FIG. 9) in a position in a transversely extending horizontally elongated slot 94 in the bottom wall 90. The opposite sides of slot 94 extend convergently downwardly from the level of bottom Wall 90. By this arrangement the aforesaid relatively thin, substantially uniform curtain of powder ejected from the belt 80 will fall through slot 94 when the endless belt 80 is moved generally counterclockwise as seen in FIG. 8.

The screws 91 are loosely received through the extensions of sidewalls 63, 66 allowing slight vertical adjustment of blade 93. The amount of powder ejected from belt 80 can be varied somewhat by increasing and decreasing the pressure of blade 93 on belt 80.

An electric motor 95 (FIG. 9) is connected with one of the pulleys 81 to rotate the latter for moving said belt. The circuit to such motor may be such that when the powder supply container is moved outwardly of the printing cylinder, as in refilling, motor 95 will be automatically switched off.

The brush assembly 57 is below the powder box assembly and comprises a housing generally designated 96.

A vertically disposed, horizontally elongated mounting plate 97 supports said housing in the lower part of the inner drum 48 by means of a pair of horizontally, extending, spaced, parallel rods 98, 99 (FIGS. 5, 6).

Rod 98 extends through a laterally outwardly opening slot 100 in one end of plate 97, and the rod 99 extends through an opening 103 formed in the opposite end of plate 97.

The rear end portion 104 of rod 98 is cylindrical and eccentrically disposed relative to the axis of said rod, and said portion extends into an opening 105 in rear wall 47, which opening is concentric with portion 104, whereby said rod and the portion of the housing supported thereon may be elevated or lowered upon rotation of the rod 98 and eccentric 104.

The rear end portion 106 of rod 99 (FIG. 5) is of reduced diameter relative to the diameter of the part of the rod disposed in opening 103 in plate 97, and extends into an opening 107 formed in rear wall 47. Openings 105 and 107 also extend through bosses 108 on the forward side of wall 47. The walls of the bosses 108 and the support for rods 98, 99, and clamping caps 109 are secured to the rear ends of rods 98, 99 by screws 110 to hold the rods 98, 99 rigid on endwall 47.

A sleeve 113 on rod 98 has radially outwardly extending flanges 114 at its ends, and said sleeve extends from and against the forward surface of mounting plate 97 to the forward end of the inner drum 48 and a similar sleeve 115 is on rod 99 and which sleeve has radially outwardly extending flanges 116 at its opposite ends.

A manually rotatable cylindrical nut 117 is threadedly supported on the forward end of rod 98 and when tightened the nut engages the flange 114 adjacent thereto and secures the rod 98 stationary. A forward end portion 118 on rod 98 is of reduced diameter, and has a manually engageable knob 119 threadedly secured thereto and which knob is secured against rotation relative to portion 118 by a set screw 120.

Upon loosening the nut 117, the rod 98, the eccentric portion 104 thereon may be rotated to raise or lower the left end of plate 97, as viewed in FIG. 6, by rotating knob 119. A stationary indicator 123 (FIG. 4) secured on housing 96 adjacent to nut 117 will indicate the elevation of the plate 97 and the elements carried thereby, since knob 119 has height designating graduations thereon.

Rod 99 also has a manually actuatable tightening nut 124 threaded on the end thereof that is at the open end of the inner drum 48, and which nut functions the same as nut 117 is that it releasably retains the mounting plate 97 including the elements carried thereby, within the inner drum or cylinder 48. Upon removal of the manually actuatable nuts 117,119 and 124, the mounting plate 97 and sleeves 113, 115 including all of the structure carried by said plate may be slid out of the open end of the inner drum or cylinder 48 for replacement or servicing. As already noted, the powder box, including structure carried thereby may be moved out of the inner cylinder for replenishing the powder supply, independently of the brush assembly 57.

At a point intermediate the rods 98, 99 is a horizontally disposed shaft 125 thatis parallel with rods 98, 99 (FIGS. 5, 6), and which shaft is rigidly, "but releasably, secured at one end to mounting plate 97. The end so secured to said plate is the inner end, and the shaft projects forwar'dly from plate 97 to approximately the open end of the inner drum 48.

Shaft 125 is formed with a radially outwardly projecting flange 126 (FIG. 5) abuts a boss 127 on plate 97, and the inner end portion of the shaft extends rearwardly from said flange through an opening in plate 97. A cap or retainer disc 128 on the terminal inner end of the shaft clamps said inner end portion to plate 97 by means ofa screw 129 extending through said retainer disc '128 .and into the inner end of shaft 125 axially of the the samev manner as cylinder 49 is connected to head 2.

(FIG. 3).

A tubular member 137 within and coaxial with cylinder 135is formed with radially outwardly projecting flanges 138 spaced from its ends that abut the opposed surfaces of heads 133, 134. The end portions of said spacer project beyond the flanges 138 and extend into and fit against the inner surfaces of coaxial central openings in heads 133, 134 within Whichball bearings 139are fitted, and

which end portions engage the opposed surfaces of the outer races of said ball bearings 139 that, in turn, rotatably support the heads 133, 134 of the roller 130 on shaft 125. Bolts 140 releasably secure flanges 138 to the heads 133, 134.

Head 134 may .be provided with a stub-shaft 142 cm axial with shaft 125 which stub-shaft is connected with a continuous duty motor 143 for rotating roller 130.

Roller 130;includes an outer cover 144 of sponge-like plastic that is formed with small surface openings adapted to releasably, hold printing powder deposited thereon throughthe slot 94 that is in the bottom of the powder container 56, said roller 130 being positioned to receive said powder along a line that is slightly offset to one side of the uppermost surface of the outer layer 144 of said roller.

The side of the roller 130 to which the discharge slot 94 is offset is in the direction of rotation of said roller, and at said same side, but spaced farther from slot 94, is a smaller distance idler roller 145 of relatively rigid plastic material that,in turn, is parallel with roller 130 and in engagement with the latter. Roller 145 is externally ribbed or threaded and its action is to insure even distribution of the powder on layer 144 of roller and to maintain the powder sufliciently loose so it will be deposited from the roller 130 at the lower side thereof onto the printing screen for movement through the latter when the lower side of the roller contacts the screen.

Said roller is rotatably supported on a shaft 146 that, in turn, has a press fit at its inner end in an opening in the mounting plate 97.

As already mentioned, a housing 96 encloses the rollers 130, 145 which housing includes arcuate walls 147 (FIG. 6) extending across the lateral and upper sides of the rollers 130, 145 and which housing is slotted to register with slot 94 of the powder box, and into which the sides defining said slot 94 project (FIG. 6). The lower side of the inner drum 48 is formed with an opening 148 for projection of the lower portion of roller 130 therethrough for engagement of layer 144 on said roller with the upper surface of the outer rotating drum 1, and the sidewalls 147 of housing 146 extend to and across the opposed lateral edges of said opening 148. Opposed vertical endwalls 149, 150 extend across the ends of the rollers, and are secured to the sidewalls 147. Endwall 150 is against the mounting plate 97 and is formed with openings for passage of shafts 125, 146. Also wall 150 may include a flange 153 (FIG. 6) that is secured to plate 97 by suit-able screws. Motor 143 may be supported on endwall 149 of housing 96, the latter being formed with an opening for the shaft 142 connecting the roller 130 with the motor. By this structure the powder deposited into housing 96 is substantially retained within the latter, except for the powder that is deposited from roller 130 onto the printing screen.

The outer drum 1 is preferably of copper and has an outer coating 154 of plastic, such as epoxy resin and Fiberglas, except for the area of each printing screen, and the fine mesh screens preferably are even with the inner surface of the drum. The plastic, being nonconductive not only may space the screen farther from the material to be printed upon than otherwise, but no arcing will occur should some portion of said material contact the drum adjacent to the screen. The drum itself will normally be spaced from the plywood 27 or other material the desired distance by manually rotating sleeve 6 and shaft 5 to eflect the raising or lowering of the drum 1. The desired pressure of roller 130 against the printing screens is accomplished by manual rotation of rod 98.

A brush 155 is pivotally supported on one end of an arm 156 in a position wipingly engaging the outer surface of drum 1 to clean off any powder that may tend to cling to the drum. The opposite end of arm 156 is pivotally connected to the bracket 8 secured to the overhead beam 9.

Mention has been made of the structure of drum 1 including an outer plastic coating of an epoxy resin incorporating Fiberglas. A shallow outwardly opening recess is formed in the drum where each screen is exposed, and the inner conductive portion of the drum is connected in an electrical D.C. current circuit during the period when the screen passes over the material to be printed upon, with the material being grounded to complete the current and to establish an electrostatic field across the air gap between the screen and the material for conducting the printing powder from the screen onto the material, as will be explained.

FIG. 6 shows one of the printing screens, and FIG. 13

As an example, in the form indicated in FIG. 13, two screens 156a and 156b are indicated as equally spaced apart circumferentially of the screen, each screen being stenciled to provide open screen areas having outlines defining the diiferent data to be printed, such as different grade marks or other symbols or designs. In the present instance, they will be considered as grade marks.

The powder deposited from roller 130 onto the screens as the latter pass below roller 130 will not be deposited onto the plywood sheet 27 unless an electrical voltage diiferential is established between the plywood and the screen. Such a potential may be established by charging the screen with a suitable DC. voltage, according to the space between the screen and plywood, and by grounding the plywood.

Drum 1 in the present example is provided with a cam member 175 adjacent the closed end thereof and mounted on sprockets 18 and 34 for rotation therewith which member extends circumferential-1y of the drum concentric with its axis, and which cam member may be of a length equal to the length circumferentially of the drum 1 of the longest over-all open mesh design or designs on each screen to be printed although it may be longer. Cam 175 is designed to actuate a pair of limit switches 176, 177 which switches in turn actuate a relay to close a circuit of direct current to a portion of drum 1 for establishing the electrostatic field during the actual printing operation.

Cam 175 is so located with respect to screens 156a, 156k and the limit switches 176, 177 that said switches are closed and direct current is applied to drum 1 only when one of said screens is in a printing position over a piece of plywood 27 (FIG. 13).

FIG. 13 schematically illustrates a grade selector system which may be used in conjunction with the drum 1 having more than one screen 156 thereon, each such screen being prepared to print different information. An application of such a selector system would be in the printing of plywood where the boards are individually graded in intermixed fashion :and the grade assigned to each board is to be printed thereon by drum 1.

In the example of printing plywood, a highly skilled grader will visually examine all pieces of plywood being passed in the intermixed fashion down a conveyor. The grader will send plywood of different grades to different storage bins to be stacked together. At the same time, he will indicate to the printer of the present invention the grade he has assigned to the particular board and that grade will be printed on the board at a point intermediate the grader and the stacking bins thereby precluding the necessity of separately passing stacks of different grades through the present printer or requiring a different printing head for each grade to be printed.

In the example of FIG. 13, provision is made for printing only two different grades of plywood, but it should be noted that any convenient number of screens 156 each having different grade (or other) information stenciled therein may be equally spaced around the periphery of drum 1. Assuming then that the two grades of plywood are simply grade A and grade B, the grader will have push buttons 1'80 and 181 representing grades A and B respectively. A description of the operation of push button 180 and the circuitry associated therewith will suffice for a description of the operation of any selector push button since the circuitry and operation is identical.

Switch 180 is in a normally open position and when depressed closes the circuit to an incoming source of current through conductor 182 and a normally closed limit switch 183 to a variable time delay relay 184. Time delay relay 184 serves as a memory device to hold a grade selection in the program while a previously graded board is being printed upon. The need for the delay will be more fully explained in conjunction with the operation of the limit switch 183.

Upon energization of relay 184, armature 185 thereof is closed thereby closing a sustaining circuit to relay 184 and to a second relay 186 which is also energized upon depressing push button 180.

Upon energization of relay 186, a first armature 1-87 thereof is closed thereby closing a circuit 190 to sustain relay 186 after time delay relay 184 has ceased to 0p erate and its armature 185 is returned to an open position.

Upon energization of relay 186, a second armature 191 thereof is actuated to close a returning circuit 192 which includes the limit switch 176.

A relay 193 for switching in the direct current during the printing operation is connected to the incoming current line 182 but is not energized until its return circuit is completed by closing the appropriate limit switch 176 or 177. Assuming grade A is to be printed upon the board 27, shown passing under drum 1 and screen 156a, the grader would have depressed push button 180 as previously described thereby making it possible to close the return circuit to relay 193 only by closing the switch 176. Said switch is so closed by its encounter with cam 175 as it rotates therepast and upon closing switch 176, relay 193 is energized and a first armature 194 is closed thereby closing the circuit from a source of direct current 195 through conductor 196 to a roller-type brush 197 which is constantly in contact with l8. copper cylinder 49 of drum 1.

Upon energization of relay 193, a second armature 200 thereof is actuated to open a grounding circuit which is connected to drum 1 by means of a roller type brush 202. For grounding the direct current passing through conductor 196 and brush 197 to drum 1, the grounding means 203 is provided beneath plank 27.

Because of the air gap which exists between drum 1, the source of direct current, and ground 203,. a static electric field is created between said drum and said ground whereby the printing powder is passed through screen 156a and onto the surface of plywood 27 When the cam 175, which is of approximately the same length as the stenciled matter on screen 154, passes limit switch 176, said switch is spring actuated to an open position thereby breaking the return circuit 192 to relay 193 and deenergizing staid relay. Upon deenergization of relay 193, the armatures 94, 200 are spring returned to the posi tions opposite those illustrated in FIG. 13, and the circuit 196 passing direct current to drum 1 is broken. Armature 200 closes a grounding circuit 201 from drum 1 to a second grounding means 204 to discharge any residual charge of direct current which may remain on drum 1.

As the plank 27 progresses from the printing mechanism to the storage bin, it will trip limit switch 183 thereby breaking the sustaining circuit 190 to relay 1 86; and upon deenergization of relay 186, the armatures 187, 191 will be spring returned to inactive positions thereby opening the return circuit 192 to relay 193.

It can be seen that if two consecutive boards are to carry the same grade designation, such as grade A, the opening of limit switch 183 by the first marked grade A plywood would break down the circuit for the succeeding piece to be marked if the push button 180 for so marking the second piece were to be depressed before the preceding piece had broken switch 183. However, time delay relay 184 will sustain the circuit through the momentary breaking of switch 183 caused by the preceding plywood. Thus when switch 183 is again closed after being momentarily opened, the entire circuit for imprinting grade A on the succeeding piece of plywood will be set for proper operation.

The circuitry for imprinting grade B on a piece of plywood or any other number of grades is exactly the same as that for imprinting grade A on such plywood.

In the event that a substantial run of a single grade of plywood is to be imprinted upon, the necessity for depressing the push button representing the grade between each board is precluded by providing a manually actuatable selector switch 205 which can be positioned to close the return circuit to relay 193 through either of the limit switches 176, 177. Switch 205 is placed on an open contact 206 while the printing mechanism is operating by push button; however if grade A were to be printed on a long succession of boards, switch 205 would be placed on contact 207 to place the return circuit 192 of relay 193 in a condition to be completed each time switch 176 is closed.

It can be seen that both switches 176 and 177 will be closed upon each rotation in a counterclockwise direction of drum 1 since the cam 175 contacts each of said switches upon each rotation. However, in the example ofprinting grade A illustrated in FIG. 13, the closing of switch 177 will be ineffectual to actuate relay 193 since the circuit in which switch 177 is positioned is opened at other points. Since relay 193 is not energized by closing switch 177 in the example illustrated, direct current will not be applied to drum 1, and no printing would be effected When screen 154b passes a printing position. Additional assurance that'only the desired screen 156 will be charged at a chosen time may be provided by const-ru-ctingupper cylinder 49 in such a way as to have each portion thereof supporting a screen 156 insulated from an adjoining portion supporting a screen with different information thereon.

It should be understood that various time-delay or memory devices can be used in place of relay 184 and would serve the same purpose even though the operation may differ slightly.

It may be noted that a drum cleaning brush 204 (FIG. 1) engages the outer surface of the drum 1 to keep it clean, and in FIG. 2, the dot-dash lines 205 merely indicate the position of another printing unit, if desired.

It is to be understood that the above detailed description discloses only the preferred form of the present invention, and it is not intended to be limited, as changes and modifications may occur to those skilled in the art which do not depart from the spirit of this invention and which come within the scope of the appended claims.

I claim:

1. In an electrostatic printing apparatus of the type for electrostatic printing by electrostatically con-ducting a dry printing powder from an electrically conductive system across an air gap onto the article to be printed upon, a cylinder including as a part thereof an electrically conductive screen having a group of openings formed thereon defining the area and shape of the design to be printed and said openings being adapted to pass said printing powder therethrough, means for supporting an article to be printed upon adjacent to and spaced from the outer surface of said cylinder in opposed relation to said screen upon rotation of said cylinder about its axis, the improvement comprising,

(-a) an endwall at one end of said cylinder closing said one end,'and the opposite end of said cylinder being open;

(b) means connected with. said endwall supporting it and said cylinder for said rotation of the latter about its axis;

(0) a powder supply container and powder dispensing means associated therewith for discharging powder from said container onto the radially inwardly facing surface of said screen;

(d) a support within said cylinder for supporting said powder supply container stationary within said cylinder during rotary movement of said cylinder and for reciprocable horizontal movement of said container into and out of the open end of said cylinder and for supporting said container when the latter is outside said open end to provide access to said container for filling the latter during rotation of said cylinder.

2. In the apparatus as defined in claim 1:

(e) means supporting said powder dispensing means for movement into and out of said open end of said cylinder to facilitate access to parts thereof when said powder dispensing means is in a position outwardly of said open end of said cylinder.

3. In an electrostatic printing apparatus of the type for electrostatic printing by electrostatically conducting a dry printing powder from an electrically conductive screen having a group of openings formed thereon defining the area and shape of the design to be printed and said openings being adapted to pass said printing powder therethrough, means for supporting an article to be printed upon adjacent to and spaced from the outer surface of said cylinder in opposed relation to said screen upon rotation of said cylinder about its axis, the improvement comprising,

(a) an endwall at one end of said cylinder closing said one end, and the opposite end of said cylinder being open;

(b) means connected with said end wall supporting it and said cylinder for said rotation of the latter about its axis;

(c) a powder supply container and powder dispensing means associated therewith for discharging powder from said container onto the radially inwardly facing surface of said screen;

(d) means within said cylinder supporting said powder supply container and said powder dispensing means stationary during rotary movement of said cylinder with said powder supply container over said powder dispensing means, said powder supply container having a downwardly directed discharge opening at its lower side;

(e) said powder dispensing means including a horizontally elongated endless belt with its upper run extending between said discharge opening for receiving powder discharged through said opening, and means carried by said container extending substantially to the upper surface of said upper run for regulating the amount of powder carried by said upper'run over one end of said belt upon longitudinal movement of said belt,

(f) pulleys carried by said powder dispensing means supporting said endless belt at its ends for said movement thereof,

(g) said powder dispensing means further including a roller rotatably supported between the ends of said belt therebelow for receiving powder deposited on said upper run of said belt upon said longitudinal movement thereof to the lower run;

(h) means supporting said roller in engagement with the radially inwardly facing surface of said screen upon revolution of said cylinder for carrying said screen past said roller; and,

(i) mean-s independently connected respectively with said cylinder, said belt and said roller, for rotating said cylinder and said roller and for actuating said belt for said longitudinal movement thereof.

4. In an electrostatic printing apparatus of the type for electrostatic printing by electrostatically conducting a dry printing powder from an electrically conductlve screen in an electrostatic field across an air gap onto an article'to be printed upon, a cylinder of electrically conductive material having a portion thereof formed with a group of openings through which powder within said cylinder is adapted to pass into said electrostatic field, and means respectively connected with said cylinder and with such article for establishing 'a voltage differential 0 between them to provide said electrostatic field, the improvement comprising;

(a) a layer of dielectric plastic material of uniform thickness outermost on said cylinder bonded and substantially covering to the outer surface of said cylinder with the exception of said portion leaving the latter exposed and providing a shallow outwardly opening recess having said portion as the radially inwardly disposed side of said recess whereby said portion will 'be spaced radially inwardly from the cylindrical outer surface of said layer;

(b) a conveyor for supporting said article for movement past the lower side of said cylinder in spaced relation to said lower side and the said means connected with such article to establish said electrostatic field being separate from said cylinder and layer and spaced from the latter;

(c) means connected with said conveyor for so moving it past said lower side of said cylinder;

(d) means for supporting said cylinder horizontally above said conveyor; and,

(e) means connecting said cylinder with said conveyor for rotating said cylinder upon movement of said conveyor. 1

5. In an electrostatic printing apparatus of the type for electrostatic printing by electrostatically conducting a dry printing powder from an electrically conductive system across an air gap onto the article to be printed upon, a cylinder including as a part thereof an electrically conductive screen having a group of openings formed thereon defining the area and shape of the design to be printed and said openings being adapted to pass said printing powder therethrough, means for supporting an article to be printed upon adjacent to and spaced from the outer surface of said cylinder in opposed relation to said screen upon rotation of said cylinder about its axis, the improvement comprising,

(a) an endwall at one end of said cylinder closing said one end, and the opposite end of said cylinder being open;

(b) means connected with said endwall supporting it and said cylinder for said rotation of the latter about its axis;

(c) a drum mounted within and concentric with said cylinder, said drum being stationary during rotary movement of said cylinder therearound;

(d) an endwall at one end of said drum closing said one end and the opposite end of said drum being open, said one end of said drum being adjacent said one end of said cylinder and said opposite end of said drum being adjacent said opposite end of said cylinder; L

(e) powder dispensing means releasably mounted within said drum on said one endwall thereof and adapted to dispense powder onto the radially inwardly facing surface of said screen; and,

(f) a powder supply container releasably mounted within said drum on said endwall thereof and adapted to discharge powder therefrom to said powder dispensing means.

6. In the apparatus as defined in claim 5:

(g) a support for so mounting said powder supply container for horizontal reciprocal movement of said container into and out of the open end of said drum and for supporting said container when the latter is outside of said open end to provide access to said container independent of the rotation of said cylinder.

7. In the apparatus as defined in claim 5:

(g) sealing means interposed between said drum and said cylinder to prevent the escape of powder into the atmosphere.

8. In electrostatic printing apparatus of the type for electrostatic printing by electrostatically conducting a dry printing powder from a screen having openings therein of predetermined configuration across an air gap and onto an article to be printed upon:

(a) a pair of cylinders concentrically mounted one within the other;

(b) each of said cylinders having adjacent closed and adjacent open ends;

(c) the outer cylinder of said pair thereof having said screen mounted in the sidewall thereof and being supported for rotary movement about its longitudinal axis;

(d) means connected with said outer cylinder for rotating the latter about its longitudinal axis;

(e) the inner cylinder of said pair thereof being supported stationary during rotary movement of said outer cylinder therearound; and,

(f) said inner cylinder having a powder dispensing means releasably mounted therein in communication with said outer cylinder for dispensing powder onto the radially inwardly directed surface of said screen as said screen rotates with said outer cylinder past said powder dispensing means.

9. In the apparatus as defined in claim 8:

(g) a powder supply container supported Within said inner cylinder and in communication with said powder dispensing means for supplying powder to the latter; and

(h) a support for supporting said container for horizontal reciprocal movement of said container to positions within and outside of said inner cylinder independent of the rotation of said outer cylinder.

10. In an electric printing apparatus of the type for electrostatic printing by electrostatically conducting a dry printing powder from an electrically conductive screen in an electrostatic field across an air gap onto material to be printed upon, a cylinder or electrically conductive material having a portion thereof formed with a group of openings through which powder within said cylinder is adapted to pass into said electrostatic field, and means connected with said cylinder and such article for establishing a voltage differential between them to provide said electrostatic field, the improvement comprising:

(a) a conveyor for supporting sheet material horizontally for movement past the lower side of said cylinder in spaced relation to said lower side,

(b) means connected with said conveyor for so moving it past said lower side of said cylinder,

(c) means for supporting said cylinder horizontally above said conveyor, and

(d) means connecting said cylinder with said conveyor for rotating said cylinder upon movement of said conveyor,

(c) said means for supporting said cylinder hori zontally including a stationary shaft coaxial with said cylinder projecting axially outwardly thereof from one end of said cylinder and means supporting said cylinder for rotation on said shaft,

(f) said means for supporting said cylinder horizontally including a stationary elongated member above said cylinder extending transversely across said conveyor and a bracket member depending therefrom at said one end only of said cylinder and outwardly of the latter and connected with said shaft adjacent to said one end for supporting said cylinder adjacent to said one end only whereby access may be had to the end of said cylinder opposite to said one end thereof, and to material on said conveyor free from interference by the said means for supporting said cylinder,

(g) means supporting said bracket member on said elongated member for movement of the latter including the cylinder suspended therefrom to different positions along said elongated member for supporting said cylinder at different positions over material on said conveyor,

(h) means supporting said shaft for vertical movement relative to said bracket for supporting said cylinder at different distances from material over said shaft, and means for securing said shaft at any one of said different distances.

15 11. In electrostatic printing apparatus of the type for electrostatic printing by electrostatically conductinga dry printing powder from a screen across an air gap and onto the article to be printed upon:

(a) a horizontally disposed cylinder including a plurality of circumferentially spaced printing screens therearound each comprising an electrically conductive section having a plurality of openings formed thereon defining different indicia to be printed by printing powder adapted to pass therethrough from within said drum and onto difierent articles passing said drum;

(b) said screens being in an electrical circuit with said articles for establishing an electrostatic field between each article and selected screens at a predetermined point at one side of said screens during revolution of said cylinder and movement of said articles past said cylinder;

(c) means in said circuit actuatable for selectively energizing said screens at said point for establishing said electrostatic field between any one of said plurality of screens and one of the articles to be moved therepast according to the indicia to be printed;

(d) conveyor means for moving said articles past said point in printing relation to said screens at said point;

(e) means connected with said cylinder for revolving said cylinder and screens about the axis of said cylinder at the same surface speed as said conveyor means and in synchronism therewith for simultaneous arrival of said articles on said conveyor means and said screens at said point;

(f) means connected with said cylinder for adjusting its position relative to said conveyor for supporting saidscreens spaced a substantially uniform distance from said articles at said point when said screens are closest to an article on said conveyor as said articles are moved past said cylinder; and,

(g) said means for selectively energizing said sections including microswitches stationarily positioned around said cylinder at spaced points corresponding to the spacing between screens, respectively actuatable for energizing said screens upon the latter revolving past said point, and means on said cylinder movable into engagement with said microswitches for actuating them upon rotation of said cylinder.

References Cited by the Examiner UNITED STATES PATENTS 3,081,698 3/ 1963 Childress et al. 3,218,967 11/1965 Childress. 3,228,326 1/1966 Childress. 3,245,341 4/ 1966 Childress.

ROBERT E. PULFR Y, Primary Examiner. E. S. BURR, Assistant Examiner.

Claims (1)

1. IN AN ELECTROSTATIC PRINTING APPARATUS OF THE TYPE FOR ELECTROSTATIC PRINTING BY ELECTROSTATICALLY CONDUCTING A DRY PRINTING POWDER FROM AN ELECTRICALLY CONDUCTIVE SYSTEM ACROSS AN AIR GAP ONTO THE ARTICLE TO BE PRINTED UPON, A CYLINDER INCLUDING AS A PART THEREOF AN ELECTRICALLY CONDUCTIVE SCREEN HAVING A GROUP OF OPENINGS FORMED THEREON DEFINING THE AREA AND SHAPE OF THE DESIGN TO BE PRINTED AND SAID OPENINGS BEING ADAPTED TO PASS SAID PRINTING POWDER THERETHROUGH, MEANS FOR SUPPORTING AN ARTICLE TO BE PRINTED UPON ADJACENT TO AND SPACED FROM THE OUTER SURFACE OF SAID CYLINDER IN OPPOSED RELATION TO SAID SCREEN UPON ROTATION OF SAID CYLINDER ABOUT ITS AXIS, THE IMPROVEMENT COMPRISING, (A) AN ENDWALL AT ONE END OF SAID CYLINDER CLOSING SAID ONE END, AND THE OPPOSITE END OF SAID CYLINDER BEING OPEN; (B) MEANS CONNECTED WITH SAID ENDWALL SUPPORTING IT AND SAID CYLINDER FOR SAID ROTATION OF THE LATTER ABOUT ITS AXIS; (C) A POWDER SUPPLY CONTAINER AND POWDER DISPENSING MEANS ASSOCIATED THEREWITH FOR DISCHARGING POWDER FROM SAID CONTAINER ONTO THE RADIALLY INWARDLY FACING SURFACE OF SAID SCREEN; (D) A SUPPORT WITHIN SAID CYLINDER FOR SUPPORTING SAID POWDER SUPPLY CONTAINER STATIONARY WITHIN SAID CYLINDER DURING ROTARY MOVEMENT OF SAID CYLINDER AND FOR RECIPROCABLE HORIZONTAL MOVEMENT OF SAID CONTAINER INTO AND OUT OF THE OPEN END OF SAID CYLINDER AND FOR SUPPORTING SAID CONTAINER WHEN THE LATTER IS OUTSIDE SAID OPEN END TO PROVIDE ACCESS TO SAID CONTAINER FOR FILLING THE LATTER DURING ROTATION OF SAID CYLINDER.

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