US3332344A

US3332344A - Powder feed mechanism and electrostatic imprinting device

Info

Publication number: US3332344A
Application number: US494326A
Authority: US
Inventors: Londahl Dickey Steele; Marlin A Schueler
Original assignee: UNIMARK CORP
Current assignee: UNIMARK CORP
Priority date: 1965-10-11
Filing date: 1965-10-11
Publication date: 1967-07-25
Anticipated expiration: 1984-07-25
Also published as: IL25608A

Description

y 1967 o. s. LONDAHL ETAL 3,33

POWDER FEED MECHANISM AND ELECTROSTATIC IMPRINTING DEVICE Filed Oct. 11, 1965 4 Sheets-Sheet l INVENTORS DICKEY S. LONDAHL BY MARLIN A. SCHUELER 7 m 351%, fa 4.

ATTORNEYS ly 5, 1967 D. s. LONDAHL ETAL 3,33

POWDER FEED MECHANISM AND ELECTROSTATIC IMPRINTING DEVICE 4 Sheets-Sheet 2 Filed Oct. ll, 1965 FIG Z INVENTORS DICKEY S. LONDAHL BY MARLIN A. SCHUELER ATTORNEYS NVENTORS 4 Sheets-Sheet 5 "w; "i I R mu E mm mm m M R SA Tm Y ,+T EL A K R P VA D M D. S. LONDAHL ET AL POWDER FEED MECHANISM AND ELECTROSTATIC IMPRINTING DEVICE July 25, 1967 Filed Oct. 11, 1965 y 1967 D. s. LONDAHL ETAL 3,33

POWDER FEED MECHANISM AND ELECTROSTATIC IMPRINTING DEVICE 4 Sheets-Sheet FlG 12 Filed Oct. 11, 1965 FlG 11 ZNVENTORS DICKEY S. LONDAHL MARLIN A. SCHUELER 134 %,;Min

ATTORNEYS United States Patent Ofiice Patented July 25, 1967 3,332,344 POWDER FEED MECHANISM AND ELECTRO- STATIC IMPRINTING DEVICE Dickey Steele Londahl, Walnut Creek, and Marlin A.

Schneler, Danville, Calif, assignors to Unimark Corporation, a corporation of California Filed Oct. 11, 1965, Ser. No. 494,326 9 Claims. (Cl. 101-120) This invention relates to apparatus and method for electrostatic printing of the type wherein a stencil screen is provided having one or more areas of unobstructed openings through which printing powder is adapted to pass from one side of the screen to the other into an electrostatic field by which the powder is conducted onto a material spaced from said other side. A voltage differential between the screen and material establishes the electrostatic field.

One of the difiiculties heretofore encountered in this type of printing has been to continuously provide an adequate and uniform distribution of powder onto the screen free from any substantial excess and loss or diffusion of the powder into the atmosphere.

One of the objects of the invention is the provision of a machine and method for overcoming the above difliculty.

Another object of the invention is the provision of an economically made and relatively .simple machine incorporating therein an improved means for feeding printing powder to the printing screen.

A still further object of the invention is the provision of a machine for effectively electrostatically printing on elongated articles, such as welding rods, or rod-like articles, and in which the impression on each article is clear and uniform in appearance.

Other objects and advantages will appear in the description and drawings, in which:

FIG. 1 is a simplified side elevation view of a machine for marking rods.

FIG. 2 is an enlarged, side elevational view partly broken away and in cross section, showing the printing portion of the machine as seen from the side thereof opposite to the side shown in FIG. 1.

FIG. 3 is a vertical cross sectional view taken along line 33 of FIG. 4.

FIG. 4 is a top plan view of the part shown in FIG. 1 including a portion of the conveyor for the rods to be marked, certain portions of the machine, such as the drum screen and a pulley housing, being broken away and in section to show structure otherwise hidden.

FIG. 5 is a fragmentary cross sectional view taken generally along line 55 of FIG. 3 and showing a portion of the printing drum in printing relation to rods on the rod-conveyor.

FIG. 6 is a cross sectional view of part of the machine at line 66 of FIG. 3.

FIG. 7 is a fragmentary, enlarged, cross sectional view of an air ejection clearing nozzle taken along line 77 s of FIG. 4.

FIG. 8 is an enlarged, fragmentary cross sectional view of a portion shown in smaller scale in FIG. 3.

FIG. 9 is a fragmentary cross sectional view of a portion of the machine taken along line 99 of FIG. 8.

FIG. 10 is a fragmentary side elevational view of a portion of the printing drum as seen from line 1010 of FIG. 4.

FIG. 11 illustrates the transfer of printing powder from a source thereof to an applicator medium intermediate said source and an object to be printed upon.

FIG. 12 illustrates the transfer of printing powder from said applicator medium through an information screen and onto the object to be printed upon.

In FIG. 1, which is a simplified view, a stationary frame, generally designated 1, includes horizontally extending upper frame portion 2 on one end of which a support 3 for the printing mechanism, generally designated 4, is provided.

Bearings 5 adjacent to the opposite ends of the upper frame portion 2 rotatably support a pair of horizontal, parallel shafts 6 in positions extending at right angles to the length of portion 2.

A horizontally extending conveyor generally designated 7 is in the form of a pair of sprocket wheels 8, each pair being secured on one of the shafts 6, and a pair of parallel horizontally elongated sprocket chains 9 extend over said sprocket wheels. The upper run of the conveyor, or the upper runs of chains 9, support horizontal equally spaced horizontal rods 10 (FIGS. 3-5) thereon in positions extending transversely across the upper runs of said chains 9.

A sprocket wheel 13 is secured on one of the shafts 6, and an endless sprocket chain 14 extends over said sprocket wheel 13 and over a sprocket wheel 15, that, in turn, is driven by motor 16 through a gear reducer 17 (FIG. 1).

A horizontally disposed shaft 11 (FIG. 1) may be rotatably secured in frame member 2 adjacent shaft 6 and secured on shafts 6 and 11 in meshing engagement is a set of gears 12. Thus, shaft 11 is driven by shaft 6 in an opposite direction thereto. Secured on the outer end of shaft 11 is a timing belt wheel 18, and a timing belt 19 connects wheel 18 with a similar wheel 20 which is secured on a shaft 23 (FIG. 4) supported in bearings 24 in the upper end of a support 25 on base 3 (FIGS. 1, 2 and 4).

Shaft 23 also has a timing belt wheel 26 (FIG. 4) secured thereon, which timing belt wheel is connected by a timing belt 27 (FIGS. 1, 4) with a timing belt wheel 28. The latter wheel is secured on one end of a hollow shaft 29 that carries a printing drum or wheel, generally designated 30. e

The foregoing structure provides means for simultaneously rotating drum 30 and for moving the upper rodcarrying run of conveyor 7 at the same rate of speed and in the same direction where the drum and upper run of the conveyor are closest together.

Referring to FIG. 4, the outer race of bearings 24 are secured in the ends of a tubular sleeve 33 that, in turn, is centrally clamped within a bore in the upper end of standard 25, one side of which is split as at 34 (FIG. 2), by means of stud bolts 35.

The outer ends of sleeve 33 project laterally outwardly of the support 25, and these outwardly projecting ends support one end of a laterally and forwardly projecting arm generally designated 36 (FIG. 2). The rear end of arm 36 is forked to provide rear extensions 37 (FIG. 4) between which the support 25 is positioned, and said extensions are formed with circular openings into which the cylindrical ends of sleeve 33 are positioned so that arm 36 is pivotally supported on the ends of said sleeve for vertical swinging of the forward end of the arm.

The forward end of arm 36 is formed with a horizontal opening or bore 38 (FIG. 3) within which one end of a shaft 39 is releasably clamped. One side of the arm at said bore is horizontally split, as at 40 (FIG. 2) and vertical stud bolts 43 (FIGS. 2, 4) extend across the split forwardly of bore 38 for clamping shaft 39 rigid relative to the arm 36.

Forward extensions 44 (FIGS. 2, 4) are rigid at one of their ends with the arm 36 above split 40 and these extensions pass to opposite sides of a vertical height adjusting screw 45. Such extensions are complementarily formed on their adjacent sides to conform to the cylindrical curvature of the unthreaded sides of screw 45 adjacent to the upper end of the latter. A clamping bolt 46 extends through extensions 44 and is held in place by engagement of a fiat side of the head 41 thereof with a shoulder on one of said extensions. A finger manipulate.- ble arm 47 threadedly received on the end of bolt 46 opposite to head 41 enables an operator to quickly tighten and loosen extensions 44 by tightening and loosening arm 47.

A lower extension 42 of arm 36 is formed with a downward projection 48 (FIG. 2) and a vertical bore therein is internally threaded for threaded engagement with the threads 49 on said screw 45. The lower end of screw 45 rests on a rigid member 50 secured on base 2. Upon rotating the screw 45 in one direction the outer end of the arm 36 will be elevated, and the latter will be lowered upon reverse rotation of the screw, while the latter will be locked against rotation upon movement of the clamp arm 47 to clamp the screw 45. O-rings, as seen in FIG. 2 around screw 45 above and below the threaded section within lower extension 48 prevent any powder from reaching the threads on said screw 45.

Shaft 39 projects at one end thereof to the side of arm 36 that is opposite to the side at which drum 30 is positioned. Said projecting end is designated 53 and is square (FIG. 2).

The timing belt wheel 28 is secured to the outer end of hollow shaft 29 by screws 54, while the opposite or inner end of the shaft 29 is secured to one end of drum 30 by screws 55 (FIG. 3), and a housing 56 extends over the timing belt 27 including the

timing belt wheels

26, 28.

A vertical member 57 (FIGS. 2, 3) is secured to one side of arm 36 for movement to different vertical adjusted positions. This arm carries a belt engaging roller 58 at its lower end adapted to engage the lower run of the timing belt 27 for tightening the latter when the member 57 is in adjusted position.

Drum 30 comprises a pair of

end walls

59, 60. End wall 59 is the one connected with the hollow shaft 29, and ball bearings 63 (FIG. 3) rotatably support hollow shaft 29 and timing belt wheel 28 on shaft 39, the latter being stationary.

The screws 55 that secure hollow shaft 29 to end wall 59 also secure an annular disc 64 against the inner side of end wall 59, or the side opposite to shaft 29, and said disc 64, in turn, is formed with a radially outwardly projecting flange 65 (FIG. 8) that extends over the inner periphery of a timing belt wheel 66 to clamp said Wheel rigid with end wall 59 for rotation of the wheel with wall 59.

A vertically elongated plate 67 (FIGS. 3, 6, 8) of electrical insulating material, preferably a plastic, is releasably clamped to shaft 39 within drum 30 in a portion adjacent to the annular disc 64. Plate 67 has an upper end portion 68 extending above shaft 39, and a lower end portion 69 below said shaft. Shaft 39 includes an end portion 70 that extends from plate 67 through drum 30 and to and through end wall 60 that is opposite to end wall 59. The outside diameter of portion 70 is smaller than the remainder and plate 67 is clamped to the larger diameter portion at the shoulder defining the juncture between said larger diameter portion and said portion 70.

A clamping bolt 73 clamps plate 67 to shaft 39, said bolt extending across a slot 74 that opens into the opening through which shaft 39 extends. Upon rotating the bolt 73 in one direction the sides of said opening will tighten against the sides of said shaft to hold the plate rigid with said shaft.

A horizontal pivot 75 (FIG. 6) swingably connects one end of a horizontally elongated arm 76 with the upper end portion 68 of plate 67. The other end of arm 76 has one end of a horizontal shaft 77 secured thereto. Shaft 77 projects to the side of arm 76 that is opposite to plate 67 and the projecting portion thereof rotatably 4 supports a horizontally elongated roller 73 thereon coaxial therewith (FIG. 8). A wire 79 is helically Wound around roller 78 and projects radially outwardly of the outer surface of said roller with the adjacent coils of the wire spaced apart. Wire 79 may be soldered, cemented, or otherwise suitably secured to roller 78.

Coaxial with and around shaft 39 within drum 30 is a powder combination feed device and holder for the printing powder. This feed device is generally designated 80 and comprises spaced opposed circular heads 83, 84 connected by an annular row of equally spaced rods 85 that extend between said heads and that are secured at their ends to the outer peripheries of said heads. A cylinder 89 of rubber-like soft resilient filter material known to the trade as Scott Foam extends around and is supported on said .row of rods, and the ends of said cylinder extend over the radially outer surfaces of said heads 83, 84. The rods indent themselves into said material, the latter being relatively thick compared to the diameters of the rods.

The central portions of

heads

83, 84 are open to pass the end portion 70 of shaft 39, and spaced around said portion 70 is a tubular sleeve 82, the ends of which are secured in the central opening in

heads

83, 84. The head 83 is bolted to end wall 60 of drum 30, which end wall supports the feed device 30 for rotation with the end wall 60.

The roller 78 is preferably directly above the cylinder 89 of the feed device with its longitudinal axis parallel with the axis of the drum 30. Said roller 78 is yieldably held against the upper side of cylinder 89 by a spring 90 (FIG. 8).

Spring 90 comprises a U-shaped spring rod disposed on its side in a vertical plane providing an upper horizontally extending leg 91 and a lower leg 92. One end of the lower leg 92 is clamped to arm 76 above the shaft 77 between a bar 93 (FIG. 8) that is secured to arm 76 in clamping relation to said one end of spring arm 92 screws 94 (FIGS. 4, 8).

The free end of upper leg 91 of spring 90 is secured to the upper end of a spring tensioning cord 95. By tightening cord 95, as by pulling it downwardly, the pressure of roller 78 against the cylinder 89 or powder feed device, will be increased, and by loosening the tension on cord 95 the pressure of roller 78 on cylinder 89 will be decreased.

As seen in FG. 8, the shaft 39 is hollow, having a central passageway or bore 96, and at a point directly below the connection between cord 95 and spring 90, the upper side of shaft 39 is formed with an opening 97 through which cord 95 extends. The side of plate 67 where cord 95 extends is recessed at 98 (FIG. 9). A horizontally disposed cylindrical dowel pin 99 ('FIG. 8) is secured within shaft 39 at the juncture between opening 97 and passageway 96 and cord 95 extends across the cylindrical surface of said dowel and into bore 96 toward the other end of the shaft 39 that terminates adjacent to, but outwardly of, wall 60 of drum 30.

Spaced within bore 96 is a horizontally elongated coupling member generally designated 101, which member extends longitudinally of bore 96. Cord 95 is secured to one end of said coupling member, while the opposite end of said coupling member is connected by a pin 100 to one end of a horizontally elongated externally threaded rod 103.

Said coupling member is formed between its ends with an elongated slot 104, and a pin 102 extends through said slot and is secured at its ends within openings in the sides of bore 96 of shaft 39 to prevent rotation of the coupling member, while permitting longitudinal movement thereof.

The threaded rod 103 extends through a rotating sleeve or tubular nut 105 that is internally threaded for threaded engagement with the threads of rod 103. Said nut 105 is rotatable in bore 96 but is held against axial movement within said bore by a transverse pin 106 that is rigid with shaft 39 and that seats in one side of an annular outwardly opening groove 107 in said nut 105.

The outer end portion 198 of nut 105 projects outwardly of the drum 30 and shaft 67 and is flattened to facilitate grasping the same and rotating the nut. Upon rotating nut 105 in one direction the cord 95 will be tightened to increase the tension of spring 90 while a reverse rotation of the nut will diminish the tension.

The outer end of shaft 39 outwardly of drum 30 and adjacent to nut 105 is externally threaded for threaded engagement with the threads of a retaining member 109.

While ball bearings 63 rotatably support the end wall 59 end of the drum 36 on shaft 39, a bearing 110 supports the end wall 60 end of said drum on portion 70 of shaft 39. The inner race 112 of bearing 110 is releasably engaged by the retaining member 169 when the latter is tightened on the outer end of portion 70 of shaft 39, and end wall 69 is moved axially when member 109 is tightened to clamp head 60 against the outer shell of the outer cylinder as will be explained later.

Referring to plate 67 in FIG. 3, a circular opening 113 is formed in the lower portion 69 of said plate, and in this opening is supported a cylindrical bearing holder 114 that projects laterally from portion 69 toward end wall 60 of the drum that is opposite thereto. Said bearing holder has a pair of coaxial ball bearings 115 supported within the ends thereof, and the outer cylindrical surface of the portion of the holder that is within opening 113 is eccentric relative to the axis of the bearing holder so that rotation of the bearing holder relative to the opening 113 will result in raising or lowering the bearing holder.

A shaft 116 is rotatably supported by bearings 115, and one end of the shaft projects from bearing 115 and from the lower portion 69 of plate 67 to the side of the latter adjacent to end wall 59 of drum 30. This projecting portion of shaft 116 has a timing belt gear 117 secured thereto. The end of shaft 116 that is in the space between

end walls

59, 60 carries a powder applying roller 118 secured thereto. Said roller 11% has an outer layer 119 of the same material as that of the layer 89 of roller 80. The roller 118 is below roller 89 and is not in contact with the latter, but the powder that filters through the cylinder 89 is evenly distributed on the layer 119. Both layers 89 and 119 will ultimately become substantially saturated with the powder and preferably there will be a slight surplus of powder at the side of layer 119 supported against the lower inner side of the outer cylindrical shell.

The roller 118 is supported by the bearing holder 114 and plate 67 in a position in which the lower side of the cylindrical layer 119 is in engagement with the inner surface of the outer cylindrical shell 120 of drum 3t), and a pin 121 extends through shaft 116 and into a recess in an end of the roller for releasably locking the shaft and roller together for rotation.

This outer cylindrical shell 120 is imperforate except for areas designated 123 (FIG. 4) within which are the perforate portions that correspond to the design symbols or letters to be printed on rods 18. These areas 123 may be called stencil or printing screens, and the openings formed thereon are usually relatively small, being from three to four hundred per inch, although the number may vary according to the requirements.

The rotation of roller 118 relative to the cylindrical shell is effected through timing belt 124 that extends over the timing belt wheel 117 (FIG. 6) which belt also extends around a relatively large diameter timing belt wheel 66, already described, and which wheel is coaxial with drum 30 and is secured against wall 59 for rotation with the latter. Thus the rotation of the roller 118 is preferably substantially faster than the rotation of the drum 30. The roller 118 may also be termed brush, since the outer lower surface brushes the inner surface of the shell 120 in the same direction as the direction of rotation of the drum. A belt tightener wheel 125 is rotatably carried on one end of an arm 126. The opposite end of said arm is pivotally connected to plate 67, and a helical spring 127 connected at one end with arm 126 at a point intermediate the ends of said arm and with a projection on plate 67 yieldably holds wheel against the inner side of belt 124 for maintaining the latter taut.

The pressure with which the brush 118 engages the I shell 120 may be varied by rotating the bearing holder 114 relative to arm 67. This adjustment of the bearing holder is effected by loosening the holder screw 122 (FIG. 6) that clamps the eccentric bearing holder and rotating the latter relative to arm 67 until the desired adjustment is made, and then tightening the screw.

An opening 128 formed in the end wall 60 (FIGS. 8, 10) adjacent to one side of the retainer member 109 is in registration with a similar opening 129 (FIG. 8) in head 83 of the feed roller 80. The powder for printing is fed through these openings to the interior of the feed roller 80, and a gate 130 (FIG. 10) is releasably held by bolts 133 in closed position closing said opening. Slots 134 may extend to the openings in gate 130 for the bolts, so the latter may be merely loosened to remove or to swing the gate 130 to open position and vice versa.

It is important that the printing drum 30 be properly timed relative to the conveyor 7, and therefore the position of the timing belt wheel 20 may be changed relative to wheel 26. This is effected by providing a laterally outwardly projecting pin 135 (FIGS. 2,4) on the timing belt wheel 20, which pin projects into a recess 136 formed in a circular plate 137 that is keyed to shaft 23. Coaxial screws 138 threadedly extend through openings in said plate 137 that open into said recess at opposite sides of the latter.

The plate 137 is bolted to the timing belt wheel 20 by bolts 139, and plate 137 has circumferentially extending slots 140 through which bolts 139 extend. To vary the position of timing belt wheel 20 relative to wheel 26 it is merely necessary to loosen bolts 139 and then rotate the screws 138 to move pin 135 in one direction or the other until the desired relative movement between

wheels

20, 26 has been accomplished.

To keep the outer surface of drum 130 clean, an air nozzle 143 (FIGS. 2, 4 and 7) is provided at the side of the drum that faces the direction of travel of the conveyor 7. This nozzle is supported on frame 1 at a point spaced a substantial distance above the lower side of drum 30, and said nozzle is formed with a horizontal, narrow slit or slot 144 that extends substantially the horizontal length of the drum. The slit communicates with a chamber 145 that extends the length of the slit, and an air passageway 146 in the body of said nozzle connects with an inlet 147 that, in turn, is connected with an intermittently controlled source of compressed air. After each printing operation the outer surface of the screen through which the printing has been effected will be cleaned without mechanically touching the screen. This is desirable, since the screens are very thin and mechanical engagement therewith for cleaning them will result in undesirable wear thereon, and possible bucking or distortion of the screen.

Referring to FIGS. 3, 8, 11 and 12, in operation, the powder for printing is deposited through the

openings

128, 129 into the interior of roller 80. The passageways through the layer 89 or outer wall of roller 80 may be approximately 60 to the linear inch, and the walls of these provide different tortuous paths extending through the layers that are resistant to direct passage of the particles of powder threthrough and the powder is thoroughly broken down and resists launching.

The roller 78 is of hard material and is yieldably held against the outer layer 89 with sufiicient force to create a shock on roller 80 each time a rod 85 passes below roller 78. The discharge of powder from the lower side of roller 80 or from layer 89 may be very accurately controlled by varying the pressure of the roller 78 against roller 80, which control extends to depositing the powder on roller 113 and the subsequent discharge therefrom.

The spiral wire '79 on roller 78 combined with the flexing of the layer 89 through the pressure exerted by roller 78 against layer 8 9 prevents caking of the powder in the passageways through the layer.

The passageways in the layer 119 of roller 118 may be even smaller than those in layer 89, or, for example, approximately 80 to the linear inch. This layer 119, like that of layer 89, becomes partially saturated with the powder and probably a small surplus will build up on the lower inner surface of the outer shell of the drum 30 ahead of the roller 119 or to the side thereof toward which the lower side of the roller 118 is moved.

As soon as the powder in the layer 119 is forced through the perforations in the outer shell such as screens 151 (FIG. 12), it is in the electrostatic field that is established between the outer shell and the material 10 onto which the powder is to be deposited.

This electrostatic field is established by connecting the screen 151 with a source of DC. current of the desired voltage, according to the distance between the screen and the article 10, and by grounding the latter.

The outer shell 120 of drum 30 is preferably a thin metal cylinder having exposed areas where the screen openings are positioned. A brush 150 is mounted in an insulated mounting in the bracket 'of nozzle 143, which brush is connected to a source of current and is adapted to continually engage shell 120 of drum 30. Thus the screens 151 are continually charged (FIGS. 2 and 12).

The material to be printed upon, such as rods 10, is continually grounded as long as it is on conveyor 7.

In order to establish the clearest printed image on the object to be printed upon, such as rods 10, the drum 30 may have to be raised or lowered as by adjusting screw 45 as previously described which, in effect, widens or narrows the air gap between the screens 151 and the rods 10.

It should be noted that the electrostatic field itself is probably insufiicient to cause the particles of printing powder to leave the screens 151 and travel through the air gap to rods 10. The powder must be freed from said screens in some manner and in the present instance this is accomplished by the roller 118. The action of roller 118 brushing over screen 151 to force powder particles into the air gap between said screens and rods 10 is effective only when a given screen is nearest a given rod. This minimizes the gap and reduces the possibility of the powder therein being subjected to air resistance and currents which could cause a distorted or fuzzy printed image.

Once the powder particles are freed from a screen 151 their path to the rod 10 therebelow is controlled by the electrostatic field established between said screen and said rod.

After the printing powder has been deposited on rods 10, conveyor 7 carries said rods beneath a fixing station 152 (FIG. 1) which is secured to frame 2 at a point remote from printing mechanism 4. At the fixing station 152 the printing powder may be subjected to heat treatment in order to fix the powder making the printing permanent; or, in some applications, the powder is fixed by spraying a hardening liquid over the powder.

It has been found that the presssure applied to screens 121 by layer 119 of transfer roller 118 affects the clarity of the impression on the article to be printed upon.

in the present device this pressure can be varied by loosening the bolt 122 (FIGS. 3, 6) which secures the bearing holder 114 in the lower end of plate 67 and rotating the bearing holder. Since the shaft 116 of roller 118 is eccentrically mounted with respect to the mounting of bearing holder 114 in plate 67, this serves to move roller 113 closer to or farther from shell 120 and screens 151 as desired. When the desired pressure is applied to screens 151, bolt 1 22 is again tightened securing bearing holder 114 in place.

It should be understood that the above detailed de- 3 scription discloses only the preferred form of the present invention and that it is not intended to be limiting, as other forms 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.

One such example would be the elimination of roller 118 whereby the layer 89' of the powder reservoir would be in direct contact with the screens 151 having thereon the information to be printed.

Applicant feels that sharper images are produced by the structure as disclosed, but in larger printing operations where fine clarity is not of greatest importance, satisfactory results may be obtained by the suggested modification.

We claim:

1. The method of electrostatically printing with a dry printing powder that includes the steps of:

(a) positioning the article to be printed upon spaced below a screen having a group of unobstructed openings corresponding in outline to the design to be printed;

(b) moving discrete particles of said powder downwardly along a plurality of closely adjacent generally vertically extending differently tortuous paths that have upper and lower open ends, which open ends and paths are of sufficient size to freely pass the particles of powder therethrough and which paths are defined by walls positioned to define the sides of said paths and to obstruct direct vertical downward movement of said particles under the influence of gravity and to cause said particles to follow said paths by administering shocks of predetermined force and regularity to said walls and particles for shifting said particles relative to said walls until the particles reach and pass through said lower open ends for movement therefrom to said openings; and thereafter;

(c) moving said particles through said unobstructed openings in said screen by application of physical force against said particles; and

(d) establishing an electrical voltage potential between said screen and the said article to provide an electrostatic field between said screen and said article for conducting the particles moved through said screen and onto said article.

2. In electrostatic printing apparatus for electrostatically depositing dry powder in the form of a desired design upon an article to be printed, and which apparatus includes a horizontal cylindrical printing screen supported for rotation about its axis and having a plurality of unobstructed openings thereon in a group the outline of which corresponds to said design, and means for establishing an electrostatic field between said cylinder and said article for electrostatically conducting powder passing through said openings from within said screen to said article, and means for rotating said screen about its said axis, the improvement comprising:

(a) a hollow cylindrical body spaced Within said screen supported for rotation about an axis parallel with the axis of said screen for feeding powder to the inner side of said screen for passage through said group of openings;

(b) said body including end walls closing the ends of said body thereby providing an enclosed drum adapted to enclose a supply of printing powder;

(0) said body being of flexible, resilient material having tortuous passageways extending therethrough from the inside of said body to the outside adapted to conduct said powder from within said body to the outer side of the latter for discharge from the outer side of said body;

(d) body engaging means engaging said body at a fixed point therearound for compressing said body at said point upon rotation of said body and within said passageways whereby said powder will move through said tortuous passageways for discharge from the outer side of said body.

3. In the improvement as defined in claim 2:

(e) means for vibrating said body during revolution thereof including a plurality of rigid elements supported against the inner side of said body at spaced points therearound for supporting said body against flexing at said points under the influence of said body engaging means upon rotation of said body, whereby the resistance to compression of said body at said points Will 'be greater than between said points to thereby cause said vibration.

4. In the improvement as defined in claim 2:

(e) a powder distributing roller supported for rotation within said screen and spaced below said body about an axis parallel with that of said screen and body;

(f) means supporting said roller for said rotation thereof in said position and against the lower side of said screen for receiving powder discharged from the openings in said body and for conducting said powder to the openings in said screen and for moving said powder through said openings.

5. In the improvement as defined in claim 4:

(g) said roller having an outer cylindrical layer of material corresponding in structure to that of said body but formed with a substantially greater number of passageways per corresponding unit of area than in said body;

(h) the passageways in said body and in said outer layer being adapted to pass said powder therethrough with the walls of said passageways distorted to resist free passage of said powder therethrough solely under the influence of gravity, whereby said layer and said body will become saturated with said powder.

6. An electrostatic printing machine comprising:

(a) a horizontally disposed printing drum having an outer cylindrical wall that includes electrically conductive screens formed with groups of unobstructed openings therein in outlines corresponding to the outlines of material to be printed, said openings being adapted to pass powder therethrough and onto an article to be printed upon;

(b) a shaft coaxial with said drum supporting said drum on one end thereof for rotation of said drum about its axis;

(c) said shaft projecting from one end of said drum;

(d) stationary means offset to one side of said projecting end of said shaft, and means pivotally connecting said stationary means with said shaft for swinging said shaft to different vertical positions whereby the level of said drum may be varied, and means connected with said shaft and movable therewith for supporting said drum at difierent levels;

(e) rotatable means within said drum supported for rotation relative to said drum for distributing printing powder to said screens;

(f) 'said rotatable means including an enclosed powder feed drum rotatable about an axis parallel with said axis of said drum for containing a supply of dry printing powder to be distributed to said screens, and having a perforate outer cylindrical Wall formed with open ended passageways extending generally radially relative to the axis of said drum for conducting powder from within said drum to outside the latter for said distribution.

7. In a machine as defined in claim 6:

(g) said rotatable means further including a roller outside said powder feed drum and offset relative to the axis of rotation of said powder feed drum and having an outer porous cylindrical wall formed with pores adapted to be filled with powder discharged from said passageways;

(h) means supporting said roller in a position for receiving powder discharged from said passageways and in engagement with the said screens upon rotation of said printing drum.

8. In a machine as defined in claim 7:

(i) said means supporting said roller being adjustable to vary the engagement between said roller and said screens.

9. The method of electrostatically printing with a dry printing powder that includes the steps of:

(a) positioning the articles to be printed upon spaced below a screen having a group of unobstructed openings corresponding in outline to the design to be printed;

(b) moving discrete particles of said powder downwardly along a plurality of closely adjacent tortuous paths that extend generally downwardly between open upper ends and open lower ends for discharge at said openings;

(c) physical moving the powder ejected from said lower ends through said openings in said screen;

((1) establishing an electrostatic field between said screen and the article therebelow for electrostatically conducting the powder moved through said openings onto said article;

(c) said paths being in an upper group and a lower group spaced apart by an air gap;

(f) administering shocks to the powder in the paths of said upper group thereof for discharge by gravity therefrom across said air gap and into the paths of said lower group for passage to said openings in said screen.

References Cited UNITED STATES PATENTS 2,173,032 12/1939 Winterrnute.

2,468,400 4/ 1949 Huebner.

2,590,321 3/1952 Huebner.

2,889,234 6/1959 Walkup l18637 X 2,940,864 6/1960 Watson.

3,052,213 9/ 1962 Schaffert.

3,081,698 3/1963 Childress et al.

3,096,198 7/ 1963 Schaffert 118-637 3,124,482 4/1964 Olden 118637 3,134,849 5/ 1964 Frohbach.

3,180,256 4/1965 Kramer et al 101129 3,245,341 4/ 1966 Childress et al.

ROBERT E. PULFREY, Primary Examiner. E. S. BURR, Assistant Examiner.

Claims

1. THE METHOD OF ELECTROSTATICALLY PRINTING WITH A DRY PRINTING POWDER THAT INCLUDES THE STEPS OF: (A) POSITIONING THE ARTICLE TO BE PRINTED UPON SPACED BELOW A SCREEN HAVING A GROUP OF UNOBSTRUCTED OPENINGS CORRESPONDING IN OUTLINE TO THE DESIGN TO BE PRINTED; (B) MOVING DISCRETE PARTICLES OF SAID POWDER DOWNWARDLY ALONG A PLURALITY OF CLOSELY ADJACENT GENERALLY VERTICALLY EXTENDING DIFFERENTLY TORTUOUS PATHS THAT HAVE UPPER AND LOWER OPEN ENDS, WHICH OPEN ENDS AND PATHS ARE OF SUFFICIENT SIZE TO FREELY PASS THE PARTICLES OF POWDER THERETHROUGH AND WHICH PATHS ARE DEFINED BY WALLS POSITIONED TO DEFINE THE SIDES OF SAID PATHS AND TO OBSTRUCT DIRECT VERTICAL DOWNWARD MOVEMENT OF SAID PARTICLES UNDER THE INFLUENCE OF GRAVITY AND TO CAUSE SAID PARTICLES TO FOLLOW SAID PATHS BY ADMINISTERING SHOCKS OF PREDETERMINED FORCE AND REGULARITY TO SAID WALLS AND PARTICLES FOR SHIFTING SAID PARTICLES RELATIVE TO SAID WALLS UNTIL THE PARTICLES REACH AND PASS THROUGH SAID LOWER OPEN ENDS FOR MOVEMENT THEREFROM TO SAID OPENINGS; AND THEREAFTER; (C) MOVING SAID PARTICLES THROUGH SAID UNOBSTRUCTED OPENINGS IN SAID SCREEN BY APPLICATION OF PHYSICAL FORCE AGAINST SAID PARTICLES; AND (D) ESTABLISHING AN ELECTRICAL VOLTAGE POTENTIAL BETWEEN SAID SCREEN AND THE SAID ARTICLE TO PROVIDE AN ELECTROSTATIC FIELD BETWEEN SAID SCREEN AND SAID ARTICLE FOR CONDUCTING THE PARTICLES MOVED THROUGH SAID SCREEN AND ONTO SAID ARTICLE.