US3886864A - Triangular drive for screen printer - Google Patents

Abstract

Briefly, apparatus embodying the invention includes a rotatable screen holder, adapted to rotate through a segment of a circle, and carrying the screen which has the pattern to be printed, and a horizontal reciprocating support table which carries the workpiece to be printed. A fixed squeegee is disposed in operative relation with the screen. The table and the rotatable screen holder are mechanically coupled together so that they move together, and the work-piece is so positioned that it and the screen come into tangent contact and the pattern is printed as the support plate and screen move together through a printing cycle.

Description

United States Patent 1 1 Larsson 1 1 TRIANGULAR DRIVE FOR SCREEN PRINTER [76| lnventor: Ivar F. Larsson. PO. Box 916.

Wellflect. Mass. 02601 [22] Filed: Oct. 25. 1973 1211 Appl. No: 409,760

[52] 1.1.5. Cl 101/126; 101/116 [51] Int. Cl. B4" 13/16: B4lf15/26 [58] Field ofSearch 101/115. 116.114.124. 101/22,23, 125. 126.118

[56] References Cited UNITED STATES PATENTS 1.856.139 5/1932 Schettler 101/22 X 1.995.403 3/1935 Smelling 101/125 2.111.207 3/1938 Denelsbeclc. 101/124 2.931.292 4/1960 Ackley 101/37 3.078.792 2/1963 Kerstun 101/35 X 3.302.560 2/1967 Edwards et al. 101/114 X 1 1 June 3, 1975 Van Der Windcn 101/118 Stommel 101/22 57 ABSTRACT Briefly. apparatus embodying the invention includes a rotatable screen holder. adapted to rotate through a segment of a circle. and carrying the screen which has the pattern to be printed. and a horizontal reciprocating support table which carries the work-piece to be printed. A fixed squeegee is disposed in operative relation with the screen. The table and the rotatable screen holder are mechanically coupled together so that they move together. and the work-piece is so positioned that it and the screen come into tangent contact and the pattern is printed as the support plate and screen move together through a printing cycle.

5 Claims, 8 Drawing Figures 1 TRIANGULAR DRIVE FOR SCREEN PRINTER BACKGROUND OF THE INVENTION Apparatus for silk-screen printing electronic products is well known and, in general, requires highprecision operation. Because of this, all such apparatus is of the reciprocating type and includes a horizontal support for the work-piece which is moved into position under a silk screen having the pattern to be printed. After the work-piece is suitably positioned, a squeegee moves across the screen and forces ink through the screen pattern onto the work-piece, after which the support is retracted and the work-piece is removed. The printing pattern is then repeated for another work-piece. It can be seen that considerable useful time is wasted by the various separate operating steps of such reciprocating apparatus. In particular, the total period of time, during which the horizontal support moves, is wasted because no useful printing work is performed during this period.

SUMMARY OF THE INVENTION Briefly, apparatus embodying the invention includes a rotatable screen holder and horizontally reciprocable work-piece holder which operate together to perform a printing operation quickly and efficiently with minimal wasted operating time of the apparatus. The screen and work-piece are so positioned that they move at the same rate with respect to each other during a printing cycle.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of silk-screen printing apparatus embodying the invention;

FIG. 2 is a side elevational view, partly in section, of a portion of the apparatus of FIG. 1 showing the silkscreen assembly;

FIG. 3 is a front elevational view, partly in section, of a portion of the apparatus of FIG. 1 showing .the silkscreen supporting mechanism;

FIG. 4 is a plan view of a portion of the apparatus of FIG. 1;

FIG. 5 is a side elevational view of a portion of the apparatus of FIG. 1 illustrating schematically means for removing a printed work-piece;

FIGS. 6 to 8 show schematically the relationship between the printing screen and work-piece at various stages in a printing cycle.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the invention, it will be seen that some structural elements include identical left and right side portions. In some of these cases, the left and right side portions carry the same reference numeral, with one numeral being primed.

BROAD PRINCIPLES OF THE INVENTION In its broadest aspects, the screen-printing apparatus of the invention 10 includes a printing-screen holder which comprises a frame in the form of an are or segment of a circle, as seen clearly in FIG. 2. The screen 30 carrying the pattern 32 to be printed is suitably supported on the frame so that its printing surface also defines an arc of a circle. The frame 20 is rotatably mounted on a horizontal shaft 40.

A horizontally reciprocatory table 50 is mounted adjacent to and beneath the screen 30 and frame 20, and the frame 20 and the table 50 are coupled together so that, in a printing cycle, as the table moves in a direction into the paper, as seen in FIG. I, or from left to right as seen in FIG. 2, the frame pivots about the shaft 40. This movement causes the screen 30 to rotate through an arc of a circle.

The table 50 also carries a work holder 60 for supporting a work-piece 70, the work holder being horizontally movable with the table and also vertically reciprocable to raise the work-piece into operating position with respect to the screen, and so that the workpiece is directly in contact with the screen during a printing operation. The screen and work-piece are positioned so that they move at the same speed with respect to each other. The apparatus 10 also includes a squeegee mounted inside the frame 20 and adapted to squeeze printing ink over the screen as the screen rotates in operation of the apparatus.

In the beginning of a cycle of operation of the apparatus 10, as described briefly above, the table 50 is retracted and the screen holder frame 20 is positioned at the maximum forward or clockwise position, clockwise as seen in FIG. 2. As the parts begin to move, the table 50 moves to the right, the frame 20 rotates counterclockwise, and the work holder 60 rises to bring the work-piece 70 into printing position, and, as the patterned area in the screen 30 reaches the work-piece, the pattern is printed thereon by the squeegee. The work-piece is then ejected as the table and screen begin to retract. As the table and screen return to their starting position, the work holder moves downwardly to a position at which it receives another work-piece, and the apparatus is ready for another printing operation.

DESCRIPTION OF A DETAILED EMBODIMENT OF THE INVENTION Referring to the drawings, the screen-printing apparatus 10 includes a floor-mounted table having a top surface 100, to which is secured a second support table spaced therefrom a suitable distance and supporting some of the operating parts of the apparatus. The apparatus 10 includes a control console and a pair of spaced-apart, rigid support members 130, 132, all suitably secured to the second support table 110.

The screen-carrying frame 20 is disposed between the rigid support member 130, 132 and is constructed as an are or segment of a circle. In one suitable arrangement, the frame 20 comprises essentially two identical side plates 140, and suitable connecting members including a horizontal connecting frame portion 150. The side plates 140, 140' are generally triangular in form and include two straight arms 160, 162 and a curved connecting base portion 164 (FIG. 2). The connecting frame portion extends between the apex of the triangle formed by each side piece, and a horizontal bore 152 is formed through this portion of the frame to receive the horizontal shaft 40 on which the frame 20 pivots or rotates.

The screen 30 may be supported on the frame 20 in any suitable manner. In one suitable arrangement, shown in FIG. 3 but not in FIG. 1, the inner wall of the base portion 164 of each side plate 140, 140 of the frame 20 includes an inwardly projecting L-shaped portion 165 which extends along the base portion and follows the curvature thereof. The L-shaped portion includes a vertical wall 167 having a top surface on which is seated, in order, a protective shim 168, the screen 30, and a backing bar 169. The screen 30 is directly secured to the first backing bar 169 by means of screws 172. The screen bears against the backing bar 169', and it is secured to a third adjustable backing bar 173 whose position with respect to the bar 169' is adjustable by means of screws 175 whereby lateral tension on the screen can be adjusted and it can be drawn taut betwee.. the side plates 164, 164. The backing bars 169, l69 and the screen 30 are held in place on the curved base portions 164, 164' of the side frames in any suitable manner, for example, by means of spring-biased toggle clamps 176 built into the curved members 164, 164', as illustrated schematically in FIG. 3.

The frame 20 is also provided, for example, on the outer surface of each of the curved side plates 140, 140, with means for rotating the frame, for example, a sector of a gear 170, 170'. The gears 170, 170' are positioned with respect to the screen 30 so that the screen is at the pitch diameter of the gears. This insures that the screen and work-piece, to be described, will move at the same speed with respect to each other in a printing cycle.

The squeegee assembly 80 is mounted vertically inside the frame and is vertically reciprocable with respect to the screen. The squeegee assembly includes a vertical holder rod 81 suitably secured to the frame by means of arm 174 thereof and carries a conventional squeegee 82 at its lower end adjacent to the screen. The squeegee holder rod 81 is preferably spring-biased, as illustrated schematically by spring 84, so that, when it is in printing position, it is biased toward the screen. An air cylinder 180 or the like is coupled to the squeegee assembly 80 to reciprocate the assembly vertically up and down, out of and into printing position with respect to the screen.

The horizontally-reciprocatory table 50 is mounted beneath and in operative relation with the screen 30 and is carried by the support table 110. The table 110 carries a pair of spaced-apart horizontal shafts 190, in which the table 50 is slidably supported by means of brackets 194 forming a portion thereof. The table 50 carries a pair of spaced-apart vertical walls 200 which carry, on their upper surfaces, gear racks 210 which, with the gear sectors 170, form a rack and pinion arrangement. The walls 200 are positioned and dimensioned so that each gear 210 engages one of the gear segments 170 carried by the side plates 140 of frame 20. The meshing gear arrangements thus provided cause the frame 20 and table 50 to move together. Other mechanical coupling arrangements could also be used.

The apparatus includes the work-piece-carrying assembly 60 which is secured to the horizontallyreciprocatory frame and is vertically-reciprocable and carries the work-piece 70 to be screened. in one arrangement, the work-piece-carrying assembly includes a vertical post 61 which is provided with a relatively large-diameter horizontal plate 220 at its upper end, on which the work-piece 70 is supported, and a plate 224 at its lower end. A horizontal stop plate 250, integral with table 50, is positioned to limit the downward movement of work holder 60. Similarly, a plate 228, integral with table 50, is positioned beneath the plate 250 to limit or control the upward movement of the work-piece holder assembly at the beginning of a screening cycle, to be described. Mechanical or suction means 225 is provided to hold the work-piece on the support plate 220. An air cylinder 246 is suitably coupled to post 61 to reciprocate the work-piece assembly.

Means is provided to adjust the upward movement of the work-piece holder assembly to work-pieces of different thickness, and this means includes, in one arrangement, an assembly including a pair of wedges 230 and 240 having mating sloping surfaces and adjustably coupled together by means of spring-biased bolts 234 extending through plate 228 and into the wedges. The wedge 230 is horizontally adjustable by a micrometer 232 or the like to set the position of the lower wedge 240, against which plate 224, secured to post 61, bears as the work holder assembly 60 moves upwardly. it can be seen that adjustment of the lateral position of the inner wedge 230 sets the position of the lower wedge 240 and determines the maximum upward travel of the work-piece holder. It is noted that post 61 is journalled in plates 250 and 228, and other suitable bearing supports may also be provided, if desired.

it is clear that other arrangements may be used to limit or adjust the upper and lower limits of motion of the work holder assembly 60. In addition, means (not shown) are also provided to permit three-dimensional adjustment of the work-piece holder to compensate for any misalignments between the screen pattern and the support apparatus.

The apparatus of the invention also includes novel drive means for driving the work-piece support apparatus 60 and the work-piece during a printing cycle. This apparatus is suitably mounted on table and includes three sprockets, gears, or the like 260, 262, 264, having a drive chain, cable, belt, or the like 266 secured thereto. One of the sprockets is driven by means of a coupling to a motor 270. The chain 266 carries a vertical post 274, to which a metal block 278, called a cam car", is secured. A pair of horizontal rods 280 are coupled to the cam car so that the cam car is slidable on the rods. A generally U-shaped frame 290, having a horizontal bar portion 294 and end portions 298, has these end portions secured to the free ends of rods 280 to provide a rigid unitary assembly. The bar portion 294 is secured to the table 50 in any suitable manner, for example, by means of a connecting post 300 suitably secured thereto.

As illustrated in plan view in FIG. 4, the three sprockets are disposed in a triangular array, with the line b between sprockets 260 and 264 representing the base of the triangle. The slope of the side S1 of the triangle formed by the line between the sprockets 260 and 262 represents the printing portion of the operating cycle of the invention and the movement of the cam car and the table 50. The smaller the angle between the side S1 and the base b of the triangle, the slower the speed of the apparatus during the printing cycle. The side S2 of the triangle formed by the line between sprockets 262 and 264 is perpendicular to the base b, and this represents the return travel of table 50 and frame 20, which takes place at maximum speed or in the shortest time. Clearly, the angles of the sprocket triangle can be arranged as desired to select the desired relative speed of movements in each phase of operation of the apparatus. Motor 270 can also be programmed to provide the desired relative speeds.

The apparatus 10 also includes means for ejecting or removing a printed work-piece 70 from support plate 220 at the end of a printing cycle and as the work table 50 and frame begin to retract and return to their starting position. As illustrated schematically in FIG. 5, an arm or blade 250 is positioned adjacent to the operating apparatus, either suitably positioned or movable into operative relation, at the end of a printing cycle so that, as the table 50 begins to reverse its direction, the screened work-piece 70 is removed from the work holder onto a suitable support (not shown). A new work-piece can be placed on the workpiece holder by hand or by means of suitable automatic feed apparatus, not shown.

In operation of the apparatus of the invention, initially, the table is retracted and the frame 20 is at a suitable clockwise retracted position, clockwise as seen in FIG. 2, which places the printing pattern 32 in the screen above the workpiece and in position to move toward the work-piece, as illustrated schematically in FIG. 6. At this time, the cam car 278 is moving horizontally, say, right to left along the rods 280. During this period of time, with the cam car moving to the left, a work-piece 70 is placed on the table 220 of the work holder, by hand or automatically. As the cam car turns and begins its travel along side s1 of the sprocket triangle, the work table is raised into printing position so that the work piece and screen will move into direct contact with each other. At a suitable time, the squeegee assembly 80 is lowered into printing position in contact with the screen, and, as illustrated schematically in FIGS. 7, 8, as the table and frame move together, the printing pattern in the screen moves into place over and in contact with the work-piece, and the squeegee squeezes the printing ink through the pattern onto the work-piece.

Now, the squeegee 80 is retracted, the work-piece holder 60 is lowered, and, as the cam car begins its travel along side S2 of the sprocket triangle, the printed work-piece is pushed off the table, and the frame 20 and table 50 are driven quickly back to their retracted position. Again, as the cam car travels along the base of the triangle, another work-piece is placed on the table, and the printing cycle can be repeated.

The apparatus of the invention has major advantages over silk-screen apparatus of the prior art and that commonly used in industry. The primary advantage of the invention is its speed of operation. A typical prior art reciprocating machine performs a printing cycle in a total time of 4 to 6 seconds; the apparatus of the invention has operated in a total printing cycle time of 1 second. As a result, prior art apparatus, typically, can print about 600 parts per hour, while the apparatus of the invention can print about 3000 parts per hour. Finally, the apparatus of the invention can be approximately 50% lower in price than typical prior art apparatus.

The broad principles of the invention have been spelled out clearly above, and it is clear that many of the specific mechanical elements described can be varied or modified or replaced by others to achieve the basic operation of the invention.

What is claimed is:

l. Silk-screen printing apparatus comprising a horizontally movable work-piece support table,

a work-piece support carried by said table,

first means coupled to said table by which said table can move horizontally forward and backward along a predetermined path,

a rotatable screen-carrying frame rotatably mounted on a horizontal shaft disposed transverse to said predetermined path in which said table moves,

mechanical means directly coupling together said table and said frame whereby when said table moves along said path, said frame rotates on said shaft, and including driving means for driving said work-piece support table backward and forward in said predetermined path,

said driving means including three sprockets disposed in a common horizontal plane parallel to said table with their centers defining a triangle having a base, a first side, and a second side,

the base of said triangle being oriented transverse to said path which said table traverses, said first side being oriented at an angle to said path, and said third side being oriented generally parallel to said path,

a drive chain threaded around said sprockets and movable along a triangular path corresponding to said triangle,

a motor coupled to one of said sprockets, and

mechanical coupling between said chain and said support table, and including a bracket slidably mounted thereon and slidable in a direction parallel to the base of said triangle and transverse to said predetermined path, said bracket exerting no force on said mechanical coupling and on said table when it moves in said direction parallel to the base of said triangle,

said bracket being secured to and moving with said chain along said triangular path, said bracket exerting a driving force on said table in one direction along said predetermined path when it moves with said chain along said first side of said triangle and in the opposite direction when it moves with said chain along said second side of said triangle.

a screen, carrying a pattern to be printed on a workpiece, secured to said frame, said screen and its pattern moving with respect to said work-piece support when said frame and said table move with respect to each other.

2. The apparatus defined in claim 1 and including means for raising and lowering said work-piece support.

3. The apparatus defined in claim 1 wherein said table is slidable on parallel rods oriented in the direction of said predetermined path and said horizontal shaft carries gears which mesh with gear racks carried by said table.

4. The apparatus defined in claim 1 and including a vertical shaft supporting said work-piece support, and

means coupled to said vertical shaft for moving it vertically up and down with respect to said table into and out of a print position.

5. The apparatus defined in claim 4 and including further means engaging said vertical shaft for adjusting the vertical position of said vertical shaft and thus adjusting the vertical position of said work-piece holder with respect to said screen.

Claims (5)

1. Silk-screen printing apparatus comprising a horizontally movable work-piece support table, a work-piece support carried by said table, first means coupled to said table by which said table can move horizontally forward and backward along a predetermined path, a rotatable screen-carrying frame rotatably mounted on a horizontal shaft disposed transverse to said predetermined path in which said table moves, mechanical means directly coupling together said table and said frame whereby when said table moves along said path, said frame rotates on said shaft, and including driving means for driving said work-piece support table backward and forward in said predetermined path, said driving means including three sprockets disposed in a common horizontal plane parallel to said table with their centers defining a triangle having a base, a first side, and a second side, the base of said triangle being oriented transverse to said path which said table traverses, said first side being oriented at an angle to said path, and said third side being oriented generally parallel to said path, a drive chain threaded around said sprockets and movable along a triangular path corresponding to said triangle, a motor coupled to one of said sprockets, and a mechanical coupling between said chain and said support table, and including a bracket slidably mounted thereon and slidable in a direction parallel to the base of said triangle and transverse to said predetermined path, said bracket exerting no force on said mechanical coupling and on said table when it moves in said direction parallel to the base of said triangle, said bracket being secured to and moving with said chain along said triangular path, said bracket exerting a driving force on said table in one direction along said predetermined path when it moves with said chain along said first side of said triangle and in the opposite direction when it moves with said chain along said second side of said triangle. a screen, carrying a pattern to be printed on a work-piece, secured to said frame, said screen and itS pattern moving with respect to said work-piece support when said frame and said table move with respect to each other.

1. Silk-screen printing apparatus comprising a horizontally movable work-piece support table, a work-piece support carried by said table, first means coupled to said table by which said table can move horizontally forward and backward along a predetermined path, a rotatable screen-carrying frame rotatably mounted on a horizontal shaft disposed transverse to said predetermined path in which said table moves, mechanical means directly coupling together said table and said frame whereby when said table moves along said path, said frame rotates on said shaft, and including driving means for driving said work-piece support table backward and forward in said predetermined path, said driving means including three sprockets disposed in a common horizontal plane parallel to said table with their centers defining a triangle having a base, a first side, and a second side, the base of said triangle being oriented transverse to said path which said table traverses, said first side being oriented at an angle to said path, and said third side being oriented generally parallel to said path, a drive chain threaded around said sprockets and movable along a triangular path corresponding to said triangle, a motor coupled to one of said sprockets, and a mechanical coupling between said chain and said support table, and including a bracket slidably mounted thereon and slidable in a direction parallel to the base of said triangle and transverse to said predetermined path, said bracket exerting no force on said mechanical coupling and on said table when it moves in said direction parallel to the base of said triangle, said bracket being secured to and moving with said chain along said triangular path, said bracket exerting a driving force on said table in one direction along said predetermined path when it moves with said chain along said first side of said triangle and in the opposite direction when it moves with said chain along said second side of said triangle. a screen, carrying a pattern to be printed on a work-piece, secured to said frame, said screen and itS pattern moving with respect to said work-piece support when said frame and said table move with respect to each other.

2. The apparatus defined in claim 1 and including means for raising and lowering said work-piece support.

3. The apparatus defined in claim 1 wherein said table is slidable on parallel rods oriented in the direction of said predetermined path and said horizontal shaft carries gears which mesh with gear racks carried by said table.

4. The apparatus defined in claim 1 and including a vertical shaft supporting said work-piece support, and means coupled to said vertical shaft for moving it vertically up and down with respect to said table into and out of a print position.

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