Patent Publication Number: US-3874289-A

Title: Screen printing press

Description:
O United States Patent 11 1 1111 ,874,289 Valentin 5] Apr. 1, 1975 SCREEN PRINTING PRESS 3.260.194 7/1966 Karlyn 101/126 x 3.518.938 7/1970 Donner et a1 [75] Inventor: 3.521.298 7/1970 Morel ct a1. lomvllleie-ponh France 3.538.845 11/1970 Peck et al.&#39;  
  3.659.523 5/1972 Olsen [73] Asslgnee Produ Basel swtzerlmd 3.792.657 2/1974 Kammann .1 101/124 x [22] Filed: Dec. 11, 1972 21 A N &#39;1 314,043 Primary E.\&#39;uminerEdgar S. Burr 1 pp 0 Assistant Examiner-R. E. Suter Attorney, Agent. or Firm-Allison C. Collard [30] Foreign Application Priority Data Dec. 10. 1971 Germany 2161385 57. ABSTRAQT [52] U S Cl 101/123 101/174 101/126 A screen printing press for printing onto objects of dif- 51 1m. (:1. B411 17/18 B4lf 17/24 1341f 17/28 shapes Pmpnsmg, 9 for SuPponmg [58] Field of Search 4,; 124 35 ob ect to be prmted, a prmtmg stencil dlsposed over ai 14 the carrier, a doctor roll or blade for contact with the stencil, means coupled to the: stencil and the doctor [56] References Cited roll or blade for reciprocating the doctor roll or blade with respect to the stencil. alternating drive means UNITED STATES PATENTS coupled to the object carrier for moving the object to 2,157,638 5/1939 Soubier 101/123 X be printed in content with the stencil and re]eusing the 2.581.775 1 1952 Wade 101 123 Object after priming 3.247.786 4/1966 Heyne ct a1 101/123 X 3.253.538 5/1966 Rudolph et a1. 101/126 X 13 Claims, 17 Drawing Figures aSZ WEIENTEDAPR H975 Szili? 2 UP 6 ll .llllPl-ll PMENTEDAPR H 2.874269 manna PATENTEDAFR&#39; 1:975 1874,2823  
 sum sag gs FIG.I3  
 FIGJL 280 SCREEN PRINTING PRESS This invention relates to screen printing presses used for printing on cylindrical, conical, elliptical, right angle, and flat surfaces. These surfaces can be separated into two groups during the printing process. One group of surfaces has a diameter which is cylindrical, conical or elliptical in shape. During the printing process, these surfaces require that a roll off process takes place, between the printing stencil and the surfaces, so that the rotational axis and longitudinal axis of the object are parallel to each other. In this conventional process, the printing stencil is moved in a reciprocating motion, so that in one moving direction, the printing medium is brought onto the object to be printed while the reverse movement is used to bring the printing stencil back into the operating position ready for the next printing position. The doctor roll or blade which is associated with the printing stencil is stationary during the printing process. During the reverse movement of the printing stencil, the doctor roll is moved from the printing stencil. The doctor roll is then brought back into position for the next printing process.  
  In the other group of surfaces which are not rolled off during the printing process, the bodies engage the printing stencil during the printing process without having a relative movement between the printing stencil and the body. The doctor roll or blade appplies the printing ink onto the body, the doctor roll being moveable with respect to the printing stencil. In this case, the printing stencil is stationary while the doctor roll moves in a reciprocating movement in one direction to transfer the ink and effect the print, and in the other direction to return the doctor roll into the operating posi tion.  
  Conventional screen printing presses are arranged to provide a reciprocating mount and a stationary mount in the press, so that the stationary mount is rigidly mounted to the frame of the press. In the reciprocating mount, the stencil print is mounted on the press while the stationary mount carries the stationary mount of the doctor roll. In the other example, when the second group of surfaces are printed, the stencil is carried by the stationary mount, while the doctor roll is mounted on the moveable mount of the press. A big disadvantage of conventional screen printing presses is that only one part is moveable during the printing process, requiring travel through a relatively long stroke in order to print a picture onto an object having certain measurements. Another disadvantage is that the press can be operated only in a stroke of fixed length. Consequently, the print volume is very low in conventional printing presses.  
  The subject invention is based on a screen printing press having a carrier for the object to be printed on, a printing stencil, and a doctor roll or blade so that one common press drive is provided. The drive provides an acceleration ofthe printing process. On the other hand, there is the possibility that a print ofa given length may be brought from the printing stencil onto the surface in the direction motion of the stencil or the doctor roll or blade. Furthermore. it is desired that the printed surfaces be continuously moved through the screen printing press. In this operation, it is essential that the transporting motion not be interrupted during the printing process. It should also be possible that a plurality of printing processes be executed during the transporting movement.  
  In the present invention, the printing stencil and the doctor roll or blade are reciprocating moveable and are associated with an alternating drive, coupled to the object carrier so that the object carrier is moveable during the printing process. It is thus possible to make the screen stencil and the doctor roll moveable in the same direction during the printing process. This occurs when the length of the screen stencil to the surface is relatively short, such as in cylindrical objects having a small diameter. It is also possible for the screen stencil and the doctor roll to move in opposite direction during the printing process. In this case, &#34;the stroke of the printing press adds to the stroke of the doctor roll so that a print mounted during the printing can have a longer dimension than normal printing presses of this type. The object carrier and the doctor roll may be moveable in a synchronous manner in a roll-off press. However, in projects where the printing stencils do not move in the roll-off fashion, it is essential that the object carrier and the printing stencil move synchronously. The object carrier may be made of a continuously moving transport element, so that objects will be printed during the carrying of the transport element. Another. arrangement may be advantageous wherein the object carrier is mounted in a reciprocating manner] In this arrangement, it is possible to add a continuously moving transport element or conveyor so that the object carrier is moved synchronously with the transport element. In all of these cases, it is possible that during the printing process, the movement of the surface to be printed constitutes a part of the transport movement.  
  The above-mentioned additional conveyor drive may engage the object carrier. On the other hand, the doctor roll and the stencil print are connected in an alternating common drive with the object carrier. The operating parts which are connected with the common drive may be in the form of of a chain, a ratchet, or any other suitable means, so as to cooperate with a reciprocal movement. It is essential that the axis of the rotational element is carried by a connecting rod. The connecting point of the connecting rod may be connected tothe drive mechanism so that it is lateral, and adjustable to both sides of the drive mechanism. A position may thus be adopted in which the axis of the rotation element is moveable in the same direction during the printing process, that is in the same direction as the object carrier. However, it should be noted that the speed of the two parts are different so that a relative movement is provided. This movement, as already mentioned, is essential when short prints are printed in the moving movement of the parts concerned. Where the printing picture has a medium length such as in roll-off printing presses, the connecting or crank point of the connecting rod may assume a neutral position. In this case, the gear which is mounted between the two threaded rods is moved by auxilliary means, without moving the axis of the rotation element. In other words, the two opposed moving objects, namely, the object and the stencil print move evenly over the same length, but in opposite direction so that the length of the picture of the object to be printed is the equal of the sum of the two strokes.  
  When articles are printed having a relatively large diameter with respect to the moving direction of the parts involved, it is essential that the movement of the axis of the rotational element is opposite to the object carrier. The doctor roll thus moves in a stroke which is the same as the twofold movement of the axis of the rotational element and the object carrier.  
  The object carrier is provided with centering elements, which may be axially moveable in the direction of the object. When the object carrier reverses its operating position, the centering elements have a larger spacing with respect to each other than during the printing process. The object carriers and/or the centering elements may be adjustable in height.  
  Essentially, the object carrier is supported by slits which are guided by carriers running parallel to rods, guides, or the like. The carriers are lateral to the transport means and parallel to the axis of the transverse rods which carry the object. The transverse rods carry a moveable base plate which engages an endless drive means. It has been shown to be very advantageous to provide two base plates. Each of these base plates are provided with a gear which engages a drive gear. This gear may be in the form of an internal gear arrangement. The invention provides for the possibility that the internal gear runs in two linear opposing and parallel paths to the transport means, and a separation exists between the two sections which are joined by arclike portions. In addition, the two base plates may be provided with a guide track which corresponds to a gear arrangement so that a roll-like guide means can engage the gear arrangement of the guide track. The axis of the drive, reverse, and guiding elements of the transport means may be arranged pivotably with respect to the plane of the transport means. In this situation, it is possible to bring the axis for printing conical objects into a position which corresponds to the incline position of theconical objects to be printed. The angle of the incline is equal to half the conical angle. Furthermore, in order to print conical or similarly formed objects, the stencil form is pivotably mounted in the plane of printing and with respect to the object carrier. Thus, at least at one connecting point, a longitudinal movement of the printing stencil is possible with respect to the object carrier. In order to provide an adjustable means with respect to objects of different size. it is essential that the connecting point be adjusted to correspond to the radius of the object to be printed. The transport means is preferably a chain means, adjustable with respect to the drive, reverse, or guide means. The chains are thus provided with holders and/or receiving elements for the objects. The arrangement for the moveability adjustment may also be at the drive elements. It is important that the object transport element move with respect to the object carrier, or any other part of the press, be adjusted without any difficulties. Furthermore, the invention provides a plurality of printing stations in series so that a plurality of objects can be printed in the course of one transport, sometimes with an intermediate drying step.  
  In the drawings wherein similar reference characters denote similar elements through the several views:  
 FIG. 1 is a side view of a screen printing press;  
 FIG. 2 is a plan view of the press;  
  FIG. 3 is a front view of a second embodiment of the invention;  
  FIG. 4 is a cross section taken along section IV-IV of FIG. 3;  
  FIGS. 5 and 6 show the position of the parts during the printing of cylindrical objects, at the beginning and at the end of the printing process;  
  FIGS. 7A, B and C show three different adjustments of the common drive for the moveable parts in relation to each other;  
  FIGS. 8 and 9 show the corresponding printing of flat and/or right angled objects in accordance with FIGS. 5 and 6;  
 FIG. 10 is a plan view of the drive for the object carrier;  
 FIG. 11 is a side view of the object carrier;  
  FIG. 12 shows the cutout from the front view of the printing means during the printing of conical objects;  
  FIG. 13 shows a plan view of a printing stencil for printing conical objects; and  
  FIGS. 14A and 14B show the movement of the printing stencil during the printing of conical objects at the beginning, and at the end of the printing cycle.  
  Referring to FIGS. 1-7, screen printing press 20 is provided with a pair of synchonuosly running endless chains or tracks 21. These chains are running over rotating wheels 22. The chains 21 run in parallel planes with respect to each other. Guide bars 23 are mounted for the objects 25 to be printed in receiving elements 24. The distance between chains 21 and guide bars 23 depends on the size of objects 25 to be printed. The upper path 26 of the chains are provided with a printing station 27. This station essentially consists of a reciprocating object carrier 28, a printing stencil 29 and a doctor roll or blade 30. (FIG. 5).  
  In the embodiment shown in FIGS. l-7, mainly cylindrical objects 25 are printed which roll over the printing stencil 29. In this case, the doctor roll or blade 30 is stationary mounted on object carrier 28. The object carrier essentially consists of a base plate 31, having two support posts 32 and 33. Support post 32 is provide with a centering element 34 and extends into the open end of the object to be printed in form of a bottle. This pin-like centering element 34 may be used, in known manner, to introduce compressed air to the bottle during the printing process. The second centering element 35 is shaped in form of a cup. This element is provided for receiving the bottom of object 25 and is provided with a shaft 36 which is supported in support post 33, and which carries a gear 37. On the upper portion, support post 33 is provided with an arm 38 which carries the doctor roll or blade 30. Furthermore, the object carrier 28 is provided with a rack 39 which runs parallel with respect to the two chains 21, and parallel with respect to the transport movement of objects 25.  
  The stencil 29 is carried by a carrier 40 which runs parallel with respect to the transport direction 41 of objects 25 and is guided by rods 42. Furthermore, carrier 40 is provided with a tooth rack 43 which runs parallel to the tooth rack 39 of object carrier 38. A common gear 44 is provided for engaging two tooth racks 39 and 43. The axis 45 of tooth wheel 44 is carried by one end of a connecting rod 46 (FIG. 4). The opposite end of connecting rod 46 is pivotably mounted with a crank pin 47 of a crank disk 48. The crank disk is provided with a guide 49 for the crank pin 47. The crank pin is radially adjustable with respect to crank disk 48, and can be stationarily adjusted to a defined position on the diameter of crank disk 48. As long as crank pin 47 is not in the center of the crank disk 48, a reciprocating movement is provided for the gear 44 by crank disk 48.  
 This movement is transmitted by connecting rod 46. Gear 44 is in engagement with tooth racks 39 and 43.  
  In FIG. 4 ofthe drawings. the center position of tooth racks 39 and 43 are shown during the printing of cylindrical objects. Crank pin 47 is arranged at the center of crank disk 48 and assumes a neutral position. FIG. 5 shows the position of printing stencil 29 and object carrier 28 together with object before the printing process. FIG. 6 shows the same parts after the printing cycle. Object carrier 28 is provided with an additional drive which will be discussed later. This drive moves or displaces the object carrier during the printing cycle synchonously with transport chains 21 in the direction of arrow 41. It is thus obvious that as long as crank pin 47 of crank disk 48 is not in the neutral position as shown in FIG. 4, two forces are in effect on gear 44. One of the forces is transmitted by connecting rod 46 via gear axis 45, and the other force is transmitted directly to gear 44 by the rack 39 of object carrier 28. Since the dimension and the speed of at least one of the transmitting forces onto gear 44 are adjustable. that is by changing the position of crank pin 47 on crank disk 48, it is possible to vary the absolute movement of printing stencil 29 on the one hand. and object 25 on the other hand. Therefore the relative movement between these two parts is adjustable.  
  It is also possible for crank pin 47, shown in FIG. 7A, to be adjusted in such a manner that during the turning movement 52 of crank disk 48, axis 45 of gear 44 moves in the same direction 41 of object carrier 28. The crank pin, as shown in FIG. 7A, is thus positioned between the rotation axis 53 and the left edge of the crank disk 48. In this position, crank pin 47 may be ad justed in such a manner that the stroke of connecting rod 46, in the direction of the arrow, corresponds to the stroke of object carrier 28. As mentioned previously, the object carrier is provided with a separate drive. In this situation, there is no relative movement between printing stencil 29 and object 25 since the gear 44 does not rotate but moves at the same speed as rack 39 in the direction of arrow 41. Therefore, it has to be assumed that crank pin 47 is initially positioned to the left of rotational axis 53, and is adjusted so that it is displaced to a point which results in a speed equal to the speed of object carrier 39 in direction of arrow 41. This setting of pin 47 is called a zero point. whereby the direction of movement from connecting rod 46 is transmitted onto gear 44 in direction of the movement indicated by at a speed equal to the speed of the rack 39. A neutral point is also achieved when the crank pin, as shown in FIGS. 4 and 7B is set on the rotational axis 53 of crank disk 48. In this position according to FIGS. 4 and 7B, crank pin 47 and connecting rod 46 do not move, so that axis 45 of the gear is at rest. In this case, only rack 39 of the object carrier, which is moved in the direction of arrow 51, is operating on gear 44. This has the effect that gear 44 rotates counter clockwise thus displacing printing stencil 29 and rack 43 in the direction of arrow 51, so that object carrier 28 and printing stencil 29 are moved with similar strokes at the same speed but opposite to each other. This adjustment is suitable for printing objects of medium diameter. for example, when the printed surface of the object is twice as long as the stroke of object carrier 28. The transmitted rotation by rack 39 onto gear 44 leads to a displacement of printing stencil 29 from the position of FIG. 5, to the position of FIG. 6, whereby the stroke of object carrier 28 is even with printing stencil 29. The displacement of crank pin 47 to the left from its neutral position according to FIG. 7B allows racks 39 and 43 to move opposite to each other. which means that object carrier 28 and the printing stencil are also moving opposite with respect to each other. However. the extent of this opposite movement decreases with increasing displacement of the crank pin to the left. This means that the displacement of axis 45 of gear 44 rotates to the right in the direction of arrow 52 during the movement of crank disk 48 causing the stroke of rack 43 and printing stencil 29 to be reduced. However, it should be noted that this stroke is still in the direction of arrow 51. In this case the gear wheel rotates counter clockwise.  
  With an increased displacement of crank pin 47 to the left. the extent of the movement of racks 39 and 43 is diminished, which means that the stroke of rack 43 is diminished until the previously mentioned zero point of crank pin 47 is reached. At this point. the speed of movement of axis 45 of gear 41, in the direction of arrow 41, is equal to the speed in which rack 39 of object carrier 28 is displaced. (in the same direction) Thus, gear 44 does not rotate. With a further displacement of crank pin 47 to the left. the stroke of axis 45 of gear 44 is increased. The same is true for the speed with which axis 45 is displaced to the right, that is, in the direction of arrow 41 by rotating the crank disk in the direction of arrow 52. Thus. axis 45 moves ahead of the rack 39 in the direction of arrow 41 so that the rotating direction of gear 44 is reversed. In this case, gear 44 rotates counter clockwise. Rack 43 and printing stencil 29 therefore also move in the direction of arrow 41, that is, in the same direction as rack 39 and object carrier 28. However, the speed of movement of object carrier 28 and printing stencil 29 are different. Therefore, there is a relative movement between the two parts so that the print from the object carrier may be rolled off from the printing stencil 29. Object carrier 28 and printing stencil 29 are thus displaced in the same direction, which is preferable in printing objects having a small diameter. This is particularly true where the circumference, or the roll-off length of the printed object is smaller than the stroke of the object carrier.  
  In objects having a diameter or a roll-off length which is larger than the double length of the stroke of object carrier 28, crank pin 47 is mounted on the other side of rotating axis 53 on crank disk 48, according to FIG. 7C. In this case, when the crank disk rotates in the direction of arrow 52, connecting rod 46 is displaced in the direction of arrow 51, that is, opposite to the direction of the movement 41 of object carrier 28. Rack 43 and printing stencil 29 thus move in one stroke, in the direction of arrow 51. This stroke is larger than the stroke of rack 39 and object carrier 28 which move in opposite directions. The stroke of the printing stencil is double that of the stroke of axis 45 of gear 44. In summary, the roll-off length is equal to the sum of the two lengths which the object carrier and the printing stencil move during the printing cycle.  
  The above-mentioned details, particularly with respect to FIGS. 7A-7C indicate that the inventive screen printing press does take into condideration all possibilities for printing objects of all types. It is interesting to note that the moving parts travel at half the speed of other known presses yet produce the same output. The drive means, during the printing cycle, provides a sinusoidal-like movement to the printing stencil so that the speed of the printing stencil reaches its greatest velocity in the center portion of the cycle. The reduction of speed also provides even travel speed. The difference between the speed at the beginning. and the maximum speed in the center. is much lower. so that an equalization takes place over the one-half revolution displaced by the crank disk. This also enhances the quality of the print. The output can also be doubled if the parts are moved at the same speed as conventional presses.  
  Another advantage of the present invention is that the transport means for the object shown in FIG. 1-7 are provided by chains 21. These chains are provided with grippers or receiving elements 24 for the objects (FIGS. 3 and 6). In conventional presses. the spacing between these grippers correspond to the largest known size to be printed. The spacing between printing stations which are in series with respect to each other is thus equally large. Therefore. when objects have smaller circumferential surfaces are printed. the press does not operate to its fullest capacity because of the enlarged spacing between grippers. Full capacity operation could only be obtained by changing the distance between the grippers on the transport means when an article is changed, an operation requiring a rigorous employment of labor. In the subject invention. the distance spacers for large objects may be shortened. according to FIG. 7C. so that a given length can be printed with a shorter lateral displacement.  
  In all of the previous cases where objects are rolledoff from printing stencil 29, the movement of printing stencil 29 in synchronism with object are made possible by gear 37 (FIG. 3). Gear 37 is connected with cup-shaped centering element by means of shaft .36. Gear 37 is threadably engaged to a rack 54 which is supported by carrier of printing stencil 29. As previously indicated with respect to FIGS. l-3, doctor roll 30 is stationarily connected with respect to object carrier 28 in the previous printing cycles. Therefore a synchronous movement is guaranteed between the object to be printed 25, and doctor roll 30. When flat objects are to be printed where the roll-off is arranged so that only a part ofthe surface of the printing stencil is available. then a relative movement between printing stencil and object is prevented when the flat surfaces are printed. The doctor roll is displaced with respect to the other two parts, that is. the printing stencil and the object. To achieve this, it is essential. that doctor roll 30 and printing stencil 29, be exchanged with respect to the drive means. that is, so that printing stencil 29 is connected with object carrier 28 to carry out the same movement. Doctor roll 30 is mounted on carrier 40 which moves relative to object carrier 29. It should be noted that the moving parts may travel in the same direction. or opposite with respect to each other. The resulting movement ofthe parts with respect toward each other are shown in FIGS. 8 and 9. FIG. 8 shows the start of the printing cycle. and FIG. 9 shows the end of the printing cycle. As shown in FIGS. 1-7, the objects to be printed are carried by an object carrier. The object carrier is synchronized with chains 121 in transport direction 141 and is displaceable therewith during the application of the print. Object 125 and printing stencil 129 are moved synchronously in the transport direction 141, and doctor roll 130 is moved in the-opposite direction 143. The length of the printed picture is thus larger in the transport direction 141 than the op- 8 posite side of the picture. opposite printing stencil 129 or larger than the stroke of doctor roll 130 in the direction of arrow 143. The movement of doctor roll 130. the movement of printing stencil 129, and the movement of object 125 relate to the total sum of length which results in the maximum length ofthe printed picture.  
  In the embodiment shown in FIGS. 8 and 9, it is essential that object 125 is advanced in the direction of arrow 141 without any interruptions during the printing process. It is also essential that receiving elements 124, carried by chains 121, are suitable to receive any shape of the objects to be printed. Lateral limiting faces on elements 124 serve to secure objects 125, which are rectangular or of any shape, in a position relative to chains 121 and thus in relation to the printing devices.  
  Figs. 12-14 show an embodimenttof the invention which is used for printing conically shaped objects. The drive and/or return wheels, and/or the axis or shafts 75 (FIG. 2) are adjusted so that the two chains 21, according to FIG. 12, assume a position wherein the longitudinal axis 276, of object 225, is in an inclined angle with respect to the stencil, so that generatrix 277, which is adjacent printing stencil 229, runs parallel thereto. Accordingly, object carrier 228 also assumes a corresponding inclined angle.  
  In order to execute the same principle of operation for the printing of conical objects as in FIGS. l-7. a circular printing picture 278, is provided on stencil 229, and the stencil is provided with a support 279 on object carrier 228, which is pivotable in the plane of printing. The support is also mounted on carrier 240 which is moved reciprocably along rod 242, and displaced in the same plane in a longitudinal direction. The movement of object carrier 228 with its associated object 225 on the one hand. and screen carrier 240 on the other hand. is the same as shown in FIGS. l-7. Therefore, the adjustment ofthe crank pin according to FIG. 7B, brings object 225 from the starting position according to FIG. 14A to the end position according to FIG. 14B. The travelling path 280 is thus established. During the printing process, stencil 229 is pivoted in the opposite direction from the starting point according to FIG. 14A, into the end position according to FIG. 148. This movement corresponds to the movement of screen carrier 240 in the direction of arrow 251. The pivot point 281 around which stencil 229 moves is arrestable by an elongated slot 282, so that pivot point 281 can be fixed depending on the prevailing conditions of the object 225 to be printed.  
  The connection opposite stencil 229 and screen carrier 240 is made by a fork-like part 283, which is provided with longitudinal slots 284. Extensions 285 of a ring 286 engage the longitudinal slots. Fork-like part 283 is pivotably mounted around a pin 287. The displacement made possible by the long slots 284 for the part 283 and therefore for stencil 229 with respect to screen carrier 240, accommodates the longitudinal balance during the pivot movement of printing screen 229 around pivot point 281, since the distance between pivot point 281 and pin 287 is changed during the pivotal movement. The path of travel 290 which is indicated in FIG. 14A indicates the spacing of the receiving elements 24 of chains 21. The drawing shows that the path of travel 280 is substantially shorter than the path of travel 290 of the objects being carried, so that the difference between the path of travel of 280 and 290 9 may be used to disengage the object. the printing stencil, and the doctor roll (not shown). When the object is taken out of contact from the object carrier. the printing stencil and the doctor roll are moved back into the starting position for the object carrier to receive the next object. thus bringing into contact again. the object. the printing stencil, and the doctor roll. In this case, the next printing process may be restarted. These steps are valid for the movements shown in the rest of the drawings. It has been already mentioned that object carrier 28 operates in a reciprocating movement. whereby the movement in the direction of transport 41 is synchronous with transport chains 21 and therefore with the movement of the objects. Furthermore. it is essential that the two centering elements 34 and 35 are moveable with respect to each other along the axis of the object so that the object may be brought between the two centering elements. and the elements are closed before the start of the printing process. After the printing cycle. the object is released by separating the centering elements from each other. FIGS. 1, 10, and 11 show the movement of the centering elements in a simple mode. At the frame of printing press 20, two parallel spaced-apart rods 56 are mounted on the upper stage 26 of chains 21. Reciprocating carriers 57 are mounted on rods 56 for movement in the direction of arrows 41 and 51. The lengths of rods 56 define the maximal length of stroke of object carrier 28. Carriers 57 carry two lateral transverse rods 58 which are lateral with respect to guide rods 56. Two base plates 59 and 60 are mounted on traverse rods 58 and are independently moveable in a reciprocating motion in the direction of arrows 61 and 62. Each of centering elements 34 and 35 (FIG. 3) is mounted on the base plates 59 and 60. For instance. base plate 59 carries centering element 35 and the base plate 60 carries the centering element 34. The latter mentioned parts are not shown in FIGS. 10 and 11.  
  Each of the two base plates 59 and 60 is provided with an internal tooth arrangement 63 which is shown only at base plate 60 for simplification. A drive pin 64 is provided in the internal tooth arrangement, and rotates in the direction of arrow 65. Furthermore. each base plate 59 and 60 is provided with a circumferential groove 66 which is engaged by a guide roller 68 which is carried on the machine frame 67.  
  The object carrier. of FIGS. 1. 10, and 11, operate as shown in FIG. 10. Starting from the position of FIG. 10, because of the rotational movement of drive pin 64 in direction 65. and a corresponding rotational movement of pin 64 (not shown) associated with base plate 59, both base plates 59 and 60 are moved simultaneously together with the traverse rods 58 which are carried by carriers 57 in the direction of arrow 41. Carriers 57 thus glide along guide rods 56 together with the synchronous movement of chains 21 during the printing cycle. In this situation. the two base plates assume the least possible spacing from each other so that the objects to be printed and the associated centering elements are in gripping engagement with the objects. (not shown in FIGS. 10 and 11). They assume a position as shown in FIG. 3. At the end of the forward movement ofobject carrier 28 in the direction of arrow 41, pin 64 engages in the curved portion 69 of the internal tooth arrangement 63, and guide roll 68 is in the correspondingly curved portion 70 of guide path 66. The turning movement of the drive pin 64 thus displaces base plate 60 outwardly, in the direction of arrow 61. Likewise. base plate 59 and its associated drive pin move the plate in the opposite direction so that the two centering pieces separate. This releases the object so that it can be transported away by chains 21 and 121.  
  When the curved range of internal teeth 69 is passed by driven pin 64, object carrier 28 is moved in the direction of arrow 51 (FIG. 10) along guide rods 56 against the transport movement 41 of chains 21 and 121 respectively. The carrier moves into the starting position when driven pin 64 arrives at the second curve 71 of the internal tooth arrangement. The next object to be printed in then located between the centering elements which are carried by the base plates 59 and 60. These centering elements move toward each other when curved 71 passes drive pin 64 at the internal tooth arrangement 63. While drive pin 64 engages the adjacent linear range of the inner tooth arrangement. that is. the position in which drive pin 64 in in engagement with internal tooth arrangement 63 as shown in FIGS. 10 and 11, the object carrier is moved forward in the direction of arrow 41 synchronously with transport chains 21 and 121. respectively. During this movement. the object is being printed.  
  In a further embodiment, the drive for the object carrier is disclosed in FIGS. 1, 10. and 11, may be changed according to FIGS. 3 and 4. Centering elements 35 and 34, carried by the base plate, may be carried by two carriers. The plates may be reciprocately moveable on two guide rods 156 which move in the same transport direction. A lateral traverse rod 158 is mounted between carriers 157. A further carrier is displaceably mounted thereon. The intermediate carrier 195 is connected to one transport element by means of a catch 196. The catch may be a disc. a chain 197, or other device to transmit a reciprocating motion with respect to the objects. The displacement of intermediate carrier 195 in the direction of the traverse rod 158 serves only to balance the movement of the objects and/or the countermovement of transport elements 197. In contrast to the embodiment according to FIGS. 1, l0, and 11, the lateral movements of the transport elements or catches 196 are not used to open or close the two centering elements 34 and 35 in the direction of arrows 61 and 62. It is essential in this embodiment that the centering elements are separately moveable in the direction of arrows 61 and 62, and that their associated supporting posts 32 and 33, move in a separate reciprocating motion.  
  In this embodiment, object carrier 28 or its parts, and in particular entering elements 34 and 35, can be arranged for a vertical up and down movement. In this case, the individual object is moved downwardly to the associated receiving element 24, and then removed at the end of the printing cycle. This vertical movement also brings the objects into and out of contact with the printing stencil as indicated by arrows 72 and 73 in FIG. 3. In the previous embodiments, an additional object carrier 28 is provided for transport element 21. In another embodiment, it has been shown that the object carrier may be removed, provided that the objects are mounted in the printing position on the transport element. This arrangement provides a transmitting means for rack 39 which is not carried by the missing object carrier. It is also essential that the reciprocating movement is synchronized with the movement of the transport means that is, with the movement of chains 21 and/or 121.  
  While only a few embodiments of the present invention have been shown and described. it will be obvious to those persons skilled in the art that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.  
 What is claimed is:  
  1. A screen printing press with at least one printing station for printing onto objects which perform a rotational movement during the printing step comprising:  
 a reciprocable object carrier for retaining and rotatably supporting the object during printing;  
 a reciprocable carrier for a printing screen disposed over the object carrier for contact with the object to be printed. the object being rotated in synchronism with the displacement of the printing screen about its longitudinal axis and in rolling engagement with the screen; reciprocable carrier for a doctor means disposed above said screen for movable contact with said screen. said doctor means being fixed to said object carrier;  
 first drive means coupled to said object carrier for reciprocating said object carrier. the reciprocating movement having a fixed stroke;  
 second drive means for reciprocating the screen. said second drive means comprising a first toothed rack mounted on said object carrier. a second toothed rack mounted on said carrier for said printing screen, parallel and adjacent to said first toothed rack. a gear meshing with said first and second toothed racks and a coupling member having one end connected to the axis of said gear for controlling the reciprocating motion between the gear and the first and second toothed racks. so that the size of the stroke of the screen can be adjusted to the length of the image to be printed on the objects.  
  2. The printing press according to claim 1 comprising a crank disk and a crank pin mounted on the opposite end of said coupling member and coupled to said crank disk. said crank pin being adjustable with respect to said crank disk.  
  3. The printing press as recited in claim 1 wherein said object carrier comprises centering elements for holding the objects and means for separating said centering elements in an axial direction to release the object so thatduring the return movement of said object carrier to a starting position after the printing step. said centering elements have a larger separation from each other.  
  4. The printing press as recited in claim 3 additionally comprising means for adjusting the height of the object carrier and the centering elements.  
  5. The printing press as recited in claim 1 wherein said object carrier comprises a pair of spaced-apart carriages supporting the object and parallel bars for longi tudinally guiding said carriages in the direction in which the object is moved during the printing step.  
  6. The printing press as recited in claim 5 wherein said carriages include at least one transverse bar interconnecting the carriages, at least one base plate displaceably mounted on said transverse bar, and a continuous drive engaging said base plate for reciprocating the base plate.  
  7. The printing press as recited in claim 6 wherein said at least one base plate includes an internal gear surface. and a driven pin for engaging the internal gear surface for displacing said at least one base plate along said at least one transverse bar.  
  8. The printing press as recited in claim 7 wherein said internal gear surface comprises two opposite linear sections which are parallel to the direction of movement of the object carrier and two connecting inte grally formed curved sections joining the ends of the linear sections.  
  9. The printing press as recited in claim 8 wherein said at least one base plate further comprises a circumferential groove having a periphery corresponding to the periphery of said internal gear surfaces, and a roller guide engaging said groove.  
  10. The printing press as recited in claim 1 additionally comprising means for adjusting the incline of the object carrier with respect to the transport for printing conical objects, the angle of incline corresponding to the inclined angle of the conical object to be printed.  
  11. The printing press as recited in claim 10 wherein one end of said printing screen is pivoted with respect to the object carrier for printing conical objects.  
  12. A screen printing press having at least one printing station for printing onto flat objects comprising:  
 a reciprocable object carrier for retaining and supporting the object during printing;  
 a reciprocable carrier for a printing screen disposed over the object carrier for contact with the object to be printed which is moved in synchronism with the screen during the printing step. said screen carrier being fixed to said object carrier;  
 at reciprocable carrier for a doctor means disposed above said screen for movable contact with said screen;  
 first drive means for reciprocating the object carrier, the reciprocating movement having a fixed stroke;  
 second drive means for reciprocating said doctor means carrier, said second means being adjustable for adjusting the length of the stroke of said doctor means to the length of the image to be printed onto the object, said second drive means for reciprocating said doctor means comprising a first toothed rack mounted on said object carrier, at second toothed rack mounted on said carrier for said doctor means adjacent and parallel to said first toothed rack, a gear meshing with said first and said second toothed racks, and a coupling member having one end connected to the axis of said gear for controlling the reciprocating motion between the gear and the first and second toothed racks, so that the size of the stroke of the screen can be adjusted to the length of the image to be printed on the objects.  
  13. The printing press according to claim 12 comprising a crank disk and a crank pin mounted on the opposite end of said coupling member and coupled to said crank disk, said crank pin being adjsutable with respect to said crank disk.