Abstract:
A silkscreen printer machine ( 8 ) includes:
       a support structure ( 48 ); and   at least one printing station ( 54 ) secured to the structure ( 48 ) and including at least one screen support ( 68 ) presenting a reception area adapted to receive a screen texture ( 70 ) having a pattern for printing placed thereon. The screen support ( 68 ) is carried by at least three support elements ( 78 ) secured to the structure ( 48 ), the support elements ( 78 ) not being in alignment and being positioned on either side of the reception area ( 69 ). The invention also provides associated printer apparatus.

Description:
FIELD OF INVENTION 
   The present invention relates to a silkscreen printer machine comprising a support structure and at least one printing station secured to the structure and including at least one screen support presenting a reception area adapted to receive a screen texture having a pattern for printing placed thereon. 
   BACKGROUND OF THE INVENTION 
   As is known per se, articles are printed in a silkscreen printer machine in a printing station by pressing a wiper blade against a silkscreen texture, the texture being squeezed between the article and the blade. 
   While printing flat articles, such as compact disks, telephone cards, or solar cells, the articles for printing are placed on a turntable suitable for transferring them between various processing and printing stations. 
   In conventional manner, the printing station comprises a support structure, a screen support secured to the structure, and a blade-carrier carriage mounted on a support beam secured to the support structure and extending along a side face of the screen support. 
   The blade-carrier carriage is guided in translation on the support beam so as to enable the screen to be wiped by the blades. During the displacement of the blade-carrier carriage, the pattern for printing is pressed against the article by the blade pressing against the mesh of the screen and by said mesh coming into contact with the surface of the article for printing. 
   Such a printer machine is described in particular in patent document FR 2 666 050. In that document, the side face of the screen support is secured at two points to the support beam. The screen support is cantilevered out from the support structure over the turntable and thus over the article for printing. 
   Nevertheless, it has been found that the printing of the pattern on the article is not uniform. Such a printer machine therefore cannot be used for printing that requires printing of great precision, as is the case for printing solar cells where precision of one hundredth of a millimeter is required. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide a printer machine of great precision. 
   To this end, the invention provides a printer machine of the above-specified type, characterized in that the screen support is carried by at least three support elements secured to the structure, said support elements not being in alignment and being positioned on either side of the reception area. 
   In particular embodiments, the printer machine includes one or more of the following characteristics:
         transport means for transporting at least one article for printing to bring it into register with the reception area, the transport means comprising at least one holding place for holding the article for printing;   lift means for the support element secured to the support structure and suitable for causing the screen support to move towards and away from the holding place;   the lift means comprise lift means common to all of the support elements;   at least fifty percent of the reception area is inscribed in a polygon whose summits are positioned at the points of contact between the support elements and the screen support;   the reception area is fully inscribed within said polygon;   the transport means comprise a circular turntable provided with a central orifice, and one of the support elements passes through said central orifice;   two support elements are positioned on a tangent to the turntable; and   the machine includes at least one locating station comprising means for determining the thickness of the article for printing, and control means for controlling the lift means of the support elements as a function of the thickness determined for the article.       

   The invention also provides printer apparatus, characterized in that it comprises:
         a printer machine as mentioned above;   at least one feed conveyor for feeding articles for printing, the conveyor having an unloading place for unloading articles for printing, and a storage place for storing articles for printing; and   at least one first transfer device for transferring articles for printing, the transfer device comprising an arm hinged about a pivot axis positioned at equal distances from the unloading place and from the storage place.       

   In particular embodiments:
         the feed conveyor is positioned relative to the printer machine in such a manner that the hinged arm of the first transfer device is adapted firstly to turn through an angle of 120° between the loading place and the holding place, while also simultaneously causing the article to turn in a horizontal plane through an angle of 120°; and   the apparatus comprises:
           at least one removal conveyor for removing correctly-printed articles, said conveyor having a first loading place for receiving printed articles;   at least one removal conveyor for removing defective articles, said conveyor including a second loading place for receiving printed articles; and   at least one second transfer device for transferring printed articles, being positioned at equal distances from the first and second loading places and from the holding place; and   
           the printer machine includes a checking station for checking articles after printing, and control means adapted to control the second transfer device so as to transfer the printed articles from the holding place to the first loading place or to the second loading place as a function of the state of each checked article.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood on reading the following description given purely by way of example and made with reference to the drawings, in which: 
       FIG. 1  is a perspective view of a first embodiment of printer apparatus of the invention; and 
       FIG. 2  is a plan view of the printer apparatus shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The printer apparatus  2  of the invention is shown diagrammatically in  FIGS. 1 and 2 . It comprises a feed conveyor  4  for feeding articles  6  for printing, a printer machine  8 , a removal-conveyor  10  for removing properly printed articles, and a removal conveyor  12  for removing articles that are badly printed or defective, and extending perpendicularly to the conveyor  10 . 
   The feed and removal conveyors  4 ,  10 ,  12  are identical, each comprising a support structure  14  and a looped conveyor belt  16  held between two parallel deflection rollers, one of which is driven by a brushless motor  18 . 
   Articles  6  for printing, such as solar cells, for example, are placed on the conveyor belt  16  one after another on support zones  20 . The support zone  20  situated at the end of the feed conveyor  4  close to the printer machine  8  defines an unloading place  22  for unloading articles for printing. The support zones  20  situated at the ends of the removal conveyors  10  and  12  close to the printer machine  8  define first and second loading places  24  and  26  for loading printed articles. 
   A storage device  28  for storing articles  6  for printing is associated with the feed conveyor  4 . It comprises a rectangular storage tray  30  and a support bracket  32  in the form of a square having one end secured to a side face of the tray  30  and its other end secured to the support structure  14 . 
   The storage tray  30  is of a size that is slightly greater than the size of the articles  6  for printing and it presents a storage zone  34  on which said articles can be stacked while the printer machine  8  is not in operation, for example while the screen texture is being washed. 
   A monitor camera  35  for monitoring the existence of articles  6  for printing on the storage place  34  and on the conveyor belt  16  is located facing the conveyor  4 . The operation of this camera is described below. 
   A feed transfer device  36  is interposed between the feed conveyor  4  and the printer machine  8 . It is suitable for moving articles  6  between the unloading place  22  and an article-holding place  38  that is situated on the printer machine  8 . It is also suitable for turning the article round on himself through an angle of 120°. 
   An opposite movement is performed by a removal transfer device  40  interposed between the printer machine  8  and the removal conveyors  10  and  12 , in order to transport printed articles  6  on the removal conveyors  10 ,  12  after printing. 
   The feed and removal transfer devices  36  and  40  are identical. Each comprises a cylindrical stand  42  extending along a vertical axis A-A′, provided with an arm  44  that is articulated about the axis A-A′ and that projects away therefrom and perpendicularly thereto. A gripper element  46  for gripping articles is secured to the free end of the arm  44 . It comprises a body in the form of a rectangular block having a suction device mounted thereon that enables articles to be lifted and held. 
   The transfer devices  36  and  40  include means (not shown) for driving the stand in an axial direction relative to the axis A-A′ and means (not shown) for driving the arm  44  to turn around the axis A-A′. 
   As can be seen in  FIG. 2 , the stand  42  of the feed transfer device  36  is positioned at equal distances from the unloading place  22 , the storage place  34 , and the holding place  38 , such that when the arm  44  turns around the axis A-A′, the gripper element  46  is adapted to take articles  6  for printing from the unloading place  22  or the storage place  34 , and to lay said articles on the storage place  34  or the holding place  38 . 
   Similarly, the stand  42  of the removal transfer device  40  is positioned at equal distances from another retaining place  38  of the printer machine and from the loading places  24  and  26  of each of the removal conveyors. 
   The printer machine  8  comprises a support structure  48  supporting a turntable  50  in the form of a disk, means (not shown) for sequentially driving the turntable about its central axis B-B′ relative to the support structure, and three processing stations  52 ,  54 , and  56  disposed at the periphery of the turntable  50 . 
   The turntable  50  moves the articles  6  from one processing station to another. It carries three holding places  38  for holding articles for printing that are disposed on the top face of the turntable  50 , on which the articles  6  are placed, and under which suction units  60  are mounted to hold the articles  6  in place. 
   The holding places  38  are rectangular or square in shape and they are situated on the turntable  50  in such a manner that two of their sides are parallel to a tangent to the turntable. They are regularly spaced apart angularly, such that they are at angles of 120° relative to one another. 
   The processing stations  52 ,  54 , and  56  disposed at the periphery of the turntable  50  in register with each holding place  38  comprise, positioned side by side and at equal distances from one another: a locating station  52  for locating the zone for printing on an article  6 ; a printing station  54 ; and a checking station  56  for checking the zone printed on the article  6 . 
   The locating station  52  comprises a locating camera  62  suitable for viewing the article  6  for printing and a sensor  64  for measuring its thickness, e.g. an infrared sensor or a laser sensor. The camera  62  and the sensor  64  are situated close to the feed conveyor  4  and facing the holding place  38  when the turntable  50  is stationary. 
   The checking station  56  for checking the article  6  for printing comprises a checking camera  66  suitable for viewing the article  6  after printing. The camera  66  is situated close to the removal conveyors  10  and  12 , and facing a holding place  38  when the turntable  50  is stationary. 
   The printing station  54  comprises a screen support  68  having an area  69  for receiving a screen texture  70  and a blade and backing blade system  72  suitable for pressing against the mesh of the screen to apply the pattern for printing on the article. 
   The blade and backing blade system  72  comprises two blades suitable for moving vertically under drive from an actuator  74 , and a carriage  76  carrying the blades and the actuator. The carriage  76  is guided on a support beam (not shown) secured to two opposite sides of the screen support  68 . 
   The screen support  68  extends over the turntable  50 . It is supported on three pillars  78  that ensure stability. These pillars  78  form support elements for the screen support  68 . They are positioned in non- aligned manner on either side of two opposite sides of the reception area  69 . 
   The reception area  69  is defined by means for securing the screen texture  70  to the screen support  68 . In order to ensure that the screen texture  70  is stable, the reception area  69  is inscribed within a triangle whose summits are situated at the three points of contact of the pillars  78  to the screen support  68 . This triangle is defined in a horizontal plane. 
   In particular, two of the pillars  78  of the screen support  68  are positioned on a tangent to the turntable  50 , while the other pillar  78  lies on the axis of the turntable  50 . 
   In the embodiment of the invention shown in the figures, one of the pillars  78  lies on the axis of rotation B-B′ of the turntable  50 , however it is also possible for this pillar  78  to be positioned away from said axis, along the rim of the screen support  68 . 
   Thus, two opposite sides of the screen support  68  are held securely, unmoving, and stable so that when the blades press the mesh of the screen texture  70  against the article  6  for printing, the distance between the mesh and the article  6  is constant along the entire length of the mesh over which the blades pass. 
   The pillars  78  are suitable for being moved vertically in order to adjust the distance between the screen texture  70  and the article  6  for printing as a function of the height of the article  6  as determined by the sensor  64 . 
   For this purpose, the pillars  78  are mounted to slide lengthwise perpendicularly to the plane of the support screen  68  on an actuator  80 . This actuator constitutes common lift means adapted to raise and lower all three pillars  78  simultaneously. 
   Thus, it is possible to adjust the distance between the screen texture  70  and the article  6  for printing in a manner that is precise so as to improve the quality of printing and avoid breaking an article that is fragile. 
   The screen support  68  is mounted to move relative to the pillars  78  in order to position the screen texture  70  exactly in register with the article  6  for printing. In particular, the screen support  68  is mounted to move radially and tangentially relative to the turntable  50  and can turn around the center of gravity defined by the positions in a horizontal plane of the three points where the pillars  78  are secured to the screen support  68 . 
   The printing station  54  further comprises means that are not shown for moving the screen support  68  in radial and tangential translation and in rotation. 
   The monitor camera  35 , the locating camera  62 , the checking camera  66 , the two transfer devices  36  and  40 , the drive means for the turntable  50 , the blade and backing blade system  72 , and the means for moving the screen support  68  are connected to a unit  82  for controlling and synchronizing the printer apparatus. 
   This control unit  82  is adapted to control the printer apparatus  2  as a whole so as to transfer and print articles  6  in series. In particular, it is suitable for controlling the pivot angle of the arm  44  of the feed transfer device  36  as a function of the operating state of the printing station  54  and as a function of the presence of articles  6  for printing on the feed conveyor  4  or on the storage device  38 , where said presence is determined as a function of images delivered by the monitor camera  35 . 
   The control unit  82  is suitable for calculating the position to be taken by the screen support  68  so that the pattern is applied accurately on the article, on the basis of the image received by the locating camera  62  and as a function of the thickness of the article for printing as measured by the sensor  64 . 
   For this purpose, the control unit  82  is adapted to compare the image viewed by the locating camera  62  with a prerecorded image where the desired printing zone is defined relative to the shape of the article or relative to previously-printed patterns, and to control the displacement of the screen support  68  as a function of the result of said comparison. 
   The control unit  82  is also suitable for controlling the angle of rotation of the arm  44  of the removal transfer device  38  as a function of the image viewed by the checking camera  66  is order to position properly-printed articles on the loading place  24  of the conveyor  10 , and poorly-printed articles on the loading place  22  of the conveyor  12 . 
   For this purpose, the control unit  82  compares the image viewed by the checking camera  66  with the prerecorded image used for determining the displacement of the support screen  68 . 
   Initially, the feed conveyor  4  transports the articles  6  for printing on the conveyor belt  16  to the unloading place  22 . 
   If the printing station  54  is in a normal operating state, the control unit  82  causes the feed transfer device  36  to transport the articles  6  for printing situated at the unloading place  22  to the holding place  38 . 
   For this purpose, the stand  42  of the transfer device  36  moves down and the gripper element  46  picks up the article  6  for printing by suction. Thereafter the stand  42  rises and turns through an angle of 120° about the axis A-A′. 
   Thereafter, the stand  42  moves down to the height of the turntable  50 . The article  6  for printing is laid on the holding place  38  of the turntable by turning of the suction device. 
   When the printing station  54  is in a non-functional state, for example while the screen texture  70  is being washed, the stand  42  turns through an angle of 90° and the article  6  for printing is unloaded onto the storage place  34 . 
   When the monitor camera  35  detects that there are no articles for printing on the feed conveyor  4 , it sends this information to the control unit  82 , which then controls the feed transfer device  36  so that it loads articles  6  for printing from the storage place  34  onto the holding place  38 . 
   At the locating station  52 , the camera  62  views the article for printing and transmits the viewed image to the control unit  82  which uses this image to determine the exact position of the article for printing, together with its shape, the center of the article, or an earlier printing thereon. 
   In parallel, the sensor  64  determines the thickness of the article  6  for printing and transmits this information to the control unit  82 . 
   The turntable  50  begins by turning through an angle of 120° so that the article for printing comes into register with the screen texture  70  of the printing station. 
   The control unit  82  calculates the position to be taken up by the screen support  62  relative to the holding place  38  to ensure that the pattern printed through the screen texture  70  is correctly positioned on the article  6  for printing. 
   Thereafter, the control unit  82  causes the actuator  80  to lift the screen support  68  as a function of the thickness of the article  6  for printing as measured at the locating station  52 . 
   The control unit  82  then causes the radial, tangential, and rotational displacement means of the screen support  68  to position the screen texture  70  in register with the zone for printing on the article as defined by the unit  82  from the image viewed by the camera  62  and from a prerecorded image. 
   Once the turntable has finished turning through 120°, and the article is in register with the screen texture, the control unit  82  causes the actuator  74  to press the blades against the mesh of the texture  70  and also causes the blade-carrier carriage drive means to operate so that the blades move right across the screen texture  70 . 
   After the blades have been raised, the control unit  82  causes the turntable  50  to turn through an angle of 120° so that the article  6  for printing is transferred to the checking station  56 . 
   In this station, the camera  66  views the zones printed on the article and transmits the resulting image to the control unit  82  which compares said image with the predefined image defining the exact position for the pattern that is to be printed on the article. 
   When the article  6  has been printed correctly, the control unit  82  controls the removal transfer device  38  so that it turns through an angle of 120° in order to position the printed article  6  on the first loading place  24  of the removal conveyor  10 . 
   When the article has been badly printed, i.e. when the printing it not sufficiently precise or when the article has broken during printing, the control unit  82  causes the removal transfer device to pivot through an angle of 90° so as to bring the printed article onto the second loading place  26  belonging to the removal conveyor  12  for taking away reject printed articles.