Abstract:
A laminating apparatus is disclosed which is particularly suited to mount holograms on plastic cards. The apparatus comprises a planar support supporting the work pieces to be laminated. A press stamp has a shape of a sector of a circular cylinder wall and is driven by means of a special gear to perform a hobbing motion along the to-be-laminated area.

Description:
This is a continuation of application Ser. No. 007,654, filed Jan. 22, 1993, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a laminating apparatus. It is well known in the art that lamination means to adhere a film or a film portion unto a substrate by means of heat bonding. The present invention is particularly suited to laminate so-called white light holograms unto plastic cards, e.g. credit cards. 
     DESCRIPTION OF THE PRIOR ART 
     A white light hologram comprises a piece of film having an embossed groove pattern representing a hologram so that it presents an apparent three-dimensional picture when viewed under certain angles even if illumination is with non-polarized light. 
     When laminating such a hologram unto a card both must be very accurately positioned and the embossed pattern must not be damaged. For this purpose two types of laminating apparatus are in use. 
     In the first type, the plastic cards are supported by a planar support, and the holograms are fed on a carrier tape. A heated stamp presses an individual hologram to be transferred unto a card, the stamp being moved orthogonally with respect to the support. There is a risk that air bubbles are trapped even if the working surface of the stamp is ground to assume a somewhat rounded shape; such rounded shape, in turn, results in a pressure which is higher in the central portion of the hologram than adjacent its edges. Consequently, there is a relatively high rejection rate. 
     The second known apparatus comprises a rotating heated stamp cooperating with a pressure roller which is also rotating. During lamination, the card and the hologram are transported through the gap between stamp and roller. It will be understood that the proper positioning causes difficulties, and in result the rejection rate is high again. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a laminating apparatus having a very low risk of entrapped air bubbles and, simultaneously, a very low risk of inadequate positioning. 
     The laminating apparatus of the present invention comprises a planar support which serves as an &#34;anvil&#34; during the lamination. Cards and holograms (or other work pieces to be laminated) are fed in superposed relation to the support whereby they may be accurately aligned. A stamp has a working surface shaped as a sector of a circular cylinder wall. A gear system is provided causing the stamp to advance relative to the support in a motion across the work pieces thereby following a partial cycloidal path. It is to be emphasized that the motion is not due to frictional engagement between the stamp and the work pieces but is uniquely caused by the particular design of the gear. Air between the hologram and the card may easily escape while proper relative positions of the laminated items is maintained because of the work pieces resting on the support during lamination. 
     A preferred embodiment of the invention is illustrated in the attached drawings and will be explained hereunder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 through 5 show schematically and in side elevation five successive phases of the operation of an apparatus according to the invention, and 
     FIG. 6 and 7 are respectively section views in accordance with lines 6--6 and 7--7. 
     It is to be noted that FIG. 1 through 5 are substantially simplified and show only those elements which are important for the invention. At first the design will be explained with reference to FIG. 1, 6, and 7. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the first instant of a laminating process. A base frame (not shown) supports a planar and horizontally arranged support 10 for plastic cards 12 fed from the right side by means of e.g. a carrier tape 11. Holograms 9 to be laminated unto the cards are supplied by means of a carrier tape 13. The holograms are optically aligned with the cards; these alignment means are not shown as they do not form a part of the present invention. Over support 10, a rocker member 16 is mounted pivotably about a shaft 14 carried by the base frame. Rocker member 16 comprises two congruent and parallel plates 18 each provided with guide tracks 20 (in FIG. 1 through 5 symbolized by a straight line), and these guide tracks 20 are congruent, too. A carriage 21 is guided by the guide tracks 20 so as to reciprocate relative thereto as illustrated in FIGS. 1 and 6. The carriage 21 has two roller bearings 22 (symbolized by small circles) which engage cam tracks 24, 26 on substantially triangular webs which are rigidly fastened on the inner faces of plates 18. 
     A stamp holder 30 is mounted on carriage 21. Holder 30 is pivotable about the axis of a shaft 32 between two end positions; a first end position is shown in solid lines and the second in phantom lines in FIG. 1. In operation, however, the stamp holder 30 is releasably connected to the carriage 21 in said first end position by means of e.g. a ball locking mechanism so that they move together. Mechanism 23 may be any type of well-known ball-locking means, such as a ball snapper commonly used in furniture. Only if maintenance of a stamp 36 is required the stamp holder 30 may be brought manually into the second end position, for example, when the working surface 34 of the stamp 36 is to be cleaned. Preferably, the stamp 36 is interchangeably mounted on the stamp holder 30. The working surface 34 has the shape of a sector of a circular cylinder wall and a size adapted to the size of a hologram to be sealed to a card. The center of curvature of the working surface 34 coincides with the axis of shaft 32. 
     A drive motor (not shown) is mounted on the base frame, and its output shaft 37 drives cam member 38 to rotate in a direction, such as indicated by the arrow illustrated. The outer circumference of cam member 38 is in engagement with cam followers 40, 42 mounted on plates 18. The cam followers 40, 42 may e.g. be the outer races of ball bearings. A crank 46 is pivotally connected to cam member 38 at 44 and its other end is pivotally connected to the carriage 21. Specifically, crank 46 is attached to carriage 21 by way of output shaft 37 and to cam 38 by way of crank pin 44, so that crank 46 rotates on both shaft 37 and on crank pin 44. Thus, upon each revolution of shaft 37 carriage 21 will perform one reciprocation. 
     Cam 38, rotating about a stationary axis, cooperates with cam followers 40, 42 which are rotatably mounted on plates 18, thereby causing a rocking motion of member 16. Driving shaft 37 has a stationary axis, while cam followers 40, 42 are mounted on plates 18 and can move so that they remain in engagement with the outer circumference of cam member 38, as illustrated in FIGS. 1-5 and FIG. 7. It is to be noted that rocker member 16 includes plates 18 and their components, as previously stated and as clearly illustrated in FIG. 7. Cam followers 40, 42 define the angular position of rocker member 16 when they are in engagement with the outer circumference of cam member 38, which rotates on stationary shaft 37. The shape of cam tracks 24, 26 is calculated or graphically designed such that the working surface 34 of the stamp 36 performs during the first half cycle (FIG. 1, 2, 3) a cycloidal motion along the hologram carrier tape 13. During this same half cycle, the working diameter of cam member 38 does not change so that rocking member 16 does not pivot either. In consequence, stamp 36 uniformly presses the hologram carrier tape 13 against the card 12. 
     During the second half cycle, however, the operative diameter of cam member 38 changes so that the rocking member 16 is pivoted away from the support 10 by a predetermined angle, as seen in FIG. 4 and 5. 
     Stamp 36 is preferably heated by means of a temperature-controlled heating element housed in the stamp 36 and interchangeable together therewith.