Abstract:
In a method and apparatus for making bonded discs, at least one of two substrates is coated with adhesive and positioned in a transfer station. A central handling system grabs the substrates from the transfer station and deposits them a joining station for subsequent bonding. The central handling system includes a carousel having gripper arms which are moved by the carousel horizontally and/or vertically into a number of indexing positions, wherein at least one gripper arm has two gripper elements arranged behind one another in radial direction. After bonding, the joining station is opened and the joined disc is withdrawn and subjected to an inspection. Handling of the substrates and the joined disc is realized in a circular manner for transport along two concentric circular paths of different diameter, thereby defining an inner circle and an outer circle, with one substrate transported on the inner circle and the other substrate transported on the outer circle.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims the priority of German Patent Application, Ser. No. 102 43 663.0-53, filed Sep. 20, 2002, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates, in general, to a method and apparatus for making bonded discs of two substrates, in particular for making DVDs (DVD audio, DVD video, DVD-R, DVD-D and other DVD formats), UDOs (Ultra Density Optical) discs or blueray discs or other types of optical data carriers.  
         [0003]     In producing a DVD, UDO or blueray disc two substrates are bonded to obtain a finished optical data carrier. Both substrates are hereby made in an injection molding machine, transferred to one or more metallizing stations in correspondence to the format of the respective data carrier, for application of one or more metal coatings, and immediately thereafter or following a temporary storage of both substrates supplied to a bonding station. The substrates pass in the bonding station initially an adhesive application station in which one or both substrates to be joined together are coated with an appropriate adhesive. Subsequently, the substrates are advanced to one or more joining stations in which the substrates are placed upon one another and bonded together. Examples of adhesives used by adhesive application station typically include hot melt, molten hot-melt adhesive, or a liquid, normally low-viscous UV-curing adhesive. Hot-melt adhesive is applied by a roller system equipped with a doctor blade, whereby the substrates move side-by-side or in sequence under the doctor blade. The UV-curing adhesive is applied by a metering needle onto one or both substrates. The substrates are joined together in the joining station and the adhesive is cured. In the case of the UV-curing adhesive, the application of UV radiation is additionally needed.  
         [0004]     European Pat. No. EP 0 735 530 A1 discloses a bonding station in which two DVD substrates are initially moved side-by-side to an adhesive application station of the hot melt type. Once the adhesive has been supplied, one of the substrates (substrate A) is transported to a station in which a UV-curable adhesive is filled in a recess of the substrate. The other substrate (substrate B) is then transferred from a substrate transfer device (so-called pick-and-place tool) to a turning device, also called flip station, and rotated there by 180°, so that the side of the substrate having the applied adhesive faces downwards. This substrate is then moved by the turning device over the first substrate and stacks it thereon. The so-joined DVD substrates are seized by a further pick-and-place tool and placed in a press where both joined DVD substrates are pressed together under pressure to make the finished DVD. Pressure application is implemented in a vacuum chamber having a bottom part with a glass window which is transparent to UV-radiation so that the DVD can be irradiated with ultraviolet for curing the UV-curing adhesive in the recess. Subsequently, the finished DVD can be extracted from the press station. Normally, the DVDs are then carried onto a quality inspection station to check for defects and, depending on the inspection, placed onto spindles for acceptable products (spindles for good parts, called “good-item spindles”) or onto spindles for parts of poor quality (called “bad-item spindles”). This type of conventional bonding station has many drawbacks. Since the DVD substrates are transported through the bonding station side-by-side before being joined together, there is a great demand for space. Moreover, the bonding station requires the use of several pick-and-place tools between the stations for adhesive application, joining, pressing and quality inspection. Each pick-and-place tool requires space so that again the demand for space is great. Also, as the transport devices and the pick-and-place tools must be synchronized to one another during operation to provide the joining station with an A substrate and a B substrate in the correct production cycle, possibly simultaneously, the electronic control and the software become complex in order to accomplish a proper interaction of the mechanical components in the correct production cycle. Further, the roller system in the hot-melt adhesive application station has to be sized wide enough to enable a simultaneous coating of both substrates A and B with adhesive. As the doctor blade becomes slightly bent hereby during application of the adhesive onto the neighboring substrates, the adhesive is applied at an uneven pressure onto the substrates. The pressure is higher in the middle of the doctor blade than at the margins so that the substrates are coated unevenly with adhesive, leading to unbalances during bonding of the substrates.  
         [0005]     International publication no. WO 01/63605 A1 discloses a bonding station which applies a hot-melt adhesive by a roller system with a doctor blade onto the DVD substrates, whereby the DVD substrates are transported to the adhesive application station in a row behind one another (A-B-A-B-A-B- . . . ). After leaving the adhesive application station, the substrates coated with adhesive are simultaneously seized by a tandem gripper and transferred to one of two joining stations. The joining stations are made of two closeable halves, with one half forming the bottom part and the other half forming the lid. The A substrate is placed in one half and the B substrate is placed in the other half. The substrates are suitably fixed and centered in both halves, e.g. on vacuum plates with centering pins. Subsequently, the lid part is moved onto the bottom part and both halves form a chamber which can be evacuated. The substrates A and B are joined together in this chamber and subjected to additional pressure to compress them. After the hot-melt adhesive has cured, the chamber can be opened and the finished DVD can be removed by a pick-and-place tool. Then, the DVD undergoes a quality inspection, normally a scanner, and is deposited, in dependence on the result of the inspection, onto a spindle for acceptable items (good-item spindle) or a spindle for unacceptable item (bad-item spindle). This bonding station has the drawback that after the adhesive application, several gripper systems, such as tandem gripper and a pick-and-place tool, are needed during transfer to the individual work stations. These gripper systems require a large operating area in the bonding station. Moreover, the movements of the tandem gripper and the pick-and-place tool must be synchronized to suit the production cycle.  
         [0006]     European Pat. Nos. 0 791 666 A2 and 0 791 667 A2 disclose the provision of a central handling system implemented as turntable which has several gripper arms with gripper elements for receiving, holding and depositing substrates. The gripper arms have a same radial length and are mounted in a plane at a certain angle relative to one another to the turntable. Thus, the gripper elements are disposed on a circle with a certain radius. Arranged on the circle are various transfer and processing stations. Through vertical movement of the turntable, the substrates can be lifted from or deposited on the respective transfer or processing station. As the turntable rotates, the individual gripper arms are moved in circumferential direction to transport the substrates from station to station. One of the gripper arms may be moved separately in circumferential direction in relation to the simultaneous movement of the remaining gripper arms so as to allow this gripper arm to target alternatingly two stations situated on a circle, typically the good-item spindle, on the one hand, and the bad-item spindle, on the other hand. This type of central handling system is unsuitable for bonding DVD substrates, because there are no provisions to transport two DVD substrates in suitable manner or to allow simultaneous grabbing of two substrates in a transfer station and to deposit them in a joining station.  
         [0007]     It would therefore be desirable and advantageous to provide an improved method and apparatus for making bonded discs, to obviate prior art shortcomings and to enable a bonding of DVD substrates in a simple manner within minimum space requirements and short cycle periods.  
       SUMMARY OF THE INVENTION  
       [0008]     According to one aspect of the present invention, a method of making bonded discs, in particular optical data carriers such as DVD, UDO disc or blueray disc, includes the steps o producing two substrates, coating at least one of the substrates with an adhesive, placing the substrates in standby position in a transfer station, transporting the substrates from the transfer station to a joining station, depositing the substrates in the joining station, bonding the substrates, opening the joining station and withdrawing the joined disc, inspecting the joined disc for compliance with quality standards, and placing the disc on a stack of acceptable discs or on a stack or rejected discs in dependence on the outcome of the inspection, wherein the substrates and the joined disc are handled in a circular manner for transport along two concentric circular paths of different diameter, thereby defining an inner circle and an outer circle, with one substrate transported on the inner circle and the other substrate transported on the outer circle.  
         [0009]     In this way, several processing stations can be targeted within a shortest possible time and operated simultaneously. This has a positive effect on the cycle period.  
         [0010]     According to another feature of the present invention, at least one of the substrates can be metallized before executing the adhesive application step.  
         [0011]     According to another aspect of the present invention, an apparatus for making bonded discs of two substrates, in particular for making optical data carriers such as DVD, UDO disc or blueray disc, includes an adhesive application station for coating at least one of the substrates with an adhesive; a plurality of processing stations, disposed downstream of the adhesive application station, for further handling the substrates, said processing stations arranged about a circle and including a transfer station for placing the substrates in a standby position for further processing, at least one joining station for joining and bonding the substrates to produce a finished disc, at least one quality inspection station for checking the disc for acceptance or rejection, a first delivery station for receiving the disc, when the disc is acceptable, and a second delivery station for receiving the disc, when the disc is unacceptable; and a central handling system in the form of a carousel which includes a plurality of gripper arms and is constructed to move the gripper arms in horizontal and/or vertical direction into a number of indexing positions, wherein a first type of the gripper arms has two gripper elements arranged behind one another in radial direction so as to enable the second gripper arm to sweep with the gripper elements over two concentric circles of different diameter, when the gripper arms are moved in circumferential direction.  
         [0012]     According to another feature of the present invention, the two gripper elements of the second gripper arm have a distance from another to allow a simultaneous seizing of the substrates.  
         [0013]     As alternative, or in addition thereto, the carousel may have a gripper arm constructed for telescopic movement in radial direction or including a part that moves in radial direction.  
         [0014]     According to another feature of the present invention, there may be provided one or more additional joining stations, wherein each of the joining stations is comprised of two halves which are provided for receiving the substrates and configured to open up and close, wherein the joining stations are so positioned that their halves extend behind one another, when the halves are in open position, with one half situated on the inner one of the two concentric circles and the other half situated on the outer one of the two concentric circles.  
         [0015]     According to another feature of the present invention, the first and second gripper arms number a total of five gripper arms which are positioned in spaced-apart relationship in such a manner that four gripper arms are spaced from one another at an angle of 60° and two gripper arms are spaced from one another at an angle of 120°.  
         [0016]     According to another feature of the present invention, the processing stations are disposed on a circle in spaced-apart relationship at an angle of 60°, whereby the carousel is indexed to rotate the gripper arms in clockwise direction as well as counterclockwise direction to pause by these processing stations as well as to pause in neutral in-between positions.  
         [0017]     Depending on the DVD to be produced, it may be necessary to supply so-called dummy substrates, i.e. uncoated substrates, or spacers to the central handling system. Spacers are necessary when the DVD is configured without stacking blocks to maintain stacked DVDs at a distance on the spindles.  
         [0018]     According to another feature of the present invention, the drive of the carousel may be constructed to move the first and second gripper arms in the horizontal direction, and there may be a further drive for separately moving the first and second gripper arms in the vertical direction. In this way, the flexibility of the bonding station can be enhanced.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0019]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0020]      FIG. 1  is a schematic top plan view of one embodiment of an apparatus for making bonded discs in accordance with the present invention, showing a central handling system with gripper arms positioned in the processing stations;  
         [0021]      FIG. 2  is a schematic top plan view of the apparatus for making bonded discs, showing the central handling system with the gripper arms in neutral position between the processing stations;  
         [0022]      FIGS. 3 . 1 - 3 - 24  are schematic top plan view of the apparatus according to the invention, showing the operation and process sequence of the components of the apparatus;  
         [0023]      FIG. 4  is a schematic illustration of a central handling system with modified gripper arms;  
         [0024]      FIG. 5  is a schematic illustration of a central handling system with a further variation of gripper arms; and  
         [0025]      FIG. 6  is a schematic top plan view of another embodiment of an apparatus for making bonded discs in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0027]     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic top plan view of an apparatus for making bonded discs in accordance with the present invention, generally designated by reference numeral  1  and being referred to in the following as hot-melt bonder. The hot-melt bonder  1  includes a substrate reservoir  2 , which contains substrates A and B, a linear guide  3  which receives the substrates A, B from the reservoir  2  and moves them to a central handling system  4  two vacuum joining stations  5 ,  6 , a quality inspection station  7  including, e.g. a scanner, a turntable  8  with six stacking spindles  9  arranged in spaced-apart relationship along a circle and intended for receiving acceptable finished discs (referred to in the following as “good-item spindles”), a flip station  10  as well as a spindle  11  for receiving unacceptable finished discs (referred to in the following as “bad-item spindles”). The linear guide  3  can be implemented, e.g. by a walking beam or, as shown in  FIG. 1 , may include round cord belts  14 ,  15  which are trained about rollers  12 ,  13 . The rollers  12 ,  13  are rotatably mounted in a frame with side walls  16 ,  17  and operated by a drive unit (not shown). Situated at a position along the linear guide  3  is an adhesive application station  18  by which the substrates can be coated with a molten hot-melt adhesive or an UV-curing adhesive. A substrate transfer station  19  is positioned downstream of the adhesive application station  18  and includes centering pins (not shown), which can move in vertical direction for lifting the substrates A, B from the belts  14 ,  15  upwards to a standby position in which the substrates A, B are ready for transfer to the central handling system  4 .  
         [0028]     As shown in  FIG. 1 , the central handling system  4  includes a carousel  20  which is adapted to index, or steppingly rotate about a vertical rotation axis  21  clockwise as well as counterclockwise and movable in vertical direction by a suitable drive assembly (not shown). The carousel  20  includes four gripper arms  22 ,  23 ,  24 ,  25  and one gripper arm  26  which can move in vertical direction as well as horizontal direction, in particular in circumferential direction, whereby the gripper arms  22 ,  23 ,  24 ,  25  are shorter than the gripper arm  26 . At their end distal to the carousel  20 , the gripper arms  22 ,  23 ,  24 ,  25 , are provided with gripper elements  27 ,  28 ,  29 ,  30 , respectively, and the gripper arm  26  is provided with gripper elements  31 ,  32 , whereby the gripper elements  27 ,  28 ,  29 ,  30 ,  31 ,  32  may be constructed, e.g., as vacuum suction units. The gripper elements  27 ,  28 ,  29 ,  30 ,  31  of the gripper arms  22 ,  23 ,  24 ,  25 ,  26  are disposed in spaced apart relationship along a circle with a diameter R 1 , whereas the gripper element  32  of the gripper arm  26  is disposed on a circle with a diameter R 2  which is greater than R 1  and dimensioned enough to enable both substrates A, B to be transported along the two circles without touching one another.  
         [0029]     The vacuum joining stations  5 ,  6  have each two halves  33 ,  34  which can be moved into an open position and moved into a closed position and which are arranged in relation to the carousel  20  in such a manner that the half  33  is situated on the inner circle and the half  34  is situated on the outer circle. In this way, the substrates A, B can be placed simultaneously in both halves  33 ,  34  of the joining stations  5 ,  6 . The mode of operation of the joining stations  5 ,  6  is generally known to the artisan (e.g. International publication no. WO 01/63605 A1) so that a further discussion thereof is omitted for the sake of simplicity.  
         [0030]     The substrate transfer station  19 , the vacuum joining stations  5 ,  6 , the quality inspection station  7 , one good-item spindle  9  as well as the substrate receiving point of the flip station  10  are arranged along a circle in six positions that are separated by one another by a 60° angle. The five gripper arms  22 ,  23 ,  24 ,  25 ,  26  are arranged on the carousel  20  in spaced apart relationship such that four 60° angles and one 120° angle are defined, whereby the bisecting line  35  of the 120° angle is in alignment with the center line of the long gripper arm  26 .  
         [0031]      FIG. 1  shows each gripper arm  22 ,  23 ,  24 ,  25 ,  26  of the carousel  20  in an operative position in which each gripper arm  22 ,  23 ,  24 ,  25 ,  26  is disposed in one processing station. In contrast thereto,  FIG. 2  shows the gripper arms  22 ,  23 ,  24 ,  25 ,  26  in a neutral position in which the gripper arms  22 ,  23 ,  24 ,  25 ,  26  are rotated clockwise by 90° and situated between the processing stations. The gripper arms  22 ,  23 ,  24 ,  25 ,  26  thus assume a mid-position between the 60° positions of the processing stations. This neutral position of the gripper arms  22 ,  23 ,  24 ,  25 ,  26  will subsequently be referred to as 30°-position.  
         [0032]     The mode of operation of the apparatus according to the invention will now be described in more detail with reference to  FIGS. 3 . 1 - 3 . 24 . For sake of simplicity, it is assumed that the gripper arms  22 ,  23 ,  24 ,  25 ,  26  are moved by the carousel  20  in a vertical movement for grabbing and depositing the substrates A, B so that this movement will not be referred to when explaining the various process steps.  
         [0033]     In  FIG. 3-1 , all substrates A, B are still retained in the substrate reservoir station  2 . The gripper arms  22 ,  23 ,  24 ,  25 ,  26  are positioned in such a manner than the long gripper arm  26  with its two gripper elements  31 ,  32  is caused to halt over the substrate transfer station  19 . When transferred to the substrate transfer station  19 , the two substrates A 1 , B 1  are picked up by the gripper elements  31 ,  32  of the long gripper arm  26 . This is shown in  FIG. 3-2 . After clockwise rotation of the gripper arms  22 ,  23 ,  24 ,  25 ,  26  by 120°, the substrates A 1 , B 1  are deposited in the joining station  6 , as shown in  FIG. 3-3 . Subsequently, the carousel  20  rotates by 30° counterclockwise so that the joining station  6  is cleared and the inner half  33  can be pivoted onto the outer half  34  to shut the joining station  6 , as shown in  FIG. 3-4 . While both substrates A 1 , B 1  are joined and bonded to form a disc AB 1 , the next two substrates A 2 , B 2  are removed from the substrate reservoir  2  and placed on the centering pins of the substrate transfer station  19  to assume the standby position. The carousel  20  turns by 30° counterclockwise to halt the gripper arms  22 ,  23 ,  24 ,  25 ,  26  over the respective 60° processing stations. This is shown in  FIG. 3-5 . The carousel  20  now turns counterclockwise by 60°, thereby halting the long gripper arm  26  over the substrates A 2 , B 2 , as shown in  FIG. 3-6 . The gripper elements  31 ,  32  take the substrates A 2 , B 2  from the centering pins, and the carousel  20  rotates counterclockwise by 120° so that the substrates A 2 , B 2  are positioned in the joining station  5  for production of disc AB 2 , as shown in  FIG. 3-7 , whereby substrate A 2  is deposited in the inner half  33  and the substrate B 2  is deposited in the outer half  34 . Subsequently, the carousel  20  is indexed further clockwise by 30° to move the gripper arms  22 ,  23 ,  24 ,  25 ,  26  into the neutral position, shown in  FIG. 3-8 , to enable a closing of the joining station  5 . Thus, both joining stations  5 ,  6  are now closed.  
         [0034]     Next, the carousel  20  is indexed by 30° clockwise to halt the gripper arms  22 ,  23 ,  24 ,  25 ,  26  again in the 60° processing stations and the joining station  6  is opened. This stage is shown in  FIG. 3-9 .  
         [0035]     Next, the carousel  20  rotates clockwise by 60° to position the long gripper arm  26  over the new substrates A 3 , B 3 , which have been moved in the meantime to the standby position on the centering pins of the substrate transfer station  19 , while the short gripper arm  24  is halted over the previously bonded disc AB 1 . Thus, the substrates A 3 , B 3  as well as the disc AB 1  can now be handled by the central handling system  4 , as shown in  FIG. 3-10 . The carousel  20  is then indexed or rotated clockwise by 120° to cause the long gripper arm  26  to move the substrates A 3 , B 3  into the previously cleared joining station  6 , while the short gripper arm  24  moves the bonded disc AB 1  into a parking position adjacent the closed joining station  5  ( FIG. 3-11 ). After depositing the substrates A 3 , B 3  into the respective halves  33 ,  34  of the joining station  6 , the carousel  20  is rotated counterclockwise by 30° to move the gripper arms  22 ,  23 ,  24 ,  25 ,  26  into the neutral position, as shown in  FIG. 3-12 . Thus, the space above the inner half  33  of the joining station  6  is cleared so that the half  33  can be flipped over the outer half  34  to close the joining station  6  and to execute the joining and bonding operations to produce disc AB 3 .  
         [0036]     The carousel  20  is then indexed counterclockwise by 30° to move the gripper arms  22 ,  23 ,  24 ,  25 ,  26  to the respective 60° processing stations, whereby the gripper arm  24  with the bonded disc AB 1  is halted adjacent the quality inspection station  7 . At the same time, the joining station  5  is opened and the previously bonded disc AB 2  is readied in the inner half  33  for further processing. This stage is shown in  FIG. 3-13 . After depositing the disc AB 1  in the quality inspection station  7 , the carousel  20  is rotated counterclockwise by 60° so that the long gripper arm  26  is again positioned in the substrate transfer station  19  to take new substrates A 4 , B 4 , which have been placed on the centering pins in the meantime. At the same time, the short gripper arm  23  removes the bonded disc AB 2  from the joining station  5  ( FIG. 3-14 ). Next, the carousel  20  is indexed to move the substrates A 4 , B 4  to the thus cleared joining station  5  for placement into the halves  33 ,  34 , while the disc AB 2  is parked adjacent the joining station  6 , as shown in  FIG. 3-15 . The short gripper arm  22  is hereby halted adjacent the quality inspection station  7  to pick up the inspected disc AB 1 .  
         [0037]     Subsequently, the carousel  20  is indexed clockwise by 30° to move the gripper arms  22 ,  23 ,  24 ,  25 ,  26  into the neutral position between the processing stations so that the space above the joining station  5  is cleared to enable the inner half  33  to move over the outer half  34  ( FIG. 3-16 ). At the same time, new substrates A 5 , B 5  are moved to the substrate transfer station  19 .  
         [0038]     The carousel  20  is now rotated clockwise by 30° so that the disc AB 2  can be carried onto the quality inspection station  7 , while the previously inspected disc AB 1  is held in the joining station  5 . The joining station  6  is opened again, with the produced disc AB 3  readied in the inner half  33  for subsequent transfer. This stage is shown in  FIG. 3-17 .  
         [0039]     Subsequently, the carousel  20  is indexed clockwise by 60° so that the disc AB 1  is positioned by the gripper arm  22  over the good-item spindle  9 , while the long gripper arm  26  is halted over the substrates A 5 , B 5  and the short gripper arm  24  has reached the joining station  6 . When disc AB 1  has passed inspection and is considered acceptable, the disc AB 1  is stacked on the good-item spindle  9 , as shown in  FIG. 3-18 . In the event, disc AB 1  has failed the inspection and is considered unacceptable, the gripper arm  22  holds on to the disc AB 1  ( FIG. 3-19 ). The carousel  20  is then rotated clockwise by 120° so that the previously bonded disc AB 3  is withdrawn from the joining station  6  and moved to the still closed joining station  5 , while the substrates A 5 , B 5  are deposited in the joining station  6  ( FIG. 3-20 ). The inspected disc AB 2  can be removed by the gripper arm  25  from the quality inspection station  7 . If disc AB 1  has previously been considered unacceptable, the gripper arm  22  now drops the disc AB 1  in the flip station  10  for subsequent transfer to the bad-item spindle  11  for unacceptable discs.  
         [0040]     In the next step, the carousel  20  is indexed counterclockwise by 30° to move the gripper arms  22 ,  23 ,  24 ,  25 ,  26  into their neutral position so that the joining station  6  can now be closed to join and bond the substrates A 5 , B 5  to form disc AB 5 , as shown in  FIG. 3-21 . This position corresponds to the one shown in  FIGS. 34 and 3 - 12 , with the difference that now the gripper arm  24  holds a not yet inspected disc, i.e. the disc AB 3 , while the gripper arm  25  holds an inspected disc, namely disc AB 2 . Next, the carousel  20  is rotated counterclockwise by 30° so as to assume again the 60° positions ( FIG. 3-22 ). The disc AB 3  is hereby deposited in the quality inspection station  7 , while the inspected disc AB 2  is positioned adjacent the joining station  6 . At the same time, the joining station  5  is opened and the bonded disc AB 4  is ready in the inner half  33  for subsequent transfer. The carousel  20  is now rotated counterclockwise by 60° so that the long gripper arm  26  is moved into the substrate transfer station  19  to pick up new substrates A 6 , B 6 , as shown in  FIG. 3-23 . The gripper arm  23  is halted over the joining station  5  to grab the disc AB 4 . In this position, the finished and inspected disc AB 2  is situated in the flip station  10 . In the event, disc AB 2  has been considered “bad”, it is dropped into the flip station  10 . Otherwise, if considered “good”, the gripper arm  25  holds on to the disc AB 2 .  
         [0041]     Next, the carousel  20  is indexed counterclockwise by 120°, as shown in  FIG. 3-24 . In this indexed position, the substrates A 6 , B 6  are deposited in the cleared joining station  5 . As the gripper arm  25  with disc AB 2  is now above good-item spindle  9  and stacks the disc AB 2  there, if previously considered “good” in the quality inspection station  7 . The position of the carousel  20  in  FIG. 3-24  corresponds to the position shown in  FIG. 3-7 . Thus, steps  3 - 8  to  3 - 23  repeat now for a new cycle. Thus, the arrival of a finished disc to the good-item spindle  9  and of a finished disc to the bad-item spindle  11  alternates. Depending on the inspection outcome, the finished disc is then either stacked on the respective spindle or carried on further by the next 120° step and then stacked on the respective spindle.  
         [0042]     Turning now to  FIG. 4 , there is shown a schematic illustration of a central handling system  4  with a modified gripper arm, here gripper arm  24  positioned in opposition to the gripper arm  22 . The gripper arm  24  has a fixed arm part  24   a , which is secured to the carousel  20 , and a telescoping arm part  24   b  which moves radially in relation to the arm part  24   a . The movement of the arm part  24   b  may be implemented by constructing the arm part  24   a  as cylinder of a piston-cylinder unit, while the telescoping arm part  24   b  represents the piston rod of the piston-cylinder unit and has one end connected to a piston  36 . As an alternative, the gripper arms  22 ,  23 ,  24 ,  25 ,  26  may all be fixed in radial direction, the carousel  20  may include additional gripper arms with telescoping feature.  
         [0043]      FIG. 5  shows, by way of example, a schematic illustration of a modified construction of a gripper arm, here gripper arm  26 , which is configured to extend through a vertical support post  20   a  of the carousel  20  and is formed with a splined portion  36  for engagement with a driven gear  37 . Any of the gripper arms  22 ,  23 ,  24 ,  25 ,  26  may be constructed in this manner, or, optionally, an additional gripper arm may be provided on the carousel  20  with such construction.  
         [0044]     Referring now to  FIG. 6 , there is shown a schematic top plan view of another embodiment of an apparatus for making bonded discs in accordance with the present invention. Parts corresponding with those in  FIG. 1  are denoted by identical reference numerals and not explained again. The description below will center on the differences between the embodiments. In this embodiment, provision is made for a second linear guide  3   a  having two side walls  16 ,  17  and two rollers  12 ,  13  disposed between the side walls  16 ,  17 . One of the rollers  12 ,  13  is driven, and a belt  36  is wrapped around the rollers  12 ,  13  for supply of, for example, uncoated substrates  37  or spacers  38  into the production process. The spacers  38  may be placed in good-item spindles  9  between the finished discs to maintain them at a distance and thus to prevent damage.  
         [0045]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. For example, is, of course possible, to use adhesives other than hot melt, and/or to use joining stations of different configuration commensurate with the adhesive being used. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.  
         [0046]     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and their equivalents: