Abstract:
An apparatus for joining two optical discs into a disc assembly having multiple layers of data has a disc processing chamber for supporting the first and second discs, wherein each of the discs has a layer of data on a first side thereof. The processing chamber is fluidly connected to a tank containing a bonding fluid. A vacuum pump is selectively connectable to the processing chamber and the tank for selectively evacuating air out of each. An actuator is operatively mounted within the processing chamber and supports the first disc. The actuator moves the first side of the first disc into contact with the first side of second disc after the processing chamber has been evacuated and a bonding fluid is placed on one of the first and second discs, thereby forming a disc assembly having multiple layers of data.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to optical disc manufacturing and more particularly, to the manufacture of multilayer optical discs. 
     Multilayer discs are now being produced that provide two or more layers of grooves or pits representing recorded or stored data or information. Such discs are generally manufactured by first producing two different discs, each having its own layer of recorded information on one side or surface of the disc. The two discs are then joined by applying an adhesive to one or both of the surfaces of the layers of recorded information and then bringing the discs together. The result is a disc having two adjacent layers of the different information in the middle of the disc in which the layers of information are separated by a transparent, intermediate bonding layer. Each of the two different layers is independently read by focusing a reading head of a laser on a layer of data to be read. Such multilayer discs are often used in DVD applications. 
     As can be appreciated, any air bubbles or other distortion in the intermediate layer of bonding fluid or adhesive can interfere with the reading of the layer of data or information behind the bonding layer, thereby potentially resulting in reading errors. Therefore, it is critical that the bonding layer be of a constant thickness and free of any air bubbles. Air bubbles can be formed in the process of storing, transferring or applying the bonding fluid or adhesive to the discs or, in the process of bringing the discs together after the adhesive has been applied. Several processes are known that attempt to eliminate air bubbles in the disc bonding process. For example, it is known to apply the bonding resin very slowly, so that air bubbles are not formed in the adhesive application process. In another process, the discs are spun at a high speed to remove air bubbles after the adhesive has been applied. In a further process, the discs are oriented and maintained in parallel as they are brought together in order to minimize the opportunity for air bubbles to form in the joining process. In still other processes, after the bonding adhesive is applied, the discs are moved to a vacuum chamber and brought together; and then, the discs are subjected to a high pressure environment in an autoclave. 
     While all of the above processes for removing air bubbles are successful, thereby improving the quality of the bonded disc, such processes achieve that success at the price of substantially increasing the processing time required to effect the bonding of the discs, or at the price of requiring additional expensive equipment, or both. Consequently, there is still a need for an improved process for joining optical discs with an intermediate layer of bonding fluid that reliably inhibits the formation of air bubbles and substantially reduces the time to implement the bonding process. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved process for joining optical discs with an intermediate layer of adhesive which eliminates the possibility of the formation of air bubbles. The process of the present invention permits a relatively fast disc bonding cycle while eliminating the formation of air bubbles. The process of the present invention has the advantage of providing the highest quality multilayer optical discs which are completely free of air bubbles. 
     According to the principles of the present invention and in accordance with the described embodiment, an apparatus for joining two optical discs into a disc assembly having multiple layers of data includes a disc processing chamber for supporting the first and second discs, wherein each of the discs has a layer of data on a first side thereof. The processing chamber is fluidly connected to a tank containing a bonding fluid. A vacuum pump is selectively connectable to the processing chamber and the tank for evacuating air out of each. An actuator is operatively mounted within the processing chamber and supports the first disc. The actuator moves the first side of the first disc into contact with the first side of second disc after the processing chamber has been evacuated and a bonding fluid is placed on one of the first and second discs, thereby forming a disc assembly having multiple layers of data. 
     In another embodiment, the present invention provides a method of using the above apparatus to evacuate the tank of air and thereafter transfer an inert gas into the tank. The two optical discs are then loaded into the processing chamber, and the processing chamber is evacuated of air. A bonding fluid is thereafter dispensed from the tank onto a data layer of one of the discs, and the discs are brought together so that the data layers are in juxtaposition with an intervening layer of bonding fluid. 
     These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a schematic block diagram of apparatus for joining two optical discs with a bonding fluid therebetween in accordance with the principles of the present invention. 
     FIG. 2 is a flowchart illustrating the method of operation of the apparatus of FIG.  1 . 
     FIG. 3 is a diametric cross-sectional view of a multilayer optical disc processed in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, the processing apparatus  20  includes a processing chamber  22  having an upper disc support  24  and a lower disc support  26 . A robotic device (not shown) is utilized in a known manner to load a first optical disc  28  having a first layer of data or information  30  onto the upper disc support  24 . The robotic device is also operable to load a second optical disc  32  having a second layer of information or data  34  onto the lower disc support  26 . With the current application, the discs are loaded in the processing chamber  22  to have a separation in the range of approximately 0.50 inches to approximately 0.75 inches or more. However, it should be noted that the magnitude of disc separation is not important to and totally independent of the successful practice of the present invention. Normally, a closer disc spacing is correlated to more efficient and faster cycle times. The processing chamber  22  also has a vent valve  35  which may be selectively opened to vent the processing chamber to atmosphere. 
     The upper disc support  24  preferably has a pneumatic vacuum chuck to secure the first disc  28  to the upper disc support  24 . The first disc  28  can alternatively be secured to the upper disc holder  24  by a mechanical locking system of a known design, for example, of the type in which a shaft expands into the center hole  38 , thereby securing the disc  28  to the upper disc support  24 . The upper disc support  24  is movable in a vertical direction by means of a cylinder  36  having a stroke of a length that the cylinder  36  may be used to lower the first disc  28  onto the second disc  32 . The cylinder  36  may be pneumatic or electric. 
     The lower disc support  26  includes a center spindle  40  extending through the center hole  42  of the second disc  32 . The spindle  40  preferably extends above the second layer  34  and thus, facilitates the accurate placement of the first disc  28  onto the second disc  32 . The lower disc support  26  is mechanically coupled to a pneumatic or electric motor  44  that rotates the lower disc support  26  and second optical disc  32  while a bonding fluid is being dispensed onto the disc  32 . 
     A bonding fluid or adhesive  47 , for example, an ultraviolet (“UV”) curable lacquer, is held within a tank  48 . A fluid conduit, for example, hard or flexible tubing,  50  carries the bonding fluid from the tank  48  to an input side of a dispensing valve  52 . The output side of the dispensing valve  52  is connected to a fluid conduit  54  that extends into the processing tank  22  and terminates with a fluid dispensing head  56 . The dispensing valve  52 , dispensing head  56  and connecting fluid conduit  54  function together as a fluid dispenser. The dispensing head  56  is supported by a robot arm or a pivot arm  58  that is powered by a pneumatic or electric motor  60 . The dispensing head  56  is supported by the robot arm  58  at a first, nondispensing position outside the peripheral boundaries of the discs  30 , 32 . The robot arm  58 , at the appropriate times, rotates or pivots the dispensing head  56  to a second, dispensing position, at which the dispensing head preferably extends radially between the discs  30 ,  32 . After dispensing the adhesive, the robot arm  58  then rotates the dispensing head back to the first position. A return fluid conduit  62  functions to return excess bonding fluid from the chamber  22  to the tank  48  through a return valve  64 . 
     A gas tank  66  provides a source of an inert gas, for example, helium, which is provided to the adhesive tank  48  by means of a fluid conduit or pipe  68  and a helium valve  70 . A vacuum pump  72  has an inlet  74  fluidly connected to a first port  78  of a 3-way vacuum valve  76 . The vacuum valve  76  has a second port  80  fluidly connected to the adhesive tank  48  by means of a fluid conduit  82 . The vacuum valve  76  has a third port  82  fluidly connected to one side of a process vacuum valve  84  by means of a fluid conduit  86 . The other side of the process vacuum valve  84  is connected to the processing chamber  22  by means of a fluid conduit  88 . 
     The processing chamber  22 , vacuum pump  72 , actuators  36 ,  44 ,  60  and the various valves  35 ,  52 ,  64 ,  70 ,  76 ,  84  are electrically connected to a controller  90 . The controller  90  can be implemented using any commercially available programmable logic controller such as those available from Allen Bradley, Modicon and others. The controller  90  is programmed to execute a serial sequence of logical operations and provides output signals via various valve and motor drivers to operate processing chamber  22 , vacuum pump  72 , actuators  36 ,  44 ,  60  and the various valves  35 ,  52 ,  64 ,  70 ,  76 ,  84  in such a manner as to perform the desired operation of the processing apparatus  20 . Generally, the output signals from the controller  90  are binary signals the states of which are operative to open or close a valve or solenoid or turn a motor pump or actuator on or off. 
     The main purpose of the processing apparatus  20  is to dispense a bonding fluid or adhesive free of air bubbles onto the upper surface of the upper directed layer  34  of the second optical disc  32  and thereafter, bring the layer  30  of the first optical disc  28  into contact with layer  34  of the second optical disc  32  such that the intermediate layer of bonding fluid continues to remain free of air bubbles. To achieve an air bubble free intermediate bonding layer, the adhesive tank  48  is evacuated and filled with an inert gas; and in addition, the bonding fluid is dispensed within an evacuated processing chamber  22 . 
     Referring to FIG. 2, the processing apparatus  20  first, at  202 , removes air from the tank  48 . To accomplish this, the controller provides output signals to maintain the helium valve  70 , the return valve  64 , the dispensing valve  52  in their initial or default, closed positions and the vent valve  35  to the processing chamber  22  in its open state. Further, output signals from the controller  90  cause the actuator  36  to maintain the upper disc support  24  in its illustrated upper position and the actuator  60  of the robot arm  58  to locate the dispenser  56  at its first default position outside the periphery of the upper disc support  24 . Further, output signals from the controller  90  turn the vacuum pump  72  on and move the three-way vacuum valve  76  to a position providing continuity between the ports  78 , 80 , thereby connecting the inlet  74  of the vacuum pump  72  to the adhesive tank  48 . The vacuum pump  72  then evacuates air from the adhesive tank  48 . 
     The controller  90  then determines that the tank  48  is evacuated to a proper less than atmospheric pressure, that is, a partial vacuum. The controller  90  achieves a desired evacuation pressure by evacuating the tank  48  with the pump  72  for a predetermined period of time as determined by a timing function within the controller  90 . Alternatively, the controller can monitor an output signal from a pressure sensor  73  in a pressure measuring relationship with the adhesive tank  48  and providing a signal representing the pressure in the tank  48  to the controller  90 . When the adhesive tank  48  is evacuated to the proper pressure, the controller  90  then provides an output signal to the valve  76  that switches the valve  76  to a state in which the ports  78 , 82  are connected within the valve, however, the closed state of the process vacuum valve  84  prevents the vacuum pump  72  from evacuating the processing chamber  22 . 
     The processing apparatus  20  next, at  204 , applies a helium blanket to the tank  48 . This is accomplished by the controller  90  providing output signals to open the helium valve  70  and also switch the three-way vacuum valve  76  such that the ports  78 ,  82  are connected within the valve  76 . Pressure from the helium tank  66  fills the evacuated space within the adhesive tank  48 , and after a predetermined period of time determined by a timer within the controller  90 , the controller provides an output signal causing the helium valve  70  to close. With an inert gas such as helium in the tank  48 , the probability of air bubbles forming in the bonding fluid within the tank and in its transfer to the processing chamber  22  is close to nil. 
     Thereafter, the processing apparatus  20 , at  206 , causes the discs  28 ,  32  to be loaded into the processing chamber  22 . The controller  90 , in a known manner, provides output signals to cause an access door  92  to open and a robot (not shown) to load the discs  28 ,  32  on the respective upper and lower disc supports  24 , 26 . Thereafter, the controller  90  provides output signals to cause the door  92  of the process chamber  22  to close. 
     Next, the processing apparatus  20 , at  208 , evacuates the processing chamber  22 . To effect this step, the controller  90  provides an output signal to open the process vacuum valve  84  which connects the interior of the processing chamber  22  to the inlet  74  of the vacuum pump  72 . The processing chamber  22  is evacuated to a desired pressure less than atmospheric pressure, that is, a partial vacuum, which is determined by the controller  90  either, by means of a passage of a period of time signaled by the expiration of an internal timer or, the detecting of a pressure value from a pressure transducer  75  connected in a pressure measuring relationship to the processing chamber  22 . 
     After the desired partial vacuum pressure in the processing chamber is achieved, the processing apparatus  20  then, at  210 , applies the bonding fluid to the upper layer  34  of the lower disc  32 . The controller  90  first provides an output signal to the motor  44  to initiate rotation of the lower disc support  26  and the lower disc  32 . In addition, an output signal is provided by the controller  90  to the motor  60  to cause the robot arm  58  and dispensing head  56  to rotate from the first position to a second, dispensing position at which the dispensing head  56  is generally above and directed radially with respect to the rotating lower disc  32 . The controller  90  then initiates a dispense timing cycle by activating a timer within the controller  90  and simultaneously providing an output signal to open the dispense valve  52 . The partial vacuum within the processing chamber  22  causes bonding fluid to be drawn from the tank  48 , through the conduit  50 , the dispensing valve  52 , the conduit  54  and out the dispensing head  56 . Dispensing the bonding fluid on the upper surface of the layer  34  of the disc  32  in combination with the rotation of the disc  32  causes the bonding fluid to distribute itself over the upper surface of the layer  34  of the lower disc  32 . Upon the internal dispensing timer timing out, the controller  90  changes the state of the output signal to the dispense valve  52 , thereby causing the dispense valve  52  to close. In addition, the controller  90  changes the states of the output signals to the motors  44 , 60 , thereby causing the motor  44  to stop the rotation of the lower support  26  and disc  32  and the robot arm  58  to return the dispensing head  56  back to its original first position. 
     Next, the processing apparatus  20 , at  212 , causes the upper disc  28  to be lowered onto the lower disc  32 . The controller  90 , therefore, provides an output signal to the cylinder  36  causing the cylinder to move the upper disc support  24  vertically downward until the upper disc  28  is contacting and resting on top of the lower disc  32  with the bonding fluid therebetween. When the cylinder  36  has reached the end of its downward stroke, the controller  90  provides an output signal to the device securing the upper disc  28  to the upper support  24  to cause the upper disc  28  to be released therefrom. For example, if the upper disc  28  is being held by a vacuum chuck, the controller  90  would provide an output signal to terminate the vacuum, thereby releasing the upper disc  28  from the upper support  24 . Alternatively, if the upper disc  28  is being held by a clamp in the center hole  30 , the controller  90  would provide an output signal to release the clamp, thereby permitting the disc  28  to drop onto the lower disc  32 . After releasing the upper disc  28  from the support  24 , the controller  90  then provides a further output signal to the cylinder  36  causing the cylinder to retract the upper support  24  to its original illustrated position. Thus, referring to FIG. 3, a multilayer disc assembly  96  is provided in which a first layer of data  30  of a first optical disc  28  is juxtaposed on top of a second layer of data  34  of a second optical disc  32  with an intervening layer  94  of bonding fluid or adhesive. 
     Next at  214 , the processing apparatus  20  vents the processing chamber  22 . To effect this, the controller  90  first provides an output signal to the process vacuum valve  84  causing the process vacuum valve to close and provides a further output signal to the vent valve  35  causing the vent valve to open, thereby releasing the partial vacuum and bringing the pressure within the processing chamber  22  to atmospheric pressure. Upon opening the vent valve  35 , the controller  90  also provides an output signal to the return valve  64  causing the return valve to open, thereby permitting excess bonding fluid to drain back into the tank 
     Thereafter, at  216 , the processing apparatus  20  causes the assembly of the upper and lower discs  28 ,  32  with the intervening layer  94  of bonding fluid to be removed from the processing chamber  22 . Thus, the controller  90  provides output signals to cause the door  92  to the processing chamber  22  to open and to command the robotic disc loader/unloader to remove the assembly of the upper and lower discs  28 , 32  with the intervening layer  94  of adhesive. The load/unload robotic device then loads two other optical discs onto the respective upper and lower supports  24 , 26  within the processing chamber  22  and provides further output signals to close the door  92 . The process of FIG. 2 as described with respect to process steps  208 - 216  is repeated, and thereafter, the process as described with respect to steps  206 - 216  is repeated to make additional disc assemblies. 
     The process of the apparatus  20  just described is effective to quickly and efficiently place the two discs  28 ,  30  in a contacting, bondable relationship with an intervening layer of bonding fluid  94  such that there are no air bubbles in the layer of bonding fluid  94 . 
     The discs are further processed in accordance with known steps, for example, the assembly of the two discs  28 ,  32  with the intervening layer of bonding fluid  94  are then spun at a high speed to provide a uniform layer  94  of bonding fluid at a consistent, desired thickness prior to being exposed to a flash of ultraviolet light for curing. 
     While the invention has been illustrated by the description of one embodiment, and while the embodiment has been described in considerable detail, there is no intention to restrict nor in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, with the illustrated embodiment, the bonding fluid is deposited on the lower one of the discs  32 ; however, as will be appreciated, the bonding fluid may be deposited on either or both of the discs  28 ,  32 . With the described embodiment, the tank  48  is evacuated and filled with an inert gas prior to the discs  28 ,  32  being loaded into the processing chamber  22 ; however, consistent with the present invention, the discs  28 ,  32  may be loaded into the processing chamber  22  prior to the tank  48  being evacuated and filled with an inert gas. 
     Further, the high speed spinning of the assembly of the two discs  28 , 32  with the intervening layer of bonding fluid  94  is performed with a separate apparatus outside the processing chamber  22 . As will be appreciated, the processing chamber  22  may be designed to provide that high speed spinning process. Further, within the processing chamber  22 , the spinning process may occur either under a partial vacuum or at atmospheric pressure. Likewise, it is also within the scope of the invention that the processing chamber  22  may be designed to include a station for exposing the intervening layer of bonding fluid  94  to the ultraviolet light. 
     The described embodiment includes a return valve  62  located between the processing chamber and the tank  48 . As will be appreciated, a return manifold may also be utilized in which return fluid is collected prior to its release into the tank  48 . With such an arrangement, the return manifold may include return valves at both ends of the manifold. 
     The described embodiment utilizes a single vacuum pump  72  and a vacuum valve  76  connected to the tank  48  and the processing chamber  22  to selectively apply a vacuum thereto. As will be appreciated, the processing chamber  22  and the tank  48  may each be connected to a separate vacuum pump, and thus, with two vacuum pumps the vacuum valve  76  can be eliminated. 
     Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.