Patent Publication Number: US-2012024233-A1

Title: Conveyor Assembly with Releasable Drive Coupling

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to the field of conveyors, and more particularly to an improved conveyor drive system for use in thin film deposition systems wherein a thin film layer, such as a semiconductor material layer, is deposited on a substrate conveyed through the module. 
     BACKGROUND OF THE INVENTION 
     Thin film photovoltaic (PV) modules (also referred to as “solar panels”) are gaining wide acceptance and interest in the industry, particularly modules based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components. Solar energy systems using CdTe PV modules are generally recognized as the most cost efficient of the commercially available systems in terms of cost per watt of power generated. However, the advantages of CdTe not withstanding, sustainable commercial exploitation and acceptance of solar power as a supplemental or primary source of industrial or residential power depends on the ability to produce efficient PV modules on a large scale and in a cost effective manner. 
     The ability to process relatively large substrates on an economically sensible commercial scale is thus a crucial consideration and, in this regard, down time of the deposition modules for maintenance and repair should be minimized. Maintenance on the module conveyor typically requires disconnecting the drives from the conveyors, which can be a tedious and timely exercise. Subsequent alignment of the drives with the conveyor components can also be problematic. Diagnosing problems with the module drives while the units are under operating temperature and vacuum conditions can also be difficult. In addition, the life of the conveyor drives can be significantly shortened by transmission of the tremendous heat generated in the deposition module to the externally mounted drive components, which also results in down time of the system to replace the components. 
     Accordingly, there exists an ongoing need for deposition modules with improved drive systems that reduce maintenance/repair down time, as well as address other disadvantages noted above. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In accordance with aspects of the invention, a module is provided for a system wherein a sublimated source material is deposited as a thin film on a substrate conveyed through one or more of the modules. In a particular embodiment, the module is a vapor deposition module configured for deposition of a thin film of photo-reactive material on a PV substrate. The module may also be one or more of the modules in the system that conveys the substrate to and from the deposition module. The module includes a drive unit mounted on an exterior wall of the module, with the drive unit having a drive shaft that extends into the module. A conveyor is operably disposed within the module and is configured to be driven in a conveying path by the drive unit. For example, in a particular embodiment, the conveyor is driven in an endless loop path between opposite sprockets within the module. A releasable drive coupling is configured between the drive unit and a drive member of the conveyor, which may be a sprocket shaft. The drive coupling has a first end that releasably engages the drive shaft and a second end that releasably engages the conveyor drive member. The drive coupling includes a torque member and at least one thermal shield spaced concentrically around the torque and extending axially between the first and second ends. 
     In a particular embodiment, the torque member includes an innermost torque transmission tube and a plurality of the concentric thermal shields disposed around the torque transmission tube. 
     The drive coupling may be axially movable along at least one of the drive shaft or conveyor drive member for disconnecting and removal of the drive coupling. A releasable locking device may be provided for axially fixing the drive coupling relative to the drive shaft and conveyor drive member. 
     To accommodate some degree of misalignment between the drive unit and conveyor drive member, a particular embodiment may include a partially rounded interface between the first end of the drive coupling and the drive shaft and between the second end of the drive coupling and the conveyor drive member. 
     In an embodiment wherein the conveyor is driven in an endless loop path between opposite sprockets, a selectively actuatable clutch may be operably configured between the drive unit and drive shaft. Another respective drive unit with associated clutch and drive coupling may be configured with a shaft on the opposite sprocket. The clutches may be operably interfaced so that the clutches cannot be simultaneously engaged. For example, the clutches may be pneumatic clutches with a controllable three-way valve disposed between an air source and the clutches, wherein the valve permits actuating airflow to only one of clutch at a time. 
     In still another embodiment, a deposition module is provided wherein a sublimated source material is deposited as a thin film on a substrate conveyed through said module. The module includes a conveyor operably disposed within the module to be driven in an endless loop path between opposite sprockets, with at least one of the sprockets being a drive sprocket. A drive unit is mounted on an exterior wall of the module for each of the sprockets, with each of the drive units having a drive shaft that extends into the module. A releasable drive coupling is configured between each drive unit and respective sprocket. The drive coupling includes a first end that releasably engages the drive shaft and a second end that releasably engages the drive sprocket. A selectively actuatable clutch is configured between each drive unit and respective drive shaft, with the clutches operably interfaced so that the clutches cannot be simultaneously engaged. 
     In a unique embodiment, the deposition module includes a conveyor housing disposed within the module, with the conveyor and sprockets configured within the conveyor housing. The conveyor housing may be removable from the module upon disconnecting the drive coupling from the drive shafts and sprockets. 
     Variations and modifications to the embodiments of the deposition module discussed above are within the scope and spirit of the invention and may be further described herein. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       A full and enabling disclosure of the present invention, including the best mode thereof, is set forth in the specification, which makes reference to the appended drawings, in which: 
         FIG. 1  is a plan view of a vapor deposition system that may incorporate one or more modules in accordance with aspects of the present invention; 
         FIG. 2  is a perspective view of a module; 
         FIG. 3  is a perspective view of the conveyor assembly from the module of  FIG. 2 ; 
         FIG. 4  is a more detailed perspective view of the components of the conveyor assembly of  FIG. 3 ; 
         FIG. 5  is a side view of an embodiment of a drive coupling for use in a conveyor assembly; 
         FIG. 6  is a perspective view of the drive coupling of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of the drive coupling of  FIG. 6 ; 
         FIG. 8  is a perspective view of a drive shaft; and, 
         FIG. 9  is an assembled view of a drive coupling between a motor drive shaft and sprocket drive shaft. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention encompass such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  illustrates an embodiment of a vapor deposition system  10  that may incorporate one or more modules  100  in accordance with aspects of the invention. The system  10  is configured for deposition of a thin film layer on a photovoltaic (PV) module substrate  14  (referred to hereafter as “substrate”). The thin film may be, for example, a film layer of cadmium telluride (CdTe). Although the invention is not limited to any particular film thickness, as mentioned, it is generally recognized in the art that a “thin” film layer on a PV module substrate is generally less than about 10 microns (μm). 
     For reference and an understanding of an environment in which the present modules  100  may be used, the system  10  of  FIG. 1  is described below, followed by a more detailed description of a particular module  100 . It should be appreciated that the modules  100  with uniquely configured conveyor drives  102  in accordance with aspects of the invention are not limited to use in the system  10  illustrated in  FIG. 1 , but may be incorporated into any suitable processing line configured for vapor deposition of a thin film layer onto a substrate  14 . 
     Referring to  FIG. 1 , the exemplary system  10  includes a vacuum chamber  12  defined by a plurality of interconnected modules  100 , one or more of which include a drive unit  102  for providing rotational drive to an internal conveyor  48 . Any combination of vacuum pumps  40  may be configured with the interconnected modules to draw and maintain a vacuum effective for the deposition process within the chamber  12 . Certain of the modules  100  are interconnected heater modules  16  that define a pre-heat section of the vacuum chamber  12  through which the substrates  14  are conveyed and heated to a desired temperature before being conveyed into a vapor deposition module  60 . Each of the heater modules  16  may include a plurality of independently controlled heaters  18 , with the heaters defining a plurality of different heat zones. A particular heat zone may include more than one heater  18 . The heaters  18  may be disposed above or below the module bodies. 
     The vapor deposition module  60  may take on various configurations and operating principles within the scope and spirit of the invention, and is generally configured for vapor deposition of a source material, such as CdTe, as a thin film on the PV module substrates  14 . In the embodiment of the system  10  illustrated in  FIG. 1 , the module  60  includes a casing in which the internal components are contained, including a vacuum deposition head mounted above a conveyor assembly. 
     The vacuum chamber  12  also includes a plurality of interconnected cool-down modules  20  within the vacuum chamber  12  downstream of the vapor deposition module  60 . The cool-down modules  20  define a cool-down section within the vacuum chamber  12  in which the substrates  14  having the thin film of source material deposited thereon are allowed to cool at a controlled cool-down rate prior to the substrates  14  being removed from the system  10 . Each of the modules  20  may include a forced cooling system wherein a cooling medium, such as chilled water, refrigerant, or other medium is pumped through cooling coils configured with the modules  20 . 
     In the illustrated embodiment of system  10 , at least one post-heat module  22  is located immediately downstream of the vapor deposition module  60  and before the cool-down modules  20 . As the leading section of a substrate  14  is conveyed out of the vapor deposition module  60 , it moves into the post-heat module  22 , which maintains the temperature of the substrate  14  at essentially the same temperature as the remaining portion of the substrate  14  within the vapor deposition module  60 . In this way, the leading section of the substrate  14  is not allowed to cool while the trailing section of the substrate  14  is still within the vapor deposition apparatus  60 . 
     As diagrammatically illustrated in  FIG. 1 , a feed device  24  is configured with the vapor deposition module  60  to supply source material, such as granular CdTe. Preferably, the feed device  24  is configured so as to supply the source material without interrupting the continuous vapor deposition process within the module  60  or conveyance of the substrates  14  through the module  60 . 
     Still referring to  FIG. 1 , the individual substrates  14  are initially placed onto a load conveyor module  26 , and are subsequently moved into an entry vacuum lock station that includes a load module  28  and a buffer module  30 . A “rough” (i.e., initial) vacuum pump  32  is configured with the load module  28  to draw an initial vacuum, and a “fine” (i.e., high) vacuum pump  38  is configured with the buffer module  30  to increase the vacuum in the buffer module  30  to essentially the vacuum within the vacuum chamber  12 . Valves  34  (e.g., gate type slit valves or rotary-type flapper valves) are operably disposed between the load conveyor  26  and the load module  28 , between the load module  28  and the buffer module  30 , and between the buffer module  30  and the vacuum chamber  12 . These valves  34  are sequentially actuated by a motor or other type of actuating mechanism  36  in order to introduce the substrates  14  (starting at atmospheric pressure) into the vacuum chamber  12  in a step-wise manner without affecting the vacuum within the chamber  12 . 
     An exit vacuum lock station is configured downstream of the last cool-down module  20 , and operates essentially in reverse of the entry vacuum lock station described above. For example, the exit vacuum lock station may include an exit buffer module  42  and a downstream exit lock module  44 . Sequentially operated valves  34  are disposed between the buffer module  42  and the last one of the cool-down modules  20 , between the buffer module  42  and the exit lock module  44 , and between the exit lock module  44  and an exit conveyor module  46 . A fine vacuum pump  38  is configured with the exit buffer module  42 , and a rough vacuum pump  32  is configured with the exit lock module  44 . The pumps  32 ,  38  and valves  34  are sequentially operated to move the substrates  14  out of the vacuum chamber  12  in a step-wise fashion without loss of vacuum condition within the vacuum chamber  12 . 
     System  10  also includes a coordinated conveyor system configured to move the substrates  14  into, through, and out of the vacuum chamber  12 . In the illustrated embodiment, this conveyor system includes a plurality of individually controlled conveyor assemblies  48  within each of the various modules in the system  10 . Although the releasable drive coupling of the present invention is particularly suited for the conveyor assembly in the vapor deposition module  60 , it should be appreciated that the drive couplings are not limited in this regard. Any combination of the respective conveyor assemblies  48  within any of the modules in system  10  may include one or more of the drive units  102  with releasable couplings  120  as discussed in greater detail below. 
     As described, each of the various modules and respective conveyors in the system  10  are independently controlled to perform a particular function. For such control, each of the individual modules may have an associated independent controller  50  configured therewith to control the individual functions of the respective module, including the conveyance rate of the conveyor assemblies  48  (and thus the speed of the drive units  102 ). The plurality of controllers  50  may, in turn, be in communication with a central system controller  52 , as illustrated in  FIG. 1 . The central system controller  52  can monitor and control (via the independent controllers  50 ) the functions of any one of the modules so as to achieve an overall desired heat-up rate, deposition rate, cool-down rate, and so forth, in processing of the substrates  14  through the system  10 . 
     Referring to  FIG. 1 , for independent control of the functions performed by the modules within the overall system configuration  10 , including individual control of the respective drive units  102 , the modules may include active-sensing viewport assemblies  54  that detect the presence of the substrates  14  as they are conveyed through the module. The viewport assemblies  54  are in communication with the respective module controller  50 , which is in turn in communication with the central controller  52 . The viewport assemblies  54  may be in direct communication with the central controller  52  in an alternate embodiment. In this manner, the individual respective conveyor assemblies  48  and drive units  102  may be controlled to ensure that a proper spacing between the substrates  14  is maintained and that the substrates  14  are conveyed at the desired constant conveyance rate through the vacuum chamber  12 . It should be appreciated that the viewport assemblies may be used for any other control function related to the individual modules or overall system  10 . 
       FIG. 2  depicts a module  100  that may be any one of the modules from the system  10  of  FIG. 1 . The module  100  includes exterior walls  104  and at least one drive unit  102  mounted on one of the exterior walls  104 . The exterior walls  104  defined an entrance  101  for conveyance of substrates  14  through the module  100  by means of an internal conveyor  108  ( FIGS. 3 and 4 ). In the illustrated embodiment, each module  100  includes two of the drive units  102  configured for driving the internal conveyor  108  in either direction, as explained more fully below. 
     The drive units  102  include a motor  103  configured on a drive unit housing  109 . Any configuration of gearing or other transmission means may be contained within the housing  109  for conveying rotational torque to a drive shaft  106  associated with the drive unit  102 . A flange  107  may be provided with the housing  109  for mounting the drive unit  102  onto a mounting surface or flange configured on the exterior wall  104  of the module  100 . 
     Referring to  FIGS. 3 through 5 , each of the drive units  102  is configured with a releasable coupling  120  operably configured between the driving member of the drive unit  102 , i.e., the drive shaft  106 , and a drive member of the conveyor  108 , such as a sprocket shaft  116 . The drive coupling  120  is releasably engaged between the respective shafts  106 ,  116  and includes a first end  124  rotationally engaged with the drive shaft  106  and a second end  126  rotationally engaged with the sprocket drive shaft  116 . This rotational engagement may be by any suitable interface, including a keyed hub  130  ( FIGS. 6 and 7 ) formed in the ends  124 ,  126  that engage with correspondingly shaped profiles on the respective drive shafts  106 ,  116 . For example, the keyed hub  130  may be a hex-shaped recess that receives a hex-shaped end section of the drive shafts  106 ,  116 , as depicted in  FIG. 8 . The shaft ends may be retained within the keyed hubs  130  (within the ends  124 ,  126 ) by any suitable releasable locking mechanism. In the illustrated embodiment, a cotter pin  146  ( FIG. 5 ) is disposed through holes  144  in the first end  124  of the coupling  120  and holes  148  ( FIG. 8 ) in the drive shaft  106  for releasably securing the components together. Other types of releasably locking mechanisms may also be used, such as a ball-detent, threaded sleeve, and so forth. 
     In the illustrated embodiment, the releasable coupling  102  is axially movable relative to the respective shafts  106 ,  116  upon releasing the locking mechanism (e.g., removing the cotter pin  146 ) for relatively simple removal of the coupling  102  from between the shafts. For example, referring to  FIG. 7 , the keyed hub  130  in the first end  124  of the coupling  120  includes an open end  134  that opens into chamber  125  that has a diameter at least as great as the widest dimension of the drive shaft  106 . Upon removing the cotter pin  146  from the holes  144 , the entire coupling  120  may be slid axially along the drive shaft  106 , which will extend into the recess  125 , until the opposite end  126  of the coupling disengages from the sprocket drive shaft  116 . The keyed hub  130  in the second end  126  has a closed end  132  against which the end of the sprocket shaft  116  abuts. It should thus be appreciated that, with this particular embodiment, a releasable locking mechanism is not needed on both of the ends  124 ,  126 . It should also be appreciated that the second end  126  may be configured with the chamber  125  such that the coupling  120  is slidable in the opposite direction. 
     Referring particularly to  FIG. 7 , the drive coupling  120  includes a torque member that transmits rotational torque from the drive shaft  106  to the sprocket drive shaft  116 . In the illustrated embodiment, the torque member is defined by an innermost transmission tube  122  that is fixed between the ends  124 ,  126 , for example mounted onto shoulders  140 ,  127  defined on each end. One or more concentric thermal shields  128  may surround the transmission tube  122  for dissipating and limiting heat transfer from the interior of the module  100  to the drive unit  102 . These shields  128  extend axially around the transmission tube  122  and are attached to one of the ends  124 ,  126 , but not to both ends. For example, in the illustrated embodiment, the two thermal shields  128  are mounted onto shoulders  142 ,  143  defined on the first end  124  and are unconnected to the second end  126 . The shields  128  may be formed from any suitable heat-dissipating material. 
     In order to accommodate relative axial misalignment between the respective shafts  106 ,  116 , a partially rounded engagement interface may be defined between the ends of the shafts and the respective keyed hubs  130 . For example, referring to  FIGS. 8 and 9 , a rounded profile  150  is defined on opposite faces of the drive shaft  106 . The same rounded profiles  150  would be defined on opposite faces of the sprocket drive shaft  116 . These rounded profiles allow for a slight canting of the axis of the drive coupling  120  relative to the axis of the shafts. For example, as seen in  FIG. 9 , although the shafts  106  and  116  may be parallel, the axis of the shaft  106  is offset relative to the axis of the shaft  116  (as indicated by lines  152 ). The coupling  120 , however, is capable of accommodating for this offset due to the partially rounded interface between the ends of the shafts  106 ,  116  within the keyed hubs  130 . It should be appreciated that the rounded surfaces  150  may, alternatively, be defined within the keyed hubs  130 . 
     The drive units  102  provide motive force to any manner of conveyor within the module  100 . A particular embodiment of a conveyor  108  is illustrated in  FIGS. 3 through 5  wherein a plurality of conveyor slats  110  form an endless conveyor that is driven around sprockets  114  by links  118  that attach the slats  118  together. Each of the sprockets  114  has a sprocket shaft  116  that may be configured as discussed above. At least one of the sprockets  114  is a drive sprocket (depending on the direction of rotation of the conveyor). The other sprocket  114  may be an idler sprocket. Typically, the upstream sprocket is the idler. The idler sprocket would not need a drive unit  102  if the conveyor  108  were configured for only unidirectional conveyance, as discussed more fully below. 
     Referring to  FIGS. 3 and 4 , a configuration of an internal conveyor  108  particularly suited for use in a vapor deposition module  60  ( FIG. 1 ) is illustrated. The conveyor  108  may be modular in construction and configured for receipt within the module  60 . The conveyor  108  may include a housing  164 , as depicted in  FIG. 3 , which has been removed in the view of  FIG. 4  for sake of clarity and explanation. The housing  164  defines an enclosed interior volume (at least around the sides and top) in which the slat conveyor  110  is driven in an endless loop having an upper leg that moves in a conveyance direction of the substrates  14  through the module  60 , and a lower leg that moves in an opposite return direction. The housing  164  includes a top member  170  that defines an open “picture frame” deposition area  184  that aligns with a deposition head of the vapor deposition module  60 . As can be seen in  FIG. 3 , the upper surface of the substrates  14  are exposed to the deposition process in the open deposition area  184 . The top wall  170  defines an entry slot  180  and an exit slot  182  for the substrates  14  that are conveyed through the vapor deposition module  60 . The clearance at these slots  180 ,  182  represents a potential source of leakage of the sublimated source material from the vapor deposition area. In this regard, it is desirable to keep the clearance between the upper surface of the substrates  14  at the entry and exit slots  180 ,  182  to a minimum. 
     Referring particularly to  FIG. 3 , the housing  164  includes end walls  166  and side walls  168 . The end walls  166 , side walls  168 , and top wall  170  are connected to each other by a tab and slot arrangement wherein tabs  172  on one wall engage within slots  174  on another wall. Pins  176  engage through the tabs  172  to retain the components in a connected assembly. This embodiment is particularly useful in that mechanical fasteners, such as screws, bolts, and the like, are not necessary to assemble the housing  164 . The components of the housing  164  simply slide together and are pinned in position relative to each other. Assembly and disassembly of the housing  164  for maintenance or other procedures is a relatively easy process in this regard. 
     The conveyor  108 , particularly the housing  164 , is configured for drop-in placement of the assembly  110  in the vapor deposition module  60 . A plurality of braces  178  are attached to the side walls  168  and extend through slots in the top wall  170 . These braces  178  define a plurality of lifting points for raising and lowering the conveyor assembly  108  into the vapor deposition module  60 . When maintenance is required, the drive units  102  are disengaged from the conveyor assembly  108  by removing the drive couplings  120  as discussed above and the housing  164  is easily lifted from the module  60 . A spare conveyor assembly  108  is readily dropped into the module  60  and engaged with the drive units  102  with the drive couplings  120 . In this way, maintenance may be conducted on the removed assembly  108  while the processing line is returned to service. This keeps the vapor deposition line running in parallel with maintenance tasks. 
     The drive units  102  may be configured with a selectively actuatable clutch  154 , as depicted in  FIGS. 3 through 5 . The clutch  154  may be, for example, a conventional pneumatic clutch supplied with actuating air via a pneumatic line  158 . When actuated, the clutch  154  couples the motor and/or internal gears to the drive shaft  106 . When deactivated, the clutch  154  uncouples to the drive shaft  106 . With the embodiment wherein a drive unit  102  is configured with each sprocket of an endless conveyor  108 , as in  FIG. 3 , a control mechanism may be provided to ensure that both drive units are not actuated at the same time. This mechanism may be, for example, a three-way valve  156  that is supplied with actuation air  160  from a suitable pressurized source. The valve  156  operates to ensure that the actuating air is directed to only one of the drive units  102 , depending on the desired conveyance direction of the conveyor  108 . Even if both drive units were reversible and drivable in the same direction (in either direction), as mentioned, it is generally preferred that the upstream sprocket  114  (of certain conveyor types) remain an idler sprocket. 
     The clutches  154  may also be torque limiting clutches that operate below a design maximum torque. If excess torque is produced, the clutches  154  slip, and may also trip an over-torque sensor. This safety feature prevents a jam from causing extensive damage to the conveyor  108 . 
     When an enclosed module  100  is under high temperature and vacuum conditions, there is no easy means to evaluate the conditions of the conveyor  108  within the module. In this regard, it may be desired to include an externally accessible male driver configured on an end of the drive shaft  106 , such as a hex head driver  162  depicted in  FIGS. 3 through 5 . This component  162  provides a simple diagnostic tool for a technician to check rotation of the drive shaft  106 , jamming of the conveyor  108 , premature wear of components, and so forth. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.