Patent Publication Number: US-6986204-B2

Title: Method of constructing panelized roof structures

Description:
REFERENCE TO RELATED APPLICATIONS 
   The present invention is related to U.S. patent application Ser. No. 10/097,916 entitled “METHODS FOR AUTOMATED ASSEMBLY OF ROOF PANEL STRUCTURES” and U.S. Pat. No. 6,742,245, entitled “APPARATUS FOR ASSEMBLY OF ROOF PANEL STRUCTURES,” having a common inventor, and hereby incorporated by reference in their entireties. 
   FIELD OF THE INVENTION 
   The present invention relates generally to roof structures, and more particularly to the fabrication of panelized roof structures. 
   BACKGROUND OF THE INVENTION 
   Roofs for contemporary buildings, particularly light industrial buildings having rectangular-shaped roofing, typically are formed from roof panel structures that are attached to main supporting beams. In general, a roof panel structure includes a purlin (i.e., a major beam) that, when installed, is attached orthogonally to the main supporting beams of the structure, subpurlins (i.e., minor beams such as lumber stiffeners) that are attached orthogonally to the purlin, and diaphragms (e.g., wood structural panels) that are nailed to the subpurlins and the purlin for structural and shear support. Completed roof panel structures may be 25 to 80 feet in length or even longer, and are often lifted to and placed on the main supporting beams by a crane or forklift. Once in place, the roof panel structures are typically nailed to the main supporting beams and adjacent roof panel structures. 
   In practice, each of the components of the roof panel structures is brought to a site and the roof panel structures are assembled by hand. Some manufacturers preassemble the subpurlins and the diaphragms offsite (typically in four-foot segments, but sometimes in eight-foot segments), and use the preassembled subpurlins and diaphragms at the site to form the roof panel structures. Even if the preassemblies are used, however, many carpenters and other construction workers are required in the roofing area to complete assembly and/or installation of the roof panel structures. Thus, although present roof panel structures work well for their intended purpose, their assembly can be time consuming and expensive. Moreover, the amount of labor involved may introduce errors into assembly, which may cause additional expenses of time, labor, and materials. In addition, the labor involved may be somewhat dangerous and/or strenuous, and very often requires young, attentive workers. 
   SUMMARY OF THE INVENTION 
   The present invention provides a portable roof panel structure assembly mechanism that may be transported to a construction site and that is used to automatically assemble roof panel structures at the site. The roof panel structure assembly mechanism includes a purlin feeder, subpurlin clamping mechanisms and feeders, and a diaphragm feeder. The purlin feeder advances a purlin into an assembly station. The subpurlin feeders insert a subpurlin into each of a plurality of subpurlin clamping mechanisms, and the clamping mechanisms advance into the assembly station and hold the subpurlins against the section of the purlin that has been already advanced into the assembly station. The diaphragm feeder places a diaphragm onto the subpurlins and the purlin at the assembly station. The components are then ready for attachment. 
   In accordance with one aspect of the present invention, one or more automatic nailers (e.g., nailing guns) may be used to attach the diaphragm, the subpurlins, and the purlin at the assembly station. The automatic nailers may be provided, for example, on a nailing carriage that moves with a lifting carriage that is used to deliver and place the diaphragm over the subpurlin and the purlin. If multiple nailing guns are used, particular guns may be fired according to the position of the gun and the length and/or width of the diaphragm. In accordance with an aspect of the present invention, once the subpurlins, purlin, and diaphragm are in place, the nailing of the components together occurs automatically. 
   In accordance with another aspect of the present invention, the purlin feeder includes a height adjustment mechanism that permits the top level of a purlin on the feeder to be adjusted to a preselected height, regardless of the height of the purlin. After the purlin has been raised or lowered to the preselected height, the purlin is advanced into the assembly station. Subpurlins and a diaphragm are moved against the purlin in the assembly station, and are attached to the purlin, such as by the automatic nailers on the nailing carriage. The purlin is then indexed the width of the diaphragm, and the next subpurlins and diaphragm are placed against the new section of the purlin, and may be attached to the purlin at the assembly station (e.g., by the nailing carriage). 
   The end of the purlin having subpurlins and diaphragm(s) attached thereto advances into an exit station. The exit station includes a support for the purlin, which is adjustable for height similar to, or the same as, the lifting mechanism for the purlin feeder. A second support is provided for the side of the assembled roof panel structure having the subpurlins and diaphragms (i.e., opposite the purlin). In accordance with another aspect of the present invention, a fork lift is provided with tines that are specially configured to lift the roof panel structure from the exit station. 
   In accordance with still another aspect of the present invention, the subpurlin clamping mechanisms are mounted on a carriage that advances the clamping mechanisms and the subpurlins into the assembly station. The carriage may, for example, include a clamping mechanism for each subpurlin. Feeders are provided to supply subpurlins to the clamping mechanisms. According to one aspect of the present invention, a separate subpurlin feeder is provided for each subpurlin clamping mechanism. The subpurlin feeders may be, for example, vertical magazines or indexing units that drop a bottom subpurlin into a subpurlin clamping mechanism while a penultimate subpurlin is supported. 
   The subpurlin clamping mechanisms may include clamps or pinchers that close on opposite sides of the subpurlin and thereby position a subpurlin in a subpurlin clamping mechanism. The clamps may include sensors for determining or confirming the thickness of a subpurlin in a subpurlin clamping mechanism. 
   A rod or other device may be used to press a subpurlin against the purlin after the carriage has advanced the subpurlins into the assembly station. A sensor may be used to determine the length of the stroke of the rod so that the subpurlin length may be detected or confirmed. 
   If the subpurlin includes brackets that are configured to extend over the purlin, in accordance with an aspect of the present invention, the carriage, the subpurlins, or the clamping mechanisms may be lifted as the brackets and subpurlins approach the purlin, so that the brackets are raised above a top edge of the purlin. This feature assures that the brackets clear the top edge of the purlin, instead of hitting the purlin as the brackets are advanced. The subpurlins, clamping mechanisms, or carriage may then be lowered, so that the brackets rest on top of the purlin. 
   In accordance with one aspect of the present invention, the diaphragm feeder includes a diaphragm carriage. In one embodiment, the diaphragm carriage includes the nailing carriage and a lifting carriage for lifting and placing the diaphragm onto the subpurlin and/or purlin. This lifting carriage may include some form of device for grasping a diaphragm, for example, suction cups. 
   The lifting carriage may lift the diaphragm from a pile of diaphragms. In accordance with another aspect of the present invention, the pile of diaphragms may be provided on a lift designed such that a top diaphragm stays at substantially the same height as diaphragms are removed. 
   In accordance with an aspect of the present invention, the lifting carriage is movable relative to the diaphragm carriage, and may, for example, be mounted on a diaphragm carriage for rotational and three dimensional movement. Sensors may be provided for aiding in proper alignment of a diaphragm held by the lifting carriage before the diaphragm is placed on the subpurlins and purlin. 
   The nailing carriage may be separate from the diaphragm carriage, or may be mounted thereon, for example, on a lower portion of the diaphragm carriage. In accordance with one aspect of the present invention, a diaphragm is lowered into place in the assembly station by the lifting carriage, and the automatic nailers nail the diaphragm to the purlin and/or subpurlin before the holding device releases the diaphragm. The holding mechanism is then released and the lifting carriage is retracted. The nailing carriage may then index so that the automatic nailers may nail the diaphragm at other locations. This process may be continued until nailing is complete. The nailing process may require turning some automatic nailers on in some locations, and off in others, depending upon the configuration of the roof panel structure and the location of the automatic nailers. To aid in aligning the automatic nailers in the proper location, the diaphragm carriage is configured to provide lateral movement of the nailing carriage, such as in the x- and y-directions. 
   The system may include a computer that permits the lengths and/or widths of the purlin, subpurlin, and diaphragms to be entered, so that the entire process is automatic once started. The sensors ensure that the appropriate size of subpurlins and diaphragms are in place and properly aligned, and serve as checks on the automated assembly. 
   The roof panel structure assembly mechanism of the present invention may be operated by a minimal number of workers, but yet generates multiple roof panel structures in a fraction of the time of conventional, manual assembly. In addition, workers that are less mobile, and that are not capable of strenuous activity may be used to operate the roof panel structure assembly mechanism. The roof panel structure assembly mechanism is fully portable, so it may be delivered to a site where assembly is needed. 
   Other advantages will become apparent from the following detailed description when taken in conjunction with the drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side perspective view of a mechanism for assembling roof panel structures in accordance with one aspect of the present invention, with parts removed to show detail; 
       FIG. 2  is an exploded perspective view a roof panel structure, used to show one typical construction of such a structure; 
       FIG. 3  is a side perspective view of a purlin feeder for the roof panel structure assembly mechanism of  FIG. 1 ; 
       FIG. 4  is a side perspective view of a lifting mechanism for the purlin feeder of  FIG. 3 ; 
       FIG. 5  is a top view of a portion of the purlin feeder of  FIG. 3 ; 
       FIG. 6  is a side view of a portion of the purlin feeder of  FIG. 3 , with a purlin shown in a lowered position; 
       FIG. 7  is a side view of a portion of the purlin feeder of  FIG. 3 , similar to  FIG. 6 , with a purlin shown in a higher position; 
       FIG. 8  is a side perspective view of the roof panel structure assembly mechanism of  FIG. 1 , with parts removed for detail, and showing an assembled roof panel structure in an exit station, the assembled roof panel structure being shown in phantom; 
       FIG. 9  shows a side perspective view, similar to  FIG. 8 , with the roof panel structure not being in phantom; 
       FIG. 10  is a side perspective view of a roof panel structure in the exit station of  FIG. 8 , with a forklift shown preparing to remove the roof panel structure from the exit station; 
       FIGS. 11–13  are side views showing various stages of a forklift removing the roof panel structure of  FIG. 10  from the exit station; 
       FIG. 14  is a side perspective view of a subpurlin station and a diaphragm station for the roof panel structure assembly mechanism of  FIG. 1 ; 
       FIG. 15  is a side perspective view showing a portion of the subpurlin station of  FIG. 14 ; 
       FIG. 16  is a rear view of the subpurlin station  FIG. 15 ; 
       FIG. 17  is a rear view of the subpurlin station  FIG. 15 , similar to  FIG. 16 , with subpurlin feeders being closed against subpurlins in the subpurlin feeders; 
       FIG. 18  is a side perspective detail view of a release mechanism for the subpurlin feeders of  FIG. 17 ; 
       FIG. 19  is a bottom view of the subpurlin feeders of  FIG. 17 ; 
       FIG. 20  is a bottom view of the subpurlin feeders of  FIG. 17 , similar to  FIG. 19 , with arms of the subpurlin feeders open so that bottom subpurlins may be released; 
       FIG. 21  is a rear view, similar to  FIG. 17 , showing the bottom subpurlins dropped from the subpurlin feeder and into subpurlin clamping mechanisms; 
       FIG. 22  is a side perspective detail view of the bottom subpurlins being dropped as in  FIG. 21 ; 
       FIG. 23  is a side perspective view of a subpurlin carriage for the subpurlin clamping mechanisms of  FIG. 21 ; 
       FIG. 24  is a top view of the subpurlin clamping mechanisms of  FIG. 23 ; 
       FIG. 25  is a side perspective detail view of a pinching mechanism for use in the subpurlin clamping mechanisms of  FIG. 23 ; 
       FIG. 26  is a side perspective view of a pinching mechanism for use in the subpurlin clamping mechanisms of  FIG. 23 , similar to  FIG. 25 , showing the pinching mechanisms closed; 
       FIG. 27  is a side view of a push bar system for use on the leading end of the subpurlin carriage of  FIG. 23 ; 
       FIG. 28  is a side view, similar to  FIG. 27 , showing the push bar engaging a purlin; 
       FIG. 29  is a side perspective view of a front end of the subpurlin carriage; 
       FIG. 30  is a diagrammatic view of a drive system for the subpurlin carriage; 
       FIG. 31  is a diagrammatic side view showing the subpurlin carriage positioned below the subpurlin feeders; 
       FIG. 32  is a diagrammatic side view, similar to  FIG. 31 , showing the subpurlin carriage advancing into an assembly station; 
       FIG. 33  is a diagrammatic side view, similar to  FIG. 32 , showing the subpurlin carriage further advanced into the assembly station; 
       FIG. 34  is a side detail view showing the subpurlin carriage as it approaches a purlin in the assembly station, with a front end of the subpurlins lifted; 
       FIG. 35  is a side detail view, similar to  FIG. 34 , showing the subpurlins being lowered against a purlin in the assembly station; 
       FIG. 36  is a top view of the subpurlin carriage in the position shown in  FIG. 35 ; 
       FIG. 37  is a diagrammatic side view, similar to  FIG. 32 , showing the subpurlin carriage in the position in  FIG. 35 ; 
       FIG. 38  is a diagrammatic side view, similar to  FIG. 37 , showing the subpurlin carriage fully retracted back to underneath the subpurlin feeders; 
       FIG. 39  is a diagrammatic side view, similar to  FIG. 38 , showing a beginning stage of movement of a diaphragm lift; 
       FIG. 40  is a top view of a diaphragm carriage in accordance with one aspect of the present invention; 
       FIG. 41  is a diagrammatic side view of the diaphragm carriage of  FIG. 40 ; 
       FIG. 42  is a top view of the diaphragm carriage of  FIG. 40 , similar to  FIG. 40 , but with a nailing carriage and a lifting carriage being raised; 
       FIG. 43  is a diagrammatic side view, similar to  FIG. 41 , with the nailing carriage and the lifting carriage being raised as is  FIG. 42 ; 
       FIG. 44  is a diagrammatic side view showing a beginning stage of lifting of a diaphragm by the lifting carriage of the diaphragm carriage; 
       FIG. 45  is a diagrammatic side view, similar to  FIG. 44 , showing the diaphragm removed from the diaphragm stack; 
       FIG. 46  is a diagrammatic side view, similar to  FIG. 45 , with the diaphragm carriage beginning movement toward the assembly station; 
       FIGS. 47–50  are diagrammatic views showing a sensor arrangement that may be used to determine the location and orientation of a diaphragm held by the diaphragm feeder, and a diaphragm being oriented relative to the sensors to determine its location and orientation; 
       FIG. 51  is a diagrammatic side view showing a diaphragm held by the lifting carriage over the assembly station; 
       FIG. 52  is a diagrammatic side view, similar to  FIG. 51 , with the diaphragm lowered against subpurlins and a purlin; 
       FIGS. 53–58  are diagrammatic side views showing a nailing process for a nailing carriage of the diaphragm carriage in accordance with one aspect of the present invention; 
       FIG. 59  is an end view of the nailing carriage of  FIGS. 53–58 ; 
       FIG. 60  is a diagrammatic view of automatic nailers for the nailing carriage of  FIG. 59 , shown relative to a portion of the lifting carriage; 
       FIG. 61  is a diagrammatic view of nailing stations for the automatic nailers of  FIG. 60 ; 
       FIG. 62  is a flow diagram generally representing exemplary steps for automatically producing a roof panel structure in accordance with an aspect of the present invention; 
       FIG. 63  is a flow diagram generally representing steps for inserting a purlin into the assembly station in accordance with an aspect of the present invention; 
       FIG. 64  is a flow diagram generally representing steps for indexing a purlin through the assembly station as subpurlins and diaphragms are added to the purlin in accordance with an aspect of the present invention; 
       FIG. 65  is a flow diagram generally representing steps for loading a subpurlin into the subpurlin clamping mechanisms in accordance with an aspect of the present invention; 
       FIG. 66  is a flow diagram generally representing steps for advancing a subpurlin via the subpurlin clamping mechanisms into the assembly station in accordance with an aspect of the present invention; 
       FIG. 67  is a flow diagram generally representing steps for advancing a diaphragm into the assembly station in accordance with an aspect of the present invention; 
       FIGS. 68–73  are diagrammatic representations of a nailing sequence that may be performed by roof panel structure assembly mechanism in accordance with one aspect of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order to not obscure the present invention. 
   Roof Panel Structures 
   Generally described, the present invention is directed to a mechanism, generally designated as  100  in  FIG. 1 , for assembling roof panel structures, an example of which is generally designated as “A” in  FIG. 2 . Although the roof panel structure A is shown as one example, variations of that structure are possible, and a person of skill in the art may utilize the features of the present invention in the construction of roof panel structures having various configurations. 
   As is known in the art, a roof panel structure A typically includes a major horizontal beam, often called a purlin P. The purlin P may be a steel girder, a glulam structure, a wooden beam, or the like, but typically includes wood or another material along a top edge that permits easy attachment of other components of the roof panel structure (e.g., by nailing). 
   Minor beams, called “subpurlins” (S in  FIG. 2 ) extend orthogonally to the purlin P, and are often attached to the purlin P by right angle brackets B that extend from an end of the subpurlin. The subpurlins S may be made of any of the materials described with above with respect to purlins P, but are typically lumber stiffeners, such as 2-by-6&#39;s or 2-by-4&#39;s, 3-by-4&#39;s, 3-by-6&#39;s, and so forth, six to ten feet in length. 
   Diaphragms D, such as wood structural panels (e.g., 4×8, 4×10, 8×8, or 8×10 structural wood panels) are mounted over the subpurlins S and the purlin P, and are typically nailed to the subpurlins and the purlin for structural and shear support. In the embodiment shown in  FIG. 2 , the diaphragms D extend beyond both ends of the subpurlins S, and a front end of the diaphragms overlaps approximately one half of the thickness of the purlin P. The back ends of the diaphragms on an adjacent roof panel structure A overlap the other half of the thickness of the purlin P. Subpurlins S are located such that the edges of the diaphragm D overlap one half of the subpurlins that extend along the side edges of the diaphragm, and other, intermediate subpurlins (two shown in  FIG. 2 , but this number may be varied) are spaced between the two subpurlins on the side edges. Adjacent diaphragms D overlap the other half of the subpurlins S at the side edges. 
   The number of diaphragms D and subpurlins S used in a roof panel structure A depends upon the spacing of the subpurlins, the width of the diaphragms, and the length of the roof panel structure. Typically, the diaphragms are 4 or 8 feet in width (although they may be less or more wide), and the subpurlins are typically spaced 24 inches on center (i.e., two edge subpurlins S and one intermediate for a 4 foot wide diaphragm, and two edge subpurlins and three intermediate subpurlins for a 8 foot wide diaphragm, and so forth). Completed roof panel structures A may be 25 to 80 feet in length, or even longer. When installed, these roof panel structures A extend orthogonally to main supporting beams (not shown, but known in the art) and are attached to the main supporting beams and adjacent roof panel structures by nailing or another appropriate attachment method. 
   General Overview 
     FIG. 1  shows a perspective view of a roof panel structure assembly mechanism  100  in accordance with the present invention. Parts have been removed for detail. In summary, the roof panel structure assembly mechanism  100  includes a purlin feeder  102 , subpurlin feeders  104 , subpurlin clamping mechanisms  106 , and a diaphragm feeder  108 . The structure and operation of an embodiment for each of these different components is described further below. However, in general, the purlin feeder  102  advances a purlin P into an assembly station, generally shown at  110  in  FIG. 1 . The subpurlin feeders  104  insert a subpurlin S into each of the subpurlin clamping mechanisms  106 , and the subpurlin clamping mechanisms advance into the assembly station  110  and hold the subpurlins against the section of the purlin P that is already in the assembly station. The diaphragm feeder  108  places a diaphragm D onto the subpurlins S and the purlin P at the assembly station  110 . 
   The components shown in  FIG. 1  are arranged relative to one another in one possible configuration. However, as will be understood from the following description, the components may be arranged differently. As nonlimiting examples, one or more of the purlin feeder  102 , the diaphragm feeder  108 , the subpurlin feeders  104 , and the subpurlin clamping mechanisms  106  may be located above another of these components, or two components may be located on the same side of the assembly station (e.g., side by side), or one or more of the components or parts of the components may be located above or below the assembly station. In addition, the functions of two or more of the purlin feeder  102 , the diaphragm feeder  108 , or the subpurlin clamping mechanisms  106  may be combined in a single station, or one or more of their functions may be provided at the assembly station  110 . In addition, the features and operation of any of the components may be distributed over multiple components or devices. As an example, one or more subpurlins and one or more diaphragms may be advanced to a first assembly station where they are attached, e.g., by nailing. The assembled structure may then be advanced to a second station where it is attached to a purlin (which may be advanced into the second station as well). As another alternative, the purlin may be advanced into the first assembly station, where it may be attached to the assembled diaphragm and subpurlin structure. Multiple variations are available. 
   Thus, multiple different arrangements are available for the purlin feeder  102 , the diaphragm feeder  108 , the subpurlin clamping mechanisms  106 , and the assembly station  110 . In addition, the functions of these components may be combined, or may be distributed over multiple stations. For ease of understanding, however, the invention will be described with reference to the arrangement shown. However, a person of skill in the art could modify the arrangement according to space constraints or particular needs. 
   In accordance with one aspect of the present invention, after the purlin P, the subpurlins S, and the diaphragm D are brought together in the assembly station  110 , the components are attached, for example by one or more automatic nailers (e.g., nailing guns). The purlin P is then advanced so that additional subpurlins S and a diaphragm D may be attached. This process proceeds until the end of the purlin P is reached. 
   The automatic nailers in the described embodiment are provided on a nailing carriage that moves with the diaphragm feeder. However, the automatic nailers may alternatively be provided on a separate carriage, and may be positioned where convenient. In addition, although the described embodiment discloses a nailing operation that occurs after the purlin P, subpurlins S, and diaphragm D have been assembled, a nailing operation may be used where subassemblies are assembled and attached (e.g., subpurlins and one or more diaphragms), and the subassemblies are then advanced to be joined with the remaining portions of the roof panel structure A (e.g., the purlin). Thus, automatic nailers may be distributed over multiple locations. Moreover, as used herein, “carriage” is meant to denote a movable part of the roof panel structure assembly mechanism  100  that may be used to deliver the respective object or part, such as the automatic nailers for the nailing carriage. 
   The forward end of the purlin P that has subpurlins S and diaphragm(s) D attached thereto advances into an exit station  112 . The exit station  112  includes supports for the assembled roof panel structure A, as described further below. The purlin P continues to index into the exit station  112  until the assembled roof panel structure A exits the assembly station  110 . The assembled roof panel structure A is then ready for removal from the exit station, and installation in a roof. 
   The components shown in  FIG. 1  may be made portable, and thus may be transported to a work site for assembly of roof panel structures A on the site. As an example, a frame  120  for housing the subpurlin feeders  104  and the subpurlin clamping mechanisms  106  may be formed integral with a frame  122  for the diaphragm feeder  108 . This integral unit may be sized so that it may be transported on a single trailer. In addition, a frame  124  for the purlin feeder  102  and a frame  126  for the exit station  112  may be integrally formed and sized so that the integral unit fits on a trailer. However, for the embodiment shown in the drawings, these two frames  124 ,  126  are separate, but individually may be transported together on a trailer or may be transported on separate trailers. The frames  124 ,  126  may include attachment structures so that they may be fixed to the frames  120 ,  122  once the roof panel structure assembly mechanism  100  has been placed at a site. The attachment of the frames  120 ,  122 ,  124 ,  126  assures that proper alignment of the various stations is maintained. 
   Although not shown so that details of the components of the roof panel structure assembly mechanism  100  are visible, the subpurlin frame  120  and the diaphragm frame  122  may include paneling on their outer surfaces. The paneling provides safety and security for the roof panel structure assembly mechanism  100 . Other paneling or appropriate covering may be incorporated in the roof panel structure assembly mechanism  100 . 
   The frames  120 ,  122 ,  124 , and  126  and the other components of the roof panel structure assembly mechanism  100  may be made steel. Other materials may be used, such as aluminum or other metals, wood for some components, and/or plastics or composites. However, the applicant has found that steel is a relatively inexpensive material that provides strength, wear resistance, and manufacturability. 
   The operation of the roof panel structure assembly mechanism  100  may be controlled by a computer  128  (shown generally by a large box in  FIG. 1 , but its size and location may be altered as appropriate). The computer  128  may be any device or devices that can execute computer-executable instructions, such as program modules. Generally, program modules include routines, programs, objects, components, data structures and the like that perform particular tasks or implement particular abstract data types. Given the description herein, the computer  128  may be programmed by a programmer of ordinary skill to perform the functions and operations described herein. Although the invention is described with reference to a single computer  128 , the features of the computer  128  may be distributed over a number of computers, microcomputers, controls, or other devices. 
   Unless described otherwise herein, the operation of the roof panel structure assembly mechanism  100  is fully automated, and the functions of the roof panel structure assembly mechanism are driven synchronously by the computer  128  with relatively little operator intervention. However, if desired, one or more of the functions of the roof panel structure assembly mechanism  100  may be performed manually instead of automatically, but without the full benefits of the described embodiment. 
   The Purlin Feeder 
   The station for the purlin feeder  102  is shown in detail in  FIG. 3 . One or more hoists  130  may be provided for lifting a purlin P (shown for simplification in phantom in  FIG. 3 , but the structure of which is known in the art) onto a series of lifting mechanisms  132 . The hoist  130  or hoists may be, for example, a single boom hoist, having a hook  134  and being capable of rotation, as shown by the arrows  136 . As shown phantom in  FIG. 3 , more than one hoist may be incorporated into the purlin feeder station  102 . Purlins P may be stacked on the frame  124 , and thus are easily accessible by the hoist  130  or by an operator. The hoist  130  is used to aid a worker in placing a purlin on the lifting mechanisms  132 , but is not necessary for operation of the present invention. 
   The details of one of the lifting mechanisms  132  are shown in  FIG. 4 . The lifting mechanism  132  is mounted on the frame  124 , and includes a vertical column  140 . The vertical column  140  has a cross section of a “U,” with sides of the U being formed by connected, parallel I-beams. 
   A carriage  142  is mounted for sliding movement up and down the face of the vertical column  140 . The carriage  142  includes wheels  144  (only one of which is shown in  FIG. 4 ) that allow the carriage to smoothly glide up and down the vertical column  140 . A bolt  146  or other fastener extends out of the back of a front plate  148  for the carriage  142 , and is connected to an endless belt or chain  150 . The chain  150  loops around an idler sprocket  152  at the top of the vertical column  140 , and a drive sprocket  154  at the bottom of the vertical column  140 . The drive sprocket  154  is arranged to engage teeth (not shown) on a horizontal shaft  156 . 
   In accordance with one aspect of the present invention, the structure thus described for the lifting mechanism  132  is included on each of the lifting mechanisms. In addition, the shaft  156  is common to all the lifting mechanisms for the purlin feeder  102 , i.e., connects to the drive sprocket  154  for each of the lifting mechanisms. 
   A plate  160  extends horizontally outward from the bottom of the carriage  142 . In accordance with one aspect of the present invention, for some of the lifting mechanisms (e.g., the right three in  FIG. 3 ), the plate includes a roller  162  or rollers along a top edge. For others (e.g., the left three in  FIG. 3 ), the plate  160  includes a pair of side rollers  164  (best shown in  FIG. 4 ). The side rollers  164  are arranged to engage and receive side edges  166  of a roller bar  168 . The roller bar  168  includes a series of rollers  170  along its top surface. 
   The side rollers  164  permit the roller bar  168  to extend beyond the frame  124  of the purlin feeder  102  and into the assembly station  110 . That is, the roller bar  168  may extend from the position shown in  FIG. 3 , where it is captured by the side rollers  164  on three lifting mechanisms  132 , to the extended position shown in phantom in  FIG. 5 . In this extended position, the roller bar  168  is supported by the leftmost two lifting mechanisms  132 , and the forward portion of the roller bar  168  extends well into the assembly station  110 . A stop may be provided to prevent the roller bar  168  from extending too far forward. By extending into the assembly station  110 , the roller bar  168  continues to provide support for a purlin P after the purlin has left the purlin feeder  102 . 
   In operation, a purlin P is lifted by the hoist  130  (if available), and is swung over to the lifting mechanisms  132 . A purlin P is shown at the beginning stage of lifting in  FIG. 5 . If not already extended into the assembly station  110 , the roller bar  168  may be thus extended prior to lifting the purlin P. Alternatively, the roller bar  168  may be extended with a purlin P. 
   The purlin P, once installed on the lifting mechanisms  132  ( FIG. 6 ), rests on the rollers  162  and the rollers  170  (e.g., the purlin P is shown on the rollers  170  in  FIG. 6 ). To this end, the rollers  162  and the rollers  170  are arranged so that their top edges are aligned. The purlin P may lean against the vertical columns  140  for stability. If desired, other rollers (not shown) may be provided on the vertical column  140  to aid in advancing a purlin P. 
   After the purlin P is placed on the lifting mechanisms  132 , the lifting mechanisms  132  may then raise or lower the purlin P so as to align the top of the purlin with a reference point. This feature is important for the embodiment of the invention shown in the drawings, because the purlin P should be at a particular level for the subpurlins to properly align with the top of the purlin in the assembly station. In alternate embodiments, the height of the subpurlins S may be altered to align with the purlin P, for example, or the subpurlins and purlin may be aligned in other manners. 
   To adjust the height of the purlin P, the shaft  156  is rotated, as shown by the arrows  172  in  FIG. 7 . Rotation of the shaft  156  causes the drive sprockets  154  to rotate, forcing the front loop of the chains  150  upward. This movement drives the carriage  142  upward, lifting the purlin along with it. 
   Because each of the lifting mechanisms  132  is driven by the same shaft  156 , the plates  160  move upward at the same rate. This feature permits the purlin P to remain horizontal and fully supported during lifting. The shaft  156  may be driven by a servo motor, shown generally as a box  174  in  FIG. 1 . 
   The proper height may be determined by a user (e.g., by visual inspection against a reference), or may be sensed. If a sensor or sensors are used, then the sensors may shut power to the servo motor  174  once the purlin P has reached the appropriate height. 
   After the purlin P is raised or lowered to the proper height, the purlin P is ready for advancing into the assembly station  110 . As such, the purlin P may be advanced (e.g., manually) on the rollers  162  and  170  into the assembly station, as is shown in  FIG. 5 . As stated above, additional rollers (not shown) may be provided on the vertical columns  140  to aid in smooth movement of the purlin P into the assembly station  110 . The roller bar  168 , because it extends into the assembly station  110 , continues to support the purlin P as it is advanced. When the purlin P reaches the assembly station  110 , it is captured between a toothed driven roller  180  ( FIG. 5 ) and a biased idler roller  182 . The idler roller  182  is pressed toward the toothed driven roller  180 , as shown by the arrow  183 , for example by a cylinder or spring (not shown). 
   Further within the assembly station  110 , just forward of the toothed driven roller  180 , is a belt  184 . The belt  184  is wrapped over a number of rollers  186 , one of which is shown in  FIG. 5 . The rotation of the outer surface of the belt  184  is synchronized with the rotation of outer surface of the toothed driven roller  180 . For example, the toothed driven roller  180  and the rollers  186  and belt  184  may have the same radius, and therefore would rotate at the same speed. 
   Once the purlin P is captured between the toothed driven roller  180  and the idler roller  182 , rotation of the toothed driven roller pulls the purlin into the assembly station  110 . The toothed surface of the toothed driven roller  180  helps to grip the purlin P, and the bias of the idler roller  182  assures constant engagement of the purlin P with the toothed driven roller. 
   Either of the toothed driven roller  180  and the idler roller  182  may include a sensor and/or a counter (not shown) for determining the start of a purlin P, and for measuring the amount the purlin has been advanced into the assembly station  110 . This feature may be provided, for example, by the toothed driven roller  180  being driven by an absolute feedback servo motor (not shown). As is known, such motors provide feedback of their functions, even if power has been cut during operation. This feature helps to automatically feed the purlin P the correct amount into the assembly station, and to maintain information regarding information about the position of the purlin as it advances into and through the assembly station  110 . In addition, the amount that the idler roller  182  is biased inward may be sensed to determine or confirm the thickness of the top of the purlin P. 
   As the purlin P continues to advance into the assembly station, it engages the belt  184 , which helps maintain alignment of the purlin, and further helps to pull the purlin forward. The idler roller  182  maintains the contact of the purlin with the front of the vertical columns  140  of the lifting mechanisms, the toothed driver roller  180 , and the belt  184 . In this manner, the purlin maintains proper alignment as it enters and passes through the assembly station  110 . 
   The lifting mechanisms  132  shown in the drawings are but one way to provide lifting and feeding of the purlin P. For example, a single column may be used, having a roller bar stabilized thereon. A platform may be provided, the height of which may be adjusted, and along which the purlin P may be fed. The purlin P may be captured between opposing rollers (up and down or side-to-side), or suspended from overhead. Many alternatives are available. However, the described embodiment is relatively inexpensive to fabricate, and provides exemplary stability and lifting ease. 
   The Exit Station 
   The exit station  112  is shown in detail in  FIGS. 8 and 9 . As the assembled panel A leaves the assembly station  110 , it enters the exit station  112 . The exit station  112  includes a number of lifting mechanisms  190  that are similar to the lifting mechanisms  132  in the purlin feeder  102 . The lifting mechanisms  190  include passive rollers  192  at their top edges, with an axis of rotation for each of the rollers being aligned vertically. 
   The lifters for the lifting mechanism  190  are similar in construction to the plates  160  and carriages  142  for the lifting mechanisms  132 . In the embodiment shown in the drawings, the left-most five lifting mechanisms  190  include rollers similar to the right-most three lifting mechanisms  132 . However, the two right-most lifting mechanisms  190  of the exit station  112  include a conveyor  196  extending between the two plates  160  for the lifting mechanisms  190 . When the assembled roof panel structures A leave the assembly station  110 , the bottom edge of the purlin P aligns with and then rides along the top of the conveyor  196 . The conveyor  196  may be driven by an absolute feedback servo motor (not shown), and preferably is synchronized with the belt  184  and the toothed driven roller  180 . 
   The shaft or other mechanism that is used to raise the lifting mechanisms  190  may be similar to, or the same as, the shaft  156  used to raise the lifting mechanisms  132  for the purlin feeder  102 . If separate mechanisms (e.g., separate shafts) are used to lift the two lifting mechanisms  132 ,  190 , then the lifting of these two lifting mechanisms is preferably synchronized so that the heights of the two mechanisms may be the same, so that the purlin P may smoothly transition from the purlin feeder  102 , through the assembly station  110 , and into the exit station  112 . As the purlin P enters and continues through the exit station  112 , the top end of the purlin aligns against the rollers  192  on the top of the lifting mechanism  190 . 
   A support  200  is provided on the opposite side of the exit station  112  from the lifting mechanisms  190 . The support  200  is arranged and configured to receive a bottom edge of the subpurlins S as the assembled roof panel structure A advances through the exit station  112 . 
   The support  200  includes an endless chain  202  running along its length. The subpurlins rest against this endless chain  202 . The rotation of the endless chain  202  is preferably synchronized with the movement of the conveyor  196 , for example by an absolute feedback servo motor (not shown). Thus, the subpurlin end of the roof panel structure A is driven through the exit station  112  at the same rate that the purlin P is driven through the exit station. The outer end of the support  200  is canted slightly inward toward the lifting mechanisms  190  relative to the inner end, so that the subpurlin end of the assembled roof panel structures A crowd or lead toward the lifting mechanisms  190 . This feature maintains the assembled roof panel structure A against the rollers  192 , and helps to maintain the alignment of the assembled roof panel structure through the exit station  112 . 
   The Forklift Tines 
   In accordance with one aspect of the present invention, a novel set of forklift tines  210  ( FIG. 10 ) is provided for removing the assembled roof panel structure A from the exit station  112 . The forklift tines  210  include an elongate bar  212  extending orthogonally to the forklift F. A series of T-bars  214  extend orthogonally from the elongate bar  212 . The T-bars  214  are attached at their base to the elongate bar  212  such that the top of the T-bars  214  is spaced from the elongate bar. The T-bars  214  are spaced from each other the same as the lifting mechanisms  190 , and the length of the top of the T-bars  214  is less than the spacing between the lifting mechanisms  190 . 
   The forklift tines  210  are rotatably mounted to the forklift, for example, about an axle  216 . This rotational mounting permits the tines  210  to be rotated upward relative to the arms of the forklift F. Vertical bars  218  extend upward from the axles  216 . 
   The use of the forklift tines  210  is shown in  FIGS. 10–13 . After an assembled roof panel structure A is complete, a forklift F having the forklift tines  210  mounted thereon is driven toward the exit station  112 , and the T-bars  214  are aligned between the lifting mechanisms  190  and under the assembled roof panel structure A. The T-bars  214  are inserted until the elongate bar  212  is adjacent the lifting mechanisms  190 . The tines  210  are then rotated about the axle  216 , and the arms of the forklift F are raised such as to remove the assembled roof panel structure from the exit station  112 . The assembled roof panel structure A may then be rotated about the axle  216  and lifted by the arms of the forklift F as appropriate so as to place the roof panel structure in position for installation. The roof panel structure A may at this point be resting against the vertical bars  218 . 
   The Subpurlin Feeders 
     FIG. 14  shows the subpurlin frame  120  and the diaphragm frame  122 , with the purlin frame  124  and the exit station  112  removed for detail.  FIG. 15  shows a detail view of a rear portion of the subpurlin clamping mechanisms  106  and the subpurlin feeders  104 . In summary, as described above, the subpurlin feeders  104  are configured and arranged to deposit subpurlins S into the subpurlin clamping mechanisms  106 . The subpurlin clamping mechanisms  106  then advance into the assembly station  110 , with the subpurlins S therein, so that the subpurlins may be aligned with and attached to the purlin P and the diaphragms D. To this end, the subpurlin clamping mechanisms  106  are mounted on a subpurlin carriage  220 , shown in  FIG. 15 . The operation and structure of the subpurlin carriage  220  and the subpurlin clamping mechanisms  106  are further described below. 
   The subpurlin feeder  104  may be any structure that is arranged and configured to deposit subpurlins S into the subpurlin clamping mechanisms  106 . In one example shown in the drawings, each subpurlin feeder  104  is a magazine that is designed to hold a plurality of subpurlins S, and to drop one subpurlin into an empty subpurlin clamping mechanism  106 . 
   A rear view of the subpurlin feeders  104  is shown in  FIG. 16 . Each of the subpurlin feeders  104  includes a vertical wall  224  that is fixed in position. An adjustable vertical wall or bracket  226  extends parallel to the fixed vertical wall  224 . Each of these walls  224 ,  226  may extend along the length of the subpurlin frame  120  or any portion thereof, but the walls are preferably arranged to maintain subpurlins S therebetween, arranged in the direction of the assembly station  110 . 
   The adjustable vertical wall  226  is rotatably attached to a fixed frame  228  by a pair of lever arms  230 ,  232 . As can be seen in  FIG. 17 , one of the lever arms  232  includes a cylinder  234  eccentrically mounted thereon. The opposite end of the cylinder  234  is attached to the frame  228 . Extending the cylinder  234  causes the two lever arms  232 ,  230  to rotate, pushing the adjustable wall  226  outward relative to the frame  228  and toward the fixed vertical wall  224 . 
   The adjustable vertical wall  226  and its movement permit the spacing between the adjustable vertical wall  226  and the fixed vertical wall  224  to be adjusted to various different thicknesses of subpurlins S. As such, the two walls  226 ,  224  may be appropriately spaced so that subpurlins can be stacked edge to edge within and between the two walls, without permitting the subpurlins S to rotate or bind between the two walls. 
   The subpurlin feeders  104  may be sized to hold an appropriate amount of subpurlins S, given space constraints and the desire of the manufacturer. The subpurlins S may be manually fed into the subpurlin feeders  104 , or some type of automated input of the subpurlins S may be provided. The subpurlin feeder  104  may include sensors (not shown) for determining that the subpurlins need to be replenished in the subpurlin feeder. These sensors may be provided, for example, by eye sensors, contact sensors, or weight sensors. 
   The spacing between the walls  224 ,  226  may be set according to the subpurlins S that are located in the subpurlin feeders  104 . The spacing between the two walls  226 ,  224  may be set, for example, by the computer  128  in response to operator input, may be manually set by an operator, or may be automatically set based upon a sensing of the width of the subpurlins S. In general, however, the spacing is slightly more than the width of the subpurlins S, e.g., two inches for 2×6&#39;s, and so forth. 
   A plunger  240  is mounted on the frame  228  so that it aligns with the second from the bottom, or penultimate subpurlin S. In the embodiment shown in the drawings, there are two of these plungers  240  per subpurlin feeder  104  ( FIG. 19 ). 
   In addition, a swivel-mounted support arm  242  is attached for rotation adjacent to the bottom of the fixed vertical wall  224 . As can be seen in  FIG. 18 , the support arm  242  is fixed to rotate with a rod  244  that extends through a bracket  246  on the fixed vertical wall  224 . A pivot arm  248  is attached for rotation with the rod  244  and extends outwardly from the top of the rod. The pivot arm  248  is attached to a lever arm  250 . The lever arm  250  attaches to a similar pivot arm  248  on another end of the purlin feeder  104 , as can be seen in  FIG. 19 . 
   A plunger  252  ( FIG. 19 ) is attached to an end of the lever arm  250 . Operation of the plunger  252  causes the lever arm  250  to retract which, in turn, causes the pivot arm  248  to rotate, rotating the support arm  242 . Rotation of the arms is shown in  FIG. 20 . As the support arms  242  rotate, they move out of the way of the bottom subpurlin S, permitting the bottom subpurlin to fall into the subpurlin clamping mechanism  106 . A subpurlin S that has dropped into the clamping mechanism  106  is shown in  FIGS. 21 and 22 . The subpurlins S may alternatively be dropped or placed in the subpurlin clamping mechanisms  106  in different ways. 
   Before the lever arm  250  is used to rotate the support arms  242 , the plungers  240  are extended to hold the penultimate subpurlin S in place. The plungers  240  continue to hold the penultimate subpurlin S during rotation of the support arms  242 . In this manner, the penultimate subpurlin S and all subpurlins above the penultimate subpurlin are supported as the bottom subpurlin drops. After the lower subpurlin S has been dropped, the plunger  252  extends, causing the support arms  242  to align back under the stack of subpurlins S. The plungers  240  then retract, allowing the penultimate subpurlin and the subpurlins S above the penultimate subpurlins to drop into place. The purlin feeder  104  is then ready for dropping of the next subpurlin S. 
   The Subpurlin Clamping Mechanisms 
   As stated above, the subpurlin clamping mechanisms  106  are mounted on a subpurlin carriage  220 . The carriage  220  includes a carriage frame  256  having wheels  258  ( FIG. 23 ). In operation, subpurlins S are provided to the subpurlin clamping mechanisms  106  by the subpurlin feeders  104 , and the subpurlin carriage  220  moves the subpurlin clamping mechanisms from the subpurlin feeders to the assembly station  110 . During this movement, the subpurlin carriage wheels  258  roll along rails  259 . The movements of the subpurlin carriage  220  and its components may be operated by absolute feedback motors, such as absolute feedback servo motors. As such, the location of the components of the subpurlin carriage and the speeds of the operation may be easily altered by the computer  128  or by a programmer or operator via the computer  128 , or may, for example, be moved precisely to a location based upon input from sensors or the computer. 
   Details of the subpurlin clamping mechanisms  106  can be seen in  FIGS. 23 and 24 . The subpurlin clamping mechanisms  106  include slots  260  for receiving the subpurlins S. The slots  260  include left rails  262  and right rails  264 . These rails  262 ,  264  are mounted on a clamping mechanism frame  266 . The clamping mechanism frame  266  is pivotally mounted to the carriage frame  256 , for example via a pivot rod  268 . The pivot rod  268  is shown in  FIGS. 22 and 23 , and the function of the clamping mechanism frame  266  pivoting relative to the carriage frame  256  is described below. 
   Mounted along the length of the subpurlin clamping mechanisms  106  are a number of clamping, or pinching mechanisms  270 . In the embodiment shown, the number of pinching mechanisms  270  per subpurlin clamping mechanism  106  is three, but this number may be varied. The pinching mechanisms  270  are configured to center the subpurlins S in the subpurlin clamping mechanisms  106 , and to hold the subpurlins in position once centered. In addition, as further described below, the pinching mechanisms  270  include sensors that detect the thickness of the subpurlins in the subpurlins clamping mechanisms  106 . 
   Details of one of the pinching mechanisms  270  are shown in  FIGS. 25 and 26 . The pinching mechanisms  270  include two different sides that are mirror images of one another. For simplicity, only one side is described. 
   The pinching mechanisms  270  include a bracket  272  mounted on the outside of the slots  260 . A rod  274  is rotatably mounted in the bracket  272 . A toothed gear  276  is mounted for rotation with the rod  274  at a bottom end of the rod. An eccentrically mounted arm  278  is mounted on the top end of the rod, also for rotation with the rod  274 . A half-circular contact  280  is mounted on the end of the eccentrically mounted arm  278 . 
   A counter-type sensor  282  is mounted on the outside of the toothed gear  276 , and is arranged and configured to index a unit as each tooth of the gear  276  passes through the sensor. The sensor  282  is located on only one side of the pinching mechanism  270 . A bar  284  having teeth along its outer edges engages the toothed gear  276  on each side of the pinching mechanism  270 . 
   In operation, the bar  284  is extended (e.g., by a cylinder, not shown) after a subpurlin S has dropped into the slot  260 . This extension causes the toothed gears  276  to rotate, forcing the half-circular contacts  280  inward. The contacts  280  engage and maintain the subpurlin S in the center of the slot  260 . In addition, the counter/sensor  282  provides real-time information to the computer  128  regarding the amount that the gears  276  on at least one side of the pinching mechanism  270  have rotated, and therefore the width of the subpurlin S may be confirmed or detected. 
   The subpurlin clamping mechanisms  106  each include a cylinder  286  at the trailing end. The cylinders  286  include a rod  288  having a T-bar  290  mounted at a distal end. The outer edges of the T-bar  290  engage left and right tracks  292 ,  294 . A sensor/counter  296  is mounted along one side of the rod  288 . 
   During operation, after a subpurlin S has been inserted into the slot  260 , and the pinching mechanisms  270  have closed around the subpurlin, the carriage  220  moves into the assembly station  110 . At the end of this movement, the cylinders  286  drive the subpurlin S against the purlin P, as further described below. The T-bar  290  engages the tracks  292 ,  294 , preventing the rod  288  from rotating, thus providing an accurate reading for the sensor  296 , and preventing the subpurlins from being twisted out of the subpurlin clamping mechanisms  106 . 
   At the front end of the subpurlin carriage  220  is mounted a pair of push bars  300 . Each of the push bars  300  includes a roller  302  mounted at its top, with a vertical axis of rotation. A bolt  304  extends through the bottom of the push bar and attaches the push bar to the clamping mechanism frame  266  or the carriage frame  256 . A spring  306  is mounted on the bolt and biases the bolt and the push bar  300  into an upright position. A stop  308  and a pair of second bolts  310  operate to maintain the position of the push bar  300  in the upright position, along with the spring  306  and the bolt  304 . 
   During operation, as the subpurlin carriage  220  is extended forward, the roller  302  engages the purlin P, and the push bar  300  rotates backward around the second bolts  310  and against the bias of the spring  306 . As such, the push bar  300  helps to assure that the purlin P is pressed appropriately against the belt  184 . Because the width of the purlin P is known, the subpurlin carriage  220  may be stopped at the appropriate location by the use of the absolute feedback servo motor that drives the subpurlin carriage. As an example, the subpurlin carriage  220  may stop at a location where the push bar  300  is bent backward approximately ¼ inch. 
   The subpurlin carriage  220  includes an assembly support  312 , shown in  FIGS. 27 ,  28  and  29 . The assembly support  312  includes rollers  314  along its top edge, and is mounted on a pair of extension bars  316 . The extension bars  316  are mounted between two pinch rollers  318  so that the extension bars  316  may extend outward and forward relative to the subpurlin carriage  220 . The extension bars  316  include teeth along a lower surface for engaging a gear  320 , shown schematically in  FIG. 30 . 
   As shown in  FIG. 30 , the gear  320  is attached, via a clutch  322 , to the drive train  324  for the subpurlin carriage  220 . The drive train  324  is connected to a motor  321 , which drives gears  328  for extending the subpurlin carriage  220 . The gears  328  may, for example, engage a gear rack (not shown) on the frame  120 . The drive train  324  is linked to an intermediate axle  323  via a drive chain  325 . The clutch  322  is arranged between the drive chain  325  and a second chain  326 , which is connected to the axle  327  for the gears  320 . 
   The gear ratio for the gear  320  is preferably the same as the ratio for the drive for the subpurlin carriage  220 . However, the gear  320  is arranged to drive the assembly support  312  in the opposite direction of the subpurlin carriage  220 , and the clutch  322  is operative to engage upon retraction of the subpurlin carriage  220 . Thus, when the clutch  322  is engaged, the assembly support  312  moves outward relative to the subpurlin carriage  220  at a rate that is substantially equal to the rate in which the subpurlin carriage is moving rearwardly. Thus, during this movement, the assembly support  312  appears to be stationary as the subpurlin carriage  220  is moving rearward. When the assembly support  312  moves outward, it is positioned to support the subpurlin and diaphragm end of the assembled roof panel structure A, after the subpurlins S and diaphragm D have been attached, so that the assembled roof panel structure A may move into the exit station  112  by rolling on the rollers  314 . The clutch  322  may also include a brake so that the assembly support may be stopped after extension. 
   The operation of the subpurlin clamping mechanisms  106 , after subpurlins S have been installed in the subpurlins clamping mechanisms  106 , is shown in  FIGS. 31–38 . Beginning at  FIG. 31 , the subpurlin feeders  104  drop subpurlins S into the subpurlin clamping mechanisms  106 . Then, at  FIG. 32 , the subpurlin carriage  220  moves forward with the subpurlin clamping mechanisms  106 , and toward the assembly station  110 . 
   When the subpurlin carriage  220  enters the assembly station, a purlin P is already in place. If the brackets B are used for the subpurlin S, there is a possibility that the edge of the bracket may hit the subpurlin S. For this reason, in accordance with one aspect of the present invention, a lift is provided on the front edge of the clamping mechanism frame  266  for raising the front edge of the subpurlins S before they reach the purlin P. In the embodiment shown in the drawings, the lift is provided as an air bag or air bags  330 . The air bags  330  may alternatively be air cylinders, mechanical lifts, or any other suitable device for lifting the front end of the subpurlins S. The air bags  330  fire as the subpurlin S approaches the purlin P, thereby lifting the bracket B to clear the top edge of the purlin. The beginning of this movement is shown in  FIG. 33 , and is shown in close detail in  FIG. 34 . In  FIG. 33 , the purlin P has been removed to show detail, but in  FIG. 34  it is shown, demonstrating how lifting the front end of the subpurlins S causes the bracket B to clear over the top edge of the purlin P. 
   While the front end of the subpurlin S is lifted, the subpurlin carriage  220  continues to move toward the purlin P. In an exemplary embodiment, the air bags  330  fire during the movement of the subpurlin carriage  220 , and thus its movement does not slow until slowed by slowing of the motor  321  that drives the subpurlin carriage  220  (i.e., when the subpurlin approaches the purlin). As the subpurlin S is adjacent the purlin P, the push bar  300  engages the purlin P, ensuring that the purlin is pushed against the belt  184 . 
   After the subpurlin S has abutted against the purlin P, the cylinder  286  presses the subpurlin against the purlin, while the sensors  296  confirm or determine the length of the subpurlin. The air bags  330  may then be released, allowing the bracket B to rest against the top of the purlin P, as shown in  FIGS. 35 and 36 . 
   After the subpurlin S is attached to the purlin P (described further below), the subpurlin carriage  220  retracts, as shown in  FIG. 37 . When it has retracted approximately halfway, the assembly support  312  is released, by engaging the clutch  322 . As the subpurlin carriage  220  continues to retract, the assembly support  312  remains in the same location, so that it may support the end of the subpurlins S, as shown in  FIG. 38 . The subpurlins S are supported on the wheels  314 , and may roll toward the exit station  112  on these wheels as the purlin P is advanced through the assembly station  110 . 
   The Diaphragm Feeder 
   The diaphragm feeder  108  is designed to advance a diaphragm D into the assembly station  110 . The diaphragms D, in the shown embodiment, are provided on a diaphragm lift  340  ( FIG. 39 ). The diaphragm lift  340  includes a stack of the diaphragms D on top of a platform  341 . The platform  341  is mounted on a scissors lift  342 . The scissors lift  342  may include appropriate cylinders or other lifting devices such as is known in the lift art. Through the use of weight or position sensors, the lift  340  may maintain a top diaphragm D in the stack at a consistent height, such that as diaphragms are removed, the scissors lift  342  indexes upward to maintain the top diaphragm at this consistent level. Wheels  344  may be provided on the bottom of the diaphragm lift  340  so that the lift may be moved in and out of the diaphragm feeder station for service or to replenish the stack of diaphragms D. 
   In accordance with one aspect of the present invention, the diaphragm feeder  108  includes a diaphragm carriage  346 . In the shown embodiment, a lifting carriage  350  and a nailing carriage  352  are configured to travel with the diaphragm carriage  346 . The lifting carriage  350  is configured to lift a diaphragm D from the diaphragm lift  340  and to properly position the diaphragm, and then place the diaphragm in the assembly station  110 . The nailing carriage  352  is configured to move automatic nailers  348  ( FIG. 41 ) into place so that the nailers may nail the diaphragms D to the subpurlins S and the purlin P. The structure and operation of the nailing carriage  352  and the lifting carriage  350  are further described below. 
   Turning now to  FIG. 40 , the lifting carriage  350  is suspended from a horizontal beam  354  by a swivel attachment  356 . The horizontal beam  354  is suspended from a pair of cross beams  358  that extend orthogonally to the horizontal beam. These cross beams  358 , in turn, are suspended from a pair of orthogonally arranged cross beams  360 . 
   The lifting carriage  350  includes a manifold  362  ( FIG. 41 ) having a central beam  364  ( FIG. 40 ). A number of suction cups  366  are attached to the manifold  362  and are fluid communication with the manifold. The manifold  362  is also connected to a vacuum system (not shown). 
   Returning now to  FIG. 40 , a worm gear  368  extends from the cross beam  364  on the manifold  362  to the cross beam  360 . A second worm gear  370  is included between the attachment of the horizontal beam  354  and the cross beam  358 . A third worm gear  372  is attached between the cross beams  358  and the orthogonally arranged cross beam  360 . 
   The three worm gears  368 ,  370 ,  372  provide rotational, x-, and y-movement of the lifting carriage  350  relative to the nailing carriage  352 . The movements of the worm gears  368 ,  370 ,  372  may be operated by absolute feedback motors, such as absolute feedback servo motors. As such, the location of the lifting carriage  350  and the speeds of the operation of the worm gears  368 ,  370 ,  372  may be easily altered by a programmer or operator via the computer  128 , or may be performed automatically by the computer. In addition, the automatic feedback motors permit the lifting carriage  350  to be accurately located relative to the nailing carriage  352 , and for that location to be known to the computer at all times. 
   Operation of the worm gear  368  causes the beam  364  of the manifold  362  to rotate, causing the lifting carriage  350  to rotate about the swivel attachment  356  in the direction of the arrows  374 . Operation of the worm gear  370  causes the horizontal beam  354  to move along the cross beams  358 , moving the horizontal cross beam in the direction of the arrows  376 . Operation of the worm gear  372  causes the cross beams  358 , and therefore the horizontal beam  354  and the lifting carriage  350 , to move along the linear bearings  378 , in the direction of the arrow  379 . All of these movements may be controlled by the computer  128 , and are smooth because of the use of the worm gears  368 ,  370 , and  372 . Other mechanisms may be used for providing the rotational, x- and y-directional movements. 
   The Nailing Carriage 
   The nailing carriage  352  includes a number of automatic nailers  348  suspended therefrom. The automatic nailers  348  may be, for example, nailing guns or other devices which are capable of pneumatically, mechanically, or otherwise driving fasteners for attaching the diaphragms D to the subpurlins S and the purlin P. As another example, the automatic nailers may be replaced with automatic screw drivers or other appropriate fastener drivers. Alternatively, if metal components are used for the roof panel structure A, the automatic nailers  348  may be welders. 
   The nailing carriage  352  may be suspended from the cross beams  360 . The cross beams  360  are mounted on linear bearings  382  that provide lateral movement in the direction up and down in  FIG. 40  of both the nailing carriage  352  and the lifting carriage  350 . A worm gear or other appropriate mechanism may be provided for movement of the cross beams  360  relative to the linear bearings  382 . 
   The lifting carriage  350  and the nailing carriage  352  may also be moved to the left and right in  FIG. 40  by rotation of a gear  384  ( FIG. 41 ) that engages the rack  386 . The gear  384  may be driven by an appropriate motor or other mechanism (not shown). To aid in movement of the lifting carriage  350  and the nailing carriage  352 , the diaphragm carriage  346  is suspended by wheels  388  ( FIGS. 40 and 41 ), which run along a track  389  ( FIG. 40 ). 
   As described thus far, it is apparent that the lifting carriage  350  may move in x, y, and rotational directions relative to the nailing carriage  352 . The nailing carriage  352  is fixed for movement with the cross beam  360 . The lifting carriage  350 , on the other hand, may move relative to the cross beam  360  in the left to right direction in  FIG. 40 , denoted by the arrow  349  and movement provided by the worm gear  372 , in the up and down directions in that drawing, denoted by the arrow  376  and provided by the worm gear  370 , and in the rotational direction by swiveling about the swivel connection  356 , denoted by the arrow  374  and provided by the worm gear  368 . 
   In addition to the above three degrees of movement, the nailing carriage  352  and the lifting carriage  350  may be moved together in x and y directions. First, the two carriages  350 ,  352  may be moved up and down in  FIG. 40  in the direction of the arrows  387  by moving the cross beams  360  along the linear bearings  382 . Second, the nailing carriage  352  and the lifting carriage  350  may be moved left and right in  FIG. 40  by rotation of the gear  384  and movement of the entire diaphragm carriage  346  along the track  389 . 
   A lift mechanism is provided to allow one more degree of movement for the lifting carriage  350  and the nailing carriage  352 . The lift mechanism permits the two carriages  350 ,  352  to move out of the page in  FIG. 40 , or upward. The lift mechanism may be provided in a number of ways, including, but not limited to, cylinders, air bags, and mechanical lifts, but a particular embodiment is shown in the drawing that utilizes wedges  390  that are driven under wheels  392 . The lifting carriage  350  and the nailing carriage  352  are suspended by the wheels  392 . Driving the wedges  390  under the wheels  392  causes the lifting carriage  350  and the nailing carriage  352  to be raised. 
   To permit the wedges  390  to be driven under the wheels  392 , the wedges  390  are mounted for sliding movement on rails  394 . The rails  394  are mounted for movement along the outer edges of the diaphragm carriage. Cross beams  396  extend between the two rails  394 , such that a rectangle is formed by the cross beams  396  and rails  394  (the rectangle is shown with stippling for ease of viewing). A rear drive  398 , such as an absolute feedback servo motor, is attached to one of the cross beams  396 . The absolute feedback motor permits the location of the rectangle and the speed of the operation to be set by the computer  128 , or to be easily altered by a programmer or operator via the computer  128 . Actuation of the rear drive  398  causes the wedges  390  to move relative to the wheels  392 , thus raising or lowering the lifting carriage  350  and the nailing carriage  352 . To assure that the movement of the lifting carriage  350  and the nailing carriage  352  is vertical only, and not lateral, wheels  402  are connected to these carriages. The wheels  402  are arranged to move along plates  404  that are attached to the diaphragm carriage  346 . Engagement of the wheels  402  with the plates  404  prevents lateral movement of the lifting carriage  350  and the nailing carriage  352 . 
   To aid in driving the wedges  390  under the wheels  392 , a second cylinder  400  may be provided that is attached to the front cross beam  396 . This cylinder  400  acts as a balancing cylinder for the rear cylinder  398 , and permits a smaller sized cylinder to be used and smoothes the lifting of lifting carriage  350  and the nailing carriage  352  relative to the diaphragm carriage. 
   Operation of the Lifting Carriage 
   Operation of the diaphragm feeder  108  begins with the diaphragm lift  340  in a raised position, with a diaphragm just below the lifting carriage  350 , such as is shown in  FIG. 39 . At this position, the lifting carriage  350  and the nailing carriage  352  are in the raised position, with the wheels  392  driven upward by the wedges  390 , such as is shown in  FIGS. 42 and 43 . 
   With the lifting carriage  350  centered over the stack of diaphragms D, the wedges  390  are driven from under the wheels  392 , causing the lifting carriage  350  and the nailing carriage  352  to lower. At the lowered position, the suction cups  366  are lowered downward into contact with the top of the diaphragm D. This action may occur, for example, by the suction cups being retractable into sleeves. The suction cups  366  are shown attached to a top diaphragm D in  FIG. 44 . 
   After the suction cups  366  are attached to the diaphragm D, the lifting carriage  350  and the nailing carriage  352  are lifted upward to the position shown in  FIGS. 45 and 46 . The movement upward is caused by the wedges  390  being driven under the wheels  392 . 
   Once in the up position, the diaphragm D may be aligned relative to the nailing carriage  352  so that the diaphragms may be properly positioned on the subpurlin S. One way of aligning the diaphragm D is shown in  FIGS. 47–50 . In accordance with one aspect of the present invention, three sensors  410 ,  412 , and  414  are provided that are aligned so that a first two of the sensors ( 410  and  412 ) are located just to one side of the diaphragm D after it is lifted, and the third sensor  414  is located just behind the diaphragm after it is lifted. 
   To properly align the diaphragm D, the diaphragm is first rotated as is shown in  FIG. 47  to the position shown in  FIG. 48 . At this location, the leading right edge of the diaphragm engages the first sensor  410 . The diaphragm D is then rotated in the opposite direction until the trailing right corner of the diaphragm engages the second sensor  412 . 
   Using the point of rotation and the amount of rotation of the diaphragm, geometry may be used to determine the orientation of the diaphragm. Using this geometry, the diaphragm D may be aligned centered properly underneath the lifting carriage  350 . Then, to establish a reference leading edge of the diaphragm, the diaphragm is moved as shown in  FIG. 50  until it engages the sensor  414 . Once engaged, the trailing edge of the diaphragm is known, and the leading edge may be calculated by knowing the length of the diaphragm. The diaphragm D may also be moved to the right in  FIG. 50  to engage the sensors  410  and  412 . This movement establishes or confirms the location of the right edge of the diaphragm. 
   Other methods may be used to align the diaphragm D properly, including but not limited to assuring that the diaphragm is properly placed on the lifting mechanism  340 . However, the presently described embodiment provides a structure and operation by which the alignment of the diaphragm D may be confirmed and/or properly set before the diaphragm enters the assembly station  110 . 
   After the diaphragm D is properly aligned, it is advanced to the assembly station  110  by rotating the gear  384  and causing the lifting carriage  350  and the nailing carriage  352  to move into the assembly station and over the subpurlins S and the purlin P. This position is shown in  FIG. 51 . 
   The movements of the lifting carriage  350  and the nailing carriage  352  are preferably operated by absolute feedback motors, such as absolute feedback servo motors. As such, the location of the lifting carriage  350  and the nailing carriage  352  and the speeds of the movement of the carriages may be easily set by the computer  128 , and altered by a programmer or operator via the computer  128 . Because the width of the purlin is known, the diaphragm D may be properly centered over the subpurlins S and aligned over the brackets B on the subpurlins using the absolute feedback motors. The wedges  390  are then driven from under the wheels  392 , causing the lifting carriage  350  and the nailing carriage  352  to lower, such as is shown in  FIG. 52 . At this lowered position, the automatic nailers  348  are slightly spaced from the top of the diaphragm D, and the suction cups  366  still hold the diaphragm in place. 
   The automatic nailers  348  are then lowered to nail the first series of nails into the subpurlin S and purlin P. Preferably, this first nailing sequence drives nails through the diaphragm D and through the brackets B and into the top of the purlin P. Other nails are driven into the subpurlins S through the diaphragm D. The nails that are driven through the brackets B and the diaphragm D and the purlin P are used to anchor the three components of the diaphragm, subpurlin S, and purlin relative to one another. 
   The position of the automatic nailers  348  in this first nailing sequence is shown in  FIG. 53 . Again, in this first nailing sequence, the suction cups remain down, as is shown in  FIG. 54 . In this manner, the suction cups  366  assure that the diaphragm D is held in the proper position during the first nailing sequence. 
   After the first nailing sequence, the suction cups are withdrawn, as is shown in  FIG. 55 . The suction cups  366  are shown fully withdrawn in  FIG. 56 . The nailing guns also slightly retract and move to the next location, described further below. At this next location, the suction cups continue to remain upward, as is shown in  FIG. 56 , even as the automatic nailers  348  are lowered. 
   Operation of the Nailing Carriage 
   After the first nails have been driven into the diaphragm by the automatic nailers  348 , the automatic nailers may be indexed to nail another series of nails. The position where the automatic nailers is indexed depends upon the number of nailers and the desired spacing of the nails. In one example, the nailing carriage  352  includes five rows of nine automatic nailers each. The automatic nailers  348  in a single row may be spaced, for example, a foot from one another. If such an embodiment is used, after the initial nailing, the automatic nailers  348  may retract ( FIG. 57 ), and index half the distance toward the adjacent automatic nailer&#39;s original location (e.g., 6 inches, as shown in  FIG. 58 ). 
   The automatic nailers  348  then drop and nail another pattern of nails. The nailers may also move perpendicular to the subpurlins S so that additional nails may be driven into the purlin P through the diaphragm D. 
   An example of the arrangement of the five rows of automatic nailers  348  is shown in  FIG. 59 . As can be seen, two rows (i.e., the rows to the right in the figure) of the automatic nailers  348  are adjacent to one another. This space corresponds to the edge of a diaphragm D of the leading subpurlin S. At this location, the trailing edge of the adjacent diaphragm D is nailed into the leading subpurlin, as well as the forward end of the diaphragm that has just been placed. If the diaphragm just placed is the first diaphragm that has been placed, then the automatic nailers  348  that would nail into the trailing end of the adjacent diaphragm do not fire. The remaining rows align with the subpurlins S. 
   The embodiment of the five rows of automatic nailers  348  may be used for a variety of different roof panel structures A. Different automatic nailers  348  fire depending upon the location along the purlin, the length of the subpurlins S and the diaphragms D, and the position of the nailers relative to the subpurlins, the diaphragms, and the purlin.  FIG. 60  shows the relation of the position of the automatic nailers  348  and the suction cups  366 , and  FIG. 61  shows possible zones for the automatic nailers  348 . The representation in  FIG. 60  includes additional automatic nailers  348  that align with the purlin. These additional automatic nailers permit the purlin to be attached with additional nails without having to index the nailers perpendicularly relative to the subpurlins. The zones represent automatic nailers  348  that may fire at the same time. Different zones are used based upon the above-listed factors. 
   In  FIG. 61 , fourteen different zones are shown. When the diaphragm feeder  108  is in the assembly station  110 , the F zones are at the purlin end of the assembly station  110 , and the R zones are at the opposite end of the assembly station. The guns within a zone fire in unison when so instructed by the computer  128 . The zones shown are but one way to separate the guns, but the particular zones shown permit a wide variety of nailing patterns for different sizes of diaphragms and different nailing locations on the diaphragms. As one example, for the initial nailing of a diaphragm that is ten feet in length and eight feet wide, and which has been placed behind another diaphragm (e.g., is not the first diaphragm on the purlin P), all of the automatic nailers  348  for all of the stations would fire. However, if a diaphragm D was the first diaphragm to be attached to the purlin P, then the stations F 1 , M 5 , and R 4  would not fire, because there would not be another, adjacent diaphragm in which to nail. 
   If, on the other hand, a diaphragm D that is being attached is only eight feet in length, then none of the R zones would fire on the initial nailing. As the nailing carriage  352  indexes down the rows, such as is shown in  FIG. 58 , then the F and M zones continue to fire as appropriate. If, however, the nailing carriage  352  indexes sideways so as to drive additional nails through the diaphragm D into the purlin P, then the stations F 1  and F 4  may be turned off and the other F stations fire as the nailing carriage is indexed. A variety of other nailing combinations may be used so as to appropriately attach the diaphragm D to the subpurlins and purlin. As can be understood, these nailing patterns may change according to the number of subpurlins S used, the length of the subpurlins and the diaphragms D, the number of nails desired in the nailing pattern, the position of the subpurlins S and diaphragms D relative to the purlin P, and other factors. 
   Operation of the Roof Panel Structure Assembly Mechanism 
     FIG. 62  is a flow diagram generally representing steps for automatically producing a roof panel structure A in accordance with one aspect of the present invention. Beginning at step  6202 , a check is made to determine whether a purlin P is in the assembly station  110 . If not, step  6202  branches to step  6204  where a purlin P is inserted into the assembly station. This operation is described in more detail with the discussion of  FIG. 63 . After the purlin is inserted, step  6204  branches to step  6206 , where the purlin P is indexed the appropriate amount into the assembly station  110 . This process is described with  FIG. 64 , below. 
   If a purlin is in the assembly station  110 , step  6202  branches to step  6208 , where a determination is made whether the end of the purlin has been reached. That is, a determination is made whether any more subpurlins S or diaphragms D will be added to the purlin P. If the end has been reached, step  6208  branches to step  6210 , where the remainder of the purlin P is fed into the exit station  112 . The assembled roof panel structure A is then removed, e.g., with the forklift F (step  6212 ). If the end of the purlin has not been reached, then step  6208  branches to step  6206 , where the purlin is indexed the appropriate amount (e.g., the width of one diaphragm D). 
   In step  6214 , the subpurlins S are advanced against a purlin P that is in the assembly station  110 . The steps for this process are discussed with  FIGS. 65 and 66 , below. In step  6216 , a diaphragm D is placed over the subpurlins S and the purlin P. This step is discussed with  FIG. 67  below. 
   The process then proceeds to step  6218 , where the diaphragm D is nailed or otherwise attached to the subpurlin S and purlin P. This process is performed by the nailing carriage  352 , was described above, and is further described with  FIGS. 68–73  below. 
   The general overview of the process is but one way to perform some of the features of the present invention, and, has been described above, different orders may be used, as well as different structures for performing the functions described herein. As one nonlimiting example, the assembly station  110  may receive two diaphragms at one time for attachment by the nailing carriage  352 . As another example, subpurlins may be added one at a time. Also, diaphragms may be placed upside down, and subpurlins may be added over the diaphragms. Other variations are within the scope of the present invention. 
   Inserting a Purlin Into the Assembly Station 
     FIG. 63  is a flow diagram generally representing steps for inserting a purlin P into the assembly station  110  in accordance with one aspect of the present invention. Beginning in step  6302 , a purlin P is lifted onto the lifting mechanisms  132  (e.g., by the hoist  130 ). The lifting mechanisms  132  then lift the purlin P or lower the purlin P to the appropriate height, for example by rotating the shaft  156  (step  6304 ). 
   In step  6306 , the purlin P is fed into the assembly station  110 . This may be done manually, for example by pushing the purlin P until it engages and is caught by the toothed driven roller  180 . 
   Once the purlin P begins to enter the assembly station  110 , the computer  128  sets the reference for the purlin to zero at step  6308 . In this manner, using the absolute feedback servo motors that are associated with the toothed driven roller  180  and the belt  184 , the exact amount the purlin P has been advanced into the assembly station  110  may be tracked. If desired, the width of the purlin P may also be sensed, for example by sensing the amount that the biased idler roller  182  is moved as the purlin is inserted into the assembly station  110 . 
   At step  6310 , the purlin P is indexed an appropriate amount into the assembly station  110 . This amount might be, for example, an appropriate lead for the end of the purlin P, plus the distance of one diaphragm width. After the purlin P has been indexed the appropriate amount, it is ready for attachment of the subpurlin S and diaphragm D. 
   Indexing the Purlin Through the Assembly Station 
     FIG. 64  is a flow diagram generally representing steps for indexing a purlin P through the assembly station  110  as subpurlins S and diaphragms D are added to the purlin. Beginning at step  6402 , the toothed driven roller  180  is rotated. Simultaneous with this rotation, the belt  184  is rotated (step  6404 ). Also simultaneous with movement of the toothed driven roller  180 , the conveyor  196  is advanced. Each of these components engages a portion of the purlin P as it is indexed through the assembly station  110 . Preferably, their movements are synchronized by the computer  128  so that none of the components is working against the others. 
   In addition to the toothed driven roller  180 , the belt  184 , and the conveyor  196 , the chain  202  advances as a purlin P is advanced through the assembly station  110  (step  6408 ). It is also desired that the computer  128  synchronizes the advancement of the chain  202  with the movement of the other components. 
   Operation of the Subpurlin Feeder 
     FIG. 65  is a flow diagram generally representing steps for loading a subpurlin S into the subpurlin clamping mechanisms  106  in accordance with one aspect of the present invention. Beginning at  6502 , a query is made as to whether the subpurlin feeders  104  are loaded. This may be done, for example, by a sensor or another suitable detection device. Alternatively, the step may be conducted by a user, e.g., via visual inspection. The step may involve determining whether any subpurlins S are in the subpurlin feeder  104 , or may involve a determination whether a certain amount of subpurlins S are within the subpurlin feeder (e.g.,  6 ). If a determination is made that the feeder is not loaded properly, then step  6502  branches to step  6504 , where the subpurlin feeder  104  is loaded. This step may be conducted automatically, or manually by an operator. 
   In either event, at step  6506 , a determination is made whether the clamping mechanism carriage  220  is in place under the feeders. If not, then the process continues to loop around until the clamping mechanism carriage  220  is in place. If the clamping mechanism carriage  220  is in place, then step  6506  branches to step  6508 , where the penultimate subpurlin S within the subpurlin feeders  104  is held (e.g., by the plungers  240 ). 
   At step  6510 , the bottom subpurlin S is released, e.g., by the arms  242 . After the subpurlins S have been released and have dropped into the subpurlin clamping mechanisms  106 , the arms  242  are closed, and the penultimate subpurlin is released at step  6512 . The process then loops back to step  6502 . 
   Advancement of the Subpurlin Clamping Mechanisms 
     FIG. 66  is a flow diagram generally representing steps for advancing a subpurlin S via a subpurlin clamping mechanism  106  into the assembly station  110 . Beginning at step  6602 , a determination is made whether a subpurlin S is present within the subpurlin clamping mechanism  106 . If not, the process continually loops back until a subpurlin S is present. If a subpurlin S is present, then step  6602  branches to step  6604 , where the pinching mechanisms  270  are closed. At step  6606 , the width of the subpurlin S is sensed or confirmed, e.g., by the sensor/counter  282 . 
   At step  6608 , the subpurlin clamping mechanisms  106  are advanced into the assembly station  110 . The front ends of the subpurlins are lifted as they approach the purlin at step  6610 . As described above, this step permits the brackets B to clear the purlin P as the subpurlin S enters the assembly station. Lifting of the subpurlins S may be provided, for example, by the inflatable bags  330 . 
   As the subpurlins S engage the purlin P, in step  6612  the front ends of the subpurlins are lowered so that the bracket B rests on top of the purlin P. The subpurlins S are then pressed against the purlin P in step  6614 . This step may be performed, for example, by the cylinders  286 . As the cylinders  286  press the subpurlin into place against the purlin, the sensors  296  detect the stroke of the cylinders  286 , so as to sense or confirm the length of the subpurlins S (step  6616 ). 
   The subpurlins S are then lowered. It is possible that the brackets B may stick on the purlin P during this lowering process. To handle such a situation, the subpurlin carriage  220  may backup slightly (e.g., ¼ inch) to prevent hanging of the brackets, and then may advance again after the lowering. These steps may be easily added to the programming of the movements for the subpurlin carriage  220 , particularly where an absolute feedback motor is used to direct its movements. 
   At step  6618 , the process waits until a diaphragm D is attached to the subpurlins and purlin P (i.e., the nailing process is completed). The process continually loops back until the diaphragm D is attached. Once the diaphragm D is attached, step  6618  branches to step  6620 , where the clamping mechanism carriage  220  is withdrawn. This process may occur, for example, after the diaphragm D has been initially nailed with the first nailing pattern, and while the suction cups  366  still hold the diaphragm and subpurlin S in place. Alternatively, the clamping mechanism carriage  220  may be withdrawn after all nailing has been done. In any event, as the clamping mechanism carriage  220  is withdrawn, the support arm  312  is extended. As described above, the support arm  312  extends out at the same rate that the clamping mechanism carriage  220  retracts, and thus the support arm  312  appears to be stationary during retraction of the clamping mechanism carriage  220 . 
   Advancing the Diaphragms Into the Assembly Station 
     FIG. 67  is a flow diagram generally representing steps for advancing a diaphragm D into the assembly station  110  in accordance with one aspect of the present invention. Beginning at step  6702 , the diaphragm lift  340  raises the top diaphragm D to a reference height, e.g., spaced just below the lifting carriage  350 . The lifting carriage  350  is then lowered at step  6704 , for example, by moving the wedges  390  from underneath the wheels  392 . 
   At step  6706 , the diaphragm D is grabbed by the lifting carriage  350 , e.g., by the suction cups  366 . The lifting carriage  350  is then raised at step  6708 . Again, this may be done by driving the wedges  390  under the wheels  392 , or in another suitable manner. At step  6710 , the diaphragm D is aligned, for example by using the sensors  410 ,  412 , and  414 . 
   At step  6712 , the diaphragm D is advanced into the assembly station  110 . This is done, for example, by rotating the gear  384  so that it moves along the rack  386 , and moves the diaphragm carriage  346  into the assembly station  110 . The diaphragm D is then lowered onto the purlin P and subpurlins S at step  6714 . This may be done, for example, by moving the wedges  390  out from under the wheels  392 . At step  6716 , the first series of nails is driven by the nailing carriage  352 . After these nails have been driven, the suction cups  366  release the diaphragm D in step  6718 . 
   Assembly Example 
   An example of steps of assembly of a roof panel structure A is shown in  FIGS. 68–73 . As is described further below, the steps taken by the roof panel structure assembly mechanism  100  are different depending upon the size of the diaphragms and the location of the purlin P relative to the assembly station  110  (i.e., how far it has been inserted). For example, one to four subpurlin clamping mechanisms  106  may be used, depending on the width of the diaphragm, and the position of the purlin P in the assembly station  110 . 
   An example of steps of assembly for a four-foot-wide diaphragm D is shown in  FIGS. 68–73 . The subpurlins S are spaced two feet on center. Thus, for an assembled roof panel structure A, there are three subpurlins S that engage each diaphragm D. Two of the subpurlins are along the edges of the diaphragms D, and one subpurlin is intermediate the two subpurlins S on the edges. 
   To begin assembly, two subpurlins S are inserted into the two leading subpurlin clamping mechanisms  106 , as is shown in  FIG. 68 . A diaphragm D is lowered onto the two subpurlins S so that it extends halfway over the first subpurlin and approximately two feet beyond the second subpurlin and over a third subpurlin clamping mechanism  106  that does not include a subpurlin therein. 
   The automatic nailers  348  lower, as is shown in  FIG. 69 . Two nailing guns fire in this sequence: The inside row of automatic nailers  348  at the first subpurlin S, and the automatic nailers at the second subpurlin. The outside row of automatic nailers  348  at the first subpurlin S do not fire, because there is not a diaphragm D on that side of the first subpurlin. 
   The purlin P, the diaphragm D, and the assembled subpurlins S are then indexed down so that the rear edge of the diaphragm D is aligned over the center of the first subpurlin clamping mechanism  106 , as is shown in  FIG. 70 . The amount of the diaphragm D that is hanging rearwardly from the previously attached subpurlin S is approximately two feet in the embodiment shown in the drawings. This amount permits the end of the diaphragm D to be flexible, so that it may bend upward. This flexibility is needed when the subpurlins S are raised upward at the end of their movement toward the purlin P, for example by the air bags  330 . This movement upward of the subpurlins S and the resultant bending of the rear portion of the diaphragm are shown in  FIG. 71 . 
   After the two subpurlins S in  FIG. 71  have been lowered into position against the purlin P, another diaphragm D is lowered against the top these two subpurlins and is aligned against the back of the adjacent diaphragm. This positioning of the second diaphragm is shown in  FIG. 72 . The automatic nailers  348  then lower and nails are driven through the back end of the leading diaphragm into a subpurlin in the first subpurlin clamping mechanism  106 , and through the front edge of the trailing diaphragm into the same subpurlin, and also into the second subpurlin. The purlin P and the attached subpurlins S and diaphragms D then are advanced. 
   The process above is continued until the end of the purlin P is reached. At this point, the last diaphragm D that has been attached has a trailing end that extends two feet beyond the last attached subpurlin S. The subpurlin feeders  104  then drop only one subpurlin S into the first subpurlin clamping mechanism  106 . A single subpurlin S shown in the first subpurlin clamping mechanisms  106  is shown in  FIG. 73 . After the single subpurlin S has been inserted, the automatic nailers  348  are lowered and only the first row of guns, i.e., the outermost of the two adjacent sets of rows fires, driving the nails in through the end of the last diaphragm D into the single subpurlin S. 
   The assembled roof panel structure A is then ready for removal from the assembly station  110 . It can be understood that the assembly process will be different than described above if the diaphragm D is wider than four feet. For example, if an eight-foot-wide diaphragm is used, then all four subpurlin clamping mechanisms  106  are filled with subpurlins S, and the diaphragm extends two feet beyond the last subpurlin clamping mechanism  106 . Nailing guns fire according to the subpurlins S that are present within the subpurlin clamping mechanisms  106 . 
   The roof panel structure assembly mechanism  100  of the present invention provides fully automated assembly of roof panel structures A. The purlins are indexed and fed using an automated system, the subpurlins are fed into the subpurlin clamping mechanisms  106  by an automated system and are advanced into the assembly station via another automated system, and the diaphragms are advanced into the assembly station via yet another automated system. These automated systems do not require user input once started. In many locations, a sensor or sensors sense or confirm the width or length of the purlin P or subpurlin S, and the automated system aligns the subpurlins S or the diaphragm D in the appropriate location due to the sensed width or length. Many of the automated movements of the components of the roof panel structure assembly mechanism  100  are operated by absolute feedback motors, such as absolute feedback servo motors. As such, the location of the components of the subpurlin carriage and the speeds of the operation may be easily and accurately set by the computer  128 . For example, operation may be altered automatically due to sensor or operator input. As such, the roof panel structure assembly mechanism  100  can save many costs and much labor involved in normal construction of roof panel structures A. 
   Other variations are within the spirit of the present invention. Thus, while the invention is susceptible to various modifications and alternative constructions, a certain illustrated embodiment thereof is shown in the drawings and has been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims.