Abstract:
An automated floor assembly machine is provided for attaching longitudinally aligned floor boards to transverse positioned cross-members of a wheeled trailer. The machine comprises a carriage for longitudinal movement relative to the floor boards, a drill mounted on the carriage so that the drill is vertically and laterally movable with respect to the carriage, a fastener driver mounted on the carriage so that the fastener driver is vertically and laterally movable with respect to the carriage, a sensor operably mounted to the carriage so that the transverse mounted cross-members are detectable by the sensor, a drive motor in communication with the carriage for moving the carriage longitudinally along the floor boards into alignment with the cross-members, and a control system having a processor in operative communication with the carriage, the drill, the fastener driver, the sensor, and the drive motor.

Description:
CLAIM OF PRIORITY 
     This non-provisional patent application claims priority to U.S. Provisional Patent Application Nos. 60/541,523, filed Feb. 2, 2004 and 60/542,719 filed Feb. 6, 2004, the entire disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to automatic fastening machines and methods, and, more specifically, to an apparatus and method for automatically assembling major subassemblies together. 
     Large objects, such as highway trailers and aircraft wings, typically comprise multiple major subassemblies fastened together. For example, a highway trailer includes major subassemblies such as a roof, side walls, and floor. The floor may include horizontal cross members connected to opposing side bottom rails. A floor deck is placed over the cross members and attached to the cross members. In the case of a sixty foot long highway trailer, the load demands and shear size of the major subassemblies require numerous points of attachment to ensure structural stability. 
     A wide variety of machines exist for attaching one major subassembly to another using bolts or rivets. These machines generally include a first unit to drill holes in the subassemblies, a supply of bolts or rivets, and a second unit to secure the bolts or upset the rivets in the subassemblies. Generally, the machines mount on a platform, and the platform moves relative to the subassemblies to position the machine at a desired attachment location. 
     To increase a trailer&#39;s structural integrity, it is preferable to attach the floor deck coincident with the cross beams. In the case of large subassemblies, however, the rivet or screw locations are often not uniformly spaced. For example, in the floor subassembly described above, adjacent cross members may be spaced at differing widths due to the presence of wheel axles, doorways and other design limitations. In addition, manufacturing tolerances result in slight variations in the distance between cross beams on each individual trailer and in the locations of cross beams on other trailers of the same general design and measurement. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes and addresses disadvantages of prior art constructions and methods and provides an automated assembly machine for attaching a work piece at sequential work sites, the machine comprising a carriage disposed proximate to the work piece for movement relative to a longitudinal axis of the work piece, at least one drill movably mounted on the carriage for transverse movement relative to the longitudinal axis of the work piece, at least one fastener driver movably mounted on the carriage proximate to the at least one drill for transverse movement relative to the longitudinal axis of the work piece, a sensor disposed on the carriage so that when the carriage is moved longitudinally along the axis of the work piece proximate to a first work site of the sequential work sites, the sensor detects the first work site, a drive motor in communication with the carriage for moving the carriage longitudinally with respect to the work piece, and a control system in operative communication with the carriage, the at least one drill, the at least one fastener driver, the drive motor, and the sensor. The control system has a processor that is operable in a first mode to move the at least one drill transverse to the work piece longitudinal axis at the first work site so as to drill one or more holes in the work piece and move the at least one fastener driver transverse to the work piece longitudinal axis at the first work site to secure fasteners in the one or more holes. In a second mode, following operation of the at least one drill and the at least one fastener driver, the processor is operable to move the carriage to a second work site of the sequential work sites responsively to the sensor. 
     In yet another embodiment, an automated assembly machine is provided for attaching a first subassembly of a cargo trailer to a second subassembly of a cargo trailer at a plurality of positions along the longitudinal axis of the first subassembly, where the second subassembly includes a plurality of structural features that are positioned transverse to a longitudinal axis of the first subassembly at the positions. The machine comprises a carriage movable with respect to the longitudinal axis of the first subassembly, a drill mounted to the carriage, a fastener driver mounted to the carriage proximate to the drill, a sensor coupled to the carriage so that the sensor detects one of the structural features to align the drill and the fastener driver with the one of the structural features; and a control system, including a processor, in operative communication with the sensor, the carriage, the drill, and the fastener driver. The control system receives a signal from the sensor when the drill and the fastener driver are aligned with the one of the structural features and the processor is configured to actuate the drill to drill a preset hole pattern through the first and the second subassemblies at one of the plurality of positions and actuate the fastener driver to drive fasteners into the holes of the preset hole pattern. The control system is also configured to move the carriage to another one of the plurality of positions responsively to the detection of the plurality of structural features by the sensor and to operate the drill and fastener driver at the second one of the plurality of positions. 
     In another embodiment of the invention, an automated floor assembly machine is provided for attaching longitudinally aligned floor boards to transverse positioned cross-members of a wheeled trailer. The machine comprises a carriage for longitudinal movement relative to the floor boards, a drill mounted on the carriage so that the drill is vertically and laterally movable with respect to the carriage, a fastener driver mounted on the carriage so that the fastener driver is vertically and laterally movable with respect to the carriage, the fastener driver being adapted to drive fasteners at the cross members, a sensor operably mounted to the carriage so that the transverse mounted cross-members are detectable by the sensor, a drive motor in communication with the carriage for moving the carriage longitudinally along the floor boards into alignment with the cross-members, and a control system having a processor in operative communication with the carriage, the drill, the fastener driver, the sensor, and the drive motor. The processor has a first mode configured to automatically move the carriage into alignment with one of the cross-members responsively to signals provided by the sensor and to automatically operate the drill and the fastener driver at the one of the cross-members to fasten the floor boards to the one of the cross-members and a second mode configured for manual movement of the carriage into alignment with one of the cross-members responsively to signals provided by the sensor. 
     Also provided is a method for automatically fastening a first plurality of longitudinal components to a second plurality of transverse components relative to a longitudinal axis of the first plurality of longitudinal components. The method comprises the steps of providing a machine on a carriage movable relative to the longitudinal axis of the first plurality of longitudinal components, wherein said machine includes a drill, a driver, a sensor, and a processor, automatically detecting one of the second plurality of transverse components using signals from said sensor that are sent to said processor, automatically drilling a plurality of holes through the first plurality of longitudinal components across the one of the second plurality of transverse components, and automatically inserting a fastener into each one of the plurality of holes to secure the first plurality of longitudinal components to the one of the second plurality of transverse components. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which: 
         FIG. 1  is a perspective view of a floor assembly machine according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of the floor assembly machine of  FIG. 1 ; 
         FIG. 3  is a top plan view of the floor assembly machine of  FIG. 1 ; 
         FIG. 4A  is a detail perspective view of a drill and driver carriage for use in the floor assembly machine of  FIG. 1 ; 
         FIG. 4B  is a detail perspective view of the drill and driver carriage of  FIG. 4A  in an extended position; 
         FIG. 5  is a perspective view of a drill and driver unit for use in the floor assembly machine of  FIG. 1 ; 
         FIG. 5A  is a perspective view of a drill and driver bank for use in the drill and driver unit of  FIG. 5 ; 
         FIG. 5B  is a detail cross-sectional view of a driver head of the drivers shown in  FIG. 5A ; 
         FIG. 6A  is a perspective view of a screw feeder for use in the floor assembly machine of  FIG. 1 ; 
         FIGS. 6B-6C  are detailed perspective views of the screw feeder shown in  FIG. 6A ; 
         FIG. 7A  is a detailed perspective view of a ball screw motor and mounting plates used to laterally move the drill and driver unit of  FIG. 5 ; 
         FIG. 7B  is a left elevation view of the ball screw and mounting plates of  FIG. 7A . 
         FIG. 8  is a perspective view of a cross member sensor for use in the floor assembly machine shown in  FIG. 1 ; 
         FIG. 9A-9D  are schematic representations of a standard drill and driver pattern for the floor assembly machine of  FIG. 1 ; and 
         FIG. 10  is a flow diagram for a control system of the floor assembly machine shown in  FIG. 1 . 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Referring to  FIGS. 1-3 , an automated floor assembly machine  10  includes a carriage  12 , drill and driver unit  14  ( FIGS. 1 and 3 ), a control panel  18  ( FIGS. 1 and 3 ), and a control box  19 . Carriage  12  mounts on a rail system  22  ( FIGS. 1 and 2 ) on which the carriage moves adjacent to a subassembly, here a floor assembly  24  ( FIGS. 1 and 2 ) that includes cross-members  26  and floor deck  28  to be attached to one another. It should be understood that automated floor assembly machine  10  can operate on any structure that has a first part that is to be connected to a plurality of discrete second parts that are spaced apart from each other, such as that shown in floor assembly  24 . 
     Referring particularly to  FIGS. 1 and 2 , rail system  22  extends generally parallel to the length of floor assembly  24  to facilitate the carriage&#39;s movement with respect to the floor assembly. The rail system generally includes a respective I-beam  30  located adjacent to each side of floor assembly  24  and a pair of angled iron tracks  32 , each located along an outer edge of a respective I-beam  30 . Tracks  32  are of a length sufficient to allow machine  10  to reach each end of the floor assembly. V-groove casters  34  ( FIG. 1 ) receive the angled iron tracks and allow carriage  12  to move along the length of rail system  22 . 
     I-beams  30  support carriage  12  as it moves along floor assembly  24 . Two tractor drives  36  ( FIGS. 1-3 ) located at the front end of automated floor assembly machine  10  each drive a respective friction wheel  38  ( FIG. 2 ) that rides on top of I-beam  30 . AC motors  40  are coupled either directly to the respective friction wheels or indirectly through a pulley to drive the wheels along the beam. To prevent friction wheels  38  from losing traction with I-beams  30 , a set of wheels  42  located under the top portion of each I-beam  30  secure the tractor drives  36  to the I-beams. 
     As should be understood in this art, the manufacturing tolerances of I-beams are substantially less stringent than for a machined track, and I-beams are typically cast from iron or other durable, relatively inexpensive, commercially available metal. Consequently, I-beams  30  provide a sufficiently straight structure that extends the length of floor assembly  24  at considerably lower cost than for a similar length of machined track. Because of their lower manufacturing tolerances, however, I-beams  30  may vary from parallel to track  32  and the edge of floor assembly  24  by up to several inches over the length of the floor assembly, and the friction wheels therefore accommodate such variances. For example, friction wheels  38  may be biased vertically downward into contact with I-beams  30  by a spring or other biasing mechanism. Interaction between V-grooved casters  34  and angled track  32  prevents the carriage from moving laterally sideways with respect to floor assembly  24  as the carriage traverses rail system  22 . 
     It should also be understood that various suitable mechanical devices may be used to move the carriage on the rail system along the floor assembly. In an alternate embodiment, for example, a pulley (not shown) mounted on the underside of carriage  12  may connect to a small electric motor (not shown) at a distal end of the rail system by way of a belt (not shown) to move the carriage along the rail system adjacent to the floor assembly. Similarly, a screw jack, scissors jack, piston, rack and pinion or similar device can be used to advance the carriage in the desired direction on the rail system. Thus, the term “drive” as used herein means any such or other suitable mechanism. 
     With reference to  FIG. 1 , carriage  12  generally includes a first drill and driver carriage  44  and a second operator carriage  46 . Generally, the operator stands in carriage  46  and controls the operations of drill and driver carriage  44  through control panel  18 . Drill and driver carriage  44  and operator carriage  46  are spaced apart from each other by about one and one-half feet and are interconnected by connectors  45 , which can be disconnected to allow the two carriages to be separated. The spacing between the two carriages allows a user to access the drill and driver unit so that drill bits can be easily replaced from above the carriages. 
     Operator carriage  46  consists of a generally flat piece of sheet metal flooring  48  of sufficient size to provide a mounting surface for other machine components. The carriage may be made of metal, aluminum, or any other material sufficiently strong and durable to support the combined weight of the other components of the automated floor assembly machine. Sheet metal  48  is attached to a frame  50  that raises the sheet metal above the height of the subassembly. V-grooved casters  34  are mounted to the underside of frame  50 . 
     The operator stands on operator carriage  46  during the floor assembly process so that the operator has access to the control panel. Referring to  FIG. 3 , control panel  18  is mounted between a plurality of screw feeders  64  that feed floor screws to the drivers in drill and driver unit  14 , as described in greater detail below. A light curtain is established by an emitter  47  in a first vertical post  49  that outputs a plurality of parallel horizontal infrared beams that are received by an infrared receiver at an opposing post  49 . Posts  49  are disposed such that the light curtain extends between operator carriage  46  and drill and driver carriage  44 . A signal generated by the received infrared beams at the receiver post  49  is output to an emergency stop circuit. Should the operator&#39;s body move from operator carriage  46  toward drill and driver carriage  44  such that the operator&#39;s body breaches the plane of the light curtain during operation of the machine, the break in the infrared signal, and a corresponding change in the signal output to the emergency stop circuit, causes the emergency stop circuit to shut down floor assembly machine  10 . Machine  10  will not resume operation until the operator manually resets the emergency stop circuit at control panel  18 . Emergency stop circuits should be understood and are therefore not discussed in detail herein. 
     Referring again to  FIG. 1 , drill and driver carriage  44  includes an upper platform  52  and a lower frame  54  connected by jack screws  56  located in each corner of lower frame  54  and that allow the operator to adjust the height of the drill and driver platform relative to floor assembly  24 . Jack screw  56  has a threaded nut and a screw threadedly received by the nut so that rotation of the nut causes the nut to move axially along the screw. Jack screws should be well known in this art, and further discussion is therefore omitted. 
     Platform  52  may be formed from a piece of sheet metal or other material sufficiently strong enough to support the combined weight of drill and driver unit  14 , control box  19 , a vacuum system  55  and other various components of the floor assembly machine. Vacuum  55  located on platform  52  connects to a central hub  58  by a hose  60 . Hub  58  has multiple input hoses  62  that terminate at a vacuum head  63  ( FIG. 5 ) mounted behind the drills so that loose debris from the drilling process can be removed. 
       FIGS. 4A and 4B  provide a detailed view of drill and driver carriage  44 . As noted above, jack screws  56  connect platform  52  to frame  54 . Jack screws  56  are actuated by an electric motor  66  through a gear and pulley  68  that drive the jack screws through a rotatable axel system  70  and gear boxes  72 . Two bearings  74  are affixed on each side of drill and driver platform  52  by bolts  76  or other suitable fastening means, for example weldments, rivets or screws. Bearings  74  traverse respective cylindrical metal tubes  78  mounted to drill and driver frame  54  at  80 . Second smaller bearings  82  are mounted above bearings  74  on platform  52  to provide additional stabilization between platform  52  and frame  54 . A pair of track restraints  84  located between rail system  22  and frame  54  have a bracket  86  coupled to the side of drill and driver frame  54  and a wheel that is positioned under track  32 . Track restraints  84  keep drill and driver carriage  44  from skipping off of V-grooved track  32  under normal operating conditions. 
     Referring to  FIGS. 5 and 5A , drill and driver unit  14  has four banks  14   a  of drills and drivers spaced across the width of drill and driver carriage  44  ( FIG. 1 ). In one preferred embodiment, each drill and driver bank  14   a  is spaced twenty-four inches on center from each adjacent drill and driver bank. Each drill and driver bank  14   a  generally includes two drills  85  and two screwdrivers  87  that are mounted to a drill driver plate  89  ( FIGS. 7A-7B ). In one preferred embodiment, drill  85  is a Model No. AFRE600-900-A6-B24 automated drill manufactured by Desoutter Limited of England, and screwdriver  87  is a Model No. SD-2040 automated screwdriver manufactured by Dixon Automatic Tool, Inc. of Rockford, Ill. 
     Each drill  85  includes a drill chuck  88  rotationally coupled to an electric motor  92  by a spindle  94 . Within each spindle  94  is a pneumatic cylinder  96  that moves drill chuck  88  vertically towards and away from floor deck  28 . The pneumatic cylinders are actuated by air provided by air lines  100  from a respective air control solenoid valve at  200 . Restrictors  120  can be manually adjusted to control the drill&#39;s feed rate. 
     A hydraulic check  96  controls the drill&#39;s feed rate at the end of the downward stroke. More specifically, greater downward pressure is exerted on the drill chuck when drilling through the wooden flooring of deck  28  than when drilling through the metal cross member. Thus, hydraulic check  96  is spaced above the drill housing a distance related to the thickness of the wooden flooring so that hydraulic check  96  operates when the drill bit engages the cross member, thereby lessening the downward pressure on drill chuck  88  as the bit drills through the cross-member. 
     Adjacent drill chucks  88  are spaced side-to-side four inches apart on center (that is, four inches apart in the left-to-right direction across the page of  FIG. 5 ) and are staggered front-and-back 1.25 inches apart on center (that is, 1.25 inches apart in the direction into and out of the page of  FIG. 5 ). As described in more detail below, the configuration of this embodiment allows for various drill patterns to be formed in floor deck  28 . 
     Each screwdriver  87  includes a screwdriver head  90  rotationally coupled to a servomotor  106  through a gear box  110 . Cables  108  provide power and feedback for the servo motors. A depth sensing rod  112  interacts with a proximity sensor (not shown) to allow the screw to be driven to any depth desired as driver  87  moves with screwdriver head  90  down into contact with floor deck  28 . Once head  90  contacts floor deck  28 , a driving tool  91  moves down towards head  90  and begins to drive the screw into floor assembly  24  to a predetermined depth, at which point depth sensing rod  112  trips the proximity sensor so that control system  20  can command the servomotor to set the screw to a particular depth. That is, servomotor  106  can be programmed to provide any number of revolutions of driving tool  91  to set the screw to any desired depth in floor deck  28  from the point where the proximity sensor trips. 
     Each screwdriver head  90  is spaced side-to-side eight inches from its adjacent drill chuck (that is, eight inches apart on center in the left-to-right direction across the page of  FIG. 5 ), and the drivers are staggered front-and-back 1.25 inches apart on center (that is, 1.25 inches apart in the direction into and out of the page of  FIG. 5 ). In this configuration, each screwdriver head  90  aligns with a drill hole made by its leading adjacent drill when drill and driver unit  14  is moved eight inches laterally across floor deck  28 . 
     As is illustrated in more detail in the discussion of  FIGS. 9A-9D , the front-and-back direction into and out of the page of  FIG. 5  corresponds to the longitudinal direction of floor deck  28 , while the left-and-right direction across the page of  FIG. 5  corresponds to the transverse direction across the floor deck. The longitudinal staggering of drill pairs  85  and adjacent screwdriver pairs  87  is related to the width of the cross members  26 , which extend transversely under the floor deck. More specifically, each cross member has an I-beam shape so that the floor boards of the floor deck  28  rest on the approximately 2.25 inches wide top flange of the I-beam. Considering the cross member top flange member divided into two longitudinal halves by the vertical plane of the center I-beam member, the drills of drill pair  85  are spaced apart longitudinally so that they may simultaneously drill holes generally in the center area of the respective halves of the cross member&#39;s top flange. Thus, the front-to-back, or longitudinal, staggering of the drills is related to the width of the cross member top flange into which the drills operate. Because the screwdrivers of driver pairs  87  follow behind respective leading drills of drill pair  85 , the screwdrivers are laterally aligned with the drills and are therefore longitudinally staggered from each other by the same distance as the drills. 
     The lateral offset between drills of drill pairs  85 , and between each leading drill and its following screwdriver, is related to the width of the floor boards comprising floor deck  28 . In the presently illustrated embodiment, for example, drill and driver unit  14  is arranged to secure a floor deck comprised of eight 12 inch wide ship-lapped boards arranged side-by-side and extending longitudinally along the floor deck. In one desirable drill pattern for such a deck, three screws are placed in each board. Moving laterally across one of the boards to an initial position, the leading drill of drill pair  85  is positioned at the center of, and drills a hole in, the 12 inch wide board. Simultaneously, the following drill, which is 4 inches behind the first drill, drills a hole 2 inches inward from the board&#39;s edge. When the holes are completed, the drill and driver unit is moved eight inches laterally, at which point the leading drill makes a hole 2 inches inward from the edge of the next board while the following drill makes a hole 2 inches from the edge of the first board. The screwdrivers, which are 8 inches behind their corresponding drills, simultaneously drive screws into the first two holes. The drill and driver unit then moves laterally another 8 inches to provide the next two holes in the second board and provide screws in the second pair of holes. 
     Accordingly, it should be apparent that the longitudinal and lateral spacing of the drills and drivers, and indeed the number and geometric placement of the drills and drivers themselves, can vary depending on the dimensions and arrangement of the structures upon which they are intended to operate. In the present example, the 1.25 inch longitudinal staggering and the 4 inch and 8 inch lateral spacing is desirable to effect a 3-hole pattern for 12 inch floor boards on I-beam shaped cross members and, as described in more detail with respect to  FIGS. 9A-9D , can be used to employ alternate hole patterns on such a structure. It should be understood, however, that this embodiment is provided by way of example only. 
     Referring now particularly to  FIG. 5B , screwdriver head  90  has jaws  116  that interact with a jaw guide  120  so that jaws  116  pivot between an opened and closed position. Jaws  116  and jaw guide  120  are housed in a sleeve  122 . In operation, a screw is delivered via tube  118  from screw feeder  64 . Jaws  116  are in the closed position prior to the screw being delivered so that the threaded portion of the screw is received between jaws  116 . As driving tool  91  engages the head of the screw, jaws  116  pivot to an opened position allowing the screw to be driven into floor deck  28 . The driver is then moved to the next adjacent hole where the process repeats. Automated screw drivers are well known in this art, and a more detailed description of there operation is therefore omitted. 
     In addition to the pneumatic system, each drill and driver bank  14   a  uses electric power, for example to operate electric motors  92 . Electricity is provided to each drill and driver bank  14   a  by a wire harness  140  ( FIGS. 3 ,  5  and  5 A) carried by a moveable arm  142 . Moveable arm  142  pivots about a first end  144  fixed to the rear of control box  19  ( FIG. 3 ). Moveable arm  142  pivots over an approximately 120 degree angle with respect to the back wall of control box  19 . 
     Referring to  FIGS. 6A-6C , screw feeders  64  generally have a screw bin  126 , a feeder head  130 , and a feeder arm  128  that transports screws from screw bin  126  to feeder head  130 . Feeder head  130  includes a thruster block  132 , a diverter  134  and a connector  136 . Diverter  134  has two bores (not shown) formed therethrough and is connected to thruster block  132 . Connector  136  connects diverter  134  to feeder arm  128  and aligns with one of the two bores. In a preferred embodiment, thruster block  132  is a linear slider manufactured by Robohand, Inc. of Monroe, Conn., and screw feeder  64  is a CLYDE-MATIC automated screw feeder manufactured by Clyde Corporation of Uyonia, Mich. 
     Each screw feeder  64  feeds companion screwdrivers  87  for a particular drill and driver bank  14   a  ( FIG. 5 ). That is, tubes  118   a  and  118   b  ( FIGS. 6B-6C ) feed independent screw driver heads  90  on a single drill and driver bank. Tubes  118   a  and  118   b  connect to one side of diverter  134  adjacent to a respective bore so that the tube is in communication with the bore. Thus, as diverter  134  is moved by thruster block  132  relative to connector  136 , one of the two bores and tubes align with connector  136 , thereby allowing a screw to be fed into a particular tube. Screw feeders  64  pneumatically feed screws to screwdriver head  90  through tubes  118   a  and  118   b . Air line  138  provides pressurized air that forces the screws down tubes  118   a  and  118   b  and into a respective screwdriver head  90 . 
     In operation, screws travel from screw bin  126  down feeder arm  128 . Thruster block  132  aligns diverter  134  with connector  136  so that a screw is fed to the first screwdriver head  90  through tube  118   a  ( FIG. 6B ). Next, thrust block  132  moves diverter  134  rearward ( FIG. 6C ) to align tube  118   b  with connector  136 . A screw is then fed to the second screwdriver head  90  through tube  118   b  . The process is reversed for the next feed cycle to reduce the number of times thruster block  132  shifts diverter  134  and to increase the speed of the operation cycle. 
     Referring to  FIGS. 7A-7B , each drill and driver bank  14   a  is capable of being positioned independently of the other drill and driver banks on a drill bank mounting plate  146 . In a preferred embodiment, each drill and driver bank  14   a  is spaced 24 apart inches on center from the next adjacent drill and driver bank. Drill and driver plate  89  couples directly to drill bank mounting plate  146  by clamps, hooks, bolts, screws or other suitable fastening means. In a preferred embodiment, drill driver plate  89  couples to drill bank mounting plate  146  by a generally L-shaped bracket  148 . Once all drill and driver banks  14   a  are secured to drill bank mounting plate  146 , each drill and driver bank  14   a  is fixed relative to each adjacent drill and driver bank so that all banks  14   a  move in unison, thereby forming drill and driver unit  14 . 
     Drill bank mounting plate  146  is coupled to a slide plate  150  by blocks  152 . In a preferred embodiment, drill bank mounting plate  146  and slide plate  150  are welded to the blocks but may also be connected by screws, bolts and other suitable fastening means. Slide plate  150  is coupled to a track plate  154  by a plurality of track cars  156  secured to the back of slide plate  150 . Track cars  156  receive a respective track  158  mounted to a front face of track plate  154 . In one embodiment, track cars  156  and tracks  158  are a THK Linear Motion Guide manufactured by THK America, Inc. of Norcross, Ga. 
     Because track plate  154  supports the full weight of the drill and driver unit under forces created by their lateral movement, a C-beam  160  is connected to the back of track plate  154  by blocks  162 . Blocks  162  may be connected to the plates by weldments but may also be connected by screws, bolts, or other suitable fastening means. In an alternate embodiment, C-beam  160  may be eliminated provided track plate  154  is of sufficient dimensions to support the weight of drill and driver unit  14  and the forces applied by it during operation of the floor assembly machine. Thus, track plate  154  would connect directly to carriage platform  52 . 
     Still referring to  FIG. 7A , a ball screw  164  moves slide plate  150  relative to track plate  154  in a direction transverse to the length of floor assembly  24 . Ball screw  164  is a rod defining a continuous thread on an outer circumference along substantially the screw&#39;s entire length. In a preferred embodiment, ball screw  164  is approximately thirty-eight inches long but may be longer or shorter depending on the lateral distance the drill and driver unit must move. Ball screw  164  threadedly couples to a nut  166  mounted to a top edge of slide plate  150 . The threaded connection allows sliding plate  150  to move relative to track plate  154  as the screw is rotated. A servo motor  168  rotationally couples to ball screw  164  and rotates the screw in a clockwise and counterclockwise direction depending on the desired direction of movement of slide plate  150 . Servo motor  168  allows for accurate placement of drill unit  14  relative to floor assembly  28  by calculating and tracking the distance slide plate  154  moves based on the number of rotations of the ball screw. More specifically, each revolution of the ball screw represents a discrete linear distance that can be tracked by servo motor  168  and relayed back to control system  20 . 
     With reference also to  FIG. 10 , a sensor system  170  generally includes one or more sensors located at desired positions on automatic floor assembly machine  10  and that communicate with control system  20  through cables. The sensors can be optical, infrared, sonic, electromagnetic, or other suitable commercially available detectors that communicate with the control system by suitable methods such as hard wiring, optical relays, infrared signals or some combination thereof. In the presently described embodiment, sensor system  170  detects the (1) location of carriage  12  with respect to cross members  26  ( FIG. 1 ), (2) height of drill and driver carriage  44 , (3) location of drill and driver unit  14 , (4) feeding of a screw and (5) location of drills  85  and drivers  87 . 
     The number and location of the sensors in a given embodiment of an automatic floor assembly machine according to the present invention will depend on the nature of the subassemblies being attached and the task for which the machine is designed. In the present example, as shown in  FIGS. 1-3 , the machine attaches floor deck  28  of a van type trailer to cross members  26  of the bottom frame. As previously described, the preferred screw positions are at the cross members so that the floor deck is secured to the cross members. Therefore, the sensor system in this embodiment should at least be capable of locating the cross members. 
     As previously discussed, tractor drives  36  ( FIG. 2 ) move automatic floor assembly machine  10  parallel to the length of floor assembly  24  along I-beams  30 . Referring also to  FIG. 8 , as the machine moves along the floor assembly, two sensors  172  determine when the machine should be stopped so that drill and driver unit  14  aligns with one of cross members  26 . Sensors  172  are mounted to drill bank mounting plate  146  by a bracket  174  so that the sensors have a direct line of sight to the cross members without interfering with the carriage&#39;s movement. Bracket  174  is aligned with the drills and drivers so that the sensors can align the center line between the staggered drills and drivers with the center line of cross member  26 . More specifically, sensors  172  emit respective beams  176  and  178  spaced two and one-quarter inches apart that detect when driver unit  14  is aligned with one of cross members  26 . The presently illustrated embodiment is designed for use with I-beam shaped cross members  26  having a top flange generally about two and one-quarter inches wide, thereby allowing both beams  176  and  178  to intersect the top flange when the drill and driver unit aligns with the cross member. 
     Sensors  172  project light beams  176  and  178  downward as machine  10  moves along the length of floor assembly  24  so that as the sensors approach one of cross members  26 , the forward beam  178  intersects with the cross member and is reflected back to the sensor. An electronic signal is generated by the sensor and is communicated to control system  20  indicating the presence of the cross member below the sensor. The tractor drives then continue to move machine  10  in a forward direction until both beams  176  and  178  simultaneously intersect cross member  26 , causing a corresponding electrical signal to be sent to control system  20 . Control system  20 , in turn, causes the forward motion of machine  10  to stop so that both beams intersect the cross member. If machine  10  should over shoot cross member  26  so that beam  176  intersects the cross member but beam  178  does not, control system  20  commands tractor drives  36  to move machine  10  in the opposite direction until both beams  176  and  178  intersect the cross member. In a preferred embodiment, each sensor  172  is a photoelectric sensor model no. BOS-26K-PA-1HC-S-4-C, manufactured by Balluf, Inc. of Florence, Ky. While a photoelectric sensor is described, other types of sensors may also be used, such as inductive sensors or optical sensors. 
     Because machine  10  positions drill and driver unit  14  over a cross member based on the cross member&#39;s location by sensors  172 , it is unnecessary to know the distance between successive cross members, and machine  10  is therefore useful in the construction of trailers in which the cross members are parallel but unevenly spaced apart from each other. Furthermore, machine  10  may locate successive cross members automatically or upon operator command. For example, upon locating a cross member and completing a drill pattern in an operator mode, control system  20  does not move the machine forward to locate the next cross member until receiving an instruction received from the operator through a button or switch at control panel  18  ( FIG. 1 ). Alternatively, in an automatic mode, the operator initially enters a desired number of cross members at which hole patterns are to be executed. If, for example, the operator instructs the control system through control panel  18  to execute ten hole patterns, machine  10  begins at the first cross member, executes a hole pattern and then automatically moves toward and locates the next cross member by sensors  172 . The machine repeats this cycle until completing ten cross members. 
     In addition to the cross member sensors, machine  10  also includes multiple proximity sensors. For example: 
     1) proximity sensors  84  ( FIG. 2 ) located on drill and driver platform  52  detect when jack screws  56  move platform  52  to its maximum and minimum height; 
     2) track plate  154  includes two proximity sensors  180  ( FIG. 7A) and 182  ( FIG. 7B ) located on opposite ends of the plate to detect when slide plate  150  has moved a maximum allowable distance in each direction relative to track plate  154 ; and 
     3) each screw feeder tube  118  includes a proximity sensor  184  that detects when a screw passes through tube  118  into driver head  90 . 
     Finally, referring to  FIG. 5A , proximity sensors  104  at each drill of drill pair  85 , and proximity sensors (not shown) at each drivers of driver pair  87 , determine when the drill and driver have been fully extended or retracted relative to floor deck  28 . To prevent damage to the drills or drivers, neither carriage  12  nor drill and driver unit  14  moves with respect to floor deck  28  until an upper proximity sensor at the respective drills and drivers trip, thereby indicating that both the drills and drivers have moved a sufficient distance from floor deck  28 . 
     In one preferred embodiment, each of proximity sensors  84 ,  104 ,  180 ,  182  and  184  are an inductive sensor model no. BES-M08MGI-PSC60F-S49G, manufactured by Balluf, Inc. of Florence, Ky. As should be well understood, inductive sensors detect a metallic flag passing in front of the sensor. While an inductive sensor is described, other types of sensors may also be used, such as a photoelectric or optical sensor. It should also be understood that each sensor of sensor system  170  communicates signals to control system  20  indicating when that particular sensor has been tripped or another event has occurred so that control system  20  can command the various components to operate. 
     Referring to  FIGS. 1 ,  3  and  10 , control panel  18  fixedly mounts on operator carriage  42  to provide the operator convenient access during operation. The control panel generally includes a display screen  186 , a keyboard  188 , and various controls  189  to allow the operator to communicate with control system  20 . Display screen  186  may be an LCD screen providing a graphic or visual display of system operating conditions. The control panel may also include other visual or audio displays. The keyboard may include a touch screen disposed over screen display  186  for providing input to control system  20 . 
     Control system  20  receives signals from key board  188 , controls  189 , ball screw servo-motor  168 , driver motors  106  and the various sensors described above, processes those signals, and directs the movement and operation of the automated floor assembly machine responsively to information carried by the signals. Referring to  FIG. 2 , the control system generally includes a central processing unit (CPU)  190  that stores software, input output cards  192  that turn each component on and off, fuses  194 , driver  196  for ball screw  168 , drill drivers  198 , screwdriver drivers  201 , a light curtain controller  202  and associated software. 
     The CPU and other associated electric devices may comprise commercially available components mounted on a circuit board housed within the control panel. Those skilled in the art should understand the construction of appropriate circuitry and software, for example written in Ladder Logic or other suitable language, to execute the functions described herein. 
     The control system directs the movement and operation of the automated floor assembly machine through control signals sent to its various components. For some components, such as the display screen and the tractor drive motors, the control system sends the signal directly to the component. The control system directs control signals for other components, such as the drill and drivers and screw feeders, through a pneumatic valve station  200 , such as that shown in detail in  FIG. 5 . Valve station  200  generally includes a valve manifold through which air passes that, in turn, drives each pneumatic powered component. Pneumatic systems should be well known in this art and further discussion is therefore omitted. 
     Floor assembly machine  10  may also include an overhead cat track (not shown) that carries power cables, air lines and other cable bundles that provide electric, hydraulic, or pneumatic power to the machine, depending on the power needs of the particular design. In the alternative, a coiled power harness (not shown) may be used that coils and uncoils as carriage  12  moves over the entire length of the subassembly without fouling or creating a work hazard. 
     In operation, and referring again to  FIGS. 1 and 8 , the presently illustrated example of automated floor assembly machine  10  is designed to attach floor deck  28  of a van type trailer to cross members  26 . In general, the machine locates a cross member, repeatedly drills holes and drives screws into the holes, moves carriage  12  toward the next cross member, locates the next cross member and drills the next set of holes and drives screws into those holes. The process is repeated until floor deck  28  has been fastened to all cross members. 
     Prior to executing the automated process, the machine powers up and executes a homing operation in which servo drive  168  ( FIG. 7A ) establishes a reference point from which to move the drill and drive unit laterally according to a hole pattern. The operator begins the homing operation by activating a homing button at control panel  18 . CPU  190  then activates servo motor  168  to the left (in the direction as shown in  FIG. 5 ) until sensor  180  ( FIG. 7A ) senses a metal flag disposed at the leading edge of slide plate  150 . Upon receiving a corresponding signal from sensor  180 , CPU  190  stops servo motor  168  through driver  196 , and this position becomes the zero position from which CPU  190  executes subsequent operations. Drill bits are manually loaded in chucks  88 , and driver tool  91  is inspected. If not already selected, the operator may select a hole pattern at control panel  18  from a list of patterns stored in memory. Once selected, the hole pattern is transferred to CPU  190  for execution. 
     Prior to inserting the floor beneath the machine, the floor&#39;s transverse cross members are placed in parallel desired positions. The longitudinal ship-lap boards are disposed over the cross members and loosely secured thereto by two single rows of screws on respective longitudinal sides of the floor. The screws may be manually applied and extend through the two outermost boards into the cross members. The floor is then moved under the machine in the longitudinal direction as shown in  FIG. 2  and is pushed to the left (from the perspective as shown in  FIG. 5 ) so that the left-hand sides of the cross members abut a guide plate (not shown in the figures) to thereby square the floor with respect to the machine. The operator then activates a button at the control panel to lower drill and driver carriage  44  toward the floor by the operation of jackscrews  56 . CPU  190  controls motor  66  to lower the carriage until proximity sensors  84  ( FIG. 2 ) determine that platform  52  has reached a desired height. Screwdriver heads  90  are cleared, and screws are automatically loaded into screwdriver heads  90  as described above. Once the drills and drivers are ready, the motor moves slide plate  150  to the right from the homing position a predetermined distance to a position where sensor  172  can detect cross members  26 . This initial distance information is programmed into the hole pattern and is based upon the predetermined homing position as described above. Thus, the length of the cross members and the width of the floor are considered in determining this distance. CPU  190  drives servo motor  168  precisely to the starting position through an appropriate number of revolutions of the ball screw. 
     Assuming manual operation, the operator actuates a button or operates a joy stick on control panel  18  in the forward direction, causing CPU  190  to drive the machine forward until sensors  172  detect that the drill and driver unit is disposed above a cross member. 
     When the machine reaches a cross member, as determined by sensors  172 , the operator activates the execution of the hole pattern through control panel  18 . The hole pattern includes the distances the drill and driver unit must move to the left in beginning the sequence. 
     Upon completing the hole pattern, the operator activates the joy stick to move the machine to the next cross member. After a cross member is completed, the control system moves drill and driver unit  14  back to the starting position at the far right to allow sensors  172  to read the next cross-member. Again, the control system knows the distance needed to move the drill and driver unit back to the starting position since it knows the positions in the hole pattern, and therefore the drill and driver unit&#39;s position at the end of the hole pattern, as well as the starting position&#39;s distance from the zero position. The carriage will not move forward or backward until the operator moves the joystick in the forward or reverse direction directing the machine to search for the next cross member. After completing the drilling and driving operation for the floor, the operator raises carriage  44  by jack screws  56 . The floor then may be removed. When a new floor is inserted, the operator may operate the machine in the reverse direction toward the opposite end of the track. 
     In beginning the drilling operation at a given cross member, if a proximity sensor  182  ( FIG. 8 ) detects the presence of the slide plate, the drill and drive unit has moved too far to the right, and the control system  20  instructs the ball screw motor to hold its position. 
       FIGS. 9A-9D  illustrate a drill and driver sequence for an exemplary hole pattern. As described above, CPU  190  uses the hole pattern to control the operation of drills  85 , drivers  87 , and ball screw servomotor  168 . More specifically, the hole pattern defines when and where a screw is inserted in a given cross member. Thus, starting with  FIG. 9A , once a cross member has been located, slide plate  150  moves to the left as defined by the hole pattern. All drills  1 - 8  drill a hole through floor deck  28  and cross member  26 . In  FIG. 9B , drill and driver unit  14  is indexed eight inches to the right, and all drills, except  1  and  8 , drill holes. Since the drivers are spaced eight inches from their corresponding drills and staggered similarly to the drills, drivers  1   a - 8   a  align with the previously drilled holes and drive a screw in each of those holes. Referring to  FIG. 9C , drill and driver unit  14  is again indexed eight inches to the right, and all drills  1 - 8  drill holes through floor deck  28  into cross member  26 . At the same time, all driver units drive screws in the previously drilled holes except for drivers  1   a  and  8   a , since their corresponding drills did not drill holes in the step illustrated in  FIG. 9B . Finally referring to  FIG. 9D , drill and driver unit  14  is indexed eight inches to the right once more and all drivers  1   a - 8   a  drive screws into the previously drilled holes, and no drills operate during this step. Drill and driver unit  14  can perform the above sequenced steps in approximately twenty seven seconds. 
     Once the steps shown in  FIGS. 9A-9D  are completed, drill and driver unit  14  returns to the appropriate position for sensors  172  to locate the cross members. Upon the operator&#39;s command, control system  20  sends a command to tractor drives  36  to move machine  10  forward in search of the next cross member. When cross member sensor beams  176  and  178  both intersect the next cross member, control system  20  stops the forward progress of machine  10 , and the drill and driver process described above repeats. When the floor is completed, drill and driver carriage  44  is raised, and floor assembly  24  is removed so that a new floor assembly can be placed in machine  10 . 
     While one or more preferred embodiments of the invention have been described above, it should be understood that any and all equivalent realizations of the present invention are included within the scope and spirit thereof. The embodiments depicted are presented by way of example only and are not intended as limitations upon the present invention. Thus, it should be understood by those of ordinary skill in this art that the present invention is not limited to these embodiments since modifications can be made. Therefore it is contemplated that any and all such embodiments are included in the present invention as may fall within the literal and equivalent scope of the appended claims.