Abstract:
An apparatus for making temporary road mats characterized by multiple layers of mutually perpendicular elongated timbers having an array of vertical intersections aligned in lateral rows. The apparatus includes a gang drill that moves relative to a roughly assembled mat for sequentially drilling the lateral rows of intersections.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. Ser. No. 10/750,272, filed on Jan. 2, 2004, which is a continuation-in-part application of U.S. Ser. No. 10/407,992 filed on Apr. 4, 2003, now U.S. Pat. No. 6,745,452, issued Jun. 8, 2004, in the name of Ronald Harrison. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to temporary road surfaces and, in particular, to apparatus for manufacturing and assembling three ply temporary road mats. 
       BACKGROUND OF THE INVENTION 
       [0003]    Temporary road mats are used extensively to allow vehicles and equipment to reach locations not serviced by permanent roads, particularly under conditions where ground surface would not support the traffic or where the temporary nature of use does not warrant the time and expense of a permanent road. The mats are generally constructed in multiple layers of heavy wood timbers in crisscrossing layers. The mats may also be provided with interlocking joints for connecting with adjacent mats as disclosed in U.S. Pat. Nos. 4,462,712 to Penland; 5,032,037 to Phillips et al.; and 4,889,444 to Pouyer. Commonly, each layer is nailed to the underlying layer. The final layer is fastened with an extended length nail having a protruding tip that crimped over to secure the assembly as disclosed in U.S. Pat. No. 5,234,204 to Hunt. The manual assembly, even with air powered nailing guns in time consuming and tiring and prone to misalignments. For heavy duty applications, three ply mats are employed. Initially, two layers are nailed as a subunit, with the third layer nailed thereto in a separate assembly sequence. This type of nailed construction provides limited torsional and bending strength, resulting loosening of the nailed joints and timber breakage. Replacing a damage timber requires time consuming removal of all overlying timbers. The entire length of timber must be replaced inasmuch as limited compression and shear strength precludes splicing with shorter lengths. Where the nail loosening occurs at the intermediate layer, supplemental nailing from both the top and bottom surfaces may be required to regain suitable strength at the joint. Such supplemental nailing can also splinter the timber resulting in a complete loss of nail holding strength. 
         [0004]    Various assembly devices have been proposed for more accurately aligning the timber layers prior to nailing. U.S. Pat. No. 4,922,598 to Pouyer discloses an assembly table having an array of alignment stops for assisting positioning the timbers prior to nailing. U.S. Pat. No. 5,234,204 to Hunt, referenced above, discloses a dual stage assembly table facilitating nailing on opposite sides of the mat. Crimped extended length nails are used on the final layer to resist a lifting of the nail heads that can damage vehicle tires. 
         [0005]    The nailing of the timbers also precludes convenient repair and replacement of damaged timbers. Typically, the mat must be substantially disassembled to access and replace damaged members. Bolted constructions have been suggested in the art, however, such mats are not known to be commercially available. Therein, holes are drilled at the intersections of the crossed timbers for receiving threaded fasteners. The resulting construction provides a smooth upper surface free of protruding nail heads. When replacement of a member is required, only the fasteners in the affected area need to be removed to allow substitution. Notwithstanding the advantages of the bolted construction, production rates, even with fixtures and assembly tables, have been limited by the cycle times of the serially required operations. 
         [0006]    Moreover, three ply mats have not been successfully produced. The cumulative tolerances in the hole arrays for the three layers present&#39;s extreme alignment problems for assembly. Approaches increasing the clearances between the holes and bolt shanks result in a loss of lateral structural stability. Leveraging the boards to align the holes for assembly results in a stressed assembly condition that can result in timber fracture and surface warping. 
         [0007]    Accordingly, a need continues to exist for three ply bolted temporary road mats that may be assembled accurately under low stress conditions. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention provides an improved method for making bolted three ply temporary road mats wherein fastener holes are drilled concurrently by a gang drill apparatus into the freely assembled mat, the apparatus and mat indexed to successive positions for drilling while the preceding rows are fastened by carriage bolts, continuing until the mat is fully assembled. Resultantly, the completed mats can use fastener holes having close sliding fits with the bolts providing increased bilateral stability. Moreover, the fasteners are connected with only compressive forces substantially reducing assembly stresses on the timbers. 
         [0009]    In one aspect of the invention, a mat assembly line includes a pair of in-line, phase opposed multilevel assembly tables supplied with precut timbers from conveyor systems including a trimming station. The precut timbers are oriented into multiple layers of mutually perpendicular timbers atop the table. A mobile gang drill carrying a plurality of drill heads travels along rails at the sides the assembly tables and sequentially drills through holes at each lateral row of timber intersections. Carriage bolts are inserted downwardly through the drilled holes as completed. At lower bays beneath the assembly tables, nuts are assembled on the bolts to provide a unitized assembly. During the drilling at the first table, another mat is assembled at the other table. Following completion at the first table the gang drill indexes to the second table and performs the drilling sequence thereat, while the bolts are fastened at the first table. The gang drill alternates between the tables, with upper and lower crews transferring between tables for continuity and efficiency. 
         [0010]    In another aspect of the invention, there is provided a mat assembly line wherein an indexing conveyor is supplied with precut timbers from conveyor systems including trimming stations. The precut timbers are oriented into multiple layers of mutually perpendicular timbers atop the table. The indexing conveyor shifts the timber stack to a stationary gang drill whereat a plurality of drill heads drills counterbored holes for a single row. After drilling, the indexing conveyor shifts the timber stack to drill the next row of holes. Concurrently, the bolts are inserted and fastened at prior set. The sequences are repeated until the mat is fully drilled and assembled. 
         [0011]    In one aspect of the invention there is provided an improved apparatus for making temporary road mats of bolted construction characterized by multiple layers of mutually perpendicular elongated timbers having an array of vertical intersections comprised of longitudinally spaced lateral rows, wherein said apparatus comprises: a pair of assembly tables spaced along an assembly line of a work floor, each of the tables having an upper layout surface spaced vertically above the work floor and providing a work bay therebelow, said layout surface having indicia for orienting the discrete timbers in each layer whereby said timber may be roughly assembled thereon into said layers with said intersections; a gang drill assembly supported for controlled movement in a longitudinal path along said assembly line with respect to said pair of assembly tables, said gang drill assembly carrying a plurality of drill units above said layout surface aligned for drilling the lateral rows of intersection; means for aligning said drill units at said lateral rows and for downwardly for moving said drill units to form through holes through said timbers at said intersections subsequent to which bolts are inserted in into said through holes from above said layout surface and fasteners are connected with said bolts in said work bay, the movement of said gang drill assembly and the sequence of said drilling being alternated between said assembly tables. 
         [0012]    Accordingly, it is an object to provide an improved temporary road mat having threaded fasteners releasably interconnecting the various components. 
         [0013]    Another object of the invention is to provide a three ply temporary road mat fastened by carriage bolts. 
         [0014]    A further object is to provide an improved apparatus for assembling temporary road mats wherein rough timbers are feed on a conveyor system through a trimming station to provide precut timbers to a pair of spaced assembly tables for positioning into multiple crossed layer orientation and a longitudinally positionable multiple drill assembly alternately drills fastener holes in the timbers at each table. 
         [0015]    Another object is to provide an apparatus for assembling bolted temporary road mats wherein a gang drill assembly is used to simultaneously drill lateral rows of through holes for receiving fasteners for interconnecting the mat components. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    The above and other features and advantages of the invention will become apparent upon reading the following written description taken in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  is a side elevational view of an apparatus for the manufacture of temporary road mats in accordance with a preferred embodiment of the invention; 
           [0018]      FIG. 2  is a top view of the conveyor and trimming station for the apparatus showing the trimming of rough timbers to length; 
           [0019]      FIG. 3  is a top view of an assembly table and surrounding walkway for the apparatus; 
           [0020]      FIG. 4  is a front elevational view of the assembly table and mobile gang drill; 
           [0021]      FIG. 5  is a cross sectional view illustrating the drilling of the timbers; 
           [0022]      FIG. 6  is a cross sectional view of the timbers and carriage bolt fasteners; 
           [0023]      FIG. 7  is a perspective view of the temporary road mat in accordance with one embodiment of manufacture; 
           [0024]      FIG. 8  is a side elevational view of the temporary road mat as shown in  FIG. 7 ; 
           [0025]      FIG. 9  is a top view of the temporary road mat as shown in  FIG. 7 ; 
           [0026]      FIG. 10  is a front view of the temporary road mat as shown in  FIG. 7 ; 
           [0027]      FIG. 11  is a front view of an apparatus for the manufacture of temporary road mats in accordance with another embodiment of the invention; 
           [0028]      FIG. 12  is a side elevational view of the apparatus illustrated in  FIG. 11  taken along line  12 - 12  in  FIG. 11 ; 
           [0029]      FIG. 13  is a fragmentary cross sectional view of the countersunk holes of the temporary road mat in the apparatus of  FIG. 11 ; 
           [0030]      FIG. 14  is a fragmentary cross sectional view of the assembled carriage bolt maintained in the countersunk holes by the pressure plate prior to assembly; and 
           [0031]      FIG. 15  is a top view of an embodiment of the temporary road mat illustrating the splicing of the timbers. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Referring to the drawings for the purpose of illustrating a preferred embodiment of the invention and not for limiting same,  FIG. 1  shows an assembly apparatus  10  for the manufacture of temporary road mats. The apparatus  10  comprises a pair of in-line multilevel assembly lines  11 . At the outer end of each line  11  rough wooden timbers  14  are delivered to a loading area  16 , transferred by conveyor  18  through trimming station  20  to produce finished timbers  22  and unloaded at transfer area  24 . The finished timbers  22  are assembled on assembly tables  26 , drilled at vertical locations by a mobile gang drill  28 , and fastened at underlying fastener bays  29 . Fully assembled mats are removed from the assembly tables  26  by suitable material equipment such as overhead cranes or mobile fork lifts. 
         [0033]    Referring to  FIGS. 7 through 10 , a completed temporary road mat  30 , according to one embodiment, comprises three mutually perpendicular layers of spaced finished timbers. The width and length of the mat are generally in two foot increments and the mat is rectangular in shape, for instance 8 feet by 12 or 16 feet. Depending on load requirements, two layers may be sufficient and in severe environments, greater than three layers may be preferable. Moreover, the ends and sides may have staggered ends adapted for interlocking assembly. Further, the top lay may be configured for distinct vehicle tracks. For each of the above and the like, the layers must be securely interlocked to maintain structural integrity during use. 
         [0034]    The mat  30  comprises a first or base layer  32  having longitudinally extending, laterally spaced members, a second or middle layer  34  having laterally extending, longitudinally spaced members, and a third or top layer  36  having longitudinally extending, uniformly laterally spaced members vertically overlying the first layer. The assembly thus forms distinct, mutually perpendicular layers of intersecting rows and columns in grid array of mutually overlying intersections. Through holes, as hereinafter described, are drilled through the overlapping members at such intersections. Suitable fastener systems  37 , as described below, extend through the holes and bolted for mutually clamping the layers together. In the present invention a carriage bolt is inserted downwardly through each hole and a nut threaded thereto at the lower surface. 
         [0035]    As shown in  FIGS. 1 and 2 , timbers roughly to length are delivered to a loading area in front of the conveyor  16 . The conveyor  16  includes a support assembly  40  having a pair of laterally spaced guide rails  42 . The guide rails  42  include upwardly curved, arcuate entry legs  44  merging with horizontal top legs  46 . A drive chain  48  is guided on sprockets for guided movement adjacent the guide rails. A control motor  50  is operatively connected to the drive chain  48  for operating the chain under manual or automatic control. Each drive chain  48  carries a plurality of spaced transfer dogs  52  that project outwardly of the guide rails  42 . The rough timbers  14  are sequentially loaded on the dogs  52  and transferred forwardly by the drive chain upwardly along the entry legs  44  and inwardly along the top legs  46 . 
         [0036]    The conveyor  16  extends through the trimming station  18  and delivers the cut timbers to the transfer area  26 . The trimming station  18 , as shown in  FIG. 2  includes a laterally adjustable circular saw unit  62 , a fence  64  and a transfer roll  66 . The transfer roll  66  is operatively connected to a drive unit  67  for rotation as shown by the arrows. The saw unit  62  is mounted for adjustable transverse movement as indicated by the arrows. As the rough timbers  14  are carried into the trimming station  18 , the transfer roll  66  laterally shifts the timbers outwardly against the fence  64 . The circular saw unit  62  is positioned downstream beyond the transfer roll  66  and laterally positioned to make a cross cut on the timbers representing a selected length between the saw blade and the fence, corresponding to the lengths in the desired mat layer. The range of adjustment between the saw unit and the fence is sufficient to handle sizing of the various timbers for the manufactured mat designs. 
         [0037]    After trimming to length, the timbers for a layer are housed at staging area  24  prior to layout on the assembly tables. The assembly tables  26  are carried on support frames  70  elevated above the work floor at a sufficient height to establish a work bay  29  therebelow to enable workers to bolt the mats together as described below. The elevation of the tables  26  is slightly above the transfer area for providing ease of manual alignment of the members on the assembly tables. The tables  26  are surrounded and mutually spaced by elevated walkways  71  for permitting movement of the workers thereabout. Depending on production rates, a single crew on the upper level may alternate between the tables, and bolting crews alternate between the bays. Alternatively, a single crew may sequentially handle upper and lower level operations. 
         [0038]    Referring to  FIG. 3 , the assembly tables  26  are provided a top frame including peripheral end supports  74  and side supports  76  interconnected with interior supporting members  78 . A lateral fence  80  is aligned and attached at one side support  76 , and a longitudinal fence  82  is aligned and attached at the inner end support  74  thereby providing an alignment surface for accurately positioning the ends of the timbers of the respective layers. Additional pivotal fences and clamps may be provided at opposed ends of the respective fences to mechanically position the timbers against the prime fences  80 ,  82 . Additionally, the lateral and longitudinal sides are provided with spaced indicia  84  and/or affirmative locators for accurately referencing and establishing respective timber placement. For assembling the bottom layer, the timbers  22  are removed from the transfer area  24 , positioned against the end fence  82 , and aligned with the indicia  84  to provide a longitudinal array of laterally spaced timbers for the bottom layer. Concurrently therewith, the trimming station  18  may be adjusted to trim the next set of timbers traversing the conveyor  16  to the determined length and in the required number for the middle layer. Alternatively, the middle layer timbers may be sized at a separate location and transferred to the assembly table for positioning atop the bottom layer. 
         [0039]    After location of the bottom layer, the ends of the middle layer timbers are positioned against the lateral fence  80  and aligned with the indicia  84  to provide an aligned lateral array perpendicular to the bottom layer. Thereafter the upper set of timbers is trimmed and aligned mutually perpendicular to the middle layer, as described above, ready for drilling with the mobile gang drill  28 . 
         [0040]    The mobile gang drill  28  comprises a shuttle  90  having side support legs  92  laterally on either side of the line  10  and interconnected by a cross member  94 . The legs include a horizontal base  93  carrying rollers  96  that are supported on longitudinal guide rails  98  spaced on the lateral sides of the assembly tables  11 . A drive motor  100  is operatively connected with the rollers  96  is operable manually or automatically to move the gang drill  28  to controlled positions along the guide rails. A tool bar  110  is supported by a parallel linkage  112  at the cross member  94  and moved vertically by actuating cylinder  114  between raised and lowered positions. A plurality of drills  116  including drill bits  118  are carried on the tool bar  110  and adjustable laterally to register with the overlapping intersections of mat timbers for the design being manufactured. A press plate  120  is slidably supported at the legs  92  for vertical movement under the manual or automatic control of actuators  122 . The press plate  120  is lowered to compressively clamp the timber layers adjacent the drills to prevent any misalignment of the timbers during the drilling. For the drilling sequence, the gang drill is indexed, manually or automatically, to position the drills over the outermost lateral row of timber intersections. Thereafter as shown in  FIG. 5 , the drills are energized and the actuator  122  extended to lower the press plate  120  to clamp the timbers. The actuator cylinders  114  are extended to lower the tool bar  110  thereby simultaneously drilling a lateral series of vertical holes completely through the three layers timbers. The drills  116  are withdrawn by the actuator cylinder  114 , the press plate  120  raised by actuator  122 , and the gang drill  28  moved to the next lateral set of intersections for repeating the foregoing drilling sequence. The drilling continues until all holes have been drilled. Thereafter, the drill assembly is parked intermediate the tables prior to undertaking the drilling sequences at the other table. 
         [0041]    Referring to  FIG. 5 , following the drilling on the first row, the carriage bolts  140  are manually inserted into the drilled holes as available and until completed. After insertion of all the carriage bolts, a cover plate  130  is lowered onto the table over the bolt heads  142  to maintain position thereof during fastening. A work crew in the assembly bay  29  then fastens the nuts  144  and washers  146  to the threaded shank  148  of the bolts  140  using powered socket wrenches to unitize the assembly. Following completion, the cover plate is removed and the finished mat transferred from the table by suitable material handling equipment such as a forklift or mobile crane. 
         [0042]    The apparatus above described allows work crews to continuously operate on both tables. During the drilling sequence at one table, the mats are rough assembled on the other table. During the fastening at the first table, drilling is done at the other table. During assembly at the first table, the fastening is performed at the other table. In this manner, both tables are continuously used with the workload shifting between the levels. Moreover, the work crews may alternate between the tables at both levels or between levels at one table thereby efficiently utilizing both labor and machine component. It will thus be appreciated that the two bays working in tandem are able to balance machine and manual time content to utilize the equipment and labor in a productive efficient manner. Compared to serial drilling and fastening wherein about 2 mats per hour could be produced, the inline dual table of the present invention outputs completed mats at the rate of about 10 per hour with comparable labor content per mat. 
         [0043]    It will be appreciated that the foregoing apparatus may be employed for the manufacture of differing sizes, layout and number of intersecting timber layers. Interlocking and/or staggered mat designs may be accommodated by table and drill layout. Further, dedicated wheel track patterns of current design may also be produced. 
         [0044]    Referring to  FIGS. 11 and 12 , there is shown another embodiment of the invention wherein the assembly apparatus is provided with stationary drilling assemblies and a mobile assembly platform. More particularly, the assembly apparatus  200  comprises a longitudinal assembly line  202  for routing timbers  2203  in layers onto a mobile assembly platform  204  including an indexing conveyor  206 , past upper and lower drill assemblies  208 ,  210  respectively, for sequentially drilling a lateral series of holes in a roughly assembled mat  212 , followed by bolting of the layers of timbers into compressive engagement to form a finished mat in upper assembly area  214  and lower assembly area  216 . 
         [0045]    The timbers  203  are transferred to the assembly platform by conveyor and trimming stations including end station  220 , and side stations  222 , and  224 . The stations  220 ,  222 , and  224  may be the same as the conveyor  18  and trimming station  20  described with reference to the first embodiment. The timbers may be inventoried at storage areas at the ends thereof or manually transferred as available to the assembly table. 
         [0046]    The apparatus  200  includes an elevated platform  230  mounted on a base  231 , such as a plant floor. The platform  230  extends along the assembly line  202  and supports the indexing conveyor  206 . The drill assemblies  208 ,  210  are carried by a support frame  234  at about the center of the platform  230 . The support frame  234  includes a pair of laterally spaced legs  236  attached to the base  231  and interconnected by cross arm  238 . The apparatus  200  provides the capability of assembling extended length platforms and accordingly the lateral timbers comprise the top and bottom layers  32 ,  36  and feed from the side stations  222 ,  224 , with the longitudinal timbers comprising the middle layer  34  and supplied from the end station  220 . 
         [0047]    The indexing conveyor  206  includes a pair of laterally spaced motor driven drive chains  240  driven by motor  241  and extending longitudinally along the frame  234 . The drive chains  240  include projecting lugs  242  engagable with the base layer timbers. By appropriate automatic or manual control, the conveyor  206  is intermittently operated to index successive lateral timbers at the drilling assemblies whereat the vertical fastener profile is formed. 
         [0048]    The upper gang drill assembly  208  is supported on the frame and is substantially the same as the drill assembly in the first embodiment and reference may be made thereto for details thereof. The lower gang drill assembly  210  comprises a laterally spaced series of drills  244  supported on a cross bar  246  carried on the legs  236  of the frame  234  for movement by a hydraulic actuator  248  between the illustrated normal lowered position to a raised drilling position. 
         [0049]    To provide for recessing on the fastener to avoid surface projections on the top and bottom surfaces of the mat, as shown in  FIG. 14 , the drilled fastener profile includes a through hole  250 , an upper counterbore  252  for the head of the bolt, and a lower counterbore  254  for the nut of the fastener. 
         [0050]    The profile is formed by a drill bit on the upper drills comprising a main drill bit for forming the through hole  250  and a counterbore bit for forming the upper counterbore  252 , and a drill bit on the lower drills  246  comprising a pilot drill and a counterbore bit for forming the lower counterbore  252 . 
         [0051]    In operation, with a lateral row of timber intersections indexed at the drill assemblies, the actuator  248  is extended to raise the lower drill assembly  210  for drilling the lower counterbores. Thereafter the upper drill assembly  206  is lowered for drilling the through hole and upper counterbores. The sequence is repeated for the remaining lateral rolls of the mat. 
         [0052]    After the first row of profiles is formed and the mat indexed, the carriage bolts are inserted. This provides for low stress assembly inasmuch as the holes are coaxial at drilling and the short transfer area presenting little opportunity for timber shifting. After assembly of the first row, the alignment becomes increasingly stable thereby allowing the close sliding fit between the fastener and holes. To prevent the upward movement of the carriage bolts during attachment of the nuts, a slightly downwardly inclined plate  250  is supported above the table and timbers, downstream of the bolt assembly area. In the lower bay  260  below the table, the nuts are assembled on the bolts to create the composite mat. Upon completion, the composite mat is transferred from the line by appropriate material handling equipment. Depending on the front length of the indexing conveyor, initial assembly may commence on another mat while the preceding mat is finishing drilling and assembly. 
         [0053]    The three layer composite mats possess substantially improved bending and torsional strength in comparison with conventional nailed mat constructions. Such strength enables assembly used sliced timbers. As shown in  FIG. 15 , the top layer may comprise columns having spliced timbers  270 ,  271  thereby permitted the use of easier to obtain and cost effective timber lengths. The spliced construction may be used for all or a portion thereof. In such a spliced construction, it is desirable to stagger the spliced joints. Similar techniques may be used for the middle row  34  using spliced timbers  272 ,  273 , and bottom layer  32  using spliced timbers  274 . 
         [0054]    Having thus described a presently preferred embodiment of the present invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the present invention. The disclosures and description herein are intended to be illustrative and are not in any sense limiting of the invention, which is defined solely in accordance with the following claims.