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 pair of assembly tables spaced along an assembly line on a work floor. Each table has an upper layout surface spaced vertically above the work floor and provides a work bay therebelow. The layout surface having indicia for orienting the discrete timbers in each layer whereby the timber may be roughly assembled. A gang drill moves in a longitudinal path along the assembly line with respect to the assembly tables. The gang drill carries a plurality of drills for sequentially drilling the lateral rows of intersections. The gang drill alternates between tables while manual assembly operations are conducted at the other table.

Description:
FIELD OF THE INVENTION 
     The present invention relates to temporary road surfaces and, in particular, to a machine for assembling temporary road mats. 
     BACKGROUND OF THE INVENTION 
     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. No. 4,462,712 to Penland; U.S. Pat. No. 5,032,037 to Phillips et al.; and U.S. Pat. No. 4,889,444 to Pouyer. Commonly, each layer is nailed to the underlying layer. The final layer is fastened with extended length nails having protruding tips 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 is time consuming and tiring and prone to misalignments. 
     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. 
     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. Such limitations have been overcome by the use of bolted mat configurations. 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. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides an improved method for making bolted temporary road mats wherein an 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 of 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. 
     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 moving said drill units to form through holes through said timbers at said intersections subsequent to which bolts are inserted 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. 
     Accordingly, it is an object to provide an improved temporary road mat having threaded fasteners releasably interconnecting the various components. 
     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. 
     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. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     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: 
     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; 
     FIG. 2 is a top view of the conveyor and trimming station for the apparatus showing the trimming of rough timbers to length; 
     FIG. 3 is a top view of an assembly table and surrounding walkway for the apparatus; 
     FIG. 4 is a front elevational view of the assembly table and mobile gang drill; 
     FIG. 5 is a cross sectional view illustrating the drilling of the timbers; 
     FIG. 6 is a cross sectional view of the timbers and carriage bolt fasteners; and 
     FIG. 7 is a perspective view of the temporary road mat in accordance with one embodiment of manufacture;. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     Referring to FIG. 7, 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. 
     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  38  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. 
     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 . 
     The conveyor  16  extends through the trimming station  20  and delivers the cut timbers to the transfer area  26 . The trimming station  20 , 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. 
     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. 
     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. 
     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 . 
     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  95  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 cylinder  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. 
     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. 
     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. 
     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. 
     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 sprit 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.