Abstract:
An apparatus nails a plurality of cross members to an underlying stringer to produce a pallet. The carriage moves in a continuous motion without stopping over the cross members until the cross members are nailed to the stringer. The carriage includes at least one nailing gun for driving nails and a hydraulic accumulator mounted on the carriage in hydraulic communication with the at least one nailing gun for supplying hydraulic fluid to provide a force to the nailing gun to nail the cross members to the stringer. The nailing gun may be pivotally secured to the carriage wherein the nailing gun pivots with respect to the carriage while driving a nail into the cross member and the underlying stringer. The nail gun is also positioned into a nail driving position pneumatically and when in the nail driving position the hydraulic cylinder is actuated to drive the nail into the cross member.

Description:
The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/553,392, filed Mar. 16, 2004, the content of which is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to an apparatus and method for driving nails into an object. In particular, the present invention relates to an apparatus and method for rapidly driving nails with a hydraulic system and a pneumatic system. 
   An item commonly used to transport goods that requires its component parts to be nailed together is a wooden pallet. Wooden pallets began being used in industry in the 1930s. Wooden pallets came into widespread use by the United States Navy during World War II to move large amounts of goods in a short period of time with forklifts. Since World War II the use of wooden pallets has steadily increased every year. 
   It is estimated that currently there are about 1.5 billion pallets used in the United States alone. There is an estimated construction of 700 million new pallets each year while an additional 700 million wood pallets are being annually repaired. 
   To keep up with the high demand, wooden pallets are being mass-produced with automated pallet making machines. The automatic pallet making machines typically include nail guns that are mounted on a frame and are aligned with stringers used to make the pallet. A majority of the mass produced pallets are built on automated machines using hydraulic nailing guns. On these machines, the relative motion between the nail gun and the material being nailed stops while the nail is driven into the material. One limiting factor in the production of wooden pallets is the average speed of the material relative to the nail gun. The relative motion between the material and the nail gun is a limiting factor because the material stops while the nail is driven. 
   Additionally, the speed at which a nail is driven by a hydraulic system requires the material be stationary while the nail is driven. The additional time required to drive the nail into the material also has made the hydraulic system a limiting factor in the mass production of pallets. 
   SUMMARY OF THE INVENTION 
   The present invention includes an apparatus for nailing a plurality of cross members to an underlying stringer in which the stringer and the plurality of cross member are positioned on a support. A carriage moves in a continuous motion without stopping over the plurality of cross members until the plurality cross members are nailed to the stringer. At least one nailing gun is secured to the carriage for driving nails in to the cross members and the underlying stringer to secure the cross members to the stringer. A hydraulic accumulator is mounted on the carriage and is in hydraulic communication with the at least one nailing gun for supplying hydraulic fluid under pressure to provide a force to the nailing gun for nailing the cross member to the stringer. 
   The at least one nailing gun may also be pivotally secured to the carriage for driving nails into the cross members and the underlying stringer wherein the nailing gun pivots with respect to the carriage while driving a nail into the cross member and the underlying stringer thereby permitting the carriage to move without stopping. 
   The apparatus may also include the at least one nail gun having a chuck portion which contacts the wood during the nailing operation and is pneumatically driven to the wood and wherein a hydraulic cylinder actuates the nail driving mechanism moving it through the wood chuck to drive nails into the cross members and the underlying stringer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of the nail gun of the present invention. 
       FIG. 2  is a perspective view of an automatic pallet-making machine employing the nail gun of the present invention. 
       FIG. 3  is a side sectional view of the nail gun of the present invention mounted to a frame. 
       FIG. 4  is a side view of the nail gun of the present invention mounted to a frame. 
       FIG. 5  is a schematic view of the control system for the nail gun of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention includes a nailing carriage that moves in a continuous fashion for nailing cross members to underlying stringers. By continuous motion is meant that the carriage does not stop while nailing. Such a carriage does not require carriage brakes as prior art devices, and also requires a relatively inexpensive electric motor with a variable frequency drive to power the movement of the nailing carriage. Prior art devices required expensive servo motors or carriage brakes in conjunction with a hydraulic motor drive to stop the carriage when the nails are being driven. The nailing carriage of the present invention moves approximately an average of 5.5 inches per second when compared to prior art devices which move approximately an average of 3 inches per second due to the stoppage that has to occur when the nailing guns drive nails into the cross members and into the underlying stringers. 
   Some of the elements that permit continuous motion of the nailing carriage of the present invention include a high speed nailing chuck having a pneumatic cylinder with a 1 inch bore that drives the chuck body of the nailing chuck down to the wood. Another aspect of the continuously moving the nailing carriage of the present invention is a hydraulic accumulator mounted on the nailing carriage in close proximity to the hydraulic nailing chuck cylinder thereby reducing hydraulic head losses. Reducing hydraulic head losses creates higher flow and reduces nail driving times. Furthermore, the nail chuck of the present invention pivots with respect to the frame allowing relative motion between the moving nailing carriage and the stationary cross members while nails are being driven. 
   A nail gun of the present invention is generally illustrated at  10  in  FIG. 1 . The nail gun  10  includes a nail chuck  12  and a hydraulic cylinder  14  and is designed to be mounted to a machine that secures at least two components together with a nail  16 . 
   One such machine is an automated pallet making machine  20  illustrated in  FIG. 2 . Throughout the application, the nail gun  10  of the present invention will be referenced in association with the automated pallet making machine  20  and the production of pallets  22 . However, the nail gun  10  can also be used in other applications besides the production of pallets. Additionally, the nail gun  10  does not have to be secured to a machine used to mass-produce goods, but rather the nail gun  10  can be mounted to any object that securely retains the nail gun  10 . 
   The exemplary automatic pallet-making machine  20  includes three nail guns  10  that are aligned with three stringers  24  of the pallet  22 . The number of nail guns  10  employed by the automatic pallet-making machine  20  varies with corresponding number of the stringers  24  used to construct the pallet  22 . 
   Referring to  FIGS. 1 ,  2  and  3 , nails  16  are fed into the nail chuck  12  through a singulating system  30 . The singulating system  30  properly aligns the nails  16  such that a head  17  of one nail  16  is proximate a pointed end of another nail. The singulating system  30  includes a vibrating bin  32  that holds a quantity of nails  16 . The aligned nails  16  exit the bin  32  through a valve  33  controlled by a programmable logic controller (PLC)  50  as illustrated in  FIG. 4 . 
   Referring to  FIGS. 1 ,  2 ,  3  and  4 , the nails  16  are fed into the nail chuck  14  through a second valve  35  also controlled by the PLC  50  and enter a tube  34  that feeds the nails  16  to the nail chuck  12 . Because the nail chuck  12  and the hydraulic cylinder  14  move to drive the nails  16  into an object, the tube  34  feeding the nails  16  to the nail chuck  14  preferably is flexible and made of a vinyl or a PVC material. 
   The nail  16  is retained in a selected position within the nail chuck  14  by a pair of opposing spring-loaded nail keepers  40  (one of which is shown). Preferably, a circular spring  42  is positioned about and biases the pair of nail keepers  40  together such that the nail  16  is retained in the selected position therebetween. 
   The nail  16  is driven into an object with a hydraulic system  46  acting upon the hydraulic cylinder  14  in combination with a pneumatic system  48  acting upon the nail chuck  12 . Preferably, the pneumatic system  48  and the hydraulic system  46  are controlled by the PLC  50  such that the PLC  50  simultaneously activates both the pneumatic system  48  to force the nail chuck  12  into contact with a cross board  23  and the hydraulic system  46  forces a hydraulic ram  52  into the nail  16  which drives the nail  16  into the cross board  23  and stringer  24 . An exemplary PLC is series  9030  controller manufactured by GE Fanuc located at 2500 Austin Drive, Charlottesville, Va. 22911. 
   The pneumatic system  48 , which is more responsive than the hydraulic system  46 , positions the nail chuck  12  proximate the cross board  23  while the hydraulic system  46  begins driving the nail  16  toward the cross board  23  and the stringer  24 . With the nail chuck  12  manipulated into a position adjacent the cross board  23  by the pneumatic system  48 , the hydraulic system  46  forces the hydraulic ram  52  from the hydraulic cylinder  16  to drive the nail  16  into the stringer  24  and the cross board  23 . The combination of the pneumatic system  48  cooperating with the hydraulic system  46  reduces the cycle time between nails  16  being driven as compared to a hydraulic system both manipulating the nail chuck  12  into position and driving the nail  16  into the pallet  22 . 
   Referring to  FIG. 1 , the nail chuck  12  is positioned within through bores  58 ,  62  of upper and lower linear motion bearings  56 ,  60 , respectively that slidably guide the movement of the nail chuck  12  toward and away from the pallet  22 . The preferred linear bearing are Oilite AA-2001-11 manufactured by Beamer Precision, Inc. located at 230 New York Drive, Fort Wash., Pa. 19034-0980. 
   The upper linear motion bearing  58  includes a nozzle  64  through which pressurized gas is forced into a chamber  66  defined by a shoulder  68  extending from the linear bearing and contacting an outer surface  13  of the nail chuck  12  and a ring  70  extending from the outer surface  13  of the nail chuck  12  and forming a seal with a surface defining the through bore  58  within the upper linear bearing  56 . The PLC  50  controls a valve  72  to begin flow of the pressurized gas into the chamber  66  as illustrated in  FIG. 4 . As pressure is built up in the chamber  66  by the compressed gas, the nail chuck  12  is forced towards the cross board  23 . Preferably, the compressed gas is compressed air. 
   While the nail chuck  12  is being forced proximate the cross board  23  with the pneumatic system  48 , the PLC  50  sends a signal to a control valve  74  that directs high pressure hydraulic fluid from an accumulator  37  mounted on the carriage  21  into an upper port  76  of a hydraulic cylinder  14  which forces a ram  52  of the hydraulic cylinder  14  towards the nail  16 . A drive pin  78  that is coupled to the ram  52  by a threaded retaining nut  80  engages the head  17  of the nail  16  and drives the nail  16  into the cross board  23  and the stringer  22 . Since the hydraulic accumulator is mounted on the carriage  21  it is in close proximity to the hydraulic cylinder. The close proximity of the hydraulic accumulator  37  to the hydraulic cylinder  14  minimizes the length of the hydraulic lines  39  reducing hydraulic head losses, creating faster flow of hydraulic fluid thereby resulting in fast nail driving. The close proximity of the hydraulic accumulator  37  to the hydraulic cylinder  14  by mounting on the carriage  21  results in nails driven in approximately 100 milliseconds or less for a typical pallet nail approximately 2.5 inches long when compared to prior art devices such as a Champion nailing carriage produced by Viking Engineering and Development Company which drives nails in approximately 180 milliseconds. The present invention, close proximity of the accumulator to the hydraulic nailing valves that control the nail chuck reduces hydraulic pressure losses about 300 pounds per square inch when compared to prior art systems such as a Champion nailing carriage in which the accumulator is not located on the nailing carriage. 
   The hydraulic system  46  is pressurized with a hydraulic pump  82 . The hydraulic system  46  includes a hydraulic fluid accumulator  84  positioned near the control valves  74 . The pump  82  is connected to the accumulator  84  and the valves  74  with a hydraulic pressure line  86 . The hydraulic accumulator  84  provides the necessary high pressure hydraulic fluid to the hydraulic system  46  to actuate as many hydraulic cylinders  16  of the nail guns  10  as necessary during a cycle. Preferably, the hydraulic accumulator  84  and the hydraulic valves  74  are positioned proximate the hydraulic cylinders  16  of the nail guns  10  to minimize pressure drop in the hydraulic system  46  such that the cycle time for driving the nails  16  is minimized. 
   Once the nail  16  is driven into the cross board  23  and the stringer  24 , the controller  50  sends another signal to the hydraulic valves  74  to redirect the high-pressure hydraulic fluid to a lower port  77  of the hydraulic cylinder  16  such that the hydraulic ram  52  is retracted back into the cylinder  14 . As the hydraulic ram  52  is retracted back into the cylinder  14 , the nail chuck  12 , which is coupled to the hydraulic ram  52  with a threaded cap  88  that threadably engages the nail chuck  12 , is also retracted from the cross board  23  by the engagement of the threaded cap  88  with the threaded nut  80 . 
   With the nail chuck  12  retracted from the cross board  23 , an electric motor  90  coupled to a frame  21  that retains the nail gun  10 , moves the frame  21  along with the nail gun  10  in the direction of arrow  25  to another selected position, as illustrated in  FIG. 3  with an encoder or high speed counter within the PLC  50  as illustrated in  FIG. 5 . The PLC  50  sends a signal to the electric motor  90  to move the frame  21  to a selected location where a nail  16  is to be driven into the cross board  23 . With the frame in the selected position, a brake  91  engages the motor  90  and retains the frame in the selected position. 
   The speed at which nails  16  driven into the cross board  23  and the stringer  24  is increased because of the pneumatic system  48  cooperation with the hydraulic system  46  in driving the chuck  12  into contact with the cross board  23 . The PLC  50  also has an interface  57  which allows the control parameters to be adjusted. 
   With the frame  21  in the selected position, the valve  35  is opened by the PLC  50  to deliver another nail  16  to the nail chuck  12  through the flexible tube  34  through a port  94  that is angled into the chuck  12 . A nut  96  threadably engages the port  94  and frictionally retains the tube  34  to the port  94 . The angle of the port  94  allows the nail  16  to slide into the chuck  12  and between the nail grippers  40 . The port  94  is secured to the chuck  12  with a holder  98  that is bolted to the chuck  12 . 
   Referring to  FIG. 1 , the nail chuck  12  also includes adjusting mechanisms for adjusting a depth of the head  17  of the nail  16  into the cross board  23 . The depth of the head  17  of the nail  16  can be adjusted such that the head  17  is above the cross board  23 , even with the cross board  23 , or countersunk into the cross board  23 . 
   The depth of the nail head  17  is adjusted by manipulating the threaded nut  80  that retains the driving pin  78  to the hydraulic ram  52 . The depth of the nail head  17  is adjusted such that an end  81  of the threaded nut contacts a shoulder  102  of a bore  100  of the chuck  12  thereby limiting the stroke of the hydraulic ram  52 . By limiting the stroke of the hydraulic ram  52 , the distance that the nail  16  can be driven is also limited or extended depending upon whether the end  81  is closer to the hydraulic ram  52  or farther from the hydraulic ram  52 , respectively. 
   The depth of the nail head  17  can also be adjusted by manipulating a nose  104  that threadably engages a threaded outer surface  106  of the chuck  12 . The nose  104  is rotated on the chuck  12  to threadably engage the chuck  12  and move the nose  104  to a selected position such that an end  105  of the nose  104  extends from the chuck  12 . One skilled in the art will recognize that by manipulating the distance that the end  105  of the nose  104  is from the chuck  12 , the depth of the nail head  17  can be adjusted because of the limited range of the hydraulic ram  52 . With the end  106  of the nose  104  proximate the nail chuck  12  the nail head  17  can be driven further into the cross board  23  than if the end  105  of the nose  104  is farther away from the nail chuck  12 . With the nose  104  in a selected position, a locking nut  108  threadably engaged with the chuck  12  is positioned to frictionally engage the nose  104  and retain the nose  104  in the selected position. 
   Referring to  FIGS. 3 ,  4  and  5 , the nail gun  10  is pivotally mounted at pivot point  27  to the movable frame  21  of the automatic pallet making machine  20  with brackets  110  that engage plates  112  that are secured to opposite sides of the linear bearings  56 ,  60  and the hydraulic cylinder  14 . Bolts  113  are positioned between through bores in the brackets  110  aligned with a through bore in each plate  112  such that the nail gun  10  pivots about the bolts  113 . 
   The nail chuck  12  is retained proximate the frame  21  with a spring  114  that is mounted to the frame  21  and the plates  112 . The spring  114  biases the nail chuck  14  toward the frame  21  such that the nose  104  is within a known proximity of a desired location. The speed at which the pallet  22  is manufactured is increased by the nail chuck being driven by the hydraulic system  46  assisted by the pneumatic system  38 . 
   Additionally, the speed at which a pallet  22  is manufactured is also increased by the pivotal attachment of the nail gun  10  to the frame  21  which allows nails  16  to be driven into the cross-boards  23  and the stringers  24  while the frame  21  with nail guns  10  is moving. With the nail gun  10  engaging the pallet  22 , the nail gun  10  moves with respect to the pallet  22  by pivoting about the bolts  113  and with the chuck  12  rotating back in the direction of arrow  29 . As the nail gun  10  disengages from the cross-board  23  the spring  114  returns the nail gun  10  to an upright position with respect to the frame  21 . 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.