Abstract:
The present invention teaches a unique drive mechanism for use in a hand held fastener driving tool. The driving mechanism comprises a pair of opposing cams coaxially positioned upon a common shaft. One of the cams is motor driven and rotatable about the common shaft but not axially translatable while the other cam is axially translatable but non-rotatable. Rotation of the rotatable cam by the motor causes the non-rotatable axially translatable cam to compress a compressible spring assembly, storing potential energy therein. Simultaneously, a driver activation cable, wrapped about the rotatable cam&#39;s periphery, unwraps thereby raising a fastener driver to its driving configuration. Upon release of the rotatable cam from the motor drive, the potential energy stored within the spring assembly causes reverse rotation of the rotatable cam thereby rewinding the drive cable about the rotatable cam&#39;s periphery and driving the fastener driver, whereby the driver drives a fastener into a workpiece.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit from U.S. Provisional Patent Application Ser. No. 60/567,263, filed Apr. 30, 2004, which application is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to fastener driving tools, in particular, to a battery operated fastener driving tool which uses the energy stored in a spring to drive the fastener. 
   2. Description of the Related Art 
   Many different types of tools have been developed over the years for the purpose of driving a fastener into wood. The most common type of fastener driving tool is the type in which the driver is actuated pneumatically. An example of this type of tool is shown in U.S. Pat. No. 3,278,106. While these tools work well, one drawback to their use is the requirement of a compressor to provide the pneumatic power. 
   In recent times, other designs for fastener driving tools have used electromechanical designs to provide the energy necessary to drive the fasteners. Some of these tools use a heavy duty solenoid to provide the driving force. Others employ the use of one or more flywheels to generate the necessary driving force. While these types of tools have been successful, it is necessary to use an electrical cord, instead of a pneumatic hose, to supply the driving power. 
   An alternative design has become popular which uses internal combustion to provide the motive force, thus allowing the tools to become truly portable, with no hose or cord necessary for the operation of the tool. An example of this type of tool is taught in U.S. Pat. No. 4,403,722. Although this type of tool has been successful, some drawbacks have been associated with internal combustion tools. First, the expense for operating these tools is higher than the pneumatic and electrical tools; in addition, the exhaust fumes from these tools can be bothersome when working in an enclosed area. 
   Some newer electric tools have been designed such that they can be operated using batteries. Examples of these types of tools can be seen in U.S. Pat. Nos. 6,607,111 and 6,669,072. When used with rechargeable batteries, theses tools are portable and can be operated at minimal cost. However, these tools are necessarily bulky and heavy, as they require high energy mechanisms to drive the fasteners. 
   U.S. Pat. No. 5,720,423 teaches a fastener driving tool which uses a drive piston within a gas chamber in which the piston is moved in a direction opposite the driving direction within the gas chamber to compress the gas above the piston such that the piston drives a fastener when released as a result of the compressed air. However, the size of this tool is dictated by the length of the gas chamber, as the gas must be compressed significantly to generate the force needed to drive larger fasteners, and it is also necessary to include an air replenishing tank to supply compressed air to the chamber when the pressure drops below a predetermined value. 
   Finally, other tools use linear compression springs as an energy storage device to provide the driving force needed to drive a fastener into a substrate. These springs do not adapt efficiently in a chamber to create a sufficient force to drive larger fasteners, and the springs generally do not have proper duty cycles, leading to premature failure. 
   SUMMARY OF THE INVENTION 
   It is therefore an object to the present invention to provide a fastener driving tool of simple construction which is compact and reliable. 
   It is a further object of the present invention to provide a battery powered fastener driving tool which needs no connection to an external power source. 
   It is a still further object of the present invention to provide a fastener driving tool which uses stored energy to efficiently drive small gauge fasteners into a workpiece. 
   These and other objects of the present invention are accomplished by a novel fastener driving tool which comprises a pair of opposed ball ramp cams positioned on a common axial shaft. One cam is rotatable about the axial shaft while the opposing cam is non-rotatable but is axially shiftable on the shaft. A motor driven mechanism rotates the rotatable cam, causing axial separation of the opposing cams, and compressing an energy storing device which is positioned on the shaft to store potential energy within the device. As the rotatable cam is released, the energy storing device forces the non-rotatable cam back to its starting position, and the balls on the ramps of the cams cause the rotatable cam to rotate in the reverse direction, causing a driver blade to drive a fastener from the tool. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary side elevational view of an exemplary fastener driving tool according to the present invention; 
       FIG. 2  is a cross-sectional view taken along section line  2 — 2  of  FIG. 1  showing the principal working elements of the invention; 
       FIG. 3  is a cross-sectional view, taken along section line  3 — 3  of  FIG. 1 ; 
       FIG. 4  is a cross-sectional view taken along section line  4 — 4  of  FIG. 3 ; 
       FIG. 5  is a cross-sectional view taken along section line  5 — 5  of  FIG. 2 ; 
       FIG. 5A  is a cross-sectional view taken along section line  5 A— 5 A of  FIG. 3 ; 
       FIG. 6  is a cross-sectional view taken along section line  6 — 6  of  FIG. 2 ; 
       FIGS. 7A–D , taken together, show the operating sequence illustrating the engagement of the driving pin of the drive gear upon the cam lobe of the rotatable cam whereby the rotatable cam is rotated until disengagement of the driving pin from the cam lobe; 
       FIG. 8  is a perspective view of the fixed cam and the rotatable cam of the present invention; 
       FIG. 9  is a block diagram of an electronic circuit for activating and controlling the fastener driving tool of the present invention; 
       FIG. 10  is a fragmentary side elevational view similar to  FIG. 1  of an alternate embodiment of the present invention; 
       FIG. 11  is a cross-sectional view taken along section line  11 — 11  of  FIG. 10  showing the principal working elements of this embodiment; and 
       FIG. 12  is a front view of the drive gear for use in the alternative embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a typical battery powered hand held fastener driving tool generally indicated at  10  comprising a main body or housing  12 , handle  14  including activation trigger  15 , a battery pack  16 , and a fastener magazine  18  including a typical guide body  19 . Main body  12  is shown having a portion of its side removed, thereby showing the general arrangement of the principal subassemblies of the tool&#39;s working mechanism in accordance with the present invention. 
   Referring now to  FIGS. 2 and 3 , the primary working mechanism comprises two major subassemblies, a fastener driving subassembly generally indicated at  20 , and a motor/gear subassembly generally indicated at  55 . 
   Fastener driving subassembly  20  comprises a central axial pin indicated at  25  having a head end  26  and an elongated shaft portion  28  rigidly affixed to a frame  30  of tool main body  12  by screw threads  32 , or any other convenient means. 
   Assembled coaxially upon axial pin  25 , between pin head end  26  and main body frame  30 , is a rotatable cam  35 , a non-rotatable fixed cam  36  and a compressible spring means  38 . Although compressible spring means  38  is illustrated in the drawings as comprising a stack of oppositely facing Belleville spring washers  22 , spring means  38  may alternately comprise a coil spring or any other suitable compressible potential energy storing system that will store potential energy when compressed. A thrust washer  34  is positioned between axial pin head  26  and rotatable cam  35 . Rotatable cam  35  contains a channel  26  within its periphery. Finally, a spacer  27  is positioned between cam  36  and Belleville spring washer stack  22 . 
   As illustrated in  FIG. 8 , the opposing surfaces of rotatable cam  35  and non-rotatable cam  36  include three ball ramps  42 A,  42 B,  42 C, and  44 A,  44 B, and  44 C respectively. Positioned between the opposing ball ramps are three ball bearings  46 A,  46 B, and  46 C. As cam  35  rotates with respect to fixed cam  36 , ball bearings  46  move within the opposing ball ramps  42  and  44 , thereby causing non-rotatable cam  36  to move away from rotatable cam  35 . Cam  36  is held in position against rotation by an extension  37  which is captured within an opening  38  within frame  30 . 
   Typically received within a fixed piston tube  40  ( FIG. 3 ) is a driving piston  47 . A rigid elongated fastener driver  50  is provided, having one end thereof affixed to driving piston  47  within driving tube  40 . A driver activating cable  52  having one end thereof affixed to driving piston  47  and the other end thereof affixed within channel  26  on the periphery of rotatable cam  35  such that when fastener driver  50  is in its rest or start position, as can be clearly seen in  FIG. 5A , driver activating cable  52  is partially wrapped within channel  26  on the periphery of rotatable cam  35 . Cable  52  is preferably composed of either a flat stiff mesh composition or a series of individual steel cables arranged to form a single flat cable, such that it has enough column strength to push piston  47  into driving position. 
   Motor/gear subassembly  55  comprises a central axial pin generally indicated at  60  having a head end  62  and an elongated shaft portion  64  rigidly affixed to frame  30  of tool main body  12  by a series of screw threads  66 , or any other convenient means. 
   Assembled coaxially upon axial pin  60  between pin head end  62  and main body frame  30  is a toothed drive gear  70 . Suitable washers  67  and  68  are positioned on either side of drive gear  70 , as illustrated in  FIGS. 2 and 3 . Drive gear  70  is driven by a motor  58  through a worm gear  72 , as illustrated in  FIG. 6 . Extending axially from drive gear  70  is a drive pin  74 . Extending axially outward from rotatable cam  35  is a cam lobe  48  as can be clearly seen in  FIG. 5 . 
   Referring now to  FIGS. 7A–7D , as drive gear  70  is rotated counterclockwise by worm gear  72 , drive pin  74 , also rotating counterclockwise, engages cam lobe  48 , as illustrated in  FIG. 7A . As drive pin  74  continues its counterclockwise rotation, the action of drive pin  74  upon cam lobe  48  causes clockwise rotation of rotatable cam  35  as illustrated in  FIGS. 7B and 7C . Upon disengagement of drive pin  74  from cam lobe  48 , as illustrated in  FIG. 7D , rotatable cam  35  is free to rotate in the counterclockwise direction and return to its initial resting position. 
   In operation, as rotatable cam  35  is rotated in a clockwise direction, as viewed in  FIGS. 5 ,  5 A, and  7 A–D, driver activating cable  52  uncoils from the periphery of cam  35 , thereby forcing driving piston  47 , along with the attached fastener driver  50 , upwardly, as viewed in  FIG. 3 , into piston tube  40 . Further, as rotatable cam  35  rotates in a clockwise direction, the axial distance between rotatable cam  35  and non-rotatable cam  36  increases, by action of ball bearings  46  and opposing ball ramps  42  and  44  of rotatable cam  35  and non-rotatable cam  36 , thereby compressing compressible spring means  38 , storing potential energy therein. 
   Upon driving piston  47  reaching the top of its driving stroke, cam lobe  48  is released from drive pin  74 , thereby permitting rotatable cam plate  35  to rotate about axial pin  25 . The potential energy stored within compressed Belleville spring washers  22  now forces fixed cam plate  36  towards the left toward cam plate  35  (as viewed in  FIGS. 1 and 2 ). As fixed cam plate  36  shifts to the left, the action of ball bearings  46  between ball ramps  42  and  44  causes rotatable cam plate  30  to rotate in the reverse direction as fixed cam plate  32  approaches rotatable cam plate  35 . 
   As rotatable cam plate  35  rotates in the reverse direction, driver activating cable  52  now wraps about channel  26  within the periphery of rotatable cam  35 , thereby pulling driver piston  47  and fastener driver  50  downwardly, driving a fastener from magazine  18  into a workpiece (not shown). 
     FIG. 9  illustrates a simple control system for operating and controlling the herein described fastener tool  10 . A magnetic sensor  73  may be conveniently positioned juxtaposed drive gear  70  as best illustrated in  FIG. 6 . A programmed electronic controller  75  may be conveniently positioned within main body  12  or handle  14  of fastener driving tool  10 . 
   Controller  75  is programmed such that when the operator squeezes trigger  15  a signal is sent from trigger  15  to controller  75 . Controller  75  then sends a signal to motor  58  to energize, thereby causing drive gear  70  to rotate. As drive gear  70  rotates, magnetic sensor  73  counts the number of gear teeth passing thereby. After sensing the passage of a given number of gear teeth, representing one full revolution of drive gear  70 , controller  75  signals motor  58  to stop, thereby repositioning drive pin  74  at its starting position. 
   As the distance moved by cam  36  under the force of spring means  38  is very small when compared to the distance traveled by driver  50  in driving a fastener, a mechanical advantage is created by this mechanism. This allows the tool to be smaller, and also allows the tool to operate more quickly. 
   Although use of a tooth counting magnetic sensor is disclosed above, any other suitable means may be used to determine the desired revolution of drive gear  70 . For example, a proximity sensor, optical or magnetic, might be used to sense the return of drive pin  74  to its start position. Further, any suitable mechanical sensing mechanism might be used to determine return of drive pin  74  to its start position. 
   Depending upon scale or size of the gear/drive subassembly  55 , it may also be suitable to provide two or more drive pins equally spaced about drive gear  70  whereby one full cycle of the fastener drive subassembly  20  would comprise 180 degrees, or less, of drive gear  70 . 
   An alternative embodiment of the present invention is shown in  FIGS. 10–12 . Note that throughout these FIGS., like elements are designated with like numerals. Referring now to  FIGS. 10 and 11 , there is shown a fastener driving tool generally indicated at  10 ′ in which fastener driving subassembly  20  and motor/gear subassembly  55  are located collinearly on a single axial pin designated at  25 . Rotatable cam  35  is positioned along elongated shaft portion  28  between drive gear  70  and fixed cam  36 . These components are held in place along pin  25  by washer  68  positioned between drive gear  70  and head end  26  of pin  25 , a pair of spaces  80 ,  82  and a thrust washer  84  positioned between drive gear  70  and rotatable cam  35 , bail bearings  46  between cam  35  and cam  36 , and a spacer  27  between cam  36  and spring means  38  comprising a stack of Belleville spring washers  22 , which contacts frame  30  of tool  10 ′. Pin  25  is affixed to frame  30  by threaded end  32 . 
   Positioned on drive gear  70  on the side facing rotatable cam  35  is a latch mechanism  90 , while positioned on cam  35  on the side facing gear  70  is a drive pin  92 . Latch mechanism  90  is fixed for rotation about a pivot pin  94  and is biased by a spring  96  such that an edge  95  of latch  90  contacts drive pin  92  of cam  35  when drive gear  70  rotates, as can be clearly seen in  FIG. 12 . Latch  90  also includes an extension  97  which overhangs the edge of drive gear  70 . 
   The operation of this alternative embodiment can now be described. When it is desired to drive a fastener, the tool user activates trigger  15  of tool  10 ′, sending a signal to motor  58 , which rotates worm gear  72 . This action causes drive gear  70  to rotate in the counterclockwise direction as seen in  FIG. 12 . The edge of latch mechanism  90  engages drive pin  92  on rotatable cam  35 , causing rotatable cam  35  to rotate in unison with drive gear  70 . This action causes ball bearings  46  to compress Belleville spring washers  22 , storing potential energy in fastener driving subassembly  20 . 
   When pin  92  has rotated cam  35  approximately 200 degrees, extension  97  of latch mechanism  98  contacts a protrusion  98  which extends from frame  30 , rotating latch  90  about pivot  94  and compressing spring  96 . As latch mechanism  90  pivots, edge  95  is released from contact with drive pin  92  of cam  35 , allowing the potential energy stored in spring means  38  to cause ball bearings  46  to rotate cam  35  in the opposite direction, activating a drive cycle of piston  47  and fastener driver  50  to drive a fastener from magazine  18 . 
   In the above description, and in the claims which follow, the use of such words as “clockwise”, “counterclockwise”, “distal”, “proximal”, “forward”, “rearward”, “vertical”, “horizontal”, and the like is in conjunction with the drawings for purposes of clarity. 
   While the invention has been shown and described in terms of preferred embodiments, it will be understood that this invention is not limited to these particular embodiments, and that many changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.