Abstract:
A preferred embodiment of a rotary tool reciprocating motion conversion attachment for a rotary power hand tool is described which is configured to be attached to a nose portion of the hand tool housing. The attachment has a rotary drive train in a housing that is connectable to the output shaft of the hand tool, the drive train driving a barrel cam having an exterior cam groove. A cam follower rides in the cam groove and produces reciprocating motion, with the cam follower being part of a cam follower assembly to which an implement holder is attached. The preferred embodiment has a cam groove configuration which causes the implement holder to move slower during a cutting stroke and faster during a return stroke, thereby tending to optimize the operation of the cutting implement. The preferred embodiment also includes a planetary gear set for reducing the rotational speed of the hand tool output shaft to reduce the speed of reciprocation of the attachment.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to power hand tools and more particularly to a rotary to reciprocating motion conversion attachment for the same.  
         [0002]     Small rotary hand tools have been marketed for many years for use in carrying out woodworking and metal working tasks by hobbyists as well as commercial artisans. Such small rotary hand tools generally have a motor unit with a rotary output shaft that is adapted to be connected to a number of implements for doing such application work as grinding, polishing, drilling and sanding, among other tasks. Such hand tools are also configured to operate with accessories, such as, for example, a long sheathed cable to which a sanding implement or rotary cutting implement can be attached, a planing attachment as well as a right angle attachment that facilitates use of implements in special applications.  
         [0003]     The drive unit of many recent models of such rotary hand tools is relatively small and lightweight and is capable of being easily used by a user. Such rotary hand tools may have a diameter less than about two inches and a length of only about six inches. The tool has a small but powerful electric motor that drives an output shaft at high speed, and a rotary implement can be typically attached to the tool&#39;s output shaft which is axially aligned with the generally cylindrical hand tool.  
         [0004]     While most of the applications that have been discussed above are directed to applications where rotary implements are used in various ways, there are other desirable uses for such rotary hand tools if an accessory were to be attached to the hand tool that would convert the rotary motion into reciprocating motion so that cutting, sawing sanding, filing, buffing and polishing implements that reciprocate could be used. Mechanisms which convert rotary motion to reciprocating motion are known in the art, but many have one or more disadvantages in that they may not provide a sufficiently large reciprocating stroke to be efficient and effective, or they may not be sufficiently robust to have a long useful life or exhibit sufficient cutting or sawing force during operation. The mechanisms for producing a reciprocating action for a saw blade or the like generally produce a sinusoidal movement in that the duration of a stroke in one direction is equal to the duration of the stroke in the reverse direction.  
         [0005]     For many saw blades, such as commercially available saber saw blades, the actual cutting action that is made by the blade is in a particular direction, i.e., the cutting stroke and the other movement is a return stroke which to returns the blade to the position where the next cutting stroke begins. Since the cutting action only occurs during one-half of the total length of movement of the blade, cutting action may be optimized by having the cutting stroke be of longer duration than the return stroke. This asymmetrical timing of the two strokes does not exist in known prior art rotary to reciprocating motion conversion apparatus.  
       SUMMARY OF THE INVENTION  
       [0006]     A preferred embodiment of a rotary tool reciprocating motion conversion attachment for a rotary power hand tool is described which is configured to be attached to a nose portion of the hand tool housing. The attachment has a rotary drive train in a housing that is connectable to the output shaft of the hand tool, the drive train driving a barrel cam having an exterior cam groove. A cam follower rides in the cam groove and produces reciprocating motion, with the cam follower being part of a cam follower assembly to which an implement holder is attached. The preferred embodiment has a cam groove configuration which causes the implement holder to move slower during a cutting stroke and faster during a return stroke, thereby tending to optimize the operation of the implement. The preferred embodiment also includes a planetary gear set for reducing the rotational speed of the hand tool output shaft to reduce the speed of reciprocation of the attachment.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a side view of a preferred embodiment of the rotary to reciprocating motion conversion attachment embodying the present invention;  
         [0008]      FIG. 2  is an exploded perspective view of the attachment shown in  FIG. 1 ;  
         [0009]      FIG. 3  is a side view of the attachment shown in  FIG. 1 , with a portion of the housing removed to show the internal components thereof, and also illustrating a representing blade implement that may be driven by the attachment;  
         [0010]      FIG. 4  is a side view of a portion of the drive train of the attachment shown in  FIG. 1 , and is shown partially in section;  
         [0011]      FIG. 5  is an exploded side view of the drive train shown in  FIG. 4 ;  
         [0012]      FIG. 6  is a top plan view of the cam follower assembly of the apparatus shown in  FIG. 1 ;  
         [0013]      FIG. 7  is a side view, partially in section, of the cam follower assembly shown in  FIG. 6 ;  
         [0014]      FIG. 8  is a front view of the cam follower assembly shown in  FIG. 6 ;  
         [0015]      FIG. 9  is a front view of the rear cam section;  
         [0016]      FIG. 10  is a cross-section taken along the line  10 - 10  of  FIG. 9 ;  
         [0017]      FIG. 11  is a front view of the front cam section of the drive train shown in  FIG. 4 ;  
         [0018]      FIG. 12  is a cross-section taken generally along the line  12 - 12  of  FIG. 11 ; and  
         [0019]      FIG. 13  is a chart illustrating a portion of the cam groove that is defined by the front and rear cam sections when they are interconnected. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Turning now to the drawings, the attachment indicated generally at  10 , is shown as a whole in  FIGS. 1-3 , with the remainder of the drawings illustrating various parts of the internal structure of the attachment. The attachment  10  is configured to be mounted on the nose portion of a high speed rotary power hand tool that is not shown in the drawings, but which is generally cylindrical in shape and has a smaller nose portion from which an output shaft extends, with the output shaft having a threaded end portion on which a chuck may be screwed on. Alternatively, a cap with an opening at the end thereof may be screwed on the shaft, with the opening being square or some other noncircular shape so that a drive coupling shaft can couple the output shaft of the hand tool to the attachment of the present invention. While not illustrated, the above described construction is known to those of ordinary skill in the art and is also disclosed in detail in U.S. Pat. No. 6,463,824 entitled Right Angle Attachment for Power Hand Tool, which is assigned to same assignee as the present invention. This patent is specifically incorporated by reference herein.  
         [0021]     The attachment  10  has a housing, indicated generally at  12 , that is comprised of two mating sections  14  and  16  with the two sections being complementary and connected together by a number of screws  18 . The housing sections are preferably made of a plastic or plastic-like material, such as ABS or glass filled nylon. Each of the housing sections  14  and  16  has a semi-cylindrical mounting portion  20  which when the sections  14  and  16  are fit together, define a generally cylindrical configuration over which have two semi-cylindrical overflow nut pieces  22  may be placed, and which are rotatable relative to the housing  12 . A sleeve  24  is configured to snap-fit onto the coupled nut pieces  22  enabling interior threads  26  thereof to engage the outer threads of the nose portion of the rotary hand tool to which the attachment  10  is to be mounted. The sleeve  24  interconnects the overflow nut pieces  22  so that the entire structure rotates on the mounting portions  20  for screwing the attachment onto the hand tool.  
         [0022]     The housing  12  has a number of vent openings  28  in each section  14  and  16  thereof for admitting and exhausting air from the interior of the housing  12  during operation. The housing also has a warning insert  30  that fits within a recess  32  of the housing section  16  which also has an elongated opening  34  which permits access to the interior of the housing for manipulating a set screw for securing or removing an implement such as a saw blade  36  as shown in  FIG. 3 . The housing has a generally transverse front portion  38  that is slightly curved as shown and which has a raised transverse generally cylindrical portion  40  formed at the front of each section  14 ,  16  of the housing which has an opening  42  through which a pivot stud  44  passes for mounting a guide foot  46  to the housing  12 .  
         [0023]     The pivot stud  44  also passes through openings  48  on opposite sides of the guide foot  46 . The guide foot is pivotal around the pivot stud  44  and the pivot stud  44  is locked in place by an inner toothed retainer  50 . Each of the housing sections  14  and  16  also has a cut out  52  which define a single opening for the blade  36  to pass. Similarly, the guide foot  46  has an opening  54  through which the blade can extend.  
         [0024]     With regard to the internal components of the preferred embodiment, the attachment  10  has a rotary drive train, indicated generally at  60 , and a cam follower assembly, indicated generally at  62 . As shown in  FIG. 2 , the drive train  60  includes a drive coupling shaft  64  that has an annular outwardly extending flange  66  for limiting axial movement of the coupling shaft relative to a fan blade  68  that is mounted to a pinion shaft  70  that has a pinion gear  72  at its rightward end portion for engaging a planetary gear set  74 . The fan  68  has a flat circular plate portion  76  to which a number of fan blades  78  are attached or formed with the plate portion. The fan  68  is a radial fan which during rotation causes air to move outwardly in the radial direction. Because the fan  68  is positioned adjacent the vent openings  28  in the housing  12 , air from within the housing can be expelled through the vent openings  28  to cool the attachment. In this regard, the planetary gear set  74  tends to generate sufficient heat that makes it desirable for the fan  68  to provide beneficial cooling. While not specifically shown, the pinion shaft  70  is configured with a recess in its left end as shown in  FIG. 2  that cooperatively engages the square cross section coupling shaft  64  so that rotation of the coupling shaft  64  will rotate the shaft  70  as well as the fan  68 . The pinion gear  72  engages components of the planetary gear set  74 .  
         [0025]     As is best shown in  FIGS. 2, 4  and  5 , the pinion shaft  70  fits within the planetary gear set  74  and particularly rides in a needle bearing  80  which is retained in an opening in a gear housing  82  of the planetary gear set  74 . The needle bearing  80  is of the type which is well known in the art and is commercially readily available. It has a number of elongated cylindrical needles that rotate within an outer cylindrical raceway. The pinion shaft  70  is therefore supported in the needle bearing  80  and the pinion gear  72  is configured to engage each of three planet gears  84  that have concentric openings so that they fit on shafts  86  that are attached to a carrier plate  88  which in turn is attached to an output shaft  90  by a press fit or other known attachment configuration, with the shaft  90  having a reduced diameter portion  92 , as well as additional reduced diameter portions  94  and  96 . The gear housing  82  has a ring gear configuration  98  on the inner surface thereof which also engages each of the planet gears  84 , it being understood that the shafts  86  and the ring gears  84  that are carried by the shafts are in a triangular arrangement relative to one another, i.e., the shafts are angularly displaced from one another by 120°.  
         [0026]     When the planet gears  84  are mounted on the shafts  86  and the assembly is inserted into the gear housing  82 , a flat circular shim plate  100  may be inserted, with the shim plate  100  having a central opening through which the pinion shaft  70  and gear  72  may pass so that the pinion gear  72  may engage the planet gears  84 . With the illustrated configuration, the output shaft  90  of the planetary gear set  74  is reduced by a factor of 9 relative to the rotational speed of the pinion shaft  70 . This therefore reduces the rotational speed of the output relative to the input, and also proportionately increases the torque that is produced by the hand tool.  
         [0027]     Referring to  FIGS. 4 and 5 , the output shaft  90  has a bushing plate  102  that is cylindrically shaped and has an outer annular flange  104  which is sized to fit within the inside of the gear housing  82  which effectively encloses the gear set  74 . Once assembled, the rim of the gear housing  82  is preferably crimped against the outer circumference of the annular flange  104  as shown at  106  in  FIG. 4  to substantially seal the interior of the housing including the carrier plate  88  and gears  84  that are located within the gear housing  82 . A bushing  108  is located within the bushing plate which is also held stationary relative to the rotating output shaft portion  90 . It should be understood that the inside diameter of the bushing  108  is sized to receive the output shaft portion  90  and firmly hold the same while permitting rotation thereof relative to the bushing  108 .  
         [0028]     A dowel pin  110  fits within an opening  112  in the reduced diameter portion  92  of the output shaft  90  so that it extends in both directions from the shaft portion  92 . It has a length sufficient to engage recesses  118  on a rear barrel cam section  112  which has an inside diameter that is sized to receive the output shaft portion  92  in close fitting engagement. The rear barrel cam section  112  is shown in  FIGS. 9 and 10 , with an inside diameter  114  having a flat portion  116  that corresponds with a flat portion of the output shaft section  92  that is not shown in detail. The corresponding flats orient the rear barrel cam section  112  in the proper angular position so that the outwardly protruding ends of the dowel pin  110  will engage the recesses  118  in the rear barrel cam section  112 . The width of the recesses  118  are slightly larger than the diameter of the dowel pin  110  so that the dowel pin will fit within the recesses  118 , but will also firmly hold the barrel cam section  112  from rotation relative to the shaft portion  92 .  
         [0029]     A front barrel cam section  120  also fits on the shaft portion  92  immediately adjacent and in front of the rear section  112 . The front barrel cam section  120  is shown in  FIGS. 11 and 12  and it has an internal opening  122  with a flat portion  124  that is provided for the same purpose as described with regard to the rear barrel cam section  112 . The front section  120  has a pair of keys  126  that fit within a pair of keyways  128 , only one of which is visible in  FIG. 5 . Each of the barrel cam sections  112  and  120  has an outwardly extending flange  130 ,  132 , which together with the outside diameter of barrel section  112  defines a cam groove that is indicated generally at  134  in the drawings. A ball bearing  136  appropriately sized to fit on the output shaft section  94  is supported by structural surfaces in the housing  12  so that the drive train is supported at both ends. A retaining ring  138  is friction fit on output shaft  96  and holds the components of the drive train together.  
         [0030]     The cam groove  134  extends completely around the joined barrel sections and defines a generally sinusoidal or near sinusoidal path around the periphery.  FIG. 13  illustrates a portion of the path, with the center of the path being shown and its extreme leftward position being marked as  0 . As the barrel cam sections rotate, the cam path center line moves to the right as shown in  FIG. 13  to its extreme right position and then returns to the zero position upon a full revolution of the barrel cam. A chart of the path in terms of movement from its extreme left or zero position through a full 360° rotation is shown in  FIG. 14 , with the amount of movement being 3.75″ of travel in the Y direction. It should be understood that the cam groove could be configured to have a greater or lesser amount of movement in the Y direction than the 0.375″ as shown, if desired. If not apparent from the foregoing description, the excursion in the Y direction is movement in the horizontal direction as oriented from  FIGS. 1 and 3  which results in reciprocating movement of the blade  36  as shown in  FIG. 3 .  
         [0031]     The cam follower assembly  62  is shown in  FIGS. 3, 6 ,  7  and  8  and comprises an elongated plunger  140  that is slideable within a pair of supports  142  which extend transversely of the length of the plunger  140  and which have ends  144  that engage recesses  146  located in both housing sections  14  and  16 , only those in section  114  being visible in  FIG. 2 . The supports  142  have a center portion that includes upper and lower sections that are sized to permit the plunger  140  to fit within them and be slideable in the left to right direction as shown in  FIG. 6 . The configuration is shown in perspective in  FIG. 2  of the drawings. Generally mid-way between the supports  142  is a cam follower mechanism that comprises a cylindrical needle bearing  148  that fits on a cylindrical sleeve  150  that has an enlarged head portion  152 . The sleeve  150  fits through an opening  154  in the plunger  140 . A washer  156  and a thin bronze thrust washer  158  provide a surface on which the needle bearing  148  can ride. The outer diameter of the needle bearing  148  is only slightly smaller than the width of the cam groove  134  so that very little play exists between the two components.  
         [0032]     As the barrel cam sections  130  and  132  rotate, the cam follower defined by the needle bearing  148  will move in the horizontal direction as shown in  FIGS. 6 and 7  in a reciprocating manner as is desired. At the front or right end of the plunger  140  is an implement holder, indicated generally at  160 , which is configured to receive a blade such as the saber saw blade  36  shown in  FIG. 3 . The holder has a generally box-like configuration with a lower slot  162  through which the right end of the plunger  140  (as shown in  FIG. 7 ) can be inserted and a dowel pin  164  is force fit into openings in both the bottom part of the holder  160  and in the end portion of the plunger  140 . Thus, the implement holder  160  is fly attached to the plunger as is desired.  
         [0033]     The plunger also has an opening  166  in the front of the holder as shown in  FIG. 8  which is configured to receive the shank end of the blade  36 . An elongated pressure pad  168  is also located in the slot  166  and generally extends from the right to the left end of the block  160  as shown in  FIG. 7 . It also extends beyond the back end and has an enlarged portion  170  through which a pin  172  is force fit into an opening therein. The front end of the pressure pad  168  is preferably curved to facilitate insertion of a blade  36  into the slot  166 . The blade  36  is secured by a set screw  174  threadably engaged in a threaded hole in the holder  160 . When the set screw is tightened by an Allen wrench fitting into a recess  176 , the inner end of the set screw will contact the pressure pad  168  forcing it against the shank of the blade  36  to firmly hold it in place. It should be understood that the set screw  174  is accessible through the housing  12  by the opening  34  as shown in  FIG. 1 . Also, while an Allen wrench configuration is shown, other configurations, such as a star configuration, square configuration, or even regular or Phillips screw configurations may be used.  
         [0034]     Referring to the chart of  FIG. 14 , the cam groove is configured to define a generally sinusoidal path, but it should be apparent that the movement from the  0  or extreme left position as shown in  FIG. 13  represents the end of the cutting stroke which occurs when the blade  36  is pulled from the right to the left as shown in  FIG. 3 . The return stroke occurs within 150° of rotation as shown in  FIG. 14  and the cutting stroke occurs when the rotational angle moves from 150° through 360°.  
         [0035]     While other near-sinusoidal paths may be used, the shape of the chart shown in  FIG. 14  is defined by the following equations.  
         [0036]     y is a function of the barrel rotation angle: 
        for 0° to 150°, y=4.7625 
       [     1   +     cos   ⁡     [       π   180     ⁢     (         c   ·   180     150     +   180     )       ]         ]       
    for 150° to 360°, y+4.7625 
       [     1   +     cos   ⁡     [       π   180     ⁢     (     180   +       180   210     ⁢     (     360   -   C     )         )       ]         ]       
 
 where C=position angle. 
       
 
         [0039]     Since more work is being done during the cutting stroke, the efficiency of the sawing operation is increased by causing the cutting action to occur through a greater rotational angle and the return stroke occur through a lesser rotational angle. It has been found that while a truly symmetrical distribution of the cutting and return stroke, i.e., 180° for each, will operate reasonably well, increased efficiency has been experienced when the above described asymmetrical cutting and return stroke is used.  
         [0040]     While the chart of  FIG. 14  illustrates a 150° return stroke and a 210° cutting stroke, the return stroke may be increased to extend over a larger angle if desired. However, using a larger angle return stroke will result in a reduction in operating efficiency compared to the smaller 150° return stroke. It should be understood that the lower the angle of the return stroke, the greater the stresses that are applied to the barrel cam structure. Since it is desired to make the barrel cam sections from glass filled nylon, it has been found that about 150° is the lower limit for the configuration illustrated in the drawings when the barrel cam sections are made of this material. Having a return stroke of about 150° results in acceptable stresses being applied to the barrel cam sections that will not damage them and also results in desirable operating efficiency.  
         [0041]     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.  
         [0042]     Various features of the invention are set forth in the following claims.