Abstract:
Embodiments of a reciprocating drive apparatus are disclosed which comprise a housing, a drive shaft rotatably mounted in the housing, an elongated plunger mounted in the housing for reciprocating motion; the plunger having a rear end portion configured to engage a wobble plate interface structure and a front end portion for attaching a tool, a first bushing positioned in the housing for retaining the front end portion in a manner whereby the plunger is not restrained from rotating about a first axis of rotation, a second bushing positioned in the housing for receiving the rear end portion of the elongated plunger in a manner whereby the plunger is not restrained from rotating along a second axis of rotation as the plunger reciprocates in the bushing, a wobble plate assembly operatively connected to the drive shaft and having an elongated arm with a wobble plate interface structure for engaging the rear end portion of the plunger and reciprocating the plunger in the first and second bushings.

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to power hand tools, and more particularly, to power reciprocating tools. 
   Reciprocating tools that are motor driven, such as saber saws, larger reciprocating saws and the like are usually driven by electric motors that have a rotating output shaft. The rotating motion must be translated into reciprocating motion for moving a saw blade or the like in a reciprocating manner. While various types of mechanisms have been known in the art for translating the rotation motion into reciprocating motion, one common type of motion conversation mechanism is known as a wobble plate drive. A wobble plate drive shaft is typically connected to the motor through a gear arrangement to reduce the speed of rotation of the motor output shaft and the wobble plate drive causes a wobble arm to reciprocate in a path that is parallel to the motion of the saw blade or the like. The blade of a reciprocating saw is mounted in a blade clamping mechanism that is located at the end of a plunger, the other end of which is operatively connected to a wobble arm. 
   In some prior art wobble plate drives, the plunger has a rectangular or square cross-section that is located in a rectangular or square opening to restrain the plunger from twisting which would undesirably affect the angular orientation of a blade attached to the drive. While these noncircular cross-section plungers operate in a desirable manner, the noncircular cross-section increases the cost relative to a tubular plunger construction which is more desirable. However, there is a tendency of wobble plate drives to exert forces on the plunger which tend to cause it to rotate. It is highly desirable to prevent such rotation using a cost effective design that operates in a highly efficient manner. 
   SUMMARY OF THE INVENTION 
   Embodiments of a reciprocating drive apparatus are disclosed which comprise a housing, a drive shaft rotatably mounted in the housing, an elongated plunger mounted in the housing for reciprocating motion; the plunger having a rear end portion configured to engage a wobble plate interface structure and a front end portion for attaching a tool, a first bushing positioned in the housing for retaining the front end portion in a manner whereby the plunger is not restrained from rotating about a first axis of rotation, a second bushing positioned in the housing for receiving the rear end portion of the elongated plunger in a manner whereby the plunger is not restrained from rotating along a second axis of rotation as the plunger reciprocates in the bushing, a wobble plate assembly operatively connected to the drive shaft and having an elongated arm with a wobble plate interface structure for engaging the rear end portion of the plunger and reciprocating the plunger in the first and second bushings. 
   An alternative embodiment has the first and second axes of rotation offset relative to one another. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a preferred embodiment of a reciprocating saw of the present invention; 
       FIG. 2  is a side view of the preferred embodiment of the wobble plate assembly shown in  FIG. 1  with portions removed to illustrate interior construction; 
       FIG. 3  is an enlarged side view of the interior construction of a front portion of the embodiment shown in  FIG. 2 ; 
       FIG. 4  is a perspective view of the interior construction of the front portion shown in  FIG. 3 ; 
       FIG. 5  is an end view of a portion of interior construction of the front portion of the embodiment shown in  FIG. 2 , shown partially in section; 
       FIG. 6  is a side view of the interior construction of the front portion of an alternative preferred embodiment, shown partially in section and with the plunger in the retracted position; 
       FIG. 7  is another side view of the interior construction of the front portion of the alternative preferred embodiment, shown partially in section and with the plunger in the extended position; and 
       FIG. 8  is a perspective view of the interior construction of the front portion of the alternative preferred embodiment, shown partially in section and with the plunger in the retracted position. 
   

   DETAILED DESCRIPTION 
   The preferred embodiment of the present invention is shown in the drawings is a reciprocating saw, the general size and shape of which is similar to saws that are currently marketed. The present invention is also adapted for other types of tools such as saber saws, for example, or other types of tools that have a reciprocating action and are powered by a motor having a rotating output shaft. A patent application assigned to the same assignee as the present invention, entitled ANTI-ROTATION SYSTEM FOR A RECIPROCATING SAW, Ser. No. 10/856,015, filed May 28, 2004, is specifically incorporated by reference herein. 
   As shown in  FIGS. 1 and 2 , the reciprocating saw, indicated generally at  10 , has an outer housing  12  which includes a nose portion  14  that is flared outwardly so that a user can hold the nose portion with one hand while holding a handle  16  with the other. A trigger switch  18  is provided in the handle portion for turning on a motor  20  that drives the tool. The saw has a shoe  22  at the nose end portion  14  and a saw blade  24  is mounted in a blade clamping mechanism  26  that is mounted at the end of an elongated plunger, indicated generally at  28 , which is slideable in front and rear bushing assemblies, indicated generally at  30  and  32 , respectively. The motor  20  has an output shaft  34  with a pinion gear  36  mounted on the shaft  34 , with the gear  36  engaging a larger gear  38  that is connected to a wobble plate assembly, indicated generally at  40 , which drives the plunger  28  in a reciprocating manner as the gear  38  drives the wobble shaft assembly. 
   More particularly, the wobble shaft assembly  40  has a drive shaft indicated generally at  42 , to which the gear  38  is attached. The shaft has an end portion  44  that is supported in a ball bearing or the like and its opposite end  46  supported in another ball bearing that is mounted in the housing  12 . It should be understood that the manner in which the motor  20 , gears  36  and  38  as well as the shaft  42  are mounted in the structure is not in and of itself part of the present invention and the manner in which the housing is constructed and the rotating parts are supported is well known to those of ordinary skill in the art. 
   With regard to the wobble plate assembly  40  and referring to  FIGS. 2 and 4 , the shaft  42  has an enlarged center portion  48  of the shaft  42  with a cylindrical shaped portion  50  that is oriented at an acute angle relative to the axis of the shaft  42  and ball bearings (not shown) are positioned to permit an elongated arm  52  to rotate relative to the cylindrical portion  50 . As the shaft  42  is rotated, the angular orientation of the cylindrical portion  50  changes so that an outer end  56  of the arm  52  is moved in a reciprocating manner, i.e., to the left and right as contrasted in  FIGS. 6 and 7 . As is shown in  FIGS. 2-5 , the arm  52  has generally flat sides  54  that extend from the bottom upwardly toward the outer end  56  which then merges into a curved portion that reduces in size and becomes circular shaped in cross-section. It then merges with a first ball-type interface  58  that in turn merges into a transition portion  60  that in turn merges into a second ball-type interface  62 . The interfaces  58  and  62  have a generally spherical form, albeit truncated, where each merges with adjacent structure  56  and/or  60 . It should be understood that these ball-type interface portions do not need to be strictly spherical but are desirably generally near-spherically shaped so that point contact is made between these interfaces and the plunger  28 . 
   Referring to  FIGS. 3 and 5 , the plunger  28  has a tubular portion  64  that merges into a right end solid generally cylindrical section  66  that has a vertical slot (see  FIG. 8 ) in which the shank end of the blade  24  may be inserted. The end  66  also has an aperture  68  in which a pin of the blade clamping mechanism  26  may be attached. At the opposite end of the plunger  28  is a receiver portion, indicated generally at  70 , that has a cylindrical extension  72  that is sized to closely fit within the interior of the tube portion  64  and which is also preferably braised to securely hold the two components together inasmuch as extreme forces are incurred by the plunger  28  during operation. 
   The receiver portion  70  has a main body portion  74  that has a circular opening  76  that merges into an elongated slot  78 , the length of which is oriented in the same direction as the axis of the tubular portion  64  as shown in  FIGS. 3 and 5 . The ends of the slot  78  are flared outwardly as shown at  80  to accommodate the reciprocating motion that is caused by the elongated arm  52  and particularly the ball-type interfaces  58  and  62  that are positioned in the opening  76  and slot  78 , respectively. As shown in  FIGS. 3 and 5 , the first ball-type interface  58  is positioned in the opening  76  with the outside of the interface being generally in a point contact with the sidewall of the opening  76 . The second ball-type interface  62  also rides in the slot  78  and as is best shown in  FIG. 5 , the diameter of the interface  62  is only slightly smaller than the width of the slot  78  and thereby effectively prevents the plunger  28  from rotating out of its vertical plane of movement. 
   Because of the preferably spherical-shaped configuration of the interfaces  58  and  62  being positioned in the respective opening  76  and slot  78 , each of which have straight wall surfaces that are contacted, there is only point contact between the interfaces and the sidewalls during the entire movement of the elongated wobble arm  52 . This point contact results in the advantages of reduced wear between the interfaces and the receiver portion  70  and less heat being generated during operation. Also, because of the curvature of the ball interface portions with the vertical walls being contacted, there is only point contact at all times, regardless of the tolerances and clearances between the parts. It is also preferred that grease be applied to the receiver portion  70  to further reduce friction between the ball-type interfaces and the receiver portion  70 . 
   An added advantage is achieved in that the point contact of the placement of the first ball interface  58  in the receiver portion  70  is at a vertical elevation relative to the tube portion  64  that is inside of the tube portion. This contact location applies reciprocating force to move the plunger close to the center of the tubular portion  64  as is desired. 
   The receiver portion  70  has a spherical rear end portion  82  that is in a slideable relation to a rear bushing  84  that is generally cylindrically shaped and has an inside diameter  86  that is only slightly larger than the outside diameter of the spherical portion  82 . The bottom of the bushing  84  has an axial slot  88  that is sized to permit non-contacting movement of the arm  52  with the bushing  84 . The use of the spherical end portion  82  does not require critical tolerances of the bushing outside diameter relative to the bushing  84  and therefore reduces manufacturing costs of the assembly  32 . 
   The center axis of the spherical end portion  82  is identified at  92  is preferably concentric with the axis of the tubular portion  64  identified at  94 . To prevent any rotational movement along the plunger axes, the wobble plate assembly  40  as well as the plunger is prevented from rotating by the provision of the second ball interface  62 . This interaction with the sidewalls of the slot  78  will prevent the arm  52  from rotating out of its vertical plane of reciprocating movement and it also keep the plunger  28  from rotating. 
   As has been described, the rear end of the plunger  28  is slideably supported in the rear by bushing assembly  32  and the front end is supported by the front bushing assembly  30 . As is best shown in  FIGS. 3 and 4 , the front bushing assembly  30  has a bushing, indicated generally at  100 , that includes a spherical front portion  102  that engages a spherically shaped cavity or seat  104  that is formed in the housing. The spherical portion  102  is free to rotate about the axis  94  of the tubular portion under the influence of forces that may be applied during operation of the tool. 
   The bushing  100  has an annular shoulder  106 , a smaller diameter cylindrical portion  108  that is larger than the tubular portion  64  and a front cylindrical portion  110 . Each of the bushing portions  102 ,  106 ,  108  and  110  have an opening through which the tubular portion  64  can pass so that the reciprocation of the plunger  28  can occur. The cylindrical front portion  110  is sized to easily fit within a larger chamber  111  in the housing when the spherical portion  102  is seated in the cavity  104 . A spring  112  bears against the shoulder  106  and against a retaining plate  114  that is attached to the housing  12  by bolts  116  in cooperation with a shoulder  118  formed in the housing. There are preferably three bolts  116 , with two being visible in  FIGS. 3 and 4 , the third being on the other side of the tubular portion  64  at the same elevation as the upper visible bolt  116 . It is preferred that the bushing  100  with its component parts  102 ,  104 ,  106 ,  108  and  110  be one piece construction, and be made of steel or other low friction metal. However it should be understood that one or more of the components may be separately fabricated if desired. 
   The spring  112  provides a biasing force for maintaining the spherical front portion  102  in contact with the spherical seat  104  but not with such force that the bushing is prevented from rotating around axis  94  during operation. It has been found that this floating interaction permits the bushing to move and align itself in a manner that reduces forces that are generally applied to it during operation of the tool. Such rotating movement contributes to an extended useful life and also produces less heat during operation. The reduction in heat that is generated during operation also contributes to an extended useful life of the tool. It is preferred that grease be packed in the volume where the front bushing assembly  30  is located. 
   An alternative embodiment is shown in  FIGS. 6 ,  7  and  8 , and is illustrated in a less detailed manner than  FIGS. 1-5  that illustrate the preferred embodiment. The alternative embodiment shown in these drawings includes modification of the receiver portion  70 ′ that has a slightly different configuration to accommodate the ball-type interface  58 ′. The circular opening  76 ′ does not have an upper slot area and in fact, the second ball-type interface  62 ′ is located at the bottom of the arm  52 ′, the ball-type interface  62 ′ riding in a slot  120  of a U-shaped bracket  122 . The width of the slot is only slightly greater than the outside diameter of the ball-type interface  62 ′ and acts to maintain the reciprocating movement of the arm  52 ″ its vertical plane, in a manner similar to the second ball-type interface  62  of the preferred embodiment. 
   The center axis of the spherical end portion  82 ′ is identified at  92  and the axis of the tubular portion  64  is identified at  94 . The axis  92  is offset relative to the axis  94  in a vertical plane to compensate for the tendency of the plunger  28 ′ to rotate along the axis of the plunger system due to inertia of the mechanism. To prevent this rotational movement along the plunger axes, the spherical end portion  82 ′ is offset relative to the tubular portion axis  94  which effectively restricts the plunger  28 ′ from rotating. The other parts of this embodiment are substantially similar to the preferred embodiment and therefore have not been given reference numbers. 
   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. 
   Various features of the invention are set forth in the following claims.