Abstract:
Embodiments are disclosed of a drive apparatus for a reciprocating tool, that comprises a housing, a rotatable drive shaft assembly located in the housing, an elongated plunger located in the housing for reciprocating motion, the plunger having a front end portion for attaching a cutting blade thereto, a rotary joint elongated rocker having a lower end portion with a lower pivot connection to the housing and an upper end with an upper pivot connection to a mid portion of the plunger, a wobble plate interface operatively connected to the drive shaft assembly, a lower portion having an effective lower pivot connection, the interface also having an upper pivot connection to a rear portion of the plunger and configured to reciprocate the plunger generally in its lengthwise direction during alternating cutting and return strokes, the distances between the upper and lower pivot connections of both the rocker and wobble plate interface together with the distance between the upper pivot connections thereof to the plunger defining a four bar mechanism that produces a path of movement of an attached cutting blade that is effective to apply a progressive non-linear cutting force to a work piece during the cutting stroke.

Description:
[0001]    This is a continuation in part of application Ser. No. 12/256,912, filed Oct. 23, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to power hand tools, and more particularly, to power reciprocating tools. 
         [0003]    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 is translated into reciprocating motion for moving a saw blade or the like in a reciprocating manner. 
         [0004]    Reciprocating tools such as jigsaws, saber saws, as well as larger reciprocating saws are typically driven by the rotating output shaft of an electric motor. Such tools have a mechanism that translates rotary motion of the output shaft into reciprocating motion. Among the types of mechanisms that convert the rotary motion to reciprocating motion includes a wobble plate drive mechanism that is well known to those of ordinary skill in the art. 
         [0005]    There has been much research and development over the years in attempting to improve the cutting efficiency of such reciprocating saws and this has been achieved by introducing an orbital path of movement for the blade as it performs its cutting stroke as well as its return stroke. Such orbital as have the effect of increasing the force that is applied to the blade during its cutting operation. The amount of orbital action can often be varied by manipulation of a control mechanism associated with the tool, so that efficient cutting can be done. The adjustment of the amount of orbital action or variation of the cut path can be made to more efficiently cut both hard and soft materials. It is generally known that existing orbit systems work better in soft materials than they do in hard materials. For this reason, saws are provided with orbit on-off switches. Knowing when to turn the orbital action on or off and remembering to do so can lead to confusion by users. 
         [0006]    Existing orbit mechanisms create a motion path that is related to the position of the plunger. The position of the plunger or plunger rod can be described as being fully forward, fully back or at mid-stroke in general. All existing orbit mechanisms cause the blade to start moving into the work piece at the start of a cut stroke and move away from or out of the work piece during the return stroke. The amount of incremental orbit motion in typical commercially marketed orbit systems is nearly constant during the entire cut stroke and the return stroke. The orbit path also can be said to be nearly symmetrical with respect to the cutting and return strokes. 
         [0007]    These conventional orbit systems work well when cutting soft materials such as wood. However, when cutting hard materials such as steel, pipe or steel plate, saws with conventional orbit systems have significant drawbacks. Conventional orbit mechanisms apply orbital action at the start of a cut stroke. The orbital action often causes the blade to bounce on the material at the beginning of the cut stroke which delays good establishment of the blade teeth in the material for a portion of the cut stroke thereby reducing cutting effectiveness. 
         [0008]    Mechanisms that can create substantial nonlinear orbit paths for aggressive orbit paths and end strokes with conventional orbit drive systems have often experienced significant mechanical limitations. These are typically cam systems that have linear motion which is basically symmetric about a mid-stroke position, with the cut stroke being one near linear path and the return stroke as another near linear path. These two paths are offset from each other by a small amount. 
         [0009]    To date, no known attempts been made to create asymmetric or to create highly nonlinear paths. Attempts have been made to create a more aggressive orbit using cam drives. However, this results in very high cam follower loads which create high friction and wear in the cam elements. Another wear problem that occurs when the cam is aggressively shaped is that the cam follower can lift off of the cam. This produces a lack of contact between the cam and the cam follower for a major portion of the cam rotation. This is called cam float and is a common problem in high-speed cams. Floating results in loss of the force pushing the blade into the work piece. In especially aggressive cams, it can require several revolutions of the cam before the follower comes back down into contact with it. The loss of cam to cam follower contact then leads to the loss of contact force between the saw blade and the work piece and reduces the cutting rate instead of increases it. 
         [0010]    There have been cam systems developed where the orbit actuation cycle of down and up is shared by two cams. However, having aggressively shaped cams is expensive because of the necessity of matching two cam profiles with a high degree of precision and the attendant wear problem still exists. Similar problems of high forces arising with aggressive orbits arise when trying to use adjustable angled slots with their associated slot followers. The forces that are experienced can be very high, even if the track is straight and too much orbital action will lead to high forces on the track follower. Since much of the action of a track follower involves sliding, high friction and wear are also a problem. 
       SUMMARY OF THE INVENTION 
       [0011]    A first preferred embodiment of the present invention is a drive apparatus for a reciprocating tool, that comprises a housing, a rotatable drive shaft assembly located in the housing, an elongated plunger located in the housing for reciprocating motion, the plunger having a front end portion for attaching a cutting blade thereto, a rotary joint elongated rocker having a lower end portion with a lower pivot connection to the housing and an upper end with an upper pivot connection to a mid portion of the plunger, a wobble plate interface operatively connected to the drive shaft assembly, a lower portion having an effective lower pivot connection, the interface also having an upper pivot connection to a rear portion of the plunger and configured to reciprocate the plunger generally in its lengthwise direction during alternating cutting and return strokes, the distances between the upper and lower pivot connections of both the rocker and wobble plate interface together with the distance between the upper pivot connections thereof to the plunger defining a four bar mechanism that produces a path of movement of an attached cutting blade that is effective to apply a progressive non-linear cutting force to a work piece during the cutting stroke. 
         [0012]    A second preferred embodiment includes a counterweight having a main portion that extends above and on opposite sides of the plunger and side portions that extend downwardly to said counterweight pivot connections and a support configuration associated with the counterweight and housing for supporting the counterweight while permitting reciprocating movement of the counterweight in said housing in a direction generally parallel to the plunger movement, said support configuration comprising a pair of spaced apart elongated rods oriented in a direction parallel to said lengthwise direction of the plunger and mounted in the housing, the counterweight having apertures in said side portions thereof in which the rods are inserted, the counterweight being movable relative to the rods. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of the preferred embodiment of the present invention, shown with portions removed to illustrate the drive mechanism; 
           [0014]      FIG. 2  is a plan view of the drive mechanism shown in the embodiment of  FIG. 1 , shown in a position at the end of a cutting stroke; 
           [0015]      FIG. 3  is a plan view of the drive mechanism shown in the embodiment of  FIG. 1 , shown in a position at the beginning of a cutting stroke; 
           [0016]      FIG. 4  is a top view of the drive mechanism shown in  FIG. 2 ; 
           [0017]      FIG. 5  is a front in view of the drive mechanism shown in  FIG. 3 ; 
           [0018]      FIG. 6  is a perspective view of a portion of the drive mechanism, particularly illustrating the pivot connection of the wobble drive assembly and the plunger; 
           [0019]      FIG. 7  is another perspective view of a portion of the drive mechanism, particularly illustrating a cross-section of the pivot connection shown in  FIG. 6 ; 
           [0020]      FIG. 8  is another perspective view of a portion of the drive mechanism, particularly illustrating another cross-section of the pivot connection shown in  FIG. 6 ; 
           [0021]      FIG. 9  is a chart of the nonlinear movement of the blade attached to the preferred embodiment of the present invention as it moves through its cutting stroke; 
           [0022]      FIG. 10  is a perspective view of another preferred embodiment of the present invention, but shown without the outer housing to illustrate the drive mechanism including a counterweight; 
           [0023]      FIG. 11  is a side view of the apparatus shown in  FIG. 10 , with the counterweight and associated structure removed; 
           [0024]      FIG. 12  is an enlarged view of a portion of the embodiment shown in  FIG. 10 , illustrating details of the counterweight mechanism; 
           [0025]      FIG. 13  is a cross-section taken generally through the center of bushings that are part of the counterweight mechanism shown in  FIG. 10 ; and 
           [0026]      FIG. 14  is a plan view of a portion of the drive mechanism of a third preferred embodiment, partially in cross section, shown with a portion of a housing. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The preferred embodiments of the present invention are reciprocating drive mechanisms for a reciprocating tool such as a reciprocating saw, the general size and shape of which is similar to saws that are currently marketed. The present invention is also applicable 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. 
         [0028]    A preferred embodiment of the present invention provides a reciprocating drive mechanism that utilizes a progressive nonlinear cut path as opposed to a traditional orbital path. The progressive cut path does this by using a nonlinear cut path that starts each cut with little contact force or a slightly negative contact force due to the blade lifting out of the work piece in which it is engaged and then applies a gradually increasing contact force through the cutting stroke. This prevents bouncing on hard materials at the beginning of the cut stroke and allows the blade teeth to establish good engagement with the material. Then the contact force is increased through the mid-stroke to approximately one third of its maximum value. Toward the end of the cutting stroke, as the plunger is slowing down as part of its sinusoidal cycle, the cut stroke is more aggressively increased to its full value. The aggressive increase of the cut stroke at the end of the cut stroke makes better use of a portion of the cutting cycle where there is usually a drop off in cutting due to the fact that the plunger is slowing down. 
         [0029]    So this type of nonlinear path improves the action of the cutting stroke by reducing bouncing of the blade on the work piece at its beginning because it has very little contact force initially. Also, at the end of the cut stroke, embodiments of the present invention compensates for a slowing plunger with an aggressive cutting path. 
         [0030]    The above operability is carried out using a drive mechanism that has far fewer parts and improved durability compared to existing mechanisms that provide orbital action. The progressive nonlinear motion is created by the action of a coupler link and a four bar mechanism that does not have any sliding interaction of components of the type which experiences wear and generates energy consuming heat. 
         [0031]    Turning now to the drawings, and referring to  FIG. 1 , a reciprocating saw, indicated generally at  10 , has a 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  16  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 . As shown in  FIGS. 1-4 , the motor  20  has an output shaft  34  with a pinion gear  36  and fan member  38  operatively attached to the shaft  34 , with the gear  36  engaging a larger gear  40  that is connected to a wobble plate assembly, indicated generally at  42 , which drives the plunger  28  in a reciprocating manner. The teeth of the pinion gear  36  and gear  40  are not shown for the sake of simplicity, but are conventional as is known to those of ordinary skill in the art. 
         [0032]    More particularly, the wobble shaft assembly  42  has a drive shaft, indicated generally at  46 , to which the gear  40  is attached. The shaft has an end portion that is supported in a needle bearing  50  or the like and an opposite end supported in another ball bearing  54  that is mounted in the housing  12 . It should be understood that the manner in which the motor  20 , gears  36  and  40  as well as the shaft  46  are mounted in the housing  12  is not shown in detail inasmuch as such is conventional and is also well known to those of ordinary skill in the art. 
         [0033]    With regard to the wobble plate assembly  42 , for and referring to  FIGS. 1-3 , the shaft  46  has generally cylindrical shaped portion  60  shown in phantom in  FIGS. 2 and 3  that is oriented at an acute angle relative to the axis of the shaft  46 . The wobble plate assembly  42  has an elongated arm  66  that is mounted in ball bearings (not shown) for rotation relative to the cylindrical portion  60 , which permits the arm  66  to move in a left and right direction relative to the cylindrical portion  60  as the shaft  46  is rotated during operation. 
         [0034]    More particularly, as the shaft  46  is rotated, the angular orientation of the cylindrical portion  60  changes, and an arm  66  of the wobble plate assembly  42  is moved in a reciprocating manner, i.e., to the left as shown in  FIG. 3 , and to the right as shown in  FIGS. 1 and 2 . As is best shown in  FIG. 1 , the arm  66  has generally flat sides  68  that extend from the bottom upwardly which then merges into a curved outer end member  70  that reduces in size and becomes circular shaped in cross-section. 
         [0035]    The end member  70  transitions into a cylindrical end portion  72  which connects to the plunger  28  by a pivot connection, indicated generally at  76 , which is shown in  FIGS. 6 ,  7  and  8 , with  FIGS. 7 and 8  being cross sections taken through the plunger  28  and portions of the pivot connection  76 . The cylindrical portion  72  interfaces with a smaller diameter cylindrical portion  78  which forms an annular shoulder  80 . A transverse cylindrical shaft  82  fits within an aperture  84  in the side walls of a receiver  86  that is formed or securely fixed to the rear end portion of the plunger  28 . The receiver  86  also has a recess  87  that is vertically oriented in which the portions  72  and  78  can be inserted. The cylindrical shaft  82  is horizontally oriented and is configured to rotate in the aperture  84  during reciprocating motion of the plunger and arm  66  of the wobble plate assembly  42 . 
         [0036]    The cylindrical shaft  82  has a circular aperture  88  that is generally vertically oriented as shown in  FIG. 8  and is sized to receive the cylindrical portion  78 . The bottom of the cylindrical shaft  82  has a flat surface  90  which contacts the shoulder  80 , and it also has an upper flat surface  92  that is configured to receive a washer  94 , with the upper end  96  of the cylindrical portion  78  being threaded to receive a nut  98  thereon. 
         [0037]    From the foregoing description, it should be appreciated that when the wobble plate assembly  42  reciprocates the arm  66  to the left and the right, the pivot connection  76  not only supports the rear end of the plunger  28 , it enables the plunger to be driven by the wobble plate assembly  42  during operation. While not essential, small holes  100  may be provided for the purpose of introducing lubricating grease or the like into the cylindrical shaft  82  and its interface with the cylindrical portion  78 . Also, while not essential, the opposite ends of the cylinder  82  may be formed or machined to provide a recess  102  for the purpose of reducing the weight of the cylinder  82 . 
         [0038]    The plunger  28  is also supported near its midpoint by an elongated rocker, indicated generally at  110 , which has a lower pivot connection, indicated generally at  112 , as well as an upper pivot connection, indicated generally at  114 . The lower pivot connection  112  consists of a shaft  116  that is preferably secured in suitable recesses of the housing with the shaft  116  having needle bearings  118  enabling the low friction rotational movement of the elongated rocker. The rocker  112  has a split upper end  120  with two side portions  122 , each of which has a needle bearing  124  in which a shaft  126  that is attached to the plunger  28  can rotate. It should be understood that the shaft  126  may actually be a unitary shaft that extends through the plunger  28 , or there may be shaft portions which extend from each side of the plunger. In any event, the pivot connections enable the plunger to be reciprocated when driven by the wobble plate assembly  42 . Referring particularly to  FIG. 3 , it has been provided with letter designations identifying the center point of pivot connections of the wobble plate assembly  42  and the front rocker  110 . More particularly, the center of the pivot connection at the base of the wobble plate assembly is identified as A whereas the center of the pivot connection  76  is marked B. Similarly, the pivot connection  112  has its center marked C and the center of the upper pivot connection  114  is marked D. As is evident from the drawing, the center C is slightly above the center A by distance d 1  has been marked on the drawing. Also, on  FIG. 3 , the rocker  110  is shown in its furthest left position which orients the rocker slightly forward by an angle θ relative to top dead center. It can be appreciated that if the mechanism is reciprocated to the right so that the rocker  110  is straight up, i.e., top dead center, the elevation of the cutting blade  24  will be at its maximum. When it is moved completely to the left as shown in  FIG. 3 , it is then going to be slightly lower than its top dead center elevation position. Similarly, if it is moved to the right as shown in  FIG. 2 , the elevation of the rocker point B will decrease and this displacement during a cutting and return stroke is shown in the chart on  FIG. 9 . 
         [0039]    As is evident from the chart, the blade height of zero is defined as when it is in the position shown in  FIG. 3 . When it is moved to the right moved approximately 6 or 7 millimeters it will be at its top dead center position. The complete cutting stroke is approximately 28 millimeters. After it has moved through top dead center, it is progressively moved in a nonlinear way so that the blade force is increased as the plunger is moved through its cutting stroke. In this regard, the cutting stroke is from the left to right as shown in  FIGS. 1-3  and the return stroke follows the same path as the plunger is moved to the left. 
         [0040]    Since it moves through the path of movement as shown in  FIG. 9 , it is evident that it does not exhibit an orbital path of movement, but one that is nonlinear and progressive. The degree of progressiveness can be changed by the geometry of the mechanism. More particularly, if it is desired to have a less progressive cut, i.e., one which has a shallower path, such as moving from 0 through −1 millimeters, for example, this can be achieved by increasing the length of the rocker  110  so that the lower pivot point C is below the pivot point A of the wobble plate drive assembly. This can be done by modifying the configuration of the housing to lower the lower pivot connection  112 . 
         [0041]    It should also be understood that with the left-most position shown in  FIG. 3  where the rocker is past top dead center, movement during the cutting stroke will cause the blade to lift relative to the initial rest position which will tend to counter the force of gravity that may otherwise result in bouncing of the blade off of the material being cut. It should be understood that changing the orientation of the lower pivot connection  112  more forwardly relative to the upper pivot connection  114  would enable the arc to start at top dead center and therefore not have the lifting characteristic as shown in  FIG. 9 . In that event, zero would be the start point and the blade height would generally extend downwardly in a curved manner with the amount of curvature being a function of the relative lengths of the rocker  110 . 
         [0042]    Second and third preferred embodiments are shown in  FIGS. 10-14  which includes identical reference numbers for those components which are essentially the same as illustrated and described in the embodiment of  FIGS. 1-8 . Where they are similar but have slight variations, the same reference number with a prime  0  designator is often used. Where such components are not included in the first preferred embodiment, they will be given new reference numbers. It is also indicated that the second preferred embodiment shown in  FIGS. 10-13  are similar to those of  FIGS. 2 ,  3  and  4  inasmuch as they include the drive mechanism without the outer housing in which they are part of. 
         [0043]    As is particularly shown in  FIGS. 10 and 11 , the second preferred embodiment is indicated generally at  200  and includes the drive mechanism that is similar to that shown in  FIGS. 1-8 , and in addition has a counterweight assembly, indicated generally at  202 , which slides on a pair of rods  204 , the near one of which is visible in the perspective view of  FIG. 10 . It should be understood that the far side of the counterweight assembly  202  is symmetrical with the visible near side shown in  FIG. 10 . In this regard, the counterweight assembly has a generally inverted U-shape top portion  206  that has downwardly extending side portions  208  that extend to enlarged mounting portions  210  which have a front portion  212  and a rear portion  214 , as well as a center recess  216  which is cut away to expose the rod  204 . 
         [0044]    The front and rear portions  212  and  214  each have an aperture  218  which is sized to receive a bushing  220  and the inside diameter of the bushing  220  is sized to approximate the outside diameter of the rods  204  so as to provide a snug fit between the two. There are a total of four bushings used to facilitate sliding engagement of the counterweight assembly  202  on the rods  204 . 
         [0045]    Each of the recesses  216  preferably has a reservoir  222  that is sized larger than the diameter of the rod  204  and is preferably determined by the thickness of the bushing  220 . A lower surface  224  is approximately co-extensive with the center of the rod  204 . An important feature of this counterweight construction is that the recesses  216  define the reservoirs  222  which are located between the front and back bushings  220 . These recesses  216  allow grease to be thrown in and accumulate in the reservoirs  222  as the counterweight reciprocates to lubricate the bushings  220 . The recesses  216  also allow air flow which is created during the reciprocation of the counterweight assembly  202  to cool the bushings. The recesses  216  thereby help to reduce friction and wear in this important area during operation of the tool. 
         [0046]    As is best shown in  FIG. 10 , the counterweight assembly  202  has a downwardly extending leg  226  that has a transverse extension  228  formed at the lower portion thereof. The transverse extension  228  has a vertically oriented slot  230  for receiving a connection to a drive rocker arm, indicated generally at  232 , which has a center pivot  234  connected to the housing, and an upper arm portion  236  that is connected to the plunger  228  by a pivot connection  238 . 
         [0047]    The drive rocker arm  232  has a lower arm portion  240  with a lower pivot connection  242  that extends into the vertical slot  230  of the transverse extension  228  of the counterweight assembly  202 . The drive rocker arm  232  effectively drives the reciprocation of the counterweight assembly  202  by virtue of the reciprocation of the plunger  28  when it is driven by the wobble drive  42 . The bottom pivot connection  242  also slides within the vertical slot  240  to compensate for the slightly vertical movement that it makes during reciprocation of the rocker arm  232 . 
         [0048]    It should be understood that the counterweight  202  is driven from the bottom of the back drive rocker  232 . Because the bottom arm portion  240  is long, the counterweight  202  is driven through a larger stroke. This is in comparison to a third preferred embodiment shown in  FIG. 14  where the counterweight  202 ′ is driven off of the bottom spherical knob  244  that is attached to the wobble arm  42 . Therefore, the drive rocker arm  232  driving the counterweight is large than a system where the counterweight is driven off of the bottom of the wobble arm  42 . Since the stroke is longer, the counterweight  202  can have less mass than one driven off of the bottom of the wobble and yet still provide the same counterbalancing force as a heavier counterweight moving through a smaller stroke. 
         [0049]    Referring to  FIG. 11 , the pivot connection  238  which interconnects the upper arm portion  236  to the plunger  28  is only a fixed pivot and has no translation movement, which is also the case with respect to the forward guide rocker  110  and connection  126 . The path of the plunger is determined by the two rocker arms  110  and  232 . That being the case, the connection  76 ′ is slightly modified from that shown in  FIGS. 6 ,  7  and  8  in that the cylindrical end portion  72 ′ must be slidable in its lengthwise direction in the arm  70 . In such an instance, the washer  92  and nut  98  may be eliminated. 
         [0050]    In addition to the feature of having the openings  216  and the reservoirs  222  allowing air flow as well as grease to be applied to the bushings, the bushings  220  are also configured to catch grease during movement of the counterweight  202  in one direction and then move toward the inside of the bushing during the opposite direction of reciprocation. This is achieved by an inside surface  250  having a pair of serrations  252  located at each end of the bushings  220 , with the serrations having inwardly directed ramp portions  254  that merge with perpendicular end portions  256 . 
         [0051]    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. 
         [0052]    Various features of the invention are set forth in the following claims.