Patent Publication Number: US-2012030955-A1

Title: Motor Driver Power Tool

Description:
The invention relates to a motor driven power tool, in particular a hand-held power tool, according to the preamble of claim  1 . 
     PRIOR ART 
     Motor driven power tools of the aforementioned type are known from DE 37 02 670 A1. They are comparatively complex in their structure, and have a lifting rod, which projects upwardly over the stroke drive and, at its upper end, at which the rotary drive for the lifting rod and for the working tool connected to the latter in a rotationally fixed manner is applied, is mounted so as to be pivotable about an axis running transversely in relation to the working plane of the tool, in order to execute the pendulum stroke operation. Overall, this results, in the longitudinal direction of the lifting rod also, in a structural length that is undesirable in some cases and that can give rise to a certain susceptibility to faults, particularly under demanding working conditions. In particular, it is at least also difficult to operate a power tool of this structure in pendulum stroke operation with the working tool rotated about its longitudinal axis to the straight ahead working direction. 
     Disclosure of the Invention 
     The invention is based on the object of simplifying in its structure a motor driven power tool of the type mentioned at the outset and, additionally, of configuring it, with a compact and robust structure, such that a pendulum stroke operation is possible, if required, with the working plane of the working tool rotated about its longitudinal axis to the straight ahead working direction, i.e., therefore, a “scrolling” operation. 
     This object is achieved, according to the invention, by means of the features of claim  1 . The dependent claims specify expedient developments. 
     In the case of the power tool configuration according to the invention, the tool driven in stroke motion is set, in its rotary position about the longitudinal axis that corresponds, at least substantially, to its stroke axis, via a carrier frame driven in rotary motion that, at the same time, is a carrier of a support member provided at the back in relation to the working tool and supporting the latter, and that additionally also constitutes the guidance and support for a drive part of the stroke drive on the lifting rod side, to which drive part the lifting rod is connected about a pivot axis running transversely in relation to its working plane. In summary, therefore, the rotary and stroke guidance of the working tool, realized, in particular, as a saw blade, and of the associated lifting rod is effected via the carrier frame that is to be driven rotatably and is mounted on the housing side, as a result of which it is also possible to realize a comparatively short lifting rod, which, in combination with the axial guidance and rotary support of the drive part of the stroke drive on the lifting rod side in relation to the carrier frame, also results in a very stiff design, with a simple structure. 
     The thereby created conditions for a directionally stable guidance of the working tool without sensitivity to vibrations are further improved in that the carrier frame is also a carrier of the support member that, at the back, supports the working tool in the working plane, irrespective of the respective rotary position, as a result of which, in particular, transverse forces on the working tool can also be controlled particularly well. Overall, a machine structure is thus obtained that, even in the case of rotary displacement of the working tool about its longitudinal axis, enables a respectively defined working line to be followed exactly by rotation of the working tool about its longitudinal axis, such that a machine designed in such a manner is also suitable, in particular, for semiautomatic application, wherein the alignment to a working line is effected by rotating the tool. Overall, a good working result can thus be achieved in all working modes, thus in straight ahead sawing or in pendulum stroke operation and also in so-called “scrolling”, the supporting of the working tool via the carrier frame against the housing also ensuring a favorable load bearing, and this in combination with a simple rotary displacement capability. 
     The combination, according to the invention, of the various support and guide functions on the carrier frame is also favorable because, via the ring-shaped carrier frame, support in respect of the housing can also be effected on a broad base, this being irrespective of the respective rotary position of the working tool, such that the support and guidance conditions do not change in dependence on rotary length, which is advantageous, in particular, in respect of the pendulum stroke operation that is also expedient in the case of a “scrolling” working mode. 
     Owing to the circular-ring shape of the carrier frame, its mounting in respect of the housing is likewise configured in a simple manner, this design offering the possibility of supporting the carrier frame in two bearing planes, which are preferably assigned to the upper and the lower end of the carrier frame, and in which the carrier frame, in the case of a cage-type structure, has an upper and a lower carrier ring. Going out from the lower carrier ring are the carrier limbs, on which the support member is mounted in a pivotally movable manner, which support member, in the case of an overall preferred Z-shaped basic shape in the region of its arm that is at a distance from and projects from the working tool, is acted upon by a positioning element of the positioning drive provided for the pendulum drive, preferably with the positioning element extending parallelwise in relation to the longitudinal axis of the working tool. 
     For exact guidance of the working tool, an additional, transverse guide for the lifting rod can also be provided, furthermore, in the transition region to the tool holder, in particular in the region of the lower carrier ring. This transverse guide can be constituted, for example, by a web-type insert having a longitudinal cutout running in the pendulum direction of the lifting rod, or by a base-type insert to the lower carrier ring, which insert would likewise be provided with a corresponding recess. 
     Also contributing to the stability of the power tool and to the exact guidance of the working tool is the fact that, in the case of the solution according to the invention, the stroke drive is supported separately from the housing in respect of its drive part, and that the lifting rod of the stroke drive, with the drive part of the stroke drive that is on the lifting rod side, is assigned to the carrier frame that is supported separately from the housing. 
     In the case of the solution according to the invention, the crank drive is realized, in particular, as a Scotch-yoke crank drive, having guides for a yoke part that run parallelwise in relation to the longitudinal axis, the yoke of which yoke part runs, perpendicularly in relation to the working plane, between the guides. Accessing the yoke is the eccentric drive of the drive wheel provided for the stroke drive, which drive wheel, with the working tool, the carrier frame, the yoke part and the guides for the yoke part, is located at the front in relation to a carrier plate, located at the back in relation to which there is a positionally fixed positioning drive for the pendulum stroke mode, i.e. the pendulum drive, which, by means of its drive element, in particular in the form of a pin, acts upon the arm, as a positioning sector, projecting at the back in relation to the support member. 
     In respect of the angular position of the yoke part in relation to the eccentric pin, which angular position varies with the rotary position of the working tool, and therefore also of the carrier frame, it is expedient if the eccentric pin is supported via a needle bearing in relation to the guide yoke, in particular is realized as a needle bearing in its engagement part in relation to the guide yoke. 
     Overall, in the case of the configuration according to the invention, a relatively short and compact structure can be achieved in the direction of the lifting rod, which structure can be realized in a manner that is also structurally favorable in respect of the drive guides for the stroke drive, the pendulum drive and also the rotary displacement of the carrier frame. 
    
    
     
       Further advantages and expedient realizations are given by the claims, the description of the figures and the drawings, wherein: 
         FIG. 1  shows a perspective, schematic general representation of a power tool according to the invention, in the form of a jigsaw, reduced to the parts essential for understanding of the invention, the housing not being represented, and 
         FIGS. 2 to 4  show representations of the power tool according to  FIG. 1  in a front view, side view and top view. 
     
    
    
     Shown in the figures, represented in a simplified manner and without a housing, is a power tool  1  in the form of a jigsaw  2 , the working tool  3  of which is constituted by a saw blade  4  driven in a stroke motion. The saw blade  4  is connected to the lifting rod  6  of a stroke drive  7  via a saw blade receiver  5 . 
     The saw blade  4 —as a working tool  3 —has a longitudinal axis  8 , which lies in the working plane of the saw blade  4 . On the front side, the saw blade is provided with a toothing  9 , the saw blade back, on the opposite side, being denoted by  10 . A support member  11  is supported, via a support roller  12 , against the saw blade back  10 . The support member  11  is constituted by a pivot lever  13 , which is linked to a carrier frame  15  via a pivot axis  14 . 
     The carrier frame  15  is designed in the manner of a cage, and has an upper carrier ring  16  and a lower carrier ring  17 , between which, in the exemplary embodiment, there extend two longitudinal struts  18 . Provided on the lower carrier ring  17  are two carrier limbs  19 , which project downwardly and are opposite one another relative to the working plane that includes the longitudinal axis  8  of the working tool  3 , and between which there extends the pivot axis  14  carried via these carrier limbs. 
     The support member  11 , which has an overall Z shape, has an arm that constitutes a position sector  20  projecting in the direction opposite to the working tool  4 . In the case of a stroke direction of the positioning element  20  that is parallel to the longitudinal axis  8 , the positioning element  21  of a positioning drive  22  is supported on the positioning sector  20 . The positioning sector  20  extends over an angular range corresponding to the pivoting range of the working tool about its longitudinal axis  8 , which angular range is usually approximately ±30°. 
     The positioning drive  22  is located at the back in relation to a carrier plate  23  that is fixed to the housing  24 , indicated in schematic form only, and provided opposite are the shown parts of the stroke drive  7 , the carrier frame  15 , and the support member  11  that acts upon the working tool  3  from the back. The positioning sector  20  extends so as to engage beneath and overlap the carrier plate  23 . 
     Via a pivot axis  33  that runs transversely in relation to the working plane, the lifting rod  6  is connected to the yoke part  26 , which constitutes part of the drive part of the stroke drive  7  on the lifting rod side, and which has a yoke guide  27 , which lies in the working plane and in which there engages an eccentric pin  28  of a drive wheel  29 . The drive wheel  29 , realized as a toothed wheel, is connected in a driving manner, not shown in greater detail, to a drive motor and, with its eccentric pin  28 , constitutes a part of the crank drive  30 . 
     The longitudinal struts  18  of the carrier frame  15  that is constructed in the manner of a cage constitute, for the yoke part  26 , a slide guide  31  extending in the working plane, and in whose groove-type guideways  32  there engage the front ends of the yoke part  26  that are opposite one another in the direction of the working plane. 
     It is not shown that the eccentric pin  28  is preferably realized as a needle bearing, or carries a needle bearing, this realization of the eccentric pin  28  preferably being provided only for the longitudinal region of the same, which longitudinal region, owing to the pivot motion of the carrier frame  15  during rotary drive of the same, is swept over by the yoke part  26 . 
     The mounting of the carrier frame  15  in relation to the housing  24  is not shown in detail in the figures, but is indicated schematically through assignment of a bearing  25  to the upper carrier ring  16 , on which there also preferably acts the rotary drive for pivoting the carrier frame  15  about the longitudinal axis  8 . For this purpose, the upper carrier ring  16  can be provided with an inner toothing, which is accessed by a drive pinion of the rotary drive, this constituting a particularly simple solution that is also favorable in respect of space. Clearly, it is within the scope of the invention for the carrier frame  15  to be supported on the housing side via a mounting provided to the carrier ring  17 , and possibly also to effect a bearing support in relation to the housing  24  in the region of the upper and the lower carrier ring  16 ,  17 .