Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    The invention is based on a hand power tool according to the preamble of claim 1.  
           [0002]    A hand power tool, in particular a motor-driven off-hand grinder, is made known in DE 199 52 108 A1, that comprises a motor with a drive shaft located in a housing. The drive shaft—by way of its side furthest from the motor—is joined via an eccentric sleeve with a sanding disk. Formed on the sanding disk—which is supported on the eccentric sleeve via a first bearing eccentrically relative to the drive shaft—is a first annular means that comprises a first, radially outwardly facing rolling face. A second annular means having a radially inwardly facing, second rolling face corresponding with the first rolling face is turnably supported on the eccentric sleeve via a second bearing coaxially in relation to the center axis of the drive shaft of the motor.  
           [0003]    The second means is enclosed—over part of its area—by an elastic band that forms a braking means. The second annular means are capable of being fixed in position in torsion-resistant fashion via the braking means for a forced drive or for a rotating drive of the sanding disk that superposes an orbital motion. The first rolling face of the first annular means can walk around the second rolling face of the second annular means, which leads to a rotary motion of the sanding disk. If the braking means are released, the second means can be rotated, and a forced drive is stopped.  
         ADVANTAGES OF THE INVENTION  
         [0004]    The invention is based on a hand power tool, in particular a disk-type sander, that comprises a motor with a drive shaft located in a housing, whereby the drive shaft—by way of its side furthest from the motor—is joined via an eccentric with a sanding disk that can walk around an annular, turnably supported means that is capable of being braked via braking means.  
           [0005]    It is proposed that the annular means are supported in the braking means. Advantageously, components—in particular bearing components—and installation space can be spared, and a robust, cost-effective device can be obtained that is compact in design, in the axial direction in particular. Moreover, an encapsulated design having inboard rubbing surfaces can be realized, by way of which said rubbing surfaces can be protected against contamination, in particular against sanding dust.  
           [0006]    If, during operation, an operator lifts the hand power tool away from a surface of a material to be worked, the sanding disk can reach a high rate of rotational speed due to the friction prevailing in a sanding disk bearing and the absence of friction between the sanding disk and the material. If the annular means have a permanent, active connection with the sanding disk, the sanding disk can be advantageously prevented from racing by means of forced rubbing between the annular means and the braking means. A separate component for reducing rotational speed, in particular a rubber lip joined with the housing in torsion-resistant fashion, can be avoided. Additional rubbing on the sanding disk and additional loading of the sanding disk resulting therefrom can be prevented.  
           [0007]    If the annular means has teeth, around which the sanding disk can walk via corresponding teeth, a secure, slip-free connection can be advantageously obtained with high efficiency. The connection between the annular means and the sanding disk can also be designed as a friction connection or a connection having undefined teeth, however.  
           [0008]    If the annular means is formed by a belt, a cost-effective standard component can be used that has low weight. If the belt is made of rubber, a high amount of friction can be obtained with only slight contact force. The belt can also be formed out of other components and/or other materials that appear reasonable to one skilled in the art, such as plastic, aluminum, etc. If the annular means is formed by a gear made of aluminum, frictional heat can be dissipated via the annular means in particularly advantageous fashion.  
           [0009]    If the cross-section of the annular means is designed trapezoidal in shape, a large contact surface can be obtained between the braking means and the annular means, with which the torque occurring between the annular means and the braking means can be advantageously transferred. Moreover, an advantageous means of guiding the annular means in the braking means can be obtained.  
           [0010]    It is feasible, in principle, that the annular means and the braking means are used solely to prevent the sanding disk from racing. Particularly advantageously, however, torque acting between the annular means and the braking means can be adjusted via a switching device. If the annular means is arrested in the braking means in torsion-resistant fashion, a forced drive can be obtained, and the sanding disk can walk around the annular means. By means of the walking-around motion, an orbital motion of the sanding disk supported eccentrically relative to the motor shaft can be combined with a rotary motion of the sanding disk, and a motion of the sanding disk can be obtained with which a high level of abrasion on the material to be worked can be achieved. If the set torque is exceeded, a slipping of the annular means in the braking means can be achieved, and an overloading of the motor—in particular when the sanding disk is obstructed—can be advantageously prevented. If the braking means are open and the annular means are turnably supported in the braking means, a free-running operation of the sanding disk can be obtained, and a particularly fine working of a surface can be achieved.  
           [0011]    If the braking means are loaded via at least one spring element, a steady-state application of the torque acting on the annular means can be achieved, and, in fact, when the spring element acts in the closing direction of the braking means, or a reliable opening of the braking means can be achieved when the spring element acts in the opening direction of the braking means. If the spring element acts in the closing direction, wear between the annular means and the braking means can be compensated. If the spring element acts in the opening direction of the braking means, a reliable opening of the braking means and operation with low material abrasion can always be ensured. The spring element can be formed by a separate component, e.g., by a tension-loaded or compression-loaded helical compression spring, etc., or it can be designed integral with the braking means, e.g., by forming the braking means out of spring steel.  
           [0012]    In a further embodiment of the invention, it is proposed that braking action is produced by means of a force acting on the braking means in the axial direction, by way of which the annular means can be reliably prevented from jamming in the braking means. Moreover, cost-effective braking means and annular means having simple cross-sectional geometries can be achieved.  
           [0013]    The braking means can be designed as a single component or having two components. If the braking means are designed with at least two components, a particularly simple assembly can be obtained, whereby the braking means can be divided into various layers appearing reasonable to one skilled in the art.  
           [0014]    It is further proposed that the braking means comprises at least two jaws capable of pivoting around a pivot axis. An even load applied by the braking means to the annular means can be advantgeously achieved using simple design means.  
           [0015]    Particularly advantageously, the pivot axis is located on a side opposite from the switching device. A large lever arm can be obtained, via which the annular means can be arrested in the braking means via a switching device using a small amount of force, and the hand power tool can be switched into the forced-drive mode with a small amount of force. The jaws can be integrally interconnected in the region of the pivot axis, or they can be designed separate in the region of the pivot axis, e.g., in that they are held together via a joint shell integral with the housing. 
       
    
    
     SUMMARY OF THE DRAWINGS  
       [0016]    Further advantages result from the description of the drawing hereinbelow. The drawings, the description, and the claims contain numerous features in combination. One skilled in the art will advantageously consider them individually as well and combine them into reasonable further combinations.  
         [0017]    [0017]FIG. 1 shows a partial sectional drawing through a disk-type sander,  
         [0018]    [0018]FIG. 2 shows a sectional drawing along the line II-II in FIG. 1, and  
         [0019]    [0019]FIG. 3 shows a section of an alternative braking means. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    [0020]FIG. 1 shows a partial sectional drawing of a disk-type sander having an electric motor  12 —located in a housing  10 —with a drive shaft  14 . On the side furthest from the electric motor  12 , the drive shaft  14  is joined with a sanding disk  16  via an eccentric  18 . The sanding disk  16  is turnably supported in the eccentric  18  eccentrically relative to the drive shaft  14  via a journal  38  and a sanding disk bearing  40 , and it is securely joined with the journal  38  via a screw  42 .  
         [0021]    On its side closest to the electric motor  12 , the sanding disk  16  comprises a sanding pad carrier  44  holding a sanding pad  66  with a flange  46  facing the electric motor  12  in the axial direction (FIG. 1). On its radially outwardly facing side, the flange  46  has teeth  26  that mesh in corresponding, radially inwardly facing teeth  24  of an annular means  20 , and said flange has a permanent, active connection with the annular means  20 .  
         [0022]    The annular means  20  formed by a rubber belt has a trapezoidal cross-section and is turnably supported in a recess  48 —having a trapezoidal cross-section—of a basically annular braking means  22  (FIGS. 1 and 2). The braking means  22 —supported in the housing  10  in torsion-resistant fashion concentrically with the drive shaft  14 —nearly completely surrounds the rubber belt  20  in its circumferential direction. The braking means  22  have a first unit facing away from the sanding disk  16 , and a second unit facing the sanding disk  16 , whereby each of the units is divided into two jaws  34 ,  36  designed semicircular in shape.  
         [0023]    The jaws  34 ,  36  are supported in a joint shell  74  integral with the housing  10  in a fashion that allows them to pivot around a pivot axis  32 . On the side opposite from the pivot axis  32 , the jaws  34 ,  36  are joined via a switching device  28  (FIG. 2).  
         [0024]    On the side closest to the switching device  28 , a first projection  50  extending in the radial direction is integrally molded on jaw  36 , and a second projection  52  extending in the radial direction is integrally molded on jaw  34  (FIG. 2). An external side of the first projection  50  has an active connection with an eccentric  54  of the switching device  28 , while an external side of the second projection  52  bears against the housing  10 . A compression-loaded helical compression spring  30  bears, with its ends, against the opposing internal sides of projections  50 ,  52  and loads the braking means  22  in its opening direction.  
         [0025]    The eccentric  54  is joined via a screw  56  with a lever  58  of the switching device  28  (FIG. 2). Torque acting between the rubber belt  20  and the braking means  22  can be adjusted on the braking means  22  by an operator via the lever  58  and the eccentric  54  of the switching device  28 .  
         [0026]    If the disk-type sander is in its free-running mode, the helical compression spring  30  presses—via the projections  50 ,  52 —the braking means  22  so far apart that the rubber belt  20  is turnably supported in the recess  48  in nearly frictionless fashion. Residual friction remaining between the braking means  22  and the rubber belt  20  prevents an undesired racing of the sanding disk  16  when, during operation, said sanding disk is lifted away from a surface to be worked.  
         [0027]    If the operator actuates the lever  58 , the braking means  22  are loaded via the eccentric  54  against a spring force of the helical compression spring  30 , and, in fact, until the rubber belt  20  is held in the braking means  22  in torsion-resistant fashion, which brings about a forced drive. With forced drive, the eccentrically supported sanding disk  16 , with its teeth  26 , can walk around the teeth  24  of the rubber belt  20  supported concentrically and in torsion-resistant fashion in the braking means  22  at a constant rotational speed. In addition to the orbital motion of the sanding disk  16 , said sanding disk also executes a rotary motion by walking around the rubber belt  20 .  
         [0028]    [0028]FIG. 3 shows a braking device  62  as an alternative to FIGS. 1 and 2. Components that essentially remain the same are labelled with the same reference numerals. Moreover, the description of the exemplary embodiment shown in FIGS. 1 and 2 can be referred to with regard for features and functions that remain the same. The description below is basically limited to the differences from the exemplary embodiment shown in FIGS. 1 and 2.  
         [0029]    The braking means  62 —divided in the axial direction into a first unit facing away from the sanding disk and a second unit facing the sanding disk—can be loaded via a switching device  28  in the axial direction to produce braking action. Each of the units has a semicircular jaw  64 ,  64 ′, each of which has a collar  68 ,  70  in the radially outer region facing the other unit, whereby a rubber ring  72  having an essentially rectangular cross-section is guided in the radial direction through the collars  68 ,  70 . A plurality of helical compression springs  60  is distributed around the circumference in the axial direction between the collars  68 ,  70 , which said helical compression springs load the braking means  62  in its opening direction. Jaw  64  is capable of being adjusted in the axial direction via an eccentric  54 .  
         [0030]    Jaws  64 ,  64 ′ could also be adjusted in the axial direction via other devices appearing reasonable to one skilled in the art, e.g., via threads, etc. Instead of numerous helical compression springs  60 , a wave disk spring could be used as well, which wave disk spring could be located between one of the two semicircular jaws  64 ,  64 ′ and the rubber ring  72 . The wave disk spring could compensate for tolerances and wear between the individual components.  
                                         Reference Numerals                                10   Housing       12   Motor       14   Drive shaft       16   Sanding disk       18   Eccentric       20   Means       22   Braking means       24   Teeth       26   Teeth       28   Switching device       30   Spring element       32   Pivot axis       34   Jaw       36   Jaw       38   Journal       40   Sanding disk bearing       42   Screw       44   Sanding pad carrier       46   Flange       48   Recess       50   Projection       52   Projection       54   Eccentric       56   Screw       58   Lever       60   Spring element       62   Braking means       64   Jaw       66   Sanding pad       68   Collar       70   Collar       72   Means       74   Joint shell

Technology Category: b