Patent Abstract:
A motor-driven machine tool has a drive motor, the motor shaft of which is driven in rotation, with a tool drive shaft, which is driven in rotation or in oscillation about its longitudinal axis, and with a coupling drive for converting the rotational movement of the motor shaft into a driving movement of the tool drive shaft. Furthermore, a coupling is provided, which compensates an angular offset or change in position between the motor shaft and tool drive shaft which deviates from an axially parallel or right-angled arrangement of the two shafts.

Full Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from German patent application 10 2013 104 271.6, filed on Apr. 26, 2013. The entire content of this priority application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a motor-driven machine tool with a drive motor, the motor shaft of which is driven in rotation, with a tool drive shaft, which is driven in rotation or in oscillation about its longitudinal axis, and with a coupling drive for converting the rotational movement of the motor shaft into a driving movement of the tool drive shaft. 
         [0003]    Machine tools of this type have been known for decades and are used in many different ways particularly as hand-held electric tools. In this context, there are both machines in which the tool drive shaft executes a rotating rotational movement, such as, for example, in drilling machines or angle grinders. Furthermore, in recent years, machines with an oscillating driving movement of the tool drive shaft have become increasingly common, and in this case the tool drive shaft can be driven in oscillation about its longitudinal axis. Oscillating machines tools of this type are used in many different ways for grinding, cutting or sawing, etc. 
         [0004]    Particularly in the case of machine tools driven in oscillation, but also in specific machine tools having a tool drive shaft driven in rotation, such as in angle grinders, there is a problem that vibrations may occur which have an adverse effect upon the service life of the machine and are felt by the user to be a disadvantage. 
         [0005]    If the motor shafts and the tool drive shaft are not oriented concentrically or axially parallel to one another, one-sided stresses upon the bearings occur, and, in course of time, overloads, premature defects or failures may possibly arise. 
         [0006]    In machine tools driven in oscillation, the rotary driving movement of the motor shaft is converted into an oscillating driving movement of the tool drive shaft by means of a suitable coupling drive. In this case, a relative movement may occur between the drive motor and the coupling drive as a result of vibrational decoupling or damping. In this case, too, concentric and axially parallel orientation of the motor axis and tool drive shaft is therefore no longer possible. 
         [0007]    EP 2 139 647 B1 discloses a machine tool driven in oscillation, according to the precharacterizing clause of Claim  1 , in which length compensation, for example using a star-shaped profile which engages into a bore with corresponding profiling, is provided between the drive shaft and motor drive shaft. 
         [0008]    However, a design of this kind allows only length compensation in the region of the drive chain. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of this, it is a first object on which the invention to disclose a machine tool which tolerates a non-axially parallel arrangement of a motor shaft and tool drive shaft. 
         [0010]    It is a second object of the invention to disclose a machine tool which reduces oscillations. 
         [0011]    It is a third object of the invention to disclose a machine tool which keeps the loads of the mounting and coupling drive between the motor shaft and tool drive shaft at a small level. 
         [0012]    In one aspect of the invention these and other objects are solved by a motor-driven machine tool, comprising: 
         [0013]    a drive motor rotatingly driving a motor shaft; 
         [0014]    a tool drive shaft having a longitudinal axis about which said tool drive shaft is driven oscillatingly; 
         [0015]    a coupling drive coupled to said tool drive shaft for driving said tool drive shaft oscillatingly about said longitudinal axis thereof; and 
         [0016]    a coupling coupled to said motor shaft at one end thereof and coupled to said coupling drive at another end thereof configured for transferring a rotary motion of said motor shaft to said coupling drive and for compensating an angular offset between said motor shaft and tool drive shaft deviating from an axially parallel or a right-angled arrangement of said motor shaft and said tool drive shaft. 
         [0017]    According to another aspect of the invention these and other objects are solved by a motor-driven machine tool, comprising: 
         [0018]    a drive motor rotatingly driving a motor shaft; 
         [0019]    a tool drive shaft having a longitudinal axis about which said tool drive shaft is driven oscillatingly or rotatingly; 
         [0020]    a coupling drive coupled to said tool drive shaft for driving said tool drive shaft about said longitudinal axis thereof; and 
         [0021]    a coupling coupled to said motor shaft at one end thereof and coupled to said coupling drive at another end thereof configured for transferring a rotary motion of said motor shaft to said coupling drive and for compensating an angular offset between said motor shaft and tool drive shaft deviating from an axially parallel or a right-angled arrangement of said motor shaft and said tool drive shaft; 
         [0022]    wherein said coupling further comprises: 
         [0023]    a coupling shaft having a drive side and a driven side; 
         [0024]    a first articulated connection comprising a first spherical head and two first drive bolts, said first spherical head being guided on an inner surface of said coupling shaft and driving said coupling shaft via said two first drive bolts; 
         [0025]    a second articulated connection comprising a second spherical head and two second drive bolts, said second spherical head being guided on an inner surface of said coupling shaft and driving said coupling shaft via said two second drive bolts; and 
         [0026]    a sliding articulated connection being arranged between said drive side and said driven side of said coupling shaft. 
         [0027]    According to another aspect of the invention these and other objects are solved by a motor-driven machine tool, comprising: 
         [0028]    a drive motor rotatingly driving a motor shaft; 
         [0029]    a tool drive shaft having a longitudinal axis about which said tool drive shaft is oscillatingly driven; 
         [0030]    an eccentric coupling being configured for converting a rotary driving movement of said motor shaft into an oscillating movement of said tool drive shaft about said longitudinal axis thereof; 
         [0031]    a coupling coupled to said motor shaft at one end thereof and coupled to said coupling drive at another end thereof configured for transferring a rotary motion of said motor shaft to said coupling drive and for compensating an angular offset between said motor shaft and tool drive shaft deviating from an axially parallel or a right-angled arrangement of said motor shaft and said tool drive shaft; 
         [0032]    wherein said coupling further comprises: 
         [0033]    a coupling shaft having a drive side and a driven side; 
         [0034]    a first articulated connection comprising a first spherical head and two first drive bolts, said first spherical head being guided on an inner surface of said coupling shaft and driving said coupling shaft via said two first drive bolts; 
         [0035]    a second articulated connection comprising a second spherical head and two second drive bolts, said second spherical head being guided on an inner surface of said coupling shaft and driving said coupling shaft via said two second drive bolts; and 
         [0036]    a sliding articulated connection being arranged between said drive side and said driven side of said coupling shaft. 
         [0037]    According to the invention, by means of the additional coupling, the risk of vibrations as a consequence of a design-induced offset or angular errors of the motor axis with respect to a concentric or axially parallel orientation to the tool drive shaft is markedly reduced. Moreover, the risk of overloads of the bearing points and of the material in the drive chain is markedly reduced. In the case of vibrationally decoupled machine tools with a tool drive shaft driven in oscillation, the risk of overloads of the bearing points is markedly reduced and at the same time the vibrational load is restricted. 
         [0038]    In an advantageous refinement of the invention, the coupling comprises a coupling shaft which is coupled on a drive shaft to the motor shaft via a first articulated connection and which is coupled on a driven side to the coupling drive via a second articulated connection, at least one sliding articulated connection being provided between the drive side and the driven side. 
         [0039]    By means of a design of this kind, angular errors and variations in position between the motor shaft and the tool drive shaft or the coupling drive arranged between them can be compensated. 
         [0040]    In this case, the first articulated connection may comprise, for example, a first spherical head which is guided on an inner surface of the coupling shaft and which drives the coupling shaft via two first drive bolts, the second articulated connection comprising a second spherical head which is guided on an inner surface of the coupling shaft and which is driven by the coupling shaft via two second drive bolts. 
         [0041]    According to a development of this design, the coupling shaft is designed as a hollow shaft with an inner surface, on which the first and the second spherical head are guided. 
         [0042]    According to a further refinement of this design, the first or the second drive bolts are received longitudinally displaceably in grooves of the coupling shaft. 
         [0043]    Preferably, both the first and the second drive bolts are guided longitudinally displaceably in slots in a wall of the coupling shaft. 
         [0044]    These measures make it possible to have a simple configuration of the coupling which compensates both an angular offset and an offset in position between the motor shaft and tool drive shaft or between the motor shaft and coupling drive. 
         [0045]    In an alternative design of the invention, at least one of the articulated connections may also be designed as a cardan joint, or both articulated connections may be designed as a cardan joint, in addition, a sliding articulated connection being integrated into the coupling shaft. 
         [0046]    In this way, too, an angular offset or variation in position between the motor shaft and tool drive shaft or between the motor shaft and coupling drive is compensated. However, the design with one or two articulated connections as a cardan joint is more complicated than the abovementioned design and may possibly lead to somewhat higher bearing stress or somewhat increased load due to vibrations. 
         [0047]    Even such a design nevertheless makes it basically possible to reduce the bearing load and the vibration load, as compared with conventional machine tools without a coupling of this type. 
         [0048]    According to a further refinement of the invention, a housing is provided, with a motor housing portion for receiving the drive motor and with a gear housing portion for receiving the tool drive shaft and preferably the coupling drive, means being provided which allow relative movements between the tool drive shaft and the drive motor. 
         [0049]    In this case, for example, the motor housing portion and the gear housing portion may be connected flexibly to one another. 
         [0050]    Alternatively or additionally, at least one damping element for vibrational decoupling may be provided between the coupling drive and the drive motor. 
         [0051]    If relative movements between the tool drive shaft and the drive motor are possible, fewer vibrations are transmitted to the drive motor. If the machine tool is held by hand in the region of the motor housing, markedly fewer vibrations are transmitted to the user. The reduction of vibrations of the drive motor and the accumulator in connection with the latter also has an advantageous effect upon the service life. 
         [0052]    Compensating movements between the drive motor and tool drive shaft or coupling drive or between the gear housing and the motor housing are absorbed by the coupling. 
         [0053]    By at least one damping element being arranged between the coupling drive and the drive motor, the vibrations are further reduced. 
         [0054]    According to a further refinement of the invention, the coupling drive has an eccentric coupling drive for converting a rotary driving movement of the motor shaft into an oscillating movement of the tool drive shaft about its longitudinal axis. 
         [0055]    In an alternative way according to the invention, the tool drive shaft is driven in rotation, the machine being designed as an angle grinder in which the coupling drive is designed as an angular gear, in particular as a bevel gear. 
         [0056]    Even in a design of this kind, the advantages of the invention are afforded by a reduction in the bearing load and the possible compensational vibrations which may occur during operation. 
         [0057]    It would be appreciated that the features of the invention which are mentioned above and those which are yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    Further features and advantages of the invention may be gathered from the description of preferred exemplary embodiments and are explained in more detail with reference to the drawing in which: 
           [0059]      FIG. 1  shows a first perspective view of a machine tool according to the invention with a tool drive shaft driven in oscillation, one housing half being removed; 
           [0060]      FIG. 2  shows a partially cut away view according to  FIG. 1 , from which further details are clear; 
           [0061]      FIG. 3  shows a longitudinal section through a machine tool according to  FIG. 1 ; 
           [0062]      FIGS. 4 and 5  show perspective views of the coupling according to  FIGS. 1 to 3  in an enlarged illustration in two different rotary positions; 
           [0063]      FIG. 6  shows in perspective a detail in the region of the drive motor, of the coupling and of the coupling gear according to  FIG. 3 ; 
           [0064]      FIG. 7  shows a view according to  FIG. 6  with a slightly changed arrangement between the motor shaft and coupling gear; 
           [0065]      FIG. 8  shows a perspective view of a further machine tool according to the invention with a rotating tool drive shaft in the form of an angle grinder; 
           [0066]      FIG. 9  shows a diagrammatic illustration of a modification of the coupling according to  FIGS. 4 and 5 , and 
           [0067]      FIG. 10  shows a simplified diagrammatic illustration of the gear arrangement in the angle grinder according to  FIG. 8 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0068]    In  FIGS. 1 to 3 , a first version of a machine tool according to the invention is designated as a whole by the numeral  10 . This is a machine tool  10  driven in oscillation, with a motor housing  12 , in which a drive motor  14  is received, and with a gear housing  13 , in which a tool drive shaft  24  is received. A rotational movement of the motor shaft  18  is converted via a coupling  22  and an assigned coupling drive  20  into an oscillatingly driven driving movement of the tool drive shaft  24  about its longitudinal axis  25 . 
         [0069]    At the outer end of the tool drive shaft  24 , which end projects outwards from the housing  12 , a tool-holding fixture  43  ( FIG. 3 ) is provided, to which an assigned tool, for example a grinding, cutting or sawing tool, can be fastened by means of a quick-action chucking device (not illustrated) with the aid of a tension lever  26 . The tool drive shaft  24  is mounted on the housing  12  with the aid of two bearings  38 ,  40  ( FIGS. 2 and 3 ). 
         [0070]    The drive motor  14 , via its motor shaft  18 , drives a coupling  22 , having a first articulated connection  44  on the side of the motor shaft  18  with a first spherical head  45  and having a second articulated connection  46  on the driven side with a second spherical head  47 . The second spherical head  47  is connected to an intermediate shaft  51  which is mounted on the housing  12  by means of two bearings  28 ,  30  and which drives the tool drive shaft  24  in oscillation via the coupling drive  20 . 
         [0071]    For this purpose, an eccentric coupling drive  32  is provided, which has on the intermediate shaft  51  an eccentric bearing  36 , on which an eccentric lever  34  connected fixedly in terms of rotation to the tool drive shaft  24  engages on both sides. The eccentric lever  34  can be seen in more detail particularly from  FIG. 2 . It has a fork of U-shaped design, both ends of which surround the eccentric bearing  36  from outside. An eccentric movement of the eccentric bearing  36  on the end of the intermediate shaft  51  is thereby converted into an oscillating movement of the tool drive shaft  24  about its longitudinal axis  25 . 
         [0072]    The eccentric coupling drive  32  and the tool drive shaft  24  are decoupled vibrationally from the drive motor  14 . For this purpose, a damping element  15  is arranged on each of the two sides in the transitional region between the motor housing  12  and the gear housing  13 , so that certain flexibility between the motor housing  12  and gear housing  13  and, in addition, vibration damping are afforded. Only a receptacle for a damping element  15  can be seen in  FIG. 1 . A rubber plug is received therein as a damping element. 
         [0073]    The transmission of vibrations from the tool drive shaft  24  and the eccentric coupling drive  32  to the drive motor  14  and the accumulator  16  connected to the latter is thereby reduced. The user who holds the machine tool  10  at the motor housing  12  experiences appreciably fewer vibrations. 
         [0074]    The more detailed configuration of the coupling  22  provided between the coupling drive  20  and the drive motor  14  can be seen particularly from  FIGS. 4 and 5 . 
         [0075]    The coupling  22  has a hollow-cylindrical coupling shaft  42  which is driven by the motor shaft  18  via a first articulated connection  44  and which drives the intermediate shaft  51  via a second articulated connection  46 . 
         [0076]    The first articulated connection  44  has a first spherical head  45  which is connected rigidly and fixedly in terms of rotation to the end of the motor shaft  18 . Two first drive bolts  48  project laterally from the first spherical head  45  towards the two sides lying opposite one another and are guided in assigned slots  52  in the surface area of the coupling shaft  42 . The first spherical head  45  is guided circumferentially on a cylindrical inner surface  49  of the coupling shaft  42 . 
         [0077]    The second articulated connection  46  has a second spherical head  47  which is connected to the tool drive shaft  24  and which is likewise guided on the hollow-cylindrical inner surface  49  of the coupling shaft  42 . Also provided on the second spherical head  47  are two second drive bolts  50  which lie opposite one another and which are guided longitudinally displaceably in assigned slots  54  in the surface area of the coupling shaft  42 . The second spherical head  47  is connected rigidly and fixedly in terms of rotation to the intermediate shaft  51 . 
         [0078]    The coupling  22  allows an angular offset and a variation in position between the motor shaft  18  and the intermediate shaft  51 . 
         [0079]    Should an exact orientation between the intermediate shaft  51  and the motor shaft  18  therefore vary, for example as a result of vibrations, the coupling  22  makes flexible compensation possible. It is likewise conceivable to arrange the intermediate shaft  51  and the motor shaft  18  so as to be offset angularly or positionally with respect to one another. 
         [0080]      FIGS. 6 and 7  show different arrangements between the intermediate shaft  51  and the motor shaft  18 . Whereas, in the version according to  FIG. 6 , these are oriented in alignment with one another, in the version according to  FIG. 7  there is a marked angular offset between the motor shaft  18  and the intermediate shaft  51 . This angular offset is compensated by the coupling  22 . 
         [0081]      FIGS. 6 and 7  additionally illustrate on the intermediate shaft  51  a balancing weight  56  which is provided for mass balancing during the rotation of the eccentric bearing  36 . 
         [0082]    One possible modification of the coupling described above is illustrated in  FIG. 9  and is designated as a whole by  22   a.  In this case, corresponding reference numerals are used for corresponding parts and are partially supplemented by “a”. 
         [0083]    In this case, the motor shaft  18  drives the coupling shaft  42   a  via a first articulated connection  44   a  in the form of a cardan joint, while the driven end of the coupling shaft  42   a  drives the intermediate shaft  51  via a second articulated connection  46   a  in the form of a cardan joint connection. The coupling shaft  42   a  comprises, furthermore, a sliding articulated connection which is indicated diagrammatically by  66  and which may comprise, for example, a slot  68 , into which an assigned slide  70  engages. 
         [0084]    It would be appreciated that other configurations of a sliding articulated connection may also be used, for example a slide, for example in the form of a polygon, which is guided on an assigned inner surface of a counterpiece. 
         [0085]    In principle, a coupling  22   a  of this type with two cardan joint connections  44   a,    46   a  and with a sliding articulated connection  66  is also possible in order to bring about angular compensation and positional compensation between the motor shaft  18  and intermediate shaft  51 . However, the above-described version of the coupling  22  according to  FIGS. 1 to 7 , which has overall a simpler set-up, is preferred. 
         [0086]    A modification of the machine tool according to the invention is illustrated in  FIGS. 8 and 10  and is designated as a whole by  10   a.    
         [0087]    This is a configuration of the machine tool in the form of an angle grinder with a gear head  58  according to  FIG. 8 , with a lateral handle  60  for holding the machine and with a conventional protective hood  62  which serves as burst protection for a tool in the form of a grinding wheel or cut-off wheel. 
         [0088]    As is clear from  FIG. 10 , in this case the coupling drive  20   a  received in the gear head  58  is constructed as an angular bevel gear. The tool drive shaft  24  mounted by means of two bearings  38 ,  40  is thus driven in rotation. The motor shaft  18  of the drive motor  14  drives the intermediate shaft, mounted by means of two bearings  28 ,  30 , via a coupling  22  according to the configuration described above with reference to  FIGS. 4 and 5 . Located on the intermediate shaft  51  is a driving pinion in the form of a bevel gearwheel which drives an assigned driven wheel in the form of a bevel gearwheel on the tool drive shaft  24 . 
         [0089]    In this version, too, the additional coupling  22  serves for the reduction of vibrations which may occur when the angle grinder is in operation. Moreover, the coupling  22  makes it possible to use an angular or positional offset between the motor shaft  18  and intermediate shaft  51 . The coupling drive  20   a  with the bevel gear could also be designed to be at an angle deviating from 90°. 
         [0090]    The coupling  22  or  22   a  allows positional and angular variations between the drive shaft  24  and motor shaft  18  during operation. It is therefore expedient to provide certain flexibility in the mounting of, for example, the coupling drive  20  or  20   a  or of the tool drive shaft  24  or motor shaft  18 , in order to permit compensating movements which may arise during operation. For this purpose, it is sufficient to provide certain flexibility between the motor housing  12  and the gear housing  13 . Advantageously, however, damping elements  15  are additionally provided for vibration damping in the transitional region between the motor housing  12  and gear housing  13 , as has already been explained above.

Technology Classification (CPC): 5