Abstract:
An oscillating tool comprises a housing that accommodates a motor which for driving a tool is coupled with a drive shaft via an oscillation drive, for driving it about its longitudinal axis rotatingly oscillatingly. For reducing vibrations, there is provided an inertial mass that is movably held on the housing via at least one spring element.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an oscillating tool with a housing that accommodates a motor which for driving a tool is coupled with a drive shaft via an oscillation drive for driving it rotatingly oscillating about its longitudinal axis. 
         [0002]    An oscillating tool of that kind is known from WO 2008/128804 A1. 
         [0003]    In the case of the known oscillating tool, the motor couples an oscillation drive in the form of an eccentric drive with a drive shaft for causing it to move about its longitudinal axis rotatingly oscillating. 
         [0004]    A mass-balancing arrangement intended to balance vibrations comprises an amplitude mass that is slidably arranged in a slide guide, and which is acted upon by the eccentric cam transmission. The amplitude mass performs an exclusively translational movement for which purpose the slide guide comprises a guide plate with a guide track, and a guide pin guided in the latter. 
         [0005]    Oscillating tools of that kind can be used in diverse ways, for example for grinding or else for sawing or cutting. A usual range of oscillation frequencies is between approximately 5,000 to 25,000 oscillations per minute, a typical oscillation angle is between approximately 0.5° and 7°. 
         [0006]    Hand tools of the before-mentioned kind provide a high degree of flexibility as regards their possible applications. However, it has been found that vibrations may occur in such hand tools of that kind that use a vibration drive, which may impair the ease of handling and which may be disagreeable to a user. 
         [0007]    Efforts have therefore been made to keep vibrations in an oscillating tool as low as possible. Although the arrangement described at the outset has the effect to minimize oscillations, it has the disadvantage that slide guides are needed and that the elements constituting such guides are subject to a certain degree of wear, due to sliding friction. This may be a disadvantage especially when the oscillating tool is driven at a high frequency and, in certain cases, with a large oscillation angle. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of this it is a first object of the invention to disclose an oscillating tool which produces less vibrations. 
         [0009]    It is a second object of the invention to disclose an oscillating tool which produces little vibrations and is well suited for continuous operation. 
         [0010]    It is a third object of the invention to disclose an oscillating tool which allows for continuous operation and has little wear. 
         [0011]    These and other objects of the invention are achieved in an oscillating tool of the type mentioned at the outset by an inertial mass that is movably held on the housing via at least one spring element. 
         [0012]    The object of the invention is thus perfectly achieved. 
         [0013]    Namely, according to the invention vibration damping is achieved by an arrangement where an inertial mass, held to be freely movable on one spring element, or a plurality of spring elements, is used for vibration damping. This provides the particular advantage that due to the inertial mass being suspended on at least one spring element a solution absolutely free of wear is achieved. Depending on the particular application, the spring-mass system constituted by the inertial mass and the respective spring element(s) can be suitably adapted to the resonant frequency or the operating frequency of the oscillation drive. In this way, especially effective vibration damping is achieved. 
         [0014]    According to another embodiment of the invention, the inertial mass has an annular shape with an opening in which the inertial mass is fixed on the housing by at least two spring elements. The design of the opening preferably is such that the center of gravity of the inertial mass lies approximately on the motor axis. 
         [0015]    This permits the inertial mass to be suspended on the housing in direct proximity to the drive so that especially effective vibration damping can be achieved. For suspension of the inertial mass, a single spring element or a plurality of spring elements can be provided. 
         [0016]    If only one spring element is used, there may be provided, for example, a guide which ensures that the inertial mass can move in one plane only. 
         [0017]    There may also be provided a plurality of spring elements which ensure that the inertial mass will move in one plane only. 
         [0018]    According to another embodiment of the invention, at least one spring element is designed as a leaf spring. 
         [0019]    It is possible in this way to guarantee high rigidity in a given direction so that it can be easily ensured that the inertial mass will move in one plane only. 
         [0020]    According to another embodiment of the invention, the oscillation drive comprises an eccentric shaft that is enclosed by the inertial mass. 
         [0021]    According to another embodiment of the invention, the motor comprises a motor shaft that is enclosed by the inertial mass. 
         [0022]    In both cases, the inertial mass may be arranged in direct proximity to the point from which the vibrations predominantly emanate. Accordingly, effective vibration damping of the drive unit can be achieved in this way. 
         [0023]    According to another embodiment of the invention, the inertial mass is arranged on an end of the motor opposite the tool 
         [0024]    Very effective vibration damping can be achieved in this way as well. The greater spacing from the point from which the predominant part of the vibrations emanate results in a longer lever arm so that a smaller inertial mass will be sufficient to achieve the desired vibration damping effect. 
         [0025]    According to another embodiment of the invention, the spring elements have a variable spring characteristic. 
         [0026]    This feature provides the advantage that the resonant frequency of the spring-mass system constituted by the inertial mass, the spring elements and the suspension can be suitably adapted to different vibration frequencies, if desired also as a function of load. 
         [0027]    To this end, the spring characteristic of the spring elements may be made variable, for example by means of an electromechanical element, for example in the form of a piezoelectric element. Alternatively, a mechanical element may be provided, for example an adjustable screw intended to vary the pretension, for example. 
         [0028]    Further, damping may be achieved, for example, by a friction element that acts on the inertial mass. The damping effect may be variable in this case. Detuning of the spring-mass system is rendered possible in this way. 
         [0029]    Accordingly, a larger range of vibration frequencies can he damped. 
         [0030]    According to a further embodiment of the invention, a plurality of inertial masses are received on the housing. 
         [0031]    That feature provides the advantage that improved tuning is rendered possible for damping different frequencies. 
         [0032]    Preferably, the inertial masses may be tuned to different resonant frequencies for this purpose. 
         [0033]    According to another embodiment of the invention, the inertial masses are arranged on the housing one beside the other. 
         [0034]    By modification of that arrangement, the inertial masses may be arranged in different positions in the area of the motor shaft, the eccentric shaft or on the end of the motor opposite the tool. 
         [0035]    This permits an optimized adaptation to be achieved for minimizing the vibrations encountered. 
         [0036]    Preferably, the resonant frequency of a spring-mass system constituted by the inertial mass in combination with the suspension on the spring elements is tuned to the operating frequency of the oscillating tool. 
         [0037]    In this way, especially effective vibration damping is achieved. 
         [0038]    It is understood that the features mentioned above and those yet to be explained below can be used not only in the respective combination indicated, but also in other combinations or in isolation in the invention, without leaving the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    Further features and advantages of the invention will become apparent from the description that follows of a preferred embodiment, with reference to the drawing. In the drawing: 
           [0040]      FIG. 1  shows a simplified partially sectioned representation of part of an oscillating tool according to the invention, in the area of its oscillation drive; and 
           [0041]      FIG. 2  shows a sectioned representation of the oscillating tool according to  FIG. 1 , taken along line II-II. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]      FIG. 1  shows a simplified view of an oscillating tool according to the invention, indicated generally by reference numeral  10 . 
         [0043]    The oscillating tool  10  comprises a housing  12 , accommodating a motor  14  and an oscillation drive indicated generally by reference numeral  13 , by which a drive shaft is driven about its longitudinal axis  28  in rotary and oscillating fashion, as indicated by double arrow  30 . The shaft is driven at a high frequency of 5,000 to 25,000 oscillations per minute, for example, and with a small oscillating angle, typically in a range of between 0.5° and 7°. 
         [0044]    The oscillation drive  13  translates the rotary movement of the motor shaft  16  into an rotatingly oscillating movement of the drive shaft  22 . The drive shaft  22 , being oscillatingly driven by an eccentric portion  18  connected with the motor shaft  16 , is positively connected with a rocker fork  20  for that purpose. 
         [0045]    The drive shaft  22  is seated in the housing  12  via bearings  19 ,  21 , and is scaled from the outside by a seal  23 . A flange  24  provided on the outer end of the drive shaft  22  is connected with the drive shaft  22  in form-locking fashion. A tool  26 , for example a triangular grinding tool, can be clamped against the flange  24  by means of a clamping element  32 , being thereby connected with the drive shaft  22  in form-locking fashion (in a manner not shown in detail). 
         [0046]    The oscillating tool  10  further comprises a quick-acting changing device of the kind known in principle from WO 2005/102605 A1, to permit rapid changing of the tool without any need for an additional tool. The necessary clamping force is produced by a set of springs (not shown) accommodated in the drive shaft  22 . A thrust pad  40  arranged on the upper end of the drive shaft  22  serves for relieving the set of springs so that the clamping element  32  can be pulled off the drive shaft  22  to permit the tool  26  to be changed. Displacing the thrust pad  40  is effected by a clamping lever  34  with an eccentric  36  that can be pivoted about an axis  37 . The details of that quick-acting changing device are known in principle so that they need not be described here in more detail. For further details, reference is made to WO 2005/102605 A1, which is incorporated herein in full by reference. 
         [0047]    For vibration damping the oscillating tool  10  comprises an inertial mass  42  which is suspended for free oscillation on the housing  12 , in the area of the motor shaft  16 , as can be seen in more detail in  FIG. 2 . The inertial mass  42  has an annular shape and comprises a central opening  44  within which the inertial mass  42  is fixed directly on the housing by two mounting elements  50 ,  52 , via two leaf spring elements  46 ,  48 . 
         [0048]    The inertial mass  42 , in combination with the two leaf springs  46 ,  48 , therefore form a spring-mass system that allows passive vibration damping. The resonant frequency of the spring-mass system is suitably tuned in that case to the resonant frequency/frequencies of the oscillation drive  13 . 
         [0049]    In the illustrated embodiment, an inertial mass of 100 g of the illustrated shape led to a resonant frequency of 300 Hz with harmonic frequencies in the range of 600 and 900 Hz so that effective vibration damping could be achieved especially in those domains. The acceleration values at 300 Hz and 900 Hz could be reduced to approximately 50% of the values obtained without the inertial mass  42 . 
         [0050]    In the case illustrated in  FIG. 2 , the inertial mass  42  is arranged on the end of the motor shaft  16 , a short way before the transition to the eccentric portion  18 . 
         [0051]    However, different other arrangements are likewise imaginable, especially an arrangement of the inertial mass  42  at a point closer to the eccentric portion  18  or in the area of the eccentric portion  18 . Further, the inertial mass  42  could also be arranged on the opposite end of the motor  14 . 
         [0052]    Finally, is would likewise be imaginable to make the spring characteristic of the spring elements  46 ,  48  variable, for example by the use of piezoelectric elements. In  FIG. 2  two piezoelectric elements are indicated optionally by reference numeral  53 . If desired, the spring elements  46 ,  48  as such could also be replaced by piezoelectric elements. A variable spring characteristic permits the resonant frequency of the spring-mass system, constituted by the spring elements  46 ,  48  and the inertial mass  42 , to be adapted to the oscillations encountered during operation. This could also be achieved by an oscillation sensor, for example in the form of a piezo-electric sensor such as shown at  41  in  FIG. 1 , which would allow an automatic adaptation system. Alternatively, or in addition, a damping system might also be provided. A friction element (see reference numeral  54  in  FIG. 2 ), may be used for damping, for example. Alternatively, piezoelectric elements such as shown at  53  in  FIG. 2  may be used for damping the movement of the inertial mass  42 .