Patent Application
20110048753
The invention relates to a motor-driven power tool, in particular a hand-held power tool, with the defining characteristics of the preamble to claim 1
DE 101 04 993 A1 has disclosed a hand-held power tool for grinding or polishing, which has a drive motor, a transmission coupled to the drive motor, and a grinding wheel operatively connected to the transmission. The hand-held power tool can be used for superfinishing in which the rotary motion of the drive shaft is converted into an eccentric rotary motion of the grinding wheel with the aid of an eccentric drive. Since grinding appliances with an eccentric drives produce imbalance oscillations that result in decreased comfort and increased material stresses, care must be taken that oscillations of this kind do not exceed a permissible intensity.
The object of the invention is to embody a low-oscillation motor-driven power tool in which the rotary motion of the drive shaft can be transmitted via an eccentric coupling device to the output shaft, which supports the tool, by means of simple structural measures.
This object is attained according to the invention with the defining characteristics of claim 1. Advantageous modifications are disclosed in the dependent claims.
The motor-driven power tool according to the invention is preferably a hand-held power tool. The rotary motion of the drive shaft, which is acted on by the drive motor, is transmitted by means of an eccentric coupling device to the output shaft that supports the tool. The eccentric coupling device produces a rotary pendulum motion of the output shaft.
In order to compensate for imbalance oscillations that are produced due to the eccentric drive motion, a mass-compensation device is provided, which is operatively connected to at least one of the shafts, i.e. either the drive shaft or the output shaft or both shafts, and executes a compensating motion in opposition to the eccentric coupling motion. This oscillation compensation results in the fact that the oscillation or vibration load in the power tool is considerably reduced in individual operating phases—advantageously at least in the idle mode of the power tool and possibly also during the working operation. To reduce oscillations, the mass-compensation device executes a compensating motion in opposition to the eccentric coupling motion, thus at least partially compensating for the rotary oscillations produced by the eccentric coupling device.
The mass-compensation device includes a stroke mass part, which is movably supported in a slot guide and is acted on by an eccentric element that is driven by one of the shafts. The stroke mass part executes a rotary compensating motion. This compensating motion is suitably situated in opposition to the eccentric drive motion, on the one hand with regard to the deflection direction and on the other hand with regard to the level of the mass compensation. In particular, the mass compensation occurs in that the bearing forces of the output shaft approach zero in idle mode. It is also possible, however, to select another operating point in which the imbalance oscillations are compensated for, e.g. an operating point during the regular operation of the power tool. It is also possible for the compensation oscillations, which are produced by means of the mass-compensation device to be amplified or attenuated in different ways, depending on the current operating mode, for example through a changed starting position of the stroke mass part.
The stroke mass part suitably executes the rotary compensating motion inside the slot guide. In this case, it is basically possible for the stroke mass part to execute an exclusively rotary motion or for it to execute a combination of rotary and translatory motion. In both cases, the mobility of the stroke mass part in the slot guide is enabled through correspondingly embodied bearings or by means of stroke curves or sliding block guides between the stroke mass part and the slot guide. In each case, the movement of the stroke mass part is produced by the eccentric element driven directly or indirectly by the drive shaft or the output shaft. The slot guide or sliding block guide in this case is suitably affixed to the housing; if need be, however, the slot guide could also be supported on a moving component of the power tool.
In order to achieve the rotary motion of the stroke mass part in the slot guide, preferably a roller bearing is provided by means of which the stroke mass part is supported in the slot guide. The stroke mass part is suitably supported in the middle of the slot guide, thus yielding a symmetrical support and suitably achieving a uniform deflection from the starting position in both directions. In addition, the eccentric element, particularly when embodied in the form of an eccentric cam, is advantageously situated in the middle of the slot guide, thus yielding a uniform impingement of force on the stroke mass part.
For example, the output shaft of the power tool is supported in cantilevered, eccentric fashion in the housing. In this type of support, the end surface of the output shaft remote from the tool is acted on by the eccentric coupling device.
Other advantages and suitable modifications can be inferred from the remaining claims, the description of the figures, and the drawings.
The hand-held power tool 1 depicted in
The eccentric coupling device 7 includes a coupling device 8 whose end remote from the output shaft 5 has a crimped section 8a in contact with an eccentric cam 9 that is mounted to the drive shaft 4 for co-rotation. The coupling fork 8 slides along the eccentric contour of the eccentric cam 9 and is thus set into the rotary pendulum oscillation that is transmitted to the output shaft 5.
When the rotary motion of the drive shaft 4 is transmitted to the output shaft 5 with the aid of the eccentric coupling device 7, this produces a mass imbalance that is at least partially compensated for by means of a mass-compensation device 10. Like the eccentric coupling device 7, the mass-compensation device 10 is situated between the drive shaft 4 and the output shaft 5. In the mass-compensation device 10, oscillations are produced in opposition to the imbalance oscillations produced by the eccentric coupling device 7.
As shown in
The eccentric cam 12 functions as a drive element for the stroke mass part 16. When the eccentric cam 12 rotates, its eccentric rotary motion is transmitted via the inner walls of the recess 19 to the stroke mass part 16, which, due to its rotary support by means of the roller bearing 22, executes a rotary pendulum motion around the rotation axis of the bearing 22 inside the slot guide part 17. This rotary pendulum motion of the stroke mass part 16 lies in a plane perpendicular to the rotation axis 18 and drive shaft 4. The deflections in this case are oriented in opposition to the deflections of the output shaft 5 and the tool 6 supported on it.
Both the rotary bearing 22 and the eccentric cam 12 are arranged symmetrically in the mass-compensation device 10. The rotary bearing 22 is situated in the middle of the slot guide part 17, as is the eccentric cam 12. The rotary pendulum motion of the stroke mass part 16 usually moves in an angular range of a few degrees, with the dimensions of the stroke mass part 16 and slot guide part 17 being adapted to each other so that the stroke mass part 16 always moves inside the contour of the slot guide part 17.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 004 638.8 | Jan 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/065277 | 11/11/2008 | WO | 00 | 7/16/2010 |
