Patent Application
20070010179
The invention is based on a handheld power grinder, a receiving flange for a grinding tool, and a balancing unit as generically defined by the preambles to the independent claims.
In a handheld power grinder, for instance, rotating structural units whose common center of gravity is not located in the axis of rotation are the source of vibration, which is quite annoying to a user, and to compensate for which balancing systems are employed. However, without compensation the grinding progress is greater than with compensation.
German Patent Disclosure DE 196 17 478 has already proposed a handheld power grinder in which two balancing masses are used that are offset from one another in the axial direction of a working shaft. The balancing masses are located on the working shaft in the interior of the housing of the handheld power grinder between two rotary bearings.
The invention is based on a handheld power grinder, having a motor located in a housing, having a receiving flange receiving a grinding tool, and having a motor-driven working shaft as well as a balancing unit that has at least one first and one second balancing mass.
It is proposed that the first balancing mass is embodied as a movable balancing mass, and the second balancing mass is embodied as a fixed balancing mass. The movable balancing mass, with the working shaft rotating, can move into a balancing position, while the fixed balancing mass forms a structural unit with the balancing unit and maintains its position in which it was installed. If an imbalance changes, then the movable balancing mass can adapt at least partially, while the fixed balancing mass remains in the installed position. Advantageously, given a change in the imbalance over time from progressive wear and tear of the grinding tool, this makes it possible to balance a working shaft and the grinding tool reliably, even over long-term use. This is because for the same balancing capacity of the fixed and movable balancing masses, for instance, twice as much balancing capacity can be handled by subtraction or addition as by a single movable balancing unit, yet that unit requires just as much installation space. Moreover, the combination of fixed and movable balancing masses makes a compact arrangement possible. Any vibration that occurs in the handheld power grinder is lessened, making the handheld power grinder more comfortable to use.
If the movable first balancing mass is formed by balls guided in a race, then they form an especially smooth-running movable balancing mass. When the working shaft is rotating, the balls automatically move into the balancing position and thus automatically achieve balancing. The balancing position is adapted automatically whenever conditions change. The adaptation takes place very quickly, since static friction of the balls is negligible. One or more races may be provided concentrically to an axis of rotation. Alternatively, rings may be provided, which move along one or more cylindrical surfaces that are concentric to the axis of rotation.
If the fixed second balancing mass is formed by a balancing sector that forms part of the circumference of the balancing unit, then a proportion of the imbalance can be compensated for.
If the receiving flange for a grinding tool has a grinding tool receptacle that is eccentric to an axis of rotation, then increased material can be removed by grinding, with simultaneous compensation of vibration and improved convenience of use of the handheld power grinder. Thus in a conventional handheld power grinder, an eccentricity of the grinding tool motion advantageously increases the grinding abrasion just as much as is the case in eccentric power grinders that are designed especially for eccentric operation.
If the receiving flange is a component of the balancing unit, a compact structural unit is created that can easily be built into handheld power grinders and can easily be replaced or retrofitted as needed.
If the fixed second balancing mass is embodied such that at least 10% of a grinding tool imbalance in the new state of the grinding tool, resulting from the eccentric chucking, is compensated for, then this makes a compact structural size possible, compared to the case where the grinding tool imbalance has to be compensated for fully. A remaining imbalance can be compensated for by the movable first balancing mass, which is also compact. The result is a favorable mass ratio between the two balancing masses as well as a favorable size ratio of the balancing unit. Preferably, 40% to 60% of the grinding tool imbalance in the new state is compensated for, and especially preferably approximately half the imbalance in the new state is compensated for. The imbalances, which originate for instance in the intended eccentric location of a tool receptacle ring, in the play between the tool receptacle ring and a grinding wheel bore, and in the intrinsic imbalance of the grinding wheel, the wheel as a rule not being entirely flat, are preferably compensated for by vectorial addition of the balancing effect of the fixed and movable balancing masses. The vectorial balancing condition for grinding wheels is Mv•e+UE+US+AB+AF=0, in which Mv=variable grinding wheel mass, e=eccentricity, UE=intrinsic imbalance of the grinding wheel, Us=imbalance from play, AB=movable balancing, and AF=fixed balancing.
The imbalance of the grinding tool, particularly a grinding wheel, changes steadily as its wear increases. The fixed second balancing mass compensates for a proportion of this, while the movable first balancing mass compensates for the remaining imbalance. With increasing wear, the fixed, second balancing mass compensates for an increasingly greater proportion. Once a state in which the fixed second balancing mass precisely compensates for the reduced weight of the grinding tool resulting from wear is exceeded, the balancing direction of the movable first balancing mass reverses and compensates for the remaining imbalance, which originates from the difference between the fixed, second balancing mass and the decreasing imbalance of the grinding tool.
If the movable first balancing mass is located on the side of the balancing unit facing away from the grinding tool receptacle, a favorable geometry of the balancing unit can be achieved. There is enough space on the back side of the balancing unit for integrating a suitable race.
The invention is also based on a receiving flange for a handheld power grinder.
An eccentric location of a grinding tool receptacle is proposed. It is attained as a result that even a conventional handheld power grinder can achieve increased grinding abrasion, by providing that the grinding tool operates eccentrically with simultaneously a central location of the center of gravity of the rotating unit.
If connecting means for a balancing unit are provided, a compact receiving flange with an integrated balancing unit can be created in a structural unit. Simultaneously, the convenience of use is enhanced, because any vibration of the handheld power grinder is compensated for while the improved grinding progress resulting from the eccentric motion of the grinding tool is preserved.
The invention is also based on a balancing unit having at least two balancing masses.
It is proposed that a movable first balancing mass and a fixed second balancing mass be provided. This advantageously makes it possible, even if the imbalance changes over time, to balance a tool reliably and provide a compact arrangement, because of the balancing masses that supplement one another.
If a receiving flange for a grinding tool is provided, a unit for balancing a working shaft and for balancing a grinding tool for a handheld power grinder can be created. The receiving flange is preferably located on end face, which makes for a small, compact arrangement. This is favorable in terms of engineering and design. The fixed, second balancing mass preferably forms part of the circumference of the balancing unit. Alternatively, the fixed, second balancing mass can form some other part of the balancing unit. The movable first balancing mass is preferably located on the side opposite from the receiving flange. Thus there is enough installation space for embodying races or cylindrical surfaces for the movable balancing mass. The movable and the fixed balancing mass are essentially offset from one another in the circumferential direction. It is equally possible, in addition or alternatively, to provide an offset in the axial direction of the axis of rotation. In an arrangement in which the balancing masses are substantially offset from one another circumferentially, a favorable ratio of forces between the fixed balancing mass and the movable balancing mass is obtained.
If the movable balancing mass is formed by balls guided in a race, these balls can easily be put into an advantageous balancing position. With the working shaft rotating, the balls automatically move into the balancing position and thus automatically achieve balancing. Other movable balancing masses, such as rings around a race, may also be provided.
If the fixed, second balancing mass is formed by a balancing sector that is part of a circumference of the balancing unit, then a favorable geometry and exertion of force of the two balancing masses can be attained.
If the balancing sector occupies an annular range of 25% to 75%, then a favorable ratio in terms of weight and size can be attained between the two balancing masses and thus also for the balancing unit. Preferably, the balancing sector occupies at most half and especially preferably approximately 40% of the circumference.
The balancing sector is preferably located counter to a direction of eccentricity of the receiving flange. This is especially favorable in the case of an eccentric receiving flange for a grinding wheel.
The invention can be employed both for conventional power grinders, in particular handheld power grinders, and for eccentric power grinders, triangular power grinders, or oscillating power grinders.
Further advantages will become apparent from the ensuing description of the drawings. In the drawings, one exemplary embodiment of the invention is shown.
The drawings, description and claims include numerous characteristics in combination. One skilled in the art will expediently consider the characteristics individually as well and put them together to make useful further combinations.
Shown are:
A detail of the arrangement of the balancing unit 22 is shown in
The fixed, second balancing mass 20 is formed by a balancing sector 28, which is part of the circumference 42 of the balancing unit 22 and extends axially along the circumference 42. Optionally, the second balancing mass 20 may also be formed by some other part of the balancing unit 22. The end face of the balancing sector 28 is offset downward somewhat relative to the receiving flange 30, so that the receiving flange 30 forms an end face of the balancing unit 22, and a grinding tool 12 can easily be installed. The balancing sector 28 extends preferably over an annular range a that encompasses at most half of the circumference 42; preferably, a is equal to approximately 120° to 180°, and especially preferably, α=150°.
The movable first balancing mass 18 is formed by balls 26 guided in a race 24. This is shown in greater detail in an exploded view in
The preferred balancing unit 22, on its side 40 opposite from the receiving flange 30, has an indentation which is located concentrically around an opening 44 for the working shaft 16 and which forms a race 24 for the movable, first balancing mass 18.
The movable balancing mass 18 is formed by a plurality of balls 26, of which only a few are identified by numerals for the sake of simplicity. They can revolve in the race 24, so that with the working shaft 16 rotating, the balls 26 automatically assume a balancing position. The race 24 is closed by a covering 36, and the balls 26 are thus enclosed in the race 24. The fixed, second balancing mass 20, in the version shown, extends from the face end 38 along the circumference 42 of the balancing unit 22 as far as the back side 40 of the balancing unit 22.
a, b, c shows a preferred receiving flange 30 in detail. This receiving flange, on its face end 38, has a grinding tool receptacle 32, while a race 24 for the movable first balancing mass 18 is let in (
The fixed, second balancing mass 20 is dimensioned such that a grinding tool imbalance in the new state of the grinding tool 12 is compensated for to a considerable extent. Favorably, from 10% to 90%, and preferably 40% to 60%, of the grinding tool imbalance in the new state is compensated for, and especially preferably, about half of it is compensated for. The race 24 of the balls 26 (
| Number | Date | Country | Kind |
|---|---|---|---|
| 103571450 | Dec 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/52843 | 11/8/2004 | WO | 11/10/2005 |
