A vibratory abrader having a grinding plate which is supported at the housing by way of elastic elements, with the abrading plate being put into an orbital movement by way of a ball bearing attached to an eccentric drive member which is equipped with a compensating weight and can be caused to rotate by the armature shaft of the drive motor. To be able to make such a vibratory grinder usable for rough as well as fine abrader work by simply changing the eccentric stroke of the abrading plate, the eccentric drive member is driven by means of an eccentric pin which is likewise mounted eccentrically with respect to the axis of the armature shaft and the armature shaft is pivotal relative to the eccentric drive member and its compensating weight, with the angle of rotation between the armature shaft and the eccentric drive member in both directions being limited to 180.degree. by corresponding abutments at the armature shaft and at the eccentric drive member, and an additional compensating weight is associated with the compensating weight of the eccentric drive member, with this additional compensating weight likewise being rotatable about 180.degree. relative to the compensating weight.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a vibratory or oscillatory sander grinder or 
abrader having a grinding plate which is supported at the housing by way 
of elastic elements, with the grinding or abrading plate being put into an 
orbital movement by way of a ball bearing attached to an eccentric drive 
member which is equipped with a compensating weight and can be caused to 
rotate by the armature shaft of the drive motor. 
2. The Prior Art 
In known vibratory grinders or oscillating sanders of this type, the 
eccentric drive member including its compensating weight is fixed to the 
armature shaft of the drive motor. The swing of the eccentric drive member 
is here defined and unchangeable. For that reason and depending on the 
design of its eccentric swing and possibly its number of revolutions, such 
a vibratory grinder is suitable either specifically for rough grinding 
(abrading) work or preferably for fine grinding work. Therefore, two 
vibratory grinders with generally different eccentricities and numbers of 
revolutions are used for rough and fine grinding work. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide a vibratory abrader such as a 
vibratory grinder which, by simply changing its eccentric stroke, is 
suitable to the same degree for rough as well as fine grinding work. 
This is accomplished according to the invention in that the eccentric drive 
member is drive by means of an eccentric pin which is likewise mounted 
eccentrically with respect to the axis of the armature shaft and the 
armature shaft is pivotal relative to the eccentric drive member and its 
compensating weight, with the angle of rotation between the armature shaft 
and the eccentric drive member in both directions being limited to 
180.degree. by corresponding abutments at the armature shaft and at the 
eccentric drive member, and an additional compensating weight is 
associated with the compensating weight of the eccentric drive member, 
with this additional compensating weight likewise being rotatable about 
180.degree. relative to the compensating weight. 
Modifications and suitable features of the invention are defined in the 
dependent claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As can be seen in FIGS. 1 and 4, the drive motor 5 is disposed vertically 
in a vibratory grinder housing 4 which is equipped with a handle 2 and a 
handhold 3. The armature shaft 1 of the motor has a bore 6 which is 
eccentric to its longitudinal axis 1' and an eccentric pin 7 is rotatably 
mounted in this bore so as to be secure against axial displacement. The 
securing of the eccentric pin against falling out of the bore 6 in the 
armature shaft may here be realized by a circlip 8 or a similar element. 
A grinding plate 10 is mounted on eccentric drive member 9 so as to be 
rotatable by means of a ball bearing 11, with the rotary movement of the 
eccentric drive member 9 being converted to orbital movement of the 
grinding plate with the aid of elastic supporting elements 12 which are 
mechanically coupled with the grinding plate and with the housing of the 
vibratory grinder. To compensate for the imbalanced mass generated during 
the conversion of the rotary movement of the armature shaft to orbital 
movement of the grinding plate, eccentric drive member 9 is provided with 
a compensating weight 13. 
An additional compensating weight 14 is attached to armature shaft 1 so as 
to be secure against rotation, for example by means of a wedge connection 
15. To secure additional compensating weight 14 against axial 
displacement, a nut 16 and counternut 17 are provided which are screwed to 
an external thread provided on the armature shaft. The additional 
compensating weight 14 has a mass ratio of 1/2:3/2 to compensating weight 
13. 
The relative rotatability of the two compensating weights 13 and 14 is 
limited to 180.degree. by an abutment 19 at the eccenytric drive member 9 
and a projection 20 at the frontal face of the armature shaft 1 (see FIGS. 
2 and 3). 
As can be seen in FIG. 2, the eccentricity of the eccentric pin 7 with 
respect to the longitudinal axis 1' of the armature shaft is r/2 and the 
eccentricity of the eccentric drive member 9 with respect to the 
longitudinal axis of the armature shaft is 2r, thus with respect to the 
longitudinal axis 7' of the eccentric pin, it is 3r/2. That means that in 
one case (FIG. 1, movement of the armature shaft to the right) a total 
eccentricity of 3r/2-r/2=r results, while in the other case (FIG. 4, 
movement of the armature shaft to the left), due to the 180.degree. 
rotation of the armature shaft relative to the eccentric drive member and 
vice versa, the total eccentricity is 3r/2+r/2=2r. 
In the position of rotation to the right shown in FIG. 1, the additional 
compensating weight 14 works counter to compensating weight 13, so that 
the compensation of masses according to the eccentricity is MA=3/2-1/2=1. 
This operating state is provided for fine grinding work. During rotation to 
the left, the armature shaft and the additional compensating weight 14 
rotate by 180.degree. relative to compensating weight 13 and eccentric 
drive member 9 around eccentric pin 7 and vice versa, with the 
eccentricity of the eccentric bore 6 in the armature shaft being doubled; 
thus a total eccentricity of 2r is realized. This operating state is shown 
in FIG. 4. The additional compensating weight 14 now is oriented in the 
direction of compensating weight 13 so that the masses are added: M.sub.A 
=3/2+1/2=2. 
While in the latter case, the compensating mass axis is identical with the 
axis of the armature shaft, if the armature shaft rotates to the right, 
the compensating mass axis shifts with respect to the armature shaft axis 
by the amount r. It has been found that this shaft is practically 
negligible. If necessary, however, a suitable compensation can be made. 
As shown in FIGS. 5 and 6, the additional compensating weight 14 may also 
be mounted so as to be rotatable in compensating weight 13. In this case, 
an abutment 22 of the additional compensating weight 14 limits the 
relative movement of the two compensating weights with respect to one 
another to 180.degree.. If the armature shaft rotates to the right, the 
additional compensating weight 14 moves until it comes to rest against a 
recess 21 in frontal face 13' of the compensating weight 13. 
The mass of additional compensating weight 14 is here subtracted from the 
mass of compensating weight 13. If movement is to the left, the additional 
compensating weight 14 is rotated by 180.degree. so that the two masses 
are added together. In this case, abutment 22 of the additional 
compensating weight runs onto frontal face 13' of compensating weight 13. 
To prevent relative movement of the two compensating weights with respect 
to one another during motor speed variation, a spherical detent 23, 24 is 
provided on the two compensating weights to fix the position of the 
compensating weights. 
The mass compensating weights are designed in such a manner that the 
resulting compensating force lies at least approximately in the plane of 
the center of gravity of the vibrating parts so that the free moments are 
compensated. 
Reversal of direction is effected electrically by means of right/left 
switching. Likewise, a reduction of rpm for a larger stroke is effected 
electronically when the vibratory grinder is switched to rotation to the 
left. 
In the case of FIGS. 7 and 8, eccentric pin 7 is a component of armature 
shaft 1. FIG. 7 here illustrates the left moving position of eccentric pin 
7 with its eccentricity r/2 and the eccentric drive member 9 with is 
eccentricity 3r/2 with respect to axis 7' of the eccentric pin, so that, 
with respect to armature shaft 1', the resulting eccentricity is 2r. FIG. 
7 also shows the position of compensating weight 13 and of the additional 
compensating weight 14 which rests on compensating weight 13 and is 
rotatable about the major eccentric. The axis of the two compensating 
masses is here identical with the armature shaft axis 1. Reference numeral 
13' identifies the frontal face of compensating weight 13. 
The position of these components while moving to the right is shown in FIG. 
8. The resulting eccentricity is here 3r/2-r/2=r. The axis of the 
compensating mass is also offset by this amount with respect to armature 
shaft axis 1.