EP0203255B1 - Balanced orbital sander - Google Patents

Balanced orbital sander Download PDF

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Publication number
EP0203255B1
EP0203255B1 EP86101186A EP86101186A EP0203255B1 EP 0203255 B1 EP0203255 B1 EP 0203255B1 EP 86101186 A EP86101186 A EP 86101186A EP 86101186 A EP86101186 A EP 86101186A EP 0203255 B1 EP0203255 B1 EP 0203255B1
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EP
European Patent Office
Prior art keywords
eccentric
rotation
output shaft
relation
grinding shoe
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP86101186A
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German (de)
French (fr)
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EP0203255A3 (en
EP0203255A2 (en
Inventor
Peter Dipl.-Ing. Maier (Fh)
Horst Dr. Haberhauer
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Festo SE and Co KG
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Festo SE and Co KG
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Priority to AT86101186T priority Critical patent/ATE56904T1/en
Publication of EP0203255A2 publication Critical patent/EP0203255A2/en
Publication of EP0203255A3 publication Critical patent/EP0203255A3/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B23/00—Portable grinding machines, e.g. hand-guided; Accessories therefor
    • B24B23/04—Portable grinding machines, e.g. hand-guided; Accessories therefor with oscillating grinding tools; Accessories therefor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T74/00—Machine element or mechanism
    • Y10T74/18—Mechanical movements
    • Y10T74/18544—Rotary to gyratory
    • Y10T74/18552—Unbalanced weight

Definitions

  • the invention is based on an orbital sander with the features of the preamble of claim 1 and claim 3.
  • the case may arise in which the elastic members with which the sanding shoe is fastened to the housing already generate significant lateral forces when the sanding shoe is brought into oscillating or orbital movement with respect to the housing.
  • a balancing weight the center of gravity of which is in the extension of the normal intersecting the two axes of rotation, would only permit inadequate balancing.
  • the sanding shoe is driven by two eccentrics arranged parallel to one another along the axis.
  • Each of the two eccentrics is non-rotatably connected to a balancing weight in order to compensate for the centrifugal force caused by the oscillating grinding shoe.
  • the eccentrics and thus the balancing weights run synchronously with the same phase position in order to generate the desired movement of the grinding shoe.
  • the object of the invention is to create an orbital sander, in particular a hand-held orbital sander, which generates less vibrations on the housing or on the handle in the grinding operation.
  • the existing balance weight slightly rotated anyway or to store it so that it is adjustable with respect to the eccentric.
  • the connecting line between the axis of rotation of the eccentric in the housing and the center of gravity of the balancing weight should be approximately parallel or opposite to the sum vector from the centrifugal force of the grinding shoe moving along the circular path and the transverse force acting on the eccentric.
  • the buzzer vector due to the comparatively low transverse forces, has no appreciably larger amount than the amount of the force vector due to the centrifugal force.
  • the mass of the at least one balancing weight and / or the distance from its center of gravity from the axis of rotation which is stationary in the housing is dimensioned such that a force and a vector arise at a specific rotational speed of the eccentric, the magnitude of which is equal to the sum vector , but this is opposite.
  • the balancing which is unchangeable in this way and which is dimensioned for the load case, results in poorer balancing when the orbital sander is lifted, which in itself is normally not particularly troublesome because the orbital sander lifted does not need to run.
  • the balancing weight is firmly connected to the eccentric, which in turn is rotatably mounted on an output shaft of the drive device.
  • the axis of rotation about which the eccentric can be rotated on the output shaft lies between the axis of rotation which is fixed in the grinding shoe and the axis of rotation which is fixed in the housing and runs parallel to both axes of rotation, the eccentric being coupled in a torsionally elastic manner to the output shaft via an elastic member.
  • both the balancing weight and the eccentric are rotatably mounted on the output shaft of the drive device, the axis of rotation of which forms the fixed axis of rotation of the eccentric in the housing.
  • the output shaft is coupled to the eccentric in a torsionally flexible manner, while a gear element is mounted in the eccentric which, when the eccentric rotates around the output shaft, rotates the balancing weight in the same direction around the output shaft, but by a larger angle.
  • This gear element thus acts much like a planet gear, which is arranged between the output shaft and the centrifugal weight, while the eccentric itself represents the planet carrier.
  • an orbital sander 1 in the housing 2 of which a drive device in the form of an electric or compressed air motor is arranged, which serves to set an abrasive thrust 3 elastically connected to the housing 2 in an oscillating movement relative to the housing 2 .
  • the housing 2 represents the fixed reference point and should remain as quiet as possible.
  • an output shaft 4 of the drive device is rotatably mounted in a bearing flange 5 of the housing 2 by means of a radial deep groove ball bearing 6 about an axis of rotation 7 which extends at right angles to a plane defined by the grinding shoe 3.
  • the oscillating movement of the grinding shoe 3 produces an eccentric 8, which is fixed in a rotationally fixed manner on the end of the output shaft 4 protruding from the deep groove ball bearing 6 and has a cylindrical outer peripheral surface, the axis of symmetry 9 of which is radially offset with respect to the axis of rotation 7 of the output shaft 4.
  • On the eccentric 8 is another radial deep groove ball bearing 11, which is pushed onto a shoulder 12 of the eccentric 8 until it abuts.
  • the axis of symmetry 9 thereby forms the axis of rotation of the eccentric 8 in the grinding shoe 3, which is parallel to the axis of rotation 7.
  • the outer bearing of the deep groove ball bearing 11 is in a bearing bore 13 which is mounted in the dome-like attachment 14 of the grinding shoe 3.
  • the dome-like attachment 14 is an integral part of the grinding shoe 3 and bulges towards the underside of the housing 2. It is located approximately in the center of the rectangular sanding shoe 3, which is glued or otherwise fastened on its underside, and carries an elastic support plate 15, which represents the contact surface for the back of an abrasive paper to be clamped.
  • the fastening devices for holding the sanding paper are omitted for the sake of clarity.
  • a balancing weight 16 is integrally formed on the eccentric 8, which rotates in the cavity which is delimited by the dome-like attachment 14 and the support plate 15.
  • the eccentric 8 is axially secured on the output shaft 4 by means of a countersunk screw 17 which is screwed into a coaxial threaded bore 19 of the output shaft 4 with the interposition of a washer 18.
  • the washer 18 forms the contact surface for the underlying end face of the eccentric 8 or the balancing weight 16.
  • Fig. 2 contains a highly schematic top view View of the grinding shoe 3 and the eccentric 8, with all other structural details that are unimportant in this context being omitted for a clear illustration of the forces acting on the eccentric 8.
  • the eccentric 8 should be understood as a one-armed lever, the length of which corresponds to the distance between the two mutually parallel axes of rotation 7 and 9. Furthermore, they assumed that the entire mass of the grinding shoe 3 is concentrated in the free end of the imaginary one-armed lever, ie in the axis of rotation 9, and that the friction and cutting forces caused by the grinding shoe 3 also act at this point. Since the eccentric 8 rotates around the axis 7, which is as spatially fixed as possible, as a forced axis of rotation, the mass of the grinding shoe 3 concentrated in the axis of rotation 9 rotates about the axis of rotation 7 with a radius corresponding to the distance between the axis of rotation 7 and the axis of rotation 9.
  • the mass of the grinding shoe 3 generates a centrifugal force according to the formula where ⁇ is the angular velocity, r is the distance between the two axes of rotation 7 and 8 and m is the mass of the grinding shoe 3.
  • This centrifugal force acts on the axis of rotation 9 and acts, as an arrow 25 illustrates, in the extension of the connecting straight line between the two axes of rotation 7 and 9, namely in the extension of the imaginary one-armed lever. Arrow 25 thus illustrates the centrifugal force vector.
  • the cutting force that arises when the orbital sander 1 is used acts at right angles to the centrifugal force, as does the frictional forces that occur between the grinding shoe 3 and the housing 2.
  • the eccentric 8 rotates counterclockwise, as indicated by an arrow 26, about the axis of rotation 7, the cutting and frictional forces act in the direction of an arrow 27, which illustrates the force vector running at right angles to the centrifugal force vector 25.
  • Both forces together result in a total force corresponding to the vectorial addition of the two force vectors 25 and 27, i.e. the cutting and friction forces on the one hand and the centrifugal force on the other.
  • the resulting sum force is represented in FIG. 2 by a sum vector according to arrow 28.
  • the center of gravity of the balance weight is therefore on the connecting straight line through the two axes of rotation 7 and 9, i.e. in extension of the centrifugal force vector 25.
  • the effective mass of the balancing weight 16 is dimensioned such that its centrifugal force compensates for the centrifugal force of the grinding shoe 3. As long as no cutting forces occur, a very low-vibration operation is obtained in this way, in which the housing 2, which is held in the hand by the operator, remains largely in ruble.
  • the balancing weight 16 is therefore arranged slightly rotated.
  • the center of gravity 29 of the balancing weight 16 lies next to the connecting straight line which intersects the two axes of rotation 7 and 9 of the eccentric 8 at right angles and is located in a plane which contains the center of gravity 29.
  • the offset of the center of gravity 29, i.e. the rotation of the balance weight 16 with respect to the eccentric 8 or the output shaft 4 is determined so that the centrifugal force acting on the center of gravity 29 of the balance weight 16 acts in a direction which runs parallel to the sum vector 28 and is opposite thereto.
  • these two balancing weights can in turn be combined in a known manner to form a single balancing weight which, compared to the balancing weight for compensating the centrifugal force according to the force vector 25, has a larger effective mass and a changed center of gravity.
  • the condition is met again in the operating case that the centrifugal force vector acting on the center of gravity 29 has the same amount as the sum vector 28, but has the opposite effect.
  • the orbital sander constructed according to FIGS. 1 and 2 shows a greater smoothness in operation or load than when it is lifted off the workpiece and freewheels, because then the fleeing from the center of gravity 29 force vector no longer runs parallel to the centrifugal force vector 25, which is now exclusively present; the cutting forces corresponding to the force vector 27 have decreased to zero in the freewheeling case. If this behavior interferes, it is possible to provide a dynamic adjustment of the position of the center of gravity 29 of the balancing weight relative to the centrifugal force vector 25 or the sum vector 28, as shown in the following figures. In these embodiments, the signal transmitted from the output shaft 4 to the grinding shoe 3 torque is used, the adjustment of the force 'vectors in the load and to realize the free-running case.
  • FIG. 3 shows a section of the region of the orbital sander that can be seen in the broken-open part of FIG. 1, insofar as it is necessary for the explanation.
  • the same reference numerals are used for the individual components, insofar as they are already shown in the previous figures.
  • An eccentrically arranged cylindrical sleeve 31 is seated on the end of the output shaft 4 protruding from the deep groove ball bearing 6, on which the eccentric 8 is in turn rotatably but axially secured.
  • the torque transmission from the output shaft 4 to the eccentric 8 takes place by means of a torsionally flexible coupling member 32, which is mounted on the one hand in a rotationally fixed manner with the output shaft 5 in the area between the deep groove ball bearing 6 and the upper end face of the eccentric sleeve 31, and on the other hand in a rotationally fixed manner with the outer peripheral surface of the Eccentric 8 is connected.
  • the balancing weight 16 in turn sits in one piece on the eccentric 8.
  • a total of three axes of rotation occur in this embodiment: the axis of rotation 7 and the axis of rotation 9, as already described above, and a new axis of rotation 33, which runs parallel to the axes of rotation 7 and 9 and extends located between them, ie the axis of rotation 33 runs at a distance from the axis of rotation 7 and also at a distance from the axis of rotation 9, but the two axes of rotation 7 and 9 are located on different sides of the axis of rotation 33.
  • the axis of rotation 7 which coincides with the axis of the output shaft 4 and is stationary in the housing 2, should remain at rest as far as possible.
  • the axis of rotation 9 runs, as previously described, on a circular path around the axis of rotation 7, so that the distance between the two axes of rotation 7 and 9 defines the grinding circle diameter from one another.
  • the rotation occurs because a torque acts on the axis of rotation 7, which acts in the clockwise direction, while the grinding force vector 27 on the axis of rotation 9 produces a counter torque, which together cause a corresponding rotation of the axes with respect to the axis of rotation 33.
  • the centrifugal force vector 25, which illustrates the centrifugal force of the grinding shoe 3 always extends in an extension of the normal through the two axes of rotation 7 and 9, it also swivels clockwise in the illustrated relative rotation between the output shaft 4 and the eccentric 8, which results in a corresponding Rotation of the cutting force vector 27 and the resulting sum vector 28 leads.
  • the centrifugal force vector 30, which illustrates the centrifugal force emanating from the balancing weight 16 and acting on the center of gravity 29, also pivots around, but counterclockwise, because this vector 30 extends through the center of gravity 29 and the axis of rotation in the extension of the normal 7.
  • the sum vector 28 and the centrifugal force vector 30 are thus rotated in the plane with respect to the axis of rotation 7 such that they act parallel to one another, but in opposite directions.
  • torsionally flexible coupling member 32 leads to a turning back of the eccentric 8 into the starting position as soon as the Cutting force, for example because of the lifting of the orbital sander 1, disappears from the workpiece, so that the position according to FIG. 4 is assumed again.
  • the eccentric 8 on the cylindrical sleeve 31 can only be rotated back and forth between two end positions, one of which corresponds to the freewheeling case according to FIG. 4, while the other end position 5 is matched to the load case.
  • 8 stops are to be provided in a known manner on the outer peripheral surface of the cylindrical sleeve 31 and in the corresponding receiving bore of the eccentric.
  • the intrinsic elasticity of the torsionally flexible coupling member 32 is dimensioned so that it ensures a reliable return of the eccentric to the position according to FIG. 4 on the one hand in the event of a freewheel, but on the other hand a rotation of the eccentric 8 in at a force which is less than the smallest cutting force 5, ie the other end position is not prevented.
  • FIG. 6 Another embodiment for a load-dependent adjustment of the balancing weight 16 is shown in a further simplified form in FIG. 6, which, similar to FIGS. 2, 4 and 5, illustrates a cross section at right angles to the output shaft 4.
  • the eccentric 8 is rotatably seated on the output shaft 4, which in turn is coupled to the output shaft 4 via a non-illustrated torsionally elastic member for torque transmission.
  • the balance weight 16 is also rotatably seated on the output shaft 4 below the eccentric 8.
  • a two-armed lever 34 is rotatably mounted, which engages on the one hand in a recess 35 of the output shaft 4 and on the other hand in a recess 36 of the balancing weight 16.
  • This two-armed lever 34 acts similarly to a planet gear of a plate gear, the output shaft 4 corresponding to the sun gear.
  • the centrifugal force vector which acts on the center of gravity of the balancing weight 16 is rotated in the direction parallel to the sum vector from the centrifugal force of the grinding shoe and the cutting force.
  • the torsionally flexible coupling member rotates the eccentric 8 back into the position shown, so that optimal balancing as in the exemplary embodiment according to FIG. 3 is also ensured for the freewheeling case.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
  • Polishing Bodies And Polishing Tools (AREA)

Abstract

An orbital sander/grinder has on one side of its housing a rotatably mounted disk holder which is brought into orbital motion by means of a drive mechanism that is inside the housing, and is coupled with an eccenter. The eccenter is rotatably mounted on one side in the housing, on the other side in the disk holder, while the rotational axis in the housing is radially offset relative to the rotational axis of the eccenter in the disk holder, but the two axes run parallel to each other. A balancing weight for compensating the unbalance rotates in synchronization with the eccenter. To ensure sanding/grinding with a minimum of vibration, means are provided to compensate for the transverse forces generated by the abrasive and/or cutting forces that are exerted at the eccenter.

Description

Die Erfindung geht aus von einem Schwingschleifer mit den Merkmalen des Oberbegriffs des Anspruches 1 bzw. des Anspruches 3.The invention is based on an orbital sander with the features of the preamble of claim 1 and claim 3.

Bei derartigen, aus der US-A-2 893 174 bekannten Schwingschleifern liegt der Schwerpunkt des Auswuchtgewichtes auf der Verbindungsgeraden zwischen den beiden Drehachsen des Exzenters, und zwar bezüglich der Drehachse in dem Gehäuse diametral zu der Drehachse des Exzenters im Schleifschuh. Bei abgehobenem Schwingschleifer werden auf diese Weise praktisch sämtliche von dem Schleifschuh ausgehenden Kräfte, die um die Drehachse des Exzenters im Gehäuse umlaufen, kompensiert.In such orbital sanders known from US-A-2 893 174, the center of gravity of the balancing weight lies on the connecting straight line between the two axes of rotation of the eccentric, with respect to the axis of rotation in the housing diametrically to the axis of rotation of the eccentric in the grinding shoe. When the orbital sander is lifted off, virtually all of the forces emanating from the grinding shoe and rotating around the axis of rotation of the eccentric in the housing are compensated in this way.

Zumindest dann, wenn der solchermaßen ausgewuchtete Schwingschleifer an die zu bearbeitende Oberfläche angepreßt wird, treten Schnittkräfte auf, die bezüglich der Drehachse des Exzenters in dem Gehäuse ein Drehmoment erzeugen und außerdem an dem Exzenter angreifende Querkräfte hervorrufen, die entsprechend der Orbitalbewegung des Schleifschuhs um die Drehachse des Exzenters im Gehäuse umlaufen. Diese ständig die Richtung ändernden Querkräfte werden vom Schleifschuh auf das Gehäuse bzw. die Handgriffe übertragen. Die am Handgriff auftretenden Querkräfte werden von der Bedienperson als lästige Schwingungen empfunden.At least when the orbital sander balanced in this way is pressed against the surface to be machined, cutting forces occur which generate a torque with respect to the axis of rotation of the eccentric in the housing and also produce transverse forces which act on the eccentric and which correspond to the orbital movement of the grinding shoe around the axis of rotation of the eccentric in the housing. These constantly changing lateral forces are transferred from the sanding pad to the housing or the handles. The lateral forces occurring on the handle are perceived by the operator as annoying vibrations.

Darüber hinaus kann zumindest bei größeren Schwingschleifern der Fall eintreten, daß die elastischen Glieder, mit denen der Schleifschuh an dem Gehäuse befestigt ist, bereits nennswerte Querkräft erzeugen, wenn der Schleifschuh in den oszillierende bzw. Orbitalbewegung bezüglich des Gehäuses gebracht wird. In solchen Fällen würde ein Auswuchtgewicht, dessen Schwerpunkt in Verlängerung der die beiden Drehachsen schneidenden Normalen liegt, nur eine ungenüngende Auswuchtung ermöglichen.In addition, at least in the case of larger orbital sanders, the case may arise in which the elastic members with which the sanding shoe is fastened to the housing already generate significant lateral forces when the sanding shoe is brought into oscillating or orbital movement with respect to the housing. In such cases, a balancing weight, the center of gravity of which is in the extension of the normal intersecting the two axes of rotation, would only permit inadequate balancing.

Bei einem anderen, aus der DE-A-3 326 854 bekannten Schwingschleifer wird der Schleifschuh von zwei achsparallel nebeneinander angeordneten Exzentern angetrieben. Jeder der beiden Exzenter ist drehfest mit einem Auswuchtgewicht verbunden, um die von dem oszillierenden Schleifschuh hervorgerufene Fliehkraft zu kompensieren. Die Exzenter und damit auch die Auswuchtgewichte laufen, um die gewünschte Bewegung des Schleifschuhs zu erzeugen, mit derselben Phasenlage synchron um.In another orbital sander known from DE-A-3 326 854, the sanding shoe is driven by two eccentrics arranged parallel to one another along the axis. Each of the two eccentrics is non-rotatably connected to a balancing weight in order to compensate for the centrifugal force caused by the oscillating grinding shoe. The eccentrics and thus the balancing weights run synchronously with the same phase position in order to generate the desired movement of the grinding shoe.

Bei dem bekannten Schwingschleifer ist ebenfalls keine Kompensation der Reib- und Schnittkräfte vorgesehen, die beim Einsatz des Schwingschleifers auftreten.In the known orbital sander, there is also no compensation for the frictional and cutting forces that occur when the orbital sander is used.

Ausgehend hiervon liegt der Erfindung die Aufgabe zugrunde, einen Schwingschleifer, insbesondere einen handgeführten Schwingschleifer zu Schaffen, der im Schleifbetrieb geringere Vibrationen am Gehäuse bzw. am Handgriff erzeugt.Proceeding from this, the object of the invention is to create an orbital sander, in particular a hand-held orbital sander, which generates less vibrations on the housing or on the handle in the grinding operation.

Diese Aufgabe wird erfindungsgemäß durch einen Schwingschleifer mit den Merkmalen des Anspruches 1 bzw. einen Schwingsschleifer mit den Merkmalen des Anspruches 3 gelöst.This object is achieved by an orbital sander with the features of claim 1 or an orbital sander with the features of claim 3.

Je nach dem, wie die Relation zwischen den Fliehkräften, die von dem auf einer Kreisbahn schwingenden Schleifschuh erzeugt werden, und den Querkräften ist, die durch die Reibung des Schleifschuhs relativ zu dem Gehäuse und den Schnittkräften beim Schleifen hergorgerufen werden, kann es ausreichen, das ohnehin vorhandene Auswuchtgewicht geringfügig gedreht anzuordnen oder es bezüglich des Exzenters verstellbar zu lagern. In beiden Fällen soll im Lastfall die Verbindungsgerade zwischen der Drehachse des Exzenters in dem Gehäuse und dem Schwerpunkt des Auswuchtgewichtes etwa parallel bzw. entgegengesetzt zu dem Summenvektor aus der Zentrifugalkraft des längs der Kreisbahn bewegten Schleifschuhs und der an dem Exzenter angreifenden Querkraft liegen. Im Falle des fest angeordneten Auswuchtgewichtes wird davon ausgegangen, daß der Summervektor infolge der vergleichsweise geringen Querkräfte keinen nennenswert größeren Betrag aufweist als der Betrag des Kraftvektors infolge der Zentrifugalkraft.Depending on the relationship between the centrifugal forces generated by the grinding shoe vibrating on a circular path and the lateral forces caused by the friction of the grinding shoe relative to the housing and the cutting forces during grinding, it may be sufficient that to arrange the existing balance weight slightly rotated anyway or to store it so that it is adjustable with respect to the eccentric. In both cases, the connecting line between the axis of rotation of the eccentric in the housing and the center of gravity of the balancing weight should be approximately parallel or opposite to the sum vector from the centrifugal force of the grinding shoe moving along the circular path and the transverse force acting on the eccentric. In the case of the fixedly arranged balancing weight, it is assumed that the buzzer vector, due to the comparatively low transverse forces, has no appreciably larger amount than the amount of the force vector due to the centrifugal force.

Bei größeren zu erwartenden Querkräften ist die Masse des mindestens einen Auswuchtgewichtes und/oder der Abstand von dessen Schwerpunkt von der in dem Gehäuse ortsfesten Drehachse derart bemessen, daß bei einer bestimmten Drehzahl des Exzenters eine Kraft und einem Vektor entsteht, der betragsmäßig gleich wie der Summenvektor, diesem jedoch entgegengesetzt ist.In the case of larger transverse forces to be expected, the mass of the at least one balancing weight and / or the distance from its center of gravity from the axis of rotation which is stationary in the housing is dimensioned such that a force and a vector arise at a specific rotational speed of the eccentric, the magnitude of which is equal to the sum vector , but this is opposite.

Die solchermaßen unveränderliche Auswuchtung, die für den Lastfall bemessen ist, bedingt jedoch eine schlechtere Auswuchtung bei abgehobenem Schwingschleifer, was an sich normalerweise deswegen nicht besonders störend ist, weil der abgehobene Schwingschleifer nicht zu laufen braucht. Zweckmäßiger ist es jedoch, den Schwingschleifer sowohl für den Lastfall als auch für den entlasteten Fall auszuwuchten. Dies ist insbesondere vorteilhaft, wenn der Schwingschleifer während des Schleifvorganges, ohne ausgeschaltet zu werden, häufig umgesetzt werden muß. In diesem Falle ist es zweckmäßig, wenn der Abstand zwischen dem Schwerpunkt des Auswuchtgewichtes und der Normalen, die die beiden Drehachsen schneidet, in Abhängigkeit von der Schnittkraft selbsttätig verstellbar ist.However, the balancing, which is unchangeable in this way and which is dimensioned for the load case, results in poorer balancing when the orbital sander is lifted, which in itself is normally not particularly troublesome because the orbital sander lifted does not need to run. However, it is more expedient to balance the orbital sander both for the load case and for the unloaded case. This is particularly advantageous if the orbital sander has to be moved frequently during the grinding process without being switched off. In this case, it is expedient if the distance between the center of gravity of the balancing weight and the normal which intersects the two axes of rotation is automatically adjustable depending on the cutting force.

Hierzu kommen grundsätzlich zwei Lösungen in Frage. Gemäß der einen Lösung ist das Auswuchtgewicht fest mit dem Exzenter verbunden, der seinerseits drehbar auf einer Ausgangswelle der Antriebseinrichtung gelagert ist. Die Drehachse, um die der Exzenter auf der Ausgangswelle drehbar ist, liegt zwischen der in dem Schleifschuh ortfesten sowie der in dem Gehäuse ortsfesten Drehachse und verläuft zu beiden Drehachsen parallel, wobei der Exzenter mit der Ausgangswelle über ein elastisches Glied drehelastisch gekuppelt ist. Diese Anordnung erreicht eine Drehung des aus Schnittkraft und Fliehkraft zusammengesetzten Summenvektors, der hierdurch zu dem Fliehkraftvektor parallel wird, der am Schwerpunkt des Auswuchtgewichtes angreift.There are basically two possible solutions. According to one solution, the balancing weight is firmly connected to the eccentric, which in turn is rotatably mounted on an output shaft of the drive device. The axis of rotation about which the eccentric can be rotated on the output shaft lies between the axis of rotation which is fixed in the grinding shoe and the axis of rotation which is fixed in the housing and runs parallel to both axes of rotation, the eccentric being coupled in a torsionally elastic manner to the output shaft via an elastic member. This arrangement achieves a rotation of the sum vector composed of cutting force and centrifugal force, which thereby becomes parallel to the centrifugal force vector which acts on the center of gravity of the balancing weight.

Eine andere Möglichkeit für die selbsttätige Verstellung sieht vor, daß sowohl das Auswuchtgewicht als auch der Exzenter drehbar auf der Ausgangswelle der Antriebseinrichtung gelagert sind, deren Drehachse die ortsfeste Drehachse des Exzenters in dem Gehäuse bildet. Wiederum ist die Ausgangswelle mit dem Exzenter drehelastisch gekuppelt, während in dem Exzenter ein Getriebeelement gelagert ist, das bei einer Drehung des Exzenters um die Ausgangswelle das Auswuchtgewicht in derselben Richtung um die Ausgangswelle dreht, jedoch um einen größeren Winkel. Dieses Getriebelement wirkt damit ählich wie ein Planetenrad, das zwischen der Ausgangswelle und dem Fliehgewicht angeordnet ist, während der Exzenter selbst den Planetenträger darstellt.Another possibility for the automatic adjustment provides that both the balancing weight and the eccentric are rotatably mounted on the output shaft of the drive device, the axis of rotation of which forms the fixed axis of rotation of the eccentric in the housing. Again, the output shaft is coupled to the eccentric in a torsionally flexible manner, while a gear element is mounted in the eccentric which, when the eccentric rotates around the output shaft, rotates the balancing weight in the same direction around the output shaft, but by a larger angle. This gear element thus acts much like a planet gear, which is arranged between the output shaft and the centrifugal weight, while the eccentric itself represents the planet carrier.

De bei den meisten Schwingschleifern sowohl im Lastfall als auch im Freilauf die jeweils auftretenden Reib- und Schnittkräfte innerhalb gewisser Toleranzen konstant sind, genügt es vollständig, wenn der Exzenter bezüglich der Ausgangswelle in seinem Drehwinkel begrenzt ist, während die Federkraft des drehelastischen Kupplungsgliedes so bemessen ist, daß im Freilauffall der Exzenter in die Ruhelage gebracht wird, während beim Überschreiten einer vorbestimmten Schnittkraft der Exzenter in seine andere, dem Lastfall entsprechende Betriebsstellung umklappt.Since most of the orbital grinders have constant friction and cutting forces within certain tolerances, both in the load case and in freewheel mode, it is sufficient if the eccentric is limited in its angle of rotation with respect to the output shaft, while the spring force of the torsionally flexible coupling member is dimensioned in this way that in the freewheeling case the eccentric is brought into the rest position, while when a predetermined cutting force is exceeded the eccentric folds over into its other operating position corresponding to the load case.

In der Zeichnung ist ein Ausführungsbeispiel des Gegenstandes der Erfindung dargestellt. Es zeigen:

  • Fig. 1 einen Schwingschleifer gemäß der Erfindung mit weilweise geöffnetem Gehäuse sowie teilweise geöffnetem Schleifschuh in einer Seitenansicht,
  • Fig. 2 eine stark schematisierte Draufsicht auf den Schleifschuh sowie den ihn antriebenden Exzenter unter Veranschaulichung der dort angreifenden Kräfte,
  • Fig. 3 einen Ausschnitt des Schwingschleifers nach Fig. 1 mit selbsttätiger Verstellung des Auswuchtgewichtes in einem Längsschnitt,
  • Fig. 4 und 5 eine stark schematisierte Draufsicht auf die Anordnung aus Exzenter und Auswuchtgewicht nach Fig. 3 unter Veranschaulichung der angreifenden Kräfte in den verschiendenen Betriebsfällen und
  • Fig. 6 ein weiteres stark schematisiertes Ausführungsbeispiel für eine selbsttätige Verstellung des Auswichtgewichtes bei einem Schwingschleifer gemäß der Erfindung.
In the drawing, an embodiment of the object of the invention is shown. Show it:
  • 1 is a side view of an orbital sander according to the invention with a partially open housing and partially open grinding shoe,
  • 2 shows a highly schematic top view of the grinding shoe and the eccentric which drives it, illustrating the forces acting there,
  • 3 shows a detail of the orbital sander according to FIG. 1 with automatic adjustment of the balancing weight in a longitudinal section,
  • 4 and 5 is a highly schematic plan view of the arrangement of the eccentric and the balancing weight according to FIG. 3, illustrating the forces acting in the various operating cases and
  • Fig. 6 shows another highly schematic embodiment for an automatic adjustment of the balance weight in an orbital sander according to the invention.

In Fig. 1 ist ein Schwingschleifer 1 veranschaulicht, in dessen Gehäuse 2 eine Antriebseinrichtung in Gestalt eines Elektro- oder Druckluftmotors angeordnet ist, der dazu dient, einen mit dem Gehäuse 2 elastisch verbundenen Schleifschub 3 relativ zu dem Gehäuse 2 in eine oszillierende Bewegung zu versetzten. Das Gehäuse 2 stellt dabei den raumfesten Bezugspunkt dar und soll möglichst in Ruhe bleiben. Zum Erzeugen der Relativbewegung ist hierzu eine Ausgangswelle 4 der Antriebseinrichtung in einem Lagerflansch 5 des Gehäuses 2 mittels eines Radialrillenkugellagers 6 um eine Drehachse 7 drehbar gelagert, die rechtwinklig zu einer durch den Schleifschuh 3 definierten Ebene verläuft. Die oszillierende Bewegung des Schleifschuhs 3 erzeugt ein Exzenter 8, der drehfest auf dem aus dem Rillenkugellager 6 herausragenden Ende der Ausgangswelle 4 befestigt ist und eine zylindrische Außenumfangsfläche aufweist, deren Symmetrieachse 9 bezüglich der Drehachse 7 der Ausgangswelle 4 radial versetzt ist. Auf dem Exzenter 8 steckt ein weiteres Radialrillenkugellager 11, das bis zur Anlage an einer Schulter 12 des Exzenters 8 aufgeschoben ist. Die Symmetrieachse 9 bildet hierdurch die Drehachse des Exzenters 8 in dem Schleifschuh 3, die zu der Drehachse 7 parallel ist.1 shows an orbital sander 1, in the housing 2 of which a drive device in the form of an electric or compressed air motor is arranged, which serves to set an abrasive thrust 3 elastically connected to the housing 2 in an oscillating movement relative to the housing 2 . The housing 2 represents the fixed reference point and should remain as quiet as possible. To generate the relative movement, an output shaft 4 of the drive device is rotatably mounted in a bearing flange 5 of the housing 2 by means of a radial deep groove ball bearing 6 about an axis of rotation 7 which extends at right angles to a plane defined by the grinding shoe 3. The oscillating movement of the grinding shoe 3 produces an eccentric 8, which is fixed in a rotationally fixed manner on the end of the output shaft 4 protruding from the deep groove ball bearing 6 and has a cylindrical outer peripheral surface, the axis of symmetry 9 of which is radially offset with respect to the axis of rotation 7 of the output shaft 4. On the eccentric 8 is another radial deep groove ball bearing 11, which is pushed onto a shoulder 12 of the eccentric 8 until it abuts. The axis of symmetry 9 thereby forms the axis of rotation of the eccentric 8 in the grinding shoe 3, which is parallel to the axis of rotation 7.

Der äußere Lagerrung des Rillenkugellagers 11 steckt in einer Lagerbohrung 13, die in dem domartigen Aufsatz 14 des Schleifschuhs 3 angebracht ist. Der domartige Aufsatz 14 ist einstückiger Bestandteil des Schleifschuhs 3 und wölbt sich der Unterseite des Gehäuses 2 entgegen. Er befindet sich etwa mittig auf dem rechteckigen Schleifschuh 3, der auf seiner Unterseite aufgeklebt oder sonst wie befestigt, eine elastische Auflageplatte 15 trägt, die die Auflagefläche für die Rückseite eines aufzuspannenden Schleifpapiers darstellt. Die Befestigungseinrichtungen zum Halten des Schleifpapiers sind der Übersichtlichkeit halber weggelassen.The outer bearing of the deep groove ball bearing 11 is in a bearing bore 13 which is mounted in the dome-like attachment 14 of the grinding shoe 3. The dome-like attachment 14 is an integral part of the grinding shoe 3 and bulges towards the underside of the housing 2. It is located approximately in the center of the rectangular sanding shoe 3, which is glued or otherwise fastened on its underside, and carries an elastic support plate 15, which represents the contact surface for the back of an abrasive paper to be clamped. The fastening devices for holding the sanding paper are omitted for the sake of clarity.

Zur Kompensation der von dem Schleifschuh 3 samt Auflageplatte 15 sowie dem Exzenter 8 und den Schnittkräften erzeugten Unwucht ist an dem Exzenter 8 ein Auswuchtgewicht 16 einstückig angeformt, das in dem Hohlraum umläuft, der von dem domartigen Aufsatz 14 und der Auflageplatte 15 begrenzt wird.To compensate for the imbalance generated by the grinding shoe 3 together with the support plate 15 and the eccentric 8 and the cutting forces, a balancing weight 16 is integrally formed on the eccentric 8, which rotates in the cavity which is delimited by the dome-like attachment 14 and the support plate 15.

Die axiale Sicherung des Exzenters 8 auf der Ausgangswelle 4 erfolgt mittels einer Senkschraube 17, die unter Zwischenlage einer Beilagscheibe 18 in eine koaxiale Gewindebohrung 19 der Ausgangswelle 4 eingeschraubt ist. Die Beilagscheibe 18 bildet dabei die Anlagefläche für die untenliegende Stirnseite des Exzenters 8 bzw des Auswuchtgewichtes 16.The eccentric 8 is axially secured on the output shaft 4 by means of a countersunk screw 17 which is screwed into a coaxial threaded bore 19 of the output shaft 4 with the interposition of a washer 18. The washer 18 forms the contact surface for the underlying end face of the eccentric 8 or the balancing weight 16.

Um beim Ingangsetzen des Exzenters 8 ein Umlaufen des Schleifschuhs 3 um die Drehachse 7 zu verhindern und um die gewünschte Orbitalbewegung zu erzwingen, befinden sich in der Nähe der vier Ecken des Schleifschuhs 3 längliche elastische Glieder oder Füße, von denen lediglich der elastische Fuß 21 im aufgebrochenen Teil des Gehäuses 2 erkennbar ist. Diese zylindrischen elastischen Füße 21 stecken, wie der elastische Fuß 21 stellvertretend zeigt, mit ihren Endabschnitten in zylinderförmigen Näpfen 22 und 23, die an dem Schleifschuh 3 bzw. dem Gehäuse 2 einander gegenüberliegend angeformt sind. Auf diese Weise verlaufen die in den Näpfen 22, 23 befindlichen Abschnitte des elastischen Fußes 21 parallel zu der Drehachse 9 bzw. der Drehachse 7. Durch Ingangsetzen des Exzenters 8, d.h. dadurch, daß er, angetrieben von der Ausgangswelle 4 um die raumfeste Drehachse 7 umläuft und sich hierbei gleichzeitig in dem Rillenkugellager 11 um seine eigene Drehachse 9 dreht, vollführen sämtliche Punkte des Scheifschuhs 3 Kreisbewegungen mit einem Radius, der dem Abstand der beiden Drehachsen 7 und 9 voneinader entspricht.In order to prevent the grinding shoe 3 from rotating around the axis of rotation 7 when the eccentric 8 is started and to force the desired orbital movement, there are elongated elastic members or feet near the four corners of the grinding shoe 3, of which only the elastic foot 21 in broken part of the housing 2 can be seen. These cylindrical elastic feet 21, as representative of the elastic foot 21, show, with their end portions in cylindrical cups 22 and 23, which are formed on the grinding shoe 3 and the housing 2 opposite one another. In this way, the sections of the elastic foot 21 located in the cups 22, 23 run parallel to the axis of rotation 9 or the axis of rotation 7. By starting the eccentric 8, i.e. characterized in that it rotates, driven by the output shaft 4 about the fixed axis of rotation 7 and at the same time rotates in the deep groove ball bearing 11 about its own axis of rotation 9, all points of the sliding shoe 3 perform circular movements with a radius which corresponds to the distance between the two axes of rotation 7 and 9 corresponds to each other.

Fig. 2 enthält eine stark schematisierte Draufsicht auf den Schleifschuh 3 sowie den Exzenter 8, wobei zur übersichtlichen Veranschaulichung der am Exzenter 8 angreifenden Kräfte alle übrigen in diesem Zusammenhang unwichtigen konstruktiven Einzelheiten weggelassen sind.Fig. 2 contains a highly schematic top view View of the grinding shoe 3 and the eccentric 8, with all other structural details that are unimportant in this context being omitted for a clear illustration of the forces acting on the eccentric 8.

Zur Erläutering der erfinderischen Maßnahme sei der Exzenter 8 als einarmiger Hebel aufgefaßt, dessen Länge dem Abstand der beiden zueinander parallelen Drehachsen 7 und 9 entspricht. Weiterhin sie angenommen, daß die gesamte Masse des Schleifschuhs 3 in dem freien Ende des gedachten einarmigen Hebels, d.h. in der Drehachse 9. konzentriert ist und daß auch an dieser Stelle die von dem Schleifschuh 3 hervorgerufenen Reib- und Schnittkräfte angreifen. Da der Exzenter 8 um die möglichst raumfeste Drehachse 7 als aufgezwungene Drehachse rotiert, läuft die in der Drehachse 9 konzentrierte Masses des Schleifschuhs 3 um die Drehachse 7 mit einem Radius entsprechend dem Abstand der Drehachse 7 von der Drehachse 9 um. Hierdurch erzeugt die Masse des Schleifschuhs 3 eine Fliehkraft gemäß der Formel

Figure imgb0001
wobei ω die Winkelgeschwindigkeit, r der Abstand zwischen den beiden Drehachsen 7 und 8 und m die Masse des Schleifschuhs 3 ist. Diese Fliehkraft greift an der Drehachse 9 an und wirkt, wie ein Pfeil 25 veranschaulicht, in Verlängerung der Verbindungsgeraden zwischen den beiden Drehachsen 7 und 9, und zwar in Verlängerung des gedachten einarmigen Hebels. Der Pfeil 25 veranschaulicht also den FliehKraftvektor.To explain the inventive measure, the eccentric 8 should be understood as a one-armed lever, the length of which corresponds to the distance between the two mutually parallel axes of rotation 7 and 9. Furthermore, they assumed that the entire mass of the grinding shoe 3 is concentrated in the free end of the imaginary one-armed lever, ie in the axis of rotation 9, and that the friction and cutting forces caused by the grinding shoe 3 also act at this point. Since the eccentric 8 rotates around the axis 7, which is as spatially fixed as possible, as a forced axis of rotation, the mass of the grinding shoe 3 concentrated in the axis of rotation 9 rotates about the axis of rotation 7 with a radius corresponding to the distance between the axis of rotation 7 and the axis of rotation 9. As a result, the mass of the grinding shoe 3 generates a centrifugal force according to the formula
Figure imgb0001
 where ω is the angular velocity, r is the distance between the two axes of rotation 7 and 8 and m is the mass of the grinding shoe 3. This centrifugal force acts on the axis of rotation 9 and acts, as an arrow 25 illustrates, in the extension of the connecting straight line between the two axes of rotation 7 and 9, namely in the extension of the imaginary one-armed lever. Arrow 25 thus illustrates the centrifugal force vector.

Die Schnittkraft, die beim Einsatz des Schwingschleifers 1 entsteht, wirkt rechtwinklig zu der Fliehkraft, ebenso wie Reibkräfte, die zwischen dem Schleifschuh 3 und dem Gehäuse 2 auftreten. Unter der Annahme, daß der Exzenter 8 im Gegenuhrzeigersinne, wie durch einen Pfeil 26 angedeutet, um die Drehachse 7 rotiert, wirken die Schnitt- und Reibkräfte in Richtung einer Pfeiles 27, der den zum Fliehkraftvektor 25 rechtwinklig verlaufenden Kraftvektor veranschaulicht. Beide Kräfte zusammen ergeben eine Summenkraft entsprechend der vektoriellen Addition der beiden Kraftvektoren 25 und 27, d.h. der Schnitt-und Reibkräfte einerseits und der Fliehkraft andererseits. Die resultierende Summenkraft ist in Fig. 2 durch einen Summenvektor entsprechend dem Pfeil 28 dargestellt.The cutting force that arises when the orbital sander 1 is used acts at right angles to the centrifugal force, as does the frictional forces that occur between the grinding shoe 3 and the housing 2. Assuming that the eccentric 8 rotates counterclockwise, as indicated by an arrow 26, about the axis of rotation 7, the cutting and frictional forces act in the direction of an arrow 27, which illustrates the force vector running at right angles to the centrifugal force vector 25. Both forces together result in a total force corresponding to the vectorial addition of the two force vectors 25 and 27, i.e. the cutting and friction forces on the one hand and the centrifugal force on the other. The resulting sum force is represented in FIG. 2 by a sum vector according to arrow 28.

Bei den bisher bekannten Schwingschleifern ist lediglich ein Ausgleichsgewicht vorgesehen, das nur dazu dient, die vom Schleifschuh 3 hervorgerufene Fliehkraft zu kompensieren. Bei diesen Schwingschleifern liegt deshalb auch der Schwerpunkt des Ausgleichsgewichtes auf der Verbindungsgeraden durch die beiden Drehachsen 7 und 9, d.h. in Verlängerung des Fliehkraftvektors 25. Die effektive Masse des Auswuchtgewichtes 16 ist dabei so bemessen, daß dessen Fliehkraft die Fliehkraft des Schleifschuhs 3 kompensiert. Solange keine Schnittkräfte auftreten, wird auf diese Weise ein recht vibrationsarmer Betrieb erhalten, bei dem das Gehäuse 2, das von der Bedienperson in der Hand gehalten wird, weitgehend in Rube bleibt. Wenn aber mit dem Schwingschleifer tatsächlich geschliffen wird und Schnitt- und Reibkräfte auftreten, geht bei den bekannten Schwingschleifern der vibrationsarme Lauf verloren, weil am Exzenter 8 die oben erläuterten Schnittkräfte angreifen. Diese Schnittkräfte rufen entsprechend Querkräfte an der Drehachse 7 und damit am Gehäuse 2 hervor, die zu entsprechenden Schwingungen des Gehäuses 2 führen.In the previously known orbital sanders, only a counterweight is provided, which only serves to compensate for the centrifugal force caused by the grinding shoe 3. With these orbital sanders, the center of gravity of the balance weight is therefore on the connecting straight line through the two axes of rotation 7 and 9, i.e. in extension of the centrifugal force vector 25. The effective mass of the balancing weight 16 is dimensioned such that its centrifugal force compensates for the centrifugal force of the grinding shoe 3. As long as no cutting forces occur, a very low-vibration operation is obtained in this way, in which the housing 2, which is held in the hand by the operator, remains largely in ruble. If, however, the orbital sander is actually used for grinding and cutting and frictional forces occur, the known low-vibration orbital sander will lose the low-vibration running because the cutting forces explained above act on the eccentric 8. These cutting forces cause corresponding lateral forces on the axis of rotation 7 and thus on the housing 2, which lead to corresponding vibrations of the housing 2.

Bei dem neuen in den Figuren gezeigten Schwingschleifer 1 ist deshalb das Auswuchtsgewicht 16 geringfügig gedreht angeordnet. Der Schwerpunkt 29 des Auswuchtgewichtes 16 liegt bei dem neuen Schwingschleifer 1 neben der Verbindungsgeraden, die rechtwinklig die beiden Drehachsen 7 und 9 des Exzenters 8 schneidet und sich in einer Ebene befindet, die den Schwerpunkt 29 enthält. Der Versatz des Schwerpunktes 29, d.h. die Verdrehung des Auswuchtgewichtes 16 bezüglich des Exzenters 8 bzw. der Ausgangswelle 4, ist so festgelegt, daß die an dem Schwerpunkt 29 des Auswuchtgewichtes 16 angreifende Fliehkraft in eine Richtung wirkt, die parallel zu dem Summenvektor 28 verläuft und diesem entgegengesetzt ist.In the new orbital sander 1 shown in the figures, the balancing weight 16 is therefore arranged slightly rotated. In the new orbital sander 1, the center of gravity 29 of the balancing weight 16 lies next to the connecting straight line which intersects the two axes of rotation 7 and 9 of the eccentric 8 at right angles and is located in a plane which contains the center of gravity 29. The offset of the center of gravity 29, i.e. the rotation of the balance weight 16 with respect to the eccentric 8 or the output shaft 4 is determined so that the centrifugal force acting on the center of gravity 29 of the balance weight 16 acts in a direction which runs parallel to the sum vector 28 and is opposite thereto.

Da bei schnellaufenden Schwingschleifern mit kleinem Schleifkreisdurchmesser die auftretenden Schnitt- und Reibkräfte um den Faktor 10 oder mehr kleiner sind als die von dem Schleifschuh 3 hervorgerufenen Fliekräfte genügt es, das bereits bekannte Auswuchtgewicht zum Ausgleich der Fliehkräfte in der oben erläuterten Weise gedreht vorzusehen. Wenn jedoch sich das Verhältnis zwischen den Schnittkräften und den Flehkräften in richtung auf die Schnittkräfte verlagert, kann möglicherweise die oben erläuterte Maßnahme noch nicht ausreichen und es ist dann zusätzlich zu dem Auswuchtgewicht 16, dessen Schwerpunkt auf der Verbindungsgeraden zwischen den beiden Drehachsen 7 und 9 liegt, ein weiteres Auswuchtgewicht an dem Exzenter 8 oder der Ausgangswelle 4 zu befestigen, das bei der Betriebsdrehzahl eine Fliehkraft erzeugt, die betragsmäßig gleich den Schnitt- und Reibkräften entsprechend dem Kraftvektor 27 ist, jedoch in entgegengesetzte Richtung wirkt und an der Drehachse 7 angreift. Selbstverständlich lassen sich diese beiden Auswuchtgewichte in bekannter Weise wiederum zu einem einzigen Auswuchtgewicht zusammenfassen, das gegenüber dem Auswuchtgewicht zur Kompensation der Fliehkraft gemäß dem Kraftvektor 25 eine größere effektive Masse und eine geänderte Schwerpunktlage aufweist. Auch hierbei ist dann im Betriebsfall wiederum die Bedingung erfüllt, daß der an dem Schwerpunkt 29 angreifende Fliehkraftvektor denselben Betrag hat wie der Summenvektor 28, diesem jedoch entgegengesetzt wirkt.Since in high-speed orbital sanders with a small grinding circle diameter, the cutting and frictional forces that occur are smaller by a factor of 10 or more than the centrifugal forces caused by the grinding shoe 3, it is sufficient to provide the already known balancing weight to compensate for the centrifugal forces in the manner explained above. If, however, the relationship between the cutting forces and the entreaties shifts towards the cutting forces, the measure explained above may not be sufficient and it is then in addition to the balancing weight 16, the focus of which is on the connecting straight line between the two axes of rotation 7 and 9 to attach a further balancing weight to the eccentric 8 or the output shaft 4, which generates a centrifugal force at the operating speed which is equal in magnitude to the cutting and frictional forces corresponding to the force vector 27, but acts in the opposite direction and acts on the axis of rotation 7. Of course, these two balancing weights can in turn be combined in a known manner to form a single balancing weight which, compared to the balancing weight for compensating the centrifugal force according to the force vector 25, has a larger effective mass and a changed center of gravity. In this case, too, the condition is met again in the operating case that the centrifugal force vector acting on the center of gravity 29 has the same amount as the sum vector 28, but has the opposite effect.

Der gemäß den Fig. 1 und 2 aufgebaute Schwingschleifer zeigt im Betriebs- oder Lastfall eine größere Laufruhe, als wenn er von dem Werkstück abgehoben ist und freiläuft, weil dann der von dem Schwerpunkt 29 ausgehende Fliehkraftvektor nicht mehr parallel zu dem nunmehr ausschließlich vorhandenen Fliehkraftvektor 25 verläuft; die Schnittkräfte entsprechend dem Kraftvektor 27 sind im Freilauffall auf null zurückgegangen. Wenn diese Verhalten stört, ist es möglich, eine dynamische Verstellung der Lage des Schwerpunktes 29 des Auswuchtgewichtes relativ zu dem Fliehkraftvektor 25 bzw. dem Summenvektor 28 vorzusehen, wie dies in den nachfolgenden Figuren gezeigt ist. Bei diesen Ausführungsbeispielen wird das von der Ausgangswelle 4 auf den Schleifschuh 3 übertragene Drehmoment dazu verwendet, die Verstellung der Kraft- 'vektoren im Last- und im Freilauffall zu verwirklichen.The orbital sander constructed according to FIGS. 1 and 2 shows a greater smoothness in operation or load than when it is lifted off the workpiece and freewheels, because then the fleeing from the center of gravity 29 force vector no longer runs parallel to the centrifugal force vector 25, which is now exclusively present; the cutting forces corresponding to the force vector 27 have decreased to zero in the freewheeling case. If this behavior interferes, it is possible to provide a dynamic adjustment of the position of the center of gravity 29 of the balancing weight relative to the centrifugal force vector 25 or the sum vector 28, as shown in the following figures. In these embodiments, the signal transmitted from the output shaft 4 to the grinding shoe 3 torque is used, the adjustment of the force 'vectors in the load and to realize the free-running case.

Fig. 3 zeigt ausschnittsweise den im aufgebrochenen Teil von Fig. 1 erkennbaren Bereich des Schwingschleifers, soweit er für die Erläuterung erforderlich ist. Für die einzelnen Bauteile werden, soweit sie bereits in den vorhergehenden Figuren dargestellt sind, dieselben Bezugszeichen verwendet.3 shows a section of the region of the orbital sander that can be seen in the broken-open part of FIG. 1, insofar as it is necessary for the explanation. The same reference numerals are used for the individual components, insofar as they are already shown in the previous figures.

Auf dem aus dem Rillenkugellager 6 herausragenden Ende der Ausgangswelle 4 stitzt drehfest eine exzentrisch angeordnete zylindrische Hülse 31, auf der wiederum drehbar, jedoch axial gesichert, der Exzenter 8 angeordnet ist. Die Drehmomentübertragung von der Ausgangswelle 4 auf den Exzenter 8 erfolgt mittels eines drehelastischen Kupplungsgliedes 32, das einerseits drehfest mit der Ausgangswelle 5 in deren Bereich zwischen dem Rillenkugellager 6 und der oberen Stirnseite der exzentrischen Hülse 31 angebracht ist, und das andererseits drehfest mit der Außenumfangsfläche des Exzenters 8 verbunden ist. Das Auswuchtgewicht 16 sitzt wiederum einstükkig an dem Exzenter 8.An eccentrically arranged cylindrical sleeve 31 is seated on the end of the output shaft 4 protruding from the deep groove ball bearing 6, on which the eccentric 8 is in turn rotatably but axially secured. The torque transmission from the output shaft 4 to the eccentric 8 takes place by means of a torsionally flexible coupling member 32, which is mounted on the one hand in a rotationally fixed manner with the output shaft 5 in the area between the deep groove ball bearing 6 and the upper end face of the eccentric sleeve 31, and on the other hand in a rotationally fixed manner with the outer peripheral surface of the Eccentric 8 is connected. The balancing weight 16 in turn sits in one piece on the eccentric 8.

Wie die Fig. 4 und 5 zeigen, treten bei dieser Ausführungsform insgesamt drei Drehachsen auf: Die Drehachse 7 und die Drehachse 9, wie sie bereits vorher beschrieben sind, sowie eine neue Drehachse 33, die parallel zu den Drehachsen 7 und 9 verläuft und sich etwa zwischen diesen befindert, d.h. die Drehachse 33 verläuft mit Abstand zu der Drehachse 7 und auch mit Abstand zu der Drehachse 9, wobei sich jedoch die beiden Drehachsen 7 und 9 an unterschiedlichen Seiten der Drehachse 33 befinden.As shown in FIGS. 4 and 5, a total of three axes of rotation occur in this embodiment: the axis of rotation 7 and the axis of rotation 9, as already described above, and a new axis of rotation 33, which runs parallel to the axes of rotation 7 and 9 and extends located between them, ie the axis of rotation 33 runs at a distance from the axis of rotation 7 and also at a distance from the axis of rotation 9, but the two axes of rotation 7 and 9 are located on different sides of the axis of rotation 33.

Unabhängig von der Belastung des Schwingschleifers 1 soll wiederum die Drehachse 7, die mit der Achse der Ausgangswelle 4 zusammenfällt, und in dem Gehäuse 2 ortsfest ist, möglichst in Ruhe bleiben. Die Drehachse 9 läuft, wie vorher beschrieben, auf einer Kreisbahn um die Drehachse 7 um, so daß der Abstand der beiden Drehachsen 7 und 9 voneinander den Schleifkreisdurchmesser festlegt. Im unbelasteten Fall, bei dem auch praktisch keine Reibungen zwischen dem Gehäuse 2 und dem Schleifschuh 3 auftreten, entstehen zwei Fliehkräfte, nämlich einmal die Fliehkraft entsprechend dem Fliehkraftvektor 25 aufgrund des oszillierenden Schleifschubs 3 und die Fliehkraft, hervorgerufen durch das synchron mit dem Exzenter 8 umlaufende Auswuchtgewicht 16, entsprechend einem Fliehkraftvektor 30, der an dem Schwerpunkt 293 angreift und in Verlängerung der Normalen durch den Schwerpunkt 29 auf die Drehachse 7 verläuft. Damit die beiden Vektoren 30 und 25 zueinander parallel und in entgegengesetzter Richtung verlaufen, ist die in Fig. 3 gezeigte Anordnung so montiert, daß das elastische Kupplungsglied 32 den Exzenter 8 in einer Stellung hält, in der die Normale durch die Drehachsen 7 und 9 auch durch den Schwerpunkt 29 verläuft.Regardless of the load on the orbital sander 1, the axis of rotation 7, which coincides with the axis of the output shaft 4 and is stationary in the housing 2, should remain at rest as far as possible. The axis of rotation 9 runs, as previously described, on a circular path around the axis of rotation 7, so that the distance between the two axes of rotation 7 and 9 defines the grinding circle diameter from one another. In the unloaded case, in which there is practically no friction between the housing 2 and the grinding shoe 3, two centrifugal forces arise, namely the centrifugal force corresponding to the centrifugal force vector 25 due to the oscillating grinding thrust 3 and the centrifugal force caused by the rotating revolving synchronously with the eccentric 8 Balance weight 16, corresponding to a centrifugal force vector 30, which acts on the center of gravity 293 and extends the normal through the center of gravity 29 to the axis of rotation 7. So that the two vectors 30 and 25 run parallel to each other and in the opposite direction, the arrangement shown in Fig. 3 is mounted so that the elastic coupling member 32 holds the eccentric 8 in a position in which the normal through the axes of rotation 7 and 9 also runs through the center of gravity 29.

Sobald an dem Schleifschuh 3 eine Schnittkraft entsprechend dem Vektor 27 abgenommen wird, wird über das elastische Glied 32 ein Drehmoment von der Ausgangswelle 4 auf den Exzenter 8 übertragen. Dieses Drehmoment bewirkt eine Verdrehung zwischen der Ausgangswelle 4 und dem Exzenter 8, und zwar um die zur Ausgangwelle 4 exzentrische Drehachse 33. Bei einer Drehrichtung entsprechend dem Pfeil 26 dreht sich die Ausgangswelle 4 um die Drehachse 33 in derselben Richtung aus der in Fig. 4 gezeigten Ruhelage in die in Fig. 5 gezeigte Arbeitslage.As soon as a cutting force corresponding to the vector 27 is taken from the grinding shoe 3, a torque is transmitted from the output shaft 4 to the eccentric 8 via the elastic member 32. This torque causes a rotation between the output shaft 4 and the eccentric 8, specifically about the axis of rotation 33 eccentric to the output shaft 4. With a direction of rotation corresponding to the arrow 26, the output shaft 4 rotates about the axis of rotation 33 in the same direction from that in FIG. 4 shown rest position in the working position shown in Fig. 5.

Mathematisch gesehen entsteht die Drehung deshalb, weil an der Drehachse 7 ein Drehmoment angreift, das im Uhrzeigesinne wirkt, während durch den Schleifkraftvektor 27 an der Drehachse 9 ein Gegendrehmoment entsteht, die zusammen eine entsprechende Verdrehung der Achsen bezüglich der Drehachse 33 hervorrufen. Da der Fliehkraftvektor 25, der die Fliehkraft des Schleifschuhs 3 veranschaulicht, immer in Verlängerung der Normalen durch die beiden Drehachsen 7 und 9 verläuft, schwenkt er bei der veranschaulichten Relativdrehung zwischen der Ausgangswelle 4 und dem Exzenter 8 ebenfalls im Uhrzeigersinne herum, was zu einer entsprechenden Drehung auch des Schnittkraftvektors 27 und des entstehenden Summenvektors 28 führt. Gleichzeitig mit der erwähnten Relativdrehung schwenkt auch der Fliehkraftvektor 30, der die von dem Auswuchtgewicht 16 ausgehende und an dem Schwerpunkt 29 angreifende Fliehkraft veranschaulicht, herum, jedoch im Gegenuhrzeigersinne, denn dieser Vektor 30 verläuft in der Verlängerung der Normalen durch den Schwerpunkt 29 und die Drehachse 7.Mathematically speaking, the rotation occurs because a torque acts on the axis of rotation 7, which acts in the clockwise direction, while the grinding force vector 27 on the axis of rotation 9 produces a counter torque, which together cause a corresponding rotation of the axes with respect to the axis of rotation 33. Since the centrifugal force vector 25, which illustrates the centrifugal force of the grinding shoe 3, always extends in an extension of the normal through the two axes of rotation 7 and 9, it also swivels clockwise in the illustrated relative rotation between the output shaft 4 and the eccentric 8, which results in a corresponding Rotation of the cutting force vector 27 and the resulting sum vector 28 leads. Simultaneously with the relative rotation mentioned, the centrifugal force vector 30, which illustrates the centrifugal force emanating from the balancing weight 16 and acting on the center of gravity 29, also pivots around, but counterclockwise, because this vector 30 extends through the center of gravity 29 and the axis of rotation in the extension of the normal 7.

Durch die Verdrehung zwischen dem Exzenter 8 und der Ausgangswelle 4 werden also bezüglich der Drehachse 7 der Summenvektor 28 und der Fliehkraftvektor 30 derart in der Ebene gedreht, daß sie parallel zueinander, jedoch in entgegengesetzte Richtungen, wirken.Due to the rotation between the eccentric 8 and the output shaft 4, the sum vector 28 and the centrifugal force vector 30 are thus rotated in the plane with respect to the axis of rotation 7 such that they act parallel to one another, but in opposite directions.

Es ist ersichtlich, daß die Relativdrehung zwischen der Ausgangswelle 7 und dem Exzenter 8 abhängig ist von der Eigenelastizität des drehelastischen Kupplungsgliedes 32, das den an der Drehachse 33 angreifenden Beiden Biegemomenten entgegenwirkt. Durch entsprechende Abstimmung der Eigenelastizität des Kupplungsgliedes 32 kann gewährleistet werden, daß bei jedem Wert der Schnittkraft immer der Summenvektor 28 parallel zu dem Fliehkraftvektor 30 verläuft.It can be seen that the relative rotation between the output shaft 7 and the eccentric 8 is dependent on the inherent elasticity of the torsionally flexible coupling member 32, which counteracts the two bending moments acting on the axis of rotation 33. By appropriate coordination of the inherent elasticity of the coupling member 32, it can be ensured that the sum vector 28 always runs parallel to the centrifugal force vector 30 for each value of the cutting force.

Es ist auch erkennbar, daß das drehelastische Kupplungsglied 32 zu einem Rückdrehen des Exzenters 8 in die Ausgangslage führt, sobald die Schnittkraft, beispielsweise wegen des Abhebens des Schwingschleifers 1 von dem Werkstück verschwindet, so daß wieder die Lage nach Fig. 4 eingenommen wird.It can also be seen that the torsionally flexible coupling member 32 leads to a turning back of the eccentric 8 into the starting position as soon as the Cutting force, for example because of the lifting of the orbital sander 1, disappears from the workpiece, so that the position according to FIG. 4 is assumed again.

Da in der Praxis die auftretenden Schnittkräfte keinen großen Streubereich aufweisen, genügt es, wenn der Exzenter 8 auf der zylindrischen Hülse 31 lediglich zwischen zwei Endstellungen hin- und herdrehbar ist, von denen die eine dem Freilauffall entsprechend Fig. 4 entspricht, während die andere Endstellung auf den Lastfall gemäß Fig. 5 abgestimmt ist. Es sind dazu in bekannter Weise auf der Außenumfangsfläche der zylindrischen Hülse 31 und in der entsprechenden Aufnahmebohrung des Exzenters 8 Anschläge vorzusehen. Die Eigenelastizität des drehelastischen Kupplungsgliedes 32 wird hierbei so bemessen, daß es einerseits im Freilauffall ein zuverlässiges Rückdrehen des Exzenters in die Stellung nach Fig. 4 gewährleistet, andererseits aber bei einer Kraft, die kleiner als die kleinste Schnittkraft ist, ein Verdrehen des Exzenters 8 in die Stellung nach Fig. 5, d.h. die andere Endstellung nicht verhindert.Since in practice the occurring cutting forces do not have a large scattering range, it is sufficient if the eccentric 8 on the cylindrical sleeve 31 can only be rotated back and forth between two end positions, one of which corresponds to the freewheeling case according to FIG. 4, while the other end position 5 is matched to the load case. For this purpose, 8 stops are to be provided in a known manner on the outer peripheral surface of the cylindrical sleeve 31 and in the corresponding receiving bore of the eccentric. The intrinsic elasticity of the torsionally flexible coupling member 32 is dimensioned so that it ensures a reliable return of the eccentric to the position according to FIG. 4 on the one hand in the event of a freewheel, but on the other hand a rotation of the eccentric 8 in at a force which is less than the smallest cutting force 5, ie the other end position is not prevented.

Eine andere Ausführungsform für eine lastabhängige Verstellung des Auswuchtgewichtes 16 zeigt in weiter vereinfachter Form Fig. 6, die ählich wie die Fig. 2, 4 und 5 einen Querschnitt rechtwinklig zu der Ausgangswelle 4 veranschaulicht.Another embodiment for a load-dependent adjustment of the balancing weight 16 is shown in a further simplified form in FIG. 6, which, similar to FIGS. 2, 4 and 5, illustrates a cross section at right angles to the output shaft 4.

Bei dem Ausführungsbeispiel nach Fig. 6 sitzt drehbar auf der Ausgangswelle 4 der Exzenter 8, der wiederum über ein nicht veranschaulichtes drehelastisches Glied zur Drehmomentübertragung mit der Ausgangswelle 4 gekuppelt ist. Unterhalb des Exzenters 8 sitzt ebenfalls drehbar auf der Ausgangswelle 4 das Auswuchtgewicht 16.In the embodiment according to FIG. 6, the eccentric 8 is rotatably seated on the output shaft 4, which in turn is coupled to the output shaft 4 via a non-illustrated torsionally elastic member for torque transmission. The balance weight 16 is also rotatably seated on the output shaft 4 below the eccentric 8.

In dem Exzenter 8 ist ein zweiarmiger Hebel 34 drehbar gelagert, der einerseits in einer Ausnehmung 35 derAusgangswelle 4 und andererseits in einer Ausnehmung 36 des Auswuchtgewichtes 16 eingreift. Dieser zweiarmige Hebel 34 wirkt ähnlich einem Planetenzahnrad eines Platenengetriebes, wobei die Ausgangswelle 4 dem Sonnenrad entspricht.In the eccentric 8, a two-armed lever 34 is rotatably mounted, which engages on the one hand in a recess 35 of the output shaft 4 and on the other hand in a recess 36 of the balancing weight 16. This two-armed lever 34 acts similarly to a planet gear of a plate gear, the output shaft 4 corresponding to the sun gear.

Wenn bei diesem Ausführungsbeispiel von der Ausgangswelle 4 über das nicht gezeigte drehelastische Kupplungsglied ein Drehmoment auf den den Schleifschuh 3 antreibenden Exzenter 8 übertragen wird, und zwar in Richtung des Pfeiles 26, verdreht sich entsprechend dem abgenommenen Drehmoment die Ausgangswelle 4 in dem Exzenter 8, um ihre Drehachse 7. Die Ausgangswelle 4 verschwenkt hierbei den in die Ausnehmung 35 eingreifenden zweiarmigen Hebel 34, der daraufhin das Auswuchtgewicht 16 entgegen der Drehrichtung des Pfeiles 26, nämlich in Richtung eines Pfeiles 37, auf der Ausgangswelle 4 dreht. Die Übertragung der anhand der vorherigen Figuren Ausführlicht erläuterten Kräftediagramme auf das Ausführungsbeispiel nach Fig. 6 zeigt, daß durch die Verschwenkung des Auswuchtgewichtes 16 im Lastfall, d.h. bei. auftretender Schnittkraft, der Fliehkraftvektor, der am Schwerpunkt des Auswuchtgewichtes 16 angreift, in Richtung parallel zu dem Summenvektor aus der Fliehkraft des Schleifschuhs und der Schnittkraft gedreht wird. Sobald die Schnittkraft verschwindet, dreht das drehelastische Kupplungsglied den Exzenter 8 wiederum in die gezeigte Lage zurück, so daß auch für den Freilauffall eine optimale Auswuchtung wie bei dem Ausführungsbeispiel nach Fig. 3 gewährleistet ist.In this exemplary embodiment, if a torque is transmitted from the output shaft 4 via the torsionally elastic coupling member (not shown) to the eccentric 8 driving the grinding shoe 3, in the direction of arrow 26, the output shaft 4 rotates in the eccentric 8 in accordance with the torque that has been removed its axis of rotation 7. The output shaft 4 pivots the two-armed lever 34 engaging in the recess 35, which then rotates the balancing weight 16 against the direction of rotation of the arrow 26, namely in the direction of an arrow 37, on the output shaft 4. The transfer of the force diagrams explained in detail with reference to the previous figures to the exemplary embodiment according to FIG. 6 shows that by pivoting the balancing weight 16 in the load case, i. at. occurring cutting force, the centrifugal force vector, which acts on the center of gravity of the balancing weight 16, is rotated in the direction parallel to the sum vector from the centrifugal force of the grinding shoe and the cutting force. As soon as the cutting force disappears, the torsionally flexible coupling member rotates the eccentric 8 back into the position shown, so that optimal balancing as in the exemplary embodiment according to FIG. 3 is also ensured for the freewheeling case.

Claims (6)

1. An orbital sander (1) having: a casing (2) which contains a driving device and to one of side of which a grinding shoe (3) is movably attached; an eccentric (8) which is coupled to the driving device and sets the grinding shoe (3) in orbital motion in relation to the casing (2) and has two parallel spaced-out axes of rotation (7, 9), one (7) of which is fixed in relation to the casing (2), the other (9) being fixed in relation to the grinding shoe (3); and at least one counterbalance weight (16) which rotates synchronously with the eccentric (8) is disposed fixed on an output shaft (4) of the driving device and compensates the imbalanced produced by the grinding shoe (3) oscillating in relation to the casing (2), characterized in that to compensate the transverse forces (27) caused by the frictional and cutting forces, the centre of gravity (29) of the at least single counterbalance weight (16) is so offset to a normal intersecting the two axes of rotation (7, 9) of the eccentric (8) and lying in a plane at right angles to the axes of rotation ((7, 9) and containing the centre of gravity (29) that the centrifugal force engaging with the centre of gravity (29) has a direction which extends substantially parallel with the summation vector (28) of the centrifugal force (25) of the grinding shoe (3) and the transverse force (17) engaging with the eccentric (8).
2. An orbital sander according to claim 1, characterized in that the mass of the at least single counterbalance weight (16) and/or the distance of its center of gravity (29) from the axis of rotation (7) fixed in the casing (2) is of a dimension such that when the eccentric (8) reaches a predetermined speed a force is generated with a vector equal in amount to but opposite from the summation vector (28).
3. An orbital sander (1) having: a casing (2) which contains a driving device and to one side of which a grinding shoe (3) is movably attached; an eccentric (8) which is coupled to the driving device and sets the grinding shoe (3) in orbital motion in relation to the casing (2) and has two parallel spaced-out axes of rotation (7, 9), one (7) of which is fixed in relation to the casing (2), the other (9) being fixed in relation to the grinding shoe (3); and at least one counterbalance weight (16) which rotates synchronously with the eccentric (8) and compensates the imbalance produced by the grinding shoe (3) oscillating in relation to the casing (2), characterized in that the eccentric (8) and the at least single counterbalance weight (16) are disposed on the output shaft (4) of the driving device to rotate in relation to the output shaft (4) and are coupled thereto via a torsionally elastic member (32), and to compensate the transverse forces (27) caused by the frictional and cutting forces, the distance of the centre of gravity of the counterbalance weight (16) can be automatically so adjusted, in dependence on the cutting force (27), in relation to a normal intersecting the two axes of rotation (7, 9) of the eccentric (8) and lying in a plane at right angles to the axes of rotation (7, 9) and containing the centre of gravity (29) that the centrifugal force engaging with the centre of gravity (29) has a direction which extends substantially parallel with the summation vector (28) of the centrifugal force (25) of the grinding shoe (3) and the transverse force (17) engaging with the eccentric (8).
4. An orbital grinder according to claim 3, characterized in that the counterbalance weight (16) is connected non-rotatably to the eccentric (8), which is rotatably mounted on the output shaft (4) of the driving device, the axis of rotation (33) around which the eccentric (8) can rotate on the output shaft being disposed between the axis of rotation (7) fixed in the grinding shoe (3) and the axis of rotation (9) fixed in the casing (2) and extending parallel to the two axes of rotation (7, 9), and the eccentric (8) is torsionally elastically coupled to the output shaft (4) via the torsionally elastic member (32).
5. An orbital sander according to claim 3, characterized in that the output shaft (4) is torsionally elastically coupled to the eccentric (8) and mounted in the eccentric (8) is a transmission element (34) which, when the eccentric (8) rotates around the output shaft (4), rotates the counterbalance weight (16) around the output shaft (4) in the same direction, but by a larger angle of rotation.
6. An orbital sander according to one of the preceding claims 3 to 5, characterized in that the angle of rotation of the eccentric (8) in relation to the output shaft (4) is limited.
EP86101186A 1985-05-25 1986-01-30 Balanced orbital sander Expired - Lifetime EP0203255B1 (en)

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ES8704109A1 (en) 1987-03-16
EP0203255A3 (en) 1988-03-30
ATE56904T1 (en) 1990-10-15
EP0203255A2 (en) 1986-12-03
DE3518984C2 (en) 1992-03-26
ES555256A0 (en) 1987-03-16
JP2558256B2 (en) 1996-11-27
DE3518984A1 (en) 1986-11-27
US4729194A (en) 1988-03-08

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