GB2338916A

GB2338916A - Orbital grinder

Info

Publication number: GB2338916A
Application number: GB9914079A
Authority: GB
Inventors: Steffen Wuensch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-06-30
Filing date: 1999-06-16
Publication date: 2000-01-12
Anticipated expiration: 2019-06-16
Also published as: CN1145542C; DE29811654U1; FR2780326B1; FR2780326A1; CN1241467A; GB9914079D0; GB2338916B

Description

2338916 Oscillafing- grinder

Prior art

The starting point of the invention is an oscillating grinder according to the precharacterising clause of claim 1.

For optimal machining of surfaces with the aid of oscillating grinders it is recommended that the grinding stroke and driving speed of the oscillating plate receiving the grinding tool be selected in a manner corresponding to the specific grinding task. Thus, for example, a large grinding stroke is expedient for removing paints and varnishes, and a small grinding stroke for intermediate and finish-grinding. Since all the known oscillating grinders possess a fixed grinding stroke, and the grinding plate therefore performs a circling oscillating movement with constant eccentricity, the craftsman or do-it-yourself enthusiast is obliged to keep on hand, and use as appropriate, a number of oscillating grinders with different grinding strokes in order to achieve results which meet demanding quality standards.

In order to produce different grinding strokes with a single oscillating grinder, it has already been proposed (DE 198 20 873.1) to construct the eccentric as an integrated component of the oscillating plate and to couple the latter to the drive shaft in such a way that it can be changed. In this event, all that remains necessary is to keep available a number of oscillating plates with different eccentricity of the eccentric, which oscillating plates are then changed on the oscillating grinder, depending upon the grinding task.

Advantages of the invention 2 By contrast, the oscillating grinder according to the invention with the features in claim I has the advantage that it can be operated with two different grinding strokes which can be selected manually in dependence upon the machining requirements. Under these circumstances, two different grinding strokes are sufficient to carry out a multiplicity of different grinding tasks in a manner approximating to the optimum. In order to set the different grinding strokes, it is merely necessary to change the direction of rotation of the working shaft by means of a hand switch which is provided, the desired coarse or fine grinding with a large or small oscillating stroke coming about automatically. Reversal of the direction of rotation is preferably produced by a reversible construction of the electric motor, which drives the working shaft either directly or else indirectly via a gear unit, and of the electrical system for switching over the direction of rotation, but can also be brought about by suitably designing a gear unit, which is disposed between the electric motor and the working shaft, and also a mechanical system for switching over the gear unit.

In addition, the switching-over of the direction of rotation of the working shaft for the purpose of obtaining different grinding strokes has the advantage that, according to a preferred form of embodiment of the invention with the system for switching over the direction of rotation, it is also possible, without any problems, to perform switching-over of the rotational speed of the working shaft at the same time, so that, for example, a low rotational speed of the working shaft can be associated with a large grinding stroke, and a high rotational speed with a small grinding stroke. In this way, a grinding speed which is suited to the material and which contributes substantially to improving the results of grinding is set automatically. In oscillating grinders with regulation of the rotational speed, the rotational speed which is predetermined in each case may additionally be varied within a limited range.

3 Advantageous further developments of, and improvements to the oscillating grinder indicated in claim I are possible as a result of the. measures set out in the other claims.

The eccentric according to the invention having eccentricity which differs in inverse directions of rotation can be produced in a particularly simple way if, according to one advantageous form of embodiment of the invention, the said eccentric is composed of a coaxial transmission member connected to the working shaft in a torsion-proof manner and an eccentric member which is held pivotably on the said transmission member, carries an eccentric jourrial extending as a prolongation of the working shaft and mounted in the oscillating plate, and interacts in such a way with an entrainment means disposed on the transmission member, that the axis of the eccentric j ourrial has a different eccentricity from the axis of the working shaft when the abutment of the eccentric member against the entrainment means changes as a result of reversal of the direction of rotation.

It is possible to construct the entrainment means and eccentric member in a different way, a fact which forms the subject of the other claims 2 to 9. What is common to all the types is that the rotation of the working shaft is transmitted to the oscillating plate through the abutment, on one side, of the eccentric member against the entrainment means with a first eccentricity and, after reversal of the direction of rotation, is transmitted to the said oscillating plate through the abutment of the eccentric member against the other side of the entrainment means with a second eccentricity, the first eccentricity giving rise to a large oscillating stroke of the oscillating plate and the second eccentricity giving rise to a small oscillating stroke of the said oscillating plate.

Drawings 4 The invention is explained in greater detail in the description below with the aid of exemplified embodiments represented in the drawings, in which:

figure 1 shows, in the form of a detail, a side view of an oscillating grinder, partially cut away, figure 2 shows a view from below, in the direction of the arrow 11 in figure 1, of an eccentric in the oscillating grinder according to figure 1, figure 3 shows a longitudinal section through an eccentric in the oscillating grinder illustrated in figure 1, according to another exemplified embodiment, figure 4 shows a view from below of the eccentric in figure 3, figure 5 shows a Jongitudinal section through an eccentric according to a third exemplified embodiment, figure 6 shows a view from below of the eccentric in figure 5, figure 7 shows a longitudinal section through an eccentric according to a fourth exemplified embodiment, figure 8 shows a view from below of the eccentric in figure 7, figure 9 shows a longitudinal section through an eccentric according to a fifth exemplified embodiment, and figure 10 shows a view from below of the eccentric in figure 9.

Description of the exemplified embodiments

The oscillating grinder represented in side view, partially cut away, in figure I has a housing 10 in which an electric motor, which is not represented here but which drives a working shaft 11, is received. A blower or fan wheel 12 belonging to a suction blower for extracting grinding dust is received, in a torsion-proof manner, on the free end of the working shaft I I which is rotatingly mounted in the housing 10. The fan wheel 12 has a fan hub 13, which is slipped onto the end of the working shaft in a torsion-proof manner, and fan vanes 14 protruding radially from the said hub, and is supported in the housing 10 via a pivot bearing 15. A connecting piece 16 for a dust-catching bag, which connecting piece forms the pressure exit of the suction blower, is constructed on the housing 10 in the vicinity of the fan wheel 12. Suspended from the underside of the housing 10 by means of elastic oscillating elements 18 is an oscillating plate 17 which can be set in circling or orbital oscillating motion via an eccentric 19 driven by the working shaft 11, and the orbital circle of which is determined by the eccentricity e, that is to say the radial offset of the eccentric axis 191 in relation to the axis I 11 of the working shaft 11. Fastened to the oscillating plate 17 is a grinding tray 20 which is constructed to receive a grinding means. For example, a grinding disc is attached to the grinding tray 20 by means of an adhesive covering provided on the latter. The eccentric 19 is, on the one hand, seated in a torsion-proof manner on the working shaft I I or in a receptacle 21 constructed in the fan hub 13 and, on the other hand, is rotatingly mounted in a bearing pot 171 constructed in one piece on the oscillating plate 17. For this purpose, a pivot bearing 22, which is constructed, for example, 6 as a grooved ball bearing with an inner bearing ring and an outer bearing ring and balls disposed between them, is received in the bearing pot 171 in an axially nondisplaceable manner. When the electric motor is switched on, the rotating working shaft I I entrains the eccentric 19 and the latter sets the oscillating plate 1-7 in circling or orbital oscillating motion, since the elastic oscillating elements 18 secure the oscillating plate 17 to the housing 10 against rotational entrainment.

For the purpose of performing different grinding tasks which require oscillating strokes of the oscillating plate 17 which differ in size in order to obtain optimum grinding results, the oscillating grinder is provided with a manual system for switching over the grinding strokes. The said system has a manual change-over switch secured to the housing 20, which switch is not represented here but by means of which the working shaft I I can be selectively switched over into one of two inverse directions of rotation. The switching-over of the direction of rotation of the working shaft 11 is brought about, for example, through the fact that the electric motor is of reversible construction with electrical switching-over of the direction of rotation and revolves in one or other direction of rotation, depending upon the switching position of the change-over switch. Furthermore, the eccentric 19 is constructed in such a way that it possesses, in inverse directionsof rotation, a different eccentricity e, and e in each case, that is to say, for example, as is indicated in figure 3, a large eccentricity el in the case of an anticlockwise direction of rotation and a small eccentricity e2in the case of a clockwise direction of rotation. The working shaft 11 revolves anticlockwise or clockwise, depending upon the direction of rotation in which the electric motor is switched on, and as a result of the different eccentricity e, or e2of the eccentric 19, the oscillating plate 17 performs a large grinding stroke with an oscillating movement having a large orbital circle diameter, or a small oscillating stroke with an oscillating movement having a small orbital circle diameter. In a manner of which no further details are 7 represented here, the reversal of the direction of rotation of the electric motor is further connected with a switching-over of rotational speed, a low rotational speed n, being associated with the direction of rotation with large eccentricity e,, and a high rotational speed n2being associated with the direction of rotation with small eccentricity e2. Because of the combining of the switching-over of rotational speed with the switching-over of the grinding stroke of the oscillating plate 17, a grinding speed which is suited to the material is always set. In the case of oscillating grinders in which it is possible to regulate the rotational speed, the rotational speed set in each case can be further varied within limits.

Five different exemplified embodiments of the eccentric 19 for producing the different eccentricities e, and 9 in inverse directions of rotation of the said eccentric are represented in the drawings. What is common to all the exemplified embodiments is that the eccentric 19 has a coaxial transmission member 23 connected to the working shaft 11 in a torsionproof manner, and an eccentric member 24 which is held on the transmission member 23 in a pivotable manner carries an eccentric journal 25 extending as a prolongation of the working shaft I I and mounted in the oscillating plate 17, namely via the pivot bearing 22, and interacts in such a way with an entrainment means 26 disposed on the transmission member 23 that, when the abutment of the eccentric member 24 against the entrainment means 26 changes as a result of reversal of the direction of rotation, the axis of the eccentric journal 25, which axis coincides with the eccentric axis 191 of the eccentric 19, has a different eccentricity e, that is to say is at a different radial distance from the axis 111 of the working shaft I I - In one direction of rotation, the eccentric member 24 abuts against one side of the entrainment means 26 and thereby transmits a large eccentricity e, to the oscillating plate 17 and, when the direction of rotation is switched over, the pivotable eccentric member 24 8 is laid against the other side of the entrainment means 26 and transmits a smaller eccentricity e2 to the oscillating plate 17.

In the exemplified embodiments in figures 1 and 2, figures 3 and 4, and also figures 5 and 6, the entrainment means 26 is constructed as a recess 27 let into the transmission member 23 and having two flanks 271, 272 located opposite one another in the direction of rotation, and the eccentric member 24 is pivotably enclosed in the recess 27 in such a way that it abuts, when the directions of rotation change, against one of the two flanks 271, 272 and is entrained in the direction of rotation. Under these circumstances, the recess 27 has the contour of a circular segment, the centre of which is offset radially in relation to the axis of the transmission member 23, which axis coincides with the axis I I I of the working shaft. The point of the segment, that is to say the transition from the flank 271 to the flank 272, is provided with a radius of curvature 273.

In the two exemplified embodiments according to figures 1 and 2 on the one hand, and figures 3 and 4 on the other, the eccentric member 24 is provided, for mounting in a pivoting manner on the transmission member 23, with a bearing stud 28 which projects axially on the side of the eccentric member 24 facing away from the eccentric journal 25, and is constructed in one piece with the said eccentric member 24. The bearing stud 28 is rotatably received in a let-in portion 29 disposed in the point of the segment of the recess 27. Under these circumstances, the radius of curvature 273 is adapted to the diameter of the bearing stud 28, or rather to the clear diameter of the let-in portion 29. The eccentric member 24 in the exemplified embodiment in figures I and 2 has a circular segment-shaped contour with a segment angle which is smaller than that of the recess 27, which is likewise circular segment-shaped, in the transmission member 23, so that the eccentric member 24 is able to pivot in the recess 27 about a 9 pivoting angle and alternately abuts, with its side flanks 241, 242, flat against the flanks 271 or 272 of the recess 27. The point of the segment of the circular segment-shaped eccentric member 24 is likewise provided with a radius of curvature 243, which is adapted to the radius of curvature 273 of the recess 27.

in the exemplified embodiment in figures 3 and 4, both the flanks 271, 272 of the recess 27 and also the flanks 241 and 242 of the eccentric member 24 are bent, the lateral flanks 241, 242 of the eccentric member 24 extending approximately parallel to one another after the bending point. Provided on the lateral flanks 24 1, 242 in each case, is a stop face 30 which projects slightly above the lateral flanks 241, 242 and by means of which the eccentric member 24 abuts against the bent flanks 271 or 272 of the recess 27, depending upon the direction of rotation.

In the exemplified embodiment in figures 5 and 6, the eccentric member 24 is constructed, for mounting in a pivoting manner inside the recess 27 inthe transmission member 23, as a rectangular crosspiece 31 which extends diametrically across the eccentricjournal 25 and is supported, by suitably shaped crosspiece ends, on the one hand in a form-locking manner against the radius of curvature 273 of the point of the segment of the recess 27, and on the other hand, displaceably on the circular arc 274 of the circular segment-shaped recess 27. In figures 5 and 6, the eccentric journal 25 is represented in a central position. If the working shaft 11, and with it the transmission member 23, rotates anticIockwise, the flank 271 of the recess 27 entrains the eccentric member 24 (crosspiece 3 1) via the crosspiece side 311, and the rotational movement of the transmission member 23 is transmitted with small eccentricity to the oscillating plate 17. If the transmission member 23 rotates clockwise, the transmission member 23 entrains the eccentric member 24 (crosspiece 3 1) via the flank 272 of the recess 27 and the crosspiece side 312 of the crosspiece 31, and the rotational movement of the transmission member 23 is transferred with larger eccentricity to the oscillating plate 17.

In the exemplified embodiment of the eccentric 19 according to figures 7 and 8, the recess 27 has a kidney-shaped contour 32 and the eccentric member 24 enclosed in the recess 27 has an outer contour 33 which is identical and kidneyshaped but is, by contrast, reduced in its dimensions to some extent. As a result of this, the eccentric member 24 is secured pivotably in one point 321 of the kidney of the kidney contour 32 and abuts, in one direction of rotation, against the concave bow 322 of the kidney of the kidney contour 32 (represented in broken lines in figure 7), and in the other direction of rotation, against the convex bow 323 of the kidney of the kidney contour 32 (represented in solid lines in figure 8). In the two abutments, there is a change in the radial distance of the axis 191 of the eccentric journal 2 5 from the axis I I I of the transmission member 23, and thereby in the eccentricity e of the eccentric 19.

In the exemplified embodiment of the eccentric 19 in figures 9 and 10, the entrainment means 26 on the transmission member 23 is formed by an axially protruding pin 34 which penetrates into an arcuate slot 35 constructed in the eccentric member 24. The eccentric member 24 is, once again, rotatably received by means of the bearing stud 28 in the let-in portion 29 which is disposed so as to be radially offset in relation to the axis 111 of the transmission member 23. The entrainment means 26 (pin 34) strikes against one or other end of the slot 35, depending upon the direction of rotation of the transmission member 23, and entrains the eccentric member 24 in one or other direction of rotation, the eccentric 19 having, in the same way, two different eccentricities el and e2

Claims

Claims

Oscillating grinder with an oscillating plate (17) for receiving a grinding tool, which oscillating plate is suspended from a housing (10) by means of elastic oscillating elements (18) and can be set, via an eccentric (19) driven by a working shaft (11), in a circling or orbital oscillating motion, the orbital circle of which is determined by the eccentricity (e) of the eccentric (19), characterised in that the working shaft (11) rotates in one of two inverse directions of rotation selectively, and that the eccentric (19) is constructed in such a way that it possesses different eccentricities (e,, e2) in inverse directions of rotation.
2. Oscillating grinder according to claim 1, characterised in that the eccentric (19) has a coaxial transmission member (23) connected to the working shaft (11) in a torsion-proof manner, and an eccentric member (24) which is held on the transmission member (23) in a pivotable manner, carries an eccentric joumal (25) extending as a prolongation of the working shaft (11) and mounted in the oscillating plate (17), and interacts in such a way with an entraimnent means (26) disposed on the transmission member (23) that, when the abutment of the eccentric member (24) against the entrainment means (26) changes as a result of reversal of the direction of rotation, the axis (191) of the eccentric journal (25) has a different eccentricity (e,, e) in relation to the axis (111) of the working shaft.

12
3. Oscillating grinder according to claim 2, characterised in that the entrainment means (26) is constructed as a recess (27) let into the transmission member (23) and having two flanks (271, 272) located opposite one another in the direction of rotation, and thar the eccentric member (24) is pivotably enclosed in the recess (27) in such a way that it abuts, when the directions of rotation change, against one of the two flanks (271, 272) in each case.
4. Oscillating grinder according to claim 3, characterised in that the recess (27) has the contour of a circular segment, the centre of which is offset radially in relation to the axis (111) of the transmission member (23), and that the point of the segment is provided with a radius of curvature (273).
5. Oscillating grinder according to claim 4, characterised in that the eccentric member (24) carries, for mounting in a pivoting manner, a bearing stud (28) which projects axially on the side facing away from the eccentric journal (25) and is rotatably received in a let-in portion inside the recess (27), which let-in portion is disposed in the point of the segment of the said recess (27).
6. Oscillating grinder according to claim 4 or 5, characterised in that the eccentric member (24) has a circular segment-shaped contour with a segment angle which is smaller than that of the recess (27), or a substantially rectangular contour which is adapted to the circular segment shape of the recess (27) in such a way that, when the directions of rotation change, one longitudinal side (241, 242) 13 of the eccentric member (24) abuts, in each case, against one flank (271, 272) of the recess (27).
7. Oscillating grinder according to claim 4, characterised in that the eccentric member (24) is constructed, for mounting it in a pivoting manner on the transmission member (23), as a" rectangular crosspiece (3 1) which extends diametrically across the eccentric journal (25) and is supported, by suitably shaped crosspiece ends, on the one hand in a form- locking manner on the radius of curvature (273) of the point of the segment of the recess (27), and on the other hand, displaceably on the circular arc (274) of the recess (27).
8. Oscillating grinder according to claim 3, characterised in that the recess (27) has a kidney-shaped contour (32) and the eccentric member (24) has an outer contour (33) which is identical and kidney-shaped but is, by contrast, reduced in its dimensions to some extent, so that the eccentric member (24) is secured pivotably in one point (321) of the kidney and abuts, in one direction of rotation, against the concave bow (322) of the kidney, and in the other direction of rotation, against the convex bow (323) of the kidney.
9. Oscillating grinder according to claim 2, characterised in that the entrainment means (26) is formed by a pin (34) axially protruding on the transmission member (23), which pin penetrates into an arcuate slot (35) constructed in the eccentric member (24), and that the eccentric member (24) carries, for mounting it in a pivoting manner, a bearing stud (28) which projects axially from the side facing away from the eccentric j ourrial (2 5) and is rotatably received 14 in a let-in portion (29) disposed in the recess (27) so as to be radially offset in relation to the axis (I 11) of the transmission member (23).
10. Oscillating grinder according to one of claims I to 9, characterised in that the switching-over of the direction of rotation of the working shaft (11) is connected with a switching-over of the rotational speed of the said working shaft (11), a low rotational speed (n) being preferably associated with the direction of rotation of the eccentric (19) with large eccentricity (e), and a high rotational speed (P being preferably associated with the direction of rotation of the eccentric (19) with small eccentricity (e2)'
11. An oscillating grinder with an oscillating plate for receiving a grinding tool, the oscillating grinder being substantially as herein described with reference to the accompanying drawings.