GB2359266A

GB2359266A - Eccentric disc sander

Info

Publication number: GB2359266A
Application number: GB0030646A
Authority: GB
Inventors: Justus Lamprecht; Joerg Dehde; Joerg Lemmel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-12-30
Filing date: 2000-12-15
Publication date: 2001-08-22
Anticipated expiration: 2020-12-15
Also published as: GB2359266B; GB0030646D0; CN1301614A; DE19963831A1; CN1165407C; JP2001219353A; DE19963831B4

Abstract

A sander comprises a housing 12 and a grinding disc 14 which is non-rotatably attached to a pin 18. The pin 18 is rotatably and eccentrically mounted relative to a drive shaft 16, whereby the grinding disc 14 can gyrate eccentrically about the drive shaft's axis and rotate about the pin's axis 24. An elastic annular braking means 26 is non-rotatably attached to the housing 10, and comprises a lip (41, Fig. 10) which rubs against the grinding disc 14 and thereby reduces its rotation speed. The braking means 26 also comprises an inwardly directed curved section (34, Figs. 2, 4, 7, 9 and 10) which supports a toothed structure (36, Figs. 2-6). Axial deformation of the braking means 26 reduces its inner diameter whereby the toothed structure (36, Figs. 2-6) engages with a corresponding toothed structure (38, Figs. 3, 5 and 6) on the grinding disc 14, resulting in forced rolling of the grinding disc 14. In one embodiment (Fig. 10), axial deformation of the braking means 26 also disengages the lip (41, Fig. 10) from the grinding disc 14.

Description

2359266 Encentric disk sander with a housing

Background art

The invention relates to an eccentric disk sander according to the preamble of the independent claims.

Eccentric disk sanders are already known, e.g. from DE 42 06 962, in which the rotational speed of the sanding disk is limitable by means of an anti-racing brake. The rotation of the drive motors is transmitted to a shaft, which at the free end carries a fan with an eccentric bore.

Supported rotatably therein is an eccentric pin, which is non-rotatably connected to the sanding disk. The working movement of the sanding disk therefore corresponds to the movement of the eccentric pin and is composed of a rotary movement about the eccentric pin axis and a gyratory movement about the shaft axis. The rotary movement about the eccentric pin axis is, in said case, a result of the bearing friction between eccentric bore and eccentric pin.

When, in the course of proper use of the eccentric disk sander, there is a braking torque acting upon the sanding disk which is greater than the torque effective as a result of the bearing friction between the eccentric bore and the eccentric pin, the sanding disk gyrates without rotating. Without braking torque upon the sanding disk, the rotational speed of the sanding disk may rise as high as the output speed of the shaft and/or fan. To counteract said effect, suitable anti-racing brakes are used. Here it is a case of, for example, a tube-like ring which, to generate friction, is supported by its free end on the sanding disk and therefore limits the rotational speed of the latter. Conversely, the transmissible torque between sanding disk and drive motor is only relatively low because it is determined only by the bearing friction between eccentric pin and the eccentric bore. This may lead, when the sanding disk is pressed hard against the workpiece to 2 be machined, to the braking torque which counteracts the rotary movement becoming too great and to the sanding disk no longer rotating but merely gyrating. The stock removal capacity is therefore reduced.

Advantages of the invention The eccentric disk sander according to the invention having the features of the main claim has the advantage that the sanding disk, as a result of being positively coupled to the braking means, may be made to roll along the braking means. The sanding disk is in said case positively coupled to the housing of the eccentric sander, which gives rise to forced rotation of the sanding disk by the braking element.

is This is particularly important when the sanding disk is pressed by the user with great force onto the surface to be machined. In said situation, despite the increased contact pressure, the rotational speed of the sanding disk is maintainable almost without any reduction because of the forced rolling.

Advantageous developments and improvements of the features indicated in the main claim are possible by virtue of the measures outlined in the subclaims.

It is particularly advantageous when the braking means is held in a nonrotatable and axially movable manner in the housing. The braking torque, which is caused by the force with which the braking means presses against the sanding disk, is, as a result of the latter's being axially displaceable, adjustable in a reproducibly precise manner.

At the same time, a cutting-in of the restricted guidance may be achieved in said manner.

When the braking means moreover takes the form of an elastic function ring and at the same time is connectable through axial deformation to the sanding disk, the result 3 is a simple and inexpensive braking means for limiting the rotational speed in an upward direction, which at the same time forms a positive drive for limiting the rotational speed in a downward direction. Thus, a stationary or merely vibrating state of the sanding disk may be avoided.

-1 It is further advantageous when the elastic function ring in axial direction comprises at least one convex or concave curvature, in particular an inward curvature. Upon axial upsetting, the radius of the curvature is therefore reduced, which leads to a reduction of the inner radius of the function ring.

When the braking means moreover comprises a first frictional/shaped structure which is bringable into engagement with a counterpart structure disposed on the sanding disk, then by merely upsetting the braking means a positive connection may be established between sanding disk and braking means. When the frictional/shaped structure and the associated counterpart structure are of a toothlike design, a further advantage arises because, in said manner, reliable engagement and hence an almost nonslip positive connection is effected.

It is particularly advantageous when the eccentric sander comprises an apparatus for axially deforming the braking means. In said manner, both the braking force of the braking means and the positive connection between braking means and sanding disk are adjustable in a reproducibly precise manner. Here, there is also the possibility of designing the apparatus in such a way that the connection is established on demand automatically, e.g. by electric displacement or upsetting of the function ring.

When the braking means is supported against the housing, a further improvement of the positive nature of the connection between sanding disk and braking means arises.

4 Furthermore, in said manner the braking action may be adjusted independently of the positive drive function. Especially if the braking means is supported, not directly against the housing, but against an adjusting apparatus connected to the housing.

The rotation of the sanding disk is moreover arrestable, with the result that the eccentric disk sander is convertible into an orbital sander because, then, the sanding disk merely gyrates without rotating.

The function ring moreover has holes for ventilation purposes, thereby creating an effective sealing of the dust chamber with limitable partial sanding disk. This prevents means upon the sanding disk great and hence prevents the unintentionally high.

Drawings vacuum in the region of the the pressure of the braking from becoming uncontrollably braking force from becoming An embodiment of the invention is illustrated in the drawings and described in detail below.

Figure 3 Figure 4 Figure 5 Figure 6 The drawings show Figure 1 a cross section through the middle of an eccentric disk sander according to the invention, Figure 2 a diagrammatic cutout of the braking means with sanding disk in braking position, a diagrammatic plan view of a sanding disk with braking means in braking position, a cutout from Fig. 1 with the braking means in positive drive position, a plan view of a sanding disk with braking means in positive drive position, a sanding disk with braking means in orbital position, Figure 7 Figure 8 a cross section of the braking means a cross section of the braking means with reinforcing bow Figure 9 a cross section of the braking means with fixed housing support and Figure 10 a cross section of the braking means with movable housing support.

Description of the embodiment

Figure 1 shows an eccentric disk sander 10 having a housing 12 and a sanding disk 14, which is driven by an output shaf t 16 via an eccentric pin 18. Said output shaf t 16 is non-rotatably coupled to an eccentric carrier 20, which is carries the eccentric pin 18. Said eccentric pin 18 is rotatable with a specific bearing friction about its axis 24 in a rolling- contact bearing 22. Said eccentric pin 18 is nonrotatably coupled to the sanding disk 14 and rotatable with a specific eccentricity Ilell relative to the output shaft 16. The sanding disk 14 therefore gyrates about the axis 24 with the eccentricity Ilel, of the output shaft 16 and simultaneously rotates about the axis of the eccentric pin 18.

Fastened to the housing 12 is a braking means 26 in the form of an elastic function ring. The latter is disposed in such a way that it rubs against the sanding disk 14 and hence limits the rotational speed of the sanding disk 14 particularly when the latter is not resting against a workpiece and is at risk of racing. Situated above the sanding disk 14 and below the motor compartment 28 is a dust chamber 30, which surrounds the rollingcontact bearing 22 and from which the dust arising during sanding may be extracted in an outward direction away from the workpiece. The braking means 26 is in said case disposed in such a way that it sealingly embraces the dust chamber 30.

6 The braking means 26 and the top of the sanding disk 14 are in the present case so designed that by means of an apparatus 32 the braking means 26 is axially displaceable and may therefore be upset. Through axial deformation a positive connection may be established between the braking means 26 in the form of an elastic function ring and the top of the sanding disk 14. The sanding disk 14 has, for said purpose, a counterpart structure 38 to the first structure 36 (not shown here) of the braking means 26.

Figure 2 shows a further embodiment of a sanding disk 14 and a braking means 26 in a sectional view. The braking means 26 in said case takes the form of an elastic function ring, which has a convex curvature 34. Here, traces of a first tooth-like structure 36 may be seen, which corresponds with the tooth-like counterpart structure 38 disposed above the sanding disk 14.

Figure 3 shows the plan view according to Figure 2. The elastic function ring 26 carries at the inside the first shaped structure 36, which corresponds with the counterpart structure 38 at the outside of the top edge of the sanding disk 14. Just as in Figure 2, in the illustrated operating position there is no positive connection but merely a frictional engagement connection between the function ring 26 and the sanding disk 14. The braking means 26 ' in said position of being axially supported against the top of the sanding disk 14, merely limits the rotational speed of the sanding disk 14.

Figure 4 shows a cutout f rom Figure 1 with the braking means in positive drive position. Here, the sanding disk 14 with the counterpart structure 38 is positively connected to the elastic function ring 26, the latter by its convex curvature 34, which comprises the first structure 36. The positive locking is achieved through 7 axial deformation, in particular upsetting, of the elastic function ring 26.

Figure 5 shows a diagrammatic plan view of 14 with the braking means 26 in the form function ring in positive drive position. function ring 26 is positively connected a sanding disk of an elastic The elastic by its f irst structure 36 to the counterpart structure 38 of the sanding disk 14 so that the sanding disk 14, as a result of its orbital movement, engages with its counterpart structure 38 into the first structure 36 and is compelled to roll along it.

Figure 6 shows a diagrammatic plan view of a sanding disk 14 with the braking means 26 in the arrested state.

Here, the braking means 26 is axially upset in such a way that the first structure 36 in a plurality of regions is positively connected to the counterpart structure 38. In said manner, a rolling of the counterpart structure 38 the sanding disk 14 in the non-rotatable structure 36 of of the braking means 26 is prevented, with the result that the sanding disk 14 itself is prevented from rotating so that it may only gyrate with the eccentricity llell, just as is the case with an orbital sander.

Figure 7 shows the prof ile of a braking means 26. In the region of the convex curvature 34 the braking means 26 is substituted by another material, which is of a high radial stiffness while being of a low axial stiffness. Thi s may be achieved, for example, by applying further materials using a multicomponent injection moulding technique or by incorporating fibre materials.

Figure 8 shows a braking means 26, which is reinforced by a bow 40. Said bow 40 may be made both of a suitable plastics material and of metal, thereby ensuring a 8 particularly high radial stiffness.

Figure 9 is a sectional view of a braking means 26, which is supported in a middle region of the housing 12. This prevents the braking force or the braking torque from becoming too great in the event of extreme axial upsetting of the braking means 26. In the present case it is also conceivable to effect the support, not directly against the housing 12, but against a displaceable element connected to the housing, thereby enabling the braking force to be adjusted independently of the axial upsetting of the elastic function ring 26.

Figure 10 shows an improved construction of the principle illustrated in Figure 9. Here, the braking ring 26 is supported in an articulated manner on the housing 12 or a support element. Consequently, upon axial upsetting, the region below the convex curvature 34 with the braking lip 41 rotates upwards about the centre of rotation 42. This leads to the reduction of the braking force and is meaningful in the positive drive position, in which the rotational speed limitation by means of the braking ring is not required; the rotational speed is determined in said situation by the gyratory frequency.

9

Claims

Claims

1.

4.

2.

3.

Eccentric disk sander having a housing (12), in which a motor via an output shaft (16) moves a sanding disk (14), wherein the output shaft (16) is non-rotatably coupled to an eccentric carrier (20), which carries an eccentric pin (18), which is rotatable, particularly in a rolling- contact bearing (22), with a specific bearing friction about its axis (24) with a specific eccentricity Ilell relative to the output shaft (16) and which is non-rotatably coupled to the sanding disk (14) so that the latter gyrates with the eccentricity Ilell about the axis of the output shaf t (16) and at the same time rotates about the axis of the eccentric pin (18), wherein braking means (26) limit the rotational speed of the, in particular, free-running sanding disk (14) especially when the sanding disk (14) is not resting against a workpiece or the like, characterized in that the at least one annular braking means (26) at its inside is at least in sections positively connectable, in particular couplable, to the sanding disk (14).

Eccentric disk sander according to one of the preceding claims, characterized in that the braking means (26) is disposed in a nonrotatable and axially movable manner in the housing (12).

Eccentric disk sander according to claim 1 or 2, characterized in that the braking means (26) takes the form of an elastic function ring and through axial deformation is connectable, in particular couplable, to the sanding disk (14).

Eccentric disk sander according to claim 3, characterized in that the function ring (26) in axial direction comprises at least one convex curvature (34), particularly in an inward direction, having an inner radius and an outer radius, wherein the inner radius decreases upon axial upsetting of the function ring (26).

is 5.

Eccentric disk sander according to one of the preceding claims, characterized in that the braking means (26) comprises a first structure (36) as a shaped structure, which is bringable into engagement with a counterpart structure (38) disposed on the sanding disk.

6. Eccentric disk sander according to claim 5, characterized in that the f rict ional /shaping structure (36) and the counterpart structure (38) are of a tooth-like design.

Eccentric disk sander according to one of the preceding claims, characterized in that the eccentric disk sander (10) comprises an apparatus for axially deforming the braking means (26).

8. Eccentric disk sander according to one of the preceding claims, characterized in that the sanding disk (14) is arrestable in its rotary movement, in particular through deformation of the braking means (26).

9.

Eccentric disk sander according to one of the preceding claims, characterized in that the braking means (26) is supportable, in particular in a region below the convex curvature (34), against the housing (12).

10. Eccentric disk sander according to claim 3, characterized in that the function ring (26) has holes, in particular to allow air to pass through.