GB2328632A

GB2328632A - Eccentric plate sander

Info

Publication number: GB2328632A
Application number: GB9818439A
Authority: GB
Inventors: Guenther Berger; Roland Walz; Stefan Heess; Mario Frank
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-09-01
Filing date: 1998-08-24
Publication date: 1999-03-03
Anticipated expiration: 2018-08-24
Also published as: DE19738095A1; GB9818439D0; ITMI981910A1; IT1301926B1; DE19738095C2; ITMI981910A0; GB2328632B

Abstract

The sander has a motor housing, in which a motor drives a shaft and the latter drives an eccentric shaft, which is non-rotatably connected to an abrasive plate and moved in an eccentrically gyrating and rotating manner relative to the axis of the shaft, the eccentric shaft being rotatable relative to the shaft and it being possible - for changing over an operating mode of the eccentric plate sander - to slow down the movement of the abrasive plate by means of a mechanically acting braking device, which is axially displaceable relative to the eccentric shaft, and a frictional engagement being achievable between the eccentric shaft and the braking device. It is provided that associated with a structural element (60) effecting the axial displacement of the braking device is a ring element (84), which is disposed coaxially with the shaft (30) and radially away from which at least one running surface (88) springs, which is in seating contact with frontal helical surfaces (92) of the structural element (setting ring 60), which ascend in a thread-like manner.

Description

2328632 1 Eccentric Iplate sande The invention relates to an eccentric

plate sander having the features described in the preamble of claim 1 -

Background art

Eccentric plate sanders of the type described are known. Here, the rotation of an electric drive motor is converted, by transmission via a right-angle gear to a shaft g an eccentric journal, into the working motion of an abrasive plate. Said working motion is composed of a rotary motion and a gyratory motion of the abrasive plate. This is achieved in that the eccentric journal forms part of an eccentric shaft which is arranged inside the shaft in the form of a hollow shaft with an eccentricity relative to said shaft. The eccentric shaft is non-rotatably connected to the abrasive plate. When the hollow shaft is set in rotation by the drive motor, the eccentric journal also rotates and gyrates jointly with the eccentric shaft and the abrasive plate with the given eccentricity about the axis of rotation of the hollow shaft. The abrasive plate and the eccentric shaft co-rotate with the hollow shaft as a result of the bearing friction at the eccentric journal. If, during use of the eccentric plate sander for its intended purpose, there is a braking torque acting upon the abrasive plate or the eccentric shaft which is greater than the torque resulting from the bearing friction of the eccentric shaft in the hollow shaft, abrasive plate and eccentric shaft gyrate without rotating.

The abrasive plate is to rotate during operation only when a relatively high removal of material is desired. Rotating of the abrasive plate is undesirable when the driven abrasive plate is not in contact with the workpiece, i.e. when there is no 2 braking torque, with the result that the rotational speed of the abrasive plate may increase m an uncontrolled manner. To counteract said so-called rev-up effect, it is known to equip the eccentric plate sander with a braking device which, during no-load operation or when a minimal abrasion capacity of the abrasive plate is desired, prevents rotation of the abrasive plate.

A known braking device comprises an miternal geared wheel, which is axially displaceable relative to the eccentric shaft and the internal gearing of which is movable into engagement with a spur-toothed wheel nonrotatably disposed on the eccentric shaft. In said case, the internal geared wheel is disposed concentrically with the axis of rotation of the shaft and the spur-toothed wheel is disposed concentrically with the axis of rotation of the eccentdc shaft. In accordance with the axial setting of the internal geared wheel, the latter is in or out of engagement with the spur-toothed wheel. For the axial setting of the internal geared wheel it is known to equip the latter with an operating element which is accessible to the operator, the internal geared wheel as a result of its rotation relative to a housing of the eccentric plate sander being in effective contact with housing-fixed supporting surfaces, which act upon helical surfaces of the internal geared wheel ascending in a thread-like manner.

Advantages of the invention The eccentric plate sander according to the invention having the features described in claim 1 offers the advantage that the axial setting of the braking device may be realized in a simple manner. By virtue of the fact that associated with a structural element effecting the axial setting of the braking device is a ring element, which is disposed coaxially with the shaft and radially away from which at least one ntrining surface springs, which is in seating contact with frontal helical surfaces 3 of the braking device ascending in a thread-like manner, a rotation of the braking device relative to a housing of the eccentric plate sander may easily be converted into an axial displacement. Particularly when the running surface comprises a seating surface coming resiliently into contact with the helical surface, it is easily possible to achieve a compensation of backlash arising as a result of manufacturing tolerances. Thus, an exact consistently reliable axial setting of the braking device is possible.

In a preferred refinement of the invention it is provided that there is simultaneously springing away from the nng element at least one arresting means, by means of which an adjusted tooth clearance of a right-angle drive of the eccentric plate sander is arrestable. A displacement of the adjusted tooth clearance, e.g. as a result of vibrations arising during the intended application, is therefore reliably prevented. It is possible to minimize wear and hence increase the life of the eccentric plate sander as a whole.

Further advaritageous refinements of the invention are evident from the remaining features described m the sub-claims.

Drawings Them follows a detailed description of an embodiment of the invention with reference to the accompanying drawings. Said drawings show:

Figure 1 a sectional view of an eccentric plate sander; Figure 2 an enlarged view of a ring element; 4 Figure J3 an iriternal geared wheel of a brakmg device; Figure 4 an enlarged detail view of the ring element; Figure 5 a detail view of arresting of a tooth clearance adjustment of a rightangle drive and a finther detail view of the ring element.

Description of the embodiment

Figure 1 shows a sectional view of an eccentric plate sander 10. The eccentric plate sander 10 comprises a motor housing 12, inside which an electric motor 14 is disposed. Flange-mounted on the motor housing 12 is a right-angle drive housing 16, which accommodates a right-angle drive 26 effectively connected to an abrasive plate 18. The right-angle drive 20 comprises a bevel wheel 24, which is disposed non-rotatably on a motor shaft 22 and meshes with a ring gear 26. The ring gear 26 concentrically and non-rotatably embraces a shaft 30 in the form of a hollow shaft, which is rotatable about an axis of rotation 28. The hollow shaft 30 is supported in the right-angle drive housing 16 in bearings 32 and 34.

The hollow shaft 30 has a stepped through-bore 36 which is eccentric relative to the axis of rotation 28. Disposed concentricafly in the bore 36 is an eccentric shaft 38, the longitudinal axis 40 of which extends parallel to the axis of rotation 28 with an eccentricity. The eccentric shaft 38 is guided in bearings 42 and 44. The eccentric shaft 38 at its bottom end carries the abrasive plate 18.

Supported on the bearing 42 is a spring element 46 which carries a spurtoothed wheel 48, an annular disc 50 with an external gearing 52, a counterpart disc 54 and, as an axial locking device, a snap ring 56.

The spur-toothed wheel 48 and the counterpart disc 54 are disposed in a nonrotatable, axially displaceable manner on the eccentric shaft 38. The annular disc 50 is rotatable in the manner of an idler wheel relative to the eccentric shaft 38. It is supported in a braking manner between the spur-toothed wheel 48 and the counterpart disc 54.

An internal geared wheel 58 and a sIMng ring 60 are disposed concentrically with the hollow shaft 30. The internal geared wheel 58 has an internal gearing 62 lying on a pitch circle tangential to an external gearing 64 of the spur-toothed wheel 48. The setting ring 60 has an internal gearing 66 lying on a pitch circle tangential to the external gearing 52 of the annular disc 50. The setting ring 60 is disposed in an axially displaceable manner so that it may be moved into and out of engagement with the annular disc 50. A long-face pinion 70, which is rotatable by means of a lever arm 72, is used as operating means 68 for axially displacing the setting ring 60. A tooth system 74 of the longface pinion 70 is meshed with a changeover tooth system 76 disposed on the outer periphery of the setting ring 60.

The right-angle drive housing 16 comprises a housing bottom part 78 and a housing cover 80. When the housing bottom part 78 and the housing cover 80 are joined by means of clamping elements 82, a ring element 84 is positioned in a defined position, the construction and fimction of said ring element being described in detail with reference to the following Figures.

6 The eccentric plate sander 10 operates as follows:

When the electric motor 14 is switched on, the bevel wheel 24 meshes with the ring gear 26 so that with the ring gear 26 the hollow shaft 30 rotates about the axis of rotation 28. The hollow shaft 30 drives the eccentric shaft 38 and the abrasive plate 18. The latter gyrate about the axis of rotation 28 with the given eccentricity and rotate about their longitudinal axis 40 as a result of the friction in the bearings 42 and 44. The spur-toothed wheel 48, the annular disc 50 and the counterpart disc 54 follow the movement of the eccentric shaft 38. Through axial displacement of the miternal geared wheel 58 by the operating means 68, the external gearing 52 of the annular disc 50 may be brought into or out of engagement with the internal gearing 66 of the setting ring 60. Said possible positions correspond to free running of the eccentric shaft 38 or positive driving of the eccentric shaft 38. When the internal gearing of the setting ring 60 is meshed with the external gearing 52 of the annular disc 50, the latter may, depending on the diametral pitch difference of the internal gearing 66 and/or the external gearing 52, oscillate without rotation along the internal gearing 66 (diametral pitch difference 0 = free running). During said process, the annular disc 50 holds the eccentric shaft 38 fast, braking the latter to an extent that allows neutralization of the torque as a result of the friction of the bearings 42 and 44. The abrasive plate 18 may therefore be adjusted so as to rotate more or less quickly without the risk of revving up.

Figure 2 shows an enlarged view of the ring element 84. The latter comprises a sheet metal shaped part made, for example, from spring steel plate. The ring element 84 has folded edges 86 springing out in an axial direction relative to the axis of rotation 28 and verging into a running surface 88. As Figure 4 shows in 7 greater detail, the running surfaces 88 - projected into a tangential viewing plane are designed so that they are curved with a radius R.

Figure 3 shows a perspective view of the setting ring 60 with its internal gearing 66. Provided at the outer periphery 90 of the setting ring 60 are helical surfaces 92, which extend with a thread-like lead and have base surfaces extending radially relative to the axis of rotation 28. In the assembled state of the eccentric plate sander 10, the running surfaces 88 of the ring element 84 lie with their radius R against the helical surfaces 92. By virtue of the spring steel plate construction, the running surfaces 88 may rest with an initial tension against the helical surfaces 92. A guidance of the setting ring 60 is effected by the running surfaces 88, the helical surfaces 92 being guided along the running surfaces 88 in accordance with a relative rotation of the setting ring 60 by the operating means 68. The axial displacement of the setting ring 60 is effected by the lead of the helical surfaces 92.

Additionally springing away from the ring element 84 is a spring tongue 94 preloaded axially in the direction of the abrasive plate 18. In Figure 5, the ring element 84 is shown in a cutout manner with its axially preloaded spring tongue 94. Provided at the end of the spring tongue 94 is an axially extending bend 96, which may be brought into engagement with a frontal tooth system 98 of an adjusting ring 100. The adjusting ring 100 (Figure 1) forms part of an adjusting arrangement for adjusting a tooth clearance of the right-angle drive 20 between the bevel wheel 24 and the ring gear 26. The adjusting ring 100 has an ext ernal "ea 102, which is in engagement with an internal thread of the housing bottom part 78. By twisting the adjusting ring 100, a bearing outer ring of the bearing 3 2 may be acted upon by an axial force so that, via the bearing 32 and the hollow shaft 30, the ring gear 26 disposed non-rotatably on the hollow shaft 30 may be adjusted 1 8 relative to the bevel wheel 24. In the assembled state of the eccentric plate'sander 10, the spring tongue 94 engages with its bend 96 into the tooth systehi 98 of the adjusting ring 100. By virtue of the initial tension of the spring tongue 94, the latter in the assembled state presses with a spring force corresponding to the initial tension onto the adjusting ring 100. By virtue of the latching of the bend 96 into the tooth system 98, the adjusting ring 100 is locked against rotation and so the adjusted clearance between the bevel wheel 24 and the ring gear 26 is maintained.

1 The ring element 84 also forms a spring tongue 102, which is preloaded axially in the opposite direction to the spring tongue 94 - in the direction of the axis of rotation 28. As the enlarged detail view of the ring element 84 in Figure 6 reveals, the spring tongue 102 verges into a supporting surface 104, which is bent at a radius and in the assembled state of the eccentric plate sander 10 lies against the helical surface 92 of the setting ring 60, which helical surface is disposed below the changeover tooth system 76. The supporting surface 104 supports the setting ring 60 in the region of the changeover tooth system 76 which meshes with the tooth system 74 of the operating means 68 (Figure 1). It is thereby ensured that an unintentional axial displacement of the setting ring 60 may not occur. The tooth system 74 therefore remains always effectively meshed with the changeover tooth system 76. Upon intentional axial displacement of the setting ring 60, the supporting surface 104 like the running surfaces 92 - is guided along the helical surface 92.

Finally, the ring element 84 has seating lugs 106, which are associated with the folded edges 86 and extend likewise axially relative to the axis of rotation 28. In positive driving mode, i.e. when the spur-toothed wheel 48 is meshed with the internal geared wheel 58, said seating lugs 106 lie as wear protection between stop cams (not shown in detail) of the housmig bottom part 78 of the right-angle drive 9 housing 16 and stop cams (likewise not shown in detail) of the internal geared wheel 58. Vibrations and impacts arising during operation of the eccentric plate sander 10 are thereby prevented from leading to excessive wear of the stop cams of both the right-angle drive housing 16 and the internal geared wheel 58.

It is on the whole evident that by means of the ring element 84 a multiflinctional structural element of the eccentric plate sander 10 is provided, which besides arresting the tooth clearance adjustment between the bevel wheel 24 and the ring gear 26 and compensating manufacturing tolerances during the changeover between free g and positive drive by means of the setting ring 60 guarantees a locking of the meshing of the changeover tooth system 76 with the tooth system 74 of the operating means 68. The ring element 84 may, as a sheet metal shaped part, be manufactured by simple production steps, e.g. punching and bending steps, inexpensively in a manner suitable for mass production.

Claims

1. Eccentric plate sander having a motor housing, in which a motor drives a shaft and the latter drives an eccentric shaft, which is non- rotatably connected to an abrasive plate and moved in an eccentrically gyrating and rotating manner relative to the axis of the shaft, the eccentric shaft being rotatable relative to the shaft and it being possible - for changing over an operating mode of the eccentric plate sander - to slow down the movement of the abrasive plate by means of a mechanically acting braking device, which is axially displaceable relative to the eccentric shaft, and a frictional engagement being achievable between the eccentric shaft and the braking device, characterized 'm that associated with a structural element (60) effecting the axial displacement of the braking device is a ring element (84), which is disposed coaxially with the shaft (30) and radially away from which at least one running surface (88) springs, which is in seating contact with frontal helical surfaces (92) of the structural element (setting ring 60), which ascend in a thread-like manner.

2. Eccentric plate sander according to claim 1, characterized in that the running surfaces (88) are formed on folded edges (86) of the ring element (84), which spring out axially relative to the axis of rotation (28), and extend radially relative to the axis of rotation (28).

3. Eccentric plate sander according to one of the previous claims, characterized in that the running surfaces (88) have a radius (R) extending tangentially relative to the ring element (84).

11

4. Eccentric plate sander according to one of the previous claims, characterized in that the ring element (84) has three running surfaces (88) disposed each offset by 120' over the periphery.

5. Eccentric plate sander according to one of the previous claims, characterized in that the running surfaces (88) are preloaded in a springlike manner in the direction of the setting ring (60).

6. Eccentric plate sander according to one of the previous claims, characterized in that springing away from the ring element (84) is an axially preloaded spring tongue (94), which is used to arrest a clearance of a right-angle drive of the eccentric plate sander (10).

7. Eccentric plate sander according to claim 6, characterized in that the spring tongue (94) engages axially onto a tooth system (98) of an adjusting ring (100), by means of which the clearance between a bevel wheel (24) and a ring gear (26) of the right-angle drive is adjustable in that the adjusting ring (100) is supported so as to he axially displaceably rotatable about the axis of rotation (28).

8. Eccentric plate sander according to one of the previous claims, characterized in that the ring element (84) has a spring tongue (102), which is preloaded axially in the direction of the setting ring (60) and supported via a supporting surface (104) against a helical surface (92) of the setting ring (60), which helical surface is disposed below a changeover tooth system (76) of the setting ring (60).

9. Eccentric plate sander according to one of the previous claims, characterized in that the ring element (84) forms seating lugs ( 106), which extend 12 axially relative to the axis of rotation (28) and engage between stop cams of a housing bottom part (78) of a right-angle drive housing (16) and of an internal geared wheel (58) of the braking device.

10. Eccentric plate sander according to one of the previous claims, characterized in that the ring element (84) is a sheet metal shaped part.

11. Eccentric plate sander according to one of the previous claims, characterized in that the material of the ring element (84) comprises spring steel plate.

12. An electric plate sander substantially as herein described with reference to the accompanying drawings.