HAND-HELD AND HAND-GUIDED POWER TOOL HAVING A WORKING ELEMENT RELEASABLY ATTACHED THERETO, AND WORKING ELEMENT IN THE FORM OF A BACKING PAD FOR SUCH A POWER TOOL

Abstract

The invention refers to a plate-like backing pad member (9) for use with a hand-held and hand-guided power tool (1). The backing pad member (9) is adapted for releasable attachment to a driving shaft (27) of the power tool (1) by means of a mechanical form fit connection arrangement comprising a protrusion member (16) connected to the driving shaft (27) and a recess member (17) connected to the backing pad member (9). The form fit connection is releasable in an axial direction running parallel to a rotational axis (13) of the backing pad member (9). The protrusion member (16) is held in the axial direction within the recess member (17) by means of an axial holding arrangement. It is suggested that the axial holding arrangement comprises at least one permanent magnet (40) on the one hand and at least one ferromagnetic element (41) or at least one further permanent magnet on the other hand exerting a magnetic force for holding the protrusion member (16) in the axial direction within the recess member (17). The at least one permanent magnet (40) or the at least one ferromagnetic element (41) or the at least one further permanent magnet is located in or makes part of the recess member (17).

Claims

1. Plate-like backing pad member (9) for use with a hand-held and hand-guided power tool (1) comprising a housing (2) with a driving motor (11) located therein for actuating a driving shaft (27) upon operation of the driving motor (11), the plate-like backing pad member (9) having a rotational axis (13), wherein the plate-like backing pad member (9) is adapted for releasable attachment to the driving shaft (27) by means of a mechanical form fit connection arrangement comprising at least one protrusion member (16) directly or indirectly connected to the driving shaft (27) and at least one recess member (17) connected to the plate-like backing pad member (9), the mechanical form fit connection arrangement being adapted for providing a torque proof connection between the at least one protrusion member (16) and the at least one recess member (17) in a plane extending perpendicular to the rotational axis (13) of the plate-like backing pad member (9), wherein the mechanical form fit connection arrangement is releasable in an axial direction running parallel to the rotational axis (13) of the plate-like backing pad member (9), wherein the at least one protrusion member (16) is held in the axial direction within the at least one recess member (17) by means of an axial holding arrangement, characterized in that the axial holding arrangement comprises at least one permanent magnet (40) and either least one ferromagnetic element (41) or at least one further permanent magnet exerting a magnetic force for holding the at least one protrusion member (16) in the axial direction within the at least one recess member (17), wherein the at least one permanent magnet (40), or the at least one ferromagnetic element (41), or the at least one further permanent magnet is located in or makes part of the at least one recess member (17).

2. The plate-like backing pad member (9) according to claim 1, wherein the plate-like backing pad member (9) has two opposing surfaces extending in parallel to each other, the surfaces comprising a first bottom surface (9a) for releasable attachment of a sheet-like polishing or abrasive member (14) by means of a hook-and-loop fastener.

3. The plate-like backing pad member (9) according to claim 2, wherein the opposing surfaces of the plate-like backing pad member (9) comprise an opposite top surface (9b) with a backing pad-connection arrangement (15) attached thereto, the backing pad-connection arrangement (15) comprising the at least one recess member (17).

4. The plate-like backing pad member (9) according to claim 1, wherein the plate-like backing pad member (9) is made of a semi-rigid plastic material and comprises a metal insert moulded into the plastic material during production of the plate-like backing pad member (9) by means of a moulding or an injection moulding process, the metal insert forming at least part of the at least one recess member (17) and constituting the at least one ferromagnetic element (41) or the at least one further permanent magnet.

5. The plate-like backing pad member (9) according to claim 1, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the plate-like backing pad member (9) has a circumferential form comprising two opposing arc-shaped sections (18a) of a circle with the rotational axis (13) running through the centre of the circle, and the plate-like backing pad member (9) further comprising two opposing straight walls (18b) running substantially parallel to one another and interconnecting the two opposing arc-shaped sections (18a).

6. The plate-like backing pad member (9) according to claim 1, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the backing pad member (9) has a circumferential form comprising a circle with the rotational axis (13) running through the centre of the circle, and the plate-like backing pad member (9) further comprising two grooves extending on opposite sides of the circle radially outwards.

7. The plate-like backing pad member (9) according to claim 1, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the plate-like backing pad member (9) has a circumferential form of a polygon, including a polygon having equal side lengths, with the rotational axis (13) running through the centre of gravity of the polygon.

8. The plate-like backing pad member (9) according to claim 1, wherein a plurality of permanent magnets (40), including four permanent magnets, are located in the recess member (17) around and equidistant to the rotational axis (13) of the plate-like backing pad member (9), with neighbouring permanent magnets (40) having opposite polarities.

9. The plate-like backing pad member (9) according to claim 8, wherein the plurality of permanent magnets (40) are located so that neighbouring permanent magnets (40) are in direct lateral abutment with one another.

10. The plate-like backing pad member (9) according to claim 8, wherein the plurality of permanent magnets (40) are located in direct contact with one another along the rotational axis (13) of the plate-like backing pad member (9).

11. The plate-like backing pad member (9) according to one of the claims 8 to 10, wherein each of the plurality of permanent magnets (40) is formed as a respective triangle having a respective vertex angle, including an isosceles triangle, and wherein all triangles are dimensioned so that the sum of all vertex angles is 360.

12. The plate-like backing pad member (9) according to claim 8, wherein each of the plurality of permanent magnets (40) is termed with a circular sector, and wherein all circular sectors are dimensioned so that all permanent magnets (40) together form a circle.

13. Hand-held and hand-guided power tool (1) comprising a housing (2) with a driving motor (11) located therein for actuating a driving shaft (27) upon operation of the driving motor (11) and further comprising a backing pad member (9) performing a working movement about its rotational axis (13) in a working plane extending perpendicular to its rotational axis (13) upon actuation of the driving shaft (27), wherein the backing pad member (9) is attached to the driving shaft (27) by means of a mechanical form fit connection arrangement comprising at least one protrusion member (16) directly or indirectly connected to the driving shaft (27) and at least one recess member (17) connected to the backing pad member (9), the mechanical form fit connection arrangement being adapted for providing a torque proof connection between the at least one protrusion member (16) and the at least one recess member (17) in a plane extending perpendicular to the rotational axis (13) of the backing pad member (9), wherein the mechanical form fit connection arrangement is releasable in an axial direction running parallel to the rotational axis (13) of the backing pad member (9), wherein the at least one protrusion member (16) is held in the axial direction within the al least one recess member (17) by means of an axial holding arrangement, characterized in that the axial holding arrangement comprises at least one permanent magnet (40) and either at least one ferromagnetic element (41) or at least one further permanent magnet exerting a magnetic force for holding the at least one protrusion member (16) in the axial direction within the at least one recess member (17), wherein at least part of the axial magnetic holding arrangement (40, 41) forms an integral part of at least part of the mechanical form fit connection arrangement (16, 17).

14. The hand-held and hand-guided power tool (1) according to claim 13, wherein the at least one permanent magnet (40), or the at least one ferromagnetic element (41), or the at least one further permanent magnet is located in or makes part of the at least one recess member (17).

15. The hand-held and hand-guided power tool (1) according to claim 13, wherein the at least one ferromagnetic element (41), or the at least one further permanent magnet, or the at least one permanent magnet (40) is attached to or makes part of the at least one protrusion member (16).

16. The hand-held and hand-guided power tool (1) according to claim 13, wherein the protrusion member (16) in the plane extending perpendicular to the rotational axis (13) of the backing pad member (9) has a circumferential form corresponding to the circumferential form of the at least one recess member (17).

17. The plate-like backing pad member (9) according to claim 2, wherein the plate-like backing pad member (9) is made of a semi-rigid plastic material and comprises a metal insert moulded into the plastic material during production of the plate-like backing pad member (9) by means of a moulding or an injection moulding process, the metal insert forming at least part of the at least one recess member (17) and constituting the at least one ferromagnetic element (41) or the at least one further permanent magnet.

18. The plate-like backing pad member (9) according to claim 2, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the plate-like backing pad member (9) has a circumferential form comprising two opposing arc-shaped sections (18a) of a circle with the rotational axis (13) running through the centre of the circle, and the plate-like backing pad member (9) further comprising two opposing straight walls (18b) running substantially parallel to one another and interconnecting the two opposing arc-shaped sections (18a).

19. The plate-like backing pad member (9) according to claim 2, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the backing pad member (9) has a circumferential form comprising a circle with the rotational axis (13) running through the centre of the circle, and the plate-like backing pad member (9) further comprising two grooves extending on opposite sides of the circle radially outwards.

20. The plate-like backing pad member (9) according to claim 2, wherein the at least one recess member (17) in the plane extending perpendicular to the rotational axis (13) of the plate-like backing pad member (9) has a circumferential form of a polygon, including a polygon having equal side lengths, with the rotational axis (13) running through the centre of gravity of the polygon.

Description

[0022] Further features and advantages of the present invention can be taken from the figures and the following detailed description. The figures show:

[0023] FIG. 1 a power tool according to the present invention in a preferred embodiment in a perspective view;

[0024] FIG. 2 the power tool of FIG. 1 in a sectional schematic view;

[0025] FIG. 3 a first type of tool-connection arrangement of a conventional power tool known in the art;

[0026] FIG. 4 a second type of tool-connection arrangement of a conventional power tool known in the art;

[0027] FIG. 5 a backing pad member of a conventional power tool known in the art;

[0028] FIG. 6 a first type of tool-connection arrangement of a power tool according to the present invention;

[0029] FIG. 7 a second type of tool-connection arrangement of a power tool according to the present invention;

[0030] FIG. 8 a first type of backing pad member according to the present invention connected to a tool-connection arrangement of FIG. 6;

[0031] FIG. 9 the first type of backing pad member according to the present invention connected to a tool-connection arrangement of FIG. 7;

[0032] FIG. 10 a second type of backing pad member according to the present invention;

[0033] FIG. 11 a tool-connection arrangement about to be connected to a backing pad-connection arrangement according to the present invention;

[0034] FIG. 12 a top view on a backing pad and its backing pad connection arrangement according to the present invention;

[0035] FIG. 13 a first embodiment of a magnetic axial holding arrangement;

[0036] FIG. 14 a second embodiment of a magnetic axial holding arrangement;

[0037] FIG. 15 a third embodiment of a magnetic axial holding arrangement;

[0038] FIG. 16 a fourth embodiment of a magnetic axial holding arrangement; and

[0039] FIG. 17 a third type of backing pad member according to the present invention adapted for connection to a hexagonal protrusion member of a tool-connection arrangement.

[0040] In FIG. 1 an example of a hand-guided and hand-held motor driven power tool according to the present invention is designated with reference sign 1 in its entirety. In this embodiment the power tool 1 is embodied as a random orbital polisher. The polisher 1 has a housing 2, essentially made of plastic material. The housing 2 has a handle 3 at its rear end and a grip 4 at its front end. An electric power supply line 5 with an electric plug at its distal end exits the housing 2 at the rear end of the handle 3. At the bottom side of the handle 3 a switch 6 is provided for turning on and off the power tool 1. The switch 6 can be continuously held in its activated position by means of a push button 7. The power tool 1 can be provided with speed adjustment means 10 (e.g. a knurled wheel) for adjusting the rotational speed of the tool's motor. The housing 2 can be provided with cooling openings 8 for allowing heat from electronic components and/or the electric motor both located inside the housing 2 to dissipate into the environment and for allowing cooling air to enter the housing 2.

[0041] As can be seen from FIG. 2, the power tool 1 has an electric motor 11 located inside the housing 2 for driving a tool-connection arrangement 12 having a protrusion member 16 protruding from the housing 2 and a plate-like backing pad member 9 releasably attached thereto. Of course, the power tool 1 according to the present invention could also be equipped with a pneumatic motor, which is especially advantageous in explosive environments, where sparks from an electric motor could provoke an explosion of an explosive mixture (e.g. oxygen and very fine dust) contained in the environment. In that case, the power tool 1 would be connected to a compressed-air line instead of the electric cable 5. Furthermore, instead of the connection of the power tool 1 to a mains power supply by means of the electric cable 5, the power tool 1 could alternatively be equipped with a rechargeable battery (not shown) located inside the housing 2. In that case the electric energy for driving the electric motor 11 and for other electronic components would be provided by the battery.

[0042] The backing pad member 9 is rotatable about a rotational axis 13. In this embodiment it performs a random-orbital working movement. However, to those skilled in the art it is clear that the backing pad 9 could also perform any other type of working movement, e.g. a purely orbital or a roto-orbital (gear driven) working movement. The backing pad member 9 has two opposing surfaces, a first bottom surface 9a for releasable attachment of a flexible sheet-like polishing or abrasive member 14 (e.g. by means of hook-and-loop fastening surfaces) and an opposite top surface 9b with a backing pad-connection arrangement 15 attached thereto. The backing pad-connection arrangement 15 may comprise a metal insert (e.g. see FIG. 12) which is moulded into the material of the backing pad member 9 and/or the backing pad arrangement 15 during its production by means of a moulding or an injection moulding process.

[0043] In the embodiment shown in the figures, the tool-connection arrangement 12 comprises the protrusion member 16 and the backing pad-connection arrangement 15 comprises a recess member 17. To those having skill in the art it is clear that the tool-connection arrangement 12 could also comprise the recess member and the backing pad-connection arrangement 15 could comprise the protrusion member. The tool-connection arrangement 12 and the backing pad-connection arrangement 15 constitute a connection arrangement. The protrusion member 16 and the recess member 17 are adapted for interacting with one another for releasably connecting the backing pad member 9 to the rest of the power tool 1 in a torque proof manner by means of a form fit connection.

[0044] As can be seen from FIG. 12, the recess member 17 of the connection arrangement 15 has an inner circumferential wall 18 rotationally asymmetrical in respect to the rotational axis 13 of the backing pad 9. As can be seen from FIG. 11, the protrusion member 16 has an outer circumferential surface 19 rotationally asymmetrical in respect to the rotational axis 13 of the backing pad 9. The protrusion member 16 and the recess member 17 are adapted for entering into mutual engagement with one another in order to realize a torque-proof connection about the rotational axis 13 of the backing pad member 9. The backing pad member 9 with its recess member 17 can be detached from the protrusion member 16 in an axial direction running parallel to the rotational axis 13 of the backing pad member 9. In order to avoid unintentional detachment of the backing pad member 9, an axial holding arrangement is provided.

[0045] Returning now to FIG. 2, the internal components of the power tool 1 are described in more detail. The electric motor 11 is powered by electricity arriving through the electric cable 5 from a mains power supply. An electronic control unit (ECU) 20 is provided inside the housing 2 for controlling the speed of the electric motor 11 and possibly other functions of the power tool 1. The speed adjustment means 10 generate a set-point signal 21 which is forwarded to the ECU 20 for controlling the rotational speed of the motor 11. The ECU 20 generates a control signal 22 which is forwarded to the motor 11. Depending on the value of the control signal 22 the motor 11 rotates at a certain speed and actuates a motor shaft 23. A gear arrangement 24 may be located between the motor shaft 23 and the tool-connection arrangement 12 in order to reduce the rotational speed and to enhance the torque output at the tool-connection arrangement 12. A bevel gear arrangement 25 may be provided in order to translate the rotation of an intermediate shaft 26 extending in an essentially horizontal direction into the rotation of a driving shaft 27 extending in an essentially vertical direction. The bevel gear 25 is necessary for realizing angular power tools. Of course, the bevel gear arrangement 25 could also realize a translation of a rotation by different angles other than 90. The tool-connection arrangement 12 is connected to the driving shaft 27 in a torque proof manner. Of course, in other embodiments of the invention the driving shaft 27 could be constituted by the motor shaft 23 or the intermediate shaft 26, when no gear arrangement 24 and/or no bevel gear arrangement 25 is present.

[0046] FIGS. 3 and 4 show two different types of tool-connection arrangements 12 for realizing a random-orbital working movement of the backing pad member 9, both types known from the prior art. In a first example according to FIG. 3 the driving shaft 27 is connected to the tool-connection arrangement 12 on the side (eccentrically) in a distance to a central axis 28 of gravity of the tool-connection arrangement 12, with the axis of gravity 28 and a rotational axis 29 of the driving shaft 27 running essentially parallel in respect to one another. The protrusion member 16 is guided freely rotatable about the rotational axis 13 in respect to the rest of the tool-connection arrangement 12. To this end, bearings 30 may be provided between the protrusion member 16 and the rest of the tool-connection arrangement 12. In this embodiment the axis of gravity 28 of the tool-connection arrangement 12 and the rotational axis 13 of the backing pad member 9 are identical.

[0047] According to another example shown in FIG. 4 the driving shaft 27 is connected to the tool-connection arrangement 12 in the center of gravity of the tool-connection arrangement 12, with the axis of gravity 28 and the rotational axis 29 of the driving shaft 27 being identical. Again, the protrusion member 16 is guided freely rotatable about the rotational axis 13 in respect to the rest of the tool-connection arrangement 12. In this example the axis of gravity 28 of the tool-connection arrangement 12 is located in a distance (eccentrically) to the rotational axis 13 of the backing pad member 9. In both examples the driving shaft 27 can be connected to the tool-connection arrangement 12 in a torque proof manner, for example by a threaded connection. In both examples a rotation of the driving shaft 27 about the axis 29 leads to a random-orbital working movement of the protrusion member 16 and, consequently, of the backing pad member 9 attached thereto. Despite the freely rotatable connection of the backing pad member 9 to the tool-connection arrangement 12 about its rotational axis 13, the recess member 17 of the backing pad-connection arrangement 15 is connected to the protrusion member 16 of the tool-connection arrangement 12 in a torque proof manner.

[0048] The flexible sheet-like polishing or abrasive member 14 is releasably attached to the bottom surface 9a of the backing pad 9. In the case of a polishing member it may comprise but is not limited to a sponge, a microfiber, and real or synthetic lambs' wool. In the case of an abrasive member it may comprise but is not limited to a sanding paper or a sanding fabric. The sheet-like polishing or abrasive member 14 is preferably attached to the backing pad member 9 by means of a hook-and-loop fastener (or Velcro). A first layer of the hook-and-loop fastener may be provided on the bottom surface 9a of the backing pad 9, wherein the top surface of the sheet-like polishing or abrasive member 14 is provided with a corresponding second layer of the hook-and-loop fastener. The two layers of the hook-and-loop fastener interact with one another in order to releasably but safely fix the sheet-like polishing or abrasive member 14 to the bottom surface 9a of the backing pad 9. Except for some aspiration openings in the backing pad member 9 and/or the sheet-like polishing or abrasive member 14, the polishing or abrasive member 14 covers the entire bottom surface 9a of the backing pad member 9. Preferably, during intended use of the power tool 1, the entire bottom surface of the sheet-like polishing or abrasive member 14 is in contact with the surface to be worked.

[0049] The backing pad member 9 is preferably made of a semi-rigid material, in particular a plastic material, which on the one hand is rigid enough to carry and support the sheet-like polishing or abrasive member 14 during the intended use of the power tool 1 and to apply a force to the polishing or abrasive member 14 in a direction essentially parallel to the backing pad's rotational axis 13 and which on the other hand is flexible enough to avoid damage or scratching of the surface to be worked by the backing pad member 9 or the polishing or abrasive member 14, respectively, during the intended use of the power tool 1. The backing pad member 9 may comprise different materials e.g. having different rigidities, which are fixed together, e.g. by means of a moulding process. The different materials may comprise different plastic materials or plastic and metal. For example, for stabilizing the backing pad member 9 it could be possible to introduce a metal support structure into the backing pad member 9 during the moulding process for manufacturing it. This metal inlay could form at least part of the recess member 17.

[0050] According to the state of the art shown in FIG. 5, the axial holding arrangement for securing the backing pad member 9 to the protrusion member 16 of the tool-connection arrangement 12 in an axial direction essentially parallel to the rotational axis 13 of the backing pad member 9 comprises a securing screw 31 having a threaded shaft 32 and a screw head 33. After bringing the recess member 17 of the backing pad-connection arrangement 15 into engagement with the protrusion member 16 of the tool-connection arrangement 12, the shaft 32 may be inserted from the bottom of the backing pad member 9 into a through hole 34 provided in the backing pad member 9 along its rotational axis 13. At the bottom surface 9a of the backing pad 9 a recessed portion 35 of the through hole 34 is adapted for receiving the screw head 33. The threaded shaft 32 is screwed into a threaded hole 36 provided in the protrusion member 16 of the tool-connection arrangement 12. In the prior art replacement of the backing pad member 9 is rather complicated and time consuming because first the screw 31 has to be loosened and unscrewed before an old backing pad member 9 can be detached from the tool-connection arrangement 12 and then the screw 31 has to be rescrewed and tightened again after a new backing pad member 9 has been attached to the tool-connection arrangement 12.

[0051] In order to overcome this drawback, the present invention suggests a magnetic axial holding arrangement for securing the backing pad member 9 in the form fit connection in respect to the protrusion member 16 of the tool-connection arrangement 12 by means of magnetic force. In particular, it is suggested that the recess member 17 of the backing pad member 9 is connected to the protrusion member 16 of the tool-connection arrangement 12 in a torque proof manner by means of the form fit connection. The form fit connection acts in a plane extending essentially perpendicular to the rotational axis 13 of the backing pad member 9. The form fit connection 16, 17 is releasable in an axial direction only. The backing pad member 9 is held within the form fit connection 16, 17 in respect to the protrusion member 16 in the axial direction by means of magnetic force. Additional force for holding the backing pad member 9 within the form fit connection 16, 17 in the axial direction may be applied by means of an additional snapping or clinching mechanism (not shown). Preferred embodiments of the invention are shown in FIGS. 6 to 17.

[0052] According to the invention it is suggested that at least one permanent magnet 40 is provided within or attached to the backing pad member 9 (see FIGS. 8-10), preferably near or inside the recess member 17 of the backing pad-connection arrangement 15. In the embodiments of FIGS. 8 and 9 one permanent magnet 40 is provided in a bottom surface of the recess member 17 of the backing pad-connection arrangement 15. Correspondingly, at least one ferromagnetic element 41 or further permanent magnet is provided within or attached to the protrusion member 16 (see FIGS. 6 and 7) of the tool-connection arrangement 12. In the embodiments of FIGS. 6 to 10 the protrusion member 16 of the tool-connection arrangement 12 is made of iron (Fe) or steel and constitutes the ferromagnetic element 41. This has the advantage that conventional power tools 1 and tool-connection arrangements 12 known from the prior art can be used together with the backing pad member 9 according to the present invention provided with the at least one permanent magnet 40. The at least one permanent magnet 40 on the one hand and the at least one ferromagnetic element 41 on the other hand are adapted for interacting with one another in order to exert the axial holding force.

[0053] In FIGS. 8 to 10 only one permanent magnet 40 and one corresponding ferromagnetic element 41 or further permanent magnet is provided in the magnetic axial holding arrangement (see FIG. 13). In a variation from what is shown in FIGS. 8 to 10 the number of permanent magnets 40 and corresponding ferromagnetic elements 41 or further permanent magnets may vary (see FIGS. 14 to 16). In particular, it is suggested there that a plurality of, preferably four, permanent magnets 40 are located in the recess member 17 around and equidistant to the rotational axis 13 of the backing pad member 9, with neighbouring permanent magnets 40 having opposite polarities. Preferably, the plurality of permanent magnets 40 are located such that neighbouring permanent magnets 40 are in direct lateral abutment with one another (see FIGS. 14 and 16). In FIGS. 14 and 16 the plurality of permanent magnets 40 are located in direct contact with one another along the rotational axis 13 of the backing pad member 9.

[0054] The plurality of permanent magnets 40 may each have the form of a triangle, preferably an isosceles triangle, wherein the triangles are dimensioned such that the sum of the vertex angles of all triangles is 360 (not shown). Hence, if four triangular permanent magnets 40 are provided they each have a vertex angle of 90. Correspondingly, six permanent magnets 40 would have a vertex angle of 60. Alternatively, the plurality of permanent magnets 40 may each have the form of a rectangle, preferably of a square (see FIG. 16). Preferably, the plurality of permanent magnets 40 each have the form of a circular sector, wherein the circular sectors are dimensioned such that the circular sectors of all permanent magnets 40 together form a circle (see FIG. 14). The form and dimensions of the ferromagnetic elements 41 or further permanent magnets correspond to the form of the respective permanent magnets 40.

[0055] Furthermore, it would also be possible that the at least one permanent magnet 40 is provided at the protrusion member 16 of the tool-connection arrangement 12, whereas the at least one ferromagnetic element 41 or the further permanent magnet is provided in the recess member 17 of the backing pad-connection arrangement 15. If the backing pad member 9 had an insert made of iron or steel (e.g. see FIG. 12) which makes part of or defines the recess member 17, the metal insert itself could constitute the ferromagnetic element 41. In that case, conventional backing pad members 9 could be used with the power tool 1 according to the present invention with at least one permanent magnet 40 located at the protrusion member 16 of the tool-connection arrangement 12.

[0056] It is understood that it would also be possible to realize the axial magnetic attachment of the backing pad member 9 to the rest of the power tool 1 by means of at least two permanent magnets of opposite polarities, one of the permanent magnets having a first polarity located in the recess member 17 of the backing pad-connection arrangement 15, and the other permanent magnet having an opposing polarity located at the protrusion member 16 of the tool-connection arrangement 12.

[0057] In the embodiments shown in FIGS. 6 to 10, when the backing pad member 9 is attached to the rest of the power tool 1, in particular when the protrusion member 16 of the tool-connection arrangement 12 is inserted into the recess member 17 of the backing pad-connection arrangement 15 in an axial direction, the ferromagnetic element 41 or the further permanent magnet is attracted by the permanent magnet 40 due to the magnetic force. The protrusion member 16 is tightly held in the recess member 17 in the axial direction by means of the magnetic force. No mechanical axial holding arrangement, like the securing screw 31 in the prior art, are needed for holding the backing pad 9 in an axial direction in respect to the rest of the power tool 1.

[0058] The present invention provides for a quick fastening and releasing mechanism for the backing pad member 9. Despite the quick attachment and detachment of the backing pad member 9, the use of magnetic force for securing the backing pad member 9 to the rest of the power tool 1 provides for a sufficiently safe and strong attachment of the backing pad member 9 to the rest of the power tool 1. The transmission of high torque values is possible, too, because the torque is transmitted by means of the form fit connection between the protrusion member 16 and the recess member 17 and the corresponding inner and outer walls 18, 19 interacting with one another. With other words, in the present invention torque may be transmitted in a plane essentially perpendicular in respect to the rotational axis 13 by means of a mechanical form fit connection and the backing pad member 9 is held in an axial direction essentially parallel to the rotational axis 13 by magnetic force.

[0059] Besides the possibility for quick attachment and detachment of the backing pad member 9, the invention has the further advantage that the backing pad member 9 as well as the tool-connection arrangement 12 can be embodied much less complicated. In particular, there is no need for the through hole 34 and the recess 35 for the securing screw 31 in the backing pad 9. Further, there is no need for the threaded hole 36 for the securing screw 31 in the protrusion member 16 of the tool-connection arrangement 12. Furthermore, detachment and attachment of the backing pad member 9 can be achieved by an operator of the power tool 1 without him having to take off working or safety gloves and without the need for specific tools for actuating separate mechanical axial holding arrangements such as a securing screw 31. Finally, the securing of the backing pad member 9 to the rest of the power tool 1 still works very safely and reliably even if abrasive dust and other small debris particles enter between the backing pad-connection arrangement 15 and the tool-connection arrangement 12.

[0060] In order to avoid damage to the at least one permanent magnet 40 when establishing the connection between the backing pad member 9 and the rest of the power tool 1, a protective cover sheet 42 may be provided, which is located between the at least one permanent magnet 40 and the respective part of the protrusion member 16 when establishing the axial attachment of the backing pad-connection arrangement 15 to the tool-connection arrangement 12 (see FIG. 10). Preferably, the cover sheet 42 is made of a material having damping characteristics such as plastic or rubber. However, the cover sheet 42 could also be made of some ferromagnetic material having the advantage that the magnetic forces from the permanent magnet 40 are better transmitted towards the tool-connection arrangement 12 resulting in a higher magnetic force acting on the ferromagnetic element 41. There could be an air gap between the at least one permanent magnet 40 and the protective cover sheet 42. The cover sheet 42 could also comprise more than one layer, the various layers preferably made of different materials, such as a first very thin layer made of plastic or rubber on top of the permanent magnet 40 and a second layer made of strong and resistant metal on top of the first layer.

[0061] FIGS. 11 and 12 show the tool-connection arrangement 12 and the backing pad-connection arrangement 15 in further detail. The protrusion member 16 with its outer circumferential walls 19 is shown in FIG. 11. Furthermore, the recess member 17 with its inner circumferential walls 18 located at the top surface 9b of the backing pad member 9 is shown in FIG. 12. It can be clearly seen that the protrusion member 16 as well as the recess member 17 have a circumferential contour, which is rotationally asymmetric (non-circular) in respect to the rotational axis 13 in order to provide for a torque proof connection. It can be further clearly seen that the outer circumferential contours of the protrusion member 16 and the recess member 17 correspond to each other in terms of allowing introduction and a precise fitting of the protrusion member 16 in the recess member 17. In particular, the form fit connection between the protrusion member 16 and the recess member 17 is such that the outer and inner walls 19, 18 abut against each other with their entire surfaces when the protrusion member 16 is inserted into the recess member 17.

[0062] As can further be seen by FIGS. 11 and 12, the form fit connection between the protrusion member 16 and the recess member 17 is releasable in the axial direction. In order to hold the protrusion member 16 of the tool-connection arrangement 12 in the recess member 17 of the backing pad-connection arrangement 15 magnetic force is used. In the embodiment of FIGS. 11 and 12 the metal insert of the backing pad-connection arrangement 15 is made of permanent magnetic material thereby constituting the permanent magnet 40. Alternatively, the at least one permanent magnet 40 is located in the bottom surface of the recess member 17. The backing pad-connection arrangement 15 visible on the top surface 9b of the backing pad member 9 may be covered with a protective sheet material such as plastic or rubber (not shown). The protrusion member 16 of the tool-connection arrangement 12 is made of ferromagnetic material thereby constituting the ferromagnetic element 41. After insertion of the protrusion member 16 into the recess member 17, the tool-connection arrangement 12 and the backing pad-connection arrangement 15 are tightly held together in their form fit connection in an axial direction by means of magnetic force, thereby firmly attaching the backing pad member 9 to the rest of the power tool 1.

[0063] In FIG. 12 it can be seen that the backing pad-connection arrangement 15 comprises a metal insert member forming the recess member 17 and having an inner circumferential wall 18, which in the plane extending perpendicular to the rotational axis 13 of the backing pad member 9 comprises two opposing arc shaped sections 18a of a circle with the rotational axis 13 running through the circle's centre. The arc shaped sections 18a are interconnected by two opposing straight walls 18b running essentially parallel to one another. The straight walls 18b form two chords of the circle spaced apart from the circle's centre and both having the same length. Preferably, the circle has a radius of appr. 19 mm, the parallel straight walls 18b are spaced appr. 17.2 mm apart. The outer contour of the protrusion member 16 is shaped correspondingly (see FIG. 11) comprising arc shaped sections 19a of a circle with the rotational axis 13 running through the circle's centre. The arc shaped sections 19a are interconnected by two opposing straight lines 19b running essentially parallel to one another.

[0064] Of course, the outer and inner contours of the outer and inner walls 19, 18 of the protrusion member 16 and the recess member 17 shown in FIGS. 11 and 12 are purely exemplary and may have almost any other form, too, which is rotationally asymmetric (non-circular) in respect to the rotational axis 13. According to another embodiment, the inner contour of the recess member 17 in the plane extending perpendicular to the rotational axis 13 of the backing pad member 9 comprises a circle with the rotational axis 13 running through the circle's centre and further two grooves extending on opposite sides of the circle radially outwards. Correspondingly, the outer contour of the protrusion member 16 comprises a circle with the rotational axis 13 running through the circle's centre and further two noses extending on opposite sides of the circle radially outwards, which fit into the grooves of the recess member 17. A further embodiment is shown in FIG. 17, where the recess member 17 has a hexagonal form with six straight walls 18c of equal length and oriented at equal angles of 60 in respect to one another. Of course, many other polygon forms, in particular polygons with equal side lengths, are conceivable, too, e.g. a triangle, rectangle, square, pentagon, heptagon, octagon and so on. Of course, the protrusion member 16 has a corresponding circumferential form, in order to allow the form fit connection between the protrusion member 16 and the recess member 17.

[0065] Although the power tool 1 is shown as a random orbital polisher in the present embodiment, the present invention is not limited to that kind of power tool. Rather, the invention may be realized with any type of power tool having a backing pad member 9 of any type releasably attached thereto. In particular, the power tool could be an oscillating sander, where the backing pad member 9 has the form of a rectangle or triangle (see FIG. 17) performing a purely oscillating working movement.

[0066] Summing up, according to the present invention the connection arrangement provided between the backing pad 9 and the rest of the power tool 1 comprises a mechanical form fit connection for providing a torque proof connection between the protrusion member 16 of the tool-connection arrangement 12 and the recess member 17 of the backing pad-connection arrangement 15 and an axial magnetic holding arrangement comprising at least one permanent magnet 40 on the one hand and at least one ferromagnetic element 41 or at least one further permanent magnet on the other hand for holding the backing pad member 9 in the form fit connection in respect to the rest of the power tool 1 in an axial direction. In particular, it is suggested that at least part of the axial magnetic holding arrangement is integrated in or forms part of the mechanical form fit connection.

[0067] It should be understood that, unless stated otherwise herein, any of the features, characteristics, alternatives or modifications described regarding a particular embodiment herein may also be applied, used, or incorporated with any other embodiment described herein. Also, the drawing herein is not drawn to scale.

[0068] Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departing from the spirit and scope of the present invention.