[0001] The present invention refers to a plate-like backing pad member for use with a hand-held
and hand-guided power tool comprising a housing with a driving motor located therein
for actuating a driving shaft upon operation of the motor. The backing pad member
has a rotational axis. The backing pad member is adapted for releasable attachment
to the driving shaft by means of a mechanical form fit connection arrangement comprising
at least one protrusion member directly or indirectly connected to the driving shaft
and at least one corresponding recess member connected to the backing pad member.
The protrusion member and the recess member are adapted to enter into engagement with
each other in order to realize the mechanical form fit connection. The mechanical
form fit connection arrangement is adapted for providing a torque proof connection
between the protrusion member and the recess member in a plane extending perpendicular
to the rotational axis of the backing pad member. The mechanical form fit connection
arrangement is releasable in an axial direction running parallel to the rotational
axis of the backing pad member. The protrusion member is held in the axial direction
within the recess member by means of an axial holding arrangement.
[0002] Furthermore, the invention refers to a hand-held and hand-guided power tool comprising
a housing with a driving motor located therein for actuating a driving shaft upon
operation of the motor and further comprising a backing pad member performing a working
movement about its rotational axis in a working plane extending perpendicular to its
rotational axis upon actuation of the driving shaft. The backing pad member is attached
to the driving shaft by means of a mechanical form fit connection arrangement comprising
at least one protrusion member directly or indirectly connected to the driving shaft
and at least one recess member connected to the backing pad member. The mechanical
form fit connection arrangement is adapted for providing a torque proof connection
between the protrusion member and the recess member in a plane extending perpendicular
to the rotational axis of the backing pad member. The mechanical form fit connection
arrangement is releasable in an axial direction running parallel to the rotational
axis of the backing pad member. The protrusion member is held in the axial direction
within the recess member by means of an axial holding arrangement.
[0003] Power tools and backing pad members of the above-identified kind are well known in
the prior art, e.g.
EP 2 669 044 A1. In the prior art, the axial holding arrangement usually comprises a securing screw
which is inserted from a bottom surface of the backing pad into an opening provided
in the centre of the backing pad member along its rotational axis and screwed into
a threaded opening located in the protrusion member. This provides for a secure attachment
of the backing pad member to the rest of the power tool, in particular of the recess
member to the protrusion member, in an axial direction parallel to the rotational
axis of the backing pad. However, it is disadvantageous that replacement of the backing
pad member is rather cumbersome and time consuming due to the fact that the securing
screw has to be untightened and unscrewed, in order to allow detachment of an old
backing pad member, and after attachment of a new backing pad member has to be inserted
into the threaded opening, has to be screwed therein and tightened again. To this
end, a special tool is required, e.g. comprising a hexagon head for insertion into
an Allen® screw of the securing screw.
[0004] Furthermore, a similar power tool and backing pad are disclosed by
DE 44 44 496 A1. This reference emanates from a power tool where a rigid polishing or abrasive disc
was directly fixed to the driving shaft of the power tool by means of a clamping nut.
In order to make replacement of the polishing or abrasive disc faster and easier,
an additional adapter is suggested which is mounted between the driving shaft and
the polishing or abrasive disc. The adapter consists of two plate-shaped parts, a
first part attached to the driving shaft of the power tool in a torque proof manner
and another part to which the polishing or abrasive disc is attached by means of a
clamping nut. The two adapter parts may be releasably attached to one another in a
torque proof manner in a plane extending perpendicular to a rotational axis of the
driving shaft by means of a form fit connection. The form fit connection can be released
in an axial direction parallel to the rotational axis. The two adapter parts are held
together in the axial direction by means of magnetic force. The abrasive or polishing
member of the known power tool performs only a purely rotational working movement.
[0005] The known power tool has the disadvantage that the proposed idea cannot simply be
transferred to a power tool comprising a backing pad member with a flexible sheet-like
polishing or abrasive material releasably attached to a bottom surface of the backing
pad member because it would not be possible to provide an additional adapter of the
type disclosed by the above reference between the driving shaft of the power tool
and the backing pad member. The power tool disclosed by the above reference is very
large, heavy, bulky and unhandy. In particular, in a power tool where the backing
pad member and, hence, also the abrasive or polishing member performs a working movement
comprising an orbital component (e.g. in purely orbital, random-orbital, roto-orbital
or gear-driven working movements), the use of a separate adaptor would lead to considerable
vibrations. Therefore, what is clearly needed is a possibility to safely and reliably
attach a backing pad member performing a working movement comprising an orbital component
to a power tool such that the backing pad member can be replaced or interchanged in
a fast and easy way. In particular, it is an object of the invention to provide for
a small, lightweight and cheap solution, preferably without an additional adapter
and without having to modify existing power tools.
[0006] In order to solve this object, the present invention suggests a backing pad member
with the features of claim 1. In particular, starting from the backing pad member
of the above identified kind, it is suggested that the axial holding arrangement comprises
at least one permanent magnet on the one hand and at least one ferromagnetic element
or at least one further permanent magnet on the other hand exerting a magnetic force
for holding the protrusion member in the axial direction within the recess member,
wherein the at least one permanent magnet or the at least one ferromagnetic element
or the at least one further permanent magnet is located in or makes part of the recess
member.
[0007] Thus, an important aspect of the present invention is the idea of attaching a backing
pad performing a working movement with an orbital component to a power tool by means
of the mechanical form fit connection arrangement in combination with a magnetic axial
holding arrangement for holding the backing pad in an axial direction. It is particularly
advantageous that at least part of the magnetic axial holding arrangement is integrated
into and forms part of the mechanical form fit connection arrangement. In particular,
one of the components for realizing the axial magnetic holding arrangement, i.e. at
least one of the permanent magnets or at least one of the ferromagnetic elements,
is located in or makes part of the recess member provided on the top side of the backing
pad member.
[0008] It is suggested that the backing pad member is made of semi-rigid plastic material.
Preferably, the backing pad member has two opposing surfaces extending in parallel
to each other, the surfaces comprising a first bottom surface for releasable attachment
of a flexible sheet-like polishing or abrasive member by means of a hook-and-loop
fastener. The opposing surfaces of the backing pad member comprise an opposite top
surface with a backing pad-connection arrangement attached thereto, the backing pad-connection
arrangement comprising the recess member. The top surface of the backing pad member
is attached to the driving shaft of the power tool without the use of additional adapters
or the like.
[0009] It is suggested that a metal insert making part of the backing pad-connection arrangement
is moulded into the backing pad during its manufacturing allowing direct access to
the backing pad-connection arrangement. Hence, the metal insert constitutes or makes
part of the recess member of the backing pad member. In particular, the protrusion
member attached to the distal end of the driving shaft can directly access and engage
with the recess member provided on the top surface of the backing pad. The metal insert
can form the at least one ferromagnetic element or the at least one further permanent
magnet, which interacts with the at least one permanent magnet of the protrusion member.
[0010] The protrusion member can be directly attached to the driving shaft in a torque proof
manner, e.g. by means of a threaded connection. However, the protrusion member could
also be indirectly attached to driving shaft, e.g. by means of a tool-connection arrangement.
The tool-connection arrangement can be directly attached to the driving shaft in a
torque proof manner, e.g. by means of a threaded connection. The protrusion member
can be connected to the tool-connection arrangement in a freely rotatable manner,
e.g. guided in one or more bearings of the tool-connection arrangement. In this manner,
a random orbital working movement of the backing pad member can be achieved. It is
also possible that the tool-connection arrangement comprises a gear mechanism for
realizing a forced rotation of the protrusion member depending on the rotation of
the tool-connection arrangement about the rotational axis of the driving shaft. In
this manner, a roto-orbital (or gear driven) working movement of the backing pad member
can be achieved.
[0011] Furthermore, the proposed backing pad allows the continuous use of conventional power
tools with conventional tool-connection arrangements and protrusion members provided
at the distal end of the tool's driving shaft. The recess members are formed at least
in part by the metal insert moulded into the top surface of the backing pad during
its manufacturing. The engagement of the protrusion member with a corresponding recess
member provides for a form fit connection between the two members. In the axial direction
running parallel to the rotational axis of the backing pad, the backing pad is held
by magnetic force in respect to the rest of the power tool. To this end the backing
pad can be provided with at least one permanent magnet adapted for interacting with
at least one respective ferromagnetic element or further permanent magnet of opposite
polarity provided in the rest of the tool, in particular in the protrusion member.
Preferably, the protrusion member itself forms a ferromagnetic element with which
the at least one permanent magnet provided in the recess interacts. The magnetic force
acting between the backing pad and the rest of the power tool, in particular between
the protrusion member and the recess member, prevents an unintentional release of
the backing pad from the protrusion member. So instead of securing screws or similar
mechanical holding arrangements, the present invention uses the magnetic force of
a magnetic holding arrangement for securing the backing pad to the rest of the power
tool, in particular to the protrusion member.
[0012] The power tool with the backing pad and the flexible sheet-like polishing or abrasive
pad is also referred to as a polisher or a sander, which is often used for working
vehicle, boat or ship bodies. Depending on the type of gear arrangement provided between
the motor and the backing pad, the backing pad may perform a purely rotational, a
purely orbital, a random-orbital or a roto-orbital (gear driven) working movement.
In a top view the backing pad member preferably has a circular form and in a sectional
view an isosceles trapezoid form with the top surface being smaller than the bottom
surface and the top and the bottom surfaces being connected by means of an inclined
external wall section. Such a circular backing pad preferably is driven in a manner
to perform a random orbital or roto-orbital (gear driven) working movement. Alternatively,
in a top view the backing pad member may also have a triangle form, preferably with
the sides of the triangle slightly convexly arched to the outside. Such a triangular
backing pad preferably is driven in a manner to perform a purely orbital movement.
Of course, the backing pad may have any other desired form, too.
[0013] Preferably, the recess member in the plane extending perpendicular to the rotational
axis of the backing pad member has a circumferential form comprising two opposing
arc shaped sections of a circle with the rotational axis running through the circle's
centre and further comprising two opposing straight walls running essentially parallel
to one another and interconnecting the arc shaped sections. Alternatively, it is suggested
that the recess member in the plane extending perpendicular to the rotational axis
of the backing pad member has a circumferential form comprising a circle with the
rotational axis running through the circle's centre and further comprising two grooves
extending on opposite sides of the circle radially outwards.
[0014] According to a preferred embodiment of the present invention it is suggested that
a plurality of, preferably four, permanent magnets are located in the recess member
around and equidistant to the rotational axis of the backing pad member, with neighbouring
permanent magnets having opposite polarities. In such a manner the magnetic force
used for holding the recess member of the backing pad in the protrusion member of
the rest of the tool, can be increased considerably. The increase is not simply a
result of the greater number of permanent magnets but rather a combination with the
advantageous flow of the magnetic flux due to the opposite polarities of neighbouring
magnets.
[0015] Preferably, the plurality of permanent magnets are located such that neighbouring
permanent magnets are in direct lateral abutment with one another. Further, it is
suggested that the plurality of permanent magnets are located in direct contact with
one another along the rotational axis of the backing pad member.
[0016] The permanent magnets may have any desired form. However, it was found that certain
forms of permanent magnets have advantages over other forms in terms of compact arrangement
in the recess member and/or higher overall magnetic force. Preferably, the plurality
of permanent magnets each have the form of a triangle, in particular an isosceles
triangle, and the triangles are dimensioned such that the sum of the vertex angles
of all triangles is 360°. Alternatively, the plurality of permanent magnets each may
have the form of a circular sector, and the circular sectors are dimensioned such
that the circular sectors of all permanent magnets together form a circle.
[0017] It is further suggested that the recess member of the backing pad-connection arrangement
has a bottom surface in which the at least one permanent magnet is located adapted
for interacting with at least one ferromagnetic element or at least one further permanent
magnet attached to or making part of the protrusion member of the tool-connection
arrangement, wherein the at least one permanent magnet is located in the bottom surface
of the recess member facing the at least one ferromagnetic element or further permanent
magnet after insertion of the protrusion member into the recess member. Of course,
it would also be possible to locate the at least one ferromagnetic element or further
permanent magnet in the bottom surface of the recess member. In that case the at least
one first permanent magnet would be attached to or make part of the protrusion member.
The integration of the at least one permanent magnet or of the at least one ferromagnetic
element or of the at least one further permanent magnet into the recess member allows
a very small and compact design of the connection arrangement provided between the
backing pad member and the tool-connection arrangement. Furthermore, metal parts of
the tool-connection arrangement or the backing pad-connection arrangement can be used
as the at least one ferromagnetic element, thereby reducing the overall number of
separate parts necessary for realising the connection arrangement.
[0018] Even if during intended use of the power tool a force is applied to a side region
of the first surface of the backing pad member carrying the polishing or abrasive
member in a distance to the rotational axis of the backing pad member, the backing
pad member will not be tilted and detached from the tool-connection arrangement due
to the strong magnetic force acting directly in the region of the mechanical form
fit connection arrangement. The risk of tilting and detachment of the backing pad
from the tool-connection arrangement due to excessive force on the side region of
the first surface of the backing pad member can be reduced, if the lateral internal
side walls of the recess member and the corresponding lateral external side walls
of the protrusion member, respectively, lie against each other along their entire
surfaces. The risk of tilting and detachment of the backing pad from the tool-connection
arrangement due to excessive force on the side region of the backing pad member can
be further reduced, if the lateral internal side walls of the recess member and the
corresponding lateral external side walls of the protrusion member, respectively,
have a sufficiently long axial extension. This prevents the backing pad member from
being tilted about a tilting axis running essentially perpendicular to the rotational
axis of the backing pad member, when attached to the tool-connection arrangement;
the backing pad member can only be disconnected from the tool-connection arrangement
in the axial direction.
[0019] Despite the safe and reliable attachment of the backing pad member to the rest of
the power tool, the backing pad member can be easily and quickly removed from the
rest of the power tool by simply holding the backing pad member in one hand and the
rest of the power tool in the other hand and by applying a force in the axial direction
along the rotational axis of the backing pad member pulling them apart thereby overcoming
the magnetic force acting between them. No additional tools are required, no threaded
connections have to be loosened and fastened and the operator of the power tool can
keep on his working or safety gloves throughout the entire process of detachment of
a backing pad from the power tool and attachment of an alternative backing pad. Finally,
the attachment of the backing pad to the tool-connection arrangement proposed by the
present invention is particularly advantageous in the rough and dirt laden environment
of vehicle and boat detailing centres, vehicle body shops and shipyards, where the
power tool according to the present invention is often used. Dust and other small
debris particles cannot significantly impair the magnetic forces acting between the
backing pad member and the rest of the power tool and, therefore, even with some dust
and other small debris particles located between the backing pad member and the rest
of the power tool, a safe and secure attachment of the backing pad member to the rest
of the power tool in the axial direction can be achieved. This is usually not the
case with the conventional mechanical axial holding arrangements.
[0020] Preferred embodiments of the present invention are the subject of the dependent claims.
[0021] Further features and advantages of the present invention can be taken from the figures
and the following detailed description. The figures show:
- Fig. 1
- a power tool according to the present invention in a preferred embodiment in a perspective
view;
- Fig. 2
- the power tool of Fig. 1 in a sectional schematic view;
- Fig. 3
- a first type of tool-connection arrangement of a conventional power tool known in
the art;
- Fig. 4
- a second type of tool-connection arrangement of a conventional power tool known in
the art;
- Fig. 5
- a backing pad member of a conventional power tool known in the art;
- Fig. 6
- a first type of tool-connection arrangement of a power tool according to the present
invention;
- Fig. 7
- a second type of tool-connection arrangement of a power tool according to the present
invention;
- Fig. 8
- a first type of backing pad member according to the present invention connected to
a tool-connection arrangement of Fig. 6;
- Fig. 9
- the first type of backing pad member according to the present invention connected
to a tool-connection arrangement of Fig. 7;
- Fig. 10
- a second type of backing pad member according to the present invention;
- Fig. 11
- a tool-connection arrangement about to be connected to a backing pad-connection arrangement
according to the present invention;
- Fig. 12
- a top view on a backing pad and its backing pad connection arrangement according to
the present invention;
- Fig. 13
- a first embodiment of a magnetic axial holding arrangement;
- Fig. 14
- a second embodiment of a magnetic axial holding arrangement;
- Fig. 15
- a third embodiment of a magnetic axial holding arrangement;
- Fig. 16
- a fourth embodiment of a magnetic axial holding arrangement; and
- 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.
[0022] 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.
[0023] 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.
[0024] 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 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.
[0025] 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.
[0026] 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 bakcing pad
member 9, an axial holding arrangement is provided.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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 figures 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.
[0045] 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. 19mm, the parallel straight walls 18b are spaced appr. 17,2mm 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.
[0046] 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.
[0047] 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.
[0048] 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.
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 motor (11), the backing pad member (9)
having a rotational axis (13),
wherein the 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 backing pad member (9),
the mechanical form fit connection arrangement being adapted for providing a torque
proof connection between the protrusion member (16) and the 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 protrusion member (16) is held in the axial direction within the recess member
(17) by means of an axial holding arrangement,
characterized in 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),
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
recess member (17).
2. Backing pad member (9) according to claim 1, wherein the 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. Backing pad member (9) according to claim 2, wherein the opposing surfaces of the
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 recess member (17).
4. Backing pad member (9) according to one of the preceding claims, wherein the 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 backing pad member (9)
by means of a moulding or an injection moulding process, the metal insert forming
at least part of the recess member (17) and constituting the at least one ferromagnetic
element (41) or at least one further permanent magnet.
5. Backing pad member (9) according to one of the preceding claims, wherein the recess
member (17) in the plane extending perpendicular to the rotational axis (13) of the
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 circle's
centre and further comprising two opposing straight walls (18b) running essentially
parallel to one another and interconnecting the arc shaped sections (18a).
6. Backing pad member (9) according to one of the claims 1 to 4, wherein the 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 circle's centre and further comprising two grooves extending
on opposite sides of the circle radially outwards.
7. Backing pad member (9) according to one of the claims 1 to 4, wherein the recess member
(17) in the plane extending perpendicular to the rotational axis (13) of the backing
pad member (9) has a circumferential form of a polygon, in particular of a polygon
with equal side lengths, with the rotational axis (13) running through the polygon's
centre of gravity.
8. Backing pad member (9) according to one of the preceding claims, wherein 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.
9. Backing pad member (9) according to claim 8, wherein the plurality of permanent magnets
(40) are located such that neighbouring permanent magnets (40) are in direct lateral
abutment with one another.
10. Backing pad member (9) according to claim 8 or 9, wherein 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).
11. Backing pad member (9) according to one of the claims 8 to 10, wherein the plurality
of permanent magnets (40) each have the form of a triangle, preferably an isosceles
triangle, and wherein the triangles are dimensioned such that the sum of the vertex
angles of all triangles is 360°.
12. Backing pad member (9) according to one of the claims 8 to 10, wherein the plurality
of permanent magnets (40) each have the form of a circular sector, and wherein the
circular sectors are dimensioned such that the circular sectors of 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 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 protrusion member (16)
and the 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 protrusion member (16) is held in the axial
direction within the recess member (17) by means of an axial holding arrangement,
characterized in 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), 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. 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 recess member (17).
15. Power tool (1) according to claim 13 or 14, 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 protrusion member (16).
16. Power tool (1) according to one of the claims 13 to 15, 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 recess member (17).