Patent Description:
Polishing or sanding power tools of the above identified kind are well known in the prior art. For instance, RUPES S. from Vermezzo (MI), Italy, was the first company to develop and launch back in <NUM> the RUPES® Big Foot® iBrid® Nano, a mini polisher of the above-identified kind. The elongated tool housing is relatively compact especially with regard to its diameter and particularly light in weight. The tubular front part of the housing has an even smaller diameter than the rear part of the tool housing permitting a user of the power tool to reach tight and cramped spaces and to work (i.e. polish or sand) small surfaces, in particular in these tight and cramped spaces.

The known polishing or sanding power tools must have an electric motor of a certain strength in order to be able to operate the backing plate or the polishing or sanding member, respectively, with enough torque. Generally, the amount of torque which can be provided by an electric motor depends (apart from the magnetic force) on the motor's external diameter, limiting a virtual lever between a rotational axis of a rotor of the motor and a point of application of the magnetic force between a stator of the motor and the rotor. Therefore, for reasons of space, the electric motor is always located in the rear part of the tool housing of the known power tools, because the rear part of the tool housing has a larger diameter than the tubular front part. Besides, the rear part usually being made of plastic material can be easily provided with venting openings allowing a cooling air stream to dissipate heat from the electric motor and other electronic components of the power tool to the environment.

Due to its small inner diameter, the tubular front part of the tool housing cannot receive any of the components of the power tool except for an extension shaft mounted therein by means of bearings and connecting a motor shaft of the electric motor with a bevel gear arrangement and/or a tool shaft to which the backing plate is attached and which drives the backing plate in order to realize its working movement. The extension shaft merely serves for transferring a rotational speed and a torque from the motor shaft in the rear part of the tool housing to the bevel gear arrangement and/or the tool shaft in the tubular front part of the housing.

The diameter of the front part of the tool housing cannot simply be enhanced in order to accommodate a conventional electric motor therein because in that case a user of the power tool could no longer reach tight and cramped spaces and work (i.e. polish or sand) small surfaces in these tight and cramped spaces. Therefore, the present invention refers to rather compact so-called mini or nano polishers and sanders.

The known power tools have the disadvantage that the electric motor occupies a large amount of space in the rear part of the tool housing leaving only little space for other components of the power tool, like an electronic control unit, switches, potentiometers, receptacles for batteries etc. Furthermore, the fact that almost all components of the power tool are located in the rear part of the tool housing leads to an overweight in the rear part and to an uneven distribution of the weight.

Therefore, it is an object of the present invention to provide for a more equilibrated power tool having more space in the rear part of the tool housing for other components, like additional batteries. In particular, it is an object to use the space available inside the entire tool housing more efficiently.

This object is solved by a power tool according to claim <NUM>. In particular, starting from the power tool of the above-identified kind, it is suggested that at least part of the electric motor is accommodated in the tubular front part of the tool housing.

The invention suggests the use of a particularly slim electric motor which fits into the tubular front part of the tool housing. The invention requires the use of an electric motor in the power tool which has a smaller external diameter than the conventional electric motors usually used in known mini or nano polishers or sanders. Conventional electric motors have an external diameter of approximately <NUM>-<NUM>, in particular approximately <NUM>-<NUM>, so they can be accommodated only in the rear part of the tool housing having an external diameter of approximately <NUM>-<NUM>, in particular approximately <NUM>-<NUM>. The tubular front part of the tool housing has an external diameter of approximately <NUM>-<NUM>, in particular of approximately <NUM>-<NUM>. This means that the electric motor used in the power tool according to the invention must have an external diameter of less than the external diameter of the front part of the tool housing, in particular of approximately <NUM>-<NUM>, particularly preferred of <NUM>-<NUM>.

To this end, it is suggested that the electric motor has an outer diameter of less than <NUM>, preferably of less than <NUM>, particularly preferred of less than <NUM>.

A theoretically (due to the reduced diameter of the electric motor) reduced torque, which can be provided by the motor of the power tool according to the invention, can be compensated by the use of new highly efficient high-performance permanent magnets in the motor. Such magnets may be made of or may comprise a rare-earth metal, for example neodym. The use of such magnets in the electric motor can compensate for the smaller diameter of the motor with a greater magnetic force. A higher efficiency and smaller dimensions of the electric motor can also be obtained by the use of a brushless electric motor.

Further, in order to reduce the diameter of the tubular front part of the tool housing, the outer wall of the tubular front part could also be used as the stator of a brushless electric motor of the inrunner type (external stator and internal rotor, in contrast to an electric motor of the outrunner type). In that case, the electric motor would constitute an integral part of the tubular front part of the tool housing, i.e. would be integrated therein.

The present invention has the advantage that it provides for a more equilibrated power tool having more space in the rear part of the tool housing for other components, like additional batteries. In particular, the space available inside the entire tool housing can be used more efficiently.

Furthermore, cooling of the electric motor during its operation can be achieved rather easily if the external housing of the electric motor, which is usually made of metal, is in thermal contact (directly or indirectly by means of heat conducting elements) with the front part of the tool housing, which is preferably also made of metal. Heat can thus be dissipated directly from the electric motor to the environment via the front part of the housing.

The invention has the above indicated advantages even if only part of the electric motor is accommodated in the tubular front part of the tool housing. The more of the electric motor is accommodated in the front part of the tool housing, the more space is created in the rear part of the tool housing for other components of the power tool.

However, according to a preferred embodiment of the invention, it is suggested that the entire electric motor is accommodated in the tubular front part of the tool housing, thereby creating a maximum amount of space in the rear part of the tool housing for other components of the power tool.

Preferably, the rear part of the tool housing is made of a plastic material and/or the tubular front part of the tool housing is made of metal or a composite material comprising metal. The rear part of the tool housing can have a basically cylindrical form. However, indentations and protrusions may be provided on the outside of the rear part of the tool housing to give the rear part an ergonomic shape that facilitates gripping and holding of the power tool with one hand of the user.

The front part of the tool housing has an essentially cylindrical form. In particular, it is suggested that most part of the tubular front part of the tool housing has the form of a hollow cylinder. At a rear end of the front part of the tool housing, at the transition to the rear part, the front part may have a continuously or stepwise increasing external diameter. A cylindrical section may also be attached to a front end of the front part of the tool housing. At the transition from the front end to the cylindrical section, the external diameter of the front part of the tool housing may also increase continuously or stepwise.

A longitudinal extension of the cylindrical section preferably runs at an angle to the longitudinal extension of the tubular front part of the tool housing. The angle is preferably <NUM>°-<NUM>°, particularly preferably <NUM>°-<NUM>°, most preferably <NUM>°. While a motor shaft extends along the longitudinal extension of the front part of the tool housing, a tool shaft extends along the longitudinal extension of the front cylindrical section. An angular gear arrangement, in particular a bevel gear arrangement, is arranged between the shafts, inside the front part of the tool housing. A gearwheel of the angular gear arrangement, in particular a bevel gear wheel, may be attached or forms an integral part of the motor shaft. Another gearwheel of the angular gear arrangement, in particular another bevel gear wheel, in mesh with the first gearwheel may be attached or forms an integral part of the tool shaft.

Thus, it is suggested that a first rotational axis of a motor shaft of the electric motor and a second rotational axis of a tool shaft of the power tool, to which the backing plate is attached and which drives the backing plate in order to realize its working movement, extend in an angle in respect to each other. The angle is preferably in the range of <NUM>° to <NUM>°, preferably in the range of <NUM>° to <NUM>°, particularly preferable <NUM>°.

The backing plate may be directly or indirectly attached to the end of the tool shaft opposite to the angular gear arrangement. In the case where the backing plate is directly attached to the tool shaft, the backing plate performs a rotary working movement in the plane of extension of the backing plate.

In the case of an indirect attachment, an eccentric element may be disposed between the backing plate and the tool shaft. Preferably, the eccentric element is attached to the tool shaft in a torque proof manner, i.e. a torque may be transmitted from the tool shaft to the eccentric element. A rotary shaft of the backing plate, preferably provided on a top surface of the backing plate and extending along a rotational axis of the backing plate, is attached to the eccentric element in a freely rotatable manner. The rotational axes of the tool shaft and of the backing plate are spaced apart and extend parallel to each other. This results in a free rotation of the backing plate in respect to the eccentric element superimposing the forced rotational movement of the eccentric element about the rotational axis of the tool shaft, resulting in an overall so-called random-orbital working movement.

In case the free rotation of the backing plate in respect to the tool housing is blocked by means of one or more elastic or magnetic elements acting between the backing plate and the tool housing, the backing plate performs a so-called orbital (or eccentric) working movement. The elastic element may comprise a circumferential collar made of an elastic material, e.g. rubber or an elastomer, which is attached to the top surface of the backing plate and to the tool housing. Alternatively, one or more magnetic elements comprising magnets and/or ferromagnetic elements are provided in the tool housing and in corresponding positions in the top surface of the backing plate. The corresponding magnetic elements attract each other magnetically, thereby limiting the free rotation of the backing plate in respect to the tool housing.

Finally, it is also possible that the backing plate is indirectly attached to the tool shaft by means of a gear arrangement, in particular an epicyclic or planetary gear arrangement. The tool shaft is attached or forms an integral part of a first gear wheel of the gear arrangement. A rotary shaft of the backing plate, preferably provided on a top surface of the backing plate and extending along a rotational axis of the backing plate, is attached to another gear wheel of the gear arrangement. The rotational axes of the tool shaft and of the backing plate are spaced apart and extend parallel to each other. During rotation of the tool shaft the backing plate performs a so-called gear-driven working movement. With that type of working movement, every complete rotation of the backing plate around its rotational axis corresponds to a fixed number of orbits of the backing plate. The fixed number of orbits depends on the design of the gear arrangement and can vary between approximately <NUM> and <NUM>, in particular between <NUM> and <NUM>, particularly preferred between <NUM> and <NUM>.

The eccentric element or the gear arrangement provided functionally between the tool shaft and the rotary shaft of the backing plate may be covered by means of a protective cap or shroud, which may be attached to a distal or bottom end of the cylindrical section of the front part of the tool housing. The protective cap or shroud is preferably made of plastic and/or rubber material. It may be detachably attached to the cylindrical section, e.g. by means of one or more magnets, snap-in connections or a threaded connection. In the latter case, the distal or bottom end of the cylindrical section may be provided with an external thread, and the top end of the cap or shroud may be provided with a respective internal thread adapted to be screwed onto the distal or bottom end of the cylindrical section.

The eccentric element is preferably detachably attached to the tool shaft allowing replacement of a first eccentric element by another eccentric element, e.g. having another orbit than the first eccentric element. In this manner, the orbit of the random-orbital working movement of the backing plate may be switched between, e.g. <NUM> and <NUM> or other values. Furthermore, the eccentric element could be replaced by a simple shaft-like extension element or the backing plate could be attached directly to the distal end of the tool shaft, resulting in a rotary working movement of the backing plate. In this manner, the working movement of the backing plate could be switched between a random-orbital and a rotary working movement.

The eccentric element could be attached to the tool shaft by means of a snap-in connection or a threaded connection or in any other way. The snap-in connection holds the eccentric element in respect to the tool shaft in an axial direction, i.e. parallel to the rotational axis of the tool shaft. In a circumferential direction, i.e. in a plane extending perpendicularly in respect to the axial direction and the rotational axis of the tool shaft, a form-fit connection may be provided preventing rotation of the eccentric element in respect to the tool shaft about the rotational axis of the tool shaft.

According to another preferred embodiment of the invention, it is suggested that a reduction gear arrangement is located functionally between the motor shaft of the electric motor and the tool shaft of the power tool to which the backing plate is attached and which drives the backing plate in order to realize its working movement. A reduction gear reduces the speed between input and output, i.e. between the motor shaft and the tool shaft, by a given ratio i > <NUM>. In return, the torque is increased accordingly in the same ratio. According to DIN, the transmission ratio i is defined as the quotient of the speed of the input and the speed of the output, i.e. the quotient of the speed of the motor shaft and the speed of the tool shaft. If the ratio i > <NUM>, the speed is reduced but the transmitted torque is increased. According to this embodiment a very high-speed motor is used, which preferably achieves a maximum speed of at least <NUM>,<NUM> rpm, preferably at least <NUM>,<NUM> rpm, particularly preferable at least <NUM>,<NUM> rpm. The rather high speed of the motor shaft is reduced by the reduction gear arrangement to a maximum speed of at least <NUM>,<NUM> rpm, preferably at least <NUM>,<NUM> rpm, particularly preferable at least <NUM>,<NUM> rpm. At the same time, the torque acting on the backing plate is significantly increased. A reduction in torque caused by the slimmer design and the reduced diameter of the electric motor can be compensated for by the reduction gear.

The reduction gear arrangement may be separate from or may form an integral part of the bevel gear arrangement, which is located functionally between the motor shaft of the electric motor and the tool shaft of the power tool to which the backing plate is attached and which drives the backing plate in order to realize its working movement. Thus, the bevel gear arrangement may have a transmission ratio i of i = <NUM> (requiring a separate reduction gear arrangement if a speed reduction and torque enhancement is desired) or of i > <NUM> (with the reduction gear arrangement forming an integral part of the bevel gear arrangement).

It is further suggested that the rear part of the tool housing is provided with actuating means for turning the electric motor on or off and/or with adjustment means for adjusting a speed of the electric motor, wherein the actuating means and/or the adjustment means are arranged and designed to be operated from outside the tool housing by a user's hand or finger. According to this embodiment, the power tool is not only held by a user's hand at the rear part of the tool housing, but can also be operated by the user with his hand from the rear part of the tool housing. Operation of the power tool may comprise turning on and/or off the electric motor thereby setting the backing plate into rotation or stopping its rotation and/or adjusting the speed of the electric motor and, consequently, of the backing plate. Additionally, operation of the power tool may comprise the control of other functions of the power tool, e.g. a light for illuminating a working surface on which the polishing or sanding member attached to the backing plate works during intended use of the power tool or a turbo mode, in which the speed of the electric motor can be temporarily further increased for a short period of time.

The actuating means and/or the adjustment means are preferably arranged in the rear part of the tool housing and designed to be operated from outside the tool housing by the user's hand or finger when holding the power tool with his hand. To this end, actuating elements in connection with the actuating means and/or the adjustment means are provided in the rear part of the tool housing, preferably in a manner protruding from the outside surface of the rear part of the housing. The actuating elements may comprise sliding elements, toggle elements, push buttons and/or rotating elements, such as knurled wheels or the like.

It is further suggested that the actuating means comprise an actuating switch or an actuating lever. The actuating lever may have a longitudinal extension running parallel to the longitudinal extension of the tool housing. The actuating lever is preferably attached to the tool housing pivotable about a pivot axis extending perpendicular to the longitudinal extension of the lever. The actuating lever may be attached to a top surface of the rear part of the tool housing permitting actuation by means of a user's handball when holding the power tool with his hand. Alternatively, the actuating lever may be attached to a bottom surface of the rear part of the tool housing permitting actuation by means of a user's fingers when holding the power tool with his hand. The actuating switch is preferably arranged in the rear part of the tool housing such that it can be actuated by a user's thumb when holding the power tool with his hand.

According to another embodiment of the invention, it is suggested that the adjustment means comprise a potentiometer, preferably with a rotating contact forming an adjustable voltage divider, or two push buttons, one for increasing and another one for decreasing the speed of the electric motor. Preferably, the potentiometer is in connection with a rotating actuating element, such as a knurled wheel or the like. The actuating element is rotatable about a rotation axis which extends radially in respect to the longitudinal extension of the tool housing. Rotation of the rotating actuating element adjusts the voltage divider and changes the output voltage (corresponding to the input voltage of the electric motor) and, thus, the speed of the electric motor.

Further features and advantages of the present invention are described in more detail in the following description referring to the accompanying drawings. The figures show:.

A hand-held electric polishing or sanding power tool <NUM> according to a preferred embodiment of the present invention is shown in <FIG>. The power tool <NUM> comprises an elongated tool housing, in which an electric motor <NUM> is accommodated. The tool housing has a rear part preferably made of plastic and adapted and formed to be gripped by a hand of a user of the power tool <NUM> thereby holding the power tool <NUM> during its intended use. In the shown embodiment, the rear part of the tool housing is made up of two halves, a right half <NUM> and a left half <NUM>, which are screwed together by means of screws <NUM>. The rear part <NUM>, <NUM> of the tool housing is preferably manufactured by means of injection moulding.

The tool housing further comprises a tubular front part <NUM> preferably made of metal, in particular aluminium, or a material compound comprising a metal. The front part <NUM> of the tool housing is preferably made by milling or by die cast. The front part <NUM> may be attached to the rear part <NUM>, <NUM> of the tool housing, e.g. by means of a threaded connection, screws or the like. It would also be conceivable for the front part <NUM> of the tool housing to be inserted between the two halves <NUM>, <NUM> of the rear part of the tool housing and to be held in place by them when the two halves <NUM>, <NUM> are closed and fastened together. It is further conceivable that the front part <NUM> of the tool housing may be attached to the rear part <NUM>, <NUM> in at least two different rotational positions about a longitudinal axis of the tool housing, the longitudinal axis extending parallel to a longitudinal extension <NUM> of the tubular front part <NUM> of the tool housing. The front part <NUM> has a smaller external diameter than the rear part <NUM>, <NUM> of the tool housing.

Furthermore, the power tool <NUM> has a moveable backing plate <NUM> protruding externally from the tool housing, in particular from the front part <NUM> of the tool housing. The electric motor <NUM> is adapted to actuate the backing plate <NUM>. Depending on the type of connection of the backing plate <NUM> to a tool shaft <NUM> of the power tool <NUM>, the backing plate <NUM> may perform a rotational, a random-orbital, an orbital (or eccentric) or a gear-driven working movement in its plane of extension. The backing plate <NUM> is preferably made of a rigid plastic material and/or metal. The backing plate <NUM> may comprise a resilient bottom layer made of an elastic plastic material, rubber or the like, and fixedly attached to a bottom surface of the rigid plastic and/or metal.

A bottom surface of the backing plate <NUM> is adapted to detachably hold a polishing or sanding member <NUM> (see <FIG>). The bottom surface may be formed by the rigid plastic and/or metal or it may be formed by the resilient bottom layer, if present. To this end, the bottom surface of the backing plate <NUM> may be provided with an adhesive layer or with a layer of a hook-and-loop fastener (Velcro®). The polishing or sanding member <NUM> may have a corresponding even top surface for attachment to the adhesive layer or a corresponding layer of the hook-and-loop fastener (Velcro®) for attachment to the layer of a hook-and-loop fastener of the bottom surface of the backing plate <NUM>. Of course, other types of releasable attachment of a polishing or sanding member <NUM> to the bottom surface of the backing plate <NUM> are conceivable, too, e.g. by means of adhesion or a detachable adhesive connection.

<FIG> shows a polishing or sanding power tool <NUM> known in the prior art. The elongated tool housing <NUM>, <NUM>, <NUM> is relatively compact especially with regard to its external diameter and particularly light in weight. The tubular front part <NUM> of the housing has an even smaller diameter than the rear part <NUM>, <NUM> of the tool housing permitting a user of the power tool <NUM> to reach tight and cramped spaces and to work (i.e. polish or sand) small surfaces, in particular in these tight and cramped spaces.

In the known power tools <NUM>, for reasons of space, the electric motor <NUM> is always located in the rear part <NUM>, <NUM> of the tool housing, because the rear part <NUM>, <NUM> has a larger diameter than the tubular front part <NUM>. The reason for this is that electric motors <NUM> providing a sufficiently large maximum torque for use in the power tools <NUM> have a respectively large external diameter which will fit in the rear part <NUM>, <NUM> of the tool housing only. Besides, the rear part <NUM>, <NUM> usually being made of plastic material can be easily provided with venting openings <NUM> allowing a cooling air stream to dissipate heat from the electric motor <NUM> and other electronic components of the power tool <NUM> to the environment.

Conventional electric motors <NUM> have an external diameter of approximately <NUM>-<NUM>, in particular approximately <NUM>-<NUM>, so they can be accommodated only in the rear part <NUM>, <NUM> of the tool housing having an external diameter of approximately <NUM>-<NUM>, in particular approximately <NUM>-<NUM>.

Due to its small inner diameter, the tubular front part <NUM> of the tool housing cannot receive any of the components of the power tool <NUM> except for an extension shaft <NUM> mounted therein by means of bearings <NUM>, <NUM> and connecting a motor shaft <NUM> of the electric motor <NUM> with a bevel gear arrangement <NUM>, <NUM> and/or a tool shaft <NUM> to which the backing plate <NUM> is attached and which drives the backing plate <NUM> in order to realize its working movement. The extension shaft <NUM> merely serves for transferring a rotational speed and a torque from the motor shaft <NUM> in the rear part <NUM>, <NUM> of the tool housing to the bevel gear arrangement <NUM>, <NUM> and/or the tool shaft <NUM> in the tubular front part <NUM> of the tool housing.

The diameter of the front part <NUM> of the tool housing cannot simply be enhanced in order to accommodate a conventional electric motor <NUM> therein because in that case a user of the power tool <NUM> could no longer reach tight and cramped spaces and work (i.e. polish or sand) small surfaces in these tight and cramped spaces. Therefore, the present invention refers to rather compact so-called mini or nano polishers and sanders.

The known power tools <NUM>, like the one shown in <FIG>, have the disadvantage that the electric motor <NUM> occupies a large amount of space in the rear part <NUM>, <NUM> of the tool housing leaving only little space for other components of the power tool <NUM>, like an electronic control unit, a printed circuit board, switches, potentiometers <NUM>, receptacles for a battery <NUM> etc. Furthermore, the fact that almost all components of the power tool <NUM> are located in the rear part <NUM>, <NUM> of the tool housing leads to an overweight in the rear part <NUM>, <NUM> and to an uneven distribution of the weight.

As can be seen in <FIG>, in order to overcome these deficiencies of the known prior art mini or nano polishing or sanding power tools <NUM>, the invention suggests that at least part of the electric motor <NUM> is accommodated in the tubular front part <NUM> of the tool housing.

The invention suggests the use of a particularly slim electric motor <NUM> which fits into the tubular front part <NUM> of the tool housing. The invention requires the use of an electric motor <NUM> in the power tool <NUM> which has a smaller external diameter than the conventional electric motors usually used in known mini or nano polishers or sanders. The tubular front part <NUM> of the tool housing has an external diameter of approximately <NUM>-<NUM>, in particular of approximately <NUM>-<NUM>. This means that the electric motor <NUM> used in the power tool <NUM> according to the invention must have an external diameter of less than the external diameter of the front part <NUM> of the tool housing, in particular of approximately <NUM>-<NUM>, particularly preferred of <NUM>-<NUM>. To this end, it is suggested that the electric motor <NUM> has an outer diameter of less than <NUM>, preferably of less than <NUM>, particularly preferred of less than <NUM>.

A theoretically (due to the reduced diameter of the electric motor <NUM>) reduced torque, which can be provided by the motor <NUM> of the power tool <NUM> according to the invention, can be compensated by the use of new highly efficient high-performance permanent magnets in the motor <NUM>. Such magnets may be made of or may comprise a rare-earth metal, for example neodym. The use of such magnets in the electric motor <NUM> can compensate for the smaller diameter of the motor <NUM> with a greater magnetic force. A higher efficiency and smaller dimensions of the electric motor <NUM> can also be achieved by the use of a brushless motor.

The present invention has the advantage that it provides for a more equilibrated power tool <NUM> having more space <NUM> in the rear part of the tool housing for other components, like additional batteries. In particular, the space <NUM> available inside the entire tool housing <NUM>, <NUM>, <NUM> can be used more efficiently.

Furthermore, cooling of the electric motor <NUM> during its operation can be achieved rather easily if the external housing of the electric motor <NUM>, which is usually made of metal, is in thermal contact (directly or indirectly by means of heat conducting elements) with the front part <NUM> of the tool housing, which is preferably also made of metal. Heat can thus be dissipated directly from the electric motor <NUM> to the environment via the metal front part <NUM> of the housing.

The invention has the above indicated advantages even if only part of the electric motor <NUM> is accommodated in the tubular front part <NUM> of the tool housing. The more of the electric motor <NUM> is accommodated in the front part <NUM> of the tool housing, the more (the larger a) space <NUM> is created in the rear part <NUM>, <NUM> of the tool housing for other components of the power tool <NUM>. However, according to a preferred embodiment of the invention, it is suggested that the entire electric motor <NUM> is accommodated in the tubular front part <NUM> of the tool housing, thereby creating a maximum amount of space <NUM> in the rear part <NUM>, <NUM> of the tool housing for other components of the power tool <NUM>.

Preferably, the rear part <NUM>, <NUM> of the tool housing is made of a plastic material and/or the tubular front part <NUM> of the tool housing is made of metal or a composite material comprising metal. The rear part <NUM>, <NUM> of the tool housing can have a basically cylindrical form. However, indentations <NUM> and protrusions <NUM> (see <FIG>) may be provided on the outside of the rear part <NUM>, <NUM> of the tool housing to give the rear part <NUM>, <NUM> an ergonomic shape that facilitates gripping and holding of the power tool <NUM> with one hand of the user.

The front part <NUM> of the tool housing has an essentially cylindrical form. In particular, it is suggested that most part of the tubular front part <NUM> of the tool housing has the form of a hollow cylinder. As can be seen in <FIG> and <FIG>, at a rear end <NUM> of the front part <NUM> of the tool housing, at the transition to the rear part <NUM>, <NUM>, the front part <NUM> may have a continuously or stepwise increasing external diameter. A cylindrical section <NUM> may also be attached to a front end <NUM> of the front part <NUM> of the tool housing. At the transition from the front end <NUM> to the cylindrical section <NUM>, the external diameter of the front part <NUM> of the tool housing may also increase continuously or stepwise.

A longitudinal extension <NUM> of the cylindrical section <NUM> preferably runs at an angle α in respect to the longitudinal extension <NUM> of the tubular front part <NUM> of the tool housing. Theoretically, the angle α may have any desired value in the range of <NUM>° to <NUM>°. The angle α is preferably <NUM>°-<NUM>°, particularly preferably <NUM>°-<NUM>°, most preferably <NUM>°. In the embodiment of <FIG> and <FIG>, the angle α is exactly <NUM>°. In the embodiment of <FIG>, the angle α is approximately <NUM>°.

While a motor shaft <NUM> extends along the longitudinal extension <NUM> of the front part <NUM> of the tool housing, the tool shaft <NUM> extends along the longitudinal extension <NUM> of the front cylindrical section <NUM>. To this end, bearings <NUM>, <NUM> may be provided inside the cylindrical section <NUM> which receive and guide the tool shaft <NUM> in a freely rotatable manner. An angular gear arrangement <NUM>, <NUM>, in particular a bevel gear arrangement, is arranged between the shafts <NUM>, <NUM>, inside the front part <NUM> of the tool housing. No or only a very small extension shaft, similar to extension shaft <NUM> of <FIG>, is provided between the motor shaft <NUM> and the bevel gear arrangement <NUM>, <NUM>. A gearwheel <NUM> of the angular gear arrangement, in particular a bevel gear wheel, forms an integral part of the motor shaft <NUM>. Of course, the gearwheel <NUM> may also be designed separately from the motor shaft <NUM> and attached thereto. Furthermore, the gearwheel <NUM> could also be attached to a short extension shaft provided between the motor shaft <NUM> and the gear arrangement <NUM>, <NUM>. Another gearwheel <NUM> of the angular gear arrangement, in particular another bevel gear wheel, in mesh with the first gearwheel <NUM> is attached to the tool shaft <NUM>. Of course, the gearwheel <NUM> may also form an integral part of the tool shaft <NUM>.

The backing plate <NUM> may be directly attached to the distal end of the tool shaft <NUM> opposite to the angular gear arrangement <NUM>, <NUM> (see <FIG>). In this case, the backing plate <NUM> performs a rotary working movement in the plane of extension of the backing plate <NUM>. A rotational axis of the backing plate <NUM> and a rotational axis of the tool shaft <NUM> are congruent and correspond to the longitudinal extension <NUM> of the front cylindrical section <NUM>. A direct attachment of the backing plate <NUM> to the tool shaft <NUM> also comprises the case where a shaft-like extension element <NUM> with one end is attached to the tool shaft <NUM> and with its opposite end is attached to the backing plate <NUM> (see <FIG>). Preferably, the extension element <NUM> is attached to the tool shaft <NUM> and to the backing plate <NUM> in a torque proof manner, i.e. a torque may be transmitted from the tool shaft <NUM> to the backing plate <NUM>.

Alternatively, the backing plate <NUM> is indirectly attached to the distal end of the tool shaft <NUM> (see <FIG>). In this case, an eccentric element <NUM> may be disposed between the backing plate <NUM> and the tool shaft <NUM> (see <FIG>). Preferably, the eccentric element <NUM> is attached to the tool shaft <NUM> in a torque proof manner, i.e. a torque may be transmitted from the tool shaft <NUM> to the eccentric element <NUM>. A rotary shaft <NUM> of the backing plate <NUM>, preferably provided on a top surface of the backing plate <NUM> and extending along a rotational axis of the backing plate <NUM>, is attached to the eccentric element <NUM> in a freely rotatable manner. To this end, a bearing <NUM> is provided in the eccentric element <NUM>, which is adapted to receive and receive in a freely rotatable manner the rotatory shaft <NUM> of the backing plate <NUM>. The rotational axes of the tool shaft <NUM> and of the backing plate <NUM> are spaced apart and extend parallel to each other. This results in a free rotation of the backing plate <NUM> in respect to the eccentric element <NUM> superimposing the forced rotational movement of the eccentric element <NUM> about the rotational axis of the tool shaft <NUM>, resulting in a so-called random-orbital working movement.

In the embodiment of <FIG>, the rotary shaft <NUM> of the backing plate <NUM> is attached thereto by means of a separate threaded seat <NUM>. Of course, it would also be possible, that the rotary shaft <NUM> is directly attached to the backing plate <NUM> or that the rotary shaft <NUM> forms an integral part of a top surface of the backing plate <NUM>, thereby allowing omission of the threaded seat <NUM>.

In case the free rotation of the backing plate <NUM> in respect to the tool housing <NUM>, <NUM>, <NUM> is blocked by means of one or more elastic or magnetic elements (not shown) acting between the backing plate <NUM> and the tool housing <NUM>, <NUM>, <NUM>, the backing plate <NUM> performs a so-called orbital (or eccentric) working movement. The elastic element may comprise a circumferential collar made of an elastic material, e.g. rubber or an elastomer, which is attached to the top surface of the backing plate <NUM> and to the tool housing <NUM>, <NUM>, <NUM>. Alternatively, one or more magnetic elements comprising magnets and/or ferromagnetic elements are provided in the tool housing <NUM>, <NUM>, <NUM> and in corresponding positions in the top surface of the backing plate <NUM>. The corresponding magnetic elements attract each other magnetically, thereby limiting the free rotation of the backing plate <NUM> in respect to the tool housing <NUM>, <NUM>, <NUM> (e.g. see <CIT>).

Finally, it is also possible that the backing plate <NUM> is indirectly attached to the tool shaft <NUM> by means of a gear arrangement, in particular an epicyclic or planetary gear arrangement (not shown). The tool shaft <NUM> is attached or forms an integral part of a first gear wheel of the gear arrangement. A rotary shaft <NUM> of the backing plate <NUM>, preferably provided on a top surface of the backing plate <NUM> and extending along a rotational axis of the backing plate <NUM>, is attached to another gear wheel of the gear arrangement. The rotational axes of the tool shaft <NUM> and of the backing plate <NUM> are spaced apart and extend parallel to each other. During rotation of the tool shaft <NUM> the backing plate <NUM> performs a so-called gear-driven working movement. With that type of working movement, every complete rotation of the backing plate <NUM> around its rotational axis <NUM> corresponds to a fixed number of orbits of the backing plate <NUM>. The fixed number of orbits depends on the design of the gear arrangement and can vary between approximately <NUM> and <NUM>, in particular between <NUM> and <NUM>, particularly preferred between <NUM> and <NUM>.

The eccentric element <NUM> or the gear arrangement provided functionally between the tool shaft <NUM> and the rotary shaft <NUM> of the backing plate <NUM> may be covered by means of a protective cap or shroud <NUM>, which may be attached to a distal or bottom end of the cylindrical section <NUM> of the front part <NUM> of the tool housing. The protective cap or shroud <NUM> is preferably made of plastic and/or rubber material. It may be detachably attached to the cylindrical section <NUM>, e.g. by means of one or more magnets (e.g. see <CIT>), snap-in connections <NUM> or a threaded connection. In the latter case, the distal or bottom end of the cylindrical section <NUM> may be provided with an external thread, and the top end of the cap or shroud <NUM> may be provided with a respective internal thread adapted to be screwed onto the distal or bottom end of the cylindrical section <NUM>. Additionally, the cylindrical section <NUM> may be completely covered by a damping cap (not shown) made of a resilient material, in order to avoid scratches or damage of the area to be worked, in particular in tight and cramped spaces, by the metal of the cylindrical section <NUM>.

The eccentric element <NUM> is preferably detachably attached to the tool shaft <NUM> allowing replacement of a first eccentric element <NUM> by another eccentric element <NUM> (see <FIG>), e.g. having another orbit than the first eccentric element <NUM>. In this manner, the orbit of the random-orbital working movement of the backing plate <NUM> may be switched between, e.g. <NUM> and <NUM> or other values. Furthermore, the eccentric element <NUM> could be replaced by a simple shaft-like extension element <NUM> (see <FIG>) or the backing plate <NUM> could be attached directly to the distal end of the tool shaft <NUM> (see <FIG>), resulting in a rotary working movement of the backing plate <NUM>. In this manner, the working movement of the backing plate <NUM> could be switched between a random-orbital and a rotary working movement.

Rotation of the tool shaft <NUM> should be blocked during detachment and attachment of the eccentric element <NUM> or the shaft-like extension element <NUM> or the backing pad <NUM> from/ to the tool shaft <NUM>. This may be achieved by means of a tool <NUM>, e.g. a wrench, to be inserted through a slit of the cap or shroud <NUM> in order to engage with the tool shaft <NUM> and to prevent it from rotating (see <FIG>). Alternatively, the rotation of the tool shaft <NUM> during detachment and attachment of the eccentric element <NUM> or the shaft-like extension element <NUM> or the backing pad <NUM> from/ to the tool shaft <NUM> may be achieved by means of a blocking mechanism making part of the power tool <NUM> and being actuated by pressing a blocking button <NUM> (see <FIG>). Of course, the blocking button <NUM> could also be located at any other position on the front part <NUM> of the tool housing.

The eccentric element <NUM> could be attached to the tool shaft <NUM> by means of a snap-in connection or a threaded connection or in any other way. The snap-in connection holds the eccentric element <NUM> in respect to the tool shaft <NUM> in an axial direction, i.e. parallel to the rotational axis (corresponding to the longitudinal extension <NUM>) of the tool shaft <NUM>. In a circumferential direction, i.e. in a plane extending perpendicularly in respect to the axial direction and the rotational axis of the tool shaft <NUM>, a form-fit connection may be provided preventing rotation of the eccentric element <NUM> in respect to the tool shaft <NUM> about the rotational axis of the tool shaft <NUM>.

According to another preferred embodiment of the invention, it is suggested that a reduction gear arrangement <NUM> is located functionally between the motor shaft <NUM> of the electric motor <NUM> and the tool shaft <NUM> of the power tool <NUM> to which the backing plate <NUM> is attached and which drives the backing plate <NUM> in order to realize its working movement. The reduction gear <NUM> reduces the speed between input and output, i.e. between the motor shaft <NUM> and intermediary output shaft <NUM> or the tool shaft <NUM>, respectively, by a given ratio i > <NUM>. In return, the torque is increased accordingly in the same ratio i. According to DIN, the transmission ratio i is defined as the quotient of the speed of the input and the speed of the output, i.e. the quotient of the speed of the motor shaft <NUM> and the speed of the output shaft <NUM> or the tool shaft <NUM>, respectively. If the ratio i > <NUM>, the speed is reduced but the transmitted torque is increased. According to this embodiment a very high-speed motor <NUM> is used, which preferably achieves a maximum speed of at least <NUM>,<NUM> rpm, preferably at least <NUM>,<NUM> rpm, particularly preferable at least <NUM>,<NUM> rpm. The rather high speed of the motor shaft <NUM> is reduced by the reduction gear arrangement <NUM> to a maximum speed of at least <NUM>,<NUM> rpm, preferably at least <NUM>,<NUM> rpm, particularly preferable at least <NUM>,<NUM> rpm. At the same time, the torque acting on the backing plate <NUM> is significantly increased. A reduction in torque caused by the slimmer design and the reduced diameter of the electric motor <NUM> can be compensated for by the reduction gear arrangement <NUM>.

The reduction gear arrangement <NUM> may be separate from or may form an integral part of the bevel gear arrangement <NUM>, <NUM>, which is located functionally between the motor shaft <NUM> of the electric motor <NUM> and the tool shaft <NUM> of the power tool <NUM>. In the embodiment of <FIG> a reduction gear arrangement <NUM> separate from the bevel gear arrangement <NUM>, <NUM> is shown. In this case, the bevel gear arrangement <NUM>, <NUM> may have a transmission ratio i of i = <NUM>. The speed reduction and torque enhancement is effected by the separate reduction gear arrangement <NUM> having a transmission ratio of I > <NUM>.

When a separate reduction gear arrangement <NUM> is used, the gear wheel <NUM> of the angular gear arrangement is preferably attached to or forms an integral part of the output shaft <NUM> of the reduction gear arrangement <NUM>. The motor shaft <NUM> acts as input shaft of the reduction gear arrangement <NUM>. The separate reduction gear arrangement <NUM> is preferably also housed by the tubular front part <NUM> of the tool housing, in particular between the electric motor <NUM> and the bevel gear <NUM>.

In the embodiment of <FIG> a reduction gear arrangement <NUM> forming an integral part of the bevel gear arrangement <NUM>, <NUM> is shown. In this case, the bevel gear arrangement <NUM>, <NUM> may have a transmission ratio i of i > <NUM> thereby providing for the speed reduction and torque enhancement.

It is further suggested that the rear part <NUM>, <NUM> of the tool housing is provided with actuating means <NUM> for turning the electric motor <NUM> on or off and/or with adjustment means <NUM> for adjusting a speed of the electric motor <NUM>. The actuating means <NUM> and/or the adjustment means <NUM> are arranged and designed to be operated from outside the tool housing <NUM>, <NUM>, <NUM> by a user's hand or finger. The actuating means <NUM> and/or the adjustment means <NUM> may comprise a switch, a potentiometer or the like.

According to this embodiment, the power tool <NUM> is not only held by a user's hand at the rear part <NUM>, <NUM> of the tool housing, but can also be operated by the user with his hand or fingers from the rear part <NUM>, <NUM> of the tool housing. Operation of the power tool <NUM> may comprise turning on and/or off the electric motor <NUM> thereby setting the backing plate <NUM> into rotation or stopping its rotation and/or adjusting the speed of the electric motor <NUM> and, consequently, of the backing plate <NUM>. Additionally, operation of the power tool <NUM> may comprise the control of other functions of the power tool <NUM>, e.g. a light for illuminating a working surface on which the polishing or sanding member <NUM> attached to the backing plate <NUM> works during intended use of the power tool <NUM> or a turbo mode, in which the speed of the electric motor <NUM> can be temporarily further increased for a short period of time.

Actuating elements <NUM>, <NUM> in connection with the actuating means <NUM> and/or the adjustment means <NUM> are provided in the rear part <NUM>, <NUM> of the tool housing, preferably in a manner protruding from the outside surface of the rear part <NUM>, <NUM> of the housing. An actuating element in connection with the adjustment means <NUM> may comprise a sliding element, a toggle element, a push button <NUM>, <NUM> and/or a rotating element <NUM>, such as s knurled wheel or the like. An actuating element in connection with the actuating means <NUM> may comprise a sliding element <NUM>, a push button, a rotating element <NUM>, such as a knurled wheel, or an actuating lever <NUM>.

The actuating lever <NUM> may have a longitudinal extension running parallel to the longitudinal extension of the tool housing <NUM>, <NUM>, <NUM>. The actuating lever <NUM> is attached to the rear part <NUM>, <NUM> of the tool housing pivotable about a pivot axis <NUM> extending perpendicular to the longitudinal extension of the lever <NUM>. In the embodiment of <FIG>, the actuating lever <NUM> is attached to a top surface of the rear part <NUM>, <NUM> of the tool housing permitting actuation by means of a user's handball when holding the power tool <NUM> with his hand. In the embodiment of <FIG>, the actuating lever <NUM> is attached to a bottom surface of the rear part <NUM>, <NUM> of the tool housing permitting actuation by means of a user's fingers when holding the power tool <NUM> with his hand. An actuating switch is arranged in the rear part <NUM>, <NUM> of the tool housing such that it may be actuated by the lever <NUM>. A spring <NUM> may be provided in order to force the lever <NUM> away from the rear part <NUM>, <NUM> of the tool housing when not actuated by the user.

The potentiometer <NUM> of the adjustment means <NUM> has a rotating contact forming an adjustable voltage divider. The rotating actuating element <NUM>, e.g. a knurled wheel, is rotatable about a rotation axis which extends radially in respect to the longitudinal extension of the tool housing. The rotating element <NUM> is located in an elevation on the top of the rear part <NUM>, <NUM> of the tool housing. The elevation has lateral cut-outs <NUM> permitting access to and actuation of the rotating element <NUM>. The rotating element <NUM> may be attached to the rotating contact of the potentiometer <NUM> thereby allowing adjustment of the output voltage of the potentiometer <NUM> when rotating the rotating element <NUM>. Rotation of the rotating actuating element <NUM> adjusts the voltage divider and changes the output voltage (corresponding to the input voltage of the electric motor <NUM>) and, thus, the speed of the electric motor <NUM>.

In an alternative embodiment shown in <FIG>, the actuating means <NUM> for turning the electric motor <NUM> on or off comprise a toggle switch <NUM> which is actuated by means of an actuating element in the form of a sliding element <NUM>. The sliding element <NUM> and the corresponding toggle switch <NUM> can be switched between a "ON"-position, indicated by "<NUM>" and an "OFF"-position, indicated by "<NUM>". The adjustment means <NUM> for adjusting the speed of the electric motor <NUM> comprise two pressure switches <NUM>, <NUM> which are actuated by means of adjustment elements comprising two push buttons <NUM>, <NUM>. One of the push buttons <NUM> is marked with "-" for reducing the speed of the electric motor <NUM> and the other push button <NUM> is marked with "+" for increasing the speed of the electric motor <NUM>.

A small display <NUM> is located between the two push buttons <NUM>, <NUM>. The display <NUM> displays numbers between "<NUM>" and "<NUM>" indicative of the currently set speed of the electric motor <NUM>.

Claim 1:
Hand-held electric polishing or sanding power tool (<NUM>) comprising an elongated tool housing (<NUM>, <NUM>, <NUM>), in which an electric motor (<NUM>) is accommodated, and a moveable backing plate (<NUM>) protruding externally from the tool housing (<NUM>, <NUM>, <NUM>),
wherein the electric motor (<NUM>) is adapted to actuate the backing plate (<NUM>), the backing plate (<NUM>) thereby performing a rotational, random-orbital, orbital or gear-driven working movement in its plane of extension,
wherein a bottom surface of the backing plate (<NUM>) is adapted to detachably hold a polishing or sanding member (<NUM>), and
wherein the tool housing has a rear part (<NUM>, <NUM>) adapted and formed to be gripped by a hand of a user of the power tool (<NUM>) thereby holding the power tool (<NUM>) during its intended use and a tubular front part (<NUM>) from which the backing plate (<NUM>) protrudes, the front part (<NUM>) having a smaller diameter than the rear part (<NUM>, <NUM>) and being attached to the rear part (<NUM>, <NUM>),
characterized in that
at least part of the electric motor (<NUM>) is accommodated in the tubular front part (<NUM>) of the tool housing.