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The present invention refers to a circular backing plate adapted for use with a hand-held polishing or sanding power tool, comprising a main body having a circular shape, a first attachment member located on a top surface of the backing plate for releasable attachment of the backing plate to a tool shaft or to an eccentric element of the power tool, a second attachment member on a bottom surface of the backing plate for releasable attachment of a polishing or sanding member to the backing plate and internal channels extending in the main body and at least some of them exiting the main body radially on an external circumferential surface of the backing plate with channel openings located above the bottom surface of the backing plate.
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Furthermore, the invention refers to a hand-held polishing or sanding power tool comprising a tool housing with a motor housed therein, a tool shaft driven by the motor and accessible from outside the tool housing and a circular backing plate protruding from the tool housing and attachable to a distal end of the tool shaft. The backing plate is of the type indicated above.
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In power tools with an integrated dust extraction functionality (see for instance
EP 3 028 811 A1 ), operation of the power tool creates an air flow aspiring dust laden air from the backing plate possibly through part of the power tool and further conveying the aspired air to an air outlet socket of the power tool. Regarding an example for the design and functioning of an integrated dust extraction functionality,
EP 3 028 811 A1 is incorporated herein by reference. A filter cartridge or a vacuum cleaner may be attached to the air outlet socket thereby filtering the dust laden air, keeping back and collecting dust and other debris contained therein and conveying filtered air to the environment. In this kind of power tools, the internal channels are part of the dust extraction system and serve for aspiring dust laden air from the working area surroundding the backing plate through the channel openings in the external circumferential surface of the backing plate and conveying the dust laden air to a central region at the top surface of the backing plate from where it is aspired by the dust extraction system. Thus, if the backing plate is provided with internal channels and respective channel openings in the external circumferential surface of the backing plate, the efficiency of the dust extraction system can be increased.
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The lower the channel openings of the internal channels are located in the external circumferential surface of the backing plate the more efficient can the integrated dust extraction system work. If the channel openings are very close to the working surface, i.e., close to the bottom surface of the backing plate, the more dust laden air can be aspired from the working surface. On the other hand, the channel openings located close to the working surface form recesses in the external circumferential surface, into which an object delimiting the working surface to be worked can engage during the intended use of the power tool. Due to the fast rotation of the backing plate, the external circumferential surface is then torn open at the channel opening by the object that has penetrated the channel opening. Thus, the channel openings located on the external circumferential surface close to the working surface and to the bottom surface of the backing plate can cause a rapid and severe damage to the backing plate during intended use of the backing plate.
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In order to avoid the risk of damaging the backing plate by objects engaging the channel openings and tearing them apart, it is known from the prior art to locate the channel openings on the external circumferential surface of the backing plate above the bottom surface of the backing plate, i.e., in a distance to the working surface. This significantly reduces the risk of the backing plate being damaged by objects extending into the working surface during intended use of the backing plate. However, the elevated channel openings located on the external circumferential surface above the bottom surface of the backing plate reduce the efficiency of the integrated dust extraction functionality, because the dust is no longer aspired on the working surface but only above and in a distance to the working surface.
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The present invention is therefore based on the object of resolving the conflict between, on the one hand, reducing the susceptibility to damage of the backing plate by objects that get caught in the channel openings on the external circumferential surface of the backing plate and, on the other hand, ensuring that dust is extracted from the work surface as efficiently as possible.
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This object is solved by a circular backing plate comprising the features of claim 1. In particular, starting from the backing plate of the above-identified kind, it is suggested that at least some of the channel openings merge into funnel-shaped outlet areas towards the external circumferential surface of the backing plate such that dimensions of the outlet areas increase continuously starting from the channel openings of the internal channels towards the external circumferential surface of the backing plate with at least part of each of the outlet areas at the external circumferential surface being located closer to the bottom surface of the backing plate than the channel openings of the internal channels.
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The object is also solved by a hand-held polishing or sanding power tool comprising the features of claim 15. In particular, starting from the hand-held polishing or sanding power tool of the above-identified kind, it is suggested that the backing plate is designed as a circular backing plate according to the present invention.
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Thus, according to the invention, the internal channels still run in a distance to the bottom surface of the backing plate. However, the funnel-shaped outlet areas of the channel openings into the external circumferential surface of the backing plate have an extension towards the bottom surface of the backing plate. Longitudinal extensions of the funnel-shaped outlet areas extend obliquely in respect to the longitudinal extensions of the internal channels. Furthermore, the dimensions of the funnel-shaped outlet areas increasing continuously starting from the channel openings of the internal channels towards the external circumferential surface provide for larger suction openings through which the dust laden air is aspired during intended use of the backing plate. At least part of each of the suction openings reaches further towards the working surface than the channel openings of the internal channels. This increases the efficiency of the internal dust extraction functionality of the power tool.
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The external suction openings of the funnel-shaped outlet areas on the external circumferential surface may have different cross-sectional forms, including where the external openings have an oval or a rectangular shape, the shape of an eyelet or of a needle eye. The funnel-shaped outlet areas may be formed by an external channel of constant or diverging diameter, the external channel extending obliquely in respect to the internal channels in the main body of the backing plate. In particular, it is suggested that the external channels extend radially downwards starting from the channel openings of the internal channels, whereas the internal channels preferably extend radially outwards and essentially parallel in respect to the bottom surface of the backing plate. Some of the internal channels may extend in a different direction, including where they extend obliquely in respect to the radial direction, but still parallel in respect to the bottom surface of the backing plate. The external channels extending radially downwards result in suction openings on the external circumferential surface of the backing plate having an oval shape (with the external channels having a round cross-section area) or a rectangular shape (with the external channels having a square cross-section area). Of course, other forms of the cross-section area of the external channels and of the suction openings are conceivable, too.
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According to a preferred embodiment of the present invention it is suggested that the funnel-shaped outlet areas have increasing dimensions compared to the dimensions of the channel openings of the internal channels only in a vertical direction. Thus, the dimensions of the funnel-shaped outlet areas increase towards the top surface of the backing plate and towards the bottom surface. With other words, the outlet areas have the same width as the channel openings of the internal channels seen in a circumferential direction.
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Preferably, the funnel-shaped outlet areas have increasing dimensions compared to the dimensions of the channel openings of the internal channels only towards the bottom surface of the backing plate. Thus, the dimensions of the funnel-shaped outlet areas increase only towards the bottom of the backing plate. With other words, the outlet areas have the same width as the channel openings of the internal channels seen in a circumferential direction and their dimensions do not increase towards the top of the backing plate.
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According to another preferred embodiment of the invention, the internal channels extend in a top surface of the main body in a manner initially open towards the top surface of the main body and wherein at least some of the initially open internal channels are closed by means of an annular shaped cover element attached to the top surface of the main body and constituting at least part of the top surface of the backing plate. The design of the internal channels as upwardly open grooves or notches and the subsequent closure of the grooves or notches with the cover element to form the closed internal channels makes the manufacturing of the backing pad with its internal channels considerably easier. Additionally, the cover element may also fulfil the function of a deflection plate, similar to what is described in
EP 2 551 056 A1 . Regarding the design and the function of the deflection plate,
EP 2 551 056 A1 is incorporated herein by reference. Preferably, the annular shaped cover element has the form of a ring-shaped disc with a flat surface extension.
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It is suggested that the annular shaped cover element is at least partially made of a rigid material. Preferably, the rigid material comprises one of Acrylonitrile Butadiene Styrene (ABS), Acrylonitrile Styrene Acrylate (ASA), Polycarbonate (PC), Polyethylene Terephthalate Glycol (PETG), Polypropylene (PP), High Impact Polystyrene (HIPS) and Polyamide (PA).
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Furthermore, it is suggested that the main body of the backing plate is at least partially made of a resilient and/or elastic material. Preferably, the resilient and/or elastic material comprises one of Polyurethane (PU), Ethylene Propylene Diene Monomer (EPDM), Polyvinyl Chloride (PVC), any other Thermoplastic Elastomer (TPE), Thermoplastic Polyurethane (TPU), Ethylene Vinyl Acetate (EVA), viscoelastic foam, Neoprene and Polyvinylidene Fluoride (PVDF).
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According to another preferred embodiment of the present invention, it is suggested that the first attachment member comprises an axial recess in the top surface of the backing plate, the axial recess being accessible from outside the backing plate and having a non-rotationally symmetric internal circumferential wall. The tool shaft or the eccentric element of the power tool is provided with a protruding element having a respective non-rotationally symmetric external circumferential wall. The axial recess of the first attachment member is designed to receive in an axial direction the protruding element of the tool shaft or of the eccentric element of the power tool, in order to establish a torque proof connection between the tool shaft or the eccentric element of the power tool and the backing plate in a plane extending perpendicular to the axial direction. The axial direction runs parallel to a rotational axis of the backing plate and of the tool shaft, respectively.
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If the backing plate is directly attached to a tool shaft in a torque-proof manner, it performs a purely rotational working motion about the rotational axis of the tool shaft. The protruding element is preferably located at a distal end of the tool shaft.
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An eccentric element may be attached to the tool shaft in a torque-proof manner resulting in a rotation of the eccentric element about the rotational axis of the tool shaft. Opposite to the attachment to the tool shaft, the eccentric element receives and holds the backing plate in a manner freely rotatable about the rotational axis of the backing plate. The rotational axes of the tool shaft and of the backing plate are spaced apart from each other and run parallel to each other. For the attachment of the backing plate to the eccentric element, the eccentric element may comprise a bearing which holds a pinion in a freely rotatable manner. A distal end of the pinion opposite to the bearing may comprise the protruding element which is received by the axial recess of the backing plate. In this case, the backing plate performs a random orbital working motion.
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After insertion of the protruding element of the tool shaft or of the eccentric element into the axial recess of the backing plate, the backing plate is held in the axial direction parallel to the rotational axis of the backing plate in respect to the protruding element. This may be achieved by means of a screw which extends through a central opening of the backing plate and is screwed into a threaded bore in the tool shaft or the pinion of the eccentric element. Alternatively, this may be achieved by magnetic force between respective magnetic elements located in or assigned to the protruding element of the tool shaft or the pinion of the eccentric element and to the axial recess of the backing plate.
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Preferably, the non-rotationally symmetric internal circumferential wall of the axial recess has the form of a polygonal, including a triangle, a square, a rectangle, a hexagonal or an octagonal, preferably of equilateral design. Similarly, it is suggested that the respective non-rotationally symmetric external circumferential wall of the protruding element has the form of a polygonal, including a triangle, a square, a rectangle, a hexagonal or an octagonal, preferably of equilateral design. The form and dimensions of the protruding element are such as to be received in an axial direction and exactly fit in the axial recess.
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Alternatively, it is suggested that the non-rotationally symmetric internal circumferential wall of the axial recess comprises two straight walls extending in a distance and parallel to each other and two arc-shaped sections each interconnecting an end of one straight wall with a respective end of the other straight wall, wherein the arc-shaped sections form part of a circle with a rotational axis of the backing plate extending through a centre of the circle. Similarly, it is suggested that the respective non-rotationally symmetric external circumferential wall of the protruding element comprises two straight walls extending in a distance and parallel to each other and two arc-shaped sections each interconnecting an end of one straight wall with a respective end of the other straight wall, wherein the arc-shaped sections form part of a circle with a rotational axis of the backing plate extending through a centre of the circle. The form and dimensions of the protruding element are such as to be received in an axial direction and exactly fit in the axial recess.
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According to another embodiment of the invention, it is suggested that the first attachment member is at least partially made of a rigid material, in particular a hard plastic material or metal, that the first attachment member is attached to a top surface of the main body by means of a co-molding process during manufacturing of the main body, and that the first attachment member attached to the top surface of the main body is located on the top surface of the backing plate.
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Furthermore, it is suggested that the second attachment member comprises a first sheet of a hook-and-loop fastener fixedly attached to the bottom surface of the backing plate. A polishing or sanding member may comprise a second corresponding sheet of a hook-and-loop fastener fixedly attached to the top surface of the polishing or sanding member. The two sheets of hook-and-loop fasteners are usually made of a fabric and comprise a hook side covered with a plurality of tiny, stiff hooks and a loop side covered with small, soft loops. When pressing the two sheets together, the hooks catch onto the loops, creating a secure bond between the polishing or sanding member and the backing plate. When pulling them apart, the hooks straighten and release from the loops, allowing the fastener to open and to detach the polishing or sanding member from the backing plate. Alternatively, the second attachment member could also comprise an adhesive surface or the like. In that case, the polishing or sanding member may comprise a corresponding adhesive surface fixedly attached to the top surface or not. The top surface of the polishing or sanding member may be attached to the adhesive surface at the bottom surface of the backing plate, with or without a corresponding adhesive surface fixedly attached to the top surface.
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Preferably, the second attachment member is attached to a bottom surface of the main body by means of gluing, welding or co-molding, thereby forming the bottom surface of the backing plate.
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According to yet another preferred embodiment of the invention, it is suggested that at least a lower part of the external circumferential surface of the backing plate extends essentially vertically and essentially parallel to a rotational axis of the backing plate. That lower essentially vertical part of the backing plate has the form of a flat cylinder, where its height is by far smaller than its diameter. The essentially vertical part of the circumferential surface may be achieved by punching or cutting after molding of the main body, where an injection mold has a form to create a circumferential surface radially extending beyond the vertical part, or it may be achieved during the molding process itself without a subsequent punching or cutting step, where the injection mold has the respective form to create the essentially vertical part of the circumferential surface. The lower essentially vertical part of the external circumferential surface gives the backing plate a greater robustness, which makes it more difficult for the external circumferential surface to be damaged during intended use of the backing plate, e.g., by sharp, protruding objects that delimit the surface to be worked by the backing plate or the sanding or polishing member attached to the backing plate, respectively.
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Furthermore, it is suggested that an upper part of the external circumferential surface of the backing plate has the form of a flat truncated cone with a diameter of the backing plate continuously decreasing towards the top surface of the backing plate. The height of the upper part is by far smaller than its diameter. When the lower part of the external circumferential surface of the backing plate extends vertically parallel to a rotational axis of the backing plate, in the flat truncated cone the diameter of the backing plate starts with the diameter of the lower part of the circumferential surface of the backing plate and continuously decreases towards the top surface of the backing plate.
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Preferably, the funnel-shaped outlet areas open only into the upper truncated cone-shaped part of the external circumferential surface and not into the lower essentially vertical part of the external circumferential surface. By opening only into the upper part of the external circumferential surface of the backing plate, the funnel-shaped outlet areas and even more the channel openings are prone much less to be damaged by objects delimiting the working surface, because the upper truncated cone-shaped part of the external circumferential surface is retracted inwards in a radial direction in respect to the lower essentially vertical part of the external circumferential surface. If at all, the external circumferential surface will collide with objects only along its smooth and even lower essentially vertical part.
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However, in another embodiment it would also be possible that the funnel-shaped outlet areas open into the upper truncated cone-shaped part of the external circumferential surface and merely touch and enter only into an upper edge of the lower essentially vertical part of the external circumferential surface. For instance, starting from the upper edge of the lower vertical part of the external circumferential surface, the funnel-shaped outlet areas enter only into less than about 30% of the overall height of the lower essentially vertical part of the external circumferential surface, preferably into less than about 20% and particularly preferred into less than about 10%.
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Further features and advantages of the present invention will become apparent from the following detailed description of the invention and the accompanying drawings. It is emphasized that the features shown in the figures may be important for the invention on their own, even if this is not shown in the figures and not explicitly mentioned in the description. Further, in the realm of the present invention, the features shown in the figures may be combined in any desired manner, even if such a combination not shown in the figures and not explicitly mentioned in the description. The figures show:
- Fig. 1
- a circular backing plate according to a first embodiment of the invention in a top view on its top surface;
- Fig. 2
- a main body of the circular backing plate of Fig. 1 in a view on its top surface, with an annular cover element detached from its top surface;
- Fig. 3
- the circular backing plate of Fig. 1 in a view on its bottom surface;
- Fig. 4
- a circular backing plate according to a second embodiment of the invention in a perspective view on its top surface;
- Fig. 5
- an enlarged view of an external circumferential surface of the backing plate of Fig. 4 with a funnel-shaped outlet area;
- Fig. 6
- a main body of the circular backing plate of Fig. 4 in a view on its top surface, with an annular cover element detached from its top surface;
- Fig. 7a
- a circular backing plate according to a further embodiment of the invention in a perspective view on its top surface.
- Fig. 7b
- a sectional view through the backing plate of Fig. 7a;
- Fig. 8
- a hand-held polishing or sanding power tool according to the invention in a schematic side sectional view; and
- Fig. 9
- an eccentric element of the hand-held polishing or sanding power tool of Fig. 8.
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The present invention refers to a circular backing plate 10 adapted for use with a hand-held polishing or sanding power tool 100. The backing plate 10 comprises a main body 12 having a circular shape, a first attachment member 14 located on a top surface 16 of the backing plate 10 for releasable attachment of the backing plate 10 to a tool shaft 102 or to an eccentric element 104 of the power tool 100. Further, the backing plate 10 comprises a second attachment member 18 on a bottom surface 20 of the backing plate 10 for releasable attachment of a polishing or sanding member 22 to the backing plate 10 and internal channels 24 extending in the main body 12 and at least some of them exiting the main body 12 radially on an external circumferential surface 26 of the backing plate 10 with channel openings 28 located above the bottom surface 20 of the backing plate 10 (see Fig. 5).
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Furthermore, the invention refers to a hand-held polishing or sanding power tool 100 comprising a tool housing 106 with a motor 108 housed therein, the tool shaft 102 driven by the motor 108 and accessible from outside the tool housing 106 and a circular backing plate 10 protruding from the tool housing 106 when attached to a distal end of the tool shaft 102 or to the eccentric element 104. The backing plate 10 is of the type indicated above.
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As shown in Fig. 8, the motor 108 is preferably an electric motor. However, it could also be a pneumatic motor. The power tool 100 may further comprise a battery 110 for providing the motor 108 and possibly other electric and electronic components of the power tool 100 with electric energy for their operation. The battery 110 is preferably rechargeable and extractable from the tool housing 106, for instance to easily replace an empty battery 110 with a fully charged battery 110. Furthermore, the power tool 100 may comprise an electronic control unit (ECU) 112 for controlling operation of the motor 108 and possibly of other electric and electronic components of the power tool 100.
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The motor 108 has a motor shaft 114 which rotates about a rotational axis 116. The motor shaft 108 may directly or indirectly drive the tool shaft 102 of the power tool 100. In the embodiment shown in Fig. 8, the motor shaft 114 indirectly drives the tool shaft 102 by means of a bevel gear 118. The bevel gear 118 translates the rotation of the motor shaft 114 about its rotational axis 116 into a rotation of the tool shaft 102 about its rotational axis 120. An angle α between the rotational axis 116 of the motor shaft 114 and the rotational axis 120 of the tool shaft 102 is preferably between 80° and 120°, in particular ≥ 90°. The bevel gear 118 may have any desired gear ratio i comprising i < 1, i = 1 and i >1. A further gear arrangement 122 may be located functionally between the motor 108 and the bevel gear 118. Again, the gear arrangement 122 may have any desired gear ratio i comprising i < 1, i = 1 and i >1.
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Furthermore, the power tool 100 may comprise many further components not shown in Fig. 8, e.g., a lever or switch for activating and deactivating the motor 108, a rotary switch or push buttons for increasing and reducing the rotational speed of the motor 108. Instead of the battery 110, the power tool 100 may also be operated through an electric cable with electric power from a mains power supply. In the case of a pneumatic power tool 100, neither the battery 110 nor the cable would be required. Instead, the power tool 100 would be connected to a compressed air line.
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According to an embodiment of the invention it is suggested that at least some of the channel openings 28 merge into funnel-shaped outlet areas 30 towards the external circumferential surface 26 of the backing plate 10 such that dimensions of the outlet areas 30 increase continuously starting from the channel openings 28 of the internal channels 24 towards the external circumferential surface 26 with at least part of the outlet areas 30 at the external circumferential surface 26 being located closer to the bottom surface 20 of the backing plate 10 than the channel openings 28 of the internal channels 24. It can be seen from Fig. 5 that a bottom surface 32 (see Figs. 4 to 6 and 7b) of an outlet area 30 extends from the channel opening 28 downwards towards the external circumferential surface 26 and towards the bottom surface 20 of the backing plate 10.
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According to the invention, the internal channels 24 run in a distance to the bottom surface 20 of the backing plate 10. However, the funnel-shaped outlet areas 30 of the channel openings 28 into the external circumferential surface 26 of the backing plate 10 have an extension towards the bottom surface 20 of the backing plate 10. Longitudinal extensions of the funnel-shaped outlet areas 30 extend obliquely in respect to the longitudinal extensions of the internal channels 24. Furthermore, the dimensions of the funnel-shaped outlet areas 30 increasing continuously in at least one direction starting from the channel openings 28 of the internal channels 24 towards the external circumferential surface 26 provide for larger suction openings 34 through which dust laden air is aspired during intended use of the backing plate 10. At least part of each of the suction openings 34 reaches further towards the working surface or the bottom surface 20 of the backing plate 10 than the channel openings 28 of the internal channels 24. This increases the efficiency of an internal dust extraction functionality of the power tool 100.
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The external suction openings 34 of the funnel-shaped outlet areas 30 on the external circumferential surface 26 may have different cross-sectional forms, including where the external suction openings 34 have an oval or a rectangular shape, the shape of an eyelet or of a needle eye. The funnel-shaped outlet areas 30 may be formed by external channels of constant or diverging diameter, the external channels extending obliquely in respect to the respective internal channels 24 in the main body 12 of the backing plate 10. In particular, it is suggested that the external channels extend radially downwards starting from the channel openings 28 of the internal channels 24, whereas the internal channels 24 preferably extend radially outwards and essentially parallel in respect to the bottom surface 20 of the backing plate 10. Some of the internal channels 24 may extend in a different direction, including where they extend obliquely in respect to the radial direction and circumferentially, but still parallel in respect to the bottom surface 20 of the backing plate 10. The external channels extending radially downwards result in suction openings 34 on the external circumferential surface 26 of the backing plate 10 having an oval shape (with the external channels having a round cross-section area) or a rectangular shape (with the external channels having a square cross-section area). Of course, other forms of the cross-section area of the external channels and of the suction openings 34 are conceivable, too.
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It is suggested that the funnel-shaped outlet areas 30 have increasing dimensions compared to the dimensions of the channel openings 28 of the internal channels 24 only in a vertical direction. Thus, the dimensions of the funnel-shaped outlet areas 30 increase towards the top surface 16 of the backing plate 10 and towards the bottom surface 20. With other words, the outlet areas 30 have the same width as the channel openings 28 of the internal channels 24 seen in a circumferential direction.
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Preferably, the funnel-shaped outlet areas 30 have increasing dimensions compared to the dimensions of the channel openings 28 of the internal channels 24 only towards the bottom surface 20 of the backing plate 10. Thus, the dimensions of the funnel-shaped outlet areas 30 increase only towards the bottom surface 20 of the backing plate 10. With other words, the outlet areas 30 have the same width as the channel openings 28 of the internal channels 24 seen in a circumferential direction and their dimensions do not increase towards the top surface 16 of the backing plate 10.
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It is suggested that the internal channels 24 extend in a top surface 36 of the main body 12 in a manner initially open towards the top surface 36 of the main body 12 and wherein at least some of the initially open internal channels 24 are closed by means of an annular shaped cover element 38 attached to the top surface 36 of the main body 12 and constituting at least part of the top surface 16 of the backing plate 10. The design of the internal channels 24 as upwardly open grooves or notches and the subsequent closure of the grooves or notches with the cover element 38 to form the closed internal channels 24 makes the manufacturing of the backing pad 10 with its internal channels 24 considerably easier. Additionally, the cover element 38 may also fulfil the function of a deflection plate, similar to what is described in
EP 2 551 056 A1 . Preferably, the annular shaped cover element 38 has the form of a ring-shaped disc with a flat surface extension.
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In Fig. 3 holes 46 in the bottom surface 20 of the backing plate 10 are shown. These holes 46 merge into vertical sections of the internal channels 24. Some of the holes 46a are covered by the annular shaped cover element 38 at the top surface 16 of the backing plate 10. Those hose 46a are provided with a shading in Fig. 3. Other holes 46b align with corresponding holes 48 in the cover element 38.
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It is suggested that the annular shaped cover element 38 is at least partially made of a rigid material. Preferably, the rigid material comprises one of Acrylonitrile Butadiene Styrene (ABS), Acrylonitrile Styrene Acrylate (ASA), Polycarbonate (PC), Polyethylene Terephthalate Glycol (PETG), Polypropylene (PP), High Impact Polystyrene (HIPS) and Polyamide (PA).
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Furthermore, it is suggested that the main body 12 of the backing plate 10 is at least partially made of a resilient and/or elastic material. Preferably, the resilient and/or elastic material comprises one of Polyurethane (PU), Ethylene Propylene Diene Monomer (EPDM), Polyvinyl Chloride (PVC), any other Thermoplastic Elastomer (TPE), Thermoplastic Polyurethane (TPU), Ethylene Vinyl Acetate (EVA), viscoelastic foam, Neoprene and Polyvinylidene Fluoride (PVDF).
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It is suggested that the first attachment member 14 comprises an axial recess 40 in the top surface 16 of the backing plate 10, the axial recess 40 being accessible from outside the backing plate 10 and having a non-rotationally symmetric internal circumferential wall 42. The tool shaft 102 or the eccentric element 104 of the power tool 100 is provided with a protruding element 124 having a respective non-rotationally symmetric external circumferential wall 126. The axial recess 40 of the first attachment member 14 is designed to receive in an axial direction the protruding element 124 of the tool shaft 102 or of the eccentric element 104 of the power tool 100, in order to establish a torque proof connection between the tool shaft 102 or the eccentric element 104 of the power tool 100 and the backing plate 10 in a plane extending perpendicular to the axial direction. The axial direction runs parallel to a rotational axis 44 of the backing plate 10.
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If the backing plate 10 is directly attached to a tool shaft 102 in a torque-proof manner, the rotational axis 44 of the backing plate 10 is congruent with the rotational axis 120 of the tool shaft 102. The backing plate 10 performs a purely rotational working motion about the rotational axes 44, 120. The protruding element 124 is preferably located at a distal end of the tool shaft 102 ready to be inserted into the axial recess 40 of the backing plate 10.
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As shown in Fig. 9, the eccentric element 104 may be attached to the tool shaft 102 in a torque-proof manner, for instance by screwing, welding, press fit or the like, resulting in a rotation of the eccentric element 104 about the rotational axis 120 of the tool shaft 102. Opposite to the attachment to the tool shaft 102, the eccentric element 104 receives and holds the backing plate 10 in a manner freely rotatable about the rotational axis 44 of the backing plate 10. The rotational axes 120, 44 of the tool shaft 102 and of the backing plate 10 are spaced apart from each other and run parallel to each other. For the attachment of the backing plate 10 to the eccentric element 104, the eccentric element 104 may comprise a bearing 128 which holds a pinion 130 in a manner freely rotatable about its rotational axis 132. A distal end of the pinion 130 opposite to the bearing 128 may comprise the protruding element 124 which is received by the axial recess 40 of the backing plate 10. With the backing plate 10 attached to the eccentric element 104, the rotational axis 44 of the backing plate 10 is congruent with the rotational axis 132 of the pinion 130. In this case, the backing plate 10 performs a random orbital working motion.
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After insertion of the protruding element 124 of the tool shaft 102 or of the eccentric element 104 into the axial recess 40 of the backing plate 10, the backing plate 10 is held in the axial direction parallel to the rotational axis 44 of the backing plate 10 in respect to the protruding element 124. This may be achieved by means of a screw which extends through a central opening of the backing plate 10 and is screwed into a threaded bore in a distal end of the tool shaft 102 or of the pinion 130 of the eccentric element 104. Alternatively, this may be achieved by magnetic force between respective magnetic elements located in or assigned to the protruding element 124 of the tool shaft 102 or the pinion 130 of the eccentric element 104 and to the axial recess 40 of the backing plate 10.
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The non-rotationally symmetric internal circumferential wall 42 of the axial recess 40 may have the form of a polygonal, including a triangle, a square, a rectangle, a hexagonal or an octagonal, preferably of equilateral design. Similarly, the respective non-rotationally symmetric external circumferential wall 126 of the protruding element 124 may have the form of a polygonal, including a triangle, a square, a rectangle, a hexagonal or an octagonal, preferably of equilateral design. The form and dimensions of the protruding element 124 are designed such that the protruding element 124 may be received by the axial recess 40 in an axial direction and exactly fits into the recess 40.
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Preferably, as shown in the Figs., the non-rotationally symmetric internal circumferential wall 42 of the axial recess 40 comprises two straight walls 42a, 42b extending in a distance and parallel to each other and two arc-shaped sections 42c, 42d each interconnecting an end of one straight wall 42a; 42b with a respective end of the other straight wall 42b; 42a, wherein the arc-shaped sections 42c, 42d form part of a circle with the rotational axis 44 of the backing plate 10 extending through a centre of the circle. Similarly, it is suggested that the respective non-rotationally symmetric external circumferential wall 126 of the protruding element 124 comprises two straight walls 126a, 126b extending in a distance and parallel to each other and two arc-shaped sections 126c, 126d each interconnecting an end of one straight wall 126a; 126b with a respective end of the other straight wall 126b; 126a, wherein the arc-shaped sections 126c, 126d form part of a circle with a rotational axis 120 of the tool shaft 102 or a rotational axis 132 of the pinion 130 extending through a centre of the circle. The form and dimensions of the protruding element 124 are designed such that the protruding element 124 may be received by the axial recess 40 in an axial direction and exactly fits into the recess 40.
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The first attachment member 14 is at least partially made of a rigid material, in particular a hard plastic material or metal. The first attachment member 14 may be attached to the top surface 36 of the main body 12 by means of a co-molding process during manufacturing of the main body 12. By attaching the first attachment member 14 to the top surface 36 of the main body 12 the attachment member 14 is located on the top surface 16 of the backing plate 10. Alternatively, as shown in Figs. 1 and 4, the first attachment member 14 may be attached to or form an integral part of the annular shaped cover element 38 fixedly attached to the top surface 36 of the main body 12 after manufacturing of the main body 12.
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Furthermore, it is suggested that the second attachment member 18 comprises a first sheet of a hook-and-loop fastener fixedly attached to the bottom surface 20 of the backing plate 10. The polishing or sanding member 22 may comprise a second corresponding sheet of a hook-and-loop fastener fixedly attached to the top surface of the polishing or sanding member 22. The two sheets of hook-and-loop fasteners are usually made of a fabric and comprise a hook side covered with a plurality of tiny, stiff hooks and a loop side covered with small, soft loops. When pressing the two sheets together, the hooks catch onto the loops, creating a secure bond between the polishing or sanding member 22 and the backing plate 10. When pulling them apart, the hooks straighten and release from the loops, allowing the fastener to open and to detach the polishing or sanding member 22 from the backing plate 10. Alternatively, the second attachment member 18 could also comprise an adhesive surface or the like.
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The radial and circumferential channels 24 and the holes 46 in the main body 12 of the backing plate 10 serve for aspiring dust laden air during a sanding process. In that case, a sanding member 22 (e.g., a sanding paper or fabric) is attached to the bottom surface 20 of the backing plate 10. In contrast thereto, Fig. 4 shows a polishing member 22 attached to the bottom surface 20 of the backing plate 10 used for a polishing process. In that case the radial and circumferential channels 24 and the holes 46 in the main body 12 of the backing plate 10 may serve for guiding a cooling air stream and for cooling the polishing member 22 during the polishing process.
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Preferably, the second attachment member 18 is attached to a bottom surface of the main body 12 by means of gluing, welding or co-molding, thereby forming the bottom surface 20 of the backing plate 10.
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It is further suggested that at least a lower part 26a (see Fig. 5) of the external circumferential surface 26 of the backing plate 10 extends essentially vertically and essentially parallel to the rotational axis 44 of the backing plate 10. The essentially vertical part 26a extends in an angle of approximately between 80° and 100° in respect to the bottom surface 20 of the backing plate 10. That lower part 26a of the backing plate 10 has the form of a flat cylinder, where its height is by far smaller than its diameter. The essentially vertical part 26a of the circumferential surface 26 may be achieved by punching or cutting after molding of the main body 12, where an injection mold has a form to create a circumferential surface 26 radially extending beyond the vertical part 26a, or it may be achieved during the molding process of the main body 12 itself without a subsequent punching or cutting step, where the injection mold has the respective form to create the essentially vertical part 26a of the circumferential surface 26.
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Furthermore, it is suggested that an upper part 26b (see Fig. 5) of the external circumferential surface 26 of the backing plate 10 has the form of a flat truncated cone with a diameter of the backing plate 10 continuously decreasing towards the top surface 16 of the backing plate 10. The height of the upper part 26b is by far smaller than its diameter. When the lower part 26a of the external circumferential surface 26 of the backing plate 10 extends vertically parallel to the rotational axis 44 of the backing plate 10, in the flat truncated cone 26b the diameter of the backing plate 10 starts with the diameter of the lower part 26a of the circumferential surface 26 of the backing plate 10 and continuously decreases towards the top surface 16 of the backing plate 10.
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Preferably, the funnel-shaped outlet areas 30 open only into the upper truncated cone-shaped part 26b of the external circumferential surface 26 and not into the lower essentially vertical part 26a of the external circumferential surface 26. By opening only into the upper part 26b of the external circumferential surface 26 of the backing plate 10, the funnel-shaped outlet areas 30 and even more the channel openings 28 are prone much less to be damaged by objects delimiting the working surface, because the upper truncated cone-shaped part 26b of the external circumferential surface 26 is retracted inwards in a radial direction in respect to the lower vertical part 26a of the external circumferential surface 26. If at all, the external circumferential surface 26 will collide with objects only along its smooth and even lower essentially vertical part 26a, which would most probably not provoke a damage of the backing plate 10.
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According to another embodiment shown in Fig. 7a, it would also be possible that the funnel-shaped outlet areas 30 open into the upper truncated cone-shaped part 26b of the external circumferential surface 26 and merely touch and enter only into an upper edge 26c of the lower essentially vertical part 26a of the external circumferential surface 26. For instance, starting from the upper edge 26c of the lower vertical part 26a of the external circumferential surface 26, the funnel-shaped outlet areas 30 enter only into less than about 30% of the overall height of the lower essentially vertical part 26a of the external circumferential surface 26, preferably into less than about 20% and particularly preferred into less than about 10%.
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As shown in Fig. 7b, the bottom surfaces 32 of the funnel-shaped outlet areas 30 each extend from the channel openings 28 of the internal channels 24 downwards towards the external circumferential surface 26, in particular towards the lower essentially vertical part 26a of the external circumferential surface 26, and towards the bottom surface 20 of the backing plate 10. The essentially vertical part 26a of the external circumferential surface 26 gives the backing plate 10, in particular the suction openings 34, a greater robustness making it more difficult for the external circumferential surface 26 and the suction openings 34, respectively, to be damaged during intended use of the backing plate 10, e.g., by sharp, protruding objects that delimit the surface to be worked by the backing plate 10 or the sanding or polishing member 22 attached to the backing plate 10, respectively. Despite the elevated position of the internal channels 24 and their respective openings 28, the funnel-shaped outlet areas 30 with their bottom surfaces 32 and suction openings 34 extending downwards manage to significantly improve the dust suction properties of the backing plate 10, so that the efficiency of the internal dust extraction functionality of the power tool 100 is significantly improved.