Patent Publication Number: US-9833871-B2

Title: Sander, especially for sanding curved surfaces

Description:
FIELD OF INVENTION 
     The invention relates to hand operated and power-driven sanding machines for sanding large plane, or convex or concave curved areas. 
     DESCRIPTION OF THE RELATED ART 
     In order to grind large plane or differently curved surface areas, a large number of different sanders or grinders are used, dividend either according to the driving mechanism (pneumatic, electrical) or particularly according to the principal (linear, belt, rotational, rotation-orbital or vibrating). All these kinds of sanders disclose substantial insufficiencies during grinding of large and curved surface areas substantial insufficiencies due to size and insufficient flexibility of their grinding surface, which is not capable of adapting to any curving of the grinding surface area and grinding of unwanted areas or holes may occur due to an inattentiveness of the operating personal. Such disadvantages have been solved by a patent application No, WO2009000219 in which a grinding segment is represented by one light flexible blade, that is pressed to the grinded surface by means of a flexible pressing plate. From the bottom, the flexible blade is provided with a grinding material and it moves between the pressing plate and the grinded surface so it gradually reaches the curving parameters as the pressing blade has. An equally distributed pressing force is obtained through a system of lever beams. However, despite numerous advantages of this technical solution, several fundamental disadvantages have occurred. One of them is the fact that the flexible blade being pressed to the grinded surface by means of the pressing plate, is significantly hindered, so a use of sufficiently designed driving mechanism and transmission mechanism are required, not only in terms of a required power but also in terms of the rate of the required torque. Driving mechanisms turned to be very bulky with high consumption of the electric power or possibly of the compressed air. Further disadvantage is a continuous mutual wear of the pressing plate and flexible blades. A third fundamental disadvantage is an insufficient torsional stiffness of so designed sanders, thus a grinding of curved surface areas is possible only in parallel with the axis of curvature of the grinded surface or transversally to it. 
     SUMMARY OF THE INVENTION 
     The above mentioned disadvantages are removed or at least substantially limited by a sander for grinding of large plane, namely but for grinding of curved surface areas, that has according to this invention a flexible grinding plate attached to the body of the sander by means of at least two lever beams, thus similarly to WO22009000219 the pressing force of the grinding plate onto a grinded surface is substantially equally distributed, whereas according to this invention the flexible grinding plate is attached to the ends of the lever beams by means of flexible connecting elements and it is connected to a driving mechanism causing to vibrate the flexible grinding plate through a shaft provided with an off-center pivot allowing a transformation of a rotational movement of the driving mechanism onto a sliding linear or orbital movement of the flexible grinding surface, i.e. to a movement carried out by the grinding plate when grinding the surface area; whereas the driving mechanism of the flexible grinding plate is designed to allow a change of relative distance between the flexible grinding plate and the body of the sander, said change being caused due to a required bending of the grinding plate, i.e. according to its deformation when being adapted to the shape of the grinded surface. According to a preferred embodiment of the invention, the lever beams are provided with arms protruding on two opposite sides from the place of the attachment of the lever beam, whereas on the and of each arm of the lever beam, a flexible connecting element is arranged, said flexible element connects the grinding plate with the lever beam. The lever beams are arranged so allow a pivotal movement in relation to the body of the sander. More preferably the lever beams are anchored on pivotal pins, whereas the pivotal movement is allowed especially in the longitudinal direction of the flexible grinding plate, thus allowing its adaption to the shape of the grinded surface. 
     Preferably the flexible connecting elements are accomplished as silent-blocks, but the can be also accomplished as springs or similar parts that allow an equally distributed pressing force onto the flexible grinding plate, and also allowing its shapeability/malleability towards the grinded surface. Adapting the shape of the flexible grinding plate is accomplished advantageously not only in the radial but also in diagonal curving direction of the grinded surface. In an embodiment of the sander according to the invention with a firmly mounted driving unit, the attachment of the flexible grinding plate by means of flexible connecting elements allows for finishing the transformation of the movement of the driving unit onto the flexible grinding surface. 
     For a purpose of this invention, a term flexible grinding plate also intends to cover an embodiment of the grinding plate consisting of several, e.g. two or more, separate grinding segments. In case of the example of the embodiment according to the  FIG. 2 , the driving unit is arranged directly on the base plate and the flexible grinding plate, rather in this case plate segments forming the flexible grinding plate, are attached to the base plate by means of flexible connecting elements, being advantageously in this case silent-blocks, allowing the grinding segments to vibrate with regard to the base plate as in the preceding case. 
     The base plate itself is pressed to the grinded surface by means of lever beams, allowing shaping of the tool according to the curvature of the grinded surface, as well as partial torsional curving, substantially regardless of the immediate deformation of the grinding plate and its mutual position in respect of the body of the sander. In this example of the embodiment of the present invention comprising the power unit connected firmly with the body of the sander, the mutual position is delimited only by the utmost positions of the grooved, telescopic, shaft, that connects the power unit with the flexible grinding plate and also by the maximal elasticity of the flexible connecting elements. Preferably such embodiment comprises a grinding plate consisting of at least two flexible grinding elements/blades/that exhibit a relative movement in relation to the body of the sander as well as to the basic flexible plate. The flexibility and stiffness of the basic plate mostly restricts also curvature parameters of the grinding segments. 
     The above described arrangement allows for a construction of a tool of substantially any length having number of grinding segments. Driving such grinding segments can be done preferably through several independent power units, each driving either one grinding segments. Possibly, one power unit can drive two or more grinding segments, whereas the drive on individual segments can be done by means of a flexible shafts etc. 
     As already mentioned, to drive grinding plates or possibly grinding segments of the sander according to this invention, it is possible to use any appropriate power unit used for handheld tools. That means, besides electric motors, also pressurized air-operated motors and similar power units can be used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject of the invention will be more apparent with a help of the drawings, on which 
         FIG. 1  illustrates the basic principle of the sander according to the invention by means of an example of the embodiment with a grinding plate in one piece; 
         FIG. 2  illustrates the principles of the sander with a grinding plate consisting of two grinding elements; and 
         FIG. 3  illustrates a detail of a connection of basic flexible plate and the flexible moving segment in a section A-A from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Example 1 
     A sander for grinding curved surface areas according to  FIG. 1  is accomplished with a body  1  of the sander, having a power unit  6  placed on it. The Power unit  6  is in the present example an electric motor having an angled transmission unit  4 , which is mounted on a bearing case  3  with a telescopic grooved shaft  11 . The grooved shaft  11  allows for a transmission of the torque from the power unit to the grinding plate  14  even in different bents of the grinding plate  14  due to its adaptation to a shape the grinded surface area. The grooved shaft  11  is provided on its end with an eccentric pivot, whereas the distance of its off-sett from the longitudinal axis of the grooved shaft imparts the relative movement, i.e. oscillation, being performed by grinding plate  14  in relation to the body  1  of the sander. The pivot is accommodated in the bearing case  12  which is firmly connected to the grinding plate  14 . The grinding plate  14  is attached to the body  1  of the sander by means of four pairs of flexible connecting elements  10 , in this example also formed by a silent-block, and by means lever beams  9 , pivotally situated on pins  7 . The flexible connecting elements  10  provide for either an equally distributed pressure of the grinding plate onto the grinded surface, an either for partial torsion deformation and flexible adaptation of the grinding plate  14  towards the grinded surface. When fixing the shape of the grinding plate  14  would be required, it is possible to fix the position of the lever beams  9  in relation to the body  1  of the sander by means of appropriate locks or possibly by means of transversal mortising etc. 
     In a preferable embodiment of the sander according to the invention, the grinding plate  14  is provided with orifices allowing extraction of sanding dust. The arrangement of the extraction system comprises a grinding plate  14  provided with a cover plate  13  with a sealing  16 . The cover plate  13  is connected with a sleeve  8  arranged so as to allow a connection of an extraction device, being place on a lever beam  9 , through a flexible bellow  15 . After connection of the extraction device, suction occurs between the grinding plate  14  and the cover plate  13  by means of which material remover by grinding is extracted. 
     In order to reduce vibrations, the sander is equipped with a counterweight  5 . The grooved shaft  11  with the counterweight  5  may be covered with a flexible sleeve in order to provide sealing against dust as well as to provide safety covering of the rotating counterweight  5 . 
     Example 2 
     A sander for grinding curved surfaces according to  FIG. 2  is in principle similar to the sander according to  FIG. 1 . The difference from  FIG. 1 . is, that the grinding plate is in this embodiment formed of a flexible base plate  26  and of flexible grinding segments (blades)  23 , 25 . The parameters as flexibility and stiffness of the tool are determined in by the flexible base plate  26  in this embodiment, instead of the grinding plate as it was in the embodiment from  FIG. 1 . The grinding itself is accomplished by two flexible grinding segments  23 ,  25  that are attached to the flexible base plate  26  through flexible connecting elements  21 ,  22  and brackets  28 . Again, the flexible connecting elements are on  FIG. 2  accomplished as silent-blocks. Each of the grinding segments  13 ,  25  is connected with the flexible base plate  26  by means of four brackets  28 , displace equally along the length of the grinding plate, and four pairs of flexible connection elements  21 . Said flexible connection elements  21  keep the grinding elements  23 , 25  in a relatively constant distance from the base plate  26 , regardless of its deformation (bending). Thus designed mounting which uses flexible connection elements, silent-blocks in the example, allows for movement of the grinding segments in relation to the flexible base plate  26 , similarly to the embodiment on  FIG. 1 . Each of these grinding segments  23 ,  25  is driven independently by a power unit  19 , provided with a shaft with an eccentric pivot so as to transform the rotational movement of the power unit onto a sliding linear or orbital movement of each grinding segments  23 ,  25 . Said power units are firmly connected to a flexible base plate  26 . The base plate  26  replaces in this embodiment the function of the body  1  of the sander on  FIG. 1 , as it is connected with the body  17  of the sander and it does not carry out any grinding movements in relation to the body  17 . The power unit  19  can be represented by e.g. a separate motor as seen on  FIG. 2 , but it can be also represented by a transmission unit, which is driven by a flexible shaft or cardan shaft from one central motor, etc. In case the transmission units are used, it is preferred to set the mutual synchronization of their movements so the grinding plates move one against the other. This way is preferred especially in case even number of the grinding segments. The flexible base plate  26  is equipped with similar system of equal distribution of the force onto the grinded surface area, as in case of the embodiment on  FIG. 1 , using the lever beams  20  connected with the flexible base plate  26  by means of silent-blocks  22 . The lever beams  20  are connected with the body  17  of the sander by means of pivots allowing turn movement of the lever beams  20  in relation to the body  17 . The flexible base plate  26  can be advantageously used in a sanding dust extraction. The flexible base plate overlaps the flexible grinding segments on its each side. To the overhang, sealing profile  27  is attached, reaching up to the grinded surface, thus creating a closed space. It is sufficient to attach properly an extraction device to the flexible base plate  26 . It is possible to fix the position of the lever beams  20  relative to the body  17 , thus fixing the respective plane or bending diameter as in case of the example 1. The technical solution according to  FIG. 2  allows for a use of substantially any number of the flexible grinding segments. So a construction of a tool with substantially any length is possible. 
     An implementation of a power unit on  FIG. 1  and  FIG. 2  is mentioned only as an example and it is possible to combine them as required. It means that any implementation is linked only for the respective embodiment of the sander. Thus it is possible to use for the embodiment of the sander from  FIG. 1  an analogous embodiment of the grinding plate from  FIG. 2  etc. 
     INDUSTRIAL APPLICABILITY 
     The design of the sander according to the invention can be used in a structure of new types of sanders or grinding machines for grinding different types of curved surface areas in all fields of industry. 
     LIST OF REFERENCE NUMERALS 
     
         
           1 —body of the sander 
           2 —grip/handle 
           3 —bearing case 
           4 —transmission unit 
           5 —counterweight 
           6 —power unit 
           7 —pivot 
           8 —sleeve for an extraction 
           9 —lever beam 
           10 —flexible connecting element 
           11 —grooved shaft with an eccentric pivot 
           12 —bearing case 
           13 —cover plate 
           14 —flexible grinding plate 
           15 —extraction bellow 
           16 —sealing elastomer 
           17 —body of the sander 
           18 —grip/handle 
           19 —power unit 
           20 —lever beam 
           21 —flexible connecting element 
           22 —flexible connecting element 
           23 —flexible grinding segment A 
           24 —shaft with an eccentric pivot 
           25 —flexible grinding segment B 
           26 —flexible base plate 
           27 —sealing 
           28 —bracket of the flexible connecting elements 
           29 —screw 
           30 —spacer