Patent Publication Number: US-2021187698-A1

Title: Polishing device

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention relate to a polishing device. 
     For finishing surfaces, in particular painted surfaces, use is made of polishing discs which are made of a very soft material, for example of a foam, foamed rubber, felt or sheepskin. The respective polishing disc is held on a support plate of the polishing device, which in turn is movable, usually in rotation, by way of a drive. 
     A highly viscous polishing paste is applied to the working side of the polishing disc located opposite the support plate, the amount of polishing agent applied being of critical importance for an optimal polishing result. 
     When using a new polishing disc, initially a relatively large amount of polishing agent is applied and is worked into the polishing disc. Then, in further, subsequent polishing operations, only a small amount of polishing agent is applied for the respective polishing process, wherein preferably flat workpieces are polished by orbital, rotational and vibrating movements of the polishing tool. 
     To avoid spatters of polish, a precise positioning of the polishing disc and/or of the polishing paste and also the pattern thereof on the polishing disc is important. The polishing result is determined by the pressing force with which the polishing disc is pressed against the workpiece, the rotational speed, and the polishing time. 
     DE 10 2017 130 805, which was not previously published, proposes a metering device by which the polishing agent is applied to the working face of the polishing disc, for which purpose the metering device has an application nozzle. In the document, the support plate together with the polishing disc moves relative to the metering device, which in this respect is arranged in a stationary manner. 
     This construction has proven to be successful in principle. However, calls are being made to shorten the cycle time losses during the polishing process, since the movement of the polishing disc towards the metering device and the application of the polishing paste are relatively time-consuming. 
     U.S. Pat. No. 1,952,910 A, WO 00/037215 A1 and DE 42 22 766 A1 each disclose a polishing device, but these are manually guided, in contrast to the generic type, and therefore they are not suitable for industrial use, which requires automated machining of surfaces. 
     Exemplary embodiments of the invention are directed to further developing a polishing device of the generic type in such a way that the usability thereof is improved with little effort in terms of construction. 
     By virtue of this construction, the machining time for a workpiece is considerably reduced since it is no longer necessary to move the support plate together with the connected polishing disc to a metering device. 
     Instead, the polishing agent is now supplied directly to the polishing disc, i.e., possibly even during the polishing process. 
     In terms of construction, this is achieved in that an application nozzle of the metering device is routed through an open central shaft of the support plate, wherein the polishing disc has a central opening for the passage of the polishing agent. 
     Preferably, the application nozzle is held in a rotary feedthrough, which may be designed as a freewheel, so that the application nozzle remains in place while the freewheel rotates with respect to the support plate and thus the polishing disc. 
     With regard to a drive that determines the polishing path, for example an eccentric movement, the application nozzle is connected thereto, as is the support plate. In other words, the application nozzle executes the same path movement as the support plate and/or the polishing disc. 
     In accordance with the generic type, the polishing device is held on a robot arm which, in a computer-controlled manner, moves the polishing device to where a flaw on the workpiece surface is detected for example by means of a sensor system. The discharged amount of polishing agent, in particular a polishing paste, is likewise computer-controlled according to the invention. 
     The amount of polishing agent supplied or to be supplied for the polishing process is preferably between 0.2-5 g. When using a new polishing disc, however, a larger amount of polishing agent is supplied on a one-off basis, namely between 1 and 10 g, wherein the volume capacity of the supply line is preferably a multiple of the maximum amount of polishing agent to be metered. The polishing agent is not supplied to the polishing disc until the latter is positioned at a distance of 3 mm from the surface to be polished. 
     The metering device is preferably provided with a reservoir, which is connected to the application nozzle via a supply line, wherein the supply line is designed in a shape-stable manner as a pipe or in a flexible manner as a suitable hose. 
     A changeover device may also be provided within the access range of the robot arm, by means of which changeover device a polishing disc can be changed in a quasi-automated manner when the maximum service life of the polishing disc has been reached. The polishing disc itself, which is held on the support plate, is preferably made of a soft material, in particular a foam or the like, and usually has a thickness of 10 to 20 mm. 
     The changeover device, which like the polishing device according to the invention contributes to an optimized workflow, is discussed in the aforementioned document DE 10 2017 130 805, which was not previously published. 
     To minimize any disruptive input of heat into the surface as a result of the polishing, according to another concept it is provided to cool the surface by means of compressed air, which moreover is routed onto the surface to be polished via the supply line for the polishing agent. 
     To minimize the input of heat, it may also be provided that the electric drive of the polishing device takes place via a toothed belt connected to an electric motor, the toothed belt being decoupled from the polishing device. 
     After the computer-controlled metering according to the invention, the polishing agent is transported to the application nozzle by compressed air, wherein the polishing disc, usually a polishing sponge, rotates at reduced speed so that the polishing agent is distributed onto the surface to be polished. 
     According to another concept of the invention, channels may be incorporated in the working face of the polishing disc, as a result of which the polishing agent is evenly distributed. Preferably, the channels extend in a star shape from the application nozzle or the central opening of the polishing disc to the outer edge thereof. 
     The channels may vary in width and length depending on requirements, wherein, according to one advantageous development of the invention, the depth of the channels decreases towards the outer edge of the polishing disc. 
     After approximately half of the polishing time, the compressed air is supplied to the polishing disc as cooling air through the supply line in order, as mentioned, to minimize any input of heat. 
     To this end, according to another concept of the invention, also the support plate is provided with a plurality of apertures, via which heat generated during the polishing can be dissipated. 
     Overall, the design according to the invention, including the advantageous developments, considerably reduces the amount of polishing agent and also the spattering of polishing agent. 
     Furthermore, cleaning of the polished surface is much easier and can now be carried out automatically by a downstream wiping device, wherein also the actuation thereof takes place in a computer-controlled manner. 
     In addition, it has been found that the polishing time is minimized and the polishing result is considerably improved. The service life of the polishing disc is also markedly increased, which has a positive effect on the cleaning effort and also the disposal of the polishing disc. 
     Exemplary embodiments of the invention will be described below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       In the drawings: 
         FIG. 1  shows the use of a polishing device according to the prior art, 
         FIG. 2  shows the polishing device according to the invention in a schematic side view, 
         FIG. 3  shows another exemplary embodiment of the polishing device according to the invention in a sectional side view. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the use of a polishing device  4  according to the prior art, wherein said polishing device is held on a robot arm  1 . 
     A changeover device  2 , positioned on a work table  6  and comprising a plurality of dispensers  3  held on a turntable, is movable in cycles such that in each case one polishing disc  10  ( FIG. 2 ) can be connected to a support plate  9 . 
     A set-up area is separated from a working area by a partition  5 , wherein the robot arm  1  with part of the changeover device  2  is arranged in the working area, while the set-up area is intended for an operator  7  to equip the changeover device  2  with dispensers  3 . The support plate  9  and respectively the polishing disc  10  is assigned a metering device  8 , by means of which a polishing agent can be applied to the working face of the polishing disc  10 . 
     The arrangement of the metering device  8  is illustrated in  FIG. 2 . 
     In the example, the support plate  9  is fastened to a rotating shaft  14  in such a way as to rotate therewith, the rotating shaft being part of an eccentric drive  13 , by means of which an eccentric polishing path is described, the path also being followed by the polishing disc  10  held on the support plate  9 . 
     The metering device  8  has a supply line  16  that opens into an application nozzle  11 , wherein the application nozzle  11 , according to the invention, is routed through the open rotating shaft  14 , which forms a central shaft, to a central opening  17  of the polishing disc  10 , from which a polishing agent, in particular a polishing paste, exits towards the working face of the polishing disc  10  in a metered manner controlled by a computer. 
     The supply line  16  and the application nozzle  11  are held in a freewheel  12 . While the rotating shaft  14  and thus the support plate  9  and the polishing disc  10  rotate, the application nozzle  11  and the supply line  16  remain in their position. In other words, the support plate  9  performs a movement relative to the application nozzle  11  and to the supply line  16 . 
     Also connected thereto is a reservoir  15 , which holds the polishing agent that is supplied to the application nozzle  11  via the supply line  16  in a metered manner controlled by a computer. 
     Since the metering device  8  is fixedly positioned with respect to the eccentric drive  13 , the metering device  8  performs the eccentric movements in the same way as the support plate  9  and the polishing disc  10 . 
     The eccentric drive  13  is to be regarded merely as an exemplary embodiment. Other drives which describe the polishing path are also conceivable, for example in order to generate an orbital movement. 
       FIG. 3  shows another exemplary embodiment of a polishing device according to the invention, wherein the same reference signs as in  FIG. 2  are used for the same functional parts. 
     The eccentric drive  13  is driven by way of an electric motor  19 , wherein the electric motor  19 , via a toothed belt  20 , drives the rotating shaft  14  and thus the eccentric drive  13  and the polishing disc  10 . Here, the rotating shaft  14  is mounted in a housing  24 , which is connected to the robot arm  1 . 
     Connected to the supply line  16  is a compressed air line  21 , via which there is routed both compressed air for transporting the polishing agent and also the compressed air for cooling the polishing disc  10  and/or the surface to be polished. The supply line  16  opens into an injection pipe  23 , which leads into a channel  18 , via which the polishing agent and the compressed air are supplied to the application nozzle  11 , which is positioned in the central opening  17  of the polishing disc  10 . 
     The central opening  17  merges into channels  22  on the working side of the polishing disc  10 , wherein said channels  22  serve to distribute the polishing agent on the surface to be polished. 
     Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description.