Abstract:
A polishing head for polishing machines, in particular for polishing optical surfaces, has a polishing plate that is connected to a rotationally drivable drive shaft. The polishing plate is articulated to, and rotates with, the drive shaft. A ball hexagonal socket joint provides the articulated connection. Rotating by means of the articulated connection, the polishing plate can follow the surface of the workpiece to be processed, so that the polishing covering on the polishing plate always rests on a maximally large area on the surface of the workpiece.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This is a Continuation Application to U.S. patent application Ser. No. 10/211,750, filed Aug. 2, 2002, which is pending. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The invention relates to a polishing head for a polishing machine, and more particularly, for polishing optical surfaces.  
         [0004]     A polishing machine for polishing spherical lens surfaces is known from EP 727 280 B1. This polishing machine has an upper slide, which can move in an x-direction. A tool spindle, which is mounted for rotation around a vertical axis, is connected to this slide. The tool spindle serves to receive a surfacing tool. A workpiece spindle, connected to a further slide, is provided for receiving the respective workpiece or lens. The workpiece spindle, and the tool spindle with the surfacing tool, are arranged at a fixed distance from one another. The slide carrying these two spindles can move in the z-direction.  
         [0005]     A polishing machine and a process for polishing optical surfaces are known from WO 97/00155. The polishing machine has a polishing head, which is provided with an elastic diaphragm. The application of force to the surface to be polished is regulated by the application of pressure to the diaphragm. In this polishing machine, it is a disadvantage that the size of the surface of the respective polishing head or diaphragm abutting the surface to be polished depends on the application of pressure. The polishing head, with the elastic diaphragm, is prestressed toward the surface to be polished by an associated spring. Hydraulic cylinders are provided in order to provide a tilting motion of the elastic diaphragm around a point situated on the rotation axis in the region of the flexible diaphragm. The application of force to the surface to be polished is detected by associated sensors, strain gages and solenoids.  
         [0006]     In the process known from this publication, the polishing of the optical surface is controlled in dependence on the rotational speed of the polishing head, and the pressing force acting on the surface to be polished is controlled by means of the application of pressure.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention has as its object to provide a polishing head for polishing a free-form surface, by means of which a qualitatively high-value optical surface can be polished, and by the use of which a constant polishing removal over the whole optical surface to be polished can be ensured.  
         [0008]     The object of the invention is attained by a polishing head, in particular for polishing optical surfaces, comprising a polishing plate having an articulated connection to a rotationally drivable drive shaft, wherein the polishing plate is connected to rotate with the drive shaft and articulated for the execution of tilting motions.  
         [0009]     By means of the feature that the polishing plate is connected, articulated to rotate with the drive shaft, it is possible for the polishing plate to rest on the surface to be processed, following the surface contour. Due to the articulated connection, the polishing plate can execute tilting motions, so that it rests on a maximum polishing surface on the surface to be polished.  
         [0010]     For the transmission of the rotational motion of the drive shaft to the polishing plate, the polishing plate is connected to the drive shaft by positive locking, so that the rotational motion of the drive shaft is transmitted to the polishing plate due to the positive locking.  
         [0011]     The articulated, commonly rotating connection is connected to the polishing plate to rotate with the drive shaft by means of a ball hexagonal socket joint. It is possible by means of this ball hexagonal socket joint to arrange the pivot point, around which the polishing plate can be pivoted in optional directions, as close as possible to the polishing surface of the polishing plate. The arrangement of the articulated connection close to the polishing surface of the polishing plate has the advantage that the polishing plate can react quickly in following the surface contours.  
         [0012]     One or more latch elements are assigned to the articulated connection, for securing the connection between the drive shaft and the polishing head. If a ball hexagonal socket joint is provided as the articulated connection, it is ensured by means of the latch element that the ball head cannot slip out of the associated recess. There are then no problems in removing the polishing plate from the surface to be polished. Furthermore, different polishing heads can easily be exchanged, due to the releasability of the connection ensured by the latch element.  
         [0013]     A pressure chamber is arranged for the polishing head, so that a translational motion of the polishing plate along a mid-axis of the polishing head results from pressurizing the pressure chamber.  
         [0014]     A piston allocated to the pressure chamber is effectively connected to the drive shaft, so that the application of pressure to the pressure chamber is transmitted via the drive shaft to the polishing plate.  
         [0015]     The drive shaft drives by means of a coaxially arranged hollow cylinder with which the drive shaft is mounted to rotate. A positive connection transmits the rotary motion.  
         [0016]     The drive shaft is mounted in the hollow cylinder by means of mounting elements, e.g., a roller bearing or a ball bearing. By this mounting the drive shaft can have a smooth-running translational motion, and accordingly the initiated translational motion is nearly completely transmitted to the polishing plate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention is described in detail hereinbelow with reference to an embodiment example.  
         [0018]      FIG. 1  shows a schematic sketch of the polishing head in a section containing its mid-axis;  
         [0019]      FIG. 2  shows a section along the plane II-II in  FIG. 1 ;  
         [0020]      FIG. 3  shows a section along the plane III-III in  FIG. 1 ; and  
         [0021]      FIG. 4  shows a section along the plane III-III, in an alternative example. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The polishing head ( 1 ) shown in  FIG. 1  has a polishing plate ( 3 ) with a polishing covering ( 5 ). The polishing covering ( 5 ) rests on a surface ( 41 ) of a workpiece ( 39 ) to be polished.  
         [0023]     The polishing plate ( 3 ) is received on a drive shaft ( 7 ) via the articulated connection. In this embodiment example shown, a ball hexagonal socket joint is provided for this commonly rotatable articulated connection. For this purpose, the drive shaft ( 7 ) is provided at the end, on the side facing toward the polishing plate, with a ball head ( 19 ) that engages in a recess ( 13 ) formed in the polishing plate ( 3 ).  
         [0024]     For securement, the connection between the ball head ( 19 ) and the polishing plate ( 3 ) is secured by means of a latch element ( 15 ). A spring element or spring pin on the polishing plate, projecting into a recess on the ball head, can for example be provided as the latch element.  
         [0025]     It is also possible to constitute the ball head on the polishing plate ( 19 ); in this case, a recess is then provided in the drive shaft ( 7 ) for rotationally secure, articulated reception of the ball head. In this case, the distance between the joint place—i.e., the point around which a tilting of the polishing plate relative to the rigid drive shaft can take place—and the surface ( 41 ) to be polished is of course greater.  
         [0026]     The drive shaft ( 7 ) can be displaced translationally by means of the mounting element ( 23 ) and is mounted in, and to rotate with, a hollow cylinder ( 49 ). The hollow cylinder ( 49 ) is driven rotationally by means of a drive (not shown) of the polishing machine, the rotational motion being fully transmitted to the drive shaft ( 7 ) for the polishing head due to the rotationally secured connection by means of the mounting element ( 23 ).  
         [0027]     A hydraulic or pneumatic system, which serves to act on the polishing head with the required polishing pressure, is provided in the hollow cylinder ( 49 ) on the side of the drive shaft ( 7 ) remote from the polishing head. This system has a pressure chamber cylinder ( 31 ) with a translationally displaceable piston ( 33 ) received therein. To decouple the piston ( 33 ) from the rotary motion of the drive shaft ( 7 ) and of the hollow cylinder, swivel bearings can be provided between the pressure chamber cylinder ( 31 ) and the hollow cylinder ( 49 ) and also between the connecting rod ( 32 ) driven by the piston ( 33 ) and the drive shaft ( 7 ). A pressure supply ( 35 ) with a pressure control valve ( 37 ) and a pressure reservoir ( 36 ) is arranged for the pressure chamber ( 29 ) formed in the pressure chamber cylinder ( 31 ), to apply pressure to the piston ( 33 ). A force on the piston ( 33 ), directed along a mid-axis ( 2 ) of the polishing head ( 1 ), is initiated by applying pressure to the pressure chamber ( 29 ). There results from this force a respective translational motion of the polishing plate or increase of the effective polishing pressure, provided that the polishing covering ( 5 ) rests on an optical surface ( 41 ) of a workpiece ( 39 ) to be polished.  
         [0028]     The translationally movable coupling for the hollow cylinder ( 49 ) to rotate with the drive shaft ( 7 ) takes place by means of a roller bearing element ( 23 ). The drive shaft ( 7 ) has for this purpose an external profile ( 43 ) that is noncircular, preferably a polygonal profile. The positive connection between the external profile ( 43 ) of the drive shaft ( 7 ) and the inner wall of the hollow cylinder is attained by means of rollers or cylinders ( 25 ) which are received in the bearing element ( 23 ) symmetrically of the external profile of the drive shaft ( 7 ) and which roll on the external profile of the drive shaft. The rotation axes of the rollers or cylinders are then directed perpendicular to the rotation axis of the drive shaft ( 7 ).  
         [0029]     Instead of the cylinder mounting of the drive shaft ( 7 ) in the hollow cylinder ( 49 ), a ball mounting can also be provided, as shown in  FIG. 4 . For a translationally displaceable connection, rotatable in common, the balls ( 53 ) are mounted in longitudinal grooves ( 51 ) of the hollow cylinder ( 49 ) and further longitudinal grooves ( 55 ) of the drive shaft ( 7 ), with the longitudinal grooves extending parallel to the rotation axis of the drive shaft ( 7 ). In this case also, the drive shaft has a non-rotationally-symmetrical external profile, in particular a polygonal profile, at least in a region corresponding to the mounting.  
         [0030]     The polishing process is described in detail hereinafter. For polishing, the polishing head, the diameter of which is smaller than the diameter of the surface to be polished, moves in a swiveling motion in the radial direction over the optical surface ( 41 ) to be polished. Both the workpiece ( 39 ) and the polishing plate are driven with nearly equal rotational speed in an identical direction. When the polishing plate moves over the optical surface ( 41 ) to be polished, it can be provided to vary the rotational speeds of the polishing plate or the rotational speed of the workpiece, in particular in dependence on the radial position of the polishing plate. This variation of rotational speed has a positive effect on a constant polishing removal.  
         [0031]     The pressure fluctuations are kept very small by the choice of a very large reservoir volume ( 36 ) in comparison with the varying volume of the piston ( 31 ), so that the polishing plate rests with a constant force on the optical surface to be polished. The pressure-regulating valve also contributes to the equalization of pressure fluctuations.  
         [0032]     By means of the arrangement described, in connection with a prior art polishing machine, in particular optical surfaces ( 41 ) which are noncircular can be polished, the polishing removal being constant over the whole optical surface. It is necessary for the uniform polishing removal that the polishing covering of the polishing plate ( 3 ) rests on the optical surface ( 41 ) to be polished over as large as possible a surface. This is in particular ensured in that, by means of the articulated connection of the polishing plate to rotate with the drive shaft ( 7 ), the polishing plate can be tilted about a point situated on the mid-axis ( 2 ) of the polishing head, and the alignment of the polishing plate can thereby follow the surface contour of the surface ( 41 ) to be polished.  
         [heading-0033]     List of reference numerals  
         [0034]    
       
         
               
               
               
               
             
           
               
                   
               
               
                   
               
             
             
               
                  1 
                 polishing head 
                 32 
                 connecting rod 
               
               
                  2 
                 mid-axis 
                 33 
                 piston 
               
               
                  3 
                 polishing plate 
                 35 
                 pressure supply 
               
               
                  5 
                 polishing covering (˜covering) 
                 36 
                 resevoir 
               
               
                  7 
                 drive shaft 
                 37 
                 pressure regulating valve 
               
               
                  9 
                 articulated connection 
                 39 
                 workpiece 
               
               
                 15 
                 recess in polishing plate 
                 41 
                 optical surface 
               
               
                 19 
                 ball head 
                 43 
                 external profile 
               
               
                 20 
                 recess 
                 49 
                 hollow cylinder 
               
               
                 23 
                 mounting elements 
                 51 
                 longitudinal grooves 
               
               
                 25 
                 cylinders or rollers 
                 53 
                 balls 
               
               
                 29 
                 pressure chamber 
                 55 
                 longitudinal groove in drive 
               
               
                 31 
                 pressure chamber cylinder 
                   
                 shaft