Abstract:
A grinding machine wherein coarse and fine grind wheels are mounted to a single rotating spindle. A multiple grind wheel mount is attached to the lower portion of the rotating spindle, the coarse and fine wheels being supported by the wheel mount, the wheel mount containing the mechanism for moving the inner coarse wheel down relative to the stationary outer fine wheel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention provides a grinding machine wherein the coarse and fine grinding wheels are driven by a single rotating spindle, a wheel mount attached to the lower portion of the spindle containing the mechanism for moving the inner coarse wheel down to the workpiece relative to the stationary outer fine wheel. 
         [0003]    2. Description of the Prior Art 
         [0004]    U.S. Pat. No. 7,118,446, assigned to the assignee of the present invention, discloses a grinding assembly for shaping work pieces that includes one or more grind spindles, each of the grind spindles including two independent grinding wheels driven by the same spindle drive. The grind spindles translate horizontally to perform both edge and face grinding with a single grind spindle. A non-contact position sensor in a work spindle measures work spindle displacement during grinding and provides feedback to the grind spindle to regulate the force imparted on the work piece by the grind spindle. 
         [0005]    The double spindle air bearing utilized in the &#39;446 system mounts a stationary outer support structure, rotating spindle, and an inner concentric shaft. The rotating spindle is supported (inside) by the stationary outer support. The rotating spindle has an inner concentric shaft which is rotationally keyed to the spindle, but is allowed to move up and down. The up/down actuation is contained in the upper section of the rotating spindle/support structure. The fine grinding wheel is attached to the lower portion of the rotating spindle, and the coarse wheel is attached to the lower portion of the inner concentric shaft. The fine and coarse wheels rotate together since the inner concentric shaft and the spindle are keyed together rotationally. In the retract position, the coarse wheel is retracted up so the fine wheel can be used for grinding. In the extend position, the coarse wheel is extended out beyond the fine wheel so the coarse wheel can be used for grinding. The actuation of the inner coarse wheel is done by the inner concentric shaft of the spindle assembly. The cost of the spindle air bearing has increased dramatically and has prompted a design that is lower in cost and can be utilized in most grinder machines to increase throughput in a dual grind application (coarse and fine). 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a device for use in a precision grind wheel bearing assembly wherein the fine and coarse wheel actuation and support member is located in a wheel mount assembly instead of the inner concentric shaft of the spindle assembly. 
         [0007]    The device of the present invention comprises a coupler/spline shaft assembly having a top coupler, a rotating spindle shaft, middle coupler and bottom coupler attached to the lower portion of the rotating spindle. When the spindle shaft rotates, the fine wheel mount rotates causing the above noted components to rotate. The middle coupler is assembled between the top coupler and the bottom coupler. Indentations on the inside diameter of the middle coupler and the outside diameter of the spline shaft create a spline interface, which prevents the middle coupler from rotating relative to the spline shaft but allows for vertical movement. Springs between the middle coupler and the bottom coupler preload the middle coupler in the retract position, the middle coupler pushing against the top coupler engaging the two mating face gears. The couplers face gears are made with the same diameter, same number of teeth, and have equal tooth geometry. Due to the number of contact points during the interface of the two face gears, the contact stresses are minimized enabling torque to be transmitted. When the coarse wheel is actuated the middle coupler moves down to interface with the bottom coupler. The interfacing face gears of the coupling provide a repeatable and stiff connection. The spline shaft and the bottom coupler are vertically stationary components mounted to the fine wheel mount. 
         [0008]    In the retract position, the coarse wheel is recessed in the wheel mount assembly allowing the fine wheel to be used for grinding. The retract position is the standard position of the wheel mount (no actuation). The springs of the coupler assembly push up the middle coupler to engage the top coupler. The face gear pair provides a repeatable and stiff interface. The middle coupler provides the mounting/support for the coarse wheel mount. In the retract position, the top coupler provides rigid positioning and enables the assembly to be balanced which is critical for high speed quality grinding surfaces (i.e. 5000 rpm). 
         [0009]    Actuation (i.e. to move coarse wheel into position for grinding work piece) is preferably provided by pressurized fluid (air or water) although other methods can be used, such as a push bar, linear motor, ball screw, etc. Pressurized fluid enters the center of the wheel mount through the hollow spindle shaft. Since the center portion of the wheel mount is sealed with a rolling diaphragm, pressure builds up creating a force which pushes down the diaphragm guide. The diaphragm guide causes the bottom shield, coarse wheel mount, coarse wheel, and middle coupler to move down, the middle coupler moving downward until it engages the bottom coupler. In the extend position, the bottom coupler transmits the torque to the coarse wheel assembly (middle coupler, coarse wheel mount, coarse wheel). In one embodiment, a pressure sensor monitors the fluid pressure to determine if the assembly is in the extend (positive pressure)/retract (no pressure) position. When the fluid pressure is relieved the wheel mount returns to its retract position by spring force. 
         [0010]    The extended wheel mount assembly of the present invention can be utilized with any grinding apparatus (such as the apparatus disclosed in the &#39;446 patent) by attaching it via bolts to the grind spindle (typically an upper air bearing spindle). In this case, an adapter plate is provided to enable the wheel mount assembly to be physically mounted to the lower portion of the grind spindle. The spindle requires a hole through its center to allow fluid (or a push bar, for example,) to actuate the assembly. The same principle would apply to other grinding apparatus. 
         [0011]    The present invention thus provides a wheel mounting assembly mounted to the lower portion of the grinding spindle, the inner wheel actuation mechanism being mounted therein, this feature eliminating the need to purchase a grinding apparatus having the inner coarse wheel activated by the spindle, thus simplifying and reducing the overall cost of the grinding apparatus. 
         [0012]    It should be noted that the extendable wheel mount assembly of the present invention is not limited to using two grind wheels (coarse and fine). In particular, the assembly may incorporate several nested components such as (from smallest to largest) an edge grinding tool, a coarse grind wheel, a fine grind wheel and a stress relief polish ring. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing wherein: 
           [0014]      FIG. 1  is a perspective view of a grinding apparatus utilizing the wheel mount of the present invention; 
           [0015]      FIG. 2  is a cross-sectional view along line  2 - 2  of  FIG. 1  showing the wheel mount in the retracted position; 
           [0016]      FIG. 3A  illustrates the wheel mount in the retract position and  FIG. 3B  illustrates the wheel mount in the extend position, both figures illustrating the coupler/spline assembly; 
           [0017]      FIG. 4  illustrates the wheel mount assembly in the retract position; 
           [0018]      FIG. 5  illustrates actuation of the coarse grind wheel; and 
           [0019]      FIG. 6  illustrates a fluid interconnect diagram. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  is a perspective view of a grinding apparatus  10  which is adapted to use the extendable wheel mount assembly  11  of the present invention (the basic operation of apparatus  10  is shown in the &#39;446 patent and will not be disclosed herein for the purposes of brevity; the teachings of the patent necessary for the understanding of the present invention being incorporated herein by reference). 
         [0021]    Apparatus  10  comprises grind spindle  12 , air bearing linear guide  14 , Zaxis force responsive servomechanism  16 , y-axis servomechanism  18 , thickness measurement sensor  20 , vacuum workchuck  22 , lower work spindle (with integrated force sensor)  24  and automatic wheel dressing  26 . 
         [0022]    Referring to  FIG. 2 ,  3  and  4 , the coupler/spline assembly  15  is made up of four components; top coupler  52 , middle coupler  54 ; spline shaft  62  and bottom coupler  56 , the last two components being vertically stationary components mounted to fine wheel mount  60 . An adapter plate  59  enables the assembly  11  to be mounted to spindle shaft  58  (a number of companies have the capability of manufacturing the type of couplers noted hereinabove). When the spindle shaft  58  rotates, the fine wheel mount  60  rotates causing the components noted above to rotate. The middle coupler  54  is assembled between the top coupler  52  and the bottom coupler  56 . The inside diameter of the middle coupler  54  and the outside diameter of spline shaft  62  create a spline interface  61  which prevents the middle coupler  54  from rotating relative to the spline shaft  62  but allowing for vertical movement. Four springs  64  (only one shown) are used between the middle coupler  54  and bottom coupler  56  to preload the middle coupler  54  to the retract position. In this position, the middle coupler  54  is pushed against the top coupler  52 , thus engaging two mating face gears. The couplers face gears are made with the same diameter, the same number of teeth, and have equal tooth geometry. The individual tooth geometry variations are averaged out over all the teeth resulting in good repeatability. Due to the high number of contact points during the interface of the two face gears, the contact stresses are low thus enabling torque to be transmitted. When coarse wheel  70  is actuated, the middle coupler  54  moves down to interface with bottom coupler  56 . The interfacing face gears of the coupling provide a repeatable and stiff connection and transmit the grinding torque and down force during coarse wheel grinding. 
         [0023]    In the retract position, the coarse wheel  70  is recessed in the wheel mount assembly allowing the fine wheel  72  to be used for grinding. The retract position is the standard position of the wheel mount assembly  11  when the system is not actuated. Spring  64  of the coupler assembly  11  forces the middle coupler  54  upwards to engage the top coupler  52 . The face gear pair (middle coupler  54  and top coupler  52 ) provides a repeatable and stiff interface. The middle coupler  54  provides the mounting/support for coarse wheel mount  74 . The coarse wheel mount  74 , in turn, provides the mounting/support for coarse wheel  70 . In the retract position, the top coupler  52  holds the coarse wheel assembly (middle coupler  54 , coarse wheel  70  and coarse wheel mount  74 ) firmly in place and keeps the assembly in balance. 
         [0024]    The preferred method for actuating the coarse grinding system is pressurized fluid (air or water) although other actuation methods can be used (such as a push bar). Pressurized fluid enters the center of the wheel mount assembly  11  through the spindle shaft  76 . Since the center portion of the wheel mount assembly  11  is sealed with rolling diaphragm  78 , the pressure buildup creating a force which pushes down diaphragm guide  80 . Diaphragm guide  80  causes bottom shield  82 , coarse wheel mount  74 , coarse wheel  70 , and middle coupler  54  to move in the downward direction. The middle coupler  54  moves down until it engages the bottom coupler  56 , the face gear of couplers  54  and  56  providing a repeatable and stiff interface. In the extend position, bottom coupler  56  transmits the torque to the coarse wheel assembly (middle coupler  54 , coarse wheel mount  74 , coarse wheel  70 ). A pressure sensor is used to monitor the fluid pressure to determine if the assembly is in the extend (positive pressure)/retract (no pressure) position. When the fluid pressure is removed, the wheel mount assembly  11  returns to its retract position. 
         [0025]      FIG. 6  is a simplified system fluid interconnect diagram. Actuating fluid (air) is forced into grinding apparatus  10  via inlet  90  by an air compressor (not shown) extending coarse grinding wheel  70 . The fluid from regulator  92  is directed to solenoid valve  94  via tubing  96 . Machine software (not part of the present invention) controls the state (on/off) of the solenoid valve  94  via tubing  96 . Rotary union  102  conducts the fluid from solenoid valve  94  via tubing  98  to the air bearing spindle  58  and is designed to withstand high levels of heat and pressure. Sensor  100  is positioned between solenoid valve  94  and the rotary union  102 . If sensor  100  detects fluid pressure below a predetermined value, then solenoid valve  94  is in the “off” state allowing the system  10  to be in the retracted position. If the sensor detects pressure above the predetermined value, then solenoid valve  94  is in the “on” state forcing the system  10  to be in the extended position. 
         [0026]    The shape of adapter plate that mounts the extendable wheel mount assembly to the upper spindle assembly will vary depending upon the upper spindle mating pilot feature and mounting home pattern in the grind apparatus provided by manufacturers of such apparatus. 
         [0027]    The present invention thus provides a compact grinding apparatus wherein the expense thereof is substantially reduced by utilizing an extendable wheel mount device attached to the grinding spindle, the wheel mount incorporating the coarse wheel actuating mechanism. 
         [0028]    While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings.