Abstract:
A method of taking up wear of a grinding wheel on a machine for grinding sheets of glass, whereby the position of an abrasive surface of the grinding wheel, initially set to an ideal work position such as to obtain a sheet of a given size, is adjusted, following wear of the grinding wheel, by moving the abrasive surface towards a reference surface on the machine, positioned facing and at a predetermined distance from the abrasive surface when the abrasive surface is in the ideal work position; determining the instant of contact between the abrasive surface and the reference surface; arresting the grinding wheel at the instant of contact; and moving the abrasive surface away from the reference surface to an adjustment distance at least equal to the predetermined distance.

Description:
[0001]    The present invention relates to a machine for grinding sheets of glass.  
         BACKGROUND OF THE INVENTION  
         [0002]    To grind outer peripheral portions of a sheet of glass, grinding machines are used, which comprise, for each side of the work sheet, a number of side by side grinding heads, each comprising a powered grinding wheel set to a respective zero position to remove a respective quantity of material to form beveled sheets or sheets to a given size or shape.  
           [0003]    To obtain sheets all of the same size and/or shape, all the wheels must be supervised constantly and the initial zero positions adjusted to take into account inevitable wear of the wheels. For which purpose, each wheel is normally fitted to a respective slide in turn fitted to the machine frame, and which is activated by a supervisor who, on detecting any deviation in size, shape and/or surface finish of the sheet coming off the machine, adjusts the wheels until the sheets coming off the machine are restored to the desired characteristics.  
           [0004]    Though widely used, the above method of checking and adjusting the wheels fails to provide for obtaining sheets all of the same shape, size and surface finish. The reason for this substantially lies in the zero position adjustment depending on the skill and experience of the supervisor, who, knowing the expected working life of the wheel under normal working conditions, and by constantly checking the characteristics of the finished sheets, manually adjusts the position of one or more wheels accordingly. When the adjustment is made, however, there is no guarantee that each wheel is actually set to the ideal work position, even if the sheets coming off the machine are, at least initially, within the given tolerance range, so that one or more wheels subjected to greater stress may undergo sudden, rapid wear, while others are subjected to less severe stress than expected.  
           [0005]    Whichever the case, adjustment as described above is a particularly time-consuming job, which is directly proportional to the number of wheels being supervised.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide a wheel wear take-up method designed to solve the aforementioned problems in a straightforward, low-cost manner.  
           [0007]    According to the present invention, there is provided a method of taking up wear of a grinding wheel on a machine for grinding sheets of glass; the method comprising the steps of setting an abrasive surface of the grinding wheel to an ideal work position, such as to obtain a sheet of desired characteristics; and adjusting the position of the grinding wheel to restore said abrasive surface to said ideal work position following wear of the grinding wheel; characterized in that adjustment of the position of the grinding wheel comprises the steps of moving said abrasive surface towards reference means on said machine, positioned facing and a predetermined distance from said abrasive surface when the abrasive surface is in said ideal work position; determining the instant of interference between said abrasive surface and said reference means; arresting said grinding wheel at said instant of interference; and moving said abrasive surface away from said reference means to an adjustment distance at least equal to said predetermined distance.  
           [0008]    The present invention also relates to a machine for grinding sheets of glass.  
           [0009]    According to the present invention, there is provided a machine for working sheets of glass, comprising a supporting frame; a grinding wheel defined by an abrasive surface; actuating means for setting and maintaining said abrasive surface in an ideal work position such as to obtain a sheet of desired characteristics; and adjusting means for adjusting the position of the grinding wheel with respect to said supporting frame, and restoring said abrasive surface to said ideal work position following wear of the grinding wheel; characterized in that said adjusting means comprise reference means fitted to said supporting frame and facing and a predetermined distance from said abrasive surface when the abrasive surface is in said ideal work position; first actuating means for moving said abrasive surface towards said reference means; detecting means for determining the instant of interference between said abrasive surface and said reference means; stop means for arresting said grinding wheel at the instant of interference; and second actuating means for moving said abrasive surface away from said reference means and to an adjustment distance at least equal to said predetermined distance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 shows a section of a preferred embodiment of a unit for taking up wear of a grinding wheel on a machine (shown partly) for grinding sheets of glass;  
         [0012]    [0012]FIG. 2 shows a larger-scale section of a detail in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Number  1  in FIG. 1 indicates as a whole a machine (shown partly) for grinding a sheet  2  of glass having a lateral surface  3  for grinding and placed horizontally on a known supporting device  4  of machine  1 .  
         [0014]    Machine  1  comprises a frame  5 ; and a number of adjustable grinding heads  6 , only one of which is shown in FIG. 1. Each head  6  comprises a grinding wheel  7 , which is housed inside a sealed chamber  8  containing cutting fluid, is rotated about a respective axis  9 —in this case, a horizontal axis—by a respective electric motor  10 , and is defined by an abrasive face surface  12 , in this case, perpendicular to axis  9  and parallel to surface  3 . Motor  10  is located outside chamber  8  and is supported, together with grinding wheel  7 , by a respective slide  13 , which is fitted movably to frame  5  and is moved, with respect to frame  5  and in a direction  15  parallel to axis  9 , by a respective, conveniently step-type, motor  16  fitted in known manner to frame  5  and connected to slide  13  by a known screw-nut screw assembly  17  (not described in detail) to move respective grinding wheel  7  to and from supporting device  4  under the control of a central control unit  18  comprising a memory  19  for storing a number of values, each corresponding to a reference or zero axial position of slide  13 .  
         [0015]    Still with reference to FIG. 1, motor  16 , assembly  17  and slide  13  form part of a positioning and adjusting assembly  20  for regulating the position of grinding wheel  7  in direction  15  as a function of the wear of grinding wheel  7 .  
         [0016]    Each assembly  20  also comprises an adjustable detecting device  21  in turn comprising a fastening frame  22  connected integrally to frame  5  of machine  1  on one side, and supporting, on the other side, a tubular body  23  having an axis  24  parallel to axis  9 , and connected integrally to frame  22  to the side of respective grinding head  6 . Each device  21  comprises a rod  25 , which has an intermediate portion  26  extending inside tubular body  23 , and is connected to tubular body  23  in axially-sliding, angularly-fixed manner. Each rod  25  also comprises two opposite lateral portions  27  and  28 . Portion  27  projects frontwards on the same side as and alongside grinding wheel  7 , projects inside chamber  8  and beyond the plane of abrasive surface  12  of grinding wheel  7 , and terminates with an eccentric plate  30 . Plate  30  extends partly facing abrasive surface  12 , and is defined by a flat surface  31  extending, in this case, over sheet  2 , facing and parallel to surface  12 , and withdrawn with respect to surface  3 .  
         [0017]    Portion  28  projects from tubular body  23  on the same side as motor  10  and inside a cup-shaped body  33  coaxial with axis  24  and comprising a cylindrical lateral wall  34  defining an extension of tubular body  23 , and an end wall  35  having an inner shoulder  36  (FIG. 2). A supporting body  37  is located between shoulder  36  and the end of portion  28 , is connected integrally to portion  28 , and projects radially beyond portion  28  to define a support for one end of a forcing spring  39  surrounding portion  28 , and the opposite end of which rests on a retaining ring  40  engaged in sliding manner by rod  25  and gripped between tubular body  23  and lateral wall  34  of cup-shaped body  33 .  
         [0018]    Still with reference to FIG. 2, device  21  also comprises a screw  42  coaxial with axis  24 , the head of which projects outside cup-shaped body  33 , and the threaded shank  43  of which engages a threaded hole in end wall  35 , and rests against supporting body  37  to keep supporting body  37  and plate  30  in a given axial reference position.  
         [0019]    Device  21  also comprises an angular stop screw  44 , the shank of which engages a threaded hole in supporting body  37  and projects outwards of cup-shaped body  33  through an axial slot  45  which it engages in axially sliding manner.  
         [0020]    With reference to FIG. 1 and, particularly FIG. 2, device  21  also comprises a switch  47 , which is fitted integrally to a lateral wall of the tubular body, is connected electrically to central control unit  18 , and has a switching member  48  on which acts an arm  49  connected integrally to portion  27  of rod  25  and extending perpendicularly to rod  25 .  
         [0021]    Operation of machine  1  and adjustment of the axial position of grinding wheel  7  as a function of the wear of grinding wheel  7  will now be described as of an ideal grinding condition, in which abrasive surface  12  of grinding wheel  7  is in an ideal work position such as to obtain a sheet  2  of desired shape, size and surface finish; screw  42  is set to keep member  48  of switch  47  pressed in a standby condition, and to keep surface  31  of plate  30  positioned over sheet  2  and at a predetermined distance A—conveniently of a few millimeters—from surfaces  3  and  12 ; and a zero value corresponding to the position of slide  13  and to said predetermined distance A is memorized in central control unit  18 .  
         [0022]    As of the above condition, and after a predetermined or random operating time of grinding wheel  7 , the sheet  2 , if any, on device  4  is removed; the grinding wheel is stopped; and central control unit  18  transmits a control signal to motor  16  to feed slide  13  forward so that abrasive surface  12  contacts surface  31  of plate  30 . On contacting plate  30 , grinding wheel  7  pushes plate  30  to overcome the action of spring  39  and feed rod  25  forward with respect to frame  5  to detach arm  49  from switch  47 , which supplies central control unit  18  with a shift-start signal. In response to the incoming shift-start signal, central control unit  18  emits a control signal which first stops and then reverses motor  16  to back up grinding wheel  7  by an adjustment quantity equal to said predetermined distance A, so that abrasive surface  12  of grinding wheel  7  is restored to the ideal work position to obtain the desired characteristics of the next sheet  2 .  
         [0023]    To compensate for any slack in the linkage mechanism, grinding wheel  7  is conveniently backed up by an adjustment quantity greater than said predetermined distance A, and, once the grinding wheel is backed up, central control unit  18  again reverses motor  16  and feeds grinding wheel  7  forward by the difference between said adjustment quantity and predetermined distance A.  
         [0024]    By backing up and, if necessary, feeding grinding wheel  7  further forward, the abrasive surface  12  of grinding wheel  7  is therefore restored at all times to the ideal work position, regardless of the wear of grinding wheel  7 , so that, by selecting the best frequency with which to reposition grinding wheel  7 , all the sheets coming off the machine are the same shape and size.  
         [0025]    Using rod  25  and respective plate  30 , switch  47  and all the electric components of device  21  in general may be located away from grinding wheel  7  and outside chamber  8  containing the cutting fluid, thus eliminating any hazards posed by the electric components and relative wiring coming into contact with the cutting fluid.  
         [0026]    By providing each grinding wheel on the machine with a respective repositioning device, the grinding wheels can be controlled independently, in use, which is extremely useful when, for any reason, only one or some of the grinding wheels on the machine need adjusting or replacing.  
         [0027]    Clearly, changes may be made to machine  1  in general, and to assembly  20  in particular, as described herein, without, however, departing from the scope of the present invention.  
         [0028]    In particular, devices other than the one described may be provided to move grinding wheel  7 , and devices other than device  21  may be provided to detect the instant surfaces  12  and  31  contact, and so control motor  16 . Reference surface  31  may, obviously, be of any shape and size, and may be selected, for example, as a function of the geometry of the abrasive surface of the grinding wheel, which may, for example, be lateral and concave, as opposed to a flat face surface. In particular, plate  30  may, obviously, be replaced with a straightforward cylindrical rod, or a rod of any shape, positioned transversely so that the lateral surface of the rod cooperates with the abrasive surface of the grinding wheel, or frontally so that the end surface of the rod—which may, obviously, be the same or a different shape and size from the cross section of the rod—cooperates with the abrasive surface of the grinding wheel. In the case of a rod with a polygonal cross section, one longitudinal edge of the rod, and therefore substantially a line, is obviously sufficient to define a reference for the abrasive surface of the grinding wheel.  
         [0029]    The reference surface may therefore be a surface other than the one described, and, in particular, a luminous surface, conveniently one defining a light beam. In which case, the instant of contact between the abrasive surface of the grinding wheel and the reference surface may be determined by detecting the variation in one or more characteristics of the light beam.  
         [0030]    In the case of two or more side by side grinding wheels, the respective bodies/reference beams for the respective surfaces of the grinding wheels may obviously be replaced with a single body/reference beam common to all the respective devices  21  of the grinding wheels.  
         [0031]    Finally, arm  49  and switch  47  may be replaced with other, e.g. optical or magnetic, devices.