Abstract:
There is provided a roll machining apparatus which can accurately support a roll by means of hydrostatic bearings while absorbing thermal expansion of the roll in the length direction e.g. due to a change in room temperature, thus enhancing the machining precision. The roll machining apparatus for machining the surface of a roll while supporting and rotating the roil in a horizontal position, includes: a first spindle to be detachably coupled to one end of the roll; a second spindle, disposed opposite to the first spindle on the same axis, to be detachably coupled to the other end of the roll; a first hydrostatic radial bearing for receiving the radial load of the first spindle and rotatably supporting the first spindle; a hydrostatic thrust bearing for receiving the thrust load of the first spindle and limiting axial movement of the first spindle, a second hydrostatic radial bearing for receiving the radial load of the second spindle and rotatably supporting the second spindle; and a floating thrust having a thrust bearing for receiving the thrust load of the second spindle, said thrust being capable of selectively limiting and permitting axial movement of the thrust bearing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a roll machining apparatus for machining the surface of a roll while supporting and rotating the roll in a horizontal position, and more particularly to a roll machining apparatus for machining a roll into a machined product which requires precision machining, such as a roll mold for the production of, for example, an optical film for use in a liquid crystal display or a lenticular lens for use in a rear projection device. 
         [0003]    2. Background Art 
         [0004]    A roll mold as described above requires fine, very high-precision machining. Therefore, when machining a roll into such a roll mold, it is necessary to precisely support the roll while suppressing shaking, displacement of the axis, etc. of the roll during its rotation. For this purpose, it is preferred to support spindles, supporting the both ends of the roll, by means of hydrostatic bearings. 
         [0005]    However, when a spindle is supported by a hydrostatic thrust bearing which receives a thrust load, because of small bearing gap of the bearing, the bearing cannot absorb thermal expansion of a roll in the length direction e.g. due to a change in room temperature, especially when the roll has a large length, causing scuffing in the bearing. 
         [0006]    Japanese Patent Laid-Open Publication No. 11-207503 discloses an apparatus for machining a crankshaft as a workpiece, in which the both ends of the workpiece are supported by two spindles which are supported by hydrostatic bearings both in the radical direction and in the thrust direction. The workpiece is not directly fixed to one of the spindles, but fixed at its one end to a piston provided in the one spindle. The workpiece is supported with a tensile force applied to the one end from the piston. 
         [0007]    Though the disclosed method makes it possible to absorb thermal expansion of a workpiece in the length direction e.g. due to a change in room temperature, involves a complicated structure of the apparatus. In addition, since one end of the workpiece is not directly fixed to the spindle, but fixed to the spindle indirectly via the piston, the workpiece cannot be supported stably, and shaking, displacement of the axis, etc. of the workpiece during its rotation are likely to occur. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to provide a roll machining apparatus which can accurately support a roll by means of hydrostatic bearings while absorbing thermal expansion of the roll in the length direction e.g. due to a change in room temperature, thus enhancing the machining precision. 
         [0009]    In order to achieve the object, the present invention provides a roll machining apparatus for machining the surface of a roll while supporting and rotating the roll in a horizontal position, said apparatus comprising: a first spindle to be detachably coupled to one end of the roll; a second spindle, disposed opposite to the first spindle on the same axis, to be detachably coupled to the other end of the roll; a first hydrostatic radial bearing for receiving the radial load of the first spindle and rotatably supporting the first spindle; a hydrostatic thrust bearing for receiving the thrust load of the first spindle and limiting axial movement of the first spindle; a second hydrostatic radial bearing for receiving the radial load of the second spindle and rotatably supporting the second spindle; and a floating thrust having a thrust bearing for receiving the thrust load of the second spindle, said thrust being capable of selectively limiting and permitting axial movement of the thrust bearing. 
         [0010]    In a preferred embodiment of the present invention, the floating thrust includes: a housing having a cylinder chamber and a hole into which the thrust bearing is inserted, together with a bearing case, movably only in the axial direction; means for fixing the thrust bearing to the rear end of the second spindle; a piston, fitted movably into the hole, for pressing the thrust bearing in the axial direction by means of a pressurized fluid supplied to the cylinder chamber, and a switching valve for switching the directions of the flow of the pressurized fluid supplied to the cylinder chamber so as to selectively allow the piston to operate either to permit axial movement of the thrust bearing or to limit axial movement of the thrust bearing and fix it at a predetermined position. 
         [0011]    According to the present invention, the first spindle of the two spindles that support the both ends of a roll is thus supported by the hydrostatic bearings both in the radial direction and in the thrust direction, while the second spindle is supported by the hydrostatic bearing in the radial direction and by the floating thrust, capable of selectively limiting axial movement of the second spindle, in the thrust direction. This enables a simple construction of the apparatus and, in addition, enables thermal expansion of the roll in the length direction, e.g. due to a change in room temperature, to be absorbed by the floating thrust while accurately supporting the roll with the hydrostatic radial bearings for the first and second spindles and with the hydrostatic thrust bearing for the first spindle, thus enhancing the processing precision. 
         [0012]    The floating thrust is to fix the axial position of the second spindle at a predetermined position with respect to the spindle head body at the time of attaching or detaching a roil to or from the first and second spindles, and to perform initial setting of the axial position of the second spindle with respect to the spindle head body. Thus, the flowing thrust does not necessarily use a hydrostatic thrust bearing. The use of a ball bearing for the floating thrust can further simplify the construction of the apparatus and can also reduce the cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view showing the main portion of a roll machining apparatus according to the present invention; 
           [0014]      FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 ; and 
           [0015]      FIG. 3  is an enlarged vertical sectional view showing the details of the floating thrust shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    The present invention will now be described in detail with reference to the drawings. 
         [0017]      FIG. 1  shows a roll machining apparatus according to an embodiment of the present invention. In  FIG. 1 , R denotes a roll to be machined, and reference numerals  10  and  11  denote a first spindle and a second spindle, respectively. The first and second spindles  10 ,  11  are disposed opposite to each other on the same horizontal axis, and detachably fix and support the both ends of the roll R and hold the roll in a horizontal position. 
         [0018]    The first spindles  10 , on their front and rear sides with respect to the roll R, is rotatably supported by first hydrostatic radial bearing which includes hydrostatic pocket member  12 ,  13 . The second spindles  11 , on their front and rear sides with respect to the roll R, is rotatably supported by second hydrostatic radial bearing members which includes hydrostatic pocket members,  14 ,  15 . The hydrostatic pocket member  12 , for example, has hydrostatic pockets  12 A,  12 B in opposing vertical pair and hydrostatic pockets  12 C,  12 D in opposing lateral pairs, as shown in  FIG. 2 . The same holds for the other hydrostatic pocket members  13 ,  14 ,  15 . 
         [0019]    Of the hydrostatic pockets  12 A,  12 B,  12 C,  12 D, the hydrostatic pocket  12 A, the upper pocket of the vertical pair to which a load is applied from the roll R, is provided with a constant-pressure ratio flow control valve  17 , provide in a pressurized oil supply circuit  16 , for changing the flow rate of a pressurized oil, supplied to the hydrostatic pocket  12 A, in response to a change in the pressure in the hydrostatic pocket  12 A so as to keep the bearing gap of the hydrostatic pocket  12 A constant. The upper hydrostatic pocket  14 A of the hydrostatic pocket member  14  on the front side of the second spindle  11  is also provided with the constant-pressure ratio flow control valve  17  provided in he pressurized oil supply circuit  16 . 
         [0020]    With reference to the hydrostatic pocket members  13 ,  15  on the rear sides of the spindles  10 ,  11  on the other hand, the lower hydrostatic pockets  13 B,  15 B are each provided with the constant-pressure ratio flow control valve  17  in the pressurized oil supply circuit  16 . The pressurized oil supply circuit  16  is connected via a temperature regulating unit  18  to an accumulator tank  19  which is the source of supply of the pressurized oil. 
         [0021]    The hydrostatic pockets (reference numerals omitted) other than the hydrostatic pockets  12 A,  14 A,  13 B,  15 B of the hydrostatic pocket members  12 ,  13 ,  14 ,  15  are connected via the temperature regulating unit  18  to the accumulator tank  19 , the source of supply of the pressurized oil, without passing through the constant-pressure ratio flow control valve  17 . 
         [0022]    Reference numerals  20 ,  21  denote hydrostatic thrust bearings for the first spindle  10 . The hydrostatic thrust bearings  20 ,  21  have pairs of opposing hydrostatic pockets on the opposite surfaces of a flange  22  provided in the first spindle  10 . Each hydrostatic pocket is connected to the accumulator tank  19  via the pressurized oil supply circuit  16  and the temperature regulating unit  18 . Reference numeral  23  denotes a drain for returning the oil, which has flowed from the hydrostatic bearings  12 - 15 ,  20 ,  21 , to a tank  24 . 
         [0023]    The second spindle  11  is provided, at its rear end (right end in  FIG. 1 ), with a floating thrust  25 . As shown in  FIG. 3 , the floating thrust  25  has ball bearings  26 ,  27  as thrust bearings, mounted to the rear end of the second spindle  11  by a nut  29  with a spacer  28  interposed between the bearings and the nut. The outer races of the ball bearings  26 ,  27  are fitted, via a bearing case  32 , into a hole  31 A of a housing  31 . A guide pin  31 B is inserted into the housing  31  in the radial direction such that the guide pin  31 B is contact with peripheral surface of the bearing case  32 . The bearing case  32   31  is supported and movable only in the axial direction by means of the guide pin  31 B. The housing  31  is mounted to a spindle head body  30  (only partly shown) that rotatably supports the second spindle  11  with the hydrostatic pocket members  14 ,  15 . 
         [0024]    In the housing  31  are formed cylinder chambers  33   a ,  34   a . Pistons  33 ,  34  for pressing the bearing case  32  backward and forward are provided in the housing  31 . With the step portions in front of and behind the hole  31 A, the forward movements of the pistons  33 ,  34  are limited, while they can each move backward a predetermined distance. The cylinder chambers  33   a ,  34   a  in the back sides of the pistons  33 ,  34 , are connected to the pressurized oil supply circuit  16  and to the tank  24  selectively via a switching valve  35 . By connecting the pistons  33 ,  34  to the pressurized oil supply circuit  16 , the pistons  33 ,  34  are pressed by the pressurized oil to the limited forward movement positions, thereby fixing the axial position of the ball bearings  26 ,  27  via the bearing case  32 . On the other hand, by connecting the pistons  33 ,  34  to the tank  24 , the pressures on the back sides of the pistons  33 ,  34  are released so as to permit axial movement of the ball bearings  26 ,  27 . 
         [0025]    Returning to  FIG. 1 , to the accumulator tank  19  is connected a receiver tank  38  for storing high-pressure air from a pressure-increasing valve  37  which increases the pressure of pressurized air from a pressurized air source  36 , e.g. factory air, so that the accumulator tank  19  can be given a pressure necessary for the hydrostatic pocket members  12 - 15 ,  20 ,  21 . 
         [0026]    Further, a pump  40  is connected via a check valve  39  to the accumulator tank  19 . The start-up and stop of the pump  40  is controlled with upper and lower liquid level indicators  41 ,  42 , provided in the accumulator tank  19 , so as to store not less than a predetermined amount of pressurized oil in the accumulator tank  19 . A rotational drive mechanism for the first and second spindles  10 ,  11 , and an axial movement mechanism for the first spindle  10  or the second spindle  11 , provided for attachment/detachment of the roll R, have no direct relation with the present invention and hence a detailed description thereof is herein omitted. 
         [0027]    The operation of the roll machining apparatus will now be described. 
         [0028]    Prior to attaching the roll R to the first and second spindles  10 ,  11 , the back sides of the pistons  33 ,  34  are connected to the pressurized oil supply circuit  16  by the switching valve  35 , so that the pressurized oil supplied presses the pistons  33 ,  34  against the step portions in front of and behind the hole  31 A as shown in  FIG. 3 , thereby fixing the ball bearings  26 ,  27  with respect to the housing  31  and fixing the axial position of the second spindle  11  with respect to the spindle head body  30 . 
         [0029]    Next, the both ends of the roll R are attached and fixed to the front ends of the first and second spindles  10 ,  11 . After the attachment of the roll R, the load of the roll R acts on the spindles  10 ,  11  whereby the bearing gaps of the lower hydrostatic pockets  12 B,  14 B of the front hydrostatic pocket members  12 ,  14  are becoming smaller, whereas the bearing gaps of the upper hydrostatic pockets  12 A,  14 A are becoming larger. On the contrary, in the case of the rear hydrostatic pocket members  13 ,  15 , the bearing gaps of the upper hydrostatic pockets  13 A,  15 A are becoming smaller, whereas the bearing gaps of the lower hydrostatic pockets  13 B,  15 B are becoming larger. 
         [0030]    The pressure of the pressurized oil in a hydrostatic picket increases as the bearing gap decreases, and conversely, the pressure of the pressurized oil in a hydrostatic picket decreases as the bearing gap increases. However, the pressurized oil is supplied from the accumulator tank  19  to the hydrostatic pockets  12 A,  14 A,  13 B,  15 B, whose bearing gaps are becoming larger, via the respective constant-pressure ratio flow control valves  17 . The flow rate the pressurized oil supplied to each of the hydrostatic pockets  12 A,  14 A,  13 B,  15 B changes in response to a change in the pressure of the pressurized oil in the hydrostatic pocket, whereby the bearing gap of each of the hydrostatic pockets  12 A,  14 A,  13 B,  15 B is kept constant. 
         [0031]    Because the bearing gaps of the hydrostatic pockets  12 A,  14 A,  13 B,  15 B, whose bearing gaps are to change by the load of the roll R, are thus kept constant, the bearing gaps of their opposing counterparts of the vertical pairs, i.e. the hydrostatic pockets  12 B,  14 B,  13 A,  15 A, are also kept constant. A change in the bearing gap of each hydrostatic pocket due to the load of the roll R can thus be suppressed. Accordingly, even when rotating the spindles  10 ,  11  at a high speed by means of a not-shown rotational drive mechanism, a difference in the rise of temperature in each hydrostatic pocket can be made small. Deformation of the spindles  10 ,  11  can therefore be suppressed, making it possible to accurately support the roll R and machine it with enhanced precision. 
         [0032]    Further according to this embodiment, the pressurized oil is supplied to the hydrostatic bearings  12 - 15 ,  20 ,  21  from, the accumulator tank  19  to which a stable pressure is given by the receiver tank  38 . This can suppress pulsing motion as will occur when supplying a pressurized oil directly from a pump, making it possible to accurately and stably support and rotate the roll R. This can also enhance the machining precision for the roll R. 
         [0033]    Furthermore, not less than a predetermined amount of pressurized oil is stored in the accumulator tank  19  through control of the start-up and stop of the pump  40  with the liquid level indicators  41 ,  42 . This enables supply of the pressurized oil to the hydrostatic pockets even upon a power failure, thus preventing damage, such as scuffing, to the bearings. 
         [0034]    After attaching the roll R to the spindles  10 ,  11  in the above-described manner and before rotating the spindles  10 ,  11  and starting machining of the roll R, the switching valve  35  for the floating thrust  25  is switched to open the back sides of the pistons  33 ,  34  to the tank  24 . This allows the ball bearings  26 ,  27  to move with respect to the housing  31  in the axial direction when the roll R expands or contracts e.g. due to a change in room temperature, thus allowing the second spindle  11  to move in the axial direction. Accordingly, no excessive load will be applied to the hydrostatic thrust bearings  20 ,  21  of the first spindle  10 . This not only prevents damage, such as scuffing, to the bearings but also makes it possible to accurately and stably support and rotate the roll R, thereby enhancing the machining precision for the roll k. 
         [0035]    In this embodiment, of the hydrostatic pockets  12 A,  12 B, etc. which are opposing hydrostatic pockets in the vertical pairs on which the load of the roll R acts, only the hydrostatic pockets  12 A, etc., whose bearing gaps increase by the load of the roll R, are connected to the respective constant-pressure ratio flow control valves  17  so as to keep the respective bearing gaps constant. However, it is also possible to connect the constant-pressure ratio flow control valves  17  to either the hydrostatic pockets  12 B, etc. whose bearing gaps decrease or all of the vertical pairs of hydrostatic pockets, the hydrostatic pockets  12 A,  12 B, etc. It is also possible not to use the constant-pressure ratio flow control valves  17 . Further, though in this embodiment the pressurized oil is supplied from the accumulator tank  19  to the hydrostatic pocket member  12 , etc. via the temperature regulating unit  18 , this is not limiting of the present invention. Thus, it is possible to omit the temperature regulating unit  18 , to change the accumulator tank  19  to the pump  40 , or to supply the pressurized oil directly from the pump  40 . 
         [0036]    In this embodiment the ball bearings  26 ,  27  are used for the floating thrust  25 . The floating thrust  25  is to fix the axial position of the second spindle  11  at a predetermined position with respect to the spindle head body  30  at the time of attaching or detaching the roll R to or from the first and second spindles  10 ,  11 , and to perform initial setting of the axial position of the second spindle  11  with respect to the spindle head body  30 . It is therefore also possible to use, instead of the ball bearings  26 ,  27 , various other types of thrust bearings, such as hydrostatic bearings or plain bearings. 
         [0037]    Further, though in this embodiment the pressurized oil in the pressurized oil supply circuit  16  for the hydrostatic bearings is used to fix the ball bearings  26 ,  27  of the floating thrust  25  to the spindle head body  30 , it is also possible to use pressurized air. Furthermore, in this embodiment the ball bearings  26 ,  27  are designed to be movable forward and backward by means of the pistons  33 ,  34  in order to respond to expansion and contraction of the roll R. However, in the case where due to machining conditions, the roll R is subject to only one of expansion and contraction, it is possible to design the pistons  33 ,  34  to be movable only backward or only forward. It will be appreciated by those skilled in the art that other changes or modifications could be made to the embodiments described above without departing from the inventive concept thereof. While the present invention can be advantageously applied to a roll machining apparatus for machining a roll into a machined product which requires precision machining, such as a roll mold for the production of, for example, an optical film for use in a liquid crystal display or a lenticular lens for use in a rear projection device, the present invention is applicable broadly to a roll machining apparatus for machining the surface of a roll while supporting and rotating the roll in a horizontal position with a first spindle and a second spindle disposed opposite to each other.