Abstract:
There is provided a spindle unit having a pressure foot whose machining efficiency may be improved even when compressed air is used as means for pressing the pressure foot. The spindle unit having the pressure foot comprises a rotor shaft provided within a base rotatably and movably along an axis, a collet chuck provided at one end of the rotor shaft, a linear motor for moving a movable element rotatably connected with the rotor shaft and movably provided within the base along the axis together with the rotor shaft to move a drill closer to or apart from the workpiece, a rotary motor for rotating the rotor shaft, a pressure foot disposed in front of the edge of the collet chuck and is capable of pressing down the workpiece, and air cylinders for connecting the movable element with the pressure foot so as to be relatively movable by a predetermined degree and for pressing the pressure foot in the direction separating from the collet chuck.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a spindle unit having a pressure foot for machining workpieces while pressing down the workpieces to a table by the pressure foot.  
         [0003]     2. Description of Related Art  
         [0004]     Hitherto, there has been a motor built-in type spindle unit whose machining efficiency is enhanced by increasing a moving speed of a drill, i.e., a machining tool, as disclosed in Japanese Patent Laid-open No. 62-197903 for example. This spindle unit is arranged so as to increase the drill moving speed, i.e., a machining speed, by moving up and down only a rotor shaft i.e., a spindle retaining the drill, in machining workpieces by rotatably and movably supporting the rotor shaft by a housing, i.e., a body portion of the unit. This arrangement allows not only the moving speed to be increased but also vibration occurring in machining to be reduced.  
         [0005]     By the way, the prior art spindle unit allows a hole to be made accurately at predetermined position by drilling a workpiece while pressing down a peripheral part of the workpiece to be machined by a pressure foot, i.e., pressure foot means, for pressing the workpiece to a table.  
         [0006]     However, the prior art spindle unit having the pressure foot has required other driving means for moving the pressure foot in addition to driving means for moving the rotor shaft so as to be able to move the pressure foot and the rotor shaft separately in machining workpieces. In this case, the driving means of the pressure foot has also played a role of pressing means for pressing the pressure foot to the workpiece and it has been difficult to increase the machining efficiency when compressed air is used for the pressing means because its response is slow in switching the pressing direction.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     It is an object of the invention to provide a spindle unit having a pressure foot whose machining efficiency can be improved even when compressed air is used for pressing means.  
         [0008]     An inventive spindle unit having a pressure foot comprises: 
        a body;     a spindle provided rotatably within the body and movably along an axis;     retaining means (collet chuck) provided at one end of the spindle for removably retaining a machining tool for machining workpieces;     holding means (vertical connecting shaft and movable element) rotatably connected with the spindle and provided within the body movably along the axis;     linear driving means (linear motor ) for moving the holding means together with the spindle along the axis to move the machining tool closer to or apart from the workpiece;     rotary driving means (rotary motor) provided within the body for rotating the spindle;     pressure foot means (pressure foot) disposed in front of the edge of the spindle for pressing down the workpiece; and     pressing means (air cylinder) for connecting the holding means with the pressure foot means so as to be relatively movable by a predetermined degree and for pressing the pressure foot means in the direction separating from the edge of the spindle.        
 
         [0017]     Since the spindle unit having the pressure foot is arranged so that the common linear driving means (linear motor) moves the spindle and the pressure foot means that is connected with the holding means through an intermediary of the pressing means (air cylinder), the pressure foot means may be moved quickly in synchronism with the spindle, thus increasing the workability. Still more, since the pressing means always presses the workpiece by a predetermined pressure during operation, it is possible to prevent the machining tool such as the drill from being damaged. This arrangement also allows the structure of the unit to be simplified and downsized.  
         [0018]     Preferably, the spindle unit having the pressure foot is also provided with resilient means (spring) between the body and the holding means (link plate connected in a body with movable element) to force the holding means in the direction of separating the edge of the spindle and the pressure foot means (pressure foot) from the workpiece.  
         [0019]     This arrangement prevents the spindle and the pressure foot means from dropping by their own weight and damaging the workpiece or the machining tool, even when the linear driving means (linear motor) is not in operation.  
         [0020]     Preferably, the spindle unit having the pressure foot is constructed so that a part of the body supporting the spindle is separable in the direction crossing with the direction of the axis.  
         [0021]     This arrangement enables a worn-out spindle to be replaced readily and swiftly.  
         [0022]     The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a front view, partly in section, of a spindle unit having a pressure foot according to an embodiment of the invention.  
         [0024]      FIG. 2  is a front view of a spindle unit having a pressure foot of the embodiment.  
         [0025]      FIGS. 3A and 3B  are section views taken along A-A in  FIG. 2 , wherein  FIG. 3A  shows a state in which a spindle is put into a base and  FIG. 3B  shows a state in which the spindle is taken out of the base.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     A spindle unit having a pressure foot of a preferred embodiment of the invention will be explained with reference to the drawings wherein like reference characters designate like or corresponding parts throughout the several views.  
         [0027]      FIG. 1  is a front view, partly in section, of the spindle unit  100  having the pressure foot of the embodiment.  
         [0028]     Disposed at the edge  1   b  of a spindle (hereinafter referred to as a rotor shaft)  1  of the spindle unit  100  are a collet chuck  2  and a spring  3  for forcing the collet chuck  2  upward in the figure. The collet chuck  2  has a plurality of slits not shown on the side of a drill  40  along an axis O, i.e., a rotational center axis of the rotor shaft  1 , so that its diameter can be reduced radially.  
         [0029]     The drill  40  is retained by the collet chuck  2 , i.e., retaining means, by radial force which is produced when the spring  3  pulls up the collet chuck  2  and a tapered face  1   a  formed at the inner face of the rotor shaft  1  presses a tapered face  2   a  formed around the outer periphery of the collet chuck  2 .  
         [0030]     The rotor shaft  1  is supported radially by a plurality of radial air bearings  5  disposed within a housing  4  and is supported and positioned in the direction along the axis O by a thrust air bearing  7  in which a flange  1   f  at its end is formed in a vertical connecting shaft  6 .  
         [0031]     A rotor  8  that is formed of an end-ring copper member is disposed around the rotor shaft  1 . A coil (stator)  9  is disposed on a face facing to the coil  8  within the housing  4 . The rotor  8 , i.e., the rotor shaft  1 , rotates when electricity is fed through the coil  9 . Thus, the coil  9  and the rotor  8  constitute a rotary motor  17 , i.e., rotary driving means.  
         [0032]     A pressure rod  10  is disposed above the collet chuck  2 . The pressure rod  10  is movable within the rotor shaft  1  along the axis O. The housing  4  is fixed to a base  16 . The housing  4  and the base  16  constitute a body portion of the unit.  
         [0033]     The vertical connecting shaft  6  is connected with a movable element  12  by means of bolts  11 . The vertical connecting shaft  6  and the movable element  12  constitute the holding means. Disposed on the side of the movable element  12  is a magnet  14  that constitutes a linear motor  18  together with a coil  13 . The coil  13  is disposed in the base  16  facing to the magnet  14 . The movable element  12  moves along the axis O when electricity is supplied to the coil  13 . It is noted that while the linear motor  18  constitutes the linear driving means, not only the linear motor  18  but also other linear driving means such as a hydraulic cylinder may be used.  
         [0034]     Bearings  15  support the movable element  12  so as to be movable within the base  16  along the axis O. The movable element  12  is connected in a body with a link plate  20  by fixing a flange  12   f  provided at the upper end of the movable element  12  to the link plate  20  by means of bolts  21 . A spring  22 , i.e., resilient means, is interposed between the link plate  20  and the base  16  to force the link plate  20  upward in the figure.  
         [0035]     A cylinder  30  is disposed above the base  16 . Guides  32  support a rod  31  of the cylinder  30  so that the rod  31  moves along the axis O. The guides  32  are provided within the movable element  12 . When the rod  31  stays at the upper end, the edge (lower end) of the rod  31  separates from the upper end of the pressure rod  10 .  
         [0036]     A pair of air cylinders  50  is fixed to the link plate  20  by means of bolts  51 . A pressure foot  53  is fixed to rods  52  of the air cylinders  50  by means of bolts  54 . The rods  52  are arranged so as to move in and out of the air cylinders  50 . The air cylinder  50  is arranged so that air is charged/discharged from the both sides. The link plate  20 , the air cylinders  50  and the pressure foot  53  move in a body when the movable element  12  is moved. However, the pressure foot  53  moves up and down separately from the link plate  20  when the direction of air to be charged to the air cylinders  50  is changed. Guides  55  retained in the base  16  support the rod  52  so as to be movable along the axis O. Air is supplied to the air cylinder  50  so that downward pressure always acts on the piston rod  52  during machining operation. The air cylinders  50  constitutes the pressing means.  
         [0037]     Next, an operation of the spindle unit  100  having the pressure foot of the embodiment will be explained.  
         [0038]     At first, steps for attaching/detaching the drill  40  will be explained.  
         [0039]     The cylinder  30  is operated in replacing the drill  40 . When the rod  31  is lowered, the pressure rod  10  moves the collet chuck  2  downward in the figure as against the force of the spring  3 . When the tapered face  2   a  of the collet chuck  2  separates from the tapered face la of the rotor shaft  1 , the force of the collet chuck  2  retaining the drill  40  is eliminated, thus detaching the drill  40  from the collet chuck  2 . Then, a new drill  40  is inserted into the inside of the collet chuck  2  in this state and the rod  31  is moved up to cause the collet chuck  2  to retain the new drill  40 .  
         [0040]     Next, a machining operation of the spindle unit  100  having the workpiece pressure foot of the embodiment will be explained.  
         [0041]     In starting to machine workpieces, the air cylinders  50  press the pressure foot  53 , i.e., the pressure foot means, downward in the figure by air within the cylinders  57 . Then, after positioning the axis O to the machining spot, electricity is fed to the coil  13  to lower the link plate  20  as against the force of the spring  22  until when the edge (chisel edge) of the drill  40  reaches to predetermined position. As the link plate  20  is lowered, the pressure foot  53  and the rotor shaft  1  start to move down together. Then, when the pressure foot  53  contacts with the workpiece  41  by its lower end, it stops from descending, presses down the workpiece  41  and relatively rises in relation to the rotor shaft  1  that continues to descend. During this time, the pressure foot  53  and the link plate  20  compress the air cylinders  50  that absorbs the relative movements of the pressure foot  53  and the rotor shaft  1 . It is noted that the predetermined air pressure is always supplied to the cylinder  57  and the pressure foot always presses the workpieces with equal pressure even when the operation for drilling the workpieces advances and a distance between the pressure foot  53  and the edge  1   b  of the rotor shaft  1  changes. It is also possible to keep the cylinder  57  to have the predetermined pressure by closing a valve while supplying the predetermined air pressure to the cylinder  57 .  
         [0042]     When the drill  40  opens a hole through the workpiece  41  to a desirable depth by its edge, the direction of the current fed to the coil  13  is reversed to raise the link plate  20  by the linear motor  18 , i.e., linear driving means. Here, the pressure foot  53  is pressed downward by the air cylinder  50 . Therefore, the drill  40  is pulled out of the workpiece  41  at first and then the pressure foot  53  separates from the workpiece  41 .  
         [0043]     Because the movable element  12 , the link plate  20 , the air cylinders  50 , the pressure foot  53 , the rotor shaft  1  and the drill  40  are linked together in the ascending/descending direction in the operation described above, the link plate  20 , the air cylinders  50 , the pressure foot  53  and others descend together  41  when the link plate  20  is lowered by the linear motor  18 , allowing the pressure foot  53  to press the workpiece without controlling air to the air cylinders  50 . Accordingly, the pressure foot  53  may be lowered simultaneously and quickly with the movable element  12  and the link plate  20  without controlling electromagnetic valves not shown connected to the air cylinders  50  to control the flow of air, thus improving the efficiency of drilling works.  
         [0044]     Still more, it is possible to raise the link plate  20 , the air cylinders  50 , the pressure foot  53  and others together in the state in which air is supplied to the air cylinders  50  in raising the link plate  20  by the linear motor  18  after ending the drilling work. In this case, the pressure foot  53  rises together because a piston of the piston  52  abuts against the bottom face of the cylinder  57 . However, when they start to rise, the pressure foot  53  is late to rise. In this case, it is also possible to separate the pressure foot  53  from the workpiece  41  sooner and to transfer to the next drilling work by supplying air to the opposite side of the air cylinders  50  to move the pressure foot  53  in the direction separating from the workpiece  41 .  
         [0045]     According to the present embodiment, the pressure foot  53  and the rotor shaft  1  are operated by the linear motor  18 , i.e., the common driving source, through the intermediary of the link plate  20 , so that the both may be moved in synchronism without providing any special means.  
         [0046]     It is noted that although the magnet  14  has been disposed on the side face of the movable element  12  in the embodiment described above, it is not necessary to provide the magnet  14  when the movable element  12  is made from a magnetic material such as iron.  
         [0047]     By the way, while a spindle body  70  needs to be replaced because it is a consumable item, the spindle unit  100  of the present embodiment is constructed so as to be able to readily replace the spindle body  70 . The spindle body  70  comprises the rotor shaft  1 , the housing  4  and the vertical connecting shaft  6 . The spindle body  70  also includes the collet chuck  2 , the spring  3  and the rotor  8  built in the rotor shaft  1 , the radial air bearings  5  and the coil  9  built in the housing  4  and thrust air bearing  7  formed in the vertical connecting shaft  6 .  
         [0048]      FIG. 2  is a front view of the spindle unit  100  of the embodiment and  FIGS. 3A and 3B  are section views taken along A-A in  FIG. 2 , wherein  FIG. 3A  shows a state in which the spindle body is put into the base, and  FIG. 3B  shows a state in which the spindle body is taken out of the base.  
         [0049]     The housing  4  fits in a U-shaped notch  61  formed in the base  16  and is fixed to the base  16  by a bowl-shaped cover  62  through an intermediary of pressure rubbers  63 . Two pressure rubbers  63  are disposed along the axis O and are compressed between the cover  62  and the housing  4  when the cover  62  is fixed to the base  16  by means of bolts  64 , thus pressing the housing  4  to the base  16  by its resilience.  
         [0050]     Because the spindle unit  100  is constructed as described above, the spindle body  70  may be removed out of the base  16  readily as shown in  FIG. 3B  by unscrewing the bolts  64  while unscrewing the bolts  11  and by removing the cover  62  from the base  16 . Accordingly, it is possible to replace the spindle body or to maintain the inside of the unit readily.  
         [0051]     It is noted that in this case, it becomes easier to replace them by removing the pressure foot  53  in advance.  
         [0052]     While the preferred embodiments have been described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts, which are delineated by the following claims.