Abstract:
There is provided a printed board machining apparatus that is capable of improving machining efficiency without hampering machining accuracy. The printed board machining apparatus includes a pressure foot which is provided with a port whose one end is opened at a lower surface of the pressure foot facing a stiffening plate, and whose other end is connected to a compressed gas source to blow out gas from the port at a pressure which does not interfere with the pressure foot pressurizing the stiffening plate and printed boards in machining the printed boards. It is noted that the gas is blown out during a period of time at least when the pressure foot and the stiffening plate are moving relatively in the horizontal direction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a printed board machining apparatus for machining workpieces by a tool while pressing down the peripheral part of the workpiece to a table by a pressure foot. 
   2. Related Background Art 
     FIG. 4  is a schematic perspective view showing an outside view of a prior art printed board hole driller, i.e., an exemplary printed board machining apparatus, and  FIG. 5  is a front section view of an edge of a spindle and a pressure foot of the printed board hole driller shown in  FIG. 4 . 
   As shown in  FIGS. 4 and 5 , the printed board hole driller  14  is constructed so that a table  1  therein moves in the direction of an arrow X by an X-axis motor  2  on a track  4  fixed on a bed  3 . A column  5  is fixed to the bed  3  so as to straddle the table  1 . A cross slide  6  is arranged to move in the direction of an arrow Y on a track  9  fixed on the column  5  by a Y-axis motor  7  and a ball screw  8 . A housing  10  is arranged so as to move up and down on a track  13  fixed to the cross slide  6  in the direction of an arrow Z by a Z-axis motor  11  and a ball screw  12 . 
   The housing  10  supports a spindle  21  that rotably supports a drill  20 , i.e., a tool. The housing  10  also supports a pressure foot body portion  22  that engages with the edge portion of the spindle  21  through a cylinder not shown so as to move up and down in the Z-axis direction. The pressure foot body portion  22  is provided with a bush  23  at the end thereof. A drill through opening  29  through which the drill  20  moves in and out is made at the axial center position of the bush  23 . A part in which the pressure foot body portion  22  is combined with the bush  23  will be referred to as a pressure foot  32  hereinafter. 
   A groove  24  connecting an outer peripheral part of the bush  23  with the drill through opening  29  is made at the lower end of the bush  23 . A space  25  made by the spindle  21  and the pressure foot  32  is connected to a dust collector  27  via a pipe  26 . ACNC unit  28  controls the motors of the respective axes. 
   A plurality of printed boards  30 , i.e., workpieces, are stacked and are fixed on the table  1  together with a stiffening plate  31  placed at the top thereof. The stiffening plate  31  is made from an aluminum plate having a thickness of about 0.5 mm. 
   In drilling the stiffening plate  31  and the printed boards  30 , the printed board hole driller  14  lowers the pressure foot  32  by an air cylinder not shown, turns on the dust collector  27  to vacuum the space  25  and lowers the spindle  21  to a predetermined height after positioning the drill  20  at a drilling position. Then, the printed board hole driller  14  presses down the stiffening plate  31  and the printed boards  30  to the table  1  by the pressure foot  32  to drill the stiffening plate  31  and the printed boards  30  by the drill  20 . 
   When the drilling ends, the printed board hole driller  14  raises the pressure foot  32  and the spindle  21  to a position where the lower end of the pressure foot  32  (lower end of the bush  23 ) does not interfere the stiffening plate  31  and moves the pressure foot  32  and the spindle  21  in the horizontal direction together with the drill  20  to position the drill  20  at a next machining position. 
   Because the prior art printed board hole driller  14  is constructed so as to cut into the stiffening plate  31  by the drill  20  while pressing down the stiffening plate  31  and the printed boards  30  to the table  1  by the pressure foot  32  as described above, it permits an accuracy of machining position to be improved. Further, because the prior art printed board hole driller  14  is constructed so as to be able to collect work chips produced in drilling the workpieces immediately within the dust collector  27  by air flowing into the space  25  through the groove  24  as shown in  FIG. 5 , it permits holes to be made accurately. 
   By the way, it is desirable to keep the position of the edge of the drill  20  as close as possible to the stiffening plate  31  (hereinafter referred to as a ‘standby position’) in moving the drill  20  to the next machining position in order to improve the drilling efficiency of the printed board hole driller  14 . However, because the position of the edge of the drill  20  in connection with the lower end of the pressure foot  32  is set in advance, the lower end of the pressure foot  32  is brought closer to the stiffening plate  31 , and a distance L 1  between the stiffening plate  31  and the pressure foot  32  is shortened when the position of the edge of the drill  20  at the standby position is brought closer to the stiffening plate  31 . 
   However, when the distance L 1  is shortened too much, there is a case when the stiffening plate  31  is lifted up because it is suctioned to the side of the pressure foot  32  by the dust collecting force of the dust collector  27  as shown in  FIG. 5 . Then, the stiffening plate  31  might be damaged if it collides with the lower end of the pressure foot  32 . When the damaged part is the part to be drilled next, drilling may not be done accurately at the predetermined position or the drill may be broken as the edge of the drill  20  may slide when it abuts the stiffening plate  31 . 
   As a printed board hole driller dealing with such a problem, Japanese Patent Laid-open No. Hei.3-3713 has proposed one that pressurizes a stiffening plate and printed boards by compressed air while lifting up a pressure foot from the stiffening plate by forming an air film between the lower face of the pressure foot and the stiffening plate by blowing compressed air from a port made at the lower face of the pressure foot in drilling the printed boards. It allows to shorten the distance L 1  and to prevent the interference between the pressure foot and the stiffening plate, thus preventing the stiffening plate from being damaged. 
   However, the prior art printed board hole driller has required a large amount of compressed air to support the pressure foot. Further, the pressurizing force fluctuates considerably, and the pressurization of the stiffening plate and the printed boards has been unstable as compared to the case of abutting the pressure foot directly to the stiffening plate. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a printed board machining apparatus whose machining efficiency is improved without dropping its machining accuracy. 
   According to one aspect of the invention, the inventive printed board machining apparatus comprises a spindle rotatably having a tool for machining workpieces placed on a table, and a pressure foot fitted to the spindle movably along the axial direction of the spindle and having a contact face that contacts the workpiece and a tool through opening which is made through the contact face and through which an edge of the tool moves in and out. The printed board machining apparatus is designed to machine the workpieces by the tool while vacuuming a space made between the spindle and the pressure foot and while pressing down the workpieces to the table by the contact face of the pressure foot. The printed board machining apparatus further comprises, at the contact face of the pressure foot, a compressed gas blowout port for blowing out compressed gas supplied from compressed gas supplying means that supplies compressed gas to prevent the workpieces from being lifted up, and a groove for communicating the outer peripheral part of the pressure foot with the tool through opening when the contact face is in contact with the workpiece. 
   The pressure of the compressed gas blown out of the compressed gas blowout port is set at a pressure which will not interfere with the contact face of the pressure foot contacting the workpiece so as to permit the contact face to contact the workpieces in machining the workpieces. 
   Preferably, the printed board machining apparatus stops the compressed gas supplying means from supplying compressed gas when the contact face of the pressure foot is in contact with the workpiece. 
   Preferably, the compressed gas supplying means blows out the compressed gas from the compressed gas blowout port when at least either one of the tool and the workpiece is moving in the direction crossing the axial direction of the spindle. 
   Preferably, the compressed gas blowout port is opened in the direction of the tool. 
   Preferably, the printed board machining apparatus is provided with a pressure sensor for measuring a negative force within the space so that the compressed gas supplying means can increase or decrease the pressure of the compressed gas in accordance with the decrease or increase of the pressure measured by the pressure sensor. 
   As described above, according to the invention, the pressure of the compressed gas blown out of the compressed gas blowout port is set at the pressure which will not interfere with the contact face of the pressure foot contacting the workpiece, so that it is possible to prevent the stiffening plate from being lifted up with a small amount of gas and to improve machining speed and accuracy. 
   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 
       FIG. 1  is a front section view of an edge part of a spindle and a pressure foot of a printed board hole driller, i.e., an exemplary printed board machining apparatus, according to an embodiment of the invention. 
       FIG. 2  is a plan view of the edge of a bush. 
       FIGS. 3   a ,  3   b ,  3   c  and  3   d  are schematic section views for explaining an operation of the printed board machining apparatus of the embodiment, wherein  FIG. 3   a  shows a state in which a drill that has moved in the horizontal direction is positioned at a standby machining position and is about to move down together with a spindle,  FIG. 3   b  shows a state in which a pressure foot is in contact with a stiffening plate,  FIG. 3   c  shows a state in which the pressure foot is about to be separated from the stiffening plate and  FIG. 3   d  shows a state in which the drill has risen to the standby position to start to move in the horizontal direction. 
       FIG. 4  is a schematic perspective view of an appearance of a printed board hole driller, i.e., an exemplary prior art printed board machining apparatus. 
       FIG. 5  is a front section view of an edge part of a spindle and a pressure foot of the printed board hole driller shown in  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A printed board hole driller, i.e., an exemplary printed board machining apparatus, of a preferred embodiment of the invention will be explained below with reference to the drawings. 
     FIG. 1  is a front section view of an edge part of a spindle and a pressure foot of the inventive printed board hole driller. 
   It is noted that in the following description, the same reference numerals as those in the prior art described above denote the same or corresponding parts, and an explanation thereof concerning the structure and operation thereof will be omitted below. 
   A pressure foot  132  is composed of a body portion  22   a , an adapter  22   b  formed hermetically in a body with the body portion  22   a , and a bush  123 . The housing  10  supports the body portion  22   a  through a cylinder (not shown) so that it fits coaxially with a spindle  21  and moves up and down in the Z-axis direction. Thus, the pressure foot  132  fits with the spindle  21  so as to be movable along the axial direction of the spindle  21 . The body portion  22   a  is provided with the adapter  22   b  at the end thereof. The adapter  22   b  is provided with the bush  123 . The bush  123  is provided with a drill through opening  129 , i.e., a tool through opening, through which the drill  20  moves up and down. 
   The bush  123  is also provided with a port  50  from which compressed gas is blown out. The port  50  is oriented so that an axial line thereof extends toward the axial line of the drill  20  (i.e., the opening of the port  50  faces a longitudinal axis of the tool  20 ). One end of the port  50  is opened to a lower surface (contact face)  123   a  of the bush  123 , and the other end is opened to an air reservoir  51  formed by the bush  123  and the adapter  22   b . A plurality of grooves  124  connecting an outer periphery  123   b  of the bush  123  with the drill through opening  129  are made at the lower (contact) surface  123   a  of the bush  123  as shown in  FIG. 2 . The contact surface  123   a  is the part that contacts with a stiffening plate  31  to press down the stiffening plate  31  and the printed boards  30  to the table  1 . It is noted that the outer periphery  123   b  of the bush  123  is also an outer periphery of the pressure foot  132 . 
   One end of a hole  52  made through the adapter  22   b  is opened to the air reservoir  51 , and the other end is connected to a compressed air source  55  via an electromagnetic valve  53  and a pressure regulator  54 . The electromagnetic valve  53 , the pressure regulator  54  and the compressed air source  55  compose a compressed gas supply device. It is noted that the pressure regulator  54  is not always necessary for the compressed gas supply device. 
   An O-ring  56  shuts off a flow of air between the air reservoir  51  and the space  25  and positions and retains the bush  123  in connection with the adapter  22   b . A CNC (control) unit  28  controls the electromagnetic valve  53 , the pressure regulator  54  and the compressed air source  55 . 
   A pressure sensor  57  is provided between the space  25  and a dust collector (i.e., suction device)  27 . The pressure sensor  57  is connected to the CNC unit  28 . 
   An operation of the printed board hole driller will be explained next. 
     FIGS. 3   a ,  3   b ,  3   c  and  3   d  are schematic section views for explaining an operation of the printed board machining apparatus of the embodiment, wherein  FIG. 3   a  shows a state in which a drill  20  that has moved in the horizontal direction is positioned at a standby machining position and is about to move down together with a spindle,  FIG. 3   b  shows a state in which a pressure foot  132  is in contact with a stiffening plate  31 ,  FIG. 3   c  shows a state in which the pressure foot  132  is about to be separated from the stiffening plate  31 , and  FIG. 3   d  shows a state in which the drill  20  rises to the standby position to start to move in the horizontal direction. 
   According to the present embodiment, the electromagnetic valve  53  is opened when the drill  20  is positioned at the standby position and compressed air is blown out of the edge of the port  50  by the compressed air source  55 . Then, when a distance between the pressure foot  132  and the stiffening plate  31  is shortened to a predetermined distance L 2  as shown in  FIG. 3   a , the electromagnetic valve  53  is closed, thus stopping the compressed air from blowing out. The electromagnetic valve  53  is closed until the state shown in  FIG. 3   d . The electromagnetic valve  53  is opened again when the state shown in  FIG. 3   d  occurs. That is, the electromagnetic valve  53  is closed while the drill  20  is positioned at the machining position, and is opened simultaneously when the drill  20 , the printed board  30  and the stiffening plate  31  move relatively in the X and Y directions. The printed boards  30  and the stiffening plate  31  are one example of the workpieces. 
   When the electromagnetic valve  53  is opened, high-pressure compressed air is blown out of the port  50 , thus pressing down the stiffening plate  31  to the printed board  30 . Then, the air that has pressed down the stiffening plate  31  to the printed board  30  is suctioned to the space  25  by the suction force of the dust collector (suction device)  27 , so that the suction force (caused by the vacuum in space  25 ) at the edge of the bush  123  decreases. As a result, the stiffening plate  31  is rarely lifted up even when the pressure foot  132  is brought closer to the stiffening plate  31 . 
   That is, it is possible to shorten the distance L 2  between the pressure foot  132  and the stiffening plate  31  in the printed board hole driller  114  of the present embodiment as compared to the distance L 1  between the pressure foot  32  and the stiffening plate  31  in the prior art printed board hole driller  14  shown in  FIG. 5 . It is also possible to shorten the distance between the pressure foot and the stiffening plate to the same degree as that described in Japanese Patent Laid-open No. Hei.3-3713. 
   Further, because the outside air is suctioned to the space  25  via the grooves  124  while the pressure foot  132  is in contact with the stiffening plate  31 , work chips are suctioned to the dust collector  27  efficiently. 
   The CNC unit  28  always monitors the output of the pressure sensor  57 . When the suction force becomes large for some reason and the pressure within the space  25  drops, the CNC unit  28  operates the pressure regulator  54  to increase the pressure of compressed air supplied to the port  50  to prevent the pressure foot  132  from contacting the stiffening plate  31 . In other words, the compressed gas supplying device is controlled so as to increase or decrease the pressure of the supplied compressed air according to the pressure (vacuum) measured by the pressure sensor  57 . 
   As described above, the present invention enables consumption of the compressed air to be cut because compressed air is supplied to the port  50  only when it is needed to prevent the stiffening plate  31  from being lifted up. 
   Further, the present invention enables the machining efficiency to improve without hampering the drilling accuracy of the stiffening plate  31  and the printed boards  30  because it enables the distance L 2  between the pressure foot  132  and the stiffening plate  31  to shorten as compared to the distance L 1  between the pressure foot  32  and the stiffening plate  31  in the prior art. 
   It is noted that although the electromagnetic valve  53  has been opened while the drill  20  is positioned at the standby position in the embodiment described above, it is possible to arrange the machining apparatus so that the electromagnetic valve  53  opens when there is a gap between the pressure foot  132  and the stiffening plate  31 . 
   Still more, it is also possible to arrange the machining apparatus so that the electromagnetic valve  53  always opens because the force required in pressurizing the stiffening plate  31  by air blown out of the port  50  may be considerably smaller than the force of the pressure foot  132  pressurizing the stiffening plate  31  and the printed board  30 . 
   The contact of the pressure foot  132  with the stiffening plate  31  is minimized because it is possible to prevent the lift of the stiffening plate  31  also when the pressure foot  132  is moving up or down. 
   It is also possible that an alarm system operates, instead of operating the pressure regulator  54 . 
   It is also possible to use other gas, e.g., nitrogen, instead of the compressed air. 
   Preferably, the grooves  124  are disposed so that they do not contact the port  50 . 
   The pressure foot main body  22   a  may be formed in a body with the adapter  22   b.    
   It is also possible to prevent the lift of the stiffening plate  31  by a small amount of compressed air by disposing an opening  50   a  of the port  50  in the lower face  123   a  of the bush  123  to be closer to the drill through opening  129  provided at the center of the bush  123 . 
   Because the port  50  is opened in the direction of the drill  20  (i.e., faces the drill), it is possible to prevent the lift of the stiffening plate  31  steadily by pressing down the part to be drilled of the stiffening plate  31  by a small amount of compressed air. Further, because the openings  50   a  of the ports  50  are made so as to surround the drill  20 , it is possible to prevent the lift of the stiffening plate  31  by pressing the part to be drilled of the stiffening plate  31  by a small amount of compressed air. 
   As described above, because the inventive printed board machining apparatus is arranged so that the air having a pressure which does not interfere with the pressure foot pressurizing the workpieces is blown out of the compressed gas blowout ports, it is possible to prevent interference between the pressure foot and the workpieces. It is also possible to improve the machining efficiency without hampering the machining accuracy because it is possible to shorten the distance between the pressure foot and the workpieces in moving the pressure foot along the upper face of the workpieces. 
   While the preferred embodiment has 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