Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 61/320,903, which was filed on Apr. 5, 2010. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a fixture that is used to support a substrate having an uneven lower face while operations are performed on the top face of the substrate. 
       BACKGROUND 
       [0003]    Support fixtures are used to support substrates, such as, for example printed circuit (PC) boards, during their manufacture. Many PC boards include chips, resistors, and other elements on both sides of the board, which are typically installed a first side of the board, and then on an opposing side of the board. After these elements have been inserted on the first side of the board, the board is flipped over and supported by the first side. Support members on the support fixture project away from the base of the support fixture and engage the elements and the board, thereby supporting the board so that additional elements can be installed on the second side of the board. 
         [0004]    Several patents disclose support fixtures with independently movable support members to engage board elements and boards, such as, for example, U.S. Pat. No. 6,702,272, which uses a ball to lock a respective pin in a desired support position. This fixture requires a complex sequence of low pressure air, high pressure air, and vacuum to set the support members, and then release the support members to reset the fixture. Additionally, the force applied by the ball to the pin may not always be sufficiently high enough to maintain the pin in its desired support position when a board element is placed onto the pin. 
         [0005]    It would be beneficial to provide a board support fixture that requires a less complex sequence of operation to set and then reset the fixture, as well as a fixture that applies a higher force to each pin to ensure that the pin is maintained in its desired support position while the PC board is being worked on. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    Briefly, the present invention provides pin locking apparatus comprising a base plate having a vertical passage having an open vertical end, a transverse passage being in fluid communication with the vertical passage, and a longitudinal passage having an open longitudinal end. The longitudinal passage is in fluid communication with the transverse passage. A pin is slidably disposed in the vertical passage and extending outwardly from the open vertical end. A magnet is slidably disposed in the transverse passage between a pin locking position wherein the magnet engages the pin and urges the pin against the base plate and a pin unlocking position wherein the pin is free to slide along the vertical passage. A means for attracting the magnet is disposed in the transverse passage, away from the pin. A wedge is disposed between the magnet and the means for magnetically attracting the magnet. The wedge is slidably disposed between a magnet locking position, wherein the wedge engages the magnet and urges the magnet against the pin and a magnet unlocking position wherein the magnet is biased away from the pin by the means for magnetically attracting the magnet. 
         [0007]    The wedge comprises a wedge piston in fluid communication with the longitudinal passage. The means for magnetically attracting the magnet comprises a second magnet. The base plate is symmetrical about a vertical plane extending along the longitudinal passage. The apparatus further comprises a pin lifting fluid passage in fluid communication with the vertical passage, away from the open vertical end. The pin lifting fluid passage comprises a first fluid connection. The pin comprises a chamfered bottom portion. 
         [0008]    Additionally, the present invention provides a pin locking apparatus having a base unit having a plurality of vertical channels formed therethrough. A first pin is slidingly disposed in a first of the plurality of vertical channels and a second pin is slidingly disposed in a second of the plurality of vertical channels. A wedge is slidingly disposed in a third of the plurality of vertical channels. The third vertical channel is located between the first and second vertical channel. A first magnet is slidingly disposed in a horizontal channel between the first pin and the wedge. A second magnet is slidingly disposed in the horizontal channel between the second pin in the wedge. The magnetic pole of the second magnet proximate to the wedge is opposite the magnetic pole of the first magnet proximate to the wedge. 
         [0009]    The wedge is biased away from the horizontal channel. The pin locking apparatus further comprises a first biasing member disposed in the first vertical channel below the first pin. The first vertical channel and the second vertical channel fluidly communicate with each other. The first and second vertical channels are fluidly communicable with a first pressurized fluid source. The third vertical channel is fluidly communicable with a second pressurized fluid source. Each of the first pin and the second pin comprises a chamfered bottom portion. The base unit comprises a lower portion containing the plurality of vertical channels and an upper portion containing the horizontal channel. 
         [0010]    Further, the present invention provides a pin locking apparatus comprising a base unit having a plurality of vertical channels and a horizontal channel extending therethrough such that the horizontal channel in fluid communication with a first vertical channel, a second vertical channel, and a third vertical channel. A first pin is slidingly disposed in the first vertical channel, a second pin is slidingly disposed in the second vertical channel, and a wedge is slidingly disposed in the third vertical channel between the first and second vertical channels. A first locking device is disposed in the horizontal channel between the first vertical channel and the third vertical channel. The first locking device is sufficiently long to engage the first pin against the base unit when the wedge is in an upward position. A second locking device is disposed in the horizontal channel between the second vertical channel and the third vertical channel. The second locking device is sufficiently long enough to engage the second pin against the base unit when the wedge is in the biasing position. 
         [0011]    The first locking device comprises a magnet. The wedge is biased toward a downward position. The first and second vertical channels are in fluid communication with a first pressurized fluid supply port. The third vertical channel is in fluid communication with a second pressurized fluid supply port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawing certain embodiments of the present invention. It should be understood, however, that the invention is not limited to the precise arrangements shown. In the drawings: 
           [0013]      FIG. 1  is a perspective view of a support fixture according to an exemplary embodiment of the present invention; 
           [0014]      FIG. 2  is a sectional view of the support fixture shown in  FIG. 1 , with the support fixture in a released condition, and with a printed circuit (PC) board located over the top of the support fixture; 
           [0015]      FIG. 2A  is a perspective view of the pin shown in  FIG. 2 ; 
           [0016]      FIG. 2B  is a side elevation view of a second exemplary embodiment of a pin used with the support fixture shown in  FIG. 2 ; 
           [0017]      FIG. 3  is a cutaway view of the support fixture of  FIG. 2 , with the support fixture in a fixed condition; 
           [0018]      FIG. 4  is top view, in section, of air passages formed in the support fixture of  FIG. 1 ; 
           [0019]      FIG. 4A  a side elevational view, in section, of the support fixture shown in  FIG. 4 ; 
           [0020]      FIG. 5  is a cutaway view of a support fixture according to another exemplary embodiment of the present invention, with the support fixture in a released condition; and 
           [0021]      FIG. 6  is a cutaway view of the support fixture of  FIG. 5 , with the support fixture in a fixed condition. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    In describing the embodiments of the invention illustrated in the drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, it being understood that each specific term includes all technical equivalents operating in similar manner to accomplish similar purpose. It is understood that the drawings are not drawn exactly to scale. 
         [0023]    The following describes particular embodiments of the present invention. It should be understood, however, that the invention is not limited to the embodiments detailed herein. Generally, the following disclosure refers to support fixtures that are used to support a substrate while operations are performed on the substrate. 
         [0024]    Referring to  FIGS. 1-4A , a support fixture  100  according to a first embodiment of the present invention is disclosed. Support fixture  100  is used to support a generally planar work piece, such as, for example, a PC board  50 , along with elements such as, for example, chips  52 , during its fabrication. While a PC board  50  is used as the exemplary work piece throughout this disclosure, those skilled in the art will recognize that other types of work pieces such as, for example, aircraft fuselage pieces or ship hull pieces, may be used on a larger scale. 
         [0025]    Support fixture  100  is a generally parallelepiped base plate  101  having a top surface  102 , an opposing bottom surface  104 , and generally orthogonal sides  106 ,  108 ,  110 ,  112 . Base plate  101  may include a plurality of plates  101   a,    101   b,    101   c  that are stacked on top of each other and secured to one another, such as with screws (not shown), for example, in order to be able to machine internal passages that extend within and through base plate  101 . Base plate  101  supports a plurality of support pins  122  that extend vertically through base plate  101 . While  FIG. 1  shows two rows of fifteen (15) support pins  122 , those skilled in the art will recognize that different numbers of support pins  122  may be used. 
         [0026]    Referring to  FIGS. 4 and 4A , base plate  101  may include pin port  114  and wedge port  116  to facilitate connection of pressurized fluid to support fixture  100  to operate support fixture  100 . In this exemplary embodiment, pin port  114  and wedge port  116  are located on the same side (side  106 ) of base plate  101 . Alternatively, although not shown, pin port  114  may be located on side  106  while wedge port  116  may be located on another of sides  108 ,  110 ,  112 . 
         [0027]    Pin port  114  is in fluid communication with a pin air channel  118  that extends from pin port  114  in side  106  toward, but does not extend through, opposing side  110 . Pin air channel  118  forms a plurality of generally parallel pin air channels  118   a  and  118   b  that are in fluid communication with each other. Similarly, wedge port  116  is in fluid communication with a wedge air channel  119  that splits into a single wedge air channel  119 . While, in the exemplary embodiment, two pin air channels  118   a  and  118   b,  as well as a single wedge air channel  119  are shown, those skilled in the art will recognize that more than two pin air channels  118   a  and  118   b  and a single wedge air channel  119  can be used. In such embodiments, not shown, however, each wedge air channel  119  corresponds to two pin air channels  118  that are located on either side of wedge air channel  119  such that there are half as many wedge air channels  119  as pin air channels  118 . 
         [0028]    Base plate  101  includes an array of vertical pin passages  120  that are generally evenly disposed in rows and columns along top surface  102  of base plate  101  and in fluid communication with one of pin air channels  118   a  or  118   b.  Each pin passage  120  has an open end at top surface  102  of base plate  101 . Alternatively, instead of a main pin air channel  118  with a plurality of pin air channels  118   a  and  118   b  extending therefrom, a single air channel (not shown) may serially connect to each pin passage  120 . Still alternatively, a single chamber (not shown) may provide fluid communication between pin port  106  and all of pin passages  120 . 
         [0029]    A support pin  122  is slidably disposed within each pin passage  120  and extends outwardly from the open end at top surface  102  of base plate  101 . Support pins  122  are used to support PC board  50  and chips  52  away from top surface  102  of base plate  101 . 
         [0030]    Each support pin  122  includes an elongated cylindrical shaft  124 . Shaft  124  may be constructed from a non-magnetic material such as, for example, aluminum or brass. Shaft  124  includes a cap  126  at a top end thereof. Cap  126  may be constructed from a soft, generally pliable material such as, for example, plastic or a compliant rubber. Cap  126  may be inserted into an opening  127  (shown in  FIG. 2B ) in the top of shaft  124 . As illustrated in  FIG. 3 , cap  126  engages PC board  50  and chips  52 . A bottom end  128  of shaft  124  is enlarged such that bottom end  128  is larger than a portion of pin passage  120  so that support pin  122  is maintained within pin passage  120 . 
         [0031]    Optionally, bottom end  128  of each support pin  122  may include a chamfered portion  128   a  as shown in  FIGS. 2A and 2B . Chamfered portion  128   a  allows a small portion of pressurized fluid in pin air channel  118  to pass around support pin  122 . By allowing the pressurized fluid to pass around support pin  122 , the pressure of the pressurized fluid does not build up sufficiently to bind support pin  122 , which may possibly keep support pin  122  from dropping in pin passage  120  when the pressurized fluid is released. In an exemplary embodiment, chamfered portion  128   a  extends in an arc of about 60 degrees around the circumference of bottom end  128  and extends at an angle ⊖ of about 50°. 
         [0032]    Referring to  FIGS. 2 and 3 , a generally cylindrical magnet  132  is slidably disposed within each transverse passage  130 . Each magnet  132  may be moved between a pin locking position in which magnet  132  drives a respective shaft  124  against the wall of its pin passage  120  to set the height of pin  122  (shown in  FIG. 3 ) and a pin unlocking position wherein pin  122  is free to slide along vertical pin passage  120  (shown in  FIG. 2 ). 
         [0033]    A non-magnetic wedge  140  may be used to drive two adjacent magnets  132  away from each other to secure their respective pins  122 . Wedge  140  is located in a wedge passage  142  that is in fluid communication with wedge port  116 . Wedge  140  includes a circumferential ridge  144  into which an o-ring  146  is inserted. O-ring  146  provides a seal between wedge  120  and the wall of wedge passage  142  so that fluid, such as, for example, pressurized air, provided into wedge passage  142  from wedge port  116  does not leak out of wedge passage  142 . In an exemplary embodiment, fixture  100  operates with a supply of between about 50 and about 80 pounds per square inch (between about 3.45 and about 5.52 bars) of pressurized fluid. 
         [0034]    Wedge  140  may include a tapered top portion  147  having a smaller top and a larger bottom. Magnet  132  may include a tapered face  134  that matches the taper of tapered top portion  147  of wedge  140  in order to provide surface-to-surface contact between magnet  132  and wedge  140 . In an exemplary embodiment, tapered face  134  is tapered at an angle of between about 7 degrees and about 22.5 degrees, and, desirably, about 15 degrees from vertical. The matching tapered surfaces reduce wear to wedge  140  and magnet  132  where magnet  140  and wedge  132  engage each other. Optionally, tapered face  134  on magnet  132  may be omitted. Further, tapered face  134  has a larger surface area than the bottom of wedge  140 , which results in a mechanical advantage of about 3.7:1. This means that, for a fluid force applied upward to the bottom of wedge  140  through wedge passage  142 , a horizontal force of 3.7 times the applied force is applied by tapered face  134  to each magnet  132  and, correspondingly, to each respective pin  122 . 
         [0035]    A biasing member, such as, for example, a helical spring  148 , is located around tapered top portion  147 , between the body of wedge  140  and magnets  132 . Helical spring  148  biases wedge  140  downward, away from magnets  132 , when pressurized fluid is not applied to wedge  140  from wedge port  116 . 
         [0036]    Adjacent magnets  132  that are separated by a mutual wedge  140  are installed in fixture  100  so that opposite poles are facing wedge  140 . As shown in  FIGS. 2 and 3 , the north pole of magnet  132   a  is facing wedge  140  while the south pole of magnet  132   b  is facing wedge  140 . The attraction of the opposing poles of magnets  132   a  and  132   b  causes magnets  132   a  and  132   b  to retract toward each other and away from their respective pins  122   a,    122   b  when wedge  140  is retracted (lowered). This feature eliminates the need for a separate biasing member to bias the pin locking elements away from pins  132  when wedge  140  is retracted (lowered). 
         [0037]    The mechanical advantage of wedge  140  against magnets  132 , forcing magnets  132   a,    132   b  apart from each other, increases the frictional locking force of magnets  132  against their respective pin  122 , compared to a prior art direct-acting piston of the same surface area and working fluid pressure. 
         [0038]    Multiple support pins  122  are locked by a single wedge  140 . As shown in  FIG. 3 , two pins  122   a,    122   b  are locked by a single wedge  140 . This configuration reduces the complexity of fixture  100  as well as eliminates potential leaking fluid seals in a system where each pin is locked by its own locking piston. 
         [0039]    Further, with the present invention, the size of the pin locking element, in this embodiment, magnet  140 , is reduced compared to prior art devices having a similar locking force. This feature improves the available stroke of pin  122  in a given base plate  101  size, allowing for increased range in topography heights of PC board  50 . 
         [0040]    Alternatively, a single support pin  122  can be locked by a single wedge  140  that drives a single magnet  132  against support pin  122 . In order to bias magnet  132  away from support pin  122  when it is desired to allow support pin  122  to retract, a fixed magnet (not shown) may be inserted into transverse passage  130  such that wedge  140  is located between magnet  132  and the fixed magnet. 
         [0041]    To operate fixture  100 , PC board  50  is moved to a position over fixture  100 . Fluid pressure is directed from pin port  114  to pin passage  120  through pin passages  118   a  and  118   b,  as shown by arrow A in  FIG. 2  to raise pins  122  such that each pin  122  engages PC board  50 . As shown in  FIG. 3 , different pins  122   a,    122   b  may be raised to different heights, depending on the topography of the bottom surface of PC board  50 . 
         [0042]    Once pins  122  are in position, fluid pressure is routed through wedge port  116  to wedge passage  142  through wedge air channel  119 , thereby moving wedge  140  upward, as indicated by arrow B in  FIG. 3 , and driving magnets  132   a,    132   b  away from each other and against their respective pins  122   a,    122   b  to lock pins  122   a,    122   b  into position for as long as fluid pressure is applied to wedge passage  142 . Once pins  122   a,    122   b  are locked, fluid pressure may be removed from pin passages  120 . This fluid pressure may be released out of pin port  114  to discharge the fluid away from fixture  100 . 
         [0043]    After operations on PC board  50  are completed, fluid pressure is removed from wedge passage  142  and exhausted from fixture  100  through wedge port  116 . Biasing member  148  biases wedge  140  downward into wedge passage  142  and the magnetic attraction between magnets  132   a,    132   b  directs magnets  132   a,    132   b  toward each other, releasing their respective pins  122   a,    122   b,  and allowing pins  122   a,    122   b  to drop through their respective pin passages  120  until bottom end  128  of each pin shaft  124  engages the narrow portion of its respective pin passage  120 . 
         [0044]    Regulation of pressurized fluid through pin port  114  and wedge port  116  may be accomplished by a programmable logic controller (not shown), and timed to operate in parallel with the movement of PC boards  50  being manufactured along an assembly line. The pressurized fluid may be air that is provided via an air compressor (not shown) or some other pressurized fluid source. Pressurized fluid that is exhausted from fixture through pin port  114  and wedge port  116  may be exhausted directly to atmosphere. 
         [0045]    An alternative embodiment of a fixture  200  is illustrated in  FIGS. 5 and 6 . Fixture  200  is structurally similar to and operates similar to fixture  100  with the following exceptions. Pin passage  220  is not in fluid communication with a pressurized fluid source. Pin passage  220  includes a closed bottom  222 . A biasing member  224 , such as, for example, a helical spring, is located in pin passage  220  below pin  122  and biases pin  122  upward. 
         [0046]    In operation, PC board  50  is moved over fixture  200  and lowered onto pins  122 , displacing pins  122  until pins  122  are in desired contact with PC board  50  and/or chips  52 . Pressurized fluid is provided to wedge passage  142  through wedge fixture  116 , as shown by arrow C in  FIG. 6 , forcing wedge  140  upward, thereby driving magnets  132   a,    132   b  apart from each other and locking their respective pins  122   a,    122   b  into position within pin passage  220 . 
         [0047]    After operations on PC board  50  are completed, PC board is lifted from pins  122 . Fluid pressure is released from wedge passage  142 , allowing biasing member  148  to bias wedge  140  downward into wedge passage  142 . Magnets  132   a,    132   b  are attracted toward each other, releasing pins  122   a,    122   b,  and allowing biasing members  224   a,    224   b  to bias pins  122   a,    122   b  to return to their unlocked position. This process is repeated for subsequent PC boards  50 . 
         [0048]    While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.

Technology Category: 7