Abstract:
A spindle assembly for a component pick and place machine includes a housing containing a spindle for movement therein along a longitudinal axis of the spindle; the housing accommodating a valve for controlling the flow of air to an inner bore of the spindle; the inner bore of the spindle having an opening at one end for communicating the flow of air for picking and placing the components; and the flow of air from the valve to the inner bore of the spindle is internal to the housing through passageways.

Description:
BACKGROUND OF THE APPLICATION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a spindle driving assembly, and, more particularly, to a high speed system for use in a spindle driving assembly in a pick and place machine.  
           [0003]    2. Description of the Related Art  
           [0004]    The present invention relates primarily, although not exclusively, to machines known in the electronics assembly industry as pick and place machines. In a pick and place machine, a spindle mounted on a spindle assembly is brought into contact with a die or other electronic component in order to pick up the die or component. The spindle assembly is then moved to another location, where the die or component picked up by the spindle is then placed in an appropriate location for assembly.  
           [0005]    In conventional pick and place machines, one type of spindle assembly utilizes a vacuum spindle. A vacuum spindle includes a nozzle at a tip at a lower end of the spindle. A vacuum is applied to the nozzle at the tip of the spindle in order to enable the spindle to pick up a die or component. The spindle is then moved to an appropriate location for placing the die or component. In order to detach the die or component from the spindle, a pulse of air, sometimes referred to as an air kiss, is applied to the nozzle in order to blow the die or component away from the tip of the spindle.  
           [0006]    In conventional pick and place machines, the vacuum is created by applying pressurized air to a venturi, which in turn, creates a vacuum. The vacuum is then directed to the spindle for picking up components. In addition, in order to discharge the die or component, the pressurized air was also applied directly to the tip of the nozzle.  
           [0007]    A conventional pick and place machine may have a pick and place head that includes a plurality of spindle assemblies in order to maximize assembly time. However, the conventional valve assemblies used in conjunction with a respective spindle assembly were relatively large. Accordingly, in order to fit as many spindle assemblies as possible in the pertinent portion of the pick and place head, the valve assembly was located remotely from the spindle assembly. A disadvantage of locating the valve assembly remotely from the spindle assembly is that the time required for a vacuum applied at the venturi to reach the tip of the nozzle added to the processing time of the pick and place machine.  
           [0008]    Some conventional valve assemblies used in a pick and place head had an actuating time of approximately 4.5 milliseconds. Accordingly, in a conventional pick and place machine, when the actuating time is factored together with the distance that the valve assembly is located from the spindle assembly, the time for the vacuum to reach the required level, typically about 20 inches of mercury, is about 40 milliseconds.  
           [0009]    In other conventional assemblies, the valves are mounted on the spindle head frame, but are connected to the spindles with tubes. Such an arrangement is difficult to assemble.  
         OBJECTS AND SUMMARY  
         [0010]    Accordingly, it is an object of the present invention to provide a pick and place head for a pick and place machine, wherein the actuating time can be reduced.  
           [0011]    It is a further object of the present invention to provide a spindle assembly for a pick and place machine, wherein the valve assembly is small enough so that it can be located adjacent the spindle in order to minimize the time required for the vacuum for air pressure to be applied to the nozzle tip.  
           [0012]    It is still another object of the present invention to provide a valve assembly for a pick and place machine, wherein the actuating time of the valve can be reduced in order to minimize processing time.  
           [0013]    According to one embodiment of the present invention, a spindle assembly for a component pick and place machine comprises a housing containing a spindle for movement therein along a longitudinal axis of the spindle; the housing accommodating a valve for controlling the flow of air to an inner bore of the spindle; the inner bore of the spindle having an opening at one end for communicating the flow of air for picking and placing the components; and the flow of air from the valve to the inner bore of the spindle is internal to the housing through passageways. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a cross-sectional view of a spindle assembly according to a preferred embodiment of the present invention, taken along line I-I of FIG. 2.  
         [0015]    [0015]FIG. 2 is a side elevational view of a spindle assembly according to the preferred embodiments of the present invention.  
         [0016]    [0016]FIG. 3 is a schematic view of a spindle assembly according to the preferred embodiments of the present invention.  
         [0017]    [0017]FIG. 4 is a schematic representation of the preferred embodiment of the present invention illustrating the air flow passages. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    [0018]FIG. 1 is a cross sectional view of a preferred exemplary embodiment of a spindle assembly  10  for a pick and place machine in accordance with the present invention. The cross sectional view is taken along line I-I of FIG. 2. The spindle assembly  10  is used in a pick and place head, for picking up electronic components and placing them at their intended locations during an assembly operation.  
         [0019]    Turning attention now to FIG. 1, the spindle assembly  10  includes a frame or housing  16  which has a vertical cavity in which the spindle  12  is supported. At a lower end of the spindle  12  is a nozzle  14 . The nozzle  14  is the portion of the spindle  12  that makes contact with the dies and components to be picked up by the spindle  12 .  
         [0020]    As can be seen in FIG. 1, at least a portion of the spindle  12  is hollow, thus creating a passage  15  through which a vacuum or air pressure may pass. The lower most end of the nozzle  14  is open so that the vacuum or air pressure may be applied to enable the die or component to be picked up and to be detached by the nozzle  14 .  
         [0021]    As can be seen in at least FIGS. 1, 3, and  4 , mounted on the spindle assembly frame  16  are two valves  18 ,  20 . Each of the valves  18 ,  20  is connected to a source of pressurized air via passage  22 . Electrical contacts  24  are provided at one end of each valve so that an electric current can be applied to actuate the valve. An exhaust port  50  is provided at a side of each of the valve bodies so as to allow compressed air to pass through the valves.  
         [0022]    According to a preferred embodiment of the present invention, it is possible to actuate the valves with a very short application of current. Specifically, the application of current for approximately  0 . 5  to  1  milliseconds at about 2.5 to 10 amps is sufficient to actuate the valves in order to open the valves. When the valves are actuated, air can flow from the air inlet port  56  through the valve body and out through the air outlet port  50 .  
         [0023]    In order to close the valve, a deactivating current is applied to the valve in an opposite polarity as the initial activating current. The deactivating current is less than the activating current. The deactivating current can be applied for about 0.1 to 0.5 milliseconds, preferably 0.12 milliseconds, at about 0.3 amps. Alternatively, the deactivating current can be a sequence of alternating degaussing currents. The preferred voltage for the valves is 12 volts. However, the present invention is not limited to the voltage, amp, and time values set forth above.  
         [0024]    The present invention is not limited to the particular details of a valve. One of ordinary skill in the art would contemplate that other types of valves could be used according to the present invention. However, it is preferable that the valve used is of a small size and of a high speed.  
         [0025]    Turning attention now to FIGS. 3 and 4, an air flow circuit of an embodiment of the present invention is illustrated. The various components of the preferred embodiment of the present invention are illustrated in schematic form, and are not necessarily drawn to scale. An air inlet  22  is connected to a source of pressurized air, and is used to deliver the pressurized air to the two valves  18 ,  20 .  
         [0026]    A venturi  36  is also mounted in the frame  16  of the spindle assembly  10 . An air passage  28  connects the outlet of valve  20  with a first end of the venturi  36 . The venturi  36  is constructed such that when an air pressure is delivered to the first end thereof, a vacuum is created at the outlet  39  of the venturi  36 . Another air passage  38  connects the outlet  39  of the venturi  36  to the spindle  12 . Accordingly, when valve  20  is actuated so as to open the valve, pressurized air from source  22  passes through an air passage  26  into the valve  20  and through the air passage  28  into the venturi  36 . A vacuum created by the venturi  36  is then applied to the spindle  12  through the air passage  38 .  
         [0027]    An exhaust passage  34  extends from a second end of the venturi  36 , through an expansion chamber  32 , and leads to an air system that is used to cool a motor that drives the pick and place head. However, it is not necessary to use the air from the exhaust passage  34  to cool the motor.  
         [0028]    The expansion chamber  32 , in its simplest form, enables an expansion of an air pulse moving from the valve  18  to the spindle  12  so as to moderate the pressure thereof. In a preferred embodiment, the expansion chamber  32  includes an enclosed space that is fixed around the second end of the venturi  36 . In the preferred embodiment, the expansion chamber includes an opening  25  in a side thereof through which air can escape. As seen in FIG. 3, the passageway  34  extends through this opening. Another air passageway  30  interconnects the output of valve  18  to the expansion chamber  32 . The air passageway  30  is constructed such that it ends at a short distance from the second end of the venturi  36 . This short distance is instrumental in moderating pulses of air passing from the passageway  30  to the venturi  36 . However, it will be appreciated that alternative arrangements can be used to moderate the air pressure.  
         [0029]    When the valve  18  is actuated so as to open the valve, compressed air from the air source  22  passes through the valve  18  and through the air passageway  30  into the expansion chamber  32 . Since the second end of the venturi  36  is spaced from the air passage  30 , when the pressurized air from the valve  18  and air passage  30  enters the expansion chamber  32 , the air pressure is moderated before it enters the venturi  36 , and a gentle pulse of air passes through the venturi  36  into the air passageway  38  and to the spindle  12 . Accordingly, a pulse of air can be delivered to the spindle  12  by activating valve  18 . The pulse of air passes through the valve  18 , the air passageway  30 , the expansion chamber  32 , the venturi  36 , the air passageway  38  to the spindle  12 . The arrangement of the expansion chamber  32 , including the volume, position, distance, and exhaust opening, is selected in such a way as to moderate the pulse of air emitted from the valve  18 . Accordingly, the expansion chamber  32  moderates the pulse of air and prevents an unnecessarily abrupt pulse of air from being applied to the spindle  12 .  
         [0030]    In a preferred embodiment, the expansion chamber  32  has an internal volume of approximately 450 cubic millimeters.  
         [0031]    In an alternative embodiment of the present invention, the second end of the venturi  36  can be connected directly to the passage  34 , and bypassing the expansion chamber  32 . In such an embodiment, an air passage from the expansion chamber  32  would be directly connected to the spindle  12 . Accordingly, the pulse of air could be directed through the expansion chamber  32  and directly into the spindle  12 , without having to pass through the venturi  36 .  
         [0032]    Because of the small, lightweight size of the valves  18 ,  20 , the valves can be actuated within about 0.5 to 0.8 milliseconds. However, in alternative embodiments of the present invention, the valves may be actuated within one or two milliseconds, or other suitable times.  
         [0033]    In a preferred embodiment of the present invention, each of the valves weighs approximately 4 grams, has a length of approximately 19 millimeters, and a diameter of 9 millimeters. However, the present invention is not limited to such valves, and valves of alternative sizes and weights may be used in accordance with the present invention. The valves of the preferred embodiment are manufactured by Sturman Industries of Woodland Park, Colo.  
         [0034]    Because of the small size of the valves, the valves may be located in the frame  16  for the spindle assembly  10 , thus enabling the valve to be arranged very close to the spindle  12 . In a preferred embodiment of the present invention, the valves are approximately 2 inches from the spindle  12 . However, in alternative embodiments, the valves may be 5, 4, or 3 inches, or less, from the spindle  12 . Because the distance between the valves and the spindles is small, there is a relatively small volume of air in the connecting passageways that needs to be evacuated during each activation. In one embodiment, the total volume in the passageways to be evacuated is about 500 cubic millimeters. Accordingly, actuation time is increased by placing the valves close to the spindles. The, small size of the valves, the fast changeover time, and the close proximity of the valves to the spindle  12  all account for very fast turnover speed.  
         [0035]    In a further aspect of the present invention, as can be seen in the preferred exemplary embodiment illustrated in FIG. 4, the passageways can be formed directly in the frame or housing  16 . Specifically, instead of providing tubing to channel the air flows throughout the system, the preferred exemplary embodiment includes passageways that are drilled, bored, molded or otherwise formed in the housing itself in order to direct the air flows throughout the system.  
         [0036]    In one embodiment, the housing  16  is molded from polyetherimide. For example, plastic sold under the tradename ULTEM™ by GE Plastics may be used. In such an embodiment, some or all of the passageways, such as passageways  22 ,  26 ,  28 ,  30 ,  34 , and  38 , are either molded directly into the housing  16  or are drilled into the housing  16  after the housing is molded. Preferably, some of the passageways will be molded directly in the housing  16  and others will be drilled.  
         [0037]    Alternatively, the housing  16  can be machined from a block of plastic. Or, the housing  16  can be molded, and after the molding process, further details of the housing can be machined.  
         [0038]    In the preferred disclosed embodiments, two valves are utilized. However, an embodiment could be used with only one valve, or more than two valves. The one valve would control only the vacuum pressure applied to the spindle. In such an embodiment, no air pulse would be available to dislodge the component from the spindle tip during placement. Such an embodiment is more useful for apparatus intended to move larger components that could easily dislodge from the spindle by gravity alone.  
         [0039]    Although only preferred embodiments are specifically illustrated and described herein, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims, without departing from the spirit and intended scope of the invention.