Abstract:
The invention provides a cooling system and method for a motor having a movable component, which may be a moving coil bracket of a linear motor. The system comprises a fluid transmission tube extending adjacent to a heat-emitting surface of the movable component to direct a cooling fluid over the heat-emitting surface, wherein the fluid transmission tube is adapted to move in conjunction with the movable component of the motor.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a system and method for cooling motors, and in particular, using fluid-cooling means to cool motors.  
         BACKGROUND AND PRIOR ART  
         [0002]    Motors are widely used to drive semiconductor packaging equipment, such as wire-bonders in wire-bonding machines. Linear motors are generally preferred to drive wire-bonders as they offer fast and precise motion. During such driving motion, a large amount of heat may be generated, whether due to a large current flowing through the motor or a significantly large resistance in the coil wires because of the compact size of the motor. Cooling is critical not only to prolong the useful life of the motor but also to maintain its performance.  
           [0003]    Electrical fans are commonly used to cool most equipment in the industry. However, although electrical fans are useful for external cooling, they are insufficient to cool internal components of linear motors, which generate and retain the most heat. In the case of linear motors comprising a coil disposed between a pair of magnets, there are small gaps between the coil and magnets. These gaps are not easily accessible to cooling air generated from an electrical fan. A practice has thus developed of trying to guide cooling air into the said gaps.  
           [0004]    One way of guiding cooling air into the said gaps is to drill holes and nozzles inside a moving coil bracket of a linear motor, and to channel cooling air through these holes and nozzles. The problem is that if the material of the coil bracket is not metallic or its machining property is poor, drilling long holes and nozzles inside the coil bracket is expensive and sometimes may not be possible. It would also increase the moving mass of the motor if additional material is formed in the coil bracket to house such holes and nozzles. Another way is to drill air nozzles on a stator of the motor. This also has limitations because such nozzles generally direct compressed air along only one axis. If in use, the moving coil moves along another axis, some portion of the cooling air will not reach the coil surface when the coil bracket moves away from the nozzle, and cooling air is wasted.  
           [0005]    Yet another method of implementing a cooling system in a linear motor is found in U.S. Pat. No. 5,834,862 for a “Linear Motor Cooling System”. This patent discloses a nozzle mounted on one end of a moving coil bracket for producing two high velocity sheets of air which are directed horizontally over the surfaces of the coil so as to bring down the temperature of the coil. This cooling structure is located outside the magnets of the linear motor and is not efficient especially if the coil area is large. Moreover, this patent disclosure introduces cooling air from one end of a coil bracket without proper sealing, allowing some of the cooling air to escape into the atmosphere. Furthermore, the nozzle area is relatively large, which serves to reduce the air pressure of the cooling air and reduces its ability to reach more remote areas of the coil. It may also not be effective if the whole coil bracket is designed to move in both the X- and Y-axes.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the invention to seek to provide an improved apparatus and method to increase cooling efficiency of cooling air introduced to cool a motor.  
           [0007]    According to a first aspect of the invention, there is provided a cooling system for a motor having a movable component comprising a fluid transmission tube extending adjacent to a heat-emitting surface of the movable component to direct a cooling fluid over the heat-emitting surface, wherein the fluid transmission tube is adapted to move in conjunction with the movable component of the motor.  
           [0008]    According to a second aspect of the invention, there is provided a method for cooling a motor having a movable component comprising the steps of arranging a fluid transmission tube so that it extends adjacent to a heat-emitting surface of the movable component, supplying a cooling fluid into the fluid transmission tube and directing the cooling fluid over the heat-emitting surface, wherein the fluid transmission tube moves in conjunction with the movable component of the motor.  
           [0009]    It will be convenient to hereinafter describe the invention in greater detail by reference to the accompanying drawings which illustrate one embodiment of the invention. The particularity of the drawings and the related description is not to be understood as superseding the generality of the broad identification of the invention as defined by the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    An example of a system and method in accordance with the invention will now be described with reference to the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is an isometric view of a typical X-Y table;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of a moving coil motor with a cooling system of the prior art;  
         [0013]    [0013]FIG. 3 is a cross-sectional view of a moving coil motor incorporating a cooling system comprising fluid transmission tubes according to the preferred embodiment of the invention;  
         [0014]    [0014]FIG. 4 is an enlarged view of a portion of FIG. 3 illustrating the fluid transmission tubes and air nozzles of the cooling system; and  
         [0015]    [0015]FIG. 5 is an isometric view of a coil bracket including fluid transmission tubes according to the preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    [0016]FIG. 1 is an isometric view of a typical X-Y table  10 . The X-Y table  10  has driving components in the form of an X motor  12  and a Y motor  14 . The X motor  12  and Y motor  14  comprise moving coil linear motors, and drive a bond head  16  in the X-axis and Y-axis respectively. An ultrasonic transducer  17  is attached to the bond head  16  to carry out wire-bonding of electronic components. Typically, wire-bonders bond conductive wires to make electrical connections between contact pads of a semiconductor chip and a leadframe to which the chip is attached.  
         [0017]    The bond head  16  is mounted on a Y stage  20  which is in turn mounted on an X stage  18 . The X stage  18  is driven by the X motor  12  whereas the Y stage  20  is driven by the Y motor  14 . The X stage  18  usually moves only along an X-axis whereas the Y stage  20 , which is on top of the X stage  18 , usually moves in both the X- and Y-axes. A combination of movement of the X stage  18  and Y stage  20  allows a tip of the ultrasonic transducer  17  to be positioned at various positions on a horizontal plane for the purpose of wire-bonding.  
         [0018]    [0018]FIG. 2 is a cross-sectional view of a moving coil linear motor  12  with a cooling system of the prior art. This is an example of a cooling system comprising air channels  50  drilled in a motor support  34  to introduce cooling air into the motor  12 . The linear motor generally comprises coils  22  that are embedded in a coil bracket  24 . The coil bracket  24  is usually made of a non-metallic material and one or more coils  22  are embedded in the material. The coils  22  and coil bracket  24  are disposed between a top magnet  26  and a bottom magnet  28 , leaving small gaps between the coils  22  and coil bracket  24  and the top and bottom magnets  26 ,  28 . There are further layers of a top iron plate  30  and a bottom iron plate  32  adjacent to the top and bottom magnets,  26 ,  28 . The bottom iron plate  32  rests on a motor base  36  and a motor support  34  supports the top iron plate  30 .  
         [0019]    When a current is passed through the coils  22 , electromagnetic interaction between the coils  22  and the top and bottom magnets  26 ,  28  produce motion of the coils  22  and coil bracket  24  relative to the magnets  26 ,  28 . An X-stage  18  attached to the coil bracket  24  is moved with it.  
         [0020]    In this prior art embodiment, air channels  50  are drilled into the motor support  34 . Air outlets  52  that lead to the air channels  50  are formed on surfaces of the motor support  34  adjacent to top and bottom surfaces of the coils  22  and coil bracket  24 . Air guides  54  are formed in the motor  12  next to the air outlets  52  to receive cooling air and guide it through the gaps between the coils  22  and coil bracket  24  and top and bottom magnets  26 ,  28  to cool the surfaces of the coils  22 . A disadvantage of this design is that the position of air cooling is fixed on the motor support  34  while the coils  22  are movable. Thus, some portion of the air may not reach the coil surfaces. It is even worse if this cooling structure is applied on a Y motor, where the coil bracket moves in both the X- and Y-axes. In order to allow the coils bracket  24  to move in both axes, the coil bracket  24  must be made much narrower or the motor must be much wider. Thus the air guide  54  would be useless. Most of the cooling air cannot get into the gaps between the coils  22  and the magnets  26 ,  28  when the bracket  24  moves away from the air guides. Thus, the cooling efficiency is not high.  
         [0021]    [0021]FIG. 3 is a cross-sectional view of a motor with a movable component, such as a moving coil motor  14 , incorporating a cooling system comprising fluid transmission tubes  36   a ,  36   b  according to the preferred embodiment of the invention. The motor  14  comprises coils  22  embedded in a coil bracket  24  disposed between top and bottom magnets  26 ,  28  and top and bottom iron plates  30 ,  32  as described above. The top and bottom magnets  26 ,  28  form a magnetic field in which the coils  22  of the coil bracket  24  are disposed. However, instead of air channels drilled in the motor support  34 , the preferred embodiment of the invention utilizes fluid transmission tubes in the form of air tubes  36   a ,  36   b  mounted to the coil bracket  24  instead.  
         [0022]    The air tubes  36   a ,  36   b  extend along a length of the coil bracket  24  and carry a cooling fluid, such as compressed air. They may be mounted onto the coil bracket  24 , whether by the use of adhesives, mounting brackets or any other means. One air tube  36   a  is mounted adjacent to a top surface of the coil bracket  24 , and another air tube  36   b  is mounted adjacent to a bottom surface of the coil bracket  24 . The top and bottom surfaces both include heat-emitting surfaces at the positions of the coils  22 , which carry electrical current. In this way, the air tubes  36   a ,  36   b  extend adjacent to the heat-emitting surfaces and move in conjunction with the coils  22  and coil bracket  24  to introduce a consistent amount of compressed cooling air directly to the top and bottom heat-emitting surfaces of the coils  22  regardless of the position of the coil bracket  24 .  
         [0023]    [0023]FIG. 4 is an enlarged view of a portion of FIG. 3 illustrating the fluid transmission tubes  38   a ,  38   b  and a plurality of apertures or air nozzles  38   a ,  38   b  of the cooling system. FIG. 4 is an illustration of the portion of FIG. 3 marked with the letter “A”. This illustration shows more clearly the air nozzles  38   a  formed in the top air tube  36   a  and the air nozzles  38   b  formed in the bottom air tube  36   b . The air nozzles  38   a ,  38   b  are positioned such that they produce air jets  40   a ,  40   b  and direct them toward the gaps adjacent to the top and bottom surfaces of the coils  22  respectively. Preferably, a number of such air nozzles  38   a ,  38   b  are formed next to locations of the coils  22  in the coil bracket  24 .  
         [0024]    [0024]FIG. 5 is an isometric view of a coil bracket  24  including fluid transmission tubes  36   a ,  36   b  according to the preferred embodiment. The coil bracket  24  shown in FIG. 5 belongs to the Y motor  14  and is allowed to move in both the X-axis and the Y-axis. Typically, the coil bracket of X motor  12  needs only to move in the X-axis due to the constraint of the X stage  18  only moving along that axis. FIG. 5 shows a coil bracket  24  with three phase coils  22  located near one end of the coil bracket  24 . A top air tube  36   a  is mounted along a length of the top surface of the coil bracket  24 . Apertures or air nozzles  38   a  are located adjacent to the positions of the three phase coils  22  as it is this heat-emitting portion of the coil bracket  24  that experiences the highest temperature rise. At an end of the air tube  36   a  that is opposite to the end of the coil bracket  24  where the coils  22  are located, there is an air input station  42  through which the air tubes  36   a ,  36   b  may receive an external supply of compressed cooling air. A hose (not shown) may be connected to the air station  42  to pump compressed cooling air to the air tubes  36   a ,  36   b.    
         [0025]    The air tubes  36   a ,  36   b  can be made from a whole host of non-magnetic materials, although stainless steel material is preferred as it is hard and is relatively cheap to fabricate and easily available. A non-magnetic material such as stainless steel is preferred because it avoids the formation of eddy currents that might affect the proper functioning of the linear motor  12 ,  14 . Positions and the numbers of the air nozzles  38   a ,  38   b  can be arranged to achieve optimum cooling efficiency.  
         [0026]    It would be appreciated that for coil brackets  24  that must move in both the X- and Y-axes, the described embodiment has the benefit of achieving the same cooling efficiency at any position of the coil bracket  24  because the air tubes  36   a ,  36   b  that generate the cooling air are fixed on the bracket  24 . There is no significant increase in the size of coil bracket  24  due to this design as the air tubes  36   a ,  36   b  are relatively tiny and affixed to the bracket  24 , and therefore does not noticeably deteriorate the dynamic performance of the motors  12 ,  14 . The air tubes  36   a ,  36   b  can have thin walls, thereby saving space and helping to achieve a compact design. The air jets  40   a ,  40   b  introduce air directly into the gaps between the coils  22  and coil bracket  24  and the top and bottom magnets  26 ,  28 . Thus, cooling efficiency is increased with a similar air volume or air consumption because of the relatively small size of the air nozzles  38   a ,  38   b  generating the compressed air directly onto the coils  22 .  
         [0027]    The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.