Abstract:
A printed circuit board includes a connection portion connectable to a control unit for driving a brushless motor; position detection element connection wiring lines respectively extending from a plurality of installation places of position detection elements to the connection portion, the position detection elements detecting a magnetic pole position of a rotor magnet of the brushless motor; a wiring line switching portion for switching over a connection state between a specific one of the position detection element connection wiring lines and another wiring line; and a neutral point connection wiring line extending from a neutral point to the wiring line switching portion, the brushless motor having a plurality of coils connected at one end to the neutral point. The specific one of the position detection element connection wiring lines are connectable to the neutral point connection wiring line by means of a conductor in the wiring line switching portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a printed circuit board for brushless motors to which a brushless motor is mounted, and a brushless motor using the same. 
       BACKGROUND OF THE INVENTION 
       [0002]    A brushless motor needs to employ a control unit that controls rotation of a rotor magnet by specifying a magnetic pole position of the rotor magnet in response to a signal outputted from a position detection element or the like and supplying an electric current to individual coils according to the magnetic pole position thus specified. For this reason, wiring lines for connecting the individual coils and the position detection element to the control unit of the brushless motor are formed in a printed circuit board for brushless motors to which the brushless motor is mounted. 
         [0003]    A method for detecting the magnetic pole position of the rotor magnet is properly selected depending on the kind of a product equipped with the brushless motor. Inasmuch as the number of signal transmission lines or the like varies depending on the magnetic pole position detection method, the wiring lines are also differently formed in the printed circuit board for brushless motors according to the position detection method employed. 
         [0004]    Examples of the position detection method include a magnetic detection method and a sensorless method. The magnetic detection method refers to a method of detecting a magnetic pole position of a rotor magnet by use of a position detection element that detects the position of a magnetic pole or the magnitude of a magnetic flux density, which is changed with rotation of the rotor magnet. The sensorless method refers to a method of detecting a magnetic pole position of a rotor magnet based on the voltage of a neutral point of coils and the counter-electromotive force generated in the respective coils. 
         [0005]    Let us consider a case where Hall elements, one example of the position detection element used in the magnetic detection method, are mounted to the printed circuit board for brushless motors. In this case, a plurality of Hall element connection wiring lines connected to the Hall elements and a plurality of current supply wiring lines, as well as coil wiring lines for supplying electric currents to individual coils, are formed in the printed circuit board for brushless motors. On the other hand, in case of a printed circuit board for brushless motors corresponding to the sensorless method, a neutral point connection wiring line connected to a neutral point of individual coils as well as coil wiring lines are formed in the printed circuit board for brushless motors. 
         [0006]    As a prior art example regarding the printed circuit board, Patent Document 1 discloses a printed circuit board capable of changing a wiring line structure. More specifically, if circuit configuration or constants that determine component characteristics cannot be specified during the process of designing a printed circuit board, a printed circuit board is first formed in such a fashion that a wiring line structure can be changed later. According to the later-fixed specification, the connection between wiring lines of the printed circuit board is switched over and components are mounted to the printed circuit board. 
         [0007]    (Patent Document 1) Japanese Patent Application Publication No. 2006-261397A 
         [0008]    Typically in the manufacture of brushless motors, a brushless motor and a printed circuit board therefor are designed, and prototypes and molds thereof are produced after settling specifications including a position detection method and the like. 
         [0009]    The brushless motor mentioned above is suitable for, e.g., a spindle motor of a disk drive apparatus that requires performance such as high speed rotation, long lifespan and so forth. It is, however, the recent trend that the model changing cycle of the disk drive apparatus becomes shorter and shorter. In keeping with this trend, the model changing cycle of the brushless motor for use in the disk drive apparatus tends to become shorter. 
         [0010]    As the model changing cycle of the brushless motor is shortened, it becomes hard to secure an ample time for designing the brushless motor and producing a prototype thereof. For the purpose of securing the design and prototype production time, it is the current practice to perform the design and prototype production according to estimated specifications before the final specifications of the brushless motor are settled. For example, if it is not yet decided whether the magnetic detection method using Hall elements or the sensorless method is employed as a position detection method, mold design and prototype production tasks are performed for both kinds of brushless motors that correspond to the respective methods. 
         [0011]    Since the mold design and prototype production of the printed circuit board for brushless motors is performed based on more than one kind of estimated specifications as noted above, there is a need to conduct the mold design and prototype production in a plural number of times, which entails a problem of reduced efficiency and increased cost. 
       SUMMARY OF THE INVENTION 
       [0012]    In view of the above, the present invention provides a printed circuit board for brushless motors capable of adapting itself to either a magnetic detection method or a sensorless method. 
         [0013]    In accordance with an aspect of the present invention, there is provided a printed circuit board for a brushless motor including a connection portion connectable to a control unit for driving the brushless motor; a plurality of position detection element connection wiring lines respectively extending from a plurality of installation places of position detection elements to the connection portion, the position detection elements detecting a magnetic pole position of a rotor magnet of the brushless motor; a wiring line switching portion for switching over a connection state between a specific one of the position detection element connection wiring lines and another wiring line; and a neutral point connection wiring line extending from a neutral point to the wiring line switching portion, the brushless motor having a plurality of coils connected at one end to the neutral point. Herein, the specific one of the position detection element connection wiring lines and the neutral point connection wiring line are connectable to each other by means of a conductor in the wiring line switching portion. 
         [0014]    It is preferable that, if the position detection elements are mounted to the installation places, the specific one of the position detection element connection wiring lines and the neutral point connection wiring line are not connected to each other in the wiring line switching portion. 
         [0015]    Further, it is preferable that, if the position detection elements are not mounted to the installation places, the specific one of the position detection element connection wiring lines and the neutral point connection wiring line are connected to each other by means of the conductor in the wiring line switching portion. 
         [0016]    Further, it is preferable that the conductor is a jumper resistor. 
         [0017]    Further, it is preferable that the conductor is solder. 
         [0018]    Further, it is preferable that the position detection elements are Hall elements. 
         [0019]    Further, it is preferable that the neutral point connection wiring line has a width greater than that of each of the position detection element connection wiring lines but smaller than that of a power source connection wiring line connected to the brushless motor. 
         [0020]    Further, it is preferable that the wiring line switching portion is arranged radially outwardly of the rotor magnet. 
         [0021]    Preferably, there is provided a brushless motor connected to the printed circuit board of the above. 
         [0022]    The printed circuit board for brushless motors in accordance with the present invention includes a plurality of position detection element wiring lines for adapting the printed circuit board to a magnetic detection method and a neutral point connection wiring line for adapting the printed circuit board to a sensorless method. In case of using the sensorless method, a specific one of the position detection element wiring lines is connected to the neutral point connection wiring line by use of a conductor such as a jumper resistor or the like so that the voltage of the neutral point of coils can be outputted to a control unit. This allows a single printed circuit board for brushless motors to be adapted to either the magnetic detection method or the sensorless method. Therefore, it is possible to assure increased efficiency and reduced cost when designing and prototyping the printed circuit board for brushless motors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0023]      FIG. 1  is a schematic view illustrating a connection state between a brushless motor and a control unit for driving the brushless motor. 
           [0024]      FIG. 2  is a schematic view showing a circuit that includes wiring lines formed in a printed circuit board for brushless motors and individual coils. 
           [0025]      FIG. 3  is a plan view showing the printed circuit board for brushless motors. 
           [0026]      FIG. 4A  is an enlarged view illustrating a surrounding region of a wiring line switching portion and  FIG. 4B  is a view depicting a state that a jumper resistor is mounted to the wiring line switching portion. 
           [0027]      FIGS. 5A ,  5 B and  5 C are views showing other examples of the wiring line switching portion. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Hereinafter, one or more embodiment of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a schematic view illustrating a connection state between a brushless motor and a control unit for driving the brushless motor. In the connection state shown in  FIG. 1 , a magnetic detection method is used as a position detection method. 
         [0029]    As shown in  FIG. 1 , a brushless motor  1  is mounted to a printed circuit board for brushless motors  4  (hereinafter simply referred to as a “printed circuit board  4 ”) and is controlled by means of a control unit  8  connected to wiring lines (see  FIGS. 2 and 3 ) formed in the printed circuit board  4 . Hall elements  5  to  7  are also mounted to the printed circuit board  4 . 
         [0030]    The brushless motor  1  is a three-phase brushless motor and is formed of a rotor magnet  2  and a stator  3 . The stator  3  is constructed by winding a U-phase coil  32 , a V-phase coil  33  and a W-phase coil  34  around slots of a stator core  31 . 
         [0031]    The printed circuit board  4  is formed of wiring lines that can adapt themselves to either a magnetic detection method for detecting a magnetic pole position of the rotor magnet  2  or a sensorless method. In other words, depending on the specifications of a product equipped with the brushless motor, the wiring lines of the printed circuit board  4  are switched over to wiring lines corresponding to either the magnetic detection method or the sensorless method. 
         [0032]    The U-phase coil  32  is connected at one end to a U-phase coil connection terminal  42  of the printed circuit board  4 . Similarly, the V-phase coil  33  and the W-phase coil  34  are connected at one end to a V-phase coil connection terminal  43  and a W-phase coil connection terminal  44  of the printed circuit board  4 . The U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34  are connected at the other end to a neutral point connection terminal  48  of the printed circuit board  4 . Also provided is a connection portion  41  that serves as an interface for electrically interconnecting the wiring lines formed in the printed circuit board  4  and the control unit  8 . 
         [0033]    The Hall elements  5  to  7  are elements that output hall signals proportional to the magnitude of a magnetic flux density changing with rotation of the rotor magnet  2 . The Hall elements  5  to  7  are mounted to the printed circuit board  4  only when the magnetic detection method is used as a method for detecting the magnetic pole position of the rotor magnet  2 . This means that the Hall elements  5  to  7  are not mounted to the printed circuit board  4  in case of using the sensorless method as a magnetic pole position detection method. 
         [0034]    The control unit  8  detects the magnetic pole position of the rotor magnet  2  to control an electric current supplied to the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34 . The control unit  8  includes a detection circuit (not shown) corresponding to one of the magnetic detection method and the sensorless method. For example, if the magnetic detection method is used as a magnetic pole position detection method, the control unit  8  includes a detection circuit that detects the magnetic pole position of the rotor magnet  2  based on the hall signals outputted from the Hall elements  5  to  7 . On the other hand, in case of using the sensorless method, the control unit  8  includes a detection circuit that detects the magnetic pole position of the rotor magnet  2  based on a counter-electromotive force generated in one of the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34  and a neutral point voltage. In this regard, the neutral point voltage refers to a voltage developed in the neutral point connection terminal  48 , which is the neutral point of the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34 . 
         [0035]    Now, the wiring lines formed in the printed circuit board  4  will be described with reference to  FIG. 2 .  FIG. 2  is a schematic view showing a circuit that includes the wiring lines formed in the printed circuit board  4  and the individual coils of the brushless motor  1 . 
         [0036]    The circuit shown in  FIG. 2  is presented merely to explain the connection state of the wiring lines formed in the printed circuit board  4  and does not correspond to one of the magnetic detection method and the sensorless method. In the circuit shown in  FIG. 2 , circuit elements and wiring lines other than the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34  are mounted to or formed in the printed circuit board  4 . 
         [0037]    First, description will be made regarding the connection portion  41 . As can be seen in  FIG. 2 , eleven terminals are formed in the connection portion  41 . These terminals are designated by reference numerals  41   a  to  41   k  one after another from the upper side in  FIG. 2 . The terminals  41   a  to  41   c  are connected to the individual coils received within the brushless motor  1 . The terminals  41   d  to  41   i  serve as output terminals of the hall signals outputted from the Hall elements  5  to  7 . The terminals  41   j  and  41   k  are used to supply a bias current to the Hall elements  5  to  7 . 
         [0038]    Next, description will be given on the connection of the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34 . The U-phase coil  32  is connected at one end to the terminal  41   a  via the U-phase coil connection terminal  42  and a U-phase coil connection wiring line  421 . The V-phase coil  33  is connected at one end to the terminal  41   b  via the V-phase coil connection terminal  43  and a V-phase coil connection wiring line  431 . The W-phase coil  34  is connected at one end to the terminal  41   c  via the W-phase coil connection terminal  44  and a W-phase coil connection wiring line  441 . 
         [0039]    The U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34  are connected at the other end to the neutral point connection terminal  48 . In other words, the U-phase coil  32 , the V-phase coil  33  and the W-phase coil  34  are connected in such a way as to make star-connection in which the neutral point connection terminal  48  constitutes the neutral point. The neutral point connection terminal  48  is connected to the terminal  41   d  via a neutral point connection wiring line  481 , a jumper resistor  491  and a Hall element connection wiring line  451 . 
         [0040]    Next, description will be made on the connection of the Hall elements  5  to  7 . The Hall element  5  will be described first. The Hall element  5  is provided with terminals  5   a,    5   b,    5   c  and  5   d.  The terminals  5   a  and  5   b  are used to output the hall signals. The terminals  5   c  and  5   d  are used to supply a bias current. 
         [0041]    The terminal  5   a  of the Hall element  5  is connected to the terminal  41   d  through the Hall element connection wiring line  451 . The terminal  5   b  of the Hall element  5  is connected to the terminal  41   e  through a Hall element connection wiring line  452 . The terminals  5   c  and  5   d  are connected to the terminals  41   j  and  41   k  through bias current supply wiring lines  453  and  454 . Although the terminal  41   d  is illustrated in  FIG. 2  as if it is connected to both the neutral point connection terminal  48  and the terminal  5   a  of the Hall element  5 , the terminal  41   d  is actually connected to either the neutral point connection terminal  48  or the terminal  5   a  of the Hall element  5  as will be described later. 
         [0042]    The Hall elements  6  and  7  are provided with the same terminals as those of the Hall element  5 . Terminals  6   a  and  6   b  of the Hall element  6  are connected to the terminals  41   f  and  41   g  through Hall element connection wiring lines  461  and  462 . Terminals  6   c  and  6   d  of the Hall element  6  are connected to the terminals  41   j  and  41   k  through the bias current supply wiring lines  453  and  454 . Likewise, the terminals  7   a  and  7   b  of the Hall element  7  are connected to the terminals  41   h  and  41   i  through Hall element connection wiring lines  471  and  472 . Terminals  7   c  and  7   d  of the Hall element  7  are connected to the terminals  41   j  and  41   k  through the bias current supply wiring lines  453  and  454 . 
         [0043]    In this regard, description will be made regarding a wiring line switching portion  49 . The connection state of the neutral point connection wiring line  481  and the Hall element connection wiring line  451  is switched over by means of the wiring line switching portion  49  so that the printed circuit board  4  can adapt itself to one of the magnetic detection method and the sensorless method. 
         [0044]    First, description will be made on a case where the magnetic detection method is used as a magnetic pole position detection method. In this case, the jumper resistor  491  of the wiring line switching portion  49  shown in  FIG. 2  is not mounted to the printed circuit board  4 . In other words, the neutral point connection wiring line  481  and the Hall element connection wiring line  451  are not connected to each other. The Hall elements  5  to  7  are mounted to the printed circuit board  4  so that the printed circuit board  4  can adapt itself to the magnetic detection method. Therefore, a drive current of the brushless motor  1  is inputted and outputted through the terminals  41   a  to  41   c  of the connection portion  41  and the hall signals or the bias current is inputted and outputted through the terminals  41   d  to  41   k.    
         [0045]    Next, description will be made on a case where the sensorless method is used as a magnetic pole position detection method. The jumper resistor  491  of the wiring line switching portion  49  is mounted to the printed circuit board  4 . In other words, the neutral point connection wiring line  481  and the Hall element connection wiring line  451  are connected to each other. The Hall elements  5  to  7  are not mounted to the printed circuit board  4 . Therefore, the drive current of the brushless motor  1  is inputted and outputted through the terminals  41   a  to  41   c  of the connection portion  41  and the neutral point voltage is outputted through the terminal  41   d.  At this time, no signal is inputted and outputted through the terminals  41   e  to  41   k  of the connection portion  41 . 
         [0046]    In this manner, the printed circuit board  4  is adapted to either the magnetic detection method or the sensorless method by switching over the connection state of the neutral point connection wiring line  481  and the Hall element connection wiring line  451  with the jumper resistor  491 . 
         [0047]    Now, the wiring lines formed in the printed circuit board  4  will be described with reference to  FIG. 3 .  FIG. 3  is a plan view showing the printed circuit board  4 . 
         [0048]    Wiring lines corresponding to the circuit diagram shown in  FIG. 2  are formed in the printed circuit board  4  illustrated in  FIG. 3 . The Hall elements  5  to  7  and the jumper resistor  491  shown in  FIG. 2  are not illustrated in  FIG. 3 . In the connection portion  41  illustrated in  FIG. 3 , the terminals  41   a  to  41   k  are formed sequentially from the right side. On the front side of the printed circuit board  4  in terms of the drawing paper surface, the brushless motor  1  is mounted to a circular area  10  indicated by a broken line in  FIG. 3 . 
         [0049]    First, description will be made on the wiring lines and the terminals formed in the printed circuit board  4 . The U-phase coil connection terminal  42 , the V-phase coil connection terminal  43  and the W-phase coil connection terminal  44  are formed inside the circular area  10  to which the brushless motor  1  is mounted. 
         [0050]    Hall element mounting regions  45  to  47  to which the Hall elements  5  to  7  are mounted are formed inside the circular area  10 . Terminals to be connected to the respective terminals of the Hall elements  5  to  7  are formed in the Hall element mounting regions  45  to  47 . The Hall element connection wiring lines  451  and  452  and the bias current supply wiring lines  453  and  454  are formed to extend from the terminals  41   d,    41   e,    41   j  and  41   k  to the Hall element mounting region  45 . This holds true for the Hall element mounting regions  46  and  47 . 
         [0051]    The neutral point connection wiring line  481  is formed to extend from the neutral point connection terminal  48  to the wiring line switching portion  49 . As illustrated in  FIG. 3 , the neutral point connection wiring line  481  has a width greater than that of the Hall element connection wiring line  451  or the like but smaller than that of the U-phase coil connection wiring line  421  or the like. The width of the wiring lines noted above are decided by the intensity of an electric current flowing through the individual wiring lines. 
         [0052]    In this connection, the wiring line switching portion  49  will be described with reference to  FIGS. 3 and 4 . FIG.  4 A is an enlarged view illustrating the Hall element mounting region  45  and the surrounding region of the wiring line switching portion  49  of the printed circuit board  4  illustrated in  FIG. 3 .  FIG. 4B  is a view depicting a state that the jumper resistor  491  is mounted to the wiring line switching portion  49 . 
         [0053]    The wiring line switching portion  49  is formed outside the circular area  10  as illustrated in  FIG. 3 . The reason is follows. In order to reduce the size of a disk drive apparatus equipped with the brushless motor  1 , it is generally necessary to reduce the axial dimension of the brushless motor  1  including the printed circuit board  4  (i.e., the dimension in a vertical direction in  FIG. 1 , which will be simply referred to as an “axial dimension” hereinbelow). For this reason, the rotor magnet  2  and the stator  3  are installed as close to the printed circuit board  4  as possible. If the wiring line switching portion  49  is formed inside the circular area  10 , however, it becomes necessary to mount the jumper resistor  491  between the printed circuit board  4  and the rotor magnet  2  and the stator  3 . As a result, the axial dimension is increased in proportion to the size of the jumper resistor  491 . Therefore, the wiring line switching portion  49  is formed outside the circular area  10  in an effort to keep the axial dimension as small as possible. 
         [0054]    Next, description will be made on a wiring state of the wiring line switching portion  49 . Referring to  FIG. 4A , the wiring line switching portion  49  includes a wiring line switching terminal  492  formed in the Hall element connection wiring line  451 . The wiring line switching portion  49  further includes an end terminal  493  formed in the neutral point connection wiring line  481  in a facing relationship with the wiring line switching terminal  492 . 
         [0055]    In case of using the magnetic detection method as a magnetic pole position detection method, the wiring line switching terminal  492  and the end terminal  493  are not connected to each other as can be seen in  FIG. 4A . On the other hand, in case of using the sensorless method, the wiring line switching terminal  492  and the end terminal  493  are connected to each other through the jumper resistor  491  as can be seen in  FIG. 4B . This allows the neutral point voltage to be outputted from the terminal  41   d  of the connection portion  41 . 
         [0056]    As illustrated in  FIG. 4A , the wiring lines corresponding to the magnetic detection method are initially formed in the wiring line switching portion  49 . In case of adapting the printed circuit board  4  to the sensorless method, the wiring line switching terminal  492  and the end terminal  493  are connected to each other through the jumper resistor  491 . This ensures that the neutral point voltage outputted from the neutral point connection wiring line  481  is prevented from being inputted to the Hall element connection wiring line  451  in case of using the magnetic detection method. 
         [0057]    As set forth above, the printed circuit board  4  of the present embodiment includes the Hall element connection wiring lines  451 ,  452 ,  461 ,  462 ,  471  and  472  and the bias current supply wiring lines  453  and  454  for use in the magnetic detection method and the neutral point connection wiring line  481  for use in the sensorless method. Furthermore, the wiring line switching terminal  492  of the Hall element connection wiring line  451  and the end terminal  493  of the neutral point connection wiring line  481  are formed in the printed circuit board  4  in an electrically connectable state. In case of using the sensorless method, the wiring line switching terminal  492  and the end terminal  493  of the wiring line switching portion  49  are connected to each other by means of the jumper resistor  491 . This makes it possible for a single printed circuit board to adapt itself to either the magnetic detection method or the sensorless method. Therefore, it is possible to assure increased efficiency and reduced cost when designing and prototyping the printed circuit board for brushless motors. 
         [0058]    Although the wiring line switching terminal  492  and the end terminal  493  in the wiring line switching portion  49  are connected to each other by means of the jumper resistor  491  in case of using the sensorless method as a magnetic pole position detection method, the present invention is not limited thereto. For example, cream solder (not shown) or the like may be used in place of the jumper resistor  491 . This helps reduce the number of parts employed in the printed circuit board  4 . In case the cream solder is used in the wiring line switching portion  49 , it is preferred that the wiring line switching terminal  492  and the end terminal  493  be formed in such a pattern as to face toward each other with an increased length. This makes it possible to reduce contact failure of the cream solder with the wiring line switching terminal  492  and the end terminal  493 . For example, the wiring line switching terminal  492  and the end terminal  493  may be formed in the patterns as illustrated in  FIGS. 5A to 5C . 
         [0059]    Furthermore, although the wiring line switching terminal  492  of the Hall element connection wiring line  451  and the end terminal  493  of the neutral point connection wiring line  481  are connected to each other in the above description, the present invention is not limited thereto. Alternatively, the neutral point connection wiring line  481  may be connected to other Hall element connection wiring lines. In other words, the neutral point voltage may be outputted from one of the terminals  41   d  to  41   i  of the connection portion  41  that output the hall signals. The Hall element connection wiring line connected to the neutral point connection wiring line  481  may be decided depending on the shape of the printed circuit board  4 , the wiring line pattern formed in the printed circuit board  4 , the arrangement of the terminals formed in the connection portion  41 , and so forth. 
         [0060]    In addition, although the Hall elements are used in the magnetic detection method according to the present embodiment, the present invention is not limited thereto. As an alternative example, MR sensors may be used in place of the Hall elements. 
         [0061]    While the invention has been shown and described with respect to the embodiment, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.