Abstract:
An electric power tool, which comprises a motor that drives a tool, a power source unit that applies voltage to the motor, a main switching circuit that makes/breaks an electrical connection between the power source unit and the motor, an illuminator that illuminates a work spot, a switching device that electrically connects the illuminator to the power source unit, and an OR circuit that is electrically connected to terminals of the motor to the base terminal is provided. The OR circuit electrically connects one of the motor terminals at which a voltage is higher to the base terminal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2007-297498, filed on Nov. 16, 2007, the contents of which are hereby incorporated by reference into the present application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electric power tool, and specifically to an electric power tool having an illuminator that illuminates a work spot. 
         [0004]    2. Description of the Related Art 
         [0005]    U.S. Pat. No. 6,318,874 B1 discloses an electric power tool that comprises a motor for driving a tool, a power source unit (battery) that applies DC voltage to the motor terminals of the motor, a main switching circuit that makes/breaks an electrical connection between the motor terminals and the power source unit, and a forward-reverse switching circuit that switches a direction of the DC voltage which is applied from the power source unit to the motor terminals via the main switching circuit. 
         [0006]    In this electric power tool, when the main switching circuit is turned ON, DC voltage is applied to the motor terminals and the DC motor starts driving the tool. When the main switching circuit is turned OFF, the DC voltage application to the motor terminals is suspended and the drive of the DC motor is stopped. 
         [0007]    Direction of the DC voltage which is applied to the motor terminals can be switched by the forward-reverse switching circuit, so that the direction to which the tool is driven by the motor is freely switched between the forward and reverse direction. 
         [0008]    The electric tool described above further comprises an illuminator that illuminates a work spot where the tool is used, and a switching device for turning ON/OFF the illuminator. The switching device has a base terminal. When a base voltage applied to the base terminal is higher than a threshold level, the switching device electrically connects the illuminator to the power source unit. In other words, light of the illuminator is turned ON. To the base terminal of the switching device, a motor side contact of the main switching circuit is electrically connected. Accordingly, when the main switching circuit is turned ON, a voltage at or higher than a threshold level is applied to the base terminal from the power source unit and the illuminator is turned ON. At the same time, the motor starts driving the tool. When the main switching circuit is turned OFF, the DC voltage application at or higher than a threshold level to the base terminal from the power source unit is suspended, and the illuminator is turned OFF. At the same time, the drive of the tool by the motor is stopped. In this electric power tool, illuminator is turned ON and OFF in conjunction with the starting and stopping of driving the tool by the motor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    Recently, switching modules in which a main switching circuit and a forward-reverse switching circuit are incorporated, and electric power tools in which such switching modules are adopted have been developed. Such switching modules enable simplification of the circuit configuration of the electric power tools, and thereby reducing costs for assembling the tools. 
         [0010]    However, the switching modules involve difficulty in leading out a signal line from the motor side contact of the main switching circuit, since the main switching circuit is incorporated therein. Accordingly, if the switching module of this type is adopted in the aforementioned electric power tool, it becomes impossible to make an electrical connection between the illuminator and the motor side contact of the main switching circuit. In other words, the circuit configuration as in the electric power tools as described above cannot adopt the switching module of this type. 
         [0011]    In cases where it is impossible to lead out a signal line from the motor side contact of the main switching circuit, the base terminal of the switching device may be electrically connected to one of the motor terminals. This circuit configuration would appear to be capable of turning the illuminator ON/OFF in conjunction with starting/stopping driving the tool by the motor. However, when the direction of the DC voltage which is applied to the motor terminals is reversed by the forward-reverse switching circuit, the base voltage then becomes incapable of turning ON the illuminator. Of course, both of the motor terminals can not be simply connected to the base terminal, which causes short circuit of the motor terminals. 
         [0012]    The teachings of the present invention solve the problem. According to the present invention, a technique for turning ON/OFF in conjunction with starting/stopping driving the tool by the motor, without using the motor side contact of the main switching circuit is provided. 
         [0013]    In an electric power tool of the present teachings, motor terminals of a motor are electrically connected to a base terminal of a switching device for an illuminator via an OR circuit. The OR circuit can electrically connect one of the motor terminals whose voltage is higher than the other motor terminal to the base terminal. Therefore, even when the direction of voltage that is applied to the motor terminals is altered, enough voltage to turn ON the switching device is applied to the base terminal in either direction. This configuration enables turning ON/OFF the illuminator in conjunction with starting/stopping driving the tool by the motor, regardless of the direction of the voltage which is applied to the motor terminals. 
         [0014]    In this electric power tool, the base terminal of the switching element does not have to be electrically connected to a motor side contact of a main switching circuit. Accordingly, a switching module in which the main switching circuit is incorporated can be advantageously adopted, in order to reduce costs for assembling the electric power tool. 
         [0015]    Preferably, the OR circuit comprises a first rectifying device that is electrically connected between the first motor terminal and the base terminal. Furthermore, the first rectifying device forbids current flowing from the base terminal to the first motor terminal. Moreover, the OR circuit further comprises a second rectifying device that is electrically connected between the second motor terminal and the base terminal. The second rectifying device forbids current flowing from the base terminal to the second motor terminal. 
         [0016]    Preferably, the electric power tool further comprises a capacitor that is electrically connected to the base terminal of the switching device. 
         [0017]    This configuration and the employment of the capacitor enables prolonged voltage application to the base terminal even after the main switching circuit is turned OFF, in order to keep the light of the illuminator to be in ON state for a predetermined period. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  shows a perspective view of the electric power screw driver. 
           [0019]      FIG. 2  shows an electrical configuration of the electric power screw driver. 
           [0020]      FIG. 3  shows a timing diagram describing operation and condition of principal configuration in forward rotation. 
           [0021]      FIG. 4  shows a timing diagram describing operation and condition of principal configuration in reverse rotation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred Features of an Embodiment of the Invention 
       [0022]    Some of the preferred features of an embodiment of the invention are described in the followings.
       (Feature 1) In a switching device, transistors such as NPN transistors or field-effect transistors are preferably used.   (Feature 2) In rectifying devices, diodes are preferably used.   (Feature 3) A main switching circuit and a forward-reverse switching circuit are preferably integrally configured as a switching module.   (Feature 4) A capacitor is connected to a base terminal of a switching device and an emitter terminal.       
 
       Embodiment of the Invention 
       [0027]    An electric power screw driver according to the invention is described with reference to the attached drawings. An electric power screw driver is one of electric power tools, which is used for screwing. The embodiment according to the invention adopts an electric power screw driver using impact method (electric power impact screw driver). It should be noted that the embodiment of the present invention is not limited to the application as hereinbelow exemplified. 
         [0028]      FIG. 1  shows a perspective view of the appearance of an electric power screw driver  10 .  FIG. 2  shows an electrical circuit configuration of the electric power screw driver  10 . As shown in the  FIG. 1 , the electric power screw driver  10  comprises a main body  12  and a battery pack  30  detachably installed to the main body  12 . The main body  12  generally comprises a chassis  14  having an approximate cylindrical shape and a grip  16  extending downward from the chassis  14 . The battery pack  30  is installed at a lower end of the grip  16 . The battery pack  30  incorporates a secondary battery  32  (refer to  FIG. 2 ), which allows repeated use by recharging. 
         [0029]    The chassis  14  of the main body  12  has a tool chuck  22 . The tool chuck  22  is rotatably retained at a distal end (left end in  FIG. 1 ) of the chassis  14 . To the tool chuck  22 , tool bits such as a driver bit or a drill bit (both not shown) can be attached. The tool chuck  22  is driven by a motor  62  incorporated in the chassis  14  (refer to  FIG. 2 ). 
         [0030]    The chassis  14  of the main body  12  has a light emitting part  24 . The light emitting part  24  is placed below the tool chuck  22 . The light emitting part  24  incorporates light-emitting diode  44  (refer to  FIG. 2 ) that emits illumination light. The light emitting part  24  emits light toward front of the tool chuck  22 . Light of the light emitting part  24  is turned ON/OFF in conjunction with the operation to a trigger switch  28  described below. 
         [0031]    The chassis  14  of the main body  12  has a forward-reverse switching button  26 . The forward-reverse switching button  26  is operated by a user. By the user&#39;s operation of the forward-reverse switching button  26 , the rotating direction of the tool chuck  22  is caused to switch either forward or reverse. The forward-reverse switching button  26  is coupled to a forward-reverse switching circuit  78  of a switching module  70  incorporated in the main body  12  (refer to  FIG. 2 ). When the forward-reverse switching button  26  is operated by the user, the forward-reverse switching circuit  78  of the switching module  70  is switched. 
         [0032]    The grip  16  of the main body  12  has the trigger switch  28 . The trigger switch  28  is operated by the user in order to start or stop rotation of the tool chuck  22 . The trigger switch  28  is coupled to a main switching circuit  76  of the switching module  70  incorporated in the main body  12  (refer to  FIG. 2 ). By the user&#39;s operation to the trigger switch  28 , the main switching circuit  76  of the switching module  70  is caused to open or close. 
         [0033]    With reference to  FIG. 2 , the electrical configuration of the electric power screw driver is described. As shown in  FIG. 2 , the electric power screw driver  10  has a motor  62 , a secondary battery  32 , a switching module  70 , and an illumination circuit  40 . The motor  62  is DC motor for driving the tool chuck  22 . The secondary battery  32  is incorporated in the battery pack  30 , which supplies DC electric power to the motor  62 . The output voltage of the battery pack  30  is approximately 12V. 
         [0034]    The switching module  70  has a first input terminal  71 , a second input terminal  74 , a first output terminal  72 , and a second output terminal  73 . The first input terminal  71  is connected to a positive electrode  32   a  of the secondary battery  32 . A second input terminal  74  is connected to a negative electrode  32   b  of the secondary battery  32 . The first output terminal  72  is connected to the first motor terminal  62   a  of the motor  62 . The second output terminal  73  is connected to the second motor terminal  62   b  of the motor  62 . 
         [0035]    Inside the switching module  70 , equipped therein are the main switching circuit  76  which works in conjunction with the trigger switch  28  (refer to  FIG. 1 ), and the forward-reverse switching circuit  78  which works in conjunction with the forward-reverse switching button  26 . The main switching circuit  76  that makes and breaks an electrical connection between the secondary battery  32  and the motor  62  is provided between the first input terminal  71  and the forward-reverse switching circuit  78 . 
         [0036]    The forward-reverse switching circuit  78  is provided between the first input terminal  71  and the second input terminal  74 , and coincidently to the aforesaid arrangement, also between the first output terminal  72  and the second output terminal  73 . The forward-reverse switching circuit  78  switches the direction of DC voltage applied to the first and second motor terminals  62   a ,  62   b  from the secondary battery  32  via the main switching circuit  76 . For example, in the case where the forward-reverse switching circuit  78  is switched in one direction (e.g. the state shown in  FIG. 2 ), the positive electrode  32   a  of the secondary battery  32  is connected to the first motor terminal  62   a  via the main switching circuit  76 , and the negative electrode  32   b  of the secondary battery  32  is connected to the second motor terminal  62   b . In this case, DC voltage is applied to the first and second motor terminals  62   a ,  62   b  in the direction from the first motor terminal  62   a  to the second motor terminal  62   b . In the case where the forward-reverse switching circuit  78  is switched in the other direction while initially being in the state as shown in  FIG. 2 , the positive electrode  32   a  of the secondary battery  32  is connected to the second motor terminal  62   b  via the main switching circuit  76 , and the negative electrode  32   b  of the secondary battery  32  is connected to the first motor terminal  62   a . In this case, DC voltage is applied to the first and second motor terminals  62   a ,  62   b  in the direction from the second motor terminal  62   b  to the first motor terminal  62   a . The forward-reverse switching circuit  78  can thus switch the rotating direction of the motor  62 , by switching the direction of DC voltage applied from the secondary battery  32  to the first and second motor terminals  62   a ,  62   b.    
         [0037]    The illumination circuit  40  is configured with a light-emitting diode  44 , a transistor  46 , an electrolytic capacitor  52 , a first diode  56 , a second diode  60  and a plurality of resistors  42 ,  46 ,  48 ,  50 ,  54 ,  58 . 
         [0038]    The light-emitting diode  44  is placed in the light-emitting part  24  (refer to  FIG. 1 ). The light-emitting diode  44  has an anode  44   a  and a cathode  44   b , and emits light when current flows from the anode  44   a  to the cathode  44   b . The light-emitting diode  44  is connected to the secondary battery  32  via the resistor  42  and the transistor  46 . As shown in  FIG. 2 , the anode of the light-emitting diode  44  is electrically connected to the positive electrode  32   a  of the secondary battery  32  via the resistor  42 . The cathode of the light-emitting diode  44  is electrically connected to the negative electrode  32   b  of the secondary battery  32 . 
         [0039]    The transistor  46  is a switching device that makes/breaks an electrical connection between the light-emitting diode  44  and the secondary battery  32 . The transistor  46  has a collector terminal  46   a , a base terminal  46   b  and an emitter terminal  46   c . The collector terminal  46   a  of the transistor  46  is connected to the positive electrode  32   a  of the secondary battery  32  via the light-emitting diode  44  and the resistor  42 . The emitter terminal  46   c  of the transistor  46  is connected to the negative electrode  32   b  of the secondary battery  32 . The transistor  46  electrically connects the collector terminal  46   a  to the emitter terminal  46   c  in a case where a base voltage (base-emitter voltage) applied to the base terminal  46   b  becomes higher than a threshold level. 
         [0040]    The base terminal  46   b  of the transistor  46  is connected to the first motor terminal  62   a  via the first diode  56 . The first diode  56  is a kind of rectifying device. The first diode  56  allows current to flow from its anode  56   a  to its cathode  56   b , but forbids current to flow from the cathode  56   b  to the anode  56   a . The anode  56   a  of the first diode  56  is electrically connected to the first motor terminal  62   a . The cathode  56   b  of the first diode  56  is electrically connected to the base terminal  46   b  of the transistor  46  via the two resistors  48 ,  54 . 
         [0041]    Further, the base terminal  46   b  of the transistor  46  is connected to the second motor terminal  62   b  via the second diode  30 . Likewise, the second diode  60  is also a kind of rectifying device. The second diode  60  allows current to flow from its anode  60   a  to the cathode  60   b , but forbids current to flow from the cathode  60   b  to the anode  60   a . The anode  60   a  of the second diode  60  is electrically connected to the second motor terminal  62   b . The cathode  60   b  of the second diode  60  is electrically connected to the base terminal  46   b  of the transistor  46  via the two resistors  48 ,  58 . 
         [0042]    As described above, the base terminal  46   b  of the transistor  46  is electrically connected to the first motor terminal  62   a  and the second motor terminal  62   b  via the first diode  56  and the second diode  60 . The first diode  56  and the second diode  60  configure a type of an OR circuit. The OR circuit  56 ,  60  electrically connects one of the first and second motor terminals  62   a ,  62   b  having higher voltage to the base terminal  46   b  of the transistor  46 . 
         [0043]    Further, the electrolytic capacitor  52  is connected to the base terminal  46   b  of the transistor  46  via the resistor  48 . The electrolytic capacitor  52  is a type of capacitor. One end of the electrolytic capacitor  52  is electrically connected to the base terminal  46   b  of the transistor  46 , and the other end of the electrolytic capacitor  52  is electrically connected to the emitter terminal  46   c  of the transistor  46 . Specifically, the base terminal  46   b  and the emitter terminal  46   c  of the transistor  46  are electrically connected to each other via the electrolytic capacitor  52  and the resistor  48 . Further, the resistor  50  is connected in parallel to the electrolytic capacitor  52 . 
         [0044]    With reference to  FIG. 3  and  FIG. 4 , operation of the electric power driver  10  is described.  FIG. 3  shows a timing diagram describing operation and condition of each unit when the electric power driver  10  is rotated in forward direction.  FIG. 4  shows a timing diagram describing operation and condition of each unit when the electric power driver  10  is rotated in reverse direction. The diagrams (a) in  FIGS. 3 and 4  show ON/OFF state of the main switching circuit  76 . The diagrams (b) in  FIGS. 3 and 4  show the electric potential of the first motor terminal  62   a . The diagrams (c) in  FIGS. 3 and 4  show the electric potential of the second motor terminal  62   b . The diagrams (d) in  FIGS. 3 and 4  show the base voltage of the transistor  46 . The diagrams (e) in  FIGS. 3 and 4  show the operation state (of light being turned ON/turned OFF) of the light-emitting diode  44 . 
         [0045]    With reference to  FIG. 3 , the case under circumstances, where the user operates the forward-reverse switching button  26  to the forward rotating direction, and the forward-reverse switching circuit  78  is switched to one direction (the state of  FIG. 2 ) is described. In this case, the main switching circuit  76  makes or breaks the electrical connection between the first input terminal  71  and the first output terminal  72 . Moreover, the second input terminal  74  is electrically connected to the second output terminal  73 . 
         [0046]    Time t 1  shows a timing at which the trigger switch  28  is turned ON by the user. At this point, the main switching circuit  76  is switched to ON state, and the electrical connection between the first motor terminal  62   a  and the positive electrode  32   a  of the secondary battery  32  is established. Accordingly, the motor  62  rotates in one direction, and the tool chuck  22  performs forward rotation. At this point, the base terminal  46   b  of the transistor  46  is electrically connected to the first motor terminal  62   a  via the first diode  56 , and electrically cut off from the second motor terminal  62   b  by the second diode  60 . As a result, the base voltage of the transistor  46  rises (e.g. to the ‘High’ level), the transistor  46  becomes ON state and the light-emitting diode  44  turns ON. Specifically, light of the light-emitting diode  44  is turned ON in conjunction with ON operation to the trigger switch  28 . At this point, the electrolytic capacitor  52  stores charge. 
         [0047]    Time t 2  after t 1  has elapsed shows a timing at which the trigger switch  28  is turned OFF by the user&#39;s operation. At this point, the main switching circuit  76  is switched to the OFF state, and the electrical connection between the first motor terminal  62   a  and the positive electrode  32   a  of the secondary battery  32  is broken. The motor  62  and the tool chuck  22  are thereby stopped. However, the base voltage of the transistor  46  is maintained at or above the threshold voltage for a predetermined period of time even after that timing t 2  by the charge stored in the electrolytic capacitor  52 . As a result, the transistor  46  maintains ON state to Time t 3 , which is after Time t 2  by a predetermined period. Thus, light of the light-emitting diode  44  is turned ON until Time t 3 . In other words, light of the light-emitting diode  44  is maintained for a predetermined period even after OFF operation is performed to the trigger switch  28  (i.e. afterglow function). 
         [0048]    With reference to  FIG. 4 , the case where the forward-reverse switching button  26  is switched to the reverse rotating direction by user&#39;s operation, and thereby the forward-reverse switching circuit  78  is switched to the other direction is described. In this case, the main switching circuit  76  makes/breaks the electrical connection between the first input terminal  71  and the second output terminal  73 . On the other hand, the second input terminal  74  is electrically connected to the first output terminal  72 . 
         [0049]    Time t 1  shows a timing at which the trigger switch  28  is turned ON by the user&#39;s operation. At this point, the main switching circuit  76  is switched to ON state, and the electrical connection between the second motor terminal  62   b  and the positive electrode  32   a  of the secondary battery  32  is established. Thus, the motor  62  rotates in the other direction, and thereby the tool chuck  22  performs reverse rotation. At this point, an electrical connection between the base terminal  46   b  of the transistor  46  and the second motor terminal  62   b  is made via the second diode  60 . On the other hand, an electrical connection between the base terminal  46   b  of the transistor  46  and the first motor terminal  62   a  is broken by the first diode  56 . As a result, the base voltage of the transistor  46  rises (e.g. to the ‘High’ level), the transistor  46  is turned to ON state, and light of the light-emitting diode  44  is turned ON. In the other words, the light-emitting diode  44  is turned ON in conjunction with ON operation to the trigger switch  28  even during reverse rotation. At this point, charge is stored in the electrolytic capacitor  52 . 
         [0050]    After that, Time t 2  shows a timing at which the trigger switch  28  is turned OFF by the user&#39;s operation. At this point, the main switching circuit  76  is switched to OFF state, the electrical connection between the second motor terminal  62   b  and the positive electrode  32   a  of the secondary battery  32  is cancelled. Thus, the motor  62  and the tool chuck  22  are thereby stopped. However, the base voltage of the transistor  46  is maintained at or above the threshold voltage for a predetermined period even after that timing by the electric power stored in the electrolytic capacitor  52 . As a result, the transistor  46  maintains ON state until Time t 3  after Time t 2  by a predetermined period. Thus, light of the light-emitting diode  44  is turned ON until Time t 3 . In other words, light of the light-emitting diode  44  is turned ON for a predetermined period even after the trigger switch  28  is turned OFF by the user&#39;s operation. 
         [0051]    As described above, according to the electric power driver  10  of this embodiment, it is possible to cause the light-emitting diode  44  of the light-emitting part  24  to turn ON in conjunction with ON operation to the trigger switch  28  regardless of a rotating direction (i.e. forward rotation or reverse rotation). Further, it is possible to cause the light-emitting diode  44  to turn OFF after a predetermined period from OFF operation to the trigger switch  28 , regardless of a rotating direction (forward rotation/reverse rotation). 
         [0052]    The electric power driver  10  of this embodiment adopts the switching module  70  having the main switching circuit  76  and the forward-reverse switching circuit  78  built therein. This switching module  70  enables simplification of internal wirings and miniaturization of the electric power driver  10 . However, this switching module  70  may make the adopting of conventional illumination circuits impossible, since the signal line which detects ON/OFF state of the main switching circuit  76  cannot be led out from the main switching circuit  76 . With consideration given to such incapability, the electric power driver  10  of this embodiment has the configuration that the first motor terminal  62   a  and the second motor terminal  62   b  are connected to the illumination circuit  40  in order to detect starting/stopping rotation of the motor  62 . Moreover, the electric power driver  10  of this embodiment is configured in order that the rotating direction of the motor  62  can be switched. Accordingly, between the first motor terminal  62   a  and the second motor terminal  62   b , the terminal to be connected to the positive electrode  32   a  of the secondary battery  32  are not fixed. Furthermore, in the illumination circuit  40  of this embodiment, the first diode  56  and the second diode  60  are provided respectively, between the first motor terminal  62   a  and the base terminal  46   b  of the transistor  46  and between the second motor terminal  62   b  and the base terminal  46   b  of the transistor  46 . According to this constitution, whichever terminal of the first motor terminal  62   a  or the second motor terminal  62   b  is connected to the positive electrode  32   a  of the secondary battery  32 , light of the light-emitting diode  44  is turned ON. 
         [0053]    The specific embodiment of the present invention is described above, but this merely illustrates some possibilities of the invention and does not restrict the claims thereof. The art set forth in the claims includes variations and modifications of the specific examples set forth above. 
         [0054]    For example, in the case where the afterglow function is not required, the electrolytic capacitor  52  may be removed from the illumination circuit  40  described in this embodiment. 
         [0055]    The technical elements disclosed in the specification or the drawings may be utilized separately or in all types of combinations, and are not limited to the combinations set forth in the claims at the time of filing of the application. Furthermore, the art disclosed herein may be utilized to simultaneously achieve a plurality of aims or to achieve one of these aims.