Abstract:
An electric working machine of an example of the present disclosure includes: a motor; a power supply portion; a controller; and a voltage detector. The power supply portion generates a DC voltage to drive the motor by rectifying an AC voltage supplied from an AC power source and smoothing by a capacitor. The controller controls energization of the motor. The voltage detector detects the AC voltage. The controller is configured to interrupt the energization when the voltage detector does not detect the AC voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Japanese Patent Application No. 2016-82851 filed on Apr. 18, 2016 with the Japan Patent Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present disclosure relates to an electric working machine that works by being supplied with electric power from an AC power source. 
         [0003]    As electric working machines such as electric power tools and so on, an apparatus has been known, which is configured to generate a DC voltage to drive a motor by rectifying an AC voltage applied from an AC power source, such as a commercial power source and so on, by a rectifying circuit, such as a diode bridge and so on, and by smoothing an output of the rectifying circuit by a capacitor (e.g., Japanese Unexamined Patent Application Publication No. 2015-9316.). 
       SUMMARY 
       [0004]    In this type of electric working machine, when a user inserts a power supply plug into an outlet of the AC power source, the AC power source supplies electric current to the electric working machine and the capacitor for smoothing is electrically charged through the rectifying circuit. 
         [0005]    Accordingly, when the power supply plug is removed from the outlet of the AC power source and electric current supply from the AC power source is interrupted, the motor is supplied with DC voltage from the capacitor and is allowed to be driven until the capacitor is electrically discharged. 
         [0006]    This type of behavior of the electric working machine is not what was intended for the user who recognizes that “the electric apparatus does not work when the power supply plug is out of the outlet,” and provides the user with a sense of discomfort. 
         [0007]    According to an aspect of the present disclosure, in an electric working machine provided with a power supply portion configured to rectify an AC voltage supplied from an AC power source and to smooth the AC voltage by a capacitor, it is preferable that a motor is not driven when electric current supply from the AC power source is interrupted. 
         [0008]    An electric working machine according to the aspect of the present disclosure includes: a motor; a power supply portion; a controller; and a voltage detector. The power supply portion generates a DC voltage to drive the motor by rectifying an AC voltage supplied from an external AC power source and smoothing the AC voltage by a capacitor. The controller controls energization to the motor from the power supply portion. The voltage detector detects the AC voltage supplied from the external AC power source. 
         [0009]    The controller interrupts the energization to the motor and stops the motor when there is no detection of the AC voltage by the voltage detector. 
         [0010]    Therefore, according to this electric working machine, when the power supply plug is pulled out of the outlet of the AC power source and the power supply from the AC power source has been interrupted, the voltage detector does not detect the AC voltage and the energization to the motor is interrupted, which leads to stopping the motor. 
         [0011]    Accordingly, for the user who recognizes that “the electric appliance does not work by pulling the power supply plug out of the outlet”, the behavior of the electric working machine of the present disclosure in the situation where the power supply plug is out of the outlet of the AC power source may reduce or eliminate discomfort. Therefore, it improves the usability of the electric working machine. 
         [0012]    It is also possible to stop the motor by interrupting the energization to the motor when the power supply from the AC power source is off due to power outage and so on. Therefore, it is also possible to inhibit the motor from rotating by electric charge stored at the capacitor in the event of a power outage. 
         [0013]    Here, the voltage detector may be configured to detect a voltage value of the AC voltage or to detect a zero-cross point of the AC voltage. In this case, the controller may be configured to determine the absence of the detection of the AC voltage when the voltage value detected by the voltage detector is smaller than a threshold value for a predetermined time or more or when the voltage detector does not detect the zero-cross point. 
         [0014]    The electric working machine of the present disclosure may include a voltage generator which receives the DC voltage outputted from the power supply portion via the capacitor and generates a drive voltage to drive the controller. 
         [0015]    In this case, electric charge stored in the capacitor is discharged by the voltage generator and the controller when the power supply from the AC power source to the electric working machine has been interrupted. Thereby, it is possible to reduce or eliminate prolonged accumulation of electric charge at the capacitor. 
         [0016]    That is, if driving the motor is stopped while the electric charge able to drive the motor has been stored at the capacitor, it takes time to discharge the electric charge from the capacitor. For example, electric shock is likely to occur when a user puts his hand inside the electric working machine for the purpose of maintenance inspection and so on and touch the capacitor. However, discharging the electric charge in the capacitor by the voltage generator and the controller can inhibit this sort of problem from occurring. 
         [0017]    The electric working machine includes a discharger that discharges an electric charge of the capacitor according to a command of the controller. The controller may be configured to output the command to the discharger and allows the discharger to discharge the electric charge of the capacitor when the voltage detector does not detect the AC voltage. Accordingly, it is possible to reduce or eliminate the above described problem by immediately discharging the electric charge stored at the capacitor when power supply from the AC power source to the electric working machine is interrupted. 
         [0018]    The discharger may include a first resistor and a transistor that is turned to an on state in response to a command from the controller and connects the first resistor to the capacitor in parallel. Accordingly, the discharger can discharge the electric charge accumulated at the capacitor rapidly when the controller determines that the power supply from the AC power source has stopped. 
         [0019]    The electric working machine may further include a second resistor connected to the capacitor in parallel. A resistance value of the first resistor may be smaller than a resistance value of the second resistor. The second resistor can gradually discharge the electric charge accumulated at the capacitor when the power supply from the AC electric current has been stopped. 
         [0020]    The power supply portion may include a diode bridge that rectifies the full waves of the AC voltage supplied from the AC power source and the capacitor that smooths rectified electric current. Accordingly, DC voltage is generated. It is therefore possible to drive the motor by use of the DC voltage generated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present disclosure will now be described by way of example with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a perspective view showing an external appearance of a circular saw according to an embodiment of the present disclosure; 
           [0023]      FIG. 2  is a block chart showing a configuration of a driving apparatus according to the embodiment; and 
           [0024]      FIG. 3  is a flowchart showing a control process implemented by an MCU illustrated in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    As shown in  FIG. 1 , a circular saw  1  as an electric working machine in the present embodiment includes a base  2  and a main body  3 . The base  2  is of approximately rectangular shape, and the base  2  is connected with an upper surface of a workpiece (illustration omitted) that is a subject of cutting. The main body  3  is arranged around the upper surface of the base  2 . 
         [0026]    The main body  3  has a round blade  4  and a blade casing  5 . The peripheral edge of the approximately half periphery at the upper side of the blade  4  is housed inside the blade casing  5  and is covered thereby. The peripheral edge of the approximately half periphery at the lower side of the blade  4  is covered by a folding cover  6 . This cover  6  rotates in a clockwise direction in  FIG. 1  in the rotation center of the blade  4  and opens gradually when the circular saw  1  is moved in a cutting direction when the workpiece is cut. The blade  4  is then exposed and the exposed portion cuts into the workpiece. 
         [0027]    When the circular saw  1  is seen along the cutting direction shown as an arrow in  FIG. 1 , the blade  4  is arranged at the right side of the main body  3  to the cutting direction and an approximately cylindrically shaped motor casing  7  is arranged at the left side of the main body  3  to the cutting direction. A motor  20  (see  FIG. 2 ) as a driving source of the circular saw  1  is housed in the motor casing  7 . A gear mechanism is housed in the center of the main body  3  between the motor casing  7  and the blade  4 . 
         [0028]    The gear mechanism works to transmit the rotation of the motor  20  to the blade  4 . According to the embodiment, the motor  20  is configured with a brushless motor. 
         [0029]    An arch shaped handle  8  is attached to the upper side at the center of the main body  3  so that a user can hold the handle  8 . That is, when the circular saw  1  is seen along the cutting direction shown as an arrow in  FIG. 1 , one end of the handle  8  is fixed to the rear end side of the main body  3  to the cutting direction and the other end thereof is fixed to the ahead of the rear end to the cutting direction. 
         [0030]    A trigger type operation switch  9  is provided at the inner peripheral side of the handle  8  so that a user can operate the operation switch  9  while holding the handle  8 . The operation switch  9  is allowed to remain at an on state for operation via a lock button (illustration omitted). 
         [0031]    A power cord  10  is led from the rear end of the main body  3  to the cutting direction. A power supply plug (illustration omitted) is attached to the tip end of the power cord  10 . By putting the power supply plug into the outlet of an AC power source  12  (see  FIG. 2 ) such as a commercial power source and so on, the power cord  10  takes power for driving the motor  20  (AC voltage) from the AC power source  12  to the main body  3 . The main body  3  is provided with a cylindrically shaped cord guard  10 A to protect the power cord  10 . 
         [0032]    A driving apparatus  30  (see  FIG. 2 ) is housed in the main body  3  and is worked by power supply from the external AC power source  12  via the power cord  10 . The driving apparatus  30  rotates the motor  20  (further blade  4 ) when the operation switch  9  is in an operation state (on state). 
         [0033]    As illustrated in  FIG. 2 , the driving apparatus  30  comprises a capacitor C 1  as a power supply portion  32  to generate a DC voltage to drive the motor  20 . The driving apparatus  30  further may include a diode bridge  34  as the power supply portion  32 . The diode bridge  34  rectifies the full waves of the AC voltage supplied from the AC power source  12  via the power cord  10  and a fuse  14 . 
         [0034]    The capacitor C 1  smooths the output of the diode bridge  34 . The DC voltage smoothed by the capacitor C 1  is outputted to a motor control circuit  36  via a power supply circuit. 
         [0035]    The operation switch  9  is provided on a power supply circuit  49  (at the positive electrode side in  FIG. 2 ) extending from the power supply portion  32  to the motor control circuit  36 . When the operation switch  9  is in the on state, the DC voltage is supplied to the motor control circuit  36  to drive the motor  20 . 
         [0036]    The motor  20  is configured with a three-phase brushless motor. The terminals of the respective phases of the motor  20  are connected, via the control circuit  36 , to the power supply circuit  49  extending from the power supply portion  32 . 
         [0037]    That is, the motor control circuit  36  is configured with a full bridge circuit (in other words, inverter circuit) provided with a high-side switch and a low-side switch to connect the terminals of the respective phases of the motor  20  to the positive and negative electrode sides of the power supply circuit  49 . The high-side switch and the low-side switch in the motor control circuit  36  are configured with at least a switching element such as a MOSFET and so on. 
         [0038]    The switching element is turned on and off in response to a control signal from the MCU (Micro Control Unit)  40  as a controller. When the switching element is in the on state, the switching element connects the terminals of the respective phases of the motor  20  to the positive or negative electrode side of the power supply circuit  49  and generates a circuit to energize the motor  20 . 
         [0039]    The MCU  40  is a known controller mainly configured with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and so on. The MCU  40  controls driving the motor  20  in accordance with a program stored in the ROM. When the motor  20  is driven, the MCU  40  turns on and off the switching element in the motor control circuit  36  and controls electric current supply to the respective phases of the motor  20 . 
         [0040]    The driving apparatus  30  includes a switch-detecting circuit  42  and a zero-cross detecting circuit  44 . The switch-detecting circuit  42  is configured to detect on and off states of the operation switch  9 . The zero-cross detecting circuit  44  is configured to detect a zero-cross point of the AC voltage supplied from the external AC power source via the power cord  10  and the fuse  14 . 
         [0041]    The switch-detecting circuit  42  is an example of a switch-detecting portion of the present disclosure. The zero-cross detecting circuit  44  is an example of a voltage detector of the present disclosure. Detection signals from the detecting circuits  42  and  44  are inputted into the MCU  40  and are employed by the MCU  40  to control driving the motor  20 . 
         [0042]    A resistance R 1  and a discharger  46  are provided at the power supply circuit  49  which supplies electric current from the power supply portion  32  to the motor control circuit  36 . The resistance R 1  and the discharger  46  are each connected to the capacitor C 1  in parallel. The resistance R 1  is employed to gradually discharge electric charge accumulated at the capacitor C 1  when the power supply from the AC power source  12  has been stopped. 
         [0043]    The discharger  46  includes a resistance R 2  and a transistor Tr 1 . The resistance R 2  discharges the electric charge accumulated at the capacitor C 1  as well as the resistance R 1 . In response to a discharge command from the MCU  40 , the transistor Tr 1  is turned to the on state and connects the resistance R 2  to the capacitor C 1  in parallel. The transistor Tr 1  is a NPN bipolar transistor in  FIG. 2 , but the transistor Tr 1  can be a field effect transistor such as MOSFET and so on. 
         [0044]    This discharger  46  is employed to rapidly discharge the electric charge stored at the capacitor C 1  when the MCU  40  determines in a control process described later that the power supply from the AC power source  12  was stopped. Therefore, a resistance value of the resistance R 2  is smaller than the resistance value of the resistance R 1 . 
         [0045]    The power supply circuit  49  to supply electric current from the power supply portion  32  to the motor control circuit  36  is connected to a DC-DC convertor (hereinafter, referred to as a convertor)  48  which generates a DC constant voltage Vcc to drive the MCU  40  and other peripheral circuits. The convertor  48  is an example of a voltage generator of the present disclosure. The MCU  40  is activated by receiving the DC constant voltage Vcc generated by the convertor  48 . 
         [0046]    Accordingly, in the circular saw  1  in the present disclosure, when the power supply plug is put into the outlet of the AC power source  12  and power supply is implemented from the AC power source  12  via the power cord  10 , DC constant voltage Vcc is generated by the convertor  48  and the MCU  40  is started. 
         [0047]    After startup, the MCU  40  performs the control process illustrated in  FIG. 3  and controls driving the motor  20 . Described below is the control process. 
         [0048]    As illustrated in  FIG. 3 , in this control process, the MCU  40  first determines in S 110  the presence or absence of the detection of the zero-cross point of the AC voltage by the zero-cross detecting circuit  44 . When there is no detection of the zero-cross point, the process at S 110  is implemented again to wait for detection of the zero-cross point. 
         [0049]    When the MCU  40  determines at S 110  the presence of the detection of the zero-cross point, the process proceeds to S 120 . At S 120 , the MCU  40  determines whether the operation switch  9  was operated and is at the on state. When the operation switch  9  is not at the on state, the process at S 120  is implemented again to wait for the operation of the operation switch  9  and switching to the on state thereof. 
         [0050]    When the MCU  40  determines at S 120  that the operation switch  9  is in the on state, the process proceeds to S 130 . At S 130 , the MCU  40  determines whether an elapsed time between the presence of the determination of the zero-cross point detection at S 110  and the determination of the on state of the operation switch  9  at S 120  is a set time Tth or more. 
         [0051]    In this determination process, when the elapsed time is short, it is thought that the power supply plug was inserted into the outlet while the operation switch  9  is at the on state. The above determination process is implemented to judge this state. 
         [0052]    For example, in a state where the operation switch  9  is at the on state by the lock button, if the power supply plug is put in the outlet, the AC voltage is supplied from the AC power source  12 , and the motor  20  is driven, it is likely that the round blade works suddenly before an operator gets ready, which may surprise the operator. 
         [0053]    Therefore, according to the embodiment, this state is determined at S 130  based upon the elapsed time. When the elapsed time is smaller than the set time Tth, the motor  20  is not started (restarted) and the process proceeds to S 140 . At S 140 , the operator is noticed that the re-start was inhibited by turning on a display lamp (not illustrated) configured with an LED and so on. 
         [0054]    After implementing the process in S 140 , the process proceeds to S 150 . At S 150 , the MCU  40  determines whether the operation switch  9  was switched to the off state to wait for switching of the operation switch  9  to the off state. When the operation switch  9  is shifted to the off state, the process proceeds to S 160 . At S 160 , the display lamp turned on at S 140  is turned off and the notice of the re-start inhabitation is cancelled. The process then proceeds to S 110  again. 
         [0055]    At S 130 , when the elapsed time is determined to be or greater than the set time Tth, the process proceeds to S 170 . At S 170 , driving the motor  20  is initiated. At S 180  following S 170 , the MCU  40  determines whether the operation switch  9  was switched to the off state. When the operation switch  9  is at the off state, the process proceeds to S 190 . Driving the motor  20  is stopped at S 190 , and the process proceeds to S 110  again. 
         [0056]    Meanwhile, when the operation switch  9  is determined at S 180  not to be at the off state, the process proceeds to S 200 . At S 200 , the MCU  40  determines the presence or absence of the detection of the zero-cross point of the AC voltage by the zero-cross detecting circuit  44 . When there is the presence of the detection of the zero-cross point, the process proceeds to S 180 . When there is the absence of the detection of the zero-cross point, the process proceeds to S 210  and driving the motor  20  is stopped. 
         [0057]    That is, when the MCU  40  determines at S 200  that the zero-cross point is not detected, it can be determined that the power supply from the AC power source  12  was interrupted during driving the motor  20 . In this case, driving the motor  20  is stopped forcedly at S 210 . 
         [0058]    At S 220  following S 210 , electric charge accumulated at the capacitor C 1  is discharged via the resistance R 2  by allowing the transistor Tr 1  of the discharger  46  to be at the on state for a predetermined period of time. The process then proceeds to S 230 . 
         [0059]    At S 230 , the MCU  40  determines whether the operation switch  9  was switched to the off state to wait for switching of the operation switch  9  to the off state. When the operation switch  9  was shifted to the off state, the process proceeds to S 110  again. 
         [0060]    As described above, in the circular saw  1  of the present embodiment, electric power is supplied to the power supply portion  32  from the external AC power source  12 . The MCU  40  is activated and the control process starts when the motor  20  is allowed to be driven. 
         [0061]    In this control process, when the zero-cross point of the AC voltage is not detected by the zero-cross detecting circuit  44 , driving the motor  20  is prohibited. When the operation switch  9  is turned to the on state when there is the detection of the zero-cross point of the AC voltage by the zero-cross detecting circuit  44 , driving the motor  20  is started. In response to the switching of the operation switch  9  to the off state, driving the motor  20  is stopped. When the zero-cross point of the AC voltage is not detected by the zero-cross detecting circuit  44  anymore during driving the motor  20 , the MCU  40  determines that the power supply from the AC power source  12  was interrupted, and driving the motor  20  is compelled to be stopped. 
         [0062]    Therefore, according to the circular saw  1  in the present embodiment, it is possible to inhibit continuing to drive the motor  20  when the power supply plug is out of the outlet of the AC power source  12 . Accordingly, it reduces or eliminates discomfort for the user, the user who recognizes that “the electric apparatus does not work by pulling out the power supply plug from the outlet,” thereby enabling to enhance usability for such users. It is also possible to inhibit the motor  20  from being rotated by electric charge accumulated at the capacitor C 1  in the event of power outage of the AC power source  12 , blow off the fuse  14 , or the like. 
         [0063]    The MCU  40  is activated by receiving power supply from the convertor  48  which generates the DC constant voltage Vcc following the output of the power supply portion  32 . Therefore, it is possible to discharge electric charge of the capacitor C 1  when the power supply from the AC power source  12  is off. 
         [0064]    The driving apparatus  30  of the present embodiment includes the discharger  46 , which discharges the capacitor C 1  immediately. When the power supply from the AC power source  12  is interrupted and driving the motor  20  is compelled to be stopped, the MCU  40  outputs a drive signal to the transistor Tr 1  of the discharger  46  so that the transistor Tr 1  is turned on and electric charge stored at the capacitor C 1  is discharged. 
         [0065]    Therefore, according to the circular saw  1  in the present embodiment, storing electric charge at the capacitor C 1  over a prolonged period of time is inhibited when the power supply from the AC power source  12  has been interrupted, so that the user is prevented from electric shocks occurred by touching the capacitor C 1 . 
         [0066]    The present disclosure should not be limited by the above-described embodiment, and can be practiced in various manners. 
         [0067]    For example, according to the above embodiment, the discharger  46  is provided at the power supply circuit  49  extending from the power supply portion  32  to the motor control circuit  36  and further to the motor  20 , but the discharger  46  is not necessarily provided. However, it is preferable to provide, at the power supply circuit  49 , an electrical load capable of discharging the capacitor C 1  such as the resistance R 1  and so on. 
         [0068]    The drive voltage to operate the MCU  40  as the controller is described above to be generated by the convertor  48 , which is activated by receiving the power supply from the power supply portion  32 . However, the MCU  40  may be operated by receiving power supply from another power source, such as a built-in battery. 
         [0069]    According to the present embodiment, the motor  20  is a brushless motor, and the motor control circuit  36  that controls energizing current to the motor  20  is housed in the driving apparatus  30 . 
         [0070]    However, for example, the motor  20  may be a brush motor. For example, the MCU  40  as the controller may be configured to turn on and off a switching element provided at the power supply circuit  49  extending from the power supply portion  32  to the motor  20  in response to the on and off states of the operation switch  9 . 
         [0071]    According to the above-described embodiment, the voltage detector is configured with a zero-cross point detecting circuit. However, the voltage detector does not necessarily employ a zero-cross point detecting circuit as far as the controller can determine the presence or absence of supply of the AC voltage. 
         [0072]    According to the above-described embodiment, the circular saw  1  is an example of the electric working machine. However, the electric working machine of the present disclosure may be provided with a power supply portion that rectifies an AC voltage supplied from an AC power source, smooths the AC voltage, and generates a DC voltage to drive a motor. Further, the electric working machine of the present disclosure is, for example, an electric tool for masonry, an electric tool for metalwork, an electric tool for woodworking, an electric tool for gardening, or so on. 
         [0073]    More specifically, the electric working machine of the present disclosure may be applied to an electric working machine, such as an electric hammer, an electric hammer drill, an electric drill, an electric driver, an electric wrench, an electric grinder, an electric reciprocating saw, an electric jigsaw, an electric cutter, an electric chain saw, an electric plane, an electric pile driver (including a riveter), an electric hedge trimmer, an electric mower, an electric lawn clipper, an electric bush cutter, an electric cleaner, an electric blower, and so on. 
         [0074]    Multiple functions of a single element according to the above embodiment may be fulfilled by multiple elements, or a single function of a single element may be fulfilled by multiple elements. Multiple functions of multiple elements may be fulfilled by a single element, or a single function fulfilled by multiple elements may be fulfilled by a single element. The configuration of the above-described embodiment may be partially omitted. At least a part of the configuration of the above-described embodiment may be added or replaced to other configurations of the above-described embodiment. Any modes encompassed in a technical idea specified by the description in the scope of claims shall be embodiments of the present disclosure. 
         [0075]    The technology of the present disclosure can also be fulfilled by various modes, such as a system including an electric working machine as an element, a program to configure a computer to function as an electric working machine, a non-transitory tangible storage media such as a semiconductor memory storing this program, a method of controlling an electric working machine, and so on.