Patent Publication Number: US-8988019-B2

Title: Electric operating machine

Description:
TECHNICAL FIELD 
     The present invention relates to an electric operating machine. 
     BACKGROUND ART 
     The above electric machine, for example, includes an electric operating machine having a driven object (such as a rotary blade) driven by a motor (for example, an electric mowing machine). As such an electric mowing machine, Patent Literature 1 discloses an electric mowing machine having adjustable motor rotation speed. This electric mowing machine has a converter to change the voltage applied to the motor so as to change the motor rotation speed. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Unexamined Japanese Patent Application KOKAI publication No. 2006-217843 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the Patent Literature 1 discloses no technique for protecting the power circuit itself of the electric operating machine; the power circuit itself is not sufficiently protected. 
     Solution to Problem 
     The present invention is invented in view of the above problem and an exemplary purpose of the present invention is to provide an electric operating machine having the power circuit properly protected. 
     In order to achieve the above purpose, the electric operating machine according to an exemplary aspect of the present invention is an electric operating machine comprising a motor and a power circuit driving the motor by the electric power supplied from a battery, wherein: 
     the power circuit comprises a voltage conversion part converting an input voltage entered in accordance with a voltage of the battery to generate an output voltage and outputting the generated output voltage to said motor, and 
     the power circuit is structured so that the voltage value of the output voltage of the voltage conversion part is changeable. 
     Possibly, the power circuit further comprises a voltage detection part outputting a first signal in accordance with the voltage of the battery, and the voltage conversion part lowers the voltage value of new output voltage being generated when the voltage detection part outputs the first signal. 
     Possibly, the voltage detection part outputs the first signal when the voltage value of the output voltage of the battery does not satisfy a given criterion. 
     Possibly, the voltage conversion part lowers the voltage value of the output voltage when the first signal is supplied. 
     Possibly, the power circuit further comprises a voltage control part outputting to the voltage conversion part a second signal of a voltage value in accordance with the output voltage output from the voltage conversion part, and 
     the voltage conversion part generates new output voltage having a voltage value in accordance with the second signal output from the voltage control part when the voltage detection part does not output the first signal. 
     Advantageous Effects of Invention 
     The present invention can provides an electric operating machine having the power circuit properly protected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an illustration showing the appearance of the electric operating machine according to Embodiment 1 of the present invention; 
         FIG. 2  is a cross-sectional view showing the motor of the electric operating machine shown in  FIG. 1 ; 
         FIG. 3  is an exploded cross-sectional view showing the output shaft and rotor of the motor shown in  FIG. 2 ; 
         FIG. 4  is a bottom view showing the fan of the rotor shown in  FIG. 3 ; 
         FIG. 5  is a block diagram for explaining the configuration of the power circuit of the electric operating machine according to Embodiment 1 of the present invention; 
         FIG. 6  is a circuit diagram for explaining an exemplary power circuit of the electric operating machine according to Embodiment 1 of the present invention; 
         FIG. 7  is a flowchart for explaining the operation of the power circuit of the electric operating machine according to Embodiment 1 of the present invention; 
         FIG. 8  is a block diagram for explaining the configuration of the power circuit of the electric operating machine according to Embodiment 2 of the present invention; 
         FIG. 9  is a circuit diagram for explaining an exemplary power circuit of the electric operating machine according to Embodiment 2 of the present invention; and 
         FIG. 10  is a circuit diagram for explaining an exemplary power circuit of the electric operating machine according to Embodiment 3 of the present invention. 
         FIG. 11  is a top view of the coil/commutator disk of the rotor in  FIG. 3   
         FIG. 12  is a top view of the coil disk part of the rotor in  FIG. 3 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The electric operating machine according to embodiments of the present invention is described hereafter with reference to the drawings. For easier understanding of the present invention, unimportant known technical matters are not explained in the following explanation as appropriate. The electric operating machine according to embodiments is an electric mowing machine having a rotary blade driven by a motor. 
     (Embodiment 1) 
     Embodiment 1 of the present invention will be described hereafter with reference to  FIGS. 1 to 7 ,  11  and  12 . As shown in  FIG. 1 , an electric operating machine  1  according to Embodiment 1 comprises a power source part  10 , an operation part  20 , a coupling part  30 , and a drive part  40 . 
     The power source part  10  comprises a power source housing  11  and a power circuit  12 . Furthermore, a battery  2  is attached to the power source part  10 . 
     The power source housing  11  constitutes the enclosure of the power source part  10  and houses the power circuit  12 . 
     The battery  2  is mounted on a battery holder provided to the power source housing  11  and electrically connected to the power circuit  12 . The battery  2  serves as the power source for supplying electric power to the power circuit  12 . 
     The power circuit  12  converts the output voltage of the battery  2  to a voltage having a given magnitude and outputs the converted voltage to a motor  50  of the drive part  40 , which will be described later. The power circuit  12  will be described in detail later. The power circuit  12  drives the motor  50  by the electric power supplied from the battery. 
     The operation part  20  comprises a handle  21  and a trigger lever  22 . 
     The handle  21  is fixed to the power source housing  11  of the power source part  10  and to one end of the coupling part  30 . 
     The trigger lever  22  is connected to a switch  113  of the power circuit  12  of the power source part  10 , which will be described later, and is operated by the user to turn on/off the switch  113 . Therefore, the trigger lever  22  drives/stops the motor  50 . 
     The coupling part  30  comprises a hollow duct  31  made of an aluminum alloy, reinforced plastic or the like. The coupling part  30  couples the operation part  20  and drive part  40 . A power cable extends from the power circuit  12  of the power source part  10  to the motor  50  of the drive part  40  through the hollow duct  31  of the coupling part  30 . The power cable electrically connects the drive part  40  and power circuit  12  for supplying electric power from the power circuit  12  to the motor  50 . 
     The coupling part  30  further comprises an additional handle  36 . The user can hold the additional handle  36  and handle  21  to operate the electric operating machine  1 . The coupling part  30  further comprises a protective cover  37  covering a part of a rotary blade  42  of the drive part  40  so that the user does not touch the rotary blade  42  while it is in use. 
     The drive part  40  comprises a motor  50  and a rotary blade  42  (working tool). Supplied with electric power from the power circuit  12  of the power source part  10 , the motor  50  rotates the rotary blade  42 . 
     The motor  50  will be described in detail hereafter with reference to  FIG. 2 . 
     The motor  50  is a commutator motor including a motor housing  51 , an output shaft  52 , a rotor  53 , a stator  54 , and sliders  55 . 
     The motor housing  51  is fixed to the other end of the coupling part  30 . The motor housing  51  has an exhaust outlet  56 . On the other hand, the coupling part  30  has an air inlet  38  communicated with the inside of the motor housing  51 . 
     The output shaft  52  is rotatably supported by bearings  57  and  58  provided in the motor housing  51 . The output shaft  52  protrudes from the motor housing  51  at one end, to which the rotary blade  42  is fixed. 
     The rotor  53  is housed in the motor housing  51  and provided integrally with the output shaft  52 . The rotor  53  includes a flange  61 , a coil/commutator disc  62 , four coil discs  63 , a rotor yoke  67 , and a fan  68 . 
     The flange  61  is made of an aluminum alloy and includes a cylindrical fixture  611  and a support member  612  in the form of a disc extending from the outer periphery of the fixture  611  in the direction nearly perpendicular thereto. With the fixture  611  being fitted on the output shaft  52  and inhibited from rotating, the flange  61  rotates together with the output shaft  52 . 
     The coil/commutator disc  62  and coil discs  63  are each in the shape of a disc with a center fitting hole. They are each a printed wiring board having an insulating substrate and a conductor pattern on the insulating substrate. One coil/commutator disc  62  and four coil discs  63  are layered so that the coil/commutator disc  62  is the topmost layer. 
     The coil/commutator disc  62  has an annular commutator region  80  on the top surface. A conductor pattern forms a commutator  81  in the commutator region  80 . The commutator  81  consists of multiple commutator segments arranged in the circumferential direction. A through-hole  83  running through the coil/commutator disc  62  is formed at the outer end of each commutator segment  82 . 
     The coil/commutator disc  62  and coil discs  63  each have, on their top surfaces, an annular coil region  90  situated outside the commutator region  80 . Nearly the same conductor pattern forms multiple coil segments  92  arranged in the circumferential direction around the output axis  52  in each coil region  90 . Multiple coil segments  92  are arranged radially about the output axis  52 . The coil segments  92  formed in each coil region  90  generate a vertical magnetic field. The coil segments  92  constitute one or more coils. The coil/commutator disc  62  and coil discs  63  are layered in a given arrangement, for example, in the manner that the coil segments  92  formed in each coil region  90  are provided at equal intervals in the circumferential direction. 
     One end and the other end of the coil segments  92  formed in the coil region  90  of the coil/commutator disc  62  are directly connected to the corresponding commutator segment  82  formed in the commutator region  80  by a conductor pattern. Furthermore, one end and the other end of the each coil segment formed in the coil regions  90  of the coil discs  63  are connected to the corresponding commutator segment  82  formed in the commutator region  80  via fitting holes or vias formed in the commutator region  80 . The outer end of each coil segment  92  is bent in a given direction about the output axis  52 . Multiple through-holes  93  running through the coil/commutator disc  62  are formed at the outer end of each coil segment  92 . 
     The conductor patterns in the commutator region  80  and coil region  90  of the coil/commutator disc  62  are formed on the same printed wiring. Furthermore, the conductive patterns on the coil/commutator disc  62  are thicker than the conductor pattern on the coil discs  63 . 
     The coil/commutator disc  62  and coil discs  63  have nearly the same inner diameter and outer diameter. Fitted on the fixture  611  of the flange  61  and supported by the top surface of the support member  612  of the flange  61 , the coil/commutator disc  62  and coil discs  63  are fixed to the flange  61 . 
     The rotor yoke  67  is an annular iron sheet member and secured to the top surface of the coil/commutator disc  62  via a not-shown insulating layer. The rotor yoke  67  has nearly the same outer diameter as the coil/commutator disc  62  and coil discs  63  and an inner diameter to cover the coil region  90 . 
     The fan  68  is an annular synthetic resin member, fitted on the outer peripheries of the rotor yoke  67 , coil/commutator disc  62 , and coil discs  63 , and secured to the top surface of the rotor yoke  67  via a not-shown adhesive layer. The fan  68  has multiple blades  681  protruding in the direction of the outer diameter. The multiple blades  681  are arranged at nearly equal intervals in the circumferential direction as shown in  FIG. 4 . 
     In order to correct any imbalance of the rotor  53  (unbalanced weight with respect to the rotation axis), a hole  671  is made in the top surface of the rotor yoke  67  as shown in  FIG. 2 . Here, a weight can be added to the top surface of the rotor yoke  67  in order to correct any imbalance of the rotor  53 . 
     The stator  54  includes a magnet  71  and a stator yoke  72 . The magnet  71  has an annular shape with magnet poles arranged in the circumferential direction. The magnet  71  faces the bottommost coil disc  63  and faces the coil regions  90  of the coil/commutator disc  62  and coil discs  63 , and is secured to the stator yoke  72 . The stator yoke  72  has an annular shape having nearly the same inner diameter and outer diameter as the magnet  71  and is fixed to the motor housing  51 . The magnet  71  generates a magnetic flax passing in the axial direction of the output shaft through the coil/commuter disc  62  and the coil disc  63 . 
     Abutting against two commutator segments  82  formed in the commutator region  80  of the coil/commutator disc  62 , two sliders  55  are held on two slider holders  59  fixed to the motor housing  51 . The sliders  55  are made of electrically conductive carbon and connected to the power circuit  12  of the above-described power source part  10  via the power cable  39  inserted in the coupling part  30 . 
     The voltage applied to the sliders  55  from the power circuit  12  of the power source part  10  is applied to the one or more coils of the rotor  53  in sequence via the commutator of the rotor  53 . Then, the attraction between the excited one or more coils and the magnet  71  of the stator  54  generates torque on the rotor  53  and the output shaft  52  fixed to the rotor  53 , rotating the rotary blade  42 . 
     The power circuit  12  will be described hereafter with reference to  FIGS. 5 and 6 . In the following explanation, the term ‘connection’ means ‘electric connection’, ‘high signals’ are signals having a voltage value higher than a given threshold, and ‘low signals’ are signals having a voltage value lower than the given threshold. The thresholds for high signals (low signals) can be all the same or different. For example, threshold for power switch control signals, threshold for voltage lowering signals, and the like may be the same or different. 
     The power circuit  12  comprises a power switch part  101 , a voltage detection part  102 , a voltage conversion part  103 , a voltage control part  104 , a current detection part  105 , a control power source part  106 , a switch state detection part  107 , a control part  108 , a temperature detection part  109 , a current amplifying part  110 , and a switch  113 . The power circuit  12  further comprises input terminals I 1 , I 2 , and I 3 . 
     The battery  2  may be a power source supplying a given direct current power. Here, the battery  2  is a battery pack. The battery  2  comprises multiple unit cells  2   a , a protection circuit  2   b , an overcurrent detection resistor  2   c , a positive terminal (+), a negative terminal (−), and a control signal output terminal (LD). 
     The multiple unit cells  2   a  are series-connected. Here, the unit cells  2   a  are lithium ion batteries. The positive end of the series-connected multiple unit cells  2   a  is connected to the positive terminal (+). The negative end thereof is connected to one end of the overcurrent detection resistor  2   c . The other end of the overcurrent detection resistor  2   c  is connected to the negative terminal (−). The overcurrent detection resistor  2   c  is used to detect the current from the unit cells  2   a  (the battery  2 ) (flowing through the battery  2 ). 
     The protection circuit  2   b  is connected to the unit cells  2   a  and overcurrent detection resistor  2   c  to detect the voltage of the unit cells  2   a  and detect the current from the unit cells  2   a  by means of the overcurrent detection resistor  2   c . The protection circuit  2   b  is also connected to the control signal output terminal (LD). The protection circuit  2   b  determines whether, for example, the detected voltage of the unit cells  2   a  or the detected current from the unit cells  2   a  is abnormal and, if abnormal, outputs control signals (battery overdischarge/overcurrent signals) to the outside of the battery  2  via the control signal output terminal (LD). Here, the control signals are low signals output when at least one of overdischarge and overcurrent occurs. For example, the protection circuit  2   b  short-circuits between the control signal output terminal (LD) and negative terminal (−) to generate and output such signals. 
     As the battery  2  is attached to the power source part  10 , the positive terminal (+) is connected to the input terminal I 1  and the negative terminal (−) is connected to the input terminal I 2 . Then, the battery  2  is ready for supplying electric power to the power circuit  12 . Furthermore, the control signal output terminal (LD) is connected to the input terminal I 3 . The input terminal I 3  is connected to the power switch part  101 . The battery overdischarge/overcurrent signals are supplied to the power switch part  101 . 
     Each element of the power circuit  12  is, connected, as appropriate, to a line, such as, a positive terminal line L 1  or a negative terminal line L 2  of the power circuit  12 , or provided at a point on one of these lines. The positive terminal line L 1  is a line to connect to the positive terminal (+) of the battery  2  via the input terminal I 1 . The negative terminal line L 2  is a line to connect to the negative terminal (−) of the battery  2  via the input terminal I 2 . The battery  2  and motor  50  are connected to the positive terminal and negative terminal lines L 1  and L 2 , whereby electric power is supplied from the battery  2  to the motor  50 . 
     The switch  113  is provided at a point on the positive terminal line L 1  between the input terminal I 1  and power switch part  101 . The switch  113  is turned on when the trigger lever  22  is pulled and turned off when the trigger lever  22  is returned to the original state. When the switch  113  is turned on, electric power is supplied to the power circuit  12  from the battery  2 . 
     When the switch  113  is turned on, electric power is supplied to the control power source part  106  from the battery  2 . The control power source part  106  serves as a constant voltage power source circuit outputting a given constant voltage Vcc (here, 5 V) to given elements of the power circuit  12  (such as the control part  108 , power switch part  101 , and current detection part  105 ) by the electric power supplied from the battery  2 . Here, the constant voltage Vcc is also applied to elements such as a comparator  105   b . The lines for applying the constant voltage Vcc to the power switch part  101 , current detection part  105 , and the like (control power source lines) have a known structure and they are omitted in  FIGS. 5 and 6  as appropriate. The elements to which the constant voltage Vcc is applied operate as they receive the constant voltage Vcc. 
     The control power source part  106  comprises a control power circuit  106   a  and capacitors  106   b  and  106   c.    
     The control power circuit  106   a  is provided at a point on the positive terminal line L 1  and connected to the negative terminal line L 2 . The control power circuit  106   a  is further connected to the control part  108  (power source part  108   e ). An output voltage, namely the voltage output from the battery  2  is applied to the control power circuit  106   a  when the switch  113  is turned on. The control power circuit  106   a  converts this voltage to the above constant voltage Vcc and outputs it to given elements of the power circuit  12  (see the above) including the control part  108  (power source part  108   e ). 
     The capacitors  106   b  and  106   c  are each connected to the control power circuit  106   a  at one end and to the negative terminal line L 2  at the other end. The capacitors  106   b  and  106   c  are used to smooth the above voltage applied to the control power circuit  106   a  and the constant voltage Vcc output from the control power circuit  106   a , respectively. 
     The switch state detection part  107  detects the ON state of the switch  113 . When the switch  113  is ON, electric power is supplied from the battery  2 . Based on this electric power supply, the switch state detection part  107  outputs control signals (switch state detection signals) in accordance with the ON state of the switch  113  to the control part  108 . In this way, the switch state detection part  107  detects the ON state of the switch  113 . 
     The switch state detection part  107  comprises resistors  107   a ,  107   b , and  107   c  and a FET (field effect transistor)  107   d.    
     The resistor  107   a  is connected to the positive terminal line L 1  at one end and to the resistor  107   b  and gate of the FET  107   d  at the other end. The resistor  107   b  is connected to the resistor  107   a  and gate electrode of the FET  107   d  at one end and to the negative terminal line L 2  at the other end. The resistor  107   c  is connected to the positive terminal line L 1  at one end and to the drain of the FET  107   d  via a node N 1  at the other end. The resistor  107   c  and FET  107   d  are series-connected. The source of the FET  107   d  is connected to the negative terminal line L 2 . Here, the FET  107   d  is an n-channel type power MOSFET (power insulated gate field effect transistor). The node N 1  is connected to the control part  108 . 
     When the switch  113  is turned on, the constant voltage Vcc is applied to the series-connected resistors  107   c  and FET  107   d . On the other hand, when the switch  113  is turned on, electric power is supplied from the battery  2  and a given voltage is applied to the series-connected resistors  107   a  and  107   b . This voltage is divided between the resistors  107   a  and  107   b . A divided voltage is applied between the source and gate of the FET  107   d . Then, the FET  107   d  is turned on and a current flows between the source and drain. Consequently, of the series-connected resistors  107   c  and FET  107   d , the potential difference between the source and drain is diminished and low signals which are control signals (switch state detection signals) are output from the node N 1  to the control part  108  (input port  108   a ). 
     The temperature detection part  109  is a part for measuring the temperature of a given site of the electric operation machine  1 . The temperature detection part  109  outputs electric signals (temperature signals) in accordance with the temperature of the given site to the control part  108 . 
     The temperature detection part  109  comprises a resistor  109   a  and a temperature-sensitive element  109   b.    
     The resistor  109   a  is connected to a power line applying the constant voltage Vcc at one end and to one end of the temperature-sensitive element  109   b  via a node N 2  at the other end. The other end of the temperature-sensitive element  109   b  is connected to the negative terminal line L 2 . The temperature-sensitive element  109   b  is an element actually used for detecting the temperature and provided in contact with or near the given site of which the temperature is to be detected. Heated by the temperature of the given site, the temperature-sensitive element  109   b  has the resistance changed. Here, the temperature-sensitive element  109   b  is a thermistor. 
     The resistor  109   a  and temperature-sensitive element  109   b  are series-connected and the constant voltage Vcc is applied to them. The constant voltage Vcc is divided between the resistor  109   a  and temperature-sensitive element  109   b . Consequently, electric signals having a voltage value divided between the resistor  109   a  and temperature-sensitive element  109   b  (temperature signals) are supplied to the control part  108  (A/D (analog/digital) converter  108   c ) from the node N 2 . The temperature-sensitive element  109   b  has the resistance changed according to the temperature. The voltage value of the temperature signals changes according to the temperature. The temperature of the given site is detected by measuring this voltage value. 
     The power switch part  101  is formed at a point on the positive terminal line L 1  and a point on the negative terminal line L 2 . More specifically, it is provided between the battery  2  and voltage conversion part  103  and after the switch  133  when seen from the battery  2 . 
     The power switch part  101  is controlled by control signals (power switch control signals) supplied from the control part  108 , which will be described later. Supplied with the power control switch signals, the power switch part  101  makes the positive terminal line L 1  conductive, whereby electric power is supplied to the motor  50  from the battery  2 . 
     Furthermore, the power switch part  101  is supplied with battery overdischarge/overcurrent signals from the battery  2 . When supplied with the battery overdischarge/overcurrent signals, the power switch part  101  makes the positive terminal line L 1  nonconductive, whereby electric power supply to the motor  50  is stopped. In this way, when the battery  2  undergoes overdischarge/overcurrent, electric power supply to the motor  50  is stopped and the entire power circuit  12  is protected. The battery  2  is also protected. 
     The power switch part  101  comprises a FET  101   a , registers  101   b  and  101   c , and a FET  101   b . The FET  101   a  is a p-channel type power MOSFET and the FET  101   b  is an n-channel type power MOSFET. 
     The FET  101   a  is provided at a point on the positive terminal line L 1  and its source and drain are connected to the positive terminal line L 1  in the manner that the source is closer to the switch  113 . The resistor  101   b  is connected to the gate and source of the FET  101   a . The gate of the FET  101   a  is further connected to one end of the resistor  101   c . The other end of the resistor  101   c  is connected to the drain of the FET  101   d . The source of the FET  101   d  is connected to the negative terminal line L 2 . The gate of the FET  101   d  is connected to the control part  108  and input terminal I 3 . 
     The FET  101   d  is turned on when the power switch control signals (here, they are high signals) are supplied from the control part  108  (output port  108   b ) to the gate of the FET  101   d . Consequently, a current flows between the source and drain of the FET  101   d . As a current flows, the gate of the FET  101   a  is connected to the negative terminal line L 2  and low signals are supplied to the gate of the FET  101   a , whereby the FET  101   a  is turned on. Consequently, the positive terminal line L 1  becomes conductive and electric power supply to the motor  50  starts. 
     The FET  101   d  is turned off when battery overdischarge/overcurrent signals (low signals) are supplied from the battery  2  to the gate of the FET  101   d . Consequently, no current flows between the source and drain of the FET  101   d  and no low signals are supplied to the gate of the FET  101   a , whereby the FET  101   a  is turned off. Consequently, the positive terminal line L 1  becomes nonconductive and electric power supply to the motor  50  is stopped, whereby the entire power circuit  12  is protected. 
     The voltage conversion part  103  receives an input voltage in accordance with the voltage output from the battery  2  (the output voltage from the battery  2 ), converts the received input voltage to generate a given voltage (the output voltage from the voltage conversion part  103 ), and outputs the generated output voltage to the motor  50  in a successive manner. Here, the voltage conversion part  103  receives the output voltage of the battery  2  as the input voltage. Here, the voltage conversion part  103  is a booster circuit boosting the output voltage of the battery  2  to an output voltage having a given voltage value. The voltage conversion part  103  is provided between the motor  50  and power switch part  101  (more specifically, between the voltage detection part  102  and voltage control part  104 ) and situated at a point on the positive terminal line L 1  and at a point on the negative terminal line L 2 . The voltage conversion part  103  is, for example, a flyback booster circuit. 
     The voltage conversion part  103  increase/decreases (the degree of change in the voltage value is preset) or maintain the voltage value of the output voltage being generated according to control signals (voltage detection signals that will be described in detail later; the second signal) supplied from the voltage control part  104  so as to generate and output an output voltage having a target voltage value. Furthermore, the voltage conversion part  103  is supplied with control signals (voltage lowering signals that will be described in detail later) from the current detection part  105  or voltage detection part  102 . Supplied with the voltage lowering signals, the voltage conversion part  103  decreases the voltage value of new output voltage being generated (the degree of change in the voltage value is preset; this degree can be the same as the above degree). In other words, the new output voltage being generated has a lowered voltage value. When supplied with the voltage lowering signals, the voltage conversion part  103  gives them priority over the voltage detection signals and generates a new voltage having a decreased voltage value. 
     The voltage conversion part  103  comprises, for example, a switching IC (integrated circuit)  103   a , a FET  103   b , a choke coil  103   c , a diode  103   d , and capacitors  103   e  and  103   f.    
     The capacitor  103   f  is provided on the input side in the voltage conversion part  103  and connected to the positive terminal line L 1  at one end and to the negative terminal line L 2  at the other end. The capacitor  103   f  smoothes the input voltage applied to the voltage conversion part  103 . 
     The switching IC  103   a  is connected to the positive terminal line L 1 , negative terminal line L 2 , FET  103   b , voltage detection part  102 , voltage control part  104 , and current detection part  105 . The source and drain of the FET  103   b  are connected to the negative terminal line L 2  and positive terminal line L 1 , respectively. The choke coil  103   c  is provided at a point on the positive terminal line L 1 . The diode  103   d  is provided at a point on the positive terminal line L 2  and connected to the choke coil  103   c  and drain of the FET  103   e  at one end. 
     The switching IC  103   a  is connected to the gate of the FET  103   b . The switching IC  103   a  supplies high signals or low signals to this gate terminal and turns on/off of the FET  103   b.    
     Here, the FET  103   b  is an n-channel type power MOSFET. When high signals are supplied to the gate of the FET  103   b , the FET  103   b  is turned on, whereby a current flows between the source and drain of the FET  103   b . When low signals are supplied to the gate of the FET  103   b , the FET  103   b  is turned off, whereby no current flows between the source and drain of the FET  103   b.    
     The choke coil  103   c  yields flyback effect as the FET  103   b  is turned on/off. By the flyback effect occurrence, the voltage between the terminals of the choke coil  103   c  is boosted. Consequently, the input voltage of the voltage conversion part  103  is converted (here, boosted) to generate and output a voltage of a given voltage value. In other words, with the switching IC  103   a  repeatedly turning on/off the FET  103   b , the voltage conversion part  103  boosts the received input voltage by means of flyback effect of the choke coil  103   c . Here, as the on/off switching duty ratio (one ON period (t)/one ON plus OFF period (T)) of the FET  103   b  is increased, the boosting amplitude of the input voltage is increased and the output voltage of the voltage conversion part  103  is increased. 
     The diode  103   d  rectifies the voltage boosted by the choke coil  103   c.    
     The switching IC  103   a  switches the signals supplied to the gate of the FET  103   b  between high signals and low signals at a frequency corresponding to the voltage value of voltage detection signals supplied from the voltage control part  104 . Here, the switching IC  103   a  compares the voltage value of the voltage detection signals to a given value (a preset value, which is termed ‘the set value’ hereafter), and switches the signals supplied to the gate of the FET  103   b  between high signals and low signals at a frequency corresponding to the comparative result. 
     For example, when the voltage detection signals have a voltage value lower than the set value, the switching IC  103   a  increases the signal duty ratio (the High period (t)/the period (T)) of high and low signals supplied to the FET  103   b  so as to increase the on/off switching duty ratio of the FET  103   b . When the voltage detection signals have a voltage value higher than the set value, the switching IC  103   a  decreases the signal duty ratio of signals supplied to the FET  103   b  so as to decrease the on/off switching duty ratio of the FET  103   b . When the voltage detection signals have a voltage value equal to the set value, the switching IC  103   a  maintains the signal duty ratio of signals supplied to the FET  103   b  so as to maintain the on/off switching duty ratio of the FET  103   b.    
     The voltage detection signals are signals having a voltage value in accordance with the voltage value of the output voltage from the voltage conversion part  103 . When the voltage detection signals have a voltage value lower than the set value, the voltage value of the output voltage from the voltage conversion part  103  is lower than a target voltage value. In such a case, the switching IC  103   a  increases the on/off switching duty ratio of the FET  103   b  so as to approximate the voltage value of new output voltage being generated (the output voltage from the voltage conversion part  103 ) to the target voltage value. On the other hand, when the voltage detection signals have a voltage value higher than the set value, the voltage value of the output voltage from the voltage conversion part  103  is higher than the target voltage value. In such a case, the switching IC  103   a  decreases the on/off switching duty ratio of the FET  103   b  so as to approximate the voltage value of new output voltage being generated to the target voltage value. Furthermore, when the voltage detection signals have a voltage value equal to the set value, the voltage value of the output voltage from the voltage conversion part  103  is equal to the target voltage value. In such a case, the switching IC  103   a  maintains the on/off switching duty ratio of the FET  103   b  so as to maintain the voltage value of new output voltage being generated. 
     The capacitor  103   e  is provided on the output side in the voltage conversion part  103  and connected to the positive terminal line L 1  at one end and to the negative terminal line L 2  at the other end. The capacitor  103   e  smoothes the output voltage output from the voltage conversion part  103 . 
     Here, with the above structure, the voltage conversion part  103  repeatedly converts (boosts) the input voltage by means of flyback effect and outputs the converted output signals in a successive manner. Furthermore, the voltage conversion part  103  increases/decreases or maintains the on/off switching duty ratio of the FET  103   b  in accordance with the voltage value of the voltage detection signals. Repeating such operation successively, the voltage conversion part  103  changes or maintains the degree to which the input voltage is converted (the difference between the input voltage and output voltage of the voltage conversion part  103 , which is termed ‘the degree of conversion’ hereafter) so as to generate an output voltage having a target voltage value based on the input voltage. The degree of change in the duty ratio is preset. 
     The switching IC  103   a  is further supplied with voltage lowering signals from the voltage detection part  102  or current detection part  105 . The voltage lowering signals have a voltage value higher than the above set value. Therefore, supplied with the voltage lowering signals, the switching IC  103   a  reduces the on/off switching speed of the FET  103   b  to lower the voltage value (the degree of conversion) of new output voltage being generated by the voltage conversion part  103 . Furthermore, the voltage value of the voltage lowering signals is sufficiently higher than the voltage value of the voltage detection signals. Therefore, even if the voltage lowering signals and voltage detection signals are simultaneously supplied to the switching IC  103   a , the voltage detection signals are invalidated due to the voltage lowering signals (the control of the voltage control part  104  is invalidated) and the switching IC  103   a  lowers the voltage value of the new output voltage being generated according to the voltage lowering signals. 
     Here, with the above structure, supplied with voltage lowering signals, the voltage conversion part  103  decreases the on/off switching duty ratio of the FET  103   b  to lower the voltage value of the output voltage being generated after the voltage lowering signals are supplied. The degree of change in the duty ratio is preset (the degree of change can be the same as the above degree of change). 
     Since the voltage conversion part  103   a  converts the output voltage of the battery  2  to generate a given voltage as described above, the electric operating machine  1  allows a battery having a different voltage or capacitance to be used for the power source part  10 . 
     The voltage control part  104  is provided after the voltage conversion part  103  when seen from the battery  2  and provides feedback on the voltage detection signals having a voltage value in accordance with the output voltage of the voltage conversion part  103  to the voltage conversion part  103 . The voltage control part  104  is connected to the positive terminal and negative terminal lines L 1  and L 2 . Furthermore, the voltage control part  104  is connected to the control part  108 . Supplied with temperature detection signals from the control part  108 , the voltage control part  104  mandatorily increases the voltage value of feedback voltage detection signals. Consequently, the voltage value of the output voltage of the voltage conversion part  103  tends to be decreased in comparison with before the temperature detection signals are supplied. When, for example, the voltage value of the output voltage is equal to a target voltage value, the voltage value of the output voltage of the voltage conversion part  103  is lower after the temperature detection signals are supplied than before the temperature detection signals are supplied. 
     The voltage control part  104  comprises resistors  104   a ,  104   b , and  104   c  and a FET  194   d . A node N 3  connecting the resistors  104   a  and  104   b  is connected to the switching IC  103   a . The voltage detection signals are output from the node N 3 . 
     The resistors  104   a ,  104   b , and  104   c  are series-connected between the positive terminal and negative terminal lines L 1  and L 2 . One end of the resistor  104   a  is connected to the positive terminal line L 1 . The source and drain of the FET  104   d  are connected to the negative terminal line L 2  and one end of the resistor  104   c , respectively. The gate of the FET  104   d  is connected to the control part  108  (output port  108   d ). The other end of the resistor  104   c  is connected to the negative terminal line L 2 . Here, the FET  104   d  is an n-channel type MOSFET. 
     The gate of the FET  104   d  is normally supplied with high signals from the control part  108  (output port  108   d ). Then, a current flows between the source and drain of the FET  104   d . Then, the voltage value of the voltage detection signals is a value resulting from dividing the voltage value of the output voltage of the voltage conversion part  103  between the resistors  104   a  and  104   b.    
     On the other hand, when the temperature detection signals (low signals) are supplied to the gate of the FET  104   d , no current flows between the source and drain of the FET  104   d . Then, the voltage value of the voltage detection signals is a value resulting from dividing the voltage value of the output voltage of the voltage conversion part  103  between the resistor  104   a  and the resistors  104   b , and  104   c . In other words, the voltage detection signals have a different voltage value depending on whether the temperature detection signals (low signals) are supplied or not, for the output voltage of the same voltage value. More specifically, when the temperature detection signals (low signals) are supplied, the voltage value of the voltage detection signals is increased. Therefore, the voltage value of the voltage detection signals tends to exceed the set value and the output voltage of the voltage conversion part  103  tends to be lowered. Then, when, for example, the voltage value of the output voltage is equal to a target voltage value, the voltage value of the voltage detection signals exceeds the set value and the output voltage of the voltage conversion part  103  becomes lower than before the temperature detection signals are supplied. 
     The voltage detection part  102  is provided between the power switch part  101  and voltage conversion part  103  and connected to the positive terminal line L 1 , negative terminal line L 2 , and voltage conversion part  103  (switching IC  103   a ). The voltage detection part  102  detects the output voltage of the battery  2  (the battery voltage) and, when the detected voltage value of the output voltage no longer satisfies a criterion A (for example, not higher than a threshold A), supplies to the voltage conversion part  103  voltage lowering signals (the first signal) that are signals for lowering the output voltage of the voltage conversion part  103 . 
     The voltage detection part  102  comprises resistors  102   a ,  102   b ,  102   c , and  102   d , a comparator  102   e , and a diode  102   f.    
     The resistors  102   a  and  102   b  are series-connected. The resistor  102   a  is connected to the positive terminal line L 1  at one end and to the minus terminal (−) of the comparator  102   e  and one end of the resistor  102   b  via a node N 4  at the other end. The other end of the resistor  102   b  is connected to the negative terminal line L 2 . 
     The resistors  102   c  and  102   d  are series-connected. The resistor  102   c  is connected to a power line applying the constant voltage Vcc at one end and to the plus terminal (+) of the comparator  102   e  and one end of the resistor  102   d  via a node N 5  at the other end. The other end of the resistor  102   d  is connected to the negative terminal line L 2 . 
     The output terminal of the comparator  102   e  is connected to the diode  102   f  and the diode  102   f  is connected to the voltage conversion part  103  (switching IC  103   a ). 
     The voltage between the positive terminal and negative terminal lines L 1  and L 2  (the voltage applied by the battery  2 , namely the battery voltage) is divided between the resistors  102   a  and  102   b . Signals having a divided voltage value are supplied to the minus terminal (−) of the comparator  102   e  from the node N 4 . The constant voltage Vcc is divided between the resistors  102   c  and  102   d . Signals having the divided voltage value are supplied to the plus terminal (+) of the comparator  102   e  from the node N 5 . 
     The comparator  102   e  compares the voltage value of the signals supplied to the minus terminal (−) with the voltage value of the signals supplied to the plus terminal (+) and, when the voltage value of the signals supplied to the minus terminal (−) is lower than the voltage value of the signals supplied to the plus terminal (+), outputs voltage lowering signals (high signals) to the voltage conversion part  103  (switching IC  103   a ). In this comparison, the battery voltage is compared with a threshold A (a value in accordance with the voltage value of the signals supplied to the plus terminal (+)) to determine whether the battery voltage satisfies the criterion A. 
     The resistors  102   a  to  102   d  have such resistance values that the comparator  102   e  outputs high signals when the battery voltage is not higher than the threshold A. The threshold A is determined so that the current flowing from the battery  2  becomes excessively large when the magnitude (voltage value) of the battery voltage is not higher than the threshold A. The threshold A is preset. 
     The diode  102   f  rectifies the voltage lowering signals and prevents back-flow of a current from the output terminal of the comparator  102   e  to the comparator  102   e.    
     The current detection part  105  is provided at a point on the negative terminal line L 2  between the voltage conversion part  103  and motor  50  (more specifically, between the voltage control part  104  and motor  50 ) and connected to the voltage conversion part  103  (switching IC  103   a ). The current detection part  105  detects the current flowing through the motor  50  (the motor current) and, when the detected magnitude (the current value) of the motor current satisfies a criterion B (for example, higher than a threshold B), supplies to the voltage conversion part  103  (switching IC  103   a ) voltage lowering signals for lowing the output voltage of the voltage conversion part  103 . 
     Here, the voltage lowering signals are output before the battery overdischarge/overcurrent signals output from the battery  2 , for example, when the current flowing through the motor  50  increases in the no-load state. 
     The current detection part  105  comprises a diode  105   a , a comparator  105   b , and resistors  105   c ,  105   d ,  105   e ,  105   f , and  105   g.    
     The resistor  105   g  is provided at a point on the negative terminal line L 2  and connected to the motor at one end. The resistor  105   g  is used to detect a current flowing through the motor  50 . The one end of the resistor  105   g  is connected to one end of the resistor  105   c . The other end of the resistor  105   c  is connected to the plus terminal (+) of the comparator  105   b.    
     The resistors  105   f  and  105   e  are series-connected. The resistor  105   f  is connected to a power line applying the constant voltage Vcc at one end and to the minus terminal (−) of the comparator  105   b  and one end of the resistor  105   e  via a node N 6  at the other end. The other end of the resistor  105   e  is connected to the negative terminal line L 2 . 
     The output terminal of the comparator  105   b  is connected to the diode  105   a . The diode  105   a  is connected to the voltage conversion part  103  (switching IC  103   a ). 
     Signals having the voltage value between the both ends of the resistor  105   g  (the voltage value proportional to the current flowing through the resistor  105   g ) are supplied to the plus terminal of the comparator  105   b  via the resistor  105   c . The constant voltage Vcc is divided between the resistors  105   f  and  105   e . Signals having a divided voltage value are supplied to the minus terminal (−) of the comparator  105   b  from the node N 6 . 
     The comparator  105   b  compares the voltage value of the signals supplied to the minus terminal (−) with the voltage value of the signals supplied to the plus terminal (+) and, when the voltage value of the signals supplied to the plus terminal (+) is higher than the voltage value of the signals supplied to the minus terminal (−), outputs voltage lowering signals (high signals) to the voltage conversion part  103  (switching IC  103   a ). In this comparison, the motor current (the current flowing through the resistor  105   g ) is compared with a threshold B (a current value in accordance with the voltage value of the signals supplied to the plus terminal (+)) to determine whether the motor current satisfies the criterion B or not. 
     The resisters  105   c  to  105   g  have such resistance values that the comparator  105   b  outputs high signals when the motor current exceeds the threshold B. The threshold B is determined so that the motor current becomes excessively large when the magnitude (the current value) of the motor current exceeds the threshold B. The threshold B is preset. 
     The diode  105   a  rectifies the voltage lowering signals and prevents back-flow of a current from the output terminal of the comparator  105   b  to the comparator  105   b.    
     The current amplifying part  110  outputs to the control part  108  signals having a voltage value in accordance with the current value of the motor current as current detection signals. The current amplifying part  110  is connected to the current detection part  105 . 
     The current amplifying part  110  comprises an amplifier  110   a  and resistors  110   b ,  110   c , and  110   d.    
     The resistor  110   d  is connected to the one end of the resistor  105   g  that is closer to the motor  50  at one end and to the plus terminal (+) of the amplifier  110   a  at the other end. The resistor  110   c  is connected to the other end of the resistor  105   g  at one end and to the minus terminal (−) of the amplifier  110   a  at the other end. The resistor  110   b  is connected to the output terminal of the amplifier  110   a  at one end and to the minus terminal (−) of the amplifier  110   a  at the other end. Furthermore, the amplifier  110   a  is connected to the control part  108  (A/D converter  108   c ). 
     With the above structure, the amplifier  110   a  amplifies the voltage in accordance with the current value of the motor current (the potential difference between the both ends of the resistor  105   g ). The amplifier  110   a  outputs to the control part  108  (A/D converter  108   c ) signals having the amplified voltage value as current detection signals. 
     The control part  108  comprises a not-shown CPU (central processing unit), ROM (read only memory), RAM (random access memory), and the like. The ROM stores programs and data. According to the programs stored in the ROM, or using the data stored in the ROM, the CPU actually executes the processes to be executed by the control part  108 . The RAM serves as a main memory for the CPU. 
     The control part  108  further comprises an input port  108   a , an output port  108   b , an A/D converter  108   c , an output port  108   d , and a power source part  108   e.    
     With switch state detection signals being supplied to the input port  108   a , the control part  108  (CPU) starts supplying power switch control signals from the output port  108   b  to the power switch part  101  (FET  101   d ). Power supply to the motor  50  is started. 
     The power source part  108   e  is applied the constant voltage Vcc, whereby the power source part  108   e  operates. 
     The A/D converter  108   c  receives temperature signals and converts the received temperature signals to digital data (temperature data). The temperature data are data specifying the temperature detected by using the temperature detection part  109 , indicating a voltage value in accordance with the temperature (the voltage value of the temperature signals). The control part  108  (CPU) acquires the converted temperature data, whereby it is assumed that the control part  108  detects the temperature of the given site of the electric operating machine  1 . The control part  108  (CPU) compares the voltage value indicated by the temperature data with a threshold C and, when the voltage value is higher than the threshold C (when the temperature specified by the temperature data satisfies (is higher than) a criterion C), supplies temperature detection signals (low signals) from the output port  108   d  to the voltage control part  104  (the gate of the FET  104   d ). Consequently, the voltage value of the voltage detection signals output from the voltage control part  104  is increased and the output voltage of the voltage conversion part  103  tends to be lowered. Here, the control part  108  normally outputs high signals from the output port  108   d.    
     The A/D converter  108   c  receives current detection signals and converts the received current detection signals to digital data (current data). The current data are data specifying the current amplified by the current amplifier  110 , indicating the voltage value amplified by the current amplifier  110  (in other words, the amplified current value is indicated by this voltage value). The control part  108  (CPU) acquires the converted current data, whereby it is assumed that the control part  108  (CPU) detects the motor current. The control part  108  (CPU) compares the voltage value indicated by the current data with a threshold D and, when the voltage value is higher than the threshold D for a given period of time (when the motor current satisfies (is higher than) a criterion D for the given period of time), stops supply of the power switch control signals from the output port  108   b . In other words, the control part  108  supplies low signals from the output port  108   b  to the power switch part  101  (the gate of the FET  104   d ). Consequently, the power switch part  101  makes the positive terminal line L 1  nonconductive to stop electric power supply to the motor  50  as in the case of the battery overdischarge/overcurrent signals being supplied. Here, the criterion D can be the same criterion as the criterion B. 
     Operation of the power circuit  12  will be described hereafter with reference to  FIG. 7 . The power circuit  12  does not operate before the battery  2  is connected and the switch  113  is turned on (Step S 101 ; NO and Step S 102 ; OFF). When the battery  2  is connected to the power circuit  12  and the trigger lever  22  is pulled to turn on the switch  113  (Step S 101 ; YES and Step S 102 ; ON), the control power source part  106  generates a constant voltage Vcc and outputs it to the control part  108 , whereby the control part  108  starts operating (Step S 103 ). Furthermore, with switch state detection signals being supplied from the switch detection part  107  to the control part  108 , the control part  108  detects the switch state (ON state) (Step S 104 ). Detecting the ON state, the control part  108  supplies power switch control signals to the power switch part  101 . Then, the power switch part  101  makes the positive terminal line L 1  conductive to start electric power supply from the battery  2  to the motor  50 . 
     Once the electric power supply starts, the voltage conversion part  103  starts operating (Step S 106 ). After Step S 106 , the power circuit  12  performs the procedures of Step S 107  and other steps in parallel. 
     In Step S 107 , the voltage conversion part  103  continuously repeats conversion from input voltage to output voltage. Here, the voltage conversion part  103  repeatedly increases/decreases or maintains the voltage value of the output voltage in accordance with the voltage detection signals supplied from the voltage control part  104  so as to generate and output an output voltage having a target voltage value. This operation is repeated until the switch  113  is turned off or the power switch part  101  stops electric power supply to the motor  50 . Here, the power switch part  101  stops electric power supply to the motor  50  when supplied with the battery overdischarge/overcurrent signals form the battery  2 . 
     In Step S 108 , the current detection part  105  detects the motor current, constantly monitors the current value of the motor current for whether the value satisfies a criterion B (by the above comparison), and outputs the voltage lowering signals when the current value satisfies the criterion B. Supplied with the voltage lowering signals, the voltage conversion part  103  generates a voltage having a lowered voltage value lower than the voltage value of the output voltage generated before the voltage lowering signals are supplied (the extent to which the voltage value is lowered is preset). Here, the procedure of lowering the voltage value in Step S 108  has priority over the procedure in Step in S 107  as described above. This procedure results in reducing the current flowing from the voltage conversion part  103 . This procedure is repeated until the switch  113  is turned off or the power switch part  101  stops electric power supply to the motor  50 . 
     Furthermore, in Step S 109 , the voltage detection part  102  detects the battery voltage, constantly monitors the voltage value of the battery voltage for whether the voltage value satisfies a criterion A (by the above comparison), and outputs the voltage lowering signals when the voltage value no longer satisfies the criterion A. Supplied with the voltage lowering signals (here, signals having the same voltage value as the voltage lowering signals output from the current detection part  105 ), the voltage conversion part  103  makes the voltage value of the output voltage being generated after the voltage lowering signals are supplied lower than the voltage value of the output voltage generated before the voltage lowering signals are supplied (the extent to which the voltage value is lowered is preset). Here, the procedure of lowering the voltage value in Step S 109  has priority over the procedure in Step in S 107  as described above. This procedure is repeated until the switch  113  is turned off or the power switch part  101  stops electric power supply to the motor  50 . 
     Furthermore, in Step S 110 , the control part  108  detects the temperature of a given site of the electric operating machine  1  using the temperature detection part  109 , constantly monitors the detected temperature for whether the temperature satisfies a criterion C, and outputs temperature detection signals to the voltage control part  104  when the voltage value satisfies the criterion C. Supplied with the temperature detection signals, the voltage control part  104  increases the voltage value of the voltage detection signals to output. In this way, the output voltage of the voltage conversion part  103  tends to be lowered. This procedure is repeated until the switch  113  is turned off or the power switch part  101  stops electric power supply to the motor  50 . 
     In Step S 111 , the control part  108  detects the motor current based on the current data based on the current detection signals output from the current amplifying part  110 , monitors the motor current for whether the current satisfies a criterion D for a given period of time (see the above comparison), and, when the motor current satisfies the criterion D for the given period of time, controls the power switch part  101  to make the positive terminal line L 1  nonconductive so as to stop electric power supply to the motor  50 . Then, the power switch part  101  stops electric power supply to the motor  50 . 
     With the above exemplary structure, the power circuit  12  of this embodiment comprises the voltage conversion part  103  converting an input voltage entered in accordance with the battery voltage of the battery  2  to generate an output voltage and outputting the generated output voltage to the motor  50  in a successive manner and the current detection part  105  outputting voltage lowering signals in accordance with the current flowing through a given part of the power circuit  12  (here, the current flowing through the motor  50  (the motor current); in other words, the given part of the power circuit  12  is a wire within the power circuit  12  that is connected to the motor  50 ). Then, with the above exemplary structure, the voltage conversion part  103  lowers the voltage value of new output voltage being generated when the current detection part  105  outputs voltage lowering signals. 
     With the above structure, the voltage value of the output voltage of the voltage conversion part  103  can be lowered in accordance with the current flowing through the motor  50 , preventing the current flowing through the motor  50  from becoming large. Then, the chance that a large current flows through at least a part of the power circuit  12  and the motor  50  is eliminated or reduced. Therefore, the electric operating machine  1  of this embodiment is an electric operating machine having the motor  50  and power circuit  12  (here, particularly the motor  50 ) properly protected. Particularly, even if the motor  50  undergoes a high load, the chance that a large current flows is eliminated or reduced, whereby the electric operating machine  1  of this embodiment machine is an electric operating machine having the motor  50  and power circuit  12  properly protected. 
     Particularly, in the electric operating machine  1  of this embodiment, the rotary blade  42  is heavy and a large current tends to flow through the motor  50 . However, the voltage value of the output voltage has an upper limit and the rotation speed is limited. The rotation speed of the rotary blade  42  is gradually increased. Therefore, the effect of protecting the motor  50  is obtained. 
     Furthermore, the electric operating machine  1  of this embodiment is structured to receive control signals (battery overdischarge/overcurrent signals) indicating abnormal states of the battery  2  from the battery  2 , and stop electric power supply to the motor  50 . The threshold is determined so that when the current supplied to the motor  50  is increased, the voltage lowering signals are output from the current detection part  105  before the battery overdischarge/overcurrent signals are output from the battery  2 . Therefore, the chance that the motor  50  stops because of the overdischarge/overcurrent signals being output is eliminated or reduced. Furthermore, even if the current detection part  105  does not work due to failure or the like, outputting the battery overdischarge/overcurrent signals from the battery  2  will minimize the chance that a large current flows through the motor  50  and power circuit  12 . 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the current detection part  105  outputs voltage lowering signals when the magnitude of the current value of the current flowing through the motor  50  satisfies a criterion B. Then, the voltage value of the output voltage of the voltage conversion part  103  is lowered when the current flowing through the motor  50  is increased. Then, the chance that a large current flows is eliminated or reduced. 
     Here, it is supposed that the current detection part  105  is provided between the battery  2  and voltage conversion part  103  and only the current before the voltage conversion is monitored. If, for example, a battery having a large battery voltage is attached as the battery  2  so that the total output is large, a large current may flow through the motor  50  even though the current before the voltage conversion is small because the voltage output from the voltage conversion part  103  is constant. Therefore, in this embodiment, the current detection part  105  is provided between the voltage conversion part  103  and motor  50 . In this way, the current flowing through the motor  50  can precisely be detected without depending on the battery voltage, proper protection is available. 
     Particularly, the conductor patterns formed on the printed wiring boards of the motor  50  of this embodiment may cause problems such as melt due to heat depending on the thickness. The above structure can prevent such problems and improves the life-span of the motor  50 . 
     Furthermore, the motor  50  has a disc shape in which the magnetic flux passes through the printed wiring boards on which coil segments  92  are formed as described above in the axial direction. Then, a lightweight and large torque electric operating machine can be constituted. 
     Furthermore, in the electric operating machine  1  of this embodiment, the rotary blade  42  is directly connected to and driven by the output shaft  52  of the motor  50 ; in other words, the rotary blade  42  is directly driven via no gears or the like. Therefore, mechanical loss is reduced and noise is prevented because no gear sound occurs. When the motor  50  and rotary blade  42  are directly connected as in this case, the motor  50  is required to produce a large torque to start rotating the rotary blade  42  because the rotary blade  42  is heavy. For this reason, the current of the battery  2  may abruptly be increased. The power circuit  12  of this embodiment eliminates or reduces the chance that a large current flows through the motor  50 . Therefore, an electric operating machine  1  having a regulation part inhibiting an excessively large current from flowing through the battery  2  can be constituted. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, supplied with the voltage lowering signals, the voltage conversion part  103  lowers the voltage value of the output voltage generated by the voltage conversion part  103 . 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the power circuit  12  further comprises the voltage control part  104  outputting (doing feedback) signals having the voltage value in accordance with the output voltage output from the voltage conversion part  103  (the voltage detection signals) to the voltage conversion part  103  and, when no voltage lowering signals are supplied, the voltage conversion part  103  successively generates an output voltage having a voltage value in accordance with the voltage detection signals. With this structure, the output voltage of the voltage conversion part  103  become a target voltage (a voltage intended to apply to the motor  50  (the drive voltage of the motor  50 )) and stabilizes at the target voltage and the voltage conversion part  103  mandatorily lowers the output voltage when the voltage lowering signals are supplied, whereby the power circuit  12  is properly protected. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the power circuit  12  controls the power switch part  101  to stop electric power supply from the battery  2  to the motor  50  when the current value of the current flowing through the motor  50  satisfies a criterion D for a given period of time. Consequently, if a large current flows through the motor  50  for the given period of time (for example, the rotary blade  42  has caught something and a high load is applied to the motor  50 ), the supply of electric power to the motor  50  is stopped. Therefore, the chance that a large current flows through the motor  50  and at least a part of the power circuit  12  is eliminated or reduced. Then, the electric operating machine  1  of this embodiment is an electric operating machine having the motor  50  and power circuit  12  properly protected. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the power circuit  12  further comprises the voltage detection part  102  outputting voltage lowering signals in accordance with the battery voltage of the battery  2 . Furthermore, the voltage conversion part  103  changes (lowers) the voltage value of new output voltage being generated when the voltage detection part  102  outputs the voltage lowering signals. In this way, the voltage conversion part  103  changes (lowers) the voltage value of new output voltage being generated in accordance with the battery voltage. 
     As the battery voltage becomes low, the voltage conversion part  103  converts (boosts) the voltage at a higher amplitude and a large current may flow through the voltage conversion part  103  and the like. Particularly, a lithium ion battery exemplified as the battery  2  of this embodiment characteristically has a battery voltage largely fluctuating and tends to cause voltage drop during operation. With the above structure, the voltage value of the output voltage of the voltage conversion part  103  is lowered in accordance with the battery voltage of the battery  2 , preventing the current flowing through the voltage conversion part  103  and the like from becoming large. Then, the electric operation machine  1  of this embodiment is an electric operation machine having the power circuit  12  properly protected. Furthermore, with the voltage value of the output voltage of the voltage conversion part  103  being lowered, the output voltage of the battery  2  is restored. 
     Furthermore, the electric operation machine  1  of this embodiment allows batteries different in voltage or capacitance to be used for the power source part  10 , which is useful because the battery can be changed depending on workability or a battery in hand can be used. Furthermore, batteries significantly different in output voltage (for example, 14 V to 36 V) are available on the market. Even though such batteries significantly different in battery voltage are used (particularly, a battery with a low battery voltage is used), the voltage conversion part  103  does not bear a large workload. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the voltage detection part  102  outputs the voltage lowering signals when the magnitude of the voltage value of the battery voltage does not satisfy a given criterion. In this way, when the battery voltage becomes low, the voltage value of the output voltage of the voltage conversion part  103  is changed (lowered), preventing the current flowing through the voltage conversion part  103  and the like from becoming large. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the voltage conversion part  103  lowers the voltage value of the output voltage when the voltage lowering signals are supplied from the voltage detection part  102 . 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the voltage conversion part  103  generates an output voltage having a voltage value in accordance with the voltage detection signals output from the voltage control part  104  when no voltage lowering signals are supplied. With this structure, the voltage conversion part  103  mandatorily lowers the voltage value of the output voltage when the voltage lowering signals are supplied, properly preventing the power circuit  12 . 
     Furthermore, in the power circuit  12  of this embodiment, with the above exemplary structure, the power circuit  12  comprises the temperature detection part  109  for detecting the temperature of a given site of the electric operating machine  1  and the control part  108  detecting the temperature of the given site using the temperature detection part  109 . The control part  108  lowers the applied voltage applied to the motor  50  when the detected temperature using the temperature detection part  109  satisfies a criterion C. Consequently, the current value of the current flowing through the motor  50  is also lowered. 
     The given site is, for example, an circuit element of the power circuit  12  such as the FET  103   b  of the voltage conversion part  103  of the power circuit  12 . With the applied voltage applied to the motor  50  being lowered, the load on the circuit element (for example, the switching intervals of the FET  103   b ) is diminished, whereby the circuit element is less heated and the power circuit  12  is properly protected. 
     Furthermore, the given site can be, for example, the motor  50 . In such a case, with the applied voltage applied to the motor  50  being lowered, the current flowing through the motor (the current flowing through the power circuit  12 ) is diminished, reducing heat generation in the motor  50 , whereby the motor  50  is properly protected from heat. The power circuit  12  is also protected as appropriate. 
     With the above structure, the given site is protected from heat and the members of the electric operating machine  1  are properly protected. 
     In the power circuit  12  of this embodiment, the applied voltage is the output voltage generated by the voltage conversion part  103 . In this way, the applied voltage applied to the motor  50  can be lowered. 
     In the power circuit  12  of this embodiment, with the above exemplary structure, the control part  108  controls the voltage control part  104  so as to control the voltage value of the voltage detection signals output from the voltage control part  104  for lowering the applied voltage applied to the motor  50 . In this way, the applied voltage applied to the motor  50  can properly be lowered. 
     (Embodiment 2) 
     Embodiment 2 of the present invention will be described hereafter with reference to  FIGS. 8 and 9 . Embodiment 2 is different from Embodiment 1 in the power circuit. The power circuit  12  according to Embodiment 2 comprises a second current detection part  205  in addition to the structure of the power circuit  12  of Embodiment 1. The other structure of the power circuit  12  is the same as in Embodiment 1 and will not be described. The current detection part  105  is referred to as the first current detection part  105  but is the same in operation and structure. 
     The second current detection part  205  is provided at a point on the negative terminal line L 2  before the voltage conversion part  103  when seen from the battery  2  (more precisely, before the power switch part  101 ) and connected to the voltage conversion part  103  (switching IC  103   a ). The second current detection part  205  detects a current flowing between the battery  2  and voltage conversion part  103  (the battery current) and, when the magnitude (current value) of the detected battery current satisfies a criterion B (for example, higher than a threshold B), supplies to the voltage conversion part  103  (switching IC  103   a ) voltage lowering signals for lowering the output voltage of the voltage conversion part  103 . When supplied with the voltage lowering signals from the second current detection part  205 , the voltage conversion part  103  operates in the same manner as when it is supplied with the voltage lowering signals from the first current detection part  105 ; therefore, the explanation is omitted (see Embodiment 1). 
     The second current detection part  205  comprises a diode  205   a , a comparator  205   b , and resistors  205   c ,  205   d ,  205   e , and  205   f.    
     The resistor  205   f  is provided at a point on the negative terminal line L 2  and connected to the input terminal I 2  (the battery  2 ) at one end. The resistor  205   f  is used to detect the current flowing between the battery  2  and voltage conversion part  103 . The other end of the resistor  205   f  is connected to one end of the resistor  205   c . The other end of the resistor  205   c  is connected to the plus terminal (+) of the comparator  205   b.    
     The resistors  205   d  and  205   e  are series-connected. The resistor  205   e  is connected to a power line applying the constant voltage Vcc at one end and to the minus terminal (−) of the comparator  205   b  and one end of the resistor  205   d  via a node N 7  at the other end. The other end of the resistor  205   d  is connected to the negative terminal line L 2  and the other end of the resistor  205   f.    
     The output terminal of the comparator  205   b  is connected to the diode  205   a  and the diode  205   a  is connected to the voltage conversion part  103  (switching IC  103   a ). 
     Signals having the voltage value between the both ends of the resistor  205   f  (a voltage value proportional to the current flowing through the resistor  2050  are supplied to the plus terminal of the comparator  205   b  via the resistor  205   c . The constant voltage Vcc is divided between the resistors  105   e  and  105   d . The signals having a divided voltage value are supplied to the minus terminal (−) of the comparator  205   b  from the node N 7 . 
     The comparator  205   b  compares the voltage value of the signals supplied to the minus terminal (−) with the voltage value of the signals supplied to the plus terminal (+) and, when the voltage value of the signals supplied to the plus terminal (+) is higher than the voltage value of the signals supplied to the minus terminal (−), outputs voltage lowering signals (high signals) to the voltage conversion part  103  (switching IC  103   a ). In this comparison, the battery current (the current flowing through the resistor  205   f ) is compared with a threshold B (a current value in accordance with the voltage value of the signals supplied to the plus terminal (+)) to determine whether the battery current satisfies the criterion B or not. 
     The resistors  205   c  to  205   f  have such resistance values that the comparator  105   b  outputs high signals when the motor current exceeds the threshold B. The threshold B is determined so that the motor current becomes excessively large when the magnitude (the current value) of the motor current exceeds the threshold B. The threshold B is preset. The threshold and the above criterion can be different from the threshold B and criterion B. 
     The diode  205   a  rectifies the voltage lowering signals and prevents back-flow of a current from the output terminal of the comparator  205   b  to the comparator  205   b.    
     In the power circuit  12  of this embodiment, with the above exemplary structure, the second current detection part  205  outputting voltage lowering signals in accordance with the battery current is provided. Then, with the above exemplary structure, the voltage conversion part  103  lowers the voltage value of new output voltage being generated when the second current detection part  205  outputs the voltage lowering signals. 
     With the above structure, the voltage value of the output voltage of the voltage conversion part  103  is lowered in accordance with the current flowing between the battery  2  and voltage conversion part  103  (when the current value is large enough to satisfy the criterion B), preventing the current flowing between the battery  2  and voltage conversion part  103  from becoming large. In this way, the chance that a large current flows through at least a part of the power circuit  12  is eliminated or reduced. Then, the electric operation machine  1  of this embodiment will be an electric operating machine having the power circuit  12  and motor  50  (here, particularly the power circuit  12 ) properly protected. Particularly, double protection is provided by the first and second current detection part  105  and  205 . 
     (Embodiment 3) 
     Embodiment 3 of the present invention will be described hereafter with reference to  FIG. 10 . Embodiment 3 is different from Embodiment 1 in the voltage control part of the power circuit  12 . A voltage control part  304  according to Embodiment 3 comprises a capacitor  304   e  in addition to the structure of the voltage control part  104  according to Embodiment 1 and a resistor  304   b  consists of a variable resistor. The other structure of the power circuit  12  is the same as in Embodiment 1 and will not be described. 
     In this embodiment, the resistor  304   b  consists of a variable resistor. With the resistance value of the resistor  304   b  being changed, the voltage value of the voltage detection signals in accordance with the output from the voltage conversion part  103  can be changed. Therefore, the effect of changing the target value of the voltage conversion part  103  can be obtained. The resistor  104   b  can be operated from outside the power source housing  11  (not shown) and the operator can change the resistance value of the resistor  304   b  on an arbitrary basis. 
     The capacitor  104   e  mandatorily increases the voltage value of voltage detection signals for feedback upon start-up of the power switch part  101 . And then, the voltage value of the voltage detection signals are gradually shifted to the voltage value in accordance with the output voltage of the voltage conversion part  103 . With the above structure, the voltage applied to the motor  50  is gradually increased upon start-up of the power switch part  101 , whereby a so-called soft start mechanism (regulation part) can be constituted. 
     In the electric operation machine  1  of this embodiment, the output signals output from the voltage conversion part  103  are changed on an arbitrary basis, whereby a desired rotation speed can be obtained. For example, even if a cutter with a nylon cord is attached in place of the rotary blade  42  mounted on the electric operation machine  1  in this embodiment, a smooth operation is ensured. 
     Furthermore, although a large current tends to flow through the motor  50  when the rotary blade  42  is activated in the electric operation machine  1  of this embodiment, the soft start mechanism that works only at the start-up gradually increases the voltage applied to the motor  50 , inhibiting an excessively large current from flowing through the battery  2 . Consequently, the load on the motor  50  and power circuit  12  is further reduced and the battery  2  is protected at the start-up. 
     (Modification) 
     In the above embodiments, the electric operation machine is applied to an electric mowing machine having an electric motor (the motor  50 ). The present invention is applicable to any electric equipment and extensively applied to other operating machines using an electric motor. Particularly, the present invention is suitable for those in which the rotation of an electric motor is directly transferred to the working tool (rotary blade, fan, etc.) via no reduction gears such as sanders, polishers, routers, and dust collectors. In the motor  50 , the rotor  52  is exchangeable with the stator  54  in structure. That is, either one of the rotor  53  and the stator  54  comprises a disc-shaped coil substrate having multiple coil segments arranged in the circumferential direction about said output shaft when seen in the axial direction of said output shaft, and the other of said rotor and stator comprises a magnet generating a magnetic flux passing through said coil substrate in the axial direction of said output shaft. 
     Having described and illustrated the principles of this application by reference to preferred embodiments, it should be apparent that the preferred embodiments may be modified in arrangement and detail without departing from the principles disclosed herein and that it is intended that the application be construed as including all such modifications and variations insofar as they come within the spirit and scope of the subject matter disclosed herein. 
     This application claims the benefit of Japanese Patent Application JP2010-006326, filed Jan. 14, 2010, the entire disclosure of which is incorporated by reference herein.