JP5879712B2 - Electric tool - Google Patents

Description

  The present invention relates to a power tool.

  Conventionally, a rectifying circuit that rectifies an AC voltage, a smoothing capacitor that smoothes the rectified AC voltage into a DC voltage, and a switching operation to sequentially apply the smoothed DC voltage to a plurality of stator windings of a brushless motor. An electric tool provided with an inverter circuit for outputting is known (for example, see Patent Document 1).

Japanese Patent No. 4487836

  However, in the conventional electric tool as described above, a smoothing capacitor having a large capacity is used, so that the power factor of the AC power is deteriorated.

  Moreover, in order to improve a power factor, the structure which equips an electric tool with a power factor improvement circuit is also considered, However, When such a structure is used, the size of an electric tool will become large and cost will increase.

  Then, this invention aims at providing the electric tool which can improve a power factor, without providing a power factor improvement circuit.

In order to solve the above-described problems, the present invention includes a stator having a plurality of stator windings and a rotor rotatable with respect to the stator, and when the rotor rotates, induced induction according to the number of rotations of the rotor is achieved. A brushless motor for generating a voltage; a rectifying circuit for rectifying an AC voltage; a smoothing capacitor that uses the rectified AC voltage as a pulsating voltage that includes a ripple; and a voltage between terminals of the smoothing capacitor as the stator. An inverter circuit that performs a switching operation for sequentially switching the stator windings that are sequentially output to the windings and energized, an input unit that receives a drive instruction for the brushless motor by a user, and a control unit that controls the inverter circuit When, with a high than the induced electromotive force voltage between the terminals corresponding to the rotational speed of the smoothing capacitor in accordance with the variation of the rectified AC voltage A first section in which a current flows in the brushless motor by varying in a region; a second section in which the voltage between the terminals balances with an induced electromotive voltage according to the rotation speed and no current flows in the brushless motor; The capacitance of the smoothing capacitor is set so as to occur alternately, and the control unit is configured to both the first and second intervals while the drive instruction is input to the input unit. The electric power tool is characterized in that the inverter circuit is controlled so that the inverter circuit performs the switching operation, and the rectifier circuit and the smoothing capacitor are provided in a tool body . According to such a configuration, a smoothing capacitor having a small capacity can be used, so that it is possible to improve the power factor of AC power without providing a power factor correction circuit.

In order to solve the above problems, the present invention further includes a stator having a plurality of stator windings and a rotor rotatable with respect to the stator, and induction according to the number of rotations of the rotor when the rotor rotates. A brushless motor that generates an electromotive voltage, a rectifier circuit that rectifies an AC voltage, a smoothing capacitor that uses the rectified AC voltage as a pulsating voltage that includes a ripple, and a voltage between terminals of the smoothing capacitor that is fixed. An inverter circuit that performs a switching operation for sequentially switching the stator windings that are sequentially output to the child windings and energized, an input unit that receives a drive instruction for the brushless motor by a user, and a control that controls the inverter circuit A voltage between the terminals of the smoothing capacitor according to the rotational speed as the rectified AC voltage rises and falls. A first section in which the current flows to the brushless motor by rising and lowering in a higher region, and a second current stops flowing to the brushless motor in balance with the induced voltage according to the rotational speed. The capacitance of the smoothing capacitor is set such that the intervals of the first and second intervals occur alternately, and the control unit is configured to output the first interval and the second interval while the drive instruction is input to the input unit. the inverter circuit in both sections of the section controls the inverter circuit so as to perform the switching operation, the rectifier circuit and the smoothing capacitor is to provide a power tool, characterized in that provided in the tool body Yes. According to such a configuration, a smoothing capacitor having a small capacity can be used, so that it is possible to improve the power factor of AC power without providing a power factor correction circuit.

  The power tool according to the present invention includes an input unit to which a driving instruction for the brushless motor is input by a user, and a magnitude of the pulsating voltage while the driving instruction is input to the input unit. It is preferable to further include a control unit that controls the inverter circuit so as to continue the switching operation even in the following section.

  According to such a configuration, the switching operation is stopped in a section where the magnitude of the pulsation voltage is equal to or less than the induced electromotive voltage, and the energy accumulated in the stator winding is prevented from flowing backward toward the smoothing capacitor.

  In addition, when the current flowing through the motor exceeds an overcurrent threshold, the control unit is configured to stop the switching operation even while a drive instruction is input to the input unit. It is preferable to control the circuit.

  According to such a configuration, it is possible to prevent current from continuing to flow through the motor even when an overcurrent occurs.

  According to another aspect of the present invention, a brushless motor having a stator having a plurality of stator windings, a rotor rotatable with respect to the stator, and a tip tool driven by the brushless motor; And an electric tool capable of applying an AC voltage from an AC power source to the stator winding, wherein the AC voltage is reduced by performing a switching operation even when the AC voltage is equal to or lower than a predetermined voltage. An electric power tool is further provided, further comprising an inverter circuit for sequentially outputting to the stator winding.

  According to the electric tool of the present invention, it is possible to improve the power factor without providing a power factor correction circuit.

Circuit diagram of power tool according to embodiment Comparison of voltage waveforms including ripples A diagram for explaining the voltage output from the smoothing capacitor and the current flowing to the motor during normal operation Comparison of current paths according to the operation of the inverter circuit The figure explaining the voltage which is output from the smoothing capacitor at the time of abnormality and the current which flows through the motor

  Hereinafter, the electric tool 1 by embodiment of this invention is demonstrated with reference to FIGS.

  FIG. 1 is a circuit diagram of a power tool 1 according to the present embodiment. As shown in FIG. 1, the electric tool 1 includes a trigger switch (input unit) 3, a control circuit voltage supply circuit 4, a motor 5, a rotor position detection element 6, a control circuit 7, and an inverter circuit 8. , A normal mode filter 9, a rectifier circuit 10, and a smoothing capacitor 11. When the trigger switch 3 is operated, an AC voltage output from the commercial power supply 2 is rectified by the rectifier circuit 10 and the smoothing capacitor 11. Smoothed and supplied to the motor 5 through the inverter circuit 8. When the trigger switch 3 is operated, the AC voltage from the commercial power supply 2 is stepped down by the control circuit voltage supply circuit 4 and supplied to the control circuit 7 as a control circuit drive voltage.

  The motor 5 is a three-phase brushless DC motor, and includes a rotor 5A made of a permanent magnet including a plurality of sets (two sets in the present embodiment) N poles and S poles, and a star-connected three-phase stator winding. And a stator 5B composed of lines U, V, and W. The motor 5 (rotor 5A) rotates when the stator windings U, V, and W through which the current flows are sequentially switched. Switching of the stator windings U, V, and W will be described later.

  The rotor position detection element 6 is arranged at a predetermined interval (for example, every angle of 60 °) in the circumferential direction of the rotor 5A at a position facing the permanent magnet of the rotor 5A, and the rotation of the rotor (rotor 6A). A signal corresponding to the position is output.

  The control circuit 7 includes a motor current detection circuit 71, a rectified voltage detection circuit 72, a control circuit voltage detection circuit 73, a switch operation detection circuit 74, an applied voltage setting circuit 75, a rotor position detection circuit 76, a motor A rotation speed detection circuit 77, a calculation unit 78, a control signal output circuit 79, and an AC input voltage detection circuit 80 are provided.

  The AC input voltage detection circuit 80 detects the peak value of the AC voltage output from the commercial power supply 2 and outputs it to the computing unit 78. In the present embodiment, it is assumed that the AC voltage is detected in a sampling period in which a value sufficiently approximate to the actual peak value can be detected.

  The motor current detection circuit 71 detects the current supplied to the motor 5 and outputs it to the calculation unit 78. The rectified voltage detection circuit 72 detects the voltage output from the rectifier circuit 10 and the smoothing capacitor 11 and outputs the detected voltage to the calculation unit 78. The control circuit voltage detection circuit 73 detects the control circuit drive voltage supplied from the control circuit voltage supply circuit 4, and outputs it to the calculation unit 78. The switch operation detection circuit 74 detects the presence / absence of operation of the trigger switch 3 and outputs it to the calculation unit 78. The applied voltage setting circuit 75 detects the operation amount of the trigger switch 3 and outputs it to the calculation unit 78.

  The rotor position detection circuit 76 detects the rotation position of the rotor (rotor 6 </ b> A) based on the signal from the rotor position detection element 6, and outputs it to the motor rotation number detection circuit 77 and the calculation unit 78. The motor rotation speed detection circuit 77 detects the rotation speed of the rotor (rotor 6 </ b> A) based on the signal from the rotor position detection circuit 76 and outputs the rotation speed to the calculation unit 78.

  The calculation unit 78 generates switching signals H 1 to H 6 based on signals from the rotor position detection circuit 76 and the motor rotation number detection circuit 77 and outputs the switching signals H 1 to H 6 to the control signal output circuit 79. The calculation unit 78 adjusts the switching signals H <b> 4 to H <b> 6 as a pulse width modulation signal (PWM signal) based on the signal from the applied voltage setting circuit 75 and outputs it to the control signal output circuit 79. Switching signals H1-H6 are output to inverter circuit 8 via control signal output circuit 79. Note that the switching signal H1-H3 may be adjusted as a PWM signal.

  Inverter circuit 8 includes switching elements Q1-Q6. The gates of the switching elements Q1-Q6 are connected to the control signal output circuit 79, and the drains or sources of the switching elements Q1-Q6 are connected to the stator windings U, V, W of the stator 5B.

  Each of the switching elements Q1-Q6 performs a switching operation based on the switching signals H1-H6 input from the control signal output circuit 79, and converts the DC voltage of the battery pack 2 applied to the inverter circuit 8 into three phases (U phase, V Power is supplied to the stator windings U, V, and W as voltages Vu, Vv, and Vw.

  Specifically, switching signals H1-H6 are input to switching elements Q1-Q6, respectively, and thereby the energized stator windings U, V, W, that is, the rotation direction of rotor 5A is controlled. At that time, the amount of power supplied to the stator windings U, V, W is controlled by H4-H6 which is also a PWM signal.

  With the above configuration, the electric tool 1 can supply a drive voltage corresponding to the operation amount of the trigger switch 3 to the motor 5.

  By the way, in the conventional electric tool, since the thing with a large capacity | capacitance was used as the smoothing capacitor 11, the power factor of alternating current power was getting worse. Moreover, in order to improve a power factor, the structure which equips an electric tool with a power factor improvement circuit is also considered, However, When such a structure is used, the size of an electric tool will become large and cost will increase.

  Therefore, in the present embodiment, a smoothing capacitor 11 having a small capacity is used in order to improve the power factor. When the smoothing capacitor 11 has a small capacity, the AC voltage output from the rectifier circuit 10 is not completely smoothed, and a pulsating voltage including ripple is output from the smoothing capacitor 11. In the present embodiment, in particular, the smoothing capacitor 11 has a capacity that smoothes the alternating voltage output from the rectifier circuit 10 into a pulsating waveform having a minimum value smaller than the induced electromotive voltage generated in the motor 5. Use.

  FIG. 2 shows (a) a voltage waveform when the ripple is 100%, (b) a voltage waveform when the ripple is 50%, and (c) a voltage waveform when the ripple is 0%. The ripple ratio decreases as the capacity of the smoothing capacitor 11 increases. Therefore, the capacity of the smoothing capacitor 11 according to the present embodiment can be determined based on such a relationship and the induced electromotive voltage generated in the motor 5. Hereinafter, a case where a ripple voltage with 100% ripple is output from the smoothing capacitor 11 will be described.

  By the way, in order to drive the motor 5, it is necessary to supply a voltage larger than the induced electromotive voltage generated in the motor 5 to the motor 5. When the pulsating voltage is supplied to the motor 5, the pulsating voltage is required. In the section Y (FIG. 3) where the magnitude of is less than the induced electromotive voltage, the motor 5 cannot be driven. That is, as shown in FIG. 4 (a), in the section X where the magnitude of the pulsating voltage is equal to or greater than the induced electromotive voltage, the current flows in the electric tool 1, but as shown in FIG. In the section Y whose magnitude is less than the induced electromotive voltage, no current flows through the electric power tool 1.

  However, since the motor 5 is once driven in the section X, the motor 5 is also rotated by the inertia in the section Y. If the motor 5 is periodically driven in the section X, the motor 5 can continue to rotate. Therefore, in the electric power tool 1 according to the present embodiment, the smoothing capacitor 11 having a capacity capable of outputting a pulsation waveform having a minimum value smaller than the induced electromotive voltage generated in the motor 5 is used. It becomes possible to improve a power factor without providing.

  By the way, in the section Y in which the magnitude of the pulsation voltage is less than the induced electromotive voltage, control of stopping the operation of the inverter circuit 8 for energy saving can be considered.

  However, if the inverter circuit 8 is stopped in the section Y, the energy accumulated in the stator windings U, V, and W of the motor 5 is smoothed in the section Z (FIG. 5) immediately after the inverter circuit 8 is stopped. It flows backward toward the capacitor 11 (FIG. 4C). As a result, the voltage of the smoothing capacitor 11 rises rapidly, and damage to the capacitor 11 and deterioration of the quality are prevented.

  Therefore, in the present embodiment, control is performed so that the operation of the inverter circuit 8 is not stopped even in the section Y where the pulsation voltage is less than the induced electromotive voltage. As a result, the energy accumulated in the stator windings U, V, and W of the motor 5 flows back toward the smoothing capacitor 11 and the voltage of the smoothing capacitor 11 rises rapidly, preventing damage to the capacitor 11 and deterioration of quality. The

  The power tool of the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made within the scope described in the claims.

  For example, in the above embodiment, control is performed so that the operation of the inverter circuit 8 is not stopped even in the section Y in which the magnitude of the pulsation voltage is less than the induced electromotive voltage. However, the current detected by the motor current detection circuit 71 is the overcurrent threshold. May be controlled so that the inverter circuit 8 is stopped.

  In the above-described embodiment, the operation of the inverter circuit 8 is not stopped in the state where the smoothing capacitor 11 is provided. However, the effects of the present invention can also be achieved in other configurations. For example, if the operation of the inverter circuit 8 is not stopped in a state where the smoothing capacitor 11 is not provided, the energy accumulated in the stator windings U, V, and W of the motor 5 flows backward toward the smoothing capacitor 11 and the capacitor It is possible to suppress a sudden increase in the voltage of 11.

DESCRIPTION OF SYMBOLS 1 Electric tool 3 Trigger switch 3 Motor 7 Control circuit 8 Inverter circuit 10 Rectifier circuit 11 Smoothing capacitor 78 Calculation part

Claims (3)

A brushless motor having a stator having a plurality of stator windings, a rotor rotatable with respect to the stator, and generating an induced electromotive force according to the rotational speed of the rotor when the rotor rotates ;
A rectifier circuit for rectifying an alternating voltage;
A smoothing capacitor that uses the rectified AC voltage as a pulsating voltage that includes ripples ;
An inverter circuit that performs a switching operation for sequentially switching the stator winding to be energized by sequentially outputting the voltage between the terminals of the smoothing capacitor to the stator winding ;
An input unit for inputting an instruction to drive the brushless motor by a user;
A control unit for controlling the inverter circuit ,
A first section in which the voltage between the terminals of the smoothing capacitor fluctuates in a region higher than the induced electromotive voltage according to the rotation speed in accordance with the fluctuation of the rectified AC voltage, and a current flows through the brushless motor; The capacitance of the smoothing capacitor is set so that the second interval in which the voltage between the terminals balances with the induced electromotive voltage according to the rotation speed and no current flows in the brushless motor alternately occurs.
The control unit controls the inverter circuit so that the inverter circuit performs the switching operation in both the first section and the second section while the drive instruction is input to the input section. Control
The rectifier circuit and the smoothing capacitor are provided in a tool body . A brushless motor having a stator having a plurality of stator windings, a rotor rotatable with respect to the stator, and generating an induced electromotive force according to the rotational speed of the rotor when the rotor rotates;
A rectifier circuit for rectifying an alternating voltage;
A smoothing capacitor that uses the rectified AC voltage as a pulsating voltage that includes ripples;
An inverter circuit that performs a switching operation for sequentially switching the stator winding to be energized by sequentially outputting the voltage between the terminals of the smoothing capacitor to the stator winding;
An input unit for inputting a driving instruction of the brushless motor by a user;
A control unit for controlling the inverter circuit,
As the rectified AC voltage rises and falls, a first interval in which the voltage between the terminals of the smoothing capacitor rises and falls in a region higher than the induced electromotive voltage according to the rotation speed and current flows to the brushless motor; The capacitance of the smoothing capacitor is set so that the second interval in which the voltage between the terminals balances with the induced electromotive voltage according to the rotation speed and no current flows in the brushless motor alternately occurs.
The control unit controls the inverter circuit so that the inverter circuit performs the switching operation in both the first section and the second section while the drive instruction is input to the input section. Control
The rectifier circuit and the smoothing capacitor are provided in a tool body .   When the current flowing through the brushless motor exceeds an overcurrent threshold, the control unit is configured to stop the switching operation even while the drive instruction is input to the input unit. The electric tool according to claim 1, wherein the circuit is controlled.

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