JP2012196723A - Power tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power tool which can protect a motor from overcurrent.SOLUTION: The power tool 1 includes a motor 5, an inverter circuit 8 for supplying a drive voltage to the motor 5, a motor current detecting circuit 71 for detecting the current value I of the current flowing to the motor 5, and a control circuit 7. The control circuit 7 controls the inverter circuit 8 so as to reduce the drive voltage when the current value I is larger than a target current value It.

Description

  The present invention relates to a power tool.

  2. Description of the Related Art Conventionally, there is known an electric tool that operates a tip tool connected to a motor by controlling the motor with an inverter circuit (see, for example, Patent Document 1).

Japanese Patent No. 4487836

  Further, in the case of a generally used motor, when a large current flows, the coating of the winding of the motor is deteriorated and the performance of the motor may be lowered. In the above inverter circuit, when a large current flows, the performance of the electrical components constituting the circuit may be deteriorated. In such a case, the performance of the electric tool may be degraded due to the degradation of the performance of the electrical component.

  Then, an object of this invention is to provide the electric tool which can make a big electric current difficult to flow into a motor.

  The power tool of the present invention includes a motor, a voltage supply unit that supplies a driving voltage to the motor, a current detection unit that detects a current value of a current flowing through the motor, and the current value is higher than a first current value. And a control unit that controls the voltage supply unit so as to decrease the drive voltage when it is large.

  According to such a configuration, it is difficult for a large current to flow through the motor. For this reason, it becomes difficult for the performance of the coating | cover of the winding of an electrical component or a motor to fall with big electric current. It is possible to reduce the deterioration of the performance of the electric component and the winding of the motor, and to reduce the deterioration of the performance of the electric tool.

  Further, the control unit controls the voltage supply unit to stop the supply of the driving voltage when the current value is larger than a second current value larger than the first current value. .

  According to such a configuration, when a large current flows, a larger current does not flow to the motor. For this reason, the performance of the coating of the electrical component and the winding of the motor is further reduced by a larger current.

  Further, the voltage supply unit supplies a drive voltage of a pulsation waveform to the motor, the current detection unit detects a peak value of a current of a pulsation waveform generated by the drive voltage of the pulsation waveform, and the control unit The voltage supply unit is controlled to reduce the drive voltage when the peak value is larger than the first current value.

  According to such a configuration, even when a drive voltage having a pulsating waveform due to the use of an AC power supply is supplied to the motor, a large current is unlikely to flow to the motor. For this reason, it becomes difficult for the performance of the coating | cover of the winding of an electrical component or a motor to fall with big electric current.

  Further, the voltage supply unit is constituted by an inverter circuit.

  According to such a configuration, it becomes difficult for a large current to flow through the inverter circuit. For this reason, the performance of the electrical components of the inverter circuit is unlikely to deteriorate due to a large current.

  An electric power tool according to another aspect of the present invention includes a motor, a voltage supply unit that supplies a driving voltage of a target value to the motor, a rotation number detection unit that detects the rotation number of the motor, and the rotation number. And a control unit that changes the target value in response.

  According to such a configuration, since the rotational speed is detected and the drive voltage is controlled based on the rotational speed, it is difficult for a large current to flow through the motor. For this reason, the performance of the electrical components of the inverter circuit is unlikely to deteriorate due to a large current. That is, if the motor rotation speed decreases, it is assumed that the current flowing through the motor has increased, and if the motor rotation speed decreases, the drive voltage can be controlled to be reduced. Become.

  An electric power tool according to another aspect of the present invention includes a power cord connectable to an AC power source, a brushless motor rotated by the AC power source, a tip tool driven by the brushless motor, and the brushless motor. An electric power tool having a current detecting unit for detecting a flowing current, wherein when the current is larger than a predetermined value, a control unit is provided for reducing the starting voltage of the brushless motor.

  According to such a configuration, when the current flowing through the motor is larger than a predetermined value, the drive voltage is lowered, so that a large current is difficult to flow through the motor.

  Further, it is preferable to provide a control unit that controls the voltage supply unit so that the driving voltage is gradually lowered when the current exceeds a predetermined value.

  According to such a configuration, since the drive voltage for driving the motor does not change suddenly, it is possible to provide an easy-to-use electric tool that does not feel uncomfortable when a person working is using the tool.

  Further, a pulse width modulation signal is used to lower the drive voltage, and the duty of the pulse width modulation signal is smaller than 100% when it is larger than a predetermined value, and 100 when it is smaller than the predetermined value. % Is preferred.

  According to such a configuration, when the current flowing through the motor is larger than a predetermined value, the drive voltage is lowered, so that a large current is difficult to flow through the motor. In addition, since the driving voltage for driving the motor does not change suddenly, it is possible to provide an easy-to-use electric tool that does not feel uncomfortable when a person working is using the tool.

  An electric power tool according to another aspect of the present invention includes a power cord connectable to an AC power source having a first frequency, a brushless motor rotated by the AC power source, and a tip tool driven by the brushless motor. And a current detection unit that detects a current flowing through the brushless motor, and an electric tool in which the current flowing through the brushless motor pulsates at the first frequency, and includes means for suppressing the peak of the pulsation. It is preferable.

  The means for suppressing the peak of the pulsation preferably uses a pulse width modulation signal.

  According to the electric tool of the present invention, it is possible to reduce a large current from flowing through the motor.

Circuit diagram of the electric power tool according to the first embodiment Diagram showing the relationship between conventional load and current Explanatory drawing of the voltage control by 1st Embodiment Flow chart of voltage control according to the first embodiment The figure which shows the relationship between the target duty by 2nd Embodiment, and the rotation speed of a motor Explanatory drawing of voltage control by 2nd Embodiment Voltage control flowchart according to the second embodiment Circuit diagram of power tool according to third embodiment Explanatory drawing when the first embodiment is implemented using an AC power supply Explanatory drawing of voltage control by 3rd Embodiment Flowchart of voltage control according to the third embodiment Explanatory drawing of voltage control by modification Flow chart of voltage control according to modification

  A first embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a circuit diagram of a power tool 1 according to the first embodiment. As shown in FIG. 1, the electric tool 1 includes a trigger switch 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. When the trigger switch 3 is operated, the voltage of the battery pack 2 is supplied to the motor 5 via the inverter circuit 8. When the trigger switch 3 is operated, the voltage of the battery pack 2 is boosted by the control circuit voltage supply circuit 4 and supplied to the control circuit 7 as a drive voltage for the control circuit.

  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 battery 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, and a motor. A rotation speed detection circuit 77, a calculation unit 78, and a control signal output circuit 79 are provided.

  The motor current detection circuit 71 detects the current supplied to the motor 5 and outputs it to the calculation unit 78. The battery voltage detection circuit 72 detects the battery voltage of the battery pack 2 and outputs it 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, the motor 5 may break down when an overcurrent flows. For example, as shown in FIG. 2, since the current is proportional to the load, when a load exceeding a predetermined value is applied to the motor 5, a current having a magnitude that damages the motor 5 flows through the motor 5. .

  Therefore, in the electric power tool 1 according to the present embodiment, as shown in FIG. 3, a target current value It smaller than the overcurrent threshold Ith is set, and the current value of the current detected by the motor current detection circuit 71 is the target current. Voltage control is performed to reduce the PWM duty of the PWM signals H4-H6 output to the switching elements Q4-Q6 when the value It exceeds the value It. As a result, the current flowing through the motor 5 is also smaller than the target current value It, so that it is possible to prevent an overcurrent from flowing through the motor 5. In addition, since the possibility of stopping the motor 5 due to overcurrent is reduced, smooth work by the electric power tool 1 is ensured. Furthermore, it is possible to protect the inverter circuit 8 that is vulnerable to overcurrent.

  Here, the voltage control performed by the calculation unit 78 will be described in detail with reference to FIG. FIG. 4 is a flowchart of voltage control according to the present embodiment. This flowchart starts when the trigger switch 3 is turned on.

  First, the calculation unit 78 acquires the current value I of the current flowing through the motor 5 from the motor current detection circuit 71 (S101), and determines whether or not the current value I is larger than the overcurrent threshold Ith (S102). ).

  When the current value I is larger than the overcurrent threshold Ith (S102: YES), the supply of power to the motor 5 is stopped by setting the target duty Dt of the PWM signals H4, H5, and H6 to 0% ( S103). This prevents overcurrent from flowing through the motor 5.

  On the other hand, when the current value I is equal to or less than the overcurrent threshold Ith (S102: NO), it is subsequently determined whether or not the current value I is larger than the target current value It (S104).

  When the current value I is less than or equal to the target current value It (S104: NO), after setting (increasing) the target duty Dt for increasing the current value I to the target current value It (S105), S101 Return to.

  More specifically, Dt = (It−I) × P + D (1) (P is a feedback gain, D is a current duty), a target duty Dt is set, and the duty is set toward the target duty Dt by Da. Increase by%. Thus, by increasing the duty by Da%, it is possible to prevent an excessive inrush current from flowing through the motor 5.

  On the other hand, when the current value I is larger than the target current value It (S104: YES), the target duty Dt is decreased by decreasing the target current value It (105), and the process returns to S101.

  Thus, in the electric power tool 1 according to the present embodiment, the target duty Dt is decreased when the current value I of the current flowing through the motor 5 is larger than the target current value It. As a result, the current flowing through the motor is also smaller than the target current value It, so that it is possible to prevent an overcurrent from flowing through the motor 5. In addition, since the possibility of stopping the motor 5 due to overcurrent is reduced, smooth work by the electric power tool 1 is ensured. Furthermore, it is possible to protect the inverter circuit 8 that is vulnerable to overcurrent.

  Next, a second embodiment of the present invention will be described.

  If the same voltage is supplied when the rotation speed of the motor 5 is low and high, a larger current flows through the motor 5 when the rotation speed is low. On the other hand, the change of the target duty takes some time before being reflected in the current. Therefore, when the rotational speed of the motor 5 is low, even if the control according to the first embodiment is performed, the control cannot follow and an overcurrent may flow through the motor 5.

  Therefore, in the present embodiment, as shown in FIG. 5, the target duty Dt is changed according to the rotation speed of the motor 5. Specifically, the target duty Dt is set such that a large voltage is not supplied to the motor 5 by setting the target duty Dt to a small value while the rotational speed of the motor 5 is low. As a result, as shown in FIG. 6, it is possible to prevent a large current from flowing through the motor 5 while the rotational speed of the motor 5 is low. Therefore, it is possible to appropriately prevent an overcurrent from flowing through the motor 5. Become.

  Next, voltage control according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart of voltage control according to the present embodiment. This flowchart starts when the trigger switch 3 is turned on. The steps from S201 to S203 are the same as S101 to S103 in FIG.

  When the current value I is equal to or less than the overcurrent threshold Ith (S202: NO), the motor N is obtained from the motor speed detection circuit 77 (S204), and the target current value is based on the speed N. After setting It and the target duty Dt for increasing the current value I to the target current value It and limiting it with the target current value It (S205), the process returns to S201. In the present embodiment, as shown in FIG. 5, the target duty Dt is increased in proportion to 100% when the rotational speed is from 0 rpm to a predetermined rpm, and is fixed to 100% after the predetermined rpm.

  As described above, in the electric power tool 1 according to the present embodiment, the target duty Dt is changed according to the rotational speed of the motor 5. Thus, since a large voltage is prevented from being supplied to the motor 5 while the rotation speed of the motor 5 is low, it is possible to appropriately prevent an overcurrent from flowing through the motor 5.

  Subsequently, a third embodiment of the present invention will be described.

  In the first embodiment, the DC power from the battery pack 2 is directly supplied to the inverter circuit 8, but a configuration in which AC power from a commercial power supply is rectified and smoothed into DC power and then supplied to the inverter circuit 8 is also considered. It is done. As such a configuration, for example, as shown in FIG. 8, a normal mode filter 21, a rectifier circuit 22, and a smoothing capacitor 23 are provided between the commercial power supply 20 and the inverter circuit 8. One having an AC input voltage detection circuit 24 is conceivable.

  In the configuration shown in FIG. 8, a smoothing capacitor 23 having a small capacity may be used for reasons such as cost reduction. The reason for using a small-capacitance capacitor is that if a large-capacity smoothing capacitor is used, the power factor deteriorates and it is necessary to add a power factor improving circuit for improving the power factor as a countermeasure. In order to provide the power factor correction circuit, a large space is required, and the power tool becomes large.

  The small-capacitance capacitor here is a capacitor having a capacitance of 47 μF or less, for example. In particular, when it is 10 μF or less, pulsation of the drive voltage is likely to occur. In the embodiment of the present invention, a 0.47 μF capacitor is employed. When this small-capacitance capacitor is used, the ripple of the power supply voltage becomes large. For example, if the ripple is 70% or more, it can be said that a large pulsation occurs. The ripple is expressed as (dV / V *) × 100% when the maximum value of the voltage of the input power supply of the tool is V * and the amount of change in voltage is dV.

  When a capacitor having a small capacity is used as the smoothing capacitor 23, the AC power is not completely smoothed by the smoothing capacitor 23, and power having a pulsating waveform of the first frequency is supplied to the inverter circuit 8. When the control according to the first embodiment is performed in such a configuration, as shown in FIG. 9, the current value I becomes equal to the time when the control follows after the current value I becomes larger than the target current value It. The duty is increased again when it starts to decrease and decreases below the target current value It.

  However, in this case, the current value I has decreased to the target current value It or lower because the AC voltage has decreased, not because the load has decreased. Therefore, a current exceeding the target current value It flows to the motor 5 every AC cycle, and the motor 5 generates unnecessary heat generation.

  Therefore, in the present embodiment, the duty is reduced when the peak value Ip of the pulsating current is larger than the target current value It. Specifically, as shown in FIG. 10, when the peak value Ip of the pulsating current is larger than the target current value It, the duty is decreased, and the decreased duty is maintained until the next peak value Ip is detected. When the peak value Ip becomes equal to or less than the target current value It, the duty is recovered stepwise. As a result, a current exceeding the target current value It does not flow to the motor 5 for each AC cycle, so that it is possible to prevent the motor 5 from generating unnecessary heat.

  Here, the voltage control according to the present embodiment will be described in detail with reference to FIG. FIG. 11 is a flowchart of voltage control according to the present embodiment. This flowchart starts when the trigger switch 3 is turned on. Note that the steps from S301 to S303 are the same as S101 to S103 in FIG.

  On the other hand, if the current value I (t) is equal to or less than the overcurrent threshold Ith (S302: NO), then the current value I (t) is smaller than the stored current value I (t-1). It is determined whether or not (S304).

  If the current value I (t) is greater than or equal to the current value I (t−1) (S302: NO), the current value I (t) is stored as the current value I (t−1) ( S305), the process returns to S301.

  On the other hand, when the current value I (t) is smaller than the current value I (t−1) (S302: YES), the current value I (t−1) is determined as the peak value Ip (S306). In the present embodiment, it is assumed that the current value I (t) is detected in a sampling period in which a value sufficiently close to the actual peak value can be detected.

  Subsequently, it is determined whether or not the peak value Ip is larger than the target current value It (S307).

  When the peak value Ip is less than or equal to the target current value It (S307: NO), after setting the target duty Dt for increasing the peak value Ip to the target current value It and limiting it with the target current value It. (S308), the process returns to S301.

  On the other hand, when the peak value Ip is larger than the target current value It (S307: YES), the target duty Dt is decreased to decrease the target current value It (309), and the process returns to S301.

  As described above, in the electric power tool 1 according to the present embodiment, the duty is reduced when the peak value Ip of the pulsating current is larger than the target current value It. Therefore, the current exceeding the target current value It is increased every time the AC cycle is performed by the motor. Therefore, unnecessary heat generation or the like can be prevented from occurring in the motor 5.

  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, the first embodiment and the second embodiment may be performed simultaneously. More specifically, the target duty Dt is changed according to the number of revolutions of the motor 5, and when the current value I is larger than the target current value It, the target duty Dt is decreased to reduce the current flowing through the motor 5. Also good.

  In this case, as shown in FIG. 12, a target duty Dt is set so that a large voltage is not supplied to the motor 5 while the rotation speed of the motor 5 is low, and the duty is set after the rotation speed of the motor 5 exceeds a predetermined value. Is fixed to 100%. After the duty is fixed at 100%, the target duty Dt is decreased when the current value I becomes larger than the target current value It.

  Here, the voltage control according to the modification will be described in detail with reference to FIG. FIG. 13 is a flowchart of voltage control according to a modification. This flowchart starts when the trigger switch 3 is turned on.

  First, the calculation unit 78 acquires the current value I of the current flowing through the motor 5 from the motor current detection circuit 71 (S401), and determines whether or not the current value I is larger than the overcurrent threshold Ith (S402). ).

  When the current value I is larger than the overcurrent threshold Ith (S402: YES), the supply of power to the motor 5 is stopped by setting the target duty Dt of the PWM signals H4, H5, and H6 to 0% ( S403).

  On the other hand, if the current value I is equal to or less than the overcurrent threshold Ith (S402: NO), then, the rotational speed N of the motor 5 is acquired from the motor rotational speed detection circuit 77 (S404). Based on the target current value It and the target duty Dt for increasing the current value I to the target current value It are set (S405).

  Subsequently, it is determined whether or not the current value I is larger than the target current value It set in S405 (S406).

  If the current value I is less than or equal to the target current value It (S406: NO), after setting the target duty Dt for increasing the current value I to the target current value It and limiting it with the target current value It. (S407), the process returns to S401.

  On the other hand, when the current value I is larger than the target current value It (S406: YES), the target duty Dt is decreased to decrease the target current value It (408), and the process returns to S401.

  As described above, by simultaneously performing the first embodiment and the second embodiment, it is possible to more effectively prevent an overcurrent from flowing through the motor 5.

  In the first embodiment, when the current value I is larger than the target current value It, the voltage is decreased at a constant decrease rate. However, even if the decrease rate is changed according to the magnitude of the current value I, Good.

  In the above embodiment, the supply of voltage to the motor 5 is stopped when the current value I is larger than the overcurrent threshold Ith. However, the current value I is higher than the target current value It for a predetermined time or more. The supply of voltage to the motor 5 may be stopped when it is largely below the overcurrent threshold Ith. In this case, the predetermined time may be changed according to the weakness against the overcurrent of the motor 5 and the inverter circuit 8.

  Further, for example, lock detection at the end of fastening when the electric power tool 1 is a driver may be performed. In this case, for example, (1) when the rotation speed N is equal to or less than a predetermined value, (2) when the rotation speed N is equal to or less than a predetermined value, and the current value I is equal to or greater than a predetermined value, (3) a current value equal to or greater than the predetermined value. If I continues for a predetermined time or more, it is conceivable to perform lock detection.

DESCRIPTION OF SYMBOLS 1 Electric tool 2 Battery pack 5 Motor 7 Control circuit 8 Inverter circuit 20 Commercial power supply 71 Motor current detection circuit 77 Motor rotation speed detection circuit 78 Calculation part

Claims (10)

A motor,
A voltage supply unit for supplying a driving voltage to the motor;
A current detection unit for detecting a current value of a current flowing through the motor;
A control unit that controls the voltage supply unit to reduce the drive voltage when the current value is greater than a first current value;
An electric tool comprising:   The control unit controls the voltage supply unit to stop the supply of the drive voltage when the current value is larger than a second current value larger than the first current value. The electric tool according to 1.   The voltage supply unit supplies a pulsating waveform driving voltage to the motor, the current detection unit detects a peak value of a pulsating waveform current generated by the pulsating waveform driving voltage, and the control unit detects the peak 3. The power tool according to claim 1, wherein the voltage supply unit is controlled to decrease the drive voltage when the value is larger than the first current value. 4.   The electric power tool according to any one of claims 1 to 3, wherein the voltage supply unit includes an inverter circuit. A motor,
A voltage supply unit for supplying a driving voltage of a target value to the motor;
A rotational speed detector for detecting the rotational speed of the motor;
A control unit that changes the target value in accordance with the rotational speed;
An electric tool comprising: A power cord that can be connected to an AC power source;
A brushless motor driven to rotate by the AC power source;
A tip tool driven by the brushless motor;
A power detection unit that detects a current flowing through the brushless motor,
An electric tool, comprising: a control unit that reduces a starting voltage of the brushless motor when the current is greater than a predetermined value.   The power tool according to claim 6, further comprising a control unit that controls the voltage supply unit so that the driving voltage is gradually decreased when the current exceeds a predetermined value.   A pulse width modulation signal is used to lower the drive voltage, and the duty of the pulse width modulation signal is smaller than 100% when it is larger than a predetermined value, and is 100% when smaller than the predetermined value. The power tool according to claim 6, wherein the power tool is provided. A power cord connectable to an AC power source having a first frequency;
A brushless motor driven to rotate by the AC power source;
A tip tool driven by the brushless motor;
A current detection unit for detecting a current flowing through the brushless motor,
An electric tool in which a current flowing through the brushless motor pulsates at the first frequency,
An electric tool comprising means for suppressing the peak of the pulsation.   The power tool according to claim 9, wherein the means for suppressing the peak of pulsation uses a pulse width modulation signal.

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