WO2010087054A1

WO2010087054A1 - Electric tool

Info

Publication number: WO2010087054A1
Application number: PCT/JP2009/066085
Authority: WO
Inventors: 秀和須田; 卓也草川; 翔洋大村
Original assignee: 株式会社マキタ
Priority date: 2009-01-29
Filing date: 2009-09-15
Publication date: 2010-08-05
Also published as: JP2010173011A

Abstract

Further cost reduction is achieved by reducing the size of a switching element by keeping the maximum current flowing through the switching element as low as possible. An electric tool is provided with a switching element (44) for driving a DC motor, a control circuit (46) for operating the switching element (44), a changeover switch (19), and a trigger-type operation switch (18), wherein when the rotational direction is changed by the changeover switch (19) and the operation switch (18) is turned on again while the DC motor (20) is rotating by inertial force after the operation switch (18) is turned off, the control circuit (46) operates the switching element (44) on the basis of an on signal of the operation switch (18) after the number of rotations of the DC motor (20) decreases to 50 percent or less of the number of rotations thereof when the operation switch (18) is on.

Description

Electric tool

The present invention includes a plurality of switching elements that drive a DC motor, a control circuit that operates the switching elements based on an input signal, and a changeover switch that inputs a signal for switching the rotation direction of the DC motor to the control circuit; And a trigger-type operation switch that inputs a signal for starting the DC motor to the control circuit.

As shown in FIG. 8A, for example, an electric tool such as a screwdriver for tightening a screw includes a trigger type operation switch 104 that controls the rotation speed of the DC motor 102 in accordance with the pulling margin of the switch, and the DC motor. And a change-over switch 105 that changes the rotation direction of 102.
Signals from the operation switch 104 and the changeover switch 105 are input to the control circuit 106. The control circuit 106 operates the switching elements FET1 to FET4 based on signals from the operation switch 104 and the changeover switch 105. That is, when the changeover switch 105 is switched to the forward rotation direction and the operation switch 104 is turned on, the switching elements FET1 and FET4 are turned on as shown in FIG. The applied voltage 102 is controlled by a pulse width modulation (PWM) method. As a result, the DC motor 102 rotates in the forward direction.

Next, when the operation switch 104 is turned off in this state, as shown in FIG. 8C, the switching elements FET1 and FET4 are turned off, and the DC motor 102 continues to rotate in the forward rotation direction with the inertial force. At this time, the current applied to the DC motor 102 is returned to the power supply through the diodes of the switching elements FET2 and FET3. Further, when the changeover switch 105 is switched in the reverse direction and the operation switch 104 is turned on while the DC motor 102 is rotating with inertial force, the switching elements FET2 and FET3 are turned on as shown in FIG. 8D. To do. As a result, a power supply voltage having a reverse polarity is applied to the DC motor 102, and the DC motor 102 receives a rotational force in the reverse direction. At this time, an excessively large current flows instantaneously through the switching elements FET2 and FET3.
In the electric power tool described in Patent Document 1, a switching element having a specification capable of withstanding the excessive current described above is used.

JP 2007-283447 A

However, a switching element having a specification capable of withstanding the excessive current described above is large in size and high in cost.
The present invention has been made to solve the above problems, and the problem to be solved by the present invention is to reduce the size of the switching element and further reduce the cost by minimizing the maximum current flowing through the switching element. It is to plan.

The above-described problems are solved by the inventions of the claims.
The invention according to claim 1 inputs a plurality of switching elements for driving the DC motor, a control circuit for operating the switching elements based on an input signal, and a signal for switching the rotation direction of the DC motor to the control circuit. An electric tool comprising a changeover switch and a trigger type operation switch for inputting a signal for starting the DC motor to the control circuit, wherein the DC motor is rotated by an inertial force after the operation switch is turned off. When the rotation direction is switched by the change-over switch and the operation switch is turned on again, the rotation speed of the DC motor decreases to 50% or less of the rotation speed when the operation switch is turned on. Operates the switching element based on an ON signal of the operation switch.

According to the present invention, the DC motor can be operated in the reverse rotation direction when the rotation speed when the DC motor is rotating by inertia force is reduced to 50% or less of the rotation speed when the operation switch is turned on. It becomes. That is, when the electromotive force of the DC motor when rotating by inertia force is halved, the switching element operates and a power supply voltage is applied to the DC motor.
For this reason, compared with the conventional method which applies the power supply voltage of reverse polarity in the state with a large electromotive force of a DC motor, the electric current which flows into a switching element at the time of reverse rotation of a DC motor can be restrained small. As a result, it is not necessary to use a switching element for large current as in the prior art, and the switching element can be reduced in size and cost can be reduced.

According to the second aspect of the present invention, when the changeover switch is not operated when the DC motor is rotating with inertial force after the operation switch is turned off, the control circuit controls the switching element based on the ON signal of the operation switch. It is characterized by operating.
As described above, when the rotation direction is the same direction, the switching element is operated by turning on the operation switch, so that the DC motor rotates following the operation of the operation switch. That is, the responsiveness of the electric tool can be maintained.
When the rotation direction is the same direction, since the polarities of the power source and the DC motor are the same, a very large current does not flow through the switching element.

According to the invention of claim 3, after the operation switch is turned off, when the DC motor is rotated by inertial force, the rotation direction is switched by the changeover switch, and when the operation switch is turned on again, the rotation of the DC motor is turned on. After the stop, the control circuit operates the switching element based on the ON signal of the operation switch.
As described above, since the reverse rotation of the DC motor is performed after the DC motor is stopped, that is, at the stage where the electromotive force of the DC motor becomes almost zero, the current flowing through the switching element during the reverse rotation of the DC motor is further increased. It can be kept small.

According to a fourth aspect of the present invention, a plurality of switching elements that drive the DC motor, a control circuit that operates the switching elements based on an input signal, and a signal that switches the rotation direction of the DC motor are input to the control circuit. An electric tool comprising a changeover switch and a trigger type operation switch for inputting a signal for starting the DC motor to the control circuit, wherein the DC motor is rotated by an inertial force after the operation switch is turned off. When the direction of rotation is switched by the change-over switch and the operation switch is turned on again, the control circuit detects the switching element based on the ON signal of the operation switch after a predetermined time from when the operation switch is turned off. It is characterized by operating.

According to the present invention, since the current flowing through the switching element during the reverse rotation of the DC motor can be suppressed, it is not necessary to use a switching element for a large current as in the prior art, and the switching element can be reduced in size and cost can be reduced. Can be planned.

It is drawing showing the structure of the motor drive circuit in the electric tool which concerns on Embodiment 1 of this invention. It is a model side view of the electric tool which concerns on Embodiment 1 of this invention. It is a time chart figure when a DC motor is normally rotated by the motor drive circuit. It is a time chart figure when a DC motor is reversely operated by the motor drive circuit. It is a time chart when the DC motor is restarted from the normal rotation direction to the reverse rotation direction by the motor drive circuit. It is a time chart figure when a DC motor is restarted in the normal rotation state by the motor drive circuit. It is a control flowchart of the electric tool which concerns on Embodiment 1 of this invention. It is a schematic diagram (A figure) showing the structure of the motor drive circuit in the conventional electric tool, and a schematic diagram (B figure, C figure, D figure) showing the switching state of a switching element.

[Embodiment 1]
Hereinafter, based on FIGS. 1-7, the electric tool which concerns on Embodiment 1 of this invention is demonstrated.
<About the outline of electric tools>
The electric tool 10 according to the present embodiment is a rotary tool that uses a DC brushless motor 20 (hereinafter referred to as a DC motor 20) as a drive source. As shown in FIG. 2, the housing 11 of the electric tool 10 includes a cylindrical housing main body 12 and a grip portion 15 formed so as to protrude from a side portion (lower portion in FIG. 2) of the housing main body 12. It is composed of The grip portion 15 includes a grip portion 15h that is gripped by the user when using the electric power tool 10, and a lower end portion 15p that is positioned below (tip end side) the grip portion 15h. A trigger-type operation switch 18 is provided at the proximal end of the grip portion 15h, which is pulled by a user with a fingertip. A changeover switch 19 for switching the rotation direction of the DC motor 20 is provided behind the operation switch 18. Furthermore, a connection mechanism (not shown) to which the battery pack 16 is connected is provided at the lower end portion 15p of the grip portion 15.

A DC motor 20 is accommodated in the rear part of the housing body 12, and a drive mechanism 24 for amplifying the rotational force of the DC motor 20 and transmitting it to the tip tool 12 is accommodated in front of the DC motor 20. .
As shown in FIG. 1 and the like, the DC motor 20 includes a rotor 22 having a permanent magnet, a stator 23 having a drive coil 23c, and three magnetic sensors for detecting the positions of the magnetic poles of the rotor 22. 32. As shown in FIG. 2, the magnetic sensor 32 is attached to the electric circuit board 30 provided at the rear end of the stator 23 at 120 ° intervals so as to surround the rotor 22. The electric circuit board 30 is attached with a three-phase bridge circuit portion 45 of a motor drive circuit 40 which will be described later.

<About the motor drive circuit 40>
The motor drive circuit 40 is an electric circuit for driving the DC motor 20, and as shown in FIG. 1, a three-phase bridge circuit unit 45 including six switching elements 44, an operation switch 18, and a changeover switch. And a control circuit 46 for controlling the switching element 44 of the three-phase bridge circuit unit 45 based on the 19 signals.
The three-phase bridge circuit unit 45 includes three (U-phase, V-phase, W-phase) output lines 41, and these output lines 41 correspond to the drive coils 23 c (U-phase, V-phase) corresponding to the DC motor 20. , W phase). In addition, the three magnetic sensors 32 are positioned with respect to each drive coil 23c of the DC motor 20 with a phase shifted by 60 °.
Here, as the switching element 44 of the three-phase bridge circuit unit 45, for example, a field effect transistor (FET) is used. Therefore, in the following description, the six switching elements 44 are represented by FETs 1 to 6. The magnetic sensor 32 is represented by Ha, Hb, and Hc.

<Operation of Motor Drive Circuit 40>
Next, the operation of the motor drive circuit 40 will be briefly described with reference to FIGS.
FIG. 3 is a time chart showing a state when the operation switch 18 is turned on and the DC motor 20 is rotating forward with the changeover switch 19 switched to the forward rotation side.
During forward rotation, as shown in FIG. 3, the U-phase positive-side FET 1 is turned on at a timing T1 when the magnetic sensor Ha changes from L to H. Further, from this state, the U-phase FET 1 is turned off at the timing T2 when the rotor 22 rotates 120 ° forward (right rotation in FIG. 1) and the magnetic sensor Hb changes from L to H, and the V-phase positive FET 3 Turns on. Further, the V-phase FET 3 is turned off and the W-phase positive-side FET 5 is turned on at the timing T3 when the rotor 22 is rotated 120 ° to the right and the magnetic sensor Hc is changed from L to H. The W-phase FET 5 is turned off at a timing T4 when the rotor 22 further rotates clockwise by 120 ° and the magnetic sensor Ha changes from L to H.
Further, the negative-side FET 2 of the U phase is turned on at a timing T5 when the magnetic sensor Ha is changed from H to L, and is turned off at a timing T6 when the magnetic sensor Hb is changed from H to L. The negative-side FET 4 of the V phase is turned on at a timing T6 when the magnetic sensor Hb is changed from H to L, and is turned off at a timing T7 when the magnetic sensor Hc is changed from H to L. The negative-side FET 6 of the W phase is turned on at a timing T7 when the magnetic sensor Hc is changed from H to L, and is turned off at a timing T8 when the magnetic sensor Ha is changed from H to L.
As a result, electromotive forces whose phases are shifted by 120 ° in the order of the U phase, the V phase, and the W phase are induced in the U-phase, V-phase, and W-phase drive coils 23c, and the electromotive force rotates clockwise. Magnetic field is generated. Then, the rotor 22 rotates clockwise by the clockwise rotating magnetic field (forward rotation operation of the DC motor 20).

FIG. 4 is a time chart showing a state when the operation switch 18 is turned on and the DC motor 20 is reversely rotated in a state where the changeover switch 19 is switched to the reverse side.
At the time of reverse rotation, as shown in FIG. 4, the U-phase positive-side FET 1 is turned on at a timing T1 when the magnetic sensor Hb changes from L to H. Further, from this state, the U-phase FET 1 is turned off and the W-phase positive-side FET 5 is turned off at the timing T2 when the rotor 22 rotates backward by 120 ° (left rotation in FIG. 1) and the magnetic sensor Ha changes from L to H. Turn on. Further, the W-phase FET 5 is turned off and the V-phase positive-side FET 3 is turned on at the timing T3 when the rotor 22 is rotated 120 ° counterclockwise and the magnetic sensor Hc is changed from L to H. The V-phase FET 3 is turned off at a timing T4 when the rotor 22 further rotates counterclockwise by 120 ° and the magnetic sensor Hb changes from L to H.
Further, the negative-side FET 2 of the U phase is turned on at a timing T5 when the magnetic sensor Hb is changed from H to L, and is turned off at a timing T6 when the magnetic sensor Ha is changed from H to L. The negative-side FET 6 of the W phase turns on at timing T6 when the magnetic sensor Ha changes from H to L, and turns off at timing T7 when the magnetic sensor Hc changes from H to L. The V-phase negative side FET 4 is turned on at a timing T7 when the magnetic sensor Hc is changed from H to L, and is turned off at a timing T8 when the magnetic sensor Hb is changed from H to L.
As a result, electromotive forces whose phases are shifted by 120 ° in the order of the U phase, the W phase, and the V are induced in the drive coils 23c of the U phase, the W phase, and the V phase, and the counterclockwise rotating magnetic field is generated by the electromotive force. Will occur. The rotor 22 rotates counterclockwise by the counterclockwise rotating magnetic field (reverse operation of the DC motor 20).

Next, when the DC motor 20 is rotating forward, the operation switch 18 is turned off, and when the DC motor 20 is rotating in the forward rotation direction by inertia force, the DC motor 20 is reversely rotated. This state will be described based on the time chart of FIG.
When the operation switch 18 is turned off at the timing T1 in FIG. 5, the FETs 1 to 6 are turned off at this time, and the power supply voltage is not applied to the drive coils 23c of the respective phases of the DC motor 20. However, since the rotor 22 of the DC motor 20 is rotating in the normal rotation direction (clockwise) by the inertial force, an electromotive force is generated in the drive coil 23c of each phase. The lower side of FIG. 5 illustrates the U-phase electromotive force as a representative. In this state, when the rotation direction is switched (see timing T2) and the operation switch 18 is turned on (timing T3), the magnetic sensor Hb is in the H level state at timing T3. The negative FET 4 is turned on (see the time chart in FIG. 4). Thereby, for example, an excessive current flows in the FET 1 and the FET 4 due to the potential difference between the state of the electromotive force of the DC motor 20 in the U phase and the state of the voltage applied by the three-phase bridge circuit unit 45 at the timing T3. It becomes like this.
On the other hand, when restarting without changing the rotation direction, as shown in FIG. 6, since the potential difference at the time of restarting (timing T1) is small, an excessive current flows through FET3 and FET2. There is no.

<About the control method of the electric tool 10 according to the present embodiment>
Next, a control method of the electric power tool 10 according to the present embodiment will be described based on the flowchart of FIG.
First, in step S101, a constant CF representing the rotation direction of the DC motor 20 and a constant NF representing the rotation state of the DC motor 20 are cleared (0). Here, the constant CF is “0” when the rotation direction of the DC motor 20 is the same as the rotation direction in the previous operation, and “1” when the rotation direction is different. The constant NF is “0” when the DC motor 20 is stopped, and “1” when the DC motor 20 is rotating. Here, whether or not the DC motor 20 is stopped is determined based on how the magnetic sensors Ha, Hb, and Hc change.
When the operation switch 18 (Trig) is pulled (YES in step S102) and the changeover switch 19 is set in the forward rotation direction (YES in step S103), the DC motor 20 rotates forward (step S104, step S105 YES). ). As a result, the constant NF = 1 (step S106).
In this state, when the operation switch 18 is turned off (YES in Step 108), the DC motor 20 maintains its rotation in the forward rotation direction by the inertial force.

In this state, when the changeover switch 19 is operated in the reverse direction (YES in step S109), the constant CF = 1 (step S110). If the DC motor 20 is rotating with inertial force, the determination in step S112 is NO and the constant NF = 1 (step S114). Even if the operation switch 18 is turned on in this state (YES in step S115), since the constant CF and the constant NF are “1”, the process returns from step S116 to step S109 via step S117. That is, while the DC motor 20 is rotating with inertial force (while NF = 1), the processes of steps S115, S116, S117, S109,... S115 are repeated, and the reverse rotation of the DC motor 20 is performed. Absent.

However, when the DC motor 20 is stopped (step S112 YES), the constant NF = 0 is set (step S113), and when the operation switch 18 is turned on (step S115 YES), NF = 0 is determined in step S117. At the current stage, since NF = 0, the determination in step S117 is YES, and the process returns to step S103 to determine forward rotation. As described above, since the changeover switch 19 is operated in the reverse rotation direction, the determination in step S103 is NO, and the DC motor 20 operates in the reverse rotation direction (step S118).
As described above, when the rotation direction of the DC motor 20 is switched, the DC motor 20 can be restarted only after it is stopped.

If the operation switch 18 is turned off after the DC motor 20 is rotated in the reverse direction in step 118 (YES in step 122), the DC motor 20 maintains the rotation in the reverse direction by the inertial force. At this time, if the changeover switch 19 is not operated (NO in step S109), the constant CF = 0 (step S111).
Then, when the operation switch 18 is turned on (step S115: YES) while the DC motor 20 is reversely rotated by the inertial force (step S112: YES), the constant CF = 0, so the determination in step S116 is YES. Thus, the process returns to step S103. In step S118, the reverse operation of the DC motor 20 is performed again.
As described above, even when the DC motor 20 is rotated by the inertial force, the DC motor 20 can be restarted following the pulling operation (ON operation) of the operation switch 18 when rotating in the same direction. It becomes like this.

<Advantages of the electric power tool 10 according to the present embodiment>
According to the electric tool 10 according to the present embodiment, the DC motor 20 cannot be operated in the reverse direction unless the DC motor 20 is stopped. That is, when the electromotive force of the DC motor 20 becomes almost zero, the FETs 1 to 6 operate and a power supply voltage is applied to the DC motor 20.
For this reason, compared to the conventional method of applying a power supply voltage having a reverse polarity while the electromotive force of the DC motor 20 is large, the current flowing through the FETs 1 to 6 during the reverse rotation of the DC motor 20 can be suppressed. As a result, it is not necessary to use a switching element FET for large current as in the prior art, and the switching element FET can be reduced in size and cost can be reduced.
Further, when the rotation direction is not switched, the switching elements FET1 to FET6 operate following the ON operation of the operation switch 18, and the DC motor 20 is restarted. Thereby, the responsiveness of the electric tool 10 can be maintained.

<Example of change>
Here, the present invention is not limited to the above-described embodiment, and can be modified without departing from the gist of the present invention. For example, in the present embodiment, when the rotation direction of the DC motor 20 is switched, an example in which the DC motor 20 can be restarted only after it has stopped has been shown. However, after the rotational speed of the DC motor 20 is reduced to, for example, 50% or less, 25% or less, or 10% or less of the rotational speed when the operation switch is turned on, the DC motor 20 can be restarted in the reverse direction. It is also possible to configure as described above.
In the present embodiment, the electric tool 10 using the DC brushless motor 20 is illustrated, but the present invention can also be applied to an electric tool using a brushed DC motor.
Also, in the case where the rotation direction of the DC motor 20 is switched, an example in which the DC motor 20 is restarted after the DC motor 20 stops or after the rotation speed becomes a predetermined value or less has been shown. A configuration in which restarting is possible later is also possible.

10 .... Electric tool 18 .... Operating switch 19 .... Switch 20 ...... DC motor 44 ... Switching elements (FETs 1 to 6)
46... Control circuit

Claims

A plurality of switching elements for driving the DC motor; a control circuit for operating the switching elements based on an input signal; a changeover switch for inputting a signal for switching the rotation direction of the DC motor to the control circuit; and the DC motor A trigger-type operation switch that inputs a signal to activate the control circuit to the control circuit,
After the operation switch is turned off, the rotation direction is switched by the changeover switch when the DC motor is rotating with inertial force, and when the operation switch is turned on again, the rotation speed of the DC motor is changed to the operation switch. An electric tool characterized in that the control circuit operates the switching element on the basis of an ON signal of the operation switch after the rotational speed is reduced to 50% or less of the on-state rotation speed.
The electric tool according to claim 1,
A configuration in which the control circuit operates the switching element based on an ON signal of the operation switch when the switch is not operated when the DC motor rotates with inertial force after the operation switch is turned off. The electric tool characterized by being.
The electric tool according to claim 1 or 2,
After the operation switch is turned off, when the DC motor is rotated by inertia force, the rotation direction is switched by the changeover switch, and when the operation switch is turned on again, after the rotation of the DC motor is stopped, The power tool, wherein the control circuit is configured to operate the switching element based on an ON signal of the operation switch.
A plurality of switching elements for driving the DC motor; a control circuit for operating the switching elements based on an input signal; a changeover switch for inputting a signal for switching the rotation direction of the DC motor to the control circuit; and the DC motor A trigger-type operation switch that inputs a signal to activate the control circuit to the control circuit,
After the operation switch is turned off, when the DC motor is rotating with inertial force, the rotation direction is switched by the changeover switch, and when the operation switch is turned on again, the operation switch is turned off for a predetermined time. An electric tool characterized in that the control circuit is configured to operate the switching element based on an ON signal of the operation switch.