JP2007110849A - Motor drive device for power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent damage/wear to a brake contact in a motor drive device for a power tool and optionally and easily adjust a braking force of a brake. <P>SOLUTION: In this motor driving device for the power tool having a power supply circuit (15) which rectifies an alternating current from an AC power supply (14) and supplies electric power to a DC motor 8, and a brake circuit (18) which makes brake current flow to the DC motor (8) by opening a main contact (16) of the power supply circuit (15), the brake circuit (18) has a field effect transistor (25) and an electronic switch control circuit (39) and the like which is synchronized with a half period of the AC power supply (14) through a photo coupler (35) when the main contact (16) is opened and supplies a gate voltage so as to switch on the field effect transistor (25) to connect a drain (D) and a source (S) of the field effect transistor (25) with two terminals (8a, 8b) of the DC motor (8), respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a motor drive device for an electric tool.

The applicant discloses Patent Document 1.
JP 2003-52195 A

  As shown in FIG. 10, the motor driving device closes the brake contact 17 by opening the main contact 16 of the power supply circuit 15 that rectifies the alternating current from the AC power supply 14 and supplies power to the DC motor 8. And a brake circuit 18 for supplying a brake current to the DC motor 8.

  The brake circuit 18 in this motor drive device includes a field effect transistor (FET) 25 and a field effect transistor that supplies a gate voltage that turns on the field effect transistor 25 via the brake contact 17 when the main contact 16 is opened. Drive means.

  The field effect transistor driving means has the following circuit configuration. That is, the resistor 26, the diode 27, and the Zener diode 28 are connected in series to the + terminal 19a and the-terminal 19b on the output side of the bridge diode 19, and the field effect transistor 25 is connected between the diode 27 and the Zener diode 28. The resistor 29 and the brake contact 17 are connected in series to the gate G of the resistor G, and the resistor 30 and the capacitor 31 are connected between the resistor 29 and the brake contact 17 and the negative terminal 19b on the output side of the bridge diode 19. A resistor 32 is connected in series. The resistor 32 is connected between the brake contact 17 and the gate G of the field effect transistor 25 and the negative terminal 19 b on the output side of the bridge diode 19. When the main contact 16 is closed and the DC motor 8 is rotating, a Zener voltage V is generated between the EFs in the Zener diode 28, the electric charge of the voltage V is accumulated in the capacitor 31, and the main contact 16 is opened. When the brake contact 17 is closed, the voltage V is applied to the gate G of the field effect transistor 25, the drain D and the source S of the field effect transistor 25 are conducted, and the brake current flows through the field effect transistor 25.

  Further, since this brake current is a direct current that continues to flow from the moment when the drain D and source S of the field effect transistor 25 are conducted, the initial value becomes a very large value and gradually decreases with the passage of time.

  According to the motor brake circuit in the motor drive device of the electric tool in Japanese Patent Application Laid-Open No. 2003-52195, when both terminals of a DC motor driven by rectifying the commercial power supply are short-circuited, the motor is braked. it can. However, at this moment, a very large brake current flows in the opposite direction to that during driving. Therefore, since a large reaction occurs at the moment when braking is applied, the tool becomes difficult to handle.

  The present invention aims to solve the above-mentioned problems and realizes a semi-permanent long-life brake by making the circuit through which the brake current flows non-contact, and arbitrarily and easily adjusts the braking force of the brake. The purpose is to greatly improve the life and workability of the motor.

  In order to solve the above-mentioned problem, the invention according to claim 1 is directed to a power supply circuit (15) for rectifying an alternating current from an alternating current power supply (14) and feeding the direct current motor (8), and a main contact of the power supply circuit (15). In the motor drive device of the electric tool provided with a brake circuit (18) for supplying a brake current to the DC motor (8) by the opening operation of (16), the brake circuit (18) includes a field effect transistor (25), Electronic switch control for supplying a gate voltage for turning on the field effect transistor (25) in synchronization with the half cycle of the AC power supply (14) via the photocoupler (35) when the main contact (16) is opened. A power tool having a circuit (39) and having a drain (D) and a source (S) of the field effect transistor (25) connected to the two terminals (8a, 8b) of the DC motor (8), respectively. Employing the motor driving device.

  According to a second aspect of the present invention, in the motor drive device for the electric tool according to the first aspect, the electronic switch control circuit (45) is connected to the AC via the photocoupler (35) when the main contact (16) is opened. A motor drive device for an electric tool that supplies a gate voltage to turn on the field effect transistor (25) in synchronization with the cycle of the power supply (14) is employed.

  Furthermore, the invention according to claim 3 is the motor drive device for the electric tool according to claim 1, wherein the electronic switch control circuit (45) is connected via a photocoupler (35) when the main contact (16) is opened. A motor drive device for an electric tool having a transmitter (47) that supplies a gate voltage that turns on the field effect transistor (25) at an arbitrary timing is adopted.

  According to a fourth aspect of the present invention, in the motor drive device for an electric tool according to any one of the first to third aspects, the field effect transistor (25) is a yoke (34) of the direct current motor (8) or a direct current. The motor drive device of the electric tool attached to the case (11) of the reducer of the motor (8) is employed.

  According to the first aspect of the present invention, there is provided a power supply circuit that rectifies alternating current from an alternating current power supply and supplies power to the direct current motor, and a brake circuit that causes the brake current Imb to flow to the direct current motor by opening the main contact of the power supply circuit. In the motor drive device of the electric tool provided, the brake circuit includes a field effect transistor and a gate that turns on the field effect transistor in synchronization with a half cycle of the AC power supply via a photocoupler when the main contact is opened. An electric switch control circuit for supplying a voltage, and a drain and a source of the field effect transistor are motor drive devices of an electric tool connected to two terminals of the DC motor, respectively, so that a minute current flows through the brake contact The field effect transistor can be driven only by passing a brake current Imb between the drain and source of the field effect transistor. Can. Therefore, it is possible to prevent the occurrence of an arc at the brake contact during braking, extend the life of the brake contact, and maintain the brake performance at a high level over a long period of time.

  Further, since the brake current Imb is intermittently generated in a pulse shape, the brake for the DC motor 8 is applied in small steps, the braking performance for the DC motor 8 is improved, and the reaction of the electric tool is reduced. Therefore, since the electric tool stops quickly without causing a large reaction by the motor, workability is improved. In particular, when the power tool is light and small, workability is remarkably improved.

  According to the second aspect of the present invention, the power supply circuit that rectifies the alternating current from the alternating current power supply and supplies power to the direct current motor, and the brake circuit that causes the brake current Imb to flow to the direct current motor by opening the main contact of the power supply circuit. In the motor drive device for an electric tool comprising: the brake circuit turns on the field effect transistor in synchronization with the period of the AC power supply via the photocoupler when the main contact is opened with the field effect transistor. An electronic switch control circuit for supplying a gate voltage, and the drain and source of this field effect transistor are motor drive devices for an electric tool connected to the two terminals of the DC motor, respectively. The field effect transistor is driven simply by flowing it, and the brake current Imb flows between the drain and source of the field effect transistor. It is possible. Therefore, it is possible to prevent the occurrence of an arc at the brake contact during braking, extend the life of the brake contact, and maintain the brake performance at a high level over a long period of time.

  Further, since this brake current Imb is intermittently generated in a pulse shape at a frequency twice as high as the brake current Imb described in claim 1, the brake for the DC motor 8 is applied in small increments, and the braking performance for the DC motor 8 is increased. Is improved, and the reaction of the power tool is reduced. Therefore, since the electric tool stops more quickly without generating a large reaction by the motor, workability is improved. In particular, when the power tool is light and small, workability is remarkably improved.

  Further, according to the invention of claim 3, a power supply circuit that rectifies alternating current from an alternating current power supply and supplies power to the direct current motor, and a brake circuit that causes a brake current Imb to flow to the direct current motor by opening the main contact of the power supply circuit The brake circuit supplies a gate voltage that turns on the field effect transistor at an arbitrary timing via a photocoupler when the main contact is opened when the motor driving device of the electric tool includes An electric switch control circuit having a transmitter, and the drain and source of the field effect transistor are motor drive devices of an electric tool connected to the two terminals of the DC motor, respectively, so that a minute current flows through the brake contact The field effect transistor is driven only by the brake current I between the drain and source of the field effect transistor. b can flow. Therefore, it is possible to prevent the occurrence of an arc at the brake contact during braking, extend the life of the brake contact, and maintain the brake performance at a high level over a long period of time.

  Further, since the brake current Imb is generated at an arbitrary frequency by the transmitter, the brake for the DC motor 8 can be adjusted so as to be optimal with respect to the shape and weight of the electric tool. Therefore, the brake for the DC motor 8 is more optimally applied, the braking performance for the DC motor 8 is further improved, and the reaction of the electric tool is reduced. Therefore, since the electric tool stops more quickly without causing a large reaction by the motor, workability is remarkably improved.

  According to a fourth aspect of the present invention, in the motor driving device for the electric tool according to any one of the first to third aspects, the field effect transistor is provided in the yoke of the DC motor or the case of the reduction gear of the DC motor. Since it is the motor drive device of the attached electric tool, the field effect transistor which generates heat by flowing the brake current Imb can be appropriately cooled in a narrow space in the electric tool housing.

(I) First Embodiment of the Present Application Next, a first embodiment of the present invention will be described with reference to FIGS.

  This motor drive device is attached to an electric tool as shown in FIGS. This electric tool is specifically an impact driver, and a DC motor 8 is provided in the housing 7 thereof. The output from the output shaft 9 of the DC motor 8 is transmitted to the spindle 10 via a reduction gear (not shown). The reduction gear is, for example, a planetary gear device, and is entirely covered with a housing 7, and a metal case 11 is attached to the distal end side of the housing 7. A trigger switch 13 for turning the DC motor 8 on and off is attached to the handle 12 integrated with the housing 7.

  1 and 2 is an impact driver, the motor driving device according to the present invention is not limited to an impact driver, and other electric tools using a DC motor, such as a portable electric drill, jigsaw, and mower. Is also available.

  As shown in FIG. 3, the motor driving device includes a power supply circuit 15 that rectifies AC from an AC power supply 14 by a bridge diode 19 and supplies power to the DC motor 8, and an opening operation of the main contact 16 of the power supply circuit 15. Is provided with a brake circuit 18 for operating a photocoupler 35 as an electronic switch to flow a brake current Imb to the DC motor 8.

  The power supply circuit 15 includes an alternating current (AC) power supply 14, a main contact 16, and a bridge diode 19 that is a rectifier circuit. The alternating current (AC) power supply 14 is an AC 100V power supply in this embodiment. The main contact 16 has a contact 20 that is in an open state (terminals a and c are ON) when the trigger switch 13 is not operated. The contact 20 is interlocked with the trigger switch 13 of the electric tool illustrated in FIG. 1, and when the trigger switch 13 is pulled, the contact 20 is closed (terminals a and b are in an ON state). The bridge diode 19 rectifies the AC power supply 14 to change to full-wave DC and supplies it to the DC motor 8.

  The DC motor 8 is a magnet motor, and its two terminals 8a and 8b are connected to the + terminal 19a and the − terminal 19b on the output side of the bridge diode 19, respectively. A forward / reverse switching unit 24 having forward / reverse switching contacts 24a and 24b for switching the rotation direction of the DC motor 8 is provided between the bridge diode 19 and the DC motor 8 as necessary. As a result, the DC motor 8 is supplied with DC power from the bridge diode 19 and rotates forward or backward. As shown in FIG. 1, the rotation of the output shaft 9 of the DC motor 8 is decelerated by a speed reducer and transmitted to the spindle 10. A cutter, a bit, and the like are attached to the spindle 10, and the electric tool performs operations such as drilling and screwing by rotating the spindle 10.

  The brake circuit 18 supplies a field effect transistor (FET) 25 and a gate voltage that turns on the field effect transistor 25 when the main contact 16 is opened (terminal a and terminal c are in an ON state). And a switch control circuit 39.

  The field effect transistor 25 is disposed in the brake circuit 18 by connecting its drain D and source S to the two terminals 8 a and 8 b of the DC motor 8, respectively.

  The electronic switch control circuit 39 includes diodes 37 and 38, a resistor 36, a light emitting diode 35a provided in the photocoupler 35, and a photodiode 35b including a plurality of photodiodes.

  The terminal c of the main contact 16 is connected to the anode of the diode 37, the cathode of the diode 37 is connected to the resistor 36, the resistor 36 is connected to the cathode of the diode 38 and the anode of the light emitting diode 35a, and the anode of the diode 38 is connected. Are connected to the cathode of the light emitting diode 35a.

  A photodiode 35 b disposed in the photocoupler 35 is connected between the gate G and the source S of the field effect transistor 25.

  When a voltage equal to or higher than the voltage value v1 necessary for starting light emission is applied between the anode and the cathode of the light emitting diode 35a, the light emitting diode 35a starts light emission. The light emitted from the light emitting diode 35a is transmitted through the photocoupler and irradiated to the photodiode 35b.

  The photodiode 35b that has received the light emitted from the light emitting diode 35a is turned on, and a voltage V is generated across the photodiode 35b. Then, the drain D and the source S of the field effect transistor 25 are brought into conduction and are turned on.

  That is, when the main contact 16 is opened (the terminals a and c are in the ON state), the voltage V of the photodiode 35b is generated between the gate G and the source S of the field effect transistor 25, and the gate of the field effect transistor 25 is A voltage V is applied to G, the drain D and the source S of the field effect transistor 25 are conducted, and the brake current Imb flows through the field effect transistor 25.

That is, as a result of the ON state between the drain D and the source S of the field effect transistor 25, the current generated by the DC motor 8 rotates in the direction of the DC motor 8 via the field effect transistor 25 as the brake current Imb. Flows in the reverse direction along the routes I _a , I _b , and I _c .

  The field effect transistor 25 generates heat due to the flow of the brake current Imb and needs to be cooled. Therefore, in this embodiment, as shown in FIGS. 1 and 2, the field effect transistor 25 is attached to the yoke 34 of the DC motor 8 so that heat generated during braking is radiated by the yoke 34. As a result, the field effect transistor 25 can be efficiently cooled without providing a dedicated heat sink in a narrow space such as the inside of the housing 7 of the electric tool.

  The place where the field effect transistor 25 is attached is not limited to the yoke 34, but may be the case 11 of the speed reducer. The field effect transistor 25 is fixed to the yoke 34 by a fixing screw 33, but can be attached by other means such as an adhesive in addition to the fixing screw 33.

  Next, the overall operation of the motor drive apparatus having the above configuration will be described with reference to FIGS.

When the operator pulls the trigger switch 13 of the electric tool, as shown in FIG. 4, the contact 20 of the main contact 16 is closed (terminals a and b are in an ON state), and an AC power supply 14 is provided in the circuit of the motor drive device. The current supplied from ₁ flows through the routes i ₁ , i ₂ , i ₃ , i ₄ , i ₅ , i ₆ . That is, a current flows through the bridge diode 19, the DC motor 8, the bridge diode 19, and the contact 20, and the DC motor 8 rotates forward or reverse. That is, the spindle 10 of the electric tool rotates. At the same time, the reverse-phase current supplied from the AC power supply 14 flows through the forward paths I ₁ , I ₂ , I ₃ , I ₄ , I ₅ , I ₆ , and I ₇ .

  In this case, since the terminals a and c of the contact 20 are in an open state, the voltage v1 is not applied to the light emitting diode 35a and the light emitting diode 35a does not emit light. Accordingly, since the voltage V is not generated in the photodiode 35b, the voltage between the gate G and the source S of the field effect transistor 25 is 0V, and the drain D and the source S of the field effect transistor 25 are in the OFF state. Therefore, the brake current Imb does not flow from the drain D to the source S of the field effect transistor 25.

  When the operator removes his / her finger from the trigger switch 13, as shown in FIG. 3, the space between the terminal a and the terminal b of the contact 20 of the main contact 16 is opened, and at the same time, the space between the terminal a and the terminal c is closed. At this moment, no current flows through the DC motor 8, but the DC motor 8 continues to rotate due to inertia. Since the DC motor 8 is a magnet motor, it generates electric power by its rotation, and a voltage of about DC 130V is generated between both terminals 8a and 8b of the DC motor 8 in an AC100V electric tool.

  In this case, since the terminals a and c of the contact 20 of the main contact 16 are closed, power is supplied from the AC power supply 14 to the diode 37, the resistor 36, and the light emitting diode 35a. The resistor 36 functions to prevent an overcurrent from flowing through the light emitting diode 35a.

  The light emitting diode 35a is supplied with an AC voltage Vac indicated by a dotted line in FIG. The light emitting diode 35a starts to emit light because the AC voltage Vac supplied to the light emitting diode 35a at the timing t1 becomes v1 which is a voltage value necessary to start light emission. The light emitted from the light emitting diode 35a is transmitted in the photocoupler 35 and received by the photodiode 35b. The photodiode 35b that receives the light emitted from the light emitting diode 35a is turned on, and a voltage V is generated. This voltage V is applied to the gate G of the field effect transistor 25, the drain D-source S of the field effect transistor 25 is turned on, and the brake current Imb having the waveform shown in FIG. Flowing.

  After that, the AC voltage Vac supplied to the light emitting diode 35a at the timing t2 becomes equal to or lower than the voltage value v1, so the light emitting diode 35a stops emitting light. In this case, since the photodiode 35b cannot receive the light emitted from the light emitting diode 35a, the photodiode 35b is turned off and the voltage V is not generated. Accordingly, the gate G and the source S of the field effect transistor 25 have the same potential, the drain D and the source S of the field effect transistor 25 are turned off, and the brake current Imb does not flow.

  Between the timings t2 and t3, the AC voltage Vac supplied to the light emitting diode 35a is equal to or lower than the voltage value v1, and thus the light emitting diode 35a maintains a state where light emission is stopped. Therefore, the drain D and the source S of the field effect transistor 25 are maintained in the OFF state, and the brake current Imb does not flow.

  Between the timing t3 and t4 and between the timing t5 and t6, the AC voltage Vac supplied to the light emitting diode 35a is equal to or higher than the voltage value v1, so that the light emitting diode 35a maintains a light emitting state. Therefore, the drain D and the source S of the field effect transistor 25 are turned on, and the brake current Imb flows.

  Further, since the AC voltage Vac supplied to the light emitting diode 35a is equal to or lower than the voltage value v1 between the timings t4 and t5, the light emitting diode 35a does not emit light. Accordingly, the drain D-source S of the field effect transistor 25 is turned off, and the brake current Imb does not flow.

As a result of the ON state between the drain D and the source S of the field effect transistor 25 as described above, the current generated by the DC motor 8 rotates in the direction of the DC motor 8 via the field effect transistor 25 as the brake current Imb. Flows in the reverse direction along the routes I _a , I _b , and I _c .

  As shown in FIG. 5A, the brake current Imb is intermittently generated in pulses in synchronization with the half cycle of the AC power supply. Therefore, the brake for the DC motor 8 is applied in small increments, and the reaction is reduced. .

  That is, the DC motor 8 is braked by the pulsed brake current Imb (regenerative braking), and the DC motor 8, that is, the electric tool is quickly stopped without causing a large reaction.

(II) Second Embodiment of the Present Application Next, a second embodiment of the present invention will be described with reference to FIGS.

  6 and 7, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The motor drive device according to the second embodiment is also mounted on an electric tool as shown in FIGS.

  FIG. 6 shows a motor drive device according to the second embodiment. This motor drive device rectifies the alternating current from the AC power supply 14 and supplies power to the DC motor 8, and the power supply circuit 15. And a brake circuit 18 for operating a photocoupler 35 as an electronic switch by opening the main contact 16 to flow a brake current Imb to the DC motor 8.

  The brake circuit 18 supplies a field effect transistor (FET) 25 and a gate voltage that turns on the field effect transistor 25 when the main contact 16 is opened (terminal a and terminal c are in an ON state). And a switch control circuit 45.

  The field effect transistor 25 is disposed in the brake circuit 18 by connecting its drain D and source S to the two terminals 8 a and 8 b of the DC motor 8, respectively.

  The electronic switch control circuit 45 includes diodes 40, 41, 42, 43, a resistor 44, a light emitting diode 35a provided in the photocoupler 35, and a photodiode 35b composed of a plurality of photodiodes.

  The terminal c of the contact 20 of the main contact 16 is connected to the anode of the diode 40 and the cathode of the diode 41, the cathode of the diode 40, the cathode of the diode 43 and the resistor 44 are connected, and the anode of the diode 43 and the diode 42 are connected. The cathode is connected, the anode of the diode 42, the anode of the diode 41, and the cathode of the light emitting diode 35a are connected, and the resistor 44 and the anode of the light emitting diode 35a are connected.

  The diodes 40, 41, 42, and 43 constitute a full-wave rectifier circuit, and when the main contact 16 is opened (terminals a and c are in an ON state), the AC power supply 14 is full-wave rectified to emit light. Vac shown in FIG. 7B is supplied between the anode and cathode of the diode 35a. The resistor 44 functions to prevent an overcurrent from flowing through the light emitting diode 35a.

  The light emitting diode 35a starts to emit light at the timing t7 in FIG. 7B because the AC voltage Vac supplied to the light emitting diode 35a becomes v1 that is a voltage value necessary to start light emission. The light emitted from the light emitting diode 35a is transmitted in the photocoupler 35 and received by the photodiode 35b. The photodiode 35b that receives the light emitted from the light emitting diode 35a is turned on and a voltage V is generated. When this voltage V is applied to the gate G of the field effect transistor 25, the drain D-source S of the field effect transistor 25 is turned on, and the brake current Imb having the waveform shown in FIG. Flows.

  Thereafter, the AC voltage Vac supplied to the light emitting diode 35a becomes equal to or lower than the voltage value v1 at the timing t8, so that the light emitting diode 35a stops emitting light. In this case, since the photodiode 35b cannot receive the light emitted from the light emitting diode 35a, the photodiode 35b is turned off and the voltage V is not generated. Accordingly, the gate G and the source S of the field effect transistor 25 have the same potential, the drain D and the source S of the field effect transistor 25 are turned off, and the brake current Imb does not flow.

  FIG. 7A shows the waveform of the pulse brake current BP21 generated between timings t7 and t8.

  Between the timing ta and tb in FIG. 7B, the AC waveform of the AC power supply 14 shows a negative voltage value. However, since the voltage applied to the light emitting diode 35a is rectified by the full-wave rectifier circuit constituted by the diodes 40, 41, 42 and 43, it becomes a positive voltage.

  However, between timing t8 and t9 and between timing t10 and t11, since the AC voltage Vac supplied to the light emitting diode 35a is equal to or lower than the voltage value v1, the light emitting diode 35a stops emitting light. maintain. Therefore, the drain D and the source S of the field effect transistor 25 are maintained in the OFF state, and the brake current Imb does not flow.

  The AC voltage Vac supplied to the light emitting diode 35a is equal to or higher than the voltage value v1 between the timing t9 and t10 and between the timing t11 and t12, so that the light emitting diode 35a maintains the light emission state. To do. Therefore, the drain D and the source S of the field effect transistor 25 are turned on, and the brake current Imb flows.

  FIG. 7A shows waveforms of a pulse brake current BP22 generated between timings t9 and t10 and a pulse brake current BP23 generated between timings t11 and t12. The current value of the pulse brake current BP22 generated between timings t9 and t10 is h22. Further, the current value of the pulse brake current BP22 is h22, which is smaller than the current value h21 of the pulse brake current BP21 generated half a cycle before the AC cycle of the power supply 14.

  The current value of the pulse brake current BP23 generated between timings t11 and t12 is h23. Further, the current value of the pulse brake current BP22 is h23, which is smaller than the current value h22 of the pulse brake current BP22 generated half a cycle before the AC cycle of the power supply 14.

  As described above, the current value of the pulsed brake current Imb generated every half cycle in the AC cycle of the power supply 14 with time passes from the time of opening the main contact 16 (terminals a and c are in the ON state). Get smaller.

As a result of the ON state between the drain D and the source S of the field effect transistor 25 as described above, the current generated by the DC motor 8 is in a direction opposite to the direction in which the DC motor 8 is rotated via the field effect transistor 25. I _a, I _b, it flows in route of I _c.

  As a result, the DC motor 8 is braked by the pulsed brake current Imb (regenerative braking), so that the DC motor 8, that is, the electric tool is quickly stopped without causing a large reaction.

  Further, since the pulse-like brake current Imb is generated twice as compared with the first embodiment, the DC motor 8, that is, the electric tool, is more stably and more quickly stopped.

  Further, since this brake current Imb is intermittently generated in a pulse shape at a frequency twice as high as the brake current Imb of the first embodiment, the brake for the DC motor 8 is applied in small steps, and the braking performance for the DC motor 8 is improved. It becomes even better, and the recoil of the power tool becomes smaller. Therefore, since the electric tool stops more quickly without generating a large reaction by the motor, workability is improved. In particular, when the power tool is light and small, workability is remarkably improved.

(III) Third Embodiment of the Present Application Next, a third embodiment of the present invention will be described with reference to FIGS.

  8 and 9, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Note that the motor driving apparatus according to the third embodiment is also mounted on an electric tool as shown in FIGS.

  FIG. 8 shows a motor drive device according to the third embodiment. This motor drive device rectifies the alternating current from the AC power supply 14 and supplies power to the DC motor 8, and the power supply circuit 15. And a brake circuit 18 for operating a photocoupler 35 as an electronic switch by opening the main contact 16 to flow a brake current Imb to the DC motor 8.

  The brake circuit 18 supplies a field effect transistor (FET) 25 and a gate voltage that turns on the field effect transistor 25 when the main contact 16 is opened (terminal a and terminal c are in an ON state). And a switch control circuit 45.

  The field effect transistor 25 is disposed in the brake circuit 18 by connecting its drain D and source S to the two terminals 8 a and 8 b of the DC motor 8, respectively.

  The electronic switch control circuit 45 includes diodes 40, 41, 42, 43, a resistor 44, a transistor 46, an oscillator (OSC) 47, a light emitting diode 35a provided in the photocoupler 35, and a plurality of photodiodes. A photodiode 35b.

  The terminal c of the contact 20 of the main contact 16 is connected to the anode of the diode 40 and the cathode of the diode 41, the cathode of the diode 40, the cathode of the diode 43 and the resistor 44 are connected, and the anode of the diode 43 and the diode 42 are connected. The cathode and the transmitter 47 are connected, the anode of the diode 42, the anode of the diode 41, and the emitter (E) of the transistor 46 are connected, the resistor 44 and the anode of the light emitting diode 35a are connected, and the cathode of the light emitting diode 35a. And the collector (C) of the transistor 40 are connected, and the base (B) of the transistor 40 and the transmitter 47 are connected.

  The diodes 41, 42, 43 and 44 constitute a full-wave rectifier circuit, and when the main contact 16 is opened (terminals a and c are in the ON state), the AC power supply 14 is full-wave rectified to emit light. Vac shown in FIG. 7B is supplied between the anode and cathode of the diode 35a. The resistor 44 functions to prevent an overcurrent from flowing through the light emitting diode 35a.

  FIG. 9 shows waveforms of the brake current Imb, the FET gate signal Vgs, and the OSC (transmitter) output signal Vos.

  The OSC output signal Vos shown in FIG. 9C is output from the oscillator (OSC) 47 to the base (B) of the transistor 46.

  The OSC output signal Vos is a waveform that is synchronized with the AC cycle of the power supply 14 but whose signal width gradually decreases with time.

  That is, the interval between timings t15 and t16 is narrower than the interval between timings t13 and t14. Further, the interval between timings t17 and t18 is narrower than the interval between timings t15 and t16. Further, the interval between timings t19 and t20 is narrower than the interval between timings t17 and t18.

  When the OSC output signal Vos applied to the base (B) of the transistor 46 is in a high state, the collector (C) and the emitter (E) of the transistor 46 are electrically connected. Between (E), a full-wave rectified AC signal of the power source 14 flows. Therefore, the light emitting diode 35 a emits light at the moment when the OSC output signal Vos is applied to the base (B) of the transistor 46. That is, the light emitting diode 35a repeats light emission in synchronization with the OSC output signal Vos. As a result, the FET gate signal Vgs (FIG. 7B) also has a waveform synchronized with the OSC output signal Vos.

  Therefore, the brake current Imb flows in synchronization with the FET gate signal Vgs. That is, at the timings t13, t15, t17, and t19, the field effect transistor 25 becomes conductive between the drain D and the source S, and the brake current Imb begins to flow. At the timings t14, t16, t18, and t20, the field effect transistor 25 becomes non-conductive between the drain D and the source S, and the brake current Imb does not flow.

  As a result, the DC motor 8 is braked by the pulsed brake current Imb (regenerative braking), so that the DC motor 8, that is, the electric tool is quickly stopped without causing a large reaction.

  Further, in the case of the present embodiment, the pulse width of the pulsed brake current Imb is initially wide and then gradually narrowed compared to the second embodiment, so that the brake is firmly applied at the start of braking, The DC motor 8, that is, the electric tool stops more stably and more quickly.

  In the present embodiment, the OSC output signal Vgs has been described in a form in which the pulse width becomes narrower as time passes while synchronizing with the AC cycle of the power supply 14, but is not limited to this embodiment, and the transmitter 47 is Arbitrary waveforms can be output. For example, the period and signal width of the OSC output signal Vgs can be arbitrarily set.

  Therefore, the degree of braking depends on the shape of the electric tool, the rotational speed of the motor, the inertial force, the weight, and the like. Therefore, the shape of the OSC output signal output from the transmitter 47 and the type of the electric tool are The period can be set.

It is a partial notch elevation view of the electric tool provided with the motor drive unit concerning the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. It is a circuit diagram which shows the motor drive device of the electric tool in the state which removed the finger | toe from the trigger switch in 1st Embodiment. It is a circuit diagram which shows the motor drive device of the electric tool in the state which pulled the trigger switch in 1st Embodiment. It is a signal waveform of each part in a 1st embodiment. It is a circuit diagram which shows the motor drive device of the electric tool in 2nd Embodiment. It is a signal waveform of each part in 2nd Embodiment. It is a circuit diagram which shows the motor drive device of the electric tool in 3rd Embodiment. It is a signal waveform of each part in 3rd Embodiment. It is a circuit diagram which shows the motor drive device of the conventional electric tool.

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 ... DC motor 8a, 8b ... Two terminals of DC motor 11 ... Metal case 14 ... AC power supply 15 ... Power supply circuit 16 ... Main contact 17 ... Brake contact 18 ... Brake circuit 25 ... Field effect transistor 34 ... Yoke 35 ... Photocoupler 36, 44 ... Resistance 47 ... Transmitter (OSC)
G ... Gate D ... Drain S ... Source B ... Base C ... Collector E ... Emitter

Claims (4)

In a motor drive device for an electric tool comprising: a power supply circuit that rectifies alternating current from an alternating current power supply and supplies power to the direct current motor; and a brake circuit that applies a brake current to the direct current motor by opening the main contact of the power supply circuit.
The brake circuit includes a field effect transistor and an electronic switch control circuit that supplies a gate voltage that turns on the field effect transistor in synchronization with a half cycle of the AC power source via a photocoupler when the main contact is opened. Have
A motor drive device for an electric tool, wherein the drain and source of the field effect transistor are connected to two terminals of a DC motor, respectively. In the motor drive device of the electric tool according to claim 1,
The electronic switch control circuit supplies a gate voltage to turn on the field effect transistor in synchronization with the cycle of the AC power supply via a photocoupler when the main contact is opened. apparatus. In the motor drive device of the electric tool according to claim 1,
The electronic switch control circuit includes a transmitter for supplying a gate voltage for turning on a field effect transistor at an arbitrary timing via a photocoupler when the main contact is opened. . In the motor drive device of the electric tool according to any one of claims 1 to 3,
The electric field effect transistor is attached to a yoke of a DC motor or a case of a reduction gear of the DC motor, and the motor driving device for an electric tool.

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