JP2017213614A - Electric tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric tool capable of actuating a brake not through an inverter circuit.SOLUTION: A brushless motor 6 comprises: a stator including a stator coil 6d composed of three-phase stator coils U, V and W of star connection and a stator core 6c; and a rotor 6b. An inverter circuit 47 has switching elements Q1 to Q6, and controls the brushless motor 6. A control part 40 controls the inverter circuit 47. A brake switch 5c is connected independently of the inverter circuit 47 with a U-phase stator coil 6d. When the brake switch 5c becomes ON, a closed circuit (a closed circuit not through the inverter circuit 47) passing the U-phase stator coil 6d and the brake switch 5c is formed, and a brake current flows through the closed circuit.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electric tool with a brake using a brushless motor as a drive source.

  In an electric tool that uses a brushless motor as a drive source, coil current generated by converting mechanical energy stored in the rotor into electrical energy through a magnetic circuit is used as an external switching element dedicated to braking, and a motor drive switching circuit (inverter circuit) There is known a configuration in which a motor is forcedly braked by being consumed in a closed circuit including a diode provided in the motor and a motor coil (Patent Document 1 below).

JP 2007-124728 A

  In the configuration of Patent Document 1, since a brake current flows through the inverter circuit, there is a risk of damaging the inverter circuit when the brake current is large.

  The present invention has been made in view of such a situation, and an object thereof is to provide an electric tool capable of operating a brake without using an inverter circuit.

One embodiment of the present invention is a power tool. This electric tool
A brushless motor having a stator having at least one coil, and a rotor facing the stator;
An inverter circuit having a plurality of first switching elements and connected to the coil to control the brushless motor;
A control unit for controlling the inverter circuit;
And a brake circuit connected to the coil independently of the inverter circuit.

  The brake circuit may form a closed circuit that passes through the coil and does not pass through the first switching element, and a brake current may flow through the closed circuit.

An operation unit for instructing to drive and stop the brushless motor;
The brake circuit may include a switch that switches the closed circuit to a closed state or an open state in conjunction with an operation of the operation unit.

  The brake circuit may include a second switching element that is turned on or off by a signal from the control unit and switches the closed circuit to a closed state or an open state.

  The second switching element may have a maximum allowable current larger than that of the first switching element.

An operation unit for instructing to drive and stop the brushless motor;
The brake circuit may include a relay switch that switches the closed circuit to a closed state or an open state in conjunction with an operation of the operation unit.

  The relay switch may close the closed circuit when there is no current supply to its electromagnet.

The brushless motor has a plurality of phases and the coils in each phase;
The brake circuit may form a closed circuit that passes through the predetermined one-phase coil and does not pass through the other-phase coil.

  It should be noted that any combination of the above-described constituent elements, and those obtained by converting the expression of the present invention between methods and systems are also effective as aspects of the present invention.

  According to the present invention, it is possible to provide an electric tool capable of operating a brake without using an inverter circuit.

The plane sectional view of the grinder 1 as an electric tool which concerns on Embodiment 1 of this invention. 1 is a side sectional view of a grinder 1. FIG. 1 is a circuit block diagram of a grinder 1. FIG. The circuit block diagram of the grinder which concerns on Embodiment 2 of this invention. The control flowchart by the control part 40 shown in FIG. The circuit block diagram of the grinder which concerns on Embodiment 3 of this invention. The top view of the grinder which concerns on Embodiment 4 of this invention. FIG. The circuit block diagram.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

Embodiment 1
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2, the front-rear, top-bottom, and left-right directions are defined. As shown in FIGS. 1 and 2, the grinder 1 includes a grindstone 2 as a rotary tool and is used for a grinding operation for flattening the surface of a welded portion. In addition, cutting work can also be performed by using a grindstone for cutting as a rotary tool. The grinder 1 includes a housing 3 (for example, made of resin) and a gear case 4.

  The housing 3 has a substantially cylindrical shape as a whole, and a brushless motor 6 as a drive source is accommodated in the housing 3. The brushless motor 6 receives power supply from a battery 7 that is detachably attached to the rear end of the housing 3. A first bevel gear 21 is provided at the front end of the output shaft 6 a of the brushless motor 6. The output shaft 6a is also provided with a cooling fan 8 such as a motor. The fan 8 is located in front of the brushless motor 6.

  In the housing 3, there is provided a switch mechanism 5 for switching on / off of an electrical connection between the battery 7 and the brushless motor 6 and opening / closing of a brake closed circuit described later. The switch mechanism 5 includes a main switch 5b (FIG. 3) for switching on / off the electrical connection between the battery 7 and the brushless motor 6, and a brake switch 5c (switching the open / close state of the brake closed circuit). ), And a button 5a for switching on and off the main switch 5b and the brake switch 5c. In the switch mechanism 5, when the button 5a is pressed, the main switch 5b is turned on and the brake switch 5c is turned off (brake is disabled). On the other hand, in the switch mechanism 5, when the button 5a is not pressed, the main switch 5b is turned off and the brake switch 5c is turned on (brake enabled).

  On the outside of the housing 3, a power lever 3b is provided as an operation unit for operating the switch mechanism 5 (operating the button 5a). The power lever 3 b can be rotated around a fulcrum 3 c provided in the housing 3. The on / off state of the switch mechanism 5 (whether or not the button 5a is pressed) is switched by a predetermined operation with respect to the power lever 3b, and the presence / absence of energization of the brushless motor 6 and the validity / invalidity of the brake are switched.

  A substrate 9 on which a plurality of switching elements 15 constituting an inverter circuit 47 (FIG. 3) described later is mounted is provided behind the brushless motor 6 in the housing 3. The switching element 15 integrally has a cooling fin 15a. Each member constituting the control unit 40 shown in FIG. 3 is mounted on the substrate 9. As shown in FIG. 2, the housing 3 is provided with a speed setting dial 3d, and the user can switch the set rotational speed of the brushless motor 6 by operating the speed setting dial 3d.

  As shown in FIG. 2, the gear case 4 includes a case main body 10 (for example, a metal such as an aluminum alloy) and a packing land 11 as a lid member that closes an opening of the case main body 10. The case body 10 is attached to the front end portion of the housing 3. Two bearings (needle bearing 12 and ball bearing 13) are provided inside the gear case 4, and the spindle 20 is rotatably held by these bearings. The spindle 20 is orthogonal to the output shaft 6 a of the brushless motor 6, and one end of the spindle 20 passes through the packing land 11 and protrudes to the outside. On the other hand, a second bevel gear 22 that meshes with a first bevel gear 21 attached to the output shaft 6 a of the brushless motor 6 is provided (attached) to the other end of the spindle 20 located in the gear case 4. The rotation of the brushless motor 6 is converted by the first bevel gear 21 and the second bevel gear 22 into a rotation direction of 90 degrees, and the rotation speed is reduced and transmitted to the spindle 20. That is, the spindle 20 is rotationally driven by the brushless motor 6.

  The grindstone 2 is fixed to the spindle 20 by a wheel washer and a lock nut, and rotates integrally with the spindle 20. The foil guard 14 is attached to the packing land 11 and covers about half of the grindstone 2 to prevent scattering of cutting powder, sparks and the like generated during the grinding operation. When the user operates the power supply lever 3b, electric power is supplied from the battery 7 to the brushless motor 6, the output shaft 6a of the brushless motor 6 rotates, and is connected to the output shaft 6a by the first bevel gear 21 and the second bevel gear 22. The spindle 20 being rotated rotates, and the grindstone 2 fixed to the spindle 20 rotates.

  FIG. 3 is a circuit block diagram of the grinder 1. The brushless motor 6 is a so-called inner rotor type and has a stator and a rotor 6b. The stator includes a stator coil 6d composed of three-phase stator windings U, V, and W connected in a star connection and a stator core 6c. The rotor 6b includes a rotor magnet 6e including a plurality of sets (two sets in the present embodiment) of N poles and S poles. The stator and the rotor 6b face each other in the radial direction of the output shaft 6a. The three position detection elements 42 are magnetic sensors such as Hall elements, for example, and are arranged at predetermined intervals in the circumferential direction, for example, every 60 degrees, in order to detect the rotational position of the rotor 6b.

  The main switch 5 b is provided between the plus terminal of the battery 7 and the inverter circuit 47. The brake switch 5c constituting the brake circuit is provided between both ends of the U-phase stator coil 6d. The main switch 5b and the brake switch 5c are set so that when one is turned on, the other is turned off according to the operation of the power lever 3b shown in FIG. 2 (depending on whether the button 5a is pressed). Composed. Both the main switch 5b and the brake switch 5c are mechanical switches.

  The rotor position detection circuit 43 generates a rotation position detection signal based on the signal from the position detection element 42 and transmits the rotation position detection signal to the calculation unit 41 and the rotation speed detection circuit 44. The rotation speed detection circuit 44 detects the rotation speed of the brushless motor 6 based on the rotation position detection signal, and transmits the rotation speed detection signal to the calculation unit 41. The rotation speed setting circuit 46 sets the rotation speed of the brushless motor 6 according to the position of the speed setting dial 3 d and transmits a rotation speed setting signal to the calculation unit 41. The calculation unit 41 controls the energization direction and time of the stator windings U, V, and W according to the rotation position detection signal, and drives the brushless motor 6 to rotate. The calculation unit 41 also controls the control signal output circuit 16 according to the rotation speed detection signal and the rotation speed setting signal to adjust the speed of the brushless motor 6.

  The inverter circuit 47 includes six switching elements Q1 to Q6 (corresponding to the switching elements 15 in FIGS. 1 and 2) such as FETs and IGBTs as first switching elements connected in a three-phase bridge form. The gates of the six switching elements Q1 to Q6 that are bridge-connected are connected to the control signal output circuit 16, and the drains or sources of the six switching elements Q1 to Q6 are star-connected stator windings. Connected to U, V, W. The six switching elements Q1 to Q6 perform a switching operation according to the switching element drive signals H1 to H6 input from the control signal output circuit 16, and the DC voltage of the battery 7 applied to the inverter circuit 47 is three-phase (U-phase). , V phase and W phase) are supplied to the stator windings U, V, W as voltages Vu, Vv, Vw.

  Of the switching element drive signals H1 to H6, signals (H4 to H6) applied to the gates of the low-side switching elements Q4 to Q6 or signals (H1 to H3) applied to the gates of the high-side switching elements Q1 to Q3. ) Is a pulse width modulation signal (PWM signal), and the amount of power supplied to the brushless motor 6 is adjusted by changing the duty of the PWM signal, and the brushless motor 6 is started, stopped, and rotated. The speed can be controlled.

  The calculation unit 41 is, for example, a microcomputer, not shown, but a central processing unit (CPU) for outputting a drive signal based on the processing program and data, a ROM for storing the processing program and control data, and data RAM, a timer, etc. are temporarily stored. The control signal output circuit 16 generates a drive signal for alternately switching predetermined switching elements Q1 to Q6 based on the output signal of the rotor position detection circuit 43 according to the control of the calculation unit 41. As a result, the predetermined windings of the stator windings U, V, and W are alternately energized to rotate the rotor 6b.

  The current value supplied to the brushless motor 6 (the current value flowing through the detection resistor Rs) is measured by the current detection circuit 48, and the value is fed back to the calculation unit 41 to monitor the load of the brushless motor 6. Based on the voltage on the brushless motor 6 side (inverter circuit 47 side) of the main switch 5b and the voltage on the negative terminal of the battery 7, the switch operation detection circuit 45 turns on / off the main switch 5b (operation of the power lever 3b by the user). ) And a switch operation detection signal is transmitted to the calculation unit 41. The calculation unit 41 turns off all the switching elements Q1 to Q6 when the main switch 5b is off.

  When the user operates the power supply lever 3b in FIG. 2 to turn off the main switch 5b while the brushless motor 6 is rotated, the brake switch connected to the U-phase stator coil 6d independently of the inverter circuit 47. 5c is turned on. Then, the voltage generated at both ends of the U-phase stator coil 6d due to the rotation of the rotor 6b causes a brake current to flow in a closed circuit (a closed circuit that does not pass through the inverter circuit 47) that passes through the U-phase stator coil 6d and the brake switch 5c. Flows to generate a braking force that decelerates the rotation of the brushless motor 6.

  According to the present embodiment, the following effects can be achieved.

(1) When the brake switch 5c is turned on, a brake current flows through a closed circuit (a closed circuit that does not pass through the inverter circuit 47) passing through the U-phase stator coil 6d and the brake switch 5c to generate a braking force. Since the brake current does not flow through the switching elements Q1 to Q6 of the inverter circuit 47, the risk that the switching elements Q1 to Q6 are destroyed by an excessive brake current can be suppressed. Further, the switching elements Q1 to Q6 do not need to have high specifications so as to withstand an excessive brake current, and the cost is low.

(2) For example, when braking is performed with the switching elements Q4 and Q5 turned on, a closed circuit is formed of the switching element Q4, the U-phase stator coil 6d, the V-phase stator coil 6d, the switching element Q5, and the switching element Q4. Since the brake current is generated by the voltage generated in the U-phase and V-phase stator coils 6d, the braking force is too great and the reaction is difficult to use. In this embodiment, when the brake switch 5c is turned on, both ends of the U-phase stator coil 6d are short-circuited, while both ends of the V-phase and W-phase stator coils 6d are open. Compared with the case of short-circuiting, the braking force is weaker, the reaction is suppressed and easy to use, and the risk of the whetstone 2 falling off can be suppressed.

(3) On / off of the brake switch 5c is switched by the user's operation of the power lever 3b and does not depend on the control of the control unit 40. Therefore, even when the main power is shut off due to the battery 7 dropping off, the user can The brake can be applied by the operation of 3b.

Embodiment 2
FIG. 4 is a circuit block diagram of a grinder according to the second embodiment of the present invention. Compared with the first embodiment, the configuration of the grinder of this embodiment is such that the brake switch 5c shown in FIG. 3 is changed to a switching element Q7 such as an FET or IGBT as the second switching element shown in FIG. The difference is that the gate as the control terminal of the switching element Q7 and the control signal output circuit 16 are connected to each other, and the other points are the same. Switching element Q7 has a larger allowable maximum current than switching elements Q1-Q6. The calculation unit 41 transmits a signal to the gate of the switching element Q7 via the control signal output circuit 16, and turns off the switching element Q7 while the main switch 5b is on, and turns off the switching element Q7 when the main switch 5b is off. turn on.

  FIG. 5 is a control flowchart by the control unit 40 shown in FIG. This flowchart starts from a state where the brushless motor 6 is stopped. When the main switch 5b is turned on (S1, Yes), the arithmetic unit 41 turns off the switching element Q7 through the control signal output circuit 16 (S2), and drives the inverter circuit 47 through the control signal output circuit 16. The brushless motor 6 is driven (S3). When the main switch 5b is turned off (S4, Yes), the calculation unit 41 stops the inverter circuit 47 (S5), that is, turns off all the switching elements Q1 to Q6 and turns on the switching element Q7 (S6). Thereafter, when the brushless motor 6 is stopped (S7, Yes), the calculation unit 41 turns off the switching element Q7 (S8).

  In the present embodiment, when the main switch 5b is turned off, a brake current flows through a closed circuit passing through the U-phase stator coil 6d and the switching element Q7, and a braking force is generated. According to the present embodiment, although the brake cannot be applied when the main power supply is shut off, the same effects as those of the first embodiment can be obtained in other respects. In the present embodiment, when the brake is applied (in step S6 in FIG. 5), the control signal output circuit 16 turns on and off the switching element Q7 by, for example, PWM control. The power can be adjusted. Note that although the brake current flows through the switching element Q7, the switching element through which the brake current flows is only the switching element Q7. Therefore, it is only necessary to increase the allowable maximum current only in the switching element Q7, and the cost is suppressed.

Embodiment 3
FIG. 6 is a circuit block diagram of a grinder according to Embodiment 3 of the present invention. In the present embodiment, the relay switch 50 is used to switch the brake between enabled and disabled. That is, the configuration of the grinder of the present embodiment is different from that of the first embodiment in that the brake switch 5c shown in FIG. 3 is replaced with the brake switch 51 of the relay switch 50 shown in FIG. Is different between the main switch 5b between the brushless motor 6 side (inverter circuit 47 side) of the main switch 5b and the negative terminal of the battery 7, and the other points are the same. In the relay switch 50, the electromagnet 52 turns off the brake switch 51 when the main switch 5b is on (when a current flows through itself), and turns off when the main switch 5b is off (when no current flows through itself). ) Turns on the brake switch 51. Therefore, when the main switch 5b is turned off, a brake current flows through a closed circuit passing through the U-phase stator coil 6d and the brake switch 51, and a braking force is generated. According to the present embodiment, the brake can be applied regardless of the operation of the power supply lever 3b when the main power is cut off, and the same effects as those of the first embodiment can be obtained in other respects.

Embodiment 4
7 is a plan view of a grinder according to Embodiment 4 of the present invention, FIG. 8 is a sectional side view thereof, and FIG. 9 is a block diagram of the same circuit. The grinder of the present embodiment is AC driven, is connected to an AC power source 60 (FIG. 9) by a power cord 62 shown in FIGS. 7 and 8, and operates with power supplied from the AC power source 60. Further, the power lever 3b shown in FIG. 2 is replaced with a slide type operation unit 3e shown in FIG. In the circuit of FIG. 9, the battery 7 shown in FIG. 3 is replaced with an AC power source 60 and a diode bridge 61 as a full-wave rectifier circuit. Other points of the present embodiment are the same as those of the first embodiment, and the same effects can be achieved. Even when the grinder is AC driven, the brake circuit may be configured as in the second and third embodiments.

  The present invention has been described above by taking the embodiment as an example. However, it is understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, modifications will be described.

  In the embodiment, an example in which the stator coil 6d is star-connected (Y-connected) has been described, but the stator coil 6d may be Δ-connected. In the embodiment, the braking force is generated by short-circuiting both ends of the U-phase stator coil 6d. However, the braking force may be generated by short-circuiting both ends of the other-phase stator coil 6d. Further, the braking force may be generated by short-circuiting both ends of the multi-phase stator coil 6d. When the closed circuit for braking is opened and closed with a switching element such as an FET or IGBT as in the second embodiment, only one direction of current can be cut off with one switching element. The two-way current may be cut off using two switching elements. The power tool is not limited to the grinder exemplified in the embodiment, and may be another type with a brake.

1 grinder (disc grinder), 2 grinding wheel (rotary tool), 3 housing, 3b power lever (operating part), 3c fulcrum, 3d speed setting dial, 4 gear case, 5 switch mechanism, 5a button, 5b main switch, 5c for brake Switch (brake circuit), 6 Electric motor (brushless motor), 6a Output shaft, 7 Battery (battery pack), 7a Latch operation part, 8 Fan, 9 Board, 10 Case body, 11 Packing land, 12 Needle bearing, 13 ball Bearing, 14 Wheel guard, 15 Switching element (first switching element), 15a Cooling fin, 16 Control signal output circuit, 20 Spindle, 21 First bevel gear, 22 Second bevel gear, 30 Filter member, 40 Control unit, 41 Calculation (Microcomputer) 50 relay switch (brake circuit), 51 a switch for brake, 52 electromagnets, 60 AC power supply, 61 a diode bridge (full-wave rectifying circuit), 62 power cord

Claims (8)

A brushless motor having a stator having at least one coil, and a rotor facing the stator;
An inverter circuit having a plurality of first switching elements and connected to the coil to control the brushless motor;
A control unit for controlling the inverter circuit;
And a brake circuit connected to the coil independently of the inverter circuit.   2. The electric tool according to claim 1, wherein the brake circuit forms a closed circuit that passes through the coil and does not pass through the first switching element, and a brake current flows through the closed circuit. 3. An operation unit for instructing to drive and stop the brushless motor;
The power tool according to claim 2, wherein the brake circuit includes a switch that switches the closed circuit to a closed state or an open state in conjunction with an operation of the operation unit.   The power tool according to claim 2, wherein the brake circuit includes a second switching element that is turned on or off by a signal from the control unit to switch the closed circuit to a closed state or an open state.   The power tool according to claim 4, wherein the second switching element has an allowable maximum current larger than that of the first switching element. An operation unit for instructing to drive and stop the brushless motor;
The power tool according to claim 2, wherein the brake circuit includes a relay switch that switches the closed circuit to a closed state or an open state in conjunction with an operation of the operation unit.   The power tool according to claim 6, wherein the relay switch closes the closed circuit when current supply to the electromagnet of the relay switch is lost. The brushless motor has a plurality of phases and the coils in each phase;
The electric power tool according to any one of claims 1 to 7, wherein the brake circuit forms a closed circuit that passes through the coil of a predetermined phase and does not pass through the coil of another phase.

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