JP2019107717A - Electric tool - Google Patents

Abstract

To provide an electric tool which can realize falling suppression of a tip tool and quick stop of the tip tool with a good balance.SOLUTION: An electric tool comprising: a motor 6; a tip tool which is rotated by the motor 6; rotation detection means which detects a rotation number of the tip tool; a control part 50 which controls rotation of the motor 6; and an operation switch 5 for instructing drive and stop of the motor 6. The control part 50 applies a brake force to the motor 6 when the operation switch 5 is so operated as to stop the motor 6, gradually reduces the brake force according to a lapse of time after reduction of the rotation number of the tip tool or start of application of the brake force, and controls the brake force so that the rotation number of the tip tool is linearly reduced in association with the lapse of time.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a power tool such as a grinder having a braking function.

  2. Description of the Related Art Conventionally, among power tools such as grinders, one that automatically performs braking (braking) when an operation switch such as a trigger is turned off is known. Patent Document 1 below discloses setting, in the grinder, the braking force to be smaller as the moment of inertia of the attached tip tool is larger. According to this, compared with the configuration in which constant braking is performed regardless of the moment of inertia of the tip tool, when the tip tool having a large moment of inertia is attached, it is suppressed that a large reaction is applied to the user at the time of braking be able to. Further, since the braking force is set in accordance with the inertia moment of the attached tip tool, it is possible to suppress the loosening of the wheel nut (lock nut) for fixing the tip tool to the spindle at the time of braking.

International Publication No. 2016/084553

  If the moment of inertia of the tip tool is the same, the force to loosen the wheel nut at the time of braking depends on the rate of decrease of the number of turns of the tip tool. If the same braking force is applied during the period from the start of braking to the stop of the tip tool, the reduction speed of the rotational speed becomes maximum immediately before the tip tool stops, and the force to loosen the wheel nut also becomes maximum. Therefore, the foil nut is detached immediately before the tip tool is stopped, and the tip tool is easily dropped. On the other hand, if the braking force is set so that the tip tool does not fall off immediately before stopping, the tip tool can not be stopped quickly.

  The present invention has been made in recognition of such a situation, and an object thereof is to provide a power tool which can realize well-balanced prevention of tip tool dropout and quick stop of the tip tool.

One aspect of the present invention is a power tool. This power tool is
Motor,
A tip tool rotated by the motor;
Rotation detecting means for detecting the number of rotations of the tip tool;
A control unit that controls the rotation of the motor;
And an operation unit for instructing to drive or stop the motor.
When the operation unit is operated to stop the motor, the control unit applies a braking force to the motor, and a lapse of time since the rotational speed of the tip tool starts to decrease or the braking force starts to be applied. Control to gradually reduce the braking force according to

  The control unit controls the braking force so that the number of rotations of the tip tool linearly decreases with time in at least a part of a period from when the application of the braking force is started to when the tip tool is stopped. May be

  The rotation detection means may include a position sensor that detects a rotational position of a rotor of the motor.

The motor is a brushless motor,
An inverter circuit including a plurality of switching elements for supplying current to the motor;
The control unit applies an electric braking force to the motor by controlling the inverter circuit, and controls the electric braking force by controlling a duty ratio of a predetermined switching element of the inverter circuit. Good.

A decelerating portion for decelerating rotation of a rotor of the motor;
A spindle connected to the speed reducing portion and extending in a direction substantially orthogonal to the rotation axis of the rotor;
The tip tool may be attached to the spindle.

  It is to be noted that arbitrary combinations of the above-described components, and those obtained by converting the expression of the present invention among methods, systems, and the like are also effective as aspects of the present invention.

  According to the present invention, it is possible to provide an electric power tool capable of achieving well-balanced control of falling off of the tip tool and quick stop of the tip tool.

The side sectional view of the state where operation switch 5 is OFF of grinder 1 concerning an embodiment of the invention. The sectional side view in the state where operation switch 5 of grinder 1 is ON. FIG. 3A is a cross-sectional view taken along the line A-A of FIG. FIG. 3B is an arrow view of the controller box 40 of FIG. 1 viewed from the B direction. FIG. 3 is a perspective view of the gear case 4 and the packing land 11 as viewed from the front of the wheel 10, the wheel washer 14, the wheel nut 15, and the spindle 20 in a disassembled state with respect to the gear case 4 and the packing land 11; FIG. 2 is a control block diagram of a grinder 1; A control flow chart of grinder 1. FIG. 7 is a graph showing an ideal (targeted) time change of the rotational speed of the motor 6 when the brake control shown in FIG. 6 is performed. The graph which shows an example of the time change of the number of rotations of motor 6 at the time of performing brake control which makes a duty ratio fixed regarding a comparative example.

  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 shown by each drawing, a member, a process, etc., and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention, and are merely examples, and all the features described in the embodiments and the combination thereof are not necessarily essential to the invention.

  The mechanical configuration of the grinder 1 as an electric tool according to the embodiment of the present invention will be described with reference to FIGS. 1 to 4. The grinder 1 includes a grindstone 10 as a tip tool (rotary tool), and is used for a grinding operation or the like to flatten the surface of concrete, stone or the like. In addition to the disc-shaped grinding stone and the cutting stone, a disc-shaped brush, a cutter, and the like can be attached as the tip tool. The grinder 1 includes a housing 3 (for example, made of resin) and a gear case 4.

  The housing 3 has a generally cylindrical shape as a whole, and a motor (electric motor) 6 as a prime mover is accommodated in the housing 3. The motor 6 is connected to an external AC power source such as a commercial power source through a power cord 7 drawn from 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 motor 6. The housing 3 is provided with an operation switch (trigger switch) 5 as an operation unit for instructing the drive and stop of the motor 6. The operation switch 5 is urged rearward (in the direction to be turned off) by the spring 5c. However, the operation switch 5 is slid forward so that the engagement convex portion 5a is engaged with the engagement concave portion of the housing 3 as shown in FIG. The operation switch 5 can be locked in the on state by hooking it to 3a.

  The gear case 4 is made of metal such as aluminum alloy, for example, and is attached to the front end of the housing 3. The opening of the gear case 4 is closed by a packing land 11 as a lid member. The packing land 11 is fixed to the gear case 4 by, for example, screwing. The packing land 11 serves as a holding member for holding a foil guard 30 described later. Two bearings (a needle bearing 12 and a 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 motor 6, and one end thereof penetrates the packing land 11 and protrudes to the outside. On the other hand, at the other end of the spindle 20 located in the gear case 4, a second bevel gear 22 meshing with the first bevel gear 21 attached to the output shaft 6 a of the motor 6 is provided (attached). The rotation direction of the motor 6 is converted by 90 degrees by the first bevel gear 21 and the second bevel gear 22, and the rotational speed is reduced at a predetermined reduction ratio and transmitted to the spindle 20. That is, the spindle 20 is rotationally driven by the motor 6.

  The grinding wheel 10 is fixed to the spindle 20 by a wheel washer 14 and a wheel nut (lock nut) 15, and rotates integrally with the spindle 20. When the operation switch 5 provided in the housing 3 is operated, the electric power is supplied to the motor 6, and the output shaft 6a of the motor 6 is rotated. Then, the spindle 20 connected to the output shaft 6 a via the first bevel gear 21 and the second bevel gear 22 rotates, and the grindstone 10 fixed to the spindle 20 rotates. A foil guard 30 is attached to the packing land 11 to cover at least half or more of the outer circumference of the grindstone 10. The wheel guard 30 is prevented from rotating so that its rotational position does not change during operation, and the rotational position can be changed according to the work content by releasing the rotation prevention.

  The motor 6 is a brushless motor in the present embodiment, and a rotor core 6b made of a magnetic material that rotates integrally with the output shaft 6a is provided around the output shaft 6a. A plurality of (for example, four) rotor magnets 6c are inserted and held in the rotor core 6b. A stator core 6d is provided (fixed to the housing 3) around the rotor core 6b. A stator coil 6e is provided on the stator core 6d via an insulator 6f.

  In the housing 3, behind the motor 6, a controller box 40 is provided. The main board 41, the sensor board 44, and the switch board 46 are accommodated in the controller box 40, and urethane 48 is filled as shown in FIGS. 3 (A) and 3 (B). On the main substrate 41, a diode bridge 42, an inverter circuit 43, a controller 54 shown in FIG. 5 and the like are provided. The sensor substrate 44 faces the sensor magnet 8 provided at the rear end of the output shaft 6 a of the motor 6. Three Hall ICs (magnetic sensors) 45 as position sensors are provided, for example, at intervals of 60 ° on the surface of the sensor substrate 44 facing the sensor magnet 8. The rotational position (rotor position) of the motor 6 can be detected by detecting the magnetic field generated by the sensor magnet 8 with the Hall IC 45. The switch substrate 46 faces the switch magnet 5 d provided at the tip of the slide bar 5 b that slides in conjunction with the operation of the operation switch 5. Two Hall ICs (magnetic sensors) 47 are provided on the surface of the switch substrate 46 facing the switch magnet 5 d. The switch magnet 5 d faces one of the Hall ICs 47 in accordance with the on / off of the operation switch 5.

  FIG. 5 is a control block diagram of the grinder 1. The diode bridge 42 is connected to the AC power supply 51 via the noise reduction filter circuit 52. An inverter circuit 43 is provided at the output terminal of the diode bridge 42 via a power factor correction circuit 53. The power factor correction circuit 53 includes, for example, a transistor Tr, which is a MOSFET, and a gate driver IC 53a that outputs a PWM control signal to the gate of the transistor Tr. Work to reduce The inverter circuit 43 is, for example, a three-phase bridge connection of switching elements Tr1 to Tr6 formed of MOSFETs, and supplies a drive current to the motor 6. The detection resistor Rs converts the current flowing through the motor 6 into a voltage.

  In FIG. 5, the operation switch detection circuit 55 is the two Hall ICs 47 mounted on the switch substrate 46 of FIG. 1, and transmits to the controller 54 a switch operation detection signal according to the position (on / off) of the operation switch 5. When the controller 54 detects that the operation switch 5 is turned on based on the switch operation detection signal, the controller 54 turns on the power supply lamp 61. The motor current detection circuit 56 identifies the current flowing through the motor 6 based on the terminal voltage of the detection resistor Rs, and transmits a motor current detection signal to the controller 54. The control signal output circuit (gate driver IC) 57 applies a drive signal such as a PWM signal to the gate of each switching element forming the inverter circuit 43 according to the control of the controller 54.

  The rotor position detection circuit 58 detects the rotational position of the rotor of the motor 6 based on the output signal of the Hall IC 45, and transmits a rotor position detection signal to the controller 54 and the motor rotation number detection circuit 59. The motor rotation number detection circuit 59 detects the rotation number of the motor 6 based on the rotor position detection signal from the rotor position detection circuit 58, and transmits a motor rotation number detection signal to the controller 54. The controller 54 controls the control signal output circuit 57 according to the switch operation detection signal, the motor current detection signal, the rotor position detection signal, the motor rotational speed detection signal, and the position of the speed setting dial 62, The respective switching elements constituting the inverter circuit 43 are driven to rotationally drive the motor 6. The controller 54 notifies the user of the rotational speed of the motor 6 by means of the speed display section 63.

  When braking is performed in the grinder 1, an electric brake (electric brake) can be used. Specifically, in FIG. 5, the control unit 50 turns off the high side switching elements Tr1, Tr3 and Tr5 among the plurality of switching elements constituting the inverter circuit 43, and switches the low side switching elements Tr2, Tr4 and Tr6. The electric braking can be performed by turning on at least one of the two. The electric braking force at this time can be changed by the duty ratio of the on period. The braking force increases as the duty ratio of the on period increases. Therefore, the control unit 50 can generate any braking force by controlling the duty ratio in the on period.

  In the present embodiment, as described later, the control unit 50 gradually reduces the duty ratio after the start of braking, so that the number of rotations of the motor 6 (the number of rotations of the grinding wheel 10) decreases linearly. Control. In other words, the control unit 50 controls the braking force so that the amount of change in the number of revolutions per hour becomes constant. Although the control unit 50 detects the number of rotations of the motor 6, the number of rotations of the motor 6 (the number of rotations of the rotor) and the number of rotations of the grinding stone 10 reduce the rotation of the rotor. Since the speed ratio of the first bevel gear 21 and the second bevel gear 22 correspond one-to-one, the control unit 50 also detects the number of revolutions of the grindstone 10.

  FIG. 6 is a control flowchart of the grinder 1. This flowchart is started by the user turning on the operation switch 5. The control unit 50 starts the motor 6 when the operation switch 5 is turned on (S1), and continues driving (rotational speed control) of the motor 6 unless the operation switch 5 is turned off (NO in S2) (S3) ). When the operation switch 5 is turned off (YES in S2), that is, when the operation switch 5 is operated to stop the motor 6, the control unit 50 starts brake control using the electric brake (S4). Specifically, the control unit 50 performs brake control to turn on / off (PWM control) a predetermined switching element with an initial duty ratio. The initial duty ratio is determined experimentally. The control unit 50 continues the brake control at the current duty ratio for a predetermined time Δt (for example, 0.1 seconds) (S5). Step S5 may continue brake control at the current duty ratio until the number of revolutions of motor 6 decreases by Δω.

Thereafter, the control unit 50 detects the number of revolutions of the motor 6 (S6), and calculates the ideal number of revolutions (target number of revolutions) at the present time (S7). The ideal rotational speed can be calculated based on the rotational speed of the motor 6 at the start of the brake control and the elapsed time from the start of the brake control. If the detected rotational speed is not 0 (NO in S8), that is, if the motor 6 is not stopped, the control unit 50 performs the brake control according to the difference between the detected rotational speed and the calculated ideal rotational speed. The duty ratio is adjusted (S9). Specifically, the adjusted duty ratio is Xn + 1, the current duty ratio is Xn, the correction coefficient is α, the detected rotation speed (angular velocity) is ωn, and the ideal rotation speed (angular velocity) is ω * n.
X n + 1 = X n + α (ω n −ω * n) equation 1
And change the duty ratio to Xn + 1. The correction coefficient α is a positive value and is determined experimentally. When the detected number of revolutions is higher than the ideal number of revolutions (ωn> ω * n), α (ωn-ω * n) becomes a positive value, and the control unit 50 increases the duty ratio of the brake control to make the braking force Will be increased. When the detected number of revolutions is lower than the ideal number of revolutions (ωn <ω * n), α (ωn-ω * n) becomes a negative value, and the control unit 50 reduces the duty ratio of the brake control to reduce the braking force Will be reduced. Thereafter, the control unit 50 repeats the adjustment of the duty ratio according to the calculation of the equation 1 every time the predetermined time Δt elapses (S5 to S9), and when the detected rotational speed becomes 0 (YES in S8), that is, the motor 6 When is stopped, the brake control is stopped (S10).

  FIG. 7 is a graph showing an ideal (targeted) time change of the rotational speed of the motor 6 when the brake control shown in FIG. 6 is performed. FIG. 8 is a graph showing an example of a time change of the number of revolutions of the motor 6 in the case of performing the brake control in which the duty ratio is constant regarding the comparative example.

  As shown in FIG. 8, in the brake control in which the duty ratio is constant, the reduction speed of the rotation speed of the motor 6 follows the passage of time (the reduction of the rotation speed of the motor 6) from the start of brake control (time t0). growing. For this reason, the foil nut 15 is removed immediately before the grinding wheel 10 stops, and the grinding wheel 10 is easily detached. On the other hand, if the duty ratio (braking force) is set so that the grindstone 10 does not fall off immediately before the stop, the grindstone 10 can not be stopped quickly.

  On the other hand, as shown in FIG. 7, according to the present embodiment, the duty ratio in brake control is gradually reduced according to the passage of time (the reduction of the number of rotations of motor 6) (the braking force is gradually By making it smaller, the number of revolutions of the motor 6 can be decreased linearly with the passage of time. For this reason, the grinding wheel 10 is rapidly stopped while suppressing the falling off of the grinding wheel 10 by setting the speed (inclination) of the rotation speed reduction of the motor 6 to the maximum within the range where the wheel nut 15 can reliably prevent the falling off. (It is possible to achieve well-balanced prevention of falling off of the grinding wheel 10 and quick stop of the grinding wheel 10).

  Although the present invention has been described above by taking the embodiment as an example, 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. It is a place. The following describes the modification.

  The control unit 50 derives the moment of inertia of the tip tool based on the rate of change in rotational speed at the time of deceleration of the motor 6, the rate of change in rotational speed at the time of acceleration (at start) of the motor 6, or the starting current of the motor 6, The initial duty ratio in the brake control, the target rotational speed reduction speed of the motor 6, and the correction coefficient α of the equation 1 may be determined according to the moment of inertia of When the moment of inertia is not derived, the initial duty ratio in brake control, the target speed reduction speed of the motor 6 as a target of the largest moment of inertia among the tip tools that can be mounted on the grinder 1, the correction coefficient of Equation 1 It is sufficient to determine α in advance.

  The control unit 50 gradually decreases the duty ratio in accordance with the passage of time (brake control in which the number of rotations of the motor 6 is linearly decreased with the passage of time), and stops the motor 6 from the start of the brake control. The braking control may be performed with a fixed duty ratio limited to a part (for example, only the second half) of the up to braking periods. Also in this case, as compared with the case where the brake control is performed at the fixed duty ratio in all of the braking period, it is possible to realize well-balanced suppression of the falling off of the grinding wheel 10 and quick stop of the grinding wheel 10.

  The power tool according to the present invention is not limited to a grinder, and may be, for example, a circular saw, a concrete cutter, a cutter, a lawn mower, or any other type of power tool to which a tip tool having a relatively large moment of inertia can be attached. . Further, the electric power tool according to the present invention is not limited to a corded type (AC drive) operated by power from an external AC power supply, and may be a cordless type (DC drive) operated by power of a battery pack.

Reference Signs List 1 grinder, 3 housing, 3a locking recess, 4 gear case, 5 operation switch (trigger switch), 5a locking protrusion, 5b slide bar, 5c spring, 5d switch magnet, 6 motor (electric motor), 6a output shaft, 6b rotor core, 6c rotor magnet, 6d stator core, 6e stator coil, 6f insulator, 7 power cord, 8 sensor magnet, 10 grindstone (tip tool), 11 packing land (holding member), 12 needle bearing, 13 ball bearing, 14 foil Washer, 15 wheel nut (lock nut), 20 spindle, 21 first bevel gear, 22 second bevel gear, 30 wheel guard, 40 controller box, 41 main board, 42 diode bridge, Reference Signs List 3 inverter circuit, 44 sensor board, 45 hole IC (magnetic sensor), 46 switch board, 47 hole IC (magnetic sensor), 48 urethane, 50 control unit, 51 AC power supply, 52 filter circuit, 53 power factor improvement circuit, 53a Gate driver IC, 54 controller, 55 operation switch detection circuit, 56 motor current detection circuit, 57 control signal output circuit (gate driver IC), 58 rotor position detection circuit, 59 motor rotation number detection circuit, 61 energizing lamp, 62 speed Setting dial, 63 speed display, Rs detection resistance

Claims (5)

Motor,
A tip tool rotated by the motor;
Rotation detecting means for detecting the number of rotations of the tip tool;
A control unit that controls the rotation of the motor;
And an operation unit for instructing to drive or stop the motor.
When the operation unit is operated to stop the motor, the control unit applies a braking force to the motor, and a lapse of time since the rotational speed of the tip tool starts to decrease or the braking force starts to be applied. The electric power tool performs control to gradually reduce the braking force according to.   The control unit controls the braking force so that the number of rotations of the tip tool linearly decreases with the passage of time during at least a part of a period from when the application of the braking force is started to when the tip tool is stopped. The power tool according to claim 1.   The power tool according to claim 1, wherein the rotation detection unit includes a position sensor that detects a rotational position of a rotor of the motor. The motor is a brushless motor,
An inverter circuit including a plurality of switching elements for supplying current to the motor;
The control unit applies an electric braking force to the motor by controlling the inverter circuit, and controls the electric braking force by controlling a duty ratio of a predetermined switching element of the inverter circuit. The power tool according to any one of Items 1 to 3. A decelerating portion for decelerating rotation of a rotor of the motor;
A spindle connected to the speed reducing portion and extending in a direction substantially orthogonal to the rotation axis of the rotor;
The power tool according to any one of claims 1 to 4, wherein the tip tool is attached to the spindle.

Images