WO2015129904A1

WO2015129904A1 - Electric tool

Info

Publication number: WO2015129904A1
Application number: PCT/JP2015/056013
Authority: WO
Inventors: Yoshikazu Kawano; Toshiaki Koizumi; Ryuichi Imamura; Yuuichi TOYOSHIMA
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2014-02-27
Filing date: 2015-02-23
Publication date: 2015-09-03
Also published as: JP6274414B2; JP2015160284A

Abstract

An electric tool includes: a motor; a control unit configured to control the motor. When the motor is accelerated from a stationary state to a target rotation number, the control unit makes an increase rate of a rotation number of the motor just after energization of the motor starts higher than the increase rate of the rotation number of the motor just before the motor reaches the target rotation number.

Description

DESCRIPTION

Title of Invention

ELECTRIC TOOL

TECHNICAL FIELD

The present invention relates to an electric tool such as a tabletop round saw and a grinder.

BACKGROUND ART

Regarding a method of controlling a rotation number of a motor of an electric tool, a constant rotation number control for keeping the motor at a set rotation number even though a load is varied has been known. The constant rotation number control is a feedback control of detecting a rotation number of the motor by a rotation number detection means and controlling a difference between the detected result and a set rotation number to be zero. In an electric tool using an AC motor, a difference between a detected rotation number and a set rotation number is reflected in a change of a conduction angle of a switching element such as a triac. The conduction angle means a phase angle, at which the triac becomes on, of an angle range (0° to 180°) from a zero cross point to a next zero cross point. In an electric tool using a DC motor, a difference between a detected rotation number and a set rotation number is reflected in a change of a duty of a PWM signal applied to a switching element such as a FET.

Patent Document 1

Japanese Patent Application Publication No. 2010-012547A

SUMMARY OF INVENTION

In the electric tool, a soft start control of gently increasing a rotation number of the motor is performed so as to suppress reaction upon startup of the motor. In the soft start control, the rotation number of the motor is gradually increased at an early stage and a gradient of the increase in the rotation number is increased over time. For this reason, a change in rotational acceleration (a gradient of the increase in the rotation number) is large before and after the motor reaches a target rotation number, so that the high reaction is applied to a user's hand when the motor reaches the target rotation number and enters a constant speed area. The reaction applied when the motor enters the constant speed area can be reduced by decreasing the rotational acceleration before the motor reaches the target rotation number. However, according to this method, the time (startup time of the motor) necessary for the motor to reach the target rotation number is prolonged. In the electric tool, the motor may be frequently ON and OFF in some cases. Therefore, it is also important to rapidly start the motor, in addition to the reaction reduction.

It is therefore an object of the present invention to provide an electric tool capable of saving time necessary for a motor to start up while suppressing reaction to be applied to a user's hand.

An aspect of the present disclosure provides the following arrangements:

(1) An electric tool comprising:

a motor; and

a control unit configured to control the motor;

wherein when the motor is accelerated from a stationary state to a target rotation number, the control unit makes an increase rate of a rotation number of the motor just after energization of the motor starts higher than the increase rate of the rotation number of the motor just before the motor reaches the target rotation number.

(2) The electric tool according to (1), wherein the control unit gradually lower the increase rate of the rotation number of the motor from a predetermined timing after the energization of the motor starts until the motor reaches the target rotation number.

(3) The electric tool according to (2), wherein the predetermined timing is a timing at which predetermined time elapses after the energization of the motor starts.

(4) The electric tool according to (2), wherein the predetermined timing is a timing at which the motor reaches a predetermined rotation number of the motor.

(5) The electric tool according to any one of (1) to (4), wherein the control unit control the motor by different control methods or different control gains during a first control time period for which predetermined time elapses after the energization of the motor starts or at which the motor reaches a predetermined rotation number and during a second control time period following the first control time period.

(6) The electric tool according to (5), wherein the control unit performs one of a proportional control during the first control time period and performs the proportional control and a differential control during the second control time period.

(7) The electric tool according to (6), wherein the control unit further performs an integral control during the first control time period and performs the integral control during the second control time period.

(8) The electric tool according to (6), wherein a control gain of the proportional control during the first control time period is smaller than the control gain of the proportional control during the second control time period.

(9) The electric tool according to any one of (5) to (8), wherein the control unit rapidly increases a valid value of a voltage applied to the motor to an initial value before the first control time period starts.

(10) The electric tool according to any one of (1) to (9) further comprising a switching element connected in series with the motor,

wherein the control unit changes one of a conduction angle of the switching element and a duty of a PWM signal applied to a control terminal of the switching element to control a valid value of the voltage applied to the motor.

(11) The electric tool according to any one of (1) to (10), wherein the control unit switches a control gain depending on a frequency of an input power supply.

(12) The electric tool according to any one of (1) to (11), wherein the motor is configured to rotate one of a round saw blade and a grind stone.

In the meantime, any combination of the above-described constitutional elements and a conversion of the expression of the present invention into a method, a system and the like are also effective as aspects of the present invention. According to the present invention, it is possible to provide the electric tool capable of saving time necessary for the motor to start up while suppressing reaction applied to a user's hand.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a circuit diagram of an electric tool according to a first illustrative embodiment of the present invention.

Fig. 2 is a flowchart showing a rotation number control in the electric tool of

Fig. 1.

Fig. 3 illustrates startup characteristics showing changes of a rotation number of a motor and a force applied to a main body of the electric tool over time when the control shown in Fig. 2 is performed.

Fig. 4 is a circuit diagram of an electric tool according to a second illustrative embodiment of the present invention.

Fig. 5 is a table showing examples of a diameter of a saw blade, an initial conduction angle of a triac 24, an initial valid value of a voltage applied to the motor 3 and startup time of the motor 3 when the electric tool of the first illustrative embodiment is a round saw.

Fig. 6 is a table showing examples of the diameter of the saw blade, an initial duty of a PWM signal applied to switching elements Ql to Q6 (at least one of switching elements of a high side or switching elements of a low side), the initial valid value of the voltage applied to the motor 3 and startup time of the motor 3 when the electric tool of the second illustrative embodiment is a round saw.

Fig. 7 shows a relation between the initial valid value (a horizontal axis) of the voltage applied to the motor 3 and an initial reaction force and startup time (a vertical axis) in the first and second illustrative embodiments.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred illustrative embodiments of the present invention will be described in detail with reference to the drawings. In the meantime, the same or equivalent constitutional elements, members, processing and the like shown in the respective drawings are denoted with the same reference numerals and the overlapping descriptions are appropriately omitted. Also, the illustrative embodiments are just exemplary, not to limit the present invention, and all features and combinations thereof described in the illustrative embodiments cannot be considered as the essentials of the present invention.

First Illustrative Embodiment

Fig. 1 is a circuit diagram of an electric tool according to a first illustrative embodiment of the present invention. An alternating current (AC) power supply 1 is a single phase 100V of 50 Hz or 60 Hz, for example, and becomes on and off by a switch 2. A rotation control device 4 has a rotation number sensor 6 configured to detect a rotation number of a motor 3, a rotation number signal amplification circuit 5 configured to amplify a rotation number signal output from the rotation number sensor 6, a microcomputer 23 functioning as a controller, a power supply circuit 7 configured to generate reference power supply in the microcomputer 23 and a control circuit, a zero cross detection circuit 8 configured to detect a zero cross point of an alternating current voltage from the AC power supply 1, a triac 24, which is an example of a semiconductor device (a switching element) for phase controlling a voltage supplied to the motor 3, a resistor 25 configured to input a gate signal of the triac 24, resistors 26, 28 and a variable resistor 27 configured to set the rotation number of the motor 3.

The rotation number signal amplification circuit 5 is an alternating current amplifier having capacitors 9, 15, resistors 10, 11, 12, 14 and a transistor 13, and is configured to amplify a rotation number signal from the rotation number sensor 6 within a range of 0V to -VCC and to output the same to the microcomputer 23. The microcomputer 23 is configured to detect the rotation number of the motor 3 using the output signal.

The power supply circuit 7 is a half wave rectification circuit having a diode 16, a resistor 17, a zener diode 18 and an electrolytic capacitor 19, and is configured to covert the AC voltage from the AC power supply 1 into a direct current (DC) voltage (- VCC) and to supply the same to the microcomputer 23 and the other circuits.

The zero cross detection circuit 8 has resistors 20, 21 and a photo coupler 22. The AC voltage from the AC power supply 1 is first attenuated by the resistor 20 and is then input to an input part (a light emitting diode) of the photo coupler 22. The input part of the photo coupler 22 is configured by arranging two light emitting diodes in parallel so that forward directions thereof are opposite to each other, and is configured to emit light when current flows in any direction and to be OFF only in the vicinity of a zero cross point at which a voltage is low. An output part of the photo coupler 22 consists of a photo transistor and becomes ON only when the light emitting diodes of the input part emit the light. That is, since the photo transistor becomes off only at the zero cross point of the AC voltage and becomes ON at the other states, the microcomputer 23 is input with 0 V through the resistor 21 only at the zero cross point of the AC voltage and is input with the DC voltage (-VCC) through the photo transistor at the other states. As the input signal from the zero cross detection circuit 8 is changed, the microcomputer 23 can obtain a reference signal for phase controlling the triac 24.

The resistors 26, 28 and a variable resistor 27 are provided to generate and input a target rotation number setting voltage to the microcomputer 23. The variable resistor 27 is a means enabling a user to freely set a rotation number by a dial from an outside in accordance with a work application, for example, a rotation number setting means attached to the electric tool and setting a rotation number of the motor 3 at several stages (for example, four (1 to 4) stages of the dial).

The rotation number control (feedback control) of the motor 3 by the microcomputer 23 is any one of a proportional control, an integral control and a differential control or a combination control of two or more controls thereof. The respective controls are described below.

^• proportional control (P control) ^■■· a control of using a product of a proportional control gain KP and a deviation of a target rotation number and a detected rotation number, as a change amount in a conduction angle of the triac 24 (an equation thereof is as follows).

change amount in a conduction angle of the triac

= proportional control gain KP χ deviation NO

^• integral control (I control) - a control of using a product of an integral control gain KI and a cumulative value of deviations of a target rotation number and detected rotation numbers, as a change amount in a conduction angle of the triac 24 (an equation thereof is as follows).

change amount in a conduction angle of the triac

= integral control gain KI χ (deviation NO of this time + deviation Nl of previous time + deviation N2 of the time before last) ^■ differential control (D control) - a control of using a product of a differential control gain KD and a difference between a deviation of this time of a target rotation number and a detected rotation number and a deviation of previous time thereof, as a change amount in a conduction angle of the triac 24 (an equation thereof is as follows). change amount in a conduction angle of the triac

= differential control gain KD ^χ (deviation NO of this time - deviation Nl of previous time)

^• proportional + integral control (PI control) - a combination control of the proportional control and the integral control. The change amounts in a conduction angle of the triac obtained by the equations of the proportional control and the integral control are summed, which is then added or subtracted to or from a current conduction angle of the triac.

^• proportional + integral + differential control (PID control) - a combination control of the proportional control, the integral control and the differential control. The change amounts in a conduction angle of the triac obtained by the equations of the proportional control, the integral control and the differential control are summed, which is then added or subtracted to or from a current conduction angle of the triac.

The integral control is to reduce an error with respect to the target rotation number and is performed to improve the rotation number precision. The differential control is to improve the control responsiveness and is performed to cope with a rapid load variation when using the electric tool. Regarding the proportional control gain KP, the integral control gain KI and the differential control gain KD, it is required to set optimal values thereof in advance by a test and the like.

Fig. 2 is a flowchart showing a rotation number control in the electric tool of Fig. 1. The flowchart starts when a user turns on the switch 2 at a state where an AC cord (not shown) of the electric tool is connected to the AC power supply 1. When the switch 2 becomes ON, an AC voltage from the AC power supply 1 is converted into a direct current constant voltage (-Vcc) by the power supply circuit 7 and is then supplied to the microcomputer 23. Also, the AC voltage from the AC power supply 1 is input to the zero cross detection circuit 8. The microcomputer 23 measures a time interval of the zero cross signal input from the zero cross detection circuit 8 and detects a frequency of the input AC power supply (S201). Then, the microcomputer 23 detects a target rotation number setting voltage of the motor 3 set by the resistors 26, 28 and the variable resistor 27 (S202) and sets a target rotation number (S203). Then, the microcomputer 23 sets an initial conduction angle of the triac 24 upon the startup of the motor (S204). Regarding the initial conduction angle, it is required to set an optimal value thereof in advance by a test and the like. The initial conduction angle is preferably 40° or larger. Then, the microcomputer 23 drives the triac 24 with the initial conduction angle set in step S204, thereby activating the motor 3 (S205).

Then, the microcomputer 23 performs a PI (proportional + integral) control, which is a primary control (S206). The microcomputer 23 controls the rotation number of the motor 3 for predetermined time (for example, 0.25 second) by the PI control (S207), again detects a target rotation number setting voltage of the motor 3 set by the resistors 26, 28 and the variable resistor 27 (S208) and sets a target rotation number (S209). The steps S208, S209 are to reset the target rotation number when the target rotation number is changed by the user.

Then, the microcomputer 23 performs a PID (proportional + integral + differential) control, which is a secondary control (S210). Here, the proportional control gain in the PID control is preferably larger than the proportional control gain in the PI control of step S206. This is to cope with a situation where a deviation of the rotation number of the motor 3 and the target rotation number becomes smaller in a time period (a second control time period) for which the PID control is performed than in a time period (a first control time period) for which the PI control is performed. Thereby, it is possible to prevent an increase rate of the rotation number of the motor 3 from being excessively slowed down in the second control time period. In the meantime, the integral control gain may be also larger in the PID control (the second control time period) than in the PI control (the first control time period). Then, the microcomputer 23 proceeds to step S211. When the switch 2 is ON, the microcomputer 23 returns to step S208 and controls the rotation number of the motor 3 (the PID control). When the switch 2 is OFF, the microcomputer 23 stops the motor 3 (S212).

The respective control gains (control constants) in the PI control in step S206 and the respective control gains (control constants) in the PID control in step S210 may be different depending on the frequency of the AC power supply detected in step S201.

Fig. 3 illustrates startup characteristics showing changes of the rotation number of the motor 3 and a force applied to a main body of the electric tool over time when the control shown in Fig. 2 is performed. In Fig. 3, the startup characteristics of the soft start control of the related art are shown with the dotted lines for comparison.

According to the startup characteristics of the related art, in order to suppress the reaction upon the startup, a valid value of the voltage applied to the motor 3 is gently increased from zero, thereby gently accelerating the rotation number of the motor 3 from zero (the increase rate of the rotation number of the motor just after the startup is small). In contrast, according to this illustrative embodiment, the microcomputer 23 is configured to rapidly increase the valid value of the voltage applied to the motor 3 to an initial value (an initial valid value) having a predetermined magnitude, thereby rapidly increasing the rotation number of the motor 3 (the increase rate of the rotation number of the motor just after the startup is large). The initial value is within a range of 24% to 76% (40° to 100° as regards the conduction angle) of a maximum value, preferably a range of 33% to 69% (50° to 90° as regards the conduction angle). In the meantime, the initial value may be different depending on the inertia moment of the rotor, and the like, which will be described later (Figs. 5 and 6).

According to the startup characteristics of the related art, a gradient (an increase rate of the rotation number) of the increase in the rotation number of the motor 3 is larger over time. On the other hand, according to the illustrative embodiment, the microcomputer 23 is configured to rapidly increase the valid value of the voltage applied to the motor 3 to the initial value, and then to linearly increase the rotation number of the motor 3 by the PI control (the first control time period) and to control the rotation number of the motor 3 by the PID control when predetermined time elapses after energization of the motor 3 starts (the second control time period). The predetermined time is within a range of 0.1 second to 1.0 second, for example, preferably a range of 0.2 second to 0.6 second. When increasing the rotation number of the motor 3 from the predetermined rotation number to the target rotation number by the PID control, the microcomputer 23 gradually lowers the increase rate of the rotation number of the motor 3. After the rotation number of the motor 3 reaches the target rotation number, the microcomputer 23 continues to control the rotation number of the motor 3 by the PID control.

According to this illustrative embodiment, following effects can be accomplished.

(1) According to the soft start control of the related art, the valid value of the voltage applied to the motor 3 is gently increased from zero and the gradient (the increase rate of the rotation number) of the increase in the rotation number of the motor 3 is larger over time. Therefore, the change in the acceleration (the gradient of the increase in the rotation number) is large at the time that the rotation number of the motor 3 reaches the target value, so that the high reaction is applied to a user's hand at the time that the motor enters a constant speed area (a steady rotation number). In contrast, according to this illustrative embodiment, while the voltage having a predetermined magnitude is applied to the motor 3 to rapidly increase the rotation number of the motor 3 at the early state, when the rotation number of the motor 3 comes close to the target rotation number of the motor 3, the increase rate of the rotation number is slowed down. Thereby, while the time (the startup time of the motor 3) for which the rotation number of the motor 3 reaches the target rotation number is made to be equivalent to or less than the related art, it is possible to reduce the reaction upon the shift to the constant speed area, as compared to the related art. In the meantime, since the voltage having a predetermined magnitude is applied to the motor 3 upon the startup, the force applied to the main body of the electric tool upon the startup is somewhat increased. However, since the rotation number of the motor 3 is small upon the startup, the user little feels the reaction. Also, since the timing at which the high reaction is applied coincides with a timing at which the user operates the switch, the user can easily know the timing at which the reaction is applied and can easily use the electric tool.

(2) The control is switched from the PI control to the PID control at a stage at which the rotation number of the motor 3 reaches a predetermined rotation number close to the target rotation number. Therefore, while rapidly increasing the rotation number of the motor 3 to the predetermined rotation number, it is possible to lower the increase rate of the rotation number from the predetermined rotation number and to gently approximate the rotation number to the target rotation number. That is, since the differential control becomes an obstacle to the rapid increase of the rotation number of the motor 3 towards the target rotation number, the differential control is not performed until the rotation number of the motor 3 reaches the predetermined rotation number close to the target rotation number, and the differential control is added after the rotation number of the motor reaches the predetermined rotation number. Thereby, it is possible not only to shorten the startup time of the motor 3 but also to reduce the reaction upon the arrival at the target rotation number.

Second Illustrative Embodiment

Fig. 4 is a circuit diagram of an electric tool according to a second illustrative embodiment of the present invention. In the first illustrative embodiment, the motor 3 is a motor having an AC brush. However, in this illustrative embodiment, the motor 3 is a DC brushless motor.

The voltage supplied from the AC power supply 1 is converted into a full rectified wave, for example, in a rectification circuit 40 such as a diode bridge, and is smoothed in a smoothing capacitor C, so that it becomes a DC voltage, which is then supplied to an inverter circuit 47. The motor 3 is a so-called inner rotor type, and has a rotor 3 a, a stator and three position detection elements 42 (a magnetic detection element such as a Hall element). The rotor 3a includes a rotor magnet 3d having a plurality of sets (two sets, in this illustrative embodiment) of N poles and S poles. The stator includes a stator coil 3c having star-connected stator windings U, V, W of three phases, and a stator core 3b. The three position detection elements 42 are arranged at a predetermined interval in a circumferential direction, for example every 60° so as to detect a rotating position of the rotor 3 a. A rotor position detection circuit 43 is configured to generate rotating position detection signals on the basis of signals from the position detection elements 42, and the microcomputer 23 is configured to control energization directions and time of the stator windings U, V, W on the basis of the rotating position detection signals, thereby rotating the motor 3. The microcomputer 23 is also configured to control a speed controller 41, depending on a position of a speed control dial 45 configured to be operated by the user, thereby controlling the speed of the motor 3.

The inverter circuit 47 includes six switching elements Ql to Q6 such as FETs connected in a three-phase bridge form. Respective gates of the six bridge-connected switching elements Ql to Q6 are connected to the speed controller 41, and respective drains or sources of the six switching elements Ql to Q6 are connected to the star- connected stator windings U, V, W. The six switching elements Ql to Q6 are configured to perform a switching operation by switching element driving signals HI to H6 input from the speed controller 41 and to supply the DC voltages applied to the inverter circuit 47 to the stator windings U, V, W, as three-phase (U phase, V phase and W phase) voltages Vu, Vv, Vw.

At least one of the signals H4 to H6 of the switching element driving signals HI to H6, which are applied to the gates of the switching elements Q4 to Q6 of a low side, or the signals HI to H3 applied to the gates of the switching elements Ql to Q3 of a high side is a pulse width modulation (PWM) signal. By changing a duty of the PWM signal, it is possible to adjust a power feeding amount (a valid value of the voltage applied to the motor 3) to the motor 3, thereby controlling the startup, stop and rotating speed of the motor 3. Although not shown, the microcomputer 23 includes a central processing unit (CPU) for outputting a driving signal on the basis of a processing program and data, a ROM for storing therein the processing program and control data, a RAM for temporarily storing therein data, a timer and the like. The speed controller 41 is configured to generate a driving signal for alternately switching the predetermined switching elements Ql to Q6 on the basis of an output signal of the rotor position detection circuit 43, under control of the microcomputer 23. Thereby, the predetermined stator windings U, V, W are alternately energized, so that the rotor 3 a is rotated. A current value (a current value flowing through a detection resistance Rs) supplied to the motor 3 is measured by a current detection circuit 48, and a measured value is fed back to the microcomputer 23, so that the load of the motor 3 is monitored. A voltage detection circuit 52 is configured to detect the voltage applied to the inverter circuit 47 and to feed back the detected voltage to the microcomputer 23.

In this illustrative embodiment, the control flow of the motor 3 is the same as the first illustrative embodiment (Figs. 2 and 3). However, when the flowchart of Fig. 2 is applied to this illustrative embodiment, because the motor 3 is a DC driving type, the detection (S201) of the power supply frequency is omitted and "initial conduction angle" (S204, S205) should be read as "initial duty", and "triac" should be read as "switching element". Also in this illustrative embodiment, it is possible to accomplish the same effects as the first illustrative embodiment.

In any of the first and second illustrative embodiments, the initial valid value of the voltage applied to the motor 3 may be changed depending on the type and size of the rotor. Fig. 5 is a table showing examples of a diameter of a saw blade, the initial conduction angle of the triac 24, the initial valid value of the voltage applied to the motor 3 and the startup time of the motor 3 when the electric tool of the first illustrative embodiment is a round saw. Fig. 6 is a table showing examples of the diameter of the saw blade, an initial duty of a PWM signal applied to the switching elements Ql to Q6 (at least one of the switching elements of a high side or the switching elements of a low side), the initial valid value of the voltage applied to the motor 3 and the startup time of the motor 3 when the electric tool of the second illustrative embodiment is a round saw. As shown in Figs. 5 and 6, when the inertia moment of the rotor is higher, the initial valid value of the voltage applied to the motor 3 is increased to accomplish the shortening of the time, which is consumed until the rotation number of the motor 3 reaches the target rotation number, and the reduction in the reaction upon the shift to the constant speed area with good balance.

Fig. 7 shows a relation between the initial valid value (a horizontal axis) of the voltage to be applied to the motor 3 and the initial reaction force and the startup time (a vertical axis) in the first and second illustrative embodiments. In Fig. 7, the startup time and the reaction force upon the shift to the constant speed area in the soft start control of the related art are also shown for comparison. As shown in Fig. 7, the higher the initial valid value of the voltage applied to the motor 3, the startup time of the motor 3 is shortened but the initial reaction force (the reaction that the user feels just after the startup) is larger. For this reason, the initial valid value of the voltage applied to the motor 3 is preferably within a range in which the startup time is not later, as compared to the related art, and the initial reaction force is remarkably reduced, as compared to the reaction force upon the shift to the constant speed area of the related art.

Although the present invention has been described with reference to the illustrative embodiments, one skilled in the art can understand that the respective constitutional elements and respective processes of the illustrative embodiments can be variously modified within the scope defined in the claims. In the below, the modified embodiments are described.

The shift timing from the first control time period (the PI control) to the second control time period (the PID control) may be a timing at which the rotation number of the motor 3 reaches a predetermined rotation number, instead of the timing at which the predetermined time elapses after the energization of the motor 3 starts. The predetermined rotation number is within a range of 50% to 90% of the target rotation number, for example, preferably 60% to 80%.

In the first control time period, the differential control gain may be made to be smaller than in the second control time period, instead of the configuration where the differential control is not performed. In the second control time period, the integral control may not be performed.

The technology described in the illustrative embodiment is particularly efficient for an electric tool configured to drive a rotor having high inertia moment, for example, an electric tool configured to drive a circular disc- shaped rotor such as a round saw and a grinder. However, the technology can be also applied to the other electric tools. The electric tool is not limited to an electric tool that is driven by the external AC power supply, and may be driven by a battery.

Claims

[Claim 1]

An electric tool comprising:

a motor; and

a control unit configured to control the motor,

[Claim 2]

The electric tool according to claim 1 , wherein the control unit gradually lower the increase rate of the rotation number of the motor from a predetermined timing after the energization of the motor starts until the motor reaches the target rotation number.

[Claim 3]

The electric tool according to claim 2, wherein the predetermined timing is a timing at which predetermined time elapses after the energization of the motor starts.

[Claim 4]

The electric tool according to claim 2, wherein the predetermined timing is a timing at which the motor reaches a predetermined rotation number of the motor.

[Claim 5]

The electric tool according to any one of claims 1 to 4, wherein the control unit control the motor by different control methods or different control gains during a first control time period for which predetermined time elapses after the energization of the motor starts or at which the motor reaches a predetermined rotation number and during a second control time period following the first control time period.

[Claim 6]

The electric tool according to claim 5, wherein the control unit performs one of a proportional control during the first control time period and performs the proportional control and a differential control during the second control time period.

[Claim 7]

The electric tool according to claim 6, wherein the control unit further performs an integral control during the first control time period and performs the integral control during the second control time period.

[Claim 8]

The electric tool according to claim 6, wherein a control gain of the proportional control during the first control time period is smaller than the control gain of the proportional control during the second control time period.

[Claim 9]

The electric tool according to any one of claims 5 to 8, wherein the control unit rapidly increases a valid value of a voltage applied to the motor to an initial value before the first control time period starts.

[Claim 10]

The electric tool according to any one of claims 1 to 9 further comprising a switching element connected in series with the motor,

[Claim 11]

The electric tool according to any one of claims 1 to 10, wherein the control unit switches a control gain depending on a frequency of an input power supply.

[Claim 12]

The electric tool according to any one of claims 1 to 11, wherein the motor is configured to rotate one of a round saw blade and a grind stone.