Power tool and control method of motor in power tool

Abstract

To suppress variation in an acceleration state of rotational speed from a motor driving start time due to the magnitude of power supply voltage.SOLUTION: A power tool includes: a motor; a drive circuit; a voltage detection section; a target calculation section; and a set duty ratio calculation section. The drive circuit applies power supply voltage to the motor in accordance with a set duty ratio. The voltage detection section detects the magnitude of power supply voltage. The target calculation section calculates a target duty ratio to rotate the motor at a target rotational speed on the basis of the detected magnitude of power supply voltage. The set duty ratio calculation section increases the set duty ratio from an initial value up to the target duty ratio with the lapse of time. An increasing rate of the set duty ratio changes according to the detected magnitude of power supply voltage.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a technique for controlling a motor in a power tool. [Background technology]

[0002] Patent Document 1 discloses an electric power tool configured to perform soft start control. In this electric power tool, a power supply voltage is applied to a motor in accordance with a PWM drive signal to drive the motor. The soft start control involves gradually increasing the duty ratio of the PWM drive signal from 0% to a target value when the motor starts to be driven. The power supply voltage is supplied from a battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-240441 A Summary of the Invention [Problem to be solved by the invention]

[0004] The magnitude of the power supply voltage when the motor starts to operate may vary depending on the remaining charge of the battery and other factors. If the power supply voltage at the start of operation is different, the degree of acceleration of the rotation speed of the motor after the start of operation may also differ. For example, the rotation speed at a certain time after the start of operation may differ depending on the magnitude of the power supply voltage.

[0005] The variation in the acceleration of the rotation speed can have an undesirable effect on the results of the work performed by the power tool. For example, when tightening a screw into a workpiece, the tightening torque can vary depending on the magnitude of the power supply voltage.

[0006] It is desirable to suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which varies depending on the magnitude of the power supply voltage, in one aspect of the present disclosure. [Means for solving the problem]

[0007] One aspect of the present disclosure provides a power tool including a motor, a drive circuit, a voltage detection unit, a target calculation unit, and a set duty ratio calculation unit. The drive circuit receives a power supply voltage and a drive signal. The drive signal has a set duty ratio. The drive circuit drives the motor by applying the power supply voltage to the motor at a period corresponding to the set duty ratio of the input drive signal.

[0008] The voltage detection unit detects the magnitude of the power supply voltage. The target calculation unit calculates a target duty ratio based on the magnitude of the power supply voltage detected by the voltage detection unit. The target duty ratio is a target value of a set duty ratio for rotating the motor at a predetermined target rotation speed.

[0009] The set duty ratio calculation unit calculates a set duty ratio. The set duty ratio calculation unit increases the set duty ratio from a predetermined initial value to a target duty ratio over time. The set duty ratio calculation unit changes an increase rate of the set duty ratio according to the magnitude of the power supply voltage detected by the voltage detection unit.

[0010] Such an electric power tool can suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which variation depends on the magnitude of the power supply voltage. In another aspect of the present disclosure, there is provided a power tool including the motor, the drive circuit, the voltage detection unit, the target calculation unit, and a set duty ratio calculation unit different from the set duty ratio calculation unit. The set duty ratio calculation unit increases the set duty ratio from a predetermined initial value to the target duty ratio over time based on the magnitude of the power supply voltage detected by the voltage detection unit. At this time, the set duty ratio calculation unit increases the set duty ratio so that the change process of the rotation speed of the motor from when the motor starts to rotate until the rotation speed of the motor reaches the target rotation speed is the same or approximately the same regardless of the magnitude of the power supply voltage.

[0011] Such an electric power tool can also suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which variation depends on the magnitude of the power supply voltage. Another aspect of the present disclosure is a method for controlling a motor in a power tool, comprising: Calculating a target value of a duty ratio for rotating the motor at a predetermined target rotation speed based on a magnitude of a power supply voltage applied to the motor; increasing the duty ratio from a predetermined initial value to the target value over time, and varying an increase rate of the duty ratio in response to a magnitude of the power supply voltage; Driving the motor in accordance with the duty ratio; It is equipped with:

[0012] This method can suppress variations in the degree of acceleration of the rotation speed from the start of driving the motor, which variations occur depending on the magnitude of the power supply voltage. [Brief description of the drawings]

[0013] [Figure 1] 1 is a side cross-sectional view of a power tool according to a first embodiment. [Diagram 2] 1 is an electric circuit diagram showing an electrical configuration of a power tool according to a first embodiment. [Diagram 3] FIG. 2 is a block diagram showing the functions of a control circuit according to the first embodiment. [Figure 4] 10A and 10B are explanatory diagrams showing an example of the operation of a motor in a power tool in which the increase rate of the set duty ratio is fixed. [Diagram 5] 5A to 5C are explanatory diagrams showing an example of the operation of a motor in a power tool to which a first method is adopted. [Figure 6] 5A to 5C are explanatory diagrams showing an example of the operation of the motor in the power tool of the first embodiment in which the first and second methods are adopted. [Figure 7] 4 is a flowchart of a motor control process according to the first embodiment. [Figure 8] 10A to 10C are explanatory diagrams showing an example of the operation of the motor in the power tool of the second embodiment. [Figure 9]10 is a flowchart of a motor control process according to a second embodiment. [Figure 10] FIG. 11 is a block diagram showing the functions of a control circuit according to a third embodiment. [Figure 11] 13A to 13C are explanatory diagrams showing an example of the operation of the motor in the power tool of the third embodiment. [Figure 12] 13 is a flowchart of a motor control process according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 1. Overview of the embodiment An embodiment may provide a power tool having at least one of the following features 1 to 5. Feature 1: Motor. Feature 2: A drive circuit configured to receive a power supply voltage and a drive signal. The drive signal has a set duty ratio. The drive circuit is configured to apply the power supply voltage to the motor at a period corresponding to the set duty ratio of the drive signal, thereby driving the motor. Feature 3: A voltage detection unit configured to detect the magnitude of the power supply voltage. Feature 4: A target calculation unit configured to calculate a target duty ratio based on the magnitude of the power supply voltage detected by the voltage detection unit. The target duty ratio is a target value of the set duty ratio for rotating the motor at a predetermined target rotation speed. Feature 5: A set duty ratio calculation unit configured to increase the set duty ratio from a predetermined initial value to the target duty ratio over time (or according to the passage of time). The set duty ratio calculation unit is configured to change an increase rate of the set duty ratio in response to the magnitude of the power supply voltage detected by the voltage detection unit. The drive signal is in the form of a pulse width modulated signal, and the set duty ratio corresponds to the duty ratio of the pulse width modulated signal.

[0015] Changing the increase rate according to the magnitude of the power supply voltage includes all manners in which the magnitude of the power supply voltage is involved in the calculation of the increase rate. Varying the rate of increase may include varying the rate of increase over time. Specifically, for example, the rate of increase may be changed continuously or intermittently.

[0016] In this case, the rate of change of the increase rate may be changed according to the magnitude of the power supply voltage. Also, for example, as described below, the increase rate may be changed (e.g., decreased) each time a specific timing at which the increase rate should be changed arrives. In this case, the specific timing may be changed according to the magnitude of the power supply voltage. The increase rate may be maintained constant other than the specific timing. The change in the increase rate at the specific timing (the rate of change or amount of change in the increase rate, or the increase rate after the change) may be configured to differ according to the magnitude of the power supply voltage.

[0017] Changing the rate of increase may include calculating the rate of increase immediately after the start of calculation of the set duty ratio (i.e., the rate of increase from the initial value) according to the magnitude of the power supply voltage. For example, as described later, the rate of increase from the initial value may be calculated to be lower as the power supply voltage is higher.

[0018] An electric power tool having at least the features 1 to 5 can suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which variation depends on the magnitude of the power supply voltage. An embodiment may include the following feature 6 in addition to or instead of at least one of the features 1 to 5 described above. Feature 6: When a switching condition for switching the increase rate is satisfied, the set duty ratio calculation unit is configured to switch the increase rate to a value lower than the increase rate at the time when the switching condition is satisfied. A power tool having at least the features 1 to 6 can reduce the processing load for changing the increase rate.

[0019] An embodiment may include the following feature 7 in addition to or instead of at least one of the features 1 to 6 described above. Feature 7: A condition setting unit configured to set the switching condition depending on the magnitude of the power supply voltage detected by the voltage detection unit. A power tool having at least the features 1 to 7 can easily achieve a change in the increase rate according to the magnitude of the power supply voltage.

[0020] An embodiment may include the following feature 8 in addition to or instead of at least one of the features 1 to 7 described above. Feature 8: The switching condition is met every time the calculated set duty ratio reaches one or more specified duty ratios. A power tool having at least the features 1 to 6 and 8 allows the switching condition to be easily set.

[0021] An embodiment may include at least one of the following features 9 and 10 in addition to or instead of at least one of the features 1 to 8 described above. Feature 9: The condition setting unit is configured to calculate one or more prescribed duty ratios based on the magnitude of the power supply voltage detected by the voltage detection unit. Feature 10: The switching condition is met every time the calculated set duty ratio reaches each of the one or more calculated prescribed duty ratios. A power tool having at least the features 1 to 7, 9, and 10 allows the switching conditions to be easily set, and thereby makes it possible to simply change the increase rate according to the magnitude of the power supply voltage.

[0022] An embodiment may include the following feature 11 in addition to or instead of at least one of the features 1 to 10 described above. Feature 11: The condition setting unit is configured to calculate each of the one or more prescribed duty ratios so that the higher the power supply voltage detected by the voltage detection unit is, the lower the prescribed duty ratio becomes. An electric power tool having at least the features 1 to 7 and 9 to 11 can simply and effectively reflect the magnitude of the power supply voltage in the one or more specified duty ratios.

[0023] An embodiment may include the following feature 12 in addition to or instead of at least one of the features 1 to 11 described above. Feature 12: The one or more prescribed duty ratios include at least two prescribed duty ratios. An electric power tool having at least the features 1 to 6, 8, and 12, or an electric power tool having at least the features 1 to 7, 9, 10, and 12, can enhance the effect of suppressing the variation in the acceleration state of the rotation speed.

[0024] An embodiment may include at least one of the following features 13 and 14 in addition to or instead of at least one of the features 1 to 12 described above. Feature 13: The switching condition is met each time one or more specified times have elapsed from a predetermined measurement start timing. Feature 14: The measurement start timing arrives when a drive condition for driving the motor is satisfied. A power tool having at least the features 1 to 6, 13, and 14 allows the switching condition to be easily set.

[0025] An embodiment may include at least one of the following features 15 to 17 in addition to or instead of at least one of the features 1 to 14 described above. Feature 15: The condition setting unit is configured to calculate one or more specified times based on the magnitude of the power supply voltage detected by the voltage detection unit. Feature 16: The switching condition is satisfied each time one or more of the calculated specified times have elapsed from a predetermined measurement start timing. Feature 17: The measurement start timing arrives when a drive condition for driving the motor is satisfied. A power tool having at least the features 1 to 7 and 15 to 17 can easily set the switching condition, and can easily change the increase rate according to the magnitude of the power supply voltage.

[0026] An embodiment may include the following feature 18 in addition to or instead of at least one of the features 1 to 17 described above. Feature 18: The condition setting unit is configured to calculate each of the one or more specified times so that the specified time is shorter as the power supply voltage detected by the voltage detection unit is higher. An electric power tool having at least the features 1 to 7 and 15 to 18 can simply and effectively reflect the magnitude of the power supply voltage at the one or more specified times.

[0027] An embodiment may include at least one of the following features 19 and 20 in addition to or instead of at least one of the features 1 to 18 described above. Feature 19: A manual switch configured to be manually operated by a user of the power tool. Feature 20: The drive condition is satisfied in response to the manual switch being manually operated by the user. A power tool having at least the features 1 to 6, 13, 14, 19, and 20 and a power tool having at least the features 1 to 7, 15 to 17, 19, and 20 can set the measurement start timing more appropriately. Furthermore, the power tool can satisfy the switching condition at an appropriate timing.

[0028] An embodiment may include the following feature 21 in addition to or instead of at least one of the features 1 to 20 described above. Feature 21: The one or more specified times include at least two specified times. A power tool having at least the features 1 to 6, 13, 14, and 21, and a power tool having at least the features 1 to 7, 15 to 17, and 21 can enhance the effect of suppressing the variation in the acceleration state of the rotation speed.

[0029] An embodiment may include the following feature 22 in addition to or instead of at least one of the features 1 to 21 described above. Feature 22: An increase rate calculation unit configured to calculate the increase rate from the initial value and / or the increase rate after switching when the switching condition is satisfied, in accordance with a magnitude of the power supply voltage detected by the voltage detection unit. A power tool having at least the features 1 to 6 and 22 can further enhance the effect of suppressing the variation in the acceleration of the rotation speed.

[0030] An embodiment may include the following feature 23 in addition to or instead of at least one of the features 1 to 22 described above. Feature 23: The increase rate calculation unit is configured to calculate the increase rate so that the increase rate decreases as the power supply voltage detected by the voltage detection unit increases. An electric power tool having at least the features 1 to 6, 22, and 23 can simply and effectively reflect the magnitude of the power supply voltage in the increase rate.

[0031] An embodiment may include the following feature 24 in addition to or instead of at least one of the features 1 to 23 described above. Feature 24: The voltage detection unit is configured to detect the magnitude of the power supply voltage before the motor is driven by the drive circuit. A power tool having at least the features 1 to 5 and 24 can appropriately reflect the magnitude of the power supply voltage in the change in the increase rate.

[0032] An embodiment may include the following feature 25 in addition to or instead of at least one of the features 1 to 24 described above. Feature 25: A drive signal generating unit configured to generate the drive signal having the calculated set duty ratio and output the drive signal to the drive circuit. An embodiment may provide a power tool having the above features 1 to 4 and the following feature 26. Feature 26: A set duty ratio calculation unit configured to increase the set duty ratio over time from a predetermined initial value to the target duty ratio. The set duty ratio calculation unit increases the set duty ratio based on the magnitude of the power supply voltage detected by the voltage detection unit. The set duty ratio calculation unit increases the duty ratio so that the process of change in the rotation speed of the motor from when the motor starts to rotate until the rotation speed of the motor reaches the target rotation speed remains the same or approximately the same regardless of the magnitude of the power supply voltage. An electric power tool having at least the features 1 to 4 and 26 can suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which variation depends on the magnitude of the power supply voltage.

[0033] An embodiment may provide a method for controlling a motor in a power tool, the method including at least one of the following features 27 to 29. Feature 27: A target value of a duty ratio is calculated based on the magnitude of a power supply voltage applied to the motor. The target value is a duty ratio for rotating the motor at a predetermined target rotation speed. Feature 28: The duty ratio is increased over time from a predetermined initial value to the target value, and an increase rate at which the duty ratio is increased is changed according to the magnitude of the power supply voltage. Feature 29: The motor is driven in accordance with the duty ratio. A method having at least Features 27 to 29 can suppress variation in the degree of acceleration of the rotation speed from the start of driving the motor, which varies depending on the magnitude of the power supply voltage.

[0034] In some embodiments, the above features 1 to 29 may be combined in any manner. In some embodiments, any of the above features 1-29 may be omitted. 2. Specific Exemplary Embodiments A specific exemplary embodiment will be described below. This specific exemplary embodiment is merely an example, and the present disclosure is not limited to this embodiment and can be implemented in any form.

[0035] 2-1. First embodiment 2-1-1. Configuration of power tools The power tool 1 of the first embodiment shown in FIG. 1 is in the form of, for example, an impact driver. The impact driver rotates various fasteners having a screw thread. The various fasteners include, for example, various screws, bolts, nuts, etc. The various screws include, for example, wood screws, drill screws, etc. The impact driver can apply a striking force to the fastener in the rotation direction while rotating the fastener. The power tool 1 of the first embodiment is driven by the power of a battery 3a (see FIG. 2) described later.

[0036] 1, the power tool 1 includes a main body 2. The power tool 1 includes a battery pack 3. The battery pack 3 of the first embodiment is detachably attached to the main body 2. The battery pack 3 supplies power to the main body 2.

[0037] The main body 2 includes a housing 4. The main body 2 includes a grip 5. The grip 5 is provided at a lower end of the housing 4. In the first embodiment, the grip 5 extends downward from the housing 4. The grip 5 is held by a user of the power tool 1.

[0038] The main body 2 includes a battery attachment section 6. The battery attachment section 6 is provided at the lower end of the grip 5. The battery pack 3 is removably attached to the battery attachment section 6. The main body 2 includes a chuck sleeve 7. The chuck sleeve 7 is provided at the front end of the housing 4. Various tool bits are removably attached to the chuck sleeve 7. The various tool bits include, for example, a driver bit and a socket bit. FIG. 1 shows a driver bit 7a in schematic form. When the chuck sleeve 7 rotates, the tool bit attached to the chuck sleeve 7 rotates together with the chuck sleeve 7 (i.e., integrally). The chuck sleeve 7 is rotated by a motor 21, which will be described later.

[0039] The main body 2 includes a trigger 8. The trigger 8 is provided at the upper front of the grip 5. The trigger 8 is manually operated by a user. Specifically, the trigger 8 in the first embodiment is pulled by the user. In other words, the trigger 8 is moved rearward and pushed into the main body 2. The power tool 1 is operated when the trigger 8 is pulled.

[0040] The main body 2 includes a direction setting switch 10. The direction setting switch 10 specifies the rotation direction of a motor 21 (and thus the rotation direction of the chuck sleeve 7), which will be described later. Specifically, the direction setting switch 10 specifies the rotation direction of the chuck sleeve 7 alternatively to a first direction or a second direction.

[0041] The direction setting switch 10 is provided near the boundary between the housing 4 and the grip 5. The direction setting switch 10 of the first embodiment is manually operated to the right or left by the user. Specifically, the direction setting switch 10 is moved to a first position or a second position by manual operation by the user.

[0042] When the direction setting switch 10 is moved to the first position, the rotation direction of the chuck sleeve 7 is set to the first direction. In other words, the rotation direction of the motor 21 is set to a direction that rotates the chuck sleeve 7 in the first direction (hereinafter referred to as the "first motor rotation direction"). That is, when the direction setting switch 10 is moved to the first position and the trigger 8 is pulled, the motor 21 is rotated in the first motor rotation direction. When the motor 21 rotates in the first motor rotation direction, the chuck sleeve 7 rotates in the first direction. The first direction may be the same as the first motor rotation direction, or may be opposite to the first motor rotation direction. In this first embodiment, the first direction is the same as the first motor rotation direction. The first direction may be, for example, clockwise (or right-handed).

[0043] The first direction corresponds to a direction in which the fastener is tightened into the workpiece. That is, a tool bit rotating in the first direction rotates the fastener in the first direction. As the fastener is rotated in the first direction, it is tightened into the workpiece.

[0044] The fastened material may be any material. Examples of the fastened material include wood, metal, concrete, gypsum board, etc. In a combination of a bolt and a nut, the bolt and the nut can be the fastening material and the fastened material, respectively. For example, in a case where the nut is rotated with a tool bit to tighten the bolt, the nut corresponds to the fastener and the bolt corresponds to the fastened material. Conversely, in a case where the bolt is rotated with a tool bit to tighten the nut, the bolt corresponds to the fastener and the nut corresponds to the fastened material.

[0045] When the direction setting switch 10 is moved to the second position, the rotation direction of the chuck sleeve 7 is set to the second direction. In other words, the rotation direction of the motor 21 is set to a direction that rotates the chuck sleeve 7 in the second direction (hereinafter referred to as the "second motor rotation direction"). That is, when the direction setting switch 10 is moved to the second position and the trigger 8 is pulled, the motor 21 is rotated in the second motor rotation direction. When the motor 21 rotates in the second motor rotation direction, the chuck sleeve 7 rotates in the second direction. The second direction may be the same as the second motor rotation direction or may be opposite to the second motor rotation direction. In the first embodiment, the second direction is the same as the second motor rotation direction. The second direction may be, for example, counterclockwise (or left-handed).

[0046] The second direction corresponds to a direction for loosening (or releasing or removing) the fastener from the fastened material. That is, the tool bit rotating in the second direction causes the fastener to rotate in the second direction. As the fastener is rotated in the second direction, it is loosened from the fastened material.

[0047] The direction setting switch 10 may be further movable to a third position. The third position may be, for example, intermediate between the first position and the second position. When the direction setting switch 10 is moved to the third position, for example, the rotation of the motor 21 may be prohibited. Specifically, the motor 21 may be configured not to rotate even when the trigger 8 is pulled, or the pulling operation of the trigger 8 itself may be mechanically restricted.

[0048] The main body 2 includes an operation panel 11. In the first embodiment, the operation panel 11 is provided in the battery mounting section 6. The operation panel 11 may include, for example, one or more buttons and / or one or more display devices.

[0049] The power tool 1 includes a motor 21. The motor 21 is accommodated in a housing 4. The motor 21 includes a shaft 21a. When the motor 21 rotates, more specifically, it means that the shaft 21a rotates.

[0050] The power tool 1 includes a drive mechanism 22. The drive mechanism 22 is accommodated in the housing 4. The drive mechanism 22 is disposed in front of the motor 21 and behind the chuck sleeve 7. The drive mechanism 22 transmits the rotation of the motor 21 (i.e., the rotation of the shaft 21a) to the chuck sleeve 7. When the motor 21 rotates, the drive mechanism 22 rotates the chuck sleeve 7.

[0051] The drive mechanism 22 includes an impact mechanism 23. The impact mechanism 23 includes a spindle 24. The spindle 24 is rotatably supported. The drive mechanism 22 includes a planetary gear mechanism 26. A shaft 21a of the motor 21 is coupled to the planetary gear mechanism 26. The planetary gear mechanism 26 transmits the rotation of the motor 21 to the spindle 24. Therefore, when the motor 21 rotates, the spindle 24 rotates.

[0052] The striking mechanism 23 includes a hammer 28, an anvil 29, and a coil spring 30. The hammer 28 is connected to the spindle 24. The hammer 28 is rotatable integrally with the spindle 24. The hammer 28 is further movable along the rotation axis of the spindle 24 (i.e., in the front-rear direction). The hammer 28 is biased forward by the coil spring 30. The anvil 29 rotates upon receiving a rotational force and / or a striking force from the hammer 28. The chuck sleeve 7 is attached to the front end of the anvil 29.

[0053] In the first embodiment, the rotation axis of the motor 21, the rotation axis of the spindle 24, the rotation axis of the hammer 28, the rotation axis of the anvil 29, and the rotation axis of the chuck sleeve 7 are aligned with one another. The hammer 28 includes, for example, a first striking protrusion 28a and a second striking protrusion 28b. The first striking protrusion 28a and the second striking protrusion 28b apply a rotational force and / or a striking force to the anvil 29. The first striking protrusion 28a and the second striking protrusion 28b are provided at an interval of, for example, 180° from each other along the rotation direction of the hammer 28. The first striking protrusion 28a and the second striking protrusion 28b are provided so as to protrude forward from the front end surface of the hammer 28.

[0054] A first striking arm 29a and a second striking arm 29b are provided at the rear end of the anvil 29. The first striking arm 29a and the second striking arm 29b are provided at an interval of, for example, 180° from each other along the rotation direction of the hammer .

[0055] When the hammer 28 is urged forward by the coil spring 30, the first striking protrusion 28a and the second striking protrusion 28b are in a state in which they can come into contact with the first striking arm 29a and the second striking arm 29b, respectively, in the rotation direction. The surfaces of the first striking protrusion 28a and the second striking protrusion 28b that come into contact with the first striking arm 29a or the second striking arm 29b, respectively, may be, for example, perpendicular or approximately perpendicular to the rotation direction of the hammer 28. The surfaces of the first striking arm 29a and the second striking arm 29b that come into contact with the first striking protrusion 28a or the second striking protrusion 28b, respectively, may be, for example, perpendicular or approximately perpendicular to the rotation direction of the anvil 29.

[0056] When the spindle 24 is rotated by the motor 21, the hammer 28 rotates integrally with the spindle 24. When the hammer 28 rotates in a state in which the first striking protrusion 28a and the second striking protrusion 28b are in contact with the first striking arm 29a and the second striking arm 29b, respectively, in the rotational direction, the rotational force of the hammer 28 is transmitted from the first striking protrusion 28a and the second striking protrusion 28b to the anvil 29 via the first striking arm 29a and the second striking arm 29b. This causes the anvil 29 to rotate. When the anvil 29 rotates, the chuck sleeve 7 rotates integrally with the anvil 29. This causes the tool bit attached to the chuck sleeve 7 to rotate.

[0057] During the rotation of the motor 21, the hammer 28 may receive torque (hereinafter referred to as "load torque") from the fastener through the chuck sleeve 7 and the anvil 29 in the opposite direction to the rotation direction of the hammer 28. When the hammer 28 receives a load torque of a predetermined magnitude or more during rotation, the hammer 28 applies a rotational force to the anvil 29 and displaces backward against the biasing force of the coil spring 30. Specifically, the first striking protrusion 28a and the second striking protrusion 28b displace backward while contacting the first striking arm 29a and the second striking arm 29b, respectively. As the hammer 28 displaces backward, the first striking protrusion 28a and the second striking protrusion 28b pass over the first striking arm 29a and the second striking arm 29b with which they are in contact, respectively, in the rotation direction. In other words, the first striking protrusion 28a and the second striking protrusion 28b move away from the first striking arm 29a and the second striking arm 29b with which they are in contact, respectively, in the rotation direction. As a result, the hammer 28 rotates idly and is displaced forward by the biasing force of the coil spring 30. As a result, the first striking protrusion 28a and the second striking protrusion 28b collide with the first striking arm 29a and the second striking arm 29b. In other words, the first striking protrusion 28a and the second striking protrusion 28b strike the first striking arm 29a and the second striking arm 29b in the rotational direction.

[0058] Such striking is repeated while the hammer 28 is receiving a load torque of a predetermined magnitude or more. In other words, while the hammer 28 is receiving a load torque of a predetermined magnitude or more, the anvil 29 is intermittently struck by the hammer 28.

[0059] When an impact occurs while the motor 21 is rotating in the first direction, the fastener is tightened to the workpiece with high torque. When an impact occurs while the motor 21 is rotating in the reverse direction, the fastener tightened to the workpiece is loosened with high torque.

[0060] The main body 2 includes a controller 16. The controller 16 controls various functions of the power tool 1, including driving the motor 21. A detailed configuration of the controller 16 will be described later with reference to Figs. 2 and 3.

[0061] The main body 2 includes a switch box 15. The switch box 15 is connected to the trigger 8. As will be described later, the switch box 15 outputs various signals to the controller 16 according to the state of the trigger 8 (specifically, the amount of pulling or the length of movement).

[0062] 2-1-2. Electrical configuration of power tools The electrical configuration of the power tool 1 will be further described with reference to Fig. 2. Fig. 2 shows the power tool 1 in a state where the battery pack 3 is attached to the main body 2.

[0063] The battery pack 3 includes a battery 3a. The battery 3a may be, for example, a secondary battery. The battery 3a may be, for example, a lithium ion battery. The battery 3a may be a secondary battery other than a lithium ion battery.

[0064] The power tool 1 includes the motor 21, the controller 16, the switch box 15 and the direction setting switch 10 described above. When the battery pack 3 is attached to the main body 2, the controller 16 is electrically connected to the battery 3a. As a result, power from the battery 3a (hereinafter referred to as "battery power") is supplied to the controller 16.

[0065] In the first embodiment, the motor 21 is, for example, a brushless DC motor. The motor 21 includes a permanent magnet rotor (not shown). The shaft 21a is fixed to the rotor and rotates together with the rotor.

[0066] The motor 21 is driven by receiving battery power. The motor 21 receives the battery power from the battery 3a via a drive circuit 32 described later. The drive circuit 32 converts the battery power into three-phase power. The motor 21 receives the three-phase power. The motor 21 of the first embodiment has three windings. Three-phase power is supplied to the three windings. The motor 21 rotates when the three-phase power is supplied to the three windings. Note that FIG. 2 shows an example in which the three windings are delta-connected to each other. However, the three windings may be connected in a manner other than delta connection.

[0067] The power tool 1 includes a rotation sensor 36. The rotation sensor 36 outputs rotation position information. The rotation position information may indicate whether the motor 21 is rotating or not. The rotation position information may change depending on the rotation position and / or rotation speed of the motor 21. The rotation position information may indicate the rotation position of the motor 21, specifically, the rotation position of the rotor 19. The rotation position information in this embodiment includes a first position signal Hu, a second position signal Hv, and a third position signal Hw. The rotation position information is input to the control circuit 31.

[0068] The rotation sensor 36 of the first embodiment includes three Hall sensors (not shown). The three Hall sensors are arranged in the vicinity of the rotor of the motor 21, spaced apart by an angle equivalent to an electrical angle of 120 degrees from each other along the rotation direction of the shaft 21a. The first to third position signals Hu, Hv, Hw are output from the three Hall sensors, respectively.

[0069] The rotation sensor 36 of the first embodiment operates by receiving power from the controller 16. Specifically, the rotation sensor 36 receives a control voltage Vcc from the controller 16. In order to receive this control voltage Vcc, the rotation sensor 36 is connected to a control power supply line and a ground line of the controller 16, which will be described later.

[0070] The switch box 15 includes a trigger switch 15a. The trigger switch 15a is linked to the movement of the trigger 8. Specifically, when the trigger 8 is pulled, the trigger switch 15a is turned on. When the trigger 8 is not pulled, the trigger switch 15a is turned off. The trigger switch 15a is provided to detect whether or not the trigger 8 is pulled. A first terminal and a second terminal of the trigger switch 15a are connected to the controller 16.

[0071] The controller 16 includes a control circuit 31 and a drive circuit 32. The control circuit 31 controls the rotation of the motor 21. The drive circuit 32 receives battery power from the battery 3a. Specifically, the drive circuit 32 is connected to the positive terminal of the battery 3a. The drive circuit 32 is further connected to a ground line in the controller 16. The ground line is connected to the negative terminal of the battery 3a.

[0072] The drive circuit 32 is connected to the motor 21. As described above, the drive circuit 32 converts battery power into three-phase power and supplies it to the motor 21. The drive circuit 32 in the present first embodiment is in the form of a three-phase full bridge circuit. The three-phase full bridge circuit includes six switches. Each switch may be in any form. In the present first embodiment, each switch is, for example, an n-channel metal oxide semiconductor field effect transistor (MOSFET).

[0073] The six switches include three high-side switches and three low-side switches. The three high-side switches are connected to the positive electrode of the battery 3a via a battery power path described later. The three low-side switches are connected to the negative electrode of the battery 3a via a ground line. As shown in FIG. 2, the sources of the three high-side switches are connected to the drains of one of the three low-side switches. The sources of the three high-side switches (in other words, the drains of the three low-side switches) are connected to the motor 21. When any one of the high-side switches and any one of the low-side switches that is not connected to the source of the high-side switch are turned on, battery power is supplied to the motor 21 via the high-side switch and the low-side switch, and the motor 21 is driven.

[0074] The controller 16 includes a voltage signal output circuit 35. The voltage signal output circuit 35 is connected to a battery power path. The battery power path runs from the positive electrode of the battery 3a to the drive circuit 32. The voltage signal output circuit 35 outputs a voltage signal Sv. The voltage signal Sv is input to the control circuit 31. The voltage signal Sv indicates the magnitude of the voltage on the battery power path.

[0075] The voltage signal output circuit 35 includes a first resistor 35a and a second resistor 35b. A first end of the first resistor 35a is connected to a battery power path. A second end of the first resistor 35a is connected to a first end of the second resistor 35b. A second end of the second resistor 35b is connected to a ground line. The voltage at the second end of the first resistor 35a (in other words, the voltage at the first end of the second resistor 35b) is input to the control circuit 31 as a voltage signal Sv.

[0076] In this first embodiment, the voltage of the battery power path is equal to or approximately equal to the voltage of the positive electrode of the battery 3a. Also, the voltage of the battery power path is equal to or approximately equal to the voltage input from the battery power path to the drive circuit 32 (hereinafter referred to as the "power supply voltage"). Therefore, in this first embodiment, the voltage signal Sv indicates the magnitude of the voltage of the battery 3a and the magnitude of the power supply voltage. In other words, in this first embodiment, the power supply voltage is equal to or approximately equal to the voltage of the battery 3a. The power supply voltage is applied to the motor 21 via the drive circuit 32.

[0077] The controller 16 includes a control power supply circuit 33. The control power supply circuit 33 receives battery power from the battery 3a. The control power supply circuit 33 generates a control voltage Vcc from the battery power and outputs it to a control power supply line. The control voltage Vcc has, for example, a constant voltage value. The control voltage Vcc is supplied to each part in the controller 16, including the control circuit 31, through the control power supply line. The control circuit 31 operates by the control voltage Vcc.

[0078] The control voltage Vcc is also supplied to the switch box 15. Specifically, the control voltage Vcc is applied to a first terminal of a trigger switch 15a via a resistor 34. A second terminal of the trigger switch 15a is connected to the ground line.

[0079] A first terminal of the trigger switch 15a is connected to the control circuit 31. The voltage at the first terminal of the trigger switch 15a is input as a trigger signal Sw to the control circuit 31. The trigger signal Sw indicates whether the trigger switch 15a is turned on or not, in other words, whether the trigger 8 is pulled or not.

[0080] The control circuit 31 of the first embodiment is in the form of a microcomputer or microcontroller unit (MCU) including a CPU 31a and a memory 31b. The memory 31b may include a semiconductor memory such as a ROM, a RAM, an NVRAM, or a flash memory.

[0081] The control circuit 31 realizes various functions by executing a program stored in a non-transient real-world recording medium. In this embodiment, the memory 31b corresponds to the non-transient real-world recording medium storing the program. In this embodiment, the memory 31b stores a program for a motor control process (see FIG. 7) to be described later.

[0082] Some or all of the various functions realized by the control circuit 31 may be achieved by execution of a program (i.e., by software processing) or may be achieved by one or more pieces of hardware. For example, the control circuit 31 may include a logic circuit including a plurality of electronic components instead of or in addition to a microcomputer. The control circuit 31 may include, for example, an application specific integrated circuit (ASIC) and / or an application specific standard product (ASSP), etc. The control circuit 31 may include a programmable logic device capable of constructing any logic circuit, such as a field programmable gate array (FPGA). Alternatively, the control circuit 31 may be in the form of a hardwired circuit.

[0083] The control circuit 31 receives rotational position information (that is, the first to third position signals Hu, Hv, Hw), the voltage signal Sv, the trigger signal Sw, and the direction setting signal Sd. The direction setting signal Sd indicates the position of the direction setting switch 10.

[0084] The control circuit 31 detects the rotational position of the motor 21 (i.e., the rotational position of the rotor) based on the rotational position information. The control circuit 31 detects the magnitude of the power supply voltage based on the voltage signal Sv. The control circuit 31 detects whether the trigger 8 is pulled based on the trigger signal Sw. The control circuit 31 detects whether the first motor direction or the second motor direction is specified based on the direction setting signal Sd. The control circuit 31 sets the rotational direction of the motor 21 to the detected direction.

[0085] The control circuit 31 outputs a drive command to the drive circuit 32 to supply three-phase power from the drive circuit 32 to the motor 21. The drive command includes six drive signals for six switches in the drive circuit 32. For example, the control circuit 31 sets one of the six switches as an on-hold switch and sets the other as a PWM switch.

[0086] More specifically, the control circuit 31 sets, for example, one of the three high-side switches as an on-hold switch and one of the three low-side switches as a PWM switch. The PWM switch corresponds to one of the two low-side switches that is not connected to the on-hold switch.

[0087] The on-hold switch is held in an on state. That is, the control circuit 31 outputs a drive signal to the on-hold switch for holding the on-hold switch in an on state. On the other hand, the PWM switch is PWM driven. PWM drive means that the PWM switch is periodically turned on and off in accordance with a pulse width modulated signal. Therefore, the drive signal output to the PWM switch (hereinafter referred to as the "PWM drive signal") is in the form of a pulse width modulated signal.

[0088] The duty ratio of the PWM drive signal (hereinafter referred to as the "set duty ratio DS") is calculated by the control circuit 31. As will be described later, in the first embodiment, the control circuit 31 gradually increases the set duty ratio DS from an initial value to a target value (hereinafter referred to as the "target duty ratio Dd") during a transitional period immediately after the motor 21 starts to be driven. The control circuit 31 determines and / or changes the rate of increase of the set duty ratio DS during that transitional period in response to the power supply voltage. The initial value may be determined in any manner. For example, the initial value may be 0% or may be greater than 0%.

[0089] When a drive command including a PWM drive signal is output from the control circuit 31 to the drive circuit 32, a power supply voltage is applied to the motor 21 at a period corresponding to the set duty ratio DS of the PWM drive signal. This drives the motor 21.

[0090] Motor control When the trigger 8 is pulled, the control circuit 31 causes the motor 21 to rotate in the rotation direction set by the direction setting switch 10 .

[0091] Specifically, when the trigger 8 is pulled, the control circuit 31 calculates a target duty ratio Dd according to the magnitude of the power supply voltage. In the first embodiment, a target rotation speed Rd of the motor 21 is determined in advance. The target duty ratio Dd corresponds to a duty ratio of a PWM drive signal for rotating the motor 21 at the target rotation speed Rd. The target rotation speed Rd may be stored in advance in, for example, the memory 31b.

[0092] Here, even if the set duty ratio DS of the PWM drive signal is constant, when the power supply voltage changes, the rotation speed of the motor 21 also changes. Specifically, even if the set duty ratio DS is constant, the lower the power supply voltage, the less power is supplied to the motor 21, and the lower the rotation speed of the motor 21 becomes.

[0093] Therefore, in the first embodiment, a target duty ratio Dd is calculated so that the motor 21 rotates at a predetermined target rotation speed Rd regardless of the magnitude of the power supply voltage. Specifically, the target duty ratio Dd is calculated according to the magnitude of the power supply voltage. More specifically, the target duty ratio Dd is calculated so that the lower the power supply voltage, the higher the target duty ratio Dd. By inputting a PWM drive signal having such a target duty ratio Dd to the PWM switch, the motor 21 can be rotated at the target rotation speed Rd regardless of the magnitude of the power supply voltage.

[0094] When the control circuit 31 starts to output the PWM drive signal (i.e., when the motor 21 starts to be driven), the set duty ratio DS is not set to the target duty ratio Dd from the beginning. The control circuit 31 first sets the set duty ratio DS to a predetermined initial value, and outputs a PWM drive signal according to the initial value. The control circuit 31 then increases the set duty ratio DS from the initial value to the target duty ratio Dd over time (or in accordance with the passage of time).

[0095] The control circuit 31 further switches the rate of increase when increasing the set duty ratio DS in accordance with a predetermined switching condition. The rate of increase means the amount of increase in the set duty ratio DS per unit time (for example, one second).

[0096] When increasing the set duty ratio DS from its initial value, the control circuit 31 first sets the increase rate of the set duty ratio DS to a first increase rate Pi1. Then, the control circuit 31 increases the set duty ratio DS from its initial value in accordance with the first increase rate Pi1.

[0097] When the switching condition is met, the control circuit 31 switches the increase rate from the first increase rate Pi1 to the second increase rate Pi2. The second increase rate Pi2 is smaller than the first increase rate Pi1. Therefore, by switching the increase rate to the second increase rate Pi2, the increase tendency of the set duty ratio DS becomes gentler.

[0098] When the switching condition is satisfied again after switching the increase rate to the second increase rate Pi2, the control circuit 31 switches the increase rate from the second increase rate Pi2 to the third increase rate Pi3. The third increase rate Pi3 is smaller than the second increase rate Pi2. Therefore, by switching the increase rate to the third increase rate Pi3, the increasing tendency of the set duty ratio DS becomes more gentle.

[0099] The configuration of the control circuit 31 that realizes the above-mentioned control of the motor 21 will be described in more detail with reference to FIG. 3. In the first embodiment, the control of the motor 21 by the control circuit 31 is realized by the CPU 31a executing a computer program, that is, by software processing. The computer program includes a motor control processing program shown in FIG. 7. The motor control processing controls the rotation of the motor 21. The control circuit 31 (more specifically, the CPU 31a) executes the motor control processing program to function as shown in FIG. 3, that is, to function as each block in the control circuit 31 shown in FIG. 3.

[0100] 3, the control circuit 31 includes a trigger detection unit 41. The trigger detection unit 41 receives a trigger signal Sw from the switch box 15. The trigger detection unit 41 detects whether or not the trigger 8 has been pulled, based on the trigger signal Sw.

[0101] The control circuit 31 includes a drive state management unit 42. The drive state management unit 42 manages the state of the motor 21. Specifically, the drive state management unit 42 determines whether or not the trigger 8 has been pulled based on the detection result by the trigger detection unit 41. If the trigger 8 has been pulled, the drive state management unit 42 operates a voltage detection unit 43, a set duty ratio calculation unit 46, and a drive command generation unit 47, which will be described later, to drive the motor 21.

[0102] The control circuit 31 includes the above-mentioned voltage detection unit 43. The voltage detection unit 43 receives the voltage signal Sv and detects the magnitude of the power supply voltage based on the voltage signal Sv. In the first embodiment, the voltage detection unit 43 detects the magnitude of the power supply voltage when the trigger 8 is pulled and before the motor 21 is driven (i.e., before a drive command is output). In other words, the voltage detection unit 43 detects the magnitude of the power supply voltage when the power supply voltage has not yet been applied to the motor 21.

[0103] The control circuit 31 includes a target calculation unit 44. The target calculation unit 44 calculates a target duty ratio Dd, for example, when the trigger 8 is pulled. The target calculation unit 44 calculates the target duty ratio Dd based on the magnitude of the power supply voltage detected by the voltage detection unit 43. Specifically, as described above, the target calculation unit 44 calculates the target duty ratio Dd so that the motor 21 rotates at a predetermined target rotation speed Rd regardless of the magnitude of the power supply voltage. More specifically, as described above, the target calculation unit 44 calculates the target duty ratio Dd so that the lower the power supply voltage, the higher the target duty ratio Dd.

[0104] The control circuit 31 includes a condition setting unit 45. As described above, in the first embodiment, when a switching condition is satisfied, the increase rate of the set duty ratio DS is switched. The condition setting unit 45 sets the switching condition based on the magnitude of the power supply voltage detected by the voltage detection unit 43. Specifically, the control circuit 31 calculates one or more prescribed duty ratios. The switching condition is satisfied each time the set duty ratio DS calculated by the set duty ratio calculation unit 46 reaches each of the one or more prescribed duty ratios.

[0105] More specifically, the condition setting unit 45 of the first embodiment calculates a first specified duty ratio Dp1 and a second specified duty ratio Dp2. The second specified duty ratio Dp2 is greater than the first specified duty ratio Dp1. Therefore, after the motor 21 starts to be driven, the set duty ratio DS reaches the first specified duty ratio Dp1, and the switching condition is met. Thereafter, the set duty ratio DS reaches the second specified duty ratio Dp2, and the switching condition is met again.

[0106] The condition setting unit 45 further changes each of the one or more prescribed duty ratios in accordance with the power supply voltage. Specifically, as illustrated on the right side of Fig. 6, the condition setting unit 45 calculates each of the one or more prescribed duty ratios (in the first embodiment, the first and second prescribed duty ratios Dp1, Dp2) so that the higher the power supply voltage, the lower the duty ratio becomes.

[0107] The one or more prescribed duty ratios may be determined in any manner. The one or more prescribed duty ratios may be determined, for example, experimentally. For example, the degree of acceleration of the rotation speed when the power supply voltage is at the maximum value in the product specifications may be set as the reference degree of acceleration. Then, the number of the one or more prescribed duty ratios and / or the magnitude of each of the one or more prescribed duty ratios may be derived experimentally or by other methods so that the degree of acceleration matches or approximately matches the reference degree of acceleration regardless of the magnitude of the power supply voltage.

[0108] The control circuit 31 includes a set duty ratio calculation unit 46. The set duty ratio calculation unit 46 calculates a set duty ratio DS. Specifically, the set duty ratio calculation unit 46 sets the set duty ratio DS to an initial value when the motor 21 starts to be driven. After the motor 21 starts to be driven, the set duty ratio DS is increased over time from the initial value to the target duty ratio Dd. Furthermore, if a switching condition is satisfied in the process of increasing the set duty ratio DS, the set duty ratio calculation unit 46 changes the increase rate of the set duty ratio DS. Specifically, as described above, the increase rate is switched to a value lower than the value at the time when the switching condition is satisfied.

[0109] The function of the set duty ratio calculation unit 46 can be expressed as follows: That is, the set duty ratio calculation unit 46 calculates the set duty ratio DS so that the change in the rotation speed from when the motor 21 starts to rotate until it reaches the target rotation speed Rd is the same or approximately the same regardless of the magnitude of the power supply voltage.

[0110] The control circuit 31 includes a drive command generating unit 47. The drive command generating unit 47 acquires the set duty ratio DS calculated by the set duty ratio calculating unit 46. The drive command generating unit 47 further acquires rotational position information. The drive command generating unit 47 further receives a direction setting signal Sd from the direction setting switch 10. The drive command generating unit 47 generates a drive command based on the set duty ratio DS, the rotational position information, and the direction setting signal Sd, and outputs the drive command to the drive circuit 32. Specifically, the drive command generating unit 47 detects the rotational position of the motor 21 (more specifically, the rotational angle of the rotor) based on the rotational position information. Then, based on the detected rotational position, the drive command generating unit 47 determines the on-maintain switch and the PWM switch so that the motor 21 rotates in the rotational direction indicated by the direction setting signal Sd, and outputs a drive command. The drive command output at this time includes a drive signal to the on-maintain switch and a PWM drive signal to the PWM switch. The set duty ratio DS calculated by the set duty ratio calculation unit 46 is set as the duty ratio of the PWM drive signal.

[0111] The control circuit 31 includes a timer 48. The timer 48 measures the elapsed time from a measurement start timing. The measurement start timing corresponds to the timing when the driving of the motor 21 starts. Specifically, the measurement start timing may be, for example, the time when the trigger detection unit 41 detects the operation of the trigger 8. Also, for example, the measurement start timing may be the time when the drive command generation unit 47 outputs a drive command to the drive circuit 32 (in other words, the time when the control circuit 31 commands the drive circuit 32 to drive the motor 21).

[0112] 2-1-4. Example of operation after drive starts An example of the operation of the motor 21 in the initial period (transitional period) from when the driving of the motor 21 is started until the rotation speed reaches the target rotation speed Rd will be described with reference to FIGS.

[0113] First, in order to facilitate understanding of the features of the present disclosure, an operation example of the motor 21 when the increase rate of the set duty ratio DS is fixed will be described as a reference example with reference to FIG. 4. FIG. 4 shows, as an example, an operation example when the value of the power supply voltage Vb is VbL and an operation example when the value of the power supply voltage Vb is VbH. VbH is greater than VbL. VbH may be, for example, the maximum value (maximum specification voltage) of the power supply voltage defined in the specifications of the power tool 1. VbL may be, for example, the minimum value (minimum specification voltage) of the power supply voltage defined in the specifications of the power tool 1. In FIG. 4, Rd indicates the target rotation speed Rd.

[0114] The motor 21 may be configured to be driven even if the value of the power supply voltage Vb exceeds the maximum specification voltage VbH, or may be configured not to drive the motor 21 when the value of the power supply voltage Vb exceeds the maximum specification voltage VbH. The same applies to the case where the value of the power supply voltage Vb is less than the minimum specification voltage VbL.

[0115] When the power supply voltage Vb is VbH, DdH is calculated and set as the target duty ratio Dd. When the power supply voltage Vb is VbL, DdL is calculated and set as the target duty ratio Dd. DdL is smaller than DdH. In other words, the target duty ratio Dd is calculated so that the motor 21 rotates at the same target rotation speed Rd regardless of the magnitude of the power supply voltage Vb.

[0116] Then, when the driving of the motor 21 starts at time t1, an initial value is set to the set duty ratio DS at time t1. The set duty ratio DS increases from the initial value to the target duty ratio Dd at a constant rate. As the set duty ratio DS increases, the rotation speed of the motor 21 also increases. Note that the right side of FIG. 4 shows a simplified waveform of the PWM drive signal and the motor current waveform near time t2 after the set duty ratio DS reaches the target duty ratio Dd. The "motor current" is the current flowing through the motor 21.

[0117] The higher the power supply voltage Vb, the lower the target duty ratio Dd. Therefore, as shown in the right side of Fig. 4, when the power supply voltage Vb is high, a period in which the motor current becomes zero may occur while the PWM switch is off. In other words, when the power supply voltage Vb is high, a period in which the motor current becomes zero may occur repeatedly in the PWM cycle.

[0118] In contrast, the lower the power supply voltage Vb, the higher the target duty ratio Dd. Therefore, as shown in the example on the right side of Figure 4, when the power supply voltage Vb is low, the motor current decreases but does not become zero even during the period when the PWM switch is turned off.

[0119] 4, the rotation speed of the motor 21 during the transitional period after the start of driving increases more rapidly when the power supply voltage Vb is low than when the power supply voltage Vb is high. In other words, the degree of acceleration during the transitional period after the start of driving varies depending on the magnitude of the power supply voltage Vb. The main reason why the rotation speed rises more slowly when the power supply voltage Vb is high than when it is low is that the motor current flows intermittently.

[0120] Incidentally, immediately after the start of driving (immediately after time t1), the load on the motor 21 is large, so the motor current is also large. Therefore, although the set duty ratio DS is small, the motor current flows continuously. Therefore, immediately after the start of driving, the variation in the acceleration state of the motor 21 caused by the magnitude of the power supply voltage Vb is small or hardly occurs.

[0121] The first embodiment proposes a first method capable of suppressing the variation in the acceleration during such a transitional period. The first method includes reducing the rate of increase of the set duty ratio DS when the set duty ratio DS reaches the specified duty ratio Dp.

[0122] Specifically, one or more prescribed duty ratios Dp are set as illustrated in Fig. 5. Fig. 5 shows an example in which first and second prescribed duty ratios Dp1 and Dp2 are set. In the first embodiment, the one or more prescribed duty ratios Dp are set within a range between a target duty ratio DdH set when the power supply voltage Vb is a maximum specified voltage (e.g., VbH) and a target duty ratio DdL set when the power supply voltage Vb is a minimum specified voltage (e.g., VbL).

[0123] 5 shows an operation example when the power supply voltage Vb has a value of VbM in addition to the operation example when the power supply voltage Vb has a value of VbL or VbH. VbM is smaller than VbH and larger than VbL. When the power supply voltage Vb is VbM, DdM is calculated and set as the target duty ratio Dd. DdM is smaller than DdH and larger than DdL. In other words, the target duty ratio DdM is calculated so that the motor 21 rotates at the same target rotation speed Rd even when the power supply voltage is VbM.

[0124] 5, after driving starts at time t11, the set duty ratio DS increases from the initial value at the first increase rate pi1. When the power supply voltage Vb is VbH, the set duty ratio DS and the rotation speed change in the same manner as in FIG.

[0125] On the other hand, when the power supply voltage Vb is VbL, the set duty ratio DS reaches the first specified duty ratio Dp1 at time t12. As a result, the increase rate of the set duty ratio DS is reduced from the first increase rate Pi1 to the second increase rate Pi2. That is, the increase rate of the set duty ratio DS becomes gentler at time t12. Then, at time t14, the set duty ratio DS reaches the second specified duty ratio Dp2. As a result, the increase rate of the set duty ratio DS is further reduced from the second increase rate Pi2 to the third increase rate Pi3. That is, the increase rate of the set duty ratio DS becomes gentler at time t14. Then, at time t15, the target duty ratio DdL is reached. As a result, as illustrated in FIG. 5, the rotation speed during the transition period is the same or almost the same when the power supply voltage Vb is VbH and when it is VbL. That is, the variation in the acceleration caused by the magnitude of the power supply voltage is reduced.

[0126] However, when the power supply voltage Vb is VbM, the degree of acceleration is different. When the power supply voltage Vb is VbM, at time t12, the set duty ratio DS reaches the first specified duty ratio Dp1, and the increase rate is reduced from the first increase rate Pi1 to the second increase rate Pi2. After that, at time t13, the set duty ratio DS reaches the target duty ratio DdM.

[0127] In this way, the first method can suppress the variation in the acceleration state caused by the magnitude of the power supply voltage. However, there is room for further improvement. Therefore, the first embodiment further proposes a second method for further suppressing the variation in the acceleration state. By adopting the first and second methods, the variation in the acceleration state can be further suppressed. The second method includes changing the aforementioned prescribed duty ratio Dp according to the power supply voltage.

[0128] Specifically, as illustrated in FIG. 6, the first and second specified duty ratios Dp1 and Dp2 are set to be lower as the power supply voltage Vb is higher. That is, the first specified duty ratio Dp1 is set to Dp1H when the power supply voltage Vb is VbH, set to Dp1M when the power supply voltage Vb is VbM, and set to Dp1L when the power supply voltage Vb is VbL. Dp1M is larger than Dp1H, and Dp1L is larger than Dp1M. The second specified duty ratio Dp2 is also set to Dp2H when the power supply voltage Vb is VbH, set to Dp2M when the power supply voltage Vb is VbM, and set to Dp2L when the power supply voltage Vb is VbL. Dp2M is larger than Dp2H, and Dp2L is larger than Dp2M.

[0129] 6, the higher the power supply voltage Vb, the earlier the timing at which the first specified duty ratio Dp1 is reached.The higher the power supply voltage Vb, the earlier the timing at which the second specified duty ratio Dp2 is reached.

[0130] For example, when the power supply voltage Vb is VbL, the set duty ratio DS reaches the first specified duty ratio Dp1L at time t23, the set duty ratio DS reaches the second specified duty ratio Dp2L at time 25, and the set duty ratio DS reaches the target duty ratio DdL at time t27. In contrast, when the power supply voltage Vb is VbM, the set duty ratio DS reaches the first specified duty ratio Dp1M at time t22, the set duty ratio DS reaches the second specified duty ratio Dp2M at time 24, and the set duty ratio DS reaches the target duty ratio DdM at time t26. Time t22 is earlier than time t23, and time t24 is earlier than time t25. In other words, the higher the power supply voltage Vb, the earlier the timing at which the increase rate of the set duty ratio DS is switched (i.e., the increase rate is reduced).

[0131] As a result, as shown in Fig. 6, the rotation speeds during the transition period are the same or nearly the same when the power supply voltage Vb is VbH, VbM, or VbL. In other words, the variation in the degree of acceleration caused by the magnitude of the power supply voltage is further reduced.

[0132] The prescribed duty ratio Dp may be set by any method. The control circuit 31 may, for example, have a formula or a table that represents the correspondence relationship between the prescribed duty ratio Dp and the value of the power supply voltage Vb. The control circuit 31 may then substitute the value of the power supply voltage Vb detected by the voltage detection unit 43 into the formula to calculate the prescribed duty ratio Dp, or may refer to the table to obtain the prescribed duty ratio Dp corresponding to that value.

[0133] The specified duty ratio Dp may also be set when the value of the power supply voltage Vb exceeds the maximum specified voltage VbH and / or when the value of the power supply voltage Vb is less than the minimum specified voltage VbL. 6, the first and second specified duty ratios Dp1 and Dp2 may both change (i.e., decrease) continuously even when the power supply voltage Vb exceeds the maximum specified voltage VbH. Also, in the region where the power supply voltage Vb is less than the minimum specified voltage VbL, the first and second specified duty ratios Dp1 and Dp2 may both change (i.e., increase) continuously.

[0134] Alternatively, in a range where the power supply voltage Vb exceeds the maximum specified voltage VbH, the specified duty ratio Dp may be maintained at the specified duty ratio Dp (Dp1H or Dp2H) when the power supply voltage Vb is the maximum specified voltage VbH. Similarly, in a range where the power supply voltage Vb is less than the minimum specified voltage VbL, the specified duty ratio Dp may be maintained at the specified duty ratio Dp (Dp1L or Dp2L) when the power supply voltage Vb is the minimum specified voltage VbL.

[0135] 2-1-5.Motor control processing The motor control process executed by the control circuit 31 (more specifically, the CPU 31a) to realize the above-mentioned operations will be described with reference to Fig. 7. When started up, the control circuit 31 executes the motor control process.

[0136] When the control circuit 31 starts the motor control process, it determines in S110 whether or not the trigger switch 15a is turned on (and thus whether or not the trigger 8 is manually operated). The process of S110 corresponds to the process executed by the trigger detection unit 41. While the trigger switch 15a is turned off, the control circuit 31 repeats the process of S110.

[0137] When the trigger switch 15a is turned off, the control circuit 31 acquires the magnitude of the power supply voltage in S120. That is, the control circuit 31 acquires the magnitude of the power supply voltage before driving the motor 21. The process of S120 corresponds to the process executed by the voltage detection unit 43.

[0138] In S130, the control circuit 31 calculates control parameters based on the magnitude of the power supply voltage acquired in S120. The control parameters calculated in S130 include a target duty ratio Dd, a first specified duty ratio Dp1, and a second specified duty ratio Dp2. The process of S130 corresponds to the process executed by the target calculation unit 44 and the condition setting unit 45.

[0139] In S140, the control circuit 31 sets the set duty ratio DS to an initial value. The process of S140 corresponds to the process executed by the set duty ratio calculation unit . In S150, the control circuit 31 starts driving the motor 21. Specifically, the control circuit 31 outputs a drive command including a PWM drive signal having the set duty ratio DS set in S140 to the drive circuit 32, and starts driving the motor 21.

[0140] In S160, the control circuit 31 determines whether the trigger switch 15a is turned off. If the trigger switch 15a is turned off, the control circuit 31 stops driving the motor 21 in S170. Specifically, for example, the control circuit 31 stops outputting a drive command. After the process of S170, the process proceeds to S110.

[0141] If the trigger switch 15a is turned on in S160, the control circuit 31 determines in S180 whether the currently calculated set duty ratio DS is less than the target duty ratio Dd. If the set duty ratio DS has reached the target duty ratio Dd, the control circuit 31 sets the set duty ratio DS to the target duty ratio Dd in S240. In other words, the state in which the set duty ratio DS has reached the target duty ratio Dd is maintained. After the process of S240, the process proceeds to S160.

[0142] If the set duty ratio DS is less than the target duty ratio Dd in S180, the control circuit 31 determines in S190 whether the currently calculated set duty ratio DS is less than the second specified duty ratio Dp2. If the set duty ratio DS is equal to or greater than the second specified duty ratio Dp2, the control circuit 31 increases the set duty ratio DS according to the third increase rate Pi3 in S230. After the process of S230, the process proceeds to S160.

[0143] If the set duty ratio DS is less than the second specified duty ratio Dp2 in S190, the control circuit 31 determines in S200 whether the currently calculated set duty ratio DS is less than the first specified duty ratio Dp1. If the set duty ratio DS is equal to or greater than the first specified duty ratio Dp1, the control circuit 31 increases the set duty ratio DS according to the second increase rate Pi2 in S220. After the process of S220, the process proceeds to S160.

[0144] If the set duty ratio DS is less than the first specified duty ratio Dp1 in S200, the control circuit 31 increases the set duty ratio DS according to the first increase rate Pi1 in S210. After the process of S210, the process proceeds to S160.

[0145] By executing such a motor control process, in the transition period after the start of driving, the motor 21 is controlled as shown in Fig. 6. This suppresses variations in the degree of acceleration caused by the magnitude of the power supply voltage Vb.

[0146] 2-1-7. Correspondence of terms The drive command generating unit 47 corresponds to an example of a drive signal generating unit in the generalization of the embodiments. The trigger 8 corresponds to an example of a manual switch in the generalization of the embodiments.

[0147] 2-2. Second embodiment In the second embodiment, another example of the switching condition will be described with reference to Figures 8 and 9. The power tool 1 of the second embodiment is basically configured similarly to the power tool 1 of the first embodiment, except for the switching condition.

[0148] In the second embodiment, the switching condition is met every time the elapsed time from the measurement start timing measured by the timer unit 48 reaches one or more specified times Tp. Specifically, in the second embodiment, the condition setting unit 45 calculates a first specified time Tp1 and a second specified time Tp2. The second specified time Tp2 is longer than the first specified time Tp1. Therefore, the switching condition is met when the measured elapsed time after the motor 21 starts to be driven reaches the first specified time Tp1. Thereafter, the measured elapsed time reaches the second specified time Tp2, and the switching condition is met again.

[0149] The condition setting unit 45 of the second embodiment further changes each of the one or more specified times Tp according to the power supply voltage. Specifically, as illustrated on the right side of FIG. 8, the condition setting unit 45 calculates each of the one or more specified times Tp (first and second specified times Tp1 and Tp2 in the second embodiment) so that the higher the power supply voltage, the shorter the specified times Tp become. The one or more specified times Tp may be determined in any manner. The one or more specified times Tp may be determined experimentally, for example, similar to the specified duty ratio Dp of the first embodiment.

[0150] An example of the operation of the motor 21 of the second embodiment will be described with reference to FIG. 8. As illustrated in FIG. 8, the first and second specified times Tp1 and Tp2 are set so as to become shorter as the power supply voltage Vb is higher. That is, the first specified time Tp1 is set to Tp1H when the power supply voltage Vb is VbH, set to Tp1M when the power supply voltage Vb is VbM, and set to Tp1L when the power supply voltage Vb is VbL. Tp1M is longer than Tp1H, and Tp1L is longer than Tp1M. The second specified time Tp2 is also set to Tp2H when the power supply voltage Vb is VbH, set to Tp2M when the power supply voltage Vb is VbM, and set to Tp2L when the power supply voltage Vb is VbL. Tp2M is longer than Tp2H, and Tp2L is longer than Tp2M.

[0151] 8, the higher the power supply voltage Vb, the earlier the first specified time Tp1 elapses from the measurement start time t31. The higher the power supply voltage Vb, the earlier the second specified time Tp2 elapses from the measurement start time t31.

[0152] For example, when the power supply voltage Vb is VbL, the first specified time Tp1L elapses at time t34, and the second specified time Tp2L elapses at time t36. At time t34, the increase rate of the set duty ratio DS switches from the first increase rate Pi1 to the second increase rate Pi2. At time t36, the increase rate switches from the second increase rate Pi2 to the third increase rate Pi3.

[0153] In contrast, when the power supply voltage Vb is VbM, the first specified time Tp1M elapses at time t33, and the second specified time Tp2M elapses at time t35. At time t33, the increase rate of the set duty ratio DS switches from the first increase rate Pi1 to the second increase rate Pi2. At time t35, the increase rate switches from the second increase rate Pi2 to the third increase rate Pi3.

[0154] Time t33 is before time t34, and time t35 is before time t36. That is, the higher the power supply voltage Vb, the earlier the timing at which the increase rate of the set duty ratio DS is switched (that is, the increase rate is reduced).

[0155] As a result, as shown in Fig. 8, the rotation speeds during the transition period are equal or almost equal when the power supply voltage Vb is VbH, VbM, or VbL. In other words, similar to the first embodiment, the variation in the acceleration caused by the magnitude of the power supply voltage is further reduced.

[0156] The motor control process executed by the control circuit 31 of the second embodiment to realize the operation as illustrated in Fig. 8 will be described with reference to Fig. 9. In Fig. 9, the same processes as those in the motor control process of the first embodiment (see Fig. 7) are denoted by the same reference numerals as in Fig. 7, and detailed description thereof will be omitted.

[0157] In the motor control process of Fig. 9, the control circuit 31 acquires the magnitude of the power supply voltage in S120, and then proceeds to S135. In S135, the control circuit 31 calculates control parameters based on the magnitude of the power supply voltage acquired in S120. The control parameters calculated in S135 include a target duty ratio Dd, a first specified time Tp1, and a second specified time Tp2. The process of S135 corresponds to the process executed by the target calculation unit 44 and the condition setting unit 45. After the process of S135, the control circuit 31 proceeds to S140.

[0158] After setting the set duty ratio DS to an initial value in S140, the control circuit 31 proceeds to S155. In S155, the control circuit 31 starts timing by the timer 48. That is, the execution timing of S155 corresponds to the above-mentioned measurement start timing, and starts measuring the elapsed time from the measurement start timing. Furthermore, in S155, driving of the motor 21 is started, similarly to S150 in FIG. 7.

[0159] If the currently calculated set duty ratio DS is less than the target duty ratio Dd in S180, the control circuit 31 proceeds to S195. In S195, the control circuit 31 determines whether the elapsed time TE from the start of measurement is less than the second specified time Tp2. If the elapsed time TE is equal to or greater than the second specified time Tp2, the control circuit 31 increases the set duty ratio DS according to the third increase rate Pi3 in S230. If the elapsed time TE is less than the second specified time Tp2, the control circuit 31 proceeds to S205.

[0160] In S205, the control circuit 31 determines whether the elapsed time TE is less than the first specified time Tp1. If the elapsed time TE is equal to or greater than the first specified time Tp1, the control circuit 31 increases the set duty ratio DS according to the second increase rate Pi2 in S220. If the elapsed time TE is less than the first specified time Tp1, the control circuit 31 increases the set duty ratio DS according to the first increase rate Pi1 in S210.

[0161] By executing such a motor control process, in the transition period after the start of driving, the motor 21 is controlled as shown in Fig. 8. As a result, similar to the first embodiment, the variation in the acceleration state caused by the magnitude of the power supply voltage Vb is suppressed.

[0162] 2-3.Third embodiment In the third embodiment, a third method is proposed to be added to the first embodiment. Specifically, the third method includes changing at least one of the first to third increase rates Pi1 to Pi3 according to the magnitude of the power supply voltage Vb. In the third embodiment, all of the first to third increase rates Pi1 to Pi3 are variably set according to the magnitude of the power supply voltage Vb.

[0163] For this reason, the control circuit 31 of the third embodiment further includes an increase rate calculation unit 51, as shown in Fig. 10. The increase rate calculation unit 51 calculates the first to third increase rates Pi1 to Pi3 based on the magnitude of the power supply voltage Vb detected by the voltage detection unit 43. Specifically, as shown in the lower part of Fig. 11, the increase rate calculation unit 51 calculates the first to third increase rates Pi1 to Pi3 so that the increase rate decreases as the power supply voltage Vb increases.

[0164] The first to third increase rates Pi1 to Pi3 may be calculated in any specific manner based on the magnitude of the power supply voltage Vb. For example, the increase rate Pi may be calculated so that the product of the increase rate Pi and the power supply voltage Vb is a constant value regardless of the magnitude of the power supply voltage Vb.

[0165] An operation example of the motor 21 of the third embodiment will be described with reference to Fig. 11. The operation example of Fig. 11 is basically the same as the operation example of the first embodiment shown in Fig. 6, except that the first to third increase rates Pi1 to Pi3 each differ depending on the power supply voltage Vb.

[0166] For example, the first increase rate Pi1 after the start of driving at time t41 differs depending on the power supply voltage Vb. Specifically, the higher the power supply voltage Vb, the lower the first increase rate Pi1. For example, when the power supply voltage Vb is VbL, the set duty ratio DS reaches the first specified duty ratio Dp1L at time t43. As a result, the increase rate of the set duty ratio DS switches to a second increase rate Pi2, which also differs depending on the power supply voltage Vb. After that, at time 45, the increase rate of the set duty ratio DS switches to a third increase rate Pi3, which also differs depending on the power supply voltage Vb.

[0167] Furthermore, when the power supply voltage Vb is VbM, the set duty ratio DS reaches the first specified duty ratio Dp1M at time t42. As a result, the increase rate of the set duty ratio DS is switched to a second increase rate Pi2, but this second increase rate Pi2 also differs depending on the power supply voltage Vb. Specifically, an increase rate lower than the second increase rate Pi2 when the power supply voltage Vb is VbL is calculated. Thereafter, at time t44, the increase rate of the set duty ratio DS is switched to a third increase rate Pi3, but this third increase rate Pi3 also differs depending on the power supply voltage Vb. Specifically, a third increase rate Pi3 lower than the third increase rate Pi3 when the power supply voltage Vb is VbL is calculated.

[0168] As a result, although not shown in FIG. 11, the variation in rotation speed during the transition period is reduced more than the variation in rotation speed shown in FIG. The motor control process executed by the control circuit 31 of the third embodiment to realize the operation as illustrated in Fig. 11 will be described with reference to Fig. 12. In Fig. 12, the same processes as those in the motor control process of the first embodiment (see Fig. 7) are given the same reference numerals as in Fig. 7, and detailed description thereof will be omitted.

[0169] As is clear from a comparison of FIG. 12 and FIG. 7, the motor control process in FIG. 12 differs from FIG. 7 in that a process in S137 is executed instead of the process in S130 in FIG. 7. That is, the control circuit 31 of the third embodiment acquires the magnitude of the power supply voltage in S120, and then proceeds to S137. In S137, the control circuit 31 calculates control parameters. Specifically, in addition to the target duty ratio Dd, the first specified duty ratio Dp1, and the second specified duty ratio Dp2, the control circuit 31 further calculates first to third increase rates Pi1 to Pi3. The control circuit 31 calculates the first to third increase rates Pi1 to Pi3 based on the magnitude of the power supply voltage acquired in S120. The first to third increase rates Pi1 to Pi3 calculated in S137 are used in S210, S220, and S230, respectively.

[0170] The third method added in the third embodiment can also be added to the second embodiment. 2-4. Other embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0171] (1) In the first and second embodiments, the increase rate of the set duty ratio DS is switched in a maximum of two stages. However, the increase rate may be switched in a maximum of one stage, or in a maximum of three stages or more.

[0172] Specifically, in the first embodiment, for example, only one prescribed duty ratio Dp may be set. In this case, the increase rate of the set duty ratio DS switches at most once. Also, for example, three or more prescribed duty ratios Dp may be set. In this case, the increase rate of the set duty ratio DS switches at most the number of times equal to the number of settings of the prescribed duty ratios Dp.

[0173] In the second embodiment, for example, only one specified time Tp may be set. In this case, the increase rate of the set duty ratio DS is switched at most once. Also, for example, three or more specified times Tp may be set. In this case, the increase rate of the set duty ratio DS is switched at most the number of times set for the specified time.

[0174] (2) In each of the above embodiments, the target rotation speed Rd is determined in advance. However, the target rotation speed Rd may be variably set depending on the amount of pulling of the trigger 8. For example, the power tool 1 may include a circuit that outputs a signal indicating the pulling amount of the trigger 8. The control circuit 31 may detect the pulling amount of the trigger 8 based on the signal from the circuit. The control circuit 31 may set the target rotation speed Rd according to the detected pulling amount. Specifically, for example, the target rotation speed Rd may be set so that the target rotation speed Rd increases as the pulling amount increases.

[0175] (3) The voltage detection unit 43 may detect the magnitude of the power supply voltage at any time (for example, periodically at a control period). Then, the target calculation unit 44 and the condition setting unit 45 may recalculate the target duty ratio Dd or reset the conditions based on the new magnitude of the power supply voltage every time the magnitude of the power supply voltage is newly detected.

[0176] (4) The present disclosure is applicable to any electric power tool that includes a motor and is configured to increase the set duty ratio DS over time during the transitional period after the start of driving. For example, the present disclosure is applicable to electric power tools for masonry, metalworking, and woodworking. More specifically, examples of electric power tools to which the present disclosure is applicable include electric impact wrenches, electric hammers, electric hammer drills, electric drills, electric wrenches, electric grinders, electric circular saws, electric reciprocating saws, electric jigsaws, electric hammers, electric cutters, electric chainsaws, electric planers, and electric nail guns (including tack guns).

[0177] (5) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. [Explanation of symbols]

[0178] 1...power tool, 3a...battery, 7...chuck sleeve, 8...trigger, 15a...trigger switch, 21...motor, 22...drive mechanism, 31...control circuit, 31a...CPU, 31b...memory, 32...drive circuit, 33...control power supply circuit, 35...voltage signal output circuit, 36...rotation sensor, 41...trigger detection unit, 42...drive state management unit, 43...voltage detection unit, 44...target calculation unit, 45...condition setting unit, 46...set duty ratio calculation unit, 47...drive command generation unit, 48...timer unit, 51...increase rate calculation unit.

Claims

1. A motor; a drive circuit configured to receive a power supply voltage and a drive signal having a set duty ratio, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty ratio of the drive signal; a voltage detection unit configured to detect the magnitude of the power supply voltage; a target calculation unit configured to calculate a target duty ratio, which is a target value of the set duty ratio for rotating the motor at a predetermined target rotation speed, based on the magnitude of the power supply voltage detected by the voltage detection unit; a set duty ratio calculation unit configured to increase the set duty ratio from a predetermined initial value to the target duty ratio over time, and to change an increase rate of the set duty ratio in accordance with the magnitude of the power supply voltage detected by the voltage detection unit; A power tool comprising:

2. The power tool according to claim 1, The set duty ratio calculation unit is configured to, when a switching condition for switching the increase rate is satisfied, switch the increase rate to a value lower than the increase rate when the switching condition is satisfied.

3. The power tool according to claim 2, The power tool further includes a condition setting unit configured to set the switching condition depending on the magnitude of the power supply voltage detected by the voltage detection unit.

4. An electric power tool according to claim 2, The power tool, wherein the switching condition is met every time the calculated set duty ratio reaches one or more specified duty ratios.

5. The power tool according to claim 3, the condition setting unit is configured to calculate one or more specified duty ratios based on the magnitude of the power supply voltage detected by the voltage detection unit, the switching condition is met every time the calculated set duty ratio reaches each of the one or more calculated specified duty ratios; Power tools.

6. The power tool according to claim 5, The condition setting unit is configured to calculate each of the one or more specified duty ratios so that the higher the power supply voltage detected by the voltage detection unit, the lower the specified duty ratio becomes.

7. A power tool according to claim 4, The one or more specified duty ratios include at least two specified duty ratios.

8. An electric power tool according to claim 2, the switching condition is satisfied each time one or more specified times have elapsed since a predetermined measurement start timing, the measurement start timing arrives when a drive condition for driving the motor is satisfied; Power tools.

9. The power tool according to claim 3, the condition setting unit is configured to calculate one or more specified times based on the magnitude of the power supply voltage detected by the voltage detection unit, the switching condition is satisfied each time one or more of the calculated specified times elapses from a predetermined measurement start timing, the measurement start timing arrives when a drive condition for driving the motor is satisfied; Power tools.

10. The power tool according to claim 9, The condition setting unit is configured to calculate each of the one or more specified times so that the higher the power supply voltage detected by the voltage detection unit, the shorter the specified time.

11. An electric power tool according to claim 8, a manual switch configured to be manually operated by a user of the power tool; the activation condition is satisfied in response to the manual switch being manually operated by the user; Power tools.

12. A power tool according to claim 8, The one or more predetermined times include at least two predetermined times.

13. A power tool according to claim 2, The power tool further includes an increase rate calculation unit configured to calculate the increase rate from the initial value and / or the increase rate after switching when the switching condition is satisfied, based on the magnitude of the power supply voltage detected by the voltage detection unit.

14. The power tool according to claim 13, The power tool, wherein the increase rate calculation unit is configured to calculate the increase rate so that the increase rate decreases as the power supply voltage detected by the voltage detection unit increases.

15. The power tool according to any one of claims 1 to 14, The power tool, wherein the voltage detection unit is configured to detect the magnitude of the power supply voltage before the motor is driven by the drive circuit.

16. A power tool according to claim 1, The power tool further includes a drive signal generating unit configured to generate the drive signal having the calculated set duty ratio and output the drive signal to the drive circuit.

17. A motor; a drive circuit configured to receive a power supply voltage and a drive signal having a set duty ratio, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty ratio of the drive signal; a voltage detection unit configured to detect the magnitude of the power supply voltage; a target calculation unit configured to calculate a target duty ratio, which is a target value of the set duty ratio for rotating the motor at a predetermined target rotation speed, based on the magnitude of the power supply voltage detected by the voltage detection unit; a set duty ratio calculation unit configured to increase the set duty ratio over time from a predetermined initial value to the target duty ratio based on the magnitude of the power supply voltage detected by the voltage detection unit so that a change process of the rotation speed of the motor from when the motor starts to rotate until the rotation speed of the motor reaches the target rotation speed is the same or approximately the same regardless of the magnitude of the power supply voltage; A power tool comprising:

18. A method for controlling a motor in a power tool, comprising: calculating a target value of a duty ratio for rotating the motor at a predetermined target rotation speed based on the magnitude of a power supply voltage applied to the motor; increasing the duty ratio from a predetermined initial value to the target value over time, and changing the rate of increase in response to the magnitude of the power supply voltage; Driving the motor in accordance with the duty ratio; A method for controlling a motor in a power tool, comprising:

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