Power tools and methods for controlling motors in power tools

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 Art

[0002] Patent Document 1 discloses a power tool configured to perform soft start control. In this power tool, a power supply voltage is applied to a motor according to a PWM drive signal to drive the motor. The soft start control includes gradually increasing the duty ratio of the PWM drive signal from 0% to a target value at the start of driving the motor. The power supply voltage is supplied from a battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Due to the remaining charge of the battery and other factors, the magnitude of the power supply voltage at the start of motor driving can vary. If the power supply voltage at the start of driving is different, the acceleration of the rotational speed of the motor after the start of driving can also be different. For example, the rotational speed at a point after a certain time has elapsed since the start of driving can vary depending on the magnitude of the power supply voltage.

[0005] Variations in the acceleration of the rotational speed can have an unfavorable impact on the work result by the power tool. For example, when performing an operation of tightening a screw to a fastening member, variations in the tightening torque may occur depending on the magnitude of the power supply voltage.

[0006] It is desirable that one aspect of the present disclosure can suppress variations in the acceleration of the rotational speed from the start of motor driving depending on the magnitude of the power supply voltage.

Means for Solving the Problems

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

[0008] The voltage detection unit detects the magnitude of the power supply voltage. The target calculation unit calculates the target duty cycle based on the magnitude of the power supply voltage detected by the voltage detection unit. The target duty cycle is the target value of the set duty cycle required to rotate the motor at a predetermined target rotational speed.

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

[0010] Such power tools can suppress variations in the rate of acceleration of the rotational speed from the start of motor operation, which can be affected by the magnitude of the power supply voltage. In another aspect of this disclosure, a power tool is provided comprising the aforementioned motor, the aforementioned drive circuit, the aforementioned voltage detection unit, the aforementioned target calculation unit, and a setting duty ratio calculation unit different from the aforementioned setting duty ratio calculation unit. The setting duty ratio calculation unit increases the setting 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 setting duty ratio calculation unit increases the setting duty ratio such that the process of change in rotational speed from when the motor starts rotating until the rotational speed of the motor reaches the target rotational speed is the same or substantially the same regardless of the magnitude of the power supply voltage.

[0011] This type of power tool can also suppress variations in the acceleration of the rotational speed from the start of motor operation, which can be affected by the magnitude of the power supply voltage. Another aspect of this disclosure is a method for controlling a motor in a power tool, The target value of the duty cycle for rotating the motor at a predetermined target rotational speed is calculated based on the magnitude of the power supply voltage applied to the motor, The duty cycle is increased over time from a predetermined initial value to the target value, and the rate of increase is varied according to the magnitude of the power supply voltage. Driving the motor according to the duty cycle, It is equipped with.

[0012] This method can suppress variations in the acceleration of the rotational speed from the start of motor operation, which can be affected by the magnitude of the power supply voltage. [Brief explanation of the drawing]

[0013] [Figure 1] This is a side cross-sectional view of the power tool according to the first embodiment. [Figure 2] This is an electrical circuit diagram showing the electrical configuration of the power tool according to the first embodiment. [Figure 3] This is a block diagram showing the functions of the control circuit of the first embodiment. [Figure 4] This is an explanatory diagram illustrating an example of motor operation in a power tool where the rate of increase of the set duty cycle is fixed. [Figure 5] This is an explanatory diagram showing an example of motor operation in a power tool employing the first method. [Figure 6] This is an explanatory diagram showing an example of motor operation in a power tool of the first embodiment in which the first and second methods are employed. [Figure 7] This is a flowchart of the motor control process in the first embodiment. [Figure 8] This is an explanatory diagram showing an example of motor operation in a power tool according to the second embodiment. [Figure 9]It is a flowchart of the motor control process of the second embodiment. [Figure 10] It is a block diagram showing the functions of the control circuit of the third embodiment. [Figure 11] It is an explanatory diagram showing an operation example of the motor in the electric tool of the third embodiment. [Figure 12] It is a flowchart of the motor control process of the third embodiment.

Modes for Carrying Out the Invention

[0014] 1. General Overview of the Embodiment A certain embodiment may provide an electric tool having at least any 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 rotational 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 as time elapses (or according to the passage of time). The set duty ratio calculation unit is configured to change the increase rate of the set duty ratio according 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 modulation signal. The set duty ratio corresponds to the duty ratio of the pulse width modulation signal.

[0015] Varying the rate of increase according to the magnitude of the power supply voltage includes any form in which the magnitude of the power supply voltage is involved in calculating the rate of increase. Changing the rate of increase may include changing 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 increase may vary depending on the magnitude of the power supply voltage. Furthermore, as will be described later, the growth rate may be changed (e.g., decreased) each time a specific timing occurs in which the growth rate should be changed. In this case, the specific timing may vary depending on the magnitude of the power supply voltage. The growth rate may be kept constant at times other than the specific timing. The degree of change in the growth rate at the specific timing (the rate of change or amount of change in the growth rate, or the growth rate after the change) may be configured to differ depending on the magnitude of the power supply voltage.

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

[0018] Power tools possessing at least features 1-5 can suppress variations in the rate of rotational speed acceleration from the start of motor operation, which can be affected by the magnitude of the power supply voltage. One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 5, the following feature 6. Feature 6: The setting duty cycle calculation unit is configured to switch the increase rate to a value lower than the increase rate when the switching condition for switching the increase rate is met. Power tools possessing at least features 1-6 can reduce the processing load required to vary the rate of increase.

[0019] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 6, the following feature 7. Feature 7: A condition setting unit configured to set the switching conditions according to the magnitude of the power supply voltage detected by the voltage detection unit. Power tools possessing at least features 1-7 can easily implement changes in the rate of increase in accordance with the magnitude of the power supply voltage.

[0020] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 7, the following feature 8. Feature 8: The switching condition is met each time the calculated set duty cycle reaches one or more specified duty cycles. Power tools possessing at least features 1-6,8 allow for easy setting of switching conditions.

[0021] One embodiment may have, in addition to or instead of, at least one of the following features 9, 10: Feature 9: The condition setting unit is configured to calculate one or more specified duty cycles based on the magnitude of the power supply voltage detected by the voltage detection unit. Feature 10: The switching condition is met each time the calculated set duty cycle reaches one or more of the calculated specified duty cycles. Power tools possessing at least features 1-7, 9, and 10 allow for easy setting of switching conditions, thereby enabling simple implementation of changes in the rate of increase in accordance with the magnitude of the power supply voltage.

[0022] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 10, the following feature 11. Feature 11: The condition setting unit is configured to calculate each of the one or more specified duty cycles such that the higher the power supply voltage detected by the voltage detection unit, the lower the duty cycle. Power tools possessing at least features 1-7, 9-11 can simply and effectively reflect the magnitude of the power supply voltage in one or more specified duty cycles.

[0023] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 11, the following feature 12. Feature 12: The one or more specified duty cycles include at least two specified duty cycles. Power tools having at least features 1-6, 8, and 12, or at least features 1-7, 9, 10, and 12, can enhance the effect of suppressing variations in the rate of rotational speed acceleration.

[0024] One embodiment may have, in addition to or instead of, at least one of the following features 13, 14: Feature 13: The switching condition is met each time one or more specified time periods have elapsed from a predetermined measurement start timing. Feature 14: The measurement start timing occurs when the driving conditions for driving the motor are met. Power tools possessing at least features 1-6, 13, and 14 allow for easy setting of switching conditions.

[0025] One embodiment may have, in addition to or instead of, at least one of the following features 15 to 17: 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 met each time one or more of the calculated specified time periods have elapsed from a predetermined measurement start timing. Feature 17: The measurement start timing occurs when the driving conditions for driving the motor are met. Power tools possessing at least features 1-7 and 15-17 allow for easy setting of switching conditions, thereby enabling simple implementation of changes in the rate of increase in accordance with the magnitude of the power supply voltage.

[0026] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 17, the following feature 18. Feature 18: The condition setting unit is configured to calculate each of the one or more specified times such that the higher the power supply voltage detected by the voltage detection unit, the shorter the specified time. Power tools possessing at least features 1-7 and 15-18 can easily and effectively reflect the magnitude of the power supply voltage during one or more specified time periods.

[0027] One embodiment may have, in addition to or instead of, at least one of the following features 19, 20: Feature 19: A manual switch configured to be operated manually by the user of the power tool. Feature 20: The driving conditions are met when the manual switch is manually operated by the user. Power tools possessing at least features 1-6, 13, 14, 19, and 20, and power tools possessing at least features 1-7, 15-17, 19, and 20, can set the measurement start timing more appropriately. Furthermore, such power tools can satisfy the switching conditions at the appropriate timing.

[0028] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 20, the following feature 21. Feature 21: The one or more specified times include at least two specified times. Power tools having at least features 1-6, 13, 14, and 21, and power tools having at least features 1-7, 15-17, and 21, can enhance the effect of suppressing variations in the rate of rotational speed acceleration.

[0029] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 21, the following feature 22. 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 met, according to the magnitude of the power supply voltage detected by the voltage detection unit. Power tools possessing at least features 1-6 and 22 can more effectively suppress variations in the rate of rotational speed acceleration.

[0030] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 22, the following feature 23. Feature 23: The increase rate calculation unit is configured to calculate the increase rate such that it becomes lower the higher the power supply voltage detected by the voltage detection unit. Power tools possessing at least features 1-6, 22, and 23 can more easily and effectively reflect the magnitude of the power supply voltage in the rate of increase.

[0031] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 23, the following feature 24. 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. Power tools possessing at least features 1-5,24 can appropriately reflect the magnitude of the power supply voltage in response to changes in the rate of increase.

[0032] One embodiment may have, in addition to or instead of at least one of the above-described features 1 to 24, the following feature 25. Feature 25: A drive signal generation unit configured to generate the drive signal having the calculated set duty cycle and output it to the drive circuit. One embodiment may provide a power tool having the above-described features 1 to 4 and the following feature 26. Feature 26: A set duty cycle calculation unit configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time. The set duty cycle calculation unit increases the set duty cycle based on the magnitude of the power supply voltage detected by the voltage detection unit. The set duty cycle calculation unit increases the duty cycle so that the process of change in rotational speed from when the motor starts rotating until the motor reaches the target rotational speed is the same or substantially the same regardless of the magnitude of the power supply voltage. Power tools possessing at least features 1-4,26 can suppress variations in the rate of rotational speed acceleration from the start of motor operation, which can be affected by the magnitude of the power supply voltage.

[0033] One embodiment may provide a method for controlling a motor in a power tool, comprising at least one of the following features 27 to 29. Feature 27: The target value of the duty cycle is calculated based on the magnitude of the power supply voltage applied to the motor. The target value is the duty cycle required to rotate the motor at a predetermined target rotational speed. Feature 28: The duty cycle is increased over time from a predetermined initial value to the target value, and the rate of increase is varied according to the magnitude of the power supply voltage. Feature 29: To drive the motor according to the duty cycle. Methods that possess at least features 27-29 can suppress variations in the rate of acceleration of the rotational speed from the start of motor operation, which can be affected by the magnitude of the power supply voltage.

[0034] In one embodiment, the above-described features 1 to 29 may be combined in any way. In one embodiment, any of the above-described features 1 to 29 may be excluded. 2. Specific exemplary embodiments Specific exemplary embodiments are described below. These specific exemplary embodiments are merely examples, and the disclosure is not limited to these embodiments and can be implemented in any form.

[0035] 2-1. First Embodiment 2-1-1. Configuration of Power Tools The power tool 1 of this first embodiment, shown in Figure 1, is, for example, an impact driver. The impact driver rotates various fasteners that have screw threads. Various fasteners include, for example, various screws, bolts, nuts, etc. Various screws include, for example, wood screws, self-drilling screws, etc. The impact driver can apply impact force in the direction of rotation while rotating the fastener. The power tool 1 of this first embodiment is powered by the power of a battery 3a (see Figure 2), which will be described later.

[0036] As shown in Figure 1, the power tool 1 comprises a main body 2. The power tool 1 also comprises a battery pack 3. In this first embodiment, the battery pack 3 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 the lower end of the housing 4. In this first embodiment, the grip 5 extends downward from the housing 4. The grip 5 is held by the user of the power tool 1.

[0038] The main unit 2 includes a battery mounting section 6. The battery mounting section 6 is located at the lower end of the grip 5. The battery pack 3 is detachably attached to the battery mounting section 6. The main body 2 is equipped with a chuck sleeve 7. The chuck sleeve 7 is located at the front end of the housing 4. Various tool bits are detachably mounted on the chuck sleeve 7. These tool bits include, for example, screwdriver bits and socket bits. Figure 1 schematically shows a screwdriver bit 7a. When the chuck sleeve 7 rotates, the tool bits mounted on the chuck sleeve 7 rotate together with the chuck sleeve 7 (i.e., as a single unit). The chuck sleeve 7 is rotated by a motor 21, which will be described later.

[0039] The main body 2 is equipped with a trigger 8. The trigger 8 is located on the upper front of the grip 5. The trigger 8 is operated manually by the user. Specifically, in this first embodiment, the trigger 8 is pulled by the user. In other words, the trigger 8 is moved backward and pushed into the interior of the main body 2. The power tool 1 is operated when the trigger 8 is pulled.

[0040] The main unit 2 is equipped with a direction setting switch 10. The direction setting switch 10 specifies the rotation direction of the motor 21 (and consequently the rotation direction of the chuck sleeve 7), which will be described later. Specifically, the direction setting switch 10 selectively specifies the rotation direction of the chuck sleeve 7 to either the first direction or the second direction.

[0041] The direction setting switch 10 is located near the boundary between the housing 4 and the grip 5. In this first embodiment, the direction setting switch 10 is manually operated by the user to the right or left. 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 the 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 coincide with the first motor rotation direction, or it may be opposite to the first motor rotation direction. In this first embodiment, the first direction coincides with the first motor rotation direction. The first direction may be, for example, clockwise (or right-hand).

[0043] The first direction corresponds to the direction in which the fastener is tightened onto the material to be fastened. That is, a tool bit rotating in the first direction rotates the fastener in the first direction. As the fastener rotates in the first direction, it is tightened onto the material to be fastened.

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

[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 the 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 coincide with the second motor rotation direction, or it may be opposite to the second motor rotation direction. In this first embodiment, the second direction coincides with the second motor rotation direction. The second direction may be, for example, counterclockwise (or leftward).

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

[0047] The direction setting switch 10 may also be movable to a third position. The third position may be, for example, an intermediate position between the first and second positions. 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 not rotate even if the trigger 8 is pulled, or the operation of pulling the trigger 8 itself may be mechanically restricted.

[0048] The main unit 2 includes an operation panel 11. In this first embodiment, the operation panel 11 is provided on 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 housed in a housing 4. The motor 21 includes a shaft 21a. When we say that the motor 21 rotates, more specifically, we mean that the shaft 21a rotates.

[0050] The power tool 1 is equipped with a drive mechanism 22. The drive mechanism 22 is housed in a housing 4. The drive mechanism 22 is positioned 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 chuck sleeve 7 rotates due to the drive mechanism 22.

[0051] The drive mechanism 22 includes a striking mechanism 23. The striking mechanism 23 includes a spindle 24. The spindle 24 is rotatably supported. The drive mechanism 22 also includes a planetary gear mechanism 26. The shaft 21a of the motor 21 is connected 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 comprises 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 also movable along the axis of rotation 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 by receiving rotational and / or striking forces from the hammer 28. A chuck sleeve 7 is attached to the front end of the anvil 29.

[0053] In this 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 each other. The hammer 28 includes, for example, a first striking projection 28a and a second striking projection 28b. The first striking projection 28a and the second striking projection 28b impart rotational and / or striking force to the anvil 29. The first striking projection 28a and the second striking projection 28b are positioned, for example, at a distance of 180° from each other along the rotational direction of the hammer 28. The first striking projection 28a and the second striking projection 28b are positioned to project forward from the front end face of the hammer 28.

[0054] The rear end of the anvil 29 is provided with a first striking arm 29a and a second striking arm 29b. The first striking arm 29a and the second striking arm 29b are positioned at a distance of, for example, 180° from each other along the rotational direction of the hammer 28.

[0055] When the hammer 28 is biased forward by the coil spring 30, the first striking projection 28a and the second striking projection 28b are in a state where they can contact the first striking arm 29a and the second striking arm 29b, respectively, in their direction of rotation. The surfaces of the first striking projection 28a and the second striking projection 28b that contact the first striking arm 29a or the second striking arm 29b may, for example, be perpendicular or substantially perpendicular to the direction of rotation of the hammer 28. The surfaces of the first striking arm 29a and the second striking arm 29b that contact the first striking projection 28a or the second striking projection 28b may, for example, be perpendicular or substantially perpendicular to the direction of rotation of the anvil 29.

[0056] When the motor 21 rotates the spindle 24, the hammer 28 rotates integrally with the spindle 24. When the hammer 28 rotates with the first striking projection 28a and the second striking projection 28b in contact with the first striking arm 29a and the second striking arm 29b in the rotational direction, the rotational force of the hammer 28 is transmitted from the first striking projection 28a and the second striking projection 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 mounted on the chuck sleeve 7 to rotate.

[0057] While the motor 21 is rotating, the hammer 28 may receive a torque (hereinafter referred to as "load torque") in the opposite direction to the rotation of the hammer 28 via the fasteners, chuck sleeve 7, and anvil 29. When the hammer 28 receives a load torque of a predetermined magnitude or greater during rotation, it displaces backward against the biasing force of the coil spring 30 while applying rotational force to the anvil 29. Specifically, the first striking projection 28a and the second striking projection 28b displace backward while contacting the first striking arm 29a and the second striking arm 29b, respectively. As the rearward displacement of the hammer 28 progresses, the first striking projection 28a and the second striking projection 28b move over the first striking arm 29a and the second striking arm 29b in the rotational direction, respectively. In other words, the first striking projection 28a and the second striking projection 28b move away from the first striking arm 29a and the second striking arm 29b in the rotational direction, respectively. As a result, the hammer 28 rotates freely and is displaced forward by the biasing force of the coil spring 30. Consequently, the first striking projection 28a and the second striking projection 28b collide with the first striking arm 29a and the second striking arm 29b. In other words, the first striking projection 28a and the second striking projection 28b strike the first striking arm 29a and the second striking arm 29b in the rotational direction.

[0058] Such blows are repeated while the hammer 28 is subjected to a load torque exceeding a predetermined magnitude. In other words, while the hammer 28 is subjected to a load torque exceeding a predetermined magnitude, the anvil 29 is intermittently struck by the hammer 28.

[0059] When the motor 21 is rotating in the first direction, a strike occurs, and the fastener is tightened to the material being fastened with high torque. When the motor 21 is rotating in the reverse direction, a strike occurs, and the fastener tightened to the material being fastened is loosened with high torque.

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

[0061] The main unit 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 pull or the length of movement).

[0062] 2-1-2. Electrical Configuration of Power Tools The electrical configuration of the power tool 1 will be explained in more detail with reference to Figure 2. Figure 2 shows the power tool 1 with the battery pack 3 attached to the main body 2.

[0063] Battery pack 3 includes a battery 3a. Battery 3a may be, for example, a rechargeable battery. Battery 3a may be, for example, a lithium-ion battery. Battery 3a may be a rechargeable battery other than a lithium-ion battery.

[0064] The power tool 1 comprises the aforementioned motor 21, controller 16, switch box 15, and direction setting switch 10. When the battery pack 3 is attached to the main unit 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 this first embodiment, the motor 21 is, for example, a brushless DC motor. The motor 21 includes a permanent magnet type rotor (not shown). The aforementioned shaft 21a is fixed to the rotor and rotates together with the rotor.

[0066] Motor 21 is driven by battery power. Motor 21 receives battery power from battery 3a via a drive circuit 32, which will be described later. The drive circuit 32 converts the battery power into three-phase power. Motor 21 receives this three-phase power. Motor 21 in this first embodiment has three windings. Three-phase power is supplied to the three windings. Motor 21 rotates as three-phase power is supplied to the three windings. Figure 2 shows an example in which the three windings are delta connected to each other. However, the three windings may be connected in a way other than delta connection.

[0067] The power tool 1 is equipped with a rotation sensor 36. The rotation sensor 36 outputs rotation position information. The rotation position information may indicate whether or not the motor 21 is rotating. The rotation position information may change according to the rotation position and / or rotation speed of the motor 21. The rotation position information may indicate the rotation position of the motor 21, more 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 this first embodiment includes three Hall sensors (not shown). The three Hall sensors are arranged near the rotor of the motor 21, separated from each other by an angle corresponding to an electrical angle of 120 degrees along the rotation direction of the shaft 21a. The first to third position signals Hu, Hv, and Hw are output from the three Hall sensors, respectively.

[0069] In this first embodiment, the rotation sensor 36 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 the control power line and ground line of the controller 16, which will be described later.

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

[0071] The controller 16 comprises 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 the 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 this 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 take any form. In this first embodiment, each switch is, for example, an n-channel metal oxide semiconductor field-effect transistor (MOSFET).

[0073] The six switches consist of three high-side switches and three low-side switches. Each of the three high-side switches is connected to the positive terminal of battery 3a via a battery power path described later. Each of the three low-side switches is connected to the negative terminal of battery 3a via a ground line. As shown in Figure 2, the source of each of the three high-side switches is connected to the drain of one of the three low-side switches. The sources of each of the three high-side switches (in other words, the drains of each 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 that high-side switch are turned on, battery power is supplied to the motor 21 via those high-side and low-side switches, 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 the battery power path. The battery power path runs from the positive terminal 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 in the battery power path.

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

[0076] In this first embodiment, the voltage in the battery power path is equal to or approximately equal to the voltage at the positive terminal of battery 3a. Also, the voltage in 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 battery 3a voltage and the power supply voltage. In other words, in this first embodiment, the power supply voltage is equal to or approximately equal to the battery 3a voltage. 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 the control power supply line. The control voltage Vcc has, for example, a constant voltage value. The control voltage Vcc is supplied through the control power supply line to each part of the controller 16, including the control circuit 31. The control circuit 31 operates according to its control voltage Vcc.

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

[0079] The 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 to the control circuit 31 as a trigger signal Sw. The trigger signal Sw indicates whether the trigger switch 15a is ON or OFF, in other words, whether the trigger 8 is pulled or OFF.

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

[0081] The control circuit 31 implements various functions by executing a program stored in a non-transitional physical recording medium. In this embodiment, the memory 31b corresponds to the non-transitional physical recording medium that stores the program. In this embodiment, the memory 31b stores the program for the motor control processing (see Figure 7), which will be described later.

[0082] Some or all of the functions implemented by the control circuit 31 may be achieved by program execution (i.e., by software processing) or by one or more hardware components. For example, the control circuit 31 may include a logic circuit containing multiple 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). 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 (i.e., the first to third position signals Hu, Hv, Hw), a voltage signal Sv, a trigger signal Sw, and a 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 has been pulled based on the trigger signal Sw. The control circuit 31 detects whether the first motor direction or the second motor direction has been specified based on the direction setting signal Sd. The control circuit 31 sets the rotational direction of the motor 21 to the direction it has detected.

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

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

[0087] The ON-hold switch is held in the ON state. That is, the control circuit 31 outputs a drive signal to the ON-hold switch to keep it in the ON state. On the other hand, the PWM switch is PWM driven. PWM driving means periodically turning the PWM switch on and off according to a pulse width modulation 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 modulation signal.

[0088] The duty cycle of the PWM drive signal (hereinafter referred to as "set duty cycle DS") is calculated by the control circuit 31. As will be described later, in this first embodiment, the control circuit 31 gradually increases the set duty cycle DS from an initial value to a target value (hereinafter referred to as "target duty cycle Dd") during the transient period immediately after the start of motor 21 operation. The control circuit 31 determines and / or changes the rate of increase of the set duty cycle DS during the transient period according to the power supply voltage. The initial value can be determined in any way. For example, the initial value may be 0% or 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, the power supply voltage is applied to the motor 21 at a period corresponding to the set duty cycle DS of the PWM drive signal. This drives the motor 21.

[0090] 2-1-3. Motor Control When the trigger 8 is pulled, the control circuit 31 rotates the motor 21 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 cycle Dd according to the magnitude of the power supply voltage. In this first embodiment, the target rotational speed Rd of the motor 21 is predetermined. The target duty cycle Dd corresponds to the duty cycle of the PWM drive signal used to rotate the motor 21 at that target rotational speed Rd. The target rotational speed Rd may be stored in memory 31b, for example.

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

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

[0094] When the control circuit 31 starts outputting the PWM drive signal (i.e., when the motor 21 starts driving), it does not initially set the set duty cycle DS to the target duty cycle Dd. The control circuit 31 first sets the set duty cycle DS to a predetermined initial value and outputs a PWM drive signal corresponding to that initial value. Then, the control circuit 31 increases the set duty cycle DS from the initial value to the target duty cycle 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 cycle DS according to predetermined switching conditions. The rate of increase refers to the amount of increase in the set duty cycle DS per unit time (e.g., 1 second).

[0096] When the control circuit 31 increases the set duty cycle DS from its initial value, it first sets the rate of increase of the set duty cycle DS to a first increase rate Pi1. Then, the control circuit 31 increases the set duty cycle DS from its initial value according to the first increase rate Pi1.

[0097] When the switching condition is met, the control circuit 31 switches the growth rate from the first growth rate Pi1 to the second growth rate Pi2. The second growth rate Pi2 is smaller than the first growth rate Pi1. Therefore, when the growth rate switches to the second growth rate Pi2, the increasing trend of the set duty cycle DS becomes more gradual.

[0098] After the control circuit 31 switches the growth rate to the second growth rate Pi2, if the switching condition is met again, it switches the growth rate from the second growth rate Pi2 to the third growth rate Pi3. The third growth rate Pi3 is smaller than the second growth rate Pi2. Therefore, when the growth rate switches to the third growth rate Pi3, the increasing trend of the set duty cycle DS becomes even more gradual.

[0099] The configuration of the control circuit 31 that realizes the control of the motor 21 as described above will be explained in more detail with reference to Figure 3. In this 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 the motor control processing program shown in Figure 7. The motor control processing controls the rotation of the motor 21. The control circuit 31 (specifically the CPU 31a) functions as shown in Figure 3, that is, as each block in the control circuit 31 shown in Figure 3, by executing the motor control processing program.

[0100] As shown in Figure 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. Based on the trigger signal Sw, the trigger detection unit 41 detects whether or not the trigger 8 has been pulled.

[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 from the trigger detection unit 41. If the trigger 8 has been pulled, it activates the voltage detection unit 43, the set duty cycle calculation unit 46, and the drive command generation unit 47, which will be described later, to drive the motor 21.

[0102] The control circuit 31 includes the aforementioned voltage detection unit 43. The voltage detection unit 43 receives a voltage signal Sv and detects the magnitude of the power supply voltage based on the voltage signal Sv. In this 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, it 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 the target duty cycle Dd, for example, when the trigger 8 is pulled. The target calculation unit 44 calculates the target duty cycle 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 cycle Dd such that the motor 21 rotates at a predetermined target rotational 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 cycle Dd such that the lower the power supply voltage, the higher the target duty cycle Dd.

[0104] The control circuit 31 includes a condition setting unit 45. As described above, in this first embodiment, the rate of increase of the set duty cycle DS switches when the switching condition is met. 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 specified duty cycles. The switching condition is met each time the set duty cycle DS calculated by the set duty cycle calculation unit 46 reaches one or more of the specified duty cycles.

[0105] More specifically, the condition setting unit 45 of this first embodiment calculates a first specified duty cycle Dp1 and a second specified duty cycle Dp2. The second specified duty cycle Dp2 is greater than the first specified duty cycle Dp1. Therefore, after the motor 21 starts driving, the switching condition is met when the set duty cycle DS reaches the first specified duty cycle Dp1. Subsequently, the switching condition is met again when the set duty cycle DS reaches the second specified duty cycle Dp2.

[0106] The condition setting unit 45 further changes each of the one or more specified duty cycles according to the power supply voltage. Specifically, as illustrated on the right side of Figure 6, the condition setting unit 45 calculates each of the one or more specified duty cycles (in this first embodiment, the first and second specified duty cycles Dp1 and Dp2) such that they become lower as the power supply voltage increases.

[0107] The above one or more specified duty cycles may be determined in any way. The above one or more specified duty cycles may be determined experimentally, for example. For example, the degree of acceleration of the rotational speed when the power supply voltage is the maximum value specified in the product specifications may be set as the reference acceleration degree. The number of the above one or more specified duty cycles and / or the magnitude of each of the above one or more specified duty cycles may be derived experimentally or by other means so that the degree of acceleration matches or approximately matches the reference acceleration degree regardless of the magnitude of the power supply voltage.

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

[0109] The function of the setting duty cycle calculation unit 46 can be rephrased as follows: The setting duty cycle calculation unit 46 calculates the setting duty cycle DS such that the rate of change in rotational speed from the start of rotation of the motor 21 to reaching the target rotational 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 generation unit 47. The drive command generation unit 47 acquires the set duty cycle DS calculated by the set duty cycle calculation unit 46. The drive command generation unit 47 further acquires rotational position information. The drive command generation unit 47 also receives a direction setting signal Sd from the direction setting switch 10. Based on the set duty cycle DS, rotational position information, and direction setting signal Sd, the drive command generation unit 47 generates a drive command and outputs it to the drive circuit 32. Specifically, the drive command generation unit 47 detects the rotational position of the motor 21 (more precisely, the rotation angle of the rotor) based on the rotational position information. Then, based on the detected rotational position, it determines the ON-hold 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-hold switch and a PWM drive signal to the PWM switch. The set duty cycle DS calculated by the set duty cycle calculation unit 46 is set as the duty cycle of the PWM drive signal.

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

[0112] 2-1-4. Example of operation after starting the drive An example of the operation of motor 21 during the initial (transitional) period from when the motor 21 is started until its rotational speed reaches the target rotational speed Rd will be explained with reference to Figures 4 to 6.

[0113] First, to facilitate understanding of the features of this disclosure, an example of the operation of the motor 21 when the rate of increase of the set duty cycle DS is fixed will be described with reference to Figure 4. Figure 4 shows, as an example, an example of operation when the value of the power supply voltage Vb is VbL and an example of operation when the value of the power supply voltage Vb is VbH. VbH is greater than VbL. VbH may be, for example, the maximum value of the power supply voltage (maximum specified voltage) specified in the specifications of the power tool 1. VbL may be, for example, the minimum value of the power supply voltage (minimum specified voltage) specified in the specifications of the power tool 1. In Figure 4, Rd represents the target rotational speed Rd.

[0114] Furthermore, the motor 21 may be configured to be driven even if the power supply voltage Vb exceeds the maximum specification voltage VbH, or it may be configured so that the motor 21 is not driven if the power supply voltage Vb exceeds the maximum specification voltage VbH. The same applies when the power supply voltage Vb is less than the minimum specification voltage VbL.

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

[0116] Then, when the motor 21 is started to run at time t1, an initial value is set for the set duty cycle DS at time t1. The set duty cycle DS then increases at a constant rate from the initial value to the target duty cycle Dd. As the set duty cycle DS increases, the rotational speed of the motor 21 also increases. On the right side of Figure 4, the waveforms of the PWM drive signal and the motor current are simply shown around time t2, after the set duty cycle DS has reached the target duty cycle Dd. "Motor current" refers to the current flowing through the motor 21.

[0117] The higher the power supply voltage Vb, the lower the target duty cycle Dd. Therefore, as illustrated on the right side of Figure 4, if the power supply voltage Vb is high, there may be periods when the motor current is zero during the time the PWM switch is off. In other words, if the power supply voltage Vb is high, periods when the motor current is zero may occur repeatedly in the PWM cycle.

[0118] In contrast, the lower the power supply voltage Vb, the higher the target duty cycle Dd. Therefore, as illustrated 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 off.

[0119] Therefore, as illustrated in Figure 4, the rotational speed of the motor 21 during the transient period after starting up increases more rapidly when the power supply voltage Vb is low compared to when the power supply voltage Vb is high. In other words, the degree of acceleration during the transient period after starting up up varies depending on the magnitude of the power supply voltage Vb. The main reason why the rise in rotational speed is slower when the power supply voltage Vb is high than when it is low is that the motor current flows intermittently.

[0120] Immediately after the start of operation (immediately after time t1), the load on motor 21 is large, so the motor current is also large. Therefore, although the set duty cycle DS is small, the motor current flows continuously. As a result, immediately after the start of operation, the variation in the acceleration of motor 21 caused by the magnitude of the power supply voltage Vb is small or almost nonexistent.

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

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

[0123] Figure 5 shows examples of operation when the power supply voltage Vb is VbL and VbH, as well as an example of operation when the power supply voltage Vb is VbM. VbM is less than VbH and greater than VbL. When the power supply voltage Vb is VbM, DdM is calculated and set as the target duty cycle Dd. DdM is less than DdH Large and DdL It is smaller. In other words, the target duty cycle DdM is calculated so that the motor 21 rotates at the same target rotational speed Rd even when the power supply voltage is VbM.

[0124] In the example in Figure 5, after the drive starts at time t11, the set duty cycle DS increases from its initial value according to the first increase rate pi1. The changes in the set duty cycle DS and rotational speed when the power supply voltage Vb is VbH are the same as in Figure 4.

[0125] On the other hand, when the power supply voltage Vb is VbL, at time t12, the set duty cycle DS reaches the first specified duty cycle Dp1. As a result, the rate of increase of the set duty cycle DS is reduced from the first rate of increase Pi1 to the second rate of increase Pi2. In other words, the rate of increase of the set duty cycle DS becomes more gradual from time t12. Then, at time t14, the set duty cycle DS reaches the second specified duty cycle Dp2. As a result, the rate of increase of the set duty cycle DS is further reduced from the second rate of increase Pi2 to the third rate of increase Pi3. In other words, the rate of increase of the set duty cycle DS becomes even more gradual from time t14. Then, at time t15, the target duty cycle DdL is reached. As a result, as illustrated in Figure 5, the transient rotational speed is the same or nearly the same when the power supply voltage Vb is VbH and when it is VbL. In other words, the variation in acceleration caused by the magnitude of the power supply voltage is reduced.

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

[0127] Thus, the first method makes it possible to suppress variations in acceleration caused by the magnitude of the power supply voltage. However, there is room for further improvement. Therefore, this first embodiment further proposes a second method for further suppressing variations in acceleration. By employing the first and second methods, variations in acceleration can be further suppressed. The second method includes changing the specified duty cycle Dp according to the power supply voltage, as described above.

[0128] Specifically, as illustrated in Figure 6, the first and second specified duty cycles Dp1 and Dp2 are set so that they decrease as the power supply voltage Vb increases. That is, for the first specified duty cycle Dp1, it is set to Dp1H when the power supply voltage Vb is VbH, to Dp1M when the power supply voltage Vb is VbM, and to Dp1L when the power supply voltage Vb is VbL. Dp1M is greater than Dp1H, and Dp1L is greater than Dp1M. Similarly, for the second specified duty cycle Dp2, it is set to Dp2H when the power supply voltage Vb is VbH, to Dp2M when the power supply voltage Vb is VbM, and to Dp2L when the power supply voltage Vb is VbL. Dp2M is greater than Dp2H, and Dp2L is greater than Dp2M.

[0129] As a result, in the example in Figure 6, the higher the power supply voltage Vb, the earlier the timing of reaching the first specified duty cycle Dp1. The higher the power supply voltage Vb, the earlier the timing of reaching the second specified duty cycle Dp2.

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

[0131] As a result, as illustrated in Figure 6, the transient rotational speeds are equal or nearly equal to each other regardless of whether the power supply voltage Vb is VbH, VbM, or VbL. In other words, variations in acceleration caused by the magnitude of the power supply voltage are further reduced.

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

[0133] The specified duty cycle Dp may also be set if the value of the power supply voltage Vb exceeds the maximum specification voltage VbH, and / or if the value of the power supply voltage Vb is less than the minimum specification voltage VbL. For example, in the graph on the right side of Figure 6, which shows the relationship between the power supply voltage Vb and the specified duty cycle Dp, both the first specified duty cycle Dp1 and the second specified duty cycle Dp2 may continue to change (i.e., decrease) even when the power supply voltage Vb exceeds the maximum specification voltage VbH. Similarly, both the first specified duty cycle Dp1 and the second specified duty cycle Dp2 may continue to change (i.e., increase) even in the region where the power supply voltage Vb is below the minimum specification voltage VbL.

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

[0135] 2-1-5. Motor Control Processing The motor control process executed by the control circuit 31 (specifically the CPU 31a) to achieve the above-described operation will be explained with reference to Figure 7. When the control circuit 31 is started, it executes the motor control process.

[0136] When the control circuit 31 starts motor control processing, it determines in S110 whether the trigger switch 15a is ON or OFF (and therefore whether the trigger 8 is manually activated or OFF). The processing in S110 corresponds to the processing performed by the trigger detection unit 41. As long as the trigger switch 15a is OFF, the control circuit 31 repeats the processing in S110.

[0137] If the trigger switch 15a is off, the control circuit 31 obtains the magnitude of the power supply voltage in S120. In other words, it obtains the magnitude of the power supply voltage before driving the motor 21. The process in S120 corresponds to the process performed 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 obtained in S120. The control parameters calculated in S130 include the target duty cycle Dd, the first specified duty cycle Dp1, and the second specified duty cycle Dp2. The processing in S130 corresponds to the processing performed by the target calculation unit 44 and the condition setting unit 45.

[0139] In S140, the control circuit 31 sets the set duty cycle DS to its initial value. The process in S140 corresponds to the process executed by the set duty cycle calculation unit 46. In S150, the control circuit 31 starts driving the motor 21. Specifically, it outputs a drive command to the drive circuit 32, which includes a PWM drive signal having the set duty cycle DS set in S140, 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, it stops outputting the drive command. After processing in S170, this process proceeds to S110.

[0141] In S160, if the trigger switch 15a is ON, the control circuit 31 determines in S180 whether the currently calculated set duty cycle DS is less than the target duty cycle Dd. If the set duty cycle DS has reached the target duty cycle Dd, the control circuit 31 sets the set duty cycle DS to the target duty cycle Dd in S240. In other words, it maintains the state in which the set duty cycle DS has reached the target duty cycle Dd. After processing in S240, this process proceeds to S160.

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

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

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

[0145] By performing this motor control process, the motor 21 is controlled during the transient period after the start of driving, as illustrated in Figure 6. This suppresses variations in acceleration caused by the magnitude of the power supply voltage Vb.

[0146] 2-1-7. Terminology Correspondence The drive command generation unit 47 corresponds to an example of a drive signal generation unit in the summary of the embodiment. The trigger 8 corresponds to an example of a manual switch in the summary of the embodiment.

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

[0148] In this second embodiment, the switching condition is met each time the elapsed time from the start of measurement, as measured by the timing unit 48, reaches one or more predetermined time Tp. Specifically, in the second embodiment, the condition setting unit 45 calculates a first predetermined time Tp1 and a second predetermined time Tp2. The second predetermined time Tp2 is longer than the first predetermined time Tp1. Therefore, after the motor 21 starts driving, the switching condition is met when the measured elapsed time reaches the first predetermined time Tp1. Subsequently, the switching condition is met again when the measured elapsed time reaches the second predetermined time Tp2.

[0149] The condition setting unit 45 of this second embodiment further changes each of the one or more specified time Tp according to the power supply voltage. Specifically, as illustrated on the right side of Figure 8, the condition setting unit 45 calculates each of the one or more specified time Tp (in this second embodiment, the first and second specified time Tp1 and Tp2) such that it becomes shorter as the power supply voltage increases. The one or more specified time Tp may be determined in any way. The one or more specified time Tp may be determined experimentally, for example, similar to the specified duty cycle Dp in the first embodiment.

[0150] An example of the operation of the motor 21 of the second embodiment will be described with reference to Figure 8. As illustrated in Figure 8, the first and second specified times Tp1 and Tp2 are set so that they become shorter as the power supply voltage Vb increases. That is, for the first specified time Tp1, it 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. Similarly, for the second specified time Tp2, it is 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] As a result, in the example in Figure 8, the higher the power supply voltage Vb, the earlier the first specified time Tp1 elapses from the measurement start timing t31. The higher the power supply voltage Vb, the earlier the second specified time Tp2 elapses from the measurement start timing t31.

[0152] For example, if 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 rate of increase of the set duty cycle DS switches from the first rate of increase Pi1 to the second rate of increase Pi2. At time t36, the rate of increase switches from the second rate of increase Pi2 to the third rate of increase 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 35. At time t33, the rate of increase of the set duty cycle DS switches from the first rate of increase Pi1 to the second rate of increase Pi2. At time t35, the rate of increase switches from the second rate of increase Pi2 to the third rate of increase Pi3.

[0154] Time t33 is before time t34, and time t35 is before time t36. In other words, the higher the power supply voltage Vb, the earlier the timing at which the rate of increase of the set duty cycle DS switches (i.e., the rate of increase is reduced).

[0155] As a result, as illustrated in Figure 8, the transient rotational speeds are equal to or nearly equal to each other regardless of whether the power supply voltage Vb is VbH, VbM, or VbL. In other words, similar to the first embodiment, variations in acceleration caused by the magnitude of the power supply voltage are further reduced.

[0156] The motor control processing performed by the control circuit 31 of the second embodiment to achieve the operation illustrated in Figure 8 will be described with reference to Figure 9. In Figure 9, the same processes as in the motor control processing of the first embodiment (see Figure 7) are denoted by the same reference numerals as in Figure 7, and their detailed explanation is omitted.

[0157] In the motor control process shown in Figure 9, the control circuit 31 obtains 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 obtained in S120. The control parameters calculated in S135 include the target duty cycle Dd, the first specified time Tp1, and the second specified time Tp2. The process in S135 corresponds to the process executed by the target calculation unit 44 and the condition setting unit 45. After the process in S135, the control circuit 31 proceeds to S140.

[0158] After setting the set duty cycle DS to its initial value in S140, the control circuit 31 proceeds to S155. In S155, the control circuit 31 starts timing using the timing unit 48. In other words, the timing of execution of S155 corresponds to the aforementioned measurement start timing, and the measurement of elapsed time from that measurement start timing begins. In S155, the motor 21 is also started to drive, similar to S150 in Figure 7.

[0159] In S180, the control circuit 31 proceeds to S195 if the currently calculated set duty cycle DS is less than the target duty cycle Dd. 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 greater than or equal to the second specified time Tp2, the control circuit 31 increases the set duty cycle 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 greater than or equal to the first specified time Tp1, the control circuit 31 increases the set duty cycle 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 cycle DS according to the first increase rate Pi1 in S210.

[0161] By performing this motor control process, the motor 21 is controlled during the transient period after the start of driving, as illustrated in Figure 8. As a result, similar to the first embodiment, variations in acceleration caused by the magnitude of the power supply voltage Vb are suppressed.

[0162] 2-3. Third Embodiment In the third embodiment, we propose adding a third method to the first embodiment. Specifically, the third method includes varying at least one of the first to third growth rates Pi1 to Pi3 in accordance with the magnitude of the power supply voltage Vb. In this third embodiment, all of the first to third growth rates Pi1 to Pi3 are variably set according to the magnitude of the power supply voltage Vb.

[0163] Therefore, the control circuit 31 of this third embodiment further includes an increase rate calculation unit 51, as shown in Figure 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 illustrated in the lower part of Figure 11, the increase rate calculation unit 51 calculates each of the first to third increase rates Pi1 to Pi3 such that the increase rate decreases as the power supply voltage Vb increases.

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

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

[0166] For example, the first growth rate Pi1 after the start of operation at time t41 differs depending on the power supply voltage Vb. Specifically, the higher the power supply voltage Vb, the lower the first growth rate Pi1 becomes. For example, if the power supply voltage Vb is VbL, the set duty cycle DS reaches the first specified duty cycle Dp1L at time t43. As a result, the rate of increase of the set duty cycle DS switches to the second rate of increase Pi2, but this second rate of increase Pi2 also differs depending on the power supply voltage Vb. Then, at time 45, the rate of increase of the set duty cycle DS switches to the third rate of increase Pi3, but this third rate of increase Pi3 also differs depending on the power supply voltage Vb.

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

[0168] As a result, although not shown in Figure 11, the variation in rotational speed during the transient period is reduced more than the variation in rotational speed shown in Figure 6. The motor control processing performed by the control circuit 31 of the third embodiment to achieve the operation illustrated in Figure 11 will be described with reference to Figure 12. In Figure 12, the same processes as in the motor control processing of the first embodiment (see Figure 7) are denoted by the same reference numerals as in Figure 7, and their detailed explanation is omitted.

[0169] As is clear from comparing Figure 12 and Figure 7, the motor control process in Figure 12 differs from that in Figure 7 in that the process in S137 is executed instead of the process in S130 in Figure 7. That is, in this third embodiment, the control circuit 31 obtains 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 cycle Dd, the first specified duty cycle Dp1, and the second specified duty cycle Dp2, it also calculates the 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 obtained in S120. These first to third increase rates Pi1 to Pi3 calculated in S137 are used in S210, S220, and S230, respectively.

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

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

[0172] Specifically, in the first embodiment, for example, only one specified duty cycle Dp may be set. In this case, the rate of increase of the set duty cycle DS will switch at most once. Alternatively, for example, three or more specified duty cycle Dp may be set. In this case, the rate of increase of the set duty cycle DS will switch at most as many times as the number of specified duty cycle Dp settings.

[0173] In the second embodiment, for example, only one specified time Tp may be set. In this case, the rate of increase of the set duty cycle DS will switch at most once. Alternatively, for example, three or more specified time Tp may be set. In this case, the rate of increase of the set duty cycle DS will switch at most as many times as the number of specified time settings.

[0174] (2) In each of the above embodiments, the target rotational speed Rd was predetermined. However, the target rotational speed Rd may be set to be variable according to the amount the trigger 8 is pulled. For example, the power tool 1 may include a circuit that outputs a signal indicating the amount the trigger 8 is pulled. The control circuit 31 may detect the amount the trigger 8 is pulled based on the signal from the circuit. The control circuit 31 may set the target rotational speed Rd according to the detected amount the trigger is pulled. Specifically, for example, the target rotational speed Rd may be set such that the target rotational speed Rd increases as the amount the trigger is pulled increases.

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

[0176] (4) The disclosure is applicable to any power tool equipped with a motor and configured to increase the transient set duty cycle DS over time after the start of operation. For example, the disclosure is applicable to power tools for masonry, metalworking, and woodworking. More specifically, examples of power tools to which the 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 nail guns).

[0177] (5) Multiple functions of one component in the above embodiment may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, some of the configurations of the above embodiment may be omitted. Furthermore, at least some of the configurations of the above embodiment may be added to or replaced with the configurations of other 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 cycle calculation unit, 47...Drive command generation unit, 48...Timekeeping unit, 51...Increase rate calculation unit.

Claims

1. Motor and, A drive circuit is configured to receive a drive signal having a power supply voltage and a set duty cycle, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty cycle of the drive signal, A voltage detection unit configured to detect the magnitude of the power supply voltage, A target calculation unit is configured to calculate a target duty cycle, which is a target value for the set duty cycle required to rotate the motor at a predetermined target rotational speed, such that the target duty cycle increases as the power supply voltage detected by the voltage detection unit decreases. A set duty cycle calculation unit is configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time, and to change the rate of increase of the set duty cycle according to the magnitude of the power supply voltage detected by the voltage detection unit. Power tools equipped with [specific features / features].

2. The power tool according to claim 1, The aforementioned duty cycle calculation unit is configured to switch the increase rate to a value lower than the increase rate when a switching condition for switching the increase rate is met, in the power tool.

3. A motor and, A drive circuit is configured to receive a drive signal having a power supply voltage and a set duty cycle, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty cycle of the drive signal, A voltage detection unit configured to detect the magnitude of the power supply voltage, A target calculation unit is configured to calculate a target duty cycle, which is a target value for the set duty cycle necessary to rotate the motor at a predetermined target rotational speed, based on the magnitude of the power supply voltage detected by the voltage detection unit. A set duty cycle calculation unit is configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time, and to change the rate of increase of the set duty cycle according to the magnitude of the power supply voltage detected by the voltage detection unit. Equipped with, The setting duty cycle calculation unit is configured to switch the increase rate to a value lower than the increase rate when the switching condition for switching the increase rate is met. Furthermore, the power tool includes a condition setting unit configured to set the switching conditions according to the magnitude of the power supply voltage detected by the voltage detection unit.

4. The power tool according to claim 2, The aforementioned switching condition is met each time the calculated set duty cycle reaches one or more specified duty cycles, in the power tool.

5. The power tool according to claim 3, The condition setting unit is configured to calculate one or more specified duty cycles based on the magnitude of the power supply voltage detected by the voltage detection unit. The aforementioned switching condition is met each time the calculated set duty cycle reaches one or more of the calculated specified duty cycles. 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 cycles such that the higher the power supply voltage detected by the voltage detection unit, the lower the duty cycle of the power tool.

7. A motor and, A drive circuit is configured to receive a drive signal having a power supply voltage and a set duty cycle, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty cycle of the drive signal, A voltage detection unit configured to detect the magnitude of the power supply voltage, A target calculation unit is configured to calculate a target duty cycle, which is a target value for the set duty cycle necessary to rotate the motor at a predetermined target rotational speed, based on the magnitude of the power supply voltage detected by the voltage detection unit. A set duty cycle calculation unit is configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time, and to change the rate of increase of the set duty cycle according to the magnitude of the power supply voltage detected by the voltage detection unit. Equipped with, The setting duty cycle calculation unit is configured to switch the increase rate to a value lower than the increase rate when the switching condition for switching the increase rate is met. The aforementioned switching condition is met each time the calculated set duty cycle reaches one or more specified duty cycles. The power tool wherein the one or more specified duty cycles include at least two specified duty cycles.

8. A motor and, A drive circuit is configured to receive a drive signal having a power supply voltage and a set duty cycle, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty cycle of the drive signal, A voltage detection unit configured to detect the magnitude of the power supply voltage, A target calculation unit is configured to calculate a target duty cycle, which is a target value for the set duty cycle necessary to rotate the motor at a predetermined target rotational speed, based on the magnitude of the power supply voltage detected by the voltage detection unit. A set duty cycle calculation unit is configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time, and to change the rate of increase of the set duty cycle according to the magnitude of the power supply voltage detected by the voltage detection unit. Equipped with, The setting duty cycle calculation unit is configured to switch the increase rate to a value lower than the increase rate when the switching condition for switching the increase rate is met. The aforementioned switching condition is met each time one or more specified time periods have elapsed from a predetermined measurement start timing. The measurement start timing occurs when the driving conditions for driving the motor are met. 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 aforementioned switching condition is met each time one or more of the calculated specified time periods have elapsed from a predetermined measurement start timing. The measurement start timing occurs when the driving conditions for driving the motor are met. 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 time periods such that the higher the power supply voltage detected by the voltage detection unit, the shorter the specified time period becomes.

11. The power tool according to claim 8, The power tool is equipped with a manual switch configured to be operated manually by the user of the power tool, The aforementioned driving conditions are met when the manual switch is manually operated by the user. Power tools.

12. The power tool according to claim 8, The aforementioned one or more specified times include at least two specified times for the power tool.

13. The power tool according to claim 2, Furthermore, the power tool 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 met, according to the magnitude of the power supply voltage detected by the voltage detection unit.

14. The power tool according to claim 13, The aforementioned increase rate calculation unit is configured to calculate the increase rate such that it becomes lower the higher the power supply voltage detected by the voltage detection unit is, in the power tool.

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

16. The power tool according to claim 1, Furthermore, the power tool includes a drive signal generation unit configured to generate the drive signal having the calculated set duty cycle and output it to the drive circuit.

17. Motor and, A drive circuit is configured to receive a drive signal having a power supply voltage and a set duty cycle, and to drive the motor by applying the power supply voltage to the motor at a period corresponding to the set duty cycle of the drive signal, A voltage detection unit configured to detect the magnitude of the power supply voltage, A target calculation unit is configured to calculate a target duty cycle, which is a target value for the set duty cycle necessary to rotate the motor at a predetermined target rotational speed, based on the magnitude of the power supply voltage detected by the voltage detection unit. A set duty cycle calculation unit is configured to increase the set duty cycle from a predetermined initial value to the target duty cycle over time, based on the magnitude of the power supply voltage detected by the voltage detection unit, so that the process of change in the rotational speed from when the motor starts rotating until the rotational speed of the motor reaches the target rotational speed is the same or substantially the same regardless of the magnitude of the power supply voltage. Power tools equipped with [specific features / features].

18. A method for controlling a motor in an electric power tool, The target duty cycle for rotating the motor at a predetermined target rotational speed is calculated such that it increases as the power supply voltage applied to the motor decreases. The duty cycle is increased over time from a predetermined initial value to the target value, and the rate of increase is varied according to the magnitude of the power supply voltage. Driving the motor according to the duty cycle, A method for controlling a motor in a power tool, comprising the features described above.

19. A method for controlling a motor in an electric power tool, The target value of the duty cycle for rotating the motor at a predetermined target rotational speed is calculated based on the magnitude of the power supply voltage applied to the motor, The process of change in rotational speed from when the motor starts rotating until the motor reaches the target value is the same or substantially the same regardless of the magnitude of the power supply voltage, by increasing the duty cycle from a predetermined initial value to the target value over time based on the magnitude of the power supply voltage. Driving the motor according to the duty cycle, A method for controlling a motor in a power tool, comprising the features described above.

20. The power tool according to claim 2, The power tool is configured such that, when the switching condition is met, the setting duty cycle calculation unit switches the increase rate to a value that is lower than the increase rate when the switching condition is met and greater than zero.

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