Impact tool

Abstract

To reduce influence caused by a condition for a work object to accurately calculate torque applied to an output shaft.SOLUTION: An impact tool 1 includes a motor 3, a hammer 42, an anvil 45, an output shaft 46, a measurement part, and a torque calculating part. The hammer 42 acquires power from the motor 3 to rotate. The anvil 45 receives impact power in a rotation direction of the hammer 42 from the hammer 42 to rotate. The output shaft 46 rotates together with the anvil 45. The measurement part measures torque current supplied to the motor 3. The torque calculation part calculates torque applied to the output shaft 46 on the basis of the variation amount of the torque current during one impact period.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to impact tools, and more particularly, to impact tools with motors. [Background technology]

[0002] The rotary impact tool described in Patent Document 1 includes a motor, a hammer, and an anvil. The rotary impact tool rotates the hammer with the motor, and generates a fastening torque by applying an impact torque from the hammer to an object to be fastened. The impact detection unit detects the impact timing from the output of the impact detection means. For each detected impact timing, the hammer speed detection unit calculates the speed of the hammer and the lead angle of the anvil at the time of impact from the output of the speed detection means. The torque calculation unit calculates the fastening torque using a formula based on the hammer speed and the lead angle of the anvil for each impact timing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-083002 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the rotary impact tool described in Patent Document 1, the calculation accuracy of the fastening torque may be insufficient depending on the conditions of the object to be fastened, which is the work target.

[0005] An object of the present disclosure is to provide an impact tool that can reduce the effects of conditions on a work target and accurately calculate the torque applied to an output shaft. [Means for solving the problem]

[0006] An impact tool according to an embodiment of the present disclosure includes a motor, a hammer, an anvil, an output shaft, a measuring unit, and a torque calculation unit. The hammer rotates by receiving power from the motor. The anvil rotates by receiving an impact force from the hammer in the rotation direction of the hammer. The output shaft is configured to hold a tool tip. The output shaft rotates together with the anvil. The measuring unit measures a torque current supplied to the motor. The torque calculation unit calculates a torque applied to the output shaft. A period from when the hammer applies the impact force to the anvil to when the hammer climbs over the anvil and then applies the impact force to the anvil again is defined as one impact period. The difference between the maximum value and the minimum value of the torque current in the one impact period is defined as the amount of fluctuation of the torque current in the one impact period. The torque calculation unit calculates the torque applied to the output shaft based on the amount of fluctuation of the torque current in the one impact period. Effect of the Invention

[0007] The present disclosure has the advantage of being able to reduce the effects of conditions on the work target and accurately calculate the torque applied to the output shaft. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic structural diagram of an impact tool according to one embodiment. [Diagram 2] FIG. 2 is an output waveform diagram of the torsion amount sensor of the impact tool. [Diagram 3] FIG. 3 is an output waveform diagram of the torsion amount sensor of the impact tool. [Figure 4] FIG. 4 is a perspective view of a main part of the impact tool. [Diagram 5] FIG. 5 is a perspective view of a main part of the impact tool. [Figure 6] FIG. 6 is a block diagram of the impact tool. [Figure 7]FIG. 7 is a graph showing the change over time of each parameter of the impact tool. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Embodiment) The impact tool 1 according to the embodiment will be described below with reference to the drawings. However, the embodiment described below is merely one of various embodiments of the present disclosure. The embodiment described below can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. In addition, each figure described in the embodiment described below is a schematic diagram, and the size and thickness ratios of each component in the figure do not necessarily reflect the actual dimensional ratios.

[0010] (overview) 1 is a diagram showing a schematic configuration of an impact tool 1 according to the present embodiment. The impact tool 1 is, for example, an impact driver, a hammer drill, an impact drill, an impact drill driver, or an impact wrench. In the following, a case where the impact tool 1 is an impact driver will be described as an example. In the following, a case where the impact tool 1 is used to screw a fastening member 52 such as a bolt into a fastened member such as wood or a metal member will be described as an example.

[0011] As shown in Fig. 1, the impact tool 1 includes a motor 3, a hammer 42, an anvil 45, an output shaft 46, a measuring unit 90 (see Fig. 6), and a torque calculation unit 84 (see Fig. 6). The hammer 42 receives power from the motor 3 and rotates. The anvil 45 receives an impact force from the hammer 42 in the rotational direction of the hammer 42 and rotates. The output shaft 46 is configured to hold a tool tip 51. The output shaft 46 rotates together with the anvil 45.

[0012] Moreover, it is preferable that the impact tool 1 further includes a torsion amount sensor 83. The torsion amount sensor 83 measures the amount of torsion of the output shaft .

[0013] Here, an impact tool according to a comparative example will be described. Components common to the impact tool 1 of this embodiment and the impact tool according to the comparative example will be denoted by common reference numerals and description thereof will be omitted.

[0014] The impact tool according to the comparative example includes a motor 3, a hammer 42, an anvil 45, an output shaft 46, and a torsion sensor 83. The impact tool according to the comparative example calculates the torque applied to the output shaft 46 based on the torsion amount of the output shaft 46 measured by the torsion sensor 83. Specifically, the impact tool according to the comparative example calculates the torque on the assumption that the torque applied to the output shaft 46 is proportional to the torsion amount of the output shaft 46. The impact tool according to the comparative example stops the motor 3 when the peak value of the calculated torque reaches or exceeds a predetermined value.

[0015] The torque applied to the output shaft 46 is, in other words, the torque applied to the fastener 52. When the impact tool 1 is used to screw the fastener 52 into a workpiece, the torque applied to the output shaft 46 is a tightening torque.

[0016] 2 and 3 show examples of waveforms of the amount of twist detected by the twist sensor 83 when the hammer 42 collides with the anvil 45 and applies an impact force. Fig. 2 shows a waveform when the fastening member 52 is a member with a relatively high hardness, and Fig. 3 shows a waveform when the fastening member 52 is a member with a relatively low hardness. Both Figs. 2 and 3 show waveforms when the hammer 42 collides with the anvil 45 only once.

[0017] 2 and 3, a first peak in the amount of twist appears at the moment (times t1 and t3) when the hammer 42 collides with the anvil 45. Thereafter, the impact force acts to compress the fastening member 52, which causes a second peak in the amount of twist to appear at time t2 in FIG. 2. The second peak is larger than the first peak. On the other hand, in FIG. 3, even if the impact force acts to compress the fastening member 52, the hardness of the fastening member 52 is low, so the phenomenon of the fastening member 52 being compressed is not detected as an amount of twist, and the second peak in the amount of twist does not appear at time t4.

[0018] The actual torque is proportional to the second peak.

[0019] The impact tool according to the comparative example calculates the peak torque as a value proportional to the maximum measured amount of twist. In Fig. 2, the peak torque is proportional to the amount of twist at time t2, and in Fig. 3, the peak torque is proportional to the amount of twist at time t3.

[0020] Therefore, in the impact tool according to the comparative example, when the fastening member 52 is a member with a relatively low hardness (as in FIG. 3), the peak value of the torque calculated based on the amount of twist is greater than the actual peak value of the torque (the torque at time t4). As described above, depending on the conditions of the work target, the torque applied to the output shaft 46 may not be calculated accurately based on the amount of twist. This is because the time during which the torque is applied to the output shaft 46 is very short when the hammer 42 collides with the anvil 45 and applies an impact force.

[0021] Furthermore, the detection signal from the torsion sensor 83 may contain high-frequency components unrelated to the tightening, which may make it impossible to accurately calculate the torque applied to the output shaft 46.

[0022] Next, we will return to the description of the impact tool 1 of this embodiment. The measurement unit 90 (see FIG. 6) of the impact tool 1 measures the torque current supplied to the motor 3. The torque calculation unit 84 (see FIG. 6) calculates the torque applied to the output shaft 46. One impact period is defined as a period from when the hammer 42 applies an impact force to the anvil 45, when the hammer 42 climbs over the anvil 45, and when the hammer 42 applies an impact force to the anvil 45 again. The difference between the maximum value and the minimum value of the torque current in one impact period is defined as the amount of fluctuation in the torque current in one impact period. For example, the difference between the maximum value V1 and the minimum value V2 in FIG. 7 is the amount of fluctuation in the torque current in one impact period. The amount of fluctuation in the torque current in one impact period is a positive value. The torque calculation unit 84 calculates the torque applied to the output shaft 46 based on the amount of fluctuation in the torque current in one impact period.

[0023] According to the impact tool 1 of the present embodiment, the torque calculation unit 84 can reduce the influence of the conditions of the work target and accurately calculate the torque applied to the output shaft 46. This is because the amount of fluctuation in the torque current during one impact period is a parameter that is highly correlated with the torque applied to the output shaft 46.

[0024] The relationship between the amount of variation in the torque current during one impact period and the torque applied to the output shaft 46 will be described with reference to Figs. 4 and 5. As shown in Fig. 4, the hammer 42 rotates from a state in which the hammer 42 is separated from the anvil 45, and as shown in Fig. 5, the hammer 42 hits the anvil 45 and applies an impact force. This causes the anvil 45 to rotate. The hammer 42 is then bounced off the anvil 45, and the hammer 42, which has retreated toward the drive shaft 41, rotates so as to get over the anvil 45. When the hammer 42 hits the anvil 45, depending on the conditions, the hammer 42 may be bounced off the anvil 45 immediately, or the hammer 42 may remain in contact with the anvil 45 for a while and rotate together with the anvil 45. The amount (rotation angle) by which the hammer 42 rotates together with the anvil 45 while in contact with the anvil 45 during one impact period is hereinafter referred to as the advance amount.

[0025] The condition where the fastening member 52 and the fastened member are relatively loosely coupled and the fastening member 52 easily rotates is hereinafter referred to as the first condition. Under the first condition, the torque (fastening torque) applied to the output shaft 46 is relatively small because the fastening member 52 easily rotates.

[0026] Moreover, under the first condition, the advancement amount when the hammer 42 collides with the anvil 45 with a certain kinetic energy is relatively large. That is, under the first condition, the rotation angle of the fastening member 52 during one striking period is relatively large.

[0027] When the hammer 42 is in contact with the anvil 45 and rotates together with the anvil 45, a load equal to or greater than a certain level continues to be applied to the motor 3 until the hammer 42 separates from the anvil 45, causing the torque current to continue to change. Therefore, the greater the amount of advance, the greater the amount of fluctuation in the torque current during one impact period. Under the first condition, the amount of advance is relatively large, and therefore the amount of fluctuation in the torque current during one impact period is relatively large. As a result, under the first condition, the torque applied to the output shaft 46 becomes relatively small, and the amount of fluctuation in the torque current during one impact period is relatively large.

[0028] Next, the condition where the fastening member 52 and the fastened member are relatively strongly bonded to each other and the fastening member 52 does not rotate easily will be referred to as the second condition below. In contrast to the first condition, under the second condition, the torque applied to the output shaft 46 becomes relatively large and the amount of fluctuation in the torque current during one strike period becomes relatively small. However, as will be described later, when the fastening member 52 is bonded to the fastened member to a certain degree or more strongly, the correlation between the torque applied to the output shaft 46 and the amount of fluctuation in the torque current during one strike period may differ from that when the fastening member 52 and the fastened member are relatively loosely bonded to each other.

[0029] As described above, the torque calculation unit 84 of the impact tool 1 of this embodiment can accurately calculate the torque applied to the output shaft 46 by using the amount of fluctuation in the torque current during one impact period. More specifically, the torque calculation unit 84 can calculate the torque according to the amount of advance by using the amount of fluctuation in the torque current during one impact period. Even when the hardness of the fastening member 52 is relatively high, the torque calculation unit 84 can calculate the torque according to the amount of advance, similarly to when the hardness of the fastening member 52 is relatively low.

[0030] In addition, since the torque current generally does not include high-frequency components unrelated to the actual fastening, it is possible to improve accuracy compared to the comparative example in which the torque is calculated based on the detection signal of the torsion amount sensor 83.

[0031] (detail) (1) Overall structure The impact tool 1 of this embodiment will be described in more detail below.

[0032] As shown in FIG. 1, the impact tool 1 includes a housing 21, an operating unit 22 (trigger switch), a battery pack 23, a motor 3, a transmission mechanism 4, a control unit 7, an inverter circuit unit 81 (see FIG. 6), a motor rotation measuring unit 82, and a torsion amount sensor 83.

[0033] (2) Housing The housing 21 accommodates the motor 3, at least a part of the transmission mechanism 4, and the control unit .

[0034] (3)Operation section The operating unit 22 is held by the housing 21. The operating unit 22 accepts operations for controlling the rotation of the motor 3. The motor 3 can be switched on and off by pulling the operating unit 22. The rotation speed of the motor 3 can be adjusted by the amount of pulling the operating unit 22. The greater the amount of pulling, the faster the rotation speed of the motor 3. The control unit 7 rotates or stops the motor 3 and controls the rotation speed of the motor 3 according to the amount of pulling the operating unit 22.

[0035] (4) Battery pack The battery pack 23 is attached to the housing 21. The battery pack 23 includes a power supply unit 230. The power supply unit 230 supplies a current for driving the motor 3. The power supply unit 230 includes, for example, one or more secondary batteries.

[0036] (5) Motor The motor 3 is, for example, a brushless motor. The motor 3 includes a rotor 31 having a rotating shaft 311 (see FIG. 1) and a permanent magnet 312 (see FIG. 6), and a stator 32 having a coil 321 (see FIG. 6). The rotor 31 rotates relative to the stator 32 due to electromagnetic interaction between the permanent magnet 312 and the coil 321. In this disclosure, "rotation of the motor 3" refers to rotation of the rotor 31 of the motor 3.

[0037] The motor 3 is a servo motor. The torque and rotation speed of the motor 3 change according to the control by the control unit 7 (servo driver). More specifically, the control unit 7 controls the operation of the motor 3 by feedback control that controls the control target parameters of the motor 3 so as to approach target values.

[0038] (6) Transmission mechanism 1, the transmission mechanism 4 transmits the rotational power of the motor 3 to the tool tip 51 to rotate the tool tip 51. In this embodiment, the side of the motor 3 on which the tool tip 51 is located is defined as the front, and the side of the motor 3 on which the tool tip 51 is located is defined as the rear.

[0039] The transmission mechanism 4 includes a drive shaft 41 , a hammer 42 , a spring 43 , a transmission 44 , an anvil 45 , an output shaft 46 , and a chuck 47 .

[0040] The transmission 44 includes, for example, a planetary gear mechanism. The transmission 44 is interposed between the rotating shaft 311 of the motor 3 and the drive shaft 41. The transmission 44 reduces the rotational power of the motor 3 at a predetermined reduction ratio and outputs it as rotation of the drive shaft 41.

[0041] The hammer 42 is attached to the drive shaft 41 via a cam mechanism. As shown in Fig. 4, the hammer 42 includes a hammer body 420 and two hammer claws 425. The hammer body 420 has a cylindrical shape. The two hammer claws 425 protrude from the front surface of the hammer body 420.

[0042] The spring 43 is a compression coil spring. The spring 43 presses the hammer 42 toward the anvil 45 (forward).

[0043] 4, the anvil 45 includes an anvil body 450 and two anvil claws 455. The anvil body 450 has a cylindrical shape. The two anvil claws 455 protrude from the anvil body 450 in the radial direction of the anvil body 450. The two anvil claws 455 are arranged on the rotational orbits of the two hammer claws 425.

[0044] The output shaft 46 has a cylindrical shape. The output shaft 46 protrudes forward from the anvil 45. The output shaft 46 is formed integrally with the anvil 45. Note that the output shaft 46 may be formed separately from the anvil 45 and fixed to the anvil 45.

[0045] The chuck 47 is attached to the output shaft 46. The chuck 47 is configured to be able to attach the tool bit 51. The output shaft 46 holds the tool bit 51 via the chuck 47. The tool bit 51 may be held directly by the output shaft 46.

[0046] The tip tool 51 (also called a bit) is, for example, a driver bit or a drill bit. The driver bit is a bit used to tighten or loosen a fastening member 52 such as a bolt. The drill bit is a bit used to drill holes in members such as wood or metal members. Of the various types of tip tools 51, a tip tool 51 appropriate for the intended use is attached to the chuck 47.

[0047] When no load (torque) greater than a predetermined magnitude is applied to the output shaft 46, the side surfaces 4250 of the two hammer claws 425 are maintained in contact with the side surfaces 4550 of the two anvil claws 455, respectively, as shown in Figure 5, and the hammer 42 and anvil 45 rotate at the same speed.

[0048] On the other hand, when a load of a predetermined magnitude or more is applied to the output shaft 46, the hammer 42 applies an impact force to the anvil 45. As shown in FIG. 5, after the hammer 42 collides with the anvil 45 and applies an impact force, the hammer 42 retreats against the spring 43 (i.e., moves away from the anvil 45) while being restricted in movement by a cam mechanism provided between the hammer 42 and the drive shaft 41. When the hammer 42 and the anvil 45 are released from the connection due to the retreat of the hammer 42, the hammer 42 rotates and gets over the anvil 45. That is, the two hammer claws 425 pass behind the two anvil claws 455, respectively. Thereafter, the hammer 42 advances (i.e., moves toward the output shaft 46) and applies an impact force in the rotational direction to the anvil 45 again, causing the output shaft 46 to rotate.

[0049] In this way, the hammer 42 repeats the operation of applying an impact force around the central axis of the output shaft 46 to the output shaft 46 via the anvil 45. While the hammer 42 advances and retreats once, one impact force is generated. More specifically, while the hammer 42 advances and retreats once, the hammer 42 rotates approximately half a turn, and the two hammer claws 425 collide with the two anvil claws 455, respectively, generating an impact force.

[0050] (7) Motor rotation measurement unit The motor rotation measuring unit 82 measures the rotation angle of the motor 3. As the motor rotation measuring unit 82, for example, a photoelectric encoder or a magnetic encoder can be adopted.

[0051] (8) Twist sensor The torsion sensor 83 is, for example, a magnetostrictive strain sensor. The magnetostrictive strain sensor includes a rotating member attached to the output shaft 46 and a fixed member disposed near the output shaft 46. The magnetostrictive strain sensor detects a change in the magnetic permeability of the rotating member, which corresponds to a distortion of the rotating member caused by torque being applied to the output shaft 46, using a coil of the fixed member, and outputs a voltage signal proportional to the distortion as a detection result.

[0052] (9) Control unit The control unit 7 shown in Fig. 6 includes a computer system having one or more processors and a memory. At least a part of the functions of the control unit 7 is realized by the processor of the computer system executing a program recorded in the memory of the computer system. The program may be recorded in the memory, or may be provided via a telecommunication line such as the Internet, or may be provided by recording it on a non-transitory recording medium such as a memory card.

[0053] 1, the control unit 7 includes a command value generating unit 71, a speed control unit 72, a current control unit 73, a first coordinate converter 74, a second coordinate converter 75, a magnetic flux control unit 76, an estimation unit 77, and a torque calculation unit 84. The impact tool 1 also includes a plurality of (two in FIG. 6) current sensors 91, 92, the inverter circuit unit 81, and the motor rotation measurement unit 82 described above.

[0054] The control unit 7 controls the operation of the motor 3. More specifically, the control unit 7 is used together with an inverter circuit unit 81 that supplies current to the motor 3, and controls the operation of the motor 3 by feedback control. The control unit 7 performs vector control that independently controls the excitation current (d-axis current) and torque current (q-axis current) supplied to the motor 3.

[0055] The two current sensors 91, 92 are included in the above-mentioned measurement unit 90. The measurement unit 90 has the two current sensors 91, 92 and the second coordinate converter 75. The measurement unit 90 measures the excitation current and torque current supplied to the motor 3. More specifically, the two-phase currents measured by the two current sensors 91, 92 are converted by the second coordinate converter 75 to obtain a measured value id1 of the excitation current and a measured value iq1 of the torque current. That is, the measurement unit 90 measures the current supplied to the motor 3 and breaks down the measured current into a torque current, which is a component that generates torque, and an excitation current, which is a component that generates magnetic flux.

[0056] Each of the multiple current sensors 91, 92 includes, for example, a Hall element current sensor or a shunt resistor element. The multiple current sensors 91, 92 measure the current supplied to the motor 3 from the power supply unit 230 (see FIG. 1) via the inverter circuit unit 81. Here, a three-phase current (U-phase current, V-phase current, and W-phase current) is supplied to the motor 3, and the multiple current sensors 91, 92 measure currents of at least two phases. In FIG. 6, the current sensor 91 measures the U-phase current to obtain a current measurement value i u 1, and the current sensor 92 measures the V-phase current and outputs a current measurement value i v Outputs 1.

[0057] The estimation unit 77 time-differentiates the rotation angle θ1 of the motor 3 measured by the motor rotation measurement unit 82 to calculate the angular velocity ω1 of the motor 3 (angular velocity of the rotor 31).

[0058] The second coordinate converter 75 converts the current measurements i measured by the multiple current sensors 91, 92 into u 1, i v The second coordinate converter 75 converts the current measurement values ​​i id 1 and i q 1 corresponding to the three-phase currents into coordinates based on the rotation angle θ 1 of the motor 3 measured by the motor rotation measurement unit 82, and calculates the measured values ​​id 1 and i q 1 . u 1, i v 1 is converted into a measurement value id1 corresponding to the magnetic field component (d-axis current) and a measurement value iq1 corresponding to the torque component (q-axis current).

[0059] The command value generating unit 71 generates a command value cω1 of the angular velocity of the motor 3. The command value generating unit 71 generates the command value cω1 according to, for example, the pull amount of the operation of pulling the operation unit 22 (see FIG. 1). That is, the command value generating unit 71 increases the angular velocity command value cω1 as the pull amount increases.

[0060] The speed control unit 72 generates a command value ciq1 based on the difference between the command value cω1 generated by the command value generation unit 71 and the angular velocity ω1 calculated by the estimation unit 77. The command value ciq1 is a command value that specifies the magnitude of the q-axis current of the motor 3. That is, the control unit 7 controls the operation of the motor 3 so that the q-axis current supplied to the coil 321 of the motor 3 approaches the command value ciq1 (target value). The speed control unit 72 determines the command value ciq1 so that the difference between the command value cω1 and the angular velocity ω1 is smaller than a predetermined value.

[0061] The magnetic flux control unit 76 generates a command value cid1 based on the angular velocity ω1 calculated by the estimation unit 77 and the measured value iq1 of the q-axis current. The command value cid1 is a command value that specifies the magnitude of the excitation current (d-axis current) of the motor 3. That is, the control unit 7 controls the operation of the motor 3 so that the d-axis current supplied to the coil 321 of the motor 3 approaches the command value cid1 (target value).

[0062] The command value cid1 generated by the magnetic flux control unit 76 is, for example, a command value for making the magnitude of the excitation current 0. The magnetic flux control unit 76 may generate a command value cid1 for always making the magnitude of the excitation current 0, or may generate a command value cid1 for making the magnitude of the excitation current greater than or less than 0 as necessary. When the command value cid1 of the excitation current becomes smaller than 0, a negative excitation current (flux-weakening current) flows in the motor 3, and the magnetic flux of the permanent magnet 312 is weakened by the flux-weakening.

[0063] The current control unit 73 generates a command value cvd1 based on the difference between the command value cid1 generated by the magnetic flux control unit 76 and the measurement value id1 calculated by the second coordinate converter 75. The command value cvd1 is a command value that specifies the magnitude of the excitation voltage (d-axis voltage) of the motor 3. The current control unit 73 determines the command value cvd1 so that the difference between the command value cid1 and the measurement value id1 is smaller than a predetermined value.

[0064] Moreover, the current control unit 73 generates a command value cvq1 based on the difference between the command value ciq1 generated by the speed control unit 72 and the measured value iq1 calculated by the second coordinate converter 75. The command value cvq1 is a command value that specifies the magnitude of the torque voltage (q-axis voltage) of the motor 3. The current control unit 73 generates the command value cvq1 so as to make the difference between the command value ciq1 and the measured value iq1 smaller than a predetermined value.

[0065] The first coordinate converter 74 converts the command values ​​CV1 and CVq1 into coordinates based on the rotation angle θ1 of the motor 3 measured by the motor rotation measuring unit 82, and outputs the command value CV u 1. CV v 1. CV w That is, the first coordinate converter 74 converts the command value CVd1 corresponding to the magnetic field component (d-axis voltage) and the command value CVq1 corresponding to the torque component (q-axis voltage) into the command value CV corresponding to the three-phase voltage. u 1. CV v 1. CV w Convert to 1. Command value cv u 1 is the U phase voltage, and the command value cv v 1 is the V phase voltage, and the command value cv w 1 corresponds to the W phase voltage.

[0066] The inverter circuit unit 81 outputs a command value cv u 1. CV v 1. CV w A three-phase voltage according to the inverter circuit unit 81 is supplied to the motor 3. The control unit 7 controls the power supplied to the motor 3 by controlling the inverter circuit unit 81 through PWM (Pulse Width Modulation).

[0067] The motor 3 is driven by the electric power (three-phase voltage) supplied from the inverter circuit unit 81, and generates rotational power.

[0068] As a result, the control unit 7 controls the excitation current so that the d-axis current flowing through the coil 321 of the motor 3 has a magnitude corresponding to the command value cid1 generated by the magnetic flux control unit 76. In addition, the control unit 7 controls the angular velocity of the motor 3 so that the angular velocity of the motor 3 becomes an angular velocity corresponding to the command value cω1 generated by the command value generating unit 71.

[0069] (10) Torque calculation section The torque calculation unit 84 calculates the torque applied to the output shaft 46 by using a trained model generated by machine learning. The trained model is generated in advance by, for example, a manufacturer of the impact tool 1. The trained model receives the amount of fluctuation in torque current during one impact period as input data, and calculates the torque applied to the output shaft 46 based on the input data.

[0070] The trained model is generated by supervised learning. The training data used in supervised learning is data that associates the amount of fluctuation in the torque current during one impact period with the torque applied to the output shaft 46. The amount of fluctuation in the torque current during one impact period is obtained by measuring the torque current in the measuring unit 90. The torque applied to the output shaft 46 is calculated based on a detection signal of a strain gauge (resistance type strain sensor) attached to a fastening member 52 such as a bolt. The magnitude of the detection signal of the strain gauge corresponds to the amount of elongation of the fastening member 52 and is proportional to the torque applied to the output shaft 46. In the training phase of machine learning, the torque applied to the output shaft 46 is calculated using a previously prepared arithmetic expression or data table based on the magnitude of the detection signal of the strain gauge.

[0071] As an example, the trained model calculates a smaller torque to be applied to the output shaft 46 as the fluctuation amount of the torque current during one impact period increases. In other words, as an example, the torque calculation unit 84 determines that the torque to be applied to the output shaft 46 is smaller as the fluctuation amount of the torque current during one impact period increases.

[0072] Furthermore, the control unit 7 stops the motor 3 when the torque calculated by the torque calculation unit 84 becomes equal to or greater than a predetermined torque. That is, at this time, the control unit 7 sets the command value of the rotational speed (angular velocity) of the motor 3 to 0. With this configuration, the fastening member 52 can be fastened so that the maximum torque applied to the fastening member 52 becomes the predetermined torque. As an example, the predetermined torque is 10 N·m (Newton·meter).

[0073] (11) Example of operation Next, a description will be given of the transition of each parameter of the impact tool 1 when an operator actually uses the impact tool 1 to screw the fastening member 52 into fastened members, with reference to FIG.

[0074] 7 illustrates a command value cω1 for the angular velocity of the motor 3, the angular velocity ω1 of the motor 3, and a measured value iq1 of the torque current. When the operator pulls in the operation unit 22 (see FIG. 1) at time T1, the command value cω1 increases accordingly, and the angular velocity ω1 increases following the command value cω1. The command value cω1 reaches an upper limit value near time T2, and thereafter, the command value cω1 is maintained at the upper limit value until the operation on the operation unit 22 is released or the torque calculated by the torque calculation unit 84 becomes equal to or greater than a predetermined torque. In FIG. 7, the control unit 7 sets the command value cω1 to 0 at time T4. This causes the motor 3 to stop.

[0075] One impact period is the period from when the hammer 42 applies an impact force to the anvil 45 until the hammer 42 applies an impact force to the anvil 45 again. In one impact period, the measurement value iq1 has a maximum value V1 and a minimum value V2. The amount of fluctuation in the measurement value iq1 of the torque current in one impact period is the difference between the maximum value V1 and the minimum value V2. The amount of fluctuation in the measurement value iq1 of the torque current in one impact period fluctuates over time.

[0076] One impact period is defined as, for example, the period from when the measured value iq1 reaches a maximum value, when the measured value iq1 drops by a certain amount to a minimum value, and thereafter, until just before the measured value iq1 reaches a minimum value. Alternatively, one impact period is defined as, for example, the period from when the measured value iq1 reaches a minimum value, when the measured value iq1 increases by a certain amount to a maximum value, and thereafter, until just before the measured value iq1 reaches a minimum value. Note that one impact period may be a period of a certain length.

[0077] In general, the torque current changes according to the magnitude of the load on the motor 3. That is, if the load on the motor 3 increases, the torque current increases, and if the load on the motor 3 decreases, the torque current decreases. While the hammer 42 is moving forward, the motor 3 does not supply energy to the hammer 42, so the load on the motor 3 decreases and the torque current decreases. Thereafter, after the hammer 42 applies an impact force to the anvil 45 again, the hammer 42 moves backward while compressing the spring 43. While the hammer 42 is moving backward, the motor 3 supplies energy to the hammer 42, so the load on the motor 3 increases and the torque current increases. As described above, when the hammer 42 collides with the anvil 45, the measured value iq1 of the torque current takes a minimum value V2, and when the hammer 42 is moved backward the most, the measured value iq1 of the torque current takes a maximum value V1.

[0078] The torque calculation unit 84 calculates the amount of fluctuation in the torque current during one impact period for each of the multiple impact periods based on the torque current measurement value iq1. In Fig. 7, the amount of fluctuation in the torque current during one impact period generally decreases over time from time T1a to time T3.

[0079] Furthermore, the torque calculation unit 84 calculates the torque applied to the output shaft 46 using the trained model. That is, the torque calculation unit 84 calculates the torque for a period corresponding to one impact period by inputting the amount of fluctuation in the torque current for one impact period into the trained model. The torque calculation unit 84 calculates the torque applied to the output shaft 46 for each of the multiple impact periods. In other words, the torque calculation unit 84 calculates the torque applied to the output shaft 46 at each point in time.

[0080] When the torque calculated by the torque calculation unit 84 becomes equal to or greater than a predetermined torque, the control unit 7 sets the command value cω1 to zero.

[0081] (Modification) Below, some modified examples of the embodiment will be described. The following modified examples may be realized in appropriate combination. Hereinafter, the configuration of the above-described embodiment will be referred to as a basic example. The same reference numerals will be used to designate the same configuration as the basic example, and the description will be omitted.

[0082] (Variation 1) The torque calculation unit 84 of the present modified example 1 calculates the torque to be applied to the output shaft 46 by different methods before and after it is determined that the amount of fluctuation in the torque current during one impact period is on the rise. More specifically, the torque calculation unit 84 calculates the torque to be applied to the output shaft 46 by using different learned models before and after it is determined that the amount of fluctuation in the torque current during one impact period is on the rise. In other words, the torque calculation unit 84 switches the learned model to be used when the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase.

[0083] The torque calculation unit 84 determines that the amount of fluctuation in the torque current during one impact period is increasing for a predetermined number of consecutive times. More specifically, the torque calculation unit 84 stores history information on the amount of fluctuation detected each time the hammer 42 applies an impact force to the anvil 45, and determines that the amount of fluctuation is increasing for a predetermined number of consecutive times when it is determined that the amount of fluctuation is greater than the amount of fluctuation in the previous impact. The "predetermined number of times" is empirically set, and is, for example, three times. That is, when the "predetermined number of times" is set to three times, the torque calculation unit 84 determines that the amount of fluctuation is increasing for a consecutive number of times when the amount of fluctuation detected in three consecutive impacts is increasing. Note that the "predetermined number of times" is not limited to three times.

[0084] The torque calculation unit 84 calculates the torque to be applied to the output shaft 46 using the first trained model from the time when the hammer 42 starts applying an impact force to the anvil 45 until it is determined that the amount of fluctuation is on the increase. The torque calculation unit 84 calculates the torque to be applied to the output shaft 46 using the second trained model from the time when it is determined that the amount of fluctuation is on the increase until the motor 3 stops.

[0085] Each of the first trained model and the second trained model receives the amount of fluctuation in the torque current during one impact period as input data, and calculates the torque to be applied to the output shaft 46 based on the input data.

[0086] The first trained model is generated using data correlating the amount of fluctuation in torque current during one impact period from when the hammer 42 starts to apply an impact force to the anvil 45 until it is determined that the amount of fluctuation is tending to increase, with the torque applied to the output shaft 46, as training data.

[0087] The second learned model is generated using data as learning data correlating the amount of fluctuation in the torque current during one impact period from when it is determined that the amount of fluctuation is on the rise until the motor 3 stops, with the torque applied to the output shaft 46.

[0088] 7, the torque calculation unit 84 determines that the amount of fluctuation is on the rise near time T3. Therefore, until time T3, the torque calculation unit 84 calculates the torque applied to the output shaft 46 using the first trained model, and after time T3, the torque calculation unit 84 calculates the torque applied to the output shaft 46 using the second trained model.

[0089] The reason for dividing the trained model before and after it is determined that the amount of fluctuation is increasing is as follows. Generally, at the start of the fastening work by the impact tool 1, the fastening member 52 has not yet been fastened, so the anvil 45 rotates together with the fastening member 52, and the rotation angle of the fastening member 52 increases each time the hammer 42 applies an impact force to the anvil 45, and the advancement amount of the anvil 45 also increases. Thus, at the start of the fastening work, the load applied to the motor 3 when the hammer 42 presses the anvil 45 while in contact with the anvil 45 is the main factor that determines the amount of fluctuation in the torque current during one impact period. However, after time has passed since the start of the fastening work by the impact tool 1 and the fastening member 52 has been fastened to a certain extent, the rotation angle of the fastening member 52 decreases each time the hammer 42 applies an impact force to the anvil 45, and the advancement amount of the anvil 45 also decreases. Therefore, as time passes from the start of the fastening operation, the load on the motor 3 at the moment when the hammer 42 hits the anvil 45 becomes the main factor that determines the amount of fluctuation in the torque current during one impact period. Such a difference before and after the amount of fluctuation starts to increase changes the correlation between the amount of fluctuation in the torque current during one impact period and the torque applied to the output shaft 46, so it is preferable to separate the trained models.

[0090] As an example, the first trained model calculates a smaller torque to be applied to the output shaft 46 as the fluctuation amount of the torque current in one impact period increases. That is, as an example, the torque calculation unit 84 determines that the torque to be applied to the output shaft 46 decreases as the fluctuation amount increases, until it is determined that the fluctuation amount is on the increase.

[0091] As an example, the second trained model calculates a larger torque to be applied to the output shaft 46 as the fluctuation amount of the torque current in one impact period increases. That is, as an example, after determining that the fluctuation amount is on the increase, the torque calculation unit 84 determines that the torque to be applied to the output shaft 46 increases as the fluctuation amount increases.

[0092] 7, at time T4, the torque calculated by the torque calculation unit 84 becomes equal to or greater than a predetermined torque, and in response, the control unit 7 sets the command value cω1 to 0. This causes the motor 3 to stop.

[0093] Incidentally, if the torque applied to the output shaft 46 becomes equal to or greater than a predetermined torque and the control unit 7 stops the motor 3 before the amount of fluctuation shows an increasing tendency, the second trained model is not used.

[0094] (Variation 2) In the first modification, when the torque calculation unit 84 determines that the amount of fluctuation is increasing, it switches the trained model to be used. On the other hand, when the torque calculation unit 84 determines that the amount of fluctuation is increasing, it may stop the process of calculating the torque applied to the output shaft 46 based on the amount of fluctuation in the torque current for one impact period.

[0095] That is, the torque calculation unit 84 calculates the torque applied to the output shaft 46 during a period in which the fluctuation amount of the torque current during one impact period is decreasing based on the fluctuation amount of the torque current during one impact period. Furthermore, when the fluctuation amount of the torque current during one impact period changes from decreasing to increasing, the torque calculation unit 84 stops the process of calculating the torque applied to the output shaft 46 based on the fluctuation amount of the torque current during one impact period.

[0096] In addition, after the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase, the torque calculation unit 84 may calculate the torque applied to the output shaft 46 based on input data other than the amount of fluctuation in the torque current during one impact period.

[0097] (Variation 3) In the first modification, the torque calculation unit 84 switches the trained model to be used when it is determined that the amount of fluctuation shows an increasing tendency. In contrast, the torque calculation unit 84 may switch the trained model to be used when the hammer 42 applies an impact force to the anvil 45 a predetermined number of times. More specifically, the torque calculation unit 84 may count the number of times that the hammer 42 applies an impact force to the anvil 45 after the motor 3 is started, and switch the trained model to be used when the number of times reaches a predetermined number. The "predetermined number of times" here is set empirically, and is, for example, 10 times.

[0098] (Variation 4) The trained model used by the torque calculation unit 84 calculates the torque applied to the output shaft 46 based on the input data. In the basic example, the input data input to the trained model is only the amount of fluctuation in the torque current during one impact period. That is, in the basic example, the input data includes only the amount of fluctuation in the torque current during one impact period. In contrast, the input data may include at least one of the rotation speed of the motor 3, the amplitude of the torsion amount measured by the torsion amount sensor 83, and the average value of the torque current during one impact period. In the training phase of machine learning, the trained model is generated using learning data including this input data.

[0099] That is, the torque calculation unit 84 may calculate the torque applied to the output shaft 46 further based on the rotation speed of the motor 3. The rotation speed of the motor 3 may be, for example, a value measured by the motor rotation measurement unit 82, or may be a value calculated based on another measurement value (for example, the rotation speed of the hammer 42).

[0100] In addition, the impact tool 1 may be provided with a torsion sensor 83 that measures the amount of torsion of the output shaft 46, and the torque calculation unit 84 may further calculate the torque applied to the output shaft 46 based on the amplitude of the torsion measured by the torsion sensor 83.

[0101] Furthermore, the torque calculation unit 84 may further calculate the torque applied to the output shaft 46 based on an average value of the torque current in one impact period. The average value of the torque current in one impact period is the average value of the torque current from the start point to the end point of one impact period. Therefore, the torque calculation unit 84 obtains one average value per one impact period, and calculates the torque applied to the output shaft 46 based on the obtained average value.

[0102] In addition, in the first modified example, the input data may be different between the first trained model and the second trained model. For example, the input data of the first trained model may include only the amount of fluctuation in the torque current during one impact period, and the input data of the second trained model may include the amount of fluctuation in the torque current during one impact period and the rotation speed of the motor 3.

[0103] (Other Modifications of the Embodiments) Other variations of the embodiment are listed below. The following variations may be implemented in appropriate combination. The following variations may also be implemented in appropriate combination with the above-mentioned variations.

[0104] As described above, the computation model (trained model) used in the torque calculation unit 84 is generated by machine learning. The torque calculation unit 84 may be implemented as any type of artificial intelligence or system. Here, the machine learning algorithm is, for example, a neural network. However, the machine learning algorithm is not limited to a neural network, and may be, for example, an eXtreme Gradient Boosting (XGB) regression, a Random Forest, a decision tree, a Logistic Regression, a Support Vector Machine (SVM), a Naive Bayes classifier, or a k-nearest neighbors method. Furthermore, the machine learning algorithm may be, for example, a Gaussian Mixture Model (GMM), or a k-means clustering method. In addition, the trained model may be updated by performing additional learning.

[0105] The torque calculation unit 84 may use a previously prepared arithmetic expression or data table to calculate the torque applied to the output shaft 46 without using the learned model. The arithmetic expression or data table indicates the correspondence relationship between the amount of fluctuation in the torque current during one impact period and the torque applied to the output shaft 46.

[0106] The fastening member 52 is not limited to a bolt, but may be, for example, a nut, a rubber vibration isolator, or a gasket.

[0107] The torsion amount sensor 83 may be, for example, a strain gauge (resistance type strain sensor) instead of a magnetostrictive type strain sensor.

[0108] The battery pack 23 does not have to be a component of the impact tool 1 .

[0109] A mask period may be set during which the torque calculation unit 84 reserves (does not execute) the process of calculating the torque applied to the output shaft 46. For example, the mask period may be set to a period until the number of collisions of the hammer 42 with the anvil 45 reaches a predetermined number, or a period until a predetermined time has elapsed since the hammer 42 first collided with the anvil 45. In Fig. 7, for example, the mask period may be set to a period until time T1a.

[0110] It is not essential for the measurement unit 90 to measure the excitation current. In other words, it is sufficient for the measurement unit 90 to measure the current supplied to the motor 3 and extract the torque current from the measured current, and it is not essential for the measurement unit 90 to extract the excitation current.

[0111] The impact tool 1 or the torque calculation method according to the present disclosure includes a computer system. The computer system is mainly composed of a processor and a memory as hardware. At least a part of the functions of the impact tool 1 or the torque calculation method according to the present disclosure is realized by the processor executing a program recorded in the memory of the computer system. The program may be pre-recorded in the memory of the computer system, provided through an electric communication line, or provided by recording it in a non-transitory recording medium such as a memory card, an optical disk, or a hard disk drive that can be read by the computer system. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large scale integrated circuit (LSI). The integrated circuits such as IC or LSI referred to here are called by different names depending on the degree of integration, and include integrated circuits called system LSI, VLSI (Very Large Scale Integration), or ULSI (Ultra Large Scale Integration). Furthermore, a field-programmable gate array (FPGA) that is programmed after the manufacture of the LSI, or a logic device that can reconfigure the joint relationship inside the LSI or reconfigure the circuit partition inside the LSI, can also be adopted as a processor. The electronic circuits may be integrated in one chip or distributed among multiple chips. The chips may be integrated in one device or distributed among multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Thus, the microcontroller is also composed of one or more electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

[0112] Furthermore, it is not essential for the impact tool 1 that multiple functions are concentrated in one housing, and multiple components of the impact tool 1 may be distributed across multiple housings.

[0113] (summary) The above-described embodiments and the like disclose the following aspects.

[0114] The impact tool (1) according to the first embodiment includes a motor (3), a hammer (42), an anvil (45), an output shaft (46), a measuring unit (90), and a torque calculation unit (84). The hammer (42) rotates by receiving power from the motor (3). The anvil (45) rotates by receiving an impact force from the hammer (42) in the rotational direction of the hammer (42). The output shaft (46) is configured to hold a tool bit (51). The output shaft (46) rotates together with the anvil (45). The measuring unit (90) measures a torque current supplied to the motor (3). The torque calculation unit (84) calculates a torque applied to the output shaft (46). One impact period is defined as the period from when the hammer (42) applies an impact force to the anvil (45), when the hammer (42) clears the anvil (45), and when the hammer (42) again applies an impact force to the anvil (45). The difference between the maximum and minimum values ​​of the torque current during one impact period is defined as the amount of fluctuation in the torque current during one impact period. The torque calculation unit (84) calculates the torque applied to the output shaft (46) based on the amount of fluctuation in the torque current during one impact period.

[0115] According to the above configuration, even if the work target (such as the fastening member 52) of the impact tool 1 easily rotates together with the output shaft 46, the torque calculation unit 84 can accurately calculate the torque applied to the output shaft 46. In this manner, the torque calculation unit 84 can accurately calculate the torque applied to the output shaft 46 while reducing the influence of the conditions of the work target.

[0116] In the impact tool (1) according to the second aspect, in the first aspect, the torque calculation unit (84) calculates the torque applied to the output shaft (46) further based on the rotation speed of the motor (3).

[0117] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0118] In addition, the impact tool (1) according to a third aspect is the impact tool (1) according to the first or second aspect, further including a torsion sensor (83). The torsion sensor (83) measures the torsion of the output shaft (46). The torque calculation unit (84) calculates the torque applied to the output shaft (46) based on the amplitude of the torsion measured by the torsion sensor (83).

[0119] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0120] In addition, in the impact tool (1) according to a fourth aspect, in any one of the first to third aspects, the torque calculation section (84) further calculates the torque applied to the output shaft (46) based on an average value of the torque current in one impact period.

[0121] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0122] In addition, in the impact tool (1) according to a fifth aspect, in any one of the first to fourth aspects, the torque calculation unit (84) calculates the torque applied to the output shaft (46) by using a trained model generated by machine learning.

[0123] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0124] In addition, in the impact tool (1) according to a sixth aspect, in any one of the first to fifth aspects, the torque calculation unit (84) calculates the torque to be applied to the output shaft (46) during a period in which the fluctuation amount of the torque current in one impact period is decreasing, based on the fluctuation amount of the torque current in one impact period.

[0125] According to the above configuration, the torque applied to the output shaft (46) can be calculated with high accuracy.

[0126] In addition, in the impact tool (1) according to the seventh aspect, in the sixth aspect, when the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase, the torque calculation unit (84) stops the process of calculating the torque applied to the output shaft (46) based on the amount of fluctuation in the torque current during one impact period.

[0127] The above-described configuration can prevent the torque calculated by the torque calculation section (84) from becoming significantly different from the actual torque.

[0128] In the impact tool (1) according to an eighth aspect, in the sixth or seventh aspect, the torque calculation unit (84) calculates the torque applied to the output shaft (46) by using a trained model generated by machine learning. When the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase, the torque calculation unit (84) switches the trained model to be used.

[0129] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0130] In addition, in the impact tool (1) according to a ninth aspect, in any one of the first to eighth aspects, the torque calculation section (84) determines that the torque applied to the output shaft (46) is smaller as the amount of fluctuation in the torque current during one impact period is larger.

[0131] According to the above configuration, the torque applied to the output shaft (46) can be calculated with higher accuracy.

[0132] The configurations other than those of the first aspect are not essential to the impact tool (1) and may be omitted as appropriate. [Explanation of symbols]

[0133] 1 Impact tool 3 Motor 42 Hammer 45 Anvil 46 Output shaft 51 Tip tool 83 Torsion sensor 84 Torque calculation section 90 Measuring part

Claims

1. A motor; a hammer that rotates by receiving power from the motor; an anvil that rotates by receiving an impact force from the hammer in the rotational direction of the hammer; an output shaft configured to hold a tool bit and rotate with the anvil; A measurement unit that measures a torque current supplied to the motor; a torque calculation unit that calculates a torque applied to the output shaft, One impact period is defined as a period from when the hammer applies the impact force to the anvil until the hammer overcomes the anvil and then the hammer applies the impact force to the anvil again. a difference between the maximum value and the minimum value of the torque current during the one impact period is defined as a fluctuation amount of the torque current during the one impact period; The torque calculation unit calculates the torque applied to the output shaft based on the amount of fluctuation of the torque current during one impact period. Impact tool.

2. The torque calculation unit calculates the torque applied to the output shaft based on a rotation speed of the motor.

2. The impact tool according to claim 1.

3. A torsion sensor for measuring a torsion amount of the output shaft is further provided. The torque calculation unit calculates the torque applied to the output shaft based on the amplitude of the torsion measured by the torsion sensor.

2. The impact tool according to claim 1.

4. The torque calculation unit calculates the torque applied to the output shaft based on an average value of the torque current during one impact period.

2. The impact tool according to claim 1.

5. The torque calculation unit calculates the torque applied to the output shaft by using a trained model generated by machine learning.

2. The impact tool according to claim 1.

6. the torque calculation unit calculates the torque applied to the output shaft during a period in which the fluctuation amount of the torque current during the one impact period is decreasing, based on the fluctuation amount of the torque current during the one impact period.

2. The impact tool according to claim 1.

7. the torque calculation unit, when the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase, stops the process of calculating the torque applied to the output shaft based on the amount of fluctuation in the torque current during one impact period.

7. An impact tool according to claim 6.

8. The torque calculation unit calculates the torque applied to the output shaft by using a trained model generated by machine learning, the torque calculation unit switches the trained model to be used when the amount of fluctuation in the torque current during one impact period changes from a decrease to an increase.

7. An impact tool according to claim 6.

9. the torque calculation unit determines that the torque applied to the output shaft is smaller as the fluctuation amount of the torque current during one impact period is larger.

2. The impact tool according to claim 1.

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