Impact tool

Abstract

To provide an impact tool which can detect an occurrence state of an instable behavior of an impact mechanism.SOLUTION: An impact tool 1 includes an electric motor 3, an impact mechanism 40, an acquisition part 90, and a detection part (retraction detection part 79). The impact mechanism 40 performs a striking operation of obtaining power from the electric motor 3 and generating a striking force. The acquisition part 90 acquires a value of a torque current supplied to the electric motor 3. The detection part detects an occurrence state of an instable behavior of the impact mechanism 40 based on a torque current acquisition value (current measurement value iq1) that is the value of the torque current acquired by the acquisition part 90.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to impact tools, and more particularly to impact tools equipped with an electric motor.

Background Art

[0002] The impact rotary tool described in Patent Document 1 includes an impact mechanism, a shock detection unit, a control unit, and a voltage detection unit. The impact mechanism has a hammer and applies a striking impact to the output shaft by motor output. The shock detection unit detects the impact by the impact mechanism. The control unit stops the rotation of the motor based on the detection result of the shock detection unit. The voltage detection unit detects the voltage of the shock detection unit. The control unit determines whether the shock detection unit is abnormal based on the voltage detected by the voltage detection unit when the motor is not rotating.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide an impact tool capable of detecting the occurrence situation of unstable behavior of the impact mechanism.

Means for Solving the Problems

[0005] An impact tool according to one aspect of the present disclosure includes an electric motor, an impact mechanism, an acquisition unit, and a detection unit. The impact mechanism performs a striking operation of obtaining power from the electric motor and generating a striking force. The acquisition unit acquires a value of a torque current supplied to the electric motor. The detection unit detects a generation state of unstable behavior of the impact mechanism based on a torque current acquisition value that is the value of the torque current acquired by the acquisition unit. The detection unit detects the generation state of the unstable behavior based on a magnitude of an alternating current component of the torque current acquisition value and an absolute value of an instantaneous value of the torque current acquisition value.

Effects of the Invention

[0006] The present disclosure has the advantage of being able to detect the occurrence situation of unstable behavior of the impact mechanism.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the impact tool 1 according to the embodiment will be described with reference to the drawings. However, each of the following embodiments is only a part of various embodiments of the present disclosure. Each of the following embodiments can be variously modified according to the design and the like as long as the object of the present disclosure can be achieved. Also, each of the figures described in the following embodiments is a schematic diagram, and the ratio of the size and thickness of each component in the figure does not necessarily reflect the actual dimensional ratio.

[0009] (1) Overview As shown in FIG. 1, the impact tool 1 of the present embodiment includes an electric motor 3 (AC motor), an impact mechanism 40, an acquisition unit 90, and a detection unit (retreat detection unit 79). The impact mechanism 40 performs a striking operation that obtains power from the electric motor 3 and generates a striking force. The acquisition unit 90 acquires the value of the torque current supplied to the electric motor 3. The detection unit (retreat detection unit 79) detects the occurrence status of unstable behavior of the impact mechanism 40 based on the torque current acquisition value, which is the value of the torque current acquired by the acquisition unit 90.

[0010] In this way, in the impact tool 1, by using the obtained torque current value, it becomes possible to detect the occurrence situation of the unstable behavior of the impact mechanism 40. As a result, it becomes possible to implement countermeasures against the unstable behavior of the impact mechanism 40. Further, the detection accuracy can be improved compared to the case of detecting the occurrence situation of the unstable behavior of the impact mechanism 40 based on the battery voltage and battery current of the battery pack which is the power source of the impact tool 1. Furthermore, when detecting the occurrence situation of the unstable behavior of the impact mechanism 40, it is not necessary to measure the battery voltage and battery current.

[0011] (2) Configuration The configuration of the impact tool 1 will be described in more detail with reference to FIGS. 2 to 4 first. In the following description, the direction in which the drive shaft 41 and the output shaft 61 described later are aligned is defined as the front-rear direction, the side of the output shaft 61 as viewed from the drive shaft 41 is defined as the front, and the side of the drive shaft 41 as viewed from the output shaft 61 is defined as the rear. Further, in the following description, the direction in which the body portion 21 and the grip portion 22 described later are aligned is defined as the up-down direction, the side of the body portion 21 as viewed from the grip portion 22 is defined as the up, and the side of the grip portion 22 as viewed from the body portion 21 is defined as the down.

[0012] The impact tool 1 of the present embodiment includes an electric motor 3, a transmission mechanism 4, an output shaft 61 (socket mounting portion), a housing 2, a trigger volume 23, and a control unit 7 (see FIGS. 1 and 3).

[0013] The housing 2 houses the electric motor 3, the transmission mechanism 4, and the control unit 7, and a part of the output shaft 61. The housing 2 has a body portion 21 and a grip portion 22. The shape of the body portion 21 is cylindrical. The grip portion 22 protrudes from the body portion 21.

[0014] The trigger volume 23 protrudes from the grip portion 22. The trigger volume 23 is an operation unit that receives an operation for controlling the rotation of the electric motor 3. By operating the trigger volume 23, the electric motor 3 can be turned on and off. Also, the rotation speed of the electric motor 3 can be adjusted by the amount of depression of the operation of pulling the trigger volume 23. The greater the amount of depression, the higher the rotation speed of the electric motor 3. The control unit 7 (see FIG. 1) rotates or stops the electric motor 3 and controls the rotation speed of the electric motor 3 according to the amount of depression of the operation of pulling the trigger volume 23. In the impact tool 1 of the present embodiment, a socket 62 as a tip tool is attached to the output shaft 61. The output shaft 61 receives the rotational force of the electric motor 3 and rotates together with the socket 62. Then, by controlling the rotation speed of the electric motor 3 by operating the trigger volume 23, the rotation speed of the socket 62 is controlled.

[0015] A rechargeable battery pack is detachably attached to the impact tool 1. The impact tool 1 operates using the battery pack as a power source. That is, the battery pack is a power source that supplies current to drive the electric motor 3. The battery pack is not a component of the impact tool 1. However, the impact tool 1 may include a battery pack. The battery pack includes an assembled battery configured by connecting a plurality of secondary batteries (for example, lithium ion batteries) in series, and a case that houses the assembled battery.

[0016] The electric motor 3 is, for example, a brushless motor. In particular, the electric motor 3 of the present embodiment is a synchronous motor, and more specifically, a permanent magnet synchronous motor (PMSM (Permanent Magnet Synchronous Motor)). The electric motor 3 includes a rotor 31 having a rotating shaft 311 and a permanent magnet 312, and a stator 32 having a coil 321. Due to the electromagnetic interaction between the permanent magnet 312 and the coil 321, the rotor 31 rotates with respect to the stator 32.

[0017] A socket 62 as a tip tool is attached to the output shaft 61. The transmission mechanism 4 transmits the rotation of the rotating shaft 311 of the electric motor 3 to the socket 62 via the output shaft 61. As a result, the socket 62 rotates. When the socket 62 rotates while being applied to a fastening member (such as a bolt, screw (wood screw, etc.) or nut), operations such as tightening or loosening the fastening member become possible. The transmission mechanism 4 has an impact mechanism 40. The impact tool 1 of the present embodiment is an electric impact driver that performs screw tightening while performing a striking operation by the impact mechanism 40. In the striking operation, a striking force is applied to a fastening member such as a screw via the output shaft 61.

[0018] Note that the socket 62 is detachable from the output shaft 61. A socket anvil can be attached to the output shaft 61 instead of the socket 62. A bit (for example, a driver bit or a drill bit) as a tip tool can be attached to the output shaft 61 via the socket anvil.

[0019] Thus, the output shaft 61 is configured to hold the tip tool (socket 62 or bit). In the present embodiment, the tip tool is not included in the configuration of the impact tool 1. However, the tip tool may be included in the configuration of the impact tool 1.

[0020] In addition to the impact mechanism 40, the transmission mechanism 4 has a planetary gear mechanism 48. The impact mechanism 40 includes a drive shaft 41, a hammer 42, a return spring 43, an anvil 45, and two steel balls 49. The rotation of the rotating shaft 311 of the electric motor 3 is transmitted to the drive shaft 41 via the planetary gear mechanism 48. The drive shaft 41 is disposed between the electric motor 3 and the output shaft 61.

[0021] The hammer 42 moves relative to the anvil 45, obtains power from the electric motor 3, and applies a rotational impact to the anvil 45. The hammer 42 includes a hammer body 420 and two protrusions 425. The two protrusions 425 protrude from the surface of the hammer body 420 on the side of the output shaft 61. The hammer body 420 has a through hole 421 through which the drive shaft 41 passes. Further, the hammer body 420 has two groove portions 423 on the inner peripheral surface of the through hole 421. The drive shaft 41 has two groove portions 413 (see FIG. 5) on its outer peripheral surface. The two groove portions 413 are connected. Two steel balls 49 are sandwiched between the two groove portions 423 and the two groove portions 413. The two groove portions 423, the two groove portions 413, and the two steel balls 49 constitute a cam mechanism. While the two steel balls 49 move, the hammer 42 is movable in the axial direction of the drive shaft 41 relative to the drive shaft 41 and is rotatable relative to the drive shaft 41. As the hammer 42 moves in a direction approaching the output shaft 61 or away from the output shaft 61 along the axial direction of the drive shaft 41, the hammer 42 rotates relative to the drive shaft 41.

[0022] The anvil 45 is integrally formed with the output shaft 61. The anvil 45 holds a tip tool (socket 62 or bit) via the output shaft 61. The anvil 45 includes an anvil body 450 and two claw portions 455. The shape of the anvil body 450 is annular. The two claw portions 455 protrude from the anvil body 450 in the radial direction of the anvil body 450. The anvil 45 faces the hammer body 420 in the axial direction of the drive shaft 41. Also, when the impact mechanism 40 is not performing a striking operation, the two protrusions 425 of the hammer 42 and the two claw portions 455 of the anvil 45 are in contact with each other in the rotational direction of the drive shaft 41, and the hammer 42 and the anvil 45 rotate integrally. Therefore, at this time, the drive shaft 41, the hammer 42, the anvil 45, and the output shaft 61 rotate integrally.

[0023] The return spring 43 is sandwiched between the hammer 42 and the planetary gear mechanism 48. The return spring 43 of the present embodiment is a conical coil spring. The impact mechanism 40 further includes a plurality (two in FIG. 3) of steel balls 50 sandwiched between the hammer 42 and the return spring 43, and a ring 51. Thereby, the hammer 42 is rotatable with respect to the return spring 43. The hammer 42 receives a force from the return spring 43 in the direction toward the output shaft 61 in the axial direction of the drive shaft 41.

[0024] Hereinafter, the movement of the hammer 42 in the direction toward the output shaft 61 in the axial direction of the drive shaft 41 is referred to as "the hammer 42 advances". Also, hereinafter, the movement of the hammer 42 in the direction away from the output shaft 61 in the axial direction of the drive shaft 41 is referred to as "the hammer 42 retreats".

[0025] In the impact mechanism 40, when the load torque becomes equal to or greater than a predetermined value, the striking operation is started. That is, as the load torque increases, among the forces generated between the hammer 42 and the anvil 45, the component force in the direction of retreating the hammer 42 also increases. When the load torque becomes equal to or greater than the predetermined value, the hammer 42 retreats while compressing the return spring 43. Then, as the hammer 42 retreats, the two protrusions 425 of the hammer 42 rotate while overcoming the two claw portions 455 of the anvil 45. After that, the hammer 42 advances by receiving the return force from the return spring 43. Then, when the drive shaft 41 makes approximately half a rotation, the two protrusions 425 of the hammer 42 collide with the side surfaces 4550 of the two claw portions 455 of the anvil 45. In the impact mechanism 40, every time the drive shaft 41 makes approximately half a rotation, the two protrusions 425 of the hammer 42 collide with the two claw portions 455 of the anvil 45. That is, every time the drive shaft 41 makes approximately half a rotation, the hammer 42 applies a rotational impact to the anvil 45.

[0026] In this way, in the impact mechanism 40, the collision between the hammer 42 and the anvil 45 repeatedly occurs. Due to the torque generated by this collision, the fastening member such as a bolt, a screw, or a nut can be tightened more strongly compared to the case where there is no collision.

[0027] Here, as shown in FIG. 6, the two groove portions 413 of the drive shaft 41 (see FIG. 5) are each formed in a V shape when viewed from the vertical direction. When the steel ball 49 is located at a position corresponding to the center of the V shape (the state shown by the solid line in FIGS. 5 and 6), the hammer 42 has advanced to the front end within the movable range. When the impact mechanism 40 is not performing a striking operation, the steel ball 49 stays at a position corresponding to the center of the V shape. When the steel ball 49 is located at a position corresponding to any one of the two ends of the V shape (the state shown by the two-dot chain line in FIGS. 5 and 6), the hammer 42 has retreated to the rear end within the movable range. In this specification, the retreat of the hammer 42 to the rear end within the movable range is referred to as "maximum retreat". That is, in this specification, the movement of the hammer 42 to the position farthest from the anvil 45 within the movable range of the hammer 42 is referred to as "maximum retreat". The maximum retreat of the hammer 42 can occur when the impact mechanism 40 is performing a striking operation, for example, when the rotational speed of the electric motor 3 is relatively high, or when the magnitude of the load applied to the output shaft 61 of the impact tool 1 suddenly increases. Further, the maximum retreat of the hammer 42 may occur when the spring force of the return spring 43 that advances the hammer 42 is insufficient. Further, the maximum retreat of the hammer 42 may also occur when the rotational speed of the electric motor 3 is not appropriately adjusted according to the type, shape, rigidity, etc. of the tip tool.

[0028] When the hammer 42 is in maximum retreat, the behavior of the hammer 42 becomes unstable as compared with the case where the retreat distance of the hammer 42 is appropriate. That is, at this time, when a force in the retreating direction acts on the hammer 42, the hammer 42 cannot retreat. Further, the force in the retreating direction will be absorbed by the hammer 42. Such a situation may reduce the life of the hammer 42.

[0029] Therefore, the retraction detection unit 79 detects the occurrence status of the maximum retraction of the hammer 42 as the occurrence status of the unstable behavior of the impact mechanism 40. In one aspect, when the retraction detection unit 79 detects the occurrence of the unstable behavior (maximum retraction) of the impact mechanism 40 (hammer 42), the control unit 7 reduces the rotational speed of the electric motor 3. Specifically, when the retraction detection unit 79 detects the occurrence of the unstable behavior (maximum retraction) of the impact mechanism 40 (hammer 42), the control unit 7 reduces the command value cω1 (see FIG. 1) of the angular velocity of the rotation of the electric motor 3. Thereby, the elimination of the maximum retraction can be achieved. That is, reducing the rotational speed of the electric motor 3 corresponds to a countermeasure against the unstable behavior of the impact mechanism 40.

[0030] (3) Control unit The control unit 7 includes a computer system having one or more processors and a memory. At least some of the functions of the control unit 7 are 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, may be provided through an electric communication line such as the Internet, or may be provided by being recorded in a non-transitory recording medium such as a memory card.

[0031] As shown in FIG. 1, the control unit 7 includes a command value generation 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, a demagnetization detection unit 78, and a retraction detection unit 79. Further, the impact tool 1 includes a control unit 7, an inverter circuit unit 81, a motor rotation measurement unit 82, and a plurality (two in FIG. 1) of current sensors 91, 92.

[0032] The control unit 7 controls the operation of the electric motor 3. More specifically, the control unit 7 is used together with the inverter circuit unit 81 that supplies current to the electric motor 3, and controls the operation of the electric motor 3 by feedback control. The control unit 7 performs vector control for independently controlling the exciting current (d-axis current) and the torque current (q-axis current) supplied to the electric motor 3.

[0033] The reverse detection unit 79 of this embodiment is included in the control unit 7. However, the reverse detection unit 79 may not be included in the control unit 7.

[0034] The two current sensors 91 and 92 are included in the acquisition unit 90 described above. The acquisition unit 90 has the two current sensors 91 and 92 and the second coordinate converter 75. The acquisition unit 90 acquires the excitation current (current measurement value id1 of the d-axis current) and the torque current (current measurement value iq1 of the q-axis current) supplied to the motor 3. The acquisition unit 90 acquires the current measurement values id1 and iq1 by calculating the current measurement values id1 and iq1 by itself. That is, the current measurement values id1 and iq1 are obtained by converting the two-phase currents measured by the two current sensors 91 and 92 with the second coordinate converter 75.

[0035] Each of the plurality of current sensors 91 and 92 includes, for example, a Hall element current sensor or a shunt resistance element. The plurality of current sensors 91 and 92 measure the current supplied from the battery pack to the motor 3 via the inverter circuit unit 81. Here, three-phase currents (U-phase current, V-phase current, and W-phase current) are supplied to the motor 3, and the plurality of current sensors 91 and 92 measure at least two-phase currents. In FIG. 1, the current sensor 91 measures the U-phase current and outputs the current measurement value i u 1, and the current sensor 92 measures the V-phase current and outputs the current measurement value i v 1.

[0036] The motor rotation measurement unit 82 measures the rotation angle of the motor 3. As the motor rotation measurement unit 82, for example, an optical encoder or a magnetic encoder can be adopted.

[0037] The estimation unit 77 calculates the angular velocity ω1 (angular velocity of the rotation axis 311) of the motor 3 by differentiating the rotation angle θ1 of the motor 3 measured by the motor rotation measurement unit 82 with respect to time.

[0038] The second coordinate converter 75 converts the current measurement values i u 1, i v1 is subjected to coordinate transformation based on the rotation angle θ1 of the electric motor 3 measured by the motor rotation measurement unit 82, and the current measurement values id1 and iq1 are calculated. That is, the second coordinate converter 75 converts the current measurement value i u 1, i v 1 into a current measurement value id1 corresponding to the magnetic field component (d-axis current) and a current measurement value iq1 corresponding to the torque component (q-axis current).

[0039] The command value generation unit 71 generates a command value cω1 for the angular velocity of the electric motor 3. The command value generation unit 71 generates, for example, a command value cω1 corresponding to the amount of retraction of the operation of pulling the trigger volume 23 (see FIG. 2). That is, the command value generation unit 71 increases the command value cω1 for the angular velocity as the amount of retraction increases.

[0040] 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 torque current (q-axis current) of the electric motor 3. That is, the control unit 7 controls the operation of the electric motor 3 so that the torque current (q-axis current) supplied to the coil 321 of the electric motor 3 approaches the command value ciq1 (target value). The speed control unit 72 determines the command value ciq1 so as to reduce the difference between the command value cω1 and the angular velocity ω1.

[0041] 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 current measurement value iq1 (q-axis current). The command value cid1 is a command value that specifies the magnitude of the excitation current (d-axis current) of the electric motor 3. That is, the control unit 7 controls the operation of the electric motor 3 so that the excitation current (d-axis current) supplied to the coil 321 of the electric motor 3 approaches the command value cid1 (target value).

[0042] The command value cid1 generated by the magnetic flux control unit 76 is, for example, a command value for setting the magnitude of the exciting current to zero. The magnetic flux control unit 76 may constantly generate the command value cid1 for setting the magnitude of the exciting current to zero, or may generate, as necessary, a command value cid1 for making the magnitude of the exciting current larger or smaller than zero. When the command value cid1 of the exciting current becomes smaller than zero, a negative exciting current (flux-weakening current) flows through the motor 3, and due to the flux-weakening, the magnetic flux of the permanent magnet 312 weakens.

[0043] 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 current measurement value id1 calculated by the second coordinate converter 75. The command value cvd1 is a command value for specifying the magnitude of the exciting voltage (d-axis voltage) of the motor 3. The current control unit 73 determines the command value cvd1 so as to reduce the difference between the command value cid1 and the current measurement value id1.

[0044] Also, 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 current measurement value iq1 calculated by the second coordinate converter 75. The command value cvq1 is a command value for specifying 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 reduce the difference between the command value ciq1 and the current measurement value iq1.

[0045] The first coordinate converter 74 performs coordinate conversion on the command values cvd1 and cvq1 based on the rotation angle θ1 of the motor 3 measured by the motor rotation measurement unit 82, and calculates the command values cv u 1, cv v 1, cv w 1. 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 values cv u 1, cv v 1, cv w 1 corresponding to the three-phase voltage. The command value cv u 1 is for the U-phase voltage, the command value cv v 1 is for the V-phase voltage, the command value cv w1 corresponds to the W-phase voltage.

[0046] The inverter circuit section 81 supplies a three-phase voltage corresponding to the command value cv u 1, cv v 1, cv w 1 to the electric motor 3. The control unit 7 controls the power supplied to the electric motor 3 by performing PWM (Pulse Width Modulation) control on the inverter circuit section 81.

[0047] The electric motor 3 is driven by the power (three-phase voltage) supplied from the inverter circuit section 81 and generates rotational power.

[0048] As a result, the control unit 7 controls the exciting current so that the exciting current (d-axis current) flowing through the coil 321 of the electric motor 3 has a magnitude corresponding to the command value cid1 generated by the magnetic flux control unit 76. Further, the control unit 7 controls the angular velocity of the electric motor 3 so that the angular velocity of the electric motor 3 becomes an angular velocity corresponding to the command value cω1 generated by the command value generation unit 71.

[0049] The out-of-synchronism detection unit 78 detects the out-of-synchronism of the electric motor 3 based on the current measurement values id1, iq1 acquired from the second coordinate converter 75 and the command values cvd1, cvq1 acquired from the current control unit 73. When out-of-synchronism is detected, the out-of-synchronism detection unit 78 transmits a stop signal cs1 to the inverter circuit section 81 to stop the power supply from the inverter circuit section 81 to the electric motor 3.

[0050] (4) Operation example Next, with reference to FIG. 7, an operation example of the impact tool 1 will be described.

[0051] In FIG. 7, "battery voltage" refers to the battery voltage of the battery pack that is the power source of the electric motor 3. Although not shown in FIG. 7, in the operation example of FIG. 7, the command value cid1 of the exciting current is always 0.

[0052] As described above, in one aspect, when the backward movement detection unit 79 detects the occurrence of unstable behavior (maximum backward movement) of the impact mechanism 40, the control unit 7 reduces the rotational speed of the electric motor 3. The temporal change of the command value cω1 of the angular velocity ω1 in such an aspect is shown by a broken line in FIG. 7. That is, when the backward movement detection unit 79 detects the occurrence of unstable behavior of the impact mechanism 40 (time point T1), the control unit 7 reduces the command value cω1.

[0053] However, it is not essential for the control unit 7 to perform such control. In the operation example of FIG. 7, the control unit 7 always keeps the command value cω1 of the angular velocity ω1 of the electric motor 3 constant (refer to the one-dot chain line portion of the command value cω1). In other words, in the operation example of FIG. 7, the control unit 7 always keeps the command value of the rotational speed of the electric motor 3 constant. Therefore, in the operation example of FIG. 7, even when the backward movement detection unit 79 detects the occurrence of unstable behavior (maximum backward movement) of the impact mechanism 40, the control unit 7 does not perform control to reduce the rotational speed of the electric motor 3.

[0054] In this way, when at least the detection result of the backward movement detection unit 79 does not indicate the occurrence of unstable behavior of the impact mechanism 40, the control unit 7 controls the operation of the electric motor 3 so that the rotational speed (angular velocity ω1) of the electric motor 3 approaches a constant target value (command value cω1). Even when the control unit 7 performs control to reduce the rotational speed of the electric motor 3 when the backward movement detection unit 79 detects the occurrence of unstable behavior of the impact mechanism 40, it is preferable to keep the command value cω1 constant when the backward movement detection unit 79 does not detect the occurrence of unstable behavior of the impact mechanism 40. If the backward movement detection unit 79 is adopted in the impact tool 1 that performs such control, the backward movement detection unit 79 can easily detect the occurrence status of unstable behavior of the impact mechanism 40 accompanying the fluctuation of the rotational speed of the electric motor 3.

[0055] The acquisition unit 90 acquires the measured value (current measurement value iq1) of the torque current (q-axis current) supplied to the coil 321 as the torque current acquisition value. The backward movement detection unit 79 detects the occurrence status of the unstable behavior (maximum backward movement) of the impact mechanism 40 based on the torque current acquisition value acquired by the acquisition unit 90. More specifically, the backward movement detection unit 79 detects the occurrence status of the unstable behavior (maximum backward movement) of the impact mechanism 40 based on the absolute value of the instantaneous value of the torque current acquisition value (current measurement value iq1) acquired by the acquisition unit 90. Even more specifically, the backward movement detection unit 79 detects that the unstable behavior (maximum backward movement) of the impact mechanism 40 has occurred when the absolute value of the current measurement value iq1 of the torque current exceeds the threshold value Th1. That is, the backward movement detection unit 79 detects the variation of the current measurement value iq1 when the maximum backward movement of the hammer 42 occurs. The threshold value Th1 is stored, for example, in the memory of the computer system constituting the control unit 7.

[0056] When the maximum backward movement has not occurred, the hammer 42 can rotate while moving backward with respect to the drive shaft 41, but when the maximum backward movement occurs, the rotation of the hammer 42 while moving backward with respect to the drive shaft 41 is restricted. As a result, when the maximum backward movement occurs, the torque of the motor 3 increases, and the absolute value of the current measurement value iq1 of the torque current increases. Therefore, the backward movement detection unit 79 detects such an increase in the absolute value of the current measurement value iq1.

[0057] In FIG. 7, it is assumed that the impact tool 1 is used as an impact driver for tightening a screw (bolt). The operator inserts the screw into the socket 62 at a time point before time T0. Thereafter, the operator performs an operation of pulling the trigger volume 23 of the impact tool 1 at a time point before time T0. As a result, a q-axis current (torque current) starts to flow through the motor 3, and the motor 3 starts to rotate. Thereafter, the rotational speed (angular velocity ω1) of the motor 3 gradually increases according to the amount of pulling of the trigger volume 23. After time T0, the impact mechanism 40 of the impact tool 1 performs a striking operation.

[0058] At time T1, the measured current value iq1 of the torque current exceeds the threshold value Th1. Therefore, the reverse detection unit 79 detects that the maximum reverse has occurred. Also, at times T2, T3, and T4, the measured current value iq1 of the torque current also exceeds the threshold value Th1. Therefore, at each of times T2, T3, and T4, the reverse detection unit 79 detects that the maximum reverse has occurred.

[0059] As described above, in the impact tool 1 of the present embodiment, the reverse detection unit 79 can detect the occurrence status of the unstable behavior (maximum reverse) of the impact mechanism 40 by using the torque current acquisition value (measured current value iq1). Thereby, it becomes possible to implement measures against the unstable behavior of the impact mechanism 40. For example, as a measure against the unstable behavior of the impact mechanism 40, it is possible to implement a measure of reducing the rotational speed of the electric motor 3 when the unstable behavior occurs.

[0060] Also, the detection accuracy can be improved compared to the case of detecting the occurrence status of the unstable behavior of the impact mechanism 40 based on the battery voltage and battery current of the battery pack that is the power source of the impact tool 1. That is, when the unstable behavior of the impact mechanism 40 occurs, the change in the torque current acquisition value appears more prominently than the changes in the battery voltage and battery current. Therefore, by using the torque current acquisition value instead of the battery voltage and battery current, the detection accuracy of the occurrence status of the unstable behavior of the impact mechanism 40 can be improved.

[0061] Furthermore, when detecting the occurrence status of the unstable behavior of the impact mechanism 40, it is not necessary to measure the battery voltage and battery current. In particular, in the impact tool 1 of the present embodiment, vector control is adopted to control the current supplied to the motor 3 based on the measured current values id1 and iq1 of the d-axis current and q-axis current. In vector control, it is possible to control the motor 3 without measuring the battery voltage and battery current. Therefore, the impact tool 1 of the present embodiment has the advantage that it is possible to control the motor 3 and detect the occurrence status of the unstable behavior of the impact mechanism 40 even without a circuit for measuring the battery voltage and battery current. As a result, it is possible to reduce the area and size of the circuit provided in the impact tool 1, and to reduce the cost required for the circuit. However, the impact tool 1 may be provided with a circuit for measuring the battery voltage and battery current. Further, the reverse detection unit 79 may detect the occurrence status of the unstable behavior of the impact mechanism 40 based on at least one of the battery voltage and the battery current in addition to the torque current acquisition value (measured current value iq1).

[0062] In addition, one of a plurality of tip tools having different types, shapes, rigidities, etc. can be attached to the output shaft 61. The reverse detection unit 79 can detect the occurrence status of the unstable behavior of the impact mechanism 40 caused by differences in the type, shape, rigidity, etc. of the tip tool. Further, since the control unit 7 controls the operation of the motor 3 based on the detection result of the reverse detection unit 79, even if the type, shape, rigidity, etc. of the tip tool are changed, the motor 3 can be controlled so that the impact mechanism 40 operates stably.

[0063] (Modification Example 1) Hereinafter, the impact tool 1 according to Modification Example 1 will be described with reference to FIG. 7. For the same configuration as in the embodiment, the same reference numerals are given and the description thereof is omitted.

[0064] In the impact tool 1 of the first modified example, the condition for the backward movement detection unit 79 to determine the presence or absence of unstable behavior (maximum backward movement) of the impact mechanism 40 is different from the condition in the embodiment. That is, in the first modified example 1, the backward movement detection unit 79 detects the occurrence status of unstable behavior (maximum backward movement) of the impact mechanism 40 based on the magnitude of the alternating current component of the torque current acquisition value (current measurement value iq1) acquired by the acquisition unit 90.

[0065] The backward movement detection unit 79 calculates the magnitude of the alternating current component of the current measurement value iq1 as follows, for example. The backward movement detection unit 79 calculates the difference between the maximum value and the minimum value of the instantaneous values of the current measurement value iq1 between a certain point in time (for example, the current time) and the point in time a predetermined time before the above-mentioned certain point in time, and regards this as the magnitude of the alternating current component of the current measurement value iq1. That is, the backward movement detection unit 79 regards the value corresponding to twice the amplitude of the current measurement value iq1 as the magnitude of the alternating current component of the current measurement value iq1. FIG. 7 shows the magnitude iac of the alternating current component of the current measurement value iq1 when the above-mentioned certain point in time is the time point T1.

[0066] Then, the backward movement detection unit 79 detects that unstable behavior (maximum backward movement) of the impact mechanism 40 has occurred when the magnitude of the alternating current component of the current measurement value iq1 exceeds a predetermined threshold value.

[0067] The magnitude of the alternating current component of the current measurement value iq1 is a value that does not depend on the magnitude of the direct current component of the torque current. Therefore, according to the first modified example 1, even when the magnitude of the direct current component of the torque current supplied to the electric motor 3 varies according to the magnitude of the load of the impact tool 1 or the like, it is easy to detect the occurrence status of unstable behavior of the impact mechanism 40.

[0068] In the first modified example 1, the backward movement detection unit 79 may calculate the difference between the instantaneous value of the current measurement value iq1 at a certain point in time (for example, the current time) and the instantaneous value of the current measurement value iq1 at the point in time a predetermined time before the above-mentioned certain point in time, and regard this as the magnitude of the alternating current component of the current measurement value iq1. The predetermined time is, for example, half of the collision cycle of the hammer 42 and the anvil 45 in the impact mechanism 40.

[0069] Alternatively, the harmonic components of the current measurement value iq1 may be removed by a low-pass filter, and the backward detection unit 79 may calculate the difference between the maximum value at the peak of the waveform of the current measurement value iq1 and the minimum value at the valley adjacent to this peak, and regard this as the magnitude of the AC component of the current measurement value iq1.

[0070] Alternatively, the backward detection unit 79 may obtain the effective value of the current measurement value iq1 and regard the obtained effective value as the magnitude of the AC component of the current measurement value iq1.

[0071] Further, the backward detection unit 79 may detect the occurrence status of the unstable behavior (maximum backward) of the impact mechanism 40 based on both the magnitude of the AC component of the current measurement value iq1 and the absolute value of the instantaneous value of the current measurement value iq1. For example, the backward detection unit 79 may detect that the unstable behavior (maximum backward) of the impact mechanism 40 has occurred when the magnitude of the AC component of the current measurement value iq1 exceeds a predetermined threshold and the absolute value of the current measurement value iq1 of the torque current exceeds the threshold Th1.

[0072] (Other modifications of the embodiment) Hereinafter, other modifications of the embodiment will be listed. The following modifications may be realized in appropriate combination. Also, the following modifications may be realized in appropriate combination with the above-mentioned modifications.

[0073] The detection unit (the backward movement detection unit 79) only needs to detect the occurrence status of the unstable behavior of the impact mechanism 40, and is not limited to a configuration that detects the occurrence status of the maximum backward movement of the hammer 42. For example, the detection unit may detect the occurrence status of the instability of the speed of the hammer 42 caused by the instability due to the rotation speed of the electric motor 3 deviating from the target value as the occurrence status of the unstable behavior of the impact mechanism 40. Further, the detection unit may detect the occurrence status of the unstable behavior related to the position of the hammer 42. The unstable behavior related to the position of the hammer 42 is, for example, the hammer 42 moving forward or backward beyond a predetermined position. Further, the detection unit may detect the sign of the occurrence of the unstable behavior of the impact mechanism 40 as the occurrence status of the unstable behavior. For example, as the hammer 42 moves backward to a position close to the position at the maximum backward movement, the absolute value of the instantaneous value of the current measurement value iq1 increases. Based on this, the occurrence status of the unstable behavior (maximum backward movement) of the impact mechanism 40 can be detected.

[0074] The acquisition unit 90 is not limited to a configuration that acquires the current measurement value iq1 as the torque current acquisition value. The acquisition unit 90 may be configured to acquire the command value ciq1 of the torque current as the torque current acquisition value. In this case, the acquisition unit 90 includes at least the speed control unit 72.

[0075] Further, the acquisition unit 90 is not limited to a configuration that acquires the current measurement value iq1 by calculating the current measurement value iq1 by itself. The acquisition unit 90 may acquire the current measurement value iq1 from a configuration other than the acquisition unit 90.

[0076] When the event that the absolute value of the current measurement value iq1 of the torque current exceeds the threshold Th1 occurs a predetermined number of times or more, the backward detection unit 79 may detect that the unstable behavior (maximum backward movement) of the impact mechanism 40 has occurred. Here, from the time when the absolute value of the current measurement value iq1 exceeds the threshold Th1, a dead time period of a predetermined length is provided, and the backward detection unit 79 may determine whether the absolute value of the current measurement value iq1 exceeds the threshold Th1 during a period other than the dead time period. Alternatively, the harmonic component of the current measurement value iq1 is removed by a low-pass filter, and the backward detection unit 79 may determine whether the peak value exceeds the threshold Th1 for each peak of the waveform of the current measurement value iq1. Alternatively, when the frequency at which the absolute value of the current measurement value iq1 of the torque current exceeds the threshold Th1 is equal to or higher than a predetermined frequency, the backward detection unit 79 may detect that the unstable behavior (maximum backward movement) of the impact mechanism 40 has occurred.

[0077] Further, when the event that the absolute value of the current measurement value iq1 of the torque current changes from a state where it is equal to or less than the threshold Th1 to a value exceeding the threshold Th1 occurs a predetermined number of times or more, the backward detection unit 79 may detect that the unstable behavior (maximum backward movement) of the impact mechanism 40 has occurred.

[0078] In one aspect of the embodiment, when the backward detection unit 79 detects the occurrence of the unstable behavior (maximum backward movement) of the impact mechanism 40, the control unit 7 reduces the rotational speed of the electric motor 3. Here, a maximum reduction width may be set in the control unit 7. Each time the backward detection unit 79 detects the occurrence of the unstable behavior of the impact mechanism 40, the control unit 7 may reduce the rotational speed of the electric motor 3 by an amount smaller than the maximum reduction width. Then, the control unit 7 may be configured not to further reduce the rotational speed of the electric motor 3 when the reduction amount of the rotational speed of the electric motor 3 reaches the maximum reduction width. Alternatively, the control unit 7 may reduce the rotational speed of the electric motor 3 at predetermined time intervals until the reduction amount of the rotational speed of the electric motor 3 reaches the maximum reduction width. Further, when the backward detection unit 79 detects the occurrence of the unstable behavior of the impact mechanism 40, the control unit 7 may immediately reduce the rotational speed of the electric motor 3 by the maximum reduction width.

[0079] The threshold Th1 may be changed according to the type, weight, and dimensions of the tip tool, as well as the type of load that is the work target. Examples of the type of load include bolts, screws, and nuts.

[0080] The impact tool 1 is not limited to an impact driver, and may be, for example, an impact wrench, an impact drill, or an impact drill driver.

[0081] The impact tool 1 of the present embodiment can replace the tip tool according to the application, but it is not essential that the tip tool be replaceable. For example, the impact tool 1 may be a power tool that can use only a specific tip tool.

[0082] The anvil 45 may hold the tip tool via an output shaft 61 or the like connected to the anvil 45, or may directly hold the tip tool.

[0083] The output shaft 61 may be formed integrally with the tip tool.

[0084] The impact tool 1 may be provided with a buffer member for mitigating the impact applied to the hammer 42 when the hammer 42 is maximally retracted. The buffer member is formed, for example, of rubber. When the hammer 42 is maximally retracted, the impact applied to the hammer 42 is mitigated when the hammer 42 hits the buffer member.

[0085] The impact tool 1 may be provided with a notification unit that notifies the detection result of the retraction detection unit 79. The notification unit has, for example, a buzzer or a light source, and notifies the maximum retraction by emitting sound or light when the retraction detection unit 79 detects the maximum retraction.

[0086] The impact tool 1 may be provided with a torque measurement unit. The torque measurement unit measures the operating torque of the electric motor 3. The torque measurement unit is, for example, a magnetostrictive strain sensor capable of detecting torsional strain. The magnetostrictive strain sensor detects a change in magnetic permeability corresponding to the strain generated when torque is applied to the output shaft 61 of the electric motor 3 with a coil installed in the non-rotating part of the electric motor 3, and outputs a voltage signal proportional to the strain.

[0087] The impact tool 1 may be provided with a bit rotation measurement unit. The bit rotation measurement unit measures the rotation angle of the output shaft 61. Here, the rotation angle of the output shaft 61 is equal to the rotation angle of the tip tool (socket 62). As the bit rotation measurement unit, for example, a photoelectric encoder or a magnetic encoder can be adopted.

[0088] (Summary) From the embodiments and the like described above, the following aspects are disclosed.

[0089] The impact tool 1 according to the first aspect includes an electric motor 3, an impact mechanism 40, an acquisition unit 90, and a detection unit (retreat detection unit 79). The impact mechanism 40 performs a striking operation that obtains power from the electric motor 3 and generates a striking force. The acquisition unit 90 acquires the value of the torque current supplied to the electric motor 3. The detection unit detects the occurrence status of unstable behavior of the impact mechanism 40 based on the torque current acquisition value (current measurement value iq1), which is the value of the torque current acquired by the acquisition unit 90.

[0090] According to the above configuration, it is possible to detect the occurrence status of unstable behavior of the impact mechanism 40 by using the torque current acquisition value (current measurement value iq1).

[0091] Further, the impact tool 1 according to the second aspect includes a control unit 7 in the first aspect. The control unit 7 controls the operation of the electric motor 3.

[0092] According to the above configuration, the impact tool 1 can perform autonomous control of the operation of the electric motor 3.

[0093] Further, in the impact tool 1 according to the third aspect, in the second aspect, when the detection result of at least the detection unit (retreat detection unit 79) does not indicate the occurrence of unstable behavior of the impact mechanism 40, the control unit 7 controls the operation of the electric motor 3 so that the rotational speed of the electric motor 3 approaches a certain target value.

[0094] According to the above configuration, it is easy to detect the occurrence status of the unstable behavior of the impact mechanism 40 accompanying the fluctuation of the rotational speed of the electric motor 3.

[0095] Further, in the impact tool 1 according to the fourth aspect, in the second or third aspect, when the detection unit (retreat detection unit 79) detects the occurrence of unstable behavior of the impact mechanism 40, the control unit 7 reduces the rotational speed of the electric motor 3.

[0096] According to the above configuration, it is possible to reduce the possibility that the life of the impact tool 1 is reduced due to the unstable behavior of the impact mechanism 40.

[0097] Further, in the impact tool 1 according to the fifth aspect, in any one of the first to fourth aspects, the acquisition unit 90 acquires the measured value of the torque current (current measurement value iq1) as the torque current acquisition value.

[0098] According to the above configuration, compared with the case where the target value (command value ciq1) of the torque current is used as the torque current acquisition value, it is possible to detect the occurrence status of the unstable behavior of the impact mechanism 40 in accordance with the actual operation of the electric motor 3.

[0099] Further, in the impact tool 1 according to the sixth aspect, in any one of the first to fifth aspects, the detection unit (retreat detection unit 79) detects the occurrence status of the unstable behavior of the impact mechanism 40 based on the magnitude of the AC component of the torque current acquisition value (current measurement value iq1).

[0100] According to the above configuration, even when the magnitude of the DC component of the torque current supplied to the electric motor 3 varies according to the magnitude of the load or the like, it is easy to detect the occurrence status of the unstable behavior of the impact mechanism 40.

[0101] Also, in the impact tool 1 according to the seventh aspect, in any one of the first to fifth aspects, the detection unit (retreat detection unit 79) detects the occurrence status of unstable behavior of the impact mechanism 40 based on the absolute value of the instantaneous value of the torque current acquisition value (current measurement value iq1).

[0102] According to the above configuration, the occurrence status of unstable behavior of the impact mechanism 40 can be detected by simple processing.

[0103] Also, in the impact tool 1 according to the eighth aspect, in any one of the first to seventh aspects, the impact mechanism 40 includes an anvil 45 and a hammer 42. The anvil 45 holds the tip tool. The hammer 42 moves relative to the anvil 45, obtains power from the electric motor 3, and applies a rotational impact to the anvil 45. The unstable behavior is the maximum retreat when the hammer 42 moves to the position farthest from the anvil 45 within the movable range of the hammer 42.

[0104] According to the above configuration, the occurrence status of the maximum retreat can be detected, and corresponding measures can be taken.

[0105] Regarding the configurations other than the first aspect, they are not essential configurations of the impact tool 1 and can be omitted as appropriate.

Explanation of Signs

[0106] 1 Impact tool 3 Electric motor 40 Impact mechanism 42 Hammer 45 Anvil 7 Control unit 79 Retreat detection unit (detection unit) 90 Acquisition unit iq1 Current measurement value (torque current acquisition value)

Claims

Claim 1. An impact tool comprising: an electric motor; an impact mechanism that receives power from the electric motor and performs an impact operation to generate an impact force; an acquisition unit that acquires a value of a torque current supplied to the electric motor; a detection unit that detects a state of occurrence of unstable behavior of the impact mechanism based on a torque current acquisition value that is the value of the torque current acquired by the acquisition unit; wherein the detection unit detects the state of occurrence of the unstable behavior based on a magnitude of an alternating current component of the torque current acquisition value and an absolute value of an instantaneous value of the torque current acquisition value; an impact tool. Claim 2. The impact tool according to claim 1, further comprising a control unit that controls an operation of the electric motor. The impact tool according to claim 1. Claim 3. The control unit controls the operation of the electric motor so as to bring the rotational speed of the electric motor closer to a constant target value when at least the detection result of the detection unit does not indicate occurrence of the unstable behavior of the impact mechanism. The impact tool according to claim 2. Claim 4. When the detection unit detects the occurrence of the unstable behavior of the impact mechanism, the control unit reduces the rotational speed of the electric motor. The impact tool according to claim 2 or 3.

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