Impact tool and method for controlling impact tool

Abstract

The present disclosure addresses the problem of providing an impact tool with which it is possible to facilitate accurate control of a motor. An impact tool (1) comprises a motor (11), a striking rotation mechanism (12), a detection unit (13), and a control unit (15). The motor (11) is capable of normal rotation and reverse rotation. The striking rotation mechanism (12) receives rotational force from the motor (11) and performs a striking operation by rotational inertial force while repeating normal rotation and reverse rotation. The detection unit (13) detects the amount of rotation of the motor (11) or the striking rotation mechanism (12) in normal rotation. The control unit (15) controls the motor (11) on the basis of at least one of the amount of rotation detected by the detection unit (13) or a change in the amount of rotation.

Description

Impact tool and control method for impact tool

[0001] The present disclosure relates to an impact tool and a method for controlling an impact tool, and more particularly to an impact tool that performs a striking action and a method for controlling such an impact tool.

[0002] Patent Document 1 describes a power tool including a motor that can rotate in either forward or reverse directions, a hammer rotated by the motor, an anvil that is intermittently struck by the hammer with a first impact force, current detection means that detects a first reverse current value that flows through the motor each time the motor rotates in the reverse direction, and control means that controls the rotation of the motor. In this power tool, when the first reverse current value falls below a predetermined value, the control means determines whether a second reverse current value detected by the current detection means upon the next reverse rotation of the motor is also substantially the same as the predetermined value. This makes it possible to confirm whether the tightening operation has been performed reliably and to avoid erroneous determination of the completion of the tightening operation due to a sudden increase in load during the tightening operation.

[0003] In the power tool described in Patent Document 1, the motor is controlled based on the reverse current value (i.e., the current generated by the rotation of the motor due to an external force) that occurs when the motor reverses due to the repulsive force of an impact. However, since the reverse current value changes with a delay relative to changes in the rotation speed of the motor during reversal, there is a possibility that correct judgments regarding tightening work may not be made.

[0004] In conventional impact tools such as the power tool described in Patent Document 1, motor rotation is generally controlled based on the motor current value (or the detection result of a strain sensor that magnetically or electrically detects the strain of the anvil). However, because there is a time lag between a change in the current value (or the detection result of the strain sensor) and a change in the rotation speed, the motor rotation speed may not be detected correctly, making it difficult to accurately control the motor. When accurate motor control becomes difficult, variations in the tightening torque occur, for example.

[0005] Japanese Patent Application Laid-Open No. 2015-30063

[0006] An object of the present disclosure is to provide an impact tool and a control method for an impact tool that can facilitate accurate control of a motor.

[0007] An impact tool according to one aspect of the present disclosure includes a motor, an impact rotation mechanism, a detection unit, and a control unit. The motor is capable of rotating in both forward and reverse directions. The impact rotation mechanism receives rotational force from the motor and performs an impact action using rotational inertia force while repeatedly rotating in the forward direction and the reverse direction. The detection unit detects the amount of rotation of the motor or the impact rotation mechanism in the forward direction. The control unit controls the motor based on at least one of the amount of rotation and a change in the amount of rotation detected by the detection unit.

[0008] A control method for an impact tool according to one aspect of the present disclosure is a control method for an impact tool including a motor and an impact rotation mechanism. The motor is capable of rotating in both forward and reverse directions. The impact rotation mechanism receives rotational force from the motor and performs an impact action using rotational inertia force while repeatedly rotating in the forward direction and the reverse direction. The control method for the impact tool includes a detection step and a control step. The detection step detects the amount of rotation of the motor or the impact rotation mechanism in the forward direction. The control step controls the motor based on at least one of the amount of rotation and a change in the amount of rotation detected in the detection step.

[0009] Fig. 1 is an external view of an impact tool according to an embodiment of the present disclosure. Fig. 2 is a block diagram of the impact tool. Fig. 3 is a flowchart illustrating part of the operation of a control unit of the impact tool. Fig. 4 is a flowchart illustrating another part of the operation of the impact tool. Fig. 5A is a comparative graph showing an output waveform of a measurement unit (magnetostrictive sensor) in an impact tool of a comparative example, and Fig. 5B is a graph showing an example of an output waveform of the measurement unit in the impact tool. Fig. 6 is a graph showing, for comparison, an output waveform of a detection unit (encoder) in the impact tool, a waveform of a current command value from the control unit to the motor, and a waveform of the motor rotation speed.

[0010] (1) Overview First, an overview of an impact tool 1 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2 .

[0011] The impact tool 1 includes a motor 11 , an impact rotation mechanism 12 , a detection unit 13 , and a control unit 15 .

[0012] (1-1) Motor The motor 11 is capable of rotating forward and reverse. The motor 11 rotates forward when supplied with a current in the forward direction, and rotates reversely when supplied with a current in the reverse direction. When not receiving a current, the motor 11 can either stop or continue to rotate by inertia.

[0013] (1-2) Impact Rotation Mechanism The impact rotation mechanism 12 performs an impact operation using rotational inertia force while repeatedly rotating forward and backward in response to rotational force from the motor 11. The rotational inertia force is the inertia force of a rotating body (for example, an anvil).

[0014] (1-3) Detector The detector 13 detects the amount of rotation of the motor 11. The detector 13 detects the amount of rotation.

[0015] The rotation amount is the amount by which the motor 11 rotates in the forward direction, and more specifically, the number of rotations or the angle of rotation. The number of rotations is the number of times the motor 11 has rotated, for example, n times. The number of rotations is the number of rotations from the start of the tightening operation, for example. The rotation angle is the angle by which the motor 11 has rotated, for example, θ degrees. The rotation angle is the angle of rotation from the position at the start of the tightening operation (initial position), for example. Note that there is a relationship of "n = θ / 360" between the number of rotations n and the angle θ.

[0016] The amount of rotation increases when the motor 11 rotates forward, remains constant when the motor 11 is not rotating, and decreases when the motor 11 rotates reversely.

[0017] The detection unit 13 repeatedly detects the amount of rotation at a predetermined cycle.

[0018] (1-4) Control Unit The control unit 15 controls the motor 11 based on at least one of the amount of rotation and the change in the amount of rotation detected by the detection unit 13.

[0019] According to the above configuration, by performing control based on at least one of the amount of rotation of the motor 11 in the forward direction and the change in such amount of rotation, it is possible to facilitate accurate control of the motor 11 compared to when control is performed based on the current value of the motor 11, etc.

[0020] Specifically, by performing control based on at least one of the amount of rotation and the change in the amount of rotation, it is possible to easily equalize the rotational impact force and thereby suppress variations in the tightening torque (details will be described later).

[0021] (2) Details Next, the impact tool 1 will be described in detail with reference to Figures 1 to 6. However, in the following, the description of the matters already mentioned will be omitted or simplified.

[0022] 1, the impact tool 1 further includes a tool body 100 and an output shaft 101. A battery pack 102 is detachably attached to the tool body 100.

[0023] 2, the tool body 100 includes a motor 11, an impact rotation mechanism 12, a detection unit 13, a measurement unit 14, and a control unit 15. The motor 11, the detection unit 13, the measurement unit 14, and the control unit 15 are supplied with power from a battery pack 102 attached to the tool body 100.

[0024] (2-1) Output Shaft and Measuring Unit The output shaft 101 outputs an impact rotation force. The impact rotation force is the result of conversion by the impact rotation mechanism 12.

[0025] The measurement unit 14 performs a measurement operation. The measurement operation is an operation of measuring the tightening torque when tightening an object with an impact rotation force and acquiring a measurement value. The measurement operation is performed every time the impact operation of the impact rotation mechanism 12 is completed.

[0026] For example, the measurement unit 14 may repeatedly perform the measurement operation at a predetermined cycle to acquire a plurality of measurement values. The acquired plurality of measurement values ​​are stored in chronological order in the internal memory of the measurement unit 14. Then, when the impact operation is completed, the measurement unit 14 may determine the measurement value of the tightening torque related to that impact operation based on the plurality of measurement values ​​stored in the internal memory.

[0027] (2-2) Details of the Impact Rotation Mechanism The impact rotation mechanism 12 alternately receives rotational force during forward rotation and rotational force during reverse rotation from the motor 11, and performs an impact operation using the rotational inertia force during forward rotation while repeatedly rotating forward and reverse. As a result, a portion of the rotational force during forward rotation of the impact rotation mechanism 12 is converted into impact rotational force, which is an impact force about the axis, and the converted impact rotational force is output via the output shaft 101. Note that the shaft referred to here is a rotational shaft common to the motor 11 and the impact rotation mechanism 12 (and also to the output shaft 101, which will be described later).

[0028] (2-2-1) Direct Connection to Motor The impact rotation mechanism 12 is directly connected to the motor 11. Direct connection here means being connected directly to the motor 11 without the intervention of springs, gears, etc. In more detail, for example, the hammer of the impact rotation mechanism 12 is fixed to the rotor of the motor 11, and the rotor of the motor 11 and the hammer of the impact rotation mechanism 12 rotate integrally.

[0029] With this configuration, compared to when the impact rotation mechanism 12 is connected to the motor 11 via a spring, gears, etc. (see "First Modified Example of Impact Rotation Mechanism" and "Second Modified Example of Impact Rotation Mechanism" described below), delay in the change in rotation of the impact rotation mechanism 12 relative to changes in rotation of the motor 11 is suppressed. Furthermore, delay in the measurement result (measured value of fastening torque) of the measurement unit 14 relative to changes in rotation of the motor 11 is also suppressed. Therefore, accurate control of the motor 11 can be further facilitated.

[0030] (2-3) Details of the control unit (2-3-1) Control to reverse the motor approximately simultaneously with completion of the impact operation The control unit 15 determines whether the impact operation has been completed based on the change in the amount of rotation detected by the detection unit 13.

[0031] In detail, if the amount of rotation is increasing, that is, if the "current amount of rotation > previous amount of rotation", the control unit 15 determines that the impact operation is not complete, and if the increase in the amount of rotation has stopped, that is, if the "current amount of rotation = previous amount of rotation", the control unit 15 determines that the impact operation is complete.

[0032] The control unit 15 then reverses the motor 11 at approximately the same time that the result of the determination changes from a negative result that the impact motion has not been completed to a positive result that the impact motion has been completed. Note that "approximately at the same time as the change" may also be rephrased as "as the change occurs."

[0033] In this way, by reversing the rotation of the motor 11 substantially simultaneously with (for example, in response to) the completion of the impact operation of the impact rotation mechanism 12, it is possible to suppress the rotational force of the motor 11 that follows the impact rotational force of the impact rotation mechanism 12. This makes it possible to achieve the tightening operation using only the impact rotational force of the impact rotation mechanism 12, and ultimately makes it even easier to accurately control the motor 11.

[0034] (2-3-2) Specific example of "reversing rotation substantially simultaneously": reversing rotation after a period of current stoppage In response to a change in the result of the judgment as to whether the impact operation is completed from a negative result to a positive result, the control unit 15 stops the current to the motor 11 (i.e., forward current) and then starts supplying a current in the opposite direction to the current (i.e., reverse current), thereby reversing the rotation of the motor 11.

[0035] Specifically, the control unit 15 changes the motor 11 from forward rotation to reverse rotation by utilizing the repulsive force against the impact torque during the current stop period from when the supply of forward current stops to when the supply of reverse current starts.

[0036] The end point of the current stop period here is, for example, in the impact tool 1 of the comparative example, immediately after "impact completion," "the anvil temporarily rotates in the reverse direction due to the repulsive force" against the impact rotational force, but continues to rotate forward "the anvil returns to normal rotation due to the rotational force of the motor," and in this series of operations, it is an appropriate point between "the anvil temporarily rotates in the reverse direction due to the repulsive force" and "the anvil returns to normal rotation due to the rotational force of the motor 11."

[0037] In other words, in the case of the impact tool of the comparative example, the control unit 15 reverses the motor 11 before the point at which the anvil would temporarily go into a reverse rotation state due to the repulsive force of the impact action and then return to a forward rotation state due to the rotational force of the motor 11, thereby maintaining the reverse rotation state.

[0038] In this way, the control unit 15 stops the supply of current to the motor 11 upon completion of the impact operation of the impact rotation mechanism 12, and then supplies current in the opposite direction. This provides a current stop period immediately after the impact operation, making it easy to reverse the rotation of the motor 11, which is rotating forward due to inertia, by utilizing the repulsive force from the impact rotation mechanism 12 to the motor 11 in response to the rotational force from the motor 11 to the impact rotation mechanism 12. Then, by supplying current in the opposite direction to the motor 11 after the current stop period, the reverse rotation of the motor 11 can be continued.

[0039] (2-3-3) Control for Reverse Rotation of Motor Until Amount of Rotation Returns to Predetermined Value The control unit 15 continues to reverse the rotation of the motor 11 until the amount of rotation detected by the detection unit 13 returns to a predetermined value.

[0040] Specifically, in response to a change in the result of the determination as to whether the impact motion is completed from a negative result to a positive result, the control unit 15 stops the current (forward current) to the motor 11 and then starts supplying a current in the opposite direction (reverse current) to the current, thereby rotating the motor 11 in the reverse direction. The control unit 15 then continues to rotate the motor 11 in the reverse direction by supplying a current in the reverse direction until the amount of rotation detected by the detection unit 13 returns to a predetermined value, and when the amount of rotation returns to the predetermined value, starts rotating the motor 11 in the forward direction by supplying a current in the forward direction.

[0041] In this way, by returning the rotation amount of the motor 11 to a predetermined value before the next striking operation (second striking), it is possible to facilitate accurate control of the motor 11 during the second striking.

[0042] In detail, by controlling the reversal of the motor 11 based on the amount of rotation of the motor 11 (reversal control based on the amount of rotation), the amount of rotation during reversal, and therefore the time interval between repeated impact movements, can be accurately controlled (e.g., made uniform) compared to, for example, reversing the motor 11 for a predetermined period of time.

[0043] Furthermore, reverse rotation control based on the rotation amount facilitates changing the rotation speed of the motor 11 during reverse rotation. In other words, the rotation amount during reverse rotation can be accurately controlled regardless of the rotation speed of the motor 11 during reverse rotation.

[0044] Furthermore, by controlling the reverse rotation based on the rotation amount, it is possible to perform control that takes into consideration the reverse rotation of the motor 11 due to the repulsive force against the rotational impact force of the impact rotation mechanism 12. In other words, even if the motor 11 rotates in the reverse direction due to the repulsive force against the rotational impact force, it is possible to perform control that takes into consideration the amount of rotation due to the repulsive force.

[0045] (2-3-4) Direction Flag The forward and reverse rotation of the motor 11 is controlled by, for example, a direction flag. The direction flag is a flag for switching the direction of current to the motor 11 between the forward and reverse directions to rotate the motor 11 forward and reverse. The direction flag is switched between "forward" and "reverse" under the control of the control unit 15.

[0046] That is, when the control unit 15 rotates the motor 11 in the forward direction, it sets the direction flag to "forward rotation", and when it rotates the motor 11 in the reverse direction, it sets the direction flag to "reverse rotation".

[0047] (2-3-5) Motor On / Off The motor 11 is turned on and off under the control of the control unit 15. When the motor 11 is on, it rotates forward or reverse according to the direction flag, and when it is off, it stops or continues to rotate by inertia.

[0048] More specifically, when the motor 11 is off and the control unit 15 sets the direction flag to "forward" and turns on the motor 11, the motor 11 receives a supply of current in the forward direction and starts rotating in the forward direction. Also, when the control unit 15 sets the direction flag to "reverse" while the motor 11 is rotating in the forward direction, the direction of the current supplied to the motor 11 changes from the forward direction to the reverse direction, and the rotation of the motor 11 changes from forward to reverse. Furthermore, when the control unit 15 sets the direction flag to "forward" while the motor 11 is rotating in the reverse direction, the direction of the current supplied to the motor 11 changes from the reverse direction to the forward direction, and the rotation of the motor 11 changes from reverse to forward.

[0049] Similarly, when the motor 11 is in the off state, if the control unit 15 sets the direction flag to "reverse" and turns on the motor 11, the motor 11 receives a current supply in the reverse direction and starts rotating in the reverse direction.

[0050] (2-3-6) Impact Completion Condition The control unit 15 determines whether the impact operation of the impact rotation mechanism 12 has been completed based on the impact completion condition. The impact completion condition is a condition for determining that the impact operation of the impact rotation mechanism 12 has been completed. For example, the impact completion condition is "the amount of rotation has changed from an increasing state to a constant state."

[0051] Specifically, the impact completion condition may be that the count value has stopped increasing. For example, the count value has stopped increasing when the difference between the current count value and the previous count value changes from a positive value to a zero value.

[0052] The control unit 15 determines that the impact operation of the impact rotation mechanism 12 is complete when the rotation amount of the motor 11 satisfies the impact completion condition. If the rotation amount of the motor 11 does not satisfy the impact completion condition, the control unit 15 determines that the impact operation of the impact rotation mechanism 12 is not complete yet.

[0053] (2-4) Hardware for Realizing Each Unit (2-4-1) Detection Unit The detection unit 13 is realized by, for example, a rotation sensor. The rotation sensor is a sensor that performs detection related to rotation. Detection related to rotation includes, for example, detection of the rotation angle, which is the angle of rotation, detection of the number of rotations, detection of the rotation speed, which is the rotation angle or number of rotations per unit time, and detection of the rotation direction (forward or reverse).

[0054] The rotation sensor in this embodiment is an encoder that detects the number of rotations of the motor 11. The encoder is, for example, an optical encoder, but may also be a magnetic or electric encoder.

[0055] (2-4-2) Measuring Unit The measuring unit 14 is realized by, for example, a magnetostrictive sensor and a processing circuit that processes the output signal of the magnetostrictive sensor to obtain a measured value of the tightening torque.

[0056] (2-4-3) Control Unit The control unit 15 is realized by, for example, a processor and a memory. The memory stores a program for causing the processor to operate as the control unit 15.

[0057] (2-5) Example of Operation of the Control Unit The control unit 15 of the impact tool 1 operates, for example, according to the flowcharts in Figures 3 and 4. The processes in Figures 3 and 4 are started, for example, when the tightening operation using the impact tool 1 is started. The processes in Figures 3 and 4 are repeatedly executed at a predetermined cycle. The processes in Figures 3 and 4 are ended, for example, when the tightening operation is completed.

[0058] First, the control unit 15 initializes a count value, which is a variable indicating the number of rotations of the motor 11, to "0" (step S1).

[0059] Next, the control unit 15 sets the direction flag, which indicates the rotation direction of the motor 11, to "normal rotation" (step S2).

[0060] Next, the control unit 15 turns on the motor 11 (step S3), which starts supplying a forward current to the motor 11, causing the motor 11 to start rotating forward.

[0061] Next, the control unit 15 causes the detection unit 13 to start counting the number of rotations of the motor 11 (step S4). In response to the counting result by the detection unit 13, the control unit 15 updates the count value and holds the count value before the update.

[0062] Next, the control unit 15 starts calculating the change in the count value, i.e., the difference between the count value before and after the update (step S5). The difference is calculated by subtracting the count value before the update from the count value after the update. Note that if the difference is a positive value, the motor 11 is rotating forward, if the difference is "0", the motor 11 is stopped, and if the difference is a negative value, the motor 11 is rotating reversely.

[0063] Next, the control unit 15 determines whether the change in the count value satisfies the impact completion condition (step S6). The impact completion condition here is a condition that "the count value has changed from an increasing state to a constant value." If it is determined that the change in the count value has not yet satisfied the impact completion condition (No in step S6), the process returns to step S6.

[0064] If it is determined in step S6 that the change in the count value satisfies the impact completion condition (Yes), the control unit 15 turns off the motor 11 (step S7), thereby stopping the supply of forward current to the motor 11, and the motor 11 enters a state in which it can rotate forward or reverse due to inertia, and switches from forward to reverse due to the repulsive force against the impact rotational force.

[0065] Next, the control unit 15 causes the measurement unit 14 to measure the tightening torque (step S8), thereby obtaining the measured value of the tightening torque at the time when the impact operation is completed.

[0066] Next, the control unit 15 sets the direction flag to "reverse" (step S9).

[0067] Next, the control unit 15 turns on the motor 11 (step S10), which starts supplying a current to the motor 11 in the reverse direction, causing the motor 11 to continue rotating in the reverse direction.

[0068] Next, the control unit 15 determines whether the count value has reached a predetermined value (step S11). If it is determined that the count value has not yet reached the predetermined value (No in step S11), the process returns to step S11.

[0069] If it is determined in step S11 that the count value has reached the predetermined value (Yes), the control unit 15 sets the direction flag to "forward rotation" (step S12). This changes the direction of the current to the motor 11 from the reverse direction to the forward direction, and the motor 11 switches from reverse rotation to forward rotation. Then, the process returns to step S6.

[0070] In the processing illustrated in Figures 3 and 4, the supply of current to the motor 11 is stopped upon completion of the impact operation (S7), and after the supply of current to the motor 11 is stopped, a measurement operation (S8) is performed. However, the measurement operation (S8) may be performed before the supply of current is stopped (S7) or simultaneously with the stop of the supply of current (S7), and it does not matter which occurs first or second.

[0071] (3) Specific Example Next, a specific example of the impact tool 1 will be described with reference to FIGS. 1, 2, 5 and 6, in comparison with an impact tool of a comparative example.

[0072] (3-1) Comparison of the Impact Rotation Mechanism of the Comparative Example and the Impact Rotation Mechanism of the Embodiment (3-1-1) Impact Rotation Mechanism of the Comparative Example The impact rotation mechanism of the comparative example includes a hammer, an anvil, a spring, gears, etc. The hammer is connected to a motor via a spring, gears, etc., and a portion of the rotational force from the motor during forward rotation is converted into potential energy of the spring, and then converted into impact rotational force by a striking motion against the anvil. The anvil is connected to an output shaft 101, receives impact rotational force from the hammer, and rotates forward together with the output shaft 101. In this way, an object to be tightened, such as a nut, is tightened by the impact rotational force repeatedly output from the output shaft 101.

[0073] In this way, in the impact rotation mechanism of the comparative example, the rotational force of the motor is stored in the spring and then output as a rotational impact force, so the rotational impact force is delayed relative to the rotational force of the motor, which makes it easy for the measurement accuracy of the tightening torque to decrease.

[0074] (3-1-2) Specific Example of Impact Rotation Mechanism of Embodiment In this specific example, the impact rotation mechanism 12 of this embodiment includes a hammer and an anvil. The hammer is directly connected to the motor 11, and when the motor 11 rotates in the forward direction, the hammer also rotates in the forward direction, and when the motor 11 rotates in the reverse direction, the hammer also rotates in the reverse direction. The hammer alternately receives rotational force in the forward direction and rotational force in the reverse direction from the motor 11, and while repeatedly rotating in the forward direction and reverse direction, performs an impact action on the anvil using the rotational inertia force in the forward direction, whereby a portion of the rotational force in the forward direction is converted into impact rotational force.

[0075] The anvil is connected to the output shaft 101. The connection to the output shaft 101 is, for example, by being attached to the output shaft 101 or by being integrally formed with the output shaft 101. The anvil receives a rotational impact force from the hammer and rotates forward together with the output shaft 101. In this way, an object to be tightened, such as a nut, is tightened by the rotational impact force repeatedly output from the output shaft 101.

[0076] In this way, in the impact rotation mechanism 12 of this embodiment, the rotational inertia force corresponding to the rotational force of the motor 11 is output as a rotational impact force, thereby suppressing the delay of the rotational impact force relative to the rotational force of the motor 11 and reducing the decrease in the measurement accuracy of the tightening torque.

[0077] (3-2) Comparison of Output Waveforms of the Measuring Unit (3-2-1) Output Waveform of the Measuring Unit in the Comparative Impact Tool Fig. 5A shows the output waveform of the magnetostrictive sensor in the comparative impact tool. This comparative impact tool is different from the impact tool 1 of the present embodiment in that the impact rotation mechanism 12 is modified so that the motor can continue to rotate in the forward direction at the time of the impact operation, and the control unit is modified so that it does not control the motor to rotate in the reverse direction upon completion of the impact operation (i.e., it has the configuration of a typical impact tool).

[0078] In the comparative example of the impact tool, the motor is connected to the hammer via springs, gears, etc., and even when the hammer strikes the anvil and the anvil stops or reverses due to the impact rotational force, the motor continues to rotate forward.

[0079] In the graph of Figure 5A, the horizontal axis corresponds to time (sec), and the vertical axis corresponds to the output (volts: V) of the measuring unit (magnetostrictive sensor), and the output waveform shows the change in strain over time. The output waveform of Figure 5A includes two pulse components, first and second, P1 and P2. The first pulse component P1 corresponds to the strain generated in the anvil in response to the rotational force of the hammer impact. The second pulse component P2 corresponds to the strain generated in the anvil in response to the rotational force of the motor.

[0080] As can be seen from the output waveform in Figure 5A, in the impact tool of the comparative example, immediately after the impact torque of the hammer (corresponding to the first pulse component P1) acts on the anvil, the torque of the motor (corresponding to the second pulse) that continues to rotate forward also acts on the anvil. In this way, the action of the motor torque on the anvil following the impact torque of the hammer contributes to an increase in the tightening torque, but on the other hand, it makes it difficult to accurately control the motor and ultimately causes variations in the tightening torque.

[0081] (3-2-2) Output Waveform of the Measuring Unit in the Impact Tool of the Embodiment Figure 5B shows the output waveform of the magnetostrictive sensor in the impact tool of the present embodiment. In the graph of Figure 5B, the horizontal axis corresponds to time (sec), the vertical axis corresponds to the output (V) of the measuring unit (magnetostrictive sensor), and the output waveform shows the change in strain over time.

[0082] The output waveform of FIG. 5B is different from the output waveform of FIG. 5A in that the second pulse component P2 of the first and second pulse components P1 and P2 is removed and only the first pulse component P1 is included.

[0083] In the impact tool 1 of this embodiment, the motor 11, under the control of the control unit 15, causes the impact rotation mechanism 12 to perform an impact operation in the forward direction, and then rotates in the reverse direction substantially simultaneously with the completion of the impact operation.

[0084] 5B, the impact tool 1 of this embodiment enables fastening work using only the impact rotational force (corresponding to the first pulse component P1) generated by the impact action of the impact rotation mechanism 12. This facilitates accurate control of the motor 11 and ultimately makes it possible to suppress variations in the fastening torque.

[0085] (3-3) Relationship between the amount of rotation of the motor, the current command value to the motor, and the rotation speed of the motor The graph in Figure 6 shows the relationship between the amount of rotation of the motor 11, the current command value to the motor 11, and the rotation speed of the motor 11. Specifically, Figure 6 shows a waveform in a dashed line indicating a change in the count value of the encoder, a waveform in a dot-dash line indicating a change in the current command value to the motor 11 from the control unit 15, and a waveform in a solid line indicating a change in the rotation speed of the motor 11.

[0086] In the graph of FIG. 6, the horizontal axis corresponds to time (msec), the left vertical axis corresponds to the count value (times), and the right vertical axis corresponds to the current command value (mA) and the rotation speed (rpm).

[0087] It is possible to switch between a forward current and a reverse current and the current command value includes, for example, a positive sign indicating a forward current or a negative sign indicating a reverse current. However, for convenience, in the graph of Figure 6, the absolute value of the current command value is shown by a thin waveform line, and the direction of the current is shown by an increase or decrease in the rotation speed of the motor 11 according to the current command value.

[0088] (3-3-1) Relationship between current command value and rotational speed When the current command value to the motor 11 changes as shown by the waveform indicated by the dashed line in Fig. 6, the rotational speed of the motor 11 changes as shown by the waveform indicated by the solid line in accordance with the change in the current command value. Comparing the waveform indicated by the dashed line with the waveform indicated by the solid line, it can be seen that the change in the rotational speed of the motor 11 is delayed relative to the change in the current command value.

[0089] Specifically, for example, at the first time point t1 (20 msec) when the current command value (waveform indicated by the dashed dotted line) first reaches a maximum, the rotation speed (waveform indicated by the solid line) is increasing, and even at the second time point t2 (40 msec) when the current command value reaches a maximum for the second time, 20 msec after the first time point t1 (20 msec), the rotation speed (waveform indicated by the solid line) is still increasing.

[0090] (3-3-2) Relationship Between Rotation Amount, Current Command Value, and Rotational Speed ​​At a first time point t1 (20 msec) when the current command value reaches its first maximum value (where the direction flag is "forward"), the motor 11 starts rotating forward, and the count value (dashed waveform) rises sharply from 0 to a reference value (58 times). Thereafter, the count value gradually rises from the reference value (58 times) to a maximum value (70 times) during the period (20 to 180 msec) from the first time point t1 (20 msec) through a second time point t2 (40 msec) when the current command value reaches its second maximum value (where the direction flag is "forward"), to a third time point t3 (180 msec) when the current command value reaches its third maximum value (where the direction flag is "forward"), as shown by the dashed waveform in FIG. 6.

[0091] Thereafter, the count value remains at the maximum value (70 times), and at the fourth time point t4 (210 msec) when the current command value reaches the fourth maximum value (however, the direction flag is set to "reverse"), it returns to a predetermined value (56 times) that is slightly below the reference value (58 times).

[0092] Thereafter, the count value is maintained at a predetermined value (56 times) or a value close to it (55 to 57 times), and begins to increase at a fifth time point t5 (280 msec) when the current command value reaches its fifth maximum value (however, the direction flag is "forward").Then, at a sixth time point t6 (330 msec) when the first impact operation of the impact rotation mechanism 12 is completed and the current command value reaches its sixth maximum value (however, the direction flag is "forward"), the count value reaches the reference value (58 times).

[0093] In response to this, that is, at the sixth time point t6 (330 msec), the current command value becomes "0" and the count value is maintained at the reference value (58 times). At the seventh time point t7 (380 msec) when the current command value reaches the seventh maximum value or the fifth maximum value (however, the direction flag is "reverse"), the count value starts to decrease, and when it returns to the predetermined value (56 times), the decrease of the count value stops.

[0094] Thereafter, the count value is maintained at a predetermined value (56 times) or a value close to it (55 to 57 times), and begins to increase again at an eighth time point t8 (450 msec) when the current command value reaches its eighth maximum value (however, the direction flag is "forward"). Then, at a ninth time point t9 (500 msec) when the second impact operation of the impact rotation mechanism 12 is completed, the current command value reaches its ninth maximum value (however, the direction flag is "forward") and the count value reaches the reference value (58 times).

[0095] In response to this, that is, at the ninth time point t9 (500 msec), the current command value becomes "0" and the count value remains at the reference value (58 times). At the tenth time point t10 (550 msec), when the current command value reaches the tenth maximum value (however, the direction flag is "reverse"), the count value begins to decrease again, and when it returns to the predetermined value (56 times), the decrease in the count value stops. Thereafter, the count value repeats the same change.

[0096] (4) Modifications Next, various modifications of the impact tool 1 of the embodiment will be described. Note that in the modifications, the description of matters common to the embodiment will be omitted or simplified.

[0097] (4-1) First Modification of Substantially Simultaneous Operation In this modification, the measurement unit 14 performs a measurement operation in response to a change in the result of the determination by the control unit 15 regarding the completion of the hitting operation from a negative result to a positive result. After the measurement operation is performed, the control unit 15 reverses the rotation of the motor 11.

[0098] In this way, the control unit 15 of this modified example causes the measurement unit 14 to measure the tightening torque in response to the completion of the impact operation, and then reverses the rotation of the motor 11. In other words, the difference from the "second modified example of substantially simultaneous rotation" described next is that the timing of the reverse rotation of the motor 11 in response to the completion of the impact operation does not have to be predetermined.

[0099] According to this modification, it is possible to suppress variations in the tightening torque and measure the tightening torque at the correct timing.

[0100] (4-2) Second Modification of Substantially Simultaneous Operation In this modification, the control unit 15 reverses the motor 11 after a predetermined time has elapsed since the result of the determination regarding the completion of the striking motion changed from a negative result to a positive result. Here, the predetermined time is, for example, a value between 0 and 40 msec. However, the predetermined time may also be a value between 0 and 60 msec, or a value between 0 and 30 msec.

[0101] The measuring unit 14 performs a measuring operation before the control unit 15 causes the motor 11 to rotate in the reverse direction.

[0102] In this manner, in this modified example, the timing for reversing the rotation of the motor 11 relative to the completion of the impact operation is predetermined, and the control unit 15 causes the measuring unit 14 to measure the tightening torque after the completion of the impact operation and before the timing for reversing the rotation of the motor 11 arrives.

[0103] According to this modification, it is possible to suppress variations in the tightening torque and measure the tightening torque at the correct timing.

[0104] (4-3) First Modification of Impact Rotation Mechanism The impact rotation mechanism 12 does not have to be directly connected to the motor 11. In this modification, the hammer that constitutes the impact rotation mechanism 12 is connected to the rotor of the motor 11 via a spring, a gear, or the like. In this modification, the motor 11 is rotating in the forward direction when the impact operation of the impact rotation mechanism 12 is completed, but the control unit 15 forcibly rotates the motor 11 in the reverse direction by switching the direction of the current to the motor 11 from the forward direction to the reverse direction approximately simultaneously with the completion of the impact operation of the impact rotation mechanism 12.

[0105] According to this modification, part of the rotational force of the motor 11 is converted into the impact rotational force of the impact rotation mechanism 12 via the potential energy of the spring, and therefore, compared to the embodiment, there is a larger delay in the change in the impact operation of the impact rotation mechanism 12 in response to a change in the rotation of the motor 11. However, even with a larger delay, by having the detection unit 13 detect the amount of rotation of the motor 11 and having the control unit 15 perform control based on the detection result of the detection unit 13, it is possible to facilitate accurate control of the motor 11 compared to when control is performed based on the current value of the motor 11, etc.

[0106] (4-4) Second Modification of Impact Rotation Mechanism In this modification, the detection unit 13 detects the amount of forward rotation of the impact rotation mechanism 12 instead of detecting the amount of rotation of the motor 11. In this modification, accurate control of the motor 11 is more difficult than in the first modification, but accurate control of the motor 11 can be made easier than in the case where control is performed based on the current value of the impact rotation mechanism 12.

[0107] (4-5) Modified example of the detection unit In this embodiment, the motor 11 and the impact rotation mechanism 12 are directly connected and rotate together, so the detection unit 13 may detect the amount of rotation of the impact rotation mechanism 12 in the forward direction instead of the amount of rotation of the motor 11 in the forward direction.

[0108] Furthermore, since the output shaft 101 is fixed to the anvil of the impact rotation mechanism 12, and the output shaft 101 rotates integrally with the motor 11 and the impact rotation mechanism 12, the detection unit 13 may detect the amount of rotation of the output shaft 101 in forward rotation instead of the amount of rotation of the motor 11 in forward rotation or the amount of rotation of the impact rotation mechanism 12 in forward rotation.

[0109] The rotation sensor that realizes the detection unit 13 in this modified example is, for example, an encoder that detects the rotation speed of the impact rotation mechanism 12 or the output shaft 101 .

[0110] (4-6) Modified Examples of the Rotation Sensor The rotation sensor may be, for example, an encoder that detects the rotation angle of the impact rotation mechanism 12 or the output shaft 101. In this case, for example, the control unit 15 calculates the number of rotations based on the rotation angle detected by the encoder.

[0111] Alternatively, the rotation sensor may be an encoder that detects the angular velocity of the impact rotation mechanism 12 or the output shaft 101. In this case, for example, the control unit 15 calculates the rotation angle and therefore the number of rotations based on the angular velocity detected by the encoder.

[0112] (4-7) Modified examples of the measuring unit The measuring unit 14 may be realized by a strain sensor other than a magnetostrictive sensor, such as a strain gauge that electrically detects strain, or by a sensor other than a strain sensor (such as a sensor that optically detects the twist of the anvil).

[0113] (5) Impact Tool Control Method The impact tool 1 control method includes steps S4 and S5 (hereinafter referred to as the "detection step") and steps S6 to S12 (hereinafter referred to as the "control step"). In the detection step, the detection unit 13 detects the amount of rotation of the motor 11 in the forward direction. Specifically, for example, the processor may detect the amount of rotation of the motor 11 or the impact rotation mechanism 12 using the detection result of the rotation sensor.

[0114] In the control step, the control unit 15 controls the motor 11 based on at least one of the amount of rotation and the change in the amount of rotation detected in the detection step. Specifically, for example, the amount of rotation detected last time is stored in memory, and the processor may determine the change in the amount of rotation based on the amount of rotation detected this time and the amount of rotation stored in memory, and control the motor 11 based on at least one of the amount of rotation detected this time and the determined change in the amount of rotation.

[0115] In the control step, the control unit 15 (processor and memory) determines whether the impact operation has been completed based on the change in the amount of rotation detected in the detection step, and reverses the motor 11 at approximately the same time that the result of the determination changes from a negative result indicating that the impact operation has not been completed to a positive result indicating that the impact operation has been completed.

[0116] In the control step, the control unit 15 (processor and memory) continues to rotate the motor 11 in the reverse direction until the amount of rotation detected in the detection step returns to a predetermined value.

[0117] (6) Summary The impact tool (1) according to the first aspect of the present disclosure includes a motor (11), an impact rotation mechanism (12), a detection unit (13), and a control unit (15). The motor (11) is capable of forward and reverse rotation. The impact rotation mechanism (12) receives rotational force from the motor (11) and performs an impact action using rotational inertia force while repeatedly rotating forward and reverse. The detection unit (13) detects the amount of rotation of the motor (11) or the impact rotation mechanism (12) in the forward direction. The control unit (15) controls the motor (11) based on at least one of the amount of rotation and a change in the amount of rotation detected by the detection unit (13).

[0118] According to this aspect, by performing control based on at least one of the amount of rotation of the motor (11) or the impact rotation mechanism (12) in the forward direction and the change in such amount of rotation, it is possible to facilitate accurate control of the motor (11) compared to when control is performed based on the current value of the motor (11), etc.

[0119] In the impact tool (1) according to the second aspect, in the first aspect, the control unit (15) determines whether the impact operation is completed based on the change in the amount of rotation detected by the detection unit (13). Then, the control unit (15) reverses the motor (11) approximately simultaneously with the result of the determination changing from a negative result indicating that the impact operation is not completed to a positive result indicating that the impact operation is completed.

[0120] According to this aspect, by reversing the rotation of the motor (11) substantially simultaneously with the completion of the impact operation, the rotational force of the motor (11) following the impact rotational force of the impact rotation mechanism (12) can be suppressed, thereby realizing the tightening operation using only the impact rotational force of the impact rotation mechanism (12), and further facilitating accurate control of the motor (11).

[0121] In the impact tool (1) according to the third aspect, in the second aspect, the control unit (15) continues to reverse the rotation of the motor (11) until the amount of rotation detected by the detection unit returns to a predetermined value.

[0122] According to this aspect, by returning the rotation amount to a predetermined value before the next striking operation (re-striking), it is possible to facilitate accurate control of the motor (11) during the re-striking.

[0123] In the impact tool (1) according to the fourth aspect, in the second or third aspect, the control unit (15) stops the current to the motor (11) in response to a change in the judgment result from a negative result to a positive result, and then starts supplying a current in the opposite direction to the current, thereby reversing the rotation of the motor (11).

[0124] According to this aspect, by stopping the supply of current to the motor (11) upon completion of the impact operation and then supplying a current in the opposite direction, i.e., by providing a current stop period immediately after the impact operation, it is possible to easily switch the motor (11) from forward rotation to reverse rotation by utilizing the rotational force from the motor (11) to the impact rotation mechanism (12) and the repulsive force from the impact rotation mechanism (12) to the motor (11). Furthermore, by supplying a current in the opposite direction to the motor (11) after the current stop period, it is possible to continue the reverse rotation of the motor (11).

[0125] The impact tool (1) according to a fifth aspect is any one of the second to fourth aspects, and further includes an output shaft (101) and a measurement unit (14). The output shaft (101) outputs an impact rotational force. The impact rotational force is the conversion result of the impact rotation mechanism (12). The measurement unit (14) performs a measurement operation. The measurement operation is an operation of measuring a tightening torque when tightening an object with the impact rotational force. The measurement unit (14) performs the measurement operation in response to a change in the judgment result from a negative result to a positive result. The control unit (15) reverses the rotation of the motor (11) after the measurement operation is performed.

[0126] According to this aspect, it is possible to suppress variations in the tightening torque and measure the tightening torque at an appropriate timing.

[0127] The impact tool (1) according to a sixth aspect is any one of the second to fourth aspects, further comprising an output shaft (101) and a measuring unit (14). The output shaft (101) outputs an impact rotational force. The impact rotational force is the conversion result of the impact rotation mechanism (12). The measuring unit (14) performs a measuring operation. The measuring operation is an operation of measuring a tightening torque when tightening an object with the impact rotational force. The control unit (15) reverses the rotation of the motor (11) after a predetermined time has elapsed since the result of the judgment changed from a negative result to a positive result. The measuring unit (14) performs the measuring operation before the control unit (15) reverses the rotation of the motor (11).

[0128] According to this aspect, it is possible to suppress variations in the tightening torque and measure the tightening torque at an appropriate timing.

[0129] In the impact tool (1) according to the seventh aspect, in any one of the first to sixth aspects, the detection unit (13) detects the amount of rotation of the motor (11) in the forward direction.

[0130] According to this aspect, even when the impact rotation mechanism (12) is not directly connected to the motor (11) (for example, when it is connected to the motor (11) via a spring, gear, etc.), accurate control of the motor (11) can be facilitated.

[0131] A control method for an impact tool (1) according to an eighth aspect is a control method for an impact tool (1) including a motor (11) and an impact rotation mechanism (12). The motor (11) is capable of rotating in both forward and reverse directions. The impact rotation mechanism (12) receives rotational force from the motor (11) and performs an impact action using rotational inertia force while repeatedly rotating in forward and reverse directions. The control method for the impact tool (1) includes detection steps (S4, S5) and control steps (S6 to S12). The detection steps (S4, S5) detect the amount of rotation of the motor (11) or the impact rotation mechanism (12) in forward rotation. The control steps (S6 to S12) control the motor (11) based on at least one of the amount of rotation and a change in the amount of rotation detected in the detection steps (S4, S5).

[0132] According to this aspect, by performing control based on at least one of the amount of rotation of the motor (11) or the impact rotation mechanism (12) in the forward direction and the change in such amount of rotation, it is possible to facilitate accurate control of the motor (11) compared to when control is performed based on the current value of the motor (11), etc.

[0133] In the control method for the impact tool (1) according to the ninth aspect, in the eighth aspect, in the control steps (S6 to S12), a determination is made as to whether or not the impact operation has been completed based on the change in the amount of rotation detected in the detection steps (S4, S5), and the motor (11) is reversed at approximately the same time as the result of the determination changes from a negative result indicating that the impact operation has not been completed to a positive result indicating that the impact operation has been completed.

[0134] According to this aspect, by reversing the rotation of the motor (11) substantially simultaneously with the completion of the impact operation, the rotational force of the motor (11) following the impact rotational force of the impact rotation mechanism (12) can be suppressed, thereby realizing the tightening operation using only the impact rotational force of the impact rotation mechanism (12), and further facilitating accurate control of the motor (11).

[0135] In the control method for the impact tool (1) according to the tenth aspect, in the ninth aspect, in the control steps (S6 to S12), the reverse rotation of the motor (11) is continued until the amount of rotation detected in the detection steps (S4, S5) returns to a predetermined value.

[0136] According to this aspect, by returning the rotation amount to a predetermined value before the next striking operation (re-striking), it is possible to facilitate accurate control of the motor (11) during the re-striking.

[0137] REFERENCE SIGNS LIST 1 impact tool 11 motor 12 impact rotation mechanism 13 detection unit 14 measurement unit 15 control unit 101 output shaft

Claims

1. An impact tool comprising: a motor capable of rotating in both forward and reverse directions; an impact rotation mechanism that receives a rotational force from the motor and repeats the forward and reverse rotation while performing an impact action using rotational inertia force; a detection unit that detects the amount of rotation of the motor or the impact rotation mechanism in the forward rotation; and a control unit that controls the motor based on at least one of the amount of rotation and a change in the amount of rotation detected by the detection unit.

2. The impact tool as described in claim 1, wherein the control unit determines whether or not the impact operation has been completed based on the change in the amount of rotation detected by the detection unit, and reverses the motor at approximately the same time that the result of the determination changes from a negative result indicating that the impact operation has not been completed to a positive result indicating that the impact operation has been completed.

3. The impact tool according to claim 2, wherein the control unit continues the reverse rotation of the motor until the amount of rotation detected by the detection unit returns to a predetermined value.

4. The impact tool according to claim 2 or 3, wherein the control unit reverses the rotation of the motor by stopping the current to the motor in response to a change in the result of the judgment from the negative result to the positive result, and then starting to supply a current in a direction opposite to the current.

5. An impact tool as described in any one of claims 2 to 4, further comprising: an output shaft that outputs an impact rotational force that is the conversion result of the impact rotation mechanism; and a measurement unit that performs a measurement operation to measure a tightening torque when an object is tightened by the impact rotational force, wherein the measurement unit performs the measurement operation in response to a change in the result of the judgment from the negative result to the positive result, and the control unit reverses the motor after the measurement operation has been performed.

6. An impact tool as claimed in any one of claims 2 to 4, further comprising: an output shaft that outputs an impact rotational force that is the conversion result of the impact rotation mechanism; and a measurement unit that performs a measurement operation to measure a tightening torque when an object is tightened by the impact rotational force, wherein the control unit reverses the rotation of the motor after a predetermined time has elapsed since the result of the judgment changes from the negative result to the positive result, and the measurement unit performs the measurement operation before the control unit reverses the rotation of the motor.

7. The impact tool according to any one of claims 1 to 6, wherein the detection unit detects the amount of rotation of the motor in the forward rotation.

8. A control method for an impact tool equipped with a motor capable of rotating in both forward and reverse directions, and an impact rotation mechanism that receives a rotational force from the motor and performs an impact action by rotational inertia force while repeating the forward and reverse rotation, the control method for an impact tool including: a detection step of detecting an amount of rotation, which is the amount by which the motor or the impact rotation mechanism rotates in the forward rotation; and a control step of controlling the motor based on at least one of the amount of rotation and a change in the amount of rotation detected in the detection step.

9. A control method for an impact tool as described in claim 8, wherein in the control step, a determination is made as to whether or not the impact operation has been completed based on the change in the amount of rotation detected in the detection step, and the motor is reversed at approximately the same time that the result of the determination changes from a negative result indicating that the impact operation has not been completed to a positive result indicating that the impact operation has been completed.

10. The control method for an impact tool according to claim 9, wherein in the control step, the reverse rotation of the motor is continued until the amount of rotation detected in the detection step returns to a predetermined value.

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