ELECTRIC TOOL, AND ELECTRIC TOOL CONTROL DEVICE

Abstract

 An electric tool (10) is provided with a power transmission unit (22) for decelerating and then transmitting the rotational power of a motor (21) to an output shaft (25), a shift actuator (27) for changing the deceleration rate of the power transmission unit, a torque detection unit (41) for detecting the load torque applied to the output shaft (25), and a control unit (23) for controlling the shift actuator (27) so as to change the deceleration rate of the power transmission unit in accordance with the detected load torque. The control unit (23) does not increase the deceleration rate of the power transmission device and determines that the motor was locked when the load torque detected by means of the torque detection unit increased within a predetermined time from a threshold value of a shifting condition set to increase the deceleration rate to a threshold value of a locking condition set to detect that the motor was locked.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electric power tool and a control device for the electric power tool.

BACKGROUND ART

[0002] In the prior art, there is an electric power tool that automatically changes a speed reduction ratio by controlling a power transmission unit, which decelerates and transmits rotational power of a motor, with a control unit (for example, refer to patent document 1). In such an electric power tool, for example, a load torque applied to an output shaft, to which a tip tool (bit) is attached, is detected from a drive current supplied to the motor, and the control unit changes the speed reduction ratio of the power transmission unit based on the detected load torque.

PRIOR ART DOCUMENT

PATENT DOCUMENT

[0003] Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-30347

SUMMARY OF THE INVENTION

PROBLEMS THAT ARE TO BE SOLVED BY THE INVENTION

[0004] The above power transmission unit is increased in size as the number of gears allowing for speed changes, that is, the number of speed reduction gears, increases. However, it is desirable that an electric power tool, particularly, a portable electric power tool, have a smaller overall size. This limits the number of speed changing gears in the power transmission unit of an electric power tool, which tends to increase the difference in the speed reduction ratio between gears.

[0005] In the above electric power tool, during an actual task, for example, a task for tightening a bolt with a drill driver, when the load torque applied to the output shaft increases as the bolt is tightened, the control unit controls the power transmission unit to shift to a speed reduction gear having a large speed reduction ratio. However, when the increase of the load torque is caused by, for example, improper fastening of the bolt to a tightening portion that locks the tip tool (output shaft), that is, locks the motor, the electric power tool may apply a large recoil force to the hand of a user or the like when shifting to a speed reduction gear having a large speed reduction ratio. Particularly, as described above, in the power transmission unit, when the difference in the speed reduction ratio between gears is large, the recoil force applied to the user by the electric power tool further increases immediately after shifting to a gear having a large speed reduction ratio.

[0006] To solve the above problem, it is an object of the present invention to provide an electric power tool and a control device for the electric power tool that properly change speeds and detect motor locking.

MEANS FOR SOLVING THE PROBLEM

[0007] One aspect of the present invention is an electric power tool. The electric power tool includes a motor, a power transmission unit configured to decelerate rotational power of the motor and transmit the rotational power to an output shaft and configured to be capable of changing a speed reduction ratio, a speed shift actuator configured to shift the speed reduction ratio of the power transmission unit, a torque detector configured to detect a load torque applied to the output shaft, and a controller configured to control the speed shift actuator to shift the speed reduction ratio of the power transmission unit in accordance with the detected load torque. When the load torque detected by the torque detector increases within a predetermined period from a speed shifting condition threshold, which is set to perform a control that increases the speed reduction ratio, to a locking condition threshold, which is set to detect locking of the motor, the controller determines that the motor is locked and does not perform the control for increasing the speed reduction ratio of the power transmission unit.

[0008] In the above configuration, preferably, when the load torque detected after performing the control for increasing the speed reduction ratio of the power transmission unit reaches a locking condition threshold that is set corresponding to the speed reduction ratio subsequent to the speed shifting, the controller determines that the motor is locked.

[0009] In the above configuration, preferably, when a change amount of the load torque detected after performing the control for increasing the speed reduction ratio of the power transmission unit reaches a locking condition threshold that is set corresponding to the speed reduction ratio subsequent to the speed shifting, the controller determines that the motor is locked.

[0010] In the above configuration, preferably, the electric power tool includes a rotation detector configured to detect rotation speed of the motor. In this case, preferably, the controller determines whether or not the motor is locked based on the load torque detected by the torque detector and the rotation speed detected by the rotation detector.

[0011] In the above configuration, preferably, the electric power tool includes an acceleration sensor configured to detect displacement of the electric power tool in a rotation direction of the output shaft. In this case, preferably, the controller determines that the motor is locked based on the displacement of the electric power tool detected by the acceleration sensor.

[0012] In the above configuration, preferably, the controller is configured to deactivate or decelerate the motor when determining that the motor has been locked.

[0013] In the above configuration, preferably, the controller is configured to perform a slow start control that increases the rotation speed of the motor more gradually than that in normal operation when reactivating the motor after the motor is deactivated.

[0014] Another aspect of the present invention is a control device of an electric power tool. The electric power tool includes a motor, a power transmission unit configured to decelerate rotational power of the motor and transmit the rotational power to an output shaft and configured to be capable of changing a speed reduction ratio, a speed shift actuator configured to change the speed reduction ratio of the power transmission unit, and a torque detector configured to detect a load torque applied to the output shaft. The control device of the electric power tool includes a controller configured to control the speed shift actuator to change the speed reduction ratio of the power transmission unit in accordance with the detected load torque. When the load torque detected by the torque detector increases within a predetermined period from a speed shifting condition threshold, which is set to perform a control that increases the speed reduction ratio, to a locking condition threshold, which is set to detect locking of the motor, the controller determines that the motor is locked and does not perform the control for increasing the speed reduction ratio of the power transmission unit.

EFFECTS OF THE INVENTION

[0015] The present invention provides an electric power tool and a control device for the electric power tool that properly change speeds and detect motor locking.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 

Fig. 1 is a schematic diagram of one embodiment of an electric power tool.

Figs. 2A to 2C are charts illustrating locking detection based on the load torque, and Fig. 2D is a chart showing reactivation after the motor locking.

Fig. 3 is a schematic diagram of another electric power tool.

Fig. 4 is a schematic diagram of another electric power tool.

EMBODIMENTS OF THE INVENTION

[0017] One embodiment of the present invention will now be described with reference to the drawings.

[0018] As shown in Fig. 1, an electric power tool 10 of the embodiment, which is used, for example, as a drill driver, includes an electric power tool main body 11 and a battery pack 12, which is coupled in a removable manner to the battery pack 12. The electric power tool main body 11 includes a motor 21, which is driven by driving power supplied from the battery pack 12, a power transmission unit 22, which decelerates and outputs rotational power of the motor 21, and a controller 23, which entirely controls the electric power tool 10 such as the motor 21. The battery pack 12 includes a rechargeable battery formed from a plurality of battery cells (for example, lithium ion batteries).

[0019] A rotation shaft 24 of the motor 21 is connected to the power transmission unit 22, which includes a speed reduction mechanism, a clutch mechanism, and the like. The power transmission unit 22 decelerates rotational power of the motor 21 and transmits the rotational power of the motor 21 to an output shaft 25. The power transmission unit 22 includes, for example, two speed reduction gears (H gear and L gear) and is capable of changing the speed reduction ratio in two stages. A tip tool 26 (bit) is attached to a distal end of the output shaft 25. Thus, in the electric power tool 10, when the rotational power of the motor 21 is decelerated by the power transmission unit 22 and output to the output shaft 25, the tip tool 26 rotates together with the output shaft 25. In the power transmission unit 22, the speed reduction ratio of the L gear is set to be larger than that of H gear. That is, the L gear rotates at a lower speed and has a larger torque than the H gear.

[0020] The power transmission unit 22 includes a speed shift actuator 27, which is used to change the speed reduction ratio. The speed shift actuator 27, which is, for example, a motor actuator, is supplied with driving power from a gearshift drive unit 28 under the control of the controller 23. The speed shift actuator 27 shifts the speed reduction gear of the power transmission unit 22 under the control of the controller 23 with the gearshift drive unit 28. The controller 23 operates on voltage-adjusted power supplied from the battery pack 12. The gearshift drive unit 28 is formed by, for example, an H bridge circuit including switching elements (for example, field effect transistors (FETs)). The gearshift drive unit 28 controls the rotation direction of a motor of the speed shift actuator 27 based on a control signal from the controller 23. Additionally, the speed shift actuator 27 controls the driving power supplied to the motor of the speed shift actuator 27 by executing pulse width modulation (PWM) control on the speed shift actuator 27 based on a control signal from the controller 23.

[0021] The motor 21 is driven to generate rotation when supplied with driving power generated by a switching drive circuit 29, which is formed by, for example, an H bridge circuit including switching elements (for example, FETs). Based on the PWM control performed by the controller 23, the switching drive circuit 29 controls the driving power supplied to the motor 21 from the power supplied by the battery pack 12. That is, the controller 23 controls the rotation speed of the motor 21 by controlling the power supplied to the motor 21 with the switching drive circuit 29.

[0022] The electric power tool main body 11 includes a trigger switch 31, which a user may operate. The trigger switch 31, which is operated to activate or deactivate the motor 21, provides the controller 23 with an output signal corresponding to an operated amount of the trigger switch 31 (pulled amount of a trigger). Then, based on the output signal received from the trigger switch 31, the controller 23 controls the power supplied to the motor 21 with the switching drive circuit 29 to activate or deactivate the motor 21 and adjust the rotation speed of the motor 21.

[0023] A current detector 41, which detects a drive current supplied to the motor 21, is arranged between the switching drive circuit 29 and the motor 21. The current detector 41 includes a detection resistor 42, which is connected between the switching drive circuit 29 and the motor 21, and an amplifier circuit 43 (operational amplifier), which amplifies the voltage between terminals of the detection resistor 42 and supplies the amplified voltage to the controller 23 as a detection signal. The current detector 41 is one example of a torque detector. The controller 23 detects the drive current based on the detection signal received from the current detector 41 in predetermined sampling intervals. Then, based on the detected drive current and the speed reduction gear of the power transmission unit 22 when the drive current is detected, the controller 23 detects the load torque applied to the output shaft 25 (tip tool 26). Additionally, based on the detected load torque, the controller 23 detects locking of the motor 21 and controls the motor 21.

[0024] The rotation shaft 24 of the motor 21 includes a rotation detector 51, which is used to detect the rotation speed of the motor 21. The rotation detector 51 includes a sensor magnet 52, which is fixed to and rotated integrally with the rotation shaft 24 and includes a plurality of magnetic poles, and a hall element 53, which is opposed to the sensor magnet 52. The hall element 53 provides the controller 23 with a detection signal when the magnetic flux changes as the sensor magnet 52 rotates. Based on the detection signal received from the rotation detector 51, the controller 23 detects the rotation speed of the motor 21. The controller 23 also detects locking of the motor 21 from the changes in the rotation speed of the motor 21.

[0025] The controller 23 controls the shifting of the speed reduction gear of the power transmission unit 22 with the speed shift actuator 27 based on the detected load torque so that gears are automatically shifted in the electric power tool 10. Here, the speed reduction mechanism of the power transmission unit 22 is, for example, a planetary gear speed reduction mechanism including a sun gear, which is driven to rotate around an axis of the rotation shaft 24 of the motor 21, planetary gears, which are located around the sun gear and meshed with the sun gear, and a ring gear, which is meshed with the planetary gears. The speed shift actuator 27 changes the position of the ring gear to change the planetary gear that is meshed with the ring gear. This allows speed reduction gears to be shifted. Here, a drive condition detector may be used to detect whether or not the ring gear has been changed to a correct position by the speed shift actuator 27. In this case, the controller 23 controls the speed shift actuator 27 based on a detection signal of the drive condition detector.

[0026] In the electric power tool 10 configured in the above manner, when the trigger switch 31 is pulled by a user, an output signal corresponding to the pulled amount is provided to the controller 23. Based on the output signal received from the trigger switch 31, the controller 23 controls the activation, deactivation, and rotation speed of the motor 21 with the switching drive circuit 29. The rotational power of the motor 21 is decelerated by the power transmission unit 22 and transmitted to the output shaft 25. This rotates the tip tool 26. Further, the controller 23 changes the speed reduction gear of the power transmission unit 22 to the H gear or the L gear based on the load torque. In this case, when the load torque is small, the H gear is selected in the power transmission unit 22. This drives the tip tool 26 at a high rotation speed with a low torque. When activated, the H gear is selected in the power transmission unit 22. As the load torque increases and exceeds a predetermined torque, the L gear is selected in the power transmission unit 22. This drives the tip tool 26 at a low rotation speed with a high torque. Based on the detection signal received from the rotation detector 51 and the detection signal received from the current detector 41, the controller 23 detects locking of the motor 21 and determines whether or not to deactivate the motor 21.

[0027] The detection of the locking of the motor 21 will now be described.

[0028] In addition to the load torque detected by the current detector 41, based on the rotation speed of the motor 21 detected by the rotation detector 51, the controller 23 performs locking detection in the motor 21. In the following description, first, the locking detection performed by the current detector 41 will be described. Then, the locking detection performed by the rotation detector 51 will be described. Then, the control of the motor 21 performed after detecting locking and deactivating the motor 21 will be described.

[0029] The lock detection based on the load torque used before shifting gears (when in the H gear) will now be described.

[0030] Fig. 2A is a graph showing the change in load torque T when the electric power tool 10 is being driven with the H gear. For example, during a task for tightening a bolt with the electric power tool 10, when the task is started at time t0, the load torque changes. The load torque starts increasing from time t1 as the bolt tightens. In this case, when the tip tool 26 (motor 21) is locked at time t2, the load torque T suddenly increases. In the controller 23, a threshold S1 is set as a speed shifting condition. When the detected load torque T exceeds the threshold S1, the controller 23 performs a control for increasing the gear reduction ratio. In the present embodiment, the controller 23 shifts the speed reduction gear from the H gear to the L gear. Also, in the controller 23, a threshold S2 is set as a locking condition. When the detected load torque T exceeds the threshold S2, the controller 23 detects locking of the motor 21. Here, the threshold S2 is set to be a larger torque value than the threshold S1.

[0031] When the load torque T exceeds the threshold S1 and quickly increases to the threshold S2 within a short predetermined period, the controller 23 determines that the motor 21 has been locked and deactivates the motor 21 (time t3). That is, when the load torque T increases from the speed shifting condition threshold S1 to the locking condition threshold S2 within the predetermined period, the controller 23 determines that the motor 21 has been locked. When detecting such locking, the controller 23 does not shift to the L gear even when the load torque T has exceeded the threshold S1.

[0032] The controller 23 does not detect the locking condition and the speed shifting condition during a predetermined period after the motor 21 is activated. More specifically, in Fig. 2A, immediately after time t0, which is when the motor 21 is activated, activation current is generated in the motor 21. When the activation current is converted to the load torque T, the drive current may have a larger value than the locking condition threshold S2. Therefore, the detections of the locking condition and the speed shifting condition are not performed during the predetermined period after time t0, which is when the motor 21 (electric power tool 10) is activated. This obviates erroneous lock detections resulting from an initial operation such as during normal operation, when resuming an interrupted task, or when loosening a tightened bolt.

[0033] The time of the period in which the locking condition is not detected may be set differently from that of the period in which the speed shifting condition is not detected. For example, the period in which the locking condition is not detected may be set to be longer than that the period in which the speed shifting condition is not detected. For example, when resuming an interrupted task that had been performed with a high torque such as the tightening of a long screw, a high current is needed during the time from the reactivation until when the rotation speed of the screw is increased. Thus, the period in which the speed shifting condition is not detected is set to be shorter than the period in which the locking condition is not detected. When resuming such a high torque task as described above, this allows for deceleration without deactivating the motor 21 due to a locking detection. Thus, the task may be preferably performed.

[0034] The locking detection based on the load torque after shifting speeds (to the L gear) will now be described.

[0035] As shown in Fig. 2B, when the electric power tool 10 is driven with the H gear and the load torque T reaches the threshold S1 at time t4, the controller 23 determines that the load torque T has reached the speed shifting condition (threshold S1) and controls the power transmission unit 22 to shift gears from the H gear to the L gear. When shifted to the L gear, the increasing rate of the load torque T is more moderate than that in Fig. 2A.

[0036] In the controller 23, a threshold S3 (locking condition) is set to detect locking based on the load torque T after shifting speeds (L gear), is set. After shifting to the L gear and generating the activation current, when the load torque T reaches the threshold S3 at time t5, the controller 23 determines that locking has occurred and deactivates the motor 21. The threshold S3, which corresponds to the L gear subsequent to the speed shifting, is set to be a smaller value than the threshold S2, which corresponds to the H gear shown in Fig. 2A. This is because the speed reduction gears have a different speed reduction ratio, which results in a different load toque T even when the drive current is the same. Therefore, the thresholds S2 and S3 are set to be different values in correspondence with the speed reduction ratios of the speed reduction gears (H gear and L gear). In this manner, the locking detection may be suitably performed for each speed reduction gear even if the load torque T is increased and the speed is changed when locking occurs.

[0037] A locking detection based on a change amount ΔT of the load torque will now be described.

[0038] In addition to the locking detection using the thresholds S2 and S3 (absolute values), the controller 23 performs a locking detection using a change amount ΔT. As shown in Fig. 2C, the controller 23 calculates the change amount ΔT of the load torque T (change amount ΔI of the drive current) in predetermined time intervals and detects locking by comparing the calculated change amount ΔT with a threshold S4 (locking condition). Here, in an example shown in Fig. 2C, when the H gear is selected, the locking detection using the change amount ΔT of the load torque T is not performed. More specifically, when the load torque T has reached the threshold S1 at time t6, the controller 23 shifts from the H gear to the L gear. Subsequent to the speed shifting, when the change amount ΔT of the load torque T exceeds the threshold S4 at time t7, the controller 23 determines that locking has occurred and deactivates the motor 21. In this case, if the locking detection were to be performed using only the thresholds S2 and S3 for the absolute value of the load torque T in the manner described in the foregoing description, the absolute value of the load torque T may be limited. Thus, the thresholds S2 and S3 for the load torque T and the threshold S4 for the change amount ΔT are employed. This eliminates the influence that limits the absolute value of the load torque T and allows the detection of locking.

[0039] The locking detection using the rotation detector 51 will now be described.

[0040] The controller 23 detects locking based on the rotation speed of the motor 21 detected by the rotation detector 51. When locking occurs, the rotation speed of the motor 21 immediately decreases. Thus, the controller 23 performs the locking detection based on the load torque T and the rotation speed. For example, even when the load torque T exceeds the threshold S2 (refer to Fig. 2A), as long as the rotation speed has not decreased or the decrease rate is small, the controller 23 determines that the lock is not occurring. This improves the accuracy for detecting locking.

[0041] The control performed after the motor 21 is deactivated due to the locking detection (determination of the lock) will now be described.

[0042] After the lock is detected and the motor 21 is deactivated, when the motor 21 is subsequently reactivated, the controller 23 selects the H gear and performs a slow start control that increases the rotation speed of the motor 21 more gradually than that in normal operation. As shown in Fig. 2D, when determining that the motor 21 has been locked at time t8, the controller 23 deactivates the motor 21. The rotation speed (rotation speed N) of the motor 21 becomes null at time t9. Even when the motor 21 is deactivated, as long as the trigger switch 31 is continuously operated, the controller 23 reactivates the motor 21 at time t10. In this case, the controller 23 performs the slow start control, which increases the rotation speed (rotation speed N) of the motor 21 more gradually than that in normal operation. This inhibits sudden increases in the torque.

[0043] The embodiment has the advantages described below.

(1) The controller 23 of the electric power tool 10 detects the load torque T applied to the output shaft 25 from the drive current, which is supplied to the motor 21 and detected by the current detector 41. Further, the controller 23 controls the shifting of the speed reduction gears of the power transmission unit 22 based on the detected load torque T so that gears are automatically shifted in the electric power tool 10. As shown in Fig. 2A, when the load torque T is increased from the speed shifting condition threshold S1 to the locking condition threshold S2 within the predetermined period, that is, when the load T is immediately increased from the threshold S1 to the threshold S2, the controller 23 does not shift to the L gear, which increases the speed reduction ratio, and determines that the motor 21 has been locked. In other words, when the increase in the load torque T is not caused by an intended operation but is caused by the locking of the motor 21, the controller 23 detects the locking and does not perform speed shifting. This allows speed shifting and the locking detection to be performed in an appropriate manner and reduces large recoil forces applied to the user from the electric power tool 10 caused by the locking of the motor 21.

(2) After the power transmission unit 22 changes the speed to increase the speed reduction ratio (shifts from the H gear to the L gear), as shown in Fig. 2B, when the load torque T reaches the locking condition threshold S3, the controller 23 determines that locking has occurred. The threshold S3 is set to be a smaller value than the threshold S2, which corresponds to the H gear. In such a configuration, even when the load torque T is increased due to the occurrence of locking and the speed is changed, the locking detection may be appropriately performed in correspondence with the speed reduction gear. This reduces recoil forces applied to the user from the electric power tool 10.

(3) After the power transmission unit 22 shifts gears to increase the speed reduction ratio, as shown in Fig. 2C, the change amount ΔT of the load torque T becomes greater than or equal to the threshold S4 (lock condition), which is set in correspondence with the speed reduction ratio, the controller 23 determines that the motor 21 has been locked. Such a configuration eliminates the influence that limits the absolute value of the load torque and allows locking detection to be performed.

(4) The electric power tool 10 includes the rotation detector 51, which detects the rotation speed of the motor 21. The controller 23 detects locking based on the load torque T and the rotation speed detected by the rotation detector 51. This improves the accuracy for detecting locking.

(5) The controller 23 performs a control that deactivates the motor 21 when detecting locking. This reduces recoil forces applied to the user from the electric power tool 10 in a further ensured manner.

(6) When deactivating the motor 21 due to a locking detection, the controller 23 performs the slow start control that increases the rotation speed N, at which the motor 21 is subsequently activated, more gradually than that in normal operation. This inhibits a sudden increase in the torque and reduces recoil forces applied to the user from the electric power tool 10.

[0044] The embodiment of the present invention may be modified as follows.

[0045] In the above embodiment, the controller 23 deactivates the motor 21 after detecting locking. However, the controller 23 may be configured to decelerate the rotation generated by the motor 21. In such a configuration, the advantages described above may be obtained. Further, instead of controlling the deactivation and deceleration of the motor 21 based on the lock detection, for example, the user may be notified that locking has been detected to prompt the user to deactivate or decelerate the motor 21.

[0046] In the above embodiment, the load torque T is indirectly detected from the drive current supplied to the motor 21. However, there is no limit to such a configuration. For example, the torque applied to the output shaft 25 may be directly measured.

[0047] In the above embodiment, the controller 23 detects locking using the thresholds S2 and S3 of the drive current (absolute value) used before and after speed shifting, the threshold S4 of the change amount ΔT (ΔI), and the rotation speed of the motor 21. Instead, the lock detection may be performed using only one or a combination of at least two of these parameters.

[0048] The above embodiment may be configured to include an acceleration sensor, which detects displacement of the electric power tool 10 (electric power tool main body 11) in the rotation direction of the output shaft 25.

[0049] For example, as shown in Fig. 3, the controller 23 is incorporated into a battery pack seat 61, to which the battery pack 12 is attached, and the acceleration sensor 62 is mounted on a substrate of the controller 23. When the tip tool 26 (output shaft 25) locks and stops rotating, the electric power tool 10 rotates, and the acceleration sensor 62 detects the displacement of the electric power tool 10 as acceleration and provides the controller 23 with a detection signal. In Fig. 3, an arrow 63 indicates the rotation direction of the electric power tool 10 when locked, and an arrow 64 indicates the direction of the acceleration component that is detected. Such a configuration allows the controller 23 to detect the displacement of the electric power tool 10 caused by locking, that is, the locking of the motor 21, from the detection signal output from the acceleration sensor 62.

[0050] The acceleration of the electric power tool 10 increases as the distance between the tip tool 26 (output shaft 25) and the rotational center increases. Thus, the accuracy for detecting locking may be improved by arranging the acceleration sensor 62 at a position as far as possible from the rotational center. The acceleration sensor 62 may be arranged between the electric power tool main body 11 and the battery pack 12 or incorporated into the battery pack 12 and provide the controller 23 with the detection signal.

[0051] Further, in the acceleration sensor 62 described above, the direction and component of the acceleration that is detected are modified in correspondence with the structure of the electric power tool 10. For example, the electric power tool 10, when used as an electric saw as shown in Fig. 4, differs from the drill driver shown in Fig. 3 in the rotation direction of the tip tool 26 (circular saw blade) and how a user holds the electric power tool 10. Thus, in the acceleration sensor 62, the acceleration component that is detected is set based on the direction of the displacement (movement) of the electric power tool 10 when locked.

[0052] In the above embodiment, the configuration of the rotation detector 51 is one example. Thus, there is no limit to such a configuration. For example, a so-called photo-interrupter may be used. The photo-interrupter includes a rotation disc, in which slits are formed at equal intervals in the rotation direction of the motor 21 and which is coupled to the rotation shaft 24. The slits are detected during the rotation of the rotation disc. Additionally, the rotation detector 51 detects the rotation speed of the rotation shaft 24 of the motor 21. However, the rotation detector 51 may detect the rotation speed of another drive shaft, for example, the rotation speed of the output shaft 25.

[0053] In the above embodiment, the power transmission unit 22 is configured to shift between two speed reduction ratios. However, the power transmission unit 22 may be configured to shift to three or more speed reduction ratios.

[0054] In the above embodiment, the speed shift actuator 27 is a motor actuator. However, there is no limit to such an actuator using a motor as the drive source. A solenoid may be used.

[0055] In the above embodiment, the electric power tool 10 is embodied in the drill driver. However, the electric power tool 10 may be another electric power tool, for example, an impact driver, an impact wrench, a hammer drill, an impact drill, a jigsaw, a sealant gun, or the like.

Claims

1. An electric power tool comprising a motor, a power transmission unit configured to decelerate rotational power of the motor and transmit the rotational power to an output shaft and configured to be capable of changing a speed reduction ratio, a speed shift actuator configured to shift the speed reduction ratio of the power transmission unit, a torque detector configured to detect a load torque applied to the output shaft, and a controller configured to control the speed shift actuator to shift the speed reduction ratio of the power transmission unit in accordance with the detected load torque, the electric power tool being characterized in that
when the load torque detected by the torque detector increases within a predetermined period from a speed shifting condition threshold, which is set to perform a control that increases the speed reduction ratio, to a locking condition threshold, which is set to detect locking of the motor, the controller determines that the motor is locked and does not perform the control for increasing the speed reduction ratio of the power transmission unit.

2. The electric power tool according to claim 1, characterized in that when the load torque detected after performing the control for increasing the speed reduction ratio of the power transmission unit reaches a locking condition threshold that is set corresponding to the speed reduction ratio subsequent to the speed shifting, the controller determines that the motor is locked.

3. The electric power tool according to claim 1 or 2, characterized in that, when a change amount of the load torque detected after performing the control for increasing the speed reduction ratio of the power transmission unit reaches a locking condition threshold that is set corresponding to the speed reduction ratio subsequent to the speed shifting, the controller determines that the motor is locked.

4. The electric power tool according to any one of claims 1 to 3, characterized by
a rotation detector configured to detect rotation speed of the motor, wherein the controller is configured to determine whether or not the motor is locked based on the load torque detected by the torque detector and the rotation speed detected by the rotation detector.

5. The electric power tool according to any one of claims 1 to 4, characterized by
an acceleration sensor configured to detect displacement of the electric power tool in a rotation direction of the output shaft, wherein the controller is configured to determine that the motor is locked based on the displacement of the electric power tool detected by the acceleration sensor.

6. The electric power tool according to any one of claims 1 to 5, characterized in that the controller is configured to deactivate or decelerate the motor when determining that the motor has been locked.

7. The electric power tool according to claim 6, characterized in that the controller is configured to perform a slow start control that increases the rotation speed of the motor more gradually than that in normal operation when reactivating the motor after the motor is deactivated.

8. A control device of an electric power tool comprising a motor, a power transmission unit configured to decelerate rotational power of the motor and transmit the rotational power to an output shaft and configured to be capable of changing a speed reduction ratio, a speed shift actuator configured to change the speed reduction ratio of the power transmission unit, and a torque detector configured to detect a load torque applied to the output shaft, the control device of the electric power tool being characterized by:

a controller configured to control the speed shift actuator to change the speed reduction ratio of the power transmission unit in accordance with the detected load torque,

wherein when the load torque detected by the torque detector increases within a predetermined period from a speed shifting condition threshold, which is set to perform a control that increases the speed reduction ratio, to a locking condition threshold, which is set to detect locking of the motor, the controller determines that the motor is locked and does not perform the control for increasing the speed reduction ratio of the power transmission unit.

Drawing