EP2724822B1

EP2724822B1 - Power tool

Info

Publication number: EP2724822B1
Application number: EP13182738.8A
Authority: EP
Inventors: Norihiro Iwamura; Masaki Ikeda
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2012-09-07
Filing date: 2013-09-03
Publication date: 2017-06-14
Anticipated expiration: 2033-09-03
Also published as: EP2724822A1; CN103659747A; JP2014050924A; JP5958817B2; CN103659747B

Description

The present invention relates to a power tool including a power transmission unit capable of shifting speed reduction ratios.
A power tool includes a power transmission unit, which reduces the speed of the rotational power produced by a motor, and a control unit, which controls the power transmission unit to automatically shift the speed reduction ratio of the power transmission unit (for example, refer to Japanese Laid-Open Patent Publication No. 2012-30347 ). Such a power tool includes an output shaft and a tip tool (bit), which is coupled to the output shaft. The load torque applied to the output shaft may be detected from the drive current supplied to the motor. The control unit shifts the speed reduction ratio of the power transmission unit based on the detected load torque.
Documents WO 2012/114815 A1 and WO 2012/114804 A1 disclose power tools comprising a speed reduction mechanism unit and a speed reduction ratio switching means. The speed reduction mechanism unit is formed from a switching member that slides in an axial direction and a gear member that engages with the switching member. The speed reduction ratio switching means has an actuator control unit which controls a drive adjustment unit so as to keep the sliding amount of the switching member constant over a given period.
Document US 2011/232933 A1 discloses a speed change device of a power tool, which reset arm is provided separately from a switch lever, which arm is operated by a reset motor.
The power transmission unit includes gears. An increase in the number of gears enlarges the power transmission unit. Since it is desirable that a power tool be compact, especially when the power tool is of a portable type, the number of gears in the power transmission unit is oftentimes limited to two. However, in such a case, when there are only two gears, the difference between two speed reduction ratios is large.
In an actual task using a power tool, such as a task for fastening a bolt with a drill driver, the load torque applied to the output shaft increases as the bolt becomes fastened. Thus, the control unit controls the power transmission unit to shift to a gear having a large speed reduction ratio. However, an increase in the load torque may occur when, for example, the bolt is not properly fastened to the fastened subject thereby causing locking of the tip tool (output shaft), that is, locking of the motor. In this case, when the power transmission unit shifts to a gear having a large speed reduction ratio, a large impact is applied from the power tool to the user. In particular, when the power tool uses a power transmission unit having a large speed reduction ratio difference, the power tool applies an even larger impact to the user immediately after shifting to the large speed reduction ratio.
It is an object of the present invention to provide a power tool that suppresses impacts applied to the user after shifting gears.
One aspect of the present invention is a power tool including a motor that generates rotational power. A power transmission unit transmits the rotational power from the motor to an output shaft. The power transmission unit is configured to reduce a rotation speed related to the rotational power and be capable of shifting a speed reduction ratio. A gear shift actuator shifts a speed reduction ratio of the power transmission unit. A torque detector detects a load torque applied to the output shaft. A control unit controls the gear shift actuator to shift the speed reduction ratio of the power transmission unit in accordance with the detected load torque. The control unit reduces an output of the motor until a predetermined time elapses from when the control unit increased the speed reduction ratio of the power transmission unit by controlling the power transmission unit.
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a schematic diagram of a power tool according to one embodiment of the present invention;
Fig. 2 is a flowchart illustrating an example of the operation of the power tool shown in Fig. 1;
Fig. 3 is a chart illustrating an example of the operation of the power tool shown in Fig. 1;
Fig. 4 is a flowchart illustrating an example of the operation in a modified power tool; and
Fig. 5 is a chart illustrating an example of the operation of the power tool shown in Fig. 4.

One embodiment of a power tool 10 will now be described.
The power tool 10 is used as, for example, a drill driver. As shown in Fig. 1, the power tool 10 includes a main body 11 and a battery pack 12, which is attached to the main body 11 in a removable manner. The main body 11 includes a motor 21, which is driven when supplied with electric power from the battery pack 12, a power transmission unit 22, which reduces the speed of the rotational power from the motor 21, and a control unit 23, which controls the power tool 10. The battery pack 12 includes a rechargeable battery formed by a plurality of battery cells (e.g., lithium-ion cells).
The motor 21 includes a rotation shaft 24. The power transmission unit 22, which includes a speed reduction mechanism and a clutch mechanism, is coupled to the rotation shaft 24. The power transmission unit 22 reduces the rotation speed of the rotational power obtained from the motor 21 and transmits the rotational power to an output shaft 25. The power transmission unit 22 includes two gears, namely, an H gear and an L gear. Thus, the speed reduction ratio of the power transmission unit 22 may be shifted between two steps. A tip tool 26 (bit) is coupled to the tip of the output shaft 25. Accordingly, the power tool 10 is configured to rotate the tip tool 26 together with the output shaft 25 by transmitting rotational power from the motor 21 via the power transmission unit 22 to the output shaft 25. The power transmission unit 22 is set so that the speed reduction ratio of the L gear is greater than the speed reduction ratio of the H gear. Thus, the L gear allows for low speed rotation with a high torque.
The power transmission unit 22 includes a gear shift actuator 27 that shifts the speed reduction ratio of the power transmission unit 22. The gear shift actuator 27 may be a motor actuator. The control unit 23 controls a gear shift driver 28 to supply the gear shift actuator 27 with a certain amount of electric power. The gear shift actuator 27 is operated by the electric power supplied from the gear shift driver 28. Accordingly, the gear shift actuator 27 shifts the gears of the power transmission unit 22 under the control of the control unit 23 via the gear shift driver 28. Further, the main body 11 of the power tool 10 includes a drive state detector 27a that detects the position of the gear shift actuator 27. Based on the position of the gear shift actuator 27 detected by the drive state detector 27a, the control unit 23 determines which one of the H gear and the L gear is selected in the power transmission unit 22. The control unit 23 runs on voltage-regulated electric power supplied from the battery pack 12. The gear shift driver 28 is formed by, for example, an H-bridge circuit using a switching element (e.g., FET). The control unit 23 provides the gear shift driver 28 with a control signal. Based on the control signal, the gear shift driver 28 changes the rotational direction of a motor for the gear shift actuator 27 and performs PWM control to supply the gear shift actuator 27 with electric power.
The main body 11 of the power tool 10 includes a switching drive circuit 29 formed by, for example, an H-bridge circuit using a plurality of switching elements (e.g., FETs). The switching drive circuit 29 supplies the motor 21 with drive power. The motor 21 generates rotation based on the electric power from the switching drive circuit 29. The control unit 23 controls the switching drive circuit 29 and performs PWM control on the electric power from the battery pack 12 to supply the motor 21 with electric power. In other words, the control unit 23 controls the electric power supplied to the motor 21 via the switching drive circuit 29. This controls the rotation speed of the motor 21.
The main body 11 of the power tool 10 includes a trigger switch 31 that may be operated by a user. The trigger switch 31, which is activated and deactivated by the user, starts and stops the motor 21. Further, the trigger switch 31 provides the control unit 23 with an output signal that is in accordance with the operation amount of the trigger switch 31 (pulled amount of trigger). The control unit 23 controls the electric power supplied to the motor 21 by the switching drive circuit 29 based on the output signal from the trigger switch 31 to start and stop the motor 21 and adjust the rotation speed of the motor 21.
The main body 11 of the power tool 10 includes a current detector 41 arranged between the switching drive circuit 29 and the motor 21 to detect the drive current supplied to the motor 21. The current detector 41 includes a detection resistor 42 and an amplification circuit 43 (operational amplifier). The detection resistor 42 is connected between the switching drive circuit 29 and the motor 21. The amplification circuit 43 amplifies the voltage across the terminals of the detection resistor 42 to generate a detection signal provided to the control unit 23. The control unit 23 detects the drive current based on detection signals from the current detector 41 taken in predetermined sampling cycles. Further, the control unit 23 detects the load torque applied to the output shaft 25 (tip tool 26) based on the detected drive current and the gear to which the power transmission unit 22 is shifted when the drive current is detected. The control unit 23 detects locking of the motor 21 based on the detected load torque and controls the motor 21 in accordance with the detection.
In the power tool 10, the control unit 23 controls the gear shift actuator 27 and automatically shifts the gears of the power transmission unit 22 based on the detected load torque. The speed reduction mechanism of the power transmission unit 22 is, for example, a planetary gear speed reduction mechanism. The speed reduction mechanism of the power transmission unit 22 includes a sun gear rotated about the axis of the rotation shaft 24 of the motor 21, planet gears engaged with the sun gear, and a ring gear engaged with the planet gears. The gear shift actuator 27 moves the ring gear to change the planet gear engaged with the ring gear. This controls the gear of the power transmission unit 22. The drive state detector 27a detects whether or not the gear shift actuator 27 has moved the ring gear to the correct position and provides the control unit 23 with a corresponding detection signal. The control unit 23 controls the gear shift actuator 27 based on the detection signal of the drive state actuator.
In the power tool 10, when the user pulls the trigger switch 31, the control unit 23 is provided with an output signal that is in accordance with the pulled amount. The control unit 23 controls the switching drive circuit 29 based on the output signal from the trigger switch 31 to start and stop the motor 21 and control the rotation speed of the motor 21. The power transmission unit 22 reduces the rotation speed of the rotational power from the motor 21 and transmits the rotational power to the output shaft 25 to rotate the tip tool 26. The control unit 23 shifts the gears of the power transmission unit 22 to the H gear or the L gear in accordance with the load torque. More specifically, the H gear is selected in the power transmission unit 22 when the load torque is small to drive the tip tool 26 at a high rotation speed with a small torque. When the power tool 10 is activated, the H gear is selected in the power transmission unit 22. When 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. Further, the control unit 23 detects locking of the motor 21 based on the detection signal from the current detector 41 and stops the motor 21 when detecting locking. After shifting to the L gear, the control unit 23 reduces the output of the motor 21.
An example of the operation of the power tool 10 will now be described.
Referring to Fig. 3, the power tool 10 is driven with the H gear, and the load torque (load current) reaches a threshold current I0 at time t0. The control unit 23 determines that the load torque T has satisfied a gear shift condition (reach threshold I0) and shifts the power transmission unit 22 from the H gear to the L gear. Here, the control unit 23 interrupts the supply of power to the motor 21.
Torque is proportional to current. Thus, until a predetermined time elapses from when the power transmission unit 22 is shifted from the H gear to the low gear L, the control unit 23 reduces the current (output) of the motor 21 in three steps in accordance with the elapsed time. The reduction of the current will now be described in detail.
Referring to Fig. 2, the control unit 23 uses the drive state detector 27a to detect the state of the gear shift actuator 27, that is, whether the H gear or the L gear is selected (step S10). When determining with the drive state detector 27a that the H gear is selected (step S10: NO), the control unit 23 continues to use the H gear.
When determining with the drive state detector 27a that the L gear is selected (step S10: YES), the control unit 23 determines whether or not a timer C has started to measure time (step S20).
When the timer C has not started time measurement (step S20: NO), the control unit 23 resets the timer C (step S21). Then, the control unit 23 starts measuring time with the timer C (step S22).
When the timer C has already started measuring time (step S20: YES) or when the timer C starts measuring time (step S22), the control unit 23 reduces the output in accordance with the elapsed time. More specifically, if the time elapsed from when the time measurement started is within time t2 (step S30: YES), the control unit 23 sets threshold I1 as the upper limit for the load current of the motor 21 (step S31). If the elapsed time from when the time measurement started is longer than or equal to time t2 (step S30: NO) but shorter than time t3 (step S32: YES), the control unit 23 sets threshold 12 as the upper limit for the load current of the motor 21 (step S33). If the elapsed time from when the time measurement started is longer than or equal to time t3 (step S32: NO) but shorter than time t4 (step S34: YES), the control unit 23 sets threshold I3 as the upper limit for the load current of the motor 21 (step S35). When the threshold I1, I2, or I3 is set in step S31, S33, or S35, the control unit 23 controls the switching drive circuit 29 so that the upper limit for the load current of the motor 21 is at the threshold I1, I2, or I3 (step S11). In this manner, by reducing the load current of the motor 21 in steps, sudden torque changes are suppressed. This reduces the impact applied to the user.
As shown in Figs. 2 and 3, if the elapsed time from when the time measurement started is longer than or equal to time t4 (step S34: NO), an upper limit is not set for the load current of the motor 21, that is, output reduction is not performed (step S36). The control unit 23 does not set an upper limit for the load current of the motor 21 and controls the switching drive circuit 29 in accordance with the pulled amount of the trigger switch 31 and the like. The control unit 23 operates the motor 21 with the maximum torque by cancelling the load current reduction control of the motor 21 so that the bolt may be completely fastened.
The present embodiment has the advantages described below.

(1) The control unit 23 reduces the output of the motor 21 until a predetermined time elapses from when the control unit 23 performs the control for increasing the speed reduction ratio of the power transmission unit 22. This reduces the impact after gears are shifted and suppresses the impact applied to the user.
(2) The control unit 23 gradually decreases the reduced amount of the load current (output) of the motor 21 as time elapses. This suppresses sudden torque changes and reduces the impact applied to the user.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.
In the above embodiment, the load current of the motor 21 is detected, and the output of the load current is suppressed. Instead, referring to the example shown in Figs. 4 and 5, since the load current of the motor 21 corresponds to the duty ratio of the switching element (FET) in the switching drive circuit 29, the duty ratio may be suppressed to obtain the same advantages of the above embodiment. In this case, the detection resistor 42 and the amplification circuit 43 that detect the load current of the motor 21 may be omitted.
The control shown in Figs. 4 and 5 will now be described. The process for using the H gear for driving and the process for shifting to the L gear are substantially the same as the above embodiment and will not be described in detail.
Referring to Fig. 5, when shifting the power transmission unit 22 from the H gear to the L gear, if the power transmission unit 22 shifts to the L gear when the supply of power to the motor 21 is interrupted, the control unit 23 reduces the duty ratio (output) of the motor 21 in three steps as time elapses until a predetermined time elapses from when the power transmission unit 22 shifted to the L gear.
Referring to Fig. 4, the control unit 23 uses the drive state detector 27a to detect the state of the gear shift actuator 27, that is, whether the H gear or the L gear is selected (step S10). When determining with the drive state detector 27a that the L gear is selected (step S10: YES), the control unit 23 determines whether or not a timer C has started to measure time (step S20).
When the timer C has not started time measurement (step S20: NO), the control unit 23 resets the timer C (step S21). Then, the control unit 23 starts measuring time with the timer C (step S22).
When the timer C has already started measuring time (step S20: YES) or when the timer C starts measuring time (step S22), the control unit 23 reduces the output in accordance with the elapsed time. More specifically, if the time elapsed from when the time measurement started is within time t2 (step S30: YES), the control unit 23 sets threshold D1 as the upper limit for the duty ratio of the motor 21 (step S41). If the elapsed time from when the time measurement started is longer than or equal to time t2 (step S30: NO) but shorter than time t3 (step S32: YES), the control unit 23 sets threshold D2 as the upper limit for the duty ratio of the motor 21 (step S42). If the elapsed time from when the time measurement started is longer than or equal to time t3 (step S32: NO) but shorter than time t4 (step S34: YES), the control unit 23 sets threshold D3 as the upper limit for the load current of the motor 21 (step S43). When the threshold D1, D2, or D3 is set in step S41, S42, or S43, the control unit 23 controls the switching drive circuit 29 so that the upper limit for the duty ratio of the motor 21 is at the threshold D1, D2, or D3 (step S11). In this manner, by reducing the duty ratio (output) of the motor 21 in steps, advantage (2) of the above embodiment is obtained.
As shown in Figs. 4 and 5, if the elapsed time from when the time measurement started is longer than or equal to time t4 (step S34: NO), an upper limit is not set for the duty ratio of the motor 21, that is, output reduction is not performed (step S44). The control unit 23 does not set an upper limit for the duty ratio of the motor 21 and controls the switching drive circuit 29 in accordance with the pulled amount of the trigger switch 31 and the like. The control unit 23 operates the motor 21 with the maximum torque by cancelling the duty ratio reduction control of the motor 21 so that the bolt may be completely fastened.
In the above embodiment, after shifting to the L gear, the output is suppressed in three steps but may be suppressed in one step or two steps. The output may also be suppressed in four or more steps.
In the above embodiment, as shown in Fig. 1, a rotation detector 51 may be used to detect locking of the motor 21 based on the rotation speed of the motor 21. The rotation detector 51 may be arranged on the rotation shaft 24 of the motor 21. The rotation detector 51 includes a sensor magnet 52, which is provided with magnetic poles fixed to and rotated integrally with the rotation shaft 24, and a Hall element 53, which is arranged opposing the sensor magnet 52. The Hall element 53 provides the control unit 23 with a detection signal indicating changes in the magnetic flux based on the rotation of the sensor magnet 52. The control unit 23 detects the rotation speed of the motor 21 based on the detection signal from the rotation detector 51. The control unit 23 also detects locking of the motor 21 from changes in the rotation speed. More specifically, the control unit 23 detects locking of the motor 21 from the rotation speed of the motor 21 detected by the rotation detector 51. When locking occurs in the motor 21, the rotation speed of the motor 21 suddenly decreases. Accordingly, the control unit 23 is configured to detect locking of the motor 21 based on both load torque T and rotation speed. For example, the control unit 23 determines that locking of the motor 21 is not occurring when the rotation speed does not decrease or the decreasing rate of the rotation speed is low. This increases the accuracy for detecting the locking of the motor 21.
In the above embodiment, the load torque T is indirectly detected from the load current supplied to the motor 21. Instead, the torque applied to the output shaft 25 may be directly measured.
In the above embodiment, the power transmission unit 22 shifts to two speed reduction ratios. Instead, the power transmission unit 22 may shift to three or more speed reduction ratios.
In the above embodiment, the gear shift actuator 27 includes a motor actuator. However, the gear shift actuator 27 does not have to use a motor as a drive source and may use a solenoid or the like instead.
In the above embodiment, the power tool 10 is embodied in a drill driver but may be embodied in a different type of power tool such as an impact driver, an impact wrench, a hammer drill, a vibration drill, a jigsaw, and a sealing gun.
The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Claims

A power tool (10) including:
a motor (21) that generates rotational power;

a power transmission unit (22) that transmits the rotational power from the motor (21) to an output shaft (25), wherein the power transmission unit (22) is configured to reduce a rotation speed related to the rotational power and be capable of shifting a speed reduction ratio;

a gear shift actuator (27) that shifts a speed reduction ratio of the power transmission unit (22);

a torque detector (41) that detects a load torque applied to the output shaft (25); and

a control unit (23) that controls the gear shift actuator (27) to shift the speed reduction ratio of the power transmission unit (22) in accordance with the detected load torque, the control unit (23) reduces an output of the motor (21) until a predetermined time elapses from when the control unit (23) increased the speed reduction ratio of the power transmission unit (22) by controlling the power transmission unit (22) the power tool being characterized in that:
the control unit (23) controls the gear shift actuator (27) to gradually decrease the reduced amount of the output of the motor as time elapses.
The power tool according to claim 1, being characterized in that:
the control unit (23) controls the gear shift actuator (27) to decrease the reduced amount of the output of the motor (21) in steps.
The power tool according to claim 2, being characterized by:
a timer (C) that measures time elapsed from when the speed reduction ratio of the power transmission unit (22) is changed,

wherein the control unit (23) controls the gear shift actuator (27) and gradually decreases the reduced amount of the output of the motor (21) in stages in accordance with the time measured by the timer (C).