CN116169908A - Electric tool and control method thereof - Google Patents

Abstract

The invention provides an electric tool and a control method thereof, comprising the following steps: a housing; a motor; a driving circuit; the current detection unit is used for acquiring motor current; torque setting means for setting an upper limit value of a rotational torque output from the electric tool; a current threshold setting unit that sets a first current threshold according to the upper limit value of the rotational torque set by the torque setting device; when the current of the motor is greater than or equal to a first current threshold, controlling the motor to be in a current limiting state, simultaneously acquiring operation parameters of the motor after the motor enters the current limiting state, and controlling the motor to exit the current limiting state when the parameters meet preset conditions; and after the motor exits the current limiting state, when the motor current is greater than or equal to the first current threshold value, the motor is turned off. By adopting the technical scheme, the electric tool with high torque control precision, low over-torque misjudgment rate and good hand feel for a user can be provided.

Description

Electric tool and control method thereof

Technical Field

The present invention relates to an electric tool, and more particularly, to an electric tool and a control method thereof.

Background

For hand-held power tools, such as power drills or screwdrivers, having a torque output function, it is often necessary to limit the torque output thereof to prevent damage to the workpiece or burnout of the motor. A mechanical overload clutch is arranged between a cutter workpiece and a motor in a common electric drill or screwdriver so as to limit output torque and prevent the occurrence of over-torsion. However, the mechanical overload clutch is relatively bulky and the accuracy of torque adjustment is relatively low. Currently, some torque output tools in the market limit output torque electronically, and turn off the motor when the motor current exceeds a preset current threshold. When the upper limit value of the output torque set by the user is smaller, the corresponding current threshold value is smaller. When the electric tool works, because the current threshold is set to be relatively small, the motor can possibly generate motor current to reach the current threshold under certain specific working conditions, but the torque output by the motor does not reach the preset upper limit value, or the motor current reaches the current threshold only in a very short time, and the torque reaches the preset torque upper limit value, but then the normal working state can be quickly restored. In this case, erroneous judgment is often caused, and particularly when the upper limit value of the torque force set by the user is relatively small, erroneous judgment is more likely to occur to turn off the motor, which seriously affects the use efficiency of the electric tool and the use feeling of the user. Accordingly, there is a need for further improvements in torque control methods employing clutches in existing power tools.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides a control method suitable for an electric tool, which can realize over-torsion protection and has low misjudgment rate, improves the use efficiency of the electric tool and enhances the use hand feeling of a user.

In order to achieve the above object, the present invention adopts the following technical scheme:

a power tool, comprising: a housing; a motor located within the housing; the driving circuit is electrically connected with the motor to drive the motor to run; a current detection unit for acquiring a motor current flowing through the motor; the torque setting device is used for receiving a torque setting instruction input by a user to set the upper limit value of the rotation torque output by the electric tool; a current threshold setting unit that sets a first current threshold according to an upper limit value of the rotational torque set by the torque setting device; the control unit is at least electrically connected with the driving circuit to control the motor to run, and obtains the motor current of the motor through the current detection unit; the control unit is configured to: when the current of the motor is greater than or equal to the first current threshold, controlling the motor to enter a current limiting state, simultaneously obtaining operation parameters of the motor after entering the current limiting state, and controlling the motor to exit the current limiting state when the parameters meet preset conditions; and after the motor exits the current limiting state, when the motor current is greater than or equal to the first current threshold value, the motor is turned off.

Further, the driving circuit includes a plurality of electronic switches;

the control module is electrically connected with the driving circuit, and outputs driving signals to control the states of the plurality of electronic switches so as to operate the motor.

Further, the operation parameter is set to an operation time, and the preset condition is set to a preset periodic time interval.

Further, the control unit is configured to:

when the motor is in the current limiting state, acquiring the motor current through the current detection unit in a periodic time interval; and when the acquired motor current exceeds the first current threshold, turning off the electronic switch in the on state in the residual time of the current time interval, and turning on the electronic switch which is controlled to be on by the control unit at present when the current time interval is over.

Further, the periodic time interval is less than or equal to the period of the drive signal.

Further, the electric tool further comprises a counting unit, wherein the counting unit is used for acquiring the rotation number of the motor.

Further, the operation parameter is set to a number of rotations of the motor, and the preset condition is set to a preset number of rotations.

Further, the current threshold setting unit sets a second current threshold according to an upper limit value of the rotational torque set by the torque setting device.

Further, the control unit is configured to:

when the motor is in the current limiting state, acquiring the rotation number of the motor through the counting unit;

when the number of rotations of the motor is smaller than the preset number of rotations, the motor current is obtained through the current detection unit, when the motor current is larger than or equal to the first current threshold, the electronic switch in a conducting state is closed, and when the obtained motor current is smaller than or equal to the second current threshold, the electronic switch which is controlled to be conducted currently by the control unit is opened.

Further, the first current threshold is greater than the second current threshold.

A control method of an electric tool, the electric tool comprising: a housing; a motor located within the housing; the driving circuit is electrically connected with the motor to drive the motor to run; a current detection unit for acquiring a motor current flowing through the motor; the torque setting device is used for receiving a torque setting instruction input by a user to set the upper limit value of the rotation torque output by the electric tool; a current threshold setting unit that sets a first current threshold according to an upper limit value of the rotational torque set by the torque setting device; the control unit is at least electrically connected with the driving circuit to control the motor to run; the control method comprises the steps that a control unit obtains motor current of the motor through the current detection unit; when the current of the motor is greater than or equal to the first current threshold, controlling the motor to enter a current limiting state, simultaneously obtaining operation parameters of the motor after entering the current limiting state, and controlling the motor to exit the current limiting state when the operation parameters meet preset conditions; and after the motor exits the current limiting state, when the motor current is greater than or equal to the first current threshold value, the motor is turned off.

Drawings

FIG. 1 is a schematic diagram of an embodiment of the present invention;

FIG. 2 is a block diagram of circuitry of the power tool of FIG. 1;

FIG. 3 is a control method flow diagram of one of the embodiments of torque control of the motor;

FIG. 4 is a flow chart of a method of controlling a motor in a second embodiment of torque control;

fig. 5 is a flowchart of a control method of the motor in the third embodiment of torque control.

Detailed Description

The invention is described in detail below with reference to the drawings and the specific embodiments.

Fig. 1 shows the present invention as an embodiment of an electric drill that provides at least torque assistance for driving a screw into a workpiece and provides an impact force for impact operation to meet different user needs. It will be apparent that the following examples are some, but not all, of the examples of the invention. The technical scheme provided by the invention can be suitable for most of torque output tools, such as impact wrenches, electric screwdrivers, electric scissors, chain saws and the like.

Fig. 1 is a schematic view of a specific example electric drill 100 as an electric power tool of the present invention. Referring to fig. 1 and 2, the electric drill 100 mainly includes a housing 11, a tool element 12, a grip portion 13, a trigger switch 14, a torque setting device 15, and a power supply device 16. The housing 11 defines an interior cavity in which the motor 111 is disposed, and in which a transmission (not shown) is also housed. The front end of the housing 11 is used for mounting the tool element 12. The motor 111 in turn drives a transmission, an output shaft (not shown) and thus the tool element 12 for performing a machining operation on the workpiece to be machined. Different tool elements 12 may be employed for different power tools. The tool element 12 in this example preferably employs a drill bit for driving a screw into the workpiece to be machined. The housing 11 is formed with a grip portion 13 for the operator's hand to grasp. The torque setting device 15 is configured to receive a torque setting command input by a user and set an upper limit value of a rotational torque output by the power tool. The power supply means 16 is electrically connected to the drill 100 to provide power to the drill 100. The power supply device 16 may be a battery pack or a mains connector. The power supply means 16 in this embodiment is preferably provided as a battery pack which is removably connected to the drill 100. The trigger switch 14 is used to implement the starting and speed regulating functions of the motor 111, and the trigger switch 14 may be, but is not limited to, a trigger, a knob, a sliding mechanism, etc. In the present embodiment, the trigger switch 14 is configured as a trigger mechanism.

As shown in fig. 2, the drill 100 further includes a control system 20 for controlling the operation state of the motor 111, and the control system 20 includes a power supply module 21, a driving circuit 22, and a control unit 23. The power supply module 21 is electrically connected to the power supply device 16 to supply the electric motor 111 with electric power for its operation. The driving circuit 22 is electrically connected to the motor 111 and the power supply module 21, and is configured to load the voltage of the power supply module 21 onto the motor 111 for the motor 111 to operate normally. The control unit 23 is electrically connected to the power supply module 21 and the driving circuit 22. The control unit 23 gives a driving signal to the driving circuit 22 to control the operation state of the motor 111.

The motor 111 is a three-phase motor having three-phase windings. The motor 111 may be an inner rotor motor or an outer rotor motor. In some embodiments, the motor 111 is an inner rotor brushless motor, alternatively, the motor 111 is an inner rotor permanent magnet synchronous brushless motor. In some embodiments, motor 111 is an external rotor brushless motor, alternatively motor 111 is an external rotor permanent magnet synchronous brushless motor. The drive circuit 22 is electrically connected to the three-phase windings of the motor 111.

The driving circuit 22 is electrically connected to the power supply module 21 to drive the operation of the motor 111. The input end of the driving circuit 22 receives the voltage from the power supply module 21, and distributes the voltage to each phase winding of the motor 111 in a certain logic relationship under the driving of the driving signal output by the control unit 23, so that the motor 111 starts and generates continuous torque. Specifically, the drive circuit 22 includes a plurality of electronic switches. The electronic switch may be a Field Effect Transistor (FET), although an insulated gate bipolar transistor (IG-BT) may be used. In some embodiments, the drive circuit 22 is a three-phase bridge circuit including three electronic switches Q1, Q3, Q5 in the high-order and three electronic switches Q2, Q4, Q6 in the low-order. The electronic switches Q1, Q3, and Q5 are provided between the power supply line of the power supply module 21 and each phase coil of the motor 111. Electronic switches Q2, Q4, Q6 are provided between each phase coil of the motor 111 and the ground. The six electronic switches Q1 to Q6 change the on or off state at a certain frequency according to the driving signal output from the control unit 23, thereby changing the power state of the power supply module 21 loaded on each phase winding of the motor 111.

The control unit 23 employs a dedicated controller, such as some dedicated control chip (e.g., MCU, microcontroller Unit). The control unit 23 is integrated with a signal processing unit, where the signal processing unit is configured to process the acquired related parameter signal, and has functions of calculation, comparison, judgment, and the like, and after the signal processing unit processes the signal, the signal processing unit can generate a driving signal and output the driving signal to the driving circuit 22 to drive the motor 111 to operate.

The control system 20 further includes a current detection unit 24, a torque setting unit 25, and a current threshold setting unit 26. The current detection unit 24 is electrically connected to the motor 111 and the control unit 23, and the control unit 23 acquires the motor current of the motor 111 through the current detection unit 24. The torque setting unit 25 acquires the instruction set by the torque setting device 15 to set the upper limit value of the output torque. The current threshold setting unit 25 is electrically connected to the torque setting unit 25 and the control unit 23. The current threshold setting unit 25 sets a corresponding current threshold according to the upper limit value of the output torque set by the torque setting unit 25.

The current detection unit 24 is used to acquire the motor current of the motor 111 during operation. It is to be understood that the motor current may be a bus current of the motor 111, and may be a phase current of each phase winding of the motor 111. In some embodiments, the current detection unit 24 includes a hall current sensor to directly detect the phase currents of the phase windings of the motor 111. In other embodiments, the current detection unit 24 includes a current sensing resistor. Specifically, the current detection unit 24 can calculate the phase current or the bus current of each phase winding by obtaining the voltages across the detection resistor, by respectively connecting the detection resistor in series between the drive circuit 22 and each phase winding of the motor 111. In other embodiments, the current detecting unit 24 obtains the internal resistance of the electronic switch in the on state in the driving circuit 22, and calculates the current passing through the electronic switch based on the internal resistance of the electronic switch in the on state and the voltage values at the two ends of the electronic switch, where the current of the electronic switch is the phase current of the winding of the corresponding motor 111. Thus, the electric tool can detect the phase current of the corresponding motor 111 winding without adding hardware, and the cost is saved.

The torque setting unit 25 is used for acquiring the instruction set by the torque setting device 15 to set the upper limit value of the output torque. In this embodiment, the torque setting device 15 uses an electronic torque ring to realize the function of torque setting. In some embodiments, the torque setting device 15 includes a dial ring disposed on the housing 11 for being shifted by a user, the dial ring is connected with a sliding rheostat, the user selects a suitable torque gear by manually operating the dial ring, and different torque gears correspond to the gears of the sliding rheostat. The torque setting unit 25 obtains the gear position of the slide rheostat to obtain the upper limit value of the output torque set by the current user.

The current threshold setting unit 26 is electrically connected to the torque setting unit 25 and the control unit 23. The current threshold setting unit 26 acquires the upper limit value of the output torque set by the torque setting unit 25 to set a current threshold corresponding to the upper limit value. The control unit 23 acquires a current threshold value corresponding to the upper limit value of the output torque set by the current user operation torque setting device 15 through the current threshold value setting unit 26.

In some embodiments, the user sets the gear of the torque output via the torque setting device 15, and then activates the trigger switch 14 to initiate operation of the motor 111. When the drill 100 is in a loaded condition, such as driving a screw into a workpiece, the torque force required by the motor 111 increases as the depth of penetration of the screw into the workpiece increases. When the screw is fully driven into the workpiece, the motor 111 will output a larger torque force to continue the load operation. The large torque force must correspond to a large current, and the torque force needs to be controlled to protect the normal operation of the motor 111, so as to avoid damage to the electric tool due to the large current. Of course, the over-twisting may occur not only when the screw is driven into the workpiece, but also when the output torque is too large. For example, the material of the workpiece is hard, and the workpiece cannot be driven continuously after the screw is driven into the part. Alternatively, the user often performs a locking operation when the locking operation is required after driving the screw. The present invention is not limited to the environment in which the control method of the present invention is used, and only some conditions in which excessive torque may occur are exemplified herein.

The flow of a control method for effectively controlling the torque force of the electric drill 100 will be described with reference to fig. 3, the method comprising the steps of:

s01: setting an upper limit value of the output torque of the motor and starting the motor;

s02: setting a current threshold of the motor;

s03: detecting motor current of a motor;

s04: judging whether the motor current of the motor is greater than or equal to a current threshold value, if so, executing step S05; if not, executing step S03;

s05: the motor is turned off.

In the control method, the motor current flowing through the motor is detected in real time and compared with a preset current threshold, and when the detected motor current is greater than or equal to the current threshold, the motor is controlled to be turned off. Before the motor is started, a user sets different torque output gears according to the needs, wherein the different torque output gears correspond to different upper limit values of the torque, and certainly correspond to different current thresholds. By the control method, the output torque of the electric tool can be controlled well under a certain environment, and damage to the electric tool caused by large current due to over-torsion is prevented. However, in the control method described above, when the upper limit value of the output torque force set by the user is small, the corresponding current threshold value is also relatively small. When the electric tool works, because the current threshold is set to be relatively small, the motor can possibly generate motor current to reach the current threshold under certain specific working conditions, but the torque output by the motor does not reach the preset upper limit value, or the motor current reaches the current threshold only in a very short time, and the torque reaches the preset torque upper limit value, but then the normal working state can be quickly restored. In this case, in the torque control method described in the above embodiment, erroneous judgment is usually generated, and particularly, when the upper limit value of the torque set by the user is relatively small, erroneous judgment is more likely to occur and the motor is turned off, which seriously affects the use efficiency of the electric tool and the use feel of the user.

It can be understood from the above embodiments that the probability of shutdown due to erroneous judgment is unavoidable, particularly when the set torque upper limit value is small. Next, a control method for reducing the false positive rate while the over-torsion protection will be described in detail.

The key of the control method for reducing the false positive rate is to delay shutdown when the control unit obtains that the motor current is equal to or greater than the first current threshold value. During the period of delayed shutdown, the current of the motor is limited to avoid the generation of large current. For the delay end judgment of the motor, the operation parameters of the motor, such as the operation time, the rotation number of the motor and the like, can be detected after the motor enters the current limiting mode. And when the motor is detected to be in the current limiting state, and the motor current is detected to be greater than or equal to a first current threshold value.

In some embodiments, the control unit 23 obtains the motor current of the motor 111 through the current detection unit 24, and controls the motor 111 to be in the first state when the motor current is greater than or equal to the first current threshold. Specifically, the first state may be understood as a current limiting state. When the motor 111 is in the current limiting state, the control unit 23 controls the motor 111 to operate at a motor current less than or equal to the first current threshold. Meanwhile, when the motor 111 is in the current limiting state, the control unit 23 acquires the operation parameters of the motor 111 and controls the motor 111 to exit the current limiting state when the operation parameters of the motor 111 satisfy the preset condition. After the motor 111 exits the current limit state, the control unit 23 continues to detect the motor current and turns off the motor when the motor current is greater than or equal to the first current threshold. Specifically, the operation parameter of the motor is set to the operation time of the motor, and the preset condition is a preset periodic time interval. When the motor 111 is in the current limiting state, the control unit 23 acquires the motor current through the current detection unit 24 at periodic time intervals; when the acquired motor current exceeds a first current threshold, the electronic switch in the on state is turned off in the residual time of the current time interval, and when the current time interval is finished, the electronic switch which is turned on and is currently controlled by the control unit is turned on.

A method for controlling the current of the motor after the over-torque to prevent erroneous judgment will be described with reference to fig. 4, which includes the steps of:

s11: acquiring motor current of a motor;

s12: judging whether a preset periodic time interval is over, if so, executing a step S17; if not, executing step S13;

s13: judging whether the motor current is greater than or equal to a first current threshold, if so, executing step S14; if not, executing step S15;

s14: turning off the electronic switch which is turned on currently;

s15: judging whether the current time interval is over, if so, executing the step S16; if not, executing step S11;

s16: starting the electronic switch which is controlled to be started currently by the control unit, and returning to the step S11;

s17: and controlling the motor to exit from the current limiting state.

The control method described above describes a current limiting strategy after the control unit 23 detects that the motor current is greater than or equal to the first current threshold in the current torque gear. It will be appreciated, of course, that the current limiting strategy described above is intended to improve the accuracy of the over-torque determination while ensuring that the current flowing through the motor does not exceed the first current threshold. In addition, it should be noted that the preset periodic time interval in the control method is set to a short time, for example, three switching cycles. The preset periodic interval period should be set according to the actual situation of the power tool, and should not be construed as limiting the present invention. It is further noted that different torque gear steps may be selected for the same predetermined periodic time interval or different periodic time intervals, without limitation.

And when the motor current is detected to be greater than the first current threshold again after the control unit controls the motor to exit the current limiting state after the operation parameters of the motor meet the preset conditions, the motor is controlled to be turned off. When the motor exits the current limit, the power tool has two possible operating conditions: in the first working condition, the motor is in a real over-torque state, and the current of the motor is larger than or equal to a first current threshold value; in the second working condition, the motor is in a normal running state, the current of the motor is smaller than a preset first current threshold, and the motor is not shut down but continues to run. It will be appreciated that in the first operating mode, the motor current may be less than the first current threshold at the moment the motor exits the current limiting state, and because of the current limiting, the control unit may control the drive circuit to be in the off state at the moment the motor exits the current limiting state, and the current at this moment may be less than the first current threshold. Thus, it is more appropriate to control the motor to be turned off when the motor current is once again detected to be equal to or greater than the first current threshold for a short time after the motor exits the current limit state.

The current control method for over-torsion judgment has obvious advantages on the electric tool with the electronic torsion ring. When the control unit 23 judges that the current motor is in an over-torque state through the motor current, the motor is not turned off immediately, the shutdown is delayed by adopting a current limiting strategy, and the current is limited to the motor during the period of time of delayed shutdown so as to protect the electric tool. And judging whether shutdown is needed or not through the motor current after the delay is finished. The technical scheme can improve the accuracy of over-torsion judgment of the electric tool, reduce the error judgment rate and improve the use hand feeling of a user. It will be appreciated that the above-described delayed shut down time (current limit time) is short and the effect of the large current caused by the motor operating at a motor current that does not exceed the first current threshold during the above-described short time is negligible.

In other embodiments, the operating parameter of the motor may be set to the number of motor revolutions after the motor enters a current limit state. The control system 20 further comprises a counting unit 27. The counting unit 27 is used to detect the number of rotations of the motor. The control unit 23 acquires the motor current of the motor 111 through the current detection unit 24, and controls the motor 111 to be in the first state when the motor current is greater than or equal to the first current threshold. Specifically, the first state may be understood as a current limiting state. When the motor 111 is in the current limiting state, the control unit 23 controls the motor 111 to operate at a motor current less than or equal to the first current threshold. Meanwhile, when the motor 111 is in the current limiting state, the control unit 23 acquires the operation parameters of the motor 111 and controls the motor 111 to exit the current limiting state when the operation parameters of the motor 111 satisfy the preset condition. After the motor 111 exits the current limit state, the control unit 23 continues to detect the motor current and turns off the motor when the motor current is greater than or equal to the first current threshold. Specifically, the operation parameter of the motor is set to the number of rotations of the motor, and the preset condition is the preset number of rotations.

Unlike the above-described embodiments, the current control method of the current limiting state in the present embodiment. Specifically, the current threshold setting unit 26 in the present embodiment sets the first current threshold and the second current threshold according to the torque upper limit value set by the current torque setting unit 25. Wherein the first current threshold in this embodiment is the same as the first current threshold in the above-described embodiments. The newly set second current threshold is smaller than the first current threshold. When the motor 111 is in the current-limiting state, the control unit 23 acquires the motor current through the current detection unit 24, turns off the currently-turned-on electronic switch when the motor current is greater than or equal to the first current threshold time, gradually decreases the motor current flowing through the motor at this time, and turns on the electronic switch currently controlled to be turned on by the control unit 23 when the control unit 23 detects that the motor current flowing through the motor is less than or equal to the second current threshold.

A method for controlling current in a current limiting state of a motor after over-twisting will be described with reference to fig. 5, which includes the steps of:

s21: acquiring motor current of a motor;

s22: judging whether the number of rotations of the motor is greater than or equal to a preset threshold value of the number of rotations, if so, executing step S27; if not, executing step S23;

s23: judging whether the motor current is greater than or equal to a first current threshold, if so, executing step S24; if not, executing step S25;

s24: turning off the electronic switch which is turned on currently;

s25: judging whether the motor current is smaller than or equal to a second current threshold, if so, executing step S26; if not, executing step S21;

s26: turning on the electronic switch which is controlled to be started currently by the control unit, and returning to the step S21;

s27: and controlling the motor to exit from the current limiting state.

The control method described above describes a current control method in which the control unit 23 enters the current limiting state in the present torque gear. It will be appreciated that the current limiting strategy described above is to improve the accuracy of the over-torque determination while ensuring that the current flowing through the motor does not exceed the first current threshold. In addition, the operation parameter of the motor in the present embodiment is set to the number of rotations of the motor, which is the number of rotations of the motor after the motor enters the current limiting state, and the count unit 27 obtains the number of rotations of the motor, which is the number of rotations of the motor after the motor enters the current limiting state. The preset condition in the present embodiment is set to a preset number of rotations, which should be set according to the actual situation of the electric tool, and is not to be construed as limiting the present invention. It is further noted that different torque gears may be selected for the same number of preset rotations or different preset rotations, without limitation.

As in the above embodiment, when the control unit controls the motor to exit the current limiting state after the operation parameter of the motor satisfies the preset condition, it again detects that the motor current is greater than the first current threshold, and controls the motor to be turned off. When the motor exits the current limit, the power tool has two possible operating conditions: in the first working condition, the motor is in a real over-torque state, and the current of the motor is larger than or equal to a first current threshold value; in the second working condition, the motor is in a normal running state, the current of the motor is smaller than a preset first current threshold, and the motor is not shut down but continues to run. It will be appreciated that in the first operating mode, the motor current may be less than the first current threshold at the moment the motor exits the current limiting state, and because of the current limiting, the control unit may control the drive circuit to be in the off state at the moment the motor exits the current limiting state, and the current at this moment may be less than the first current threshold. Thus, it is more appropriate to control the motor to be turned off when the motor current is once again detected to be equal to or greater than the first current threshold for a short time after the motor exits the current limit state.

Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims (11)

1. A power tool, comprising:

a housing;

a motor located within the housing;

the driving circuit is electrically connected with the motor to drive the motor to run;

a current detection unit for acquiring a motor current flowing through the motor;

the torque setting device is used for receiving a torque setting instruction input by a user to set the upper limit value of the rotation torque output by the electric tool;

a current threshold setting unit that sets a first current threshold according to an upper limit value of the rotational torque set by the torque setting device;

the control unit is at least electrically connected with the driving circuit to control the motor to run, and obtains the motor current of the motor through the current detection unit;

it is characterized in that the method comprises the steps of,

the control unit is configured to:

when the current of the motor is greater than or equal to the first current threshold, controlling the motor to enter a current limiting state, simultaneously obtaining operation parameters of the motor after entering the current limiting state, and controlling the motor to exit the current limiting state when the parameters meet preset conditions;

and after the motor exits the current limiting state, when the motor current is greater than or equal to the first current threshold value, the motor is turned off.

2. The power tool of claim 1, wherein the power tool comprises a power tool,

the driving circuit comprises a plurality of electronic switches;

the control module is electrically connected with the driving circuit, and outputs driving signals to control the states of the plurality of electronic switches so as to operate the motor.

3. The power tool according to claim 2, wherein,

the operation parameter is set to be operation time, and the preset condition is set to be a preset periodic time interval.

4. The power tool according to claim 3, wherein,

the control unit is configured to:

when the motor is in the current limiting state, acquiring the motor current through the current detection unit in a periodic time interval; and when the acquired motor current exceeds the first current threshold, turning off the electronic switch in the on state in the residual time of the current time interval, and turning on the electronic switch which is controlled to be on by the control unit at present when the current time interval is over.

5. The power tool of claim 4, wherein the power tool comprises a power tool,

the periodic time interval is less than or equal to the period of the drive signal.

6. The power tool according to claim 2, wherein,

the electric tool further comprises a counting unit, wherein the counting unit is used for acquiring the rotation number of the motor.

7. The power tool of claim 6, wherein the power tool comprises a power tool,

the operation parameter is set as the number of rotations of the motor, and the preset condition is set as the preset number of rotations.

8. The power tool of claim 7, wherein the power tool comprises a power tool,

the current threshold setting unit sets a second current threshold according to an upper limit value of the rotational torque set by the torque setting device.

9. The power tool of claim 8, wherein the power tool comprises a power tool,

the control unit is configured to:

when the motor is in the current limiting state, acquiring the rotation number of the motor through the counting unit; when the number of rotations of the motor is smaller than the preset number of rotations, the motor current is obtained through the current detection unit, when the motor current is larger than or equal to the first current threshold, the electronic switch in a conducting state is closed, and when the obtained motor current is smaller than or equal to the second current threshold, the electronic switch which is controlled to be conducted currently by the control unit is opened.

10. The power tool of claim 9, wherein the power tool comprises a power tool,

the first current threshold is greater than the second current threshold.

11. A control method of an electric tool, the electric tool comprising:

a housing;

a motor located within the housing;

the driving circuit is electrically connected with the motor to drive the motor to run;

a current detection unit for acquiring a motor current flowing through the motor;

the torque setting device is used for receiving a torque setting instruction input by a user to set the upper limit value of the rotation torque output by the electric tool;

a current threshold setting unit that sets a first current threshold according to an upper limit value of the rotational torque set by the torque setting device;

the control unit is at least electrically connected with the driving circuit to control the motor to run;

the control method comprises the following steps:

the control unit obtains the motor current of the motor through the current detection unit;

when the current of the motor is greater than or equal to the first current threshold, controlling the motor to enter a current limiting state, simultaneously obtaining operation parameters of the motor after entering the current limiting state, and controlling the motor to exit the current limiting state when the operation parameters meet preset conditions;

and after the motor exits the current limiting state, when the motor current is greater than or equal to the first current threshold value, the motor is turned off.

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