Patent Publication Number: US-2021187635-A1

Title: Power tool  and method for starting the same

Description:
RELATED APPLICATION INFORMATION 
     The present application claims the benefit of Chinese Patent Application No. 201811085427.0, filed on Sep. 18, 2018, and Chinese Patent Application No. 201910021260.X, filed on Jan. 10, 2019, in the CNIPA (China National Intellectual Property Administration), each of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Power tools such as angle grinders and circular saws have a relatively large working current. The relatively large working current is generally carried by a high-current switch provided in a main circuit. The contacts of the high-current switch are prone to sparks, which may lead to deformation or failure of the contacts, bringing safety hazards. Therefore, there is an urgent need for a solution that prevents the failure of switch control when carrying a large current and improves the accuracy of switch control in power tools, and further improves power tool safety. 
     SUMMARY 
     The present application provides a power tool enabled to carry large currents and the switch control is not easy to fail. 
     This application adopts the following technical solutions: 
     A power tool including: a tool accessory; a motor for driving the tool accessory; a control module for controlling the operation process of the motor; a power supply module for providing electric power for the motor and the control module; an operating switch includes: a trigger mechanism; a current switch for connecting and disconnecting the electrical connection between the power supply module and the motor; the current switch is coupled to the trigger mechanism to be actuated by the trigger mechanism; a signal switch at least configured to output a control signal to the control module to control the start of the motor; the signal switch is coupled to the trigger mechanism to be actuated by the trigger mechanism. 
     A method for starting the power tool, the power tool further including: a drive circuit electrically connected to the motor and the power supply module; a power storage element operably connected with the drive circuit in parallel; the method for starting the power tool includes: turning on the current switch; after the current switch is turned on, charging the power storage element after delaying a predetermined time period. 
     A method for starting the power tool, the power tool further including: a drive circuit electrically connected to the motor and the power supply module; a power storage element operably connected with the drive circuit in parallel; the method for starting the power tool includes: turning on the current switch; after the current switch is turned on, charging or discharging the power storage element with a first current and then a second current; the value of the first current is less than the value of the second current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view of a power tool according to an example; 
         FIG. 2  is a schematic diagram of an example of a circuitry of the power tool shown in  FIG. 1 ; 
         FIG. 3A  is a structural diagram of an operating switch of the power tool shown in  FIG. 1 ; 
         FIG. 3B  is a schematic diagram of the relationship between the states of a current switch and a signal switch and the position of a trigger mechanism; 
         FIG. 4  is an external view of a power tool according to another example; 
         FIG. 5  is a schematic diagram of an example of a circuitry of the power tool shown in  FIG. 4 ; 
         FIG. 6  is an internal structure diagram of a handle portion of the power tool shown in  FIG. 4 , wherein a trigger mechanism of an operating switch is in a first position; 
         FIG. 7  is a structural diagram of the operating switch of the power tool shown in  FIG. 4 , wherein the trigger mechanism of the operating switch is in a second position; 
         FIG. 8  is an internal structure diagram of the handle portion of the power tool shown in  FIG. 4 , in which the trigger mechanism of the operating switch is in a third position; 
         FIG. 9  is a flowchart of the working process of the trigger mechanism being actuated to move from an initial position to an end position; 
         FIG. 10  is a flowchart of the working process of the trigger mechanism being actuated to move from the end position to the initial position; 
         FIG. 11A  is a schematic diagram of the state of each switch and the position of the trigger mechanism when the trigger mechanism is actuated to move from the initial position to the end position; 
         FIG. 11B  is a schematic diagram of the state of each switch and the position of the trigger mechanism when the trigger mechanism is actuated to move from the end position to the initial position; 
         FIG. 12  is a schematic diagram of an example of a circuitry of the power tool shown in  FIG. 4 ; 
         FIG. 13  is a flowchart of the working process of the operating switch and the working state of the power tool according to an example; 
         FIG. 14  is a structural diagram of the operating switch of the power tool shown in  FIG. 4 ; 
         FIG. 15  is a structural diagram of the operating switch of the power tool shown in  FIG. 4  from another perspective; 
         FIG. 16  is a structural diagram of the operating switch of the power tool shown in  FIG. 4  from another perspective; 
         FIG. 17  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 18  is a flowchart of the method for starting the power tool shown in  FIG. 17 ; 
         FIG. 19  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 20  is a flowchart of the method for starting the power tool shown in  FIG. 19 ; 
         FIG. 21  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 22  is a flowchart of the method for starting the power tool shown in  FIG. 21 ; 
         FIG. 23  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 24  is a flowchart of the method for starting the power tool shown in  FIG. 23 ; 
         FIG. 25  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 26  is a flowchart of the method for starting the power tool shown in  FIG. 25 ; 
         FIG. 27  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 28  is a flowchart of the method for starting the power tool shown in  FIG. 27 ; 
         FIG. 29  is a schematic diagram of the change of the output voltage of a battery pack when using the method for starting the power tool shown in  FIGS. 26 and 28 ; 
         FIG. 30  is a simplified diagram of an example of the circuitry of the power tool shown in  FIG. 12 ; 
         FIG. 31  is a flowchart of the method for starting the power tool shown in  FIG. 30 ; 
         FIG. 32  depicts the predetermined rotational speed thresholds corresponding to each duty cycle interval in the method for starting the power tool shown in  FIG. 31 ; and 
         FIG. 33  is a schematic diagram of the change of the rotational speed of the motor over time when using the method for starting the power tool shown in  FIGS. 26, 28 and 31 . 
     
    
    
     DETAILED DESCRIPTION 
     The application will be specifically introduced below in conjunction with the drawings and examples. 
     In this application, power tools can be hand-held power tools, gardening tools and so on. The power tools of this application may include the following: speed adjusting power tools such as screwdrivers, electric drills, wrenches, angle grinders, etc.; polishing power tools such as sanders, etc.; cutting power tools such as reciprocating saws, circular saws, jig saws, etc.; impacting power tools such as electric hammers, etc. The power tools may also be gardening tools, such as hedge trimmers and chain saws; in addition, these tools may also be used for other purposes, such as mixers. As long as these power tools adopt the substance of the technical solutions disclosed below, they fall within the protection scope of this application. 
     A power tool includes: a tool accessory for realizing the function of the power tool; a motor for driving the tool accessory; a control module for controlling the operation process of the motor; a power supply module for providing electric power for the motor and the control module; an operating switch operable to control the power tool; wherein the operating switch includes: a trigger mechanism to be operably actuated; a current switch for connecting and disconnecting the electrical connection between the power supply module and the motor; the current switch is coupled to the trigger mechanism to be actuated by the trigger mechanism; a signal switch at least configured to output a control signal to the control module to control the start of the motor; the signal switch is coupled to the trigger mechanism to be actuated by the trigger mechanism. 
     The following illustrates the implementation of the present application with two typical power tools as examples. 
     Referring to  FIGS. 1 and 2 , in an example, a power tool  10  takes a drill as an example, the structure of the drill shown in  FIG. 1  includes: a housing  11 , a tool accessory  12 , a motor  13 , and an operating switch  16 . Wherein the housing  11  is configured to accommodate the motor  13 , the circuit board, etc.; one end of the housing  11  is also configured to mount the tool accessory  12 . In the front-back direction, the housing  11  further includes a body housing portion  111  and a head housing portion  112 , wherein the body housing portion  111  can accommodate the motor  13  and a circuit board, and the head housing portion  112  can connect the tool accessory  12 . Taking the head housing portion as the front, in the left-right direction, the body housing portion  111  can be symmetrically arranged with respect to the section plane of the structure shown in  FIG. 1 . On two sides of the section plane, the body housing portion  111  may include mutually symmetrical left housing portion and right housing portion. 
     The housing  11  is formed with a handle, and the operating switch  16  is provided on the handle for the user to operate. The operating switch  16  is actuated by user operation to control the operation process of the power tool  10 . The tool accessory  12  is configured to realize the function of the power tool  10 . For an electric drill, the tool accessory  12  may be a drill bit. 
     As an alternative, the power tool further includes a transmission device  14 . The transmission device  14  is configured to transmit the power output by the motor  13  to the tool accessory  12 , thereby driving the tool accessory  12  to output power. 
     Referring to  FIG. 2 , to control the operation of the motor  13 , the power tool  10  further includes: a power supply module  18 , a control module  21 , a current switch SW 1  and a switch signal SW 2 . 
     The power supply module  18  is used to provide electric power for the power tool  10 , and the power supply module includes a DC power supply or an AC power supply. In some examples, the power supply module  18  includes a DC power supply, and in some examples, the power supply module  18  includes a battery pack. In other examples, the power supply module  18  includes an AC power supply, and the power tool  10  uses AC power supply. The AC power supply can be 120V or 220V AC mains. The power supply module includes an AC-DC power conversion circuit, which is connected to the AC power supply and converts the alternating current into electric power for the power tool  10 . 
     Optionally, the power tool further includes a drive circuit  22 , and the control module  21  is electrically connected to the drive circuit  22  for outputting drive signals for controlling operation of the drive circuit  22 . In some examples, the control module  21  uses a dedicated control chip, for example, a single chip microcomputer (MCU, Microcontroller Unit). 
     The drive circuit  22  is configured to drive the motor  13  to output power and is electrically connected to the motor  13 . The drive circuit  22  is also electrically connected with the control module  21  to receive drive signals from the control module  21 . The drive circuit  22  is electrically connected to the three-phase electrodes U, V, and W of the motor  13  to drive the motor  13  to operate. The drive circuit  22  shown in  FIG. 2  includes a plurality of drive switches VT 1 , VT 2 , VT 3 , VT 4 , VT 5 , and VT 6 ; the plurality of drive switches VT 1 , VT 2 , VT 3 , VT 4 , VT 5 , and VT 6  compose a three-phase bridge. The drive switch can be a MOSFET or an IGBT. The plurality of drive switches VT 1 -VT 6  change the connection state according to the drive signals output by the control module  21 , thereby changing the voltage state of the battery pack loaded on the windings of the motor  13  and generating an alternating magnetic field to drive the rotor to rotate, thereby realizing the drive of the motor  13 , driving the motor  13  to run. 
     The operating switch  16  includes a trigger mechanism  161 ; the trigger mechanism  161  can be operated by a user. The trigger mechanism  161  may be, for example, a trigger. The operating switch  16  further includes a current switch SW 1  and a signal switch SW 2 . The current switch SW 1  and the signal switch SW 2  are coupled to the trigger mechanism  161  to be actuated by the trigger mechanism  161 . 
     The current switch SW 1  is configured to switch on or off the electrical connection between the power tool  10  and the power supply module  18 . In some examples, one end of the current switch SW 1  is electrically connected to the power supply module  18 , and the other end is electrically connected to the drive circuit  22 . The drive circuit  22  can be electrically connected or disconnected from the power supply module  18  through the current switch SW 1 . The current switch SW 1  is actuated by the trigger mechanism  161  to switch between the on state and the off state. When the current switch SW 1  is in the on state, the power tool  10  is electrically connected to the power supply module  18 , and the power supply module  18  supplies power to the power tool  10 . When the current switch SW 1  is in the off state, the electrical connection between the power tool  10  and the power supply module  18  is disconnected, and the power supply module  18  stops supplying electric power to the power tool  10 . 
     The signal switch SW 2  at least enables the control module  21  to control the motor  13  to start. In some examples, one end of the signal switch SW 2  is electrically connected to the control module  21 ; the control module  21  can obtain electrical signals indicating on or off state of the switch SW 2 . The signal switch SW 2  is coupled to the trigger mechanism  161  to be actuated by the trigger mechanism  161 . The signal switch SW 2  is actuated by the trigger mechanism  161  to switch between the on state and the off state. The signal switch SW 2  is electrically connected to the control module  21 . When the signal switch SW 2  is in different states, it outputs different electrical signals to the control module  21 . The control module  21  outputs a control signal according to the electrical signal output from the signal switch SW 2  to control the drive circuit  22  to control the motor  13  to start or not to start. 
     Referring to  FIG. 3B , the trigger mechanism  161  may be actuated to reach different positions. When the trigger mechanism  161  is actuated to reach the first position L 11 , the current switch SW 1  is actuated and changes its on-off state to enable the electrical connection between the power supply module  18  and the power tool  10 ; when the trigger mechanism  161  is actuated to reach the second position L 12 , the signal switch SW 2  is actuated and changes its on-off state, so that the control module  21  controls the motor  13  to start. During the process that the trigger mechanism  161  is actuated to move from an initial position Ls 1  to an end position Le 1 , the trigger mechanism  161  sequentially reaches a first position L 11  and the second position L 12 . The “on-off state” refers to the on state and the off state of the current switch SW 1  and the signal switch SW 2 . In other words, during the startup process of the motor  13 , the current switch SW 1  and the signal switch SW 2  are actuated by the trigger mechanism  161  in a different order. The “initial position Ls 1 ” of the trigger mechanism  161  in this application refers to the position where the operating switch  16  is not operated and the trigger mechanism  161  is not actuated, and the “end position Le 1 ” refers to the position far from the initial position when the trigger mechanism  161  stops moving forward after the motor  13  is started. The “end position Le 1 ” may be a third position L 13 , or may be a position farther from the original position Ls 1  with respect to a third position L 13 . The trigger mechanism  161  is, for example, a trigger, and the “position” of the trigger mechanism  161  may refer to the angular position of rotating the trigger. 
     The current switch SW 1  at least includes two pairs of contacts, and each pair of contacts is connected by a metal conductor. Optionally, the metal conductor is a copper sheet. 
     Referring to  FIGS. 2 and 13 , the current switch SW 1  has two pairs of contacts, wherein contact A and contact B composes a pair of contacts; contact A′ and contact B′ composes a pair of contacts, wherein contact A and contact A′ are movable contacts; contact B and contact B′ are stationary contacts. Contact A may follow the movement of the trigger mechanism  161  to connect or disconnect contact B; contact A′ may follow the movement of the trigger mechanism  161  to connect or disconnect contact B′. The two pairs of contacts are connected in parallel, and the current switch SW 1  uses at least two pairs of contacts to carry all the current output by the power supply module  18 , which prevents the contacts of the current switch SW 1  from sparking due to carrying large currents. 
     In this example, a copper sheet may be used as the structure of electrical connection between contact A and contact B; another copper sheet may be used as the structure of electrical connection between contact A′ and contact B′. The two branches connected to the copper sheet carry the current from the power supply module  18  in parallel. Because the copper sheet has good conductivity and good heat dissipation characteristics, this connection method, on the one hand, effectively solves the problem of sparking between the switch contacts at the moment of high current being turned on, and on the other hand, cools the current switch with the copper sheet arranged on the surface of the switch. 
     The trigger mechanism  161  is coupled to the movable contacts of the current switch SW 1 , so that the current switch SW 1  is switched between the ON state and the OFF state by the trigger mechanism  161 . In some examples, when the trigger mechanism  161  is pressed down such that the current switch SW 1  is in the ON state, as shown in  FIG. 2 , contact A and contact B of the current switch SW 1  are connected, contact A′ and contact B′ of the current switch SW 1  are connected, at the same time, contact A′ and contact B′ of the current switch SW 1  are electrically connected; the electrical connection between the power supply module  18  and the power tool  10  is turned on; the power supply module  18  supplies power to the power tool  10 . In some examples, the power supply module  18  supplies power to the drive circuit  22 , the control module  21  and motor  13 . When the trigger mechanism  161  is pressed down such that the current switch SW 1  is in the OFF state, as shown in  FIG. 2 , contact A and contact B of the current switch SW 1  are electrically disconnected, at the same time, contact A′ and contact B′ of the current switch SW 1  are electrically disconnected, the power supply module  18  stops supplying power to the power tool  10 . In some examples, the power supply module  18  stops supplying power to the drive circuit  22 , the control module  21 , and the motor  13 . 
     The trigger mechanism  161  is provided with a projection on the surface, and the projection is used to trigger the signal switch SW 1 . Referring to  FIG. 3A , the above mentioned trigger mechanism  161  is provided with a projection  162  on the upper portion, the projection  162  can be pressed or released with the trigger mechanism  161 , and correspondingly actuate the signal switch SW 2  through a rocker  163 , allowing the signal switch SW 2  to be actuated by the trigger mechanism to switch between the on state and the off state. The signal switch SW 2  outputs different electrical signals to the control module  21  in the on state and the off state, and the control module  21  outputs different drive signals according to the different electrical signals to control the drive circuit  22 . 
     The current switch SW 1  and the signal switch SW 2  are actuated by the trigger mechanism  161  in a different order. During the process that the trigger mechanism  161  is actuated to move from the initial position Ls 1  to the end position Le 1 , the trigger mechanism  161  sequentially reaches the first position L 11  and the second position L 12 . 
     In some examples, after the operating switch  16  is manipulated and the trigger mechanism  161  is actuated, firstly, when the trigger mechanism  161  is actuated to reach the first position, the current switch SW 1  is turned on, the main circuit is turned on, and the power tool  10  and the power supply module  18  are electrically connected, the power tool  10  is powered on; then, when the trigger mechanism  161  is actuated to reach the second position, the trigger mechanism  161  presses the signal switch SW 2  through the projection  162  and the rocker  163  to switch it to the on state. When the signal switch SW 2  is switched to the on state, the electrical signal (for example, current signal) generated is transmitted to the control module  21 , and the control module  21  outputs drive signals in the form of PWM (Pulse Width Modulation) to the drive circuit  22  according to the electrical signals generated by the signal switch SW 2  being actuated. Thus, the drive circuit  22  drives the motor  13  according to the drive signals, the motor  13  starts, and then the motor  13  enters normal operation. 
     Optionally, the current switch SW 1  and the signal switch SW 2  are configured as one integral structure. In other words, the current switch SW 1  and the signal switch SW 2  are integrated. 
     The control module  21  may be implemented as a DSP (Digital Signal Processor) chip, an ARM (Advanced RISC (Reduced Instruction Set Computer) Machine, RISC Microprocessor) chip, or a single-chip microcomputer (MCU, Microcontroller Unit) according to the internal data signal processing requirements of the power tool  10 . 
     Referring to  FIG. 4 , another example of a power tool  40  takes a hand-held circular saw as an example, and the mechanical structure includes: a base plate  48 , for contacting with a workpiece; a housing  41 , the housing is mounted on the base plate  48 ; a saw blade guard  49 , the blade guard  49  and the housing  41  being connected; a saw blade shaft  42  for supporting the saw blade to rotate within the saw blade guard  49  to cut the workpiece; a motor  43  disposed in the housing  41  including a stator, a rotor and a motor shaft  431 , the motor shaft  431  being driven by the rotor of the motor  43 ; a transmission device  44 , the transmission device  44  being configured to transmit the power output by the motor  43  to a tool accessory. For a circular saw, the tool accessory is a saw blade. In some examples, the transmission device  44  connects the motor shaft  431  and the saw blade shaft  42 , transmitting the rotational movement of the motor shaft  431  to the saw blade shaft  42  to drive the saw blade to operate. The transmission device  44  may include a speed reduction mechanism, for example, an intermeshing worm gear mechanism. The worm gear mechanism may include gear structures with different gear ratios, or synchronous belt transmission structures with different synchronizing wheel radius. Optionally, the motor  43  is a brushless motor. 
     The hand-held circular saw further includes a handle  48  to be held by the user, the handle  48  can be formed by the housing  41 , or can be formed or installed separately; an operating switch  46  for the user to operate. The operating switch  46  is arranged at the handle  48  for convenience. The operating switch  46  includes a trigger mechanism  461 , and the trigger mechanism  461  can be actuated. 
     Referring to  FIG. 5 , to control the operation of the motor  43 , the circuitry  50  of an example of a power tool  40  includes: a power supply module  54 , a control module  51 , a current switch SW 1 ′, a first signal switch SW 2 ′ and a second signal switch SW 3 ′ etc. Optionally, the power tool  40  further includes a drive circuit  52 . 
     The cooperative working modes of the aforementioned circuit components of the power tool  40  are similar to the electronic components of the power tool  10  shown in  FIGS. 1-3  and will not be repeated here. Compared with the aforementioned power tool  10 , the power tool  40  of this example adds one signal switch, so the signal switch includes a first signal switch SW 2 ′ and a second signal switch SW 3 ′. The first signal switch SW 2 ′ is coupled to the trigger mechanism  461  to be actuated by the trigger mechanism  461 , and the second signal switch SW 3 ′ is coupled to the trigger mechanism  461  to be actuated by the trigger mechanism  461 . The first signal switch SW 2 ′ is at least configured to output a signal to the control module  54  to brake the motor  43 . The second signal switch SW 3 ′ is configured to output a signal to the control module  54  to start the motor  43 . 
     As shown in  FIGS. 6 and 8 , the operating switch  46  includes the above-mentioned trigger mechanism  461 , the current switch SW 1 ′, the first signal switch SW 2 ′, and the second signal switch SW 3 ′. When the trigger mechanism  461  is actuated to reach different positions, the on-off states of the current switch SW 1 ′, the first signal switch SW 2 ′, and the second signal switch SW 3 ′ will change accordingly with the position of the trigger mechanism  461 , that is, the current switch SW 1 ′, the first signal switch SW 2 ′ and the second signal switch SW 3 ′ are respectively switched between the on state and off state according to the current position of the trigger mechanism  461 . The trigger mechanism  461  is, for example, a trigger; and the “position” of the trigger mechanism  461  may refer to the angular position of rotating the trigger. The “on-off state” refers to the on state and off state of the current switch SW 1 ′, the first signal switch SW 2 ′, and the second signal switch SW 3 ′. 
     The trigger mechanism  461  can be actuated to reach different positions. For example, when the trigger mechanism  461  is actuated to reach a first position L 21 , the first signal switch SW 2 ′ changes its on-off state; when the trigger mechanism  461  is actuated to reach a second position L 22 , the current switch SW 1 ′ changes its on-off state; when the trigger mechanism  461  is actuated to reach a third position L 23 , the second signal switch SW 3 ′ changes its on-off state. During the process that the trigger mechanism  461  is actuated to move from an initial position Ls 2  to an end position Le 2 , the trigger mechanism  461  reaches the first position L 21 , the second position L 22 , and the third position L 23  in sequence. The “initial position Ls 2 ” of the trigger mechanism  461  in this application refers to the position where the operating switch  46  is not operated and the trigger mechanism  461  is not actuated, and the “end position Le 2 ” refers to the position far from the initial position where the trigger mechanism  161  stops moving forward. The “end position Le 2 ” may be the third position L 23 , or may be a position farther from the initial position Ls 2  than the third position L 23 . 
     The surface of the trigger mechanism  461  is provided with a projection, and the projection is used to trigger the first signal switch SW 2 ′ and the second signal switch SW 3 ′. In some examples, the trigger mechanism  461  is provided with a first projection  462  on the surface; the first projection  462  follows the movement of the trigger mechanism  461 . When the trigger mechanism  461  moves to the first position L 21 , the first projection  462  triggers the first signal switch SW 2 ′ coupled to the first projection  462 . Alternatively, when the trigger mechanism  461  moves to the first position L 21 , the first projection  462  triggers the first signal switch SW 2 ′ to power on the control module  51 . 
     The trigger mechanism  461  is provided with a second projection  463  on the surface, the second projection  463  follows the movement of the trigger mechanism  461 . When the trigger mechanism  461  moves to the third position L 23 , the second projection  463  triggers the second signal switches SW 3 ′ coupled to the second projection  463 . The second signal switch SW 3 ′ outputs electrical signals to the control module  51 . The control module  51  controls the drive circuit  52  to start the motor  43  according to the electrical signals output by the second signal switch SW 3 ′. 
     When the trigger mechanism  461  is actuated to reach the second position L 12 , the current switch SW 1 ′ is actuated; the on-off state of the current switch SW 1 ′ changes so that the power tool  40  and the power supply module  54  are electrically connected. 
     In some examples, the operating switch  46  further includes a first rocker  464  and a second rocker  465 . The first rocker  464  is connected to the first signal switch SW 2 ′. When the trigger mechanism  461  is actuated to reach the first position L 21 , the first projection  462  and the first rocker  464  move relative to each other, and the first projection  462  presses or moves away from the first rocker  464 , the first rocker  464  actuates the first signal switch SW 2 ′ to change the on-off state, and the on-off state of the first signal switch SW 2 ′ changes. The second rocker  465  is connected to the second signal switch SW 3 ′. When the trigger mechanism  461  is actuated to reach the third position L 23 , the second projection  463  actuates the second rocker  465 , and the second rocker  465  actuates the second signal switch SW 3 ′, and the on-off state of the second signal switch SW 3 ′ changes. 
     Referring to  FIGS. 6-10 , the working process of the above example will be described. 
     The user operates the operating switch  46 , the trigger mechanism  461  is actuated to start moving, and the trigger mechanism  461  first moves to the first position L 21  ( FIG. 6 ). For example, the trigger mechanism  461  rotates from the initial position Ls 2  to an angular position of 12°. At this time, the first projection  462  and the first rocker  464  move relatively, the first signal switch SW 2 ′ is actuated, and the first rocker  464  actuates the first signal switch SW 2 ′ to change the on-off state. Optionally, when the trigger mechanism  461  is moved to the first position L 21 , the first projection  462  triggers the first signal switch SW 2 ′ to power on the control module  51 . At this time, since the trigger mechanism  461  has not reached the second position L 22  and the third position L 23 , the current switch SW 1 ′ and the second signal switch SW 3 ′ are not actuated, and the motor  43  will not start. 
     In some examples, when the trigger mechanism  461  is not actuated, the first switch signal SW 2 ′ is in the ON state; at this time the first projection  462  is pressed against the first rocker  464 . At first, when the trigger mechanism  461  reaches the first position L 21 , the first projection  462  releases the first rocker  464 , and the first signal switch SW 2 ′ is turned off. In other examples, when the trigger mechanism  461  is not actuated, the first signal switch SW 2 ′ is in the off state; at this time, the first projection  462  is not in contact with the first rocker  464 . When the trigger mechanism  461  is actuated to reach the first position L 21 , the first projection  462  presses the first rocker  464 , and the first signal switch SW 2 ′ is turned on. 
     The user further presses the trigger mechanism  461  to reach the second position L 22  ( FIG. 7 ). For example, the trigger mechanism  461  rotates from the initial position to an angular position of 24°. At this time, the current switch SW 1 ′ is switched to the on state. At this time, the first signal switch SW 2 ′ is still in the aforementioned state after being actuated. Since the trigger mechanism  461  has not yet reached the third position L 23 , the second signal switch SW 3 ′ will not be actuated, the second signal switch SW 3 ′ will not generate a power-on signal. At this time, the current switch SW 1 ′ passes a large current, but because the second signal switch SW 3 ′ is not actuated and no power-on signal is generated, therefore, the motor  43  still does not start. 
     Referring to  FIGS. 5 and 7 , the trigger mechanism  461  is coupled to contact A, contact B, contact A′, and contact B′ of the current switch SW 1 ′. When the trigger mechanism  461  pressed to reach the second position L 22 , the current switch SW 1 ′ is switched to the on state, contact A and contact B of the current switches SW 1 ′ thereby form an electrical connection, contact A′ and contact B′ also form an electrical connection thereby; the electrical connection between the power supply module  54  and the power tool  40  is turned on, and the power supply module  54  can output electric power to provide electricity to the power tool  40 . Contact A and contact B, contact A′ and contact B′ of the current switch SW 1 ′ are respectively connected, the current switch SW 1  carries all the current output by the power supply module  43 . Similar to the previous example, in order to avoid sparking between the contacts of the current switch SW 1  due to a large current, in this example, a copper sheet can be used as the electrical connection structure between contact A and contact B, and another copper sheet can be used as the electrical connection structure between contact A′ and contact B′. The two branches connected to the copper sheet carry the current from the power supply module  18  in parallel. Because the copper sheet has good conductivity and good heat dissipation characteristics, this connection method, on the one hand, effectively solves the problem of sparking between the switch contacts at the moment of high current being turned on, and on the other hand, cools the current switch with the copper sheet arranged on the surface of the switch. 
     The user further presses the trigger mechanism  461  to reach the third position ( FIG. 8 ), and the trigger mechanism  461  rotates from the initial position to an angular position of 27°. At this time, the second projection  463  actuates the second rocker  465 , and the second rocker  465  actuates the second signal switch SW 3 ′. The second signal switch SW 3 ′ is actuated to change the on-off state and generate and output a power-on electrical signal to control module  51 . At this time, the current switch SW 1 ′ is still in the on state, the first signal switch SW 2 ′ is still in the aforementioned state after being actuated, and the control module  51  receives the electrical signal from the second signal switch SW 3 ′ to control the motor  43  to start running. In some examples, the control module  51  outputs a drive signal to the drive circuit  52 , and the drive circuit  52  starts the motor  43 . 
     Referring to  FIGS. 9 and 11A , the process that the trigger mechanism  461  is actuated to move from the initial position Ls 2  to the end position Le 2  is as follows: 
     Step S 11 : the operating switch  46  is actuated, and the trigger mechanism  461  starts moving after being pressed. 
     Step S 12 : the trigger mechanism  461  reaches the first position L 21 . 
     The first signal switch SW 2 ′ is actuated to change the on-off state. Optionally, the first signal switch SW 2 ′ is actuated to power the control module  51 . 
     Step S 13 : the trigger mechanism  461  reaches the second position L 22 . 
     At this time, the current switch SW 1 ′ is switched to the on state, the power supply module  54  and the power tool  40  are connected, and current flows through the current switch SW 1 ′. 
     Step S 14 : the trigger mechanism  461  reaches the third position; the second signal switch SW 3 ′ is actuated to change the on-off state so that the control module  51  controls the motor  43  to start. 
     When the user releases the trigger mechanism  461 , the trigger mechanism  461  is released and restored, and at the same time drives the first projection  462  and the second projection  463  to return. When the user releases the trigger mechanism  461 , the trigger mechanism  461  returns from the end position Le 2  to the initial position Ls 2 , and sequentially reaches a fourth position L 24 , a fifth position L 25 , and a sixth position L 26 . In some examples, when the trigger mechanism  461  reaches the fourth position L 24 , the second signal switch SW 3 ′ first changes the on-off state again, but because the first signal switch SW 2 ′ is still in the aforementioned state after being actuated, that is, the first signal switch SW 2 ′ has not changed its state again and will not output a brake signal. The motor  43  continues to run and the power tool  40  works normally; then, the trigger mechanism  461  reaches the fifth position L 25 , and the first signal switch SW 2 ′ changes the on-off state again, outputs a brake signal to the control module  51 , while the second signal switch SW 3 ′ is still in the aforementioned state after the change again, the control module  51  controls the motor  43  to brake; finally, the trigger mechanism  461  reaches the sixth position L 26 , the current switch SW 1 ′ is turned off, and the power tool  40  is powered off. 
     Referring to  FIGS. 10 and 11B , the process that the trigger mechanism  161  is released from the end position Le 2  to the initial position Ls 2  is as follows: 
     Step S 15 : the operating switch  46  is released, and the trigger mechanism  161  is released to start the return journey. 
     Step S 16 : the trigger mechanism  461  reaches the fourth position L 24 . 
     The on-off state of the second signal switch SW 3 ′ is changed again, however, since the first signal switch SW 2 ′ is still in the aforementioned state after being actuated, that is, the first signal switch SW 2 ′ has not changed its state again, and will not output a brake signal, the motor  43  continues to run and the power tool  40  works normally. 
     Step S 17 : the trigger mechanism  461  reaches the fifth position L 25 , the on-off state of the first signal switch SW 2 ′ is changed again so that the control module  51  controls the motor  43  to brake. 
     Step S 18 : the trigger mechanism  461  reaches the sixth position L 26 , the current switch SW 1 ′ is turned off, and the power tool  40  is powered off. 
     The current switch SW 1 ′ is turned off after the first signal switch SW 2 ′ and the second signal switch SW 3 ′ are turned off, which ensures that the control module  51  can still work for some time to control the braking time and braking current, so that the braking of the power tool is under control, and the braking process is more stable and safer. 
     Due to the return journey difference resulted from the mechanical structure of the trigger mechanism  461 , the first position L 21 , second position L 22 , and third position L 23  in the process of the trigger mechanism  461  moving from the initial position Ls 2  to the final position Le 2  are different from the fourth position L 24 , the fifth position L 25 , and the sixth position L  26  in the process of the trigger mechanism  461  moving from the final position Le 2  to the initial position Ls 2 . 
     Optionally, the fifth position L 25  is closer to the initial position Ls 2  with respect to the second position L 22 . That is, compared with the second position L 22  reached during the advancement of the trigger mechanism  461 , the fifth position L 25  reached during the return journey of the trigger mechanism  461  needs to be released by a greater distance. The advantage is that, when braking is required, the trigger mechanism  461  needs to be released for a longer travel distance to be able to trigger the brake of the motor  43 , so as to prevent the user from accidentally actuating the trigger mechanism and causing undesired consequences. For example, the first position L 21 , the second position L 22 , and the third position L 23  in the process of the trigger mechanism  461  moving from the initial position Ls 2  to the end position Le 2  are 12° angular position, 24° angular position, and 27° angular position, respectively. The fourth position L 24 , the fifth position L 25 , and the sixth position L 26  in the process of the trigger mechanism  461  moving from the final position Le 2  to the initial position Ls 2  are 22° angular position, 7° angular position, and 5° angular position, respectively. 
     The first projection  462  and the second projection  463  are staggered to each other, so that the trigger mechanism  461  actuates the first signal switch SW 2 ′ and the second signal switch SW 3 ′ at different times, so that the first signal switch SW 2 ′ and the second signal switch SW 3 ′ will not be actuated at the same time, thereby generating electrical signals representing different information to the control module  51 . In the present example, the first signal switch SW 2 ′ is used to power up the control module  51  during the startup process of the power tool  10  and generate a brake signal during the braking process of the power tool  10 . When the control module  51  receives the brake signal, it controls the motor  43  to brake. The second signal switch SW 3 ′ is used to generate a power-on signal during the startup process of the power tool. Upon receiving the power-on signal, the control module  51  determines that the current switch SW 1 ′ has been turned off, and then controls the drive circuit  52  to control the operation of the motor  43 . 
     Referring to  FIG. 12 , as another example, the circuitry of the power tool  40  includes: a control module  61 , a drive circuit  62 , a motor  43 , a power supply module  64 , a power circuit  66 , a current switch SW 1 ′, a first switch signal SW 2 ′, a second signal switch SW 3 ′, a first signal switch state detection circuit  67 , a second signal switch state detection circuit  68 , and a current switch state detection circuit  69 . 
     In this example, the control module  61 , the drive circuit  62 , the motor  62 , and the power supply module  64  are similar to those of the aforementioned example, and their cooperative functioning methods are similar, and will not be repeated here. 
     In this example, the drive circuit  62  is electrically connected to or disconnected to the power supply module  64  through the current switch SW 1 ′. 
     The power circuit  66  is configured to convert the electric power from the power supply module  64  into electric power for the control module  61  and each switch state detection circuit. 
     In this example, when the trigger mechanism  461  is actuated to move from the initial position Ls 2  to the end position Le 2 , that is, during the startup process of the power tool, the first signal switch SW 2 ′ is configured to trigger the power circuit  66  to work, thereby to provide power to the control module  61 , and to power on the power tool  40 ; and when the trigger mechanism  461  moves from the end position Le 2  to the initial position Ls 2 , the first signal switch SW 2 ′ is configured to provide a brake signal to the control module  61  to brake the motor  61 . 
     The first signal switch state detection circuit  67  is used to detect the on-off state of the first signal switch SW 2 ′ and send the detected state information of the first signal switch SW 2 ′ to the control module  61 , and the control module  61  controls the motor  43  to brake according to the state of the first signal switch SW 2 ′. 
     The current switch state detection circuit  69  is electrically connected to the current switch SW 1 ′ for detecting the on-off state of the current switch SW 1 ′. The first signal switch state detection circuit  67  is connected to the first signal switch SW 2 ′ for detecting the on-off state of the first signal switch SW 2 ′. The second signal switch state detection circuit  68  is connected to the first signal switch SW 3 ′ for detecting the on-off state of the second signal switch SW 3 ′. 
     The other ends of the first signal switch state detection circuit  67 , the second signal switch state detection circuit  68 , and the current switch state detection circuit  69  are all connected to the control module  61 , and the control module  61  controls the operation of the motor  43  according to the received electrical signals of each switch state detection circuit. With the above-mentioned switch state detection circuits, it is possible to effectively prevent the power tool from malfunction when the mechanical structure of the operating switch fails and the above-mentioned current switch or signal switches is not effectively actuated or is falsely actuated. Through the software method formed by the above-mentioned hardware switches and the switch state detection circuits, a double protection is formed to avoid undesired malfunction of the power tool  40 . 
     Referring to  FIG. 13 , in an example, a control method of the power tool  40  includes: 
     Step S 21 : actuate the operating switch  46 , and the trigger mechanism  461  starts to move. 
     Step S 22 : determine whether the trigger mechanism  461  has reached the first position L 21 , if yes, go to step S 23 ; if not, proceed to step S 22 . 
     Step S 23 : actuate the first signal switch SW 2 ′ to change its on-off state so that the control module  61  is powered on. 
     In a specific implementation, the first signal switch SW 2 ′ brings the power supply circuit  69  to work, and powers on the control module  61 . 
     Step S 24 : determine whether the trigger mechanism  461  has reached the second position L 22 , if yes, go to step S 25 ; if not, proceed to step S 24 . 
     Step S 25 : switch the current switch SW 1 ′ to the on state, the power supply module  64  is electronically connected with the power tool, the main circuit of the power tool  40  is closed, and current flows through the current switch SW 1 ′. 
     Step S 26 : determine whether the trigger mechanism  461  has reached the third position L 23 , if yes, go to step S 27 ; if not, proceed to step S 26 . 
     Step S 27 : actuate the second signal switch SW 3 ′ to change its on-off state, and the motor  43  has started. 
     In a specific implementation, the second signal switch SW 3 ′ is actuated to change the on-off state, the control module  61  receives the power-on signal, determines that the current switch SW 1 ′ is turned on, and the control module  61  controls the drive circuit  62  to start the motor  43 . 
     Step S 28 : determine whether the operating switch  46  has been released, if yes, go to step S 39 ; if not, proceed to step S 28 . 
     Step S 29 : determine whether the trigger mechanism  461  has reached the fourth position L 24 , if yes, go to step S 30 ; if not, proceed to step S 29 . 
     Step S 30 : change the on-off state of the second signal switch SW 3 ′ again, and the power tool  10  continues working. 
     After the trigger mechanism  461  reaches the fourth position L 24 , the on-off state of the second signal switch SW 3 ′ changes again, but because the first signal switch SW 2 ′ is still in the aforementioned state after being actuated, that is, the first signal switch SW 2 ′ has not changed its state again and will not output a brake signal. The motor  43  continues to run and the power tool  40  works normally. 
     Step S 31 : determine whether the trigger mechanism  461  has reached the fifth position L 25 , if yes, go to step S 32 ; if not, proceed to step S 31 . 
     Step S 32 : change the on-off state of the first signal switch SW 2 ′ again, start the braking process, and the motor  43  brakes. 
     Step S 33 : determine whether the trigger mechanism  461  has reached the sixth position L 26 , if yes, go to step S 34 ; if not, proceed to step S 33 . 
     Step S 34 : switch the current switch SW 1 ′ to the off state, and the power tool  40  is powered off. 
     Therefore, the present application provides the first signal switch state detection circuit  67 , the second signal switch state detection circuit  68 , and the current switch state detection circuit  69 , and the control module  61  controls the motor  43  to start, run, brake or stop according to the received electrical signals of each switch state detection circuit, which can effectively prevent the power tool from malfunction when any one of the operating switch, the trigger mechanism, the above-mentioned current switch, and the two signal switches is not effectively actuated or is falsely actuated. Through the software method formed by the above-mentioned hardware switches and the switch state detection circuits, a double protection is formed to avoid undesired malfunction of the power tool. 
     Referring to  FIGS. 14-16 , the plane that bisects the handle  48  is defined as the handle central plane S, and the first signal switch SW 2 ′ and the second signal switch SW 3 ′ are distributed on both sides of the handle central plane S. Optionally, the handle  48  is arranged symmetrically about the handle central plane S. Optionally, the handle  48  is not strictly symmetrical about the handle central plane S, but minimizes the space volume or surface area of the two parts of the handle  48  bisected by the handle central plane S. The projection of the first signal switch SW 2 ′ on handle central plane S and the projection of the second signal switch SW 3 ′ on handle central plane S at least partially overlap. This is advantageous in that the first signal switch SW 2 ′ and the second signal switch SW 3 ′ occupy a smaller space, so that the handle  48  is more compact. 
     For the convenience of explanation, “front”, “rear”, “left” and “right” are defined as shown in  FIGS. 14 and 15 , the “front”, “rear”, “left” and “right” are the “front”, “rear”, “left” and “right” of the power tool  40 , as well as the “front”, “rear”, “left” and “right” of the handle  48 . In  FIG. 15 , the handle central plane S is perpendicular to the paper surface. 
     Existing brushless DC motors drive the drive circuit through a control module. A capacitor for reducing ripple and performing filtering is arranged in parallel at both ends of the drive circuit. The capacitor will be charged at the moment the current switch is closing, and a relatively large charging current will be generated during charging. When the current switch is not completely closed, the charging current will cause a huge impact on the current switch contacts, which can easily cause the contacts to burn and stick, and the switch to fail. 
     In the power tool  40  of the present application, the above-mentioned problems can be avoided.  FIG. 17  shows a simplified diagram of the circuitry  60  of the power tool  40  shown in  FIG. 12 . 
     The power tool  40  further includes a power storage element C. The power storage element C is used to reduce ripple and perform filtering, so as to avoid the surge voltage generated when the control module  61  controls the drive circuit  62  through the pulse width modulation method and damage the drive switch. In particular, under a large current, the ripple generated by the drive switch increases when it turns on and off, and the power storage element C can reduce the ripple current in the circuit and perform filtering. The power storage element C is electrically connected to one end of the current switch SW 1 ′ and the first driving end  62   b  of the drive circuit  62 . In some examples, the power storage element C is an electrolytic capacitor. Optionally, a resistor R is also connected in parallel at both ends of the power storage element C to provide another discharge circuit for the power storage element C, so that the power storage element C can discharge faster when discharging, and the power stored in the power storage element C can also get discharged through a switch element Q. In some examples, the resistance value of the resistor is equal to or greater than 1 megohm. The advantage of this is that the power storage element C can be guaranteed to work normally without being affected by the resistor R. 
     To protect the current switch SW 1 ′, the power tool  40  further includes a switch circuit  700  to avoid the charging current of the power storage element C from impacting the current switch SW 1 ′. The switch circuit  700  is connected in series with the power storage element C and then connected in parallel with the drive circuit  62 . 
     The control module  61  is configured to: turn on the switch circuit  700  with a delay after the current switch SW 1 ′ is turned on. In other words, only after the current switch SW 1 ′ is turned on, does the control module  61  output a control signal to the switch circuit  700  to turn on the electrical connection between the power storage element C and the power supply module  64 , thereby delaying the charging of the power storage element C. In this example, after the current switch SW 1 ′ is completely closed, the control module  61  outputs a control signal to the switch circuit  700  to charge the power storage element C. Optionally, the switch circuit  700  includes a switch element Q, and the switch element Q is connected in series with the power storage element C and is electrically connected with the control module  61 . The switch element Q is used to control the charging of the energy storage element C such that the charging of the energy storage element C is delayed until the current switch SW 1 ′ is turned on; in some examples, the control module  61  outputs a control signal to the switch element Q to charge the energy storage element C after the current switch SW 1 ′ is completely closed. This method can avoid the impact of high current on the switch contacts of the switch SW 1 ′ and the power storage element C, which may cause sparking and sticking of the switch contacts and reduce the usage life of the power storage element C. 
     Optionally, the switch element Q is a field effect transistor, the gate of which is electrically connected to the control module  61 , one of the drain or the source is connected in series with the power storage element C, and the other of the drain or source is electrically connected to the drive circuit  62 . 
     Referring to  FIG. 18 , in an example, the method for starting the power tool  10  includes: 
     Step S 41 : turn on the current switch SW 1 ′. 
     In a specific implementation, the user actuates the trigger mechanism  461  so that the current switch SW 1 ′ is switched to the on state, so that the power supply module  64  and the drive circuit  62  are electrically connected. 
     Step S 42 : turn on the switch circuit  700  after a delay. 
     After the current switch SW 1 ′ is turned on, turn on the switch circuit  700  after waiting for a predetermined time period, which is greater than or equal to the time period from when the current switch SW 1 ′ starts to close until it is completely closed. Optionally, the value of the predetermined time period ranges from 50 milliseconds to 200 milliseconds. Optionally, the value of the predetermined time period ranges from 70 milliseconds to 120 milliseconds. Such a setting not only ensures that the current switch SW 1 ′ is completely closed, but also guarantees the user&#39;s hand feeling. 
     In a specific implementation, after the current switch SW 1 ′ is turned on, the control module  61  outputs a control signal to the switch element Q in the switch circuit  700  to turn on the switch element Q, so that the power storage element C starts to get charged. In this way, the power storage element C can be recharged after the current switch SW 1 ′ is completely closed, thereby avoiding the impact of high current on the switch contacts of the switch SW 1 ′ and the power storage element C, which may cause sparking and sticking of the switch contacts and reduce the usage life of the power storage element C. 
     After the current switch SW 1 ′ is closed, the control module  61  outputs a control signal to the drive circuit  62  such that the timing of starting the motor  43  can be set reasonably according to actual needs. Optionally, the control module  61  outputs a control signal to the drive circuit  62  to start the motor  13  after the power storage element C is almost fully charged or fully charged. Optionally, the duration from the start of switching the current switch SW 1 ′ to the start of the rotation of the motor  43  has a value range from 50 milliseconds to 250 milliseconds, so as to guarantee the user&#39;s hand feeling. 
     Referring to  FIG. 19 , according to another example, the simplified diagram of the circuitry of the power tool  40  differs from  FIG. 17  in that another switch circuit  702  is added in this example. In other words, in this example, the power tool  40  has two switch circuits, which are a first switch circuit  701  and a second switch circuit  702 , respectively. 
     The first switch circuit  701  is connected in series with the power storage element C and then connected in parallel with the drive circuit  62 . The control module  61  is configured to delay turning on the first switch circuit  701  after the current switch SW 1 ′ is turned on. The first switch circuit  701  includes: a first switch element Q 1 , which is connected in series with the power storage element C and electrically connected with the control module  61 . 
     The second switch circuit  702  is connected in parallel with the first switch circuit  701  and is electrically connected to the control module  61 . In other words, after the second switch circuit  702  and the first switch circuit  701  are connected in parallel, the parallel connection of the two is then connected in series with the power storage element C. 
     The first switch circuit  701  allows a first current to flow through, and the second switch circuit  702  allows a second current to flow through; the current value of the first current is greater than the current value of the second current. 
     The control module  61  is further configured to: turn on the second switch circuit  702  to allow the second current to charge the power storage element C after the current switch SW 1 ′ is turned on and before the first switch circuit  701  is turned on. That is, after the current switches SW 1 ′ turned on, the control module  61  first controls the first switch circuit  701  to turn on, and then controls the second switch circuit  702  to turn on, so that the power storage element C is charged with a small current after the current switch SW 1 ′ is turned on, and then the power storage element C works normally to reduce ripple and perform filtering, so as to avoid the impact of high current on current switch SW 1 ′, prevent the switch contacts from sparking and sticking, and prolong the usage life of the electrolytic capacitor. 
     The first switch circuit  701  includes: a first switch element Q 1 , which is connected in series with the power storage element C and electrically connected with the control module  61 . Optionally, one end of the first switch element Q 1  is electrically connected with the power storage element C, and the other end of the first switch element Q 1  is electrically connected with the second end  62   b  of the drive circuit  62 . 
     Optionally, the first switch element Q 1  is a field effect transistor, the gate of which is electrically connected to the control module  61 , and the other one of the source or drain is electrically connected to the second end  62   b  of the drive circuit  62 . 
     The second switch circuit  702  includes: a second switch element Q 2 , which is electrically connected to the control module  61 ; and a current limiting element, which is connected in series with the second switch element Q 2 , the current limiting element is a resistive element, and the parameters of the resistive element can be adjusted to control the charging current of the power storage element C. The second switch element Q 2  is first connected in series with the current limiting element and then connected in parallel with the first switch circuit  701 . The first switch circuit  701  and the second switch circuit  702  are two independent branches, both of which can be used to control the charging of the power storage element C. 
     Optionally, the second switch element Q 2  is a field effect transistor, and the current limiting element is a resistor R 1 . 
     Referring to  FIG. 20 , in an example, the method for starting the power tool  40  includes: 
     Step S 51 : turn on the current switch SW 1 ′. 
     In a specific implementation, the user actuates the trigger mechanism  461  so that the current switch SW 1 ′ is in the on state; in this way, the power supply module  64  and the drive circuit  62  are electrically connected. 
     Step S 52 : turn on the second switch circuit  702  to allow the power storage element C to be charged with the second current. 
     In a specific implementation, after the current switch SW 1 ′ is turned on, the control module  61  may immediately turn on the second switch circuit  702  to allow the power storage element C to be charged with the second current. In a specific implementation, the control module  61  outputs a control signal to the switch element Q 2  of the second switch circuit  702  to turn it on. In this way, due to the existence of the current limiting element, the second switch circuit  702  allows a small current to flow through, and the power storage element C is charged with the small current. In this way, there is no need to delay turning on the second switch circuit  702 , because charging the power storage element C with a small current will not generate a large current impacting the contacts of the current switch SW 1 ′. 
     Step S 53 : turn on the first switch circuit  701  to allow the power storage element C to be charged or discharged with the first current. 
     After the second switch circuit  702  is turned on, the control module  61  then outputs a control signal to the first switch circuit  701  to turn on the first switch circuit  701 . Optionally, after the second switch circuit  702  is turned on, the control module  61  outputs a control signal to the first switch circuit  701  to turn on the first switch circuit  701  after waiting for a predetermined time period. The value of the predetermined time period ranges from 5 milliseconds to 20 milliseconds. After the predetermined time period, the power storage element C will not generate a large charging current. In this way, the user&#39;s hand feeling can be guaranteed, and the charging current of the power storage element C will not impact the contacts of the current switch SW 1 ′. 
     Optionally, after the second switch circuit  702  and the first switch circuit  701  are turned on, the control module  61  outputs a control signal to the drive circuit  62  to start the motor  43 . 
     The timing at which the control module  61  outputs the control signal can be set reasonably according to actual needs. Optionally, the control module  61  outputs a control signal to the drive circuit  62  to start the motor  43  after the power storage element C is fully charged or almost fully charged with the second current. In this way, it can be ensured that there will not be a large current impact on the switch contacts, nor will the user&#39;s feeling be affected. Optionally, the duration from the start of switching the current switch SW 1 ′ to the start of the rotation of the motor  43  has a value range from 50 milliseconds to 250 milliseconds. 
     Optionally, before the first switch circuit  701  is turned on, the control module  61  outputs a control signal to turn off the switch element Q 2  of the second switch circuit  702 . 
     The first switch circuit  701  and the second switch circuit  702  are two independent circuits for controlling the charging of the power storage element C, and are used for controlling the current of the power storage element C. 
     Through the two switch circuits ( 701 ,  702 ) provided above, the charging timing and the charging current of the power storage element C can be controlled, and the switch contacts of the current switch SW 1 ′ can be effectively prevented from loading a large current when the current switch SW 1 ′ is not completely closed. Moreover, the charging current of the power storage element C can be changed by adjusting the resistor R 1 , and the circuit of the power storage element C will not be affected by the current limiting element when the power tool  40  is working normally, thereby reducing the ripple reduction and filtering performance. In addition, in this example, by arranging two switch elements Q 1  and Q 2 , the switch element is saved from having to withstand the impact of the charging current of the power storage element C during every starting up, as well as the charging or discharging current of the power storage element C during the normal operation of the drive circuit  62 . Therefore, the requirements for selecting the switch element is not very high, which reduces the cost, and also alleviates the problem of poor performance and reduced reliability of the switch element after bearing many current impacts. 
     In this application, the power tool  40  includes a transmission device  44 ; the transmission device  44  is configured to transmit torque output by the motor  43  to the tool accessory. The transmission device  44  is provided with a lubricant that at least partially solidifies when the temperature of the power tool  40  is lower than a predetermined temperature threshold. Especially, if the transmission device is a worm gear mechanism that meshes with each other, when starting in a low temperature environment, the starting torque of the power tool  40  increases due to the solidification of lubricating oil. At this time, if it is forced to start with the normal starting method, a larger starting current will be required. Excessive starting current can easily damage the electronic switch elements (e.g., field effect transistors) in the power tool, causing overcurrent protection and unsuccessful startup of the power tool  40 . 
     The power tool  40  further includes a detection module  71  ( FIG. 12 ), which is connected with the control module  61 , for detecting relative parameters during the start-up process of the motor  43 , including at least one of the current of the motor  43 , the temperature of the power tool  40 , and the output voltage of the power supply module  64 . 
       FIG. 21  is a simplified diagram of the circuitry of the power tool  40  shown in  FIG. 12 . The detection module  71  includes a temperature sensor  711 , which is disposed inside the power tool  40 , for detecting the temperature of the power tool  40 . Optionally, the temperature sensor  711  may be a thermistor, especially an NTC thermistor. 
     The temperature sensor  711  is electrically connected with the control module  61 . The control module  61  is configured to: control the startup speed of the motor  43  according to the temperature of the power tool  40 . When the temperature of the power tool  40  is higher than a predetermined temperature threshold, the rotational speed of the motor  43  is gradually increased to a predetermined rotational speed at the first rate of change; when the temperature of the power tool  40  is lower than the predetermined temperature threshold, the rotational speed of the motor  43  is gradually increased to the predetermined rotational speed at the second rate of change lower than the first rate of change. 
     Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     In an example, the ratio of the first rate of change to the second rate of change is greater than or equal to 2. 
     In some examples, the temperature sensor  711  is disposed inside the power tool  40  close to the drive switch (VT 1 , VT 2 , VT 3 , VT 4 , VT 5 , and VT 6 ) of the drive circuit  62 , so as to detect the temperature of the drive switch. The control module  61  is further configured to control the drive circuit  62  to stop driving the motor  43  when the temperature of the drive switch is higher than a second predetermined temperature threshold. The second predetermined temperature threshold is higher than the first predetermined temperature threshold. Optionally, the value of the second predetermined temperature threshold ranges from 60° C. to 90° C. In this way, the temperature sensor  711  can be configured to detect environment temperature to adopt a low temperature control strategy for the motor  43  at low temperatures, and to detect the temperature of the drive switch to stop the motor  43  when the temperature of the motor  43  is too high. There is no need to set up two additional temperature detection circuits or temperature sensors, which not only saves costs, but also simplifies the circuitry design. 
     In an example, the power supply module  64  includes a battery pack  45 , and the battery pack  45  is detachably mounted to the power tool  40  for providing electric power for the power tool  40 . The battery pack  45  includes a plurality of electrically connected cells, and the cells can be repeatedly charged and discharged. The battery pack  45  also includes a positive power supply terminal B+ and a negative power supply terminal B−. The power tool  40  includes a positive connection terminal T+ and a negative power supply T−, which are respectively configured to connect with the positive power terminal B+ and the negative power terminal B− of the battery pack  45  to transmit electric power. Of course, the power supply module  64  may also include an AC power source. The power tool  40  uses AC power supply. The power supply module  64  also includes some power conversion circuits for converting AC power into electric power for the power tool  40 . 
     The present application also discloses a method for starting a power tool, including: obtaining the temperature of the power tool  40 ; and control the starting speed of the motor  43  according to the temperature of the power tool  40 . 
     In a specific implementation, when the temperature of the power tool  40  is higher than the first predetermined temperature threshold, the motor  43  is controlled to gradually increase the rotational speed of the motor  43  at a first rate of change; when the temperature of the power tool  40  is lower than the predetermined temperature threshold, the rotational speed of the motor  43  is gradually increased to a final rotational speed at a second rate of change lower than the first rate of change. The final rotational speed is the rotational speed at which the power tool  40  runs at a constant speed. 
     In an example, a ratio of the first rate of change to the second rate of change is greater than or equal to 2. 
     Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     In actual operation, this can be achieved by controlling the duty cycle of the PWM signal output by the module  61 . In some examples, the first rate of change of the rotational speed of the motor  43  corresponds to the first rate of change of the duty cycle of the PWM signal, and the second rate of change of the rotational speed of the motor  43  corresponds to the second rate of change of the duty cycle of the PWM signal. The second rate of change of the duty cycle is lower than the first rate of change of the duty cycle. Optionally, the ratio of the first rate of change of the duty cycle to the second rate of change of the duty cycle is greater than or equal to 2. 
     Referring to  FIG. 22 , in an example, according to the method for starting the power tool  40 , the power tool  40  is started in the following steps: 
     Step S 61 : power on the power tool. 
     Step S 62 : obtain the temperature of the power tool and determine whether the current temperature of the power tool  40  is higher than the first predetermined temperature threshold, if yes, go to step S 43 , otherwise go to step S 44 . 
     Step S 63 : in a normal starting mode, gradually increase the rotational speed of the motor  43  to the final rotational speed at the first rate of change, and the power tool  40  works normally at the final rotational speed. 
     Step S 64 : in a low temperature starting mode, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the second rate of change lower than the first rate of change. 
     Step S 65 : the power tool  40  has started, that is, the motor  43  runs normally at the predetermined speed, and the power tool  40  works normally. 
     The aforementioned example can ensure the normal and safe startup of the power tool  40  under low temperature conditions. Setting the temperature sensor  711  to directly detect the environment temperature of the power tool  40  enables the timely recognition of whether the working environment of the power tool  40  is in a low temperature environment that requires a large starting torque. When the temperature sensor  711  detects a temperature lower than the predetermined threshold temperature, reduce the rate of change of the starting speed of the motor  43 , thereby reducing the starting current of the motor  43 , and avoiding the problem of increased starting torque at low temperature and increased starting current, which causes the drive switch to be damaged or the power tool  40  to enter the overcurrent protection and start unsuccessfully. 
       FIG. 23  is a simplified diagram of an example of the circuitry of the power tool  40  shown in  FIG. 12 , wherein the detection module  71  includes a current detection circuit  712 , and the current detection circuit  712  is electrically connected to the windings of the motor  43  through a detection resistor that detects the current of the motor  43 . As an optional solution, the current detection circuit  712  detects the phase current of the motor  43  by sampling the single current of the DC bus. The current detection circuit  712  is electrically connected with the control module  61 . 
     The control module  61  controls the starting speed of the motor  43  according to the detection result of the current detection circuit  712 : when the current of the motor  43  is lower than the predetermined current threshold, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the first rate of change; when the current of the motor  43  is higher than the predetermined current threshold, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the second rate of change lower than the first rate of change. 
     In an example, the ratio of the first rate of change to the second rate of change is greater than or equal to 2. 
     Optionally, the value of the predetermined current threshold ranges from 30A to 120A. 
     The present application also discloses a method for starting a power tool, including: obtaining the current of the power tool  40 ; and control the starting speed of the motor  43  according to the current of the power tool  40 . 
     In a specific implementation, when the current of the motor  43  of the power tool  40  is lower than the predetermined current threshold, the motor  43  is controlled to gradually increase the rotational speed of the motor  43  at the first rate of change; when the current of the motor  43  of the power tool  40  is higher than the predetermined current threshold, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the second rate of change lower than the first rate of change. 
     In an example, the ratio of the first rate of change to the second rate of change is greater than or equal to 2. 
     Optionally, the value of the predetermined current threshold ranges from 30A to 120A. 
     In actual operation, this can be achieved by controlling the duty cycle of the PWM signal output by the module  61 . In a specific implementation, the first rate of change of the rotational speed of the motor  43  corresponds to the first rate of change of the duty cycle of the PWM signal, and the second rate of change of the rotational speed of the motor  43  corresponds to the second rate of change of the duty cycle of the PWM signal. The second rate of change of the duty cycle is lower than the first rate of change of the duty cycle. Optionally, the ratio of the first rate of change of the duty cycle to the second rate of change of the duty cycle is greater than or equal to 2. 
     When the rotational speed of the power tool  40  changes at the first rate of change, the duty cycle of the PWM signal is gradually increased to the duty cycle corresponding to the predetermined rotational speed at the first rate of change of the duty cycle, so as to start normally. 
     When the rotational speed of the power tool  40  changes at the second rate of change lower than the first rate of change, the duty cycle of the PWM signal is gradually increased to the duty cycle corresponding to the predetermined rotational speed at the second rate of change of the duty cycle lower than the first rate of change of the duty cycle, so as to start under low temperature. 
     Referring to  FIG. 24 , in an example, the method for starting the power tool  40  includes: 
     Step S 71 : power on the power tool; 
     Step S 72 : obtain the current of the motor and determine whether the current of the motor is lower than the predetermined current threshold, if yes, go to step S 73 , otherwise go to step S 74 ; 
     Step S 73 : in a normal starting mode, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the first rate of change; the predetermined rotational speed is the speed at which the power tool  40  works normally. 
     Step S 74 : in a low temperature starting mode, gradually increase the rotational speed of the motor  43  to the predetermined rotational speed at the second rate of change lower than the first rate of change. 
     Step S 75 : the power tool  40  has started, that is, the motor  43  runs at the final rotational speed, and the power tool  40  works normally. 
     The aforementioned example can ensure the normal and safe startup of the power tool  40  under low temperature conditions. Setting the current detection circuit  712  to detect the current of the power tool  40  enables the timely recognition of low environment temperature of the power tool  40 . This is because when the motor is started in a low temperature environment, the starting torque is increased due to the solidification of the lubricating oil of the transmission device  44 . At this time, if the starting torque is forced to start according to the normal starting mode, the starting current is also larger. Therefore, detecting the current of the motor  43  also enables the timely recognition of low environment temperature of the power tool  40 . When the current of the motor is detected to be higher than the predetermined threshold current, reduce the rate of change of the starting speed of the motor  43 , thereby reducing the starting current of the motor  43 , and avoiding the problem of increased starting torque at low temperature and increased starting current, which causes the drive switch to be damaged or the power tool  40  to enter the overcurrent protection and start unsuccessfully. 
     Referring to  FIG. 25 , the detection module  71  of the power tool  40  includes a voltage detection module  713 , for detecting the output voltage of the battery pack  45 , which is electrically connected to the control module  61 , for transmitting the detected results to the control module  61 . Optionally, the voltage detection module  713  includes detection resistors and the like. 
     In the present example, the control module  61  is configured to: obtain the output voltage of the battery pack  45 ; dynamically adjust the duty cycle of the PWM signal output to the drive circuit  62  according to the output voltage of the battery pack  45  so that the output voltage of the battery pack  45  is greater than the first undervoltage protection threshold. 
     Optionally, when the temperature of the power tool  40  is lower than a predetermined temperature threshold, set up a first undervoltage protection threshold; when the temperature of the power tool  40  is higher than the predetermined temperature threshold, set up a second undervoltage protection threshold; wherein, the first undervoltage protection threshold is less than the second undervoltage protection threshold. Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     In some examples, the ratio of the first undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.25 to 0.75. In some examples, the ratio of the second undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.3 to 0.8. For example, taking a battery pack  45  with a rated voltage of 48V as an example, the first undervoltage protection threshold is, for example, 24V, and the second undervoltage protection threshold is 30V. 
     In other words, different undervoltage protection thresholds are set according to the temperature of the power tool  40 . The undervoltage protection threshold at low temperature is less than the undervoltage protection threshold at normal temperature. 
     The control module  61  is further configured to: if the output voltage of the battery pack is less than the predetermined voltage threshold, reduce the duty cycle of the PWM signal output to the drive circuit so that the output voltage of the battery pack is greater than or equal to the predetermined voltage threshold. 
     The method that the control module  61  dynamically adjusts the duty cycle of the PWM signal output to the drive circuit  62  according to the output voltage of the battery pack  45  includes: if the output voltage of the battery pack  45  is less than a predetermined threshold voltage, reduce the duty cycle of the PWM signal output to the drive circuit so that the output voltage of the battery pack  45  is greater than or equal to the predetermined voltage threshold. Wherein, the predetermined voltage threshold is greater than the first undervoltage protection threshold and less than the second undervoltage protection threshold. For example, taking a battery pack  45  with a rated voltage of 48V as an example, the first undervoltage protection threshold is 24V, for example, and the second undervoltage protection threshold is 30V, then the predetermined voltage threshold is set between 24V and 30V, for example 27V. 
     Since the predetermined voltage threshold is set between the undervoltage protection threshold of normal temperature and the undervoltage protection threshold of low temperature, under normal temperature, when the output voltage of the battery pack  45  drops to the second undervoltage protection threshold, the power tool  40  enters the undervoltage protection and shuts down, which will not reach the lower first undervoltage protection threshold and trigger a low-temperature startup. When the output voltage of the battery pack  45  drops to the first undervoltage protection threshold, the low-temperature startup starts. 
     In the low temperature startup, the control module  61  is configured to: if the output voltage of the battery pack  45  is less than the predetermined voltage threshold, reduce the duty cycle of the PWM signal output to the drive circuit  62  such that the output voltage of the battery pack  45  is greater than or equal to the predetermined voltage threshold. 
     That is, when the voltage of the battery pack  45  has dropped to reach the predetermined voltage threshold, and about to reach the undervoltage protection threshold at low temperature (i.e., the first undervoltage protection threshold), the control module  61  reduces the duty cycle of the PWM signal output to the drive circuit  62 , in such a way as to reduce the output current of the battery pack  45  to the motor  43 , and due to the internal resistance of the battery pack  45 , the output voltage of the battery pack  45  increases, so that the voltage of the power tool  40  rises, so as to avoid the situation that the power tool  40  enters the undervoltage protection at low temperature and shuts down, causing unsuccessfully startup. 
     In the initial stage of startup, the temperature of the power tool  40  is low, the lubricating oil is in a solidified state, and the starting torque of the motor  43  is relatively large. When starting, the output voltage of the battery pack  45  rises briefly and then drops below the predetermined voltage threshold. Once detecting that the output voltage of the battery pack  45  drops below the predetermined voltage threshold, the control module  61  reduces the duty cycle of the PWM signal output to the drive circuit  62 . 
     If the output voltage of the battery pack  45  is determined to be greater than the predetermined voltage threshold, then gradually increase the duty cycle of the PWM signal, for example, each time increase the duty cycle of the PWM signal by a predetermined duty cycle increment and stop increasing once the duty cycle of the PWM signal reaches the final duty cycle. After that, the motor  43  enters the normal operation stage with the final duty cycle, and the motor  43  has started. In other words, if the output voltage of the battery pack  45  is greater than the predetermined voltage threshold, determine whether the current duty cycle is equal to the final duty cycle; if the current duty cycle is equal to the final duty cycle, then output the final duty cycle of the PWM signal to control the drive circuit  62  to make the motor  43  run normally. Optionally, the final duty cycle is set to 100%. Of course, the final duty cycle can also be another predetermined duty cycle to ensure that the motor can run normally. 
     And in the whole process, the output voltage of the battery pack  45  needs to be monitored in real time to determine whether the duty cycle of the PWM signal needs to be reduced. Once the output voltage of the battery pack  45  is detected to drop below the predetermined voltage threshold, the control module  61  reduces the duty cycle of the PWM signal output to the drive circuit  62 . 
     Referring to  FIG. 26 , the method for starting the power tool  40  shown in  FIG. 2  includes: 
     Step S 81 : power on the power tool  40 ; 
     The power tool  40  is powered on, the control module  61  is powered on, and the motor  43  is ready to start. 
     Step S 82 : control the drive circuit  62  with the PWM signal of an initial duty cycle; 
     In a specific implementation, the control module  611  first outputs the initial duty cycle to the drive circuit  62  to start the motor. The initial duty cycle is less than the final duty cycle. Optionally, the ratio of the initial duty cycle to the final duty cycle ranges from 5% to 20%, for example, the initial duty cycle is 10%, and the final duty cycle is generally set to 100%. 
     Step S 83 : determine whether the output voltage of the battery pack  45  is less than the predetermined voltage threshold, if yes, go to step S 84 ; if not, go to step S 85 . 
     In a specific implementation, the control module  61  obtains the output voltage of the battery pack  45  detected by the voltage detection module  713  and determines whether the output voltage of the battery pack  45  is less than the predetermined voltage threshold, if yes, go to step S 14 ; if not, go to step S 15 . 
     Step S 84 : decrease the duty cycle such that the output voltage of the battery pack  45  is greater than or equal to the predetermined voltage threshold. 
     In a specific implementation, if the output voltage of the battery pack  45  is less than the predetermined voltage threshold, the control module  61  reduces the duty cycle of the PWM signal output to the drive circuit  62  such that the output voltage of the battery pack  45  is greater than or equal to the predetermined voltage threshold; the predetermined voltage threshold is greater than the first undervoltage protection threshold and less than the second undervoltage protection threshold. 
     Wherein the first undervoltage protection threshold and the second undervoltage protection threshold are set as follows: if the temperature of the power tool  40  is lower than the predetermined temperature threshold, the undervoltage protection threshold of the power tool  40  is set to the first undervoltage protection threshold; if the temperature of the power tool  40  is higher than the predetermined temperature threshold, the undervoltage protection threshold of the power tool  40  is set to the second undervoltage protection threshold; wherein the first undervoltage protection threshold is less than the second undervoltage protection threshold. 
     Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     Optionally, the ratio of the first undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.25 to 0.75. 
     Optionally, the ratio of the second undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.3 to 0.8. 
     That is, the predetermined voltage threshold is greater than the undervoltage protection threshold of the power tool  40  at low temperature, and less than the undervoltage protection threshold of the power tool  40  at normal temperature. For example, taking a battery pack  45  with a rated voltage of 48V as an example, the first undervoltage protection threshold is 24A, the second undervoltage protection threshold is 30A, and the predetermined voltage threshold is 27A. 
     Step S 85 : determine whether the duty cycle of the PWM signal reaches the predetermined final duty cycle, if yes, go to step S 86 ; if not, go to step S 83 . 
     The control module  61  determines whether the duty cycle of the PWM signal output to the drive circuit  62  reaches the predetermined final duty cycle, if yes, then go to step S 86 , the motor  43  has started, the motor  43  enters normal operation, and the control module  61  controls the motor  43  to enter the normal operation phase at a speed corresponding to the final duty cycle. Optionally, the final duty cycle is set to 100%. Of course, the final duty cycle can also be another predetermined duty cycle. 
     Step S 86 : the motor  43  has started. 
     The power tool  40  completes the startup process and enters the normal operation stage. 
     Referring to  FIG. 27 , a simplified diagram of a circuitry of the power tool  40  according to another example, the difference between the present example and the previous example is the addition of a current detection circuit  712  and a current detection module  713  for detecting the current of the motor  43 . In some examples, the current detection circuit  712  is configured to detect the bus current or phase current of the motor  43 . The current detection circuit  712  is electrically connected to the control module  61 . 
     In the present example, as compared with the preceding examples, the duty cycle of the PWM signal output to the drive circuit  62  is dynamically adjusted according to the output voltage of the battery pack  45  so that the output voltage of the battery pack  45  is greater than the first undervoltage protection threshold. The specific implementation is the same as or similar to the foregoing implementation and will not be repeated here. The difference is that, in the present example, the control module  61  is configured to: before determining whether the output voltage of the battery pack  45  is less than the predetermined voltage threshold, it needs to: obtain the current of the motor  43 ; determine whether the current of the motor  43  is less than a predetermined current threshold: when the current of the motor  43  is less than the predetermined current threshold, output a first PWM signal with a gradually increasing duty cycle to the drive circuit  62  so that the rotational speed of the motor  43  gradually increases to the predetermined rotational speed at the first rate of change; when the current of the motor  43  is greater than or equal to the predetermined current threshold, output a second PWM signal with a gradually increasing duty cycle to the drive circuit so that the rotational speed of the motor gradually increases to the predetermined rotational speed at the second rate of change; the increasing rate of the duty cycle of the second PWM signal is less than the increasing rate of the duty cycle of the first PWM signal. 
     That is, in the initial stage of starting the motor  43 , when the current of the motor  43  is small, the duty cycle increases at a faster rate, and when the current of the motor  43  is large, the duty cycle increases at a slower rate, thereby starting slowly when the current of the motor  43  is large, and starting quickly when the current of the motor  43  is small, so as to prevent the motor  43  from a large starting current exceeding the overcurrent protection threshold, which causes unsuccessful startup of the motor  43 , while at the same time prevent the battery pack  45  from a large starting current, which causes undervoltage protection and startup failure of the motor. 
     Optionally, the value of the predetermined current threshold ranges from 50A to 100A. The predetermined current threshold is set to prevent excessive starting current, which causes overcurrent protection and startup failure. The present application uses the predetermined current threshold as a reference and starts to decrease the duty cycle after the current of the motor  43  reaches the predetermined current threshold, so that the current of the motor  43  will not exceed the current of the overcurrent protection. The current value of the overcurrent protection is greater than the predetermined current threshold. Optionally, the current value of the overcurrent protection ranges from 110A to 130A. 
     Optionally, the increase rate of the duty cycle of the second PWM signal is in a negative correlation with the current of the motor  43 . That is, the rate at which the duty cycle of the second PWM signal increases is related to the current of the motor  43 . The larger the current of the motor  43 , the lower the rate at which the duty cycle of the second PWM signal increases, that is, increases in a slower manner. 
     Optionally, the increase rate of at least one of the duty cycle of the first PWM signal and the duty cycle of the second PWM signal when it is less than the predetermined duty cycle is greater than the increase rate of the duty cycle of that PWM signal when it is greater or equal to the predetermined duty cycle. 
     For example, if the predetermined current threshold is set to 80A, when the current of the motor  43  is less than 80A, at least one of the duty cycle of the first PWM signal and the duty cycle of the second PWM signal is controlled to increase at a rate of 1% every 3 ms within the range of 0-50%, and increase at a rate of 2% every 3 ms within the range of 50%-100%. When the motor  43  current is greater than or equal to 80A, the increase rate is changed according to the magnitude of the current, for example: when the value of the bus current is between 80A and 90A, the duty cycle is controlled to increase at a rate of 0.1% every 3 ms within the range of 0-50%, and increase at a rate of 0.2% every 3 ms within the range of 50%-100%. 
     With the above configuration, the motor  43  adjusts the duty cycle of the PWM signal according to the current of the motor  43  in the initial stage of starting, so that the current of the motor  43  will not become too large and enter the overcurrent protection. 
     Referring to  FIG. 28 , in an example, the method for starting the power tool  40  includes: 
     Step S 91 : start the motor  43 ; 
     Power on the power tool  40 , and the control module  61  first controls the drive circuit  62  with the PWM signal of the initial duty cycle to start the motor  43 . 
     Step S 92 : determine whether the current of the motor  43  is less than the predetermined current threshold, if yes, go to step S 93 ; if not, go to step S 94 . 
     In a specific implementation, the control module  61  obtains the detected current of the motor  43  from the current detection module  713  and determines whether the current of the motor  43  is less than the predetermined current threshold. 
     Step S 93 : control the drive circuit  62  with the first PWM signal; 
     In a specific implementation, when the current of the motor  43  is less than the predetermined current threshold, the control module  61  outputs the first PWM signal with a gradually increasing duty cycle to the drive circuit  62  to increase the rotational speed of the motor  43  at the first rate of change. 
     Step S 94 : control the drive circuit  62  with the second PWM signal; 
     In a specific implementation, when the current of the motor  43  is greater than or equal to the predetermined current threshold, the control module  61  outputs the second PWM signal with a gradually increasing duty cycle to the drive circuit  62  such that the rotational speed of the motor  43  increases at the second rate of change that is less than the first rate of change; wherein the increase rate of the duty cycle of the second PWM signal is less than the increase rate of the duty cycle of the first PWM signal. 
     In other words, if the current of the motor  43  is small, then start in the normal soft-start process, wherein the duty cycle increases in a normal increase rate. If the current of the motor  43  is large, i.e., greater than the predetermined current threshold, then reduce the increase rate of the duty cycle to make the motor  43  start slower than normal so as to avoid a large current, which causes overcurrent protection and startup failure of the motor  43 . 
     Optionally, the increase rate of the duty cycle of the second PWM signal is in a negative correlation with the current of the motor  43 . That is, the rate at which the duty cycle of the second PWM signal increases is related to the current of the motor  43 . The larger the current of the motor  43 , the lower the rate at which the duty cycle of the second PWM signal increases, that is, increases in a slower manner. 
     Optionally, the increase rate of at least one of the duty cycle of the first PWM signal and the duty cycle of the second PWM signal when it is less than the predetermined duty cycle is greater than the increase rate of the duty cycle of that PWM signal when it is greater or equal to the predetermined duty cycle. 
     For example, if the predetermined current threshold is set to 80A, when the current of the motor  43  is less than 80A, at least one of the duty cycle of the first PWM signal and the duty cycle of the second PWM signal is controlled to increase at a rate of 1% every 3 ms within the range of 0-50%, and increase at a rate of 2% every 3 ms within the range of 50%-100%. When the motor  43  current is greater than or equal to 80A, the increase rate is changed according to the magnitude of the current, for example: when the value of the bus current is between 80A and 90A, the duty cycle is controlled to increase at a rate of 0.1% every 3 ms within the range of 0-50%, and increase at a rate of 0.2% every 3 ms within the range of 50%-100%. 
     Step S 95 : determine whether the output voltage of the battery pack  45  is less than the predetermined voltage threshold, if yes, go to step S 96 ; if not, go to step S 97 . 
     In a specific implementation, the control module  61  obtains the output voltage of the battery pack  45  detected by the voltage detection module  713  and determines whether the output voltage of the battery pack  45  is less than the predetermined voltage threshold, if yes, go to step S 96 ; if not, go to step S 97 . 
     Step S 96 : decrease the duty cycle so that the output voltage of the battery pack is greater than or equal to the predetermined voltage threshold. 
     In a specific implementation, if the output voltage of the battery pack  45  is less than the predetermined voltage threshold, the duty cycle of the PWM signal output to the drive circuit  62  is reduced to make the output voltage of the battery pack  45  greater than or equal to the predetermined voltage threshold; the predetermined voltage threshold is set to be greater than the first undervoltage protection threshold and less than the second undervoltage protection threshold. 
     Wherein the first undervoltage protection threshold and the second undervoltage protection threshold are set as follows: if the temperature of the power tool  40  is higher than the predetermined temperature threshold, the undervoltage protection threshold of the power tool  40  is set to the second undervoltage protection threshold; if the temperature of the power tool  40  is lower than the predetermined temperature threshold, the undervoltage protection threshold of the power tool  40  is set to the first undervoltage protection threshold; wherein the first undervoltage protection threshold is less than the second undervoltage protection threshold. 
     Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     Optionally, the ratio of the first undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.25 to 0.75. 
     Optionally, the ratio of the second undervoltage protection threshold to the rated voltage of the battery pack  45  ranges from 0.3 to 0.8. 
     That is, the predetermined voltage threshold is greater than the undervoltage protection threshold of the power tool  40  at low temperature and less than the undervoltage protection threshold of the power tool  40  at normal temperature. For example, taking a battery pack  45  with a rated voltage of 48V as an example, the first undervoltage protection threshold is, for example, 24A, and the second undervoltage protection threshold is, for example, 30A, and the predetermined voltage threshold can be set to 27A. 
     Step S 97 : determine whether the duty cycle has reached the predetermined final duty cycle, if yes, go to step S 67 ; if not, go to step S 62 . 
     The control module  61  determines whether the duty cycle of the PWM signal output to the drive circuit  62  has reached the predetermined final duty cycle. If so, the motor has started and enters the normal operation stage. The control module  61  controls the motor  43  to enter the normal operation stage at the final rotational speed corresponding to the final duty cycle. Optionally, the final duty cycle is set to 100%. Of course, the final duty cycle can also be another predetermined duty cycle. 
     Step S 98 : the motor  43  has started and enters the normal operation stage. 
     The power tool  40  completes the startup process and enters the normal operation stage. 
     Referring to  FIG. 29 , the above two examples dynamically adjust the duty cycle output to the drive circuit  62  according to the output voltage of the battery pack  45 . The output voltage of the battery pack  45  fluctuates around the predetermined voltage threshold within a predetermined time range, and within the predetermined time range, the rotational speed of the motor  43  changes repeatedly, and each repeated change of the rotational speed of the motor  43  includes a rise and a drop and then another rise of the rotational speed. In other words, with the above method, the rotational speed of the motor can repeatedly rise and drop; and the motor can start over and over again ( FIG. 33 ), thereby accelerating the melting of the lubricating oil and ensuring the successful startup of the motor at low temperatures, also at a faster speed. 
     It should be noted that, the low-temperature startup process of the motor  43  of the present application is a process of adjusting the duty cycle so that in the early stage after the output voltage of the battery pack  45  has fallen to the predetermined voltage threshold, the output voltage of the battery pack  45  fluctuates around the predetermined voltage threshold, that is, basically stays around the predetermined voltage threshold, so as not to enter undervoltage protection. In the later stage of the startup process, due to the effect of repeated startup, the lubricating oil gradually melts and the starting torque decreases, the duty cycle of the PWM signal gradually increases to the final duty cycle, after which the motor  43  runs with the final duty cycle and enters the normal operation stage, and the motor  43  startup completes. 
     Referring to  FIG. 30 , according to an example of the simplified diagram of the circuitry of the power tool  40 , the detection module of the power tool  40  includes a temperature sensor  711  and a speed detection module  714 . 
     The temperature sensor  711  is configured to detect the temperature of the power tool  40 . Optionally, the temperature sensor  711  is provided inside the power tool  40 . As an optional solution, the temperature sensor  711  may be a thermistor, especially an NTC thermistor. The temperature sensor  711  is electrically connected to the control module  61 . 
     The speed detection module  714  is configured to detect the rotational speed of the motor  43 . The speed detection module  714  may include some sensors, such as Hall sensors arranged near the rotor inside the motor  43 , a photoelectric encoder, and a magnetic encoder, etc. Of course, the speed detection module  714  may also calculate the rotational speed by detecting the phase current or the bus current of the motor. 
     In the present application, the control module  61  is configured to output a control signal to the drive circuit  62  such that the rotational speed of the motor  43  changes repeatedly; wherein each repeated change of the rotational speed of the motor  43  includes a rise and a drop and then another rise of the rotational speed. 
     As an optional solution, the control signal is a PWM signal; the control module  61  is configured to: obtain the rotational speed of the motor  43 ; dynamically adjust the duty cycle of the PWM signal output to the drive circuit  62  according to the rotational speed of the motor  43 , so that the rotational speed of the motor  43  is greater than or equal to the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle. 
     The power tool  40  has a plurality of predetermined rotational speed thresholds and a plurality of duty cycle intervals; the plurality of predetermined rotational speed thresholds and the plurality of duty cycle intervals are mapped in one-to-one correspondence. In some examples, when the duty cycle is in the first duty cycle interval, the predetermined rotational speed threshold is set to the first predetermined rotational speed threshold; when the duty cycle is in the second duty cycle interval, the predetermined rotational speed threshold is set to the second predetermined rotational speed threshold. A duty cycle in the first duty cycle interval is less than a duty cycle in the second duty cycle interval. The first predetermined rotational speed threshold is less than the second predetermined rotational speed threshold. 
     Referring to  FIG. 32 , for example, when the duty cycle of the PWM signal output by the control module  61  to the drive circuit  62  is in the interval of 10%-20%, the predetermined rotational speed threshold is set to n 1 ; when the duty cycle of the PWM signal output by the control module  61  to the drive circuit  62  is in the interval of 20%-30%, the predetermined rotational speed threshold is set to n 2 ; when the duty cycle of the PWM signal output by the control module  61  to the drive circuit  62  is in the interval of 30%-40%, the predetermined rotational speed threshold is set to n 3 , . . . , when the duty cycle of the PWM signal output by the control module  61  to the drive circuit  62  is in the interval of 90%-100%, the predetermined rotational speed threshold is set to n 9 . The predetermined rotational speed threshold corresponding to each duty cycle interval increases as the duty cycle corresponding to the duty cycle interval increases. For example, the values of the aforementioned predetermined rotational speed thresholds n 1 , n 2 , . . . , n 9  increase in sequence. Each predetermined rotational speed threshold is set as the under speed protection threshold of the motor  43  corresponding to the duty cycle within the range of the duty cycle interval. When the rotational speed of the motor  43  is lower than the under speed protection threshold, the motor  43  has a tendency to stall. 
     Optionally, when the rotational speed of the motor  43  is less than the predetermined rotational speed threshold, the control module  61  reduces the duty cycle of the PWM signal to the predetermined duty cycle threshold. In an example, the value of the predetermined duty cycle threshold ranges from 5% to 15%. That is, when the rotational speed of the motor  43  has not reached the predetermined rotational speed threshold corresponding to the duty cycle interval, the duty cycle is reduced to ensure that the current of the motor  43  does not exceed the overcurrent protection threshold and start unsuccessfully. The predetermined duty cycle threshold is greater than or equal to an initial duty cycle output by the control module  61  to the drive circuit  62  when the motor begins to start, and the initial duty cycle is used to start the motor  43 . In an example, the value of the initial duty cycle ranges from 5% to 10%. 
     In an example, after the duty cycle of the PWM signal is reduced to the predetermined duty cycle threshold, the control module  61  then increases the duty cycle of the PWM signal by a predetermined duty cycle increment. The power tool  40  may have a plurality of predetermined duty cycle increments, and the control module  61  gradually increases the duty cycle of the PWM signal by the plurality of predetermined duty cycle increments. Wherein, the predetermined duty cycle increment of this time is less than the predetermined duty cycle increment of the next time. In other words, every time the duty cycle decreases to the predetermined duty cycle threshold, the control module  61  increases the duty cycle of the PWM signal by different predetermined duty cycle increments. For example, after the duty cycle of the PWM signal decreases to the predetermined duty cycle threshold for a first time, the duty cycle increases by 20%; and after the duty cycle of the PWM signal decreases to the predetermined duty cycle threshold for a second time, the duty cycle is increased by 30%. The advantage is: when the rotational speed of the motor  43  has not reached the predetermined rotational speed threshold corresponding to the duty cycle interval, the duty cycle is decreased and then increased, resulting in the effect of repeated startup. During the process that the duty cycle is repeatedly increased, decreased and then increased again, the effect of repeated startup of the motor  43  is generated, and the starting torque is gradually reduced. Therefore, two PWM signals with the same duty cycle before and after can correspond to different rotational speeds of the motor  43  before and after, and the rotational speed of the latter one is greater than that of the earlier one. 
     After increasing in the duty cycle of the PWM signal each time, the control module  61  determines whether the rotational speed of the motor  43  is greater than the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle; if the rotational speed of the motor  43  is greater than the predetermined rotational speed threshold, increase the duty cycle of the PWM signal by another predetermined duty cycle increment. 
     It should be noted that after increasing the duty cycle of the PWM signal by another predetermined duty cycle increment, the duty cycle of the PWM signal after the increase, i.e., the current duty cycle, may be increased to another duty cycle interval that is different from the aforementioned duty cycle interval. At this point, the current rotational speed of the motor must be compared with the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle to determine whether to increase or decrease the duty cycle. 
     Through such a dynamic adjustment of the duty cycle, the duty cycle is repeatedly increased or decreased, so that the motor generate the effect of repeated startup impacts, so that the lubricating oil gradually melts, the starting torque is reduced, and the rotational speed is increased, so as to start the motor  43  successfully, and to ensure that the rotational speed of the motor  43  is not too low to stall, which leads to startup failure. 
     Before the control module  61  dynamically adjusts the duty cycle of the PWM signal output to the drive circuit  62  according to the rotational speed of the motor  43  such that the rotational speed of the motor is greater than or equal to the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle, it is necessary to obtain the temperature of the power tool and determine whether the temperature of the power tool  40  is less than the predetermined temperature threshold. 
     Based on the temperature determination result, determine whether to dynamically adjust the duty cycle of the PWM signal output to the drive circuit  62  according to the rotational speed of the motor  43  such that the rotational speed of the motor is greater than or equal to the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle. Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. 
     If the temperature of the power tool  40  is less than the predetermined temperature threshold, it is determined that the power tool  40  is in a low temperature environment, and a low temperature start strategy needs to be adopted. The low temperature start strategy is to dynamically adjust the duty cycle of the PWM signal output to the drive circuit  62  according to the rotational speed of the motor  43  such that the rotational speed of the motor is greater than or equal to the predetermined rotational speed threshold corresponding to the duty cycle interval of the current duty cycle. 
     In an example, the temperature sensor is arranged in the power tool  40  near the drive switch of the drive circuit  62 , so that it can also detect the temperature of the drive switch. The control module  61  is also configured to control the drive circuit  62  to stop driving the motor  43  when the detection result of the temperature sensor is higher than the second predetermined temperature threshold. The second predetermined temperature threshold is higher than the predetermined temperature threshold. Optionally, the value of the second predetermined temperature threshold ranges from 60° C. to 90° C. 
     Referring to  FIG. 31 , in an example, the method for starting the power tool  40  includes: 
     Step S 101 : power on the power tool  40 . 
     Step S 102 : determine whether the current temperature of the power tool  40  is lower than the predetermined temperature threshold, if yes, go to step S 103 ; if not, go to step S 104 . 
     In a specific implementation, the control module  61  obtains the temperature detected by the temperature sensor  711  and determines whether the current temperature of the power tool  40  is lower than the predetermined temperature threshold, if yes, go to step S 103 ; if not, go to step S 104 . Optionally, the value of the predetermined temperature threshold ranges from −20° C. to 10° C. If the current temperature is lower than the predetermined temperature threshold, it is determined that the power tool  40  is in a low temperature environment and needs to be started in a low temperature starting mode. 
     Step S 103 : control the motor  43  to start with the PWM signal of the initial duty cycle. 
     The power tool  40  enters the low-temperature startup process, and the control module  61  first outputs the PWM signal of the initial duty cycle to the motor  43  so that the motor  43  starts to rotate at a low speed. The value of the initial duty cycle ranges from 5% to 15%. For example, the initial duty cycle is 10%. 
     Step S 104 : soft-start the power tool  40  normally. 
     If the current temperature of the power tool  40  is greater than or equal to the predetermined temperature threshold, the power tool  40  starts in a normal soft-start mode. In other words, the duty cycle of the PWM signal output from the control module  61  to the drive circuit  62  gradually increases until the final duty cycle is reached, and then the motor runs normally. The normal soft-start method is a common method used in the art and will not be repeated here. 
     Step S 105 : determine whether the rotational speed of the motor  43  is less than the predetermined rotational speed threshold corresponding to the duty cycle interval, if yes, go to step S 106 ; if not, go to step S 107 . 
     The predetermined rotational speed threshold is set in correspondence to the interval range of the duty cycle of the PWM signal output by the control module  61  to the drive circuit  62 . The power tool  40  has a plurality of predetermined rotational speed thresholds and a plurality of duty cycle intervals; the plurality of predetermined rotational speed thresholds and the plurality of duty cycle intervals are mapped in one-to-one correspondence. 
     Step S 106 : decrease the duty cycle of the PWM signal to the predetermined duty cycle threshold. 
     When the rotational speed of the motor  43  is less than the predetermined rotational speed threshold, the control module  61  reduces the duty cycle of the PWM signal output to the drive circuit  62  to the predetermined duty cycle threshold. In an example, the value of the predetermined duty cycle threshold ranges from 5% to 15%. 
     Step S 107 : increase the duty cycle of the PWM signal by the predetermined duty cycle increment. 
     The control module  61  increases the duty cycle of the PWM signal output to the drive circuit  62  by the predetermined duty cycle increment. In an example, the predetermined duty cycle increment gradually increases, that is, the predetermined duty cycle increment of this time is less than the predetermined duty cycle increment of the next time. 
     Step S 108 : determine whether the duty cycle of the PWM signal has reached the predetermined final duty cycle, if yes, go to step S 109 ; if not, go to step S 105 . 
     The control module  61  determines whether the current duty cycle of the PWM signal has reached the predetermined final duty cycle, if yes, then go to step S 109 ; if not, go to step S 105 . Optionally, the predetermined final duty cycle is 100%. Of course, the predetermined final duty cycle may also be other values. 
     Step S 109 : the motor completes the startup process and enters normal operation. 
     When the duty cycle of the PWM signal reaches the predetermined final duty cycle, the control module  61  controls the motor  43  to run with the predetermined final duty cycle, the motor  43  completes the startup process and enters the normal operation stage. 
     In this example, the duty cycle is increased and the current (after-increase) rotational speed of the motor is compared with the current (after-increase) predetermined rotational speed threshold corresponding to the duty cycle interval to determine whether to further increase the duty cycle or directly decrease the duty cycle to the predetermined duty cycle threshold. 
     Through such a dynamic adjustment of the duty cycle, the duty cycle is repeatedly increased and decreased, so that the motor  43  generates the effect of repeated startup impacts, so that the lubricating oil gradually melts, and the starting torque is reduced. When the duty cycle of the PWM signal is at the same duty cycle twice before and after, the rotational speed of the latter one is greater than that of the earlier one. In this way, the rotational speed of the motor  43  changes repeatedly, wherein each repeated change of the rotational speed of the motor  43  includes a rise and a drop and then another rise of the rotational speed. In this way, the motor gradually rises to the final rotational speed ( FIG. 33 ) and ensures that the rotational speed of the motor  43  is not too low to stall, which leads to startup failure. 
     In the present application, the addition of a signal switch coupled to the trigger mechanism in the power tool avoids switch control failure when the power tool carries a large current and improves the accuracy of switch control in the power tool.