Power tool and power tool braking method

Abstract

The embodiment of the application discloses an electric tool and a braking method of the electric tool. The electric tool comprises: a motor comprising a stator winding and a rotor; a driving circuit connected with the motor and used for providing an excitation signal to the motor; and a controller connected with the driving circuit and used for outputting a control signal to the driving circuit. The controller is configured to: when a shutdown signal is received, output a first control signal to control the driving circuit to output an excitation signal with a preset intensity or pause the output of the excitation signal, so that the motor runs at a reduced speed; and when the rotating speed of the motor reduces to a first rotating speed threshold, output a second control signal to control the driving circuit to output an excitation signal that short-circuits the stator winding, thereby braking the motor. By reducing the rotating speed of the motor to a certain rotating speed first and then performing braking control, an excessively large braking force can be avoided, and the rotating speed of the motor is prevented from being reduced too quickly, thereby avoiding the risk of loosening and falling off of functional parts of the electric tool during the braking process.

Description

Technical Field

[0001] The embodiments of the present invention relate to power tool technology, and more particularly to a power tool and a power tool braking method. Background Art

[0002] For angle grinding tools, if they have a brake function, the time interval between repeated startup operations can be shortened, thereby greatly improving the efficiency of tool use.

[0003] However, because the grinding disc of angle grinders is secured with a flange, excessive braking can easily cause the disc to loosen, posing a safety risk of it falling off. Rapid braking also draws high braking currents, posing a challenge to electronic components. Summary of the Invention

[0004] Embodiments of the present invention provide an electric tool and an electric tool braking method, which improve the use safety and extend the life of the electric tool by controlling the braking time of the electric tool.

[0005] In a first aspect, an embodiment of the present invention provides an electric tool, comprising:

[0006] an electric motor, including a stator winding and a rotor;

[0007] a driving circuit, connected to the motor, and configured to provide an excitation signal to the motor;

[0008] a controller connected to the driving circuit and configured to output a control signal to the driving circuit,

[0009] The controller is configured to:

[0010] When a shutdown signal is received, a first control signal is output to control the drive circuit to output an excitation signal of a preset intensity or to stop outputting the excitation signal, so that the motor runs at a reduced speed;

[0011] When the rotation speed of the motor decreases to a first rotation speed threshold, a second control signal is output to control the drive circuit to output an excitation signal for short-circuiting the stator winding, thereby braking the motor.

[0012] Optionally, the driving circuit includes a plurality of electronic switches, and the controller is configured to:

[0013] upon receiving a shutdown signal, outputting a first control signal that turns on the plurality of electronic switches in a preset sequence, wherein the first control signal has a first duty cycle that is smaller than the duty cycle of the control signal output by the controller before receiving the shutdown signal; or

[0014] When a shutdown signal is received, a first control signal is outputted to turn off all of the plurality of electronic switches.

[0015] Optionally, the plurality of electronic switches include high-side switches and low-side switches; and the controller is configured to:

[0016] When the rotation speed of the motor decreases to a first rotation speed threshold, a second control signal is output to control the high-side switch or the low-side switch to be turned on.

[0017] Optionally, the second control signal is a PWM control signal with a constant duty cycle, so that the conduction time of the high-side switch or the low-side switch is fixed; or

[0018] The second control signal is a PWM control signal that gradually increases according to a preset duty cycle increment, so that the conduction time of the high-side switch or the low-side switch gradually increases according to the preset increment.

[0019] Optionally, when the second control signal is a PWM control signal that gradually increases according to a preset duty cycle increment, an initial duty cycle of the PWM control signal is less than or equal to 30%.

[0020] Optionally, the controller is further configured to:

[0021] If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period;

[0022] When the speed of the motor decreases to a second speed threshold, outputting the second control signal of a preset duration;

[0023] Based on a comparison result between the rotation speed of the motor and a corresponding rotation speed threshold, the first control signal and the second control signal are alternately output until the motor stops rotating.

[0024] Optionally, it further includes: a power supply module, used to receive alternating current to power the stator winding;

[0025] The voltage conversion module is used to receive the AC power received by the power module and output a DC bus voltage.

[0026] In a second aspect, an embodiment of the present invention further provides a power tool braking method, which is applied to the power tool described in any embodiment of the present invention, and the method includes:

[0027] When a shutdown signal is received, a first control signal is output to control the drive circuit to output an excitation signal of a preset intensity or to stop outputting the excitation signal, so that the motor runs at a reduced speed;

[0028] When the rotation speed of the motor decreases to a first rotation speed threshold, a second control signal is output to control the drive circuit to output an excitation signal for short-circuiting the stator winding, thereby braking the motor.

[0029] Optionally, the driving circuit includes a plurality of electronic switches; and outputting a first control signal to control the driving circuit to output an excitation signal of a preset intensity or to pause outputting the excitation signal, so that the motor runs at a reduced speed, includes:

[0030] outputting a first control signal that turns on the plurality of electronic switches in a preset sequence, wherein the first control signal has a first duty cycle that is smaller than the duty cycle of the control signal output by the controller before receiving the shutdown signal; or

[0031] A first control signal is outputted to turn off all of the plurality of electronic switches.

[0032] Optionally, the plurality of electronic switches include high-side switches and low-side switches; and outputting a second control signal to control the drive circuit to output an excitation signal for short-circuiting the stator winding to brake the motor includes:

[0033] A second control signal is output to control the high-side switch or the low-side switch to be turned on to brake the motor, wherein the on-time of the high-side switch or the low-side switch is fixed or gradually increases according to a preset increment.

[0034] Optionally, after outputting the second control signal to control the drive circuit to output an excitation signal for short-circuiting the stator winding, the method further includes:

[0035] If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period;

[0036] When the speed of the motor decreases to a second speed threshold, outputting the second control signal of a preset duration;

[0037] Based on a comparison result between the rotation speed of the motor and a corresponding rotation speed threshold, the first control signal and the second control signal are alternately output until the motor stops rotating.

[0038] The electric tool provided by the embodiment of the present invention has the following characteristics: when the electric tool is turned off, the controller first outputs a first control signal to make the motor coast or decelerate, so that the motor speed decreases; when the motor speed drops to a first speed threshold, the controller outputs a second control signal, so that the drive circuit outputs an excitation signal to short-circuit the stator winding of the motor, and the motor generates a braking torque under the action of the excitation signal to brake the motor. By first allowing the motor speed to drop to a certain speed before performing braking control, it is possible to avoid generating excessive braking force and preventing the motor speed from dropping too quickly, thereby avoiding the risk of functional parts of the electric tool loosening and falling off during braking, and improving the safety of the electric tool. At the same time, after the motor speed drops to a certain speed, performing braking control can avoid the stator winding from generating a large braking current, thereby avoiding damage to the electronic components in the motor and extending the life of the electric tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A structural block diagram of an electric tool provided by an embodiment of the present invention;

[0040] Figure 2 Shown is a block diagram of a control system of an electric tool as an embodiment;

[0041] Figure 3 A schematic structural diagram of a driving circuit provided by an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of a PWM control signal with increased duty cycle provided by an embodiment of the present invention;

[0043] Figure 5 A structural block diagram of another electric tool provided by an embodiment of the present invention;

[0044] Figure 6 This is a flow chart of a power tool braking method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0046] Figure 1 This is a schematic diagram of the structure of an electric tool provided by an embodiment of the present invention. The electric tool is not limited to angle grinders, grinders, screwdrivers, and sanders. Any electric tool driven by a brushless motor can adopt the technical solution provided by the embodiment of the present invention. Taking an angle grinder as an example, the angle grinder 100 includes:

[0047] The shield 101 , the output shaft 102 , the motor (not shown), the transmission mechanism (not shown), the housing 105 , the AC unit 106 and the operation switch 107 .

[0048] The protective cover 101 at least partially covers the grinding disc to provide a protective function. The output shaft 102 is used to mount or secure the grinding disc. The output shaft 102 is connected to a motor, which drives the output shaft 102 to rotate. Specifically, the motor includes a motor shaft, which is connected to the output shaft 102 via a transmission mechanism, transmitting the driving force of the motor shaft to the output shaft 102.

[0049] The AC unit 106 is used to access AC power to power the angle grinder 100. In some embodiments, the AC unit 106 includes an AC plug and a peripheral circuit electrically connected to the AC plug. The AC plug is inserted into an AC socket to access AC mains power, thereby providing a source of power for the power tool. In another embodiment, the AC unit 106 includes other structural forms and peripheral circuits that can access AC power. For example, the AC plug is connected to a movable substation or other means to access AC power. It should be noted that the AC unit 106 only needs to be able to access AC power, and the specific structure and form are not limited here. The value range of the AC power that the AC unit 106 can access is 110V~130V or 210V~230V.

[0050] The housing 105 is formed with a handle portion 1051 for the user to hold and a head shell portion 1052 located at the front end of the handle portion.

[0051] The head shell portion 1052 defines a head shell space capable of accommodating the motor and transmission mechanism. The handle portion 1051 defines a space for at least accommodating the motor control unit. Furthermore, the front end of the handle portion is formed with a generally tubular grip for the user to grasp. A downwardly extending protrusion is formed at the rear end of the handle portion, located between the grip portion and the AC unit.

[0052] The angle grinder 100 further includes an operating switch 107 for starting or stopping the motor 103. The motor starts when the operating switch 107 is triggered, and the motor stops when the operating switch 107 is released. The operating switch 107 is provided on the head shell 1052.

[0053] Figure 2 FIG. 1 is a block diagram of a control system of an electric tool as an embodiment. Figure 2 The electric tool further includes a motor 10 , a drive circuit 20 and a controller 30 .

[0054] The motor 10 further includes a stator winding and a rotor. In some embodiments, the motor 10 is a three-phase brushless motor including a rotor having permanent magnets and electronically commutated three-phase stator windings U, V, and W. In some embodiments, the three-phase stator windings U, V, and W are connected in a star configuration, while in other embodiments, the three-phase stator windings U, V, and W are connected in a delta configuration. However, it should be understood that other types of brushless motors are also within the scope of this disclosure. A brushless motor may include fewer than or more than three phases.

[0055] The drive circuit 20 is connected to the motor 10 and is used to provide an excitation signal to the motor 10. The drive circuit 20 is a circuit used to rotate and drive the motor 10 by switching the power-on state of each phase winding of the motor 10 and controlling the current flowing through each phase winding. The conduction order and time of each phase winding depend on the position of the rotor. In order to rotate the motor 10, the drive circuit 20 has multiple drive states. In one drive state, the stator winding of the motor 10 generates a magnetic field. The controller 30 outputs a control signal based on different rotor positions to control the drive circuit 20 to switch the drive state so that the magnetic field generated by the stator winding rotates to drive the rotor to rotate, thereby driving the motor 10. In this embodiment, under the action of the control signal output by the controller 30, the drive circuit 20 is used to output an excitation signal to the stator winding of the motor 10 to control the motor 10 to slow down and brake.

[0056] In some embodiments, the input side of the drive circuit 20 is connected to the converted DC voltage signal of the power supply of the power tool 100, and the control end of the drive circuit 20 is connected to the controller 30. The controller 30 outputs a control signal so that the drive circuit 20 distributes the power of the DC voltage on the input side to each phase winding on the stator of the motor 10 in a certain logical relationship, so that the motor 10 starts and generates continuous torque.

[0057] The controller 30 is connected to the drive circuit 20 and is used to output a control signal to the drive circuit 20. Optionally, the power tool 100 also includes a drive chip 31, which is used to control the on or off state of the electronic switch in the drive circuit 20. The drive chip 31 is connected in series between the controller 30 and the drive circuit 20, and controls the on or off state of the electronic switch in the drive circuit 20 according to the control signal from the controller 30. In some embodiments, the control signal from the controller 30 is a PWM control signal. In this embodiment, the drive chip 31 is shown as being separated from the controller 30. In other embodiments, the drive chip 31 and the controller 30 can be integrated into one.

[0058] In this embodiment, the controller 30 is configured as follows:

[0059] When receiving the shutdown signal, the first control signal is output to control the driving circuit 20 to output the excitation signal of the preset intensity or to stop outputting the excitation signal, so that the motor 10 runs at a reduced speed;

[0060] When the speed of the motor 10 decreases to a first speed threshold, a second control signal is output to control the drive circuit 20 to output an excitation signal that short-circuits the stator winding, thereby braking the motor 10 .

[0061] When shutting down the power tool 100, it is usually necessary to brake the motor as quickly as possible while ensuring the safety of the power tool 100. Considering that the speed of the power tool 100 is relatively high before shutting down, if forced braking is performed, functional components of the power tool 100 may become loose or even fall off, causing a safety accident. This embodiment outputs different brake signals to control the power tool 100 to brake as quickly as possible without causing safety hazards.

[0062] Specifically, the first control signal acts on the drive circuit 20, causing the drive circuit 20 to output the power signal on the input side to the stator winding of the motor 10 at a certain intensity. Under this working condition, the intensity of the excitation signal is less than the intensity of the excitation signal output by the drive circuit 20 before receiving the shutdown signal, which is equivalent to reducing the driving force for the motor 10, thereby reducing the speed of the motor 10 and the motor 10 running at a reduced speed.

[0063] Alternatively, the first control signal acts on the drive circuit 20, causing the drive circuit 20 to disconnect the power supply from the motor 10. Under this operating condition, the drive circuit 20 suspends outputting the excitation signal to the stator winding of the motor 10, so that the rotor of the motor 10 is in a gliding state, and the speed of the motor 10 decreases accordingly, and the motor 10 runs at a reduced speed.

[0064] When the stator windings of motor 10 are short-circuited, the motor 10, in its generating state, is equivalent to a short-circuited power supply. Because the stator windings have relatively low resistance, a large short-circuit current is generated. This effectively dissipates the kinetic energy of the rotor through the stator resistance and dissipates it as heat, generating a significant braking torque for rapid braking. The higher the speed of motor 10, the greater the short-circuit current and the greater the braking force.

[0065] In this embodiment, when the speed of the motor 10 decreases to a first speed threshold, the controller 30 outputs a second control signal to control the short-circuiting of the stator windings of the motor 10, thereby braking the motor 10. This arrangement has the advantage of, on the one hand, being able to brake the motor 10 after the speed has decreased to a certain value, resulting in a smaller short-circuit current that does not exceed the tolerance of the electronic switch in the drive circuit 20; and, on the other hand, being able to brake the motor 10 after the speed has decreased to a certain value prevents the speed of the motor 10 from decreasing too rapidly. Thus, the braking process does not cause the functional components of the power tool 100 to become loose, thereby reducing the risk of functional components falling off. For example, if the power tool 100 is an angle grinder, braking the motor 10 when the speed is too high would generate a large braking torque, which could cause the grinding wheel of the angle grinder to fly out, resulting in a safety accident. Therefore, being able to brake the motor 10 after the speed has decreased to the first speed threshold can avoid generating an excessively large braking torque, i.e., preventing the speed of the motor 10 from suddenly decreasing from a high speed to a low speed, thereby reducing the risk of functional components falling off of the power tool 100 and causing a safety accident.

[0066] In the power tool 100 provided in an embodiment of the present invention, when the power tool 100 is turned off, the controller 30 first outputs a first control signal to decelerate the motor 10. When the speed of the motor 10 drops to a first speed threshold, the controller 30 outputs a second control signal, causing the drive circuit 20 to output an excitation signal that short-circuits the stator winding of the motor 10. Under the action of the excitation signal, the motor 10 generates a braking torque to brake the motor 10. By first allowing the speed of the motor 10 to drop to a certain speed before performing braking control, it is possible to avoid generating excessive braking force and preventing the speed of the motor 10 from dropping too quickly, thereby reducing the risk of functional parts of the power tool 100 loosening and falling off during the braking process. At the same time, after the speed of the motor 10 drops to a certain speed, braking control is performed, and the short-circuit current generated by the stator winding of the motor is small, which will not damage the electronic components in the drive circuit.

[0067] Optionally, based on the above embodiment, the driving circuit 20 includes a plurality of electronic switches, and the controller 30 is configured as follows:

[0068] Upon receiving the shutdown signal, outputting a first control signal that turns on the plurality of electronic switches in a preset sequence, wherein the first control signal has a first duty cycle that is smaller than the duty cycle of the control signal output by the controller 30 before receiving the shutdown signal; or

[0069] When a shutdown signal is received, a first control signal is output to turn off all of the multiple electronic switches.

[0070] The preset sequence refers to the turn-on sequence of the electronic switches in the driving circuit 20 when the motor 10 is operating normally.

[0071] The first duty cycle is less than the duty cycle of the control signal output by the controller 30 before shutdown, so that the intensity of the excitation signal output by the drive circuit 20 to the motor stator winding is less than the intensity of the excitation signal output by the drive circuit 20 to the motor stator winding before shutdown, and the driving force of the motor 10 decreases, causing the motor 10 to run at a reduced speed. For example, before shutdown, the duty cycle of the control signal output by the controller 30 is 100%, then the duty cycle of the first control signal can be any duty cycle less than 100%, which can cause the motor to run at a reduced speed. Of course, in order to quickly reduce the motor speed to the first speed threshold, the duty cycle of the first control signal can be set to be significantly different from the duty cycle of the control signal before shutdown.

[0072] When all the electronic switches are turned off, the drive circuit 20 stops outputting the excitation signal. The motor 10 loses its driving force due to the lack of the excitation signal, the motor rotor is in a coasting state, and the speed of the motor 10 decreases.

[0073] The action process of the first control signal will be further described below with reference to the accompanying drawings. Figure 3 A schematic diagram of a driving circuit according to an embodiment of the present invention is provided. Figure 3 The drive circuit 20 includes a plurality of electronic switches. In some embodiments, the electronic switches include field effect transistors (FETs), while in other embodiments, the electronic switches include insulated gate bipolar transistors (IGBTs), etc. In some embodiments, the drive circuit 20 is a three-phase bridge circuit. Specifically, the drive circuit 20 includes three drive switches Q1, Q3, and Q5 configured as high-side switches and three drive switches Q2, Q4, and Q6 configured as low-side switches.

[0074] The three drive switches Q1, Q3, and Q5, which serve as high-side switches, are respectively arranged between the power supply line and the phase coils of the motor 10. The three switching elements Q2, Q4, and Q6, which serve as low-side switches, are respectively arranged between the phase coils of the motor 10 and the ground line. The gate terminals UH, UL, VH, VL, WH, and WL of the six drive switches Q1-Q6 are electrically connected to the controller 30, and each drain or source of the drive switches is connected to the stator winding of the motor 10. The drive switches Q1-Q6 change the on or off state at a certain frequency according to the control signal output by the controller 30, thereby changing the power state loaded by the power module on the winding of the motor 10.

[0075] For example, the control signal before shutdown is a PWM control signal with a duty cycle of 100%, and the first control signal is a PWM control signal with a duty cycle of 80%. The PWM control signal with a duty cycle of 80% controls the electronic switches in the drive circuit 20 to be turned on in the conduction sequence of Table 1, so that the speed of the motor rotor decreases.

[0076] Table 1

[0077] Q1 and Q4 are on All other switches are off Q1 and Q6 are turned on All other switches are off Q3 and Q6 are turned on All other switches are off Q3 and Q2 are turned on All other switches are off Q5 and Q2 are turned on All other switches are off Q5 and Q4 are turned on All other switches are off Q1 and Q4 are on All other switches are off

[0078] Exemplarily, the first control signal controls all six electronic switches Q1-Q6 of the upper and lower bridge arms to be closed. At this time, the stator winding of the motor 10 has no excitation signal, so that the rotor of the motor 10 loses driving force and is in a coasting state, and the speed of the motor decreases.

[0079] Optionally, based on the above embodiment, the controller 30 is further configured to: output a second control signal to control the high-side switch or the low-side switch to be turned on when the speed of the motor 10 decreases to a first speed threshold.

[0080] Continue to refer Figure 3 The second control signal controls the three electronic switches Q1, Q3, and Q5 of the upper bridge arm to be all turned on and the three electronic switches Q2, Q4, and Q6 of the lower bridge arm to be all turned off, or controls the three electronic switches Q2, Q4, and Q6 of the lower bridge arm to be all turned on and the three electronic switches Q1, Q3, and Q5 of the upper bridge arm to be all turned off. Under this working condition, the stator of the motor 10 is short-circuited, generating a short-circuit current, and the kinetic energy of the motor rotor is converted into heat energy on the stator of the motor 10, causing the motor to be in a braking state, and the speed of the motor rotor drops rapidly.

[0081] Optionally, the second control signal is a PWM control signal with a constant duty cycle, so that the conduction time of the high-side switch or the low-side switch is fixed; or,

[0082] The second control signal is a PWM control signal that gradually increases according to a preset duty cycle increment, so that the conduction time of the high-side switch or the low-side switch gradually increases according to the preset increment.

[0083] When the second control signal is a PWM control signal with a constant duty cycle, the high-side switch or the low-side switch in the on state is turned on for a fixed duration.

[0084] Figure 4 Schematic diagram of PWM control signal with increased duty cycle provided by an embodiment of the present invention, refer to Figure 4 When the second control signal is a PWM control signal that increases according to a preset duty cycle increment, the conduction time of the high-side switch or the low-side switch in the on state gradually increases according to the preset increment. The advantage of this setting is that because the rotor speed has been reduced, a greater braking torque is obtained by increasing the conduction time, so that the motor 10 can stop rotating as soon as possible without affecting the user's feel.

[0085] Optionally, when the second control signal is a PWM control signal that gradually increases according to a preset duty cycle increment, an initial duty cycle of the PWM control signal is less than or equal to 30%.

[0086] The above analysis indicates that the higher the motor speed, the greater the short-circuit current generated during short-circuit braking. Even after the motor has initially decelerated, a relatively large short-circuit current may still be generated if a control signal with a larger duty cycle is used. This embodiment, by setting the initial duty cycle of the PWM control signal to less than or equal to 30%, can prevent the generation of excessive short-circuit currents that exceed the tolerance of the MOS transistor when the motor 10 is running at high speed. After the motor 10 speed is reduced to a low speed, even using a control signal with a 100% duty cycle to increase the braking torque will not generate an excessive short-circuit current. Therefore, using a PWM control signal with a gradually increasing duty cycle for braking will not damage the MOS transistor.

[0087] Optionally, based on the above embodiment, the controller 30 is further configured to:

[0088] If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period;

[0089] When the speed of the motor 10 decreases to a second speed threshold, a second control signal of a preset duration is output;

[0090] Based on a comparison result between the rotation speed of the motor 10 and the corresponding rotation speed threshold, the first control signal and the second control signal are alternately output until the motor 10 stops rotating.

[0091] As analyzed above, under the action of the second control signal, the stator winding of the motor 10 generates a short-circuit current. To obtain a larger braking torque and quickly stop the motor 10, the duty cycle of the second control signal is large, causing the speed of the motor 10 to drop rapidly. This rapid drop in speed can cause the user's hand feel to deteriorate. To address this issue, in this embodiment, when using a PWM control signal with a constant duty cycle as the second control signal, the controller 30 alternately outputs the first control signal and the second control signal according to the speed of the motor 10, causing the motor 10 to alternately operate between a deceleration state and a braking state. On the one hand, the second control signal is used to brake the motor 10, causing it to stop rotating as quickly as possible; on the other hand, the first control signal is used to decelerate the motor 10, making the entire braking process more gentle and helping to improve the user's hand feel during the braking process.

[0092] For example, a speed threshold list can be pre-configured in the controller 30. The controller 30 compares the current speed of the motor 10 obtained with the various thresholds in the list. Whenever the speed of the motor 10 drops to the corresponding speed threshold, the controller 30 outputs a second control signal to short-circuit brake the motor 10. In this alternating operation, the motor 10 is braked quickly and gently.

[0093] Optional, Figure 5This is a structural block diagram of another electric tool provided by an embodiment of the present invention. Figure 5 The power tool also includes:

[0094] A power module 40 is used to receive AC power to power the stator winding;

[0095] The voltage conversion module 41 is configured to receive the AC power from the power module 40 and output a DC bus voltage.

[0096] The power module 40 is used to access AC power to power the motor 10. In some embodiments, the power module 40 includes an AC plug and a peripheral circuit electrically connected to the AC plug. The AC plug is inserted into an AC socket to access AC mains power, thereby providing a source of power for the motor 10. In another embodiment, the power module 40 includes other structural forms and peripheral circuits that can access AC power, for example, the AC plug is connected to a movable substation to access AC power. It should be noted that the power module 40 only needs to be able to access AC power, and the specific structure and form are not limited here. The AC power that the power module 40 can access ranges from 110V to 130V or 210V to 230V.

[0097] The voltage conversion module 41 is used to receive the AC power received by the power module 40 and operatively output a DC bus voltage. The voltage conversion module 41 includes a rectifier circuit 411 and a filter capacitor 412 .

[0098] Rectifier circuit 411 is used to convert AC power into DC power for output. Rectifier circuit 411 is connected in series between power module 40 and filter capacitor 412 to receive AC power and convert it into pulsating DC power. In some specific embodiments, rectifier circuit 411 includes four rectifier bridges.

[0099] Filter capacitor 412 is used to filter the pulsating DC power from rectifier circuit 411. Filter capacitor 412 is connected in series between rectifier circuit 411 and driver circuit 20. In some embodiments, filter capacitor 412 is a small electrolytic capacitor. In other embodiments, filter capacitor 412 is a thin film capacitor.

[0100] Optionally, in some embodiments, the power tool further includes a power submodule 42, which is used to power the driver chip 31 and / or the controller 30. In some embodiments, the power submodule 42 is connected to the power module 40 to convert the AC power received through the power module 40 into a power supply voltage output suitable for the driver chip 31 and / or the controller 30. For example, in some embodiments, in order to power the driver chip 31, the power submodule 42 reduces the AC power supply voltage from the power module 40 to 15V to power the controller 30, and reduces the power supply voltage to 3.2V to power the driver chip 31. In another embodiment, the power submodule 42 is connected to the voltage conversion module 41 to convert the AC power received through the power module 40 into a power supply voltage output suitable for the driver chip 31 and / or the controller 30.

[0101] Optionally, in some embodiments, the power tool further includes a switch device, which is used to start or shut down the motor 10. The switch device is located between the power submodule 42 and the driver chip 31. In some embodiments, the switch device serves as a trigger switch of the power tool. When the user presses the trigger switch device to the on position, the driver chip 31 and / or the controller 30 receives an electrical signal from the power submodule 42, and the motor 10 is powered on; when the user presses the trigger switch device to the off position, the electrical connection between the driver chip 31 and / or the controller 30 and the power submodule 42 is cut off, the controller receives a shutdown signal, and the controller controls the motor 10 to brake.

[0102] Optional, Figure 6 This is a flow chart of a method for braking an electric tool provided by an embodiment of the present invention. This method can be applied to the electric tool described in any embodiment of the present invention and is used to control the braking process of the electric tool to prevent the electric tool's braking speed from being too high and affecting the mechanical structure of the electric tool. For example, when an angle grinder with a braking function is braking, if the braking speed is too high, the grinding disc is likely to loosen and there is a risk of falling off. The method of the embodiment of the present invention can be used to solve this problem. Figure 5 , the method specifically comprises the following steps:

[0103] S610: When a shutdown signal is received, output a first control signal to control the driving circuit to output an excitation signal of a preset intensity or to suspend outputting the excitation signal, so that the motor runs at a reduced speed.

[0104] The controller outputs a first control signal to the drive circuit. The drive circuit allocates the input voltage signal according to the first control signal to output an excitation signal of a certain intensity to the motor, thereby driving the motor. Specifically, in this embodiment, the drive circuit outputs a deceleration excitation signal to the motor according to the first control signal, thereby reducing the motor speed.

[0105] In one embodiment, the drive circuit includes multiple electronic switches; the controller outputs a first control signal that causes the multiple electronic switches to turn on in a preset order, and the first control signal has a first duty cycle, which is smaller than the duty cycle of the control signal output by the controller before receiving the shutdown signal.

[0106] Among them, compared with the working condition where the driving circuit drives the motor to operate normally, under the action of the first control signal, the driving circuit does not change the conduction sequence of each electronic switch, but only reduces the intensity of the excitation signal output to the electronic switch to reduce the driving force of the motor and control the motor to operate at a reduced speed.

[0107] In one embodiment, the controller outputs a first control signal to turn off all of the plurality of electronic switches.

[0108] Among them, when multiple electronic switches in the drive circuit are all turned off, the drive circuit stops outputting excitation signals to the motor, the motor loses driving force and is in a sliding state, and the speed gradually decreases.

[0109] S620: When the speed of the motor decreases to a first speed threshold, output a second control signal to control the drive circuit to output an excitation signal that short-circuits the stator winding, thereby braking the motor.

[0110] The second control signal is used to brake the motor, rapidly reducing its speed. Specifically, under the action of the second control signal, the motor's stator winding is short-circuited, and the motor is now in a generating state. The short-circuited stator winding generates a short-circuit current, generating a large amount of heat that consumes the kinetic energy of the motor's rotor, causing the motor's speed to rapidly decrease.

[0111] In one embodiment, the multiple electronic switches in the drive circuit include a high-side switch and a low-side switch; the controller outputs a second control signal to control the high-side switch or the low-side switch to be turned on to brake the motor, wherein the on-time of the high-side switch or the low-side switch being turned on is fixed or gradually increases according to a preset increment.

[0112] Among them, when all the high-side electronic switches in the drive circuit are turned on or all the low-side electronic switches are turned on, the stator winding of the motor is short-circuited, and the motor in the generating state generates a short-circuit current in the short-circuited stator winding. The braking force generated by the short-circuit current hinders the rotation of the motor, thereby controlling the motor to decelerate.

[0113] When the second control signal is a PWM control signal whose duty cycle gradually increases according to a preset duty cycle increment, the on-time of the high-side switch or the low-side switch gradually increases according to the preset increment. The advantage of using a PWM control signal with a gradually increasing duty cycle for braking control is that during the braking process, as the motor speed continues to decrease, the short-circuit current generated also continues to decrease, and accordingly, the braking torque also gradually decreases. At this time, increasing the duty cycle of the PWM control signal can increase the short-circuit current of the motor stator winding to compensate for the short-circuit current reduced due to the speed decrease, that is, to compensate for the braking torque reduced due to the speed decrease, making the braking torque relatively stable, thereby quickly stopping the motor and achieving rapid braking.

[0114] It is worth noting that before shutdown, the motor's speed is relatively high. If the motor is directly short-circuited to brake, the high speed will generate a large short-circuit current. This large short-circuit current may not only damage the switch in the drive circuit, but also, because the speed drops too quickly, it may cause the motor's functional components to loosen and fall off, causing a safety accident. This embodiment avoids this problem by first outputting a first control signal to reduce the motor's speed before short-circuiting the motor.

[0115] The electric tool braking method provided by an embodiment of the present invention is as follows: when the electric tool is turned off, the controller first outputs a control signal to decelerate the motor, causing the motor's speed to decrease. When the motor's speed drops to a set speed threshold, the controller outputs a control signal to brake the motor, causing the motor's stator winding to generate a short-circuit current. The short-circuit current generates a braking torque that hinders the rotation of the motor's rotor. Under the action of the braking torque, the motor is able to slow down. By first controlling the motor to slow down and reduce its speed before braking the motor to quickly stop it, it is possible to avoid immediate braking at high speeds to generate excessive short-circuit current and damage the switch in the drive circuit, and to avoid the motor's speed dropping too quickly, thereby reducing the risk of loosening or falling off of the functional parts of the electric tool.

[0116] Optionally, based on the above technical solution, after outputting the second control signal to control the drive circuit to output an excitation signal for short-circuiting the stator winding, the method further includes:

[0117] If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period;

[0118] When the speed of the motor decreases to a second speed threshold, a second control signal of a preset duration is output;

[0119] Based on a comparison result between the rotational speed of the motor and a corresponding rotational speed threshold, a first control signal and a second control signal are alternately output until the motor stops rotating.

[0120] Among them, when the duty cycle of the second control signal is constant, on the one hand, the short-circuit current must be smaller than the rated current of the electronic switch tube in the drive circuit, and on the other hand, the deceleration of the motor must be controlled to be smaller than the acceleration of the motor before shutdown. When the above conditions are met, in order to stop the motor as quickly as possible, it is necessary to output a control signal with a larger duty cycle to obtain a relatively large braking torque. When the braking torque is large, the speed of the motor will drop too fast, resulting in a decrease in the user's feel. For this reason, when the present embodiment uses a PWM control signal with a constant duty cycle for braking, the controller alternately outputs the first control signal and the second control signal according to the speed of the motor to control the motor to alternately operate in a deceleration state and a braking state, making the entire braking process more gentle, thereby achieving the goal of stopping the motor as quickly as possible while improving the user's feel.

[0121] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. An electric tool comprising: an electric motor, including a stator winding and a rotor; a driving circuit, connected to the motor, and configured to provide an excitation signal to the motor; a controller connected to the driving circuit and configured to output a control signal to the driving circuit, It is characterized in that the controller is configured to: When a shutdown signal is received, a first control signal is output to control the drive circuit to output an excitation signal of a preset intensity so that the motor runs at a reduced speed; When the speed of the motor decreases to a first speed threshold, a second control signal is output to control the drive circuit to output an excitation signal for short-circuiting the stator winding, thereby braking the motor; If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period; When the speed of the motor decreases to a second speed threshold, outputting the second control signal of a preset duration; Based on a comparison result between the rotation speed of the motor and a corresponding rotation speed threshold, the first control signal and the second control signal are alternately output until the motor stops rotating.

2. The electric tool according to claim 1, wherein: The driving circuit includes a plurality of electronic switches, and the controller is configured to: When a shutdown signal is received, a first control signal is output to turn on the multiple electronic switches in a preset order, wherein the first control signal has a first duty cycle, which is smaller than the duty cycle of the control signal output by the controller before the shutdown signal is received.

3. The electric tool according to claim 2, wherein: The plurality of electronic switches include high-side switches and low-side switches; and the controller is configured to: When the rotation speed of the motor decreases to a first rotation speed threshold, a second control signal is output to control the high-side switch or the low-side switch to be turned on.

4. The electric tool according to claim 3, wherein: The second control signal is a PWM control signal with a constant duty cycle, so that the conduction time of the high-side switch or the low-side switch is fixed.

5. The electric tool according to claim 1, wherein: Also includes: a power supply module, configured to receive alternating current to supply power to the stator winding; The voltage conversion module is used to receive the AC power received by the power module and output a DC bus voltage.

6. A method for braking a power tool, The electric tool comprises: an electric motor, including a stator winding and a rotor; a driving circuit, connected to the motor, and configured to provide an excitation signal to the motor; Characterized in that, the braking method comprises: When a shutdown signal is received, a first control signal is output to control the drive circuit to output an excitation signal of a preset intensity, so that the motor runs at a reduced speed; When the speed of the motor decreases to a first speed threshold, a second control signal is output to control the drive circuit to output an excitation signal for short-circuiting the stator winding, thereby braking the motor; After outputting the second control signal to control the drive circuit to output an excitation signal for short-circuiting the stator winding, the method further includes: If the second control signal is a PWM control signal with a constant duty cycle, the first control signal is output after the second control signal is output for a preset time period; When the speed of the motor decreases to a second speed threshold, outputting the second control signal of a preset duration; Based on a comparison result between the rotation speed of the motor and a corresponding rotation speed threshold, the first control signal and the second control signal are alternately output until the motor stops rotating.

7. The electric tool braking method according to claim 6, characterized in that: The drive circuit includes a plurality of electronic switches; the outputting of a first control signal to control the drive circuit to output an excitation signal of a preset intensity so as to cause the motor to run at a reduced speed includes: A first control signal is output to turn on the plurality of electronic switches in a preset sequence, wherein the first control signal has a first duty cycle that is smaller than the duty cycle of the control signal output by the controller before receiving the shutdown signal.

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