Electric tool and control method thereof

Abstract

The present invention discloses an electric tool, comprising: a motor; a power supply for supplying power to the motor; a drive circuit electrically connected to the motor so that the power supply applies voltage to the motor; a voltage detection module for detecting the voltage of the motor; and a controller configured to perform the following operations: if the voltage of the motor is greater than or equal to a preset voltage, the drive circuit is controlled to apply voltage to the motor at a second slope; wherein the value range of the second slope is greater than or equal to zero and less than or equal to 0.3. The present invention also discloses a control method for starting an electric tool with load. The electric tool and the control method thereof disclosed in the present invention not only avoid the excessive starting current when the lawn mower is started with load, but also shorten the starting time of the lawn mower, thereby improving the user experience.

Description

Technical Field

[0001] The invention relates to an electric tool, in particular to a garden-type electric tool and a control method thereof. Background Art

[0002] When the existing electric tool is started under load, the starting voltage of the motor is increased to increase the initial speed of the motor, thereby causing the motor to rotate to start the electric tool.

[0003] On the one hand, the increase in the motor starting voltage will cause a larger starting current to flow through the motor, which may cause the motor or other circuit components to burn out.

[0004] On the other hand, if the starting voltage of the motor is increased slowly, the power tool will start more slowly when loaded, affecting the user experience. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, an object of the present invention is to provide an electric tool that can be quickly started under load conditions and a control method for starting the electric tool under load.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An electric tool comprises: a motor; a power supply for supplying power to the motor; a drive circuit electrically connected to the motor so that the power supply applies voltage to the motor; a voltage detection module for detecting the voltage of the motor; and a controller configured to perform the following operations: if the voltage of the motor is greater than or equal to a preset voltage, control the drive circuit to apply voltage to the motor with a second slope; wherein the value range of the second slope is greater than or equal to zero and less than or equal to 0.3.

[0008] Furthermore, it also includes: a speed detection module for detecting the speed of the motor; the controller is configured to perform the following operations: if the speed of the motor is greater than or equal to a preset speed, the control drive circuit is used to apply a voltage to the motor with a third slope; wherein the third slope is greater than the second slope.

[0009] Furthermore, the value range of the preset speed n is: n≤60%n0, where n0 is the no-load speed of the motor.

[0010] Furthermore, it also includes: a trigger switch, used to enable the drive circuit to start applying voltage to the motor; the controller is configured to perform the following operations: if the voltage of the motor is less than a preset voltage, the drive circuit is controlled to apply voltage to the motor with a first slope; wherein the first slope is less than or equal to the third slope.

[0011] Further, the controller determines the preset voltage based on a maximum current that the internal circuit of the power tool can withstand.

[0012] Further, the controller selects the preset voltage based on one of: a maximum current that the drive circuit can withstand; and a load of the motor.

[0013] Furthermore, the driving circuit includes a switching power tube; the controller uses a pulse width modulation method to control the conduction or closing of the switching power tube so that the driving circuit is used to apply a voltage value to the motor with a second slope.

[0014] Furthermore, the power supply is a battery pack that is detachably connected to the power tool, and the voltage of the battery pack is greater than or equal to 30V.

[0015] Furthermore, the electric tool is a lawn mower.

[0016] A control method for an electric tool, the electric tool includes a motor and a drive circuit, the control method includes the following steps: detecting the voltage of the motor; when the voltage of the motor is greater than or equal to a preset voltage, enabling the drive circuit to apply a voltage to the motor with a second slope; the value range of the second slope is greater than or equal to zero and less than or equal to 0.3.

[0017] Furthermore, when the voltage of the motor is less than a preset voltage, the driving circuit is used to apply a voltage to the motor with a first slope; wherein the first slope is less than or equal to the third slope.

[0018] Further, the speed of the motor is detected; if the speed of the motor is greater than or equal to the preset speed, the drive circuit is used to apply a voltage value to the motor with a third slope; the value range of the preset speed n is: n≤60%n0, where n0 is the no-load speed of the motor.

[0019] Furthermore, a preset voltage is obtained based on a maximum current that the driving circuit can withstand.

[0020] As another aspect of the present invention, a method for starting an electric tool under load is provided, wherein the electric tool includes a motor, and the method includes the following steps: detecting the voltage of the motor; when the electric tool is in a first starting stage, applying a voltage that gradually increases according to a first slope to the motor; when the electric tool is in a second starting stage, applying a voltage that changes according to a second slope to the motor; when the voltage of the motor is greater than or equal to a preset voltage, the electric tool switches from the first starting stage to the second starting stage.

[0021] Furthermore, the value range of the second slope is greater than or equal to zero and less than or equal to 0.3.

[0022] Furthermore, the third slope is greater than or equal to the first slope.

[0023] Furthermore, a preset voltage is obtained based on a maximum current that the electric tool can carry or a load of the motor.

[0024] Further, the rotation speed of the motor is detected; if the rotation speed of the motor is greater than or equal to the preset rotation speed, the electric tool switches from the second starting stage to the third starting stage;

[0025] When the electric tool is in the third starting stage, a voltage gradually increasing according to a second slope is applied to the motor.

[0026] Furthermore, the value range of the preset speed n is: n≤60% n0, where n0 is the no-load speed of the motor.

[0027] The invention is beneficial in that it avoids excessive starting current when the lawn mower is started under load, shortens the starting time of the lawn mower, and improves the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a structural diagram of a lawn mower as an embodiment;

[0029] Figure 2 is a circuit block diagram of a lawn mower as one embodiment;

[0030] Figure 3a shows a curve of the voltage applied to the motor changing over time as an implementation mode;

[0031] Figure 3b shows a curve of a PWM control signal changing over time as an implementation method;

[0032] Figure 3c shows a curve of the speed of a motor changing over time as an implementation mode;

[0033] Figure 3d A curve showing the change of the motor starting current over time as an implementation method is shown;

[0034] Figure 4a FIG. 4 shows a curve of a voltage applied to a motor changing over time as another embodiment;

[0035] Figure 4b shows a curve of a PWM control signal changing over time as another embodiment;

[0036] Figure 5 is a flow chart of a control method for a lawn mower as one embodiment;

[0037] Figure 6 is a flow chart of a control method for a lawn mower as another embodiment. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0039] The electric tools of the present invention include but are not limited to the following: screwdrivers, electric drills, wrenches, angle grinders and other electric tools that require speed regulation, sanders and other electric tools that may be used to grind workpieces, reciprocating saws, circular saws, jigsaws and other electric tools that may be used to cut workpieces; electric hammers and other electric tools that may be used for impact. These tools may also be garden tools, such as lawn mowers, snow blowers, vacuum blowers, pruning machines and chain saws; in addition, these tools may also be used for other purposes, such as blenders. As long as these electric tools can adopt the substantive content of the technical solutions disclosed below, they can fall within the protection scope of the present invention.

[0040] For the convenience of description, a lawn mower 100 is taken as an example for description. The lawn mower 100 may be a push lawn mower or a riding lawn mower.

[0041] refer to Figure 1 As shown, the lawn mower 100 includes: a power supply 110 , a motor 120 , a housing 130 , a handle 140 , wheels 150 , a blade (not shown), and a chassis 160 .

[0042] The power supply 110 is used as a power source to provide kinetic energy for the lawn mower 100. In some embodiments, the power supply 110 is a battery pack, and the battery pack is detachably connected to the housing 130. Figure 1 As shown, the housing 130 is provided with a battery compartment 1311 for accommodating a battery pack, and the battery compartment 131 is provided on the upper part of the chassis 160. In some embodiments, the lawn mower 100 includes a plurality of battery packs. In some embodiments, the voltage of the battery pack is greater than or equal to 30V. Further, the voltage of the battery pack is greater than or equal to 48V.

[0043] The blade is a tool accessory of the lawn mower 100 , and is used to realize the mowing function of the lawn mower 100 . The blade is arranged in the chassis 160 .

[0044] The motor 120 is used to drive the blade to rotate. The motor 120 is operably connected to the blade to drive the blade to rotate, thereby achieving a mowing function. In some embodiments, the blade is directly connected to the motor 120 shaft of the motor 120. In other embodiments, the blade can be connected to the motor 120 through a transmission device or a reduction structure.

[0045] The chassis 160 is used to carry and install the motor 120. The chassis 160 is formed with a cutting cavity (not shown).

[0046] The handle 140 is used for the user to hold, so that the user can push the lawn mower 100. The lawn mower 100 also includes a self-propelled motor, which is used to drive the wheels 150 to rotate so as to realize the walking function of the lawn mower 100.

[0047] refer to Figure 2 As shown, the lawn mower 100 further includes a power supply circuit 121 , a drive circuit 122 , a voltage detection module 123 , a rotation speed detection module 124 , a trigger switch 125 and a controller 126 .

[0048] The power supply circuit 121 is electrically connected to the power supply 110 and is used to convert the power supply voltage from the power supply 110 to power various functional circuits. The functional circuits mentioned here include but are not limited to circuits, chips or electronic devices inside the lawn mower 100 for realizing functions such as detection, driving, control, and calculation. In some embodiments, multiple power supply circuits 121 may be included to power each functional module respectively.

[0049] The driving circuit 122 is electrically connected to the motor 120 so that the power supply 110 applies voltage to the motor 120. In some embodiments, the motor 120 is a three-phase brushless motor 120 including a three-phase winding. Figure 2 As shown, the three-phase windings U, V, and W form a star connection. The drive circuit 122 includes six switching elements, and the switching elements can be field effect tubes or IGBI transistors. For convenience of explanation, taking IGBT transistors as an example, the gates of the switching elements Q1-Q6 are connected to the controller 126, and the collectors and emitters of the switching elements Q1-Q6 are connected to the three-phase windings. The switching elements Q1-Q6 are turned on and off according to the drive signal output from the controller 126 to adjust the voltage applied to the motor 120 to control the speed and commutation of the motor 120.

[0050] The speed detection module 124 is used to detect the speed of the motor 120. In some embodiments, the speed detection module 124 includes a Hall sensor. Three Hall sensors are arranged at intervals of 60 degrees along the rotation direction of the motor 120 near the rotor of the motor 120 to detect the speed of the motor 120. In some embodiments, the speed detection module 124 can also use a sensorless method or other types of sensors, such as an optical or magnetic encoder or a rotary transformer.

[0051] The voltage detection module 123 is used to detect the voltage of the motor 120. In some embodiments, the voltage detection module 123 includes a voltage sensor and other peripheral circuits connected thereto. In some embodiments, the voltage monitoring module is integrated with the controller 126. It should be noted that the voltage detection module 123 can adopt any other solution that can detect the voltage of the motor 120.

[0052] The trigger switch 125 is disposed on the housing 130 for the user to operate to start the lawn mower 100. In this embodiment, the trigger switch 125 is disposed on a trigger on the housing. When the user operates the trigger switch 125, the power supply 110 supplies power to the lawn mower 100, and the lawn mower 100 enters a start state.

[0053] The controller 126 generates corresponding control signals according to the detection signals input by the speed detection module 124 and / or the voltage detection module 123 to control the driving circuit 122 to output a corresponding voltage to load to the motor 120 until the lawn mower 100 is started.

[0054] The following will combine the actual starting conditions of the lawn mower 100 and Figure 3a-3d The start-up control of the lawn mower 100 will be described in detail.

[0055] The user operates the trigger switch 125 and the lawn mower 100 enters the start state. The controller 126 responds to the input signal of the trigger switch 125 and controls the driving circuit 122 to apply a voltage to the motor 120 with a first slope when the voltage of the motor 120 is less than the preset voltage V0.

[0056] In some embodiments, the voltage detection module 123 detects the voltage of the motor 120. When the voltage of the motor 120 is less than a preset voltage, the lawn mower 100 is in the first startup stage. When the lawn mower 100 is in the first startup stage, the controller 126 is configured to output a control signal to the drive circuit 122 to control the drive circuit 122 to apply a gradually increasing voltage to the motor 120 at a first slope. In this stage, the speed of the motor 120 increases as the voltage applied to the motor 120 increases.

[0057] Specifically, the control signal output by the controller 126 is a PWM signal. When the lawn mower 100 is in the first startup stage, the controller 126 outputs a PWM signal with a gradually increasing duty cycle, such as Figure 3b As shown, when the lawn mower 100 is in the first startup stage, the duty cycle of the PWM signal gradually increases with a first slope.

[0058] When the voltage of the motor 120 is greater than or equal to the preset voltage, the lawn mower 100 switches from the first startup stage to the second startup stage. When the lawn mower 100 is in the second startup stage, the controller 126 is configured to control the driving circuit 122 to apply voltage to the motor 120 with a second slope.

[0059] In some embodiments, the control signal output by the controller 126 is a PWM signal. The voltage detection module 123 detects the voltage of the motor 120. When the voltage of the motor 120 is greater than or equal to a preset voltage value, the controller 126 outputs a PWM signal with a fixed duty cycle to the drive circuit 122. Figure 3bAs shown, the lawn mower 100 is in the second startup stage at this time, and the duty cycle of the PWM signal is a fixed value. In this stage, the motor 120 has a certain speed, and the motor 120 rotates to drive the blade to cut vegetation such as weeds, so that the load of the motor 120 changes, and the speed of the motor 120 also changes with the load of the motor 120 (such as Figure 3c as shown).

[0060] In other embodiments, if the voltage of the motor 120 is greater than or equal to the preset voltage value, the controller 126 outputs a PWM signal with a duty cycle changing at a second slope to the driving circuit 122. Figure 4a and Figure 4b As shown, the lawn mower 100 is in the second starting stage, and the duty cycle of the PWM signal changes with a second slope.

[0061] In one or more embodiments, the value range of the second slope is greater than or equal to zero and less than or equal to 0.3. If the second slope is zero, that is, the controller 126 outputs a PWM signal with a constant duty cycle to the drive circuit 122, and the drive circuit 122 applies a constant voltage to the motor 120. Since the voltage loaded to the motor 120 remains constant, on the one hand, it can prevent the generation of excessive starting current when starting the motor 120, and on the other hand, the rotation of the motor 120 drives the blade to cut soft vegetation such as weeds, and the load of the motor 120 will be reduced. The speed of the motor 120 increases as the load of the motor 120 decreases, so that the motor 120 can be started quickly. If the second slope is greater than 0.3, the voltage loaded to the motor 120 increases too fast, generating an excessive starting current. The excessive current increases the temperature of the components, potentially causing the motor 120, the drive circuit 122, etc. to burn out.

[0062] The preset voltage is obtained based on the maximum current that the power tool can withstand or the load of the motor 120. The maximum current that the power tool can withstand includes the maximum current that the drive circuit 122 can withstand, the maximum current that the motor 120 can withstand, or the maximum current that other electronic components can withstand.

[0063] In some embodiments, a preset voltage is obtained based on the maximum current that the driving circuit 122 can withstand, and the preset voltage value is written into the controller 126. In some embodiments, a one-to-one correspondence between the maximum current that the driving circuit 122 can withstand and the preset voltage value is established, and stored in a storage unit of the power tool in a table form, and the storage unit can be integrated into the controller 126 or exist separately.

[0064] When the voltage of the motor 120 reaches the preset voltage, the lawn mower 100 switches from the first starting stage to the second starting stage to change the voltage applied to the motor 120. The selection of the preset voltage and the change of the voltage both shorten the starting time of the motor 120 and ensure that the starting current is maintained within the range that allows the lawn mower 100 to operate normally.

[0065] The speed detection module 124 detects the speed of the motor 120. If the speed of the motor 120 is greater than or equal to the preset speed n, the controller 126 controls the driving circuit 122 to apply a voltage to the motor 120 with a third slope.

[0066] In some embodiments, the control signal output by the controller 126 is a PWM signal. If the speed of the motor 120 is greater than or equal to the preset speed n, the controller 126 outputs a PWM signal with a duty cycle changing at a third slope to the drive circuit 122. Figure 3b As shown, the lawn mower 100 is in the third startup stage, and the duty cycle of the PWM signal increases with a third slope. In this stage, the voltage applied to the motor 120 also gradually increases with a third slope, and the speed of the motor 120 increases until the lawn mower 100 is started.

[0067] In at least one embodiment, the preset speed n has a value range of n≤60%n0, where n0 is the no-load speed of the motor 120. If the preset speed n is greater than 60% of the preset speed, the voltage applied to the motor 120 will be too high, generating an excessive starting current.

[0068] In at least one embodiment, the third slope is greater than or equal to the first slope, which shortens the startup time and reduces the startup current.

[0069] Figure 3a A curve showing the change of the voltage loaded to the motor over time is shown, wherein the dotted line represents the conventional on-load starting process of the lawn mower 100 , and the solid line represents the on-load starting process of the lawn mower 100 as one of the embodiments using the above starting scheme.

[0070] Figure 3b The curve of the PWM signal changing with time is shown, wherein the dotted line represents the conventional on-load starting process of the lawn mower 100 , and the solid line represents the on-load starting process of the lawn mower 100 as one of the embodiments adopting the above starting scheme.

[0071] Figure 3c The curve of the rotation speed of the motor 120 changing with time is shown, wherein the dotted line represents the conventional on-load starting process of the lawn mower 100, and the solid line represents the on-load starting process of the lawn mower 100 as one of the embodiments adopting the above starting scheme.

[0072] Figure 3dA curve of starting current changing with time is shown, wherein the dotted line represents the conventional on-load starting process of the lawn mower 100 , and the solid line represents the on-load starting process of the lawn mower 100 as one of the embodiments using the above starting scheme.

[0073] refer to Figure 3a-3d Compared with conventional load-starting schemes, the load-starting scheme for lawn mowers described in the present disclosure makes the current of the lawn mowers lower during the entire load-starting process, avoiding the frequent starting problem caused by excessive starting current when the lawn mowers are started. At the same time, the starting time of the lawn mowers is also shortened. It is particularly suitable for starting lawn mowers under heavy load.

[0074] refer to Figure 5 The on-load starting method for a lawn mower shown in the figure comprises the following steps:

[0075] S501. Detect the voltage V of the motor.

[0076] In this step, the voltage detection module detects the voltage of the motor. Here, the voltage of the motor can be a phase voltage or a bus voltage. In some embodiments, the voltage monitoring module includes a voltage sensor and other peripheral circuits connected thereto. In some embodiments, the voltage monitoring module is integrated with the controller.

[0077] S502. Determine whether the voltage of the motor is greater than or equal to a preset voltage V0; if not, execute step S503; if yes, execute step S504.

[0078] In this step, the controller compares the voltage of the motor inputted by the voltage detection module with the preset voltage V0 in the controller to output a corresponding control signal to the driving circuit.

[0079] The preset voltage is obtained based on the maximum current or motor load that the electric tool can withstand, wherein the maximum current that the electric tool can withstand includes the maximum current that the drive circuit can withstand, the maximum current that the motor can withstand, or the maximum current that other electronic components can withstand.

[0080] In some embodiments, a preset voltage is obtained based on the maximum current that the driving circuit can withstand, and the preset voltage value is written into the controller. In some embodiments, a one-to-one correspondence between the maximum current that the driving circuit can withstand and the preset voltage value is established, and the values ​​are stored in a storage unit of the power tool in a table form. The storage unit can be integrated into the controller or exist separately.

[0081] S503. Enable the driving circuit to apply a voltage to the motor with a first slope.

[0082] In this step, the controller outputs a control signal to enable the driving circuit to apply a voltage to the motor at a first slope. In some embodiments, the control signal output by the controller is a PWM signal.

[0083] S504. Enable the driving circuit to apply a voltage value to the motor with a second slope.

[0084] In this step, the controller outputs a control signal to enable the drive circuit to apply a voltage value to the motor at a second slope. In some embodiments, the control signal output by the controller is a PWM signal. The PWM signal changes at a second slope. The second slope has a value range of greater than or equal to zero and less than or equal to 0.3.

[0085] S505. Detect the rotation speed of the motor.

[0086] In this step, the speed detection module detects the speed of the motor. In some embodiments, the speed detection module includes a Hall sensor. Three Hall sensors are arranged at intervals of 60 degrees along the motor rotation direction near the rotor of the motor 120 to detect the speed of the motor. In some embodiments, the speed detection module can also use a sensorless method or other types of sensors, such as an optical or magnetic encoder or a rotary transformer.

[0087] S506. Determine whether the motor speed is greater than or equal to the preset speed; if not, return to step S505; if so, execute step S507.

[0088] In this step, the controller outputs a control signal to the drive circuit according to the motor speed detected by the speed detection module. The value range of the preset speed n is: n≤60%n0, n0 is the no-load speed of the motor.

[0089] S507. Enable the driving circuit to apply a voltage value to the motor with a third slope.

[0090] In this step, the controller outputs a control signal to enable the drive circuit to apply a voltage value to the motor at a third slope. In some embodiments, the control signal output by the controller is a PWM signal. The third slope is greater than the second slope.

[0091] refer to Figure 6 Another method for starting a lawn mower with load shown in the figure comprises the following steps:

[0092] S601. Detect the voltage V of the motor;

[0093] S602. Detect the motor speed;

[0094] S603. Determine whether the voltage of the motor is greater than or equal to the preset voltage, if so, go to step S604, if not, go to step S605;

[0095] S604. Enable the driving circuit to apply a voltage value to the motor 120 at a second slope;

[0096] The value range of the second slope is greater than or equal to zero and less than or equal to 0.3.

[0097] S605. Enable the driving circuit to apply a voltage value to the motor 120 at a first slope;

[0098] S606. Determine whether the motor speed is greater than or equal to the preset speed; if so, go to step S607; if not, go to step S603.

[0099] Among them, the value range of the preset speed n is: n≤60%n0, n0 is the no-load speed of the motor 120.

[0100] S607 . Enable the driving circuit to apply a voltage value to the motor 120 at a third slope.

[0101] Figure 6 The on-load starting method for the lawn mower is shown in Figure 5 The difference of the load-starting method for the lawn mower shown is that during the load-starting process, the voltage V of the motor and the speed of the motor 120 can be detected simultaneously, which will not be described in detail here.

[0102] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. An electric tool comprising: Motor; A power supply, used to supply power to the motor; a drive circuit electrically connected to the motor so that the power supply applies a voltage to the motor; A voltage detection module, used for detecting the voltage of the motor; The controller is configured to do the following: When the electric tool is in a starting state, if the voltage of the motor is greater than or equal to a preset voltage, controlling the drive circuit to apply a voltage to the motor with a second slope; The value range of the second slope is greater than or equal to zero and less than or equal to 0.3; Also includes: A rotation speed detection module, used for detecting the rotation speed of the motor; The controller is configured to perform the following operations: If the rotation speed of the motor is greater than or equal to a preset rotation speed, controlling the driving circuit to apply a voltage to the motor with a third slope; wherein the third slope is greater than the second slope; The value range of the preset speed n is: n≤60%n0, where n0 is the no-load speed of the motor.

2. The electric tool according to claim 1, characterized in that: Also includes: a trigger switch for causing the drive circuit to begin applying voltage to the motor; The controller is configured to perform the following operations: If the voltage of the motor is less than the preset voltage, controlling the driving circuit to apply a voltage to the motor with a first slope; The first slope is less than or equal to the third slope.

3. The electric tool according to claim 1, characterized in that: The controller determines the preset voltage based on a maximum current that an internal circuit of the electric tool can withstand.

4. The electric tool according to claim 1, characterized in that: The controller selects the preset voltage based on one of the following: The maximum current that the driving circuit can withstand; and The load of the motor.

5. The electric tool according to claim 1, characterized in that: The driving circuit includes a switching power tube; The controller uses pulse width modulation to control the on or off of the switch power tube so that the drive circuit is used to apply a voltage value to the motor with a second slope.

6. The electric tool according to claim 1, characterized in that: The power supply is a battery pack detachably connected to the power tool, and the voltage of the battery pack is greater than or equal to 30V.

7. The electric tool according to claim 1, characterized in that: The electric tool is a lawn mower.

8. A control method for an electric tool, the electric tool comprising a motor and a drive circuit, the control method comprising the following steps: detecting a voltage of the motor; When the electric tool is in a starting state, when the voltage of the motor is greater than or equal to a preset voltage, the drive circuit is used to apply a voltage to the motor with a second slope; The value range of the second slope is greater than or equal to zero and less than or equal to 0.3; Detecting the rotation speed of the motor; If the rotation speed of the motor is greater than or equal to a preset rotation speed, the driving circuit is used to apply a voltage value to the motor with a third slope; wherein the third slope is greater than the second slope; The value range of the preset speed n is: n≤60%n0, where n0 is the no-load speed of the motor.

9. The control method according to claim 8, characterized in that: When the voltage of the motor is less than the preset voltage, the driving circuit is used to apply a voltage to the motor with a first slope; The first slope is less than or equal to the third slope.

10. The control method according to claim 8, characterized in that: The preset voltage is obtained based on a maximum current that the driving circuit can withstand.

11. A method for starting an electric tool under load, the electric tool comprising a motor, the method comprising the following steps: detecting a voltage of the motor; When the electric tool is in a first starting stage, applying a voltage gradually increasing at a first slope to the motor; When the electric tool is in a second starting stage, applying a voltage varying with a second slope to the motor; When the voltage of the motor is greater than or equal to a preset voltage, the electric tool switches from the first starting stage to the second starting stage; The value range of the second slope is greater than or equal to zero and less than or equal to 0.3; Detecting the rotation speed of the motor; If the rotation speed of the motor is greater than or equal to the preset rotation speed, the electric tool switches from the second starting stage to the third starting stage; When the electric tool is in the third starting stage, applying a voltage gradually increasing at a third slope to the motor; wherein the third slope is greater than the second slope; The value range of the preset speed n is: n≤60% n0, where n0 is the no-load speed of the motor.

12. The method according to claim 11, characterized in that The preset voltage is obtained based on a maximum current that the electric tool can carry or a load of the motor.

13. The method according to claim 11, characterized in that The third slope is greater than or equal to the first slope.

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