Power tool and control method thereof

Abstract

The application provides an electric tool, comprising: a power supply unit; a brushless motor comprising a stator and a rotor; an inverter circuit comprising a plurality of switching elements, the switching elements performing switching actions to control driving of the brushless motor; a controller electrically connected with the inverter circuit and the brushless motor, the controller comprising a load detection module detecting a parameter indicative of a working load of the brushless motor; when the parameter is less than a set threshold, the controller controls the brushless motor to maintain a first target rotating speed; when the parameter is greater than or equal to the set threshold, the controller controls the brushless motor to maintain a second target rotating speed; wherein the first target rotating speed is greater than the second target rotating speed. By controlling the motor rotating speed of the electric tool to maintain at a lower second target rotating speed, the electric tool is prevented from being damaged due to large motor rotating speed fluctuation under heavy load. By controlling the motor rotating speed of the electric tool to maintain at a higher first target rotating speed, the working efficiency of the electric tool before entering the heavy load state is improved.

Description

[0001] This application claims priority to Chinese Patent Application No. 202110528366.6, filed May 14, 2021, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the field of control, and in particular to an electric power tool and a control method thereof. BACKGROUND

[0003] Electric power tools have been widely used in home, garden and other working environments, bringing great convenience to people's life and work. Electric power tools can be powered by a battery pack. After the switch of the electric power tool is turned on to connect the power supply, the motor rotates and drives the transmission mechanism to achieve various power operations.

[0004] To achieve the desired output power, ordinary electric power tools usually use open-loop or closed-loop regulation of PWM duty cycle. However, for the purpose of obtaining greater or more stable output power, the PWM duty cycle regulation method is difficult to meet the expectations. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, one object of the present application is to provide an electric power tool and a control method thereof, which can meet the user's expectations for output power.

[0006] According to a first aspect of the present application, an electric power tool is provided, comprising:

[0007] a power supply unit;

[0008] a brushless motor including a stator and a rotor;

[0009] an inverter circuit including a plurality of switching elements, the switching elements performing switching actions to control driving of the brushless motor;

[0010] a controller electrically connected to the inverter circuit and the brushless motor, the controller including a load detection module to detect a parameter indicative of a working load of the brushless motor;

[0011] when the parameter is less than a set threshold, the controller controls the brushless motor to maintain a first target speed;

[0012] when the parameter is greater than or equal to the set threshold, the controller controls the brushless motor to maintain a second target speed;

[0013] wherein the first target speed is greater than the second target speed.

[0014] In one of the embodiments, the controller adjusts the PWM duty cycle and / or the conduction angle of the switching element to keep the brushless motor at a first target speed or a second target speed.

[0015] In one of the embodiments, the controller can also adjust the advance angle of the switching element.

[0016] In one of the embodiments, when the parameter is less than the set threshold and the actual motor speed is less than the first target speed, or when the parameter is greater than or equal to the set threshold and the actual motor speed is less than the second target speed, the PWM duty cycle and / or the conduction angle of the switching element is increased, wherein the PWM duty cycle has a higher priority than the conduction angle.

[0017] In one of the embodiments, when the parameter is less than the set threshold and the actual motor speed is greater than the first target speed, or when the parameter is greater than or equal to the set threshold and the actual motor speed is greater than the second target speed, the PWM duty cycle and / or the conduction angle of the switching element is decreased, wherein the conduction angle has a higher priority than the PWM duty cycle.

[0018] In one of the embodiments, the brushless motor is a three-phase brushless motor, the brushless motor includes a position sensor, the controller calculates the actual motor speed according to the signal transmitted by the position sensor, and the minimum value of the conduction angle of each phase of the three-phase brushless motor is 120° and the maximum value is 180°.

[0019] In one of the embodiments, the conduction angle is adjusted by a fixed increment, and the increment is any value in the range of 0.1-0.5°.

[0020] In one of the embodiments, the power tool is an impact fastening tool, the impact fastening tool includes an impact mechanism, and when the parameter is greater than or equal to the set threshold, the impact mechanism performs an impact action.

[0021] According to a second aspect of the present application, a control method of a power tool is provided, including the following steps:

[0022] A controller detects a parameter indicating the working load of a brushless motor, and determines the working state of the power tool according to the parameter;

[0023] When it is determined that the parameter is less than a set threshold, the controller controls the brushless motor to keep a first target speed;

[0024] When it is determined that the parameter is greater than or equal to the set threshold, the controller controls the brushless motor to keep a second target speed;

[0025] wherein the first target speed is greater than the second target speed.

[0026] In one embodiment, the controller controls the brushless motor to maintain a first target speed or the controller controls the brushless motor to maintain a second target speed includes: the controller calculates an actual motor speed of the brushless motor, when the actual motor speed is less than the first target speed or the actual motor speed is less than the second target speed, the controller increases a PWM duty cycle and / or a conduction angle of driving the brushless motor, wherein the PWM duty cycle has a higher priority than the conduction angle.

[0027] In one embodiment, the controller controls the brushless motor to maintain a first target speed or the controller controls the brushless motor to maintain a second target speed includes: the controller calculates an actual motor speed of the brushless motor, when the actual motor speed is greater than the first target speed or the actual motor speed is greater than the second target speed, the controller decreases the conduction angle and / or the PWM duty cycle of driving the brushless motor, wherein the conduction angle has a higher priority than the PWM duty cycle.

[0028] In one embodiment, the controller can also adjust a lead angle of driving the brushless motor.

[0029] According to a third aspect of the present application, there is provided an electric power tool, comprising:

[0030] a power supply unit;

[0031] a brushless motor including a stator and a rotor;

[0032] an inverter circuit including a plurality of switching elements, the switching elements performing switching actions to control driving of the brushless motor;

[0033] a controller electrically connected to the inverter circuit and the brushless motor, the controller including a load detection module to detect a parameter indicative of a load of the brushless motor;

[0034] when the parameter is greater than or equal to a set threshold, the controller controls the brushless motor to maintain a target speed;

[0035] when the parameter is less than the set threshold, the controller controls the brushless motor in an open loop manner, the brushless motor having a maximum speed under the open loop manner control;

[0036] wherein the maximum speed under the open loop manner control is greater than the target speed.

[0037] In one embodiment, the controller adjusts a PWM duty cycle and / or a conduction angle of the switching elements to maintain the target speed of the brushless motor.

[0038] In one embodiment, when the parameter is greater than or equal to a set threshold, and the actual motor speed is less than the target speed, the PWM duty cycle and / or the conduction angle of the switching element is increased, wherein the PWM duty cycle has a higher priority than the conduction angle.

[0039] In one embodiment, when the parameter is greater than or equal to a set threshold, and the actual motor speed is greater than the target speed, the conduction angle and / or the PWM duty cycle of the switching element is decreased, wherein the conduction angle has a higher priority than the PWM duty cycle.

[0040] According to a fourth aspect of the present application, a control method of an electric power tool is provided, comprising the steps of:

[0041] The controller detects a parameter indicative of the load of the brushless motor, and determines the working state of the electric power tool according to the parameter;

[0042] When the parameter is determined to be less than a set threshold, the brushless motor is controlled in an open loop mode, and the brushless motor has a maximum speed in the open loop mode;

[0043] When the parameter is determined to be greater than or equal to a set threshold, the controller controls the brushless motor to maintain a target speed;

[0044] Wherein the maximum speed in the open loop mode is greater than the target speed.

[0045] In one embodiment, the controller controlling the brushless motor to maintain a target speed comprises: the controller calculating the actual motor speed of the brushless motor, and when the actual motor speed is less than the target speed, the controller increasing the PWM duty cycle and / or the conduction angle of the switching element driving the brushless motor, wherein the PWM duty cycle has a higher priority than the conduction angle.

[0046] In one embodiment, the controller controlling the brushless motor to maintain a target speed comprises: the controller calculating the actual motor speed of the brushless motor, and when the actual motor speed is greater than the target speed, the controller decreasing the conduction angle and / or the PWM duty cycle of the switching element driving the brushless motor, wherein the conduction angle has a higher priority than the PWM duty cycle.

[0047] According to the present application, by controlling the motor speed of the electric power tool to maintain at a lower second target speed, the electric power tool is prevented from being damaged due to the large fluctuation of the motor speed under heavy load. By controlling the motor speed of the electric power tool to maintain at a higher first target speed, the working efficiency of the electric power tool is improved before entering the heavy load state. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0049] Figure 1 The structural schematic diagram of the impact fastening tool provided by the embodiment one of the present application is shown.

[0050] Figure 2 The circuit block diagram of the control system of the impact fastening tool provided by the embodiment one of the present application is shown.

[0051] Figure 3A The schematic diagram of the power inverter module provided by the embodiment one of the present application is shown.

[0052] Figure 3B The driving sequence diagram of the initial conduction angle provided by the embodiment one of the present application is shown.

[0053] Figure 4 The driving sequence diagram of the increased conduction angle provided by the embodiment one of the present application is shown.

[0054] Figure 5 The relationship curve between the trigger switch stroke and the motor control provided by the embodiment one of the present application is shown.

[0055] Figure 6 The flowchart of the control method provided by the embodiment one of the present application is shown.

[0056] Figure 7A The flowchart of the increased PWM duty ratio or conduction angle provided by the embodiment one of the present application is shown.

[0057] Figure 7B The flowchart of the decreased conduction angle or PWM duty ratio provided by the embodiment one of the present application is shown.

[0058] Figure 8 The flowchart of the control method provided by the embodiment two of the present application is shown. DETAILED DESCRIPTION

[0059] In order to solve the above problems, the embodiments of the present application propose an electric tool and a control method thereof. The embodiments of the present application will be described in detail below with reference to the drawings.

[0060] The technical solutions in the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0061] It should be noted that when an element is referred to as being "provided on" another element, it can be directly on the other element or there can be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there can be an intervening element. The terms "vertical", "horizontal", "left", "right", and similar expressions used herein are for illustrative purposes only and are not intended to be limiting.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0063] Embodiment One

[0064] Figure 1 The structure of the impact fastening tool provided by the first embodiment of the present application is shown. It should be understood that the embodiments of the present application can also be applied to other fastening tools, grinding tools, cutting tools, cleaning tools, garden tools, etc.

[0065] The impact fastening tool 100 includes a housing 101, a motor 102, an output end 103, a controller 104, an impact mechanism 106, and a battery pack 105.

[0066] The motor 102 is disposed in the upper cavity of the housing 101 and includes a rotor and a stator. In this embodiment, the motor 102 is a three-phase brushless direct current (BLDC) motor that is powered by the battery pack 105 under the control of the controller 104. Other forms of motors can also be used, which are not limited here.

[0067] The trigger switch 107 can be disposed on the handle of the housing 101 and used to provide user input to the controller 104 so that the controller 104 controls the operation of the impact fastening tool 100 according to the user's input instructions. The trigger switch 107 can be a trigger switch based on a displacement sensor, or other forms of switches can also be used, such as switches based on touch sensors, capacitive sensors, etc.

[0068] The controller 104 can be disposed in a cavity of the lower portion of the handle, and the controller 104 can include a central processing unit (CPU) or other forms of processing units having data processing capability and / or instruction execution capability.

[0069] The battery pack 105 can be detachably mounted on the housing 101, or can be disposed in the housing 101 in a built-in manner, or can be connected to the impact fastening tool 100 and the battery pack 105 in a length by an external power line. Although the impact fastening tool of the present embodiment adopts a battery pack as a power supply unit, it should be clear that the impact fastening tool can also adopt a conventional alternating current power supply as a power supply unit.

[0070] The impact mechanism 106 includes a tripping unit mainly formed by a hammer and an anvil. When the working load of the output end 103 increases to a certain extent, the hammer and the anvil change from integrated rotation to relative rotation with impact action, so that the hammer repeatedly applies impact force in the radial direction of the anvil, i.e., a tripping state.

[0071] Figure 2 The circuit block diagram of the control system 110 of the impact fastening tool of the present embodiment is shown. The control system 110 includes a motor control circuit 111, a battery pack 105, a motor 102, and a position detection module 112. The position detection module 112 is usually mounted in the motor for detecting the position information of the rotor on the motor 102 and transmitting the position information to the controller. The position detection module 112 of the present embodiment adopts a Hall sensor, and other types of position sensors such as a magneto-electric sensor and a photoelectric sensor can also be adopted. The main control module 202 receives the position signal from the position detection module 112 and calculates the actual motor speed of the motor 102 according to the position signal. Compared with a motor without a position detection module, the motor with the position detection module in the present embodiment can have a larger conduction angle and a leading angle adjustment interval.

[0072] Because the motor coil is an inductive load, the current in the coil will have a certain time delay relative to the loading voltage on the coil, and a leading angle setting method is usually adopted to improve this problem. In the present embodiment, the installation position of the Hall sensor is adjusted to achieve the setting of the leading angle. As a transformation, a program can also be implanted in the control software to set a fixed or variable leading angle, and the effect is similar to the present embodiment.

[0073] The motor control circuit 111 is used for driving control of the motor 102. The motor control circuit 111 includes a power inverter module 201, a main control module 202, a driving module 203, and a sampling module 204.

[0074] The sampling module 204 is configured to collect the working load parameter of the motor 102 and send the parameter to the controller 104, so that the controller 104 determines the working state according to the parameter.

[0075] Figure 3A The power inverter module 201 is a three-phase bridge inverter circuit, which includes six switching elements, divided into upper and lower bridge arms. The six switching elements include three upper side switches and three lower side switches, which are driven by high drive signals UH, VH and WH and low drive signals UL, VL and WL, respectively. The source of the upper side switch of each phase is connected to the drain of the lower side switch to output a power signal for driving the motor 102. The main control module 202 determines the switching frequency of the switching elements in the power inverter module 201 and the commutation timing according to the signal feedback, thereby controlling the speed of the motor 102.

[0076] The conventional constant speed electric tool adjusts the motor speed by adjusting the PWM duty cycle. The duty cycle in the conduction time of each phase conduction angle determines the voltage duration provided to the motor. Generally, the greater the duty cycle, the longer the voltage duration provided to the motor in the conduction time, and the greater the motor speed. The actual motor speed can be calculated according to the position information measured by the position detection module. If the actual motor speed is lower than the target speed, the motor speed can be increased by increasing the PWM duty cycle. However, when the PWM duty cycle increases to the maximum value of 100%, if the actual motor speed still does not reach the target speed, it is not possible to increase the voltage duration in the conduction time, so it is not possible to increase the motor speed by increasing the PWM duty cycle, resulting in the electric tool not reaching the expected output.

[0077] Figure 3B The driving sequence diagram of the power inverter module 201 is shown when the PWM duty cycle of the three-phase brushless motor is 100%, the conduction angle of each phase is the initial value of 120°, and the lead angle is 0°. As can be seen, the conduction time of the conduction angle between adjacent two phases (for example, U phase and V phase) does not overlap. In this embodiment, in order to further increase the speed of the electric tool to reach the expected output, the conduction angle of the adjacent two phases is partially overlapped by increasing the conduction angle, which helps to increase the total voltage provided to the motor, thereby further improving the motor speed. Figure 4

[0078] ​Specifically, when the actual motor speed is less than the target speed, the PWM duty cycle adjustment is prior to the conduction angle adjustment; when the actual motor speed is greater than the target speed, the conduction angle adjustment is prior to the PWM duty cycle adjustment. Priority refers to adjusting the variable with high priority first, and then adjusting the variable with low priority when the variable with high priority reaches the maximum value or the minimum value. For example, if the actual motor speed is less than the target speed, the PWM duty cycle is increased to increase the motor speed. When the PWM duty cycle reaches the maximum value, if there is still a demand for speed, the conduction angle is increased. If the actual motor speed is greater than the target speed, and the conduction angle is greater than the initial value at this time, the conduction angle is reduced to reduce the motor speed. When the conduction angle is reduced to the initial value, there is still a demand for speed reduction, and then the PWM duty cycle is reduced. The combination of the two adjustment methods greatly widens the adjustment range of the motor speed and improves the flexibility of the motor speed adjustment. It should be understood that the lead angle adjustment can also be added on the basis of the above to further improve the range and flexibility of the speed adjustment.

[0079] In the embodiment, the maximum value of the PWM duty cycle is set to 100%, and the maximum value of the PWM duty cycle can also be set to 95% or other in the software program. The initial value and the maximum value of the conduction angle basically depend on the parameters of the motor. In the embodiment, the initial value of the conduction angle of the three-phase brushless DC motor is 120°, and the maximum value is 180°. The initial value of the lead angle is 0°, and the maximum value is 60°.

[0080] Specifically, when the conduction angle is adjusted, the slope adjustment with a fixed increment is preferably used, and the increment range is 0.1-0.5°. Preferably, the increment value is 0.1°, so that the motor speed adjustment is more stable. In addition, the slope adjustment with a floating increment can also be considered, for example, the slope adjustment with a small increment is used when the difference between the actual motor speed and the target speed is less than a preset threshold, and the slope adjustment with a large increment is used when the difference between the actual motor speed and the target speed is greater than or equal to the preset threshold, so as to improve the adjustment efficiency. If the conduction angle reaches 180° and the actual motor speed still does not reach the target speed, the conduction angle can be kept at 180° without further increasing the conduction angle, so as to avoid the decrease of the working efficiency of the motor.

[0081] Since the motor tool usually requires a high speed, the conduction angle is preferably increased by using the advanced commutation method, which is beneficial to increasing the speed in the medium and high speed conditions. However, it should be understood that according to the working conditions and power of the specific motor tool, the conduction angle can also be increased by using the lagging commutation method. Furthermore, the conduction angle can also be adjusted by using the combination of the advanced commutation method and the lagging commutation method.

[0082] For example, when the current flowing through the motor 102 is less than a set threshold, the sampling module 204 determines that the motor is in the first working state, and the main control module 202 controls the motor 102 to keep the first target speed by adjusting the PWM duty cycle and / or the conduction angle; when the current is greater than or equal to the set threshold, the main control module 202 determines that the motor 102 is in the second working state, and controls the motor 102 to keep the second target speed by adjusting the PWM duty cycle and / or the conduction angle. It should be clear that the parameter indicating the load of the motor can also be the vibration of the motor, the stress of the working head, and the speed of the motor, as well as other parameters that can represent the size of the load. In order to be accurate, more than two parameters can be used to indicate the load of the motor.

[0083] Preferably, the current threshold is any value in the range of 10A to 20A, and more preferably, the threshold is 15A. The first working state can refer to the impact fastening tool being in an idle or light load state, such as the impact mechanism 106 not performing impact fastening actions; the second working state can refer to the impact fastening tool being in a heavy load state, such as the impact mechanism 106 performing impact fastening actions.

[0084] In this embodiment, the first target speed is greater than the second target speed. By controlling the motor speed of the impact fastening tool to keep at a lower second target speed in the second working state, the impact fastening tool is prevented from being damaged due to large fluctuations in motor speed under heavy load. At the same time, the motor speed of the impact fastening tool is kept at a first target speed higher than the second target speed in the first working state, so that the working efficiency of the impact fastening tool before the motor enters the heavy load state is improved.

[0085] Specifically, the first target speed is any value in the range of 21850 to 24150 RPM (revolutions per minute), and preferably, the first target speed is 23000 RPM; the second target speed is any value in the range of 12350 to 13650 RPM, and preferably, the second target speed is 13000 RPM. It should be understood that both the first target speed and the second target speed can be set to a range value.

[0086] The first target speed and the second target speed can be default built-in parameters of the impact fastening tool out of the factory, or can be set by the user through hardware or software, for example, the impact fastening tool can receive the first target speed and the second target speed selected by the user through a function panel (not shown) provided on the shell 101 of the impact fastening tool. The first target speed and the second target speed can have different values according to different user needs or technical parameters of impact fastening tools of different power. The numerical values mentioned in this embodiment are only for illustration and are not limited thereto.

[0087] Since the first target speed is high, in order to make the speed-up in the starting stage smooth, the trigger switch can be set to a front displacement, for example, before 70% displacement, and the speed-up is performed in a linear increase of PWM duty ratio. After the trigger switch is displaced to 70%, the starting detection load parameter is detected and the working state is judged. For example, after the trigger switch is pressed to 70%, the motor speed reaches 23000 RPM. When the load parameter is detected to be greater than the set threshold, according to the embodiment, the motor is controlled in the second working state to keep the motor speed at 13000 RPM, as shown in Figure 5

[0088] Figure 6 The flowchart of the control method of the embodiment is shown.

[0089] Step S301: detecting a parameter indicating the working load of the motor;

[0090] Step S302: judging whether the first working state or the second working state is in according to the parameter;

[0091] Step S303: when it is judged that the first working state is in, in which the parameter is less than the threshold, judging whether the actual motor speed calculated by the controller is less than the first target speed;

[0092] Step S304: when it is judged that the actual motor speed is less than the first target speed, increasing the PWM duty ratio or the conduction angle to increase the motor speed;

[0093] Step S305: when it is judged that the actual motor speed is not less than the first target speed, decreasing the conduction angle or the PWM duty ratio to decrease the motor speed;

[0094] Step S306: when it is judged that the second working state is in, in which the parameter is not less than the threshold, judging whether the actual motor speed calculated by the controller is less than the second target speed;

[0095] Step S307: when it is judged that the actual motor speed is not less than the second target speed, decreasing the conduction angle or the PWM duty ratio to decrease the motor speed;

[0096] Step S308: when it is judged that the actual motor speed is less than the second target speed, increasing the PWM duty ratio or the conduction angle to increase the motor speed.

[0097] By repeatedly executing the above series of S301-S308, the PWM duty ratio and / or the conduction angle of the driving motor are controlled, and finally the motor speed is kept at the first target speed or the second target speed.

[0098] Specifically, Figure 7A ​The specific process of increasing the PWM duty ratio or the conduction angle in the above S304 and S308 processes is shown. When it is determined that the PWM duty ratio or the conduction angle needs to be increased, the steps are as follows:

[0099] Step S309: Determine whether the current PWM duty ratio is the maximum value.

[0100] Step S310: When it is determined that the PWM duty ratio is not the maximum value, increase the PWM duty ratio.

[0101] Step S311: When it is determined that the PWM duty ratio is the maximum value, increase the conduction angle.

[0102] By repeatedly performing the above series of S309-S311 control, when the PWM duty ratio or the conduction angle needs to be increased, the adjustment of the PWM duty ratio is given priority over the adjustment of the conduction angle.

[0103] Specifically, Figure 7B The specific process of reducing the conduction angle or the PWM duty ratio in the above S305 and S307 processes is shown. When it is determined that the conduction angle or the PWM duty ratio needs to be reduced, the steps are as follows:

[0104] Step S312: Determine whether the current conduction angle is the minimum value.

[0105] Step S313: When it is determined that the current conduction angle is the minimum value, reduce the PWM duty ratio.

[0106] Step S314: When it is determined that the current conduction angle is not the minimum value, reduce the conduction angle.

[0107] By repeatedly performing the above series of S312-S314 control, when the conduction angle or the PWM duty ratio needs to be reduced, the adjustment of the conduction angle is given priority over the adjustment of the PWM duty ratio.

[0108] Example Two

[0109] The structure of the impact fastening tool of this example is the same as that of Example One, and the motor speed control scheme when the motor is in the second state is the same, which will not be repeated here. The difference from the first example is that when the motor is in the first working state, this example uses an open-loop control method to control the motor.

[0110] Specifically, the open-loop control mode adopts a manner of linearly adjusting the PWM duty ratio and / or the conduction angle according to the displacement of the trigger switch. For example, the displacement of the trigger switch changes from 0% to 100%, and the PWM duty ratio also changes from 0% to 100% linearly, and the conduction angle remains the initial value during the process. For another example, the trigger switch changes from 0% to 70%, the PWM duty ratio changes from 0% to 100% linearly, the trigger switch changes from 70% to 100%, and the conduction angle increases from the initial value to the set value, which can be a built-in parameter by default or set by the user according to the speed requirement.

[0111] In the first state, the open-loop control mode is adopted, and the motor runs according to the program setting. Generally, when the trigger switch is displaced to 100%, the running speed of the motor at no load is the maximum speed of the motor in the open-loop control mode.

[0112] By controlling the motor speed of the impact fastening tool to be stable at the second target speed in the second working state, the impact fastening tool is prevented from being damaged due to large motor speed fluctuation under heavy load. In the first working state, the open-loop control mode is adopted to control the motor speed, so that the impact fastening tool can be controlled by the user according to the actual need in the first working state. The second target speed is less than the maximum speed of the motor in the open-loop control mode.

[0113] In the first working state, the open-loop control is selected in the embodiment, which not only optimizes the control program, but also reduces the power loss in the first working state.

[0114] FIG. 7 shows a flowchart of the control method of the embodiment.

[0115] Step S401: detecting a parameter indicating the load of the motor;

[0116] Step S402: determining whether the first working state or the second working state is in according to the parameter;

[0117] Step S403: when it is determined that the first working state is in, the open-loop control is adopted;

[0118] Step S404: when it is determined that the second working state is in, determining whether the actual motor speed is less than the second target speed;

[0119] Step S405: when the result is yes, increasing the PWM duty ratio or the conduction angle to increase the motor speed;

[0120] Step S406: when the result is no, reducing the conduction angle or the PWM duty ratio to reduce the motor speed.

[0121] By repeatedly performing the above series of regulations S401-S406, the PWM duty ratio and / or the conduction angle of the driving motor are controlled, and finally the motor speed is kept at the second target speed or the motor is open-loop controlled.

[0122] In the present embodiment, the way of increasing the PWM duty ratio or the conduction angle and decreasing the conduction angle or the PWM duty ratio is consistent with the flowchart shown in FIG. 6, and will not be described here again. Figure 7A and 7B The flowchart shown in FIG. 6 is consistent with the flowchart shown in FIG. 5, and will not be described here again.

[0123] In addition, it should be noted that the combination of the technical features in the present case is not limited to the combination of the claims in the present case or the combination of the embodiments described in the present case. All the technical features described in the present case can be freely combined or combined in any way, unless contradictory to each other.

[0124] It should be noted that the above-mentioned is only a specific embodiment of the present application, and obviously the present application is not limited to the above-mentioned embodiments, and there are many similar changes. All the modifications directly derived or thought from the disclosure of the present application by those skilled in the art should belong to the protection scope of the present application.

[0125] It should be understood that the adjectives first, second, etc. mentioned in the embodiments of the present application are only used to more clearly describe the technical solutions of the embodiments of the present application, and cannot be used to limit the protection scope of the present application.

[0126] The above-mentioned is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A power tool, characterized in that, include: Power supply unit; Brushless motor, consisting of a stator and a rotor; The inverter circuit includes multiple switching elements that perform switching actions to control the drive of the brushless motor. A controller is electrically connected to the inverter circuit and the brushless motor. The controller includes a load detection module that detects parameters indicating the operating load of the brushless motor. When the parameter is less than the set threshold, the controller controls the brushless motor to maintain the first target speed; When the parameter is greater than or equal to the set threshold, the controller controls the brushless motor to maintain the second target speed; Wherein, the first target rotational speed is greater than the second target rotational speed; The controller adjusts the PWM duty cycle and / or conduction angle of the switching element to keep the brushless motor at a first target speed or a second target speed. When the parameter is less than a set threshold and the actual motor speed is less than the first target speed, or when the parameter is greater than or equal to the set threshold and the actual motor speed is less than the second target speed, the PWM duty cycle and / or conduction angle of the switching element are increased, wherein the adjustment priority of the PWM duty cycle is higher than that of the conduction angle; or, When the parameter is less than the set threshold and the actual motor speed is greater than the first target speed, or when the parameter is greater than or equal to the set threshold and the actual motor speed is greater than the second target speed, the PWM duty cycle and / or conduction angle of the switching element are reduced, wherein the adjustment priority of the conduction angle is higher than that of the PWM duty cycle.

2. The power tool according to claim 1, characterized in that, The conduction angle is adjusted using a fixed increment ramp, with the increment being any value between 0.1 and 0.5°.

3. The power tool according to claim 1, characterized in that, The brushless motor is a three-phase brushless motor. The brushless motor includes a position sensor. The controller calculates the actual motor speed based on the signal transmitted by the position sensor. The conduction angle of each phase of the three-phase brushless motor is a minimum of 120° and a maximum of 180°.

4. The power tool according to claim 1, characterized in that, The controller can also adjust the lead angle of the switching element.

5. The power tool according to claim 1, characterized in that, The power tool is an impact fastening tool, which includes an impact mechanism. When the parameter is greater than or equal to the set threshold, the impact mechanism performs an impact action.

6. A control method for an electric tool, characterized in that, Includes the following steps: The controller detects parameters indicating the workload of the brushless motor and determines the working status of the power tool based on these parameters. When the parameter is determined to be less than the set threshold, the controller controls the brushless motor to maintain the first target speed; When the parameter is determined to be greater than or equal to a set threshold, the controller controls the brushless motor to maintain the second target speed. Wherein, the first target rotational speed is greater than the second target rotational speed; The controller controlling the brushless motor to maintain a first target speed or the controller controlling the brushless motor to maintain a second target speed includes: the controller calculating the actual motor speed of the brushless motor; when the actual motor speed is less than the first target speed or the actual motor speed is less than the second target speed, the controller increases the PWM duty cycle and / or conduction angle driving the brushless motor, wherein the adjustment priority of the PWM duty cycle is higher than that of the conduction angle; or... The controller calculates the actual motor speed of the brushless motor. When the actual motor speed is greater than the first target speed or the actual motor speed is greater than the second target speed, the controller reduces the conduction angle and / or PWM duty cycle of the brushless motor. The adjustment priority of the conduction angle is higher than that of the PWM duty cycle.

7. The control method as described in claim 6, characterized in that, The controller can also adjust the lead angle driving the brushless motor.

8. A power tool, characterized in that, include: Power supply unit; Brushless motor, consisting of a stator and a rotor; The inverter circuit includes multiple switching elements that perform switching actions to control the drive of the brushless motor. A controller is electrically connected to the inverter circuit and the brushless motor. The controller includes a load detection module that detects parameters indicating the operating load of the brushless motor. When the parameter is greater than or equal to the set threshold, the controller controls the brushless motor to maintain the target speed; When the parameter is less than the set threshold, the controller controls the brushless motor in an open-loop manner, and the brushless motor has a maximum speed under the open-loop control. Wherein, the maximum rotational speed under the open-loop control is greater than the target rotational speed; The controller adjusts the PWM duty cycle and / or conduction angle of the switching element to keep the brushless motor at the target speed; When the parameter is greater than or equal to a set threshold, and the actual motor speed is less than the target speed, the PWM duty cycle and / or conduction angle of the switching element are increased, wherein the adjustment priority of the PWM duty cycle is higher than that of the conduction angle; or, When the parameter is greater than or equal to the set threshold, and the actual motor speed is greater than the target speed, the conduction angle and / or PWM duty cycle of the switching element are reduced, wherein the adjustment priority of the conduction angle is higher than that of the PWM duty cycle.

9. A control method for an electric tool, characterized in that, Includes the following steps: The controller detects parameters indicating the workload of the brushless motor and determines the working status of the power tool based on these parameters. When the parameter is determined to be less than the set threshold, the brushless motor is controlled in an open-loop manner, and the brushless motor has a maximum speed under the open-loop control. When the parameter is determined to be greater than or equal to a set threshold, the controller controls the brushless motor to maintain the target speed. Wherein, the maximum rotational speed in the open-loop mode is greater than the target rotational speed; The controller controls the brushless motor to maintain a target speed by: calculating the actual motor speed of the brushless motor; when the actual motor speed is less than the target speed, the controller increases the PWM duty cycle and / or conduction angle of the brushless motor, wherein the adjustment priority of the PWM duty cycle is higher than that of the conduction angle; or... The controller calculates the actual motor speed of the brushless motor. When the actual motor speed is greater than the target speed, the controller reduces the conduction angle and / or PWM duty cycle of the brushless motor. The adjustment priority of the conduction angle is higher than that of the PWM duty cycle.

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