Impact tool and control method

Abstract

The application discloses an impact tool and a control method. The impact tool comprises a motor, a plurality of phase windings of the motor, an output shaft for outputting torque, and an impact mechanism for applying impact force to the output shaft. A controller is configured to obtain a demagnetization time after phase conversion of the motor windings, the demagnetization time being a time difference between a rising edge of phase voltage and a falling edge of the phase voltage after the phase conversion of the windings. When the impact mechanism applies the impact force to the output shaft according to the demagnetization time, the controller controls the motor to operate in a first preset state. The above scheme can simplify debugging and judgment parameters.

Description

Technical Field

[0001] This application relates to a power tool, specifically an impact tool and its control method. Background Technology

[0002] Impact tools are tools capable of outputting rotational motion with a certain impact frequency, including but not limited to impact wrenches and impact screwdrivers. For example, impact wrenches are used to tighten bolts and nuts, while impact screwdrivers are typically used to loosen or tighten screws. To achieve rotational motion with a certain impact frequency, impact tools need to include an output component for outputting rotational force, as well as an impact mechanism for periodically impacting the output component.

[0003] The impact mechanism includes an impact block, an anvil that engages with the impact block, and a main shaft connected to a motor. When the conditions for activating the impact mechanism are met, the impact block periodically engages with the anvil to output an impact force in the direction of rotation.

[0004] In related technologies, the control logic of impact tools is generally divided into a non-impact stage and an impact stage. Whether an impact has occurred is determined by detecting physical properties such as impact noise or by detecting current. Summary of the Invention

[0005] The purpose of this application is to provide an impact tool and control method, so as to provide an impact tool with better impact detection performance.

[0006] To achieve the above objectives, this application adopts the following technical solution: An impact tool includes: a motor having a plurality of phase windings; a drive circuit having a plurality of semiconductor switching elements to switch the energizing state of the motor windings; an output shaft for outputting torque; an impact mechanism for applying an impact force to the output shaft; and a controller electrically connected at least to the motor and / or the drive circuit. The controller is configured to: acquire the demagnetization time after commutation of the motor windings, the demagnetization time being the time difference between the rising edge and the falling edge of the phase voltage after commutation; determine the impact state of the impact mechanism based on the demagnetization time; and when the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state.

[0007] In some embodiments, the controller is configured to determine that the impact mechanism applies an impact force to the output shaft when the demagnetization time is greater than or equal to a first time threshold within a preset detection cycle of the motor.

[0008] In some embodiments, the controller is configured to: determine that the impact mechanism applies an impact force to the output shaft when the demagnetization time is less than a first time threshold and the change in demagnetization time is greater than or equal to a second time change threshold within a preset detection cycle of the motor.

[0009] In some embodiments, when the first demagnetization time is less than a first time threshold and the change in demagnetization time is greater than or equal to a second time change threshold within a preset detection cycle of the motor, and the second demagnetization time is greater than a third time threshold, it is determined that the impact mechanism applies an impact force to the output shaft.

[0010] In some embodiments, the first demagnetization time is the maximum value of the demagnetization time within a preset detection cycle of the motor, the second demagnetization time is the minimum value of the demagnetization time within the preset detection cycle of the motor, and the change in demagnetization time includes: a change value of demagnetization time and / or a change rate of demagnetization time, wherein the change value of demagnetization time is the difference between the first demagnetization time and the second demagnetization time, and the change rate of demagnetization time is the change value of demagnetization time divided by the first demagnetization time.

[0011] In some embodiments, when it is determined from the demagnetization time that the impact mechanism has not applied an impact force to the output shaft, the controller controls the motor to operate in a second preset state.

[0012] In some embodiments, in the first preset state, the controller outputs a first control signal with a first duty cycle to control the motor to run; in the second preset state, the controller outputs a second control signal with a second duty cycle to control the motor to run, wherein the first duty cycle is different from a duty cycle smaller than the second duty cycle.

[0013] A control method for an impact tool, the impact tool comprising: a motor having a plurality of phase windings; a drive circuit having a plurality of semiconductor switching elements to switch the energizing state of the motor windings; an output shaft for outputting torque; an impact mechanism for applying an impact force to the output shaft; and a controller, which is electrically connected to at least the motor and / or the drive circuit; the control method comprising: acquiring the demagnetization time after the motor windings are commutated, the demagnetization time being the time difference between the rising edge and the falling edge of the phase voltage after the windings are commutated; determining the impact state of the impact mechanism based on the demagnetization time; and, when it is determined that the impact mechanism applies an impact force to the output shaft based on the demagnetization time, controlling the motor to operate in a first preset state.

[0014] In some embodiments, the method for determining the impact state of the impact mechanism based on the demagnetization time includes: when the demagnetization time is greater than or equal to a first time threshold within a preset detection cycle of the motor, determining that the impact mechanism applies an impact force to the output shaft.

[0015] In some embodiments, the method for determining the impact state of the impact mechanism based on the demagnetization time includes: within a preset detection cycle of the motor, when the first demagnetization time is less than a first time threshold and the change in demagnetization time is greater than or equal to a second time change threshold, and at the same time the second demagnetization time is greater than a third time threshold, determining that the impact mechanism applies an impact force to the output shaft. This application provides an impact tool that, when using demagnetization time to determine the impact state, reduces the preset threshold and simplifies the debugging and judgment parameters. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an embodiment in this application; Figure 2 This is a circuit block diagram of an embodiment in this application; Figure 3 This is a schematic diagram of the demagnetization time according to one embodiment of this application; Figure 4 This is a schematic diagram illustrating the demagnetization time generated during motor commutation in an electric tool according to one embodiment of this application; Figure 5 This is a flowchart illustrating the control method of the impact tool in an embodiment of this application; Figure 6 This is a schematic diagram of the process for determining the impact state based on demagnetization time in an embodiment of this application. Detailed Implementation

[0017] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0019] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0020] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] To clearly illustrate the technical solution of this application, the following are also defined: Figure 1 and Figure 2 The top, bottom, left, right, front, and back sides are shown.

[0022] like Figure 1 and Figure 2 An impact wrench 100 according to a first embodiment of this application is shown. The impact wrench 100 includes a housing 11, a motor 12, an output mechanism 13, a transmission mechanism 14, and an impact mechanism 15. The motor 12 includes a motor shaft 121 that rotates about a first axis 101.

[0023] The output mechanism 13 includes an output shaft 131 for connecting and driving the working attachment to rotate. The front end of the output shaft 131 is provided with a clamping assembly, which can clamp the corresponding working attachment, such as a screwdriver, drill bit, wrench, etc., when performing different functions.

[0024] The output shaft 131 is used to output power. The output shaft 131 rotates about an output axis, which in this embodiment is the second axis 102. In this embodiment, the first axis 101 and the second axis 102 coincide. In other alternative embodiments, the second axis 102 and the first axis 101 are set at a certain angle. In other alternative embodiments, the first axis 101 and the second axis 102 are parallel to each other but do not coincide.

[0025] The impact mechanism 15 provides impact force to the output shaft 131. The impact mechanism 15 includes a main shaft 151, an impact block 152 sleeved around the outer periphery of the main shaft 151, a hammer anvil 153 disposed at the front end of the impact block 152, and an elastic element 154. The hammer anvil 153 is connected to the output shaft 131. In this embodiment, the hammer anvil 153 includes an anvil seat 1531, and the output shaft 131 is formed at the front end of the anvil seat 1531. It is understood that the anvil seat 1531 and the output shaft 131 can be integrally formed or separate independent parts. The impact block 152 is driven by the main shaft 151, and the hammer anvil 153 cooperates with and is struck by the impact block 152. Because the working principle of the impact mechanism and the impact force generated on the output shaft by such an impact mechanism are well disclosed to those skilled in the art, detailed descriptions are omitted here for the sake of brevity.

[0026] The transmission mechanism 14 is disposed between the motor 12 and the impact mechanism 15, and is used to transmit power between the motor shaft 121 and the main shaft 151. In this embodiment, the transmission mechanism 14 adopts a planetary gear reduction. Since the working principle of planetary gear reduction and the reduction generated by such a transmission mechanism have been fully disclosed to those skilled in the art, a detailed description is omitted here for the purpose of brevity.

[0027] The impact wrench 100 also includes an operating switch 16, a power interface 31, a drive circuit 17, and a controller 18.

[0028] The operating switch 16 allows the user to perform on / off operations. Optionally, the operating switch 16 can be a mechanical switch or an electronic switch.

[0029] In this embodiment, the motor 12 can be a three-phase brushless motor, and the three-phase stator windings A, B, and C are connected in a delta or Y configuration.

[0030] The power interface 31 is used to connect the power supply device 30 to supply power to the motor 12. In one embodiment, the power supply device 30 can be selected as an AC power source, and the power interface 31 can be connected to 120V or 220V AC mains power. In another embodiment, the power supply device 30 can be selected as a battery pack, which can be composed of a group of battery cells. For example, the battery cells can be connected in series to form a single power branch, forming a 1P battery pack. The output voltage of the battery pack is varied by a specific power control module, such as a DC-DC module, to output a suitable supply voltage for the drive circuit, motor, etc., to power them. Those skilled in the art will understand that the DC-DC module is a mature circuit structure and can be selected according to the specific parameter requirements of the power tool.

[0031] In one embodiment, the impact wrench 100 also integrates a control module, which includes a drive circuit 17 and a controller 18, primarily used to regulate the power supply from the power interface 31 to the motor 12. In one embodiment, the control module may be housed within the housing 11, specifically below the motor 12. It is understood that the location of the control module depends on the shape and specifications of the power tool and can be located anywhere on the impact wrench 100.

[0032] The drive circuit 17 is electrically connected to the stator windings A, B, and C of the motor 12, and is used to transfer current from the power supply circuit 20 to the stator windings A, B, and C to drive the motor 12 to rotate. As one embodiment, such as... Figure 2 As shown, the drive circuit 17 includes multiple switching elements Q1, Q2, Q3, Q4, Q5, and Q6. The gate of each switching element is electrically connected to the controller 18 to receive a control signal from the controller 18. Each drain or source of the switching element is connected to the stator windings A, B, and C of the motor 12. Switching elements Q1-Q6 receive control signals from the controller 18 and change their respective conduction states, thereby changing the current applied by the power supply circuit 20 to the stator windings A, B, and C of the motor 12. In one embodiment, the drive circuit 17 may be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g., FETs, BJTs, IGBTs, etc.). It is understood that the aforementioned switching elements may also be any other type of solid-state switch, such as an insulated-gate bipolar transistor (IGBT), a bipolar junction transistor (BJT), etc.

[0033] To enable the motor 12 to rotate, the drive circuit 17 has multiple drive states. In one drive state, the stator winding of the motor generates a magnetic field. The controller 18 outputs a corresponding PWM control signal to the switching element in the drive circuit 17 based on the rotor position or back electromotive force of the motor, causing the drive circuit 17 to switch drive states. This causes the stator winding to generate a changing magnetic field to drive the rotor to rotate, thereby realizing the rotation or commutation of the motor 12. It should be noted that any other circuit and control method capable of driving the rotation or commutation of the motor 12 can be used in this disclosure. This disclosure does not limit the circuit structure of the drive circuit 17 or the control of the drive circuit 17 by the controller 18.

[0034] In one embodiment, the user triggers the operation switch 16 to start the power tool. When the tool starts, the controller 18 outputs a first control signal with a first duty cycle to the drive circuit, causing the motor to start rotating. When the impact tool is unloaded or under light load, the impact mechanism does not impact, that is, the impact mechanism does not apply impact force to the output shaft. The impact mechanism plays a transmission role, transmitting the rotation of the motor to the output shaft.

[0035] When a load is applied to the impact tool, the rotation of the output shaft is hindered. Depending on the load, the output shaft may rotate at a reduced speed or stop completely. When the output shaft stops rotating completely, the hammer anvil also stops rotating. Due to the circumferential limiting effect of the hammer anvil on the impact block, the impact block also stops rotating. However, the main shaft continues to rotate, and the impact block rotates integrally with the main shaft, sliding back and forth relative to the main shaft along the first axis with a predetermined stroke to periodically engage with the hammer anvil. The impact mechanism applies an impact force to the output shaft. Under the action of this impact force, the output shaft overcomes the load and continues to rotate at a certain angle. Then, the output shaft stops rotating again, and the above process is repeated, thus allowing the impact tool to work continuously.

[0036] Based on the working principle of the impact tool described above, the controller needs to control the motor differently when the impact mechanism is in the impact state and when it is not in the impact state. For example, the motor speed needs to be different.

[0037] In related technologies, determining whether an impact mechanism has entered an impact state is based on detecting current parameters in the drive circuit. However, the current parameter is affected by the duty cycle and the voltage in the circuit. In some embodiments, the impact wrench has preset adjustable speed levels, so different speed levels correspond to different duty cycles. In impact wrenches using a battery pack as a power source, the battery pack voltage changes as the battery charge decreases. Therefore, when setting the current parameter judgment threshold, multiple thresholds need to be set according to different duty cycles and voltages. This increases both the complexity of the judgment and the complexity of debugging.

[0038] In this embodiment, the controller acquires the demagnetization time after the motor windings are commutated and determines the impact state of the impact mechanism based on the demagnetization time. When the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state. It can be understood that the demagnetization time refers to the time difference between the rising edge and falling edge of the phase voltage after the motor windings are commutated, when the motor windings are conducting in pairs. This means that the phase current cannot abruptly become zero due to the motor inductance (i.e., the phase current on the windings will not abruptly become zero after commutation). The demagnetization time is the duration of this freewheeling current through the reverse-parallel diodes. Alternatively, the demagnetization time can be understood as the time difference between the rising edge and falling edge of the phase voltage after the motor windings are commutated.

[0039] In this embodiment, when it is determined, based on the demagnetization time, that the impact mechanism is not applying impact force to the output shaft, the controller controls the motor to operate in a second preset state. In the first preset state, the controller outputs a first control signal with a first duty cycle to control the motor to operate. In the second preset state, the controller outputs a second control signal with a second duty cycle to control the motor to operate, wherein the first duty cycle is less than the second duty cycle. It can be understood that during the motor state adjustment process, the first control signal is used to control the motor speed to decrease, and the second control signal is used to control the motor speed to increase. That is to say, when the impact mechanism enters the impact state, the motor speed decreases.

[0040] In this embodiment, if the demagnetization time is greater than or equal to a first time threshold within the motor's preset detection cycle, it is determined that the impact mechanism applies an impact force to the output shaft. The motor's preset detection cycle is a time period longer than the interval between two adjacent current peaks. In some embodiments, the specific value of the motor's preset detection cycle can be set according to actual detection requirements, and is not specifically limited here. The specific value of the first time threshold is set according to actual detection requirements. The value of the first time threshold is adjusted according to the different output speeds and torques of different impact tools.

[0041] When the demagnetizing time is less than a first time threshold within the motor's preset detection cycle, the demagnetizing time change is detected again. When the demagnetizing time change is greater than or equal to a second time change threshold, it is determined that the impact mechanism applies an impact force to the output shaft. Therefore, the controller is equipped with a storage unit to store the demagnetizing times detected within the preset detection cycle. Specifically, the controller compares and determines the maximum and minimum values ​​of the demagnetizing times detected within the preset detection cycle. The maximum value is set as the first demagnetizing time, and the minimum value is set as the second demagnetizing time. Therefore, when it is determined that the demagnetizing time is less than the first time threshold, it is necessary to compare the first demagnetizing time with the first time threshold; that is, the first demagnetizing time is less than the first time threshold. It can be understood that if the first demagnetizing time is less than the first time threshold, it can be determined that all demagnetizing times in the storage unit are less than the first time threshold.

[0042] The demagnetizing time change includes: the demagnetizing time change value and / or the demagnetizing time change rate. The demagnetizing time change value is the difference between the first demagnetizing time and the second demagnetizing time. The demagnetizing time change rate is the demagnetizing time change value divided by the first demagnetizing time. Both the demagnetizing time change value and the demagnetizing time change rate can characterize the demagnetizing time change. In use, either one or both can be detected, depending on different needs. There are no restrictions.

[0043] In this embodiment, the specific values ​​of the first time threshold and the second time change threshold are set according to the actual detection requirements. Depending on the different impact tools, their output rotational speed and output torque vary, and the values ​​of the first time threshold and the second time change threshold are adjusted accordingly.

[0044] In some embodiments, when determining the impact state of the impact mechanism, the judgment is made simultaneously based on the first demagnetization time, the second demagnetization time, and the change in demagnetization time. When the first demagnetization time is less than a first time threshold within the motor's preset detection cycle, the change in demagnetization time is detected again. When the change in demagnetization time is greater than or equal to a second time change threshold, and simultaneously the second demagnetization time is greater than a third time threshold, it is determined that the impact mechanism applies an impact force to the output shaft. Adding a judgment on the second demagnetization time can reduce misjudgments of the impact state. The applicant found that when using a program to control the demagnetization time detection, when the demagnetization time is less than a certain value, there is a microsecond-level error during the sampling process, which can lead to misjudgments of impact. When using hardware to detect the demagnetization time, this error does not occur, therefore, the judgment on the second demagnetization time is not required.

[0045] When using demagnetization time to determine the impact state, only the first time threshold, the second time change threshold, and the third time threshold need to be set when setting preset thresholds. This simplifies the debugging and judgment parameters.

[0046] Specifically regarding the acquisition of demagnetization time, in this embodiment, the controller can obtain the demagnetization time after motor commutation based on the relative relationship between the bus voltage and the phase voltage. It is understood that the relative relationship between the bus voltage and the phase voltage includes situations where the bus voltage is greater than the phase voltage or less than the phase voltage. The controller can compare the time points at which the relative relationship between the half-bus voltage and the phase voltage changes.

[0047] like Figure 3 As shown, assuming the bus voltage is Us and the phase voltage is Ua, the time point at which the relative relationship between the two changes is denoted as the first time point. Soon The time node is the first time node And this is the first time it has appeared since then. The time node is the second time node First time node Second time node The duration Δt between these points is defined as the time nodes mentioned above. and The duration Δt is the freewheeling time after commutation, i.e., the demagnetization time. Therefore, the demagnetization time during commutation can be determined based on the motor's bus voltage and phase voltage. The demagnetization time can be referenced... Figure 4The illustrated motor commutation diagram shows that during any commutation of the motor, the voltage of the commutated phase undergoes a sudden change. The duration of this voltage change is the demagnetization time. In one embodiment, the phase voltage change typically occurs from a high value Us to 0 or from 0 to a high value Us. For example, after commutation from AC to BC on the upper bridge, the time it takes for the voltage of phase A to drop from Us to 0 is the demagnetization time after phase A commutation. In another embodiment, the demagnetization time can also be obtained through AD sampling. It is understood that this application does not limit the acquisition of the demagnetization time, and any other method of acquiring the demagnetization time is within the scope of protection of this application.

[0048] It is understandable that using only the demagnetization time as a criterion for judging the impact state may lead to deviations in the acquisition of the demagnetization time due to changes in the power supply voltage, thus affecting the accuracy.

[0049] In one embodiment, the controller can also acquire relevant operating parameters of the motor after startup, such as the motor's operating voltage, current, or temperature. For example, based on the product of demagnetization time and bus voltage. Using the phase voltage as a compensation quantity avoids the problem of reduced accuracy caused solely by changes in power supply voltage.

[0050] The following will combine Figure 5 This describes a method for controlling impact tools, which includes the following steps: S101, collects bus voltage.

[0051] S102, collects phase voltage.

[0052] S103 calculates the demagnetization time of the motor after commutation based on the bus voltage and phase voltage.

[0053] S104. Determine the impact state of the impact mechanism based on the demagnetization time. If the impact mechanism applies an impact force to the output shaft based on the demagnetization time, proceed to step S105; otherwise, proceed to step S106.

[0054] S105, the motor operates in the first preset state.

[0055] S106, the motor operates in the second preset state.

[0056] Combination Figure 6 The method shown for determining the impact state of an impact mechanism based on demagnetization time includes the following steps: S1041, Begin.

[0057] S1042, Obtain the demagnetization time within the preset detection cycle, specifically by obtaining and storing all demagnetization times within the preset detection cycle.

[0058] S1043, compare the obtained demagnetization time.

[0059] Understandably, the controller compares and determines the maximum and minimum values ​​of the demagnetization time detected within a preset detection cycle. The maximum value is set as the first demagnetization time, and the minimum value is set as the second demagnetization time. S1044, determine whether the demagnetization time is greater than the first time threshold. If yes, proceed to step S1047; otherwise, proceed to step S1045.

[0060] S1045, determine whether the current demagnetization time is the first demagnetization time. If yes, proceed to step S1046; otherwise, proceed to step S1044.

[0061] Understandably, it's necessary to determine if the first demagnetization time is less than the first time threshold. When the first demagnetization time is less than the first time threshold, it means that the demagnetization time of all cells within the storage unit is less than the first time threshold.

[0062] S1046, if the change in demagnetization time is greater than the second time change threshold and the second demagnetization time is greater than the third time threshold, then proceed to step S1047.

[0063] S1047, determine that the impact mechanism applies an impact force to the output shaft.

[0064] S1048, End.

[0065] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that the above embodiments do not limit this application in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of this application.

Claims

1. An impact tool, comprising: An electric motor has several phase windings; The drive circuit has several semiconductor switching elements to switch the energizing state of the motor windings; The output shaft is used to output torque externally. An impact mechanism is used to apply an impact force to the output shaft; The controller is electrically connected to at least the motor and / or the drive circuit; The controller is characterized in that it is configured to: The demagnetization time after the motor winding is commutated is obtained, and the demagnetization time is the time difference between the rising edge and the falling edge of the phase voltage after the winding is commutated. When the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state, wherein, within the preset detection cycle of the motor, when the demagnetization time is greater than or equal to a first time threshold, it is determined that the impact mechanism applies an impact force to the output shaft.

2. The impact tool according to claim 1, characterized in that, When the controller determines that the impact mechanism has not applied an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a second preset state.

3. The impact tool according to claim 2, characterized in that, In the first preset state, the controller outputs a first control signal with a first duty cycle to control the motor to run. In the second preset state, the controller outputs a second control signal with a second duty cycle to control the motor to run, wherein the first duty cycle and the second duty cycle are different.

4. An impact tool, comprising: An electric motor has several phase windings; The drive circuit has several semiconductor switching elements to switch the energizing state of the motor windings; The output shaft is used to output torque externally. An impact mechanism is used to apply an impact force to the output shaft; The controller is electrically connected to at least the motor and / or the drive circuit; The controller is characterized in that it is configured to: The demagnetization time after the motor winding is commutated is obtained, and the demagnetization time is the time difference between the rising edge and the falling edge of the phase voltage after the winding is commutated. When the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state. Within the preset detection cycle of the motor, if the first demagnetization time is less than a first time threshold and the change in demagnetization time is greater than or equal to a second time change threshold, it is determined that the impact mechanism applies an impact force to the output shaft. Here, the first demagnetization time is the maximum value of the demagnetization time within the preset detection cycle of the motor.

5. The impact tool according to claim 4, characterized in that, Within the preset detection cycle of the motor, when the first demagnetization time is less than the first time threshold and the change in demagnetization time is greater than or equal to the second time change threshold, and at the same time the second demagnetization time is greater than the third time threshold, it is determined that the impact mechanism applies an impact force to the output shaft, wherein the second demagnetization time is the minimum value of the demagnetization time within the preset detection cycle of the motor.

6. The impact tool according to claim 5, characterized in that, The demagnetization time change includes: the demagnetization time change value and / or the demagnetization time change rate, wherein the demagnetization time change value is the difference between the first demagnetization time and the second demagnetization time, and the demagnetization time change rate is the demagnetization time change value / the first demagnetization time.

7. The impact tool according to claim 4, characterized in that, When the controller determines that the impact mechanism has not applied an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a second preset state.

8. The impact tool according to claim 7, characterized in that, In the first preset state, the controller outputs a first control signal with a first duty cycle to control the motor to run. In the second preset state, the controller outputs a second control signal with a second duty cycle to control the motor to run, wherein the first duty cycle and the second duty cycle are different.

9. A control method for an impact tool, the impact tool comprising a motor having a plurality of phase windings; and a drive circuit having a plurality of semiconductor switching elements to switch the energizing state of the motor windings; An output shaft for outputting torque; an impact mechanism for applying impact force to the output shaft; The controller is electrically connected to at least the motor and / or the drive circuit; the control method includes: The demagnetization time after the motor winding is commutated is obtained, and the demagnetization time is the time difference between the rising edge and the falling edge of the phase voltage after the winding is commutated. When the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state. The method for determining the impact state of the impact mechanism based on the demagnetization time includes: when the demagnetization time is greater than or equal to a first time threshold within a preset detection cycle of the motor, it is determined that the impact mechanism applies an impact force to the output shaft.

10. A control method for an impact tool, the impact tool comprising a motor having a plurality of phase windings; and a drive circuit having a plurality of semiconductor switching elements to switch the energizing state of the motor windings; An output shaft for outputting torque; an impact mechanism for applying impact force to the output shaft; The controller is electrically connected to at least the motor and / or the drive circuit; The control method includes: The demagnetization time after the motor winding is commutated is obtained, and the demagnetization time is the time difference between the rising edge and the falling edge of the phase voltage after the winding is commutated. When the impact mechanism applies an impact force to the output shaft based on the demagnetization time, the controller controls the motor to operate in a first preset state. The method for determining the impact state of the impact mechanism based on the demagnetization time includes: within a preset detection cycle of the motor, when the first demagnetization time is less than a first time threshold and the change in demagnetization time is greater than or equal to a second time change threshold, and at the same time the second demagnetization time is greater than a third time threshold, it is determined that the impact mechanism applies an impact force to the output shaft. The first demagnetization time is the maximum value of the demagnetization time within the preset detection cycle of the motor, and the second demagnetization time is the minimum value of the demagnetization time within the preset detection cycle of the motor.

Images