Patent Publication Number: US-2023163706-A1

Title: Power tool, impact wrench, and tool control method

Description:
RELATED APPLICATION INFORMATION 
     This application claims the benefit under 35 U.S.C. § 119(a) of Chinese Patent Application No. CN 202111392151.2, filed on Nov. 23, 2021, which application is incorporated herein by reference in its entirety. 
     BACKGROUND 
     With the development of power tools, the intelligent control technology of power tools is more and more widely applied. For example, a controller is used for adjusting a power supply voltage of an electric motor so that a power tool has characteristics such as quick starting and smooth braking. 
     However, if an existing power tool working at a low speed performs an impact action, cases such as a locked rotor will occur due to the low speed and low torque. Thus, it is difficult for the power tool to complete a working task in a special working condition. For example, the so-called special working condition refers to that when an object to be impacted is relatively soft wood or another relatively soft material or when an impact drill bit is relatively small, the tool needs to perform the impact action at a relatively low rotational speed. 
     SUMMARY 
     An example of the present application provides a power tool. The power tool includes an electric motor, an output shaft, a commutation detection device, and a controller. The output shaft is electrically connected to the electric motor. The commutation detection device is electrically connected to the electric motor and used for detecting and obtaining commutation information about each commutation of the electric motor. The controller is electrically connected to at least the electric motor and the commutation detection device and capable of outputting a control signal to control the electric motor to rotate. The controller is configured to receive the commutation information of the electric motor and when the commutation information does not match a preset commutation condition, adjust the control signal based on the commutation information such that a rotational speed of the electric motor is maintained to be a target rotational speed. 
     In an example, the controller is configured to, when a current commutation of the electric motor is not completed, update commutation information about the current commutation according to commutation information about a last commutation and adjust the control signal according to the updated commutation information about the current commutation such that the rotational speed of the electric motor is maintained to be the target rotational speed. 
     In an example, the controller is configured to calculate the rotational speed of the electric motor according to the updated commutation information about the current commutation and adjust and output the control signal when the rotational speed of the electric motor does not satisfy the target rotational speed such that the rotational speed of the electric motor is maintained to be the target rotational speed. 
     In an example, the commutation information about each commutation of the electric motor includes at least a commutation start point of the each commutation, a commutation end point of the each commutation, and duration required for the each commutation. 
     In an example, the controller is configured to update commutation duration of the current commutation using a commutation end point of the last commutation as a commutation start point of the current commutation and calculate the rotational speed of the electric motor according to the updated commutation duration of the current commutation. 
     In an example, that the current commutation of the electric motor is not completed includes that commutation duration of the current commutation of the electric motor is longer than commutation duration of the last commutation or that no commutation is performed within commutation duration of the current commutation. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 300 RPM. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 200 RPM. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 150 RPM. 
     In an example, the electric motor is a sensorless motor. 
     In an example, the controller is configured to, when the commutation duration of the electric motor is longer than or equal to a set threshold, control the electric motor to perform locked rotor protection in a process in which the electric motor rotates at the target rotational speed. 
     An example of the present application further provides an impact wrench. The impact wrench includes an electric motor, an output shaft, a commutation detection device, and a controller. The output shaft is connected to the electric motor. The commutation detection device is electrically connected to the electric motor and used for detecting and obtaining commutation information about each commutation of the electric motor. The controller is electrically connected to at least the electric motor and the commutation detection device and capable of outputting a control signal to control the electric motor to rotate. The controller is configured to: receive commutation information of the electric motor; and when the commutation information does not match a preset commutation condition, adjust the control signal based on the commutation information such that a rotational speed of the electric motor is maintained to be a target rotational speed. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 300 RPM. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 200 RPM. 
     In an example, the target rotational speed is greater than or equal to 100 RPM and less than or equal to 150 RPM. 
     An example of the present application further provides a control method for a power tool. The control method is performed by the power tool. The power tool includes an electric motor, an output shaft, a commutation detection device, and a controller. The output shaft is connected to the electric motor. The commutation detection device is electrically connected to the electric motor and used for detecting and obtaining commutation information about each commutation of the electric motor. The controller is electrically connected to at least the electric motor and the commutation detection device and capable of outputting a control signal to control the electric motor to rotate. The control method includes: receiving the commutation information of the electric motor; and when the commutation information does not match a preset commutation condition, adjusting the control signal based on the commutation information such that a rotational speed of the electric motor is maintained to be a target rotational speed. 
     In an example, the control method further includes: when a current commutation of the electric motor is not completed, updating commutation information about the current commutation according to commutation information about a last commutation and adjusting the control signal according to the updated commutation information about the current commutation such that the rotational speed of the electric motor is maintained to be the target rotational speed. 
     In an example, the commutation information about each commutation of the electric motor includes at least a commutation start point of the each commutation, a commutation end point of the each commutation, and duration required for the each commutation. 
     In an example, the control method further includes: updating commutation duration of a current commutation using a commutation end point of a last commutation as a commutation start point of the current commutation and calculating the rotational speed of the electric motor according to the updated commutation duration of the current commutation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram of a circuit structure of a power tool in an example of the present application; 
         FIG.  2    is a structural view of an impact tool in an example of the present application; and 
         FIG.  3    is a flowchart of a control method for a power tool in an example of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     The present application is further described in detail hereinafter in conjunction with the drawings and examples. It is to be understood that the examples described herein are merely intended to illustrate the present application and not to limit the present application. Additionally, it is to be noted that for ease of description, only part, not all, of structures related to the present application are illustrated in the drawings. 
     As shown in  FIGS.  1  and  2   ,  FIG.  1    is a block diagram of a circuit structure of a power tool  100  according to an example of the present application, and  FIG.  2    is a structural view of an impact tool according to an example of the present application. It is to be noted that in addition to the power tool  100  shown in  FIG.  2   , any other impact power tool  100  that uses a sensorless brushless motor or a sensored brushless motor and can perform low-speed control may use a control method described in the present application. 
     Referring to  FIG.  1   , the power tool  100  includes an electric motor  10 , an output shaft  20 , a commutation detection device  30 , and a controller  40 . The output shaft  20  is electrically connected to the electric motor  10 . The commutation detection device  30  is electrically connected to the electric motor  10  and used for detecting and obtaining commutation information about each commutation of the electric motor  10 . The controller  40  is electrically connected to at least the electric motor  10  and the commutation detection device  30 . The controller  40  is configured to receive the commutation information of the electric motor  10  and when the commutation information does not match a preset commutation condition, adjust a control signal based on the commutation information such that a rotational speed of the electric motor  10  is maintained to be a target rotational speed. 
     The electric motor  10  may be a sensorless brushless direct current motor and performs multiple commutations within one electrical period. The output shaft  20  is connected to the electric motor  10  and can be driven by the electric motor  10  to rotate so that a drill bit or another tool accessory mounted on the output shaft  20  is driven to rotate. The commutation detection device  30  is electrically connected to the electric motor  10  and the controller  40  separately and used for detecting and obtaining the commutation information about each commutation of the electric motor  10  and sending the commutation information to the controller  40 . The controller  40  is used for receiving the commutation information about each commutation of the electric motor  10  and when the commutation information does not match the preset commutation condition, adjusting the control signal based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. It is to be understood that with control information output by the controller  40 , switching elements in a driver circuit (not shown) in the tool can be controlled to change driving states such that the electric motor  10  is driven to change a rotation state. The commutation detection device  30  may estimate a position of a rotor of the electric motor  10  during the rotation of the electric motor  10  to determine the commutation information of the electric motor  10 . 
     It is to be noted that the preset commutation condition may be: whether the electric motor  10  completes a commutation action when performing each commutation; whether the electric motor  10  completes the commutation when a duration of a current commutation of the electric motor  10  reaches a duration of a last commutation; or the like. The preset commutation condition may be specifically set according to actual situations and is not specifically limited herein. 
     In the technical solution in this example, the power tool  100  may be an impact tool, for example, an impact wrench. For example, in conjunction with  FIGS.  1  and  2   , the power tool  100  is the impact wrench. The impact wrench is typically used for performing an impact operation at a relatively low speed such as impact on a very soft board and alignment of a drill bit with a relatively small size. However, since it is very difficult for the impact wrench to work at a relatively low speed and maintain the output of a constant and low speed, operations such as the impact on the board and the alignment of the drill bit are difficult to perform smoothly. Therefore, the power tool  100  provided by the present application can implement the following: when a user needs to operate the power tool  100  to perform the operations at a constant and low speed, such as the impact on the board and the alignment of the drill bit, the commutation detection device  30  detects and obtains the commutation information about each commutation of the electric motor  10  in real time and sends the commutation information to the controller  40 , the controller  40  receives the commutation information of the electric motor  10  and compares the commutation information with the preset commutation condition, and when the commutation information does not match the preset commutation condition, the controller  40  adjusts the control signal based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed and thus, the output shaft  20  can also output the target rotational speed continuously and stably so that the user can perform the impact on the board continuously, align the drill bit, and the like. 
     For example,  FIG.  2    shows the structural view of the impact tool. Referring to  FIG.  2   , the impact wrench includes a housing  50 , a trigger  60 , a grip  70 , a battery pack  80 , the electric motor  10 , the output shaft  20 , the commutation detection device  30 , and the controller. The housing  50  is formed with the grip  70  for the user to grip. Of course, the grip  70  may be a separate part. The housing  50  constitutes a main body of the impact tool and is used for accommodating the electric motor  10 , the controller, a transmission assembly, and other electronic components such as a circuit board. The output shaft  20  may be used for mounting a functional part such as the drill bit. 
     Optionally, the target rotational speed may be greater than or equal to 100 RPM and less than or equal to 300 RPM, for example, 100 RPM, 150 RPM, 200 RPM, 250 RPM, 300 RPM, or the like. 
     According to the technical solution in this example, the power tool  100  is provided, which includes the electric motor  10 , the output shaft, the commutation detection device  30 , and the controller, where the output shaft is electrically connected to the electric motor  10 , the commutation detection device  30  is electrically connected to the electric motor  10  and used for detecting and obtaining the commutation information about each commutation of the electric motor  10 , and the controller  40  is electrically connected to at least the electric motor  10  and the commutation detection device  30  and configured to receive the commutation information of the electric motor  10  and when the commutation information does not match the preset commutation condition, adjust the control signal based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. It can be seen that the power tool  100  can solve the problem that it is difficult for an existing power tool  100  working at a low speed to complete a target working task due to the low speed and low torque. In a working process, the power tool  100  receives the commutation information of the electric motor  10  and can adjust the control signal based on the commutation information when the commutation information does not match the preset commutation condition such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the case can be avoided where the power tool  100  cannot complete the working task in the process since the electric motor  10  outputs a relatively low speed or has an unstable rotational speed, and the power tool  100  can be controlled to work at a constant and low speed. 
     Optionally, when the commutation information does not match the preset commutation condition, the control signal is adjusted based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed in a manner that includes the operation described below. 
     When the current commutation of the electric motor  10  is not completed, commutation information about the current commutation is updated according to the commutation information about the last commutation, and the control signal is adjusted according to the updated commutation information about the current commutation such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. 
     The preset commutation condition may be whether the electric motor  10  completes the commutation when performing each commutation. Specifically, the current state of the electric motor  10  is defined as the current commutation state. The electric motor  10  is in a state of performing the current commutation, if the commutation detection device  30  detects that the current commutation of the electric motor  10  is not completed, the controller  40  updates the commutation information about the current commutation according to the commutation information about the last commutation of the electric motor  10  and adjusts the output of the control signal using the updated information about the current commutation as the commutation information about the current commutation state such that the electric motor  10  can maintain its running at the target rotational speed. 
     Optionally, the control signal is adjusted according to the updated commutation information about the current commutation such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed in a manner that includes the operation described below. 
     The rotational speed of the electric motor  10  is calculated according to the updated commutation information about the current commutation, and when the rotational speed of the electric motor  10  does not satisfy the target rotational speed, the control signal is adjusted and output such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. 
     The rotational speed of the electric motor  10  is related to the commutation information of the electric motor  10 . Therefore, in order that the electric motor  10  can output a stable target rotational speed, the controller  40  calculates the rotational speed of the electric motor  10  according to the updated information about the current commutation and compares the calculated rotational speed with the target rotational speed, and when the calculated rotational speed does not satisfy the target rotational speed, the controller  40  adjusts and outputs the control signal. For example, the control signal is output in the form of increasing a duty cycle such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the output shaft can output the target rotational speed constantly so that the user can implement the operations such as the impact on a very soft board and the alignment of the drill bit with a relatively small size. 
     The control signal may be a control signal with a certain duty cycle and is used for driving the electric motor  10  to run constantly at the target rotational speed. The manner of adjusting the control signal may be to output an adjusted signal by increasing the duty cycle or decreasing the duty cycle. For example, the target rotational speed is 100 RPM. Assuming that the rotational speed of the electric motor  10  calculated according to the updated commutation information about the current commutation is less than 100 RPM, the controller  40  outputs the adjusted signal by increasing a pulse-width modulation (PWM) duty cycle such that the rotational speed of the electric motor  10  is maintained to be 100 RPM. It is to be noted that the adjustment has certain hysteresis, which does not affect the capability of the power tool  100  to bear a load at a low speed. For example, when the rotational speed of the electric motor  10  drops to 80 RPM, the power tool  100  can still perform impact in the process in which the PWM duty cycle is adjusted according to the updated commutation information about the current commutation to increase the rotational speed to 100 RPM. 
     Optionally, the commutation information about each commutation of the electric motor  10  includes at least a commutation start point of each commutation, a commutation end point of each commutation, and duration required for each commutation. 
     When running, the electric motor  10  performs multiple commutations according to a certain period, for example, the electric motor  10  performs six commutations within one period. Normally, within the same period, the electric motor  10  has the same commutation duration for each commutation. However, due to a locked rotor of the electric motor  10  or the like, commutation duration of the current commutation of the electric motor  10  is longer than commutation duration of the last commutation, or no commutation is performed within the duration of the current commutation. Therefore, within the same period, the commutation duration of each commutation of the electric motor  10  is different. Since the commutation duration of the electric motor  10  is related to the rotational speed of the electric motor  10 , the commutation duration, the commutation start point, and the commutation end point of each commutation of the electric motor  10  need to be detected. 
     Optionally, the rotational speed of the electric motor  10  is calculated according to the updated commutation information about the current commutation in a manner that includes the operation described below. 
     The commutation duration of the current commutation is updated using a commutation end point of the last commutation as a commutation start point of the current commutation, and the rotational speed of the electric motor  10  is calculated according to the updated commutation duration of the current commutation. 
     Specifically, when the commutation information about the current commutation of the electric motor  10  does not satisfy the preset commutation condition, the update is performed using the commutation end point of the last commutation as the commutation start point of the current commutation. The commutation duration of the current commutation is calculated and updated according to an updated commutation start point of the current commutation and a commutation end point at which the current commutation is actually completed. The rotational speed of the electric motor  10  is recalculated by the updated duration of the current commutation, and the calculated rotational speed is compared with the target rotational speed. When the calculated rotational speed does not satisfy the target rotational speed, the control signal is adjusted and output. For example, the control signal is output in the form of increasing the duty cycle such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the output shaft can output the target rotational speed constantly so that the user can implement the operations such as the impact on a very soft board and the alignment of the drill bit with a relatively small size. 
     Optionally, that the current commutation of the electric motor  10  is not completed includes that the commutation duration of the current commutation of the electric motor  10  is longer than the commutation duration of the last commutation or that no commutation is performed within the duration of the current commutation. 
     The rotational speed of the electric motor  10  is related to the commutation duration of each commutation. For example, the target rotational speed is 100 RPM. When the rotor of the electric motor  10  is not locked, the rotational speed of the electric motor  10  is calculated according to the commutation duration. However, when the rotor of the electric motor  10  is locked, the duration required for the commutation becomes longer because of the locked rotor. If the rotational speed is still calculated according to an original commutation duration, the calculated rotational speed will be greater than an actual rotational speed. Moreover, the rotational speed of the electric motor  10  has been less than the target rotational speed of 100 RPM. Since the calculated rotational speed is still 100 RPM, the controller  40  will not increase the PWM duty cycle automatically and so the actual rotational speed of the electric motor  10  will not reach the target rotational speed. In addition, if the rotational speed continues to drop, the power tool  100  cannot continue the impact at a low speed (for example, 100 RPM) and thus cannot bear a load at the low speed. Therefore, when the commutation duration of the current commutation of the electric motor  10  is longer than the commutation duration of the last commutation or no commutation is performed within the duration of the current commutation, the update is performed using the commutation end point of the last commutation as the commutation start point of the current commutation. The commutation duration of the current commutation is calculated and updated according to the updated commutation start point of the current commutation and the commutation end point at which the current commutation is actually completed. The rotational speed of the electric motor  10  is recalculated by the updated duration of the current commutation, and the calculated rotational speed is compared with the target rotational speed. When the calculated rotational speed does not satisfy the target rotational speed, the control signal is adjusted and output. For example, the control signal is output in the form of increasing the duty cycle such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the output shaft can output the target rotational speed constantly so that the user can implement the operations such as the impact on a very soft board and the alignment of the drill bit with a relatively small size. 
     Optionally, the electric motor  10  may be a sensored motor, and the commutation detection device  30  may be a Hall sensor. The Hall sensor is used for detecting the commutation start point of each commutation of the electric motor  10 , the commutation end point of each commutation of the electric motor  10 , and the duration required for each commutation. 
     In the process in which the electric motor  10  is started at a constant and low speed, the rotor of the electric motor  10  is likely to be locked. Therefore, a relatively high locked-rotor current may cause damage to power elements in a control circuit. To avoid this case, in the process in which the electric motor  10  rotates at the target rotational speed, the controller  40  may continuously monitor the commutation duration. If the commutation duration exceeds a set threshold, the control signal is no longer changed, that is, a duty cycle of a PWM signal is no longer increased, and the electric motor  10  is controlled to enter a locked rotor protection program. That is to say, in the process in which the electric motor  10  is started at the constant and low speed, it may be determined whether the electric motor  10  is started successfully according to commutation time. If the commutation time does not exceed the set threshold, it may be considered that the electric motor  10  is started successfully, and otherwise, the electric motor  10  is not started successfully. If the electric motor  10  is not started successfully, the electric motor  10  directly enters the locked rotor protection program to prevent an excessively high current from burning the power elements in the tool. 
       FIG.  3    is a flowchart of a control method for a power tool  100  according to an example of the present application. This example is applicable to an implementation process of the control method for a power tool  100 . The method may be performed by the power tool  100  provided in the example of the present application. The power tool  100  includes an electric motor  10 , an output shaft, a commutation detection device  30 , and a controller. The output shaft is electrically connected to the electric motor  10 . The commutation detection device  30  is electrically connected to the electric motor  10  and used for detecting and obtaining commutation information about each commutation of the electric motor  10 . The controller  40  is electrically connected to at least the electric motor  10  and the commutation detection device  30 . 
     Referring to  FIG.  3   , the control method for a power tool  100  includes the steps described below. 
     In step  110 , the commutation information of the electric motor  10  is received. 
     Specifically, the power tool  100  includes the electric motor  10 , the output shaft, the commutation detection device  30 , the controller, and the like. The commutation detection device  30  is electrically connected to the electric motor  10  and the controller  40  separately. The commutation detection device  30  such as a Hall sensor may detect and obtain the commutation information about each commutation of the electric motor  10  and send the commutation information to the controller. 
     In step  120 , when the commutation information does not match a preset commutation condition, a control signal is adjusted based on the commutation information such that a rotational speed of the electric motor  10  is maintained to be a target rotational speed. 
     Specifically, the controller  40  receives the commutation information of the electric motor  10  and compares the commutation information of the electric motor  10  with the preset commutation condition. When the commutation information does not match the preset commutation condition, the control signal is adjusted based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the output shaft can output the target rotational speed constantly so that a user can implement operations such as impact on a very soft board and alignment of a drill bit with a relatively small size. 
     According to the technical solution in this example, the control method for a power tool  100  is provided. The control method for a power tool  100  is performed by the power tool  100 , and the power tool  100  includes the electric motor  10 , the output shaft, the commutation detection device  30 , and the controller, where the output shaft is electrically connected to the electric motor  10 , the commutation detection device  30  is electrically connected to the electric motor  10  and used for detecting and obtaining the commutation information about each commutation of the electric motor  10 , and the controller  40  is electrically connected to at least the electric motor  10  and the commutation detection device  30 . The control method for a power tool  100  includes: receiving the commutation information of the electric motor  10 ; and when the commutation information does not match the preset commutation condition, adjusting the control signal based on the commutation information such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. The control method for a power tool  100  can solve the problem that it is difficult for an existing power tool  100  working at a low speed to complete a target working task due to the low speed and low torque. In a working process, the power tool  100  receives the commutation information of the electric motor  10  and can adjust the control signal based on the commutation information when the commutation information does not match the preset commutation condition such that the rotational speed of the electric motor  10  is maintained to be the target rotational speed. Thus, the case can be avoided where the power tool  100  cannot complete the working task in the process since the electric motor  10  outputs a relatively low speed or has an unstable rotational speed, and the power tool  100  can be controlled to work at a constant and low speed. 
     Optionally, the commutation information about each commutation of the electric motor  10  includes at least a commutation start point of each commutation, a commutation end point of the commutation, and duration required for each commutation. 
     It is to be noted that the above are only preferred examples of the present application and the technical principles used therein. It is to be understood by those skilled in the art that the present application is not limited to the examples described herein. For those skilled in the art, various apparent modifications, adaptations, and substitutions can be made without departing from the scope of the present application. Therefore, while the present application is described in detail in conjunction with the preceding examples, the present application is not limited to the preceding examples and may include equivalent examples without departing from the concept of the present application. The scope of the present application is determined by the scope of the appended claims.