Method for detecting recoil of power tool

Abstract

An electric tool (1) and a method for detecting recoil of said tool (1). The electric tool (1) comprises a housing (2), a power supply module, an electric motor (4), a working part (3), a control module (5) and a detection module (6). The detection method (6) predicts the position of the center of gravity (C) of the working part (3) of the electric tool (1) in the near future by means of the linear speed and rotational speed of the working part (3) captured by the detection module (6), compares the displacement between the predicted position and the actual position with a preset threshold value, and determines that a recoil is about to occur when the displacement exceeds the preset threshold value.

Description

Technical Field

[0001] The present invention relates to an operating method of an electric tool, and in particular to a method for detecting a recoil of an electric tool and an electric tool for executing the method. Background Art

[0002] Power tools such as electric angle grinders and electric circular saws rely on the rotation of electric motors to drive working parts to perform corresponding work. During the operation of some high-torque power tools such as high-power angle grinders and circular saws, when a blade such as a grinding wheel or saw blade comes into contact with the material being processed, the material being processed may exert a reaction force on the blade, causing the power tool to jam or recoil, thereby generating a recoil phenomenon.

[0003] Many electric tools are known to have implemented recoil detection. In most existing recoil detection solutions, the occurrence of recoil is determined based on comparing the actual value of the acceleration sensor with a set threshold. For example, patent document US2018038546A discloses a solution that allows the recoil of the electric tool from the material being processed to be accurately detected based on the movement of the electric tool body. The electric tool includes a detection module for detecting the posture change of the device body; when the motor is performing a driving action, if the degree of posture change of the device body detected by the detection module exceeds a preset threshold, then it is determined that the device body is recoiled from the material being processed. With the degree of posture change of the device body, the detection module detects at least one of the moving speed and the moving amount of the device body in one or more axial directions, and the control module is configured so that: if the moving speed or the moving amount detected by the detection module exceeds the threshold, then it is determined that the device body is recoiled from the material being processed, and the driving action of the motor is terminated. If recoil has occurred, it may cause the electric tool to lose control, and the operator of the electric tool may be injured. Therefore, a solution is needed that allows the trend of tool movement to be predicted and thus predicts possible recoil. The tool can then be stopped as quickly as possible to avoid injury to the tool operator.

[0004] Furthermore, in the prior art, it is often not possible to differentiate between true kickback and manual kickback detection. In some cases, it may be manually tested for an office demonstration of a kickback feature, or in the case of a user testing the kickback detection function, no true kickback occurs - it is just a manual test. In this case, it is desirable for the power tool to be able to identify whether it is true kickback or a manual test, so that different braking schemes are used to avoid wear on mechanical parts due to hard braking. Summary of the invention

[0005] An object of the present invention is to provide a method for detecting the recoil of an electric tool, which method can predict and accurately detect the occurrence of recoil and can reduce the risk of injury to the user of the electric tool and damage to the electric tool.

[0006] Another object of the present invention is to provide a power tool and a method for detecting the recoil of the power tool to distinguish between true recoil and manual recoil test.

[0007] In addition, the present invention also provides an electric tool for executing the recoil method.

[0008] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0009] A method for detecting recoil of an electric tool, the electric tool comprising a housing, a power module, an electric motor, a working component, a control module and a detection module, the detection module being designed to detect the linear acceleration and angular velocity of the working component, and the detection module being at a distance r from the center of gravity of the working component; the detection method comprising:

[0010] a. Detecting the linear acceleration by means of the detection module, subtracting the gravity acceleration from the linear acceleration to obtain the adjusted linear acceleration; then integrating the adjusted linear acceleration to obtain the linear velocity;

[0011] b. Detecting the angular velocity by means of the detection module and multiplying it by the distance r between the detection module and the center of gravity of the working member to obtain the rotational speed;

[0012] c. Calculate the total translation speed based on the linear speed and the rotational speed, and predict the center of gravity position of the working part of the power tool after the time constant τ milliseconds;

[0013] d. Detect the actual position of the center of gravity of the working part of the power tool;

[0014] e. Comparing the displacement between the predicted position of the center of gravity of the working component and the actual position of the center of gravity of the working component with a preset threshold, and determining that backlash is about to occur when the displacement exceeds the preset threshold.

[0015] The method for detecting the recoil of an electric tool according to the present invention only needs to collect the acceleration and angular velocity signals of the electric tool, so as to simply and reliably predict whether the electric tool is about to recoil, thereby quickly braking or stopping the electric motor in time, thereby protecting the user from injuries caused by the recoil of the electric tool in a simple way.

[0016] In the method for detecting backlash according to the present invention, the predicted position of the center of gravity of the working part of the power tool after τ milliseconds is calculated by the following algorithm:

[0017]

[0018] Where s(t+τ) represents the predicted position, s(t) represents the actual position, υ(t) represents the vector sum of the linear velocity and the rotational speed, and α(t) represents the linear acceleration. Therefore, the predicted position of the center of gravity of the working part is the position after τ milliseconds based on the actual position. The algorithm of the present invention is independent of the electric motor current or speed information and does not require comparison of acceleration changes, but determines that the power tool is about to recoil by predicting the position of the power tool in the near future. Predicting the movement trend of the center of gravity of the working part is the most accurate method to determine the position of the power tool, thereby more accurately predicting whether recoil will occur.

[0019] According to a preferred embodiment of the present invention, the linear acceleration is filtered to eliminate noise generated during operation of the power tool.

[0020] According to another preferred embodiment of the present invention, the preset threshold of the user safety zone is fixed. This means that the detection module and the control module of the present invention can operate without any further information; that is, signals other than the acceleration and rotation speed signals, such as the electric motor current or speed, are not necessary information for detecting the kickback in the power tool of the present invention.

[0021] According to another preferred embodiment of the present invention, the detection method further collects a speed and / or current signal from the electric motor, and the preset threshold value can be changed according to the speed or current from the electric motor. For example, when the speed of the electric motor drops significantly, the preset threshold value of the user safety zone can be adjusted.

[0022] According to another preferred embodiment of the present invention, the detection method further comprises: if a significant decrease in the speed of the electric motor or a significant increase in the current is detected while the displacement exceeds a preset threshold, then it is determined to be a true recoil; otherwise, if there is no significant change in the speed of the electric motor or the current, then it is determined to be a manual recoil test. In the case of a true recoil, the speed of the tool will also drop significantly. This means that if the speed drops significantly when the recoil is detected, the threshold of the prediction algorithm can be adjusted, which means that the recoil is detected faster so that a suitable braking method can be selected. In the case of a manual recoil test, the speed of the electric motor will not drop, so that a true recoil and a non-true recoil situation can be distinguished. Therefore, very fast braking can be avoided to avoid wear of mechanical parts due to hard braking.

[0023] In addition, the present invention also provides an electric tool, including a housing, a power module, an electric motor, a working part, a control module and a detection module, wherein the detection module is designed to detect the linear acceleration and angular velocity of the center of gravity of the working part, and the detection module is at a distance r from the center of the working part; the electric tool is designed to perform the method for detecting recoil described in more detail above. The advantages described in relation to the detection method according to the present invention are also correspondingly applicable to the electric tool designed according to the present invention. By using the electric tool designed according to the present invention, the occurrence of recoil of the electric tool can therefore be simply and reliably predicted to prevent harm to the user.

[0024] Preferably, in the electric tool according to the present invention, the detection module comprises an acceleration sensor for determining linear accelerations in three specific spatial directions, and a gyro sensor for determining angular velocities in three spatial directions.

[0025] According to a preferred embodiment of the present invention, the working part includes a saw blade, a drill bit or a grinding wheel. The power tool of the present invention includes but is not limited to tools for grinding, hammer drilling or cutting, specifically, power tools such as angle grinders, circular saws, jig saws or saber saws, drills, hammer drills or chisel hammer drills. Therefore, for the above-mentioned power tools, the working part also correspondingly includes a saw blade, a drill bit or a grinding wheel, etc. The selection of the working part should match the power tool. The center of gravity of the working part is preferably located at the center of the saw blade, or the working axis of the drill bit or the center of the grinding wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] When reading the accompanying drawings, the above embodiments can be better understood through the following detailed description. It should be emphasized that the various components are not necessarily drawn to scale. In fact, for the sake of discussion, the size can be enlarged or reduced at will. In the accompanying drawings, the same reference numerals represent the same elements.

[0027] Figure 1 It is a simplified structural schematic diagram of the electric tool provided in an embodiment of the present invention.

[0028] Figure 2 The present invention is a flowchart of a method for detecting electric tool recoil. DETAILED DESCRIPTION

[0029] Reference below Figure 1 and Figure 2 The electric tool and the electric tool recoil detection method of the present invention are described.

[0030] Figure 1A power tool 1 according to the invention is shown, which in the illustration shown is designed as an angle grinder. According to alternative embodiments, the power tool 1 can also be designed as a drill, a hammer drill, a chisel hammer drill or a saw, such as a circular saw, a jig saw or a saber saw, etc. Preferably, the power tool 1 of the invention is a handheld power tool.

[0031] Figure 1 The electric tool 1 designed as an angle grinder in the embodiment includes a housing 2, a power module (not shown), a working part 3, an electric motor 4, a control module 5 and a detection module 6. The housing 2 preferably has at least one handle area, in which the user can hold and operate the electric tool 1. The electric motor 4 is powered by means of a power module (not shown) connected to the electric tool 1. For a cordless tool, the power module can be a battery, and for a corded tool, the power module can be a power cable. The electric motor 4 is arranged inside the housing 2 together with a gear mechanism (not shown) and a drive shaft 7 for the purpose of driving the working part 3 (e.g., a grinding wheel) to perform a working process by rotation, axial movement, rotational movement or the like. For example, in this embodiment, the torque generated by the electric motor 4 is transmitted to the gear mechanism and finally to the drive shaft 7. The center of the working part 3 (e.g., a grinding wheel) is connected to the drive shaft 7, so that the torque of the drive shaft 7 can be transmitted to the working part 3, so that the working part 3 can rotate in the direction of the arrow R.

[0032] The electric tool 1 also has a control module 5 and a detection module 6. The detection module 6 is electrically connected to the control module 5, or alternatively wirelessly connected to the control module 5. Signals can be sent between the detection module 6 and the control module 5. The control module 5 is in turn connected to the electric motor 4 and the power module, or alternatively wirelessly connected to the electric motor 4 and the power module. Signals can be sent between the detection module 6 and the electric motor, and between the detection module and the power module.

[0033] According to a preferred embodiment of the present invention, the detection module 6 is designed as a hybrid acceleration and / or gyroscope sensor. In an alternative embodiment, only an acceleration sensor may be provided, or a separate acceleration sensor and a gyroscope sensor may be provided. In this embodiment, the detection module 6 is designed to be able to detect the linear acceleration α_sensor in three axial directions (i.e., the x-axis, the y-axis, and the z-axis) in the 3D space. In addition, the detection module 6 can also detect the angular velocity ω_sensor in the rotation direction around the rotation axis x, y, and z.

[0034] If the working part 3 designed as a grinding wheel gets stuck in the material to be processed while performing the working process, the working part 3 will no longer rotate relative to the material to be processed, and the torque generated by the electric motor 4 will act on the housing 2 of the power tool 1. As a result, the housing 2 will begin to accelerate or shift around the rotation axis y in a direction opposite to the rotation direction R. Such a sudden acceleration or sudden shift of the housing 2 of the power tool 1 may be dangerous for the user. In order to prevent the grinding wheel from injuring the user or other people, when a sudden acceleration or sudden shift of the housing 2 of the power tool 1 is detected, the control module 5 will shut down the electric motor as soon as possible with the help of the detection of the detection module 6 and the algorithm stored in the control module 5 and described by the method according to the present invention.

[0035] like Figure 1 As shown in , the detection module 6 is usually arranged in the handle area of ​​the housing 2 along the longitudinal direction x of the power tool 1. Therefore, the detection module 6 is at a distance r from the center of gravity C of the working part 3. Alternatively, the detection module 6 is arranged at the center of gravity C of the working part 3, in which case the distance r is equal to zero.

[0036] See also Figure 2 , the recoil detection method of the present invention specifically includes: detecting at least one linear acceleration by means of the detection module 6. Preferably, the detection module 6 detects the linear acceleration α_x in the x-axis direction, α_y in the y-axis direction, and α_z in the z-axis direction. As is well known, the x, y, and z directions defined in the 3D space are perpendicular to each other; the x direction corresponds to the longitudinal direction of the power tool 1, the y direction corresponds to the vertical direction of the power tool 1, and the z direction corresponds to the lateral direction of the power tool 1. The linear accelerations α_x, α_y, and α_z in these three directions are integrated into the linear acceleration α_sensor.

[0037] Preferably, when the power tool 1 is in operation, for example during grinding, cutting, sawing or drilling, disturbances such as severe vibrations and noise may occur, which may cause the power tool 1 to shut down unexpectedly. In order to be able to avoid this in a simple manner, such as Figure 2 The measured acceleration α_sensor is filtered, as represented by S1 shown in . For example, a low-pass filter can be provided, wherein a typical frequency of the low-pass filter is between 0.1 Hz and 6 Hz, and in particular about 1 Hz. In a power tool 1 having an oscillating working part 3 (such as a saw), interference signals may affect the rotational speed values, and low-pass or band-pass filters can be used to filter these values. The frequencies of these filters are adapted to the frequency of the oscillating motion, so that the filters are attenuated to the desired extent.

[0038] In addition, the gravity acceleration (g=9.81 m / s2) detected by the detection module 6 continuously acts on the power tool 1. Since this is destructive to determining the critical state of the power tool 1, such as Figure 2 As represented by S2 in FIG. 1 , the relevant component of the gravitational acceleration g is subtracted from the first, second and third linear accelerations to form an adjusted linear acceleration α_user. The specific algorithm for removing the gravitational acceleration is known, for example, the method disclosed in CN114174002 can be referred to. The adjusted linear acceleration α_user is then integrated to obtain the linear velocity v1.

[0039] In parallel with the above steps, the detection module 6 detects at least one angular velocity. Preferably, the detection module 6 detects the angular velocities ω_x, ω_y and ω_z in three spatial directions (i.e., the x-axis, the y-axis and the z-axis) and integrates them into an angular velocity ω_sensor. The angular velocity ω_sensor is multiplied by the distance r between the detection module and the center of the working part to obtain the rotational speed v2.

[0040] Then, if Figure 2 As represented by S3, the center of gravity position of the working part of the power tool after τ milliseconds is predicted based on the following formula:

[0041]

[0042] In this formula, the total speed Total υ translaslanal , linear acceleration, and the actual position of the center of gravity of the working part are used for prediction after τ milliseconds, where s(t+τ) represents the predicted position, s(t) represents the actual position, and u(t) represents the total velocity Total υ translational , and α(t) represents the linear acceleration. In this paper, Total υ translational is the vector sum of the linear velocity v1 and the rotational speed v2. The time constant τ may be a fixed time period between 50 ms and 100 ms, and it may specifically be about 70 ms.

[0043] The displacement between the predicted position of the center of gravity of the working component 3 and the actual position of the center of gravity of the working component 3 is compared with a preset displacement threshold, such as Figure 2 As indicated by S4 in FIG. 1 , when the displacement exceeds a preset displacement threshold, it is determined that a recoil is about to occur. The algorithm of the present invention is independent of the current or speed information from the electric motor 4 and does not require comparison of acceleration changes. Instead, it determines that the electric tool is about to recoil by predicting the position of the electric tool 1 in the near future. Predicting the movement trend of the center of gravity of the working part 3 is the most accurate method for determining the position of the electric tool 1, thereby more accurately predicting whether a recoil will occur.

[0044] According to another preferred embodiment of the present invention, the preset displacement threshold is fixed. This means that the detection module 6 and the control module 5 of the present invention can operate without any further information; that is, other signals besides the acceleration and the rotation speed of the working part 3, such as the electric motor current or the rotation speed of the electric motor 4, are not necessary information for detecting the kickback in the power tool 1 of the present invention.

[0045] Alternatively, according to another preferred embodiment of the present invention, the preset threshold value may be varied according to the rotation speed or current signal from the electric motor 4. The preset displacement threshold value for the user safety zone may be adjusted.

[0046] According to another preferred embodiment of the present invention, the detection method further comprises: the detection method also collects the speed and / or current signal from the electric motor 4, and as shown in S5, if it is detected that the speed of the electric motor 4 decreases significantly or the current increases significantly, then a logic evaluation is performed. Figure 2 As indicated by S6, if the displacement of the working part 3 exceeds the preset displacement threshold at the same time, then this is determined to be a true recoil; otherwise, if there is no significant change in the speed or current of the electric motor 4, then this is determined to be a manual recoil test. In the case of a true recoil, the threshold of the prediction algorithm can be adjusted to select a suitable braking method. For example, when it is determined to be a true recoil, the control module 5 will brake or stop the electric motor, and / or send an alarm signal. In the case of a manual recoil test, the speed of the electric motor 4 will not drop, so that a true recoil and a recoil test situation can be distinguished. Therefore, very rapid braking can be avoided to avoid wear of mechanical parts due to hard braking.

[0047] As described above, although the exemplary embodiments of the present invention have been described herein with reference to the accompanying drawings, the present invention is not limited to the specific embodiments described above and may have many other embodiments. The scope of the present invention should be defined by the claims and their equivalents.

Claims

1. A method for detecting recoil of an electric tool, the electric tool comprising a housing, a power module, an electric motor, a working component, a control module and a detection module, the detection module being designed to detect the linear acceleration and angular velocity of the working component, and the detection module being at a distance r from the center of gravity of the working component; the detection method comprising: a. detecting the linear acceleration by means of the detection module, subtracting the gravity acceleration from the linear acceleration to form an adjusted linear acceleration; The adjusted linear acceleration is then integrated to obtain the linear velocity; b. detecting the angular velocity by means of the detection module, and multiplying the angular velocity by the distance r between the detection module and the center of gravity of the working member to obtain the rotational speed; c. calculating the total translation speed based on the linear speed and the rotational speed, and predicting the center of gravity position of the working member of the power tool after a time constant τ milliseconds; d. detecting the actual position of the center of gravity of the working member of the power tool; e. Comparing the displacement between the predicted position of the center of gravity of the working component and the actual position of the center of gravity of the working component with a preset threshold, and determining that backlash is about to occur when the displacement exceeds the preset threshold.

2. The method for detecting recoil according to claim 1, characterized in that: The predicted position of the center of gravity of the working part of the power tool after τ milliseconds is calculated by the following algorithm: Where s(t+τ) represents the predicted position, s(t) represents the actual position, v(t) represents the vector sum of the linear velocity and the rotational speed, and α(t) represents the linear acceleration.

3. The method for detecting recoil according to claim 2, characterized in that: The detection module detects linear acceleration and / or angular velocity in three spatial directions including an x-axis, a y-axis, and a z-axis.

4. The method for detecting recoil according to claim 3, characterized in that: Filter the linear acceleration.

5. The method for detecting recoil according to claim 4, characterized in that: The preset threshold is fixed.

6. The method for detecting recoil according to claim 4, characterized in that: The detection method further collects a rotation speed and / or current signal from the electric motor, and the preset threshold value can be changed according to the rotation speed or current from the electric motor.

7. The method for detecting recoil according to claim 6, characterized in that: The detection method also includes: if it is detected that the speed of the electric motor decreases significantly or the current increases significantly when the displacement exceeds the preset threshold, then this is determined to be a true recoil; otherwise, if there is no significant change in the speed or current of the electric motor, then this is determined to be a manual recoil test.

8. The method for detecting recoil according to claim 7, characterized in that: The detection method further includes braking or stopping the electric motor and / or issuing a warning signal when true recoil is determined.

9. An electric tool, comprising a housing, a power module, an electric motor, a working component, a control module and a detection module, wherein the detection module is designed to detect at least one linear acceleration and / or at least one angular velocity of the working component, and the detection module is at a distance r from the center of the working component, characterized in that: The electric tool is designed to perform the method for detecting kickback according to any one of claims 1-8.

10. The electric tool according to claim 9, characterized in that: The detection module includes an acceleration sensor for determining linear acceleration in three specific spatial directions, and a gyroscope sensor for determining angular velocity in three spatial directions.

11. The electric tool according to claim 10, characterized in that: The working part includes a saw blade, a drill bit or a grinding wheel.

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