Motor control method and power tool

Abstract

The application discloses a motor control method, which solves the problems of the prior art and comprises the following steps: detecting a motor working voltage, setting corresponding starting protection current threshold I1 and exiting protection current threshold I2 according to the working voltage; detecting a motor working current, starting timing when the working current exceeds the starting protection current threshold I1, stopping timing when the working current is lower than the exiting protection current threshold I2, and calculating the time t between the starting protection monitoring and the exiting protection monitoring; if the time t is greater than the locked-rotor protection time T1, stopping the motor and starting motor reverse rotation, stopping the motor after exiting the operating position and restarting the motor.

Description

Technical Field

[0001] This invention relates to the field of motor technology, and in particular to a motor control method and a power tool. Background Technology

[0002] In some power tools, the motor output exhibits asymmetrical load characteristics. For example, in cutting tools, when the motor rotates forward, the cutting edge of the blade faces the workpiece, resulting in a larger output load; when rotating in reverse, the cutting edge faces away from the workpiece, resulting in a smaller output load. If such tools encounter a sudden stall during operation, the extrusion deformation from the motor output shaft, transmission mechanism, and workpiece creates a reverse force. Since the reverse torque is much smaller than the forward torque, a sudden stall can easily cause the motor to reverse. For instance, in machines using single-phase induction motors, which have low starting torque and can operate in both directions, even after a sudden stall and reverse rotation, the motor can still operate normally. The control system often cannot distinguish the change in the motor's operating state, causing the machine to continue operating in an incorrect state.

[0003] Existing methods for resolving motor stall and reverse rotation include: 1. User monitoring and control of motor operation, with the operator stopping the machine, repositioning the workpiece, and restarting it when reverse rotation occurs. However, user-controlled monitoring and control, especially when frequent, reduces the user experience. 2. Increasing motor power or reducing cutting power through limit switches or reduced cutting radius, thereby decreasing the probability of stall and reverse rotation. However, this method increases product cost or reduces product usability. 3. Adding speed and direction recognition to the motor to implement corresponding control and protection measures when reverse rotation occurs. However, this increases the complexity of the motor, control system, and the entire machine, increasing costs. In summary, existing methods for resolving motor stall rely on experience-based judgment, or can only reduce the likelihood of stall and reverse rotation, but cannot effectively identify stall situations. Furthermore, these methods increase the cost of power tools, increase their complexity, and limit their usability. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing methods for solving motor stall, which rely on the experience of relevant personnel to make judgments, or can only reduce the possibility of stall and reverse rotation, but cannot effectively identify the situation of motor stall. At the same time, these methods increase the cost of power tools, make power tools more complex, and limit their use. This invention provides a motor control method.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A motor control method includes the following steps:

[0007] Detect the motor operating voltage and set the corresponding protection start current threshold value I1 and protection exit current threshold value I2 according to the operating voltage;

[0008] The motor operating current is detected. Timing starts when the operating current exceeds the protection activation current threshold value I1 and stops when the operating current falls below the protection deactivation current threshold value I2. The time t between the activation of protection monitoring and the deactivation of protection monitoring is calculated.

[0009] If t is greater than the stall protection time T1, stop the motor and start the motor in reverse. After exiting the operating position, stop the motor and restart the motor.

[0010] This solution detects voltage and current changes and their duration based on the characteristics of the power tool's motor and load. This allows for the determination and control of the motor's operating status, enabling accurate and timely detection of motor stall and ensuring safe operation of the power tool. The solution also considers the time t between activating and deactivating protection monitoring, avoiding the traditional method of automatically determining motor stall upon exceeding the current threshold I1. In actual operation, the current threshold I1 may briefly exceed the threshold due to the workpiece being processed, but this is still within the normal operating range. If the motor is stopped immediately in this situation, it would degrade the user experience and reduce motor efficiency. This solution addresses these shortcomings.

[0011] Preferably, within the time range t, if the peak value of a certain operating current cycle is lower than the current threshold value I1 but higher than the current threshold value I2, then that current cycle is recorded. The total time of all current cycles with peak values ​​lower than the current threshold value I1 and higher than the current threshold value I2 is t1. If t-t1 is greater than the set stall protection time T1, it is determined that the motor is continuously stalled. The situation where the peak value of the current cycle is lower than the current threshold value I1 but higher than the current threshold value I2 can be judged as the power tool possibly still being in normal working condition. In this case, the excessive current value caused by the workpiece should not be included in the stall protection time T1. Therefore, this design further optimizes the judgment condition for whether the motor is stalled.

[0012] Preferably, if t is less than or equal to the set stall protection time T1, then it continues to determine if t is greater than the set reverse protection time T2. If t is greater than the set reverse protection time T2, it is determined that the motor has reversed. If t is less than the set reverse protection time T2, it is determined that the motor is working normally. If the motor reverses, the motor continues to reverse, and after exiting the operating position, the motor restarts and begins working in the forward direction. The magnitude of the protection time T2 depends on the inertia that the motor needs to overcome from forward to reverse. Therefore, the response time of the machine from normal operation to stall and reverse does not change much. This solution is applied to power tools with asymmetrical load characteristics. That is, these power tools have different resistances when rotating forward and in reverse. For example, in cutting tools, the resistance is high when the blade cuts the workpiece in forward rotation and low when rotating in reverse. In tools controlled by induction motors, due to the small starting torque of the induction motor, these tools are very prone to reverse rotation due to stall. Therefore, the design of this solution can accurately determine whether the motor is stalled or reversed, and take different measures according to whether the motor is stalled or reversed, further improving the user experience.

[0013] Preferably, the ratio between the stall protection time T1 and the reverse protection time T2 is 1.5:1 to 10:1.

[0014] Preferably, the operating voltage waveform is smoothed and filtered before acquisition, and the operating current waveform is smoothed and filtered before acquisition.

[0015] An electric tool includes a motor that performs the motor control method described above when in operation.

[0016] The power tool mentioned is a shredder, used to prune the leaves, branches, and trunks of plants.

[0017] The beneficial effects of this invention are: the design of this solution can accurately determine whether the motor is stalled or reversed based on the amplitude and time characteristics of the voltage and current, and take different measures according to whether the motor is stalled or reversed, thus further improving the user experience. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention;

[0019] Figure 2 This is a waveform diagram of the motor of the present invention;

[0020] Figure 3 This is another waveform diagram of the motor of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Example 1: A motor control method, such as Figure 1 As shown, it includes the following steps:

[0023] Detect the motor operating voltage and set the corresponding protection start current threshold value I1 and protection exit current threshold value I2 according to the operating voltage;

[0024] The motor operating current is detected. Timing starts when the operating current exceeds the protection activation current threshold value I1 and stops when the operating current falls below the protection deactivation current threshold value I2. The time t between the activation of protection monitoring and the deactivation of protection monitoring is calculated.

[0025] If t is greater than the stall protection time T1, stop the motor and start the motor in reverse. After exiting the operating position, stop the motor and restart the motor.

[0026] The method for detecting the motor's operating voltage is to acquire the waveform of the operating voltage, calculate the peak value of the operating voltage cycle based on the waveform, and calculate the current actual operating voltage using the peak value. The method for detecting the motor's operating current is to acquire the waveform of the operating current, and calculate the peak value of the operating current in a single cycle based on the waveform.

[0027] This solution detects voltage and current changes and their duration based on the characteristics of the power tool's motor and load. This allows for the determination and control of the motor's operating status, enabling accurate and timely detection of motor stall and ensuring safe operation of the power tool. The solution also considers the time t between activating and deactivating protection monitoring, avoiding the traditional method of automatically determining motor stall upon exceeding the current threshold I1. In actual operation, the current threshold I1 may briefly exceed the threshold due to the workpiece being processed, but this is still within the normal operating range. If the motor is stopped immediately in this situation, it would degrade the user experience and reduce motor efficiency. This solution addresses these shortcomings.

[0028] If t is less than or equal to the set stall protection time T1, then it continues to check if t is greater than the set reverse protection time T2. If t is greater than the set reverse protection time T2, it is determined that the motor has reversed. If t is less than the set reverse protection time T2, it is determined that the motor is working normally. If the motor reverses, the motor continues to reverse. After exiting the operating position, the motor restarts and begins working in the forward direction. The magnitude of the protection time T2 depends on the inertia that the motor needs to overcome from forward to reverse. Therefore, the response time of the machine from normal operation to stall and reverse does not change much. This solution is applied to power tools with asymmetrical load characteristics. That is, these power tools have different resistances when rotating forward and in reverse. For example, in cutting tools, the resistance is high when the blade is cutting the workpiece in forward rotation and low when rotating in reverse. In tools controlled by induction motors, due to the small starting torque of the induction motor, these tools are very prone to reverse due to stall. Therefore, the design of this solution can accurately determine whether the motor is stalled or reversed, and take different measures according to whether the motor is stalled or reversed, further improving the user experience.

[0029] like Figure 2 , Figure 3 As shown in the figure, the threshold values ​​for the start-up protection current I1, the threshold values ​​for the exit protection current I2, the stall protection time T1, and the reverse protection time T2 are marked on the graph. Figure 2 In the process, the time exceeding the current threshold value I1 is greater than the locked rotor protection time T1, therefore it can be determined that a locked rotor has occurred. Figure 3 If the time t between the activation and deactivation of protection monitoring is greater than the reverse protection time T2, then it can be determined that the motor has reversed.

[0030] The ratio between the stall protection time T1 and the reverse protection time T2 is 1.5:1 to 10:1.

[0031] Before acquiring the waveform of the operating voltage, a smoothing filter is applied to the operating voltage; before acquiring the waveform of the operating current, a smoothing filter is applied to the operating current.

[0032] Example 2: A motor control method, whose principle and implementation are basically the same as Example 1, except that within the time range t, if the peak value of a certain working current cycle is lower than the current threshold value I1 but higher than the current threshold value I2, then the current cycle is recorded. The total time of all current cycles with peak values ​​lower than the current threshold value I1 and higher than the current threshold value I2 is t1. If t-t1 is greater than the set stall protection time T1, it is determined that the motor is continuously stalled. The situation where the peak value of the current cycle is lower than the current threshold value I1 but higher than the current threshold value I2 can be judged as the power tool possibly still being in normal working condition. In this case, the excessive current value caused by the workpiece should not be included in the stall protection time T1. Therefore, the design of this scheme further optimizes the judgment condition for whether the motor is stalled.

[0033] Example 3: An electric tool, comprising a motor, which executes the motor control method described in Example 1 or Example 2 during operation. The electric tool is a wood chipper, used for pruning numerous branches and trunks. A wood chipper is a garden machinery tool that integrates slicing and shredding, capable of cutting branches and trunks with a diameter of 1-20 cm. It is mainly used for processing materials such as pine, mixed wood, poplar, fir, and raw bamboo. However, when encountering large pieces of material, or branches or knots in the branches, it is prone to jamming and reverse rotation, thus interrupting normal shredding work and posing certain safety hazards.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A motor control method, characterized in that, Includes the following steps: Detect the motor operating voltage and set the corresponding protection start current threshold value I1 and protection exit current threshold value I2 according to the operating voltage; The motor operating current is detected. Timing starts when the operating current exceeds the protection activation current threshold value I1 and stops when the operating current falls below the protection deactivation current threshold value I2. The time t between the activation of protection monitoring and the deactivation of protection monitoring is calculated. If t is greater than the stall protection time T1, stop the motor and start the motor in reverse. After exiting the operating position, stop the motor and restart the motor. Within the time range t, if the peak value of a certain working current cycle is lower than the current threshold value I1 but greater than the current threshold value I2, then the current cycle is recorded. The total time of all working current cycles with peak values ​​lower than the current threshold value I1 and greater than the current threshold value I2 is t1. If t-t1 is greater than the set stall protection time T1, it is determined that the motor is continuously stalled.

2. The motor control method according to claim 1, characterized in that, If t is less than or equal to the set stall protection time T1, then it continues to determine whether t is greater than the set reverse protection time T2. If t is greater than the set reverse protection time T2, then it is determined that the motor has reversed. If t is less than the set reverse protection time T2, then it is determined that the motor is working normally. If the motor reverses, then the motor continues to reverse. After exiting the operation position, the motor restarts and begins to work in the forward direction.

3. The motor control method according to claim 2, characterized in that, The ratio between the stall protection time T1 and the reverse protection time T2 is 1.5:1 to 10:

1.

4. A motor control method according to any one of claims 1-3, characterized in that, The operating voltage waveform is smoothed and filtered before acquisition, and the operating current waveform is smoothed and filtered before acquisition.

5. A power tool, characterized in that, The power tool includes a motor, which, when in operation, performs the motor control method as described in any one of claims 1-4.

6. A power tool according to claim 5, characterized in that, The power tool mentioned is a shredder, used to prune the leaves, branches, and trunks of plants.

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