Three-section type control method for screw thread slipping prevention of impact screwdriver

Abstract

The invention discloses a three-section type control method for preventing screw teeth during screw hitting of an impact screwdriver. The three-section type control method aims at solving the problem that in the prior art, when an impact screwdriver is used for hitting a screw on a thin plate, the screw teeth are prone to loosing. According to the key points of the technical scheme, the three-section type control method for the impact screwdriver to screw anti-slip teeth comprises the following procedures: in the first stage, an impact screwdriver outputs according to a set rotating speed n1, whether a screw approaches to penetrate through a plate or not is judged by collecting load current changes in a motor according to the judgment basis that whether the load current is obviously reduced or not, and if yes, the step 2 is executed; automatically switching the program to the next stage; in the second stage, the impact screwdriver outputs according to the set rotating speed n2, n2 is smaller than n1, whether the screw is nearly screwed or not is judged by collecting load current changes in the motor according to the judgment basis that whether the load current is sharply increased or distributed according to a specific waveform, and if yes, the program is automatically switched to the next stage; and in the third stage, the impact screwdriver outputs according to a set pulse mode.

Description

Technical Field

[0001] This invention relates to a control method for an impact screwdriver, and more specifically, to a three-stage control method for using an impact screwdriver to drive anti-slip screws. Background Technology

[0002] As a power tool used for tightening and loosening screws, the impact screwdriver's core advantage over a conventional electric drill lies in its integrated dedicated impact module. This module can adaptively switch between two working states based on the load amplitude of the output shaft to meet the torque requirements of different work scenarios: When the output shaft is under low load (such as tightening unloaded screws, tightening low-hardness materials such as wood and plastic), the impact module remains locked or in synchronous transmission mode, stably transmitting output energy from the spindle to achieve continuous linear torque output; this working mode is defined as the non-impact output state. When the output shaft encounters high load (such as tightening screws to their mechanical limits, working on relatively high-hardness materials, or removing rusted screws), the impact module releases the lock and enters intermittent transmission mode, intermittently transmitting output energy from the spindle to intermittently output high-intensity pulse torque (energy) to efficiently overcome high load resistance; this working mode is defined as the impact output state.

[0003] In actual operation, especially when using self-tapping screws to drive into aluminum profiles, gypsum board, iron plates, and other materials, the load borne by the self-tapping screw at different driving stages exhibits significant stage-specific changes. Specifically, it can be divided into three continuous operation stages: The first stage is the initial driving stage, where the self-tapping screw gradually cuts into (or grinds) the material. As the driving depth increases, the frictional resistance and compressive resistance of the material to the screw increase linearly and synchronously. Correspondingly, the output power of the impact screwdriver also increases linearly to match the load increase and ensure smooth driving. The second stage is the near-penetration stage, where the self-tapping screw continues to penetrate and gradually penetrates the material. The material's wrapping force and resistance to the screw decrease sharply until the screw completely penetrates the material. At this point, the load borne by the screw drops to an extremely low level, almost unloaded, and then the screw continues to be screwed in. The third stage is the final tightening stage, where after the self-tapping screw penetrates the material, its nut or matching washer begins to abut against the surface of the material. As the impact screwdriver continues to output torque, the tightening load borne by the screw increases sharply until the preset tightening force is reached.

[0004] Regardless of the material of the sheet metal being screwed in, the load in the first and second stages is relatively low. Based on the switching logic of the two working states of the impact screwdriver, the load generated in these two stages is below the non-impact trigger threshold of the impact screwdriver. Therefore, the impact screwdriver always maintains the non-impact output state. However, the third stage varies greatly depending on the material of the sheet metal. For example, on wood, gypsum board, or thin aluminum alloy sheets, even the load generated in the third stage cannot exceed the "impact" threshold. On thicker iron sheets, the load of the screw in the third stage will increase sharply, quickly exceeding the impact trigger threshold of the impact screwdriver, causing the impact screwdriver to switch to the impact output state.

[0005] The aforementioned phased load changes easily trigger two typical "stripping" problems: First, in the second phase, due to the sharp decrease in the resistance of the sheet metal, while the output power of the impact screwdriver remains at the high level of the first phase, the output shaft will drive the self-tapping screw to rotate at high speed or at an accelerated speed, resulting in excessive friction and engagement failure between the screw thread and the sheet metal thread, thus causing "stripping." Second, in the third phase, the load increases sharply. When the sheet metal is of medium to low strength, due to the material properties, the material itself will undergo structural damage, leading to "stripping." However, when the sheet metal is of high strength, such as thick iron plates, the impact screwdriver will automatically switch to impact output mode. Its instantaneous output pulse torque and energy are extremely high, and the impact frequency is very fast. If the operator cannot accurately control the impact duration, the screw thread may be subjected to torque exceeding its bearing limit, resulting in thread stripping and damage, i.e., "stripping." Once a "stripping" failure occurs, the self-tapping screw will completely lose its tightening function, not only affecting the quality and efficiency of the work, but also requiring additional manpower and resources for rework and repair, increasing operating costs.

[0006] Currently, to avoid the two risks of "slipping threads" mentioned above, extremely high requirements are placed on the operator's skill and concentration. Operators need to rely on experience to accurately judge the screw's driving stage and adjust the output parameters of the impact screwdriver in time or stop the operation. However, even with rich operating experience, it is difficult to completely and accurately control the instantaneous and sudden nature of load changes, and it is impossible to fundamentally avoid the occurrence of "slipping threads".

[0007] Therefore, in the power tool industry, how to solve the technical problem of "stripping" caused by the mismatch between the output energy and the stage load when impact screwdrivers drive self-tapping screws (especially when driving into thinner plates), and improve the reliability and stability of operation, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] This invention provides a three-stage control method for preventing screw slippage when using an impact screwdriver; it solves the problem in the prior art where impact screwdrivers easily "slip" when screwing into thin sheet metal.

[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a three-stage control method for anti-slip screw driving with an impact screwdriver, comprising the following program: First stage (S1), the impact screwdriver outputs at a set speed n1, and at the same time, the change of load current in the motor is collected to determine whether the screw is close to penetrating the plate. The determination is based on whether the load current decreases significantly. If so, the program automatically switches to the next stage; Second stage (S2), the impact screwdriver outputs at a set speed n2, where n2 is less than n1. The change of load current in the motor is collected to determine whether the screw is close to being tightened (the nut abuts against the plate). The determination is based on whether the load current surges or follows a specific waveform distribution. If so, the program automatically switches to the next stage; Third stage (S3), the impact screwdriver outputs according to a set pulse mode.

[0010] When the impact screwdriver is in the thick iron setting, the object being screwed is a hard iron plate with a certain thickness. The surge in load in the third stage will cause the impact screwdriver to quickly enter the "impact state". Therefore, the criterion for judging whether the impact screwdriver has entered the third stage is: whether the collected load current is distributed according to a specific continuous waveform. If so, it means that the impact screwdriver is in the "impact state", which means that the screwing has entered the third stage.

[0011] When the impact screwdriver is in the drywall / wooden board setting, the object being screwed is a thin board with a relatively soft material. Even if it enters the third stage, it will not cause an "impact state", but there will be a significant surge in load. Therefore, the criterion for judging whether the impact screwdriver has entered the third stage is: whether the load current increases significantly. If so, it means that the screwing has entered the third stage.

[0012] Regardless of the gear setting, once pulse mode is activated, the user must determine when to stop. In pulse mode, the instantaneous output power is sufficient, but each power output is very short, resulting in a small number of rotations per pulse, typically between 0.3 and 2 rotations. This prevents the screw from rotating too many times in a short period, making it difficult for the user to stop in time and causing "stripping".

[0013] This invention employs a three-stage control method that precisely adjusts the output mode of the impact screwdriver according to different screw-driving stages. In the first stage, the output is set to a rotation speed n1, ensuring that the self-tapping screw can smoothly cut into the board, laying the foundation for subsequent operations. In the second stage, the rotation speed is reduced to n2, effectively avoiding high-speed free-spinning or accelerated rotation of the screw due to a sharp decrease in board resistance, greatly reducing the risk of "stripping". In the third stage, specific judgment criteria are used to determine whether to enter this stage based on different gears, and a set pulse mode is output. This short-duration, small-rotation-number output method gives the user more time to control the operation and avoids "stripping" caused by excessive output energy.

[0014] Meanwhile, this control method also reduces the workload and stress on operators. Previously, extensive experience and high concentration were required to minimize the risk of stripped threads. Now, through the automatic adjustment of this three-stage control method, even inexperienced operators can easily complete screw-driving operations, reducing stripped threads caused by human error and improving the overall stability and operability of power tool operations. In practical applications, this control method is expected to be widely adopted in the power tool industry, providing strong technical support for improving the reliability and quality of screw-driving operations.

[0015] In summary, the present invention has the following beneficial effects: 1. By using the three-stage control method provided by this invention to screw, the power tool can autonomously determine which of the three stages it is currently in and output power according to the preset program, so that the output energy matches the current load, thereby reducing the technical pain point of "slipping threads" and improving the reliability and stability of the operation. 2. The third stage uses pulse output. This power output mode can ensure sufficient instantaneous output power, but the power output time is very short each time. This can avoid the screw rotating too many times in a short time, which would cause "stripping". 3. The entire screw-driving process only requires pressing the switch, eliminating the need to manually control the switch's travel to adjust the output power, resulting in a better user experience. Attached Figure Description

[0016] Figure 1 This is a circuit diagram for load current acquisition. Figure 2 The current waveform diagram is shown in Example 1; Figure 3 This is a flowchart of the impact judgment and detection procedure. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0018] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "set up / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The present invention will now be described in detail with reference to the accompanying drawings.

[0021] Example 1: A three-stage control method for anti-slip screw driving with an impact screwdriver. This example is applied to the thick iron setting. The three-stage control method includes: In the first stage (S1), the impact screwdriver outputs at the set speed n13700 (duty cycle preset to 94%). During this stage, the screw is in the grinding state of thick iron, and the load is relatively small. High-speed rotation helps to improve grinding efficiency. At the same time, the load current change is collected in real time through the acquisition circuit. When the load current is detected to decrease significantly, the program automatically switches to the second stage. In the second stage (S2), the impact screwdriver outputs at the set speed n21800 (duty cycle reduced to 45%). In this stage, the screw immediately penetrates the iron plate and enters the tapping state. It is necessary to reduce the output speed to avoid "stripping" due to excessive speed during tapping. At the same time, the load current change is collected in real time through the acquisition circuit. When the collected load current is distributed according to a specific continuous waveform (the condition for judging impact), the program automatically switches to the third stage. In the third stage (S3), the impact screwdriver outputs according to the set pulse mode with a duty cycle of 50% and a pulse frequency of approximately 2 pulses per second. The duration of the motor's work within one pulse cycle is approximately 54ms (calculated based on the machine's transmission ratio, which takes the output shaft to rotate one revolution). The entire "impact-stop" pulse process lasts approximately 510ms (the impact frequency can be adjusted). During this stage, the screw nut abuts against the thick iron, resulting in a huge load.

[0022] In the third stage, one pulse corresponds to one rotation of the output shaft, and the load is high at this time. The impact screwdriver outputs in an impact state, that is, it impacts twice per second. This low-frequency impact can significantly reduce the tightening speed of the screw, making it easier for users to judge whether it is tightened and reducing the probability of stripping.

[0023] Load current acquisition principle: In the load circuit (i.e., between the power supply + and power supply -), a sampling resistor is connected in series. When current flows through it, a voltage drop is generated. Using Ohm's law: V=I*R, we get I=V / R. The current is calculated by measuring the voltage drop. The voltage value across the sampling resistor is relatively small (the resistance of the sampling resistor is usually very small), so it needs to be amplified by an internal operational amplifier circuit. Finally, it is processed by a filter circuit to obtain the current sample value.

[0024] The condition for switching from the second stage to the third stage is whether the system has entered an impact state. When the impact screwdriver begins its impact, the intermittent changes in load cause the current to fluctuate intermittently as well. Utilizing this characteristic, the impact detection program works as follows: The current detection module in the main control chip detects a change in the current sampling value and determines whether the current is rising or falling. When an upward trend is detected, it further checks whether the rising segment meets the check time window. If it does, the upward detection is successful, the detection count is incremented by 1, and the system switches to detecting a downward trend. It checks whether the current is falling. If it is, it checks whether the falling segment meets the check time window. If it does, the falling detection is successful, and the system switches back to detecting an upward trend. Each detection time window has a threshold. If the condition is met, the detection trend switches; if the condition is not met, it times out and returns to the initial detection stage. This process continues until all detection pairs are completed, indicating that the system is in an "impact state."

[0025] Example 2: A three-stage control method for anti-slip screws on impact screwdrivers. This example is applied to the drywall / wood panel setting, where impact is never triggered throughout the process. The three-stage control method includes: In the first stage (S1), the impact screwdriver outputs at the set speed n11400 (duty cycle preset to 35%). During this stage, the screw is in the state of driving into the plate and the load is moderate. At the same time, the load current change is collected in real time through the acquisition circuit. When the load current is detected to decrease significantly, the program automatically switches to the second stage. In the second stage (S2), the impact screwdriver outputs at the set speed n21000 (duty cycle reduced to 25%). In this stage, the screw immediately penetrates the plate, and the load decreases sharply. It is necessary to reduce the output power to avoid the "stripping" caused by the sharp increase in speed. At the same time, the load current change is collected in real time through the acquisition circuit. When the collected load current increases significantly (the screw nut is in contact with the plate, and the load increases), the program automatically switches to the third stage. In the third stage (S3), the impact screwdriver outputs according to the set pulse mode with a duty cycle of 50% and a pulse frequency of approximately (2) times / second. The duration of the motor's work within one pulse cycle is approximately (55) ms (the time required for the output shaft to rotate half a turn is calculated based on the machine's transmission ratio). The duration of a complete "impact-stop" pulse process is approximately (510) ms (the impact frequency can be adjusted). During this stage, the screw nut contacts the plate, and the load increases significantly.

[0026] In the third stage, one pulse corresponds to half a rotation of the output shaft, and the load is relatively low at this time. The impact screwdriver outputs in a non-impact state, which means it rotates once per second. This can greatly reduce the tightening speed of the screw, making it easier for users to judge whether it is tightened and reducing the probability of stripping.

[0027] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A three-stage control method for anti-slip screw driving with an impact screwdriver, characterized in that, The program includes the following steps: In the first stage, the impact screwdriver outputs at the set speed n1, while simultaneously determining whether the screw is close to penetrating the plate. If so, the program automatically switches to the next stage. In the second stage, the impact screwdriver outputs at the set speed n2, where n2 is less than n1. Simultaneously, it determines whether the screw is close to being tightened. If so, the program automatically switches to the next stage. In the third stage, the impact screwdriver outputs according to the set pulse mode.

2. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 1, characterized in that: The basis for determining whether a screw is close to penetrating the plate is to collect the load current change in the motor. If the load current decreases significantly, it indicates that the screw is close to penetrating the plate.

3. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 1, characterized in that: The basis for determining whether a screw is close to being tightened is to collect the load current changes in the motor. If the load current increases significantly or follows a specific waveform distribution, it indicates that the screw is close to being tightened.

4. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 3, characterized in that: If the load current increases significantly when the impact screwdriver is in the drywall / wooden board setting, it indicates that the screw is close to being tightened.

5. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 3, characterized in that: When the impact screwdriver is in the thick iron setting, if the load current is distributed according to a specific waveform, it indicates that the impact screwdriver is in the "impact state" and the screw is close to being tightened.

6. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 5, characterized in that: The specific procedure for detecting whether an impact screwdriver is impacting is as follows: The current detection module in the main control chip detects a change in the current sampling value and determines whether the current is in an upward or downward trend. When an upward trend is detected, it further checks whether the upward segment meets the inspection time window. When it is, the upward detection is considered successful, the detection pair is incremented by 1, and then the detection switches to detecting a downward trend to determine whether the current is in a downward trend. If it is in a downward trend, it checks whether the downward segment meets the inspection time window. When the condition is met, the downward detection is successful, and the detection switches to detecting an upward trend. Each detection time window has a threshold. If the condition is met, the detection trend switches; if the condition is not met, the timeout occurs, and the system returns to the initial detection stage. This process continues until all detection pairs are completed, at which point the device is determined to be in an "impact state".

7. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 1, characterized in that: When the impact screwdriver is in the drywall / wooden board setting, n1 is 1400, corresponding to a duty cycle of 35%, and n2 is 1000, corresponding to a duty cycle of 25%. In pulse mode, the corresponding duty cycle is 50%, and the pulse frequency is 2 times / second.

8. The three-stage control method for anti-slip screw driving with an impact screwdriver according to claim 1, characterized in that: When the impact screwdriver is in the thick iron setting, n1 is 3700, corresponding to a duty cycle of 94%, and n2 is 1800, corresponding to a duty cycle of 45%. In pulse mode, the corresponding duty cycle is 50%, and the pulse frequency is 2 times / second.

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