A control method for a threaded fastener tightening device

Abstract

The application discloses a control method of a threaded fastener tightening device, the tightening device comprising a tightening head, a motor, a torque sensor and a speed reducer, the motor driving the tightening head to rotate and tighten the threaded fastener; the method comprising: monitoring the number of rotations of the tightening head after the tightening head starts to tighten the threaded fastener into a fastened object, and the tightening head uniformly tightening the threaded fastener into the fastened object at an initial speed; when the number of rotations of the tightening head reaches a preset number of rotations, controlling the speed reducer to reduce the rotating speed of the tightening head to a first speed, and triggering the torque sensor to monitor the output torque of the motor; when the output torque of the motor reaches a first torque, controlling the speed reducer to reduce the rotating speed of the tightening head from the first speed to a second speed; when the output torque of the motor reaches a second torque, controlling the motor to stop; the second torque is greater than the first torque. The application can improve the efficiency of tightening on the basis of ensuring the accuracy of tightening.

Description

Technical Field

[0001] This invention relates to the field of tightening device technology, and more particularly to a control method for a threaded fastener tightening device. Background Technology

[0002] Typically, bicycle axles are tightened by screwing on bolts. However, the screws must be tightened with the correct force; excessive force can cause them to break or break during riding, leading to safety issues. Insufficient force, on the other hand, can result in a loose axle, causing instability or even wheel detachment. Therefore, existing bicycle axle bolts are tightened to a predetermined, safe torque to ensure product quality and safety. Furthermore, bicycle production lines often have dedicated axle tightening lines, with each operator having 30-40 seconds of usable time, thus requiring highly efficient torque wrenches.

[0003] In response, three types of torque wrenches have emerged on the market. The first is a single-speed torque wrench, which pre-sets a torque to meet safety requirements and operates at a very high speed. Due to the time delay in wrench control and the high speed, the final tightening torque often exceeds the set torque. The second is a slow-speed torque wrench, which reduces the speed compared to the first type, making the final tightening torque closer to the set torque. However, its speed is too slow and inefficient, making it unsuitable for bicycle axle locking assembly lines. The third is a dual-speed torque wrench, which pre-sets two torques to meet safety requirements, with the second torque achieved by reducing the speed. This approach results in a final tightening torque that is close to the set second torque, also known as the "initial tightening followed by final tightening" method in existing technology, such as the method used in patent CN202763750U. However, to achieve a final torque close to the preset torque, the speed corresponding to the second torque in the third type of torque wrench is often set much lower than the speed corresponding to the first torque, leaving the second approach still inefficient.

[0004] Therefore, it is very important to improve tightening efficiency while ensuring tightening accuracy, so that torque wrenches can be adapted to the assembly line of bicycle axle locking. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a control method for a threaded fastener tightening device, which can improve tightening efficiency while ensuring tightening accuracy.

[0006] To address the aforementioned technical problems, the first aspect of this invention discloses a control method for a threaded fastener tightening device. The tightening device includes a tightening head, a motor, a torque sensor, and a reducer. The motor drives the tightening head to rotate and tighten the threaded fastener. The method includes:

[0007] Once the tightening head begins to screw the threaded fastener into the object being fastened, the number of rotations of the tightening head is monitored, and the tightening head screws the threaded fastener into the object being fastened at a constant initial speed.

[0008] When the number of rotations of the tightening head reaches a preset number, the speed reducer is controlled to reduce the speed of the tightening head to a first speed, and the torque sensor is triggered to detect and monitor the output torque of the motor.

[0009] When the output torque of the motor reaches the first torque, the reducer is controlled to reduce the speed of the tightening head from the first speed to the second speed;

[0010] When the output torque of the motor reaches the second torque, the motor is controlled to stop; the second torque is greater than the first torque.

[0011] As an optional implementation, in a first aspect of the invention, the first speed and / or the first torque are determined based on a preset delay time and the threaded fastener tightening model corresponding to the model parameters of the threaded fastener.

[0012] As another optional implementation, in the first aspect of the present invention, the delay duration is the duration between the start and the end when the number of rotations of the tightening head reaches a preset number of rotations.

[0013] As another alternative implementation, in the first aspect of the invention, the first torque is 75% of the second torque.

[0014] As another alternative implementation, in the first aspect of the invention, the first speed is 50% of the initial speed.

[0015] As another alternative implementation, in the first aspect of the invention, the second speed is 10% of the initial speed.

[0016] As another alternative implementation, in the first aspect of the invention, the threaded fastener is a screw used for fastening a bicycle axle.

[0017] A second aspect of the present invention discloses a tightening device, characterized in that it is used to perform the steps in the control method of the threaded fastener tightening device.

[0018] A third aspect of the present invention discloses a computer storage medium, characterized in that the computer storage medium stores computer instructions, which, when invoked, are used to execute steps in the control method of the threaded fastener tightening device.

[0019] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0020] Compared to existing technologies, this invention initially screws most of the threaded fastener into the object at a higher speed and lower torque. When a preset depth is reached (by setting a preset number of turns), it switches to a mode that increases the torque of the tightening head by reducing the rotation speed. This allows the threaded fastener to be screwed into the object with higher torque, thus meeting the preload requirements of the threaded fastener. Specifically, in the mode of increasing the torque of the tightening head by reducing the rotation speed, the speed is reduced twice consecutively. Compared to directly reducing the speed to a low speed, this achieves less tightening time, improves efficiency, and also achieves a more stable increase in torque, improving accuracy and safety. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating a control method for a threaded fastener tightening device disclosed in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram illustrating the relationship between the number of turns and the torque (N*m) of a tightening head based on a 10-thread screw tightening device disclosed in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram illustrating the change of tightening head torque (N*m) with time (s) when a threaded fastener is screwed into the object at a uniform rotation speed, as disclosed in an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] See Figure 1 , Figure 1This is a flowchart illustrating a control method for a threaded fastener tightening device according to an embodiment of the present invention. The tightening device includes a tightening head, a motor, a torque sensor, and a reducer. The motor drives the tightening head to rotate and tighten the threaded fastener. The control method includes:

[0028] 101. After the tightening head begins to screw the threaded fastener into the object to be fastened, the number of rotations of the tightening head is monitored, and the tightening head screws the threaded fastener into the object to be fastened at a uniform initial speed.

[0029] 102. When the number of rotations of the tightening head reaches the preset number of rotations, the speed reducer is controlled to reduce the speed of the tightening head to the first speed, and the torque sensor is triggered to detect and monitor the output torque of the motor.

[0030] 103. When the output torque of the motor reaches the first torque, the reducer is controlled to reduce the speed of the tightening head from the first speed to the second speed.

[0031] 104. When the output torque of the motor reaches the second torque, the motor is controlled to stop; the second torque is greater than the first torque.

[0032] In this embodiment of the invention, the second torque is set to a torque that gives the threaded fastener a good preload.

[0033] In this embodiment of the invention, after the tightening head begins to screw the threaded fastener into the object being tightened, the number of rotations of the tightening head corresponds to the depth of the threaded fastener in the object being tightened. As the depth increases, the torque output by the motor also changes accordingly.

[0034] For example, when the threaded fastener is a 10-thread screw, the preset number of turns is 9, the first torque is 30 N*m, and the second torque is 40 N*m, the relationship between the number of turns and the torque (N*m) of the tightening head in a 10-thread screw tightening device using the control method of this embodiment is as follows: Figure 2As shown. Within one revolution, as the screw enters, the pressure exerted by the screw head on the contact surface with the fastened object increases, leading to greater friction on the screw head. At this point, the work done by the tightening head against friction per unit time increases, and the torque of the tightening head continuously increases with a constant rotation speed. After one revolution, the pressure exerted by subsequent screws on the contact surface with the fastened object is much less than that of the screw head. Since friction is only related to the pressure and the coefficient of friction, the friction experienced by the screw after one revolution but before nine revolutions is essentially equal to the friction at the end of one revolution. At this point, the work done by the tightening head against friction per unit time remains constant, i.e., the power remains constant. With a constant rotation speed, the torque of the tightening head will be approximately equal to the torque at the end of one revolution. The torque of the tightening head remains constant and essentially unchanged. When 9 turns are reached, the speed of the tightening head decreases, for example, to 50% of the initial speed. Since the friction force is only related to the squeezing force and the coefficient of friction, the friction force remains unchanged at this time. Therefore, the work done to overcome the friction force per unit time remains unchanged, that is, the power remains unchanged. As the speed decreases continuously (due to inertia, the speed gradually decreases to 50%), the torque of the tightening head will continuously increase. When the torque of the tightening head reaches 30 N*m, the speed of the tightening head decreases again. Similarly, at this time, the friction force and the power remain unchanged. As the speed decreases continuously, the torque of the tightening head will increase again, but the rate of torque increase will decrease. When the number of turns is 10, the screw is completely inserted into the fastened object.

[0035] As can be seen, the embodiments of the present invention initially screw most of the threaded fastener into the object being fastened using a higher speed and lower torque. When a preset depth is reached (by setting a preset number of turns), the method switches to a mode that increases the torque of the tightening head by reducing the rotation speed. This allows the threaded fastener to be screwed into the object with a higher torque, thus meeting the preload requirements of the threaded fastener. Specifically, in the mode of increasing the torque of the tightening head by reducing the rotation speed, the rotation speed is reduced twice consecutively. Compared to directly reducing the speed to a low speed, this achieves both less tightening time and improved efficiency, as well as a more stable increase in torque, improving accuracy and safety.

[0036] In an optional embodiment, the first speed and / or the first torque are determined based on a preset delay time and the tightening model corresponding to the threaded fastener. The tightening model corresponding to the threaded fastener is the tightening model corresponding to the model parameters of the threaded fastener, including a model showing the relationship between the torque of the threaded fastener at different speeds and time.

[0037] Optionally, the delay duration is the time between the start and the end when the number of rotations of the tightening head reaches a preset number of rotations.

[0038] In another alternative embodiment, the second torque can be 40 N*m or other torque values, as long as they provide sufficient preload to the threaded fastener.

[0039] In yet another optional embodiment, the first torque can be 30 N*m. Based on practical experience, Figure 3 This diagram illustrates the change in torque (N*m) of the tightening head over time (s) when a threaded fastener is screwed into an object at a uniform rotational speed. The rate of torque change is higher when the torque is greater than 30 N*m than when the torque is less than 30 N*m. Because it takes 20-30 ms for the reducer to decelerate after the torque sensor detects that the torque has reached the first torque, an error occurs between the actual torque at the start of deceleration and the first torque during this 20-30 ms period. Specifically, the torque error is higher when the first torque is greater than 30 N*m than when it is less than or equal to 30 N*m. Therefore, to ensure a better torque error, the first torque should be set to less than or equal to 30 N*m. Furthermore, since deceleration occurs after reaching the first torque and the rate of torque increase decreases, this embodiment sets the first torque to 30 N*m to shorten the time it takes for the torque to reach the second torque, while also considering the torque error.

[0040] In yet another alternative embodiment, the first torque can be 75% of the second torque. For example, when the second torque is set to 40 N*m, the first torque can be 30 N*m.

[0041] In another optional embodiment, the initial speed can be 600-800 r / min. The motor speed is 3000-4000 r / min, and the motor speed is reduced to 600-800 r / min by a reduction gearbox at a ratio of 1:5, thus driving the tightening head to rotate at 600-800 r / min.

[0042] In yet another optional embodiment, the first speed may be 50% of the initial speed. Figure 2 It can be seen that when the speed decreases, the torque change rate at relatively higher speeds is greater than that at lower speeds. However, if the speed is too high, it can easily lead to a higher torque error; if the speed is too low, it will affect the efficiency. This embodiment is based on multiple experiments and found that the torque error and efficiency are more balanced when the speed is reduced to 50% of the initial speed.

[0043] In another alternative embodiment, the second speed can be 10% of the initial speed. The second speed is used to precisely achieve the second torque; therefore, a speed smaller than the first speed is chosen to achieve higher torque accuracy.

[0044] In yet another alternative embodiment, the threaded fastener may be a screw used to fasten a bicycle axle.

[0045] Example 2

[0046] A computer storage medium, characterized in that the computer storage medium stores computer instructions, which, when invoked, are used to execute steps in the control method of the threaded fastener tightening device as described in Embodiment 1.

[0047] Example 3

[0048] A tightening device for performing steps in the control method of the threaded fastener tightening device as described in Embodiment 1.

[0049] The content disclosed in the embodiments of this invention is only a preferred embodiment of the invention and is used only to illustrate the technical solutions of the invention, not to limit it. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this invention.

Claims

1. A control method of a threaded fastener tightening device, the tightening device comprising a tightening head, a motor, a torque sensor and a speed reducer, the motor driving the tightening head to rotate to tighten the threaded fastener; characterized in that, The method comprises: monitoring the number of rotations of the tightening head when the tightening head starts to screw the threaded fastener into the fastened object, and the tightening head uniformly screws the threaded fastener into the fastened object at an initial speed; when the number of rotations of the tightening head reaches a preset number of rotations, controlling the speed reducer to reduce the rotation speed of the tightening head to a first speed, and triggering the torque sensor to monitor the output torque of the motor; when the output torque of the motor reaches a first torque, controlling the speed reducer to reduce the rotation speed of the tightening head from the first speed to a second speed; the first torque is 75% of a second torque; when the output torque of the motor reaches the second torque, controlling the motor to stop; the second torque is greater than the first torque; the first speed and / or the first torque are determined according to a preset delay time and a threaded fastener tightening model corresponding to the model parameter of the threaded fastener; the threaded fastener tightening model comprises a relationship model of the torque of the threaded fastener varying with time at different speeds; the delay time is a time length between a start time when the number of rotations of the tightening head reaches the preset number of rotations and an end time when the speed reducer starts to reduce the rotation speed of the tightening head to the first speed.

2. The control method according to claim 1, characterized by, the first speed is 50% of the initial speed.

3. The control method according to claim 1, characterized by, the second speed is 10% of the initial speed.

4. The control method according to claim 1, characterized by, the threaded fastener is a screw for fastening a bicycle axle.

5. A tightening device, characterized in that A control method for performing the steps in the threaded fastener tightening device according to any one of claims 1-4.

6. A computer storage medium, characterized in that The computer storage medium stores computer instructions, which are called when used to perform the steps in the control method for the threaded fastener tightening device according to any one of claims 1-4.

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