Method and device for controlling thread pre-tightening force

Abstract

The invention discloses a method and device for controlling thread pre-tightening force. The method comprises the following steps: fixing a reflection target on a measurement calibration piece, measuring the initial position L0 of a reference point on the surface of the reflection target by using a laser feedback range finder, continuously measuring the actual position Lt of the reference point by using the laser feedback range finder, and calculating the actual displacement delta L = L0-Lt of the reference point in real time, the actual displacement delta L is compared with the maximum displacement delta Lmax and the minimum displacement delta Lmin, and if delta Lmin is larger than delta L, the threaded fastener continues to be tightened; and if delta L is greater than or equal to delta Lmax and greater than or equal to delta Lmin, stopping tightening the threaded fastener. The device comprises a laser feedback range finder (2) and a reflection target (6) for feeding back laser beams, the laser feedback range finder (2) is in communication connection with the controller (1), the controller is electrically connected with the electric tightening tool (7), and the reflection target (6) is fixed on a measurement calibration piece.

Description

Technical Field

[0001] This invention relates to a method for precisely controlling the preload of threaded fasteners (screws, bolts, nuts) during the assembly of power and electronic equipment; it also relates to an apparatus for implementing the method. This invention belongs to the field of precision mechanical assembly and automatic control technology. Background Technology

[0002] In the assembly of secondary power modules such as aerospace transformers and rectifiers, numerous connections are made using threaded fasteners such as screws and bolts. Examples include fixing transformer components inside the chassis, installing heat sink components, mounting PCB boards, and fixing busbars. The uniformity and accuracy of the preload of these threaded fasteners directly affect the contact thermal resistance, heat dissipation performance, mechanical vibration and noise, and long-term reliability of the secondary power equipment. Currently, torque control or torque-angle control methods are commonly used to control the preload of these threaded fasteners.

[0003] Torque control uses a digital torque wrench to tighten threads. Its disadvantage is that the relationship between preload and torque is F=T / (K·d), where K is the torque coefficient, which is significantly affected by thread friction and end-face friction. Fluctuations in the friction coefficient can lead to significantly different preloads even with the same torque, resulting in some threaded connections being too tight or too loose, affecting the uniformity of force distribution between the connected parts.

[0004] The torque-angle method involves first applying an initial torque to eliminate thread backlash, then rotating the component by a specific angle. While this method offers some improvement, for connected components such as radiators and insulating gaskets that are sensitive to changes in rigidity, even slight deviations in component thickness or minor differences in material properties can lead to variations in elastic deformation and preload even with the same angle of rotation.

[0005] This is because existing methods described above all involve "indirect control" of the elastic deformation of the connecting parts, failing to "see" the physical effect of thread tightening in real time. In other words, the actual elastic deformation of the connected parts cannot be "seen," and the consistency of assembly quality depends on the machining accuracy of the parts and the operator's experience. Therefore, there is an urgent need for a method and device that can directly sense and control the elastic deformation of the connected parts during thread tightening. Summary of the Invention

[0006] In view of the above-mentioned defects in the prior art, the present invention aims to provide a method for controlling thread preload; another object of the present invention is to provide an apparatus for implementing the method.

[0007] To achieve the above objectives, the method of the present invention adopts the following technical solution: 1) Fix the reflective target on the measuring calibration component, ensuring that the reflective target is as close as possible to the connecting thread; the measuring calibration component is any one of the connected parts connected by threaded fasteners, or a component rigidly connected to any one of the connected parts; 2) Measure the initial position L0 of the reference point located on the surface of the reflective target using a laser feedback rangefinder; 3) During the tightening of the threaded fasteners, the actual position L of the reference point is continuously measured using a laser feedback rangefinder. t And calculate the actual displacement of the reference point ΔL=L0-L in real time. t ; 4) Compare the actual displacement ΔL with the preset maximum displacement ΔL max The preset minimum displacement ΔL min Comparison: If ΔL min If the value is greater than ΔL, continue tightening the threaded fasteners; If ΔL max ≧ΔL≧ΔL min If the threaded fastener is not tightened, then stop tightening it.

[0008] To achieve the above method, the device provided by the present invention includes a laser feedback rangefinder with a laser emitter, a receiver and a signal processing unit inside, and a reflective target for feeding back the laser beam; the laser feedback rangefinder is communicatively connected to a controller, which is electrically connected to an electric tightening tool, and the reflective target is fixed on a measuring calibration component; the measuring calibration component is any one of the connected components connected by threaded fasteners, or other components rigidly connected to any one of the connected components.

[0009] Compared with the prior art, the present invention adopts the above-mentioned technical solution, which fixes the reflective target on the measuring calibration part (the connected part, or other parts rigidly connected to one of the connected parts). Therefore, during the thread tightening process, the micron-level elastic deformation generated by the connected part can be directly measured in real time in a non-contact manner, and the amount of elastic deformation is transmitted to the controller as a feedback signal for closed-loop control, thereby controlling the action of the electric tightening tool, thereby controlling the magnitude of the thread preload, and finally achieving the goal of high consistency of thread preload for each device.

[0010] This invention directly targets the physical quantity that affects the magnitude of the preload—"elastic deformation"—as the control objective. It can completely eliminate the influence of factors such as fluctuations in the coefficient of friction and deviations in the thickness of parts on the preload. This not only ensures the consistency of the preload at each threaded connection, but also ensures the good contact surface between the connecting parts, reduces contact thermal resistance, and improves the rigidity and vibration resistance of the mechanical connection, thereby enhancing the overall electrical performance and reliability of the equipment. Attached Figure Description

[0011] Figure 1 The measurement principle of the method of this invention Figure 1 ; Figure 2 The measurement principle of the method of this invention Figure 2 .

[0012] In the diagram: 1. Controller; 2. Laser feedback rangefinder; 3. First connected component; 4. Second connected component; 5. Threaded fastener; 6. Reflector target; 7. Electric tightening tool; 8. Other components. Detailed Implementation

[0013] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings: Example

[0014] like Figure 1 As shown, the method provided by this invention is as follows: 1) Fix the reflective target 6 onto the measuring calibration component, ensuring that the reflective target 6 is as close as possible to the connecting thread; the measuring calibration component can be either the first connected component 3 or the second connected component 4 connected by threaded fasteners 5, or other components 8 rigidly connected to the first connected component 3 or the second connected component 4. In this example, the measuring calibration component refers to the second connected component 4; 2) Measure the initial position L0 of the reference point located on the surface of the reflective target 6 using the laser feedback rangefinder 2; 3) During the tightening of the threaded fastener 5, the actual position L of the reference point is continuously measured using a laser feedback rangefinder 6. t And calculate the actual displacement of the reference point ΔL=L0-L in real time. t ; 4) Compare the actual displacement ΔL with the preset maximum displacement ΔL max The preset minimum displacement ΔL min Comparison: If ΔL min If the value is greater than ΔL, then continue to tighten the threaded fastener 5; If ΔL max ≧ΔL≧ΔL min If the threaded fastener 5 is not tightened, then stop tightening. Example

[0015] Each step is the same as in Example 1. The measurement calibration refers to the calibration of other components 8 that are rigidly connected to the second connected component 4 (see Example 1). Figure 2 ). Example

[0016] The device provided by the present invention employs, as follows Figure 1 , Figure 2 The structure shown is as follows: The laser feedback rangefinder 2 has a laser emitter (not shown in the figure), a receiver (not shown in the figure), and a signal processing unit (not shown in the figure). The laser feedback rangefinder 2 is communicatively connected to the controller 1, which is electrically connected to the electric tightening tool 7. The reflective target 6 used to feed back the laser beam is fixed on the measuring calibration component. The surface of the reflective target 6 has a reference point. The measuring calibration component can be either the first connected component 3 or the second connected component 4 connected by threaded fasteners 5, or other components 8 rigidly connected to the first connected component 3 or the second connected component 4.

[0017] In the above embodiments, the electric tightening tool 7 is an electric screwdriver or electric wrench driven by a servo motor. The controller 1 receives the distance data collected in real time by the laser feedback rangefinder 2 and calculates the actual displacement ΔL in real time, based on ΔL and ΔL... max ΔL min The comparison result generates a control command and sends it to tightening tool 7. ΔL max ΔL min It is determined in advance through testing, and is the amount of elastic deformation of the connected parts when the corresponding threaded fastener 5 reaches the maximum ideal preload or the minimum ideal preload.

Claims

1. A method for controlling thread preload, characterized in that... The method is as follows: 1) Fix the reflective target on the measuring calibration component, ensuring that the reflective target is as close as possible to the connecting thread; the measuring calibration component is any one of the connected parts connected by threaded fasteners, or a component rigidly connected to any one of the connected parts; 2) Measure the initial position L0 of the reference point located on the surface of the reflective target using a laser feedback rangefinder; 3) During the tightening of the threaded fasteners, the actual position L of the reference point is continuously measured using a laser feedback rangefinder. t And calculate the actual displacement of the reference point in real time ΔL=L0-L t ; 4) Compare the actual displacement ΔL with the preset maximum displacement ΔL max The preset minimum displacement ΔL min Comparison: If ΔL min If the value is greater than ΔL, continue tightening the threaded fasteners; If ΔL max ≧ΔL≧ΔL min If the threaded fastener is not tightened, then stop tightening it.

2. An apparatus for implementing the method of claim 1, comprising a laser feedback rangefinder (2) having a laser emitter, a receiver, and a signal processing unit internally, and a reflective target (6) for feeding back the laser beam; characterized in that: The laser feedback rangefinder (2) is connected to the controller (1), which is electrically connected to the electric tightening tool (7). The reflective target (6) is fixed on the measuring calibration component. The measuring calibration component is any one of the connected parts connected by the threaded fastener (5), or other components (8) rigidly connected to any one of the connected parts.

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