A bolt pretightening force monitoring and loosening early warning method for a speed sensor of a visual perception-based ATP system

Abstract

The application relates to the field of rail transit technology, in particular to a bolt pre-tightening force monitoring and loosening early warning method for a speed sensor of an ATP (Automatic Train Protection) system based on visual perception, compared with the prior art, according to the method, the equivalent stress of the bolt under the pre-tightening force reduction condition when the initial pre-tightening force and the beginning loosening are more accurately obtained. The application obtains a color chart of multiple gravity-induced color-changing materials under certain stress conditions; a ring groove is formed on the free end surface of a nut or the free end surface of a bolt in a precision machine, a ring made of the multiple gravity-induced color-changing materials is arranged in the ring groove, the pre-tightening force size is simply and effectively predicted or the bolt loosening is monitored, and the function completeness, safety and stable operation of the equipment are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rail transit technology, in particular to a bolt pretightening force monitoring and loosening early warning method for a speed sensor of an ATP system based on visual perception. BACKGROUND

[0002] The train speed supervision system (ATP system) in subway transportation can monitor the speed of the vehicle in stages or continuously, and output a brake or emergency brake signal when the actual speed of the train exceeds the allowed value, and then give the train the existing speed, target distance or target speed information through the instrument, so that the driver only needs to operate the vehicle according to these information to ensure the safe arrival of the vehicle. The speed sensor of the ATP system is installed on the axle box, which is assembled on the wheel shaft outside the wheel, and its sensing accuracy is obviously crucial to the safety of the train, and the reliability of the installation and fixation of the speed sensor of the ATP system has a significant impact on its sensing accuracy.

[0003] During the operation of the train, due to vibration and impact, material aging and fatigue, design defects and improper installation, gasket creep and thermal expansion, etc., the fixing bolt of the speed sensor of the ATP system may gradually reduce its axial pretightening force, which will affect its sensing accuracy. Even cause serious deviation of function or failure of the system. Therefore, the bolt pretightening force of the fixing bolt of the speed sensor of the ATP system is crucial to the normal function of the ATP system, and once the axial force is weakened, the functions of the fastener will also be reduced or even completely lost, which may cause functional deviation, even disconnection, slipping or loosening of the connected parts, and thus may cause major safety accidents. Therefore, effective prediction or monitoring of the bolt pretightening force is of great significance to determine whether the bolt is loose, ensure the complete function of the equipment, and safe and stable operation.

[0004] Currently, the methods for predicting or detecting whether the bolt connection is loose mainly include visual inspection, tool testing, wear mark observation, acoustic-elastic effect method, vibration and guided wave method, electromechanical impedance method, and machine learning algorithm. Each method has its advantages and disadvantages, but most of the methods in engineering practice require special equipment for detection, and other methods that do not require special equipment for detection require a lot of experience summary of engineers and cannot be applied to engineering practice with large number of bolt connections and complex engineering conditions. For the determination of the bolt pretightening force value, the existing technology mainly uses the method of installing a mechanical sensor at a certain position, but this method has few measurement points and is not suitable for small-sized bolts, and is not suitable for large number of bolt connections or precision mechanical engineering such as ATP system. SUMMARY

[0005] In view of the technical problems existing in the prior art, the application provides a bolt pretightening force monitoring and loosening early warning method for a speed sensor of an ATP system based on visual perception.

[0006] According to one aspect of the application, the application provides the following technical solutions:

[0007] A bolt pretightening force monitoring and loosening early warning method for a speed sensor of an ATP system based on visual perception comprises the following steps:

[0008] S1, multiple gravity-induced color-changing materials are packaged at specific positions of experimental bolts or experimental nuts, and a color chart is prepared based on the colors of the multiple gravity-induced color-changing materials under different axial force values of the bolts or nuts;

[0009] S2, multiple gravity-induced color-changing materials are arranged on the bolts or nuts for precision machinery, and the positions, sizes and materials of the multiple gravity-induced color-changing materials are the same as those of the experimental bolts or nuts, during the working process of the precision machinery, the bolt pretightening force and the loosening degree are obtained by observing the multiple gravity-induced color-changing materials and comparing the color chart, and the bolt pretightening force monitoring and loosening early warning for the precision machinery are realized.

[0010] As a preferred scheme of the bolt pretightening force monitoring and loosening early warning method for a speed sensor of an ATP system based on visual perception, in the step S1,

[0011] First, the bolt usually applies an initial fastening pretightening force F After the bolt is tightened, the friction force is used to ensure that the bolt does not loosen; assuming that the nominal diameter of the bolt is d , the diameter of the friction contact surface is Ф (if there is no washer, the outer diameter of the nut or the nut is used), and the friction contact area is

[0012] (1)

[0013] Assuming that the ratio of the friction contact surface to the diameter of the bolt is , then

[0014] (2)

[0015] Assuming that the pressure generated by the pretightening force is uniformly distributed, the micro area at a distance r from the center is

[0016] (3)

[0017] The pressure on the micro area is

[0018] (4)

[0019] If the friction coefficient is μ , the friction force on the micro area is

[0020] (5)

[0021] Moment due to friction on micro area

[0022] (6)

[0023] Thus the moment due to friction on the whole contact surface is

[0024] (7)

[0025] Shear stress due to moment

[0026] (8)

[0027] where ρ is the distance from the center of torsion;

[0028] Second, the initial tightening preload F Calculation:

[0029] Usually the initial tightening preload of bolt F Can be calculated as follows

[0030] (9)

[0031] where is the bolt strength, is the bolt stress cross-sectional area;

[0032] Third, determine the friction coefficient between different materials μ ;

[0033] Finally, determine the equivalent stress ;

[0034] For the bolt head and nut, the free end surface in the bolt locking state condition is the main deformation form due to the friction moment leading to torsional deformation, i.e. pure shear stress state.

[0035] Then the maximum principal stress and the minimum principal stress are respectively

[0036] (10)

[0037] (11)

[0038] Thus the equivalent stress

[0039] (12)

[0040] Based on the equivalent stress of the bolt under the initial pre-tightening force and the pre-tightening force reduction condition when starting to loosen, multiple gravity-induced color-changing materials are selected for experiments, the colors under the corresponding stress conditions are obtained, and a color chart is made.

[0041] As a preferred scheme of the bolt pre-tightening force monitoring and loosening early warning method for the speed sensor of the ATP system based on visual perception, in the step S1, a ring-shaped groove is opened on the free end surface of the nut or the free end surface of the bolt for arranging the multiple gravity-induced color-changing materials, and the multiple gravity-induced color-changing materials are multiple gravity-induced color-changing polymer rings.

[0042] As a preferred scheme of the bolt pre-tightening force monitoring and loosening early warning method for the precision machinery of the ATP system based on visual perception, in the step S1, a glass light-transmitting packaging ring is covered on the multiple gravity-induced color-changing materials.

[0043] The beneficial effects of the present application are as follows:

[0044] The present application provides a bolt pre-tightening force monitoring and loosening early warning method for the speed sensor of the ATP system based on visual perception. Compared with the prior art, according to the method of the present application, the equivalent stress of the bolt under the initial pre-tightening force and the pre-tightening force reduction condition when starting to loosen can be more accurately obtained. The present application obtains a color chart of multiple gravity-induced color-changing materials under certain stress conditions, opens a ring-shaped groove on the free end surface of the nut or the free end surface of the bolt for the precision machinery, and installs a ring made of multiple gravity-induced color-changing materials, so that the size of the pre-tightening force or whether the bolt is loosened can be simply and effectively predicted or monitored, and the complete, safe and stable operation of the equipment is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to the structures shown in the drawings without creative labor for those skilled in the art.

[0046] Figure 1 A schematic diagram for calculating the contact surface area is shown.

[0047] Figure 2 A schematic diagram for bolt connection is shown.

[0048] Figure 3 A schematic diagram for stress state analysis is shown.

[0049] Figure 4 A schematic diagram for designing the free end surface of the nut is shown.

[0050] Figure 5 Figure 3 shows a schematic diagram of the free end surface of the bolt.

[0051] Figure 6 Figure 3 shows a schematic diagram of the free end surface of the bolt.

[0052] Figure 7 Figure 3 shows a schematic diagram of the free end surface of the bolt.

[0053] Figure 3 shows a schematic diagram of the free end surface of the bolt.

[0054] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0056] To realize the bolt pre-tightening force measurement and intuitive visual prediction of loosening, the present application encapsulates the force-induced color-changing material at a specific position of the bolt or nut. When the axial force of the bolt changes, the color of the material changes due to the force change, and thus the bolt pre-tightening force and loosening can be intuitively judged, and the complete, safe and stable operation of the equipment is ensured.

[0057] According to one aspect of the present application, the present application provides the following technical solutions:

[0058] A bolt pre-tightening force monitoring and loosening early warning method for a speed sensor of an ATP system based on visual perception, comprising the following steps:

[0059] S1, encapsulating multiple force-induced color-changing materials at a specific position of the experimental bolt or the experimental nut, and preparing a colorimetric card based on the colors of the multiple force-induced color-changing materials under different axial force values of the bolt or the nut;

[0060] S2, setting the multiple force-induced color-changing materials with the same position, size and material as those of the experimental bolt or the experimental nut on the bolt or the nut for precision machinery, and obtaining the bolt pre-tightening force and the loosening degree by observing the multiple force-induced color-changing materials and comparing the colorimetric card during the working process of the precision machinery, so as to realize the bolt pre-tightening force monitoring and loosening early warning of the precision machinery.

[0061] Preferably, in the step S1, first, the bolt usually applies an initial fastening pre-tightening force FAfter the bolt is tightened, the friction force ensures that the bolt does not loosen; for example Figure 1 As shown in the figure, let the nominal diameter of the bolt be d , the diameter of the friction contact surface be Ф (if there is no washer, then the outer diameter of the nut or the nut), and the friction contact area be

[0062] (1)

[0063] Let the ratio of the friction contact surface to the diameter of the bolt be , then

[0064] (2)

[0065] Assuming that the pressure generated by the pre-tightening force is uniformly distributed, as shown in the figure, the micro-area at a distance r from the center is Figure 1

[0066] (3)

[0067] The pressure on the micro-area is

[0068] (4)

[0069] If the friction coefficient is μ , the friction force on the micro-area is

[0070] (5)

[0071] The moment generated by the friction force on the micro-area is

[0072] (6)

[0073] Therefore, the moment generated by the friction force on the entire contact surface is

[0074] (7)

[0075] The shear stress generated by the moment is

[0076] (8)

[0077] where ρ is the distance from the center of torsion;

[0078] Secondly, the initial tightening pre-tightening force F is calculated as follows:

[0079] The initial tightening pre-tightening force of the bolt F can be calculated as follows

[0080] (9)

[0081] where​ and Table 1 and Table 2 can be referred to.

[0082] Table 1 Bolt strength

[0083]

[0084] Table 2 Bolt stress cross-sectional area

[0085]

[0086] Again, the friction coefficient between different materials is determined as μ ;

[0087] Table 3 Friction coefficient between different materials μ

[0088]

[0089] Finally, the equivalent stress is determined as ;

[0090] For the bolt head and nut as shown in Figure 2 , the main deformation form of the free end surface of the nut under the condition of bolt locking is the torsional deformation caused by the friction torque, that is, the pure shear stress state as shown in Figure 3 .

[0091] Then the maximum principal stress and the minimum principal stress are respectively

[0092] (10)

[0093] (11)

[0094] Thus, the equivalent stress

[0095] (12)

[0096] Based on the equivalent stress of the bolt under the condition of the initial pre-tightening force and the pre-tightening force reduction when starting to loosen, a plurality of gravity-induced color-changing materials are selected for experiments to obtain the color under the corresponding stress condition, and then a colorimetric card is made.

[0097] Preferably, in the step S1, according to the nut size under different standard conditions listed in Table 4, an annular groove is opened on the nut free end surface 11 of the nut 1 for setting a plurality of gravity-induced color-changing polymer rings 3, and a glass light-transmitting packaging ring 4 is covered on the plurality of gravity-induced color-changing materials, as shown in Figure 4-5As shown. Also can be in the screw free end face 21 of the screw 2 open a ring groove for setting multiple gravity-induced color change polymer ring 3, on the multiple gravity-induced color change polymer ring cover glass light package ring 4, such as Figure 6-7 As shown.

[0098] In the ring groove into the same size of multiple gravity-induced color change material made of circular ring, and ensure fastening. To ensure the integrity and stability of the force-induced color change material, while facilitating the observation of the material discoloration caused by bolt loosening, which is covered with a corresponding size of glass light package ring, to ensure that the color change of the multiple gravity-induced color change polymer can be directly observed.

[0099] Table 4 Nut size parameters

[0100]

[0101] Compared with the prior art, the method according to the present application can more accurately obtain the equivalent stress of the bolt under the condition of the initial pre-tightening force and the pre-tightening force reduction when starting to loosen. A multiple gravity-induced color change polymer is selected for experiment, and the color under the corresponding stress condition is obtained, and then a colorimetric card is made. A ring groove is opened on the free end face of the nut or the free end face of the bolt, a circular ring made of a multiple gravity-induced color change polymer of force-induced color change material is loaded in the groove, and fastening is ensured. In order to ensure the integrity and stability of the force-induced color change material, while facilitating the observation of the material discoloration caused by bolt loosening, which is covered with a corresponding size of glass light package ring, to ensure that the color change of the multiple gravity-induced color change polymer can be directly observed, and then the bolt loosening can be directly judged, and the safety and stable operation of the equipment can be ensured. The present application has reasonable design, can realize simple and effective prediction of the pre-tightening force or monitoring of the bolt loosening, and has good practical application value.

[0102] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made according to the content of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A bolt pre-tightening force monitoring and loosening early warning method for a speed sensor of a visual perception-based ATP system, characterized in that, It comprises the following steps: S1, encapsulating multiple gravity-induced color-changing materials at specific positions of the experimental bolt or experimental nut, and making a color chart based on the colors of the multiple gravity-induced color-changing materials under different axial force values of the bolt or nut; In the step S1, First, the bolt applies an initial tightening preload F After the bolt is tightened, the friction ensures that the bolt does not loosen; the nominal diameter of the bolt is d , the diameter of the friction contact surface is Ф, and the friction contact area （1） Let the ratio of the frictional contact surface to the diameter of the bolt be then （2） Assuming that the pressure generated by the pre-tightening force is uniformly distributed, the micro-area with a distance r from the center of the circle is （3） wherein dθ is an integral infinitesimal of angle; The pressure on the micro-area is （4） If the friction coefficient is μ the friction force on a micro-area （5） The moment generated by the friction force on the micro-area is （6） Thus, the moment generated by the friction force on the entire contact surface is （7） The shear stress generated by the moment is （8） wherein ρ is the distance from the center of the twist circle; Second, the initial fastening preload F Calculation: Typically the initial tightening preload of the bolts F This can be calculated as follows （9） wherein is the bolt strength, is the bolt stress cross-sectional area; Again, the friction coefficient between different materials is determined to be μ ; Finally, the equivalent stress is determined ; For the bolt head and the nut, the main deformation form of the surface at the free end under the condition of bolt locking is the torsional deformation caused by the friction moment, i.e. pure shear stress state; the maximum principal stress and the minimum principal stress respectively （10） （11） Thus, the equivalent stress is （12） Based on the equivalent stress of the bolt under the condition of pre-tightening force reduction from the initial pre-tightening force to the beginning of loosening, multiple gravity-induced color-changing materials are selected for experiment, the colors under the corresponding stress conditions are obtained, and then a color chart is made; S2, multiple gravity-induced color-changing materials are arranged on the bolt or nut for precision machinery, which are the same as those arranged on the experimental bolt or experimental nut in terms of position, size and material. During the working process of the precision machinery, the pre-tightening force and loosening degree of the bolt are obtained by observing the multiple gravity-induced color-changing materials and comparing the color chart, so as to realize the pre-tightening force monitoring and loosening early warning of the bolt for precision machinery.

2. The bolt pre-load monitoring and loosening warning method for speed sensor of visual perception based ATP system according to claim 1, characterized in that, In the step S1, a ring groove is opened on the free end surface of the nut or the free end surface of the bolt for arranging the multiple gravity-induced color-changing materials.

3. The bolt pre-load monitoring and loosening warning method for speed sensor of visual perception based ATP system according to claim 2, characterized in that, In the step S1, a glass transparent encapsulation ring is covered on the multiple gravity-induced color-changing materials.

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