A gear crack fault diagnosis method based on electromechanical coupling model

Abstract

The application discloses a gear crack fault diagnosis method based on an electromechanical coupling model and belongs to the field of gear crack fault diagnosis. The method comprises the following steps: establishing a global coupling dynamic model of a coal mining machine cutting part electromechanical transmission system driven by a permanent magnet motor; constructing a dynamic load model of a coal mining machine cutting drum; determining a permanent magnet synchronous motor controller architecture and control parameters; determining a gear crack fault model and fault feature representation parameters; obtaining signal features of motor currents in the electromechanical coupling model to accurately extract gear transmission system crack fault feature parameters; and ending the design. The application provides a non-invasive method for detecting mechanical faults through electrical features, solves problems such as difficulty in ensuring monitoring quality of an additional sensor from the source, and achieves the purpose of accurately extracting typical features in a fault working condition directly from motor current signals, thereby providing an important theoretical basis for studying health state monitoring and fault prediction of a coal mining machine cutting transmission system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of gear crack fault diagnosis, and particularly relates to a gear crack fault diagnosis method based on an electromechanical coupling model. BACKGROUND

[0002] The shearer cutting transmission system is a nonlinear electromechanical coupling transmission system with characteristics such as multiple meshing points and multiple-stage transmission. During long-time operation, the transmission gears of the shearer cutting part are prone to wear, cracks, broken teeth and other faults, which further affect the normal operation of the shearer. At present, in the fault diagnosis of the transmission gears of the shearer, the vibration signals are collected by installing an acceleration sensor to monitor the gear motion state. However, in the harsh working environment of the coal mine, the installation of additional sensors is limited by the space position, and the quality of the monitoring signals is difficult to guarantee. Therefore, it is very important to make reasonable and effective judgments on the possible faults of the transmission system of the shearer cutting part and determine the effective typical fault features in view of the harsh working environment of the shearer cutting transmission system.

[0003] Considering that the shearer cutting transmission system is composed of a permanent magnet synchronous motor, a speed reducer, a cutting drum and some parts, and is a typical electromechanical coupling system, many scholars have carried out research on the electromechanical coupling model of the transmission system at home and abroad. However, in the process of studying the gear faults, most of the existing researches adopt the form of oil detection, ferrography analysis and torque sensor post-processing to judge the gear faults. However, it is inconvenient to install a torque sensor in the complex working conditions of the coal mine, and the oil detection and ferrography analysis monitoring have a large time delay. Therefore, how to extract effective current signals to diagnose the faults of the shearer cutting transmission system becomes a problem to be solved. SUMMARY

[0004] Technical problem: The purpose of the present application is to solve the technical problems of the prior art, and to provide a gear crack fault diagnosis method based on an electromechanical coupling model, which does not need to install additional sensors and realizes non-invasive fault detection of the machine through current signals.

[0005] Technical solution: To achieve the above object, a gear crack fault diagnosis method based on electromechanical coupling model, characterized by: from the perspective of electromechanical coupling, the motor current signal is collected through a non-intrusive method to detect mechanical faults through electrical characteristics, first, a permanent magnet motor driven coal mining machine cutting part electromechanical transmission system coupling dynamics model is established, then a coal mining machine cutting drum end dynamic load model is constructed, then the permanent magnet synchronous motor controller architecture and control parameters are determined, the gear crack fault model and fault feature representation parameters are determined, the gear transmission system crack fault feature parameters are accurately extracted by analyzing the signal characteristics of the motor current in the electromechanical coupling model, without additional sensors, the current signal is easy to obtain quickly, and the purpose of directly extracting typical features under fault working conditions from the motor current signal is achieved.

[0006] The specific steps are as follows:

[0007] S1: A global electromechanical coupling dynamics model of the electromechanical transmission system of the permanent magnet motor driven coal mining machine cutting part is established, which includes all kinds of typical complex electromechanical systems in the electromechanical transmission system of the coal mining machine cutting part, including permanent magnet motor subsystem, gear transmission subsystem, and end load subsystem model;

[0008] S2: The cutting drum load is calculated to obtain the average load torque of the coal mining machine end cutting drum, the relationship between the cutting load torque of the coal mining machine and the traction speed and the drum cutting speed is established by establishing the mathematical model of the cutting drum, and the dynamic load model of the cutting drum of the coal mining machine is constructed;

[0009] S3: According to the physical model of the electromechanical transmission system coupling dynamics of the permanent magnet motor driven coal mining machine cutting part, the dynamics model of the electromechanical transmission system of the coal mining machine cutting part is established, the permanent magnet synchronous motor controller architecture is determined, and the motor control parameters are determined;

[0010] S4: Since the physical parameters of the electromechanical transmission system of the coal mining machine cutting part will directly affect the dynamic response of the gear transmission, for gear crack fault, first, calculate and determine the key parameters of each rotor component in the electromechanical transmission system of the coal mining machine cutting part, including rotational inertia, concentrated mass, stiffness, and damping, then model and numerically solve the electromechanical transmission system of the coal mining machine cutting part; According to the crack depth, the gear crack fault is divided into two cases, the bending deformation and shear deformation stiffness of the gear teeth with crack fault are calculated, the time-varying meshing stiffness of the gear teeth with crack fault on the driving gear is calculated, and the mapping relationship between crack fault and current is established for fault diagnosis;

[0011] S5: According to the global electromechanical coupling dynamics model of the electromechanical transmission system in S1 and the dynamics models of the permanent magnet motor subsystem, the gear transmission subsystem and the end load subsystem respectively, the signal characteristics of the permanent magnet motor current in the electromechanical coupling model are obtained, the meshing stiffness of the gear crack fault state is taken as the evaluation index, the crack fault characteristics of the gears in each subsystem of the electromechanical transmission system of the coal mining machine cutting part are accurately extracted, the mapping relationship between the q-axis current characteristics of the permanent magnet synchronous motor and the gear crack fault is established, and the gear crack fault in the gear transmission system is judged by monitoring the motor current signal; the accuracy of fault diagnosis is changed by adjusting the control parameters of the permanent magnet motor and the fault characteristic representation parameters of the gear, until it is consistent with the actual fault result, and finally the accurate diagnosis method of the gear crack fault of the coal mining machine cutting part is determined.

[0012] Further, the electromechanical coupling effect of the electromechanical transmission system of the coal mining machine cutting part refers to the coupling system composed of the electromagnetic parameters of the permanent magnet synchronous motor and the mechanical parameters of the gear transmission system and the load system, which includes the complete input to output, and the mapping relationship between the gear crack fault and the current is represented by the dynamics model of the coupling system:

[0013] (1),

[0014] In the formula, represents the charge, i q represents the q-axis current, R represents the resistance, L d is the d-axis inductance, L q is the q-axis inductance, and are PI control parameters of the current loop, and are PI control parameters of the speed loop, is the motor set speed, is the motor actual measured speed, θ m is the speed difference, η m is the integral of the speed difference, J i (i=m, L, 1~6) is the moment of inertia of each element, θ i (i= m, L, 1~6) is the torsion angle of each element, K 12 , K 34 , K 56 are the meshing stiffness of each gear pair, C 12 , C 34 , C 56 are the meshing damping of each gear pair K m1 , K 23 , K 45 , K 6L are the torsional stiffness of each transmission shaft, C m1 , C23 , C 45 , C 6L is the torsional damping of each transmission shaft, F 12 , F 34 , F 56 is the meshing force between the gear pairs, T m is the electromagnetic torque of the permanent magnet motor, T L is the load torque of the cutting drum, the dynamic models of the permanent magnet motor subsystem, the gear transmission subsystem, and the end load subsystem are established respectively, and finally the dynamic models of each subsystem are integrated.

[0015] Further, when calculating the load of the cutting drum, the average cutting force Z d experienced by a single blunt pick on the drum is:

[0016] (2),

[0017] In the formula, is the cutting force experienced by a single sharp pick, is the increase in traction when the pick is worn blunt, and ; is the unidirectional compressive strength of coal, the empirical formula , 10~50MPa; f is the coal rock firmness coefficient; is the projection area of the worn surface on the cutting plane after the pick is worn blunt; is the stress state volume coefficient of the ore body; is the cutting resistance coefficient; is the average cutting resistance of the coal seam; is the calculated width of the working part of the pick, and for a gage pick, it is half the diameter, is the external leakage free performance coefficient; is the influence coefficient of the truncated ; is the rake face shape influence coefficient of the pick, ranging from is the pick arrangement mode coefficient, 1 for sequential arrangement and 1.25 for chessboard arrangement; is the influence coefficient of ground pressure on the coal wall of the working face; is the brittleness degree coefficient of coal; is the deflection angle of the pick on a cutting line relative to the traction direction;

[0018] The average load torque of the end cutting drum is:

[0019] (3),

[0020] In the formula, D is the diameter of the drum, and from formula (3), it can be seen that the mathematical model of the cutting drum is a three-variable function with the drum rotating speed, the traction speed and the coal rock firmness coefficient as independent variables.

[0021] Further, the coupling system composed of the electromagnetic parameters of the permanent magnet synchronous motor and the mechanical parameters of the gear transmission system and the load system, the dynamic model of the coupling system is set as follows when mathematical modeling is performed:

[0022] 1) Ignore the core saturation, and do not consider the eddy current and hysteresis loss;

[0023] 2) The air gap is uniformly distributed, the magnetic circuit is independent of the position of the rotor, that is, the self-inductance of each winding and the mutual inductance between windings are independent of the position of the rotor, and the stator winding is star-connected;

[0024] 3) There is no damping winding on the rotor, and the permanent magnet has no damping effect;

[0025] 4) The back electromotive force waveform is a sine wave.

[0026] Further, based on the coupling relationship and mechanical relationship of the cutting transmission system of the coal mining machine, the models of the motor subsystem and the gear transmission subsystem are as follows:

[0027] The stator voltage equation of the permanent magnet synchronous motor in the dq axis coordinate system is:

[0028] (4),

[0029] In the formula, u d , u q are the dq axis components of the stator voltage, i d , i q are the dq axis components of the stator current, L d , L q are the dq axis inductance components, and for the surface-mounted PMSM, L d =L q ; represents the flux linkage;

[0030] The electromagnetic torque equation of the permanent magnet synchronous motor in the dq coordinate system is:

[0031] (5),

[0032] In order to eliminate the coupling relationship between the d-axis voltage and the q-axis voltage of the permanent magnet synchronous motor, the control mode of i d =0 is adopted to realize the static decoupling of the motor:

[0033] In order to make the permanent magnet synchronous motor have better speed and torque performance, PI control is added, and the speed loop expression of the q-axis reference current is:

[0034] (6),

[0035] Active damping B a is expressed as:

[0036] (7),

[0037] The adjustment parameter setting formula is:

[0038] (8),

[0039] In the formula, β is the expected frequency band bandwidth of the speed loop; K pω and K iω are the current parameters of the speed loop, ω * m is the set speed of the permanent magnet motor, ω m is the actual mechanical angular velocity, B a is the active damping coefficient; the q-axis voltage is calculated by formula (9):

[0040] (9)

[0041] Substitute formula (6) and (9) into formula (4) to obtain the current equation:

[0042] (10),

[0043] Further, when the crack fault of a gear tooth root in any gear in the transmission system of the global electromechanical coupling dynamics model of the electromechanical transmission system occurs, the bending deformation and shear deformation stiffness can be calculated in the following two cases:

[0044] Case one, when the cracked fault tooth satisfies h g <h r or h g ≥ h r & α1 < α g :

[0045] Wherein, h g represents the distance from the crack end point G to the tooth center line when the crack of the cracked fault tooth does not reach the tooth center line, h r represents half of the tooth thickness at the top of the tooth, α1 represents the angle between the force component F b and the tangent force F acting on the gear base circle, and α g corresponds to the force point G.

[0046] In this case, the bending deformation and shear deformation stiffness of the gear tooth root crack fault tooth are as follows,

[0047] (11),

[0048] (12),

[0049] where a represents the integral variable; v represents the Poisson's ratio of the gear material; a2represents the half of the addendum angle on the base circle; -a1represents the opposite of a1; k bcrack represents the bending stiffness of the gear with crack failure, k scrack represents the shear stiffness of the gear with crack failure;

[0050] Case II, when the gear tooth with crack failure satisfies h g ≥ hrand a1> a g :

[0051] In this case, the meshing point between the gear tooth with crack failure and another normal gear moves between point G and the dedendum, thus, there are two cases to calculate the moment of inertia I xg and the cross-sectional area A xg , one is x≤d (corresponding to a≤a g ) and x>d (corresponding to a>a g ), where x represents the length integral variable corresponding to the angle integral variable a, d represents the distance from the meshing point to the dedendum, thus in the integral calculation of the bending deformation stiffness K b and the shear deformation stiffness K s , the integral is divided into two segments: for the first segment integral, corresponding to a≤a g , the upper and lower limits of the integral are a2and -a g 1respectively; for the second segment integral, corresponding to a>a g, , the upper and lower limits of the integral are a g 1and -a1respectively; the sum of the two segment integrals is the bending deformation and shear deformation stiffness equation of the gear tooth with crack failure under the condition of case II:

[0052] (13),

[0053] (14),

[0054] In summary, for the time-varying meshing stiffness of the gear tooth with crack failure on the driving gear, it is expressed as follows

[0055] (15),

[0056] where k t is the time-varying meshing stiffness under the crack failure of the dedendum, k h is the Hertz contact stiffness, k a1 and k a2 represent the axial compression stiffness, kscrack represents the shear stiffness of the gear with crack fault, k s2 represents the shear stiffness, k bcrack represents the bending stiffness of the gear with crack fault, k b2 represents the bending stiffness of the gear.

[0057] Further, the optional pair of mutually meshing gears of the cutting unit of the coal mining machine is set with a rotating speed, the current signal is taken as the analysis object, the frequency spectrum characteristics of the current are researched, the relationship between the current signal and the fault is determined, when the rotating speed curve of the fault gear tooth is maintained at the set rotating speed quickly after starting, it is indicated that the permanent magnet synchronous motor controller has good control effect, the torque and the current curve are periodically stable, if the rotating speed cannot reach the set rotating speed after exceeding the preset time, it is indicated that the selected gear has crack fault.

[0058] Beneficial effects: compared with the prior art, the present application provides a non-invasive method for detecting mechanical faults through electrical characteristics from the motor current signal when diagnosing the gear crack fault from the angle of electromechanical coupling, solves many problems that it is difficult to guarantee the monitoring quality by using an external sensor from the source, makes the current signal easy to obtain, achieves the purpose of extracting typical characteristics under the fault working condition from the motor current signal, and provides an important theoretical basis for researching the health state monitoring and fault prediction of the cutting transmission system of the coal mining machine. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 Fig. 1 is a flowchart of the gear crack fault diagnosis method based on the electromechanical coupling model of the present application;

[0060] Figure 2 Fig. 2 is a schematic diagram of the electromechanical coupling dynamics model of the cutting unit of the coal mining machine in the present application;

[0061] Figure 3 Fig. 3 is a schematic diagram of the permanent magnet motor control model;

[0062] Figure 4 Fig. 4 is a schematic diagram of the gear crack fault;

[0063] Figure 5 Fig. 5 is a curve diagram of (a) rotating speed, (b) torque, (c) q-axis current and (d) q-axis current spectrum characteristics of the motor under the fault-free condition; DETAILED DESCRIPTION

[0064] One embodiment of the present application will be further described below in combination with the drawings.

[0065] As Figure 1As shown, a gear crack fault diagnosis method based on an electromechanical coupling model of the application, from the perspective of electromechanical coupling, the motor current signal is summarized through a non-invasive method to detect mechanical failure through electrical characteristics, first, the permanent magnet motor drive coal mining machine cutting part electromechanical transmission system coupling dynamics model is established, then the coal mining machine cutting drum end dynamic load model is constructed, then the permanent magnet synchronous motor controller architecture and control parameters are determined, the gear crack fault model and fault feature representation parameters are determined, the signal characteristics of the motor current in the electromechanical coupling model are analyzed to accurately extract the gear transmission system crack fault feature parameters, without additional sensors, the current signal is easy to quickly obtain, and the purpose of directly extracting the typical characteristics of the motor current signal under fault working condition is achieved.

[0066] The step flow of the specific technical solution is as follows:

[0067] S1: Establishing a permanent magnet motor driven coal mining machine cutting part electromechanical transmission system coupling dynamics model

[0068] The coal mining machine cutting part electromechanical transmission system is a typical complex electromechanical system containing multiple subsystems. The electromechanical coupling effect of the system mainly refers to the coupling of the electromagnetic parameters of the permanent magnet synchronous motor and the mechanical parameters of the gear transmission system and the load system, forming a complete coupling system from input to output. The dynamics model diagram of the system is as shown in Figure 2 , wherein the rotor m in the permanent magnet motor is connected to the cutting drum L through gears 1, 2, 3, 4, 5 and 6;

[0069] (1),

[0070] In the figure: J i (i=m, L, 1~6) is the moment of inertia of each element, θ i (i=m, L, 1~6) is the torsion angle of each element, K 12 , K 34 , K 56 is the meshing stiffness of each gear pair, C 12 , C 34 , C 56 is the meshing damping of each gear pair, e 12 , e 34 , e 56 is the static transmission error of each gear pair, K m1 , K 23 , K 45 , K 6L is the torsional stiffness of each transmission shaft, C m1 , C 23 , C 45 , C 6L is the torsional damping of each transmission shaft, Tm T is the electromagnetic torque of the permanent magnet motor L T is the load torque of the cutting drum.

[0071] S2: Establish the load model of the cutting drum of the coal mining machine

[0072] Z is the average cutting force on a single blunt pick on the drum d T is:

[0073] (2),

[0074] In the formula, Z is the cutting force on a single sharp pick, ΔT is the increase in traction when the pick is blunt, and ; σc is the unidirectional compressive strength of coal, and the empirical formula is 10~50MPa; f is the coal rock firmness coefficient; A is the projection area of the worn surface on the cutting plane after the pick is blunt; is the stress state volume coefficient of the ore body; is the cutting resistance coefficient; is the average cutting resistance of the coal seam; is the calculated width of the working part of the pick, and for a pick, it is half the diameter, is the external leakage free performance coefficient; is the influence coefficient of the truncated corner ; is the rake face shape influence coefficient of the pick, ranging from is the pick arrangement mode coefficient, 1 for sequential arrangement, and 1.25 for chessboard arrangement; is the influence coefficient of the ground pressure on the coal wall of the working face; is the brittleness degree coefficient of coal; is the deflection angle of the pick on a cutting line relative to the traction direction.

[0075] The average load torque of the end cutting drum is:

[0076] (3),

[0077] In the formula, D is the drum diameter. As can be seen from formula (3), the mathematical model of the cutting drum is a three-variable function with the drum speed, traction speed, and coal rock firmness coefficient as independent variables.

[0078] S3: Determine the permanent magnet synchronous motor controller architecture and control parameters:

[0079] According to the simplified model of Figure 2 , the dynamics equation of the system is established, and the following assumptions are made when mathematical modeling is performed,

[0080] 1) Ignore the core saturation, not to eddy current and hysteresis losses. (2) The air gap is uniform, the magnetic circuit and the position of the rotor is irrelevant, that is, the self-inductance of each winding and the mutual inductance between the windings are independent of the rotor position, and the stator winding is star connected. (3) There is no damping winding on the rotor, and the permanent magnet has no damping effect. (4) The back electromotive force waveform is a sine wave.

[0081] The stator voltage equation of the permanent magnet synchronous motor in the dq axis coordinate system is:

[0082] (4),

[0083] In the formula, u d , u q are the dq axis components of the stator voltage, i d , i q are the dq axis components of the stator current, L d , L q are the dq axis inductance components, and for surface-mounted PMSM, L d =L q .

[0084] The electromagnetic torque equation of the permanent magnet synchronous motor in the dq coordinate system is:

[0085] (5),

[0086] From the voltage equation and mathematical model of the permanent magnet synchronous motor in formula (1), it can be seen that the d-axis voltage u d is not only affected by the d-axis current i d , but also affected by the q-axis current i q , which shows that there is a certain coupling relationship between the d-axis voltage and the q-axis voltage of the permanent magnet synchronous motor. In the actual control process, the coupling will have a great harm to the performance of the controller. In order to eliminate this problem, the control method of i d =0 is adopted to realize the static decoupling of the motor.

[0087] The system control diagram of the permanent magnet synchronous motor is shown in Figure 3 In order to make the permanent magnet synchronous motor have better speed and torque performance, PI control is added, and the speed loop of the q-axis reference current can be expressed as:

[0088] (6),

[0089] Active damping (7),

[0090] Adjustment parameter setting formula:

[0091] (8),

[0092] β is the desired frequency band bandwidth of the speed loop.

[0093] where K pω and K iω are speed loop current parameters, ω * m is the set speed of the permanent magnet motor, ω m is the actual mechanical angular speed, B a is the active damping coefficient.

[0094] (9),

[0095] Substituting equations (6), (9) into equation (4), the current equation can be obtained as follows:

[0096] (10),

[0097] S4: Determine the gear crack fault model and fault feature representation parameters:

[0098] The key physical parameters inside the system will directly affect the dynamic response of the gear transmission. Before modeling and numerically solving the transmission system, the important internal parameters in the system are first determined through specific calculation. Considering that the gear transmission system of the coal mining machine cutting part is operated in harsh conditions such as heavy load and impact for a long time, the gear transmission system is always subjected to external disturbances such as alternating load and overload impact. The stress on the gear tooth root during gear meshing is relatively concentrated, and cracks are extremely prone to occur. Therefore, this patent will focus on gear crack faults, establish a mapping relationship between faults and currents, and be used for fault diagnosis.

[0099] The bending deformation and shear deformation stiffness of the gear tooth with crack fault can be calculated in the following two cases, as shown in Figure 4 .

[0100] Case I, h g < h r or h g ≥ h r & α1< α g ,

[0101] In this case, the bending deformation and shear deformation stiffness of the gear tooth with crack fault are as follows,

[0102] (11),

[0103] (12),

[0104] Case II, h g ≥ h rand a1> a g ,

[0105] In this case, the meshing point of the two teeth moves between point G and the root, so there are two cases to calculate the moment of inertia I xg and the area A xg , one is x≤d (corresponding to a≤a g ) and x>d (corresponding to a>a g ). Therefore, the integral of the bending deformation stiffness k b and the shear deformation stiffness k s is also divided into two sections. For the first section, corresponding to a≤a g , the upper and lower limits of the integral are a2 and -a g respectively; for the second section, corresponding to a>a g, , the upper and lower limits of the integral are a g and -a1 respectively; the sum of the two sections is the bending deformation and shear deformation stiffness calculation formula of the tooth with root crack fault under the condition of the second case:

[0106] (13),

[0107] (14),

[0108] In summary, the time-varying meshing stiffness of the gear with root crack fault on the driving gear can be expressed as:

[0109] (15),

[0110] S5: Accurate extraction of gear transmission system crack fault feature parameters through signal feature analysis of motor current in electromechanical coupling model

[0111] The dynamic models of the permanent magnet motor subsystem, the gear transmission subsystem, and the end load subsystem have been established respectively. Finally, the dynamic models of each subsystem are integrated. Based on the data analysis of the parameters of each gear in the system, in order to further analyze the gear fault diagnosis method through the electromechanical coupling model, the crack fault is selected as the research type, and the meshing stiffness under the fault state is selected as the evaluation index. A tooth crack fault is set. In order to determine that the fault can be reflected in the output torque signal, the speed is selected as 400 r / min, and the current signal is selected as the analysis object. The frequency spectrum characteristics of the current are studied to determine the relationship between the current signal and the fault. The results are shown in Figure 5 .

[0112] Figure 5The characteristic curves of the rotating speed, torque, q-axis current and q-axis current spectrum under the fault conditions of gear pairs 1 and 2 are given, the rotating speed curve is quickly stabilized at 400 r / min after 4s of starting, which shows that the controller has good control effect, the torque and current curves are periodically stable, and the q-axis current spectrum can find three additional frequencies besides the original three fitting frequencies of gear pairs and the load frequency, which are 9, 10 and 11 times of the fault frequency of gear pair 1. Figure 5 (d)It can be seen that the load frequency is 0.8Hz, the meshing frequency of gear pair 1 is 126.6Hz, the meshing frequency of gear pair 2 is 61.7Hz, and the meshing frequency of gear pair 3 is 26.3Hz, which is consistent with the calculation result, which shows that the q-axis current contains important information of the gear transmission system, and the q-axis current spectrum can find three additional frequencies besides the original three fitting frequencies of gear pairs and the load frequency. Figure 5 (d)The q-axis current spectrum can find three additional frequencies besides the original three fitting frequencies of gear pairs and the load frequency, which are 9, 10 and 11 times of the fault frequency of gear pair 1.

[0113] S6: the design is completed.

[0114] The whole design process of the application is divided into six steps, the first step is to establish a coupled dynamics model of the electromechanical transmission system of the permanent magnet motor driving the cutting part of the coal mining machine, the second step is to determine the controller architecture and control parameters of the permanent magnet synchronous motor, the third step is to establish a load model of the cutting drum of the coal mining machine, the fourth step is to determine the gear crack fault model and fault feature representation parameters, the fifth step is to accurately extract the gear transmission system crack fault feature parameters through the signal feature analysis of the motor current in the electromechanical coupling model, and after the above steps, the design is completed.

[0115] It is found that the established electromechanical coupling model can be used for gear fault analysis, mainly through monitoring the current signal to realize the monitoring of gear fault. In summary, the typical characteristics under the gear crack fault working condition can be extracted through the established electromechanical coupling dynamics model, which is an important theoretical basis for studying the health state monitoring and fault prediction of the cutting transmission system of the coal mining machine.

Claims

1. A method for diagnosing gear crack faults based on an electromechanical coupling model, characterized in that: From the perspective of electromechanical coupling, this method summarizes motor current signals and uses a non-invasive approach to detect mechanical faults through electrical characteristics. First, a coupled dynamic model of the electromechanical transmission system of the coal mining machine's cutting section driven by a permanent magnet motor is established. Then, a dynamic load model of the end of the coal mining machine's cutting drum is constructed. After that, the architecture and control parameters of the permanent magnet synchronous motor controller are determined, and the gear crack fault model and fault characteristic parameters are determined. By analyzing the signal characteristics of the motor current in the electromechanical coupling model, the characteristic parameters of the gear transmission system crack fault are accurately extracted. No external sensors are required, making it easy and quick to acquire current signals, thus achieving the goal of directly extracting typical characteristics under fault conditions from the motor current signal. The specific steps are as follows: S1: Establish a global electromechanical coupling dynamic model of the electromechanical transmission system of the coal cutting machine driven by a permanent magnet motor. This model includes a typical complex electromechanical system of all subsystems in the electromechanical transmission system of the coal cutting machine, including the permanent magnet motor subsystem, gear transmission subsystem, and end load subsystem model. S2: Calculate the load on the cutting drum to obtain the average load torque of the cutting drum at the end of the coal mining machine, establish a mathematical model of the cutting drum to obtain the relationship between the cutting load torque of the coal mining machine and the traction speed and the drum cutting speed, and construct a dynamic load model of the end of the cutting drum of the coal mining machine. S3: Based on the coupled dynamic physical model of the electromechanical transmission system of the coal cutting part driven by the permanent magnet motor, mathematical modeling is carried out to establish the dynamic model of the electromechanical transmission system of the coal cutting part, determine the architecture of the permanent magnet synchronous motor controller, and determine the motor control parameters; S4: Since the physical parameters of the electromechanical transmission system of the coal mining machine cutting section directly affect the dynamic response of the gear transmission, for gear crack faults, the key parameters of each rotor component in the electromechanical transmission system of the coal mining machine cutting section are first calculated and determined one by one, including moment of inertia, concentrated mass, stiffness, and damping. Then, the electromechanical transmission system of the coal mining machine cutting section is modeled and numerically solved. According to the crack depth, the gear crack fault is divided into two cases. The bending deformation and shear deformation stiffness of the teeth with crack faults are calculated, the time-varying meshing stiffness of the teeth with tooth root crack faults on the drive gear is obtained, and the mapping relationship between crack faults and current is established for fault diagnosis. S5: Based on the global electromechanical coupling dynamic model of the electromechanical transmission system in S1, and the dynamic models of the permanent magnet motor subsystem, gear transmission subsystem, and end load subsystem respectively, the signal characteristics of the permanent magnet motor current in the electromechanical coupling model are obtained. Using the meshing stiffness under gear crack fault state as the evaluation index, the crack fault characteristics of the gears in each subsystem of the electromechanical transmission system of the coal mining machine cutting section are accurately extracted. The mapping relationship between the q-axis current characteristics of the permanent magnet synchronous motor and the gear crack fault is established. The gear crack fault in the gear transmission system is judged by monitoring the motor current signal. The accuracy of fault diagnosis is changed by adjusting the control parameters of the permanent magnet motor and the gear fault characteristic characterization parameters until it is consistent with the actual fault result. Finally, the accurate diagnosis method of the middle gear crack fault in the coal mining machine cutting section is determined.

2. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 1, characterized in that: The electromechanical coupling effect of the coal mining machine's cutting section electromechanical transmission system refers to the coupling system formed by the electromagnetic parameters of the permanent magnet synchronous motor and the mechanical parameters of the gear transmission system and load system. This coupling system includes a complete input-output process. The mapping relationship between gear crack faults and current is represented by the dynamic model of this coupling system. (1)， In the formula Represents electric charge, i q Represents the q-axis current, R represents resistance, and L represents the resistance. d For the d-axis inductance, L q For the q-axis inductance, K pq and K iq K is the PI control parameter for the current loop. pω and K iω These are the PI control parameters for the speed loop. Set the motor speed, ω m θ represents the actual measured speed of the motor. m For the speed difference, η m J is the integral of the speed difference. i (i=m, L, 1~6) represents the moment of inertia of each component, θ i (i=m, L, 1~6) represents the torsion angle of each component, K 12 K 34 K 56 C represents the meshing stiffness of each gear pair. 12 C 34 C 56 The meshing damping K of each gear pair m1 K 23 K 45 K 6L C represents the torsional stiffness of each drive shaft. m1 C 23 C 45 C 6L F represents the torsional damping of each drive shaft. 12 F 34 F 56 T is the meshing force between the gear pairs. m T is the electromagnetic torque of the permanent magnet motor. L To cut off the load torque of the drum, dynamic models of the permanent magnet motor subsystem, gear transmission subsystem, and end load subsystem are established separately, and then the dynamic models of each subsystem are integrated.

3. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 1, characterized in that: When calculating the load on the cutting drum, the average cutting force Z on a single blunt cutting tooth on the drum is... d for: (2)， In the formula, The cutting force borne by a single sharp cutting tooth. This is the increase in traction force when the cutting teeth become dull, and ; The empirical formula for the uniaxial compressive strength of coal. , 10~50MPa; f is the coal and rock firmness coefficient; This refers to the projected area of ​​the worn surface on the cutting plane after the cutting teeth have become dull. The volume factor for the stress state of the ore body; It is the coefficient of cutting resistance; The average cutting resistance of the coal seam; Calculate the width of the working part of the cutting tooth, with the pick tooth being half its diameter. The external free expression coefficient; For truncated angle Influence coefficient; The influence coefficient of the rake face shape of the cutting tooth is given, and its range is: The coefficient represents the arrangement of the cutting teeth; a sequential arrangement is set to 1, and a checkerboard arrangement is set to 1.

25. This is the coefficient representing the influence of ground pressure on the coal face of the working face; This is the brittleness coefficient of coal; The deflection angle of the cutting tooth on a cutting line relative to the traction direction; The average load torque of the end cutting drum is (3)， In the formula, D is the diameter of the drum. As can be seen from equation (3), the mathematical model of the cutting drum is a ternary function with the drum speed of the coal mining machine, the traction speed and the coal and rock firmness coefficient as independent variables.

4. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 2, characterized in that: The dynamic model of the coupled system, consisting of the electromagnetic parameters of the permanent magnet synchronous motor and the mechanical parameters of the gear transmission system and the load system, is defined as follows during mathematical modeling: 1) Ignore core saturation and disregard eddy current and hysteresis losses; 2) The air gap is uniformly distributed, and the magnetic circuit is independent of the rotor position. That is, the self-inductance of each winding and the mutual inductance between windings are independent of the rotor position. The stator winding is star-connected. 3) The rotor has no damping winding, and the permanent magnet has no damping effect; 4) The back electromotive force waveform is a sine wave.

5. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 4, characterized in that: Mathematical modeling is performed based on the coupling and mechanical relationships of the coal mining machine's cutting transmission system. The models for the motor subsystem and gear transmission subsystem are shown in the following formulas: The stator voltage equation of the permanent magnet synchronous motor in the dq axis coordinate system is: (4)， In the formula u d u q These are the dq-axis components of the stator voltage, i d i q These are the dq-axis components of the stator current, L d L q These are the dq axis inductance components, and for a surface-mount PMSM, there is L... d =L q Ψ f Indicates magnetic flux; The electromagnetic torque equation of a permanent magnet synchronous motor in the dq coordinate system is: (5)， To eliminate the coupling relationship between the d-axis voltage and the q-axis voltage of a permanent magnet synchronous motor, i d The =0 control mode achieves static decoupling of the motor: To improve the speed and torque performance of the permanent magnet synchronous motor, PI control is incorporated, where the speed loop expression of the q-axis reference current is as follows. (6)， Active damping B a Represented as: (7)， The formula for adjusting the parameters is: (8)， In the formula, β is the desired bandwidth of the rotational speed loop; K pω and K iω For the velocity loop current parameter, ω * m To set the speed of the permanent magnet motor, ω m B is the actual mechanical angular velocity. a The active damping coefficient is used; the q-axis voltage is calculated using formula (9): (9)， Substituting equations (6) and (9) into equation (4), we obtain the current equation: (10)。 6. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 5, characterized in that: In the global electromechanical coupling dynamics model of the electromechanical transmission system, the bending deformation and shear deformation stiffness of a gear tooth root failure in any stage gear can be calculated in the following two cases: Case 1: When the cracked gear tooth meets the h condition. g <h r Or h g ≥h r &α1<α g Situation: Among them, h g This represents the distance h from the crack endpoint G to the tooth centerline when the crack in the tooth with the crack has not reached the tooth centerline. r α1 represents half the thickness of the tooth tip, and α1 represents the force component F. b The angle α between the forces F that are tangent to the base circle of the gear and the gear base circle. g Corresponding to the point of application of the force, G; In this case, the bending and shear stiffness of the gear teeth with root cracks are as follows. (11)， (12)， In the formula, α represents the integral variable; ν represents the Poisson's ratio of the gear material; α2 represents the half-tooth angle on the base circle; -α1 is the negative of α1; k bcrack k represents the bending stiffness under gear crack failure. scrack Indicates the shear stiffness under gear cracking failure; Scenario 2: When the cracked gear tooth satisfies h g ≥hr and α1>α g Situation: In this case, the meshing point between the cracked gear tooth and another normal gear moves between point G and the tooth root. Therefore, there are two scenarios for calculating the moment of inertia I. xg and cross-sectional area A xg One form is x≤d, corresponding to α≤α g Another possibility is x>d, corresponding to α>α. g Where x represents the length integral variable corresponding to the angle integral variable α, and d represents the distance from the meshing point to the tooth root. Therefore, in calculating the bending deformation stiffness k of the gear teeth... b and shear deformation stiffness k s The integration is divided into two parts: for the first part, the integration is performed in segments corresponding to α ≤ α. g The upper and lower limits of its integration are α² and -α, respectively. g The second integral corresponds to α>α g, The upper and lower limits of its integration are α and α, respectively. g Summing the two integrals, we can obtain the bending and shear stiffness equations for the tooth with root cracks under condition two: (13)， (14)， In summary, the time-varying meshing stiffness of the tooth with root cracks on the driving gear is expressed as follows: (15)， k in the formula t k represents the time-varying meshing stiffness under tooth root crack fault conditions. h For Hertzian contact stiffness, k a1 and k a2 k represents axial compressive stiffness. scrack k represents the shear stiffness under gear cracking failure. s2 k represents shear stiffness. bcrack k represents the bending stiffness under gear crack failure. b2 This indicates the bending stiffness of the gear.

7. The gear crack fault diagnosis method based on the electromechanical coupling model according to claim 6, characterized in that: Select any pair of meshing gears in the cutting section of the coal mining machine and set their speed. Using the current signal as the analysis object, study the spectral characteristics of the current and determine the relationship between the current signal and the fault. When the faulty gear rotates, its speed curve quickly stabilizes at the set speed after startup, indicating that the permanent magnet synchronous motor controller has a good control effect and the torque and current curves are periodically stable. If the speed still cannot reach the set speed after the preset time, it indicates that the selected gear has a crack fault.

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