Coal mining machine transmission fault simulation test bench and test method based on motor current characteristics

Abstract

The invention relates to a coal cutter transmission fault simulation test bench based on motor current characteristics and a test method. The test bench comprises a driving module, a fault simulation module, a load module and a signal acquisition module, the signal acquisition module comprises a three-phase current sensor, and the driving module and the load module are respectively connected with an input shaft and an output shaft of the fault simulation module. The driving module and the load module are connected with a power grid through a common direct current bus, the driving module and the direct current bus form a first regenerative rectification unit, and the load module and the direct current bus form a second regenerative rectification unit. The second regenerative rectification unit rectifies alternating current generated by the load module into direct current through a diode and feeds the direct current back to the direct current bus, and the first regenerative rectification unit inverts the direct current and drives the driving motor. According to the test bed and the test method, the accuracy of diagnosing the transmission fault of the coal mining machine based on the motor current characteristics is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining machine fault simulation; in particular, the present application relates to a coal mining machine transmission fault simulation test bench based on motor current characteristics and a test method. BACKGROUND

[0002] The transmission system of a coal mining machine works in harsh conditions of heavy load, impact, vibration and moisture for a long time, and key components such as gears and bearings are prone to failure, resulting in unplanned shutdown and causing significant economic losses. Therefore, it is of great significance to build a transmission fault simulation test bench that can accurately simulate the actual working conditions of a coal mining machine in a laboratory, to study the fault evolution mechanism, develop state monitoring and early fault diagnosis algorithms, and verify the reliability and durability of the equipment.

[0003] With the development of intelligent coal mining machines, using the stator current of the drive motor to monitor the health status of the cutting part transmission system has become a research hotspot. Its development process evolved from the initial simple current effective value monitoring to the analysis of current spectrum, especially the side frequency component for rotor broken bar and other electrical faults. In recent years, researchers have begun to explore the use of current signals to diagnose mechanical transmission faults, the principle of which is that mechanical faults will cause slight fluctuations in the load torque, which in turn modulates the motor stator current. At present, the test benches used for the study of coal mining machine transmission systems at home and abroad mainly have the following forms, and they have obvious defects when it comes to fault diagnosis technology research based on current characteristic analysis.

[0004] One of the existing technologies is to use a magnetic powder brake, an eddy current brake and other energy-consuming loads. This type of technology converts the mechanical energy of the system into heat energy dissipation through the shear force of the magnetic powder chain or the electromagnetic eddy current effect to achieve load simulation, which has the following defects: first, the inherent load noise results in extremely low signal-to-noise ratio. The magnetic powder brake has physical phenomena such as magnetic powder agglomeration and slip during operation, and the eddy current brake has magnetic flux fluctuations, resulting in inherent, random nonlinear pulsation and noise in the load torque. These load fluctuations, which have nothing to do with the faults of the equipment being tested, will directly act on the motor as a strong interference signal and produce a large amplitude of interference components in the stator current, seriously confusing and even masking the true torque fluctuation characteristics produced by early-stage cracks and other minor mechanical faults, resulting in extremely low signal-to-noise ratio in separating fault components from the current and high misdiagnosis rate. Second, the key "minor fault-low load" working condition simulation is missing. Due to the physical characteristics of the magnetic powder / eddy current brake, it is difficult to achieve stable and accurate load control in the area of extremely low torque close to no load. However, since the fault characteristics are the weakest at no load or light load, this is often the most challenging working condition for current diagnosis and the most valuable test scenario for researching "feature enhancement methods". This blind spot of the existing technology limits the verification of related diagnosis algorithms.

[0005] The second existing technology involves using a DC generator set as a resistive load or a closed-loop test bench with coarse control. This type of technology utilizes the energy generated by the DC generator or uses early analog circuits / low-bandwidth frequency converters for simple load application. This technology has the following drawbacks: First, severe electromagnetic spectrum pollution. When using a DC generator as a load, its inherent armature reaction and the commutation sparks generated by the contact between the carbon brushes and the commutator introduce complex broadband high-frequency electromagnetic noise into the system. This noise is directly coupled into the electrical circuit of the drive system, causing severe "pollution" of the current signal spectrum, easily interfering with the identification and extraction of specific mechanical fault characteristic frequencies, which are usually located in the high-frequency range or appear as weak sidebands. Second, poor dynamic response, making it impossible to establish a quantitative "fault-current" mapping relationship. Such test benches have low dynamic response bandwidth, making it impossible to achieve high-fidelity, precisely programmable instantaneous torque control. Therefore, researchers cannot simulate a single fault mode by inputting torque fluctuations of specific frequency and amplitude, and thus cannot quantitatively study the transfer function relationship between "mechanical torque fluctuations" and "motor current modulation response." This results in a lack of accurate physical benchmarks for parameter calibration of the current diagnostic model, leading to poor generalization ability of the algorithm. Summary of the Invention

[0006] In view of this, the present invention provides a coal mining machine transmission fault simulation test bench and test method based on motor current characteristics, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0007] To achieve the aforementioned objectives, a first aspect of the present invention provides a coal mining machine transmission fault simulation test bench based on motor current characteristics. The test bench includes a drive module, a fault simulation module, a load module, and a signal acquisition module, wherein...

[0008] The drive module includes a drive motor and a first controller for controlling the drive motor. The first controller is communicatively connected to a first host computer, and the first host computer controls the first controller through a direct torque control strategy.

[0009] The fault simulation module includes a gearbox, which comprises removable and replaceable normal components and faulty components.

[0010] The load module includes a load motor and a second controller for controlling the load motor. The second controller is communicatively connected to a second host computer, which controls the second controller using a direct torque control strategy.

[0011] The signal acquisition module includes a three-phase current sensor disposed at the input terminal of the drive motor.

[0012] The driving motor is connected with an input shaft of the gear box, and the load motor is connected with an output shaft of the gear box through a shaft coupling,

[0013] The driving motor and the load motor are connected with a power grid through a shared bidirectional reversible DC bus,

[0014] The driving motor and the load motor are of the same type, the first controller and the second controller are of the same type, the driving motor, the first controller, the first upper computer, the DC bus and the inverter on the DC bus constitute a first regenerative rectification unit, the load motor, the second controller, the second upper computer and the DC bus and the inverter on the DC bus constitute a second regenerative rectification unit, when the load motor is in a power generation mode, the second regenerative rectification unit rectifies the alternating current generated by the load motor into direct current through a diode and feeds back to the DC bus, and the first regenerative rectification unit inverts the direct current and drives the driving motor.

[0015] In the coal mining machine transmission fault simulation test bench as described above, optionally, the signal acquisition module further comprises a vibration sensor arranged on the box body of the gear box and a voltage sensor arranged on the DC bus.

[0016] In the coal mining machine transmission fault simulation test bench as described above, optionally, the second upper computer sends a torque instruction to the second controller based on a random cutting resistance model of the coal mining machine.

[0017] In the coal mining machine transmission fault simulation test bench as described above, optionally, the gear box comprises a single-double-stage adjustable parallel gear box and a single-double-stage adjustable planetary gear box, the parallel gear box comprises normal straight gears, normal helical gears, normal rolling bearings, a fault straight gear set, a fault helical gear set and a fault rolling bearing set which can be disassembled and replaced, and the planetary gear box comprises normal planetary gears, normal sun gears, normal planetary gear bearings, normal sun gear bearings, a fault planetary gear set, a fault sun gear set, a fault planetary gear bearing set and a fault sun gear bearing set which can be disassembled and replaced, wherein the fault types of the fault straight gear set, the fault helical gear set, the fault planetary gear set and the fault sun gear set include tooth breakage, tooth surface wear and pitting, and the fault types of the fault rolling bearing set, the fault planetary gear bearing set and the fault sun gear bearing set include outer ring crack, inner ring crack, ball peeling and mixed fault.

[0018] In the coal mining machine transmission fault simulation test bench as described above, optionally, a radial loading device is integrated on the output shaft of the gear box.

[0019] To achieve the foregoing object, the second aspect of the present application provides a coal mining machine transmission fault simulation test method, which can be realized based on the coal mining machine transmission fault simulation test bench as described above, and the test method comprises:

[0020] Step one: according to the test requirements, the fault elements are loaded in the gear box;

[0021] Step two: the protection parameters are set in the second controller, and the random cutting resistance model of the coal mining machine is set in the second upper computer;

[0022] Step three: the driving motor is started and driven by the first controller to drive the gear box to run;

[0023] Step four: the second upper computer controls the load motor to generate a reverse torque on the gear box through the second controller based on the random cutting resistance model;

[0024] Step five: the driving motor stator current signal collected by the three-phase current sensor is recorded in real time, and a mapping relationship between the fault type and the signal characteristics of the driving motor stator current signal is established.

[0025] In the coal mining machine transmission fault simulation test method as described above, optionally, the test method further comprises step six: the fault elements in the gear box are replaced with corresponding normal elements, steps two to five are repeated, and the differences between the motor stator current signals collected under the two different states of the fault elements and the normal elements are compared.

[0026] In the coal mining machine transmission fault simulation test method as described above, optionally, in the step five: the vibration signal of the gear box is collected in real time by the vibration sensor arranged on the box body of the gear box, the voltage fluctuation signal of the DC bus is collected in real time by the voltage sensor arranged on the DC bus, and the mapping relationship between the fault type and the signal characteristics of the vibration signal, and the mapping relationship between the fault type and the signal characteristics of the voltage fluctuation signal are established.

[0027] In the coal mining machine transmission fault simulation test method as described above, optionally, in the step one, the fault elements include fault spur gear sets, fault bevel gear sets, fault planetary gear sets and fault sun gear sets with fault types of broken teeth, tooth face wear and pitting, and fault rolling bearing sets, fault planetary bearing sets and fault sun bearing sets with fault types of outer ring crack, inner ring crack, ball peeling and mixed fault, the transmission configuration of the gear box is set to single-stage parallel gear transmission, double-stage parallel gear transmission, single-stage planetary gear transmission or double-stage planetary gear transmission by loading the fault elements into the gear box, and a radial loading device is arranged on the output shaft of the gear box to apply radial pressure to the bearing outer ring of the gear box.

[0028] In the coal mining machine transmission fault simulation test method as described above, optionally, in the step four, the second controller controls the load motor to periodically generate positive torque on the gear box.

[0029] The coal mining machine transmission fault simulation test bench of the application adopts a bidirectional circulating electrical topology structure of a double-stage regenerative rectifier unit, directly connects the inverters of the drive motor and the load motor through a shared DC bus, and constructs an "electric-motor-electric" strongly coupled energy closed-loop test environment. Since the gear box generates a transient torque pulse on the transmission chain when a fault occurs, the load motor in the test bench of the application can sensitively capture the speed fluctuation and generate a back electromotive force fluctuation based on a high-bandwidth direct torque control mode, and directly pumps the back electromotive force fluctuation into the DC bus. Since the drive motor is also connected to the same DC bus, a slight fluctuation in the bus voltage will be instantaneously fed back to the input end of the drive motor, forcing the drive motor to adjust the current to maintain the speed. This "back-to-back" electrical connection is equivalent to increasing the "electromechanical gain" inside the test bench, physically amplifying the small mechanical fault signal in the electrical circuit, significantly increasing the fault sideband amplitude in the current spectrum, and improving the sensitivity and accuracy of fault diagnosis analysis based on motor current characteristics.

[0030] At the same time, the test bench feeds back the electrical energy generated by the load motor to the DC bus and uses it to drive the drive motor, avoiding the huge waste caused by converting energy into heat energy, realizing internal power efficient recycling, and saving electricity by 80-90%, while eliminating the dependence on brake resistors or other complex external heat dissipation systems, reducing the operating cost and thermal load of the test bench.

[0031] In an optional embodiment, the test bench detects the vibration signal of the gearbox and the voltage fluctuation signal on the DC bus through a signal acquisition module, using the vibration signal and voltage fluctuation signal as auxiliary observation variables strongly correlated with the stator current signal. By introducing a new feature signal dimension, non-stationary random interference in the current signal can be effectively eliminated, further improving the confidence of fault feature identification, and thus training a more accurate multi-source data fault fusion diagnostic model.

[0032] In an optional embodiment, the second host computer of the test bench performs direct torque control on the second controller of the load motor based on the random cutting resistance model of the coal mining machine, thereby improving the fidelity of the test bench in simulating the actual working conditions of the coal mining machine.

[0033] In an optional embodiment, a modular gearbox and its components containing multiple fault types are selected, and a radial loading device is integrated on the gearbox. By replacing the internal components, multiple transmission configurations can be flexibly assembled, enabling the test bench to not only simulate single component failures, but also to realize multi-physics field coupled fault simulation of "gear meshing failure - bearing damage - structural radial stress", providing a more comprehensive and realistic test environment for the reliability study of the coal mining machine transmission system.

[0034] The present invention further provides a method for simulating transmission failure of a coal mining machine, and therefore this method also has the above-mentioned advantages. Attached Figure Description

[0035] The disclosure of this invention will become more apparent from the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings:

[0036] Figure 1 This is a schematic block diagram of an embodiment of the coal mining machine transmission fault simulation test bench of the present invention. Detailed Implementation

[0037] Referring to the accompanying drawings and specific embodiments, the structure, composition, features, and advantages of the coal mining machine transmission fault simulation test bench and test method of the present invention will be described below by way of example. However, all descriptions should not be construed as limiting the present invention in any way.

[0038] Furthermore, for any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the various figures, the present invention still allows for any combination or deletion of these technical features (or their equivalents) without any technical obstacle, and thus these further embodiments according to the present invention should also be considered within the scope of this description.

[0039] It should also be noted that the terms "inner" and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship of the coal mining machine transmission failure simulation test bench shown in the accompanying drawings. They are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this disclosure.

[0040] Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," "third," or "fourth" may explicitly or implicitly include at least one of those features.

[0041] Figure 1 This is a schematic block diagram of an embodiment of the coal mining machine transmission fault simulation test bench of the present invention.

[0042] As shown in the diagram, the coal mining machine transmission fault simulation test bench can include a drive motor and a first controller for controlling it, a gearbox, a load motor and a second controller for controlling it. The drive motor is connected to the input shaft of the gearbox, and the load motor is connected to the output shaft of the gearbox via a coupling. The drive motor and the load motor are connected to the power grid through a shared DC bus, which is bidirectional and reversible. The drive motor and the first controller constitute the drive module of the test bench, while the load motor and the second controller constitute the load module.

[0043] In this embodiment, the drive motor and load motor are both variable frequency servo motors of the same model, eliminating parameter errors and improving the accuracy and reliability of the fault simulation test. Meanwhile, the servo motor features low inertia and high response, enabling it to execute complex load commands with millisecond-level response speeds. This allows the test bench to generate non-stationary current signals whose frequency and amplitude change rapidly over time, a crucial foundation for subsequent analysis algorithms. Furthermore, the first and second controllers are identical variable frequency controllers, and the drive module and load module form a mirror-symmetric electrical structure, allowing for functional interchange and bidirectional feedback.

[0044] In an optional embodiment, the test bench further includes a horizontally placed vibration isolation mounting platform. The upper part of the vibration isolation mounting platform may be provided with a T-slot structure to facilitate the adjustment of the positions of the modules on it. Simultaneously, the T-slot design facilitates the alignment and adjustment of the modules on it, eliminating interference from installation errors on fault signals and improving the repeatability and accuracy of fault simulation tests.

[0045] The drive motor, gearbox, and load motor are all mounted on this T-slot structure. During the test bench setup phase, laser alignment can be used to ensure that the axes of these devices are aligned. Laser alignment is a method that utilizes the directionality and monochromaticity of laser light, employing a laser alignment instrument's transmitter and receiver to precisely align the equipment. In other alternative embodiments, alignment methods such as dial gauges or dynamic tracking methods can also be used, as long as they can eliminate axial deviations between modules.

[0046] In this embodiment, a three-phase current sensor is installed at the input terminal of the drive motor, a vibration sensor is installed on the gearbox housing, a first voltage sensor is installed on the side of the DC bus near the drive motor, and a second voltage sensor is installed on the side of the DC bus near the load motor. These sensors constitute the signal acquisition module of the test bench.

[0047] As shown in the figure, a radial loading device is integrated at the output shaft bearing housing of the gearbox. This device applies radial pressure to the outer ring of the bearing in the gearbox via hydraulic pressure or a screw-driven loading mechanism. A built-in force sensor monitors the loading force in real time, simulating the effect of the radial component force generated by gear meshing on the bearing. The radial loading device expands the types of transmission fault simulations possible with the test bench of this invention. Furthermore, by altering the gear meshing stiffness, it physically amplifies the vibration energy of mechanical faults, providing a stronger signal source for subsequent current feature extraction.

[0048] In optional embodiments, the gearbox is a quick-change modular structure, which can include two types of gearboxes: a single-stage / double-stage adjustable parallel gearbox and a single-stage / double-stage adjustable planetary gearbox, both with multiple bearing seat holes pre-drilled on the housing. This design allows the gearbox to be switched to four different transmission configurations by simply changing its internal shaft and gear combinations: single-stage parallel gear transmission, double-stage parallel gear transmission, single-stage planetary gear transmission, and double-stage planetary gear transmission. For example, without moving the base of the fault simulation module, the single-stage parallel gearbox can be reconstructed into a double-stage parallel gearbox by opening the gearbox's top cover and adding an intermediate shaft and gear pair, and then used for subsequent simulation tests. In other optional embodiments, different component replacement methods can also be used. This single-stage / double-stage adjustable gearbox design allows for simple and quick switching of the transmission configuration of the fault simulation module without the need for large lifting equipment, improving the efficiency of fault simulation tests.

[0049] In the parallel gearbox and planetary gearboxes described above, a removable and replaceable set of normal component libraries and a set of faulty component libraries are provided to simulate different types of transmission faults. In the parallel gearbox, the normal component library can contain normal spur gears, normal helical gears, and normal rolling bearings. The faulty component library can contain faulty spur gears and helical gears with broken teeth, tooth surface wear, and pitting, as well as faulty rolling bearings with outer ring cracks, inner ring cracks, ball spalling, and mixed fault types. In the planetary gearbox, the normal component library can contain normal planet gears, normal sun gears, normal planet gear bearings, and normal sun gear bearings. The faulty component library can contain faulty planet gear sets and sun gear sets with broken teeth, tooth surface wear, and pitting, as well as faulty planet gear bearing sets and sun gear bearing sets with outer ring cracks, inner ring cracks, ball spalling, and mixed fault types.

[0050] In a further optional embodiment, multiple fault components of the broken tooth type can be provided according to different degrees of fracture, and multiple fault components of the tooth surface wear type can be provided according to different wear depths, and so on for other fault types. In other optional embodiments, other fault type components can also be provided according to actual test requirements, such as gear sets with tooth surface scuffing or tooth surface plastic deformation, or bearing sets with fretting corrosion, etc. The present invention does not limit the number and type of supporting components for the gearbox.

[0051] With its radial loading device and flexibly assembled component library, the test bench of this invention can not only simulate single component failures, but also perform multi-physics field coupling failure simulations of gear failures, bearing damage, and structural radial stress, thereby improving the adaptability and effectiveness of coal mining machine transmission failure simulation.

[0052] As shown in the figure, the first controller is controlled by a first host computer, and the second controller is controlled by a second host computer. The first and second host computers can be located locally on the test bench or remotely. In an optional embodiment, control commands are sent to the first and second controllers respectively via an industrial bus communication protocol. This invention does not limit the communication connection method between the host computers and controllers.

[0053] In an optional embodiment, the control command from the second host computer is a torque command generated by a direct control strategy based on real-time estimation of stator flux linkage and electromagnetic torque, used to control the load motor to generate reverse torque on the gearbox. This command is a random load spectrum generated based on the cutting resistance model of the coal mining machine. It can be a constant value simulating a stable coal seam or a random waveform, used to simulate the impact load when the coal mining machine cuts hard interbedded rock and the sudden load drop when cutting brittle coal. In the experiment, the torque command is set according to the actual simulation requirements, such as inputting a sinusoidal torque waveform superimposed with random noise to simulate the fluctuation of the coal mining machine drum load.

[0054] As shown in the figure, the first controller is connected to the drive motor via the first inverter and to the power grid via the second inverter. The drive motor is connected to the power grid sequentially via the first inverter, the DC bus, and the second inverter. The second controller is connected to the load motor via the third inverter and to the power grid via the fourth inverter. The load motor is connected to the power grid sequentially via the third inverter, the DC bus, and the fourth inverter. The drive motor, the first controller, the first host computer, the first inverter, the second inverter, and the DC bus constitute the first regenerative rectifier unit. The load motor, the second controller, the second host computer, the third inverter, the fourth inverter, and the DC bus constitute the second regenerative rectifier unit. The first and second regenerative rectifier units share a common DC bus, enabling bidirectional power flow and forming an electrically closed loop.

[0055] With this electrical topology, when the load motor is in regenerative braking and power generation mode, the second controller can naturally rectify the AC power generated by the load motor through the diodes in the second regenerative rectifier unit and feed it back to the DC bus, causing the DC bus voltage to continuously rise. Subsequently, in response to the rise in DC bus voltage, the first controller controls the first regenerative rectifier unit to start the active inverter function, inverting the DC power into AC power and feeding it back to the drive motor, thus realizing energy circulation.

[0056] Based on the nonlinear conduction characteristics of the diodes in the second regenerative rectifier unit, the test bench of this invention can convert the instantaneous back EMF fluctuations caused by mechanical faults into current ripples injected into the DC bus without control dead zone or algorithm lag, directly mapping them to the pulsation of the DC bus current. This avoids the suppression of fault features by traditional closed-loop control algorithms, thereby maximizing the preservation of the modulation depth of the fault signal and improving the integrity of feature extraction in the stator current signal of the drive motor.

[0057] Based on the active inverter of the first regenerative rectifier unit, the test bench of this invention can reduce the total harmonic distortion of the grid-side input current. At the same time, it isolates the DC bus from the test circuit, so that the voltage of the DC bus is not affected by the grid voltage fluctuation. This eliminates the ripple interference and grid background noise caused by traditional diode rectification, reduces the noise floor in current spectrum analysis, and makes the fault characteristic peaks that were originally submerged in noise, especially the weak characteristic peaks of early mechanical faults such as bearing microcracks, clearly visible. This provides a higher signal-to-noise ratio environment for the stator current signal of the drive motor, and improves the purity and reliability of the stator current signal of the drive motor.

[0058] This bidirectional energy transfer path, constructed on the drive and load sides as "diode natural rectification - DC bus floating - isolated active inverter," effectively amplifies the modulation effect of mechanical faults on the electrical system. This significantly increases the amplitude of the fault sideband component in the stator current of the drive motor, enhancing the fault characteristic representation in the current signal. Consequently, it improves the accuracy of the test bench and test method for acquiring the stator current signal of the drive motor. Simultaneously, the drive motor and load motor are electrically interconnected via a common DC bus and mechanically interconnected via a rigid transmission chain, forming a mechanical-electrical dual closed-loop energy circulation system. The electrical energy generated by the load motor is rectified and directly supplied to the drive motor via the DC bus. In the braking or reverse drag mode of the load motor, bidirectional energy flow can be achieved, with excess energy fed back to the power grid.

[0059] Based on such Figure 1 The test bench shown can be used to implement the coal mining machine transmission fault simulation test method of the present invention.

[0060] First, the drive motor, gearbox, and load motor are sequentially installed on the vibration isolation mounting platform. In an optional embodiment, these modules can be laser-aligned to ensure the accuracy and repeatability of subsequent tests. Depending on the test requirements, faulty components are incorporated into the gearbox to form a specific transmission configuration and fault type. For example, the gearbox can be configured as a two-stage planetary transmission with an inner ring crack in the sun gear bearing, broken teeth in the planet gears, and normal components. In a further optional embodiment, a radial loading device integrated into the gearbox output shaft can be used to enhance the fault characteristics. For example, setting the radial preload to 2 kN can simulate the weight of the coal mining machine's drum and change the gear meshing stiffness, physically amplifying the vibration energy of the mechanical fault, thereby providing a stronger signal source for subsequent current feature extraction. This invention does not limit the transmission configuration, fault coupling type, or the magnitude of the radial preload.

[0061] Secondly, protection parameters such as overcurrent, overvoltage, and overspeed are set in the second controller of the load motor, and the electrical topology of the test bench is configured. At this time, the first and second regenerative rectifier units are connected, and operating logic is set in both controllers: when the load motor is in generator mode, the second regenerative rectifier unit is forced to operate in diode natural rectification mode, and the inverter start-up threshold of the first regenerative rectifier unit is set higher than the no-load voltage of the DC bus. Simultaneously, the random cutting resistance model of the coal mining machine used in this fault simulation test is set in the second host computer.

[0062] Next, the drive motor is started via the first controller and driven to the required test speed, such as 2880 rpm, thereby driving the gearbox. The drive motor in the test bench is a high-power variable frequency servo motor, which can perform high-speed overspeed tests such as 5000 rpm for a short time when required by the test. At this time, the first controller is in speed control mode, used to simulate the constant speed traction or variable frequency speed regulation of the coal mining machine cutting motor, providing the input speed for the entire transmission chain; the drive motor is in electric mode. In this test method, the stator current of the drive motor is the main signal source for fault diagnosis, directly responding to the fault torque fluctuations transmitted by the load module.

[0063] Subsequently, the gearbox is simulated under load via the load module. The second host computer, based on a pre-defined random cutting resistance model, controls the load motor to generate reverse torque on the gearbox via a second controller. For example, the second controller can input a sinusoidal torque waveform superimposed with random noise to simulate the load fluctuations of the coal mining machine drum. At this time, the load motor is in generator mode, and the reverse electromagnetic torque of the load motor is controlled to simulate the load resistance encountered by the coal mining machine's cutting drum. Based on the electrical topology of the test bench described above, the load module can form a low-noise fault transmission channel and enhance the fault characteristic representation in the current signal, providing a high-quality test environment for subsequent fault diagnosis algorithms. Simultaneously, the mechanical energy generated by the load motor is converted into electrical energy, injected into the DC bus via the diodes of the second regenerative rectifier unit, and then fed back to the drive motor via the first regenerative rectifier unit to drive the drive motor.

[0064] Finally, the stator current signal of the drive motor acquired by the three-phase current sensors is recorded in real time. Due to the low-noise electrical architecture described above, the stator current spectrum of the drive motor will display modulation sidebands caused by component faults. In optional embodiments, an analysis algorithm such as HHT (Hilbert-Huang Transform), wavelet packet analysis, and deep learning models can be used to establish a mapping relationship between fault types and signal characteristics of the drive motor stator current signal. This invention does not limit the type or specific process of the analysis algorithm.

[0065] In an optional embodiment, the test method of the present invention further includes comparative verification. The faulty component in the gearbox is replaced with a corresponding normal component, the test steps described above are repeated, and the energy difference of the motor stator current signal collected under these two different conditions is compared to verify the amplification effect of the test bench of the present invention on weak fault characteristics in the drive motor stator current signal.

[0066] In an optional embodiment, the vibration signal of the gearbox and the voltage fluctuation signal of the DC bus can also be used as auxiliary observation variables that are strongly correlated with the stator current signal of the drive motor to increase the signal observation dimension, thereby establishing a multi-dimensional feature fusion fault diagnosis algorithm.

[0067] During the experiment of this invention, when the load motor is in power generation mode, the second controller controls the second regenerative rectifier unit to rectify the AC power generated by the load motor into DC power through diodes and inject it into the DC bus. The first controller controls the first regenerative rectifier unit to invert the DC power and feed it back to the drive motor. At this time, the voltage fluctuation signals are collected in real time by the first voltage sensor and the second voltage sensor installed on the DC bus. On the one hand, the energy feedback mechanism of the test bench is verified to confirm that when the DC bus voltage rises due to the power generation of the load motor, the first regenerative rectifier unit can normally intervene and feed electrical energy back to the drive motor, thereby reducing the total power consumption of the system. On the other hand, a mapping relationship between the fault type and the signal characteristics of the DC bus voltage fluctuation signal is established. In a further optional embodiment, based on the DC bus voltage fluctuation signal and the drive motor stator current signal, cross-correlation analysis or joint probability density function can be used to eliminate non-stationary random interference in the stator current signal, further improving the confidence of fault feature identification.

[0068] In traditional DC bus test bench systems, the impact of mechanical faults on the DC bus voltage signal is suppressed by voltage loop control, resulting in the loss of this information. The test bench and method of this invention can retain and analyze the DC bus voltage fluctuation signal in conjunction with the stator current signal of the drive motor using multi-dimensional fault diagnosis algorithms, further improving the reliability of fault simulation in the coal mining machine transmission system.

[0069] In a further optional embodiment, the test method of the present invention not only applies resistance to the gearbox through a load motor, but also periodically applies power to the gearbox, realizing rapid switching of the gearbox's transmission chain between the driving tooth surface and the non-working tooth surface. This torque zero-crossing oscillation test mode, based on the four-quadrant control capability of the bidirectional frequency conversion system, can analyze the current distortion waveform of the drive motor at the moment of torque zero-crossing, thereby identifying wear gaps and keyway loosening in the transmission chain. Through this test design, the test bench of the present invention can not only simulate the conventional cutting state of a coal mining machine, but also simulate the instantaneous tooth-jamming and drum sliding conditions of the coal mining machine. It improves the sensitivity and reliability of feature capture and fault diagnosis for mechanical gaps and wear faults that are only exposed during torque direction switching, thus enhancing the functionality compared to traditional unidirectional loading test benches.

[0070] In practical operation, the test bench of the present invention conducted a low-noise energy feedback test based on a dual-unit topology to verify that the test bench of the present invention can effectively reduce the background noise of the stator current signal of the drive motor while realizing energy feedback.

[0071] In the simulation of the traditional fully controlled test bench, the second regenerative rectifier unit is forced to operate in PWM (Pulse Width Modulation) active rectification mode. At this time, the power analyzer shows that the stator current of the drive motor contains a large number of high-frequency harmonics related to the switching frequency, resulting in high noise floor. In the simulation of the test bench of this invention, the second regenerative rectifier unit operates in diode natural rectification mode. At this time, due to the turn-off of the switching devices in the load module, the oscilloscope shows that the stator current waveform of the drive motor is smoother, high-frequency glitches are significantly reduced, and the noise floor is lowered, demonstrating the excellent electromagnetic interference suppression capability of the dual-unit hierarchical isolation architecture.

[0072] In addition, the test bench of the present invention has also conducted experimental verification on the effectiveness of weak fault feature enhancement and current diagnosis, in order to prove that the test bench of the present invention has a significant feature enhancement effect on fault diagnosis based on motor current characteristics.

[0073] In this experiment, the gearbox was configured as a single-stage parallel gear transmission, with a slightly worn gear mounted on its drive shaft. The fault energy of this type of early fault is extremely weak, making it very difficult to identify on conventional test benches. The drive motor was set to a constant speed of 1500 rpm, and the load simulated the rated coal seam resistance. A conventional fully controlled closed-loop test bench was set as the control group, while the test bench of this invention was set as the test group, for comparative experiments on fault signal acquisition and analysis.

[0074] In the control group, when the load module adopted full-loop control, FFT (Fast Fourier Transform) analysis of the stator current of the drive motor revealed no obvious fault spectrum lines at characteristic frequencies (such as the meshing frequency sidebands). This is because the closed-loop control algorithm suppressed weak torque fluctuations, and the signal was submerged by background noise. In the experimental group, when the load module was switched to the diode "escape" mode unique to this invention, the stator current signal of the drive motor clearly showed fault sideband components with significant amplitudes at the same frequency. Synchronous monitoring revealed that the DC bus voltage fluctuation signal exhibited tiny periodic ripples consistent with the fault frequency, proving that the mechanical fault energy successfully "escaped" through the diode channel and was converted into an electrical signal.

[0075] Experimental results demonstrate that the test bench of this invention, through its diode natural rectification channel and low-noise electrical topology, successfully overcomes the suppression of fault characteristics and noise interference inherent in traditional test benches. Under the same weak fault conditions, the test bench of this invention can significantly enhance the fault characteristic representation in the stator current signal of the drive motor, providing a high-quality, high-signal-to-noise ratio test environment for verifying high-sensitivity fault diagnosis algorithms.

[0076] The test bench and test method of this invention can not only provide fault diagnosis and mechanism research based on multi-source fault signal acquisition for the transmission system of heavy machinery such as coal mining machines, but also be used for product development and testing verification of the reliability, durability and other performance of gearboxes or transmission systems. At the same time, it can serve as a data platform for predictive maintenance and multi-source fusion intelligent fault diagnosis algorithms for the transmission system of coal mining machines, and for the development and verification of fault diagnosis algorithms.

[0077] The technical scope of this invention is not limited to the contents of the above specification. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the scope of this invention.

Claims

1. A coal mining machine transmission fault simulation test bench based on motor current characteristics, characterized in that, The test bench includes a drive module, a fault simulation module, a load module, and a signal acquisition module, wherein... The drive module includes a drive motor and a first controller for controlling the drive motor. The first controller is communicatively connected to a first host computer, and the first host computer controls the first controller through a direct torque control strategy. The fault simulation module includes a gearbox, which comprises removable and replaceable normal components and faulty components. The load module includes a load motor and a second controller for controlling the load motor. The second controller is communicatively connected to a second host computer, which controls the second controller using a direct torque control strategy. The signal acquisition module includes a three-phase current sensor disposed at the input terminal of the drive motor. The drive motor is connected to the input shaft of the gearbox, and the load motor is connected to the output shaft of the gearbox via a coupling. The drive motor and the load motor are connected to the power grid via a shared bidirectional reversible DC bus. The drive motor and the load motor are of the same model, and the first controller and the second controller are of the same model. The drive motor, the first controller, the first host computer, the DC bus and the inverter thereon constitute a first regenerative rectifier unit. The load motor, the second controller, the second host computer, the DC bus and the inverter thereon constitute a second regenerative rectifier unit. When the load motor is in power generation mode, the second regenerative rectifier unit rectifies the AC power generated by the load motor into DC power through diodes and feeds it back to the DC bus. The first regenerative rectifier unit inverts the DC power and uses it to drive the drive motor.

2. The coal mining machine transmission fault simulation test bench as described in claim 1, characterized in that, The signal acquisition module also includes a vibration sensor mounted on the gearbox housing and a voltage sensor mounted on the DC bus.

3. The coal mining machine transmission fault simulation test bench as described in claim 1, characterized in that, The second host computer sends torque commands to the second controller based on the random cutting resistance model of the coal mining machine.

4. The coal mining machine transmission fault simulation test bench as described in claim 1, characterized in that, The gearbox includes a single- or double-stage adjustable parallel gearbox and a single- or double-stage adjustable planetary gearbox. The parallel gearbox includes removable and replaceable normal spur gears, normal helical gears, normal rolling bearings, faulty spur gear sets, faulty helical gear sets, and faulty rolling bearing sets. The planetary gearbox includes removable and replaceable normal planetary gears, normal sun gears, normal planetary gear bearings, normal sun gear bearings, faulty planetary gear sets, faulty sun gear sets, faulty planetary gear bearing sets, and faulty sun gear bearing sets. The fault types of the faulty spur gear sets, the faulty helical gear sets, the faulty planetary gear sets, and the faulty sun gear sets include broken teeth, tooth surface wear, and pitting. The fault types of the faulty rolling bearing sets, the faulty planetary gear bearing sets, and the faulty sun gear bearing sets include outer ring cracks, inner ring cracks, ball spalling, and mixed faults.

5. The coal mining machine transmission fault simulation test bench as described in claim 1, characterized in that, A radial loading device is integrated on the output shaft of the gearbox.

6. A method for simulating transmission faults in a coal mining machine based on motor current characteristics, which can be implemented using the coal mining machine transmission fault simulation test bench as described in claim 1, characterized in that, The test method includes: Step 1: According to the test requirements, install the faulty component into the gearbox; Step 2: Set the protection parameters in the second controller and set the random cutting resistance model of the coal mining machine in the second host computer; Step 3: Start and drive the drive motor through the first controller to drive the gearbox; Step 4: Based on the random cutting resistance model, the second host computer controls the load motor to generate reverse torque on the gearbox through the second controller; Step 5: Record the stator current signal of the drive motor collected by the three-phase current sensor in real time, and establish a mapping relationship between the fault type and the signal characteristics of the stator current signal of the drive motor.

7. The method for simulating transmission failures of a coal mining machine as described in claim 6, characterized in that, The test method further includes step six: replacing the faulty component in the gearbox with the corresponding normal component, repeating steps two to five, and comparing the differences in the motor stator current signals collected under the two different states of the faulty component and the normal component.

8. The method for simulating transmission failures of a coal mining machine as described in claim 6, characterized in that, In step five: the vibration signal of the gearbox is collected in real time by a vibration sensor installed on the gearbox housing, and the voltage fluctuation signal of the DC bus is collected in real time by a voltage sensor installed on the DC bus. A mapping relationship is established between the fault type and the signal characteristics of the vibration signal, and between the fault type and the signal characteristics of the voltage fluctuation signal.

9. The method for simulating transmission failures of a coal mining machine as described in claim 6, characterized in that, In step one, the faulty components include faulty spur gear sets, faulty helical gear sets, faulty planetary gear sets, and faulty sun gear sets with fault types of tooth breakage, tooth surface wear, and pitting; and faulty rolling bearing sets, faulty planetary gear bearing sets, and faulty sun gear bearing sets with fault types of outer ring cracks, inner ring cracks, ball spalling, and mixed faults. By installing the faulty components into the gearbox, the transmission configuration of the gearbox is set to a single-stage parallel gear transmission, a double-stage parallel gear transmission, a single-stage planetary gear transmission, or a double-stage planetary gear transmission. At the same time, a radial loading device is set on the output shaft of the gearbox to apply radial pressure to the outer ring of the bearings of the gearbox.

10. The method for simulating transmission failures of a coal mining machine as described in claim 6, characterized in that, In step four, the second controller controls the load motor to periodically generate positive torque on the gearbox.

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