It is difficult to fully mine the information from that one-dimensional vibration signal that expresses the state characteristics and then early recognize the wear of the valve plate of a piston pump. In view of the excellent image processing capabilities of the convolutional neural networks(CNN), we proposed an optimized VMD-CWT-CNN model to solve the above-mentioned problem. Firstly, continuous wavelet transform(CWT) was used to preprocess the signal to obtain a two-dimensional time-frequency diagram of the signal, which iwasused as one input of the CNN model to convert the state recognition problem into a CNN image recognition problem. Secondly, after optimizing variational mode decomposition(VMD) parameters based on correlation coefficient, the vibration signal was preprocessed by using the optimized VMD, and then based on the principle of maximizing the correlation coefficient and the kurtosis value, three groups of Intrinsic mode function(IMF) with fault characteristics were selected and reorganized into a three-channel one-dimensional signal as another input of the CNN model. Finally, in the CNN model, two paths were converged, and the results of the recognition and classification of the valve plate wear states of the piston pump were obtained. In the experiment, the proposed method we first use the optimized VMD and the CWT to preprocess the vibration signal, respectively, and then combined with the CNN to classify the wear states of valve plates. Experimental results show the recognition effect of the proposed method on the three states of valve plate wear is significantly better than that of the single-input CNN model, the typical deep learning method and the machine learning classifier. The optimized VMD-CWT-CNN method can more accurately recognize the valve plate wear states of the piston pump.

Rolling bearing is a critical component in the rotating machinery,which directly affects the reliability of the equipment. The artificial intelligence-enabled bearing fault diagnosis model has achieved impressive successes over the years. However,rolling bearings' imbalanced data sets (normal samples are much larger than failure samples) degrade the diagnostic performance. To address this issue,a bidirectional generative adversarial network(BiGAN) based fault diagnosis method was proposed. First,the signal was denoised via the ensemble empirical mode decomposition(EEMD) to automatically distribute it to a suitable reference scale and avoid modal aliasing. Then,the BiGAN model with gradient penalty term was constructed to expand the fault samples,where the min-max normalization was included. Finally,based on the enhanced training set,the convolutional neural network was established with batch normalization and maximum pooling layers. Experimental results proved that the proposed method improved fault diagnosis accuracy and robustness.

The stability of the output speed of a hydraulic system has a great influence on the working performance of hydraulic equipment. It changes with the system working conditions. The increase in leakage caused by the wear of the hydraulic kinematic pair and the slip of the motor lead to the instability of the output speed. Although the hydraulic system can satisfy the output requirements of the active control scheme with ex ante decision making or the passive feedback control strategy with ex post compensation, it also causes an increase in system complexity and manufacturing cost. The speed stiffness as a basic characteristic of the output of the hydraulic system has not been sufficiently investigated and evaluated. In this paper, the IFMDH (inverter-fed, motor-driven hydraulic) system is taken as the object, and the coupling relationship of each link of the system is revealed by mathematical modelling. The reliability of the model is verified under a wide range of speed and load variations in combination with experiments. By redefining the speed stiffness quantification method, the effects of load conditions, motor stiffness, and speed ratio at the output end on the speed stability of the system are discussed in conjunction with the system coupling mechanism model. The conclusions show that the motor stiffness and the addition of a speed reducer have a significant effect on the system speed stiffness, where changing the output speed ratio has a significant effect on the speed stiffness. The conclusions of the study provide technical support for the rapid design, selection, and system optimisation of hydraulic systems in common scenarios.

Due to the intense noise interference in hydraulic systems, it is extremely difficult to detect component faults through vibration signals. Diagnostic performance is also constrained by highly time-varying and non-stationary operating conditions. This study proposes to use instantaneous angular speed (IAS) signals that are both operational and state parameters as sources of information. Firstly, the instantaneous angular speed fluctuation (IASF) of a piston pump is analyzed theoretically, and it is concluded that its fluctuating components contain the health status information of the components. The IASF can then be obtained by subtracting the speed trend term from IAS signals obtained via a magneto-electric speed sensor. A synchro-extraction of the normal S transform (SNST) is proposed to process it via line-pass filtering. Finally, the filtered and reconstructed IASF signal is utilized to draw a two-dimensional polar coordinate map online. A non-stationary-condition test is carried out on the test platform to monitor the morphological characteristics of the valve plate under normal, slight, and severe wear conditions. The polar plot shows significant increases in speed fluctuations and oscillation times within a range from 180° to 270°. The relevant research results reflect that the IAS signal can provide a new method for monitoring the operating status of and conducting fault diagnoses for hydraulic equipment.

The transient and dynamic loading accuracy of the valve controlled cylinder force loading system of the undercarriage actuator cylinder wear and life experiment platform is low, which cannot meet the accuracy requirements of the load spectrum, thus affecting the safety and reliability judgment of the actuator. An improved nonlinear active disturbance rejection control (INADRC) algorithm with higher accuracy and anti-interference ability is proposed based on control algorithm. First, the AMESim/Simulink co-simulation model of the electro-hydraulic servo force loading system is established. Secondly, in order to optimize its parameters, the INADRC controller is designed, and the genetic particle swarm algorithm is used. Finally, the performance of the controller is verified by simulating and experiment with three target signal tracking. The simulation and experimental results show that compared with PID control, nonlinear ADRC (NADRC) and other improved nonlinear ADRC (ONADRC), the average accuracy of the INADRC is improved by 4.15％, 1.15％ and 0.65％, which reflects the characteristics of high servo force transient, dynamic loading accuracy and strong anti-interference ability.

An accurate digital model is of great significance to system operation inversion and behavior prediction. The multi-energy domain coupling mechanism of the Electro-mechanical and Hydraulic (EMH) system is complex and has strong nonlinear characteristics. At present, the research mainly focuses on the mechanical-hydraulic coupling characteristics, while the research on the large operating range and the influence of electric motor and load characteristics on the nonlinear dynamics of the EMH system are less. Based on the first principle description, the nonlinear characteristics of the system components are described in this paper. Furthermore, the nonlinear dynamic model of the EMH system described in multi-state space is established based on the Quasi-LPV system. Combined with the experimental data, the structural and non-structural uncertain parameters of system are identified. Finally, the influence of the mechanical characteristics of electric motor, load on the nonlinear dynamics of the EMH system are discussed. Experiments show that the Quasi-LPV models proposed in this paper can accurately reproduce and predict system behavior. It provides technical support for rapid design, selection, and scheme optimization of hydraulic systems in general scenarios.

The multi-lip combined seal has the advantages of multi-lip coupling, large supporting force, and can withstand high-pressure shocks. It is an irreplaceable structure for single-lip seals. However, most of the seal wear analysis focuses on the simulation method of the single-lip seal under the influence of macro factors, and very little involves the wear characteristics of multi-lip seals. In this paper, a micro numerical method is established, which combines the elastohydrodynamic lubrication theory with the modified Archard equation. The performance of a multi-lip combined seal under different working conditions is analyzed through simulation, including macro and micro factors. It is found that some of the characteristics of single-lip seals are also reflected in multi-lip seals, and there is a critical speed that makes the sealing behavior of each seal lip different.

Considering that the vibration of the piston pump shell includes not only motion state information, but also energy state information, this study discloses the relationship between the piston pump vibration signal and the operating state by the piston pump shell vibration phase trajectory. Firstly, the high pressure fluid excitation and the vibration speed, displacement, and vibration energy of the pump shell are related. This relationship can be set forth by analysis of the piston pump fluid vibration transmission path. Secondly, according to the vibration frequency traceability, multi-synchrosqueezing transform (MSST) method is used to reconstruct signal. After the integral transformation of the reconstructed signal, the information of vibration speed and displacement can be obtained further. Finally, the trajectory diagram of the shell vibration is constructed based on the vibration speed and displacement. The experiment under different operating conditions are carried out to expound the variation rules of the kinetic energy and potential energy of the piston pump contained in the phase trajectory diagram of the shell vibration. The results show that combined with vibration frequency traceability, MSST can accurately extract the vibration frequency and phase information of shell vibration acceleration signal caused by hydraulic excitation. The operating condition of piston pump has significant influence on kinetic energy and potential energy of piston pump shell. With the increase of system pressure, the distance between the phase trajectory and the vertical zero-shift axis, and the potential energy of the shell increase significantly. With the increase of speed, the maximum vibration speed of phase trajectory diagram and the kinetic energy of shell increase significantly. The phase trajectory diagram of axial piston pump can reflect the kinetic energy and potential energy of the shell more intuitively. This study can provide a theoretical basis and method support for the fault diagnosis and health assessment of key components such as hydraulic pumps, motors.

Considering that the vibration of the piston pump shell includes not only motion state information, but also energy state information, this study discloses the relationship between the piston pump vibration signal and the operating state by the piston pump shell vibration phase trajectory. Firstly, the high pressure fluid excitation and the vibration speed, displacement, and vibration energy of the pump shell are related. This relationship can be set forth by analysis of the piston pump fluid vibration transmission path. Secondly, according to the vibration frequency traceability, multi-synchrosqueezing transform(MSST) method is used to reconstruct signal. After the integral transformation of the reconstructed signal, the information of vibration speed and displacement can be obtained further. Finally, the trajectory diagram of the shell vibration is constructed based on the vibration speed and displacement. The experiment under different operating conditions are carried out to expound the variation rules of the kinetic energy and potential energy of the piston pump contained in the phase trajectory diagram of the shell vibration. The results show that combined with vibration frequency traceability, MSST can accurately extract the vibration frequency and phase information of shell vibration acceleration signal caused by hydraulic excitation. The operating condition of piston pump has significant influence on kinetic energy and potential energy of piston pump shell. With the increase of system pressure, the distance between the phase trajectory and the vertical zero-shift axis, and the potential energy of the shell increase significantly. With the increase of speed, the maximum vibration speed of phase trajectory diagram and the kinetic energy of shell increase significantly. The phase trajectory diagram of axial piston pump can reflect the kinetic energy and potential energy of the shell more intuitively. This study can provide a theoretical basis and method support for the fault diagnosis and health assessment of key components such as hydraulic pumps, motors.

For variable speed pump-controlled hydraulic cylinder system,the nonlinear change of hydraulic system parameters is brought in by large-scale change of speed or load.It causes the control system,which is designed by the linear model,to have the problems such as difficult correction of control parameters,unstable precision or even control instability.In this paper,a multi-model adaptive PID(MMA-PID)control method is proposed by analyzing the state space of a typical variable speed pump-controlled hydraulic cylinder system.According to the nonlinear change of the bulk elastic modulus of oil caused by the change of the system pressure,the system behavior is described by using multiple linear sub-models.A reasonable controller is designed for each sub-model.During the control process,the output weight coefficient of each sub-model is estimated separately through the Kalman filter,and the weighted fusion of all the sub-models control output is used as the final control input of the system.The simulation and experimental results demonstrate that when the working conditions are vary widely,the MMA-PID can adapt to the nonlinear change of system parameters better than the traditional PID,and it owns better control effect and dynamic performance.

We investigate an optimization problem of robust control for the Delta-type parallel manipulator. The task is to render the uncertain Delta-type parallel manipulator to follow the pre-specified active constraints. Uncertainties in this paper are deemed to be (possibly fast) time-varying and bounded, and the information of boundaries is creatively depicted via a fuzzy set. By this fuzzy depiction, a robust control scheme, which is deterministic and not the traditional if-then rules-based, is designed. On top of that, we construct an optimization problem that targets the choice of the performance-dependent control parameter. Then, the existence and uniqueness of the global solution to this problem, which could be solved by minimizing a fuzzy performance index, is proven. In addition to meeting active constraints, the Delta-type parallel manipulator under the proposed control scheme assures two attractive performances: the deterministic performance and the fuzzy performance. The results of simulations illustrate the validity and practicability of the control scheme.

The improvement of data-driven soft sensor modeling methods and techniques for the industrial process has strongly promoted the development of the intelligent process industry. Among them, ensemble learning is an excellent modeling framework. Accuracy and diversity are two key factors that run through the entire stage of building an ensemble learning-based soft sensor. Existing base model generating methods or ensemble pruning methods always consider the two factors separately, which has limited the development of high-performance but low-complexity soft sensors. To work out this issue, a selective ensemble learning-based soft sensor modeling method based on multi-kernel latent variable space and evolutionary multi-objective optimization is proposed, referred to as MOSE-MLV-VSPLS. This method designs a multiple diversity enhancement mechanism in the base model generation stage. Diversified input variable subspaces are first constructed using the maximum information coefficient on the bootstrapping random resampling subset. Then a set of base models that combine accuracy and diversity are generated on supervised latent variable subspaces under multiple kernel function perturbations. Further, two quantifiable parameters are designed for accuracy and diversity, and the multi-objective gray wolf optimization algorithm is used to select the base models that maximize these two important parameters to achieve effective ensemble pruning at the model ensemble stage. The MOSE-MLV-VSPLS method is applied to two typical industry processes, and the experimental results show that the method is effective and superior in selective ensemble-based soft sensor modeling.

针对液压马达驱动负载系统中,马达输出轴的转速波动特性直接影响负载工作稳定性和可靠性的问题,建立典型液压马达-负载系统的动力学模型,阐明液压马达等效弹簧扭转刚度的计算方法;根据非线性动力学原理,分析等效液压弹簧扭转刚度和摩擦转矩对系统转速波动特性的影响机制,提出利用高频采样计数方法对转速波动进行测试与分析.理论分析与实验结果均表明:非线性摩擦转矩、输出容积脉动、负载转矩、油液有效体积弹性模量等因素的变化影响系统的转速波动特性.

The pressure pulsation of axial piston pump is not only an important cause of rotation speed fluctuation,vibration noise and output stability of the hydraulic system,but also the main information source for obtaining fault information.Hydraulic system is characterized by strong noise interference,which leads to low signal-to-noise ratio(SNR)of detection signals.Therefore,it is necessary to dig deep into the system operating state information carried by pressure signals.Firstly,based on flow loss mechanism of the plunger pump,the mapping relationship between flow pulsation and pressure pulsation is analyzed.After that,the pressure signal is filtered and reconstructed based on standard Gabor transform.Finally,according to the time-domain waveform morphology of pressure signal,four characteristic indicators are proposed to analyze the characteristics of pressure fluctuations under different working conditions.The experimental results show that the standard Gabor transform can accurately extract high-order harmonics and phase frequencies of the signal.The reconstructed time-domain waveform of pressure pulsation of the axial piston pump contains a wealth of operating status information,and the characteristics of pulsation changes under various working conditions can provide a new theoretical basis and a method support for fault diagnosis and health assessment of hydraulic pumps,motors and key components.

为在线监测液压系统的运行状态及功率匹配信息,识别其在典型工况下的功率匹配关系,以变转速泵控缸液压系统为例,基于多源信息融合思想,提出了李萨如图和功率圆图的动态功率匹配图示化监测方法.基于LabVIEW开发了测控程序进行变工况下的功率软测量,验证并分析了系统的能效特性.结果 表明:恒定转速下,系统总效率随负载增大先升高后降低;阶跃加载时,系统存在功率冲击;溢流工况下,系统总效率为0;恒定负载下,系统总效率随转速增大先升高后降低;电机转速与负载相匹配时,可提高系统总效率.李萨如图和功率圆图特征参量可反映系统的功率及运行工况,该方法能够对液压系统的动态变化进行实时监测,为液压系统的功率监测和匹配研究提供了新思路.

Multi-lip reciprocating seals are extensively used in the subject of engineering equipment. However, the current research on the tribology of reciprocating seals mainly focused focuses on the numerical analysis of single-lip seals. In order to study the sealing performance of multi-lip seals, this paper takes double-acting seal (DAS) as the research object, and establishes a multi-lip mixed elastohydrodynamic lubrication (M-EHL) numerical simulation model from the perspective of solid mechanics, fluid mechanics, contact mechanics, and deformation mechanics. The sealing characteristics under different working conditions (sealed pressure, piston rod extension speed, and seal surface roughness) were analyzed by numerical calculation, and the variation trend of friction force corresponding to the experimental results was obtained. The model can provide a modeling guidance basis for the M-EHL characteristic analysis and structural optimization design of multi-lip reciprocating seals in the mechanical field.

由于存在测量误差,直接测量的时域转速波动并不是其真实的波动.为了获得非平稳转速工况下的瞬时转速波动,提出了在阶次谱中提取瞬时转速波动幅值的方法.将时域中测得的瞬时转速信号从时域转换到角度域,再进行短时傅立叶变换得到阶次频谱图,通过提取一阶次的转速波动信号从而得到转速波动幅值特征.实验研究表明,此方法能较好地提取转速斜坡、正弦、阶跃工况下的波动,为非平稳工况下的瞬时转速波动幅值特征提取提供了参考和借鉴.

In the electro-hydraulic servo control system, there are some problems, such as low position control accuracy, uncontrollable speed, speed impact, and asymmetric control due to the asymmetry of hydraulic cylinder. To solve the above problems, this paper proposes a Fuzzy PID control algorithm with load force compensation based on improved PSO optimization. This improved particle swarm optimization algorithm introduces crossover and mutation operations in genetic algorithm to improve the optimization performance of traditional particle swarm optimization algorithm. The mathematical model of valve controlled asymmetric cylinder is established, and the Amesim linearization analysis function is used to identify the system, establish the transfer function, and build the control system. The joint simulation and test results of Amesim and MATLAB show that the proposed control strategy can realize the simultaneous control of speed and position. Under different loads, different speeds, and different input follow signals, it does not need to adjust any parameters. Regardless of forward or reverse operation, the optimal dynamic performance and minimum steady-state error are obtained, which greatly improves the response speed of the system. The effectiveness and superiority of the improved PSO compound control strategy are verified.

Compression loss is one of the volumetric losses of bent-axis piston pumps, and its accurate evaluation is the basis for predicting the effective flow rate and volumetric efficiency of bent-axis piston pumps. The effect of changes in gas content on the effective bulk modulus rarely is considered in the existing compression loss models, which does not apply to the compression loss of bent-axis piston pumps under cavitation. However, cavitation exists in the actual work, especially in increasing the speed of the bent-axis piston pump. To solve this problem, a compression loss model is proposed. Firstly, the modified Henry’s law and the simplified transport equations of gas are used to describe the oil gas content under cavitation, and the effective bulk modulus equation is established. Then, combined with the definition of compressibility, the compression loss model of the bent-axis piston pump is proposed. Finally, the compression loss of the bent-axis piston pump under different operating conditions is analyzed through simulation, and the results are verified by experiment. The results show that the model prediction results are a good agreement with the experimental results under different operating conditions. The conclusions provide a new method for evaluating the effective flow rate and volumetric efficiency in the bent-axis piston pump.

Purpose This paper aims to revel the leakage characteristics of the bent-axis piston pump considering elastohydrodynamic deformation via a dynamic leakage model. Design/methodology/approach A dynamic leakage model of bent-axis piston pump based on elastohydrodynamic lubrication theory is proposed, which is used to present the leakage characteristics of bent-axis piston pump. The model is composed of three parts. First, the dynamic gap in the piston ring-cylinder bore interface (PRCB) is described via the elastohydrodynamic lubrication equations. Then, the PRCB leakage is presented based on the dynamic gap. Finally, combined with leakage equation of the valve plate-cylinder block interface (VPCB), the total leakage model is proposed. Through the numerical simulation and experiment, the leakage characteristics of bent-axis piston pump considering elasto-hydrodynamic deformation are studied. Findings The PRCB leakage is negatively correlated with VPCB leakage under the range of 800–1400 r/min and 1–25 MPa. When the discharge pressure is less than the critical pressure, the PRCB leakage is the main factor affecting the total leakage in bent-axis piston pump. On the contrary, the VPCB leakage is the main factor. The critical pressure increases with increasing speed Originality/value The effect of operating parameters has a significant effect on the elastic deformation of piston ring without considering wear of friction pairs in bent-axis piston pump. There is a critical phenomenon in the leakage, which is related to the operating parameters, and provides a novel idea for extracting wear information from leakage and evaluating the status of bent-piston pump.