Water pumps as fluid mechanical equipment are widely used in modern industrial production. Impeller damage is a common failure mode of pump, which will reduce the flow and head of pumps and affect the efficiency of the overall system. The normal operation of the pump can be ensured by timely diagnosis of impeller failure. Aiming at the problem of pump impeller fault, a method of pump fault diagnosis based on wavelet analysis and BP neural network is proposed. The wavelet analysis is introduced to extract the frequency band energy of the pump vibration signal, and the fault diagnosis is carried out by detecting the energy changes of each frequency component. The intelligent diagnosis of pump impeller fault is realized by obtaining the fault characteristics with energy. This method has high diagnostic accuracy and feasibility for further improving pump fault diagnosis.
In the pilot relief valve design, it is often necessary to estimate the flow value of the pilot valve when the main valve is opened. Generally, the empirical method is used to directly take 1% of the rated flow of the relief valve. In this paper, taking a certain type of relief valve as an example, through the valve and the data fitting analysis, the recommended range of the pilot valve flow valve when the design of the main valve is opened is proposed.
Increasingly stringent national emission standards for construction machinery and rising fuel prices have promoted excavator manufacturers to improve energy efficiency. When the hydraulic excavator boom lowers, the gravitational potential energy is converted into heat, which results in poor energy efficiency. To solve this problem, a novel flywheel based energy recovery system (FESS) is proposed in this paper. A hydraulic pump/motor (PM) is employed as the energy conversion element and a flywheel is used as the energy storage element. To reduce the power loss when the flywheel is idling, a clutch is installed between the PM and the flywheel. The working principle of the system is analyzed in detail. A 4 t hydraulic excavator is taken as the research object, and the key parameters of the system are matched. The model of the FESS is developed in AMESim. The influence of the key parameters such as the PM displacement and the moment of inertia of the flywheel on the energy recovery and reutilization efficiency in the typical working cycle are simulated and analyzed, and the specific value of the energy recovery and reutilization is obtained, up to 65% for 4 t excavator and 60% for a 21 t excavator. The simulation results show that the FESS can significantly improve the energy efficiency of the hydraulic system.
In this paper, An adaptive dynamic surface controller (ADSC) is developed for the pneumatic servo systems with the single-rod pneumatic actuator. The ADSC scheme contains a nonlinear feedback part, a parametric adaption part, and a disturbance observer part in the parallel structure. The nonlinear feedback part is synthesized by the backstepping method, while the explosion of complexity in traditional backstepping design is avoided by utilizing dynamic surface control technique. Since precision motion control of pneumatic servo system is always disturbed by unknown model parameters and disturbance, the gradient adaption laws are employed to further estimate and compensate those factors. Experimental results obtained verify the effectiveness of the proposed ADSC controller and its performance robustness to parameter variations and external disturbance in practical implementation.
To improve the flow control quality of an engine flow regulator, the synchronous control strategy of multi-servo mechanism driving flow regulator was studied. The position loop model of servo mechanism is constructed and an adaptive fuzzy PID tracking controller is designed to replace the traditional PID controller to realize the on-line real-time adjustment of servo control parameters under load disturbance. Based on the analysis of the constraints of different position servo mechanisms of the flow regulator, a new control strategy of improved deviation coupling synchronization is proposed by introducing a nonlinear coupling factor, which is related to the deviation and the position information. The simulation and experimental results show that the synchronization control strategy has higher synchronization accuracy, smaller load disturbance response than the conventional coordinated control strategy, and reduces the influence of parameters difference of servo mechanism.
An adaptive control system with good following characteristics is designed for the electro-hydraulic servo system which is seriously nonlinear. The model of position servo system on flexible nozzle is discussed with the uncertain system equivalent to the one with parametric variable double input and single output to establish a Popov-MRAC system. The simulation results show that the adaptive control system has good following characteristics and robustness.
This paper reports a study of the Independent Metering System of a four-valve configuration controlling an asymmetric hydraulic cylinder. The four-valve consists of four proportional cartridge valves connected with exchangeable control software that the meter-in orifice and meter-out orifice can be separately controlled. The potential energy saving of this system is analyzed via the mathematical analysis of the correlation of the transform efficiency ratio and systematic parameters. There are many metering modes which are the increasing ways of the meter-in and meter-out opening ratios. The 7 typical increasing ways of the meter-in and meter-out opening ratios is analyzed by the mathematical analysis of the transform efficiency and output velocity. Aiming at obtaining a high transform efficiency ratio to realize the energy saving efficiency of the Independent Metering System, the optimal metering mode has been obtained, which is the meter-in orifice is opening proportionally and the meter-out orifice is opening fully.
The precise control of the feet-end is the key link to realize the functions of the robots. Through the forward and inverse kinematics analysis and feet-end trajectory planning, the thesis proposes a method to solve the problem of feet-end trajectory deviation of robots by analyzing the relative position between the target planning point of feet-end trajectory and the actual planning point. First, it will support the body's trajectory that it is equivalent to the feet-end , then through the relative position between the target planning point of the feet- end trajectory and the actual planning point , the method of calculating the trajectory of the ideal planning point is given. Finally , it is analyzed that the deviation of the feet-end trajectory target point and the actual planning point under 4 kinds of relative position of robots in the swing phase and support phase.
As an important component of hydraulic system, hydraulic cylinder is a kind of energy conversion element that converts pressure energy into mechanical energy, and its performance directly affects the performance of the hydraulic system. Because the first generation of hydraulic cylinder with sealing parts has great friction resistance, the development of hydraulic cylinder towards high speed and high frequency is restricted. The second generation of hydraulic cylinder with constant clearance non-sealing parts has low friction resistance and improves dynamic response, however, the capacity efficiency is reduced and the requirement of machining precision is high. On the basis of the second generation of hydraulic cylinder, the third generation of hydraulic cylinder with pressure automatic compensation variable clearance sealing is developed by applying the elastic-plastic theory and the gap flow theory of fluid mechanics. Through analysis, modeling, simulation and experiments, it is proved that the third generation of hydraulic cylinder has characteristics of good static and dynamic performance, high volumetric efficiency and long working life, and is suitable for hydraulic system with high frequency and high speed. The pressure automatic compensation variable clearance sealing technology can also be applied to other hydraulic components and related fields.
For the powder-paved 3D printing technology, an effective conveying glue control system is proposed. Taking the speed control of piston that squeezes the glue as the core of this design, a set of hydraulic control system for glue conveying is designed. The test model of the glue conveying control system is established. The system is simulated based on the MATLAB/ Simulink module, and the PID controller is applied to improve the dynamic performance of the system. The simulation results show that this design of the glue conveying control system for powder-paved 3D printer has good stability, accuracy and rapidity under the premise of ensuring safety, and can meet the requirements of glue conveying.
Aiming at satisfying the demand of electric power supply for small power secondary instrument of sewage and heating flowmeter, the study designed a small-sized impeller hydroelectric generating device without external lead wire or battery. The flow field of impeller hydroelectric power plant is analyzed by means of finite element analysis. The effects of wheelbase, impeller stages and blade number of single impeller on the efficiency of impeller plant are studied. The influence weights of blades number impeller stages and wheelbase on the efficiency of hydroelectric impeller are obtained, and the small structure of high efficiency and low loss hydropower generating device with impeller installed is proposed.
Spring-loaded pressure safety valves are the key devices used for protecting pressure vessels and systems. In order to facilitate the design progress of spring-loaded pressure safety valves and get a better understanding of the flow forces, this paper conducted a series of numerical simulations for predicting the flow forces acting on the disc at various valve opening positions for different pressures ranging from 3 to 4 bar. 2D and 3D geometries as well as different turbulence models have been developed for improving the accuracy of the simulation. The results indicate that the two-dimensional model along with transition on SST model can simulate the turbulent flow within the flow domain effectively , according to the comparison with experimental data. In addition , it reveals that this study can be of great help to predict flow forces at the similar mechanical structure.
Most of today's hydraulic quadruped robots use a single-pump multi-actuator structure. Due to the dissimilarity of the mechanical characteristics of the joints of the quadruped robot during the movement, the mismatch between the constant pressure oil supply and the pressure required by the system causes considerable energy waste and reduces the system efficiency. Aiming at the phenomenon that the pressure demand of the quadruped robot joint actuator does not match the oil supply pressure, this paper proposes a variable oil supply pressure control strategy. Firstly, through load prediction and anti-cavitation pressure of the hydraulic cylinder, we can determine the minimum supply pressure of the system. Secondly, combined with the actual work requirements of the quadruped robot, two grouping oil supply strategies are proposed, which are joint-based grouping and leg-based grouping. Finally, the simulation and experiment of constant pressure oil supply and variable oil supply pressure control strategies are carried out. Analyze its influence on the control characteristics of the quadruped robot and the energy saving effect. The results of Matlab/Simulink, ADAMS and AMEsim co-simulation and single leg experiment show that the grouping oil supply strategy based on variable oil supply pressure can achieve good energy saving effect without affecting the control performance of the quadruped robot.
Axial piston hydraulic motor pump is an innovative type of electro-hydraulic integrated power unit which combines the structure and principle of axial piston hydraulic pump with high-speed motor. With developmental frontier and application prospects, high-speed motor pump has attracted much attention. However, the heat problem of high speed motor pump is an important obstacle to its design and development. In this paper, the basic structure and the operation principle of high-speed motor pump are initially introduces and the causes and calculation method of heat loss are analyzed. With the finite element method and analytical method, the losses of each part of high-speed permanent magnetic hydraulic pump plunger motor are calculated and the influence of key parameters on the loss are analyzed. This study provides evidence for a further analysis of the temperature field of high-speed motor pump and a reference for the design of high-speed motor pump.
The hydraulic motor is usually controlled by the servo valve, with the speed encoder composing a closed loop system. While considering the power efficiency, the secondary control which changes the displacement of the motor is always a direct method, though the response time may be a bit longer. For the purpose of accuracy and efficiency, a control method of both valve control and secondary regulation is proposed in this paper. Compared with the traditional valve-controlled motor system, the throttling loss of the servo valve can be reduced. The simulation using AMESim is carried out to verify the effectiveness and feasibility of the principle.
To meet the test requirements of the key structural part in the super high-rise building, a 108MN 6-dof advanced structural testing system is developed. And for the high-speed shear test of the large rubber bearing, the instantaneous flow demand of the testing system is far more than the conventional hydraulic testing equipment. For this, the piston accumulator group with the separated nitrogen cylinder is adopted as the system auxiliary hydraulic power. In the paper, the optimization design of the accumulator group is implemented though continuously optimizing the volume ratio of the accumulator and the nitrogen cylinder. And when the accumulator group works, its pressure decreases from the precharge pressure to the working pressure constantly, which will impact the loading accuracy, and the excessive pressure is also not conducive to the protection for the specimen. To restrain the pressure fluctuation, a pressure control loop with the large-flow cartridge valve is presented, the associated model is set up and the control method is developed. The results show that with PD control the oil supply pressure of the accumulator group can be stabilized within the required range, and the control precision is high.
In a T-junction microdroplet generator, a mathematical model which can describe the linear relation between the droplet length and the flow-rate ratio for different geometries of the T-junctions is established. For different viscosity of the fluids, the droplet length as a function of the flow-rate ratio is measured experimentally. We observe that the droplet length is a linear function of the flow-rate ratio for different Capillary numbers, while the droplet length varies nonlinearly with the flow-rate ratio at a high Capillary number. Particularly, two geometries of the T-junction microchannels are designed for droplet formation, and good agreements are found between the predicted and the measured droplet length for low Capillary numbers. More importantly, the linear model of droplet formation is only determined by the geometry of a T-junction and independent of the viscosity of the fluids for high Capillary numbers. As a result, our linear model can be experimentally validated, and the size of the droplets can be precisely predicted for different geometries of the T-junctions.
It is of great significance to develop the high- precision and high-reliability hydraulic force servo control system to promote the application of hydraulic fatigue machine in the field of structural and machine parts fatigue testing. The dynamic characteristics considering the variation of load stiffness is analyzed by establishing the model of hydraulic fatigue machine. The dual inertia loop is adopted to enhance the stability of the force control system of the fatigue testing machine. For the sinusoidal force loading signal, an adaptive amplitude and phase control algorithm is proposed to improve the sinusoidal force tracking accuracy in spite of the existence of parameter uncertainties and nonlinearities of the hydraulic system. The digital control system of fatigue machine is built based on xPC rapid prototyping method. The experimental results show the effectiveness and real-time of the proposed control algorithm mentioned above.
Generally, water hydraulic piston pump (WHAPP) can use oil as working media due to good lubrication of oil. The noise of pump is a very important performance and paid many attentions. How about the noise of WHAPP when using oil as working media is worth being concerned. In this paper, the noise of a WHAPP with valve plate is experimentally investigated using water and oil as working media respectively. The experimental results show that the volumetric and mechanical efficiency of oil is larger than that of water. However, the noise, vibration and pressure pulsation when using oil are also larger, although the volumetric elastic modulus of water is larger than that of oil. It is analyzed that the pre-compression angle of valve plate for water hydraulic pump is too small for oil pump, which will result in the back-flow and aggravate the noise of oil pump.
The energy dissipation mechanism of hydraulic viscous damper was studied considering the shear thinning effect of dimethyl silicone oil. The analysis indicates that most of the energy loss occurs in the damping hole, which is mainly manifested as the damping loss along the path. The calculation formula of damping loss is simplified by assuming boundary conditions and the theoretical curve is drawn. The result shows that for the damping holes with the same size, the velocity and viscosity of oil are the key parameters to determine damping loss. But for different sizes damping structures, length- diameter ratio is the main factor affecting the energy loss, which in essence affects the pressure capacity of damping holes. Subsequently, the rationality of the above conclusions is verified by experiment, and two kinds of low-index hydraulic viscous damper were designed. The experimental results show that the algorithm can predict the mechanical properties of the damper well.
