| Hydraulic system is widely used in engineering machinery,aerospace and many other fields because it has high density of the power,step less speed regulation,and is easy to control remotely.With the process of modern industrialization,the transmission power of hydraulic systems is getting larger and the information interaction is becoming more and more complex.The problems of safety,reliability and stability during service are of great concern.It is of great significance to carry out condition monitoring of equipment.The hydraulic system integrates hydraulics,electricity,and hydraulics.The monitoring of the operating state of the hydraulic system cannot be limited to mechanical and fluid parameters.It should also explore new methods of condition monitoring from the system level.The hydraulic system is integrated with machine,electricity and liquid.We cannot be confined to the parameters of the machine and fluid only when monitor the operating state of the hydraulic system.And a new state monitoring method should be explored from the system level.Under the coupling effect of the rotor of the motor,the system’s running state will be reflected in the three-phase electrical signals.As the voltage and current signal are easier to acquire and more sensitive than the monitoring signals of pressure,flow and vibration,it become a new carrier for the study of the system’s running state.In order to obtain the complete information of the electrical signal,this paper proposes a state monitoring method which combines the voltage and current signals from the motor input side into the electric power graph.Then completes the development of the monitoring platform.Firstly,the energy conversion mechanism and coupling process in the working process of hydraulic system were analyzed.The dynamic model of each subsystem of the hydraulic system were designed.The global coupling dynamic model of the system was formed.The energy consumption of the system was analyzed from the perspective of power flow.The results showed that the input power of the hydraulic system can reflect the power matching condition of the load conditions of the system,which provided a theoretical basis for the system status monitoring based on the electric power.Secondly,a state monitoring technology was proposed,which integrated voltage and current signals into electrical power graphics.According to the principle that voltage and current signals are in the same frequency,we chose to use the Lissajous figure method for the fusion of electric power graphics.The mathematical method of using the voltage and current signal to fuse the electric power Lissajous Figure was deduced.The functional relationship between electric power parameters and electric power Lissajous figure features was analyzed.The electrical power parameters were drew into a power circle graphs.The operating status and load conditions of the system were monitored through the electric power Lissajous figure and the power circle graphs.Then,a hydraulic system condition monitoring platform based on electric power graphics was developed on the virtual instrument.The monitoring platform was developed from two aspects: the selection of hardware virtual instruments and the software monitoring system design.I chose the signal acquisition equipment through the signal acquisition route on my hardware;Lab VIEW was selected as a software development platform on the software.The program and interface were designed for each module of the status monitoring,and a hydraulic system condition monitoring platform covering four functions of signal acquisition,signal processing,online monitoring,and off-line processing was formed.Finally,in order to verify the feasibility of the electrical power-based graphical monitoring method,a condition monitoring test was conducted on a motor-drag hydraulic system test stand.The on-line/off-line monitoring of the state of the hydraulic system under the conditions of constant load,slope plus and minus load,and step plus and minus load conditions were conducted.The results show that under various load conditions,the condition monitoring results based on the electrical power pattern method are feasible and effective.The graphical method of electric power provided a new approach for the study of hydraulic system condition monitoring,and it also provides new ideas for further equipment fault diagnosis and energy saving control. |
