| Due to the development of adjustable speed with variable frequency motor and the considerable energy saving effectiveness,the variable speed hydraulic system has been widely applied to the industry.In the variable speed hydraulic pump control motor system,it is necessary to obtain the instantaneous speed(IS)of hydraulic motor and its fluctuations information in some application for the demand of high-precision.Therefore,there are continued challenges in some key technology on IS of hydraulic motor,such as the algorithm of measurement,the mechanism and relevant control measures of measurement error,the dynamic response and control precision with different control strategies,monitoring the system operating status,etc.Now,the method of variable speed hydraulic system condition monitoring is mainly showed through monitoring the pressure,flow and temperature to get the running status information of system.However,the above-mentioned methods are intrusive measurement and the collected signal is sensitive to noise,which is not convenient for installation sensors in hydraulic circuits.Based on the above background,using the method of theoretatical analysis and experimental validation,the related research issues of IS of hydraulic motor,such as the measurement,control performance,and the instantaneous speed fluctuation(ISF)of hydraulic motor recognition method,were studied by using IS measurement and ISF extraction in this paper.The study of this paper would be helpful to provide a new method for performance evaluation,condition monitoring and fault diagnosis on the variable speed hydraulic pump control motor system.The IS measurement algorithm,mechanism and influencing factors of quantization error were analyzed on electro-magnetic sensor in this paper.With the method of A/D sampling software counting,the sampling point number of the original square wave produced by the magnetoelectric speed sensor was counted in a single cycle,and the average speed of a square wave cycle was obtained.The average speed can be approximately regarded as the IS of hydraulic motor when the gear turned an angle of a tooth through the sensor.The sampling point was not in the square wave time of high and low voltage conversion,which leads to the time measured a square-wave cycle time be not the actual time.Therefore,the quantization error is introduced into the IS measurement algorithm.Theoretical and experimental studies showed that increasing the sample frequency and decreasing the measured speed can reduce the quantization error.When the hydraulic motor speed is under the unsteady state condition,the method of wavelet filter can reduce the influence of quantization error.Once the IS approximate truth value of hydraulic motor is obtained,the relative quantization error can be calculated.The new method on the hydraulic system state recognition and monitoring has been proposed by using the ISF amplitude of hydraulic motor.The signal of IS is converted from the time domain to the angle domain.By tracking the first order spectrum,the changing rule on ISF can be obtained under different working conditions.The ISF of the hydraulic motor can be affected by the moment of inertia,the motor speed and the load pressure,the temperature of oil and the system state.The ISF of the hydraulic motor is closely related to the efficiency of hydraulic system,and their tendency of the changes is reverse.The typical control modes and characteristics of the hydraulic motor were analyzed.Under the same condition,the differences between the control accuracy and dynamic response characteristics of three kinds of control speed modes,directly openloop and closed loop PID and fuzzy,were studied.When the hydraulic motor target speed step changes from 600 r/min to 800 r/min,the peak time of open-loop control is 0.4 s,the peak time of closed loop PID is 1.1 s,and the peak time of fuzzy control is 2 s.The steady state error is produced by open-loop control,while it can be eliminated by closed-loop PID and fuzzy control.Under the condition of the same load disturbance,the hydraulic motor speed decreased with open-loop control,while the influence of load disturbance can be corrected with closed-loop PID and fuzzy control,and the hydraulic motor speed can be maintained in the set value.The efficiency of hydraulic system among three kinds of control method is close and the input and output power of the open loop control is smaller than the others.Compared to the fuzzy control,the ISF of the closed-loop PID on the local is slightly smaller.The influence on actual output hydraulic motor speed has been studied in flow feedback closed-loop PID control,when the high frequency noise interference signal is introduced into acquisition system.Under the same experimental conditions,compared to the flow feedback signal without filter,with butterworth low-pass digital filter and wavelet filter,the comparison experiment has processed in order to anysis the change rule of the hydraulic motor speed output performance.Without a filter,the average of actual flow can reach the target value,but the fluctuation of the hydraulic motor speed and output flow is large.Butterworth low-pass digital filter is not a zero phase filter.Thus,flow feedback signal after filtering,the data is moved,which lead to actual flow be low and not reach the target value.Wavelet filter is a zero phase filter.Flow feedback signal after filtering,the actual flow can reach the target value.The technology makes sure that the output curves of the actual flow,hydraulic motor and motor speed are smooth. |
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