Regulating characteristics of an electro-hydraulic vibrator multiply controlled by the combination of a two-dimensional valve and a standard servo valve

For extending the frequency bandwidth greatly and controlling the vibration characteristic variables precisely, the electro-hydraulic high-frequency vibrator controlled by the parallel design of a two-dimensional valve (named as 2D valve) and a standard servo valve is preserved. The frequency of the vibrator is proportional to the product of the rotary speed of the spool of the two-dimensional valve and the switching numbers between grooves in the spool and windows in sleeve in one circle, so that it is convenient to extend the working frequency range by coordinating these parameters. In this study, the load is considered to be an elastic force and the relationships between the characteristic variables of the vibration and the control parameters are investigated using the analytic method. For the solution to the expression of the bias of the vibration, the electro-hydraulic vibration system is considered to be equivalent to a symmetrical hydraulic cylinder controlled by a single slide valve with a neutral pre-opening, which is determined by the throttling area of the two-dimensional valve. For the waveform of the vibration, the system is assumed to be a hydraulic cylinder controlled only by the two-dimensional valve and the effect imposed by the parallel servo valve on hydraulic cylinder is treated as an external load. The equations of the waveform superimposed on the bias are finally solved using the analytic method, where the expressions of the vibration amplitude are derived. It is found that coupling relationships exist between the characteristic variables of the vibration and the control parameters, where the vibration amplitude is not only determined by the axial displacement of the spool of the two-dimensional valve but is also reciprocally proportional to the rotary speed of the spool of the two-dimensional valve. While the bias is only dependent on the ratio of the throttling area of the parallel servo valve to that of the two-dimensional valve, the working frequency is exclusively dependent on the rotary speed of the spool of the two-dimensional valve and the vibration amplitude is almost independent of the throttling area variation of the parallel servo valve. The experimental system is built to verify the analytic results of the relationships between characteristic variables and control parameters. It is demonstrated that the theoretical analysis is consistent well with measured results and it is also verified that by means of proposed multiple control to the hydraulic vibrator, the vibration can be sustained at the level of high accuracy.