To precisely control the bias position of an electro-hydraulic vibration exciter

a scheme of a digital servo valve connected in parallel with a two-dimensional valve(2D valve)is proposed and investigated. The mathematical model of the electro-hydraulic vibration exciter is constructed

a vibration central position is analytically derived by assuming that the paralleled valves are equivalent to a single slide valve with neutral positive opening and identical time-average flow rate. Then the analytic solutions to excited waveforms superimposed on the bias position are further obtained. The experimental system is established to verify the theoretical analysis in the range of 5-200 Hz. The results reveal that when the opening area of 2D valve is constant

the bias position follows a linear relation with the throttling areas of the parallel valve

but there is a virtual limitation on the maximum position. The excited waveform is close to the sinusoidal waveform. In the same opening area of the parallel valve

the bias position is reduced as the area coefficient of 2D valve increases. In this process

maximum position of vibration goes up after a sharp reduction. When the frequency is 200 Hz and throttling area of parallel valve is 25%

the maximum bias poison gets the minimum at 20% of the throttling area of 2D valve. The proposed scheme ensures not only the frequency and the amplitude to be controlled independently but also the bias position to be adjusted precisely.