## 4 Active Control Experiment  
In order to verify the performance of the active-passive hybrid vibration isolation system and the effectiveness of the adaptive suppression algorithm, the algorithm is developed using NI LabVIEW, and an active control experimental platform is built by combining the NI PXI real-time acquisition and control system. A low, medium and high multiline spectrum excitation experiment was carried out taking the vibration exciter as the control object, the hybrid vibration isolation system as the active control actuator and the ASFXLMS algorithm as the control law. The experimental model is shown in Figure 17. The upper layer of the experimental bench was equipped with an electromagnetic vibration exciter, and the lower plate was fixed on the ground. The periphery of the lower plate was provided with a column guide rail using bolts, and the upper plate matched the column with roller sliding bearings. The hybrid vibration isolation system was bolted between the upper and lower plates. The vibration exciter, upper plate and lower plate were each equipped with an acceleration sensor to collect the active control reference signal, upper primary vibration signal and lower residual vibration signal. The lower residual vibration signal was used as the error signal of the active control algorithm. The experimental equipment mainly included the NI PXI control system (including the PXI 8840 adaptive controller, PXI 4498 AD acquisition board and PXI 6733 DA output board), Copley Xenus servo drive, PCB acceleration sensors, electromagnetic vibration exciter, WYK-20040K DC stabilized current power supply, etc. The electromagnetic exciter was independently developed, which is essentially an electromagnetic actuator, and the output force had a linear relationship with the input current amplitude in the low-frequency excitation range. The signal generation module generated an excitation signal, which was generated by the servo drive to the electromagnetic exciter to conduct vibration interference. The PCB acceleration sensors acquire the reference signal, the upper primary signal and the lower  
Figure 17: Schematic diagram of the active vibration isolation experimental bench. error signal into the PXI 8840 adaptive controller via the PXI 4498 AD acquisition board. The output control signal enters the Copley Xenus servo drive via the PXI 6733 DA output board, which drives the active and passive hybrid vibration isolation system to generate secondary vibration to suppress the primary vibration. Superimposed harmonic signals of 37 Hz, 60 Hz and 110 Hz with currents of 8 A were generated with the signal generator as the initial excitation signals. The length of the control filters was 300 orders. The iterative step size of the algorithm was 0.00001. The sampling frequency was set to 10 kHz, which not only satisfied the sampling theorem but also ensured the real-time tracking of the signal. A Butterworth band-stop filter was designed in the experiment to filter out the 50 Hz power frequency interference in the signal collected by AD board. The drop between the primary vibration signal and the residual vibration signal was taken as the evaluation standard, and the passive vibration isolation and active-passive vibration isolation effects were obtained before and after the control was turned on. After the experiment was carried out for 2 s, the algorithm control was started. The obtained time-frequency domain control effect and input current amplitude are shown in Figures 18 and 19. The passive vibration isolation effect of the hybrid vibration isolation system is shown before the active control was turned on. From the time-domain diagram, it can be seen that the residual vibration was reduced by 25% compared to the primary vibration, and there  
Figure 18: Diagram of the effect of the active and passive control in the time–frequency domain: (a) time history before and after control; (b) frequency-response function before and after control.