# A High-Precision Active Vibration Isolation Control System: Experimental Study
## 4 Experimental Study
### Experimental Results and Discussions
the rear edge of the top platform and 8 [mm] below its top surface. This disturbs the top platform motion in the \(x_{t}\)-, \(\theta_{zt}\)-, and \(\theta_{yt}\)-directions. The velocity of the \(x_{t}\)-direction motion of the top platform in the passive case needs 5 [s] to reach the zero steady state. The proposed controller only needs 0.5 [s], whereas the robust controller and the PD controller need approximately 0.6 [s] and 0.7 [s], respectively. The amplitude of the top platform motion is also smaller in the cases of AVISs. The peak velocity of the proposed AVIS is only 5 [mm/s] compared to 7 [mm/s], 12 [mm/s], and 13 [mm/s] of the robust control, the PD control, and the passive system, respectively. The resulting motions of the top platform in the other directions show a similar trend to those in the first experimental case. That is, the PD control system is the worst among the AVISs, in both terms of settling time and peak velocity. On the other hand, the proposed control system suppresses the vibration the most effectively. The control efforts show that the proposed controller reacts with the interactions within the system better than the robust controller, and the PD controller is the worst. In some cases, such as in the \(\dot{\theta}_{zt}\)- and \(\dot{\theta}_{xt}\)-direction, the PD controller has the most torque but still can not maintain a good vibration suppression performance. In summary, the experimental results in Figures 6 and 7 indicate that all considered controllers are efficient in isolating the vibration for the top platform of the system. They provide significantly better results in comparison to the passive system, i.e., the one without a controller. Moreover, the proposed robust decoupling controller proves to be superior to the other controllers, not only in the direction of the disturbance vibrations but also in all other directions. That is, the proposed system attains the best performance in terms of vibration isolation and mutual interference compensation. The results from the two other experimental cases are shown in Figures 8 and 9. In these cases, a device weighing 2.8 [kg] is mounted on the top platform, thus acting as a payload. The impact forces depicted in Figure 5 and the points of impact are as same as in the first two experiments. One can easily see that, for the passive system, the peak velocities are much smaller, and the settling times are much longer than those in the first two experiments, even though the impact forces are roughly the same in all situations. This is due to the payload leading to the increment of the total mass of the oscillating system, resulting in a smaller amplitude and lower natural frequency. The control performances show a similar trend to the cases without a payload. That is, the PD-controlled system is the worst, then the robust control without the feedforward compensators, and the proposed controlled system is the most effective one. Especially, the performance of the PD-based AVIS becomes significantly worse in the loaded cases compared with the unloaded cases. For example, in the third experiment, the passive system needs 6.5 [s] to settle the vertical vibration. The proposed controller only needs 0.9 [s], whereas the robust controller and the PD controller need approximately 1.4 [s] and 1.6 [s]. The amplitude of the motion in the PD-controlled system is initially smaller than in the passive one, then increases and remains at a notable width before completely settling at 1.6 [s]. Figure 7: Experimental results in case 2: (**a**) velocities at the center of the top platform; (**b**) control efforts. Figure 8: Experimental results in case 3: (**a**) velocities at the center of the top platform; (**b**) control efforts. The worsened performance indicates that the PD-controlled system is easily affected by uncertainties, i.e., the payload in this case. The robust control system and the proposed  
Figure 9: Experimental results in case 4: (**a**) velocities at the center of the top platform; (**b**) control efforts.