A novel 3-DOF active vibration isolation method for TBM’s laser target

In the process of full-face tunnel boring machine (TBM) tunneling, pitch angle measurement accuracy of the laser target is greatly reduced by low frequency vibrations with large amplitude and multiple degrees of freedom. In order to improve pitch angle measurement accuracy of laser target under vibration, a three-degree-of-freedom (3-DOF) active vibration isolation system is designed in this paper. A plate-type voice coil motor with large air gap and large thrust is designed based on genetic algorithm. In order to increase damping of the vibration isolation system, an eddy current damper is designed by combining copper plate and permanent magnet of the voice coil motor. An active vibration isolation device for laser target was built by using the designed plate-type voice coil motor and eddy current damper, and the dynamic model of the system was established. Aiming at control and stability problems caused by the nonlinear factors, a High-Frequency sliding mode controller which can ensure system asymptotically stable is designed in this paper. A 1–30 Hz sinusoidal sweep excitation experiment was performed on a shaking table. The experimental results show that the active vibration isolation system has a good damping effect. The root mean square (RMS) of acceleration in Y direction can be attenuated by 90.5%, in Z direction can be attenuated by 95.8%. The active isolation system effectively attenuates the vibration transmitted to the laser target, and pitch angular fluctuation of the laser target is reduced by 75.8%. The designed active vibration isolation system improves the pitch angle measurement accuracy of the laser target.