Three Degrees of Freedom Active Control of Pneumatic Vibration Isolation Table by Pneumatic and Time Delay Control Technique

Based on previous feasibility study on one degree of freedom (1DOF) pneumatic active control of pneumatic springs, this paper presents procedures and results of a more realistic 3DOF active control of a pneumatic vibration isolation table. The 3DOF motion of the pneumatic table, consisting of heaving, rolling, and pitching, is controlled directly by adjusting air pressure in four pneumatic cylinders in a dynamic manner with pneumatic valves, without any external actuator such as an electromagnet or voice coil. The time delay control, which is a software chosen in this study, together with the hardware, i.e., the pneumatic actuator, is shown to be very powerful in enhancing the performance of vibration isolation for ground excitation as well as in settling time reduction for payload excitation through simulations and measurements on the 3DOF motion control system. New key results found in the experimental approach are that the pneumatic actuator shows a dynamic behavior of a second-order system, instead of a first-order system, which has been used in existing literatures so far, and that just feed-forward control of the pneumatic actuator by the second-order model can compensate for the inherently slow response characteristics of the pneumatic actuator very successfully. Effectiveness of the proposed active pneumatic control technique in the multi-input and multi-output system is shown via singular value decomposition analysis on the transmissibility matrix. Promising future of the proposed control and performance analysis technique is further discussed based on the results in the case of payload excitations as well.