Active control of precise vibration isolation table using two degrees of freedom controller

精密仪器，如电子显微镜和目前感兴趣的微型机器必须安装在精密隔振台上，通常由空气弹簧组成。表必须同时具有吸振和快速准确定位的功能。吸收需要软弹簧，定位需要硬弹簧。为了应对这种相互矛盾的要求，传统的被动隔离系统是不够的，应该主动控制。考虑振动吸收作为干扰抑制和定位作为对期望输入的跟踪，二自由度控制的概念可能有效地协调这两种要求。此外，由于工作台是一个多自由度的运动机构，在控制中出现了各个自由度之间的耦合问题。将耦合力作为扰动的一种，由于扰动抑制函数而产生的解耦是可以预期的。研究了气动隔振台两自由度控制器的有效性，并提出了一种设计方法。将其控制性能与PI控制器的控制性能进行了比较，验证了二自由度控制对气动隔振台的有效性。

Precise instruments such as an electron microscope and a micro machine currently interested have to be installed on a precision vibration isolation table generally comprising air springs. The table must provide with functions of both the vibration absorption and the fast and accurate positioning. The absorption requires the soft spring, the positioning does the hard one. To cope with such a mutually contradictory requirements, a conventional passive isolation system is not sufficient, which should be actively controlled.Considering the vibration absorption as a disturbance suppression and the positioning as a tracking to desired inputs, the concept of a two degrees of freedom control may be effective to reconcile both requirements. Further, as the table is a motion mechanism with multi-degrees of freedom, some problems of coupling among each degree of freedom appear in the control. Regarding coupling forces as a kind of disturbance, the decoupling owing to the disturbance suppression function may be expected. This study investigates the availability of two degrees of freedom controller to a pneumatic vibration isolation table, also of which a design approach is proposed. Comparing its control performance with that obtained from PI controller, the effectiveness of the two degrees of freedom control to the pneumatic vibration isolation table is assured.