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Six degrees of freedom

Electro-pneumatic vibration isolation

The Active Isolation System (AIS) from Bilz (Germany) consists of a PLC, a CAN network, 16-bit controllers, electro-pneumatic servo-valves, and the company’s Bi-Air air springs and/or HAB horizontal air springs.

The isolation system features a CAN network (Photo: Bilz)

THE SYSTEM WORKS FROM WITH A MINIMUM OF THREE DEGREES OF FREEDOM to six degrees of freedom. A range of sizes is available for both the vertical and horizontal air springs. One 16-bit controller and one electro-pneumatic servo-valve are used for each air spring or group of air springs. The 16-bit controllers can be mounted directly to the air-spring itself or to the machine, in the same direction as the isolator motion. Located inside each controller is a microprocessor, a position sensor with a resolution of 0,2 μm, an acceleration sensor with a resolution of 8 μg, and an air-pressure sensor with a resolution of 0,2 mbar. The signals from each of these sensors are sampled at the rate of 4 kHz.

Since each controller has a microprocessor along with a pneumatic servo valve, no feed forward signal is required. The 16 bit-controllers are connected to the PLC via a CAN network. The PLC can be connected to a PC by the standard EIA-232 for initial set-up and diagnosis. The primary function of the PLC is to manage and watch over the 16-bit controllers. In addition, the PLC has digital inputs and outputs, for example: ready, motion complete, inspection of position, pressure and power supply, or emergency stop.

The PLC also provides the ability to switch from scanning mode to loading mode using a digital I/O. The PLC takes care of downloading all necessary parameters to each 16 bit-controller to achieve the two different modes. The advantage of providing two different modes is that the performance of the system can be optimized for each mode. For example, during the scanning mode when the machine is performing sensitive operations the system should be soft and not be too rough, otherwise forces which are created by the isolation system can affect the machine performance.

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