Design of an Open Source, Hard Real Time, Controls Implementation Platform for Active Magnetic Bearings

Suspension of an active magnetic bearing (AMB) system involves significant computational and monitoring effort. Modern AMB systems need 1) logically complex and computationally expensive controller algorithms and I/O; 2) real time data storage of plant information such as states, inputs, and outputs; 3) real time plotting capabilities (such as rotor displace- ment as a function of time, actuator forces as a function of time, and FFTs); 4) real time controller parameter updates; and 5) real time access to reference signals; and 6) remote monitoring for safety purposes. Control systems based upon embedded Digital Signal Processors (DSP) boards often require specialized programming and development tools, may lack flexibility when computational requirements change, are often financially expensive, and may not directly address the aforementioned needs. Even worse, newer and faster DSPs may not be fully pin compatible with their predecessors, thus requiring total redesign of the embedded electronics for a given project. A novel DSP-less controller implementation system - the Real Time Controls Laboratory (RTiC-Lab) - has been developed explicitly to address these problems. It uses the concept of Real Time Operating Systems to guarantee hard real time constraints. Its design is based on the use of both commodity personal computers and RT-Linux, a free and Open Source modification of Linux intended to support hard real-time computation. RTiC-Lab is also free and Open Source and is intended to serve as a communal effort among the controls engineers in both the controls and AMB community. Discussion is presented on the design of the software architecture, defining timing requirements of the control tasks, and measuring the predictability of RTiC-Lab. An example application is presented which uses RTiC-Lab in the controls implementation on a five degree of freedom AMB.