FixedtimeSteuerung

FixedtimeSteuerung, literally fixed-time control, is a concept in automation and digital control where the controller and related processing tasks run at a predetermined, regular interval. It is commonly used in embedded systems, programmable logic controllers (PLCs), and real-time control platforms that rely on cyclic scheduling to guarantee deterministic timing.

In practice, a fixed-time controller operates with a fixed sampling period, often denoted as T. At each tick, the latest sensor data is read, the control law is computed using a discrete-time model of the plant (for example, a discretized PID or state-space controller), and an actuator command is issued. This periodic execution makes timing predictable, simplifies integration with digital networks, and supports straightforward timing analysis in many industrial environments.

Key design considerations include choosing an appropriate sampling period that balances control bandwidth with processor load, ensuring proper discretization of the continuous-time controller, and accounting for communication and actuator delays. Stability and performance must be assessed in the discrete domain, taking into account quantization effects, dead-time, and potential jitter from the task scheduler.

Benefits of fixed-time control include deterministic behavior, repeatable performance, and compatibility with cyclic tasking in PLCs and microcontrollers. Challenges involve aliasing and reduced control bandwidth if the period is too long, hardware and software overhead, and the need to guarantee that all periodic tasks meet their deadlines in a multi-task system.

Applications span industrial automation, process control, robotics, automotive and aerospace controllers, and any setting where reliable, periodic digital control is required. The term is sometimes used interchangeably with fixed-sample-time control in German-language literature.