The Impact of Deadline Misses on the Control Performance of High-End Motion Control Systems

Abstract

Abstract-In high-end motion control systems the real-time computational platform must execute tasks from multiple control loops operating at high sampling rates. In recent years traditional special-purpose platforms have been replaced by generalpurpose multi-processor platforms, which introduce significant fluctuations in execution times. While considering worst-case execution times would severely reduce the sampling rates, accepting deadline misses and assuring that the control system still meets the desired specifications is challenging. In this paper, we provide a framework to model and assert the impact of deadline misses in a real-time control loop. We consider stochastic models for deadline misses and characterize the mean and the variance of closed-loop output variables based on a time-domain analysis. We illustrate the usefulness of our framework in the control of a benchmark motion control experimental setup and in the control of a wafer stage in a lithographic machine.

Minimization of Network Induced Jitter Impact on FPGA-Based Control Systems for Power Electronics through Forward Error Correction

“…The added delay for the Hamming coding is even lower, and at only 200 ns its impact is low enough for this technique to be directly applicable to most power electronics control architectures. For systems with particular requirements in terms of extremely wide control bandwidth or minimal latencies, further techniques for the characterization and compensation of the network latencies are available from modern control theory [28]. However, it is worth noting that by comparing these results with others achieved by similar works [16], the measured latency, even in the case of the RS code, was significantly lower.…”

“…However, the specific typology and magnitude of these effects is highly dependent on the specific control methodology and the parameters of the controlled system. In [28,29], a much more in-depth analysis of these phenomenons in two specific real world scenarios is presented. For these reasons, it is not possible to specify a typical or maximum allowed network latency, that can generally be valid for large classes of applications.…”

Comparing Platform-aware Control Design Flows for Composable and Predictable TDM-based Execution Platforms

“…The mechanical setup is composed of two masses connected to each other by a flexible bar. The motor is connected directly to one of the masses, and two encoders measure the rotation in each mass [Geelen et al 2016]. The electrical circuit converts the digital actuation signal to an analog input that is applied to the plant.…”

“…The mechanical and electrical circuits are described with the CT LTI model from Equation 1, where the state of the plant x(t) = θ 1 θ 2 ω 1 ω 2 ′ is composed of angular positions (θ 1 , θ 2 ), angular velocities (ω 1 , ω 2 ), and the state and input matrices are defined by (adapted from the model presented in [Geelen et al 2016])…”

Weakly-hard Real-time Guarantees for Earliest Deadline First Scheduling of Independent Tasks

“…However, many practical embedded real-time systems can de facto sustain a bounded number of deadline-misses. In control engineering, which is the natural application domain of real-time computing, papers have been published [10,16,32,41] showing that it is sometimes possible to guarantee the performance of a control system despite some missed deadlines. Such systems are called weakly-hard real-time systems [4].…”