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Feedforward in manual control

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Daan Marinus Pool
added a research item
The human controller (HC) in manual control of a dynamical system often follows a visible and predictable reference path (target). The HC can adopt a control strategy combining closed-loop feedback and an open-loop feedforward response. The effects of the target signal waveform shape and the system dynamics on the human feedforward dynamics are still largely unknown, even for common, stable, vehicle-like dynamics. This paper studies the feedforward dynamics through computer model simulations and compares these to system identification results from human-in-the-loop experimental data. Two target waveform shapes are considered, constant velocity ramp segments and constant acceleration parabola segments. Furthermore, three representative vehicle-like system dynamics are considered: 1) a single integrator (SI); 2) a second-order system; and 3) a double integrator. The analyses show that the HC utilizes a combined feedforward/feedback control strategy for all dynamics with the parabola target, and for the SI and second-order system with the ramp target. The feedforward model parameters are, however, very different between the two target waveform shapes, illustrating the adaptability of the HC to task variables. Moreover, strong evidence of anticipatory control behavior in the HC is found for the parabola target signal. The HC anticipates the future course of the parabola target signal given extensive practice, reflected by negative feedforward time delay estimates.
Frank Drop
added 7 research items
The human in manual control of a dynamical system can use both feedback and feedforward control strategies and will select a strategy based on performance and required effort. Literature has shown that feedforward control is used during tracking tasks in response to predictable targets. The influence of an external disturbance signal on the utilization of a feedforward control strategy has never been investigated, however. We hypothesized that the human will use a combined feedforward and feedback control strategy whenever the predictable target signal is sufficiently strong, and a predominantly feedback strategy whenever the random disturbance signal is dominant. From the data of a human-in-the-loop experiment we conclude that feedforward control is used in all the considered experimental conditions, including those where the disturbance signal is dominant and feedforward control does not deliver a marked performance advantage.
Pure feedback and pure open-loop feedforward helicopter pilot models are currently applied for predicting the performance of pilot-helicopter systems. We argue that feedback models are likely to underestimate performance in many realistic helicopter maneuvers, whereas inverse simulation models, which have an open-loop feedforward structure, are likely to overestimate performance as they neglect typical human-in-the-loop characteristics. True verification of feedback and feedforward elements in helicopter pilot control behavior was never performed, however. This paper proposes a pilot model containing a feedback and feedforward controller acting simultaneously and presents a method to identify the hypothesized feedforward action from human-in-the-loop data collected in a simulator experiment. The results of the human-in-the-loop experiment show that actual human performance is better than predicted by a pure feedback model and worse than predicted by an (inverse dynamics) feedforward model. The identification results suggest that the human pilot indeed utilizes feedforward strategies, but it was not possible to either confirm or refute the model by means of the collected data and the developed analysis method. © 2013 by the American Helicopter Society International, Inc. All rights reserved.