A Method to Measure the Relationship Between Biodynamic Feedthrough and Neuromuscular Admittance

Abstract

Biodynamic feedthrough (BDFT) refers to a phenomenon where accelerations cause involuntary limb motions, which can result in unintentional control inputs that can substantially degrade manual control. It is known that humans can adapt the dynamics of their limbs by adjusting their neuromuscular settings, and it is likely that these adaptations have a large influence on BDFT. The goal of this paper is to present a method that can provide evidence for this hypothesis. Limb dynamics can be described by admittance, which is the causal dynamic relation between a force input and a position output. This paper presents a method to simultaneously measure BDFT and admittance in a motion-based simulator. The method was validated in an experiment. Admittance was measured by applying a force disturbance signal to the control device; BDFT was measured by applying a motion disturbance signal to the motion simulator. To allow distinguishing between the operator's responses to each disturbance signal, the perturbation signals were separated in the frequency domain. To show the impact of neuromuscular adaptation, subjects were asked to perform three different control tasks, each requiring a different setting of the neuromuscular system (NMS). Results show a dependence of BDFT on neuromuscular admittance: A change in neuromuscular admittance results in a change in BDFT dynamics. This dependence is highly relevant when studying BDFT. The data obtained with the proposed measuring method provide insight in how exactly the settings of the NMS influence the level of BDFT. This information can be used to gain fundamental knowledge on BDFT and also, for example, in the development of a canceling controller.

A practical biodynamic feedthrough model for helicopters

“…1 are shown for a much larger frequency range than used by Mayo, as the BDFT dynamics also show interesting features outside the 1-5 Hz frequency range [20]. The frequency range used by Mayo was limited and it is therefore likely that the model's quality will reduce outside this range.…”

“…Each task was trained before the experiment started. In earlier studies, it was shown that the neuromuscular admittance and BDFT strongly depend on these control tasks [21,20]. The three tasks combined with the three directions results in a 3x3 repeated-measures design, each condition was repeated 6 times.…”

“…The signals were separated in frequency to allow distinguishing the response due to each disturbance in the measured signals [31,20]. The frequency content of the disturbance signals was equal in all conditions, only the magnitude varied for each task.…”

“…The frequency content of the disturbance signals was equal in all conditions, only the magnitude varied for each task. The magnitude was varied in such a way that the standard deviation of the control device deflections was approximately similar in each condition to allow comparison across conditions [20]. To obtain a full bandwidth estimate of the admittance, a range between 0.05 Hz and 21.5 Hz was selected for the force disturbance signal F dist .…”

“…Once more, in many publications the possibility that BDFT dynamics may vary over time, as results of 'muscle activity' or 'control strategy', is mentioned, but generally not investigated in any detail. Recently, a method was developed to measure BDFT and neuromuscular admittance (a measure for limb dynamics) simultaneously [20]. Neuromuscular admittance, or simply admittance, is a measure for describing the limb dynamics of the subject's body and represents a dynamical relationship between force input and position output.…”