The feel system is an extension of both the vehicle and neuromuscular systems

Abstract

In an aircraft with powered controls, a manual tracking task employs limb neuromuscular (NM) control of an inceptor, which can then provide input to a control system through an artificial feel system. Traditionally inceptors have been passive and hand-gripped, and the resulting inceptor-limb dynamics allowed the open-loop NM element to be represented as a self-contained second-order transfer function with a fixed damping ratio and natural frequency. However, active inceptors and gaming devices present themselves as candidate human-vehicle interfaces, and it is shown through elementary mechanical modeling how limb-inceptor interaction can influence the NM system. A physical example of this is provided. It is well-established that inceptor force feedback is an important NM cue to the pilot. An experiment using a passive joystick with and without spring restoring force investigated the effect of force feedback on tracking performance and NM response. The preliminary results suggest the role of NM equalization changes depending on whether force feedback is present, and that the presence or absence of force feedback influences the role of visual equalization. When it is available, force (rather than stick deflection) appears to be the signal employed to close the loop around the NM element. Neurophysiological research and this work’s observations suggest that muscle tension arising from limb co-contraction drives operator gain, which in turn governs crossover frequency. This muscle tension affects the mechanical NM response by changing the muscle stiffness and damping. This work proposes a NM model that first integrates both limb and inceptor dynamics, from which the open-loop NM system can then be isolated using the feel system dynamics and loop closure made with the force output. The location of the NM mode can have a key influence on the extent that an operator can generate frequency compensation, and the degree to which the Crossover Model is adhered to.