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0.1 sec and 10 sec. The low-frequency poles shown in figure A1 are those determined in a later study by Jones et al., who assumed that the torsional pendulum dynamics developed a sensation of angular velocity (ref. 33). The dynamical differences among axes do not have a satisfying physical explanation and may lie at the behavioral level as suggested by Zacharias (ref. 31). The delay from the central nervous system was included by Levison et al. (ref. 35) for the yaw axis and was carried over to the other axes. The thresholds shown are based on a summary given by Zacharias (ref. 31). Differences among individuals have been noted in both the dynamics and the thresholds, and it is known that the thresholds can vary up to an order of magnitude, depending on whether a subject has to perform a task (such as flying a simulator) (ref. 36). While the semicircular canals act as effective rate gyros, the utricles in the inner ear act as effective linear accelerometers. Peters (ref. 28) provides a block diagram of the sensing path for the utricles, which is shown in figure A2. The transfer function was developed by Meiry (ref. 22) with a subject experiencing longitudinal motion only. No dynamic data have been determined in the vertical or lateral axes. The dynamics of the utricles act as a bandpass filter between 0.1 and 1.5 rad/sec. The cutoff frequency of 1.5 rad/sec suggests that high-frequency accelerations must be sensed by the tactile mechanisms in the body and not by the vestibular system. A wide variance exists in the literature for the translational specific force sensing threshold, which is dmin in figure A2. Peters reviewed thresholds from seven sources and found that they ranged from 0.002 and 0.023 g’s (ref. 28). In addition to these vestibular models, nonvestibular motion sensing plays a prominent role in motion perception. Gum states that “For man in flight the component of the vestibular apparatus, semicircular canals and otolith, do not seem to be very reliable or useful force- and motion-sensing mechanisms” (ref. 30). He summarizes nonvestibular models, with a model of the control of lateral head motion shown in figure A3. Here, the head is essentially an inverted pendulum with respect to the pilot’s body that is strapped into a moving cockpit. Taps of the physiological feedback system that regulates the head position serve as an effective motion cueing source. The closed-loop dynamics of the head-control model have a real-axis pole at 3 rad/sec with the rest of the poles at frequencies higher than 10 rad/sec. Thus, the bandwidth of the head-positioning control is twice that of the vestibular system. The final sensing model covers body pressure sensing; very few quantitative data are available to describe its dynamic response. The body-pressure model shown in figure A4 is from Gum (ref. 30); it has a natural frequency of 34 rad/sec. This bandwidth would make the body’s pressure response dynamics the highest of all of its motion-sensing capabilities. The 1-sec time-constant high-pass filter in the model is due to the adaptation effect wherein the receptors in the skin lose their sensitivity to sustained acceleration. 直升机网 www.helicopter.cn 直升机翻译 www.aviation.cn 本文链接地址：Helicopter Flight Simulation Motion Platform Requirements(60) |
