Cassoni, G.

Marchesoli, D.

Masarati, P.

Talamo, C.

Zanoni, A.

English

Archivio istituzionale della ricerca - Politecnico di Milano

ECCOMAS Thematic Conference on Multibody DynamicsJuly 24 - 28, 2023, Lisbon, PortugalMultibody analysis of helicopter pilot biomechanics for real-time end point impedance estimationAndrea Zanoni1, Davide Marchesoli1, Carmen Talamo1, Gianni Cassoni1, Pierangelo Masarati11 Department of Aerospace Science and TechnologyPolitecnico di Milanovia La Masa 34, 20156, Milano, Italyandrea.zanoni@polimi.itEXTENDED ABSTRACT1 Introduction and motivationThe design of aircraft human-machine interface has received increasing attention in the last several years, both regarding thedevelopment of innovative control systems [1] and the extended analysis of established layouts [2]. The latter is focused onassessing the control system performance and its robustness in allowing the pilots to safely accomplish operative targets. Animportant aspect, to this end, is the robustness of the control system design with respect to rotorcraft-pilot couplings (RPC), i.e.to potentially adverse dynamic couplings between the pilot and the vehicle [3]. When the pilots biomechanics interacts withthe helicopter dynamics in a frequency range outside of the bandwidth of voluntary control action - typically identified in the[0−1] Hz range - the interaction takes the name of Pilot-Assisted Oscillation (PAO).The principal indicator of the potential interaction between the pilot and the vehicle is the Bio-Dynamic Feed-Through, or BDFT,which is the frequency domain relationship between the involuntary control inceptor deflection δ and the vehicle acceleration a,typically measured at the seat reference point. The most common shape of the BDFT is that of a second-order filter:HBDFT(s) =δ (s)a(s)=µs2 +2ξpωps+ω2p(1)where µ is the static gain, a function of pilot modal mass associated with the normal mode dominating the pilot-control leverinteraction, ξp and ωp its damping ratio and natural frequency.The shape of the BDFT makes it possible, in principle, to reduce its identification to the identification of three parameterscontributing to the pilot arms end-point impedance related to the control lever rotations: a mass mp, a damping coefficient cp anda stiffness coefficient kp, such that ξp = cp/2√mpkp and ωp =√kp/mp. The total impedance is not only a function of the pilot"static" bio-mechanical characteristics, but also to the instantaneous muscular activation, which in turn depends on numerousfactors, among which the most important can be regarded as the pilots workload in the specific task they are required to performand the operational environment [4, 5]. It is thus important to assess the robustness of the helicopter design to RPC consideringthe range of variation of the pilot BDFT.Estimating the pilot end-point impedance on line, possibly in real time, will enable to assess the BDFT immediate variation dueto the variation of exogenous parameters, like task demands, operational environment, flight control system mode switches, etc...This work is dedicated to the development of a virtual testing framework in which the development of algorithms for the realtime estimation of the pilot-helicopter BDFT.2 MethodsThe biomechanics of the pilot upper body, coupled with the dynamics of the control inceptors, is simulated using a multibodymodel of the human upper body [6], (Cf. Figure 1) developed in the open source multibody solver MBDyn. Simple trackingtasks, in which the virtual pilot is asked to maintain a constant inceptor reference position, are employed initially. Only thecollective control channel is analyzed, in this preliminary work.The basic test to calculate the BDFT consists in an open loop excitation of the pilot in the vertical axis, the most relevant forthe collective channel. A sufficient number of tests is performed changing the parameters governing the muscular activation,whereas the pilot biometric parameters are kept constant . Parameters controlling the muscular activation are changed in order torepresent either more relaxed tasks or more challenging tasks, requiring a higher precision and effort.As per real pilots, stricter demands results in an increase of the aggressiveness towards the control inceptors as well as morefrequent inputs injected by the pilot. These two effects reflect in an increased muscular activation and consequently in a variationof pilot mechanical impedance and pilot exerted force on the inceptor. Thus, a quantity related to force spectrum and derivativenorm together with the impedance are used to estimate the total workload of the pilot. Given the impossibility to get a subjectiveworkload evaluation from the pilot, the total workload is estimated only from objective physical quantities.The task assigned to the virtual pilot is a pure Point Tracking, representative of an attitude tracking task while subjected toexternal disturbances. In these type of tasks, the difficulty is strongly related to the precision demands and to the total amountof underwent vibration in the [1.5−7]Hz range [7]. To validate the results, the new indices are compared to the Gray’s 2D PilotInceptor Workload [8], an quantitative index estimating the pilot workload from the inceptor time history.Figure 1: The multibody model of the human upper body.3 Expected resultsA identification algorithm able to produce robust estimates of the end-point stiffness as a function of the objective workloadmeasures is sought, with its structure currently under development.The identification algorithm will then be tested for its real-time performance by feeding it with time histories coming from simu-lations in which both the pilot biometric parameters and muscular activation are varied, simulating a context-switching from morerelaxed tasks to more challenging ones, and vice versa. Comparison between the results obtained by the identification algorithmand the reference BDFT data will provide for a initial validation of the methods.At future stages, the comparison between the numerical simulations and experimental tests, performed on a dedicated testfacility[9] is envisioned.References[1] von Grünhagen, W., Müllhäuser, M., Abildgaard, M., and Lantzsch, R., “Active Inceptors in FHS for Pilot Assistance Systems,” 36thEuropean Rotorcraft Forum, September 7–9 2010.[2] Klyde, D., Liang, C.-Y., Alvarez, D., Richards, N., Adams, R., and Cogan, B., “Mitigating Unfavorable Pilot Interactions with AdaptiveControllers in the Presence of Failures/Damage,” AIAA Atmospheric Flight Mechanics Conference, August 2011.doi: 10.2514/6.2011-6538[3] Pavel, M. D., Jump, M., Dang-Vu, B., Masarati, P., Gennaretti, M., Ionita, A., Zaichik, L., Smaili, H., Quaranta, G., Yilmaz, D., Jones, M.,Serafini, J., and Malecki, J., “Adverse rotorcraft pilot couplings — Past, present and future challenges,” Progress in Aerospace Sciences,Vol. 62, doi:10.1016/j.paerosci.2013.04.003, October 2013, pp. 1–51.[4] Venrooij, J., Abbink, D. A., Mulder, M., van Paassen, M. M., and Mulder, M., “Biodynamic feedthrough is task dependent,” 2010 IEEEInternational Conference on Systems Man and Cybernetics (SMC), doi:10.1109/ICSMC.2010.5641915, October 10–13 2010.[5] Zanoni, A., Zago, M., Paolini, R., Quaranta, G., Galli, E., and Masarati, P., “On task-dependence of helicopter pilot biodynamic feedthroughand neuromuscular admittance. An experimental and numerical study,” IEEE Transactions on Human-Machine Systems, Vol. 51, (5),doi:10.1109/THMS.2020.3044971, 2021, pp. 421–431.[6] Zanoni, A., Cocco, A., and Masarati, P., “Multibody dynamics analysis of the human upper body for rotorcraft–pilot interaction,” NonlinearDynamics, Vol. 102, (3), doi:10.1007/s11071-020-06005-7, 2020, pp. 1517–1539.[7] Niewind, I., “Investigations on boundary avoidance tracking and pilot inceptor workload,” CEAS Aeronautical Journal, Vol. 2, (1-4),December 2011, pp. 147–156.doi: 10.1007/s13272-011-0037-1[8] Gray, W., “A Generalized Handling Qualities Flight Test Technique Utilizing Boundary Avoidance Tracking,” 2008 U.S. Air Force T&EDays, February 2008.doi: 10.2514/6.2008-1648[9] Zanoni, A., Cocco, A., Marchesoli, D., Talamo, C., Masarati, P., Colombo, F., Kemp, S., and Fosco, E., “Pilot Biomechanics for theDefinition of a Rotorcraft-Pilot Interaction Experiment,” 78th Vertical Flight Society Annual Forum and Technology Display, FORUM2022, May 2022.

Multibody Analysis of Helicopter Pilot Biomechanics for Real-Time End Point Impedance Estimation

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Multibody Analysis of Helicopter Pilot Biomechanics for Real-Time End Point Impedance Estimation

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