Nonlinear robust control of tail-sitter aircrafts in flight mode transitions

© 2018 Elsevier Masson SAS In this paper, a nonlinear robust controller is proposed to deal with the flight mode transition control problem of tail-sitter aircrafts. During the mode transitions, the control problem is challenging due to the high nonlinearities and strong couplings. The tail-sitter aircraft model can be considered as a nominal part with uncertainties including nonlinear terms, parametric uncertainties, and external disturbances. The proposed controller consists of a nominal H∞controller and a nonlinear disturbance observer. The nominal H∞controller based on the nominal model is designed to achieve the desired trajectory tracking performance. The uncertainties are regarded as equivalent disturbances to restrain their influences by the nonlinear disturbance observer. Theoretical analysis and simulation results are given to show advantages of the proposed control method, compared with the standard H∞control approach

Effect of ROCK inhibition studied by single cell morphological statistics.

<p>(a),(b),(k)&(l) Histograms of frequency distribution of cell orientation for untreated cells on NFES gelatin patterns (NF-0), ROCK-inhibited cells on NFES gelatin patterns (NF-I(5 M)), untreated cells on PDMS (PDMS-0), and ROCK inhibited cells on PDMS (PDMS-I(5 M)). (c),(f),(g)&(j) The corresponding histograms of frequency distribution of cell perimeters. (d,e,h,i) The corresponding scatter plots of the cell perimeter <i>vs</i> cell orientation.</p

Dependence of cell morphology w.r.t. H1152 concentration.

<p>(a–d) Scatter plots of cell perimeter <i>vs.</i> orientation for ECs subject to no ROCK inhibition, and H1152 concentration at 2.5 M, 25 M, and 50 M respectively. (e–h) Scatter plots of cell perimeter <i>vs.</i> area for ECs subjected to the same treatment.</p

Versatile gelatin fibril patterns can be formed by near-field electrospinning over a large area.

<p>(a) Scheme of the NFES patterning process. (b) A 2 inch PDMS sheet containing arrays of gelatin patterns. (c)–(e) Confocal images of fibril patterns with bead-on-strings, coils, and uniform straight fibrils respectively. (f)–(h) Scanning electron micrographs showing typical regions of the fibril patterns illustrated in (c)–(e).</p

Physical and chemical properties of gelatin fibrils.

<p>(a) FTIR spectra of as-received gelatin powder (P), a cast gelatin film (F), the crosslinked gelatin film (Fx), NFES gelatin fibrils (NF), crosslinked NFES gelatin fibrils (NFx), and crosslinked gelatin films post cell culturing for 18 hrs (Fx(C18)). (b) AFM profiles of a crosslinked gelatin fibril before being immersed in water (left), and after being immersed in water for 24 hrs and dried (right). (c) Cross-sectional profile of the fibrils presented in (b). (d) In-situ AFM imaging of a hydrated gelatin fibril. (e) Young's modulus mapping of a central fibril region. (f) Histogram showing the range of Young's modulus values for the gelatin fibril and PDMS respectively.</p

Fibril assay elucidating the drug effectiveness of H1152.

<p>Plot of and <i>Orientation Deviation</i> w.r.t. H1152 concentration for the ECs interfaced with the gelatin fibril assay. Immunofluorescence images for the selected inhibition experiments are included as examples.</p

Solution properties controls global fibril morphology.

<p>Different solution properties are plotted against the total acid-acyl contents (A.A.E.A.) for (a) conductivity, (b) pH, and (c) surface tension. The approximate regimes of fibril morphology are highlighted in each graph. For (b) and (c), a pair of blue lines are drawn to enclose the range of conditions which resulted in the formation of straight fibers. It is to note that for G10-A70, the A.A.∶E.A. ratios of 1, 1.5 and 4 were tested, and this can be seen as the increase in conductivity in (a).</p