3.3. Results and discussions
To demonstrate the effectiveness of the proposed
method, several numerical simulations are performed
and the input torques, obtained in Figure 7 as the control
input, are employed. Figure 8 shows the comparison
among the unshaped, ZVD shaped, and optimal
multi-input shaped responses for the pitch and roll
angles.
When !o ¼ !p
o ¼ !d, as indicated by the curves in
Figure 8(a), both the ZVD and optimal shapers yield
lower residual vibration levels than the unshaped
response in the pitch direction. Further, the optimal
shapers with improved settling time result in a better
performance than the ZVD shapers. Figure 8(b) indicates
that the ZVD shapers and optimal shapers do not
give rise to significant vibration in the roll direction. It
is because of this insignificant impact that the vibration
frequency in the pitch direction only is necessary to
design shapers in Subsection 3.2.
Approaches to develop robust shapers loosely fall
into four categories: derivative methods, tolerable
vibration limit methods, ad hoc methods and numerical
optimization methods. In this paper, the numerical
optimization is used to improve the robustness.
Next, in order to examine the robustness, the design
frequency is fixed as !d ¼ 15:49 rad/s, and change the
operating frequency !o through changing the relative
height of CG.
Figure 9 shows the vibratory responses with the
frequency !o ¼ 0:78!d ¼ 12:08 rad/s and !o ¼ 1:34!d
¼ 20:76 rad/s. To allow comparison, the performance
of the unshaped command is superimposed on the
curves. From Figure 9(a) it is observed that the optimal
input shapers with the improved robustness give a
better performance than the ZVD shapers when
!o ¼ 0:78!d. This advantage results from the considerations
of robustness with respect to frequency in the
cost function. However, when the operating frequency
!o2= ½ 0:75!d, 1:25!d , as shown in Figure 9(b), th
3.3. Results and discussionsTo demonstrate the effectiveness of the proposedmethod, several numerical simulations are performedand the input torques, obtained in Figure 7 as the controlinput, are employed. Figure 8 shows the comparisonamong the unshaped, ZVD shaped, and optimalmulti-input shaped responses for the pitch and rollangles.When !o ¼ !po ¼ !d, as indicated by the curves inFigure 8(a), both the ZVD and optimal shapers yieldlower residual vibration levels than the unshapedresponse in the pitch direction. Further, the optimalshapers with improved settling time result in a betterperformance than the ZVD shapers. Figure 8(b) indicatesthat the ZVD shapers and optimal shapers do notgive rise to significant vibration in the roll direction. Itis because of this insignificant impact that the vibrationfrequency in the pitch direction only is necessary todesign shapers in Subsection 3.2.Approaches to develop robust shapers loosely fallinto four categories: derivative methods, tolerablevibration limit methods, ad hoc methods and numericaloptimization methods. In this paper, the numericaloptimization is used to improve the robustness.Next, in order to examine the robustness, the designfrequency is fixed as !d ¼ 15:49 rad/s, and change theoperating frequency !o through changing the relativeheight of CG.Figure 9 shows the vibratory responses with thefrequency !o ¼ 0:78!d ¼ 12:08 rad/s and !o ¼ 1:34!d¼ 20:76 rad/s. To allow comparison, the performanceof the unshaped command is superimposed on thecurves. From Figure 9(a) it is observed that the optimalinput shapers with the improved robustness give abetter performance than the ZVD shapers when!o ¼ 0:78!d. This advantage results from the considerationsof robustness with respect to frequency in thecost function. However, when the operating frequency!o2= ½ 0:75!d, 1:25!d , as shown in Figure 9(b), th
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