A time-delay limitation from the hydraulic Seliciclib CDK2 actuator further limits the achievable closed loop performance. Clearly, a drastic improvement in the overall system performance cannot be achieved solely by feedback control design. To eliminate or decrease the undesirable mechanical characteristics, the mechanical system needs to be redesigned. For example, by replacing the tires with tracks, the DOFs for the system reduce to one and the system becomes fully actuated. Alternatively, active suspensions can be added between the tires and the combine body to increase the number of actuators and therefore eliminate the underactuation in the system. Other possibilities include redesigning key parameters in the system, such as suspension elements, to improve the low natural frequency and lightly damped characteristics of the passive DOFs.

As can be seen, there are multiple ways to address the mechanical system problem. However, all of these must be considered in light of realistic Inhibitors,Modulators,Libraries cost and design constraints. As for the actuator delay problem arising from the electrohydraulic system, it may be Inhibitors,Modulators,Libraries possible to reduce or eliminate the delay with very high performance servo hydraulics. As with the mechanical redesign, these types of system changes would have to be performed under realistic cost and design constraints. High performance servo-actuators may not be appropriate for an all-weather all-terrain agricultural vehicle and may not meet market price points. The work presented here illustrates a practically relevant problem; the search for an optimal solution remains an open control engineering question.

Acknowledgment The authors appreciate the support of Deere & Company for this Inhibitors,Modulators,Libraries paper. Dustin Denault’s assistance for the experimental testing performed on the combine and the test stand was essential and greatly appreciated. Glossary Nomenclature a,b = the distance in x direction between front/rear Inhibitors,Modulators,Libraries wheel axis and gravity center of combine body (2m;1.3m)1 bf,br = the damping constant of front and rear tires (22,400kg/s; 26,300kg/s) h0 = the original height of the A point (1.2m) ��0 = the original value of angle �� (0.113m) Icom,Ih = the inertias of combine body and header with respect to the gravity center and point A separately (66,000kg m2; 22,000kg m2) lt1,lt2,lcgh = structural length (refer to Fig. Fig.3)3) (2.9m, 3m, 2m, 0.8m) lins,lh,lf = structural length (refer to Fig.

Fig.4)4) (4.6m, 1.7m) mcom,mh = the masses Inhibitors,Modulators,Libraries of the combine body and the header (15,000kg; 5000kg) kf,kr = the spring constant of front and rear tires (1,303,720N/m; 1,673,600N/m) khydr = coefficient from valve current to the velocity of the cylinder (0.032m/s/A) ��h,��cgh = structural angle (refer to Fig. Fig.3)3) (0.3rad, 0.1rad) ?t1,?t2 = structural Cilengitide angle (refer to Fig. Fig.4)4) (0.3rad, 0.