Classifying Facial Expressions Based on Topo-Feature Representation
Xiaozhou Wei, Johnny Loi, Lijun Yi · 2008
Nowadays, control design of Unmanned Aerial Vehicles (UAVs) has emerged as an attractive research area, due to the wide range of UAV applications in various military and civilian areas such as terrain and utility inspections, coordinated surveillance, search and rescue missions, disaster monitoring, rapid emergency response, aerial mapping, traffic monitoring, and reconnaissance missions (see, e.g., (Metni et al., 2007), (Kuroki et al., 2010 ), (Campbell & Campbell, 2010 )).They can also be used as complex test-bed dynamic systems for implementation and verification of the control schemes for different research purposes (Kim & Sukkarieh, 2007), (Saripalli et al., 2003), (Bortoff, 1999).Several research groups are involved in the modeling and control of UAVs (Bortoff, 1999), (Gavrilets et al., 2000), (Cai et al., 2006).The control methods such as the neural network approach (Enns & Si, 2003), the differential geometry method (Isidori et al., 2003), feedback control with decoupling approach (Peng et al., 2009), and the model predictive approach (Shim et al., 2003) have been applied for the flight control of the UAV helicopters.In this chapter, however, we have used an analytical approach to design and analyze the whole system including the inner-loop and the outer-loop controllers for a small-scale UAV helicopter.Here, in the proposed hierarchical structure, the inner-loop is responsible for the internal stabilization of the UAV in the hovering state and control of the linear velocities and heading angle angular velocity whereas the outer-loop is used to drive the system, which is already stabilized by the inner-loop, to follow a desired path while keeping the system close to the hovering state.This hierarchical strategy is an intuitive way of controlling such a complex system.However, there is another reason that compels us to employ such a control structure.Indeed, the UAV model cannot be fully linearized, since, in practice, we cannot expect the heading angle of the UAV to be restricted to a small range of variation as depending on the mission, the heading of the UAV could be in any direction.This will impose some kind of nonlinearity on the system, which can be modeled by a simple transformation.To handle this semi-linearized model of the UAV, we can separate the linear and nonlinear parts, and then control the linear part in the inner-loop and the nonlinear part in the outer-loop.In this hierarchy, for the inner-loop, we have used an H ∞ controller to both stabilize the system and suboptimally achieve the desired performance of the UAV attitude control.Assuming that the inner-loop has already been stabilized by an H ∞ controller, a proportional feedback controller combined with a nonlinear compensator block have been used in the outer-loop to bring the UAV into the desired position with desired heading angle.