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                              motor or a hydraulic cylinder using a servo valve. The actuator output shaft drives a linkage
                              connected to the moveable control surface. The nominal hydraulic supply line pressure
                              in commercial airplanes today is in the range of 3000–5000 psi. In order to increase the
                              hydraulic power density (hydraulic power delivered/mass of the hydraulic components),
                              the future operating pressures are expected to get higher.
                                   The current trend in the aerospace industry is towards the so-called “more-electric
                              aircraft” (or ultimately, the “all-electric aircraft“). As this name suggests, it is desired to
                              replace hydraulic powered systems by electrically powered ones. Historically, flight control
                              systems have evolved through four different stages (Figure 1.28) in terms of the way the
                              aerodynamic surfaces are controlled and powered,

                                1. mechanically control signaled (via mechanical linkages and cables), hydraulically
                                   powered flight control systems of the past (Figure 1.28a),
                                2. pilot-hydraulically control signaled, hydraulically powered flight control systems of
                                   the past (Figure 1.28b),
                                3. electrically control signaled, hydraulically powered flight control systems of the
                                   present (Figure 1.28c),
                                4. electrically (or optically) control signaled, electrically powered flight control systems
                                   of the future (Figure 1.28d).
                              In the so called hydro-mechanical control systems (Figure 1.28b), there are no electronic
                              components. All of the control decisions and sensing are accomplished via mechanical and
                              hydraulic means (Figure 1.6).
                                   The main reasons for the push for more electric aircraft lies in:
                                1. easier installation and maintainability of electric wiring compared to hydraulic piping,
                                2. improved efficiency of power usage (at generation, transmission, and actuation stages)
                                   due to on-going improvement in electric motor and power electronics technology.


                       1.3 EMBEDDED CONTROL SOFTWARE DEVELOPMENT
                             FOR MECHATRONIC SYSTEMS


                              The trend in industrial practice is that the embedded control software development part of
                              modern mechatronics engineering is done involving three phases (Figures 1.29, 1.30, 1.31):
                                  Phase 1: Control software development and simulation in non-real-time environment.

                                    Phase 2: Hardware in-the-loop (HIL) simulation and testing in real-time environment.
                                  Phase 3: Testing and validation on actual machine.

                                   In phase 1, the control software is developed by using graphical software tools,
                              such as Simulink ®  and Stateflow, simulated and analyzed on a non-real-time computer
                              environment (Figure 1.29). The “plant model,” which is the computer model of the machine
                              to be controlled, is a non-real-time detailed dynamic model. Simulations and analysis are
                              done in this non-real-time environment.
                                   In phase 2, the “same control software” is tested on a target embedded control mod-
                              ule (ECM). That “same control software” is a C-code which is auto-generated from the
                                                       ®
                              graphical diagrams of Simulink and Stateflow using auto-code generation tools such as
                                     ®
                                                                       ®
                              Simulink Coder, Embedded Coder, and MATLAB Coder. That real-time controller soft-
                              ware is run on the target embedded controller module (ECM) hardware in real-time, which
                              can be connected to another computer which simulates the controlled process dynamics
                              in real-time. This case is called the hardware in-the-loop (HIL) simulation (Figure 1.30).
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