The force equalization of a hybrid actuation system combining one servo-hydraulic actuator and one electro-mechanical actuator operated in position control and in active/active mode is addressed for safety critical applications such as primary flight controls. In a first step, an accurate virtual test bench is built to facilitate the analysis of force fighting and the assessment of the performance and robustness of the proposed force equalization strategies. It is validated from real experiments performed for the aileron actuator of a single-aisle commercial aircraft. Static force equalization is achieved first by adding equalization offsets in the position control loops as a function of the integral of the force difference between actuators. In order to keep a high level of segregation, the authority for this action is limited to 4% of the total actuator stroke. The dynamic force equalization is performed by forcing the two actuators to follow the same path. Thus, a trajectory generator is introduced to output the required position, velocity and acceleration from the position set point with realistic reproduction of the actuator power limits. Feedforward actions are used to compensate the major and invariant effects such as servo-hydraulic actuators functional flow and electro-mechanical actuator inertial torque. In this way, the pursuit errors are significantly reduced without decreasing robustness. Then, the accurate virtual test bench is used to assess the robustness of the force equalization strategy by analyzing the sensitivity of performance indicators to parameters and operating conditions. It is shown that the proposed force equalization scheme meets all the requirements, including segregation, robustness and simplicity.

This paper deals with safety-critical, high-power actuation in aerospace applications. Using a system-level synthetic view, it identifies, explains and discusses the reasons why electrically supplied, or power-by-wire, solutions have not spread rapidly enough to become a generalized replacement of the conventional, hydraulically supplied ones. Once the actuation needs have been summarized, the drawbacks of conventional actuation and the merits of electrically supplied actuation are listed and analyzed. Then, the challenges to be met in order to mitigate the intrinsic disadvantages of power-by-wire are addressed in detail with a focus on the solutions under development or research. Numerous examples, numerical data and orders of magnitude are provided to support the discussion.

The influence of load and temperature on friction is addressed in a practical way to provide a step forward in simulation-based design through the development and the numerical implementation of realistic system-level models of frictional losses. Hydraulically and electrically supplied actuators are considered at both individual component level (e.g. gear pairs, nut–screws or bearings) and integrated equipment level (e.g. reducers or even complete actuators). The need for more realistic modelling of friction for embedded and more electrical systems is highlighted, and the influence of load and temperature is illustrated from measurements. The state of the art is reviewed considering knowledge models with special focus on physical effects and data commonly supplied by components’ manufacturers. Then, special attention is paid to global representation models developed as a parameterized combination of generic friction effects, and a generic framework for introducing load and temperature effects in system-level friction models is proposed. Candidate options for model structure, parameterization, numerical implementation and inverse simulation are discussed. The last part of this article supports the development of friction models from mechanical efficiency data, the parameter most widely handled by designers and suppliers, with special attention to aiding or opposite load and to sticking. Throughout this article, measured friction forces are extensively reported and compared with the proposed models.

The work reported here was aimed at improving the practical efficiency of the model-based development and integration of electromechanical actuators. Models are proposed to serve as preliminary design, virtual prototyping, and validation. The first part focuses on the early phases of a project in order to facilitate the identification of modelling needs and constraints, and to build a top-level electromechanical actuator model for preliminary studies and sub-specification. Detailed modelling and simulation are then addressed with a mixed view on the control, power capability, and thermal balance. Models for the power chain are firstly considered by focusing on the key practical issues in modelling the electric motor, power electronics, and mechanical power transmission. The same logic is applied to the signal and control chain with practical considerations concerning the parameters of the controller, its digital implementation, the sensors, and their signal conditioning. Numerous orders of magnitude are provided to justify the choices made and to facilitate decision-making for and through simulation activities.