Fundamental design concepts in multi-lane smart electromechanical actuators

Abstract

The most fundamental concept in designing multi-lane smart electromechanical actuation systems, besides meeting performance requirements, is the realization of high integrity. The essential requirements for realizing high integrity (and in any safety-critical system) are hardware redundancy and intelligent monitoring. To correctly detect, identify, isolate and replace redundant components, an intelligent fault detection and fault isolation scheme is required. The effectiveness of any fault detection and fault isolation system is assessed by examining promptness of detection, sensitivity, missed fault detection, the rate of false alarms, and incorrect fault identification. These terms are very much dependent on the threshold values of the monitoring devices imbedded in the system.The main aim of this paper is to provide fundamental consolidation designs and monitoring schemes in different architectures. It will address single-type and two-type summing architectures and highlight feedback sensor integration and monitoring strategies in the former, and explore the suitability of different threshold setting methodologies such as a simulation-graphical based Monte Carlo method, decision theory and analysis of variance. The paper will also address other fundamentals that are essential at the design stage, such as control surface load estimation, force fight (between mismatch lanes) reduction through lane equalization, and threshold setting concepts (scheduled and unscheduled) in a multi-mode operation system. The analysis is based on a four-lane actuation system capable of driving aerodynamic and inertial loads (with two lanes failed) of an aileron control surface similar to that of the Sea Harrier.

Introduction

“…To implement an anti-jamming function, the mechanical transmission must be disconnected from the external load, but for many aircraft applications, it is not acceptable to have a free-wheeling load motion. For this reason, redundant sections have to be designed and integrated to obtain a jamming-free EMA, which, after the failure, keeps partial or full operability [12,25,41,59].…”

“…The redundancy can be implemented either at actuator level by using nonredundant actuators (simplex EMAs) working in parallel, or at subsystem level with EMAs including redundant components (fault-tolerant EMAs) [12,15,16,23]. In any case, EMAs for flight controls must implement a fail-safe capability.…”

Hardware versus lumped cross-monitoring in smart multilane torque-summed electromechanical actuators

“…In this paper a single-type torque-summing architecture will be considered (Fig. 1), where the output torque is the algebraic sum of the individual lane torques [14]. Such configuration has the advantage of eliminating the problem of lane gradual speed runaway, but it has the possible disadvantage of a force fight between mismatched lanes.…”

Technology transfer of aircraft actuation to marine and propulsion

“…Detailed description may be found in (Annaz, 2005), however, here are some of the main key points that should be taken into account: In both architectures, logic ensures that failures in any of the feedback sensors would result in their isolation and feedback signals in the control system will always have the average value of the remaining active sensors.…”