Umfassende Abwägungsverfahren im Vorfeld komplexer Investitionsvorhaben

Umfassende Abwägungsverfahren, wie sie bei erweiterten Umweltverträglichkeitsprüfungen auf der Basis des EG-Richtlinien-Entwurfs unumgänglich werden, haben sich mit einer Mehrzahl von Problembereichen auseinanderzusetzen: Argumentations- und Akzeptanz- sowie Darstellungs- und Verständigungsproblemen, aufgrund der Vielzahl heterogener, kaum vergleichbarer quantitativ und/oder qualitativ erfaßter Indikatoren und deren unterschiedlichen Bewertungsmaßstäben, Prognose- und Zielbestimmungsproblemen, aufgrund der indikatorenspezifisch unterschiedlichen Einschätzung möglicher Verlaufsentwicklungen bei gleichzeitig differierenden zeitlichen und räumlichen Bezugsdimensionen, sowie dem unvermittelten Nebeneinander von generellen bzw. regions-/problemspezifischen Zielsetzungen

Spall Fault Quantification Method for Flight Control Electromechanical Actuator

Flight control electro-mechanical actuators (EMAs) are among the primary onboard systems that significantly influence the reliability and safety of unmanned aerial vehicles. Recent reliability studies have shown that the ball-screw element of a flight control EMA is subject to oscillating operating conditions that may initiate rapid degradation, such as fatigue spall defects. Accordingly, detecting and quantifying such faults are crucial for developing efficient fault prognostic and remaining useful life estimation capabilities. In this study, a vibration-based fault quantification method is developed to quantify the fatigue faults of a ball-screw mechanism of an EMA. The method is based on identifying the ball passing instants through a localized surface defect on the vibrational jerk rather than the vibrational acceleration measurement. The jerk is numerically determined from conventional accelerometers using a Savitzky–Golay differentiator. This method was successfully tested for ball bearings and it is adjusted in this paper for ball-screw faults. The experimental validation is investigated on a set of fault-seeded samples on NASA’s Ames Research Center Flyable Electro-Mechanical Actuator test stand

Towards a Reusable First Stage Demonstrator: CALLISTO - Technical Progresses & Challenges

In order to investigate the capabilities of a reusable launch system, JAXA, CNES and DLR have jointly initiated the project CALLISTO ("Cooperative Action Leading to Launcher Innovation for Stage Toss-back Operations"). The goal of this cooperation is to launch, recover and reuse a first stage demonstrator to increase the maturity of technologies necessary for future operational reusable launch vehicles (RLV) and to build up know-how on such vehicles under operational and developmental aspects. As the project has now turned into the detailed design phase, significant technical progresses have been made in definition, analysis and testing of systems and subsystems. The CALLISTO vehicle itself constitutes a subscale vertical take-off vertical landing (VTVL) stage with an overall length of 13.5 m and a take-off mass of less than 4 tons, which is propelled by a throttleable LOX/LH2 engine. It is capable to perform up to 10 consecutive flights during the planned flight campaign in French Guiana. Globally, the development effort on this system is equally shared between the three project partners. This paper presents the recent achievements in development of the key technologies for the reusable launch vehicle. While the design of critical subsystems has reached PDR level, detailed analyses and first breadboard tests have been performed successfully. These results are presented and discussed within the perimeter of the CALLISTO development roadmap. Possible technical challenges are indicated and their resolution methods are examined. Finally, the upcoming development steps are described which are foreseen to move forward to the qualification and maiden flight campaign

Fault detection of bearing defects for ballscrew based electro-mechanical actuators

Electro-mechanical actuators (EMAs) are considered a promising energy-efficient technology for actuating flight controls of future aircrafts. When it comes to aerospace systems, the EMAs degradation should be checked in regular maintenance events or through condition-based maintenance. Ball bearings have a significant failure rate for flight control EMAs and they are usually monitored by vibration noise. A challenge for detecting bearing faults, using state-of-the-art industrial methods, is the presence of a ballscrew mechanism that produces a nominal vibration noise similar to that of faulty bearings. No prior research has investigated this problem. This paper explores vibration noises generated from a set of healthy and faulty bearings included in a typical ballscrew EMA. In addition, a method is introduced for evaluating fault diagnosis performance for different time and frequency vibration features. The technique has been validated on an EMA actuator at the German Aerospace Center (DLR)

Anisotropy Identification for Electromechanical Flight Actuators With Sensorless Rotor Angle Detection

Electromechanical actuation of flight control surfaces based on permanent magnet synchronous motors (PMSMs) becomes an important technology for more electric aircraft architectures. Demanding requirements for fault tolerance and small space envelopes make sensorless control modes a promising technology in this field. However, sensorless rotor angle detection is not always feasible because it requires differential magnetic anisotropy properties of the motor. This article investigates this prerequisite for a PMSM with flux concentrating magnet topology and fractional slot concentrating windings. A nonlinear model that approximates inductance with respect to current and in particular rotor angle variations is identified. The observable anisotropic operating domain is conservatively determined through testing and finite element analysis (FEA)

A potential study of prognostic-based maintenance for primary flight control electro-mechanical actuators

The operating costs of civilian aircraft are crucial to air carriers. These costs currently offset more than 95% of their revenues, and maintenance represents around 10-20% of these operating costs. Thus, minimizing unscheduled maintenance is an important cost saving opportunity. Currently, primary flight actuators are based on electro-hydraulic technologies, and they are maintained by scheduled operational tests in accordance with the Maintenance Steering Group-3 (MSG-3) process. This paper discusses the potential of utilizing Prognostic-Based Maintenance (PrM) to minimize unscheduled maintenance of primary flight control actuators. Two perspectives will be considered: the MSG-3 based maintenance program and electro-mechanical actuation (EMA) - EMA is a promising technology for actuation in future aircraft. PrM and some of MSG-3 maintenance tasks have similar features that may be used to implement new PrM applications. Further, the EMA perspective involves a case study of a PrM system dedicated to monitoring the rolling contact fatigue of an EMA ball bearing. The PrM potential for aircraft systems has been investigated in numerous studies on the system level; however, practical utilization necessitates more focus on the component level related to specific failure modes

Fault detection of ball screw-based electromechanical actuators using electrical, ultrasound and accelerometer sensors

Electromechanical actuators (EMAs) are considered a promising energy-efcient technology for actuating the flight controls of future aircraf. When it comes to aerospace systems, the degradation of EMAs should be checked during regular maintenance events or through condition-based maintenance. Ball bearings have a signifcant failure rate for flight control EMAs and are usually monitored by vibration noise. A challenge for detecting bearing faults, using state-of-the-art industrial methods, is the presence of a ball-screw mechanism that produces nominal vibration noise similar to that of faulty bearings. No prior research has investigated this problem. Tis paper explores vibration noise generated fom a set of healthy and faulty bearings included in a typical ball-screw EMA. In addition, a method is introduced for evaluating fault diagnosis performance for different time and fequency vibration features. Te technique has been validated on an EMA actuator at the German Aerospace Center (DLR)

A Strategy on Selection of Condition Monitoring Methods and Techniques

High-maintenance or critical systems require a robust but affordable Condition Monitoring (CM) to be economical. Existing CM concepts can only be suitable for a limited number of applications and their real monitoring performance can only be estimated after intensive tests or while in actual operation. Due to the large number of methods available, it is difficult to decide for a specific one. Additionally, expert knowledge is required to select the most suitable technique for each method. This paper wants to show a strategy to master this problem by example results from investigations on monitoring electro-mechanical actuators supposed to be used as primary flight control servo drive. In detail, it will present how the proposed strategy works within test data of the main actuator component bearing only and subsequently discusses the implication for the actuator in its entirety. The example applies the strategy on combinations between signal processing techniques and statistical values analysis. This conduces to the comparison of two different monitoring methods: current signature and vibration signal. The suggested strategy can ensure the most suitable CM method for a certain application. Furthermore, it can extend the use of conventional monitoring concepts by demonstrating the potentials of the proposed technique combinations

Simplified Sensorless Torque Estimation Method for Harmonic Drive Based Electro-Mechanical Actuator

Torque measurements can significantly enhance control and monitoring loops for many mechatronic and aerospace applications. A typical challenge is to justify incorporating a torque sensor in terms of cost, system complexity, and reliability. Recently, sensorless torque estimation methods have been developed for robotic joints that include harmonic drive transmissions (HDTs). The principle is based on their relatively low torsional stiffness, which allows for estimating the transmitted torque by measuring the torsional angles (via existing joint encoders) and a compliance model. However, these methods are based on nonlinear models that are difficult to identify and tune. In this study, a simplified torque estimation method is introduced based on the structural damping friction of the HDTs. The structural damping can be correlated to the HDT torque using a simplified linear dynamic model and torsional rate measurements. Experimental results have validated the proposed method, using a robotic joint setup with an external torque sensor that has been previously utilized for testing several torque estimation method