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  • 1
    Electronic Resource
    Electronic Resource
    On the effects of production and maintenance variations on machinery performance (2002)
    Bingley : Emerald
    Journal of quality in maintenance engineering 8 (2002), S. 226-238 
    Details
    ISSN: 1355-2511
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Technology , Economics
    Notes: The variations introduced during the production and maintenance of rotating machinery components are correlated with the vibration and noise emanating from the final system during its operational lifetime. Vibration and noise are especially unacceptable elements in high-risk systems such as helicopters and aircraft engines, resulting in premature component degradation and a potentially unsafe flying environment. In such applications, individual components often are subject to 100 per cent inspection following production and during operation through rigorous maintenance, resulting in increased product development cycles and high production and operation costs. In this work, the aim is to provide engineers with a technique to evaluate vibration modes and levels for each component or subsystem prior to putting them into operation. This paper presents a preliminary investigation of the correlation of manufacturing and assembly variations with vibrations, using an experimental test rig. A factorial design is used to study the effects of various factors. Challenges in developing a process monitoring and inspection methodology to predict performance quality are identified, followed by a discussion of future work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/13552510210439801
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Automatic speech recognition research at NASA-Ames Research Center (1977)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A trainable acoustic pattern recognizer manufactured by Scope Electronics is presented. The voice command system VCS encodes speech by sampling 16 bandpass filters with center frequencies in the range from 200 to 5000 Hz. Variations in speaking rate are compensated for by a compression algorithm that subdivides each utterance into eight subintervals in such a way that the amount of spectral change within each subinterval is the same. The recorded filter values within each subinterval are then reduced to a 15-bit representation, giving a 120-bit encoding for each utterance. The VCS incorporates a simple recognition algorithm that utilizes five training samples of each word in a vocabulary of up to 24 words. The recognition rate of approximately 85 percent correct for untrained speakers and 94 percent correct for trained speakers was not considered adequate for flight systems use. Therefore, the built-in recognition algorithm was disabled, and the VCS was modified to transmit 120-bit encodings to an external computer for recognition.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NADC, Proceedings: Voice Technology for Interactive Real-Time Command(Control Systems Application; p 143-170
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Evaluating Manufacturing and Assembly Errors in Rotating Machinery to Enhance Component Performance (2001)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Manufacturing and assembly phases play a crucial role in providing products that meet the strict functional specifications associated with rotating machinery components. The errors resulting during the manufacturing and assembly of such components are correlated with the vibration and noise emanating from the final system during its operational lifetime. Vibration and noise are especially unacceptable elements in high-risk systems such as helicopters, resulting in premature component degradation and an unsafe flying environment. In such applications, individual components often are subject to 100% inspection prior to assembly, as well as during operation through rigorous maintenance, resulting in increased product development cycles and high production and operation costs. In this work, we focus on providing designers and manufacturing engineers with a technique to evaluate vibration modes and levels for each component or subsystem prior to putting them into operation. This paper presents a preliminary investigation of the correlation between vibrations and manufacturing and assembly errors using an experimental test rig, which simulates a simple bearing and shaft arrangement. A factorial design is used to study the effects of: 1) different manufacturing instances; 2) different assembly instances; and, 3) varying shaft speeds. The results indicate a correlation between manufacturing or assembly errors and vibrations measured from accelerometers. Challenges in developing a tool for DFM are identified, followed by a discussion of future work, including a real-world application to helicopter transmission vibrations.
    Keywords: Mechanical Engineering
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Classification of Aircraft Maneuvers for Fault Detection (2002)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Automated fault detection is an increasingly important problem in aircraft maintenance and operation. Standard methods of fault detection assume the availability of either data produced during all possible faulty operation modes or a clearly-defined means to determine whether the data provide a reasonable match to known examples of proper operation. In the domain of fault detection in aircraft, the first assumption is unreasonable and the second is difficult to determine. We envision a system for online fault detection in aircraft, one part of which is a classifier that predicts the maneuver being performed by the aircraft as a function of vibration data and other available data. To develop such a system, we use flight data collected under a controlled test environment, subject to many sources of variability. We explain where our classifier fits into the envisioned fault detection system as well as experiments showing the promise of this classification subsystem.
    Keywords: Aircraft Design, Testing and Performance
    Type: Fourth International Workshop on Multiple Classifier Systems; Unknown
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Maneuver Classification for Aircraft Fault Detection (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Automated fault detection is an increasingly important problem in aircraft maintenance and operation. Standard methods of fault detection assume the availability of either data produced during all possible faulty operation modes or a clearly-defined means to determine whether the data provide a reasonable match to known examples of proper operation. In the domain of fault detection in aircraft, identifying all possible faulty and proper operating modes is clearly impossible. We envision a system for online fault detection in aircraft, one part of which is a classifier that predicts the maneuver being performed by the aircraft as a function of vibration data and other available data. To develop such a system, we use flight data collected under a controlled test environment, subject to many sources of variability. We explain where our classifier fits into the envisioned fault detection system as well as experiments showing the promise of this classification subsystem.
    Keywords: Numerical Analysis
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Influence of Design Variations on Systems Performance (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: High-risk aerospace components have to meet very stringent quality, performance, and safety requirements. Any source of variation is a concern, as it may result in scrap or rework. poor performance, and potentially unsafe flying conditions. The sources of variation during product development, including design, manufacturing, and assembly, and during operation are shown. Sources of static and dynamic variation during development need to be detected accurately in order to prevent failure when the components are placed in operation. The Systems' Health and Safety (SHAS) research at the NASA Ames Research Center addresses the problem of detecting and evaluating the statistical variation in helicopter transmissions. In this work, we focus on the variations caused by design, manufacturing, and assembly of these components, prior to being placed in operation (DMV). In particular, we aim to understand and represent the failure and variation information, and their correlation to performance and safety and feed this information back into the development cycle at an early stage. The feedback of such critical information will assure the development of more reliable components with less rework and scrap. Variations during design and manufacturing are a common source of concern in the development and production of such components. Accounting for these variations, especially those that have the potential to affect performance, is accomplished in a variety ways, including Taguchi methods, FMEA, quality control, statistical process control, and variation risk management. In this work, we start with the assumption that any of these variations can be represented mathematically, and accounted for by using analytical tools incorporating these mathematical representations. In this paper, we concentrate on variations that are introduced during design. Variations introduced during manufacturing are investigated in parallel work.
    Keywords: Aircraft Design, Testing and Performance
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Experimental Analysis of Steady-State Maneuvering Effects on Transmission Vibration Patterns Recorded in an AH-1 Cobra Helicopter (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Flight experiment was designed primarily to determine the extent to which steady-state maneuvers influence characteristic vibration patterns measured at the input pinion and output annulus gear locations of the main transmission. If results were to indicate that maneuvers systematically influence vibration patterns, more extensive studies would be planned to explore the response surface. It was also designed to collect baseline data for comparison with experimental data to be recorded at a later date from test stands at Glenn Research Center. Finally, because this was the first vibration flight study on the Cobra aircraft, considerable energy was invested in developing an in-flight recording apparatus, as well as exploring acceleration mounting methods, and generally learning about the overall vibratory characteristics of the aircraft itself.
    Keywords: Aircraft Design, Testing and Performance
    Type: American Helicopter Society Annual Forum; May 02, 2000 - May 05, 2000; Virginia Beach, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    An Exploration of Discontinuous Time Synchronous Averaging for Helicopter HUMS Using Cruise and Terminal Area Vibration Data (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Recent research using NASA Ames AH-1 and OH-58C helicopters, and NASA Glenn test rigs, has shown that in-flight vibration data are typically non-stationary [l-4]. The nature and extent of this non-stationarity is most likely produced by several factors operating simultaneously. The aerodynamic flight environment and pilot commands provide continuously changing inputs, with a complex dynamic response that includes automatic feedback control from the engine regulator. It would appear that the combined effects operate primarily through an induced torque profile, which causes concomitant stress modulation at the individual internal gear meshes in the transmission. This notion is supported by several analyses, which show that upwards of 93% of the vibration signal s variance can be explained by knowledge of torque alone. That this relationship is stronger in an AH-1 than an OH-58, where measured non-stationarity is greater, suggests that the overall mass of the vehicle is an important consideration. In the lighter aircraft, the unsteady aerodynamic influences transmit relatively greater unsteady dynamic forces on the mechanical components, quite possibly contributing to its greater non-stationarity . In a recent paper using OH-58C pinion data [5], the authors have shown that in computing a time synchronous average (TSA) for various single-value metric computations, an effective trade-off can be obtained between sample size and measured stationarity by using data from only a single mesh cycle. A mesh cycle, which is defined as the number of rotations required for the gear teeth to return to their original mating position, has the property of representing all of the discrete phase angles of the opposing gears exactly once in the average. Measured stationarity is probably maximized because a single mesh cycle of the pinion gear occurs over a very short span of time, during which time-dependent non-stationary effects are kept to a minimum. Clearly, the advantage of local stationarity diminishes as the temporal duration of the cycle increases. This is most evident for a planetary mesh cycle, which can take several minutes to complete.
    Keywords: Aircraft Stability and Control
    Type: American Helicopter Society 2003; May 01, 2003; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Classification of Aircraft Maneuvers for Fault Detection (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Automated fault detection is an increasingly important problem in aircraft maintenance and operation. Standard methods of fault detection assume the availability of either data produced during all possible faulty operation modes or a clearly-defined means to determine whether the data is a reasonable match to known examples of proper operation. In our domain of fault detection in aircraft, the first assumption is unreasonable and the second is difficult to determine. We envision a system for online fault detection in aircraft, one part of which is a classifier that predicts the maneuver being performed by the aircraft as a function of vibration data and other available data. We explain where this subsystem fits into our envisioned fault detection system as well its experiments showing the promise of this classification subsystem.
    Keywords: Air Transportation and Safety
    Type: NIPS 2002; Dec 01, 2002; Vancouver; Canada
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Threshold Assessment of Gear Diagnostic Tools on Flight and Test Rig Data (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A method for defining thresholds for vibration-based algorithms that provides the minimum number of false alarms while maintaining sensitivity to gear damage was developed. This analysis focused on two vibration based gear damage detection algorithms, FM4 and MSA. This method was developed using vibration data collected during surface fatigue tests performed in a spur gearbox rig. The thresholds were defined based on damage progression during tests with damage. The thresholds false alarm rates were then evaluated on spur gear tests without damage. Next, the same thresholds were applied to flight data from an OH-58 helicopter transmission. Results showed that thresholds defined in test rigs can be used to define thresholds in flight to correctly classify the transmission operation as normal.
    Keywords: Quality Assurance and Reliability
    Type: NASA/TM-2003-212220/Rev1 , E-13812 , NAS 1.15:212220/Rev1 , 59th Annual Forum and Technology Display; May 06, 2003 - May 08, 2003; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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