Advanced hydraulic systems for next generation of skid steer loaders

Fluid power systems have been extensively used in off highway applications like skid steer loaders, wheel loaders, excavators since many years. Work has been done by both industry and academia to improve efficiency, reduce noise and leakages in these systems. With increasing competition in the market, importance is now also given to operator comfort and machine productivity in off highway applications. Mobile, off – highway vehicles like Skid-steer loaders are widely used in labour saving applications like loading earth into a truck, dig and move material on construction sites to, clean roads, clear snow from roads etc. To carry out these jobs in limited spaces, skid steer loaders need tight turning radius. For this reason, these machines have a short wheelbase which prevents the use of suspensions in these vehicles. The absence of a suspension system exposes the vehicle to ground vibrations of high magnitude and low frequency. Vibrations reduce operator comfort, productivity and life of components. This thesis will discuss control strategies for vibration damping of skid steer loader using the hydraulic boom cylinder as the active suspension element, which is equivalent to a spring–damper. Along with vibrations, the machine productivity is also hampered by material spillage which is caused by the tilting of the bucket due to the extension of the boom. This dissertation will discuss the development of a robust path-planning control algorithm which adapts to the position of the boom to maintain a level load to achieve bucket self-leveling. Another reason for reduced productivity in skid steer loaders is slow in site travel speeds. This dissertation also concentrates on reducing the in-job cycle time by developing a control strategy to smooth speed shift the drive motors keeping the pump flow constant. To synthesize these proposed control algorithms, high fidelity hydraulic and mechanical models of the skid steer loader are created. Ultimately, the control algorithms derived in this dissertation help in improving operator comfort and machine productivity

Fractal Dimension Analysis of Transient Visual Evoked Potentials: Optimisation and Applications

Purpose The visual evoked potential (VEP) provides a time series signal response to an external visual stimulus at the location of the visual cortex. The major VEP signal components, peak latency and amplitude, may be affected by disease processes. Additionally, the VEP contains fine detailed and non-periodic structure, of presently unclear relevance to normal function, which may be quantified using the fractal dimension. The purpose of this study is to provide a systematic investigation of the key parameters in the measurement of the fractal dimension of VEPs, to develop an optimal analysis protocol for application. Methods VEP time series were mathematically transformed using delay time, τ, and embedding dimension, m, parameters. The fractal dimension of the transformed data was obtained from a scaling analysis based on straight line fits to the numbers of pairs of points with separation less than r versus log(r) in the transformed space. Optimal τ, m, and scaling analysis were obtained by comparing the consistency of results using different sampling frequencies. The optimised method was then piloted on samples of normal and abnormal VEPs. Results Consistent fractal dimension estimates were obtained using τ = 4 ms, designating the fractal dimension = D2 of the time series based on embedding dimension m = 7 (for 3606 Hz and 5000 Hz), m = 6 (for 1803 Hz) and m = 5 (for 1000Hz), and estimating D2 for each embedding dimension as the steepest slope of the linear scaling region in the plot of log(C(r)) vs log(r) provided the scaling region occurred within the middle third of the plot. Piloting revealed that fractal dimensions were higher from the sampled abnormal than normal achromatic VEPs in adults (p = 0.02). Variances of fractal dimension were higher from the abnormal than normal chromatic VEPs in children (p = 0.01). Conclusions A useful analysis protocol to assess the fractal dimension of transformed VEPs has been developed

Aeronautical Engineering. A continuing bibliography, supplement 115

This bibliography lists 273 reports, articles, and other documents introduced into the NASA scientific and technical information system in October 1979

Research and Technology

Langley Research Center is engaged in the basic an applied research necessary for the advancement of aeronautics and space flight, generating advanced concepts for the accomplishment of related national goals, and provding research advice, technological support, and assistance to other NASA installations, other government agencies, and industry. Highlights of major accomplishments and applications are presented

Proceedings of the fifth workshop on digital fluid power, October 24-25, 2012, Tampere, Finland

The Digital Fluid Power workshops have been arranged annually since 2008 alternating between Linz and Tampere. This is the third time in Tampere and the number of participants is as high as 114 from 11 countries, 33 companies and 8 universities despite bad economic situation. The digital fluid power technology is developing rapidly and new principles still emerges. The component availability is better and several papers present research results with commercial digital valves. The good old days with self-wound coils and fuming power electronics seem to be ending. Other trends are sophisticated control methods, which consider digital nature of the systems, energy efficient fully digital solutions, and faster and more compact valves

The insertion of human dynamics models in the flight control loops of V/STOL research aircraft. Appendix 2: The optimal control model of a pilot in V/STOL aircraft control loops

An overview is presented of research work focussed on the design and insertion of classical models of human pilot dynamics within the flight control loops of V/STOL aircraft. The pilots were designed and configured for use in integrated control system research and design. The models of human behavior that were considered are: McRuer-Krendel (a single variable transfer function model); and Optimal Control Model (a multi-variable approach based on optimal control and stochastic estimation theory). These models attempt to predict human control response characteristics when confronted with compensatory tracking and state regulation tasks. An overview, mathematical description, and discussion of predictive limitations of the pilot models is presented. Design strategies and closed loop insertion configurations are introduced and considered for various flight control scenarios. Models of aircraft dynamics (both transfer function and state space based) are developed and discussed for their use in pilot design and application. Pilot design and insertion are illustrated for various flight control objectives. Results of pilot insertion within the control loops of two V/STOL research aricraft (Sikorski Black Hawk UH-60A, McDonnell Douglas Harrier II AV-8B) are presented and compared against actual pilot flight data. Conclusions are reached on the ability of the pilot models to adequately predict human behavior when confronted with similar control objectives