620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Abstract Classical ballet requires dancers to exercise significant muscle control and strength both while stationary and when moving. Following the Royal Academy of Dance (RAD) syllabus, 8 male and 27 female dancers (aged 20.2 + 1.9 yr) in a full-time university undergraduate dance training program were asked to stand in first position for 10 seconds and then perform 10 repeats of a demi-plié exercise to a counted rhythm. Accelerometer records from the wrist, sacrum, knee and ankle were compared with the numerical scores from a professional dance instructor. The sacrum mounted sensor detected lateral tilts of the torso in dances with lower scores (Spearman’s rank correlation coefficient r = -0.64, p < 0.005). The 5RMS6 acceleration amplitude of wrist mounted sensor was linearly correlated to the movement scores (Spearman’s rank correlation coefficient r = 0.63, p < 0.005). The application of sacrum and wrist mounted sensors for biofeedback during dance training is a realistic, low cost option.
The use of manually fed machines (e.g. table saws) bares risks of injury that are clearly above the average level of other high risk workplaces.
The wide use of such machines causes severe problems for occupational safety and implies high costs for medical treatments and accident annuities.
This thesis presents a new concept of a multispectral sensor to monitor an area in front of a danger zone to detect the user’s limbs and trigger safeguarding measures to prevent an accident in time.
The sensor concept realizes a contact-free material classification, which comprises the development of a system design and specific safety requirements with respect to international safety standards.
Furthermore, a prototypical implementation using four wavebands, which were determined for skin detection through an analysis of reflectance spectra acquired specifically for this purpose, was built.
Arbeitssicherheit: Allein in Deutschland passieren an Produktionsmaschinen fast täglich schwere Unfälle. Tisch- und Formatkreissägen gehören mit zu den gefährlichsten Maschinen. Informatiker entwickelten nun eine neue Sensortechnik, die solche Unfälle verhindert, indem sie Haut unabhängig von Hautfarbe, Alter und Geschlecht sicher vom Werkstück unterscheidet.
Cost efficient energy monitoring in existing large buildings demands for autonomous indoor sensors with low power consumption, high performance in multipath fading channels and economic implementation. Good performance in multipath fading channels can be achieved with noncoherent chaotic modulation schemes such as chaos on-off keying (COOK) or differential chaos shift keying (DCSK). While COOK stands out in the area of power consumption, DCSK excels when it comes to its performance in noisy and multipath fading channels. This paper evaluates a combination of both schemes for autonomous indoor sensors. The simulation results show 50% less power consumption than DCSK and more than 3dB SNR gain in Rayleigh fading channels at BER=10-3 as compared to COOK, making it a promising candidate for low power transmission in autonomous wireless indoor sensors. We further present an enhanced version of this scheme showing another 1 dB SNR improvement, but at 25% less power consumption than DCSK.
Hybrid system models exploit the modelling abstraction that fast state transitions take place instantaneously so that they encompass discrete events and the continuous time behaviour for the while of a system mode. If a system is in a certain mode, e.g. two rigid bodies stick together, then residuals of analytical redundancy relations (ARRs) within certain small bounds indicate that the system is healthy. An unobserved mode change, however, invalidates the current model for the dynamic behaviour. As a result, ARR residuals may exceed current thresholds indicating faults in system components that have not happened. The paper shows that ARR residuals derived from a bond graph cannot only serve as fault indicators but may also be used for bond graph model-based system mode identification. ARR residuals are numerically computed in an off-line simulation by coupling a bond graph of the faulty system to a non-faulty system bond graph through residual sinks. In real-time simulation, the faulty system model is to be replaced by measurements from the real system. As parameter values are uncertain, it is important to determine adaptive ARR thresholds that, given uncertain parameters, allow to decide whether the dynamic behaviour in a current system mode is the one of the healthy system so that false alarms or overlooking of true faults can be avoided. The paper shows how incremental bond graphs can be used to determine adaptive mode-dependent ARR thresholds for switched linear time-invariant systems with uncertain parameters in order to support robust fault detection. Bond graph-based hybrid system mode identification as well as the determination of adaptive fault thresholds is illustrated by application to a power electronic system easy to survey. Some simulation results have been analytically validated.
Für die Entwicklung steuerungstechnischer Sicherheitsfunktionen muss ab 2012 die Normen EN ISO 13849-1 oder EN 62061 befolgt werden, die sowohl Anforderungen an die Hardware als auch Anforderungen an die Software beschreibt. Die Anforderungen an die Software spielten bis vor einigen Jahren kaum eine Rolle, da Sicherheitsfunktionen vorzugsweise in Hardware realisiert wurden. Heutzutage ist es jedoch sehr häufig üblich, Sicherheitsfunktionen mit einer dafür geeigneten programmierbaren SPS zu realisieren. Die neuen Normen bzgl. der sicheren Steuerung von Maschinen verlangen neben der Quantifizierung der Hardware-Ausfallraten von Sicherheitsfunktionen noch ein Management der Sicherheitsfunktionen. Dazu gehört auch ein Management der Softwareentwicklung für Sicherheitsfunktionen, um systematische Fehler zu minimieren. Dieses Management der Softwareentwicklung wird im Wesentlichen durch das V-Modell repräsentiert. Für die Maschinebauindustrie darf dieser Managementprozess nicht zu aufwendig sein, ansonsten wird dieser in der Praxis nur schwer angenommen. Eine Möglichkeit der Abarbeitung des V-Modells wird vorgestellt. Wahrscheinlich ist diese aufgezeigte Möglichkeit für die Industrie noch zu aufwendig.
In this paper, the performance evaluation of Frequency Modulated Chaotic On-Off Keying (FM-COOK) in AWGN, Rayleigh and Rician fading channels is given. The simulation results show that an improvement in BER can be gained by incorporating the FM modulation with COOK for SNR values less than 10dB in AWGN case and less than 6dB for Rayleigh and Rician fading channels.
Die Anforderungen an die Tragfähigkeit von Seilrollen aus Guss-Polyamiden nehmen aufgrund der Erwartungen hinsichtlich der maximal zu realisierenden Hublasten bei neueren Förder- und Hebegeräte stetig zu. Die heutige Konstruktionspraxis erlaubt für normale Betriebsbedingungen eine gesicherte Auslegung der Seilrollen. Aus jahrelanger Erfahrung sind hierfür Grenzwerte für maximal zulässigen Belastungen im Betrieb unter verschiedensten Betriebsbedingungen gewonnen worden. Jedoch ist bei steigenden Lasten, besserer Ausnutzung des Werkstoffpotenzials oder Modifikationen des Basiswerkstoffs nur noch eine eingeschränkte Bestimmung der tatsächlichen "Worst-Case"-Tragfähigkeit mit dieser Konstruktionspraxis möglich. Berechnungsmodelle einer neuen Bemessungsgrundlage basieren auf der Anwendung der Finite Elemente Methode. Die ersten Berechnungsmodelle aus der modifizierten Bemessungsgrundlage ermöglichen den Einfluss von geometrischen Änderungen der Form bzw. der Ausführung, von lokalen Materialeigenschaften und von realistischere Lastzustände auf den Deformationsund Spannungszustand einer Seilrolle theoretisch zu beschreiben. Weitere Berechnungsmodelle, die z.B. die Erwärmung der Seilrolle durch die Rollreibung zwischen Seil und Seilrolle sowie des Walkens durch die Bewegung des Seiles bei dynamischer Belastung beschreiben können, sind in der Entwicklung. Für den Konstrukteur werden zudem parametrisierte Geometrie-, Last- und FE-Modelle entwickelt, die eine schnelle und betriebssichere Dimensionierung von Seilrollen aus Guss-Polyamiden ermöglichen. Alle theoretischen Ergebnisse werden z.Z. durch umfangreiche Versuche abgesichert.
The small and remote households in Northern regions demand thermal energy rather than electricity. Wind turbine in such places can be used to convert wind energy into thermal energy directly using a heat generator based on the principle of the Joule machine. The heat generator driven by a wind turbine can reduce the cost of energy for heating system. However the optimal performance of the system depends on the torque-speed characteristics of the wind turbine and the heat generator. To achieve maximum efficiency of operation both characteristics should be matched. In the article the condition of optimal performance is developed and an example of the system operating at maximum efficiency is simulated.
Automated force field optimisation of small molecules using a gradient-based workflow package
(2010)
In this study, the recently developed gradient-based optimisation workflow for the automated development of molecular models is for the first time applied to the parameterisation of force fields for molecular dynamics simulations. As a proof-of-concept, two small molecules (benzene and phosgene) are considered. In order to optimise the underlying intermolecular force field (described by the (12,6)-Lennard-Jones and the Coulomb potential), the energetic and diameter parameters ε and σ are fitted to experimental physical properties by gradient-based numerical optimisation techniques. Thereby, a quadratic loss function between experimental and simulated target properties is minimised with respect to the force field parameters. In this proof-of-concept, the considered physical target properties are chosen to be diverse: density, enthalpy of vapourisation and self-diffusion coefficient are optimised simultaneously at different temperatures. We found that in both cases, the optimisation could be successfully concluded by fulfillment of a pre-defined stopping criterion. Since a fairly small number of iterations were needed to do so, this study will serve as a good starting point for more complex systems and further improvements of the parametrisation task.