A Predictive maintenance model for heterogeneous industrial refrigeration systems

The automatic assessment of the degradation state of industrial refrigeration systems is becoming increasingly important and constitutes a key-role within predictive maintenance approaches. Lately, data-driven methods especially became the focus of research in this respect. As they only rely on historical data in the development phase, they offer great advantages in terms of flexibility and generalisability by circumventing the need for specific domain knowledge. While most scientific contributions employ methods emerging from the field of machine learning (ML), only very few consider their applicability amongst different heterogeneous systems. In fact, the majority of existing contributions in this field solely apply supervised ML models, which assume the availability of labelled fault data for each system respectively. However, this places restrictions on the overall applicability, as data labelling is mostly conducted by humans and therefore constitutes a non-negligible cost and time factor. Moreover, such methods assume that all considered fault types occurred in the past, a condition that may not always be guaranteed to be satisfied. Therefore, this dissertation proposes a predictive maintenance model for industrial refrigeration systems by especially addressing its transferability onto different but related heterogeneous systems. In particular, it aims at solving a sub-problem known as condition-based maintenance (CBM) to automatically assess the system’s state of degradation. To this end, the model does not only estimate how far a possible malfunction has progressed, but also determines the fault type being present. As will be described in greater detail throughout this dissertation, the proposed model also utilises techniques from the field of ML but rather bypasses the strict assumptions accompanying supervised ML. Accordingly, it assumes the data of the target system to be primarily unlabelled while a few labelled samples are expected to be retrievable from the fault-free operational state, which can be obtained at low cost. Yet, to enable the model’s intended functionality, it additionally employs data from only one fully labelled source dataset and, thus, allows the benefits of data-driven approaches towards predictive maintenance to be further exploited. After the introduction, the dissertation at hand introduces the related concepts as well as the terms and definitions and delimits this work from other fields of research. Furthermore, the scope of application is further introduced and the latest scientific work is presented. This is then followed by the explanation of the open research gap, from which the research questions are derived. The third chapter deals with the main principles of the model, including the mathematical notations and the individual concepts. It furthermore delivers an overview about the variety of problems arising in this context and presents the associated solutions from a theoretical point of view. Subsequently, the data acquisition phase is described, addressing both the data collection procedure and the outcome of the test cases. In addition, the considered fault characteristics are presented and compared with the ones obtained from the related publicly available dataset. In essence, both datasets form the basis for the model validation, as discussed in the following chapter. This chapter then further comprises the results obtained from the model, which are compared with the ones retrieved from several baseline models derived from the literature. This work then closes with a summary and the conclusions drawn from the model results. Lastly, an outlook of the presented dissertation is provide

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Review of Condition Based Maintenance approaches for vapor compression refrigeration systems

Vapor compression refrigeration systems are subject to performance degradation over time due to the presence of faults. However, latest work in the field of condition-based maintenance shows promising results in the automatic early detection of anomalous behaviour as well as in accurate machine diagnostics and can, therefore, increase the overall system reliability by simultaneously preventing machine downtimes. In this paper, the latest research works carried out within the last decade are reviewed and the approaches are classified regarding their working principles. Furthermore, the work at hand depicts the current research trend in this field and outlines current obstacles

Automatisierte Erkennung von Messarealen bei robotergestützten In Vivo Messungen

Dieser Beitrag schlägt ein Bildverarbeitungsmodell zur automatisierten Bestimmung von Messarealen bei robotergestützten In Vivo Messungen vor. Es wird angenommen, dass moderne Verfahren der Deep-Learning-Objekterkennung in der Lage sind die einzelnen Areale wiederholbar genau genug zu erkennen, um die benötigten Messareale im dreidimensionalen Raum einzupassen. Für das Einpassen werden Tiefeninformationen aus einer stereoskopischen Kamera verwendet. Weiter wird untersucht inwiefern diese Tiefeninformationen als zusätzlicher Eingang für die Deep-Learning-Modelle verwendet werden können. Hierfür wird ein Konzept ausgearbeitet, ein Datensatz erstellt und Modelle zur Objekterkennung in verschiedenen Implementierungen trainiert. Das Verwenden von Tiefeninformationen führt zu einer besseren Generalisierbarkeit der Modelle, insbesondere auf tätowierten Hautarealen. Das Bildverarbeitungsmodell erreicht beim Einpassen der Messareale eine gemittelte Wiederholgenauigkeit bzw. Abweichung von 6, 1 mm bei einer Bildwiederholrate von 2, 3 bis 3, 3 Bildern die Sekunde

Data-driven fault diagnosis for heterogeneous chillers using domain adaptation techniques

Automatic fault diagnosis is becoming increasingly important for assessing a chiller’s degradation state and plays a key role in modern maintenance strategies. Data-driven approaches have already become well established for this purpose as they rely on historical data and are therefore more generally applicable compared to their model-based counterparts. Existing chiller fault diagnosis models, however, require labelled data from the target system, which are often not available. Therefore, in this paper, a data-driven fault diagnosis model is proposed that deploys domain adaptation techniques to enable the transfer of knowledge amongst heterogeneous chillers. In particular, the model utilizes transfer component analysis (TCA) and a support vector machine with adapting decision boundaries (SVM-AD) to diagnose faults by aggregating labelled source and unlabelled target domain data in the training phase. Furthermore, it is demonstrated how the model parameters can be tuned to ensure effective classification performance, which is then evaluated by use of fault data stemming from different chiller types. Experimental results show that with the proposed approach faults can be diagnosed with high accuracy for cases when labelled target domain data are not available

Vernetzung physischer und virtueller Entitäten im CPPS : Augmented Reality als Mensch-Maschine Schnittstelle

Konventionelle Fertigungsstrategien werden künftig zunehmend durch komplexe cyberphysische Produktionssysteme (CPPS) ersetzt. Es entstehen durchgehend verbundene Wertschöpfungsnetzwerke mit großer Informationsdichte, die den Menschen mit einer signifikant gestiegenen Datenmenge konfrontieren, auf deren Basis er agieren muss. Daher nimmt die Mensch-Maschine-Schnittstelle einen wichtigen Stellenwert innerhalb des Produktionsprozesses ein, wobei sich neuartige Visualisierungsverfahren wie Augmented Reality (AR) vielversprechend zeigen. Für entsprechende Anwendungen bedarf es einer durchgängigen Kommunikation aus dem Feld bis hin zur Applikation. Der Artikel beschreibt, wie existierende Kommunikationsstandards dafür nutzbar gemacht werden können und zeigt eine beispielhafte Umsetzung. Zudem wird eine Kommunikationsarchitektur vorgeschlagen, die auf Grundlage der Verwaltungsschale den interoperablen Informationsaustausch zwischen physischen und virtuellen Entitäten ermöglicht

A Data-Driven Approach Towards the Application of Reinforcement Learning Based HVAC Control

Refrigeration applications consume a significant share of total electricity demand, with a high indirect impact on global warming through greenhouse gas emissions. Modern technology can help reduce the high power consumption and optimize the cooling control. This paper presents a case study of machine-learning for controlling a commercial refrigeration system. In particular, an approach to reinforcement learning is implemented, trained and validated utilizing a model of a real chiller plant. The reinforcement-learning controller learns to operate the plant based on its interactions with the modeled environment. The validation demonstrates the functionality of the approach, saving around 7% of the energy demand of the reference control. Limitations of the approach were identified in the discretization of the real environment and further model-based simplifications and should be addressed in future research

Modellansatz zur Prozessoptimierung beim hydroadhäsiven Greifen

Der Produktlebenszyklus von Kleidung ist vor allem durch lange Lieferketten von Niedriglohnländern in Hochlohnländer gekennzeichnet. Die Eliminierung solcher Transportwege könnte dazu führen, dass der komplette Lebenszyklus von Kleidungsware nachhaltiger und umweltfreundlicher wird. Der Aufbau von Produktionsstätten in Hochlohnländern wird aktuell durch technische Herausforderungen des Produktionsprozesses von Kleidung bzw. allgemein biegeschlaffen Materialien verhindert. Aufgrund der Eigenschaften biegeschlaffer Materialien können die Entnahme bzw. definierte Ablage von Textilteilen heutzutage nur teilautomatisiert bzw. mit einem hohen Anteil manueller Tätigkeiten gelöst werden. Das Hydroadhäsive Greifen könnte eine Lösung sein, die oben genannten Prozesse zu automatisieren und die Produktion für Hochlohnländer zu vergünstigen. Jedoch verfügt das Verfahren noch über lange Zykluszeiten und die Haltekräfte sind nicht reproduzierbar. Weiterhin ist die Findung von Einstellparametern sehr zeitaufwendig und komplex. Die Lösung könnte eine intelligente Steuerung sein, dessen Kernstück ein datengetriebenes Modell für die Parameteroptimierung und -findung ist. Im Rahmen der Forschungsarbeiten wird ein Modellansatz zur Optimierung der Taktzeit beim hydroadhäsiven Greifen erarbeitet. Dabei wird die Gewinnung der Datengrundlage, das zu entwickelnde Modell sowie die eigentliche Validierung diskutiert

Impact of COVID-19 on Diagnostic Cardiac Procedural Volume in Oceania: The IAEA Non-Invasive Cardiology Protocol Survey on COVID-19 (INCAPS COVID)

Objectives: The INCAPS COVID Oceania study aimed to assess the impact caused by the COVID-19 pandemic on cardiac procedure volume provided in the Oceania region. Methods: A retrospective survey was performed comparing procedure volumes within March 2019 (pre-COVID-19) with April 2020 (during first wave of COVID-19 pandemic). Sixty-three (63) health care facilities within Oceania that perform cardiac diagnostic procedures were surveyed, including a mixture of metropolitan and regional, hospital and outpatient, public and private sites, and 846 facilities outside of Oceania. The percentage change in procedure volume was measured between March 2019 and April 2020, compared by test type and by facility. Results: In Oceania, the total cardiac diagnostic procedure volume was reduced by 52.2% from March 2019 to April 2020, compared to a reduction of 75.9% seen in the rest of the world (p&lt;0.001). Within Oceania sites, this reduction varied significantly between procedure types, but not between types of health care facility. All procedure types (other than stress cardiac magnetic resonance [CMR] and positron emission tomography [PET]) saw significant reductions in volume over this time period (p&lt;0.001). In Oceania, transthoracic echocardiography (TTE) decreased by 51.6%, transoesophageal echocardiography (TOE) by 74.0%, and stress tests by 65% overall, which was more pronounced for stress electrocardiograph (ECG) (81.8%) and stress echocardiography (76.7%) compared to stress single-photon emission computerised tomography (SPECT) (44.3%). Invasive coronary angiography decreased by 36.7% in Oceania. Conclusion: A significant reduction in cardiac diagnostic procedure volume was seen across all facility types in Oceania and was likely a function of recommendations from cardiac societies and directives from government to minimise spread of COVID-19 amongst patients and staff. Longer term evaluation is important to assess for negative patient outcomes which may relate to deferral of usual models of care within cardiology