Parametrisierte Modelle zur konstruktiven Auslegung optimierter elektrischer Steckverbinderkontakte

Steckverbinder für die Leistungsübertragung müssen geometrisch-stofflich so dimensioniert werden, dass sie eine vorgegebene Grenztemperatur nicht überschreiten. Zunächst werden analytische Modelle aus verschiedenen physikalischen Phänomenen (mechanische, elektrische, thermische und kontaktphysikalische) miteinander gekoppelt, um die Stromerwärmung von Steckverbinderkontakten analytisch zu berechnen. Die Modelle werden durch Experimente und FE-Analysen verifiziert. Mit erweiterten Modellen werden wichtige Fragestellungen bei der konstruktiven Auslegung geklärt (z.B. zulässiger Durchgangswiderstand, Zusammenhang zwischen Widerstand und Stromerwärmung, optimale Anzahl an Kontaktfedern). Zudem werden Sensitivitätsanalysen durchgeführt. Schließlich wird ein berechnungsgestütztes Vorgehen zur systematischen Auslegung von Steckverbinderkontakten erarbeitet. Unter Berücksichtigung geeigneter Randbedingungen ist eine direkte Berechnung der wesentlichen Abmessungen und Werkstoffkennwerte möglich.The aim of this work is to investigate the design of connector contacts according to a specific current carrying capacity. At first established analytical models of different physical phenomena (mechanic, electric, thermal and contact physical) are combined. Thus, the heating of connector contacts including the connected wire can be calculated analytically. The models are verified by experiments and by FE-Analysis. Afterwards, these analytical models are transformed in order to calculate important parameters for the design process of connector contacts. This includes the maximum permissible power loss of a connector contact, the relationship between the transition resistance and the heating, as well as the optimal number of contact springs for a connector contact. Additionally, sensitivity studies are conducted, in order to illustrate the influence of several design parameters on the heating of connector contacts. Using the obtained results, a systematic approach for dimensioning connector contacts with respect to the current carrying capacity is presented. This approach uses analytical models (parametrized models) in order to calculate the main geometrical and material parameters. Thus, connector contacts can be designed using a uniform method, which maximises the performance potential and which is scalable for different current ratings. Therefore, this work presents an approach for the parametric design of connector contacts.Im Rahmen dieser Arbeit wird die konstruktive Auslegung von Steckverbindern hinsichtlich der Stromtragfähigkeit untersucht. Zunächst werden bekannte analytische Modelle aus verschiedenen physikalischen Phänomenen (mechanische, elektrische, thermische und kontaktphysikalische) miteinander kombiniert, um die Stromerwärmung von Steckverbinderkontakten incl. der angeschlossenen Leitung analytisch zu berechnen. Die Modelle werden mit Hilfe von Experimenten und FE-Analysen verifiziert. Anschließend werden die analytischen Modelle umgeformt, um wichtige Fragestellungen bei der konstruktiven Auslegung von Steckverbinderkontakten zu berechnen. Dazu zählen unter anderem der maximal zulässige Durchgangswiderstand von Steckverbinderkontakten, der Zusammenhang zwischen Durchgangswiderstand und Stromerwärmung, sowie die optimale Anzahl an Kontaktfedern für einen Steckverbinderkontakt. Zudem werden Sensitivitätsanalysen durchgeführt, um den Einfluss konstruktionsrelevanter Parameter auf die Stromerwärmung von Steckverbinderkontakten darzustellen. Durch die gewonnenen Ergebnisse wird schließlich ein Vorgehen zur systematischen Auslegung von Steckverbinderkontakten hinsichtlich der Stromtragfähigkeit erarbeitet. Dieses nutzt analytische Modelle (parametrisierte Modelle), mit denen sich wesentliche geometrische Abmessungen und Werkstoffkennwerte berechnen lassen. Dadurch können Baureihen von Steckverbinderkontakten entwickelt werden, die einer einheitlichen Methodik folgen, eine Überdimensionierung vermeiden und sich für verschiedene Stromstärken skalieren lassen. Die Arbeit stellt damit einen Ansatz zur parametrischen Konstruktion von Steckverbindern dar

Model-Based Control of a Large-Scale Ball-on-Plate System With Experimental Validation

A ball-on-plate system is a widespread education oriented laboratory experiment for automation in mechatronics. The setup combines elements of mechanical, electrical and control engineering and is an adequate setup for learning the combination of theory and practice. This paper presents an example of a workshop result on automatic control in mechatronics. The aim of the workshop is to develop and compare model-based approaches for ball position control in a given large-scale ball-on-plate system. The result includes the derivation of a non-linear state space model of the system. The equations are linearized in the center of the horizontal plate as an operating point in order to apply cascade control, linear-quadratic optimal control and PI optimal state feedback control. The algorithms are implemented on a microcontroller and tested in the experimental setup. The results show a successful control development which achieves the control goal with good performance in terms of command response

Bone Mass Distribution of the Distal Tibia in Normal, Osteopenic, and Osteoporotic Conditions: An Ex Vivo Assessment Using HR-pQCT, DXA, and Computational Modelling.

Osteoporosis leads to bone loss and structural deterioration, which increase the risk of fractures. The aim of this study was to characterize the three-dimensional (3D) bone mass distributions of the distal tibia in normal, osteopenic, and osteoporotic conditions. High-resolution peripheral quantitative computed tomography (HR-pQCT) of the 33 % of the distal tibia and local dual-energy X-ray absorptiometry were applied to 53 intact, fresh-frozen tibiae. The HR-pQCTs were graded to assign local T-scores and merged into three equally sized average normal, osteopenic, and osteoporotic surface models. Volumetric bone mineral density (vBMD) was determined using categorized T-scores, volumetric visualization, and virtual bore probes at the dia-, meta-, and epiphyseal sites (T-DIA, T-META, and T-EPI). We observed a distinct 3D bone mass distribution that was gradually uninfluenced by T-score categories. T-DIA was characterized by the lowest bone mass located in the medullary cavity and a wide homogenous cortex containing the maximum vBMD. The T-META showed decreased cortical thickness and maximal vBMD. At the T-EPI, the relatively low vBMD of the mostly trabecular bone was similar to the maximal cortical vBMD in this sub-region. Four trabecular regions of low bone mass were identified in the recesses. The bone content gradually decreased at all sites, whereas the pattern of bone mass distribution remained essentially unchanged, with the exception of disproportionate losses at T-DIA, T-META, and T-EPI that consistently showed increased endocortical, intracortical, and trabecular bone loss. Extra information can be obtained from the specific pattern of bone mass distribution, potential disproportionate bone losses, and method used

Histomorphometric Assessment of Cancellous and Cortical Bone Material Distribution in the Proximal Humerus of Normal and Osteoporotic Individuals Significantly Reduced Bone Stock in the Metaphyseal and Subcapital Regions of Osteoporotic Individuals

Osteoporosis is a systemic disorder predominantly affecting postmenopausal women but also men at an advanced age. Both genders may suffer from low-energy fractures of, for example, the proximal humerus when reduction of the bone stock or/and quality has occurred. The aim of the current study was to compare the amount of bone in typical fracture zones of the proximal humerus in osteoporotic and non-osteoporotic individuals. The amount of bone in the proximal humerus was determined histomorphometrically in frontal plane sections. The donor bones were allocated to normal and osteoporotic groups using the T-score from distal radius DXA measurements of the same extremities. The T-score evaluation was done according to WHO criteria. Regional thickness of the subchondral plate and the metaphyseal cortical bone were measured using interactive image analysis. At all measured locations the amount of cancellous bone was significantly lower in individuals from the osteoporotic group compared to the non-osteoporotic one. The osteoporotic group showed more significant differences between regions of the same bone than the non-osteoporotic group. In both groups the subchondral cancellous bone and the subchondral plate were least affected by bone loss. In contrast, the medial metaphyseal region in the osteoporotic group exhibited higher bone loss in comparison to the lateral side. This observation may explain prevailing fracture patterns, which frequently involve compression fractures and certainly has an influence on the stability of implants placed in this medial region. It should be considered when planning the anchoring of osteosynthesis materials in osteoporotic patients with fractures of the proximal humerus

Clinical observation of diminished bone quality and quantity through longitudinal HR-pQCT-derived remodeling and mechanoregulation.

High resolution peripheral quantitative computed tomography (HR-pQCT) provides methods for quantifying volumetric bone mineral density and microarchitecture necessary for early diagnosis of bone disease. When combined with a longitudinal imaging protocol and finite element analysis, HR-pQCT can be used to assess bone formation and resorption (i.e., remodeling) and the relationship between this remodeling and mechanical loading (i.e., mechanoregulation) at the tissue level. Herein, 25 patients with a contralateral distal radius fracture were imaged with HR-pQCT at baseline and 9-12 months follow-up: 16 patients were prescribed vitamin D3 with/without calcium supplement based on a blood biomarker measures of bone metabolism and dual-energy X-ray absorptiometry image-based measures of normative bone quantity which indicated diminishing (n = 9) or poor (n = 7) bone quantity and 9 were not. To evaluate the sensitivity of this imaging protocol to microstructural changes, HR-pQCT images were registered for quantification of bone remodeling and image-based micro-finite element analysis was then used to predict local bone strains and derive rules for mechanoregulation. Remodeling volume fractions were predicted by both average values of trabecular and cortical thickness and bone mineral density (R2 > 0.8), whereas mechanoregulation was affected by dominance of the arm and group classification (p < 0.05). Overall, longitudinal, extended HR-pQCT analysis enabled the identification of changes in bone quantity and quality too subtle for traditional measures

Staphylococcus Aureus Infective Endocarditis: JACC Patient Pathways.

A 19-year-old female patient presented with Staphylococcus aureus infective endocarditis, with suspected subdural brain hemorrhage, disseminated intravascular coagulopathy, and septic renal as well as spleen infarcts. The patient had extensive vegetations on the mitral and tricuspid valves and underwent urgent mitral and tricuspid repair. This paper discusses the clinical case and current evidence regarding the management and treatment of Staphylococcus aureus endocarditis.S

Internet based multicenter study for thoracolumbar injuries: a new concept and preliminary results

This article reports about the internet based, second multicenter study (MCS II) of the spine study group (AG WS) of the German trauma association (DGU). It represents a continuation of the first study conducted between the years 1994 and 1996 (MCS I). For the purpose of one common, centralised data capture methodology, a newly developed internet-based data collection system ( http://www.memdoc.org ) of the Institute for Evaluative Research in Orthopaedic Surgery of the University of Bern was used. The aim of this first publication on the MCS II was to describe in detail the new method of data collection and the structure of the developed data base system, via internet. The goal of the study was the assessment of the current state of treatment for fresh traumatic injuries of the thoracolumbar spine in the German speaking part of Europe. For that reason, we intended to collect large number of cases and representative, valid information about the radiographic, clinical and subjective treatment outcomes. Thanks to the new study design of MCS II, not only the common surgical treatment concepts, but also the new and constantly broadening spectrum of spine surgery, i.e. vertebro-/kyphoplasty, computer assisted surgery and navigation, minimal-invasive, and endoscopic techniques, documented and evaluated. We present a first statistical overview and preliminary analysis of 18 centers from Germany and Austria that participated in MCS II. A real time data capture at source was made possible by the constant availability of the data collection system via internet access. Following the principle of an application service provider, software, questionnaires and validation routines are located on a central server, which is accessed from the periphery (hospitals) by means of standard Internet browsers. By that, costly and time consuming software installation and maintenance of local data repositories are avoided and, more importantly, cumbersome migration of data into one integrated database becomes obsolete. Finally, this set-up also replaces traditional systems wherein paper questionnaires were mailed to the central study office and entered by hand whereby incomplete or incorrect forms always represent a resource consuming problem and source of error. With the new study concept and the expanded inclusion criteria of MCS II 1, 251 case histories with admission and surgical data were collected. This remarkable number of interventions documented during 24 months represents an increase of 183% compared to the previously conducted MCS I. The concept and technical feasibility of the MEMdoc data collection system was proven, as the participants of the MCS II succeeded in collecting data ever published on the largest series of patients with spinal injuries treated within a 2 year period

Multidisciplinary inpatient rehabilitation improves the long-term functional status of geriatric hip-fracture patients

Background As the world population ages, the number of hip-related fractures in the elderly is steadily increasing. These fractures generate a major worldwide healthcare problem and frequently lead to deterioration of life quality, mobility and independence in activity of daily life of geriatric patients. At present, many studies have investigated and proved benefits of multidisciplinary orthogeriatric care for elderly hip-fracture patients. Only few studies however, have analyzed treatment concepts for those patients directly following discharge from hospital in specialized rehabilitation centers. The aim of this study was to evaluate effects of a multidisciplinary inpatient rehabilitation on the short- and long-term functional status of geriatric patients who suffered from hip fracture. Methods A total of 161 hip-fracture patients aged 80 years and above, or additionally 70 years and above suffering from age-typical multimorbidity were included in this study. Patients who had an initial Barthel Index lower than 30 points were excluded from this study, as most of these patients were not able to attend a therapy at the rehabilitation center due to a poor functional status. The patients were separated into two subgroups dependent on the availability of treatment spots at the rehabilitation center. No other item was used to discriminate between the groups. Group A (n = 95) stayed an average of 21 days at an inpatient rehabilitation center that specialized in geriatric patients. Group B (n = 66) underwent the standard postoperative treatment and were sent home with further treatment by their general practitioner, nursing staff and physiotherapists. To evaluate the patients’ functional status over the course of time we used the Barthel Index, which was evaluated for every patient on the day of discharge, as well as during checkups after 3, 6 and 12 months. Results The average Barthel Index at the day of discharge was 57.79 ± 14.92 points for Group A and 56.82 ± 18.76 points for Group B (p = 0.431). After 3 months, the average Barthel Index was 82.43 points for Group A and 73.11 points for group B (p = 0.005). In the 6-month checkup Group A’s average Barthel Index was 83.95 points and Group B’s was 74.02 points (p = 0.002). After 12 months, patients from Group A had an average Barthel Index of 81.21 while patients from Group B had an average Barthel Index of 69.85 (p = 0.005). Conclusion The results of this study reveal a significantly better outcome concerning both, short-term and long-term functional status after 3, 6 and 12 months for geriatric hip-fracture patients, who underwent an inpatient treatment in a rehabilitation center following the initial therapy