Statischer Stiffness-Index von zwei Multikomponenten-Bandagen-Kompressionssystemen: Ergebnisse einer randomisierten kontrollierten Studie an gesunden Probanden

Zusammenfassung Zweck Vergleich der Leistung von zwei Mehrkomponenten-Kompressionssystemen. Methoden In dieser randomisierten, kontrollierten Studie wurden beide Beine von 25 gesunden Probanden nach dem Zufallsprinzip entweder mit einem Kompressionssystem der neuen Generation (UrgoK1, eine einzige Binde) oder einem etablierten System (UrgoK2, zwei Binden) als Kontrolle bandagiert. Beide Systeme wurden Tag und Nacht getragen. Arbeits- und Ruhegrenzflächendruck wurden unmittelbar nach dem Anlegen und nach 4 h, 24 h, 48 h und 72 h gemessen und der Static Stiffness Index (SSI) berechnet. Ergebnisse Nach 4 Stunden wurden mit beiden Systemen ähnlich hohe Arbeitsdrücke und mäßige Ruhedrücke registriert. Im Zeitverlauf folgten die Druckänderungen und des SSI den gleichen Kurven. Nach 48 h wurde ein SSI ≥ 10 mmHg bei 88 % der getesteten und 76 % der Kontrollsysteme erreicht, was die Nichtunterlegenheit des Testsystems bestätigt (p = 0,016). Beide Systeme wiesen gute Halteeigenschaften auf und waren gut verträglich, aber das getestete System wurde von der Mehrheit der Probanden als deutlich angenehmer empfunden und schließlich dem Kontrollsystem vorgezogen. Schlussfolgerung Das neue Kompressionssystem erreichte ähnliche Leistungen wie die Kontrolle, aber seine bessere Akzeptanz könnte ein Vorteil für die Patientencompliance sein. Diese vielversprechenden Ergebnisse müssen in einer klinischen Studie an Patienten mit Unterschenkelulcera und/oder Ödemen bestätigt werden.

About the weight and size parameters of electromagnetic stiffness correctors

A significant reduction in the levels of general ship vibrations can be achieved by using vibration isolators with a “floating” section of zero stiffness in vibration protection suspensions. In such devices, in parallel to the main elastic element, the so-called stiffness corrector (compensator) is switched on - a device with a negative coefficient of static stiffness, equipped with a restructuring system that ensures the retention of the corrector elements when the relative position of the vibrating and protected objects, caused by a change in static forces acting on these objects. One of the variants of the corrector is an electromagnetic stiffness corrector, in which the power characteristic with a negative stiffness coefficient is provided by two electromagnets with a common armature turned on in opposite directions. The disadvantage of such correctors is the dependence of their overall dimensions on the value of the permissible relative displacement of the vibrating and protected objects. The article deduced mathematical expressions that approximately determine the dependence of the overall dimensions of the stiffness corrector electromagnets on the value of the calculated relative displacement of the vibrating and protected objects, the possible field of application of vibration isolators Xwith electromagnetic stiffness correctors is determined.

Numerical and experimental study on the static performance of externally pressurized thrust bearings lubricated with refrigerant gases

Purpose Oil-free heat pumps that use the system refrigerant gases as lubricants are preferred for thermal management in future space applications. This study aims to numerically and experimentally investigate the static performance of externally pressurized thrust bearings lubricated with refrigerant gases. Design/methodology/approach The refrigerant gases R22, R410A and CO2 were chosen as the research objects, while N2 was used for comparison. Computational fluid dynamics was used to solve the full 3 D Navier–Stokes equations to determine the load capacity, static stiffness and static pressure distribution in the bearing film. The numerical results were experimentally verified. Findings The results showed that the refrigerant-gas-lubricated thrust bearings had a lower load capacity than the N2-lubricated bearings, but they presented a higher static stiffness when the bearing clearance was less than 9 µm. Compared with the N2-lubricated bearings, the optimal static stiffness of the R22- and CO2-lubricated bearings increased by more than 46% and more than 21%, respectively. The numerical and experimental results indicate that a small bearing clearance would be preferable when designing externally pressurized gas thrust bearings lubricated with the working medium of heat pump systems for space applications. Originality/value The findings of this study can serve as a basis for the further investigation of refrigerant gases as lubricants in heat pump systems, as well as for the future design of such gas bearings in heat pump systems for space applications.

Stiffness Evaluation and fast matching method of mechanical composite structure

Stiffness evaluation can improve the reliability and safety of combined machinery, which is often used to evaluate the performance of combined machinery. In order to study the stiffness evaluation method and rapid matching of mechanical composite structure, the composite machinery composed of high-power diesel is taken as the research object. The results show that the error between test mode and calculation mode is no more than 10%, indicating the reliability of finite element simulation model; two characterization methods of static stiffness and dynamic stiffness are determined, and the analysis methods of two characterization methods of combined machinery are discussed one by one. Taking the combined machinery of body, main bearing cap and oil pan as the research object, the overall stiffness characterization data of three parts are obtained one by one; finally, the principles of mechanical combination Stiffness Evaluation and rapid matching are summarized. This study provides a reference for Stiffness Evaluation and rapid matching of combined mechanical structures.

Quasi-Static Compliance Calibration of Serial Articulated Industrial Manipulators

This article presents a procedure for the quasi-static compliance calibration of serial articulated industrial manipulators. Quasi-static compliance refers to the apparent stiffness displayed by manipulators at low-velocity movements, i.e., from 50 to 250 mm/s. The novelty of the quasi-static compliance calibration procedure lies in the measurement phase, in which the quasi-static deflections of the manipulator’s end effector are measured under movement along a circular trajectory. The quasi-static stiffness might be a more applicable model parameter, i.e., representing the actual manipulator more accurately, for manipulators at low-velocity movements. This indicates that the quasi-static robot model may yield more accurate estimates for the trajectory optimization compared with static stiffness in the implementation phase. This study compares the static and apparent quasi-static compliance. The static deflections were measured at discretized static configurations along circular trajectories, whereas the quasi-static deflections were measured under circular motion along the same trajectories. Loads of different magnitudes were induced using the Loaded Double Ball Bar. The static and quasi-static displacements were measured using a linear variable differential transformer embedded in the Loaded Double Ball Bar and a Leica AT901 laser tracker. These measurement procedures are implemented in a case study on a large serial articulated industrial manipulator in five different positions of its workspace. This study shows that the measured quasi-static deflections are bigger than the measured static deflections. This, in turn, indicates a significant difference between the static and apparent quasi-static compliance. Finally, the implementation of the model parameters to improve the accuracy of robots and the challenges in realizing cost-efficient compliance calibration are discussed.

Theoretical and Experimental Research of Viscoelastic Damping Limb-Like-Structure Device with Coupling Nonlinear Characteristics

The nonlinear characteristic of vibration control systems has attracted increasing attention for its advantage in improving structural performance. In this paper, a new type of viscoelastic damping limb-like-structure (VE-LLS) device is proposed by combing the viscoelastic (VE) damper and limb-like-structure (LLS) together, which possesses coupling nonlinearity characteristic caused by geometric and material factors, as well as a remarkable advantage in improving the control performance. First, to explore the nonlinear geometrical effects on the static stiffness of the VE-LLS device, a formula is derived from static stiffness, and the results are discussed. Second, dynamic analysis is performed of the proposed device considering the coupling geometrical and material nonlinearities in frequency domain, with the real-time effect of frequency and temperature on the mechanical properties of the viscoelastic damper considered in solving the nonlinear vibration equation. The harmonic balance method (HBM) is used to solve the nonlinear dynamic equation. Then, the displacement transmissibility of the VE-LLS device is calculated and assessed. The results indicate that the proposed device possesses excellent vibration isolation performance, and the geometric parameters of the viscoelastic damper have significant nonlinear effect on the performance. Finally, an experiment is carried out of the VE-LLS device to verify the accuracy of the static stiffness analysis. The results show that the theoretical results agree well the experimental ones, and that the theoretical results have high accuracy and reliability.

Analysis of the nodal beam isolation system based on application of helical spring

A nodal beam isolation system allows the transmission of vibration from the source to an isolated element to be limited using nodal points on the elastic beam connecting them. These points are selected in such a way that their position during vibration is constant. The application of a helical spring as an elastic beam reduces the dimensions of the system and increases its applications. An effective computational model of the nodal beam isolation system based on a helical spring application as an elastic beam is presented in the paper. The model allows the position of nodal points to be determined for a given excitation frequency. It also allows the influence of system parameters on spring vibration amplitudes and static stiffness of the connection between the source and isolated element to be analysed. The analysis makes it possible to formulate conclusions facilitating the designer to select the proper system parameters for the given operating conditions. The results of numerical and experimental tests exhibit high compliance with the results of the presented model.