High Radial Stiffness Research Articles

ACCURACY OF INSTALLATION AND MACHINING OF BLANKS IN CAM ARBORS

The cam arbors are widely used for machining of axially symmetrical blanks with the medium and high radial stiffness. GOST 31.1066.04–97 is developed for cam arbors, but it lacks information on the accuracy of installation and machining of blanks on different metal-cutting machines, does not contain recommendations on engineering of such devices, and also contradicts other technical documentation and catalogues of western companies. In order to clarify such contradictions and to determine the data on the accuracy of cam arbors a number of articles are published. In the first article, which was published earlier, the consideration is given to deficiencies and contradictions to the mentioned GOST, and the material support for execution of complex investigations on the accuracy of installation and machining of blanks in cam arbors is described. The first part of this study is dedicated to the experimental investigations to determine the accuracy of installation of reference rings in the pilot samples of cam arbors with different design parameters. Upon analysis of the obtained data concerning the accuracy of installation the scope of experiments on the accuracy of machining of a batch of blanks in cam arbors was determined, methods of procedures were developed and the necessary pilot samples of fittings and other equipment were defined. The second part of the study is dedicated to the description of the results of experiments concerning the accuracy of turning and milling of blanks in different pilot samples of cam arbors. A batch of blanks (at least 30 blanks in a batch) with the same nominal parameters was machined during each experiment, then, the obtained results were processed by statistical methods. The third part of this study is dedicated to investigation of the precision reliability of cam arbors; to this end, a work bench was developed and manufactured which could make it possible to fix the pilot blank with the specified axial force, to hold it in the fixed state and to unfix. A number of cycles was brought to 200 thousand and it was determined that the cam arbors have the increased precision reliability.

Subjective approach to optimal cross-sectional design of biodegradable magnesium alloy stent undergoing heterogeneous corrosion

Existing biodegradable Magnesium Alloy Stents (MAS) have several drawbacks, such as high restenosis, hasty degradation, and bulky cross-section, that limit their widespread application in a current clinical practice. To find the optimum stent with the smallest possible cross-section and adequate scaffolding ability, a 3D finite element model of 25 MAS stents of different cross-sectional dimensions were analysed while localized corrosion was underway. For the stent geometric design, a generic sine-wave ring of biodegradable magnesium alloy (AZ31) was selected. Previous studies have shown that the long-term performance of MAS was characterized by two key features: Stent Recoil Percent (SRP) and Stent Radial Stiffness (SRS). In this research, the variation with time of these two features during the corrosion phase was monitored for the 25 stents. To find the optimum profile design of the stent subjectively (without using optimization codes and with much less computational costs), radial recoil was limited to 27 % (corresponding to about 10 % probability of in-stent diameter stenosis after an almost complete degradation) and the stent with the highest radial stiffness was selected.The comparison of the recoil performance of 25 stents during the heterogeneous corrosion phase showed that four stents would satisfy the recoil criterion and among these four, the one having a width of 0.161 mm and a thickness of 0.110 mm, showed a 24 % – 49 % higher radial stiffness at the end of the corrosion phase. Accordingly, this stent, which also showed a 23.28 % mass loss, was selected as the optimum choice and it has a thinner cross-sectional profile than commercially available MAS, which leads to a greater deliverability and lower rates of restenosis.

Design and evaluation of a novel anti-reflux biliary stent with cone spiral valve.

Endoscopic placement of biliary stent is a well-established palliative treatment for biliary obstruction. However, duodenobiliary reflux after stent placement has been a common problem which may lead to dreadful complications. This paper designed a novel anti-reflux biliary stent with a cone spiral valve. Fluid-Structure Interaction (FSI) simulations were established to evaluate the efficiency of the anti-reflux stent comparing with a clinically applied standard stent. According to the stress distribution of the valve, the fatigue performance in the stress concentration area was analyzed. The results show that when the antegrade flow through the valve, the cone spiral valve could stretch and open to realize adequate drainage under the normal physiological pressure of biliary tract; When the duodenal reflux through the valve, the valve would be compressed and close with a result of nearly zero at the outlet flow rate. Furthermore, the anti-reflux stent achieved improved radial mechanical performance with 2.7 times higher radial stiffness than standard stent. Finite element analysis (FEA) also indicates that compared with the standard stent, the addition of the anti-reflux valve had little negative effect on flexibility of the stent. Fatigue analysis results showed that the valve was reliable. This research provides the new stent with a cone spiral valve and proves that it is technically feasible and effective for preventing the duodenobiliary reflux while ensuring the antegrade bile flow without compromising the other biomechanical performances.

A Pneumatic/Cable-driven Hybrid Linear Actuator with Combined Structure of Origami Chambers and Deployable Mechanism

Pneumatic actuators have been widely used in robotics due to their inherent compliance and relatively high strength. In this letter, the authors report on the design, analysis and experimental validation of a novel pneumatic/cable-driven hybrid linear actuator whose structure is a combination of origami chambers and passive deployable mechanism. Under the joint actuation of the cable and compressed air, the proposed actuator can generate bidirectional motion; meanwhile, both thrust and tensile force can be produced. The combined structure of the rigid deployable mechanism and the axially soft origami chambers possesses high radial stiffness and an extension ratio up to 200% without radial expansion. The position can be controlled at whole motion range through a simple strategy and the actuation pressure can be as low as 2 kPa at no load. The kinematic as well as the quasi-static model is developed to accurately predict the behavior of the actuator and design the control strategy. A prototype is built based on a new fabrication method, on which the validation experiments are conducted. The experimental results prove the effectiveness of the model and show that the prototype possesses acceptable positioning accuracy, even when an external load is exerted on its moving plate.

The Complementary Functions Method Solution to the Functionally Graded Polar Orthotropic Rotating Hyperbolic Disks with Both Radially and Circumferentially Aligned Fibers

In the present study, efforts have been made to numerically evaluate elastic displacements and stresses in a convergent or divergent hyperbolic disk subjected to a centrifugal force of constant circular velocity. The disk material is assumed to be continuously radially functionally graded (FG) with two orthotropic materials based on the simplest Voigt rule with a power of volume fraction of two constituents. The fibers are assumed to be aligned along either radial (RR) or circumferential (CR) directions. Having been a second order differential equation with variable coefficients, the governing equation so-called Navier equation is first derived and then put in the form of two differential equations of first order. These two ordinary differential equation set is originally solved based on the initial value problem (IVP) by employing the Complementary Functions Method (CFM). The numerical results are verified with the corresponding benchmark results for uniform thickness FG polar orthotropic disks. The radial variation of the elastic fields in a hyperbolic disk is investigated for several boundary conditions, disk profile parameters, and the gradient parameter for both the radially and circumferentially aligned fibers. Some numerical results are also presented. Under the case that is considered in this study, it is revealed that the CR disk offers much higher elastic fields than RR disk under all boundary conditions. For a composite rotating disk rotating at a constant speed, it will be better to align fibers along the radial directions, to use convergent disk profiles, and to locate the material having higher radial stiffness at the outer surface. It is also disclosed that the location of the maximum Von-Mises equivalent stress in fixed-free disks varies regarding the fiber orientation.

Nonlinear dynamic analysis of a rotor-bearing system with porous tilting pad bearing support

Porous tilting pad bearings (PTPBs) show a potential for using in high-speed, high precision rotating machinery that requires high bearing stiffness and good stability. In this study, the nonlinear characteristics of a rotor supported on PTPBs are investigated. The Darcy equations and the modified Reynolds equations are adopted to establish the gas flow model in porous materials and gas film region, respectively. The pad motions and rotor motions are also included in the numerical nonlinear model. The advantages of PTPBs over tilting pad journal bearings are discussed. PTPBs with externally pressurized gas can avoid friction during startup and shutdown, improve the load capacity at low rotational speeds, and effectively suppress subsynchronous vibrations at high rotational speeds. The nonlinear characteristics of the rotor-bearing system with various bearing parameters, such as supply pressure ratio, nominal bearing clearance, pad tilting and radial stiffness, are analyzed. Poincare maps, predicted rotor orbit and bifurcation diagrams are used. High supply pressure ratio and small nominal bearing clearance can significantly decrease the orbit size and increase the critical speed. Low tilting and high radial stiffness can improve system stability. This study reveals the complex nonlinear characteristics of the system and provides guidance for designing PTPBs for using in high-speed rotating machinery.

Design and Development of Double Spiral Shaped Flexural Feed Stage for Micro-drilling Workstation

Flexure based system is class of compliant mechanisms which allows motion by bending the load elements. Accurate linear motion is one of the features of the flexure based systems. Due to these advantages flexural based mechanisms are used in various applications demanding micro and nano-positioning accuracy. The established high positioning accuracy of flexural mechanisms sets the motivation and promise for its utility in development of economical micro-drilling work station. This paper presents development of flexural guideways for micro-drilling workstation. Flexural systems are light in weight, possess low friction and require no lubrication. Use of spiral shape flexural guideways is the key element for accurate linear motion in feed direction in the developed system. In this paper, proposed spiral shape flexural mechanism is analyzed for its linear motion and strength using finite element analysis. The linear motion of the flexural feed stage is observed under feed force and undesirable lateral forces. The low axial stiffness and high radial stiffness is required to provide accurate linear motion even under presence of the undesirable lateral forces. Based on finite element analysis, the flexural design is converged and then accordingly fabricated for its implementation. The experimental results have shown that the flexural mechanism is capable of providing linear motion within ±5 µm accuracy. Further implementation of flexural stage could reduce the positioning errors. The inherent accuracy in linear motion of the flexural guideways has enabled to make micro-drilling up to 50 µm with ease and simplicity in design.

A new flow diverter stent for direct treatment of intracranial aneurysm

The use of a stand-alone flow diverter (FD) stent has demonstrated itself as an efficacious endovascular approach to intracranial aneurysm treatment. FD stents that are currently available adopt an interwoven braided design. The relatively low radial stiffness intrinsic to this design could cause difficulty in deployment and poor stent–wall apposition, leading to high complication rates. A new FD stent is proposed to overcome the problems of the interwoven FD stents. The new device is manufactured from a Nitinol tube through a laser-cutting technique, and its unique structure allows for both low porosity and high packaging efficiency. Computational simulation using Abaqus has been conducted to investigate the radial stiffness and longitudinal flexibility of the new device. The new device exhibits high radial stiffness when compared to interwoven FD stents and superior longitudinal flexibility. Results from on-going in-vivo experiments and CFD simulations have also demonstrated the efficacy of the new device as a FD stent.

Modeling and simulation for the critical bending force of power chucks to guarantee high machining precision

The progressive development of hard turning technology places greater demands upon clamping devices. The chuck is required not only to grip the workpiece securely but also to have high and stable radial chucking stiffness to guarantee high machining accuracy. As a primary property of a chuck, the clamping force, which greatly affects the security and precision of the machining process, must be meticulously determined. However, existing approaches for determining the required clamping force of jaw-chucks have mainly focused on their security. This is especially true for the crucial computation model for determining the critical bending force, which has more influence on the machining accuracy than other components of the cutting force. A new analytic computation model for determining the critical bending force of three-jaw power chucks, taking machining precision into account, is introduced in this study. The finite element method was applied and experiments performed to assist the modeling work. The results show that, when the jaw contacts the workpiece along its full clamping length, the variation in apparent radial chucking stiffness with respect to the direction of the bending force can be eliminated. In addition, an entirely uniformly distributed clamping force is desirable for the maintenance of larger critical bending forces, and a tiny negative initial angle is preferable. Furthermore, the critical bending force and radial chucking stiffness can be improved dramatically by enlarging the clamping length. This approach is helpful in the substitution of hard turning for grinding as the last process of machining.

Comparison of c-type flexures with different bending radius

The flexure bearing is one of the key components of linear motor. Due to its frictionless, wearless, high radial and low axial stiffness; it is a very critical part of any linear actuator. The flexure bearing has increased the reliability and life of operation of linear actuators used in cryocoolers. This paper discusses the failure aspects of C-Type flexure with 3 mm bending radius in comparison with flexure bearing of different bending radii. Experimental results of 3 mm and 8 mm bending radii flexures are also discussed.

Inspiration from nature: dynamic modelling of the musculoskeletal structure of the seahorse tail

Technological advances are often inspired by nature, considering that engineering is frequently faced by the same challenges as organisms in nature. One such interesting challenge is creating a structure that is at the same time stiff in a certain direction, yet flexible in another. The seahorse tail combines both radial stiffness and bending flexibility in a particularly elegant way: even though the tail is covered in a protective armour, it still shows sufficient flexibility to fully function as a prehensile organ. We therefore study the complex mechanics and dynamics of the musculoskeletal system of the seahorse tail from an engineering point of view. The seahorse tail derives its combination of flexibility and resilience from a chain of articulating skeletal segments. A versatile dynamic model of those segments was constructed, on the basis of automatic recognition of joint positions and muscle attachments. Both muscle structures that are thought to be responsible for ventral and ventral-lateral tail bending, namely the median ventral muscles and the hypaxial myomere muscles, were included in the model. Simulations on the model consist mainly of dynamic multi-body simulations. The results show that the sequential structure of uniformly shaped bony segments can remain flexible because of gliding joints that connect the corners of the segments. Radial stiffness on the other hand is obtained through the support that the central vertebra provides to the tail plating. Such insights could help in designing biomedical instruments that specifically require both high bending flexibility and radial stiffness (e.g. flexible stents and steerable catheters).

Design Considerations for Achieving High Radial Stiffness in an Attraction-Type Magnetic Bearing With Control in a Single Direction

In past work, the authors have proposed a radial magnetic bearing architecture where the rotor was kept suspended only by means of magnetic forces produced by permanent magnets working in attraction mode and the rotor was actively controlled only in one degree of freedom (d.o.f.), i.e., its axial direction. Although the presented architecture is simpler than those bearings with active control in two or more d.o.f., it presented limitations mainly of low radial stiffness. So, in this context this paper discusses ways to enhance the radial stiffness in this kind of bearing and presents simplified analytical methods used to find magnets and actuator optimal dimensions that gives both ring magnets radial stiffness and actuator force/current ratio maximum intensities.

Mechanical Properties of Open-Cell, Self-Expandable Shape Memory Alloy Carotid Stents

Mechanical properties of carotid stents are important for the selection of the implantable device. The efficacy of cell design is usually investigated on the basis of clinical follow-ups; however, for the specific carotid application the relative importance of the cell design on the stenting outcome is debated. Ideally, a carotid stent should have at the same time low bending stiffness (i.e., high flexibility) to correctly conform to the vessel curvatures in the stenotic region and high stiffness to sustain the vessel wall in the radial direction. In this study, experimental tests on six carotid open-cell design self-expandable stents were carried out to assess bending and radial stiffness. A four-point bending test was adopted to measure the bending stiffness. Radial stiffness was obtained by measuring the stent resistance to local compression in a V-shaped support. Geometrical features, such as the link positioning and their length, were examined as a possible determinant of the mechanical properties of the tested stents. The tested stents showed very different geometrical features and mechanical properties despite similar material and a common open-cell structure consisting in rings connected by roughly straight links. In particular, different strategies are evident regarding the link position. Three distinct behaviors were observed: stents with both low radial and bending stiffness, moderate bending and high radial stiffness, and high bending and moderate radial stiffness. In general, a large link length allows the stent to be more flexible under bending condition, whereas the mutual links positioning plays a key role in the radial stiffness of these devices. Furthermore, for a fixed strut layout, a correlation was found between the strut cross area, as well as metal-to-artery ratio and the resultant radial and bending stiffness.

Finite Element Analysis of Different Flexure Springs

Flexure spring suspensions have demonstrated the ability to provide long operating lifetimes for cryocoolers. The good flexure spring need high radial stiffness and high fatigue life. The profile curves are very important for flexure spring. In this paper, based on the finite element analysis software (ANSYS), geometrically nonlinear static structural analysis and nonlinear dynamics structural analysis were made to several different flexure springs. The fatigue strength, axial and radial stiffness, modal frequency were calculated and listed. The different performance between linear flexure spring and spiral flexure spring were discussed, which would provide an advisory opinion for the design and application of flexure spring in space cryocooler.

008 Biomechanical design of the intracranial stent for the cerebral aneurysm treatment

Introduction: The mechanical characteristic required for an aneurysm stent is high longitudinal flexibility and low radial stiffness. Longitudinal flexibility is necessary to navigate the tortuous shape inherent to the intracranial...

CHARACTERISTICS OF OIL-LUBRICATED PARTIALLY HERRINGBONE GROOVED JOURNAL BEARING

An experimental investigation of the performance of oil-lubricated partially herringbone- grooved journal bearing (HGJBs) which have a beveled-step groove profile have been carried out. The bearing groove parameters (groove angle α, groove width ratio β , groove depth ratio Γ ) have been optimized for a wide range of bearing operating conditions in search of the best stability characteristics. Hydrodynamic lubrication unit with some accompanying apparatuses are used to measure the pressure distribution, attitude angle, Eccentricity, contact and friction torque. The optimized values are (α = 26.78o , β =0.55, Γ =2.2). The test results are compared to experimental results for the completely grooved bearing which have the same beveled-step groove profile [1] ,and rectangular groove profile . In comparison of the previous work the introduced grooved configurations showed high radial stiffness and load capacity, low friction torque and better stability characteristics.

1216 ステントにおけるセル・リンクの寸法比が剛性におよぼす影響の実験的評価(G02-2 医療とバイオエンジニアリング(2),G02 バイオエンジニアリング)

High radial stiffness and longitudinal flexibility are essential mechanical properties of a stent. These mechanical properties depend on stent structures and dimension. A stent is composed of a cell and a link. We calculated effect of design factor on stent structures. The objective of this paper was to investigate the influence between longitudinal lengths of a cell (A) and a link (B) and these mechanical properties using compression test machine. The results showed that the radial stiffness increased with the cell-link length ratio (B/A). Radial stiffness is independent of compression position.

ステントにおけるセル・リンクの寸法比が力学特性におよぼす影響 : 実験による検討(S04-1 医療とバイオエンジニアリング,工学技術の医療応用(1),S04 医療とバイオエンジニアリング,工学技術の医療応用)

High radial stiffness and longitudinal flexibility are essential mechanical properties of a stent. A stent consists of cell and link, which is minimal structure unit. Mechanical properties of a stent are depended on these configuration and dimension. In this paper, the relation between mechanical properties and the longitudinal length of cell and link was investigated. Six stents were constructed and measured the bending stiffness using 4-points bending test machine. The result showed that the bending stiffness decreased with the cell-link length ratio (B/A). The result was-not consistent with the numerical analysis. The disagreement suggests that the deformation mode under bending condition changes with B/A.

피스톤계 마찰 측정 장치 개발

This paper presents a novel piston friction force measurement system that has characteristics of relieving the pressure force acting on the upper surface of the liner; the system uses general rubber O-rings for combustion chamber scaling, and does not need special changes to the piston top land. The lower supporter of the floating liner increases stiffness in liner axial direction, and results in the increase of natural frequency. The upper supporter has multi-layer structure designed for low axial stiffness and high radial stiffness. With the use of the present system, the effects of variation in clearance and piston ring tension were studied.

Modeling and control of a new horizontal-shaft hybrid-type magnetic bearing

This paper reports on the development of a new horizontal-shaft hybrid-type magnetic bearing system. The bearing system will be used for a horizontal-shaft machine. The rotor is levitated due to the repulsive force between a stator and a rotor permanent magnet (PM). A lower cost and higher radial stiffness have been achieved by using a strontium-ferrite magnet on the rotor and an Nd-Fe-B PM above and below the rotor magnet. A finite-element analysis was performed to calculate the levitation force and radial stiffness. An upper stator magnet subtending an angle of 45/spl deg/ provides the best compromise between a large levitation force and radial stiffness. A model for the horizontal-shaft hybrid magnetic bearing system has been developed and includes the effect of the rotor dynamics and the electromagnetic forces. An integral servocontroller was designed to stabilize the axial position. The controller has been implemented in a digital signal processor. Experimental results performed on a prototype system are in agreement with the theoretical results.