Preload Method Research Articles

Development of a newly structured variable preload control device for a spindle rolling bearing by using an electromagnet

For high speed and high efficiency machining, the spindle of modern machine tools simultaneously requires high speed and high stiffness characteristics, and its range of use rotation is becoming wider. Both heavy cutting at low speed and light cutting at high speed must be carried out successively in series with a single machine tool spindle. As such, many studies are being carried out on variable preload control methods that apply a preload to a spindle rolling bearing, as an alternative to the existing fixed position preload and constant pressure preload methods. This paper introduces a newly structured variable preload control device that can arbitrarily adjust the preload applied to spindles employing a rolling bearing. The device controls the coil current on an electromagnet and thereby uses the magnetic force between the electromagnet and a magnetic substance to arbitrarily control the preload applied to the rolling bearing during operation. A prototype for the variable preload control device of the proposed structure was created and a functionality test was then carried out with a test bench prepared using a load cell. The operating principle of the proposed device was verified and the interrelationships between the coil current on the electromagnet and the preload applied to rolling bearing were analyzed through the functionality test. Lastly, the fabricated variable preload control device was applied to a prototype of a spindle system, and a rigidity test was carried out. The test results confirmed that the variable preload control device operates properly and smoothly.

A Method to Increase the Lateral Reversible Region of Bulk YBCO Above a Permanent Magnet Guideway

Lateral reversible region of the bulk high-Tc superconductor (HTSC) above the permanent magnet guideway (PMG) is a key parameter for the high-Tc superconducting (HTS) maglev system. The lateral stability and guidance force are proportional to the width of the lateral reversible region. When the lateral displacement of the bulk HTSC exceeds the reversible region, the maglev system will return to a new lateral equilibrium position. The method with the use of pre-displacement can successfully increases the lateral reversible region of the bulk HTSC. By the correct choice of the maximum lateral offset and a new starting point, the instability of flux motion can be suppressed. Unsuitable usage of this method will cause the intersection of guidance force and reduce the reversible region. Analyses based on the magnetizing history and pinning metamorphoses well explain the experimental results. Difference between this method and the pre-load method is also discussed in this article.

Investigation of variable optimum preload for a machine tool spindle

Angular contact ball bearings have been widely used in machine tool spindles, and the bearing preload plays an important role on the performance of the spindle. With the development of high speed machining, especially for high speed milling, heavy cutting at a low speed and light cutting at a high speed are often performed on a single machine tool spindle, thus, high stiffness at low speed and low temperature rise at high speed are required. The traditional constant pressure preload method cannot meet the technical requirement of this kind of spindle any more. The variable preload technology is systematically investigated in this paper. At high speed range, FEM method is used to analyze the temperature distribution of the spindle, and the variable spindle preload is determined according to the constraint of temperature rise of bearings. At low speed range, the spindle preload is resolved by the fatigue life of bearings. The dynamic stiffness of the variable preload spindle is analyzed utilizing the Transfer Matrix Method (TMM) and a nonlinear bearing model that includes the centrifugal force and gyroscopic effects. An experimental set-up for the variable preload spindle is developed using hydraulic pressure that can automatically adjust the bearing preload. The proposed method to determine variable preload is verified experimentally by measuring the dynamic stiffness of the spindle and the temperature rise of the test bearing. The results show that the variable preload spindle gives outstanding behavior that the temperature rise at high speed is lower than that of the constant pressure preload spindle, and the dynamic stiffness at low speed range is significantly increased.

Characteristic of the Guidance Force in the High-T c Superconducting Levitation System with Pre-Load Process

The stable levitation above permanent magnet is an important characteristic of the bulk high-Tc superconductor (HTS). When an external force pushes the bulk HTS up, down or sideways, or tries to tilt it, a restoring force can return it to its initial position. The HTS Maglev relied on this characteristic can overcome the external force from wind or pass the curve lines successfully. The change of guidance force (GF) during many times lateral movement is studied. Experiments show that GF increases during the lateral movement, no matter what kind of PMG or HTS is used, and the change of the GF slows down after 5 times lateral movement. The pre-load method can reduce the levitation force decay during lateral movement. So the influence of GF by the pre-load method is needed to be studied. It is found that the pre-load method can increase GF and reduce the change of the GF during lateral movement. The Halbach permanent magnetic guideway (PMG) can offer much more GF but the change is larger just as the levitation force decays. The GF of cylindrical bulk HTS increases more than of the rectangular bulk HTS in the pre-load case. The characteristics of the GF during the lateral movement are explained. These results are important for further HTS Maglev vehicle system designs.

Development of automatic variable preload device for spindle bearing by using centrifugal force

Machine tool spindles of late require high stiffness and fast rotation characteristics all at once for high-speed, high-efficient processing, as well as for a wide range of use rotation. As such, many studies are being carried out on automatic variable preload control methods that apply a preload to a spindle rolling bearing as an alternative to the existing fixed position preload and constant pressure preload methods. This paper introduces a newly structured automatic variable preload device that can automatically adjust the preload applied to spindles employing a rolling bearing. It proposes an automatic variable preload device with a completely new composition comprising of a main bearing to which the preload is applied, an auxiliary bearing that conveys the force and a centrifugal element that converts the centrifugal force into a force in the axial direction, and a constant pressure preload spring that applies the initial preload to the main bearing. Other changes in the centrifugal force are also presented. The proposed composition was validated through a contact nonlinear analysis, and the design data necessary to create a prototype were obtained. A prototype for the automatic variable preload device using centrifugal force was then created and tested to confirm that the preload device of the proposed structure runs properly and smoothly.

Characteristic study of high- Tc superconducting maglev under side-loading

In practical application of High- T c Superconducting (HTS) maglev, slant is an observable defect. It was caused by constantly one side on and off the vehicle by passengers. So far, this phenomenon has not been reported yet. In order to understand its influence on the stability of the HTS maglev, we experimentally studied the dynamic characteristic and slant effect of HTS maglev under center-load and side-load. It was found that load destabilizes the vehicle, and the side-load can obviously slant the vehicle body. In the end, the pre-load method was proposed to enhance the dynamic stability and suppress the slant, which proved to be considerably effective. These results are critical in practical running of HTS maglev.

Dynamic Force Properties of a High Temperature Superconducting Maglev Test Vehicle

In order to investigate the feasible application of a high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting (HTS) levitation system to a maglev train or a space vehicle launcher, we construct a demonstration maglev test vehicle consisting of two linear permanent magnets (PM) guideways and a test levitator with multi-block melt-processed YBaCuO superconductors. By using a vibration testing technique, we measure the dynamic force properties of the test vehicle in different field cooling (FC) and loading conditions. In both vertical and lateral vibration directions, resonance frequencies and related magnetic stiffness show large dependence on the FC height (FCH) and the load weight. The resonance frequencies increase as the FCH decreases or the load weight is reduced. The magnetic stiffness is also increased by using the low FCH or adding the load weight. It is shown that the dynamic properties of the HTS levitation system are closely related to the flux history in superconductors and the motion process of the system. Finally a low FC scheme and a preloading method are proposed to improve the stability of the HTS maglev vehicle.

Method to reduce levitation force decay of the bulk HTSC above the NdFeB guideway dueto lateral movement

A magnetic levitation vehicle using bulkhigh-Tc superconductors (HTSC) is considered as a promising transportation type thanks to itslateral inherent stability, but previous studies have found that the levitation force (LF)decays due to lateral movement. In this paper, a pre-load method is presented to reduce theLF decay, and the experimental results indicate that this method is very applicable insupressing this decay in spite of the applied field and material property of the bulkHTSC, and this effect can be ascribed to the reduction of the hysteresis loss inthe bulk HTSC, i.e. more trapped magnetic flux after the pre-load case. In theend, experimental results indicate that the Halbach PMG has an advantage toreduce the cost of the PMG, but its rate of LF decay is also larger due to lateralmovement

Studies on the levitation height decay of the high temperature superconducting Maglev vehicle

The levitation height decay was found in the high temperature superconducting (HTS) Maglev test vehicle system during man-loading running. Experimental results show that the no-load levitating system would drift to a new equilibrium position by the external loaded history, but the new equilibrium position will almost not drift by the second-round same loaded history. A new method is proposed to improve the stability of the HTS Maglev vehicle, that is, a pre-load was applied to the HTS Maglev vehicle before running. The impulse responses are performed on the HTS Maglev vehicle before the pre-load and after the pre-load. The results show that the pre-load method is considerably effective to improve the stiffness and damping coefficient of the HTS Maglev vehicle. Moreover, it helps to suppress the levitation height decay and enhance the stability of the HTS Maglev vehicle in practical operation.

Soil improvement for a storage yard using the combined vacuum and fill preloading method

This paper presents a case study of using the combined vacuum and fill surcharge preloading method to improve the foundation soil for a storage yard at Tianjin Port, China. A vacuum load of 80 kPa was applied for 4-8 weeks before fill surcharge was added in stages. The site to be improved was recently reclaimed using dredged clay slurry. Both the consolidated clay slurry fill and the seabed soils were very soft. After the combined vacuum and fill surcharge preloading, the ground settled more than 1 m. The average degree of consolidation achieved was more than 80%. The undrained shear strength of the soil increased twofold. The water content of the soil also decreased substantially. The soil improvement procedure using the combined vacuum and fill surcharge preloading method and the instrumentation scheme are described, the field monitoring data are presented and analyzed, and methods to estimate the degree of consolidation and several other issues related to the combined preloading method are discussed.Key words: case history, consolidation, ground improvement.

Dual-Stack Piezoelectric Device with Bidirectional Actuation and Improved Performance

Piezoelectric stacks can normally take significant compressive loads but cannot tolerate tension. Therefore, conventional piezoelectric stack actuators are mainly designed for the push-only actions and usually incorporate a compressive preload mechanism to protect the stack from experiencing tensile stresses. A common preload method is to include a mechanical spring in parallel with the stack, which may reduce the free stroke capability of the actuator and affect performance. In this research, a new bi-directional (can operate in both push and pull directions) actuator design is introduced, utilizing a pair of matching piezoelectric stack elements within the actuator housing. The stack elements are integrated in a mechanically opposing configuration and are electrically operated out of phase. To examine the performance advantages of the new concept, both analytical and experimental studies are conducted. The dual-stack actuator is compared with two internally preloaded single stacks integrated in a parallel configuration, thus both actuator systems are utilizing equivalent volumes of the piezoelectric material. The analysis indicates that the dual-stack actuator produces greater free stroke, output energy, and energy efficiency than the two parallel single-stack actuators. For experimental evaluations, a dual-stack actuator and an internally preloaded single-stack actuator are fabricated using the same materials, similar construction techniques, and the same piezoelectric stack elements. A testing procedure is formulated to determine the free stroke and blocked force of both the actuators. The experimental results verified the trends observed in the analytical predictions. That is, in addition to being bi-directional, the dual-stack arrangement can produce higher free stroke, blocked force, output energy, specific output energy, and energy efficiency, as compared to two preloaded, parallel-configured single-stack actuators. It is also concluded that by tailoring the dual-stack actuator, it will be 62% volume and weight of a conventional single-stack actuator that produces the same amount of blocked force and free strain.

Retinaldehyde, a Potent Inhibitor of Gap Junctional Intercellular Communication

Retinaldehyde and retinoic acid are derivatives of vitamin A, and retinaldehyde is the precursor for the synthesis of retinoic acid, a well-known inhibitor of gap junctional intercellular communication. In this investigation, we asked the question if retinaldehyde has similar effects on gap junctions. Gap junctional intercellular communication was measured by scrape-loading and preloading dye-transfer methods, and studies were carried out mainly on cultured liver epithelial cells. Retinaldehyde was found to be a more potent inhibitor (dye transfer reduced by 50% at 2.8 microM) than retinoic acid (dye transfer reduced by 50% at 30 microM) and glycyrrhetinic acid (dye transfer reduced by 50% at 65 microM). Both the 11-cis and all-trans forms of retinaldehyde were equally effective. Retinaldehyde inhibited dye transfer of both anionic Lucifer yellow and cationic Neurobiotin. Inhibition by retinaldehyde developed in less than two minutes at 50 microM, but unlike the reported case with retinoic acid, recovery was slower, though full. In addition to liver epithelial cells, retinaldehyde inhibited gap junctional communication in lens epithelial cells, retinal pigment epithelial cells and retinal ganglion cells.

Suppression of rotor fall for radial-type high-temperature superconducting magnetic bearing

The superconducting flywheel energy storage systems (SFESS) using superconducting magnetic bearings (SMBs) have been studied actively to contribute to electric daily load leveling. In development of SMBs, which are key technology of SFESS, it is one of the important issues to minimize descent of the rotor due to decline with time in levitation force of SMBs. Thus we have evaluated the levitation force of a module of 126 mm diameter class radial SMB in order to study of this subject. We have confirmed the effectiveness of a method using the temperature characteristic of a superconductor (SC) (the supercooling method), a method using the hysteretic characteristic of a SC (the pre-loading method), and a combination of these two methods. Therefore we have confirmed the characteristics and effectiveness of these methods.

Method of preload reduction during LVPVR analysis of systolic function: airway pressure elevation and vena cava occlusion.

A graded preload reduction during analysis of the left ventricular pressure-volume relationship (LVPVR) is required for derivation of end-systolic elastance (Ees) and preload recruitable stroke work (PRSW). The authors aimed to measure serial changes in these systolic function parameters before and during planned circulatory interventions using two different methods of preload alteration: a positive airway pressure plateau (APP) and inferior vena cava occlusion (IVCO). In eight animals, measurements were made at 38 degrees, 30 degrees, 32 degrees, 34 degrees, and posthypothermia 38 degrees C. In an additional eight animals, isoflurane, adrenaline, and aorta occlusion (balloon catheter occluder) were administered in series, each with a preintervention control measurement. Left ventricular volume was measured by conductance. Paired measurements of the systolic function parameters Ees and PRSW, each derived with two preload methods, were analyzed for bias. Circulatory alterations were achieved with the temperature, isoflurane, adrenaline, and aorta occlusion interventions. Measured changes in Ees and PRSW from control to intervention showed a strong correlation and no significant bias for APP in relation to IVCO. The APP-derived absolute values for Ees and PRSW demonstrated a consistent positive bias compared with IVCO. The APP method for preload reduction during LVPVR analysis detected changes in Ees and PRSW during the circulatory interventions in this model that were not different than those detected using another preload reduction method, IVCO. APP and IVCO are not interchangeable methods for preload reductions during LVPVR absolute quantitation of systolic function, and each needs to be used serially.

ラジアル型超電導磁気軸受におけるロータ降下の抑制

Superconducting flywheel energy storage systems (SFESS) using superconducting magnetic bearings (SMBs) have been studied to contribute to daily load leveling. It is known that the levitation force of SMBs used for SFESS varies with time due to flux creep. In providing noncontact support to the whole weight of the SFESS rotor using a SMB, it should be noted that a decline in the levitation force of the bearing would result in rotor over time. Accordingly, an important consideration in providing long-time noncontact support to the rotor of an SFESS by a SMB is to control and minimize rotor descent. Among promising techniques to control descent are a method using the temperature characteristics of superconductors (a supercooling method), a method using the hysteretic characteristics of superconductors (a pre-load method), and a combination of these two methods. A study was conducted on these rotor descent control methods to examine their respective effects. In this study, a series of tests was carried out on the control methods using a radial superconducting magnetic bearing of the 126mm diameter class, The test results were compared and analyzed to find major characteristics and effects of the three rotor descent control methods as applied to the radial SMB of an SFESS.

Recent development and improvement of vacuum preloading method for improving soft soil

This paper discusses the use of the vacuum preloading method (VPM) in China. During the use and application of the VPM in China, Tianjin Port Engineering Institute introduced sufficient modifications and improvements to the equipment and technology to achieve an increase in the vacuum beneath the sealing membrane, thus improving the consolidation of the soft clay being treated. When the preloading loads imposed by the VPM are incapable of meeting the operational requirements, a method of vacuum preloading in combination with surcharge fill may be employed. In some cases the surcharge fill was placed up to a height of 5·5 m with an imposed load of 100 kPa. Slopes often develop excessive displacement, destabilising the foundation, owing to the cutting operations and loads along the sides of the slopes. The VPM can be used to effectively solve such problems. Case studies of engineering projects are also presented, where (a) the VPM was used to improve and consolidate the slopes in coastal marine works and (b) clay-mixed retaining walls were erected in soft soil overburdened with a thick layer of sand when the method was used to improve soft soils. Le présent article examine l'utilisation de la méthode préchargée à vide (VPM) en Chine. Pendant l'utilisation et l'application de cette méthode en Chine, l'Institut d'Ingénierie du Port de Tianjin a apporté des modifications et des améliorations aux équipements et à la technologie afin d'augmenter le vide sous la membrane d' étanchéité, consolidant du même coup l'argile tender à traiter. Quand les Contraintes de précharge imposées par la méthode VPM ne peuvent satisfaire les besoins opérationnels, on pourra employer une méthode de préchargement à vide, en combinaison avec un remblayage en surcharge. Bans certains cas, le remblayage atteint une hauteur de 5,5 m avec une charge imposée de 100 kPa. Les talus développent souvent un déplacement excessif ce qui déstabilise les foundations à cause des opérations de déblaiement et à cause des charges le long du talus. La méthode VPM peut être utilisée pour résoudre ces probl`mes avec efficacité. Nous présentons aussi des études de projets d'ingénierie où, dans un premier cas, la méthode VPM a été utilisée pour améliorer et consolider les talus lors de travaux maritimes côtiers et où, dans un second cas, des murs de soutènement constitués d'un mélange argileux ont été érigés dans un sol tendre surchargéd'une épaisse couche de sable quand la méthode était utilisée pour améliorer les sols tendres.

A study on the relaxation of levitation property in an HTSC magnetic bearing

For realization of the flywheel system using high T c superconductors (HTSCs), AC loss is one of the serious problems to be solved. An un-uniformity of magnetization of permanent magnets rotating at high speed generates AC field around HTSC. This causes AC losses. In this study we assumed that AC field generated by a rotating permanent magnet is equivalent to AC field generated by coil current. Based on this model the experiments were done. These results were compared with those of numerical simulation. Furthermore, to suppress AC loss, a pre-loading method was suggested.

In vitro axial preload application during spine flexibility testing: towards reduced apparatus-related artefacts

Presently, there is little consensus about how, or even if, axial preload should be incorporated in spine flexibility tests in order to simulate the compressive loads naturally present in vivo. Some preload application methods are suspected of producing unwanted “artefact” forces as the specimen rotates and, in doing so, influencing the resulting kinematics. The objective of this study was to quantitatively compare four distinct types of preload which have roots in contemporary experimental practice. The specific quantities compared were the reaction moments and forces resulting at the intervertebral disc and specimen kinematics. The preload types incorporated increasing amounts of caudal constraint on the preload application vector ranging from an unconstrained dead-load arrangement to an apparatus that allowed the vector to follow rotations of the specimen. Six human cadaveric spine segments were tested (1-L1/L2, 3-L2/L3, 1-L3/L4 and 1-L4/L5). Pure moments were applied to the specimens with each of the four different types of compressive preload. Kinematic response was measured using an opto-electronic motion analysis system. A six-axis load cell was used to measure reaction forces and moments. Artefact reaction moments and shear forces were significantly affected by preload application method and magnitude. Unconstrained preload methods produced high artefact moments and low artefact shear forces while more constrained methods did the opposite. A mechanical trade-off is suggested by our results, whereby unwanted moment can only be prevented at the cost of shear force production. When comparing spine flexibility studies, caution should be exercised to ensure preload was applied in a similar manner for all studies. Unwanted moments or forces induced as a result of preload application method may render the comparison of two seemingly similar studies inappropriate.

Vacuum consolidation of soda-ash tailings

The Solvay process, widely used in industrial production of soda ash, generates a large quantity of tailings. The tailings consist of fine solids suspended in alkaline water that remain in a loose state, causing environmental concerns. An alternative solution for the management of sodaash tailings is presented in this paper, that is, the use of a vacuum pre-loading technique to consolidate the tailings so that they can be used as a foundation material in industrial sites. This paper presents the procedure and results of vacuum pre-loading consolidation of soda-ash tailings in a field trial. A vacuum pressure of approximately 90 kPa was applied to a 45 × 45 m area to a depth of 8 m via prefabricated vertical drains. The results showed that after 66 days of vacuum pre-loading treatment, the water content of the soda-ash tailings was reduced by 12·3% to 42·4%. Also, densification was shown by changes in void ratio, unit weight and settlement. The tailings were consolidated to a material with the undrained shear strength ranging from 22·3 to 34·4 kPa, compared with the initial value of 7·1–14·5 kPa. The allowable bearing capacity of the tailings reached 120 kPa as tested from the static loading plate test. The vacuum pre-loading method has shown to be a fast, effective and economically feasible alternative for in situ consolidation of soda-ash tailings.

N‐Methyl‐d‐Aspartate Releases γ‐Aminobutyric Acid from Rat Striatum In Vivo: A Microdialysis Study Using a Novel Preloading Method

In vivo microdialysis was used in conjunction with a novel dual-label preloading method to monitor changes in extracellular levels of gamma-aminobutyric acid (GABA) and glutamate due to N-methyl-D-aspartate (NMDA) infusion in the striatum of conscious, unrestrained rats. [14C]GABA and [3H]glutamate were applied in the dialysis stream for a preloading period of 30 min, after which dialysis perfusion was continued for up to 6 h and dialysate samples were collected for analysis by liquid scintillation spectrometry. NMDA (300 microM in the dialysate) caused significant rises in both 14C and 3H content measured in the dialysates, the majority of which remained associated with the preloaded GABA and glutamate, respectively. The NMDA-evoked release of both GABA and glutamate was blocked by the specific NMDA receptor antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP), indicating that the response was receptor mediated. The NMDA-stimulated release of glutamate was also totally abolished by concomitant application of the adenosine agonist 2-chloroadenosine or by prior frontal decortication. However, these two treatments caused little change in NMDA-evoked GABA release. These results show that NMDA causes release of GABA from the striatum in vivo by an NMDA receptor-mediated mechanism and that the majority of this release is not secondary to glutamate release from terminals of the corticostriate pathway. In addition, they confirm the results of previous studies investigating the effect of NMDA on endogenous glutamate release.