scholarly journals Model Research on the Influence of Bearing Preload Change on the Frequency and Form if Natural Vibrations of the Spindle System

2020 ◽  
Vol 14 (4) ◽  
pp. 284-297
Author(s):  
Paweł Turek ◽  
Wacław Skoczyński
Keyword(s):  
Natural Vibrations ◽  
Spindle System ◽  
Model Research ◽  
Bearing Preload

A State-Space Model for Monitoring Thermally Induced Preload in Anti-Friction Spindle Bearings of High-Speed Machine Tools

1994 ◽  
Vol 116 (3) ◽  
pp. 372-386 ◽  
Author(s):  
J. L. Stein ◽  
J. F. Tu
Keyword(s):  
State Space ◽  
Machine Tools ◽  
High Speed ◽  
The State ◽  
Spindle Speed ◽  
Spindle System ◽  
Thermally Induced ◽  
On Line ◽  
Bearing Preload ◽  
High Speed Machine

Catastrophic and premature bearing failure caused by excessive thermally induced bearing preload is a major design problem for spindle bearings of high-speed machine tools. Due to a lack of a low cost and easy to maintain on-line preload measuring technique, the traditional solution is to limit the maximum spindle speed and the initial bearing preload. This solution is incompatible with the need to increase machining productivity, which requires increasing the spindle speed, and to increase product quality (surface finish, dimensional accuracy), which requires increasing (or at least not decreasing) the preload to keep the spindle system stiff. This paper proposes a dynamic mathematical model of the spindle system, which can be used as part of a model-based monitoring system for estimating the spindle bearing preload. The model is derived from physical laws of heat transfer and thermoelasticity and represents the transient preload behavior induced by uneven thermal expansions within a bearing. The state-space structure of the model provides for efficient sensor selection and easy conversion into a state observer for on-line preload estimation. The state variables defined in the model are the temperatures of the outer ring/housing, the rolling elements, and the inner ring, while the induced preload is an algebraic function of these states. The model, which is successfully validated for two typical configurations of high speed spindle assemblies, provides a tool for understanding the basic mechanics of induced preload as a function of initial preload, spindle speed, and housing cooling conditions. Most importantly, the model meets the requirements as the basis of a preload observer developed by the authors. While the observer is not presented in this paper, basic issues related to its development are discussed.

Study of the Relationship between the Vibration Response and Milling Instability

2014 ◽  
Vol 945-949 ◽  
pp. 571-575
Author(s):  
Sheng Long Nong ◽  
Shang Han Gao
Keyword(s):  
Finite Element ◽  
System Design ◽  
Close Relationships ◽  
Ball Bearing ◽  
Vibration Response ◽  
Design Stage ◽  
Spindle System ◽  
Maximum Peak ◽  
The Relationship ◽  
Bearing Preload

This paper is concerned with the milling instability of spindle-ball bearing milling system. The finite-element analyzes is adopted. It is verified that there existed close relationships between the vibration response and the milling instability contributed by the same spindle mode. The spindle mode, which excites the maximum peak spectrum value, will produce the milling instability most likely. The front bearing preload has much more remarkable influences on spindle modes and milling stability than the rear one. It is therefore very important to adjust the front bearing preload according to the actual processing situations and stability demands in the spindle system design stage.

Factors Affecting the Organizational Justice in Ho Chi Minh City, Vietnam

2018 ◽  
Vol 9 (6) ◽  
pp. 523-528
Author(s):  
Vu Ba Thanh ◽  
◽  
Ngo Van Toan ◽  
Keyword(s):  
Organizational Culture ◽  
Quantitative Analysis ◽  
Organizational Justice ◽  
Survey Data ◽  
Internal Communication ◽  
Ho Chi Minh City ◽  
Research Model ◽  
Factors Affecting ◽  
Feedback Training ◽  
Model Research

The study was conducted to examine the factors affecting organizational justice in Ho Chi Minh City. Through quantitative analysis from the survey data for 242 civil servants working in Ho Chi Minh city to evaluate the scale and research model. Research results show that four factors: feedback, training, organizational culture and internal communication affect organizational justice in Ho Chi Minh city.

Why Are Children with Cochlear Implants at Risk for Executive Functioning Delays?

2020 ◽  
pp. 247-267
Author(s):  
William G. Kronenberger ◽  
David B. Pisoni
Keyword(s):  
Executive Functioning ◽  
Cochlear Implants ◽  
Family Environment ◽  
Fluid Intelligence ◽  
Deaf Children ◽  
Data Set ◽  
Theoretical Approaches ◽  
Model Research ◽  
Psychosocial Influences ◽  
Auditory Experience

Prelingually deaf children with cochlear implants (CIs) have about 2 to 5 times more risk for delays in specific domains of executive functioning (EF) than normal-hearing (NH) children, with about 25% to 40% of children with CIs showing delays in specific EF subdomains. This chapter reviews the rationale and evidence for two theoretical approaches to explaining this elevated risk for EF delay: language-focused approaches and biopsychosocial systems theories, such as the auditory neurocognitive model. Research supporting language-focused approaches, which attribute risk of EF delays entirely to language delays, has significant limitations. Furthermore, results from an extensive data set of EF outcomes in CI users are inconsistent with language-focused approaches. In contrast, biopsychosocial systems theories, which attribute risk for EF delay to a system of factors, including auditory experience, language, family environment/experiences, fluid intelligence, and psychosocial influences, provide the strongest evidence and potential for explaining EF delays and outcomes in children with CIs.

Population Genetics ofCaenorhabditis elegans: The Paradox of Low Polymorphism in a Widespread Species

Genetics ◽  
2003 ◽  
Vol 163 (1) ◽  
pp. 147-157 ◽  
Author(s):  
Arjun Sivasundar ◽  
Jody Hey
Keyword(s):  
Genetic Variation ◽  
Microsatellite Loci ◽  
Population Expansion ◽  
Widespread Species ◽  
C Elegans ◽  
Model Research ◽  
The World ◽  
Natural Isolates ◽  
History Of ◽  
Low Levels

AbstractCaenorhabditis elegans has become one of the most widely used model research organisms, yet we have little information on evolutionary processes and recent evolutionary history of this widespread species. We examined patterns of variation at 20 microsatellite loci in a sample of 23 natural isolates of C. elegans from various parts of the world. One-half of the loci were monomorphic among all strains, and overall genetic variation at microsatellite loci was low, relative to most other species. Some population structure was detected, but there was no association between the genetic and geographic distances among different natural isolates. Thus, despite the nearly worldwide occurrence of C. elegans, little evidence was found for local adaptation in strains derived from different parts of the world. The low levels of genetic variation within and among populations suggest that recent colonization and population expansion might have occurred. However, the patterns of variation are not consistent with population expansion. A possible explanation for the observed patterns is the action of background selection to reduce polymorphism, coupled with ongoing gene flow among populations worldwide.

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