scholarly journals Construction of meta-GGA functionals through restoration of exact constraint adherence to regularized SCAN functionals

2021 ◽  
Author(s):  
James William Furness ◽  
Aaron David Kaplan ◽  
Jinliang Ning ◽  
John P. Perdew ◽  
Jianwei Sun
Keyword(s):  
Exact Constraint

scholarly journals Exact Constraint

2009 ◽  
Vol 131 (09) ◽  
pp. 32-36
Author(s):  
James G. Skakoon
Keyword(s):  
Degrees Of Freedom ◽  
Two Dimensions ◽  
Washing Machine ◽  
Design Engineers ◽  
Successful Design ◽  
Tapered Roller ◽  
Tapered Roller Bearings ◽  
Exact Constraint ◽  
Three Degrees Of Freedom

This article discusses the significance of knowing exact constraint in successful design. Although not traditionally taught in mechanical engineering curricula, and not universally known among mechanical engineers, principles of exact constraint have been around for over a century. Designers of precision instruments have for decades used exact constraint, without which they simply would not achieve the precision required by many devices. Exact constraint has a well-developed theory applicable for design engineers. Applying it improves designs by avoiding over-constraint. Over-constrained designs lead to high stresses, tight tolerances, looseness, binding, and difficult assembly. Exact constraint is easier to picture in two dimensions than in three. In two dimensions, there are three degrees of freedom: two translations and one rotation. Some useful compromises to exact constraint are pinned and bolted connections, ball bearings, and tapered roller bearings. Another is in-situ adjustment of over-constraint as in, for example, the thread-adjusted foot pads of a clothes dryer or washing machine.

Using Exact Constraint to Design Flexure Mechanisms

2000 ◽  
Author(s):  
Douglass L. Blanding
Keyword(s):  
Machine Design ◽  
Qualitative Technique ◽  
Exact Constraint

Abstract This paper presents a qualitative technique, known as “Exact Constraint Machine Design”, for synthesizing and analyzing the design of flexure mechanisms. This technique is presented more fully in the book: Exact Constraint: Machine Design using Kinematic Principles.

Computer Aided Tolerance Analysis of Parts and Assemblies

1989 ◽  
Author(s):  
R. T. Scott ◽  
G. A. Gabriele
Keyword(s):  
Real World ◽  
Probability Distributions ◽  
Three Dimensional ◽  
Tolerance Analysis ◽  
The Real ◽  
Assembly Tolerance ◽  
Computer Aided ◽  
Probability Information ◽  
Exact Constraint

Abstract An exact constraint scheme based on the physical contacting constraints of real part mating features is used to represent the process of assembling the parts. To provide useful probability information about how assembly dimensions are distributed when the parts are assembled as intended, the real world constraints that would prevent interference are ignored. This work addresses some limitations in the area of three dimensional assembly tolerance analysis. As a result of this work, the following were demonstrated: 1. Assembly of parts whose assembly mating features are subjected to variation; 2. Assemble parts using a real world set of exact constraints; 3. Provide probability distributions of assembly dimensions.

Elastic Averaging in Flexure Mechanisms: A Three-Beam Parallelogram Flexure Case Study

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Shorya Awtar ◽  
Kevin Shimotsu ◽  
Shiladitya Sen
Keyword(s):  
Improve Performance ◽  
Mathematical Basis ◽  
Element Analysis ◽  
Redundant Constraints ◽  
Flexure Mechanism ◽  
Design Paradigm ◽  
Constraint Model ◽  
Effective Use ◽  
Exact Constraint

Redundant constraints are generally avoided in mechanism design because they can lead to binding or loss in expected mobility. However, in certain distributed-compliance flexure mechanism geometries, this problem is mitigated by the phenomenon of elastic averaging. Elastic averaging is a design paradigm that, in contrast with exact constraint design principles, makes deliberate and effective use of redundant constraints to improve performance and robustness. The principle of elastic averaging and its advantages are illustrated in this paper by means of a three-beam parallelogram flexure mechanism, which represents an overconstrained geometry. In a lumped-compliance configuration, this mechanism is prone to binding in the presence of nominal manufacturing and assembly errors. However, with an increasing degree of distributed-compliance, the mechanism is shown to become more tolerant to such geometric imperfections. The nonlinear elastokinematic effect in the constituent beams is shown to play an important role in analytically predicting the consequences of overconstraint and provides a mathematical basis for elastic averaging. A generalized beam constraint model is used for these predictions so that varying degrees of distributed compliance are captured using a single geometric parameter. The closed-form analytical results are validated against finite element analysis, as well as experimental measurements.

AN EXACT SOLUTION TO THE FITTING PROBLEM IN THE APPLICATION SPECIFIC STATE MACHINE DEVICE

1994 ◽  
Vol 04 (02) ◽  
pp. 173-190 ◽  
Author(s):  
MAREK A. PERKOWSKI ◽  
MALGORZATA CHRZANOWSKA-JESKE ◽  
EDMUND PIERZCHALA ◽  
ALAN COPPOLA
Keyword(s):  
Graph Isomorphism ◽  
Isomorphism Problem ◽  
State Machine ◽  
Logic Device ◽  
Graph Isomorphism Problem ◽  
Complex Programmable Logic Device ◽  
High Level ◽  
Exact Constraint ◽  
Application Specific ◽  
Fitting Problem

In this paper the fitting problem for a new Application Specific State Machine Device, CY7C361, from Cypress Semiconductor is formulated and the solution is proposed. This fitting problem consists of mapping a netlist obtained from high-level synthesis into the chip’s physical resources. In general, a mapping (fitting) problem can be formulated as one of the labeled graph isomorphism between the netlist graph and the subgraph of the resources graph. However, the specific architecture-related constraints of the CY7C361 device cause the fitting problem to be generalized as a graph isomorphism problem with some additional mapping constraints and node multiplication (placing some nodes of the netlist graph in more than one node of the physical graph). Such formulation is quite general for a class of Complex Programmable Logic Device (CPLD) fitting problems, and has not been found in the literature. We implemented an exact, constraint-based, tree searching algorithm with several kinds of backtracking.

Quasi-Exact-Constraint Design of Wind Turbine Gearing

2010 ◽  
Author(s):  
Hani A. Arafa ◽  
Mostafa Bedewy
Keyword(s):  
Wind Turbine ◽  
Degrees Of Freedom ◽  
Gear Tooth ◽  
Elastic Deformations ◽  
Helical Gears ◽  
Design Concepts ◽  
Cylindrical Gears ◽  
The Past ◽  
Bearing Loads ◽  
Exact Constraint

In the past two decades the wind turbine industry has witnessed a considerable number of catastrophic accidents, many of which were due to gearbox failure. Ever increasing power ratings at decreased rotor speeds result in rotor torques of some million Nm. This imposes tooth loads and planet/pinion bearing loads on the order of a hundred tons within the first step-up stage. Such heavily loaded gearboxes, correctly (or rather innocently) designed according to the relevant codes, can be self-destructive. Due consideration should be given to the elastic environment in which the gears exist. Otherwise, appreciable, unsymmetrical/unequal elastic deformations in unwanted directions lead to gear tooth edge loading, in addition to overloading the bearing(s) near that edge. Designers of wind turbine gearing have in recent years identified several concepts and measures to be taken for counteracting the asymmetry of elastic deformations or mitigating their effects. In addition to giving a brief survey of such new design concepts, this paper suggests the use of selected types of curved-tooth cylindrical gears (so-called C-gears), primarily for their self-aligning capability; they allow four degrees of freedom (4-DOF), in contrast to the 3-DOF spur and helical gears and the 2-DOF double-helical gears. In addition, these gears offer a unique set of further advantages. When used in at least the most heavily loaded, first step-up stage, the design will be rendered quasi-exactly constrained; largely tolerant of misalignment due to elastic deformations, and the gearbox reliability should be improved, by design.

scholarly journals Shifted axis angular positioning mechanisms – unconventional use of exact constraint design

2018 ◽  
Vol 157 ◽  
pp. 01018
Author(s):  
Ksawery Szykiedans ◽  
Maciej Bujwan
Keyword(s):  
Angular Displacement ◽  
Driving Mechanism ◽  
Kinematic Structure ◽  
Axis Of Rotation ◽  
Exact Constraint ◽  
Constraint Method

Paper presents some remarks about designing angular positioners having significant angular displacement and shifted axis of rotation. Those driving mechanism are useful in specific applications where mechanism wraps around other object or there is a need of rotation around virtual axis. Examples of those applications like orthotic robots or gimbals for panoramic motions where developed at Faculty of Mechatronics WUT. Usage of exact constraint method was described including its influence to a kinematic structure of designed mechanism.

Passive micro-assembly of modular, hot embossed, polymer microfluidic devices using exact constraint design

2009 ◽  
Vol 19 (12) ◽  
pp. 125025 ◽  
Author(s):  
Byoung Hee You ◽  
Pin-Chuan Chen ◽  
Daniel S Park ◽  
Sunggook Park ◽  
Dimitris E Nikitopoulos ◽  
...  
Keyword(s):  
Microfluidic Devices ◽  
Micro Assembly ◽  
Exact Constraint
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