The Optimum Quality Index for the Stability of In-Parallel Planar Platform Devices

1999 ◽  
Vol 121 (1) ◽  
pp. 15-20 ◽  
Author(s):  
J. Lee ◽  
J. Duffy ◽  
M. Keler
Keyword(s):  
Optimal Design ◽  
Equilateral Triangle ◽  
Quality Index ◽  
Optimal Shape ◽  
Geometrical Meaning ◽  
Moving Platforms ◽  
Maximum Value ◽  
Dimensionless Ratio ◽  
Parallel Platform ◽  
The Stability

The paper investigates primarily the geometrical meaning of the determinant of the Jacobian (det j) of the three connector lines of a planar in-parallel platform device using reciprocity. A remarkably simple result is deduced: The maximum value of det j namely, det jm is simply one-half of the sum of the lengths of the sides of the moving triangular platform. Further, this result is shown to be independent of the location of the fixed pivots in the base. A dimensionless ratio λ = |det j|/det jm is defined as the quality index (0 ≤ λ ≤ 1) and it is proposed here to use it to measure “closeness” to a singularity. An example which determines the optimal design by comparing different shaped moving platforms having the same det jm is given and demonstrates that the optimal shape is in fact an equilateral triangle

The Optimum Quality Index for the Stability of In-Parallel Planar Platform Devices

1996 ◽  
Author(s):  
Jaehoon Lee ◽  
Joseph Duffy ◽  
Max Keler
Keyword(s):  
Optimal Design ◽  
Equilateral Triangle ◽  
Quality Index ◽  
Optimal Shape ◽  
Geometrical Meaning ◽  
Moving Platforms ◽  
Maximum Value ◽  
Dimensionless Ratio ◽  
Parallel Platform ◽  
The Stability

Abstract The paper investigates primarily the geometrical meaning of the determinant of the Jacobian (det j) of the three connector lines of a planar in-parallel platform device using reciprocity. A remarkably simple result is deduced : The maximum value of det j namely, det jm is simply one-half of the sum of the lengths of the sides of the moving triangular platform. Further, this result is shown to be independent of the location of the fixed pivots in the base. A dimensionless ratio λ = |det j| / det jm is defined as the quality index (0 ≤ λ ≤ 1) and it is proposed here to use it to measure “closeness” to a singularity. An example which determines the optimal design by comparing different shaped moving platforms having the same det jm is given and demonstrates that the optimal shape is in fact an equilateral triangle.

The Optimum Quality Index for a Spatial Redundant 8-8 In-Parallel Manipulator

2000 ◽  
Author(s):  
Yu Zhang ◽  
Joseph Duffy ◽  
Carl D. Crane
Keyword(s):  
Quality Index ◽  
Parallel Manipulator ◽  
Jacobian Matrix ◽  
Static Stability ◽  
Space Structure ◽  
Maximum Value ◽  
Deployable Space Structure ◽  
Symmetrical Configuration ◽  
Dimensionless Ratio ◽  
Optimal Quality

Abstract The quality index for a redundant 4-4 in-parallel manipulator with a square platform and a square base was obtained in [1]. Following this, the quality index for a redundant 4-8 manipulator with a square platform and an octagonal base was determined in [2]. In this paper the optimal quality index for a redundant 8-8 manipulator is determined. The device has an octagonal platform and a similar octagonal base connected by eight legs. The quality index is defined as a dimensionless ratio which takes a maximum value of 1 at a central symmetrical configuration that is shown to correspond to the maximum value of the square root of the determinant of the product of the manipulator Jacobian by its transpose. The Jacobian matrix is none other than the normalized coordinates of the eight leg lines. It is shown that the quality index can be used as a constructive measure of not only acceptable and optimum design proportions but also an acceptable operating workspace (in the static stability sense). The analysis of the redundant 8-8 manipulator described here can be used to model and design a self-deployable space structure that has a pair of flexible octagonal antenna platforms in the base and top platform.

Optimal Design of the Large-Diameter Spinning Torispherical Head

2012 ◽  
Vol 544 ◽  
pp. 194-199
Author(s):  
Di Zhang ◽  
Shui Ping Sheng ◽  
Zeng Liang Gao
Keyword(s):  
Finite Element ◽  
Optimal Design ◽  
Large Diameter ◽  
General Purpose ◽  
Design Tool ◽  
Crown Area ◽  
Finite Element Software ◽  
The Stability

Two important parameters of torispherical head that are (interior radius of spherical crown area) and r (interior radius of transition corner) have been optimized by the module of the large general-purpose finite-element software ANSYS, targeting the strength and stability of the head. This paper provides an optimized torispherical head, which improves the stability of the edge of the head with acceptable strength of the head. The procedure is generally applicable as a design tool for optimal design.

scholarly journals An experimental study on the effects of swirling oxidizer flow and diameter of fuel nozzle on behaviour and light emittance of propane-oxygen non-premixed flame

2017 ◽  
Vol 21 (3) ◽  
pp. 1453-1462 ◽  
Author(s):  
Alireza Javareshkian ◽  
Sadegh Tabejamaat ◽  
Soroush Sarrafan-Sadeghi ◽  
Mohammadreza Baigmohammadi
Keyword(s):  
Reynolds Numbers ◽  
Flame Length ◽  
Nozzle Diameter ◽  
Fuel Flow ◽  
Maximum Value ◽  
Fuel Nozzle ◽  
Flame Shape ◽  
The Stability ◽  
Blue Flame

In this study, the stability and the light emittance of non-premixed propane-oxygen flames have been experimentally evaluated with respect to swirling oxidizer flow and variations in fuel nozzle diameter. Hence, three types of the vanes with the swirl angles of 30?, 45?, and 60? have been chosen for producing the desired swirling flows. The main aims of this study are to determine the flame behaviour, light emittance, and also considering the effect of variation in fuel nozzle diameter on combustion phenomena such as flame length, flame shape, and soot free length parameter. The investigation into the flame phenomenology was comprised of variations of the oxidizer and fuel flow velocities (respective Reynolds numbers) and the fuel nozzle diameter. The results showed that the swirl effect could change the flame luminosity and this way could reduce or increase the maximum value of the flame light emittance in the combustion zone. Therefore, investigation into the flame light emittance can give a good clue for studying the mixing quality of reactants, the flame phenomenology (blue flame or sooty flame, localized extinction), and the combustion intensity in non-premixed flames.

scholarly journals A Precise and GNSS-Free Landing System on Moving Platforms for Rotary-Wing UAVs

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 886 ◽  
Author(s):  
Francisco Alarcón ◽  
Manuel García ◽  
Ivan Maza ◽  
Antidio Viguria ◽  
Aníbal Ollero
Keyword(s):  
Relative Position ◽  
Unmanned Helicopter ◽  
Landing Position ◽  
Moving Platforms ◽  
Landing Platform ◽  
Aerial Vehicle ◽  
The Stability ◽  
Novel Concept ◽  
High Level ◽  
Rotary Wing

This article presents a precise landing system that allows rotary-wing UAVs to approach and land safely on moving platforms, without using GNSS at any stage of the landing maneuver, and with a centimeter level accuracy and high level of robustness. This system implements a novel concept where the relative position and velocity between the aerial vehicle and the landing platform are calculated from the angles of a cable that physically connects the UAV and the landing platform. The use of a cable also incorporates a number of extra benefits, such as increasing the precision in the control of the UAV altitude. It also facilitates centering the UAV right on top of the expected landing position, and increases the stability of the UAV just after contacting the landing platform. The system was implemented in an unmanned helicopter and many tests were carried out under different conditions for measuring the accuracy and the robustness of the proposed solution. Results show that the developed system allowed landing with centimeter accuracy by using only local sensors and that the helicopter could follow the landing platform in multiple trajectories at different velocities.

scholarly journals Increasing the range of ultra wideband radars based on antenna arrays

2019 ◽  
Vol 30 ◽  
pp. 05017
Author(s):  
Boris Lagovsky ◽  
Alexander Samokhin ◽  
Malay Tripathy
Keyword(s):  
Cross Section ◽  
Antenna Arrays ◽  
Numerical Solutions ◽  
Narrow Band ◽  
Variational Problems ◽  
Optimal Shape ◽  
Ultra Wideband ◽  
Maximum Value ◽  
Efficient Processing ◽  
Processing Algorithms

Analytical and numerical solutions are presented for increasing the range of ultra wideband radars based on antenna arrays by optimizing their characteristics. It is shown that the shape of UWB pulses significantly affects the maximum value of the reflected signal. Solutions of variational problems of searching for the optimal shape of probing UWB pulses are investigated. Optimization of the form allows to obtain good results when using even approximate data on the dispersion dependences of the radar cross-section. The use of new efficient processing algorithms for UWB signals that do not have direct narrow-band analogs is substantiated.

ANALYSIS OF SURFACE ROUGHNESS AT OVERLAPPING LASER SHOCK PEENING

2016 ◽  
Vol 23 (03) ◽  
pp. 1650012 ◽  
Author(s):  
F. Z. DAI ◽  
Z. D. ZHANG ◽  
J. Z. ZHOU ◽  
J. Z. LU ◽  
Y. K. ZHANG
Keyword(s):  
Surface Roughness ◽  
Theoretical Analysis ◽  
Equilateral Triangle ◽  
Experimental Results ◽  
Laser Shock Peening ◽  
Laser Shock ◽  
Minimum Value ◽  
Maximum Value ◽  
Shock Peening ◽  
Iso 25178

The overlapping effects on surface roughness are studied when samples are treated by laser shock peening (LSP). Surface roughness of overlapped circular laser spot is calculated by ISO 25178 height parameters. The usually used overlapping styles namely isosceles-right-triangle-style (AAP) and equilateral-triangle-style (AAA) are carefully investigated when the overlapping degree in x-axis ([Formula: see text]) is below 50%. Surface roughness of isosceles-right-triangle-style attains its minimum value at [Formula: see text] of 29.3%, and attains its maximum value at [Formula: see text] of 43.6%. Surface roughness of equilateral-triangle-style attains its minimum value at [Formula: see text] of 42.3%, and attains its maximum value at [Formula: see text] of 32%. Experimental results are well consistent with theoretical analysis.

The stability of a viscous liquid in a vertical tube containing porous material

1959 ◽  
Vol 252 (1268) ◽  
pp. 120-134 ◽  
Keyword(s):  
Porous Medium ◽  
Porous Material ◽  
Density Gradient ◽  
Capillary Tube ◽  
Saturated Porous Medium ◽  
Vertical Tube ◽  
Neutral Stability ◽  
Molecular Diffusivity ◽  
Dimensionless Ratio ◽  
The Stability

If a long vertical tube filled with porous material contains a viscous solution, the density of which increases with height as a result of the presence of the dissolved substance, the equilibrium of the liquid is stable provided that the density gradient does not anywhere exceed the value d ρ /d Z = 3·390 μκ / gkb 2 Here κ , the diffusivity of the solute through the saturated porous medium, is defined to be the quantity of solute diffusing across unit area within the porous medium per unit time under unit density gradient. The above expression for the density gradient at neutral stability has been compared experimentally with Taylor’s value for the corresponding density gradient in a vertical capillary tube. For a porous medium consisting of randomly packed glass spheres of mean diameter about 0·2 mm and porosity ϵ = 0·365, it has been found that the two results are consistent provided that the ratio κ / Dϵ = 0·633, where D is the molecular diffusivity of the solute when the porous medium is absent. As this dimensionless ratio is a property of the porous material alone, it can be determined directly by diffusion measurements. An alternative method of measuring κ / Dϵ , based upon an electrical analogue, has led to a value of 0·641 for the same porous material, which is in good numerical agreement.

In-vitro method for assessing femoral implant—bone micromotions in resurfacing hip implants under different loading conditions

2007 ◽  
Vol 221 (8) ◽  
pp. 943-950 ◽  
Author(s):  
L Cristofolini ◽  
E Varini ◽  
M Viceconti
Keyword(s):  
Hip Replacement ◽  
Hip Implants ◽  
Motor Tasks ◽  
Preliminary Screening ◽  
Maximum Value ◽  
Gap Opening ◽  
Hip Stems ◽  
The Stability ◽  
Peak Value

Although prosthesis-bone micromotion is known to influence the stability of total hip replacement, no protocol exists to investigate resurfacing hip implants. An in-vitro protocol was developed to measure prosthesis-bone micromotions of resurfaced femurs. In order to assess the effect of all loading directions, the protocol included a variety of in-vitro loading scenarios covering the range of directions spanned by the hip resultant force in the most typical motor tasks. Gap-opening and shear-slippage micromotions were measured in the locations where they reach the maximum value. The applicability of the protocol was assessed on two commercial designs and different head sizes. Intra-specimen repeatability and inter-specimen reproducibility were excellent (comparable with the best protocols for cemented hip stems). Results showed that the protocol is accurate enough to detect prosthesis-bone micromotions of the order of a few microns. Statistically significant differences were observed in relation to the direction of the applied force. Using the whole range of hip loads enabled detection of maximum micromotions for any design (the peak value could be different for different loading directions). Application of the protocol during a test to failure indicated that the system could track micromotion up to the last instant prior to failure. The protocol proposed is thus completely validated and can be applied for preliminary screening of new epiphyseal designs.

Sign in / Sign up

Export Citation Format

Share Document