On the Synthesis of Straight Line, Constant Velocity Scanning Mechanisms

1991 ◽  
Vol 113 (4) ◽  
pp. 464-472 ◽  
Author(s):  
P. H. Hodges ◽  
A. P. Pisano
Keyword(s):  
Constant Velocity ◽  
Transverse Velocity ◽  
Grid Search ◽  
Planar Mechanisms ◽  
Kinematic Synthesis ◽  
Velocity Error ◽  
Straight Line ◽  
Transmission Angle ◽  
Point Motion ◽  
Input Motion

This paper presents a kinematic synthesis of constant-velocity, straight-line coupler-point motion of two planar mechanisms. After the derivation of synthesis equations, the numerical results of a grid search to determine the linkage dimensions for maximum constant velocity, with minimal straight line error, are presented. Plots of acceleration magnitude, transmission angles, and transverse velocity are presented as a function of the percentage of the constant velocity portion of a cycle of input motion. For a 5R2P Stephenson 6-bar linkage, normalized velocity errors as small as 2 percent can be maintained over 40 percent, or more, of the input cycle. A 7R Watt 6-bar linkage, while not achieving quite as high values as the 5R2P linkage, nevertheless can maintain normalized velocity errors as low as 2.5 percent over as much as 39 percent of the input cycle. These levels of performance must be weighed against unfavorable transmission angles, and in many cases, other undesirable effects, such as large accelerations and large transverse travel. The results show that, in order to maintain minimally acceptable transmission angle requirements, the velocity error and scan fraction requirements may be as little as 2.0 percent and as much as 35 percent, respectively.

Coarse-To-Fine 3D Randomized Hough Transform for Dim Target Detection

2014 ◽  
Vol 519-520 ◽  
pp. 1040-1045
Author(s):  
Ling Fan
Keyword(s):  
Target Detection ◽  
Hough Transform ◽  
Constant Velocity ◽  
Three Dimensional ◽  
Randomized Hough Transform ◽  
Straight Line ◽  
Memory Complexity ◽  
Coarse To Fine

This paper makes some improvements on Roberts representation for straight line in space and proposes a coarse-to-fine three-dimensional (3D) Randomized Hough Transform (RHT) for the detection of dim targets. Using range, bearing and elevation information of the received echoes, 3D RHT can detect constant velocity target in space. In addition, this paper applies a coarse-to-fine strategy to the 3D RHT, which aims to solve both the computational and memory complexity problems. The validity of the coarse-to-fine 3D RHT is verified by simulations. In comparison with the 2D case, which only uses the range-bearing information, the coarse-to-fine 3D RHT has a better practical value in dim target detection.

scholarly journals Extended Kalman Filter for Bearings-Only Tracking

2019 ◽  
Vol 8 (6) ◽  
pp. 637-640 ◽  
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
Constant Velocity ◽  
Target Motion ◽  
Passive Mode ◽  
Crucial Issue ◽  
Straight Line ◽  
Optimal Linear ◽  
Target Motion Analysis ◽  
Line Path

Target tracking using bearings-only measurements in passive mode operation of sonar is a crucial issue of underwater tracking. Target motion in underwater scenario is analyzed using bearings-only measurements and calculating parameters like range, course and speed of the target. This is called Target Motion Analysis (TMA). TMA process is highly non-linear as the measurements chosen are nonlinearly related to the selected target state vector and the traditional, optimal linear Kalman filter will not be appropriate to use. It is presumed that the target is moving in straight line path with constant velocity, so Extended Kalman Filter (EKF) is proposed in this paper. The algorithm is simulated for several scenarios using MATLAB. Monte-Carlo runs are performed to evaluate the capability of the algorithm.

Synthesis of a Large Oscillation Four-Bar Mechanism

1997 ◽  
Author(s):  
Gloria K. Starns ◽  
Donald R. Flugrad
Keyword(s):  
Reduced Gradient Method ◽  
Large Oscillation ◽  
Oscillation Mechanism ◽  
Straight Line ◽  
Transmission Angle ◽  
Reduced Gradient ◽  
Generalized Reduced Gradient ◽  
Angular Oscillations ◽  
Four Bar Linkage ◽  
Effective Transmission

Abstract This paper demonstrates procedures implemented for the synthesis of a four-bar mechanism that produces large angular oscillations of the output member while maintaining effective transmission angles. The mechanisms are modeled as being driven by a force applied at the coupler link. Additionally this force’s line of action is constrained to occur along an approximate straight line. This research was conducted out of the need for a device that is capable of retraction of the horizontal tool bar housed on the back of a tractor. The tool bars accommodate the implements required to accomplish the numerous tasks of the farmer, i.e. row markers, sprayer arms, planters, etc. Upon retraction of the tool bar so that it is parallel to ground, the appropriate tools are lowered to their working position. As the length of these bars increases, a savings of time and increased productivity is realized. Kurt Hain makes the following observation regarding large oscillation mechanisms in [1]: “It would be very difficult to solve this problem with one four-bar linkage, because it is difficult to design a four-bar linkage having such a large oscillation of a crank without running into problems of poor transmission angle characteristics; it might be possible to use linkages in combinations with gears, but this would make the mechanism more expensive, less efficient, and probably noisier.” In this study simulated annealing, a genetic algorithm and the generalized reduced gradient method are used to produce mechanisms with large angular oscillations of the output member and transmission angles that vary by as little as 20° from 90°. A comparative analysis of each of the optimization procedures is presented with observations regarding the efficacy of each method in the solution of the large oscillation mechanism.

Velocity estimates derived from three‐dimensional seismic data

Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1486-1497 ◽  
Author(s):  
Kwame Owusu ◽  
G. H. F. Gardner ◽  
Wulf F. Massell
Keyword(s):  
Seismic Data ◽  
Constant Velocity ◽  
Three Dimensional ◽  
Logarithmic Scale ◽  
Model Data ◽  
Reconstruction Process ◽  
Input Field ◽  
Scattering Center ◽  
Straight Line ◽  
The Matrix

A new computer algorithm is described by which velocity estimates can be derived from three‐dimensional (3-D) multifold seismic data. The velocity estimate, referred to as “imaging velocity,” is that which best describes the diffraction hyperboloid due to a scatterer. The scattering center is best imaged when this velocity is used in the reconstruction process. The method is based on the 3-D Kirchhoff summation migration before stack. The implementation consists of two basic phases: (1) differentiating the input field traces and resampling them to a logarithmic time scale, and (2) shifting, weighting, and summing each resampled trace to a range of depth levels also chosen on a logarithmic scale. Peak amplitudes in the resulting image matrix give a time T and depth Z from which velocity is obtained using the relation [Formula: see text] The locus of constant velocity is a slanted straight line in the coordinate system of the matrix. In the usual application of migration for velocity analysis, each input trace of N samples is migrated for each of M constant velocity functions requiring [Formula: see text] moveout shift calculations. In the new method presented here, a constant shift is calculated for a given resampled trace, for each depth into which it is summed. This reduces the number of calculations per trace to about N, resulting in a significant improvement in computing efficiency. The operation of the algorithm is illustrated using synthetic and physical model data.

Kinematic Synthesis and Analysis of the Rack and Pinion Multi-Purpose Mechanism

1992 ◽  
Vol 114 (3) ◽  
pp. 428-432 ◽  
Author(s):  
G. K. Ananthasuresh ◽  
S. N. Kramer
Keyword(s):  
General Procedure ◽  
Full Range ◽  
Mechanism Synthesis ◽  
Kinematic Synthesis ◽  
Function Generation ◽  
Monotonic Functions ◽  
Transmission Angle ◽  
Velocity Condition ◽  
Method Of Solution ◽  
Design Requirements

The general procedure for synthesizing the rack and pinion mechanism up to seven precision conditions is developed. To illustrate the method, the mechanism has been synthesized in closed form for three precision conditions of path generation, two positions of function generation, and a velocity condition at one of the precision points. This mechanism has a number of advantages over conventional four bar mechanisms. First, since the rack is always tangent to the pinion, the transmission angle is always 90 deg minus the pressure angle of the rack. Second, with both translation and rotation of the rock occurring, multiple outputs are available. Other advantages include the generation of monotonic functions for a wide variety of motion and nonmonotonic functions for a full range of motion as well as nonlinear amplified motions. In this work the mechanism is made to satisfy a number of amplified motions. In this work the mechanism is made to satisfy a number of practical design requirements such as completely rotatable input crank and others. By including the velocity specification, the designer has considerably more control of the output motion. The method of solution developed in this work uses the complex number method of mechanism synthesis. A numerical example is included.

The Problems of Random Flight and Conduction of Heat

1924 ◽  
Vol 22 (2) ◽  
pp. 167-168
Author(s):  
W. Burnside
Keyword(s):  
Constant Velocity ◽  
Time Interval ◽  
Straight Line ◽  
Random Flight ◽  
Image Position

In a paper on random flight Lord Rayleigh proved the following result: A number is formed by adding together n numbers each of which is equally likely to have any value from − a to + a. Then, if f (n, s) ds is the probability that the number so formed lies between s and s + ds, and if n is sufficiently great,This result may be stated as follows: A point moves discontinuously in a straight line. For a time τ it has a constant velocity. During the next time-interval τ it again has a constant velocity, and so on. Then if each of these velocities is equally likely to have any value from − v to + v, the probability that in the time nτ, the point moves a distance lying between s and s + ds is f (n, s) ds, with vτ written for a.

Design of a Continuum Mechanism that Matches the Movement of an Eight-bar Linkage

2020 ◽  
pp. 1-11
Author(s):  
Xueao Liu ◽  
J. Michael McCarthy
Keyword(s):  
Finite Element Analysis ◽  
Rigid Body ◽  
Design Methodology ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Initial Structure ◽  
Element Analysis ◽  
Kinematic Synthesis ◽  
Generic Structure ◽  
Straight Line

Abstract This paper presents a design methodology for mechanisms consisting of a single continuous structure, continuum mechanisms, that blends the kinematic synthesis of rigid-body mechanisms with topology optimization for compliant mechanisms. Rather than start with a generic structure that is shaped to achieve a required force deflection task for a compliant mechanism, our approach shapes the initial structure based on kinematic synthesis of a rigid body mechanism for the required movement, then the structure is shaped using Finite Element Analysis to achieve the required force deflection relationship. The result of this approach is a continuum mechanism with the same workpiece movement as the rigid link mechanism when actuated. An example illustrates the design process to obtain an eight-bar linkage that guides its workpiece in straight-line rectilinear movement. We show that the resulting continuum mechanism provides the desired rectilinear movement. A 210 mm physical model machined from Nylon-6 is shown to achieve 21.5mm rectilinear movement with no perceived deviation from a straight-line.

A Modified Design for λ-Type Double-Cranks to Approximate a Straight Line

1988 ◽  
Vol 110 (4) ◽  
pp. 446-451
Author(s):  
E. A. Dijksman
Keyword(s):  
Degrees Of Freedom ◽  
Maximum Deviation ◽  
Straight Line ◽  
Transmission Angle ◽  
The One ◽  
Straight Line Mechanism

Double-cranks containing a Chebyshev-dyad are investigated for their use as a straight-line mechanism. The three available design degrees of freedom have been used for the optimization of the minimum transmission angle, for the minimization of the maximum deviation and for the length L of the straight-stretch in the coupler curve. The resulting double-cranks are shown to have deviations that are about half as large as for those in which the coupler point lies on the extension of the coupler. For any maximum deviation, the length L of the straight-stretch also appears to be about 1.5 times as long as the one obtained when Ball’s point lies at the base of the design. A graph showing the maximum deviation as a function of L allows the designer to pick his choice mechanism. A table also will be of help to find accurate dimensions of the mechanism that yields a given deviation or a given length L of the straight part in the coupler curve.

Dynamic Propagation of a Kinked or Bifurcated Crack in Antiplane Strain

1982 ◽  
Vol 49 (2) ◽  
pp. 371-376 ◽  
Author(s):  
P. Burgers
Keyword(s):  
Constant Velocity ◽  
Crack Tip ◽  
Crack Initiation And Propagation ◽  
Crack Line ◽  
Kinked Crack ◽  
Dynamic Propagation ◽  
Straight Line ◽  
Initiation And Propagation ◽  
Cauchy Singular Integral ◽  
Cauchy Singular Integral Equation

An initially unloaded, semi-infinite, stationary crack is assumed to kink or bifurcate at time t=0 and the new crack tip(s) propagate out along a straight line at a constant velocity vCT. A Green’s function, consisting of a dislocation whose Burgers vector is growing linearly with time, that is suddenly emitted from the tip of a stress-free semi-infinite crack and propagates out along the kinked crack line at constant velocity u, is used to form a Cauchy singular integral equation. This equation is solved using standard numerical techniques and the stress-intensity factor is obtained as a function of crack-tip speed vCT and kink angle δ. The bifurcation case is treated in a similar manner. Finally, some conclusions concerning crack initiation and propagation are drawn.

Synthesis of Spring Parameters to Satisfy Specified Energy Levels in Planar Mechanisms

1977 ◽  
Vol 99 (2) ◽  
pp. 341-346 ◽  
Author(s):  
G. K. Matthew ◽  
D. Tesar
Keyword(s):  
Energy Storage ◽  
Potential Energy ◽  
Energy Levels ◽  
Planar Mechanisms ◽  
Algebraic Form ◽  
Kinematic Synthesis ◽  
Nonlinear Motion

The potential energy storage capabilities of linear springs are integrated with the nonlinear motion of mechanisms to provide approximation of desired counter-loading functions. The approximating function is required to be identical to the desired function at a number of precision points. The work is directly analogous to the algebraic form of kinematic synthesis, thus enabling an immediate conceptual grasp by those already familiar with kinematics.

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