First Paper: Imperfections in Vacuum Remelted Precision Steel Balls Which Affect Ball Race Performance

1970 ◽  
Vol 185 (1) ◽  
pp. 353-365
Author(s):  
D. J. Haines
Keyword(s):  
Centre Of Mass ◽  
Ball Surface ◽  
Steel Balls ◽  
Race Performance ◽  
Mass Position ◽  
Ball Motion

In a study of ball motion in an angular contact ball race the author found that precision steel balls having their centre of mass displaced from the true geometric centre of the ball show tendencies to run in a ‘heavy end outwards’ condition resulting in preferential wear of parts of the ball surface. Three techniques are described which permit the sorting of balls and the elimination of those which limit race life due to errors in ball sphericity and errors in centre of mass position.

scholarly journals A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility

PLoS ONE ◽  
2015 ◽  
Vol 10 (9) ◽  
pp. e0137284 ◽  
Author(s):  
John A. Nyakatura ◽  
Vivian R. Allen ◽  
Jonas Lauströer ◽  
Amir Andikfar ◽  
Marek Danczak ◽  
...  
Keyword(s):  
Body Mass ◽  
Three Dimensional ◽  
Joint Mobility ◽  
Centre Of Mass ◽  
Mass Centre ◽  
Mass Position ◽  
Skeletal Reconstruction

scholarly journals The influence of sagittal trunk lean on uneven running mechanics

2020 ◽  
Vol 224 (1) ◽  
pp. jeb228288
Author(s):  
Soran AminiAghdam ◽  
Reinhard Blickhan ◽  
Kiros Karamanidis
Keyword(s):  
Centre Of Mass ◽  
Leg Length ◽  
Mass Model ◽  
Ankle Stiffness ◽  
Trunk Posture ◽  
Step Down ◽  
Posterior Trunk ◽  
Running Mechanics ◽  
Mass Position

ABSTRACTThe role of trunk orientation during uneven running is not well understood. This study compared the running mechanics during the approach step to and the step down for a 10 cm expected drop, positioned halfway through a 15 m runway, with that of the level step in 12 participants at a speed of 3.5 m s−1 while maintaining self-selected (17.7±4.2 deg; mean±s.d.), posterior (1.8±7.4 deg) and anterior (26.6±5.6 deg) trunk leans from the vertical. Our findings reveal that the global (i.e. the spring-mass model dynamics and centre-of-mass height) and local (i.e. knee and ankle kinematics and kinetics) biomechanical adjustments during uneven running are specific to the step nature and trunk posture. Unlike the anterior-leaning posture, running with a posterior trunk lean is characterized by increases in leg angle, leg compression, knee flexion angle and moment, resulting in a stiffer knee and a more compliant spring-leg compared with the self-selected condition. In the approach step versus the level step, reductions in leg length and stiffness through the ankle stiffness yield lower leg force and centre-of-mass position. Contrariwise, significant increases in leg length, angle and force, and ankle moment, reflect in a higher centre-of-mass position during the step down. Plus, ankle stiffness significantly decreases, owing to a substantially increased leg compression. Overall, the step down appears to be dominated by centre-of-mass height changes, regardless of having a trunk lean. Observed adjustments during uneven running can be attributed to anticipation of changes to running posture and height. These findings highlight the role of trunk posture in human perturbed locomotion relevant for the design and development of exoskeleton or humanoid bipedal robots.

Limit Steady State Vehicle Handling

1987 ◽  
Vol 201 (4) ◽  
pp. 281-291 ◽  
Author(s):  
J C Dixon
Keyword(s):  
Steady State ◽  
Load Transfer ◽  
Limit State ◽  
Lateral Acceleration ◽  
Design Parameters ◽  
Centre Of Mass ◽  
Vehicle Handling ◽  
Specific Proposal ◽  
Turning Radius ◽  
Mass Position

Previously, limit steady state handling has always been restricted to the qualitative statement that a vehicle has final understeer or final oversteer; it cannot be analysed by the conventional understeer gradient concept. A specific proposal is made for quantification of final understeer or oversteer. This is called the understeer number, and is defned by Nu = (ArAf)-1, where Af and Ar are the lateral acceleration capabilities of the front and rear axles. Thus Nu is non-dimensional, is zero for a notional final neutral vehicle, positive for final understeer and negative for final oversteer. A typical value is 0.150 (rear drive) or 0.220 (front). The various design parameters that influence the understeer number are investigated, and equations are obtained and quantified, including centre of mass position, lateral load transfer distribution, longitudinal load transfer, traction, the components of aerodynamic forces and moments, the effect of non-free differentials and the effect of load increments. The effect of turning radius and slopes is also investigated. Thus the limit state of handling is subject to a quantitative assessment, showing the degree of a vehicle's commitment to final understeer or oversteer.

LONG JUMP: MECHANICAL AND ENERGETIC ASPECTS

2004 ◽  
Vol 04 (04) ◽  
pp. 535-557 ◽  
Author(s):  
T. K. KARALIS
Keyword(s):  
Contact Point ◽  
Reaction Force ◽  
Vertical Component ◽  
Centre Of Mass ◽  
Force Vector ◽  
Direct Measurements ◽  
Long Jump ◽  
The Mean ◽  
Vector Formula ◽  
Mass Position

The use of variation techniques is applied to investigate jumper's posture at take-off, resulting in maximum distance of jump. Explicit expressions have been derived between: (i) the take-off angle ϕT (formed by the line connecting the contact point of the leg driving the jump with the ground to the centre of mass position and the horizontal), (ii) the ratio [Formula: see text] of the mean vertical component of the ground reaction force vector to athlete's weight at take-off, (iii) the time spent for the mid-support/take-off phase TT, and (iv) the change in the vertical component of the displacement of the centre of mass compared with the take-off foot ΔyT, measured between two extreme postures, i.e. the mid-support and the take-off phase. The method is illustrated by calculating the state vector [Formula: see text] at take-off, in connection with the take-off angle ϕT. The results are compared to direct measurements from real long jumps.

Design of Deployment Mechanim of Steel Ball and Surface Defects Recognition

2013 ◽  
Vol 274 ◽  
pp. 245-248 ◽  
Author(s):  
Yan Ling Zhao ◽  
Wan Bo Che ◽  
Kai Zhou ◽  
Jia Ping Xuan
Keyword(s):  
Mathematical Model ◽  
Image Processing ◽  
Motion Analysis ◽  
Surface Defects ◽  
Steel Ball ◽  
Simulation Based ◽  
Ball Surface ◽  
Low Efficiency ◽  
The Mathematical Model ◽  
Ball Motion

At present, the steel ball surface defects are usually detected by manual work, but it has low efficiency and low reliability. For the current situation, in this paper, we design the steel ball deployment mechanism based on image processing technology, establish the mathematical model of the shooting point trajectory and determine the amount and location of the shooting points by the steel ball motion analysis. By the simulation based on Mathematica and Java, verify the effectiveness of the steel ball deployment mechanism in steel ball unfolding and defects recognition. Thus, the steel ball surface can be completely detected.

Failure Analysis of GCr15 Steel Balls in Ball Screw Pair

2014 ◽  
Vol 651-653 ◽  
pp. 24-28
Author(s):  
Cheng Nan Li ◽  
Ye Yan ◽  
Yu Hong Gai ◽  
Bao Min Li ◽  
Wei Du ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Raw Materials ◽  
Steel Ball ◽  
Ball Screw ◽  
Failure Characteristics ◽  
Gcr15 Steel ◽  
Microstructure Observation ◽  
Ball Surface ◽  
Steel Balls

Based on macro morphology, metallographic microstructure, field emission scanning electron microscope observations and microhardness testing, failure analysis of the GCr15 steel balls in the ball screw pair was dealt with in this paper. The experimental results showed that small scratches and pits were evenly distributed on the surface of the A steel ball which showed features of wear failure. Characteristics of the B steel ball surface morphology were contacted to fatigue failure. Microstructure observation on the cross-section of the B steel ball showed that martensite and carbides were uneven distributed which were caused by the uneven elements distribution in the raw materials. It was the main cause of this abnormal failure. Therefore, the quality of the raw materials needed to be strictly controlled and the reasonable heat treatment process should be adopted to ensure the quality of the steel balls.

A fast methodology to determine the characteristics of thousands of grains using three-dimensional X-ray diffraction. I. Overlapping diffraction peaks and parameters of the experimental setup

2012 ◽  
Vol 45 (4) ◽  
pp. 693-704 ◽  
Author(s):  
Hemant Sharma ◽  
Richard M. Huizenga ◽  
S. Erik Offerman
Keyword(s):  
Data Analysis ◽  
Three Dimensional ◽  
Experimental Setup ◽  
Centre Of Mass ◽  
X Ray Diffraction ◽  
X Ray ◽  
Overlapping Peaks ◽  
Diffraction Peaks ◽  
Mass Position

A data-analysis methodology is presented for the characterization of three-dimensional microstructures of polycrystalline materials from data acquired using three-dimensional X-ray diffraction (3DXRD). The method is developed for 3DXRD microscopy using a far-field detector and yields information about the centre-of-mass position, crystallographic orientation, volume and strain state for thousands of grains. This first part deals with pre-processing of the diffraction data for input into the algorithms presented in the second part [Sharma, Huizenga & Offerman (2012).J. Appl. Cryst.45, 705–718] for determination of the grain characteristics. An algorithm is presented for accurate identification of overlapping diffraction peaks from X-ray diffraction images, which has been an issue limiting the accuracy of experiments of this type. The algorithm works in two stages, namely the identification of overlapping peaks using a seeded watershed algorithm, and then the fitting of the peaks with a pseudo-Voigt shape function to yield an accurate centre-of-mass position and integrated intensity for the peaks. Regions consisting of up to six overlapping peaks can be successfully fitted. Two simulations and an experiment are used to verify the results of the algorithms. An example of the processing of diffraction images acquired in a 3DXRD experiment with a sample consisting of more than 1600 grains is shown. Furthermore, a procedure for the determination of the parameters of the experimental setup (global parameters) without the need for a calibration sample is presented and validated using simulations. This is immensely beneficial for simplifying experiments and the subsequent data analysis.

scholarly journals The system of airplane centre-of-mass position-finding in the flight mode

2011 ◽  
Vol 4 (30) ◽  
Author(s):  
А.П. Козлов ◽  
О.В. Мельников ◽  
Ю.М. Кеменяш
Keyword(s):  
Centre Of Mass ◽  
Flight Mode ◽  
Mass Position

scholarly journals Estimation of the Centre of Mass From Motion Capture and Force Plate Recordings: A Study on the Elderly

2011 ◽  
Vol 8 (1) ◽  
pp. 67-84 ◽  
Author(s):  
S. Cotton ◽  
M. Vanoncini ◽  
P. Fraisse ◽  
N. Ramdani ◽  
E. Demircan ◽  
...  
Keyword(s):  
Motion Capture ◽  
Force Plate ◽  
The Elderly ◽  
The Body ◽  
Estimation Methods ◽  
Centre Of Mass ◽  
Joint Angles ◽  
Biomechanical Models ◽  
The Subject ◽  
Mass Position

The estimation of the centre of mass position in humans is usually based on biomechanical models developed from anthropometric tables. This method can potentially introduce errors in studies involving elderly people, since the ageing process is typically associated with a modification of the distribution of the body mass. In this paper, an alternative technique is proposed, and evaluated with an experimental study on 9 elderly volunteers. The technique is based on a virtual chain, identified from experimental data and locating the subject's centre of mass. Its configuration defines the location of the centre of mass, and is a function of the anatomical joint angles measured on the subject. This method is a valuable investigation tool in the field of geronto-technology, since it overcomes some of the problems encountered with other CoM estimation methods.

Sign in / Sign up

Export Citation Format

Share Document