• Title, Summary, Keyword: Stiffness

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Lower Extremity Stiffness Characteristics in Running and Jumping: Methodology and Implications for Athletic Performance

  • Ryu, Joong Hyun
    • Korean Journal of Sport Biomechanics
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    • v.28 no.1
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    • pp.61-67
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    • 2018
  • Objective: The human body is often modelled as a spring-mass system. Lower extremity stiffness has been considered to be one of key factor in the performance enhancement of running, jumping, and hopping involved sports activities. There are several different classification of lower extremity stiffness consisting of vertical stiffness, leg stiffness, joint stiffness, as well as muscle and tendon stiffness. The primary purpose of this paper was to review the literature and describe different stiffness models and discuss applications of stiffness models while engaging in sports activities. In addition, this paper provided a current update of the lower extremity literature as it investigates the relationships between lower extremity stiffness and both functional performance and injury. Summary: Because various methods for measuring lower extremity stiffness are existing, measurements should always be accompanied by a detailed description including type of stiffness, testing method and calculation method. Moreover, investigator should be cautious when comparing lower extremity stiffness from different methods. Some evidence highlights that optimal degree of lower extremity stiffness is required for successful athletic performance. However, the actual magnitude of stiffness required to optimize performance is relatively unexplored. Direct relationship between lower extremity stiffness and lower extremity injuries has not clearly been established yet. Overall, high stiffness is potentially associate risk factors of lower extremity injuries although some of the evidence is controversial. Prospective injures studies are necessary to confirm this relationship. Moreover, further biomechanical and physiological investigation is needed to identify the optimal regulation of the lower limb stiffness behavior and its impact on athletic performance and lower limb injuries.

Analysis of Stiffness Bounds for Parallel Devices Using Eigenvalues (고유치를 이용한 병렬형 기구의 강성범위 해석)

  • Kim, Taek-Soo;Kim, Hyun;Hong, Dae-Hee
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.699-702
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    • 2000
  • In order to use a parallel device fur machine tool feed mechanism, it is very important to analyze its stiffness over the workspace. Generally, the stiffness of a rod varies with its length. In this paper, the stiffness of the leg is modeled as a linear function. With the linear stiffness model, the methods that can determine stiffness bounds and max/min stiffness directions are presented utilizing eigenvalues and eigenvectors of the stiffness matrix. The stiffness variation along a tool-path and stiffness mapping over a workspace are presented with cubic-shaped parallel device which is originally designed for machine tool feed mechanism.

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Semi-Singularity in Stiffness Generation of an Anthropomorphic Robot

  • Kim, Sungbok;Sungho Moon;Cho, Doo-San
    • Proceedings of the Korea Institute of Convergence Signal Processing
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    • pp.113-116
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    • 2000
  • This paper analyzes the singularity of an anthropomorphic robot associated with joint and operational stiffness generation from muscle stiffness. The singularity analysis is made simply based on the signs of the actual and the desired coupling joint stiffness. First, the relationships of the muscle stiffness and the actual joint stiffness, and the operational stiffness and the desired joint stiffness are examined. Second, according to the sign restriction on the actual coupling joint stiffness, the operational space is divided into the semi-singular(SS), the regular(R), and the semi-regular(SR) regions. Third, from the sign comparison of tile actual and the desired coupling joint stiffness, the sufficient condition for the semi-singularity in operational stiffness generation is derived. The limitation on the allowable operational stiffness when a task point belongs to SS, R, and SR regions is also discussed. Simulation results are given.

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Development of On-line Bending Stiffness Tester (2) - Lab experiment - (종이 휨강성 자동 측정방식의 개발과 그 이용 (2) - 실험실 측정 -)

  • Seo, Yung-Bum;Jung, Suk-Myun;Jung, Tae-Young
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.39 no.4
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    • pp.21-28
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    • 2007
  • A simple method of on-line stiffness measurement using the wrinkling behavior of paper web between two rollers was presented. The theory and the equation were presented, and lab and mill tests were executed. We called the stiffness measured by Taber tester as 'Taber stiffness', and by tension wrinkling measurement as 'wrinkle stiffness', respectively. Lab experimental results showed Taber and wrinkle stiffness are almost equivalent. In the mill experiment, we could measure the stiffness in the wet state and in the dry state. The dry wrinkle stiffness was close to the taber stiffness, but the wet wrinkle stiffness was much lower than the corresponding taber stiffness.

Design of high stiffness and lightweight body for stiffness distribution ratio (강성 배분비를 괴려한 고강성 경량화 차체 설계)

  • Yang, Hee-Jong;Kim, Ki-Chang;Yim, Hong-Jae;Kim, Chan-Mook
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.562-566
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    • 2006
  • Lightweight body can cause a low stiffness due to the decrease of panel thickness and reinforcing member. The other way, high stiffness body demands an increase of mass. Front pillar section area is decreased due to driver's visual field. Global vehicle stiffness is affected by stiffness distribution ratio between upper part and lower part at side body structure. This paper will describe a process used to evaluate the stiffness distribution ratio based on research of strain energy analysis of the tip rotation method. In addition, optimum design schemes are presented for high stiffness and lightweight body structure considering the investigated stiffness distribution ratio. In this way the designer will be aided by a defined design guide and a set of supporting tool to help him work towards a good design

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A new method to calculate the equivalent stiffness of the suspension system of a vehicle

  • Zhao, Pinbin;Yao, Guo-Feng;Wang, Min;Wang, Xumin;Li, Jianhui
    • Structural Engineering and Mechanics
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    • v.44 no.3
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    • pp.363-378
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    • 2012
  • The stiffness of a suspension system is provided by the bushings and the stiffness of the wheel center controls the suspension's elasto-kinematic (e-k) specification. So the stiffness of the wheel center is very important, but the stiffness of the wheel center is very hard to measure. The paper give a new method that we can use the stiffness of the bushings to calculate the equivalent stiffness of the wheel center, which can quickly and widely be used in all kinds of suspension structure. This method can also be used to optimize and design the suspension system. In the example we use the method to calculate the equivalent stiffness of the wheel center which meets the symmetric and positive conditions of the stiffness matrix.

Performance analysis of vehicle suspension systems with negative stiffness

  • Shi, Xiang;Shi, Wei;Xing, Lanchang
    • Smart Structures and Systems
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    • v.24 no.1
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    • pp.141-155
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    • 2019
  • This work evaluates the influence of negative stiffness on the performances of various vehicle suspension systems, and proposes a re-centering negative stiffness device (NSD). The re-centering NSD consists of a passive magnetic negative stiffness spring and a positioning shaft with a re-centering function. The former produces negative stiffness control forces, and the latter prevents the amplification of static spring deflection. The numerical simulations reveal that negative stiffness can improve the ride comfort of a vehicle without affecting its road holding abilities for either passive or semi-active suspension systems. In general, the improvement degree of ride comfort increases as negative stiffness increases. For passive suspension system, negative stiffness brings in negative stiffness feature in the control forces, which is helpful for the ride comfort of a vehicle. For semi-active suspensions, negative stiffness can alleviate the impact of clipped damping in semi-active dampers, and thus the ride comfort of a vehicle can be improved.

A Study on the Development of High Stiffness Body for Suspension Performance (서스펜션 성능 확보를 위한 고강성 차체 개발 프로세스 연구)

  • Kim, Ki-Chang;Kim, Chan-Mook
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.358-361
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    • 2004
  • This paper describes the development process of high stiffness body for ride and handling performance. High stiffness and light weight vehicle is a major target in the refinement of passenger cars to meet customers' contradictable requirements between ride and handling performance and fuel economy. This paper describes the analysis approach process for high stiffness body through the data level of body stiffness. According to the frequency band, we can suggest the design guideline about Is cornering static stiffness, torsional and lateral stiffness, body attachment stiffness. The ride and handling characteristic of a vehicle is significantly affected by vibration transferred to the body through the chassis mounting points from front and rear suspension. It is known that body attachment stiffness is an important factor of ride and handling performance improvement. And high stiffness helps to improve the flexibility of bushing rate tuning between Handling and road noise. It makes it possible to design the good handling performance vehicle at initial design stage and save vehicles to be used in tests by using mother car at initial design stage. These improvements can lead to shortening the time needed to develop better vehicles.

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Torsional Stiffness Analysis of a Cycloid Reducer using Hertz Contact Theory (Hertz 접촉이론을 이용한 사이클로이드 감속기의 비틀림 강성해석)

  • Lee S.Y.;Park J.S;Ahn H.J.;Han D.C.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.816-821
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    • 2005
  • The cycloid reducer has very high efficiency, high ratios, high stiffness and small size, in comparison with a conventional gear mechanism, which makes it an attractive candidate for limited space and precision application such as industrial robot. There are several publications on analysis and design of the cycloid reducer, however, it was assumed that the contact stiffness of pin rollers and cycloid disk is constant regardless of their contact geometry. Moreover, the torsional stiffness of the cycloid reducer couldn't be calculated due to the assumption. In this paper, we present a new procedure of calculating torsional stiffness of the cycloid reducer using Hertz contact theory. First, conventional force analysis of the cycloid reducer is briefly reviewed. Then, iterative numerical calculation procedure of the contact stiffness is proposed based on the Hertz contact theory where the contact stiffness depends on the contact force. In addition, total torsional stiffness of the cycloid reducer is estimated considering its rolling element bearing stiffness. The torsional stiffness of the cycloid reducer is dominated by the rolling element bearing stiffness since the contact stiffness of the cycloid disk is too large.

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A Study on the Development of High Stiffness Body for Suspension Performance (서스펜션 성능 확보를 위한 고강성 차페 개발 프로세스 연구)

  • Kim, Ki-Chang;Kim, Chan-Mook
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.7
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    • pp.799-805
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    • 2005
  • This paper describes the development process of high stiffness body for ride and handling performance. High stiffness and light weight vehicle is a major target in the refinement of Passenger cars to meet customers' contradictable requirements between ride and handling performance and fuel economy This paper describes the analysis approach process for high stiffness body through the data level of body stiffness. According to the frequency band. we can suggest the design guideline about lg cornering static stiffness, torsional and lateral stiffness, body attachment stiffness. The ride and handling characteristic of a vehicle Is significantly affected by vibration transferred to the body through the chassis mounting points from front and rear suspension. It is known that body attachment stiffness is an important factor of ride and handling performance improvement. And high stiffness helps to improve the flexibility of bushing rate tuning between handling and road noise. It makes possible to design the good handling performance vehicle and save vehicles to be used in tests by using mother car at initial design stage. These improvements can lead to shortening the time needed to develop better vehicles.