• Title, Summary, Keyword: Leg stiffness

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Relationship between Leg Stiffness and Kinematic Variables According to the Load while Running

  • Hyun, Seung Hyun;Ryew, Che Cheong
    • Korean Journal of Sport Biomechanics
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    • v.27 no.2
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    • pp.109-116
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    • 2017
  • Objective: This study aimed to investigate the relationship between leg stiffness and kinematic variables according to load while running. Method: Participants included eight healthy men (mean age, $22.75{\pm}1.16years$; mean height: $1.73{\pm}0.01m$; mean body weight, $71.37{\pm}5.50kg$) who ran with no load or a backpack loaded with 14.08% or 28.17% of their body weight. The analyzed variables included leg stiffness, ground contact time, center of gravity (COG) displacement and Y-axis velocity, lower-extremity joint angle (hip, knee, ankle), peak vertical force (PVF), and change in stance phase leg length. Results: Dimensionless leg stiffness increased significantly with increasing load during running, which was the result of increased PVF and contact time due to decreased leg lengths and COG displacement and velocity. Leg length and leg stiffness showed a negative correlation (r = -.902, $R^2=0.814$). COG velocity showed a similar correlation with COG displacement (r = .408, $R^2=.166$) and contact time (r = -.455, $R^2=.207$). Conclusion: Dimensionless leg stiffness increased during running with a load. In this investigation, leg stiffness due to load increased was most closely related to the PVF, knee joint angle, and change in stance phase leg length. However, leg stiffness was unaffected by change in contact time, COG velocity, and COG displacement.

Changes of Lower Limb Joints Stiffness with Gait Speed in Knee Osteoarthritis (무릎 골관절염 환자의 보행속도에 따른 하지 관절 강성 변화)

  • Park, Hee-Won;Park, Su-Kyung
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.7
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    • pp.723-729
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    • 2012
  • Spring-like leg models have been employed to explain various dynamic characteristics in human walking. However, this leg stiffness model has limitations to represent complex motion of actual human gait, especially the behaviors of each lower limb joint. The purpose of this research was to determine changes of total leg stiffness and lower limb joint stiffness with gait speed in knee osteoarthritis. Joint stiffness defined as the ratio of the joint torque change to the angular displacement change. Eight subjects with knee osteoarthritis participated to this study. The subject walked on a 12 m long and 1 m wide walkway with three sets of four different randomly ordered gait speeds, ranging from their self-selected speed to maximum speed. Kinetic and kinematic data were measured using three force plates and an optical marker system, respectively. Joint torques of lower limb joints calculated by a multi-segment inverse dynamics model. Total leg and each lower limb joint had constant stiffness during single support phase. The leg and hip joint stiffness increased with gait speed. The correlation between knee joint angles and torques had significant changed by the degree of severity of knee osteoarthritis.

Relationship between Dimensionless Leg Stiffness and Kinetic Variables during Gait Performance, and its Modulation with Body Weight

  • Hyun, Seung Hyun;Ryew, Che Cheong
    • Korean Journal of Sport Biomechanics
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    • v.26 no.3
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    • pp.249-255
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    • 2016
  • Objective: This purpose of this study was to analyze the relationship between dimensionless leg stiffness and kinetic variables during gait performance, and its modulation with body weight. Method: The study sample consisted of 10 young women divided into 2 groups (Control, n=5 and Obese, n=5). Four camcorders (HDR-HC7/HDV 1080i, Sony Corp, Japan) and one force plate (AMTI., USA) were used to analyze the vertical ground reaction force (GRF) variables, center of pressure (COP), low limb joint angle, position of pelvis center and leg lengths during the stance phase of the gait cycle. Results: Our results revealed that the center of mass (COM) displacement velocity along the y-axis was significantly higher in the obese group than that in control subjects. Displacement in the position of the center of the pelvis center (Z-axis) was also significantly higher in the obese group than that in control subjects. In addition, the peak vertical force (PVF) and dimensionless leg stiffness were also significantly higher in the obese group. However, when normalized to the body weight, the PVF did not show a significant between-group difference. When normalized to the leg length, the PVF and stiffness were both lower in the obese group than in control subjects. Conclusion: In the context of performance, we concluded that increased dimensionless leg stiffness during the gait cycle is associated with increased velocity of COM, PVF, and the change in leg lengths (%).

Effect of Leg Stiffness on the Running Performance of Milli-Scale Six-Leg Crawling Robot with Payload (소형 6족 주행 로봇의 페이로드와 다리 강성이 로봇의 주행 성능에 미치는 영향)

  • Chae, Soo-Hwan;Baek, Sang-Min;Lee, Jongeun;Yim, Sojung;Ryu, Jae-Kwan;Jo, Yong-Jin;Cho, Kyu-Jin
    • The Journal of Korea Robotics Society
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    • v.14 no.4
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    • pp.270-277
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    • 2019
  • Inspired by small insects, which perform rapid and stable locomotion based on body softness and tripod gait, various milli-scale six-legged crawling robots were developed to move rapidly in harsh environment. In particular, cockroach's leg compliance was resembled to enhance the locomotion performance of the crawling robots. In this paper, we investigated the effects of changing leg compliance for the locomotion performance of the small light weight legged crawling robot under various payload condition. First, we developed robust milli-scale six-leg crawling robot which actuated by one motor and fabricated in SCM method with light and soft material. Using this robot platform, we measured the running velocity of the robot depending on the leg stiffness and payload. In result, there was optimal range of the leg stiffness enhancing the locomotion ability at each payload condition in the experiment. It suggests that the performance of the crawling robot can be improved by adjusting stiffness of the legs in given payload condition.

Effect of Functional Ankle Instability and Surgical Treatment on Dynamic Postural Stability and Leg Stiffness Variables during Vertical-Drop Landing

  • Jeon, Kyoung Kyu;Kim, Kew Wan;Ryew, Che Cheong;Hyun, Seung Hyun
    • Korean Journal of Sport Biomechanics
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    • v.28 no.2
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    • pp.135-141
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    • 2018
  • Objective: The purpose of this study was to investigate the effect of functional ankle instability (FAI) and surgical treatment (ST) on postural stability and leg stiffness during vertical-drop landing. Method: A total of 21 men participated in this study (normal [NOR]: 7, FAI: 7, ST: 7). We estimated dimensionless leg stiffness as the ratio of the peak vertical ground reaction force and the change in stance-phase leg length. Leg length was calculated as the distance from the center of the pelvis to the center of pressure under the foot. Furthermore, the analyzed variables included the loading rate and the dynamic postural stability index (DPSI; medial-lateral [ML], anterior-posterior [AP], and vertical [V]) in the initial contact phase. Results: The dimensionless leg stiffness in the FAI group was higher than that of the NOR group and the ST group (p = .018). This result may be due to a smaller change in stance-phase leg length (p = .001). DPSI (ML, AP, and V) and loading rate did not show differences according to the types of ankle instability during drop landing (p > .05). Conclusion: This study suggested that the dimensionless leg stiffness was within the normal range in the ST group, whereas it was increased by the stiffness of the legs rather than the peak vertical force during vertical-drop landing in the FAI group. Identifying these potential differences may enable clinicians to assess ankle instability and design rehabilitation protocols specific for the impairment.

Stiffness Analysis of Planar Parallel Manipulators with Serially Connected Legs (직렬체인 다리를 갖는 평면 병렬형 기구의 강성해석)

  • Kim, Han Sung
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.23 no.2
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    • pp.164-172
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    • 2014
  • This paper presents a method for analyzing the stiffness of full and low DOF (degree of freedom) planar parallel manipulators with serially connected legs. The individual stiffness of each leg is obtained by applying reciprocal screws to the leg twist using passive joints and elastic elements consisting of actuators and links. Because the legs are connected in parallel, the manipulator stiffness is determined by summing the individual leg stiffness values. This method does not require the assumption that springs should be located along reciprocal screws and is applicable to a planar parallel manipulator with a generic or singular configuration. The stiffness values of three planar parallel manipulators with different DOFs are analyzed. The numerical results are confirmed using ADAMS S/W.

Establishment of Design Variable of Leg Stiffness Artificial Tendon Actuator ($LeSATA^{TM}$) for Actual Control in Dorsiflexion of Metatarsophalangeal Joint at the Initial Contact while the Bi-pedal Human Walking : (1) Realization of Lagrangian Equation and Impulsive Constraint (2족 보행시 중족지절관절 초기접지기 배측굴곡의 능동적 통제를 위한 Leg Stiffness Artificial Tendon Actuator($LeSATA^{TM}$)의 설계변수 확립 : (1) Lagrangian 방정식 및 Impulsive Constraint 적용법 구현)

  • Kim, Cheol-Woong;Han, Gi-Bong;Eo, Eun-Kyoung
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.651-652
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    • 2010
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Vertical Limb Stiffness Increased with Gait Speed in the Elderly (노인군 보행 속도 증가에 따른 하지 강성 증가)

  • Hong, Hyun-Hwa;Park, Su-Kyung
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.6
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    • pp.687-693
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    • 2011
  • Spring-mass models have been widely accepted to explain the basic dynamics of human gait. Researchers found that the leg stiffness increased with gait speed to increase energy efficiency. However, the difference of leg stiffness change with gait speed between the young and the elderly has not been verified yet. In this study, we calculated the lower limb stiffness of the elderly using walking model with an axial spring. Vertical stiffness was defined as the ratio of the vertical force change to the vertical displacement change. Seven young and eight elderly subjects participated to the test. The subjects walked on a 12 meter long, 1 meter wide walkway at four different gait speeds, ranging from their self-selected speed to maximum speed randomly. Kinetic and kinematic data were collected using three force plates and motion capture cameras, respectively. The vertical stiffness of the two groups increased as a function of walking speed. Maximum walking speed of the elderly was slower than that of the young, yet the walking speed correlated well with the optimal stiffness that maximizes propulsion energy in both groups. The results may imply that human may use apparent limb stiffness to optimize energy based on spring-like leg mechanics.

Stiffness Analysis of a Low-DOF Parallel Manipulator using the Theory of Reciprocal Screws (역나선 이론을 이용한 저자유도 평행구조 기구의 강성해석)

  • Kim, Han-Sung
    • Proceedings of the KSME Conference
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    • pp.573-578
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    • 2004
  • This paper presents a methodology for the stiffness analysis of a low-DOF parallel manipulator. A low-DOF parallel manipulator is a spatial parallel manipulator which has less than six degrees of freedom. The reciprocal screws of actuations and constraints in each leg can be determined by making use of the theory of reciprocal screws, which provide information about reaction forces due to actuations and constraints. When pure force is applied to a leg, the leg stiffness is modeled as a linear spring along the line. For pure couple, it is modeled as a rotational spring about the axis. It is shown that the stiffness model of an F-DOF parallel manipulator consists of F springs related to actuations and 6-F springs related to constraints connected from the moving platform to the base in parallel. The $6{\times}6$ Cartesian stiffness matrix is obtained, which is the sum of the Cartesian stiffness matrices of actuations and constraints. Finally, a 3-UPU parallel manipulator is used as an example to demonstrate the methodology.

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Stiffness Analysis of a Low-DOE Parallel Manipulator using the Theory of Reciprocal Screws (역나선 이론을 이용한 저자유도 병렬형 기구의 강성해석)

  • Kim Han Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.5
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    • pp.680-688
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    • 2005
  • This paper presents a methodology for the stiffness analysis of a low-DOF parallel manipulator. A low-DOF parallel manipulator is a spatial parallel manipulator which has less than six degrees of freedom. The reciprocal screws of actuations and constraints in each leg can be determined by making use of the theory of reciprocal screws, which provide information about reaction forces due to actuations and constraints. When pure farce is applied to a leg, the leg stiffness is modeled as a linear spring along the line. For pure couple, it is modeled as a rotational spring about the axis. It is shown that the stiffness model of an it_DOF parallel nipulator consists of F springs related to actuations and 6-F springs related to constraints connected from the moving platform to the base in parallel. The 6x f Cartesian stiffness matrix is derived, which is the sum of the Cartesian stiffness matrices of actuations and constraints. Finally, the 3-UPU, 3-PRRR, and Tricept parallel manipulators are used as examples to demonstrate the methodology.