• Title/Summary/Keyword: Joint Stiffness

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A hybrid method for dynamic stiffness identification of bearing joint of high speed spindles

  • Zhao, Yongsheng;Zhang, Bingbing;An, Guoping;Liu, Zhifeng;Cai, Ligang
    • Structural Engineering and Mechanics
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    • v.57 no.1
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    • pp.141-159
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    • 2016
  • Bearing joint dynamic parameter identification is crucial in modeling the high speed spindles for machining centers used to predict the stability and natural frequencies of high speed spindles. In this paper, a hybrid method is proposed to identify the dynamic stiffness of bearing joint for the high speed spindles. The hybrid method refers to the analytical approach and experimental method. The support stiffness of spindle shaft can be obtained by adopting receptance coupling substructure analysis method, which consists of series connected bearing and joint stiffness. The bearing stiffness is calculated based on the Hertz contact theory. According to the proposed series stiffness equation, the stiffness of bearing joint can be separated from the composite stiffness. Then, one can obtain the bearing joint stiffness fitting formulas and its variation law under different preload. An experimental set-up with variable preload spindle is developed and the experiment is provided for the validation of presented bearing joint stiffness identification method. The results show that the bearing joint significantly cuts down the support stiffness of the spindles, which can seriously affects the dynamic characteristic of the high speed spindles.

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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    • 2000.08a
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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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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.

Rotator cuff tear with joint stiffness: a review of current treatment and rehabilitation

  • Park, Hyung-Seok;Choi, Kyung-Ho;Lee, Hyo-Jin;Kim, Yang-Soo
    • Clinics in Shoulder and Elbow
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    • v.23 no.2
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    • pp.109-117
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    • 2020
  • Repair of the rotator cuff tear is a joint-tightening procedure that can worsen joint stiffness. This paradoxical phenomenon complicates treatment of rotator cuff tear with joint stiffness. As a result, there is controversy about how and when to treat joint stiffness. As many treatments have been published, this review discusses the latest findings on treatment of rotator cuff tear with joint stiffness.

Static Stiffness Tuning Method of Rotational Joint of Machining Center (머시닝센터 회전 결합부의 정강성 Tuning 기법)

  • Kim, Yang-Jin;Lee, Chan-Hong
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.19 no.6
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    • pp.797-803
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    • 2010
  • A method has been developed to tune the static stiffness at a rotation joint considering the whole machine tool system by interactive use of finite element method and experiment. This paper describes the procedure of this method and shows the results. The method uses the static experiment on measurement model which is set-up so that the effects of uncertain factors can be excluded. For FEM simulation, the rotation joint model is simplified using only spindle, bearing and spring. At the rotation joint, the damping coefficient is ignored, The spindle and bearing is connected by only spring. By static experiment, 500 N is forced to the front and behind portion of spindle and the deformation is measured by capacitive sensor. The deformation by FEM simulation is extracted with changing the static stiffness from the initial static stiffness considering only rotation joint. The tuning static stiffness is obtained by exploring the static stiffness directly trusting the deformation from the static experiment. Finally, the general tuning method of the static stiffness of machine tool joint is proposed using the force stream and the modal analysis of machine tool.

NUMERICAL APPROXIMATION OF VEHICLE JOINT STIFFNESS BY USING RESPONSE SURFACE METHOD

  • Lee, S.B.;Park, J.R.;Yim, H.J.
    • International Journal of Automotive Technology
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    • v.3 no.3
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    • pp.117-122
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    • 2002
  • Joint stiffness can affect the vibration characteristics of car body structures. Therefore, it should be included in vehicle system model. In this paper, a numerical approximation of joint stiffness is presented considering joint flexibility of thin walled beam-jointed structures. Using the proposed method, it is possible to optimize joint structures considering the change of section shapes in vehicle structures. The numerical approximation of joint stiffness is derived using the response surface method in terms of beam section properties. The study shows that joint stiffnesses can be effectively determined in designing vehicle structures.

Influence of the joint stiffness on the segment design (이음부 강성계수가 세그먼트 설계에 미치는 영향)

  • Choi, Woo-Yong;Park, Jong-Deok;Lee, Seok-Won
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.16 no.1
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    • pp.63-74
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    • 2014
  • The lining of shield TBM tunnel is composed of segments, therefore segment joints are induced by connecting each segment. Segment joint is considered as joint stiffness in the design of TBM tunnel. Depending on the choice among the different stiffness equations, the joint stiffness values determined can be varied largely. Therefore, the influence of joint stiffness value on the design of segment lining should be verified. In this study, the joint stiffness values were determined firstly by using various equations and total change boundary was justified. Within the change boundary determined, the member forces were calculated by changing the joint stiffness through the numerical analysis and consequently the stability of segment lining was investigated by applying nominal strength. The results showed that the segment joint stiffness did not affect the design of segment lining largely.

Flexural Strength and Rotational Stiffness Estimation of Joint between Vertical and Horizontal Members in System Support (시스템 동바리 수직재와 수평재 연결부의 휨강도와 회전 강성 평가)

  • Won, Jeong-Hun;Lee, Hyung Do;Choi, Myeong-Ki;Park, Man Cheol
    • Journal of the Korean Society of Safety
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    • v.33 no.4
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    • pp.46-53
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    • 2018
  • This study examined the maximum resistant moment and nonlinear rotational stiffness of wedge joint between the vertical and horizontal members of system supports. To examine the maximum resistant moment and propose the nonlinear rotation stiffness of wedge joint, 6 specimens were tested and additional 3 specimens, where the horizontal member was welded to the vertical member, were tested to compare the moment capacity of wedge joints. The average maximum moment in the tested wedge joint was 1.183 kNm which represented about 70 % of the maximum moment developed in the welded specimens. And, as simulating nonlinear rotational stiffness of the wedge joint, a tri-linear model was suggested. The rotational stiffness was estimated as 23.095 kNm/rad in first stage, 7.945 kNm/rad in second stage, and 3.073 kNm/rad in third stage. For the failure mode, the specimen with the wedge joint showed the failure of joint between vertical and horizontal members. However, the specimen with welded joint represented the yielding of horizontal members.

A Design on the chassis frame of passenger car using beam and spring Elements (빔과 스프링 요소를 이용한 승용차의 차체 프레임 설계)

  • 이동찬;이상호;한창수
    • Transactions of the Korean Society of Automotive Engineers
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    • v.7 no.9
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    • pp.89-96
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    • 1999
  • This paper presents the optimization design technique on the joint stiffness and section characteristic factors of chassis frame, by using beam and spring elements in a given design package. Two correction methods are used for the optimization design of chassis frame. First is the equivalent inertia of moment method in relation to the section characteristic factors of joint zones, which are thickness , width and height of frame channel section. Second is the rotational spring element with joint stiffness of joint zones. The CAE example shows that the relationship of section characteristic factors and joint stiffness can effectively be used in designing chassis frame. In this point, if static and dynamic targets are given, the joint-zone and section characteristic factors of chassis frame intended may be designed and defined by using beam and rotational spring elements.

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Analysis on Rehabilitation of Elbow Joint Using Elastic String (탄성 줄을 이용한 팔꿈치 관절 재활 분석)

  • Kim, Byoung-Ho
    • Journal of the Korean Institute of Intelligent Systems
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    • v.26 no.3
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    • pp.196-201
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    • 2016
  • This paper analyses the characteristics of a stiffness-based rehabilitation mechanism for improving the function of the elbow joint of a human. We consider an elastic string as a tool for the elbow joint rehabilitation, where the string has been modeled as a linear spring with a stiffness. For effective rehabilitation training by using such a mechanism, we need to analyse the available torque characteristics of the elbow joint according to the stiffness of the string. Through various simulations, the torque pattern and its range of the elbow joint by assigning the stiffness of the string have been identified for a pre-defined trajectory of motion of the elbow joint. Finally, we show that the specified stiffness-based rehabilitation scheme can be used for effective rehabilitation of the elbow joint.