• Title, Summary, Keyword: singularity

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Task Reconstruction Method for Real-Time Singularity Avoidance for Robotic Manipulators : Dynamic Task Priority Based Analysis (로봇 매니플레이터의 실시간 특이점 회피를 위한 작업 재구성법: 동적 작업 우선도에 기초한 해석)

  • 김진현;최영진
    • Journal of Institute of Control, Robotics and Systems
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    • v.10 no.10
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    • pp.855-868
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    • 2004
  • There are several types of singularities in controlling robotic manipulators: kinematic singularity, algorithmic singularity, semi-kinematic singularity, semi-algorithmic singularity, and representation singularity. The kinematic and algorithmic singularities have been investigated intensively because they are not predictable or difficult to avoid. The problem with these singularities is an unnecessary performance reduction in non-singular region and the difficulty in performance tuning. Tn this paper, we propose a method of avoiding kinematic and algorithmic singularities by applying a task reconstruction approach while maximizing the task performance by calculating singularity measures. The proposed method is implemented by removing the component approaching the singularity calculated by using singularity measure in real time. The outstanding feature of the proposed task reconstruction method (TR-method) is that it is based on a local task reconstruction as opposed to the local joint reconstruction of many other approaches. And, this method has dynamic task priority assignment feature which ensures the system stability under singular regions owing to the change of task priority. The TR-method enables us to increase the task controller gain to improve the task performance whereas this increase can destabilize the system for the conventional algorithms in real experiments. In addition, the physical meaning of tuning parameters is very straightforward. Hence, we can maximize task performance even near the singular region while simultaneously obtaining the singularity-free motion. The advantage of the proposed method is experimentally tested by using the 7-dof spatial manipulator, and the result shows that the new method improves the performance several times over the existing algorithms.

Singularty Control of Robot Wrist Joints using Euler Parameters (오일러 파라미터를 이용한 로보트 손목관절의 특이성 회피제어)

  • Jeon, Ui-Sik;Park, Su-Heung
    • Journal of the Korean Society for Precision Engineering
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    • v.9 no.1
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    • pp.137-145
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    • 1992
  • Considering the singularity of robot, singularity avoidance control of robot is very important. Because it is very difficult structurally to exclude the wrist singularity. Then new control policy is needed to overcome wrist singularity. In this paper, the singularity states of robot wrist was analyzed and control algorithms for 3 and 4 axes robot wrist were proposed. Application results of the proposed control algorithms to the path including singularity showed us their usefulness and validity.

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Analysis of Stress Singularity for the Excess Adhesive of Interface in Adhesively Bonded Joint (접착이음의 계면덧살에 대한 응력특이성 해석)

  • Chung, Nam-Yong;Park, Cheol-Hee
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.21 no.3
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    • pp.439-445
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    • 2012
  • The stress singularity for the excess adhesive on interface of adhesively bonded joint was investigated by using the 2-dimensional elastic boundary element method (BEM). To establish a reasonable strength evaluation method and a fracture criterion for the excess adhesive of interface in adhesively bonded joint, it is necessary to evaluate fracture parameters with various bonding conditions. Under the variations of adhesively bonded thickness (h) and diameter (d) for the excess adhesive, a stress analysis was performed, and from the results, the stress singularity index (${\lambda}$) and the stress singularity factor (${\Gamma}$) were calculated. The variations have a great influences on the stress singularity for the excess adhesive of interface in adhesively bonded joint, and the ${\Gamma}$ is reduced as the "h" and "d" increase.

Analysis of Stress Singularities on Interfaces of Friction Welded Dissimilar Materials (마찰용접에 의한 이종재 접합계면에 대한 응력특이성의 해석)

  • Chung, Nam-Yong;Park, Chul-Hee
    • Transactions of the Korean Society of Automotive Engineers
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    • v.13 no.2
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    • pp.142-148
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    • 2005
  • In this paper, the stress singularity on interface of friction welded dissimilar materials was investigated by using 2-dimensional elastic boundary element method. It is required that stress distributions and stress singularities on an interface for friction welded dissimilar materials analize to establish strength evaluation. The stress singularity index ($\lambda$) and stress singularity factor ($\Gamma$) were calculated from the results of stress analysis. The stress singularities on variations for shapes and thickness of friction welded flashes were analized and discussed. This paper suggested that the strength evalution by using the stress singularity factors as fracture parameters, considering the stress singularity on an interface edge of friction welded dissimilar materials were very useful.

A Unified Framework for Overcoming Motion Constraints of Robots Using Task Transition Algorithm (작업 전이 알고리즘 기반 로봇 동작 제한 극복 프레임워크)

  • Jang, Keunwoo;Kim, Sanghyun;Park, Suhan;Park, Jaeheung
    • The Journal of Korea Robotics Society
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    • v.13 no.2
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    • pp.129-141
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    • 2018
  • This paper proposes a unified framework that overcomes four motion constraints including joint limit, kinematic singularity, algorithmic singularity and obstacles. The proposed framework is based on our previous works which can insert or remove tasks continuously using activation parameters and be applied to avoid joint limit and singularity. Additionally, we develop a method for avoiding obstacles and combine it into the framework to consider four motion constraints simultaneously. The performance of the proposed framework was demonstrated by simulation tests with considering four motion constraints. Results of the simulations verified the framework's effectiveness near joint limit, kinematic singularity, algorithmic singularity and obstacles. We also analyzed sensitivity of our algorithm near singularity when using closed loop inverse kinematics depending on magnitude of gain matrix.

Strength Evaluation of Bonded Dissimilar Materials by Using Stress Singularity Factor (응력특이성계수에 의한 이종 접합재료의 강도평가)

  • Jeong, Nam-Yong;O, Bong-Taek
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2087-2096
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    • 1996
  • Recentrly advantages in composite and light weight material techniques have led to the increased use of bonded dissimilar materials such as ceramics/metal bonded joints, IC package, brazing, coating and soldering in the various industries. It is required to analyze the evaluation method of fracture strength and design methodology of bonded joints in dissimilar materials. Stress singularity according to changes of scarf angles for bonded scarf joints in dissimilar materials was investigated by the boundary element method and static experiments. In this paper, effect of the stress singularity factors at the interface edges of scarf joints on various dissmilar materials combinations were investigated by analysis of its stress and stress singularity index using 2-dimensional elastic program of boundary element method. And the variations of stress singularity index by changes for Young's modulus ratios of materials and scarf angles were investigated. Also, it is found that stress singularities at bonded interface edges are disappeared for certain combination of scarf angle in a pair of bonded dissimilar materials. As the results, it is proposed that the strength evaluation by using stress singularity factors, $\Gamma$, considering stress singularity at the interface edges of bonded dissimilar materials, is very useful.

Viscoelastic Stress Analysis of Polymeric Thin Layer Under Moisture Absorption (수분 흡수로 인해 고분자 박막에서 발생하는 점탄성 응력 해석)

  • 이상순;장영철
    • Journal of the Microelectronics and Packaging Society
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    • v.10 no.1
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    • pp.25-29
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    • 2003
  • This paper deals with the stress singularity induced at the interface corner between the elastic substrate and the viscoelastic thin film as the polymeric film absorbs moisture from the ambient environment. The boundary element method is employed to investigate the behavior of interface stresses. The order of the singularity is obtained numerically for a given viscoelastic model. It is shown that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model considered.

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Boundary Element Analysis of Singular Stresses in a Viscoelastic Thin Film due to Moisture Absorption (수분 흡수로 인해 점탄성 필름에 발생하는 특이 응력의 경계요소해석)

  • Lee, Sang-Sun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.3
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    • pp.685-690
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    • 2000
  • This paper deals with the stress singularity induced at the interface corner between the viscoelastic thin film and the rigid substrate as the film absorbs moisture from the ambient environment. Th e time domain boundary element method is employed to investigate the behavior of interface stresses. The order of the free-edge singularity is obtained numerically for a given viscoelastic model. It is shown that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model considered.

Prediction Fracture Strength on Adhesively Bonded scarf Joints in Dissimilar Materials (이종재료의 경사접착이음에 대한 파괴강도의 예측)

  • 정남용
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.4 no.4
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    • pp.50-60
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    • 1995
  • Recently advantages joining dissimiliar materials and light weight material techniques have led to increasing use of structural adhesives in the various industries. Stress singulartiy occurs at the interface edges of adhesively bonded dissimilar materials. So it is required to analyze its stress singularity at the interface edges of adhesively bonded joints indissimilar materials. In this paper, the analysis method of stress singularity is studied in detail. Also, effects of the stress singularity at the interface edge of adhesively bonded scarf joints in combinations of dissimilar materials are investigated by using 2-dimensional elastic program of boundary element method. As the results, the strength evaluation method of adhesively bonded dissimilar materials using the stress singularity factor, $\Gamma$,is very useful. The fracture criterion, method of strength evaluation and prediction of fracture strength by the stress singularity factor on the adhesively bonded dissimilar materials are proposed.

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Stress Singularity Behaviour in the Frictional Complete Contact Problem of Three Bodies (세 물체 간 마찰 완전 접촉 문제의 응력 특이성 거동)

  • Kim, Hyung-Kyu
    • Tribology and Lubricants
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    • v.35 no.4
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    • pp.229-236
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    • 2019
  • This study investigates the stress singularity that occurs at the contact edge of three bodies in a frictional complete contact. We use the asymptotic analysis method, wherein we constitute an eigenvalue problem and observe the eigenvalue behavior, which we use to obtain the order of the stress singularity. For the present geometry of three bodies in contact, a contact between a cracked indenter and half plane is considered. This is a typical geometry of the PCMI problem of a nuclear fuel rod. Thus, this paper, specifically presents the characteristics of the PCMI problem from the perspective of stress singularity. Consequently, it is noted that the behavior of the stress singularity varies with the difference in the crack angle, coefficient of friction, and material dissimilarity, as is observed in a frictional complete contact of two bodies. In addition, we find that the stress singularity changes essentially linearly with respect to the coefficient of friction, regardless of the variation in the crack angle and material dissimilarity. Concurrently, we find the order of singularity to be 0.5 at a certain coefficient of friction, irrespective of the crack angle, which we also observe in the crack problem of a homogeneous and isotropic body. The order of singularity can also exceed 0.5 in the frictional complete contact problem of three bodies. This implies that the propensity for failure when three bodies are in frictional complete contact can be even worse than that in case of a failure induced by a crack.