• 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.

• The Journal of Korea Robotics Society
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• v.16 no.2
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• pp.137-146
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• 2021

When controlling manipulator, degree of freedom is lost in singularity so specific joint velocity does not propagate to the end effector. In addition, control problem occurs because jacobian inverse matrix can not be calculated. To avoid singularity, we apply Deep Deterministic Policy Gradient(DDPG), algorithm of reinforcement learning that rewards behavior according to actions then determines high-reward actions in simulation. DDPG uses off-policy that uses 𝝐-greedy policy for selecting action of current time step and greed policy for the next step. In the simulation, learning is given by negative reward when moving near singulairty, and positive reward when moving away from the singularity and moving to target point. The reward equation consists of distance to target point and singularity, manipulability, and arrival flag. Dual arm manipulators hold long rod at the same time and conduct experiments to avoid singularity by simulated path. In the learning process, if object to be avoided is set as a space rather than point, it is expected that avoidance of obstacles will be possible in future research.

• 제어로봇시스템학회:학술대회논문집
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• 1989.10a
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• pp.138-143
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• 1989

In considering the singularities of robot, singularity avoidance control of robot wrist is very important. Because it is more difficult structurally to exclude the wrist singularity than the arm singularity. Since control policies with Jacobian may bring about mathematical singularities, control policies with Euler parameters that never cause mathematical singularities are necessary. In this research, singular status 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 usefulness and validity.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.427-427
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• 2000

In this study, singularity of two types of mobile robots for various input joints are investigated: One is the mobile robot with three caster wheels and the other is the mobile robot with two conventional wheels and one caster wheel. Kinematic models are derived via the transfer method of generalized coordinates. Then, determinants of the Jacobian of the mobile robots are used to identify the singularity configurations.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.137-142
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• 2002

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.

• Journal of the Korean Mathematical Society
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• v.36 no.3
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• pp.459-467
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• 1999

A complete analysis of the equation x'=y, y'=$\beta$y-$\alpha$x2+$\alpha$x2+$\delta$xy, where $\alpha$ and $\beta$ small, describing a particular unfolding of the Takens-Bogdanov singularity is presented.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.58-68
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• 1998

Advantages of adhesively bonded joints and techniques of weight reduction have led to increasing use of structural adhesives such as LSI(large scale integration) package, automobile, aircraft in the various industries. In spite of such wide applications of adhesively bonded joints, the evaluation method of bonding strength has not been established. Stress singularity occurs at the interface edges of adhesively bonded joints and it is required to analyze it. In this paper, the stress singularity using 2-dimensional elastic boundary element method (BEM) with the changes of the lap length and adhesive for single lap joint was analyzed, and experiments of strength evaluation were carried out. As the results, the evaluating method of bonding strength considering stress singularity at interface edges of adhesively bonded joints and stress intensity factor of interface crack have been proposed in static and fatigue test.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.12
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• pp.1041-1047
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• 2002

It is known that parallel-type mechanisms have many singularities than serial-type mechanisms. In haptic application, these singularities deteriorate the system performance when the haptic system displays the reflecting force. Moreover, different from general manipulators, haptic systems can't avoid the singular point because they are operated by user's random motion command. Although many singularity-free algorithms for serial mechanisms have been proposed and studied. singularity-free algorithms for parallel haptic application have not been deeply discussed. In this paper, various singularity-free algorithms, which are appropriate to parallel haptic system, will be discussedand evaluated.

• Journal of Ocean Engineering and Technology
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• v.17 no.6
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• pp.72-76
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• 2003

This paper deals with the stress singularity developed in a polymer layer that is coated to a concrete surface, due to temperature change. The boundary element method is employed to investigate the behavior of interface stresses. The polymeric layer is assumed to be a linear viscoelastic material, and is thermorheologically simple. The order of the singularity is obtained, numerically, for a given viscoelastic model. Numerical results exhibit the relaxation of interface stresses, and large gradients are observed in the vicinity of the free surface. Results show that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model.

• Korean Institute of Interior Design Journal
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• v.14 no.6 s.53
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• pp.47-56
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• 2005

The purpose of this paper is to understand the meaning of 'institution' in Louis Kahn's architecture and to reveal that it is expressed through singularity and commonality, which have two aspects; formal-material(eidos-hyle) aspect and phenomenological aspect. Under these recognitions, this paper shows the detail analysis on design process of Phillips Exeter Academy Library, focusing on his writings and sketches. The results are as follows. First, the basic form is maintained through the design process of the Exeter library, and it is derived from the consideration of the human activities in the library. And second, each 'room' of the library acquires its singularity through structure and light. And the 'plan' is based on the commonality inherent in the singularity of each room. And the last, singularity and commonality are revealed not only In the relation of architectural elements but also In the relation with man and architecture.