• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.781-786
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• 1996

In this paper, output precision characteristic of planar 3 and 6 degree-of-freedom parallel mechanisms are investigated. The 6 degree-of-freedom mechanism is formed by adding an additional small link along with an actuated joint in each of serial subchain of the 3 degree-of-freedom mechanism. First, kinematic analysis for two parallel mechanisms are performed, then their first-order kinematic characteristics are examined via isotropic index and minimum velocity transmission ratio of the mechanisms. It can be concluded that the planar 6 degrees-of-freedom parallel mechanism can be very effectively employed as a high-precision macro-micro manipulator from the analysis results when its link lengths are properly chosen.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.105-106
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• 2007

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.3
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• pp.360-371
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• 1998

In this paper, output precision characteristics of a planar 6 degree-of-freedom parallel mechanisms are investigated, where the 6 degree-of-freedom mechanism is formed by adding an additional link along with an actuated joint in each serial subchain of the planar 3 degree-of-freedom parallel mechanism. Kinematic analysis for the parallel mechanism is performed, and its first-order kinematic characteristics are examined via kinematic isotropic index, maximum and minimum input-output velocity transmission ratios of the mechanisms. Based on this analysis, two types of planar 6 degrees-of-freedom parallel manipulators are selected. Then, dynamic characteristics of the two selected planar 6 degree-of-freedom parallel mechanisms, via Frobenius norms of inertia matrix and power modeling array, are investigated to compare the magnitudes of required control efforts of both three large actuators and three small actuators when the link lengths of three additional links are changed. It can be concluded from the analysis results that each of these two planar 6 degrees-of-freedom parallel mechanisms has an excellent control-in-the-small characteristics and therefore, it can be very effectively employed as a high-precision macro-micro manipulator when both its link lengths and locations of small and large actuators are properly chosen.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.8
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• pp.79-88
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• 2009

This paper presents the analytical stiffness analysis method for a low-DOF planar parallel manipulator. An n-DOF (n<3) planar parallel manipulator to which 1- or 2-DOF serial mechanism is connected in series may be used as a positioning device in planar tasks requring high payload and high speed. Differently from a 3-DOF planar parallel manipulator, an n-DOF planar parallel counterpart may be subject to constraint forces as well as actuation forces. Using the theory of reciprocal screws, the planar stiffness is modeled such that the moving platform is supported by three springs related to the reciprocal screws of actuations (n) and constraints (3-n). Then, the spring constants can be precisely determined by modeling the compliances of joints and links in serial chains. Finally, the stiffness of two kinds of 2-DOF planar parallel manipulators with simple and complex springs is analyzed. In order to show the effectiveness of the suggested method, the results of analytical stiffness analysis are compared to those of numerical stiffness analysis by using ADAMS.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.7
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• pp.648-653
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• 2015

The kinematics with the instantaneous motion and statics of a manipulator has generally been proven algebraically. The algebraic solutions give very simple and straightforward results but the solutions do not have any meaning in physics or geometry. Therefore it is not easy to extend the algebraic results to design or control a robotic manipulator efficiently. Recently, geometrical approach to define the instantaneous motion or static relation of a manipulator is popularly researched and the results have very strong advantages to have a physical insight in the solution. In this paper, the instantaneous motion and static relation of a planar manipulator are described by geometrical approach, specifically by an axis screw and a line screw. The mass center of a triangle with weight and a perpendicular distance between the two screws are useful geometric measures for geometric analysis. This study provides a geometric interpretation of the kinematics and statics of a planar manipulator, and the method can be applied to design or control procedure from the geometric information in the equations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1045-1049
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• 2005

In this paper, the dynamic crawling of a five-bar planar mechanism is investigated. One complete cycle of the crawling selected in this study consists of four different steps, i) sliding at one contact point between the mechanism and the ground, ii) changing its configuration without sliding at two contact points, iii) sliding at the other contact point, and iv) again changing its configuration without sliding at two contact points. In this type of crawling, the crawling mechanism maintains the shape of the parallel structure throughout a complete crawling cycle. The modeling algorithm for serial manipulators proposed by M. Thomas and et al.[1] is employed by introducing imaginary joints and links which represent the contact interfaces between the one end of the mechanism and the ground, while the other end of the mechanism is regarded as an end-effector of the imaginary serial manipulator which treats the reaction force and torque at the contact point as external forces. Then, a complete cycle of dynamic crawling of the mechanism is investigated through various computer simulations. The simulation result show that the stable crawling characteristics of the mechanism could be secured when the proper configurations depending on specified frictional constraints are met.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.04a
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• pp.395-400
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• 1994

Most of Commercial Remote Center Compliance(RCC) devices have been designed using deformable structures. In this work, we propose another type of assembly devices which generate the compliance effects by attaching the compliances (or spring) at the joints of the given mechainsm. The compliance models are derived for a serial-type, parallel-type, and hybrid-type mechanisms, respectively. In particular, a planar three-degree of freedom parallel structure is shown to have RCC points at the center of the workspace for its symmetric configuratings.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.60-68
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• 1998

Parallel link manipulators have an ability of more precise positioning than serial open-loop manipulators. However. general parallel link manipulators have been restricted to the real applications since they have limited workspace due to interference among actuators. In this study, we suggest a closed-loop manipulator with 6 degrees-of-freedom and with enlarged workspace. It consists of two parts for minimizing the interference among actuators. One part is lower structure with planar 3 degrees-of-freedom and the other is upper one with spatial 3 degrees-of-freedom. Forward kinematics and inverse kinematics are solved, research about singularity points are carried out and workspace is evaluated. The comparison of workspace between Stewart platform, which is the typical parallel link manipulator, and the suggested manipulator shows that the workspace of the latter is wider than that of the former. Especially, simulation results also show that the suggested manipulator is more suitable when there needs rotation in the end-effector.