• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.631-637
• /
• 2005

This paper presents a stiffness analysis method for a low-DOF parallel manipulator, which takes into account of elastic deformations of joints and links. A low-DOF parallel manipulator is defined as a spatial parallel manipulator which has less than six degrees of freedom. Differently from the case of a 6-DOF parallel manipulator, the serial chains in a low-DOF parallel manipulator are subject to constraint forces as well as actuation forces. The reaction forces due to actuations and constraints in each limb can be determined by making use of the theory of reciprocal screws. It is shown that the stiffness model of an F-DOF parallel manipulator consists of F springs related to the reciprocal screws of actuations and 6-F springs related to the reciprocal screws of constraints, which connect the moving platform to the fixed base in parallel. The $6{times}6$ stiffness matrix is derived, which is the sum of the stiffness matrices of actuations and constraints. The six spring constants can be precisely determined by modeling the compliance of joints and links in a serial chain as follows; the link can be considered as an Euler beam and the stiffness matrix of rotational or prismatic joint can be modeled as a $6{times}6$ diagonal matrix, where one diagonal element about the rotation axis or along the sliding direction is zero. By summing the elastic deformations in joints and links, the compliance matrix of a serial chain is obtained. Finally, applying the reciprocal screws to the compliance matrix of a serial chain, the compliance values of springs can be determined. As an example of explaining the procedure, the stiffness of the Tricept parallel manipulator has been analyzed.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
• /
• pp.203-209
• /
• 1999

In this study, the structural deflection analysis of robot manipulator for removing nuclear fuel rod from nuclear reactor vessel is performed by using general purpose finite element code (ANSYS). The structural deflection analysis results reported in this study is very required for the accurate design of robot system. The structural deflection analysis for the manipulator's structural status at which the gripper grasps and draws up the nuclear fuel rod is done, For this beginning structural status of robot manipulator's removing motion, the reaction forces at each joint have static maximum values as reported in the reference(6), and so these forces may cause the maximum deflection of robot structure. The structural deflection analysis is performed for selected four working cases of the proposed structural model and results on deformation, stress for the manipulator's solid body and the deflection at the end of robot manipulator's gripper are calculated. And further, the same analysis is performed for the slenderer manipulator with cross section reduced by one-fifth of each side length of proposed model. The analysis is performed not only for the nuclear fuel rod with weight load of 300kg but also for nuclear fuel rods with weight loads of 100kg, 200kg, 400kg and 500kg. The static structural deflection analysis results show that the deflection value increases as the load increases and the largest value (corresponding to the weight load of 500kg in case 1) is much smaller than the gap distance between nuclear fuel rods. but the largest value for the slenderer manipulator is almost as large as the gap distance, Hence, conclusively, the proposed manipulator's structural model is acceptably safe for mechanical design of robot system.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• 제10권2호
• /
• pp.87-96
• /
• 2012

With a view to determine a safe speed the limit of a manipulator arm, several experiments was performed with a multi-jointed manipulator in maintenance and decommissioning tasks of nuclear facilities. Under the simulated emergency conditions, which were generated with random combinations of manipulator arm speed, failure probability and failure type, response characteristics of human operators to various malfunctions of a manipulator arm were measured in terms of reaction time, number of false alarm, and number of misses. This paper demonstrated that failure type, manipulator axes and manipulator arm speed has significant effects on human reaction time. As a whole the reaction time was slightly increased with manipulator arm speed, which is showed somewhat different pattern due to failure type. The reaction time to an axis acting on a workpiece directly, which could flex and extend, was fastest and much more its standard deviation was small. Various factors which may affect safe speed were also described.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.48-53
• /
• 2004

In this paper, the task-oriented optimal configuration in the sense of Velocity and Force manipulability measure of manipulator mounted on ROV is considered. Manipulability is a quantitative measure of manipulator's capability obtained under the limits of joint velocities or torques. The base arrangements and optimal joint configuration of manipulator, that maximize the manipulability measure under the constraints of given task, are investigated. With the two types of base arrangements of manipulator, workspace analysis is carried out to investigate merits and demerits of each arrangement on the view of manipulability measure. To find optimal joint configuration for a given task with each arrangement, the SQP(Sequential Quadratic Programming) optimization are performed. Weighted linear combination of velocity and force manipulability measure is object function for SQP optimization. The kinematic parameters of Dual Orion manipulator which will be mounted on KORDI ROV are used for simulation.

• Proceedings of the KSME Conference
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.573-578
• /
• 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.

• Journal of Institute of Control, Robotics and Systems
• /
• 제16권9호
• /
• pp.883-890
• /
• 2010

This paper proposes tip position control system which uses a visual marker to determine the tip position of a robot manipulator. The main idea of this paper is to introduce visual marker for the tracking control of a robot manipulator. Existing researches utilize stationary markers to get pattern information from them. Unlike existing researches, we introduce visual markers to get the coordinates of them in addition to their pattern information. Markers need not be stationary and the extracted coordinate of markers are used as a reference trajectory for the tracking control of a robot manipulator. To build the proposed control scheme, we first obtain intrinsic parameters through camera calibration and evaluate their validity. Secondly, we present a procedure to obtain the relative coordinate of a visual marker with respect to a camera. Thirdly, we derive the equation for the kinematics of the SCORBOTER 4pc manipulator which we use for control of manipulator. Also, we provide a flow diagram of entire visual marker tracking system. The feasibility of the proposed scheme will be demonstrated through real experiments.

• Journal of Mechanical Science and Technology
• /
• 제14권6호
• /
• pp.605-621
• /
• 2000

A mobile manipulator-a serial connection of a mobile platform and a task robot-is redundant by itself. Using its redundant freedom, a mobile manipulator can move in various modes, i. e., can perform dexterous tasks. In this paper, to improve task execution efficiency utilizing redundancy, optimal configurations of the mobile manipulator are maintained while it is moving to a new task point. Assuming that a task robot can perform the new task by itself, a desired configuration for the task robot can be pre-determined. Therefore, a cost function for optimality can be defined as a combination of the square errors of the desired and actual configurations of the mobile platform and of the task robot. In the combination of the two square errors, a newly defined mobility of a mobile platform is utilized as a weighting index. With the aid of the gradient method, the cost function is minimized, so the tasle that the mobile manipulator performs is optimized. The proposed algorithm is experimentally verified and discussed with a mobile manipulator, PURL-II.

• Journal of Mechanical Science and Technology
• /
• 제19권3호
• /
• pp.756-767
• /
• 2005

This paper presents a decentralized motion control method of welding mobile manipulators which use for welding in many industrial fields. Major requirements of welding robots are accuracy, robust, and reliability so that they can substitute for the welders in hazardous and worse environment. To do this, the manipulator has to take the torch tracking along a welding trajectory with a constant velocity and a constant heading angle, and the mobile-platform has to move to avoid the singularities of the manipulator. In this paper, we develop a kinematic model of the mobile-platform and the manipulator as two separate subsystems. With the idea that the manipulator can avoid the singularities by keeping its initial configuration in the welding process, the redundancy problem of system is solved by introducing the platform mobility to realize this idea. Two controllers for the mobile-platform and the manipulator were designed, respectively, and the relationships between two controllers are the velocities of two subsystems. Control laws are obtained based on the Lyapunov function to ensure the asymptotical stability of the system. The simulation and experimental results show the effectiveness of the proposed controllers.

• Journal of Biosystems Engineering
• /
• 제26권6호
• /
• pp.535-544
• /
• 2001

This study developed a manipulator for robotic harvester to harvest cucumber. The manipulator was designed and built fur transferring an end-effecter from a fixed point to a specified cucumber. Its development involved the integration of a manipulating system with a PC compatible, DC motors, geared boxes, timing belts, and a motor controller board. Software, written in Quick basic. combined the functions of motor control with various circumstances. In order to move smoothly and rapidly the manipulator, it's shoulder link and elbow link were minimized by using rotational inertial moment without a motor and a geared box. After 30 replications of exercising the manipulator, it was concluded that the precision values of the X, Y and Z axes were less than 0.5mm, 7.25mm and 0.35mm, respectively. The precision data indicated the manipulator was not missing any steps fur the harvester to reach a target cucumber.

• Journal of Institute of Control, Robotics and Systems
• /
• 제11권7호
• /
• pp.609-614
• /
• 2005

Parallel manipulators have been used for a variety of applications, including the motion simulators and mechanism for precise machining. Since the ball screws used for linear motion of legs of the Stewart-Gough type parallel manipulator provide wider contact areas than revolute joints, parallel manipulators are usually more affected by frictional forces than serial manipulators. In this research, the method for detecting the frictional forces arising in the parallel manipulator using the gravitational force is proposed. First, the reference trajectories are computed from the dynamic model of the parallel manipulator assuming that it is subject to only the gravitational force without friction. When the parallel manipulator is controlled so that the platform follows the computed reference trajectory, this control force for each leg is equal to the friction force arising in each leg. It is shown that control performance can be improved when the friction compensation based on this information is added to the controller for position control of the moving plate of a parallel manipulator.