• 제어로봇시스템학회논문지
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• 제10권10호
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• pp.869-877
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• 2004

This paper deals with motion planning algorithm for kinematically redundant manipulators that are not fixed to the ground. Differently from usual redundant manipulators fixed to the ground, the stability issue should be taken into account to prevent the robot from falling down. The typical ZMP equation, which is employed in human walking, will be employed to evaluate the stability. This work proposes a feed forward ZMP planning algorithm. The algorithm embeds the 'ZMP equations' indirectly into the kinematics of the kinematic model of a manipulator via a ZMP stability index The kinematic self motion of the redundant manipulator drives the system in such a way to keep or plan the ZHP at the desired position of the footprint. A sequential redundancy resolution algorithm exploiting the remaining kinematic redundancy is also proposed to enhance the performances of joint limit index and manipulability. In addition, the case exerted by external forces is taken into account. Through simulation for a 5 DOF redundant robot model, feasibility of the proposed algorithms is verified. Lastly, usual applications of the proposed kinematic model are discussed.

• Transactions on Control, Automation and Systems Engineering
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• 제1권1호
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• pp.8-15
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• 1999

One of the main reason advocating redundant manipulators' superiority in application is that they can afford to optimize a dexterity measure, for example the manipulability measure. However, to obtain the gradient of the manipulability is not an easy task in case of general manipulator with high degrees of redundancy. This article proposes a method to compute the gradient of the manipulability, based on recursive algorithm to compute the Jacobian and its derivative using Denavit-Hartenberg parameters only. To characterize the null motion of redundant manipulators, the null space matrix using square minors of the Jacobian is also proposed. With these capabilities, the inverse kinematics of a redundant manipulator system can be done automatically. The result is easily extended to dual manipulator system using the relative kinematics.

• 제어로봇시스템학회논문지
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• 제8권11호
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• pp.963-969
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• 2002

Design method of a robust impedance control is proposed for the kinematically redundant manipulators. To achieve this objective, we first use the momentum feedback disturbance observer(MFDOB) scheme which can handle the nonlinear dynamics of a manipulator in Joint space. An extended task space formulation to describe the behaviors of task and null spaces of redundant manipulator is employed. Using the extended task space formulation and disturbance observer scheme, a robust impedance control method is designed. The performance of the proposed extended impedance controller is verified through experiments with a planar three links direct-drive manipulator.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.456-459
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• 1995

The problem of compliant motion control using a redundant manipulator is addressed in this article. Specifically, a hybrid-control type and impedance-control type controllers are extended to general redundant manipulators based on the kinematically decomposed and geometrically compatible modeling of its joint space. In the case of the hybrid controller, it leads to the linear and decoupled closed-loop dynamics in the three motion spaces, that is the motion-controlled, force-controlled, and the null motion-controlled spaces of the redundant manipulator. When the proposed impedance controller is applied, the decoupled impedance models in three motion spaces are obtained. The superiority of the proposed controllers is verified with the numerical experiments.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1150-1155
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• 1990

This paper proposes an optimal redundancy resolution of a kinematically redundant manipulator while considering homotopy classes. The necessary condition derived by minimizing an integral cost criterion results in a second-order differential equation. Also boundary conditions as well as the necessary condition are required to uniquely specify the solution. In the case of a cyclic task, we reformulate the periodic boundary value problem as a two point boundary value problem to find an initial joint velocity as many dimensions as the degrees of redundancy for given initial configuration. Initial conditions which provide desirable solutions are obtained by using the basis of the null projection operator. Finally, we show that the method can be used as a topological lifting method of nonhomotopic extremal solutions and also show the optimal solution with considering the manipulator dynamics.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.811-814
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• 1997

In this paper, the torque optimization of a kinematically redundant manipulator for minimizing the torque demands is discussed. The minimum torque solution based on a local optimization has been known to encounter the instability problem and then the global torque optimization was suggested as one of the alternatives. Herein, by adopting the infinity-norm rather than the 2-norm for the magnitude of torques, we are to propose a new cost function more advantageous to the avoidance of torque limits. By the way, a solution to the global torque optimization formulated with the new cost function can not be obtained by the previous methods due to their difficulties such as inability to treat discontinuous cost functions and various constraints on the joint variables. Thus, to overcome those deficiencies, we are developing a new approach using the dynamic programming. The effectiveness of the proposed method is shown through simulation examples for a 3-link planar redundant manipulator.

• 로봇학회논문지
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• 제6권4호
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• pp.308-316
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• 2011

This work deals with development of effective redundancy resolution algorithms for the motion control of manipulator. Differently from the typical kinematically redundant robots that are attached to the fixed ground, the ZMP condition should be taken into account in the manipulator motion in order to guarantee the system stability. In this paper, a new motion planning algorithm for redundant manipulator not fixed to the ground is introduced. A sequential redundancy resolution algorithm is proposed, which ensures the ZMP (Zero Moment Point) stability, the planned operational motion, and additional sub-criteria such as joint limit index. A geometric constraint equation derived by reshaping the existing ZMP equation enables one to employ the sequential redundancy algorithm. The feasibility of the proposed algorithm is verified by simulating a redundant manipulator model.

• 한국정밀공학회지
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• 제10권4호
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• pp.227-235
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• 1993

In this paper, the development of a high performance flexible controller is described. The hardware of the controller, based on VME-bus, consists of four M68020 single-board computers (32-bit) with M68881 numerical coprocessors, two M68040 single board donputers, I/O devices (such as A/D and D/A converters, paraller I/O, encoder counters), and bus-to-bus adaptor. This software, written in C and based on X-window environment with Unix operating system, includes : text editor, compiler, downloader, and plotter running in a host computer for developing control program ; device drivers, scheduler, and mathemetical routines for the real time control purpose ; message passing, file server, source level debugger virtural terminal, etc. The hardware and software are structured so that the controller might have both flexibility and extensibility. In papallel to the controller, a three degrees of freedom kinematically redundant robot has been developed at the same time. The development of the same time. The development of the robot was undertaken in order to provide, on the one hand, a computationally intensive plant to which to apply the controller, and on the other hand a research tool in the field of kinematically redundant manipulator, which is, as such, an important area. By using the controller, dynamic control of the redundant manipulator was successfully experimented, showing the effectiveness and flexibility of the controller.

• Transactions on Control, Automation and Systems Engineering
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• 제2권1호
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• pp.56-61
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• 2000

Majority of industrial robots are controlled by a simple independent joint control of joint actuators rather than complex controllers based on the nonlinear dynamic model of the robot manipulator. In this independent joint control scheme, the performance of actuator control is influenced significantly by the joint disturbance torques including gravity, Coriolis and centrifugal torques, which result in the trajectory tracking error in the joint control system. The control performance of a redundant manipulator under independent joint control can be improved by minimizing this joint disturbance torque in resolving the kinematic redundancy. A 3 DOF planar robot is studied as an example, and the dynamic programming method is used to find the globally optimal joint trajectory that minimize the joint disturbance torque over the entire motion. The resulting solution is compared with the solution obtained by the conventional joint torque minimization, and it is shown that joint disturbance can be reduced using the kinematic redundancy.

• 대한기계학회논문집
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• 제18권9호
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• pp.2284-2296
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• 1994

Force control of robotic mechanisms continues to be a challenging area. Previous implementation have seldom produced satisfactory results, and researchers in the past have experienced significant instability problems associated with their force controllers. In this study, a new stability factor in force control will be pointed out. When a manipulator is constrained to an environment(force-controlled), geometric instability due to the relationship between the manipulator configuration and the force-controlled direction is shown to be a significant factor in overall system stability. This exploratory study points out a rather intuitive, geometrically based stability factor in terms of an effective system stiffness and analyzes the phenomenon both analytically and graphically. Also, a stiffness control algorithm using the kinematic redundancy of a kinematically redundant manipulator is proposed to improve the overall stability in force control.