Whang Cho

RCC Characteristics of Planar/Spherical Three Degree-of-Freedom Parallel Mechanisms With Joint Compliances

A three degree-of-freedom (DOF) planar parallel manipulator has been extensively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupled compliance characteristic at the object space, which is the important operational requirement for a RCC device. As the first condition to have a RCC point, this mechanism should maintain symmetric configurations. As the second condition, the same magnitude of revolute joint compliance should be symmetrically placed at the same joint location of each chain. We also investigate the compliance characteristics of a spherical 3 DOF mechanism which has a similar kinematic structure to the planar mechanism through simulation. It turns out that the spherical mechanism also has a RCC point at the intersection point of all nine joint axes in its symmetric configuration. Further, more general output compliance model is derived for those mechanisms with redundant joint compliances. It is expected that these two parallel mechanisms not only can be used as excellent 3 DOF RCC devices, but also can be integrated into the design of a new six DOF RCC device.

A Bond Graph Approach to the Modeling of General Multibody Dynamic Systems

A vector bond approach which effectively leads to a compact form of Hamiltonian bond graph structure and naturally to Hamilton’s equation of motion is proposed for the modeling of general multibody dynamic system. The methods for determining required bond graph elements are formulated in terms of kinematic influence coefficients. All moduli of transformers and their time rate of changes are found by pure vector (matrix) operations for the readiness for computer simulation of the resulting bond graph.

Open-loop stability of overconstrained parallel robotic systems

The authors derive the object-based effective stiffness of antagonistically actuated, backdrivable, parallel linkages and show how to use this result to synthesize the generalized input loads required to create a desired system stiffness. They investigate the open-loop stability characteristics of such antagonistically actuated systems as a simple four-bar linkage, a dual-arm system, and a multifingered hand. In addition, they compare object-based and joint-based load distribution schemes in terms of their effect on system stability and input load requirements for an overconstrained planar mechanism. These investigations show an extreme interdependence between system geometry, actuation mode, and stability.<<ETX>>

MPPT and yawing control of a new horizontal-axis wind turbine with two parallel-connected generators

Commonly used horizontal-axis wind turbines (HAWT) have the following structure: two or three blades, a nacelle which contains power converting equipments, generators, and a tower which supports the nacelle. The generated power is transmitted from the nacelle to the ground. Due to this structure, the power transmission lines are twisted when the nacelle is yawing. Thus, slip ring or additional yaw control mechanism is required. We propose a new structure of HAWT which is free of this transmission line problem. Moreover, the size of inverter can be reduced since two generators are connected in parallel in our mechanism so that power is distributed. A controller for yawing is developed so that it works in harmony with the controller for power generation. An MPPT (Maximum Power Point tracking) algorithm is implemented for the proposed system and is validated by simulation.

Constraint Embedding in Kinematics and Dynamics of Hybrid Manipulator Systems

An approach to kinematics and dynamics based on kinematic influence coefficient matrices is proposed for applications to the analysis and control of motion controlled multibody systems, e.g., hybrid robotic manipulator systems. The scheme is unique in a sense that all the kinematic constraints are completely embedded into the formulations at the kinematics level and equation of motion of the system is obtained in a closed form with respect to the minimal set of independent joint coordinates. Furthermore, all kinematic and dynamic formulations are expressed compactly in the same format by using two special algebraic operators. This isomorphic formalism allows systematic transformations of kinematic and dynamic informations between different sets of coordinates in a purely algebraic way.

Study on the Development of Multi-Agents Position Tracking System Using Ultrasonic Transducers

In This paper, through simulation, proposes a system which makes it possible for freely moving multiple agents with ultrasonic receivers to estimate their own position by themselves using the ultrasonic signals sequentially emitted from multiple ultrasonic transmitters. This system possesses an advantage that there is no limit in the number of agents existing in the space covered by more than three transmitters fixed at proper locations. Hence, the proposed system can be utilized effectively in position tracking control of multiple robotic agents system and motion capturing system.

Theoretical analysis and design for a multilayered ionic polymer metal composite actuator

Ionic polymer metal composites with a flexible large deformation have been used as biomimetic actuators and sensors in various fields. This work mainly focuses on the validation of the proposed theoretical prediction for various ionic polymer metal composite applications, such as a field needing a large resultant force, large tip deflection, or high response frequency. Such properties can be controlled by the number of layers and the thickness ratio of a multilayered ionic polymer metal composite actuator. Thus, we considered major design factors such as the number of layers and the thickness ratio in analysis of the proposed theoretical model and performed experiments to verify the static and dynamic electromechanical responses of multilayered (multimorph) ionic polymer metal composite structures acting as actuators. The relation between the polymer (Nafion) and electrode or substrate is represented by β. From this theoretical analysis, three properties were analyzed and predicted based on the Euler–Bernoulli beam theory, considering the dynamics of the ionic polymer metal composite, electrode, and bonding layers (substrate layers). The predicted results of a symmetric ionic polymer metal composite multimorph were compared with results of finite element analysis and experiments using ionic polymer metal composite multimorphs with one to five layers. Finally, this work examined how the number of layers and thickness affect the dynamic properties. This can contribute to predicting and optimally designing a multilayered ionic polymer metal composite actuator for satisfying a specific requirement.

Modelling and control of dual generator type wind turbine (DGWT)

This paper deals with the dynamic model and controller for dual generator type wind turbine (DGWT). DGWT is kept distinct from typical horizontal axis wind turbine (HAWT) by following structure, four bevel gears are equipped in the nacelle, the parallel generators installed on the ground like a vertical axis wind turbine (VAWT). This structure was already proposed in previous research which shows the advantages for transmission line problem or minimize the converter size, but the dynamic model was not addressed in detail. In this paper, we derive the the dynamic model of DGWT from Euler-Lagrange equation. Moreover, simulation and experimental results are also included to validate the performance of DGWT.

Nonlinear and Adaptive Back-Stepping Speed Control of IPMSM

In this paper, a nonlinear controller based on adaptive back-stepping method is proposed for high performance operation of Interior Permanent Magnet Synchronous Motor (IPMSM). First, in order to improve the performance of speed tracking, a nonlinear back-stepping controller is designed. In addition, since it is difficult to achieve the high quality control performance without considering parameter variation, a parameter estimator is included to adapt to the variation of load torque in real time. Finally, for the efficiency of power consumption of the motor, controller is designed to operate motor with the minimum current for the required maximum torque. The proposed controller is tested through experiment with a 1-hp Interior Permanent Magnet Synchronous Motor (IPMSM) for the angular velocity reference tracking performance and load torque volatility estimation, and to test the Maximum Torque per Ampere (MTPA) operation. The result verifies the efficacy of the proposed controller.

A study on the advanced PLC system using the MIB and SNMP

This paper presents the design and implementation of an advanced PLC (power line communication) system using the MIB (management information base) and SNMP (simple network management protocol). Various information of PLC instruments are defined using MIB. The peripheral functions to improve the performance of PLC are devised. ACF is for auto connecting instruments without intervention of the user. DEC is for checking the loss of data and the presence of error. DLPF is for preventing the loss of data and error. To evaluate the proposed system, the experimental set-up is developed and the experiments are successfully carried out. The conclusion points that the proposed PLC using the MIB contributes the betterment of the conventional PLC instruments.