• Journal of Institute of Control, Robotics and Systems
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• v.19 no.12
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• pp.1160-1166
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• 2013

This paper presents feedforward controllers to improve the control performance of the motion and grasping force of a surgical instrument used in an MIS (Minimally Invasive Surgery) robot. The surgical instrument has a long distance between the drive motors and its active joints. Therefore, the gripper on the instrument is controlled by a cable drive mechanism, which generates a coupled motion between the wrist joint and the grip direction. In order to solve the problem, this paper analyzes the pulley composition of the surgical instrument and proposes feedforward controllers to eliminate the coupled motion. Furthermore, feedforward controllers to regulate the grasping force are proposed to deal with another coupling problem between the grasping force of the instrument and the motion of the instrument joints. The experimental results demonstrate the improved control performance of the motion and grasping force of the instrument.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.427-432
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• 2018

Tidal current power is one of the energy sources of the ocean. Electricity can be generated by converting the flow energy of the current into the rotational energy of a turbine. Unlike tidal barrage, tidal current power does not require dams, which have a severe environmental impact. A floating-type tidal current power device can reduce the expensive support and installation cost, which usually account for approximately 41% of the total cost. It can also be deployed in relatively deep water using tensioned wires. The dynamic behavior of a floater and turbine force are coupled because the thrust and moment of the turbine affect the floater excursion, and the motion of the floater can affect the incoming speed of the flow into the turbine. To maximize the power generation and stabilize the system, the coupled motion of the floater and turbine must be extensively analyzed. However, unlike pile-fixed devices, there have been few studies involving the motion analysis of a moored-type tidal current power device. In this study, the commercial program OrcaFlex 10.1a was used for a time domain motion analysis. In addition, in-house code was used for an iterative calculation to solve the coupled problems. As a result, it was found that the maximum mooring load of 200 kN and the floater excursion of 5.5 m were increased by the turbine effect. The load that occurred on the mooring system satisfied the safety factor of 1.67 suggested by API. The optimum mooring system for the floating tidal current power device was suggested to maximize the power generation and stability of the floater.

• Coupled systems mechanics
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• v.6 no.4
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• pp.377-398
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• 2017

The present paper deals with the influence of the inclination of cables' system on the decrease of the lateral-torsional motion because of dynamic loadings. For this goal, a mathematical model is proposed. A 3-D analysis is performed for the solution of the bridge model. The theoretical formulation is based on a continuum approach, which has been widely used in the literature to analyze such bridges. The resulting uncoupled equations of motion are solved using the Laplace Transformation, while the case of the coupled motion is solved through the use of the potential energy. Finally, characteristic examples are presented and useful results are obtained.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.5
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• pp.44-51
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• 2008

In this paper, the optimal tuning of a cross-coupled controller linked with the feedforward controller is studied to reduce contouring and tracking errors of a bi-axial servomechanisms by using the previously developed integrated tuning method. The CCC system for an arbitrary curve, which is combined with the feedforward controller, is formulated by a state-space based on a series of linear motion trajectories. An optimal tuning problem is formulated as a nonlinear constrained optimization problem including relevant controller parameters of the servo. To verify the effectiveness of the proposed optimal tuning procedure, linear and circular motion experiments are performed on the xy-table. Experimental results confirm that both tracking and contouring errors are significantly reduced by applying the proposed control and tuning system.

• Structural Engineering and Mechanics
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• v.38 no.2
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• pp.195-210
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• 2011

Bernoulli-Euler beam theory is used to develop an exact dynamic stiffness matrix for the flexural-torsional coupled motion of a three-dimensional, axially loaded, thin-walled beam of doubly asymmetric cross-section. This is achieved through solution of the differential equations governing the motion of the beam including warping stiffness. The uniform distribution of mass in the member is also accounted for exactly, thus necessitating the solution of a transcendental eigenvalue problem. This is accomplished using the Wittrick-Williams algorithm. Finally, examples are given to confirm the accuracy of the theory presented, together with an assessment of the effects of axial load and loading eccentricity.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.103-111
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• 2009

Multi-climbing hydraulic robots are used to lift construction factory (CF) synchronously for applications in the automation of a high-rise building construction. In this study, synchronous motion controller is proposed for the hydraulic robots, whose strategy is not only to make each robot follow the reference path basically by sliding-mode control, but also to synchronize motions of two adjacent cent robots consecutively by cross-coupled control technique. Simulations are performed by using SIMULINK for a system similar to a practical application that includes unbalance in CF and wind disturbance. The results show that the proposed controller significantly reduces synchronous errors, compared to the individual controller for each hydraulic robot.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.212-217
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• 2001

This paper presents the stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing. The proportional and derivative controls including coupled motion are adopted for the control algorithm to control the hydrodynamic journal bearing with a circumferentially groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. The stability characteristics are investigated with the Routh-Hurwitz criteria using the linear dynamic coefficients which are obtained from the perturbation method. The stability characteristics of the rotor-bearing system supported by active controlled hydrodynamic journal bearing are investigated for various control gain. It is found that the speed at onset of instability is increased for both proportional and derivative control of the bearing, and the proportional and derivative control of coupled motion is more effective than proportional and derivative control of uncoupled motion.

• Coupled systems mechanics
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• v.2 no.4
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• pp.303-327
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• 2013

The coupled free vibration of flexible structures and on-board liquid in zero gravity space was analyzed, considering the spacecraft main body as a rigid mass, the flexible appendages as two elastic beams, and the on-board liquid as a "spring-mass" system. Using the Lagrangians of a rigid mass (spacecraft main body), "spring-mass" (liquid), and two beams (flexible appendages), as well as assuming symmetric motion of the system, we obtained the frequency equations of the coupled system by applying Rayleigh-Ritz method. Solving these frequency equations, which are governed by three system parameters, as an eigenvalue problem, we obtained the coupled natural frequencies and vibration modes. We define the parameter for evaluating the magnitudes of coupled motions of the added mass (liquid) and beam (appendages). It was found that when varying one system parameter, the frequency curves veer, vibration modes exchange, and the significant coupling occurs not in the region closest to the two frequency curves but in the two regions separate from that region.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.275-294
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• 2013

Side-by-side offloading operations are widely utilized in engineering practice. The hydrodynamic interactions between two vessels play a crucial role in safe operation. This study focuses on the coupled effects between two floating bodies positioned side-by-side as a shuttle tanker-FPSO (floating production, storage and offloading) system. Several wave directions with different side-by-side distances are studied in order to obtain the variation tendency of the horizontal hydrodynamic coefficients, motion responses and mean drift forces. It is obtained that the coupled hydrodynamics between two vessels is evidently distinguished from the single body case with shielding and exaggerating effects, especially for sway and yaw directions. The resonance frequency and the peak amplitude are closely related with side-by-side separation distance. In addition, the horizontal hydrodynamics of the shuttle tanker is more susceptible to coupled effects in beam waves. It is suggested to expand the gap distance reasonably in order to reduce the coupled drift forces effectively. Attention should also be paid to the second peaks caused by hydrodynamic coupling. Since the horizontal mean drift forces are the most mainly concerned forces to be counteracted in dynamic positioning (DP) system and mooring system, prudent prediction is beneficial in saving consumed power of DP system and reducing tension of mooring lines.

• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.37-46
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• 2017

This paper is concerned with the numerical study on the resonance response of a rigid spar-type floating platform in coupled heave and pitch motion. Spar-type floating platforms, widely used for supporting the offshore structures, offer an economic advantage but those exhibit the dynamically high sensitivity to external excitations due to their shape at the same time. Hence, the investigation of their dynamic responses, particularly at resonance, is prerequisite for the design of spar-type floating platforms which secure the dynamic stability. Spar-type floating platform in 2-D surface wave is assumed to be a rigid body having 2-DOFs, and its coupled dynamic equations are analytically derived using the geometric and kinematic relations. The motion-variance of the metacentric height and the moment of inertia of floating platform are taken into consideration, and the hydrodynamic interaction between the wave and platform motions is reflected into the hydrodynamic force and moment and the frequency-dependent added masses. The coupled nonlinear equations governing the heave and pitch motions are solved by the RK4 method, and the frequency responses are obtained by the digital Fourier transform. Through the numerical experiments to the wave frequency, the resonance responses and the coupling in resonance between heave and pitch motions are investigated in time and frequency domains.