• Journal of Ocean Engineering and Technology
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• v.35 no.3
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• pp.229-237
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• 2021

A numerical hydrodynamic performance analysis of the pitch-type multibody wave energy converter (WEC) is carried out based on both linear potential flow theory and computational fluid dynamics (CFD) in the unidirectional wave condition. In the present study, Salter's duck (rotor) is chosen for the analysis. The basic concept of the WEC rotor, which nods when the pressure-induced motions are in phase, is that it converts the kinetic and potential energies of the wave into rotational mechanical energy with the proper power-take-off system. This energy is converted to useful electric energy. The analysis is carried out using three WEC rotors. A multibody analysis using linear potential flow theory is performed using WAMIT (three-dimensional diffraction/radiation potential analysis program), and a CFD analysis is performed by placing three WEC rotors in a numerical wave tank. In particular, the spacing between the three rotors is set to 0.8, 1, and 1.2 times the rotor width, and the hydrodynamic interaction between adjacent rotors is checked. Finally, it is confirmed that the dynamic performance of the rotors slightly changes, but the difference due to the spacing is not noticeable. In addition, the CFD analysis shows a lateral flow phenomenon that cannot be confirmed by linear potential theory, and it is confirmed that the CFD analysis is necessary for the motion analysis of the rotor.

• Journal of Drive and Control
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• v.18 no.2
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• pp.46-55
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• 2021

A forklift is a powered industrial vehicle used to lift and move materials over short distances. Nowadays, almost all forklifts are equipped with an automatic transmission due to its improved operator comfort and increased productivity. Thanks to marked improvement of transmission control unit equipped with highly-advanced microcontrollers, recently developed automatic transmission for forklift have various auxiliary functions such as creep, auto retardation, and automatic shift with excellent shift quality. This paper deals with the creep function which enables one to maneuver a forklift at the designated low speed by slip control of clutches. The design of creep function was based on four modes of creep operation depending on the status of the operator's shift lever and accelerator pedal. Control algorithms and control parameters for each mode were designed to achieve the desired static and dynamic performance. Vehicle test for the designed creep function was carried out with an independently developed embedded controller. Test results confirmed good creep speed control without speed error at a steady state with a mild shift shock during mode changes by stepping or releasing the accelerator.

• Journal of Drive and Control
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• v.18 no.2
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• pp.9-19
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• 2021

The spool displacement signal of a directional control valve, including the servo valve, can be considered as the standard signal to measure dynamic characteristics. When the spool displacement signal is not available, the velocity signal of a metering cylinder piston can be used. In this study, the frequency response characteristics of the metering cylinder are investigated for the spool displacement input. The transfer functions of the servo valve-metering system are derived taking into consideration the oil inertia effect in the transmission lines. The theoretical results of the transfer functions are verified through computer simulations and experiments. The oil inertia effect in the transmission lines was found to have a very significant effect on the bandwidth frequency of the servo valve-metering cylinder system. In order to more precisely measure the dynamic characteristics of a servo valve, the metering cylinder should be set up to minimize the oil inertia effect by increasing the inner diameters of the transmission lines or shortening their lengths.

• Journal of Drive and Control
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• v.18 no.2
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• pp.20-31
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• 2021

An excavator is a construction machine that can perform various tasks such as trenching, piping, excavating, slope cutting, grading, and rock demolishing. In the 2010s, unmanned construction equipment using ICT technology was continuously developed. In this paper, the path design process was studied to implement the output data of the decision stage, and the path design algorithm was developed. For example, the output data of the decision stage were terrain data around the excavator, excavator mechanism information, excavator hydraulic information, the position and posture of the bucket at key points, the speed of the desired bucket path, and the required excavation volume. The result of the path design was the movement of the hydraulic cylinder, boom arm, bucket, and bucket edge. The core functions of the path design algorithm are the function of avoiding impact during the excavation process, the function to calculate the excavation depth that satisfies the required excavation volume, and the function that allows the bucket to pass through the main points of the excavation process while maintaining the speed of the desired path. In particular, in the process of developing the last function, the node tracking method expressed in the path design table was newly developed. The path design algorithm was verified as this path design satisfied the JCMAS H02 requirement.

• Journal of Drive and Control
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• v.18 no.2
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• pp.38-45
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• 2021

In recent years, the demand for an onboard scale system which can directly monitor load distribution and overload of vehicles has increased. Depending on the suspension type of the vehicle, the onboard scale system could use different types of sensors, such as, angle sensors, pressure sensors, load cells, etc. In the case of a vehicle equipped with leaf spring suspension system, the load of the vehicle is measured by using the deflection or displacement of the leaf spring. Leaf springs have hysteresis characteristics that vary in displacement depending on the load state. These characteristics cause load measurement errors when moving or removing cargoes. Therefore, this study aimed at developing an onboard scale device for cargo vehicles equipped with leaf springs. A sectional modeling method which can reduce measurement errors caused by hysteresis characteristics was also proposed.

• Journal of Drive and Control
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• v.17 no.4
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• pp.80-86
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• 2020

Autonomous driving is one of the most important new technologies of our time; it has benefits in terms of safety, the environment, and economic issues. Path following algorithms, such as automated lane keeping systems (ALKSs), are key level 3 or higher functions of autonomous driving. Pure-Pursuit and Stanley controllers are widely used because of their good path tracking performance and simplicity. However, with the Pure-Pursuit controller, corner cutting behavior occurs on curved roads, and the Stanley controller has a risk of divergence depending on the response of the steering system. In this study, we use the advantages of each controller to propose a hybrid control strategy that can be stably applied to complex driving environments. The weight of each controller is determined from the global and local curvature indexes calculated from HD map information and the current driving speed. Our experimental results demonstrate the ability of the hybrid controller, which had a cross-track error of under 0.1 m in a virtual environment that simulates K-City, with complex driving environments such as urban areas, community roads, and high-speed driving roads.

• Journal of Drive and Control
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• v.17 no.4
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• pp.31-37
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• 2020

We are concerned with the dual-arm manipulation for disaster-responding special-purpose machinery. This paper presents a control strategy for performing complex work in an irregular environment, the control algorithm, the hydraulic circuit, and the master devices. The occurrence of collapse accidents at disaster sites such as natural disasters and building collapses is increasing, which is emerging as a social problem. In particular, for the initial response, various tasks must be performed in an irregular environment. The Marionette algorithm for intuitive control of 'as if the operator's arm is moving' was presented as a control strategy for dual-arm manipulators with attachments and the prototype. Next, the hydraulic circuit, control system, and wearable-type master device presented to implement the Marionette algorithm were explained and verified through an experiment in which rebar-cutting, drum-lifting, and lifting a bottle with one arm and pouring the water into the bucket with the other arm were tested.

• Journal of Drive and Control
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• v.17 no.4
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• pp.97-102
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• 2020

This paper presents the basic research for the design and fabrication of a 3D-printed load cell made of NCPC (nano-carbon piezo-resistive composite). We designed a structure that can resonate at a low frequency range of about 5-6 Hz with ANSYS using sensitivity analysis and a response surface method. The design was verified by fabricating the device with a low-quality commercial 3D printer and ABS filament. We conducted a feasibility test for a commercial sensor using 1000 cyclic load tests at 0.3 Hz in a material testing system. A manufacturing process for the 3D printer filament based on the NCPC was also developed using the nano-composite process.

• Journal of Drive and Control
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• v.18 no.1
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• pp.24-30
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• 2021

There is an increasing interest in condition-based maintenance for the prevention of economic loss due to failure. Moreover, immense research is being carried out in related technologies in the field of construction machinery. In particular, data-based failure diagnosis methods that employ AI (machine & deep learning) algorithms are in the spotlight. In this study, we have focused on the failure diagnosis and mode classification of reduction gear of excavator's travel device by using the AI algorithm. In addition, a remote monitoring system has been developed that can monitor the status of the reduction gear by using the developed diagnosis algorithm. The failure diagnosis algorithm was performed in the process of data acquisition of normal and abnormal under various operating conditions, data processing and analysis by the wavelet transformation, and learning. The developed algorithm was verified based on three-evaluation conditions. Finally, we have built a system that can check the status of the reduction gear of travel devices on the web using the Edge platform, which is embedded with the failure diagnosis algorithm and cloud.

• Journal of Drive and Control
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• v.17 no.4
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• pp.103-112
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• 2020

Field robots are used in various fields, such as agriculture, forestry, manufacturing, and construction; their use has recently expanded to include submarine areas. Field robots can aid in various tasks, such as soil transport, ground clearance, and dismantling of buildings. As field robots are used in a variety of different areas, the difficulty of the work is also quite varied. Increased difficulty is associated with an increased risk of accidents involving the field robot. In order to reduce the accident rate of field robot workers, the need for digitalization and automation of field robots is becoming more of an issue. To this end, it is necessary to study a system that enables workers to do their work without directly contacting a field robot. Therefore, in this paper, we introduce a control system for wireless remote control of a small field robot. The field robot can be wirelessly controlled by a worker in a remote location if the worker cannot be present at the work site. The implemented remote system is tested according to the type of work, and the operating characteristics of the remote system are assessed.