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Hydraulic Control Systems

Although the off-road mobility characteristics of wheeled or tracked vehicles are generally recognized as being inferior to those of man and cursorial animals, the complexity of the joint-coordination control problem has thus far frustrated attempts to achieve improved vehicular terrain adaptability through the application of legged locomotion concepts. Nevertheless, the evident superiority of biological systems in this regard has motivated a number of theoretical studies over the past decade which have now reached a state of maturity sufficient to permit the construction of experimental computer-controlled adaptive walking machines. At least two such vehicles are known to have recently demonstrated legged locomotion over smooth hard-surfaced terrain. This paper is concerned with an extension of the present theory of limb coordination for such machines to the case in which the terrain includes regions not suitable for weight-bearing and which must consequently be avoided by the control computer in deciding when and where to successively place the feet of the vehicle. The paper includes a complete problem formalization, a heuristic algorithm for solution of the problem thus posed, and a preliminary evaluation of the proposed algorithm in terms of a computer simulation study.

Adaptive Locomition of a Multilegged Robot over Rough Terrain

This paper proposes enhanced hysteresis-based current regulators in the field-oriented vector control of doubly fed induction generator (DFIG) wind turbines. The proposed control scheme is synchronized with the virtual grid-flux space vector, readily extractable by a quadrature phase-locked loop (QPLL) system. Identical equidistant-band vector-based hysteresis current regulators (VBHCRs) are then used to control the output currents of the rotor-side and grid-side converters. The proposed hysteresis-based technique has excellent steady-state performance and reveals several advantages in comparison with the commonly used proportional-integral (PI) current regulator, including very fast transient response, simple control structure, and intrinsic robustness to the machine parameters variations. Moreover, the fixed hysteresis bands in VBHCRs are replaced with equidistant bands to limit the instantaneous variations of the switching frequency and reduce the maximum switching frequencies experienced in the converters. Extensive simulation studies are carried out for a 1.5 MW DFIG-based wind turbine to examine the operation of the proposed vector control scheme under changing wind speed and compare its transient and steady-state performances with the conventional PI current regulators.

Enhanced Hysteresis-Based Current Regulators in Vector Control of DFIG Wind Turbines

Conventional hysteresis current controllers have the disadvantage of a variable switching frequency. This paper presents a novel hysteresis current control method which uses the adjacent current error zero-crossing time to calculate the upper/lower hysteresis bandwidth after the measured half current error period. This strategy makes the algorithm independent of load parameters and thus it can achieve a stable switching frequency. An improved switching scheme has been successfully applied to a single-phase three-level H-bridge voltage source inverter driving a vibration test bench based on the novel hysteresis current. It can select appropriate switching states to overcome dead-time effects without dead-time compensation according to the relation of the current switching state, the current error, and the upper/lower hysteresis bandwidth. Field-programmable gate array has enough computational power to allow multiple sampling within a current error period and logic control power to implement state machine transitions. The simulation and experimental results are given to demonstrate the validity and features of the novel hysteresis current controller with the improved switching scheme.

A Hysteresis Current Controller for Single-Phase Three-Level Voltage Source Inverters

This paper presents a new vector-based hysteresis current controller (HCC) for three-phase pulsewidth modulation (PWM) voltage-source inverters (VSI). The HCC is intrinsically robust to the load parameters variations, exhibits very fast transient performance, and is suitable for simple implementations. Despite these advantages, the conventional HCC has a major drawback when applied to the three-phase PWM-VSI: interphases dependency leads to very high-switching frequencies in the inverter. This paper starts with a review on the vector-based HCCs reported in the literature to address this problem. Then, a new vector-based method is proposed using multilevel hysteresis comparators integrated with a switching table. The proposed method works with the inverter current vector represented in the stationary α- β frame and produces a coordinated switching pattern. The current error is kept inside a square tolerance region without significant increase in the complexity of the hardware implementation. Simulation results show that the proposed vector-based method can retain the advantages of the conventional HCC. However, the steady-state performance of the proposed current regulator is significantly improved by reducing the switching frequency and minimizing oscillations of the inverter current vector. The proposed current controller is finally compared with other reported vector-based methods and its advantages are illustrated.

A New Vector-Based Hysteresis Current Control Scheme for Three-Phase PWM Voltage-Source Inverters

Hysteresis current controllers having fixed bands are used in inverters of high-performance AC drives. The switching frequency of such controllers varies over the fundamental period of the modulating signal. The maximum switching frequency (MSF) of these controllers is high. To limit the MSF within the limit of inverter switches, fixed carrier lockouts are usually incorporated. The incorporation of carrier lockouts causes current distortion, and load currents do not confine within the predetermined band. In this paper, two new controllers are proposed. One is a mixed-mode controller of sinusoidal band added to a fixed band, and the other is an equidistant-band current controller, performances of the proposed controllers are compared with the performances of the conventional fixed-band and sinusoidal-band controllers.

Variable-band hysteresis current controllers for PWM voltage-source inverters

Investigation of stresses at the fixed end of deep cantilever beams

Human gait is the identity of a person's style and quality of life. Reliable cognition of gait properties over time, continuous monitoring, accuracy of evaluation, and proper analysis of human gait characteristics have demonstrated their importance not only in clinical and medical studies, but also in the field of sports, rehabilitation, training, and robotics research. Focusing on walking gait, this study presents an overview on gait mechanisms, common technologies used in gait analysis, and importance of this particular field of research. Firstly, available technologies that involved in gait analysis are briefly introduced in this paper by concentrating on the usability and limitations of the systems. Secondly, key gait parameters and motion characteristics are elucidated from four angles of views; one: gait phases and gait properties; two: center of mass and center of pressure (CoM-CoP) tracking profile; three: Ground Reaction Force (GRF) and impact, and four: muscle activation. Thirdly, the study focuses on the clinical observations of gait patterns in diagnosing gait abnormalities of impaired patients. The presentation also shows the importance of gait analysis in sports to improve performance as well as to avoid risk of injuries of sports personnel. Significance of gait analysis in robotic research is also illustrated in this part where the study focuses on robot assisted systems and its possible applicability in clinical rehabilitation and sports training.

Gait analysis: systems, technologies, and importance

Problem statement: Wheeled robots are not very well suited for navigation over uneven terrains. Hexapod robots have some advantages over wheeled robots when negotiating and navigating on rugged terrain. Approach: Different gaits of hexapods can be developed for different kinds of locomotion and obstacle avoidance. Results: In this research a novel algorithm has been developed for hexapod robots navigation. Conclusion: Implementation of the developed algorithm on a hexapod prototype showed desirable performance in terms of stable navigation with simultaneous gait transition over different terrains.

A novel navigation algorithm for hexagonal hexapod robot

The concentration of pollutants emitted from industrial production are generally toxic and hazardous, which can be a serious health risk to humans not limited to respiratory ailments (asthma, bronchitis, tuberculosis, etc) but also to the photosynthesis in plants. In this study, a pilot scrubber system for PM10 control has been designed using data obtained from cement industry. A model for the overall collection efficiency of counter current scrubber system and Langmuir’s approximations were used to predict the performance of the system by considering droplet sizes of 500µm, 1000µm, 1500µm and 2000µm. The range of liquid to gas ratio recommended by the US Environmental Protection Agency (EPA) has been used to investigate the appropriate ratio for optimum performance of the system. Due to reversed flow in the Langmuir’s approximation, negative collection efficiencies for the 1µm dust particle were obtained. For 5µm and 10µm dust particles, the maximum collection efficiencies were determined to be 99.988% and 100.000% at 500µm droplet size and 2.7 l/m 3 while the minimum was obtained to be 43.808% and 58.728% at 2000µm droplet size and 0.7 l/m 3 . The predicted performance of the scrubber system was then validated using the World Health Organization (WHO) air quality standard for PM10.

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Md. Raisuddin Khan

Papers

Variable-band hysteresis current controllers for PWM voltage-source inverters

Investigation of stresses at the fixed end of deep cantilever beams

Gait analysis: systems, technologies, and importance

A novel navigation algorithm for hexagonal hexapod robot

Performance evaluation of wet scrubber system for industrial air pollution control