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CONTENTS
Volume 11, Number 2, February 2013
 

Abstract
This work presents a test platform for the assessment and benchmarking of modern actuators which have been specifically developed for the new field and service robotics applications. This versatile platform has been designed for the comparative analysis of actuators of dissimilar technology and operating conditions. It combines a modular design to adapt to linear and rotational actuators of different sizes, shapes and functions, as well as those with different load capacities, power and displacement. This test platform emulates the kinematics of robotic joints while an adaptive antagonist-load actuator allows reproducing the variable dynamic loads that actuators used in real robotics applications will be subjected to. A data acquisition system is used for monitoring and analyzing test actuator performance. The test platform combines hardware and software in the loop to allow actuator performance characterization. The use of the proposed test platform is demonstrated through the characterization and benchmarking of three controllable impedance actuators recently being incorporated into modern robotics.

Key Words
benchmarking of actuators; experimental testing; test bench design; modular and versatile design; instrumentation; force control

Address
Elena Garcia and Pablo Gonzalez-de-Santos : Field and Service Robotics Group, Centre for Automation and Robotics -CSIC-UPM 28500 Madrid, Spain

Abstract
Control systems have been greatly studied in recent years and can be classified as: passive, active, semi-active or hybrid systems. Most forms of control systems have been applied in a centralized manner where all the information is sent to a central node where control the algorithm is then calculated. One of the possible problems of centralized control is the difficulty to scale its application. In this paper, a completely decentralized control algorithm is analytically implemented. The algorithm considers that each of the control systems makes the best decision based solely on the information collected at its location. Semi-active control is used in preference to active control because it has minimal energy consumption, little to no possibility of destabilization, a reduction in the possibility of data saturation, and a reduction in the response time in comparison to centralized control.

Key Words
control; passive; active; semi-active; decentralized

Address
M.E. Ruiz-Sandoval and E. Morales : Department of Materials, Universidad Autonoma Metropolitana – Azcapotzalco. Av. San Pablo #180 Col. Reynosa-Tamaulipas, Mexico D.F.

Abstract
We developed a simultaneous strain measurement and damage detection technique using a pair of surface-mounted piezoelectric transducers and a fiber connecting them. This is a novel sensor configuration of the fiber acoustic wave (FAW) piezoelectric transducer. In this study, lead-zirconate-titanate (PZT) transducers are installed conventionally on a plate\'s surface, which is a technique used in many structural health monitoring studies. However, our PZTs are also connected with an optical fiber. A FAW and Lamb wave are simultaneously guided in the optical fiber and the structure, respectively. The dependency of the time-of-flight of the FAW on the applied strain is quantified for strain sensing. In our experimental results, the FAW exhibited excellent linear behavior and no hysteresis with respect to the change in strain. On the other hand, the well-known damage detection function of the surface-mounted PZT transducers was still available by monitoring the waveform change in the conventional Lamb wave ultrasonic path.

Key Words
fiber acoustic wave; lamb wave; strain measurement; ultrasonic measurement; structural health monitoring

Address
J.R. Lee : 1Department of Aerospace Engineering and LANL-CBNU Engineering Institute Korea, Chonbuk National
University, Jeonju, South Korea
C.Y. Park : Aeronautical Technology Directorate, Agency for Defense Development, Daejeon 305-600, South Korea
C.W. Kong : Structures and Materials Department, Korea Aerospace Research Institute, Daejeon, South Korea

Abstract
During the service life of a structure, design complications and unexpected events may induce unforeseen vibrations. These vibrations can be generated by malfunctioning machinery or machines that are modified or placed without considering the original structural design because of a change in the intended use of the structure. Significant vibrations occurred at a natural gas plant cooling structure during its operation due to cavitation effect within the hydraulic system. This study presents findings obtained from the in-situ vibration measurements and following finite-element analyses of the cooling structure. Comments are made on the updated performance level and damage state of the structure using the results of these measurements and corresponding numerical analyses. An attempt was also made to assess the applicability of traditional displacement-based vulnerability estimation methods in the health monitoring of structures under vibrations with a character different from those due to seismic excitations.

Key Words
vibration; finite element method; cooling structure; accelerometers; vulnarability analysis

Address
Ozgur ANIL, Sami Oğuzhan AKBAŞ and A. Cem GEL : 1Civil Eng. Department, Gazi University, Ankara, Turkiye
Erkan KANTAR : Civil Eng. Department, Celalbayar University, Manisa, Turkiye

Abstract
In this paper, practical methods to utilize PZT\'s dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material\'s dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.

Key Words
PZT\'s dynamic strain; E/M impedance; damage detection; structural health monitoring; beam structures

Address
Khac-Duy Nguyen and Jeong-Tae Kim : Department of Ocean Engineering, Pukyong National University, Busan, Korea
Duc-Duy Ho : Faculty of Civil Engineering, Ho Chi Minh City University of Technology, Vietnam


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