12-04-2011, 04:21 PM
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Structural Applications of Smart Materials in Construction Engineering Using Robotics
Abstract -Sensors and Actuators designs have mimicked nature to a large extent. Similar to our five senses - sight, sound, smell, taste and touch -correspondingly visual/optical, acoustic/ultrasonic, electrical, chemical and thermal/magnetic sensors have been developed. The response from these primary sensors is converted to electrical signals, which are transmitted to the brain (central processing unit) for further processing. In addition to the processing, the role of the processor is to make decision based on these inputs. This is currently done manually by an experienced operator who has an understanding of the sensing and processing technology. To aid the operator in making a more judicious decision, the conditioned signal has to be presented with as much pertinent information displayed in an arresting way. A further development would be to provide the virtual machine itself to make the judgment - smart sensor. The next stage in this would be for the processor to decide on the course of action and the actuation mechanism to respond accordingly. Virtual human robots can be equipped with sensors, memory, perception, and behavioural motor. This eventually makes these virtual human
robots to act or react to events. The design of a behavioral animation system raises questions about creating autonomous actors, endowing them with perception, selecting their actions, their motor control and making their behaviour believable and the behavior should be spontaneous and unpredictable.
Keywords- smart materials, structures, smart sensors, actuators.
INTRODUCTION
There is an increasing awareness of the benefits to be derived from the development and exploitation of smart materials and structures in applications ranging from hydrospace to aerospace. With the ability to respond autonomously to changes in their environment, smart systems can offer a simplified approach to the control of various material and system characteristics such as light transmission, viscosity, strain, noise and vibration etc. depending on the smart materials used [1]. There are a number of materials that act as both sensors and actuators that can monitor and respond to their environment. However, with the ability to also modify their properties in response to an environmental change, they can be 'very smart' and, in effect, learn. While the scope of sensors and actuators is quite broad, three main sub-programs have been identified – Smart Structures and Materials, Miniature Sensor and Actuators and Automated Testing, Inspection Monitoring and Evaluation. These are exciting times for Sensors and Actuators with the maturing of the enabling technologies of Photonics and Electronics paving the way for inventive and innovative system designs. For the modeling of sensor behaviours, the ultimate objective is to build intelligent autonomous virtual humans with adaptation, perception and memory. These virtual humans should be able to act freely and emotionally. They should be conscious and unpredictable. The virtual humans are expected in the near future to represent computer the concepts of behaviour, intelligence, autonomy, adaptation, perception, memory, freedom, emotion, consciousness, and unpredictability. Behavior for virtual humans may be defined as a manner of conducting themselves. It is also the response of an individual, group, or species to its environment.
Intelligence may be defined as the ability to learn or understand or to deal with new or trying situations[1].
A. Mechatronic devices
The essential ingredients of any robotic system are sensors, computation and actuators. Appropriate choices of sensors and actuators can simplify a robotic system or may even be the difference between its success and failure. Mechatronic devices are the novel actuators including those based on shape memory alloy, electrorheological fluids, magnetic fluids and the piezoelectic effect as well as a wide range of sensors for measuring quantities of importance for robotic systems [1].
B. Robotic mechanisms
All of the sensors, actuators [1]-[2] and algorithms that are developed should be tested by incorporating them into a mobile robot platform, humanoid robot or fixed manipulator/ gripper system. An extensive experience of building legged, wheeled and tracked land vehicles, submersibles and flying robots as well as robotic grippers and complete humanoid robots are required.
II. VIRTUAL REALITY APPLICATION
Virtual human robots (Fig. 1) can be equipped with sensors, memory, perception, and behavioral motor. This eventually makes this to act or react to events. The design of a behavioral animation system raises questions about creating autonomous actors, endowing them with perception, selecting their actions, their motor control and making their behaviour believable and the behavior should be spontaneous and unpredictable. They should give an illusion of life, making the people believe that that they are really alive. A virtual human can be developed which include the basic components of a smart system embedded sensor(s), an information processing (software) system for data analysis, logic and decision making and system hardware (e.g., multiplexers, actuators
etc) interfaced to a computer for control, actuation and feedback [4].
III. SENSORS AND ACTUATORS
Development of the research and technology base in Sensors and Actuators (Fig. 2) requires a basic understanding of the principles and mechanics of the components. Programs identified within the Sensors and Actuators SRP, include
* Optical Sensors and Digital Imaging
* Smart Materials and Structures
* Non-Destructive Testing and Evaluation
* Bio-chemical Sensors
* Other related programmes
Being a fairly broad discipline, the Sensors and Actuators SRP has common ground and overlap with most of the other SRP's. For example, with the MEMS programme, there is the development of optical sensors for characterization and reliability of MEMS devices. Similarly a suite of techniques is developed for NDT and stress management of electronic packaging systems. With the biomedical group, there is work on development of fiber optic biosensors for bacterial sensing and detection. While the research focus is on development of novel sensors and actuators, industrial support requires integrated system development as well. The Smart Structures and Materials program is a particular case in point of an integrated system incorporating sensors, processing and decision making capabilities and actuation. It can be defined as "a system or material which has built-in or intrinsic sensor(s), actuator(s), and control mechanism(s) whereby it is capable of sensing a stimulus, responding to it in a predetermined manner and extent, in a shortlappropriate time, and reverting to its original state as soon as the stimulus is removed". The term stimulus may include stress, strain, incident light, electric field, gas molecules, temperature, hydrostatic pressure etc. whereas, the response could be any of a number of possibilities, such as motion or change in optical properties, conductivity, surface tension,
dielectric, piezoelectric or pyroelectric properties, mechanical modulus or permeability [5]. Although Japanese and American scientists have rather different views of smart/intelligent materials, they are generally regarded to be a group of materials that have varying degrees of sensing and actuating functions that can be incorporated into systems having feedback loops to constantly vary or "tune" one or more material property such as size, shape, color, structure or composition. Using sophisticated hardware (control devices e.g., actuators) and software these materials can be incorporated into what is described as a smart/intelligent system, that possesses a higher level of intelligence such as selfdiagnosis, self-repair, learning ability, ability to discriminate shapes and forms, ability to judge etc.
A. Optical Sensors and Digital Imaging
Optical components such as optical fibers, lasers and detectors are only recently being
developed fueled by the applications in the communications industry. Electronics and Optics have been competing technologies in sensor and actuator system over the years. Indeed, the evolution of electronics and optics has taken similar routes. Optical Sensors offer some advantages over electrical sensors, such as use of passive, dielectric and insulating components. No electrical power at the measurement point is required, thus no heat generation, electrical shorting and fire hazard problems. Remote non-contact sensing and whole-field visual display of the measure and rounds of the positive aspects of optical sensors. However, electrical sensors have a longer industrial history and thus components and devices for these sensors are readily available. Thus electrical sensors are more prevalent. The cost of these components is competitive and various off-the-shelf systems are becoming available. Optoelectronics has merged these two competing technologies, taking the best of each. Optics has the advantage in the primary sensing capabilities, while electronics is currently leading in the processing and actuating technologies. Thus this has a lot to offer in development of novel sensor processor- actuator systems
