Mechanical actuators are integral components of many engineered systems. Many of the presently available actuator systems lack the desired stroke, power, controllability and reliability. The hierarchical actuator is a natural extension of the trend toward improving the performance of actuators through increments in geometric complexity and control. The hierarchical concept is to build integrated actuators out of a combination of smaller actuators. The smaller actuators are arranged geometrically and controlled so as to extend the performance of the total actuator into ranges that are not possible with actuators that are based on a few active elements and levels of control. Precision, speed increase, force output, load sharing, efficiency under smooth load/displacement control, smooth motion, stroke amplification/reduction and redundancy are all possible. Mechanics and mechanisms of hierarchical actuators are examined, along with a few experiments to demonstrate the operating principles.
Electrical, optical and hydraulic conductors are vital components of most modern engineered systems. Damage to wiring and other conductors can degrade system performance, require expensive maintenance, and may cause catastrophic failures. This paper describes some efforts at developing active methods for self-healing wiring and conductor insulation. The concept is that there may be situations where it is beneficial to use self-healing cabling. One-part and two-part self-healing systems are fabricated and tested. Localized toughening in the face of localized damage has been realized in bench top experiments.
Membrane masks are thin (2 micron x 35 mm x 35 mm) structures that carry the master exposure patterns in proximity (X-ray) lithography. With the continuous drive to the printing of ever-finer features in microelectronics, the reduction of mask-wafer overlay positioning errors by passive rigid body positioning and passive stress control in the mask becomes impractical due to nano and sub-micron scale elastic deformations in the membrane mask. This paper describes the design, mechanics and performance of a system for actively stretching a membrane mask in-plane to control overlay distortion. The method uses thermoelectric heating/cooling elements placed on the mask perimeter. The thermoelectric elements cause controlled thermoelastic deformations in the supporting wafer, which in turn corrects distortions in the membrane mask. Silicon carbide masks are the focus of this study, but the method is believed to be applicable to other mask materials, such as diamond. Experimental and numerical results will be presented, as well as a discussion of the design issues and related design decisions.
KEYWORDS: Sensors, Sensing systems, Robots, Data acquisition, Signal processing, Robotics, Structural sensing, Magnetism, Imaging systems, Control systems
Structural sensing systems that employ adaptive strategies have the potential to achieve superior performance over nonadaptive counterparts. Adaptation is a means that many systems use to improve performance to compensate for varying and uncertain circumstances. Structural sensing systems can use several different adaptive sensing techniques including adaptive signal processing, adaptive data acquisition protocols, rapidly deployable sensors and mobile sensors. Adaptive signal processing is where the processing that is applied to a given set of data is modified according to the information content in the data or external circumstances. Adaptive data acquisition can be implemented through modifying the acquisition parameters and through the modification of sensor location and spatial sensitivity. The adaptive deployment of sensors requires mobile sensors and mechanisms, such as robots, to move the sensors into more advantageous positions. While the enabling technologies of adaptive sensing systems are readily emerging, optimal and effective adaptive strategies remain largely unexplored. This paper will also discuss some of the issues related to developing effective adaptation strategies for sensing systems and present example applications of adaptive signal processing and mobile robotic sensing applications.
This paper will present the concept of utilizing various mobile robotic platforms for homeland security. Highly specialized mobile robots equipped with the proper sensors and data processing capabilities have the ability to provide security and surveillance for a wide variety of applications. Large infrastructure components, such as bridges, pipelines, dams, and electrical power grids pose severe challenges for monitoring, surveillance, and protection against man-made and natural hazards. The structures are enormous, often with awkward and dangerous configurations that make it difficult, if not impossible, for continuous human surveillance. Properly outfitted robots have the potential to provide long-term surveillance without requiring continuous human supervision. Furthermore, these robotic platforms can have disaster mitigation capabilities such as evaluation of infrastructure integrity at the disaster site. The results presented will include proof-of-concept robotic platforms equipped with various sensor arrays, as well as discussion of design criteria for numerous homeland security applications.
This paper describes the mechanics and control of mechanical distortions imposed on membrane masks during proximity (X-ray) lithography. Two sources of mechanical distortions are examined. The first is aeroelastic distortion caused by the coupling of aerodynamic fluid forces in the gap between the membrane and the wafer with the elastic mechanics of the membrane. Aerodynamic loadings on the membrane arise when the gap between mask and wafer is adjusted and during lateral stepping maneuvers. Results of stepping and gap closing experiments are presented. The results are correlated with numerical calculations based on Reynolds lubrication equation. Possible methods for reducing these aeroelastic distortions are examined. The second set of mechanical distortions contains those that give rise to some of the in-plane overlay errors. A thermoelastic technique for controlling in-plane errors using thermoelectric devices placed on the mask perimeter is described. Numerical and experimental results are presented.
This paper describes the application of active damping systems to the reduction of weight of aerospace electronics. Aerospace electronics are subject to extremely harsh vibratory environments throughout their service lives. Present methods of protecting and reinforcing circuit boards from vibration and their associated stresses and strains in such applications add significant weight to these electronic systems. The vibration protection they provide is crucial, however, as the nature of aerospace vehicles requires an extremely robust, durable design to prevent premature failure of any of the components of the electronics system. By directly mounting an active mass damping system onto each circuit board, it is possible to reduce significantly the weight and volume of the complete electronic circuit board system, while maintaining equal or superior vibration protection. This paper presents results of electronic circuit board active vibration reduction of damping sinusoidal excitations near resonance, free vibration damping, as well as future strategies for the active vibration control system.
This paper describes efforts at monitoring microfloor vibrations in a newly-constructed research building. This building is intended to house a variety of delicate precision scientific instruments with performances that are deleteriously affected by even small floor vibrations. The building is five stories with welded steel construction. Upon completion of the construction, the initial occupants anecdotally complained of excessive floor vibrations. This resulted in an effort to measure the vibrations and to reduce them at their sources, including the mechanical systems for the building. The measurements are compared with industry standards and with measurements taken at nearby reinforced concrete buildings. The success of efforts at reducing the vibrations due to the mechanical systems of the building are also assessed.
The bulge testing technique determines the mechanical properties of solid thin films by measuring the deformation that forms in response to the application of a controlled differential pressure to a thin film window. By comparing the pressure-displacement relation with a mechanical model, the elastic modulus and residual stress in the film can be measured. While the bulge testing technique can be quite effective, the technique is not routinely used because of difficulties that often arise with using this technique. The difficulties include specimen preparation and mounting, automated bulge height measurement and the correlation of bulge deformation with the mechanical properties of the thin film. This paper describes developments in the bulge testing technique that alleviate many of these difficulties, as well as presenting results from the testing of single and dual layer thin films. Single film tests were conducted on samples of B-doped-Si, SiC, and diamond-like carbon. A total of 135 windows with three different window aspect ratios and two different thicknesses were investigated. In a preliminary study to determine the feasibility of extending the technique to the testing of multilayer films, the mechanics of a dual layer system were measured. The dual layer system was an Al layer on top of B-doped-Si. The results from the single film test were that the elastic moduli of the B-doped-Si were close to nominal bulk values and the diamond-like carbon was about half that of diamond. The SiC elastic moduli measurements were inconclusive because of the large prestress. Elastic moduli measurements from nanoindentation were about 50% higher. It should be noted that neither the variation of the aspect ratio nor the variation of the film thickness led to different results. The measured prestresses agreed quite well with wafer curvature measurement. The dual-layer measurements yielded values for the elastic modulus of thin film Al that were within 5% of the nominal bulk values.
The inspection of structures by humans is often hampered by safety and accessibility concerns. One method of reducing human inspection activities is to use remotely located sensors, such as strain gages and accelerometers. Running cables to power the sensors and transmit data can be expensive and inconvenient. This paper describes a development effort in which a robot is used to power and interrogate remotely placed sensors. The sensors are powered by a noncontact inductive system, which eliminates the need for batteries or interconnecting lead wires. The data are sent by a wireless connection back to a central data logger and processor. The power demands of telemetering data are decreased by close proximity of robot. The system utilizes existing microminiature, multichannel, wireless programmable Addressable Sensing Modules (ASM's) to sample data from a wide variety of sensors. Demonstration style robots are built and tested with ASMs in simple tabletop design, and a more robust task specific I-beam crawler robot for structural application.
Determining the health of concrete structural members, such as bridge columns and retaining walls is often difficult because a large portion of the interesting features, including damage are buried underneath the surface. This paper describes a development effort in which high-frequency electromagnetic waves (0.5 to 6 GHz) are used to interrogate reinforced concrete bridge columns, retaining walls and roadways. This technology, often known as ground penetrating radar (GPR), has previously been used to examine roadways and geological formations, primarily with lower frequencies. Rebar locations, concrete degradation and some cracks can be identified. However, most of the presently available GPR systems are bulky and specifically designed for examining horizontal surfaces. It is envisioned to use GPR technology to also examine non-horizontal surfaces, such as columns and walls. A prototype handheld system has been developed and tested on columns and retaining walls in the field as well as in the laboratory. The design of the system, field data compared with visual and historical information, as well as design concepts for an improved system will be presented.
Ground Penetrating Radar (GPR) can be an effective technique for assessing internal damage levels in concrete roadways. Damage to concrete roadways, particularly those on bridges, can have large economic consequences. Damage often takes the form of corrosion of reinforcing bars, the promotion of internal cracking, eventually large-scale spalling, and the formation of deep potholes. This damage usually initiates internally and does not appear on the surface until it is at an advanced state. The use of asphalt overlays further exacerbates this problem. One of the most important, yet difficult to identify, defects is a delamination, which can be due to expansion associated with reinforcing bar corrosion. The GPR reflections from a delamination can be relatively weak, whereas the reflection from a reinforcing bar can be fairly strong. Identifying the damage levels at an early stage can be used as a guide for efficiently planning maintenance activities. This paper presents the results of a laboratory and field study that focused on GPR methods of detecting delaminations in concrete roadways. The measurement technique used 0.5 to 6.0 GHz air-coupled waves to probe the roadways. Delaminations as small as 0.5 mm were simulated and detected in the laboratory. Field measurements are suggestive that this technique can be effective for field use.
Assessing internal damage levels in concrete roadways is an excellent opportunity for the application of nondestructive evaluation techniques, such as ground penetrating radar (GPR). Concrete roadways, particularly those on bridges, are high- performance structural elements that are subjected to severe environmental and mechanical stresses. These stresses cause corrosion of reinforcing bars, the promotion of internal cracking, eventually large-scale spalling, and the formation of deep potholes. This damage usually initiates internally and does not appear on the surface until it is at an advanced state. The use of asphalt overlays further exacerbates this problem. One of the most important, yet difficult to identify, defects is a delamination, which can be due to expansion associated with reinforcing bar corrosion. The GPR reflections from a delamination can be relatively weak, whereas the reflection from a reinforcing bar can be fairly strong. This paper presents the results of a laboratory and field study that focused on GPR methods of detecting delaminations in concrete roadways. The measurement technique used 0.5 to 6.0 GHz air-coupled waves to probe the roadways. Delaminations as small as 0.5 mm were stimulated and detected in the laboratory. Field measurements are suggestive that this technique can be effective for field use.
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