Brian Esser

Wireless inspection of structures aided by robots

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 (ASMs) 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.

Damage detection in roadways with ground penetrating radar

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.

Hierarchical actuator systems

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.

Adaptive, robotic, and mobile sensor systems for structural assessment

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.

Bulge testing of single- and dual-layer thin films

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.

Monitoring of microfloor vibrations in a new research building

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.

Damage assessment in roadways with ground-penetrating radar

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.

Active membrane masks for improved overlay performance in proximity lithography

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.

Membrane mask aeroelastic and thermoelastic control

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.

Aerospace electronics weight reduction through the use of active mass damping

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.