S. Andrew Gadsden

Advances of the smooth variable structure filter: square-root and two-pass formulations

Abstract. The smooth variable structure filter (SVSF) has seen significant development and research activity in recent years. It is based on sliding mode concepts, which utilize a switching gain that brings an inherent amount of stability to the estimation process. In an effort to improve upon the numerical stability of the SVSF, a square-root formulation is derived. The square-root SVSF is based on Potter’s algorithm. The proposed formulation is computationally more efficient and reduces the risks of failure due to numerical instability. The new strategy is applied on target tracking scenarios for the purposes of state estimation, and the results are compared with the popular Kalman filter. In addition, the SVSF is reformulated to present a two-pass smoother based on the SVSF gain. The proposed method is applied on an aerospace flight surface actuator, and the results are compared with the Kalman-based two-pass smoother.

Fabrication of a Cell Culture Plate With a Three-Dimensional Printed Mold and Thermal Analysis of PDMS-Based Casting Process

Polydimethylsiloxane (PDMS)-based casting method was used to fabricate PDMS cell culture platforms with molds printed by a fused deposition modeling (FDM) printer. Cell viability study indicated that the produced plates have the suitable biocompatibility, surface properties, and transparency for cell culture purposes. The molds printed from acrylonitrile-butadiene-syrene (ABS) were reusable after curing at 65 C, but were damaged at 75 C. To understand thermal damage to the mold at elevated temperatures, the temperature distribution in an ABS mold during the curing process was predicted using a model that considers conduction, convection, and radiation in the oven. The simulated temperature distribution was consistent with the observed mold deformation. As the maximum temperature difference in the mold did not change appreciably with the curing temperature, we consider that the thermal damage is due to the porous structure that increases the thermal expansion coefficient of the printed material. Our study demonstrated that FDM, an affordable and accessible three-dimensional (3D) printer, has great potential for rapid prototyping of custom-designed cell culture devices for biomedical research. [DOI: 10.1115/1.4040134]

Development of a variable structure-based fault detection and diagnosis strategy applied to an electromechanical system

Signal processing techniques are prevalent in a wide range of fields: control, target tracking, telecommunications, robotics, fault detection and diagnosis, and even stock market analysis, to name a few. Although first introduced in the 1950s, the most popular method used for signal processing and state estimation remains the Kalman filter (KF). The KF offers an optimal solution to the estimation problem under strict assumptions. Since this time, a number of other estimation strategies and filters were introduced to overcome robustness issues, such as the smooth variable structure filter (SVSF). In this paper, properties of the SVSF are explored in an effort to detect and diagnosis faults in an electromechanical system. The results are compared with the KF method, and future work is discussed.