Experimental apparatus has been developed for physically testing control systems for pointing flexible structures, such as limber spacecraft, in the event that control actuators cannot be colocated with the sensors. (An example is the Galileo spacecraft, whose television camera at one end of a flexible beam must be pointed by torquiiig at the other end of the beam). With colocation, good stable control is very easy to achieve. With noncolocation it is extremely difficult, particularly if structural damping is very low and spacecraft stiffness and inertia values are uncertain and changing, as they are typically. For the apparatus we have built, structural damping ratios are less than 0.003, each basic configuration of sensor/actuator noncolocation is available, and inertias can be halved or doubled abruptly during control maneuvers, thereby imposing in particular a sudden reversal in the plant's pole-zero sequence, a most difficult problem for the controller. First experimental results are presented, including stable control with both colocation and noncolocation. The inherent robustness of the former is clearly seen, as is the great difficulty of achieving robustness for the latter. (Schemes for doing so are now being explored, and future experiments will establish what the best achievable robust but nonadaptive control is, and will develop adaptive control.) What we hope to contribute here is a "red flag" warning about noncolocated control of flexible structures: there are configurations, indeed, simple ones, for which there may be no practical alternative to adaptive control.

A digital state vector feedback controller with integral and preview actions, which can be called a proportional plus integral plus derivative plus preview (PIDP) controller, is derived based on linear quadratic optimal control theory. The preview action is a generalization of the feedforward concept which has been exercised in many process control situations. Preview of future system disturbance inputs is shown to be effective to improve the performance of the control system.

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Articles you may be interested inVertical directionality-controlled metal-assisted chemical etching for ultrahigh aspect ratio nanoscale structures J. Vac. Sci. Technol. B 32, 06FI01 (2014); 10.1116/1.4898199 Influence of catalytic gold and silver metal nanoparticles on structural, optical, and vibrational properties of silicon nanowires synthesized by metal-assisted chemical etching J. Appl. Phys. 112, 073509 (2012); 10.1063/1.4757009Nanofabrication of x-ray zone plates using ultrananocrystalline diamond molds and electroforming Integration of benzocyclobutene polymers and silicon micromachined structures using anisotropic wet etchingIn-plane control of morphology and tunable photoluminescence in porous silicon produced by metal-assisted electroless chemical etching Ordered arrays of high-aspect-ratio micro/nanostructures in semiconductors stirred a huge scientific interest due to their unique one-dimensional physical morphology and the associated electrical, mechanical, chemical, optoelectronic, and thermal properties. Metal-assisted chemical etching enables fabrication of such high aspect ratio Si nanostructures with controlled diameter, shape, length, and packing density, but suffers from structure deformation and shape inconsistency due to uncontrolled migration of noble metal structures during etching. Hereby the authors prove that a Ti adhesion layer helps in stabilizing gold structures, preventing their migration on the wafer surface while not impeding the etching. Based on this finding, the authors demonstrate that the method can be used to fabricate linear Fresnel zone plates.

Sample were identified. Hospitalizations were trended over years using Poisson regression and expressed as average annual percent change (AAPC), stratified by race. A yearly aggregate sum of HF-related procedures (valvular interventions, heart transplants, and left ventricular assist device implants) similarly trended by race. Results: Overall, 1,472,565 hospitalizations were identified. Total as well as primary cardiovascular hospitalizations significantly increased across all races (AAPC: White 8% and 7%, respectively; Black 9% and 9%, Hispanic 8% and 8%, other 7% and 8%). Rates of HF-related procedures were 145 per 1000 hospitalizations in White patients, 57 per 1000 in Black patients, 103 per 1000 in Hispanic patients, and 138 per 1000 in patients of other races. From 2000 to 2017, procedural rates increased in patients of all races: White (130 per 1000 to 163, p<0.0001), Black (51 per 1000 to 65, p<0.0001), Hispanic (75 per 1000 to 129, p<0.0001), and other races (71 per 1000 to 147, p<0.0001), (Figure). Similar trends were seen for each race when stratified by primary insurance. Conclusion: Rate of hospitalizations and HF-related procedures increased in patients with CHD from 2000 to 2017. Black and Hispanic patients had significantly fewer procedures compared to White patients regardless of insurance type. Further studies are needed to better ascertain the causes behind demographic disparities in procedural volumes in patients with CHD and to raise awareness among patients and providers.

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Concurrent design and analysis of mechanisms offer significant improvements in product quality while greatly reducing design cycle time. Recent advances in CAE software now give very powerful analysis and design capability directly to the design engineer. The key advances are intuitive graphical interfaces, adapation of analysis software to the design process, and seamless integration with existing CAD/CAM/CAE products. Several examples of concurrent mechanism design and analysis are given along with an overview of CAE mechanism design and analysis software, including Applied Motion® from Rasna Corporation.