A digital signal processor based optical position sensor and its application to flexible beam control

A Digital Signal Processor (DSP) based optical position sensor was developed. The sensor system consists of the following components: 1) analog electronics, 2) the DSP based synchronous demodulation software, 3) PC based interface software which samples and saves the data, and 4) PC based control codes for a flexible beam. experiment. The ability of the system to determine the distance from the optical sensor to the power modulated light source was assessed by the following tests: 1) a stationary drift test to evaluate the system\u27s noise, 2) a short-range test to determine the resolution of the optical sensor over a 25mm range and, 3) a long-range test to evaluate the ability of the system to predict the location of the optical sensor over a 600mm range. It was found that the resolution of the system is approximately 0.5mm for the short range test and 5mm for the long range test. Finally, the sensor was deployed for the position feedback of a flexible beam experiment. Performance indices used to evaluate the response of the system were: 1) the sum of the squared position error, 2) the final steady state position error of the end of the flexible beam, and 3) the 5% settling time of the flexible beam. A number of control laws were evaluated and it was determined that a variable PID controller produced the best overall performance. The system can consistently position the end of the flexible beam from a +1-20cm to within 5mm of the command position in approximately 8 seconds with a properly tuned controller

An Observational Overview of Solar Flares

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.Comment: This is an article for a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011