Controlling a contactless planar actuator with manipulator

An existing magnetically levitated planar actuator with manipulator has been studied and improved from a control point of view. This prototype consists of a magnetically levitated six-degree-of-freedom (6-DOF) planar actuator with moving magnets, with a 2-DOF manipulator on top of it. This system contains three different contactless technologies: contactless bearing and propulsion of the planar actuator, wireless powering of the manipulator, and wireless communication and control of the manipulator. The planar actuator (PA) consists of a Halbach magnet array, which is levitated and controlled in all six DOF’s above a stationary coil array. The PA is propelled in two horizontal translational DOF’s while the other four DOF’s are stabilized to accomplish a stiff bearing. Each active coil contributes to the production of forces and torques acting on the magnet array. Since the number of active coils is much larger than the number of DOF’s, the desired force production can be distributed over many coils. Therefore, a commutation algorithm has to be used to invert the mapping of the forces and torques exerted by the set of active coils as a function of the coil currents and the position and orientation of the translator. One method for linearization and decoupling of the forces and torques was developed in the past. The method is called direct wrench decoupling and guaranties minimal dissipation of energy. However, no constraints on the maximum current can be given. This study proposes two novel, norm-based commutation methods: l8-norm and clipped l2-norm based commutation. Both methods can put bounds on the maximum currents in the coils to prevent saturation of the current amplifiers. The first method focuses on minimization of the maximum current whereas the second method limits the peak current while it minimizes the power losses. Consequently, a higher acceleration of the translator can be achieved and/or less powerful (cheaper) current amplifiers can be utilized and/or fewer commutation errors arise. Only a long-stroke translational movement of the moving magnet planar actuators has been considered in the past. The possibility of a completely propelled and controlled rotation about the vertical axis instead of just stabilizing it for bearing has been analyzed in this thesis from a control point of view. Enhancing the planar actuator with a long-range rotation will increase its utility value and opens new application areas. Based on this investigation, a novel coil array with a triangular grid of rounded coils has been proposed for better controllability in any orientation of the PA. In addition, other coil and magnet topologies have been studied from a control point of view for their suitability for full rotation. The influence of different kinds of error-causes on the commutation precision has been studied. From this investigation, it has been found that the offsets of the measurement system have the highest influence on the precision of the commutation. Investigation of the convergence of the procedure for estimation and elimination of these offsets has been performed. Although it was not proven that the procedure could be applied on the whole workspace of the PA, the convergence has been shown at least for all the investigated points. From this investigation, convergence for any position in the workspace of the PA is expected. It was found that it is possible to use the procedure also with different topologies and with different commutations. A novel wireless link has been developed for the real-time control of a fast motion system. The wireless link communicates via infrared-light transceivers and the link has a delay and a packet-loss ratio almost indistinguishable from the wired connection for the bandwidth of the system up to several kilohertz. The clipped l2-norm based commutation method has been successfully tested on the experimental setup after improving the measurement system, the contactless energy transfer and the wireless communication. With a new, interferometer sensor system, a well-controlled PA with two long-stroke DOF’s has become available. Improved contactless energy transfer does not cause increased electromagnetic interference during switching between the primary coils any more and the wireless connection using the infrared link provides a reliable communication channel between the manipulator and the fixed world. Several control approaches have been tested on the experimental setup. Both, the classical PID control, Sliding-mode control and Iterative learning control have been implemented. Each controller brought better performance than the previous one. Also, a fourth-order trajectory and enhanced feedforward control helped to improve performance. Finally, the tracking errors, in comparison to the initial situation, were reduced by a factor 10 (and even more than by a factor 50 with deactivated contactless energy transfer) while the velocity and acceleration of the system were a factor 4 and 14, respectively, higher

Identification and parameter-varying decoupling of a 3-DOF platform with manipulator

The paper describes identification and a new parameter-varying decoupling method for a 3-degree-of-freedom (DOF) platform with a manipulator on top of it, which is magnetically levitated by 9 voice-coil actuators. The identification has been performed in closed-loop using two different indirect approaches. In the first approach time-domain data of the system were processed using Ho-Kalman algorithm. The second approach was based on frequency-response measurements. The 3 DOFs of the platform are coupled and the coupling is even varying as the manipulator on top is moving. In order to design separate SISO controllers for each DOF of the platform, a new decoupling method has been developed which uses frequency response measurements of the system obtained for different positions of the manipulator

Identification and parameter-varying decoupling of a 3-DOF platform with manipulator

The paper describes identification and a new parameter-varying decoupling method for a 3-degree-of-freedom (DOF) platform with a manipulator on top of it, which is magnetically levitated by 9 voice-coil actuators. The identification has been performed in closed-loop using two different indirect approaches. In the first approach time-domain data of the system were processed using Ho-Kalman algorithm. The second approach was based on frequency-response measurements. The 3 DOFs of the platform are coupled and the coupling is even varying as the manipulator on top is moving. In order to design separate SISO controllers for each DOF of the platform, a new decoupling method has been developed which uses frequency response measurements of the system obtained for different positions of the manipulator

Human Febrile Illness Caused by Encephalomyocarditis Virus Infection, Peru

Encephalomyocarditis virus was identified in the serum of 2 febrile patients in Peru

Risk behaviors in a rural community with a known point-source exposure to chronic wasting disease

<p>Abstract</p> <p>Background</p> <p>The emergence and continuing spread of Chronic Wasting Disease (CWD) in cervids has now reached 14 U.S. states, two Canadian provinces, and South Korea, producing a potential for transmission of CWD prions to humans and other animals globally. In 2005, CWD spread for the first time from the Midwest to more densely populated regions of the East Coast. As a result, a large cohort of individuals attending a wild game feast in upstate New York were exposed to a deer that was subsequently confirmed positive for CWD.</p> <p>Methods</p> <p>Eighty-one participants who ingested or otherwise were exposed to a deer with chronic wasting disease at a local New York State sportsman's feast were recruited for this study. Participants were administered an exposure questionnaire and agreed to follow-up health evaluations longitudinally over the next six years.</p> <p>Results</p> <p>Our results indicate two types of risks for those who attended the feast, a <it>Feast Risk </it>and a G<it>eneral Risk</it>. The larger the number of risk factors, the greater the risk to human health if CWD is transmissible to humans. Long-term surveillance of feast participants exposed to CWD is ongoing.</p> <p>Conclusion</p> <p>The risk data from this study provide a relative scale for cumulative exposure to CWD-infected tissues and surfaces, and those in the upper tiers of cumulative risk may be most at risk if CWD is transmissible to humans.</p

Fifty-Year Fate and Impact of General Medical Journals

Background: Influential medical journals shape medical science and practice and their prestige is usually appraised by citation impact metrics, such as the journal impact factor. However, how permanent are medical journals and how stable is their impact over time? Methods and Results: We evaluated what happened to general medical journals that were publishing papers half a century ago, in 1959. Data were retrieved from ISI Web of Science for citations and PubMed (Journals function) for journal history. Of 27 eligible journals publishing in 1959, 4 have stopped circulation (including two of the most prestigious journals in 1959) and another 7 changed name between 1959 and 2009. Only 6 of these 27 journals have been published continuously with their initial name since they started circulation. The citation impact of papers published in 1959 gives a very different picture from the current journal impact factor; the correlation between the two is non-significant and very close to zero. Only 13 of the 5,223 papers published in 1959 received at least 5 citations in 2009. Conclusions: Journals are more permanent entities than single papers, but they are also subject to major change and their relative prominence can change markedly over time

Disease concepts and treatment by tribal healers of an Amazonian forest culture

<p>Abstract</p> <p>Background</p> <p>The extensive medicinal plant knowledge of Amazonian tribal peoples is widely recognized in the scientific literature and celebrated in popular lore. Despite this broad interest, the ethnomedical systems and knowledge of disease which guide indigenous utilization of botanical diversity for healing remain poorly characterized and understood. No study, to our knowledge, has attempted to directly examine patterns of actual disease recognition and treatment by healers of an Amazonian indigenous culture.</p> <p>Methods</p> <p>The establishment of traditional medicine clinics, operated and directed by elder tribal shamans in two remote Trio villages of the Suriname rainforest, presented a unique investigational opportunity. Quantitative analysis of clinic records from both villages permitted examination of diseases treated over a continuous period of four years. Cross-cultural comparative translations were articulated of recorded disease conditions through ethnographic interviews of elder Trio shamans and a comprehensive atlas of indigenous anatomical nomenclature was developed.</p> <p>Results</p> <p>20,337 patient visits within the period 2000 to 2004 were analyzed. 75 disease conditions and 127 anatomical terms are presented. Trio concepts of disease and medical practices are broadly examined within the present and historical state of their culture.</p> <p>Conclusion</p> <p>The findings of this investigation support the presence of a comprehensive and highly formalized ethnomedical institution within Trio culture with attendant health policy and conservation implications.</p