Performance evaluation of a six-axis generalized force-reflecting teleoperator

Work in real-time distributed computation and control has culminated in a prototype force-reflecting telemanipulation system having a dissimilar master (cable-driven, force-reflecting hand controller) and a slave (PUMA 560 robot with custom controller), an extremely high sampling rate (1000 Hz), and a low loop computation delay (5 msec). In a series of experiments with this system and five trained test operators covering over 100 hours of teleoperation, performance was measured in a series of generic and application-driven tasks with and without force feedback, and with control shared between teleoperation and local sensor referenced control. Measurements defining task performance included 100-Hz recording of six-axis force/torque information from the slave manipulator wrist, task completion time, and visual observation of predefined task errors. The task consisted of high precision peg-in-hole insertion, electrical connectors, velcro attach-de-attach, and a twist-lock multi-pin connector. Each task was repeated three times under several operating conditions: normal bilateral telemanipulation, forward position control without force feedback, and shared control. In shared control, orientation was locally servo controlled to comply with applied torques, while translation was under operator control. All performance measures improved as capability was added along a spectrum of capabilities ranging from pure position control through force-reflecting teleoperation and shared control. Performance was optimal for the bare-handed operator

Inverse Modelling to Obtain Head Movement Controller Signal

Experimentally obtained dynamics of time-optimal, horizontal head rotations have previously been simulated by a sixth order, nonlinear model driven by rectangular control signals. Electromyography (EMG) recordings have spects which differ in detail from the theoretical rectangular pulsed control signal. Control signals for time-optimal as well as sub-optimal horizontal head rotations were obtained by means of an inverse modelling procedures. With experimentally measured dynamical data serving as the input, this procedure inverts the model to produce the neurological control signals driving muscles and plant. The relationships between these controller signals, and EMG records should contribute to the understanding of the neurological control of movements

Condensate splitting in an asymmetric double well for atom chip based sensors

We report on the adiabatic splitting of a BEC of $^{87}$Rb atoms by an asymmetric double-well potential located above the edge of a perpendicularly magnetized TbGdFeCo film atom chip. By controlling the barrier height and double-well asymmetry the sensitivity of the axial splitting process is investigated through observation of the fractional atom distribution between the left and right wells. This process constitutes a novel sensor for which we infer a single shot sensitivity to gravity fields of $\delta g/g\approx2\times10^{-4}$. From a simple analytic model we propose improvements to chip-based gravity detectors using this demonstrated methodology.Comment: 4 pages, 5 figure

Precision measurements of s-wave scattering lengths in a two-component Bose-Einstein condensate

We use collective oscillations of a two-component Bose-Einstein condensate (2CBEC) of \Rb atoms prepared in the internal states $\ket{1}\equiv\ket{F=1, m_F=-1}$ and $\ket{2}\equiv\ket{F=2, m_F=1}$ for the precision measurement of the interspecies scattering length $a_{12}$ with a relative uncertainty of $1.6\times 10^{-4}$. We show that in a cigar-shaped trap the three-dimensional (3D) dynamics of a component with a small relative population can be conveniently described by a one-dimensional (1D) Schr\"{o}dinger equation for an effective harmonic oscillator. The frequency of the collective oscillations is defined by the axial trap frequency and the ratio $a_{12}/a_{11}$, where $a_{11}$ is the intra-species scattering length of a highly populated component 1, and is largely decoupled from the scattering length $a_{22}$, the total atom number and loss terms. By fitting numerical simulations of the coupled Gross-Pitaevskii equations to the recorded temporal evolution of the axial width we obtain the value $a_{12}=98.006(16)\,a_0$, where $a_0$ is the Bohr radius. Our reported value is in a reasonable agreement with the theoretical prediction $a_{12}=98.13(10)\,a_0$ but deviates significantly from the previously measured value $a_{12}=97.66\,a_0$ \cite{Mertes07} which is commonly used in the characterisation of spin dynamics in degenerate \Rb atoms. Using Ramsey interferometry of the 2CBEC we measure the scattering length $a_{22}=95.44(7)\,a_0$ which also deviates from the previously reported value $a_{22}=95.0\,a_0$ \cite{Mertes07}. We characterise two-body losses for the component 2 and obtain the loss coefficients ${\gamma_{12}=1.51(18)\times10^{-14} \textrm{cm}^3/\textrm{s}}$ and ${\gamma_{22}=8.1(3)\times10^{-14} \textrm{cm}^3/\textrm{s}}$.Comment: 11 pages, 8 figure

Miniature Telerobots in Space Applications

Ground controlled telerobots can be used to reduce astronaut workload while retaining much of the human capabilities of planning, execution, and error recovery for specific tasks. Miniature robots can be used for delicate and time consuming tasks such as biological experiment servicing without incurring the significant mass and power penalties associated with larger robot systems. However, questions remain regarding the technical and economic effectiveness of such mini-telerobotic systems. This paper address some of these open issues and the details of two projects which will provide some of the needed answers. The Microtrex project is a joint University of Washington/NASA project which plans on flying a miniature robot as a Space Shuttle experiment to evaluate the effects of microgravity on ground-controlled manipulation while subject to variable time-delay communications. A related project involving the University of Washington and Boeing Defense and Space will evaluate the effectiveness f using a minirobot to service biological experiments in a space station experiment 'glove-box' rack mock-up, again while subject to realistic communications constraints

Pupillometry, a bioengineering overview

The pupillary control system is examined using a microprocessor based integrative pupillometer. The real time software functions of the microprocessor include: data collection, stimulus generation and area to diameter conversion. Results of an analysis of linear and nonlinear phenomena are presented

Mean-field dynamics of two-mode Bose-Einstein condensates in highly anisotropic potentials: Interference, dimensionality, and entanglement

We study the mean-field dynamics and the reduced-dimension character of two-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means of perturbative techniques, we show that the tightly confined (transverse) degrees of freedom can be decoupled from the dynamical equations at the expense of introducing additional effective three-body, attractive, intra- and inter-mode interactions into the dynamics of the loosely confined (longitudinal) degrees of freedom. These effective interactions are mediated by changes in the transverse wave function. The perturbation theory is valid as long as the nonlinear scattering energy is small compared to the transverse energy scales. This approach leads to reduced-dimension mean-field equations that optimally describe the evolution of a two-mode condensate in general quasi-1D and quasi-2D geometries. We use this model to investigate the relative phase and density dynamics of a two-mode, cigar-shaped $^{87}$Rb BEC. We study the relative-phase dynamics in the context of a nonlinear Ramsey interferometry scheme, which has recently been proposed as a novel platform for high-precision interferometry. Numerical integration of the coupled, time-dependent, three-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers shows that this model gives a considerably more refined analytical account of the mean-field evolution than an idealized quasi-1D description.Comment: 35 pages, 10 figures. Current version is as publishe

Hormonal contraceptive methods and risk of HIV acquisition in women : a systematic review of epidemiological evidence

Peer reviewedPublisher PD