One of the big research topics in modern cosmology is the mystery of dark Energy. To unveil the secret, cosmologists want to measure precisely the evolution of large scale structures in the universe. One way of doing so is to measure the 3D location of a high number of galaxies. By measuring the redshift of a galaxy, it is possible to find its distance. In order to measure a high number of galaxies in a practical amount of time, we need to observe multiple objects in parallel. Instead of a spectrograph, thousands of optical fibres are placed in the focal plane of a telescope. They will transmit the light of many objects to a spectrograph. Each fibre has to be positioned to several μm precision in the focal plane of a telescope for each exposure. Each fibre is positioned by a 2-axis fibre positioner. In this paper such a fibre positioner with 24-mm diameter is presented. It is driven by two brushless DC motors in combination with a backlash free gearbox. The positioner has an optimal central fibre path and improved angular alignment. The fibre runs through the centre of the positioner and is only bent at the top to reach its target position. In this way, the flexion and torsion of the fibre are minimal. In addition to the high positioning accuracy, the design is optimized to allow a minimal tilt error of the fibre. This is demonstrated using a novel optical tilt measurement system.
The next generation of large-scale spectroscopic survey experiments such as DESI, will use thousands of fiber positioner robots packed on a focal plate. In order to maximize the observing time with this robotic system we need to move in parallel the fiber-ends of all positioners from the previous to the next target coordinates. Direct trajectories are not feasible due to collision risks that could undeniably damage the robots and impact the survey operation and performance. We have previously developed a motion planning method based on a novel decentralized navigation function for collision-free coordination of fiber positioners. The navigation function takes into account the configuration of positioners as well as their envelope constraints. The motion planning scheme has linear complexity and short motion duration (2.5 seconds with the maximum speed of 30 rpm for the positioner), which is independent of the number of positioners. These two key advantages of the decentralization designate the method as a promising solution for the collision-free motion-planning problem in the next-generation of fiber-fed spectrographs. In a framework where a centralized computer communicates with the positioner robots, communication overhead can be reduced significantly by using velocity profiles consisting of a few bits only. We present here the discretization of velocity profiles to ensure the feasibility of a real-time coordination for a large number of positioners. The modified motion planning method that generates piecewise linearized position profiles guarantees collision-free trajectories for all the robots. The velocity profiles fit few bits at the expense of higher computational costs.
In the large-scale, Dark Energy Spectroscopic Instrument (DESI), thousands of fiber positioners will be used. Those are
robotic positioners, with two axis, and having the size of a pen. They are tightly packed on the focal plane of the
telescope. Dedicated micro-robots have been developed and they use 4mm brushless DC motors. To simplify the
implementation and reduce the space occupancy, each actuator will integrate its own electronic control board. This board
will be used to communicate with the central trajectory generator, manage low level control tasks and motor current
feeding. In this context, we present a solution for a highly compact electronic. This electronic is composed of two layers.
The first is the power stage that can drive simultaneously two brushless motors. The second one consists of a fast
microcontroller and deals with different control tasks: communication, acquisition of the hall sensor signals,
commutation of the motors phases, and performing position and current regulation. A set of diagnostic functions are also
implemented to detect failure in the motors or the sensors, and to sense abnormal load change that may be the result of
two robots colliding.
High-speed laser manipulation is a key technology in applications such as fast optical switches for coupling light into
optical fibres, 2D beam steering for optical scanners, laser printers or 2D sensors. A novel design of a Polyvinylidene
Fluoride (PVDF) bimorph actuator is proposed in this work as high speed switching element in the kHz range. The
actuator of several cm length and 200 microns thickness takes advantage of the structural and electromechanical
capabilities of the PVDF. A 0.164 g compact mirror is placed at the tip of the PVDF bimorph actuator allowing scanning
of the beam in two directions. Tests made by an autocollimator have been performed in order to characterize the
precision, repeatability and also the long term stability at low frequencies. To complete this characterization, a
photodiode was used to measure the response of the mirror at high frequencies up to 3 kHz. Results of the FE element
confirm the trends observed in the experimental setup. Experimental results indicate that the PVDF actuator responds
conveniently to manipulate the laser beam at kHz frequency. In addition, due to the intrinsic properties of the PVDF, the
system is compact and light-weight. This is of advantage in several domains such as e.g. aerospace or micro-engineering.
PRIMA, the instrument for Phase-Referenced Imaging and Micro-arcsecond Astrometry at the VLTI, is currently being
developed at ESO. PRIMA will implement the dual-feed capability, at first for two UTs or ATs, to enable simultaneous
interferometric observations of two objects that are separated by up to 1 arcmin. PRIMA is designed to perform narrow-angle
astrometry in K-band with two ATs as well as phase-referenced aperture synthesis imaging with instruments like
Amber and Midi. In order to speed up the full implementation of the 10 microarcsec astrometric capability of the VLTI
and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Genève, Max
Planck Institute for Astronomy, and Landessternwarte Heidelberg, has built Differential Delay Lines for PRIMA and is
developing the astrometric observation preparation and data reduction software. When the facility becomes fully
operational in 2009, we will use PRIMA to carry out a systematic astrometric Exoplanet Search program, called ESPRI.
In this paper, we describe the narrow-angle astrometry measurement principle, give an overview of the ongoing hardand
software developments, and outline our anticipated astrometric exoplanet search program.
ESPRI is a project which aims at searching for and characterizing extra-solar planets by dual-beam astrometry with
PRIMA@VLTI. Differential Delay Lines (DDL) are fundamental for achieving the micro-arcseconds accuracy required
by the scientific objective. Our Consortium, consisting of the Geneva Observatory, the Max-Planck Institut for
Astronomy Heidelberg, and the Landessternwarte Heidelberg, in collaboration with ESO, has built and tested these
DDLs successfully and will install them in summer 2008 at the VLTI. These DDLs consist of high quality cat's eyes
displaced on a parallel beam-mechanics and by means of a two-stage actuation with a precision of 5 nm over a stroke
length of 70 mm. Over the full range, a bandwidth of about 400 Hz is achieved. The DDLs are operated in vacuum. We
shall present, in this paper, their design and their exceptional performances.
Based on the concept of Mazzone et al., we have designed a novel system to be used simultaneously as an input and output device for designing, presenting, or recognizing objects in three-dimensional space. Unlike state of the art stereoscopic display technologies that generate a virtual image of a three-dimensional object, the proposed system, a “digital clay” like device, physically imitates the desired object. The object can not only be touched and explored
intuitively but also deform itself physically. In order to succeed in developing such a deformable structure, self-actuating ionic polymer-metal composite (IPMC) materials are proposed. IPMC is a type of electro active polymer (EAP) and has recently been drawing much attention. It has high force to weight ratio and shape flexibility, making it ideal for robotic applications. This paper introduces the first steps and results in the attempt of developing such a structure. A strip consisting of four actuators arranged in line was fabricated and evaluated, showing promising capabilities in deforming two-dimensionally. A simple model to simulate the deformation of an IPMC actuator using finite element methods (FEM) is
also proposed and compared with the experimental results. The model can easily be implemented into computer aided engineering (CAE) software. This will expand the application possibilities of IPMCs. Furthermore, a novel method for creating multiple actuators on one membrane with a laser machining tool is introduced.
The PRIMA facility will implement dual-star astrometry at the VLTI. We have formed a consortium that will build the PRIMA differential delay lines, develop an astrometric operation and calibration plan, and deliver astrometric data reduction software. This will enable astrometric planet surveys with a target precision of 10μas. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around stars that are not amenable to high-precision radial-velocity observations, and a search for large rocky planets around
nearby low-mass stars.
A convenient method for exact recognitions of the curved shape and amplitudes of vibrated micro cantilevers is presented. The method includes the analysis based on preliminary introduction of the formulas for the shapes of deviated cantilevers to get the intensity distribution R(ξ) of the optical pattern of image. The feature of this method is the possibility to get high accuracy for MEMS orientation.
This paper presents a signal analysis method with the purpose of detecting frequency chande and acceleration amplitude of vibrating-type accelerometer's output. The method has potential application for newly developed oscillating micro accelerometers.
The Monolithic PiezoActuator (MPA) described in this work proposes the amplification of the piezoelectric deformation by a lever mechanism designed in a bulk piezoceramic plate. The advantages of the monolithic approach are to make the structure compact and to avoid problems of assembling reducing consequently production costs. In addition, several DOF (Degree Of Freedom) MPA can be designed with this approach. The total displacement using the MPA can reach some microns for a few millimeters size device. A numerical model has been used to simulate the static and dynamic behavior of a 1 DOF MPA. Static and dynamic measurements show a maximum displacement of around 6 mm and bandwidths as high as 5 kHz. The second part of this work is devoted to the open-loop position control of the MPA. The piezoelectric actuation is generally known to have a static behavior with a good linearity. Actually, when such an actuator is controlled by the electrical voltage, the typical hysteresis between this voltage and the corresponding deformation of the actuator can reach 20% for a soft PZT. Experimental results show an hysteresis under 10% and weak non-linearity for the MPA compared to standard piezoactuators. In order to linearize the open-loop motions, an open-loop control device which control the quantity of free electrical charges on the micro-actuator has been developed. The implementation of the control method has also given very encouraging results for MPA prototypes used in the laboratory.
An automated assembly technique for small optical components has been developed. It concerns components such as, e.g., laser diodes and LEDs, fibers, lenses beamsplitters, polarizers, mirrors, crystals, prisms, diffractive elements or photodiodes. It is based on the flexible 2-dimensional arrangement of a universal tripod holder (10 by 10 by 4 mm) on a planar mounting plate. Its particular mechanical structure allows to align the optical elements on-line and to attach them to the mounting plate in a one step procedure. The different elements are aligned with an accuracy of plus or minus 1 micrometer and attached one after the other. Very good position stability (plus or minus 0.7 micrometer, plus or minus 0.2 mrad) during the attachment procedure has been achieved by laser point welding. They are optically interconnected by free-space propagation of a light beam with diameter of up to 8 millimeters. Mass production has been shown with a collimator as test vehicle. The collimator is composed of two elements (laser diode and collimating lens) and is mounted entirely automatically by two co-working robots. Easy prototyping has been shown with the realization of the optical position sensing system featuring a high precision linear magnetic bearing. Flexibility, simple handling, high packaging density and low cost make this new assembly technique satiable to both mass production and prototyping of small opto electronical devices.