Dimensional Position Information Research Articles

Particle tracking stereomicroscopy in optical tweezers: Control of trap shape

We present an optical system capable of generating stereoscopic images to track trapped particles in three dimensions. Two-dimensional particle tracking on each image yields three dimensional position information. Our approach allows the use of a high numerical aperture (NA=1.3) objective and large separation angle, such that particles can be tracked axially with resolution of 3 nm at 340 Hz. Spatial Light Modulators (SLMs), the diffractive elements used to steer and split laser beams in Holographic Optical Tweezers, are also capable of more general operations. We use one here to vary the ratio of lateral to axial trap stiffness by changing the shape of the beam at the back aperture of the microscope objective. Beams which concentrate their optical power at the extremes of the back aperture give rise to much more efficient axial trapping. The flexibility of using an SLM allows us to create multiple traps with different shapes.

The structure of molecular clouds and the universality of the clump mass function

Using an SPH simulation of a star-forming region in a molecular cloud, we show that the emergence of a clump mass function (CMF) resembling the stellar initial mass function (IMF) is a ubiquitous feature of molecular cloud structure, but caution against its over-interpretation. We employ three different techniques to extract the clumps in this study. In the first two, we interpolate the SPH particle data to 2 and 3 dimensional grids before performing the clump-find, using position-position (PP) and position-position-velocity (PPV) information respectively. In the last technique, the clump-finding is performed on the SPH data directly, making use of the full 3 dimensional position information. Although the CMF is typically similar to that observed in regions of nearby star formation, the individual clumps and their masses are found to be unreliable since they depend strongly on the parameters and the method of the clump-finding. In particular we find that the resolution and orientation of the data make a significant difference to the resulting properties of the identified clumps in the PP and PPV cases. We conclude that making comparisons between a CMF and the stellar IMF should be done with caution, since the definition of a clump boundary, and hence the number of clumps and their properties, are arbitrary in the extraction method. This is especially true if molecular clouds are truly scale free.

Acquisition of Weld Seam Dimensional Position Information for Arc Welding Robot Based on Vision Computing

Recognition and identification of weld environment and seam dimensional position by computer vision is a key technology for developing advanced autonomous welding robot. Aiming at requirements for recognition of weld seam image characteristics, this paper first presents an improved algorithm of subpixel edge detection based on Zernike moments. Comparing with the Ghosal’s original algorithm, the improved algorithm deals with mask effect and first derivative model on edge gradient direction so that it has the strong robust to noise, self-thinning ability and higher locating precision. An algorithm based on ZMs to extract line is also proposed, the comparative results with SHT and RHT show the method has the highest calculation speed and accuracy. The stereovision technology is developed to identify dimensional position of weld seam by computing dimensional coordinates of the weld seam. According to characteristics of weld seam, view field scope model and stereovision model based on baseline are studied and a stereo matching method is presented. In order to evaluate the algorithms and models presented in this paper, a welding robot systems with single camera fixed on the weld torch end-effector has been established for the robot to identify the dimensional position of typical weld seam by one-item and two-position method. The experiment results on S-shape and saddle-shape weld seams show that the vision computing method developed in this paper can be used for acquiring weld seam dimensional position information in welding robot system. Thus the welding path is mapped before the welding operation is executed.

A 3-Dimensional Robotic Vision Sensor

Abstract A video camera based vision system is very helpful for some robotic vision problems. But for real time object recognition and localisation requirements, video data cannot be treated fast enough to be feeded back into the control loop. In this work a new approach and a new related sensor is developed in order to acquire three dimensional position information about the external world of the robot. The developed sensor uses active triangulation technique and makes use of coherent monochromatic light. The sensor is very compact and may be integrated within the end effector of the robot. The device may deliver punctual three dimensional information of profile data, within a field of wiew of 40 degrees and a range of up to three meters.

A Spherical Drift Chamber Area Detector for X-Ray Crystallography

A multiwire proportional chamber system has been built as an area detector for use in x-ray crystallography with Cu Kα radiation (1.54Å). The chamber, constructed by Charpak and collaborators at CERN, consists of a 10cm thick spherical interaction region with a radial electric field, a transition from spherical to plane geometry and a 50cm × 50cm multiwire proportional chamber and subtends a 90° opening angle. Two dimensional position information is obtained from orthogonal cathode planes using a high speed analog centroid finding technique. Data on spatial and energy resolution as a function of angle and depth of interaction in the spherical drift region using a collimated, pulsed, x-ray source are presented. Ionization loss as a function of drift distance and field and loss due to field shaping grids has also been measured.

A frameless, cylindrically shaped, multiwire proportional chamber using charge division readout

We have constructed PWCs in the shape of cylindrical quandrants, placed them around the bicone in an experiment at the CERN ISR, and operated them in a charge division mode to obtain two dimensional position information. A pair of PWCs share a cylindrical styrofoam shell as the basic support member, and contain ∼0.008 radiation lengths of material. The observed charge division resolution is δx/ L∼0.5% in reasonable agreement with an expected resolution of ∼0.3% due primarily to digitization noise. Reduction of digitization noise is limited by available dynamic range of the electronics and the width of the pulse height distributions. A method is described, using X-rays from 55Fe strip sources for calibrating the electronics, which is sufficiently accurate to match the observed resolution.