Andrew K. Forrest

A Low Friction Bearing Based on Liquid Slip at the Wall

In recent years it has been shown experimentally by a number of workers that simple, Newtonian liquids can slip against solid surfaces when the latter are both very smooth and lyophobic. It has also been shown theoretically how, based on a half-wetted bearing principle, this phenomenon may be used to significantly reduce friction in lubricated sliding contacts and thus make possible the hydrodynamic lubrication of very low load contacts. This paper describes the experimental validation of this concept. A low load bearing is constructed and the influence of surface roughness and the wetting properties of the surfaces on friction are investigated over a wide range of sliding speeds. It is shown that liquid slip can be used to considerably reduce friction in full film, hydrodynamic conditions.

Measurement of Sub-Nanometer Lubricant Films Using Ultra-Thin Film Interferometry

The ultra-thin film interferometric method of measuring the thickness of very thin films in lubricated contacts has been refined so as to be able to measure films down to 0.3 nm with a standard deviation of 0.15 nm. The main remaining source of measurement variation for films below 3 nm thick is the surface roughness of the contacting solids. This modified technique has been applied to study the film-forming properties of three fluids, hexadecane, a dilute solution of surfactant in hexadecane, and cyclohexane. Purified hexadecane shows a very slightly enhanced oil-film thickness below 1 nm. The long-chain surfactant forms a boundary film 2 nm thick. Cyclohexane behaves as though it forms a surface layer about 1 nm thick with viscosity three times the bulk fluid viscosity.

Occlusion detection in early vision

The authors show that occlusion can be detected by early visual processes derived directly from the image data. Two methods are demonstrated. The first method is based on detecting binocular rivalry during binocular fixation. The feasibility of this technique also supports the hypothesis that stereo fusion and rivalry coexist in human vision. Stereo fusion gives rise to smooth disparity whereas rivalry signals depth discontinuity. The second method uses focal information that results from a change in depth of field. This method does not involve changes of viewpoint and hence avoids the correspondence problem. These two methods together with cues from motion, as has been suggested elsewhere, form robust occlusion detection in early visual processing.<<ETX>>

Transformation calibration of a camera mounted on a robot

The paper describes the accurate calibration of the camera transformation for a vision system consisting of a camera mounted on a robot. The calibration includes an analysis of the linearity of the camera. A knowledge of the camera transformation allows the three-dimensional position of the object points to be determined using triangulation.

Visual detection of differential movement: applications to robotics

A method has been developed for accurately determining the differential movement of known objects from multiple camera views. The method has been applied to a robot System to find the repeatability and accuracy of the robot in both rotational and translational terms and also for tracking an object using visual feedback.

Multichannel telecentric flying spot scanner for real-time surface inspection

A telecentric flying spot scanner consisting of a rotating multifaceted mirror and a 500 mm diameter parabolic mirror for the inspection of large flat and embossed surfaces up to 400 mm wide is described. Real time high resolution 2-D images at three different angles are obtained providing various types of intensity profiles of the surface. These channels are linearly combined to form pseudo-color images. The image size per channel is limited to about 4 Mbytes by the maximum direct memory access buffer area used by the image grabber card. Images with variable resolutions (for example, 2048 X 2048 pixel or 10000 X 400 pixel) are therefore feasible. Photomultiplier tubes are used for light detection to offer good signal-to-noise ratio and to cover a wide dynamic signal detection range varying from scattered to specular light. Composite images for ceramic tiles with different textures, colors and surface features are presented. These images show some interesting features of the surface profile and texture which otherwise could not be observed using a CCD camera or a single channel scanner. Subtle flaws such as fine scratches and finger marks on the surface and the surface texture variations can be easily identified.

Use of vision in dispensing control and inspection of adhesives

A prototype system utilizing a vision technique to monitor the parameters of adhesive beads or sealants is presented. The system uses a structured light technique to investigate adhesive beads and extract information about the shape of the bead from binary images. The geometrical model of the bead, the relationship between this model and the shape of a line of light on the image are investigated. The models for calculating the parameters of the bead and the height of the camera are analyzed. Control strategies are suggested.

Depth reversal in binocular vision with symmetrical convergence

Binocular vision is the coordinated behavior of the two eyes by which a single perception of the external world is obtained and by which, the specific sensation of stereoscopic depth perception, is made possible. This perception, however, can be reversed by interchanging the left- and right-eye views. In this paper, the mathematical expression of the Vieth-Mueller circle is derived. A point on the line of the primary direction is found which only relates to the convergence angle and the interocular distance. A relation is developed between the position of a point in real space and its reversal if viewed pseudoscopically. It is shown that in some circumstances a concave surface is not necessarily perceived as a convex surface under pseudoscopic viewing conditions. The difference in perceiving real objects and stereograms is briefly discussed.

A Technique for the Detection of Liquid Slip at a Load-Bearing, High Shear Contact

This research aims to exploit the physical phenomenon of simple liquids slipping against very smooth solid surfaces, to create a new type of bearing where the lubricant slips against one surface but not the other. To demonstrate the feasibility of this idea, a special test rig capable of measuring milli-Newton forces has been employed to measure friction in high-speed, sliding contacts between a steel roller and sapphire window, lubricated by hexadecane. Sapphire was made either lyophobic by coating with a self-assembled silane monolayer, or lyophilic by O2 -plasma cleaning. The roller was made lyophilic. A significant reduction in friction was achieved with lyophobic sapphire but not with lyophilic sapphire. This reduced friction is believed to result from lubricant slip against the lyophobic surface. One possible application of such a bearing will be in microsystems and devices.Copyright

Color metric for production quality control

A real-time color quality control metric for planar surfaces has been developed. This is a differencing method that compares the color histogram of a test object with that of a standard obtained off-line. To reduce computational effort, three 1D histograms are formed by projecting the reference color histogram on to its principal axes. A metric value for each of the axes is then obtained by taking the RMS value of the differences between the corresponding entries in the histograms of the sample and reference objects. A model of the behavior of the metric has been developed and compared to the practical case where one of the color channels is attenuated. The major axis is generally observed to form the least sensitive color metric component for the purposes of quality control. It is argued that the projections on to the minor axis are theoretically expected to produce the most sensitive component because this is a null channel with respect to the reference image. In practice it is observed that this is often the case. The method has been evaluated using production samples of ceramic tiles. Results are presented showing clustering of the experimental data corresponding to tiles of different grades.