Optical contact measurement system

Alternatively non-contacting measurement systems may be considered for distinguishing between the different textile families, e.g. based on analyses of the optical or infrared optical spectra of the textiles. However, difficulties will arise, considering the variety of textiles in use. 

Some studies analyze and compare the methodologies and precisions obtained with non-contact measurement systems showing its high sensitivity to various external factors inherent to the measurement process or the optical characteristics of the object [1,2]. 

E2208-02(2010)e1 Standard Guide for Evaluating Non-Contacting Optical Strain Measurement Systems... 

The reaction between the analjrte and the bioreceptor produces a physical or chemical output signal normally relayed to a transducer, which then generally converts it into an electrical signal, providing quantitative information of analytical interest. The transducers can be classified based on the technique utilized for measurement, being optical (absorption, luminescence, surface plasmon resonance), electrochemical, calorimetric, or mass sensitive measurements (microbalance, surface acoustic wave), etc. If the molecular recognition system and the physicochemical transducer are in direct spatial contact, the system can be defined as a biosensor [76]. A number of books have been published on this subject and they provide details concerning definitions, properties, and construction of these devices [77-82]. 

In laser-optic measurement systems (such as Optalign), a combined laser source -sensor unit is placed on the reference shaft and the relative displacement vector and the alignment angle is calculated from the position of the incoming laser beam reflected by a prism unit, which is attached to the other shaft. This is an optical counterpart of the rim-and-face method. It is thus also relative, contact, manual and static in nature. 

The digital optical measurement systems have achieved wide spread in recent years in industry, reaching a share of around 20 % of the world market. These systems present interesting advantages over the coordinate measuring machines (CMM) with probing mechanical methods, mainly the speed of data acquisition, automation of measurement functions and, above all, the absence of contact. 

Conceptually an optical measuring machine can be divided into two subsystems, a "machine system" and an "optical system". The "machine system" consists of a monoblock structure holding the measuring table and allows the displacement of the axes. The "optical system" consists of a charged-coupled device (CCD) which allows the acquisition and transfer of images to a computer connected to the "machine system" as well as the necessary lenses and objectives to obtain images of a given resolution. The system made up of CCD camera replaced the "contact sensor system" used in a CMM. This subdivision allows us to analyze separately the two systems in order to achieve a model as a basis for the evaluation of uncertainty. 

Non-contact optical technologies can be used to obtain the full rail profile at speeds up to 350 km/h. Rail profile measurement systems (RPMS) can use high level laser and video technology to provide accurate and instantaneous report on the rail profile condition. The video cameras capture full cross-sectional rail profiles from the base to the top of the rail surface to allow useable and accurate measurements. Such a system can measure the following parameters rail profile vertical and horizontal wear, rail inchnation and head width. By comparison with a reference profile, parameters out of tolerance can be identified immediately. 

An important consideration for the direct physical measurement of adhesion via pull-off measurements is the influence of the precise direction of the applied force. In AFM the cantilever does not usually lie parallel to the surface, due to the risk that another part of the cantilever chip or chip holder will make contact with the surface before the tip. Another problem relates to the fact that the spot size in the optical beam deflection method is usually larger than the width of the lever. This can result in an interference effect between the reflection from the sample and the reflection from the cantilever. This is reduced if the cantilever and sample are not parallel. Most commercial AFM systems use an angle in the range of 10°-15° between the sample and the cantilever. Depending on this angle and the extent to which the cantilever is bent away from its equilibrium position, there can be a significant fraction of unintentional lateral forces applied to the contact. 

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