The topographic instruments as an alternative in industrial measurement

In this way, two sciences as seemingly disparate, metrology, and the topografía-geodesia approach to solve geometric problems. In any case it should not be forgotten that modern metrology arises in the 19th century together with geodesy, and the first definition of the metre is derived from geodetic steps of the arc of the Meridian, measured among others by the Spaniards Jorge Juan and Antonio de Ulloa.

The Ibáñez Ibero general founder and first director of the geographical Institute was the first President of the International Committee of weights and measures, which explains the path in the company of both Sciences in Spain, until not many years ago.

In topography get lower to the centimeter measurement uncertainties requires specific methodologies, however in metrology 0.1 mm tends to be overly high accuracy. The major contributions to the uncertainty in conventional topographical works are those associated to the error that is committed to make the aim on the object and the error due to place the instrument on a particular point. In industrial surveying the first aspect is minimized using very precise aim plates adapted to short distances and it solves the second dramatically, by parking not overhang the instrument on a fixed point.

In classical topography field, are two work type that can be made: the uprising lead us to the role (computer) field and the layout or mark on the ground the elements for a draft of which is available on the computer. In industrial surveying the three-dimensional determination of an object would be tantamount to lifting and mounting to the layout.

As for accessories, some typically metrological adapt to these instruments to allow their industrial use. Micrometers of flat plates parallel, eye of autocollimation, pentaprismas, targets, mirrors, eye motors, self-leveling mirrors, objectives of self-reflection, etc., allow these instruments designed for use in geographical sciences, to adapt to industrial purposes.

Usually have micrometre of plates flat parallel that allow read rules graduated with resolutions of 10 µm.

More modern levels replace the human eye by CCD cameras and the prescription rules conventional by others of "bar code", so that it evaluates the height intercepted by a correlation between the image and a reference code. These instruments sacrifice precision, but allow the automation in the gathering of data. They are widely used in the control of deformation of nuclear power stations.

Obviously both the horizontal position of the optical axis of the instrument and the graduation of the used rules must be properly calibrated.

In various industrial applications van fitted with an autocollimation eyepiece, used for the determination of flatness and righteousness, the alignment of axis of rotation of machinery, the calibration of rotary tables or the extent of the angles formed by the faces of a satellite.

Using two Theodolites conveniently oriented is an alternative to traditional measurement machines by coordinates.

The accuracy of this method of optical intersection depends, in addition to the type of theodolite used, the geometry of the measure, the stability of the object to be measured and the Theodolites and environmental conditions. Details of the order of 10-5 in the measures dimension can achieve.

The main advantages of this method of measure 3D contact is not to move the equipment to the room where the piece is placed to measure and to enable the extent of pieces of any size. However, because it is a method of a certain complexity with long measurement times, it can affect the stability of the system and therefore its accuracy.

Some applications of the method of space intersection using Theodolites are the control of robots, naval, space industry and automotive, although it has given way in many of its applications to laser tracking systems.

These systems, like the previous method, are associated with metrological software, enabling them to increase its versatility.

An evolution of this system, improving its accuracy to a large extent, are tracking laser systems. Polar dynamic meters solve the lack of accuracy of the tachometers in the measurement of distances, incorporating a Laser Interferometer. As it does not provide absolute distances, some systems incorporate meters similar to topographic use distances, but resolution Metrology (1 µm). On the other hand, they maintain the dynamism and versatility. The laser trackers eliminated the optical aspect of the instruments topographic incorporating a system of follow-up to the reflector.

This system, is implemented in the industry little by little, though its high price precludes greater use.

Obtaining the 3D coordinates of a point are given by the intersection of the lines defined by the coordinates of the focal point of each House and the fotocoordenadas of the image of the point to be determined. The use of modern digital metric cameras facilitates the process. The accuracy of this method can reach up to 10 µmm, depending on the distance of the object to the cameras and the geometry of the intersection

1. Santos Mora, Antonio. Industrial applications of the topography, COITT. Madrid 1998.
2. Fdez. Couple, Teresa; Bisbal, Javier. Assurance of quality in topography. Topographic instruments, Topcart 2000 metrological control.
3. Prieto, Emilio; Bisbal, Javier. The quality and the topographic instrumentation, Congress Galego da Calidade (2001).

Need for calibration

It has become clear the wide applicability of the topographic instruments in various sectors of the industry. But it should not only be present the end of measurement of the system, but that should include the needs of calibration that this entails. That is why, in the area of length of the Spanish Center of metrology instruments Topográficos laboratory to offer this service has been enabled.

In those cases where not yet be available sufficient information on the most appropriate calibration procedures, are being developed relevant, as e.g. with laser tracking systems studies.