The invention relates to a method for positioning a measuring device emitting and receiving optical radiation for measuring wear in the lining of a container, said method comprising fixing the coordinate systems set for the measuring device and the container, said fixing comprising mathematically combining the coordinate systems of the measuring device and the container by measuring the position of specific fixing points in the coordinate system of the measuring device.
It is extremely significant to measure wear in the lining of converters or ladles used in steel making. This renders it possible to optimize the service life of the container and to prevent excessive wear in the lining from causing risks pertaining to production or industrial safety. Wear linings of converters must be renewed relatively often, as their life time varies from a week or two normally to no more than a few months, depending on what is melted in the converter, on the material of which the lining is made, and naturally on the number of meltings for which the converter is used. Generally speaking, a converter can last for about 100 to 5000 meltings.
The wear in a lining is measured by a method based on measuring the propagation time or phase difference of a laser beam: the laser beam is directed to the lining on the inner surface of a converter, from which it is reflected back to the measuring device. In the method based on measuring the propagation time, the distance between the measuring device and each measured point on the lining to be measured in the coordinate system of the measuring device can be calculated on the basis of the time difference between the emitting time and the return time of the laser beam. The measured points define the wear profile of the lining, which may be output for instance to a display terminal, by which the wear profile measured from a converter in use can be compared graphically and numerically with the profile that was measured of the inner surface of the same container during the modelling step before the container was actually brought into use, i.e. before the first melting.
To measure wear in the lining of three-dimensional objects, such as converters, ladles and other containers used in the steel industry, by non-contacting methods, such as laser measurement, requires that the measuring device and the object to be measured be represented in the same coordinate system. Combining the coordinate systems of the measuring device and the object to be measured is called fixing. In other words, the measuring device is positioned in relation to the object. For the fixing, it is necessary to use at least three fixing points to each of which the laser beam of the measuring device is directed in turn, and from which the coordinates of each fixing point in the coordinate system of the measuring device are measured. Even if the measuring device has a fixed or semi-fixed position in the vicinity of the container, it is necessary, in any case, to perform the fixing separately for each lining measurement; thus it is ensured that a change in the ambient conditions, and other factors do not cause any errors. To perform fixing each time all over again is also necessary in order that to estimate whether the fixing has succeeded.
In the so-called direct procedure normally used for positioning, or fixing, stationary fixing points are mounted on the object to be measured such as a container--more specifically, in the vicinity of the container opening. By means of the fixing points, the coordinate systems of the object and the measuring device can be mathematically combined. In the direct procedure, the object to be measured and the measuring device can be included in the same coordinate system by measuring at a time both the fixing points and the points to be actually measured.
In a special case where the object to be measured is supported by a pivoted axle, it is possible to use indirect angle measurement fixing, in which the fixing points are located outside the container. An angle measuring device can be mounted, for example, on the pivoted axle of the container or elsewhere in the container if a so-called inclinometer is employed. At present, fixing by means of angle measurement is an indirect method which is used when it is impossible to provide the object to be measured with necessary fixing points which are clearly visible and whose position is even otherwise suitable. Angle measurement fixing has been performed using fixing points in structures outside the object to be measured and an angle value obtained from the angle measurement device; this has allowed the coordinate systems to be mathematically combined. The fixing points have been attached to the frame structures of a factory wall, for example, in proximity to the converter. When angle measurement is used in the known methods, the angle measurement device informs the measuring device of the position of the object, or container, in relation to the known environment.
In both direct and indirect angle measurement fixing, the fixing points are, for example, small steel plates, to which the laser beam emitted by the measuring device is manually directed, for instance by means of binoculars or some other instrument. In these known methods, the aim is to direct the laser beam manually to the centre of the fixing point; in order that the fixing could succeed, the operators of the measuring device are thus required to perform several operations before all fixing points have been measured. The drawback of these known methods is that it is difficult to automate the fixing operation; in addition, when the fixing is performed by a human being, there is a risk of errors in both the estimation of the centre of the fixing point and the actual directing step.