A new method for measuring the downward deflection

2022-08-16
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A new method for measuring the deflection value of the main beam of a crane after loading

during the regular inspection and acceptance inspection of the crane, the deflection value of the main beam at rated load and the permanent deformation of the main beam during static load test must be measured. Usually, the traditional measurement method is to use a level gauge, theodolite or arch gauge to align the ruler pasted in the middle of the main beam span, and measure the difference between the changes before and after the lifting load, so as to calculate the deflection value of another 10 in the large plastic market

however, when measuring with a level, it will be limited by the site, and in most cases, the level cannot be erected; When measuring with theodolite, it will produce visual error and bad field light. Especially at the beginning of lifting, the crane sometimes moves horizontally because the lifted weight does not leave the ground at the same time, which makes the measurement fail; However, the workload of sticking and taking scales each time is large, and the labor intensity is also great. In case of electric single beam crane, it is more difficult to stick and take the ruler, and there is a certain danger. It is quite tedious and inaccurate to measure with the arch measuring instrument. In view of the above situation, distotm classic5a handheld laser rangefinder (with a measurement accuracy of ± 1.5mm) from LecA geosystemsag of Switzerland can be used to measure the deflection value

the specific method is:

use the tripod of the level or theodolite, use the horizontal bubble on the laser rangefinder to adjust the tripod, and adjust the basic level of the installation plane on the upper part of the tripod. Place the laser rangefinder vertically upward on the installation plane on the upper part of the tripod, align it with any point on the lower plane of the main beam midspan, and measure the distance difference between the lower plane of the main beam before and after the lifting load and the laser rangefinder, that is, the downward deflection value. With this method, the measurement is quite accurate, because the repeatability of sudden heat cooling is good; And convenient, fast, greatly reducing the labor intensity. At present, this kind of measurement method is rarely used in China, and it is a more advanced downward deflection measurement method at present

when the crane is lifted, a small horizontal movement will have a great impact on the measurement results. In addition, even if there is a certain error in the perpendicularity of the laser rangefinder on the installation plane on the upper part of the tripod, due to the poor machining accuracy and assembly quality of the hydraulic components, the vertical deflection angle is very small, and the error of the length change in the vertical direction is almost 0, which can be ignored. So the measurement is very accurate. Moreover, the accidental horizontal movement of the crane during lifting has little impact on the measurement results

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