In the field of gear measurement, the measurement of large and small gears has always been a technical problem, among which the measurement of super large gears and micro gears belong to the category of “absolute end measurement”. Gear measurement is generally divided into the following three types: analytical measurement based on tooth profile, helix and pitch measurement; functional measurement based on comprehensive measurement (double-sided and single-sided mesh measurement); gear overall error measurement integrating single and comprehensive measurement. For large gears, analytical measurement is mainly used. There are many methods to measure the big gear. According to the position relationship between the machine tool, the measured gear and the instrument, it can be divided into two categories: gear out of position measurement and gear in position measurement.
Gear out of position measurement means that the gear must be removed from the machine tool and moved to the instrument for measurement. Measuring instruments include large-scale gear measuring center and large-scale CMM, which have high precision, good measuring conditions and can measure multiple error items of gears. It is a way of thinking to measure large gear with large-scale instrument, that is to say, to measure large-scale workpiece, we need to develop a larger-scale measuring instrument.
Large gear measuring center
The large gear measuring center is the “amplification” of the conventional medium and small gear measuring center. In addition to the corresponding improvement of the instrument structure, the measurement principle is also different. In general, electronic generating measurement is used in small and medium-sized gear measurement centers, while the large-scale gear measurement center is the synthesis of electronic generating polar coordinate, normal polar coordinate and rectangular coordinate measurement.
China, Germany, the United States and Japan have a number of gear meter factories to produce large gear measuring centers [7]. For example, the 3920 type gear measuring center developed by Harbin Electric Machinery Group Co., Ltd. in 2004 can measure 2 m gear, module 1-32 mm, and the maximum workpiece mass is 10 T. the principle of electronic generation measurement is adopted.
The p150-p350 series gear measuring center (Figure 3) is developed by Klingelnberg company in Germany for the measurement of large gears. The horizontal measuring arm and horizontal three-dimensional series probe are used, and the normal coordinate measurement principle of electronic expansion is generally used for the tooth profile measurement; the polar coordinate measurement principle is used for the gear whose expansion length is greater than the tangent guide stroke of the instrument. The measuring accuracy of this series of instruments can meet the requirements of class 3 gear measurement of iso1328, and the individual error items have reached class 2. Among them, P350 can measure the maximum diameter of workpiece 3.8 m, modulus 1-32 mm, and weight up to 20 t. In addition, the company developed p150w-p350w series gear measuring center according to the particularity of wind power gear measurement. The vertical measuring arm and vertical three-dimensional parallel socket mounted probe are adopted, which are more suitable for the measurement of inner ring gear, planetary gear and sun gear.
WGT series gear measuring center of Wenzel company in Germany can also be used for the measurement of large gears, among which wgt4000 can measure large gears with an outer diameter of 4 m, and the maximum bearing mass can reach 30 t.
The sigma series gear measuring center of Gleason company can measure the maximum diameter of gear 3 m, module 0.8-32 mm, and the maximum weight of workpiece 9 t. Sigma series gear measuring center is equipped with a set of analytical measurement software Gama, which has the characteristics of simple operation, controllable process and real-time display of results. Compared with the same level of instruments, the measurement can save half of the time.
Large CMM
As a universal, automatic and high-precision measurement system, CMM is widely used in industrial production and scientific research. In the last 10 years, the research focus is to use the universal CMM to measure the big gear. This kind of task is usually only the precision CMM can meet the measurement accuracy requirements. The large three coordinate measuring machine is also developed from the traditional medium and small three coordinate measuring machine; up to now, some well-known measuring instrument companies in the world have developed the corresponding large three coordinate measuring machine to solve the measurement problems of large workpieces. For example, Leitz company of Germany has developed pmm-c, pmm-f and pmm-g series of large-scale CMM which can measure large gears. Among them, pmm-g is the most representative (Figure 4) [9], it is a gantry type mechanism, the maximum space measurement range is 6000 mm × 4000 mm × 3000 mm, and there are many kinds of gears that can be measured. For segmented gears, pmm-g has more advantages. As shown in Figure 5, the scheme of measuring 4 segments of 5-m ring gear with pmm-g is adopted.
Zeiss company of Germany also produces MMZ series large gantry CMM for large workpieces, among which mmz-g3000 has the largest space measurement range, which is 3000 mm × 6000 mm × 2000 mm. The instrument is equipped with special software equipped with vast active scanning probe and measuring wind energy system components, which can be used in the production workshop.
German Wenzel company has produced LH series and LHF series of large-scale coordinate measuring machines. In 2008, it also developed a super large measuring machine lhf3020, with a measuring range of 3000 mm × 100000 mm × 2000 mm, which is particularly suitable for the measurement of large gears.
In theory, the problem of measuring big gear with diameter less than 5 m has been solved, but in practice, these bench type measuring instruments are generally installed in the measuring room rather than in the production site. Because of the inconvenient handling of big gear, the installation and debugging of the instruments are also very troublesome, and the high price of the instruments, the application of such instruments is affected. In view of the limitation of the bench type measuring instrument, it is a reasonable choice to put the instrument on the gear or to measure the gear in place on the machine tool.