3.d round eccentricity correction. At this time, the correction target is the cycle error of the worm pair, and the principle and method are the same as the above 2. This method will make the d wheel (or e wheel) fixed, thus reducing the choice of the matching gear wheel, that is, limiting the range of machining teeth.
4. Use the differential chain to correct. This method is similar to the principle of the above-mentioned measurement and control scheme, that is, using the machine differential system to provide an additional opposite motion to cancel according to the error. But just add a cam here. As shown in Figure 1. The gears a', b', c', d'4 are differential hanging wheels, where a' is replaced by a cam, b' is regarded as a swinging lever, and c' and d' are amplification ratio adjusting gears. a′′～b′′ is the feed suspension wheel set, and a~e are the split tooth suspension wheel sets. Adjust the feed hanging wheel so that the axis of the differential hanging wheel a' rotates synchronously with the machine table, install the cam on the a' shaft, install a swing rod on the b' shaft, and use the spring to ensure that the swing rod and the cam are unidirectional. Closely, the increase in cam will increase the b' axis by a rotary motion that brings an additional motion to the table through c', d', differential mechanisms e, f, a, b, c, d and the worm To offset the previously measured transmission error.
The machining of the cam is based on the test error curve, and the shape of the cam envelope is the shape of the test curve. Early limited to processing means, only cam processing according to the long-period error test curve, and need to leave a certain margin first, then mount the cam and then test, according to the test results, then use the boring tool to correct the cam (the cam material is made of plexiglass) To facilitate processing), so repeated several times. This method is mainly to correct the long cycle error of the machine tool. With the development of computer technology and CNC machining technology, corrections have been made based on transmission error (including long-period error and short-term cycle error) curves. The test curve obtained by the FMT test system [1][2] is composed of 1024 test points per week. After converting these points into the CNC milling machine, the cam with a fairly accurate shape can be processed. Therefore, the long cycle error of the machine tool and most of the short cycle error (a small number of high frequency errors are not reflected due to interference between the wheel and the cam on the pendulum) can be compensated and corrected, and the accuracy is more remarkable.
Third, the conclusion
The premise of realizing mechanical refinement is precision measurement, and after measurement, according to the measurement and analysis results, some large error links in the transmission chain, such as the shaft bent, the hole is biased, the teeth are missing, the sleeve is loose... ...and the first replacement, this work is very easy to do with the FMT test system. On this basis, the inaccurate replacement process, such as the cumulative error caused by the worm pair and the cycle error caused by the bevel gear, can achieve good results.
Also note that once the machine tool is adjusted, do not disassemble it at will, otherwise the accuracy will deteriorate immediately if the gear phase is disordered.
The author once modified an old gear hobbing machine in a factory. In two days, the cumulative error was reduced from 13.6′′ to 5.2′′. The factory immediately moved the machine tool to the constant temperature workshop as a master machine. It can be seen that this scheme is simple and easy to implement, and is very popular among users, and this technology is also easy to be promoted to the transformation of other gear processing machines.
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