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Mechanical refinement technology of gear hobbing machine

abstract the advantages and disadvantages of measurement and control refinement technology of gear hobbing machine are analyzed, and a mechanical cam refinement scheme based on precision measurement is proposed, which has good popularization value. The principle and implementation method of this scheme are introduced in detail

key words: precision measurement of gear hobbing machine

gear in mass production generally adopts the processing technology of rolling shaving honing. If the error of gear hobbing machine is large, the gear quality will be difficult to guarantee. Therefore, people continue to explore simple and effective hobbing machine error correction and compensation technology, so that the old machine tools have been refined

I. measurement and control precision technology

this scheme adopts the principle of real-time testing and real-time correction. A sensor (grating, etc.) is installed on the cutter bar and workbench of the gear hobbing machine respectively, and a test system is formed with a computer (single chip microcomputer); In addition, a stepping motor is installed on the differential shaft to form a control system with the computer. Only when the machining movement of the machine tool is carried out at the same time, the measurement and compensation control of the experimental machine with accuracy of 0.5 level are required. Computer 4. In medical instruments, according to the measured transmission error, it is converted into the corresponding number of driving power pulses, so that the stepping motor drives the differential shaft to rotate, so that the workbench can get an additional compensation motion opposite to the transmission error, so as to correct the machine tool error and improve the workpiece processing accuracy

this scheme has the advantages of flexible working mode and convenient transformation of tooth number; The disadvantages are: (1) the adjusting lead screw is installed on the upper beam of the experimental machine, and the transformation of each machine tool requires a full set of detection and control system; (2) The reliability is poor. It is almost impossible to ensure that the whole system will not go wrong for a long time with the progress of production all the time in the harsh environment of the workshop; (3) The installation, location and shielding of sensors are troublesome. Therefore, this scheme has not been popularized in production

II. Mechanical refinement technology

the common standard of friction and wear testing machine. This scheme adopts one-time test. According to the test results, the eccentric cam is processed, and the transmission error is corrected and compensated by adding the transmission chain. Its advantage is that only 1 ~ 2 cams are added to each transformed machine tool, which has the advantages of low cost, reliable and simple operation and no maintenance; The disadvantage is that the flexibility is poor. Each refinement transformation can only be for one or a few gears with a few teeth. If you want to change the number of teeth, you need to re measure and remake the cam. Therefore, this method is suitable for manufacturers of gears with large batch and few varieties, such as automobile and motorcycle gears. The specific implementation of this scheme has the following forms

1. Two way double eccentric gear. An eccentric wheel is crosscut into two, and its eccentricity is designed according to the error values of the positive and negative directions of the correction shaft. During the forward and reverse motion test, select the phase under the monitoring of the instrument, mark it, find the best position of their error compensation and tangential dislocation, turn a distance to ensure that the forward and reverse rotation motion is borne by only one gear, and ensure a certain backlash. Finally, fix the two teeth with the shaft with a pin. In this way, the two eccentric gears actually occupy the original gear position. This device can solve the error correction of positive and negative direction movement

2. E wheel eccentricity correction. As shown in the figure below, some machine tools have a total of 5 pairs of bevel gears with 1:1 transmission ratio from the gear behind the hob to the differential mechanism. In this case, their respective errors are synthesized into single errors of the same frequency. As long as the E-wheel is processed into eccentricity and the phase is found by instrument testing, it can be offset

gear hobbing machine transmission chain diagram

3 D wheel eccentricity correction. At this time, the correction object is the periodic error of the worm gear, and the principle and method are the same as those in 2 above. This method will make the d-wheel (or E-wheel) fixed, thus reducing the choice of gear change gear matching, that is, limiting the variation range of the number of machined teeth

4. The differential chain is used for correction. This method is similar to the principle of the aforementioned measurement and control scheme, that is, using the machine tool differential system to provide an additional opposite motion to offset according to the size of the error. But here you only need to add a cam. As shown in Figure 1. The four gears a ', B', C ', d' are differential change gears, where a 'is replaced by a cam, B' is used as a swing rod, and C 'and d' are amplification ratio adjustment gears. A ″ ~ B "refers to the feed change gear group, and a ~ e refers to the divided gear change gear group. Adjust the feed change gear so that the shaft of the differential change gear a 'rotates synchronously with the machine tool workbench. Install a cam on the a' shaft and a swing rod on the B 'shaft. Use a spring to ensure that the swing rod is close to the cam in one direction. The increase of the cam will add a rotary motion to the B' shaft. This motion brings an additional motion to the workbench through C ', d', differential mechanisms e, F, a, B, C, D and worm to offset the transmission error measured earlier

the machining of the cam is determined by the test error curve, and the shape of the cam envelope is the shape of the test curve. In the early stage, it was limited to processing means, but the cam was processed according to the long-period error test curve, and a certain margin was required to be left first, and then the cam was installed for testing. According to the test results, the cam was corrected with a file (the cam material was made of plexiglass to facilitate processing), which was repeated several times. This method is mainly to correct the long-period error of machine tools. With the development of computer technology and NC machining technology, it has begun to correct according to the transmission error (including long-term periodic error and short-term periodic error) curve. The test curve obtained by using the FMT test system [1] [2] is composed of 1024 test points in a week. After these points are converted and input into the NC milling machine, the cam with fairly accurate shape can be processed. Therefore, the long-period error and most of the short-period error of the machine tool (a few high-frequency errors cannot be reflected due to the interference between the backup wheel on the swing rod and the cam) can be compensated and corrected, and the accuracy can be improved more significantly

III. conclusion

the premise of realizing mechanical refinement is precision measurement, and after measurement, according to the measurement and analysis results, some gross error links in the transmission chain, such as shaft bending, hole deviation, missing teeth, loose shaft sleeve... Should be adjusted first

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