Mass-produced gears typically follow the rolling-shaving-turning process. However, if the gear hobbing machine has significant errors, it becomes difficult to ensure the quality of the final product. To address this issue, researchers have continuously explored simple and effective error compensation technologies for hobbing machines, enabling the modernization and refinement of older equipment. **First, Measurement and Control-Based Refinement Technology** This approach relies on real-time testing and correction. Sensors, such as gratings, are installed on the tool bar and workbench of the hobbing machine, forming a testing system with a computer or microcontroller. A stepping motor is also mounted on the differential axis, creating a control system. During machining, the system measures transmission errors and converts them into drive pulses, which activate the stepping motor to adjust the differential axis. This results in an opposing motion that compensates for the machine's errors, improving the precision of the workpiece. The advantages of this method include flexible operation and easy tooth conversion. However, there are several drawbacks: (1) high costs due to the need for a complete measurement and control system per machine; (2) low reliability, as maintaining a fully functional system in a harsh workshop environment is challenging; and (3) complex installation and shielding of sensors. As a result, this technique has not been widely adopted in industrial settings. **Second, Mechanical Refinement Technology** This method involves one-time testing and the use of eccentric cams to correct transmission errors. By adding one or two cams to each modified machine, the cost remains low, and the system is reliable, simple, and maintenance-free. However, its flexibility is limited—each modification is tailored to specific numbers of teeth, and changing the number of teeth requires retesting and re-machining the cam. This makes it ideal for mass production of gears with few variations, such as those used in automobiles and motorcycles. There are several forms of implementation: 1. **Two-Way Double Eccentric Gear**: One eccentric is split into two, with eccentricity designed based on bidirectional error values. During forward and reverse testing, optimal positions are selected and marked to compensate for errors and misalignment. The gear is then adjusted to ensure smooth rotation and backlash, with pins securing the two teeth in place. This setup effectively corrects errors during both forward and reverse movements. 2. **E-Wheel Eccentric Correction**: Some machines use 5 pairs of bevel gears with a 1:1 ratio, combining their errors into a single frequency. E-wheels are machined with eccentricity, and the phase is calibrated using instruments to offset the errors. 3. **D-Wheel Eccentric Correction**: This method targets periodic errors in worm gears, following a similar principle to the E-wheel approach. It fixes the D-wheel (or E-wheel), reducing the range of possible tooth counts and limiting flexibility. 4. **Differential Chain Correction**: This method uses the differential system to provide additional counter-motion based on measured errors. A single cam is added, with gears and a swinging rod adjusting the motion to compensate for transmission errors. The cam shape is derived from test curves, and with CNC technology, highly accurate corrections can be made, significantly improving machine tool accuracy. **Third, Conclusion** The foundation of mechanical refinement lies in precise measurement. Using systems like FMT, it’s easy to identify and eliminate coarse errors in the drive chain, such as shaft bending or misalignment. Once these are addressed, refinement can focus on hard-to-replace components, like cumulative errors from worm pairs or periodic errors from bevel gears. It’s important to note that once a machine is properly adjusted, it should not be disassembled, as this can disrupt the gear alignment and reduce accuracy. In one case, an old gear hobbing machine was reconstructed in just two days, reducing accumulated error from 13.6 arcseconds to 5.2 arcseconds. The factory immediately moved the machine to a controlled-temperature workshop, highlighting the effectiveness and practicality of this method. This technology is not only simple and user-friendly but also easily adaptable to other types of gear processing machines.

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