Stepper motor bearing grinder and its control system

The use of stepper motor and its control system on the bearing grinder in our country started from the nineties of the last century. For more than ten years, the bearing grinder adopting stepper motor control technology has developed rapidly. At present, Wuxi, Shijiazhuang, Chengdu and Several cities in Henan bearing equipment manufacturers are mass-produced stepper motor control of the bearing grinder. With a large number of stepper motor controlled bearing grinders to the market, the problem of stepper motor system control is also more and more surfaced, single-axis stepper motor control system, the problem is less, but more than two axes Of the stepper motor system, often appear such as the two systems are not synchronized, the size of the instability and other failures. Stepping motor system problems are many. We have done in the ball bearing groove grinder analysis, has tried several brands of stepper motor, found that the two systems are not synchronized very serious. Out-of-sync error tests begin with PLCs, Position Control Modules, stepper motor drivers, and stepper motors. Ball screw lead 4mm, harmonic reducer deceleration ratio of 1:80, step angle of 0.9 ° stepper motor positioning error has exceeded the accuracy of machine tool inspection standards 3 times. According to the pulse equivalent of 0.125 μm calculation, the total station positioning error has reached 0.003 after 20 times. The data in Table 1 shows that not only the error of the stepping motor but also the error of the mechanical system is more obvious. We analyzed the feeding mechanism and the compensation mechanism of this machine and found that the mechanical problems were also serious. First, the nominal diameter of the ball screw is too small (Φ20), the accuracy level of 3 is low, and feel the phenomenon of crawling more serious; Second, the feed cylinder and ball screw fast positioning, assembly position deviation can not be eliminated; Third, the harmonic reducer and ball screw only screw locking no key connection or pin link; fourth, did not use ball screw bearings and so on. Then we analyzed the electrical system of the machine tool and found that the frequency converter, transformer and stepper motor controller placed in close proximity, the data cable output from the PLC is not shielded, with a plate of strong and weak cable mixing, and so on . These problems are all factors that affect the instability of the stepper motor system. , The pulse equivalent is 0.125 μm. Due to the poor anti-interference ability of the stepper motor system in our country at present, the unreasonable layout of these electrical designs will directly produce the accidental feed system and the compensation system error. Combined with the systematic error of the mechanical system, the machine tool will be in an unstable work status. Not to say that as long as the machine's hydraulic feed compensation system into a stepper motor feed compensation system, the machine's overall performance will certainly be significantly improved. Stepper motor replaces the original complex hydraulic feed compensation system, the original hydraulic fluctuations and mechanical parts processing transmission chain error eliminated, and the stepper motor feed process can be divided into several stages, each stage can choose different Of the pulse frequency control feed rate, you can use the number of pulses to control the machine table refined to give, which is indeed a hydraulic system than the original bearing grinder a big step forward. However, what follows is that other related parts of the machine tool should also be updated with the design to meet the requirements of machine tool grinding. No matter the design of the mechanical structure or the design of the electrical system, the weak anti-interference ability of the stepping motor system should not be neglected. If our solutions to the above problems are not properly addressed, the bearing grinder controlled by a stepper motor system would not be inherently provided that the overall components of a machine tool, especially the critical components, are still standards for the original machine tool hydraulic system Improve. Of course, the most thorough way is to adopt the most advanced servo motor control system in the world. Servo motor control system using the bearing grinder, the fast cylinder and harmonic reducer removed, the use of ball screw and servo motor direct-coupled structure, making the smallest mechanical system error. Although the majority of our country adopts the servo motor control system of the bearing grinder most of the pulse control, but the servo motor's comprehensive ability to drive, anti-interference ability and repeat positioning accuracy than the stepper motor bearing grinder has taken a big step forward. Because of the characteristics of the stepper motor system and many BUG, ​​it is only a transitional product of mechanical hydraulic control to the middle of the servo system control. Almost few foreign countries now see the use of precision motor controlled stepper motor grinder, and our country is CNC machine tools On the application of stepping motor system longest time countries. As China's bearing industry to speed up technological innovation, with more and more high-quality processing bearing the development of enterprises, stepper motor control of the bearing grinder will eventually be replaced by a servo motor.