Design of high-precision AC servo shearing system

In the plate and strip production enterprises of roll assembly lines, such as rolled steel, aluminum platinum, roll paper, etc., their cutting systems, many enterprises are basically still using the previous closed-loop control system composed of DC or AC frequency conversion. Although the cutting accuracy can meet the basic requirements, it is often not very high. With the development of society, production enterprises keep improving, and it is becoming increasingly important to improve their own brand image, while also meeting customers' increasingly high requirements for products.

System Principle

Figure 1: AC servo shearing system of Kangerda Company.

Assuming the length to be cut is S, the circumference of the active roller is L, and the number of turns of the main roller is N (or angle), then S=LN, which is a linear equation, that is, S and N are proportional. Assuming the ratio of the belt-reducing machine gear is K, S and the number of turns of the motor X can be calculated, S=L*X/K. This formula shows that S and X are still a linear equation. To obtain the required length S, it is only necessary to control the number of turns of the motor. In the original system, the control system is composed of a frequency converter, PLC, encoder and high-speed counting module, in which the PLC given value (the pulse amount corresponding to the length) is sent to the frequency converter to drive the motor to run, and the motor operation drives the encoder to rotate and generate pulses, which are fed back to the high-speed counter and sent to the PLC for comparison with the original given value until the motor stops when they are equal. In actual use, although this system introduces the first and second acceleration and deceleration times to reduce the inertia of the motor by adjusting the frequency converter, the motor stops when it is extremely slow and creeping. However, the accuracy of this system is still not very high. Its disadvantages are: (1) the encoder and the motor are not coaxial and are not integrated; (2) the motor needs to be braked to stop, and the speed and strength of the brake will affect the accuracy.

Process Equipment

■ Operation table - The automatic and manual functions of the length-fixing system are controlled by the main electrical appliance, and the required cutting size is provided by the 8421-coded dial switch.
■ PLC - FX1N-40MT is used. This PLC has a low cost and is equipped with the required high-speed pulse output. One PLC unit can output 2 points of 100KHz pulses at the same time. The PLC is equipped with 7 special instructions, including zero return, absolute position reading, absolute or relative drive, and special pulse output control. It has strong anti-interference ability, is easy to program, has a wide range of uses, and is easy to purchase.
■ Servo motor and driver - The servo motor uses Panasonic servo motor MDMA202A1G. This motor has a coaxial high-precision rotary encoder. The encoder is incremental 2500p/r with a resolution of 10000. The driver uses Panasonic MDDA203A1A and the servo motor system has good control performance. This system has good stability. After setting the parameters, no manual intervention is required. It has high reliability and basically does not require maintenance, so there is no maintenance cost.

Figure 2: Control system hardware diagram.

Control system software

Because Mitsubishi FX1N-40MT is used, ladder diagram language programming is performed with the attached FXGP/WIN software, which is very intuitive and easy to understand. The entire program is concise and convenient to communicate with the driver, which can be completed with relatively simple wiring.

Figure 3: Block diagram.

Figure 4: Process diagram.

Advantages of using AC servo

■ Smooth operation, no vibration at low speed;
■ High control accuracy, the control accuracy of the AC servo is guaranteed by the rotary encoder at the rear end of the motor shaft;
■ Fast response speed, acceleration and deceleration can be completed in a very short time;
■ Constant torque output is not affected by the speed;
■ Has strong overload capacity;
■ The AC servo drive system itself forms a closed loop, and the control is more reliable.

Conclusion

After our company adopted this system, the stability and accuracy were greatly improved, the loss was reduced, the higher requirements of customers were met, and the economic benefits were remarkable. At the same time, it also accumulated experience for future promotion. In the following years, our company successively changed other production lines, and achieved good results at a lower cost. Later, it was also recognized and promoted by peers. All the production lines later adopted similar systems, and abandoned the original variable frequency clamping and feeding method.