Stepping motor has the characteristics of fast starting and stopping speed, accurate stepping and positioning, so it is often used as the control element of industrial process control and instruments. At present, the typical control method is to control the stepping motor with the pulse sequence generated by single chip microcomputer. However, the adoption of single-chip microcomputer control not only requires the design of complex control programs and I /O interface circuits, but also has poor adaptability and low reliability to the harsh environment of industrial sites. The stepper motor based on PLC control has the advantages of simple design, convenient implementation, high positioning accuracy and flexible parameter setting. Used in industrial process control, with high reliability and convenient monitoring.

Main characteristics of stepping motor

(1) step angle and static step error: the step angle of stepping motor is an important parameter to determine the pulse equivalent of open-loop servo system. The step angle of reactive stepping motor in CNC machine tools is generally 0.5 ~ 0.3. Generally speaking, the smaller the step angle, the higher the machining accuracy. Static step error refers to the difference between theoretical step angle and actual step angle, which is expressed in minutes and is generally 65430. The stepping error is mainly caused by the manufacturing error of pitch angle of stepping motor, uneven air gap between stator and rotor, and uneven electromagnetic torque of each phase. Stepping error directly affects the machining accuracy and dynamic characteristics of stepping motor.

(2) Dynamic frequency fd: When there is no load, the stepping motor suddenly starts from the static state, and the maximum frequency allowed for normal operation without losing step is called starting frequency or jumping frequency, which is expressed by fd. If the starting frequency is greater than the jumping frequency, the stepping motor cannot be started normally. Fd is related to the load inertia and generally decreases with the increase of the load inertia. When starting with no load, the change frequency of the energized state of the stator winding of the stepping motor cannot be higher than the jump frequency.

(3) The highest working frequency fmax for continuous operation is the acceptable limit frequency fmax for stepping motor to keep running without losing step, which is called the highest working frequency. It is a parameter that determines the highest change frequency of stator winding electrification state, and it determines the highest speed of stepping motor. Its value is greater than fq and varies with the nature and size of the load and the driving power supply.

(4) Acceleration and deceleration characteristics: The acceleration and deceleration characteristics of stepping motor describe the acceleration and deceleration process of stepping motor from static to working frequency and from working frequency to static, and the stator windings are connected.

Relationship between frequency and time of electrical state change. When the stepping motor is required to start and stop at a working frequency greater than the jump frequency, the speed change must be gradually reduced. The acceleration time and deceleration of ascending and descending should not be too small, otherwise there will be out of step or out of step. We use the acceleration time constant to describe the acceleration and deceleration characteristics of the stepping motor, as shown in figure 1.

(5) Moment-frequency characteristics and dynamic torque. Torque-frequency characteristic M=F(f), and figure 1.2 is a curve describing the relationship between torque and frequency. The torque corresponding to each frequency on this characteristic curve is called dynamic torque. It can be seen that the dynamic torque increases or decreases with the continuous frequency.

Except for the first item, the main characteristics of the above stepping motors are closely related to the power supply. The performance of driving power supply is good, and the performance of stepping motor may be improved obviously.

The basic idea of programming

When programming, we must first make clear the specific control requirements of the object. Because of the serial scanning mode of CPU, the input and output will be delayed, and the longest delay time caused by scanning mode can reach two multi-scanning cycles _1j. The longer the program, the more obvious the delay and the lower the control accuracy. Therefore, on the basis of realizing the control requirements, the program should be as simple and compact as possible. On the other hand, for the same control object, the control requirements or control sequence will change according to the different production processes. At this time, it is required that the program modification is convenient and simple, that is, the program should be flexible. Programming with SIMATIC shift instruction as the main body of step control can better meet the above design requirements.

2. Design tasks and requirements

"PLC Programming and Application" is a practical and applied course, and the purpose of learning is application. This course design is an important practical teaching link to cooperate with PLC programming and application teaching. It can consolidate the knowledge learned in class and books, strengthen the comprehensive ability, improve the system design and application ability, and inspire innovative thinking.

I. Control requirements:

1. A five-phase stepping motor has five windings: A, B, C, D, E,

Forward rotation sequence: ABC → BC → BCD → CD → CDE → DE → DEA → EA → EAB → AB.

Reverse order: ABC ← BC ← BCD ← CD ← CDE ← DE ← DEA ← EA ← EAB ← AB.

2. Use five switches to control its operation:

1 switch controls its operation (start/stop).

The No.2 switch controls its low-speed operation (it takes 0.5 seconds to turn a step angle).

The No.3 switch controls the medium-speed operation (it takes 0. 1 second to turn a step angle).

The No.4 switch controls its low-speed operation (it takes 0.03 seconds to turn a step angle).

The No.5 switch controls its steering (turning forward to open and turning backward to close).

Second, the subject requirements:

1. According to the requirements of the topic, draw the PLC terminal wiring diagram and control ladder diagram.

2. Complete the PLC terminal wiring, use the programmer to input the ladder diagram control program, and complete the debugging.

3. Complete the curriculum design specification

According to the above specific control requirements, the program block diagram of stepping motor when starting and running can be made.

If you don't understand, I'll give you extra points and improve. I have a cousin who does this.