Application selection of stepper motor drive control system

    The stepper motor is an open-loop control element that converts an electrical pulse signal into an angular displacement or a linear displacement. In the case of non-overload, the speed and stop position of the motor depend only on the frequency and number of pulses of the pulse signal, and are not affected by the load change, that is, when a pulse signal is added to the motor, the motor rotates a step angle. The existence of this linear relationship, coupled with the characteristics of the stepper motor having only periodic errors and no cumulative errors, makes it very simple to use stepper motors to control speed, position and other control fields.
Although stepper motors have been widely used, stepper motors cannot be used under normal conditions like ordinary DC motors and AC motors. It must be composed of a control system consisting of dual-ring pulse signals, power drive circuits, etc. before it can be used. Therefore, it is not easy to use stepper motors well, and it involves many professional knowledge such as machinery, motors, electronics and computers.
At present, there are indeed many manufacturers that produce stepper motors, but there are very few manufacturers that have professional technicians and can develop and research on their own. Most manufacturers have only one or twenty people, and do not even have the most basic equipment. They are only in a blind imitation stage. This causes a lot of trouble for users in product selection and use. The stepper motor is an open-loop linear actuator that converts electrical pulse signals into angular displacement or linear displacement. It has the characteristics of no cumulative error, low cost and simple control. The products are divided into two, three, four and five phases in terms of the number of phases, 0.9°/1.8°, 0.36°/0.72° in terms of step angle, 42~φ130 in terms of specifications, and 0.1N•M~40N•M in terms of static torque.
The use and control of stepper motors must be composed of a control system composed of ring pulses, power amplifiers, etc.
1. Generation of pulse signals. Pulse signals are generally generated by a single-chip microcomputer or CPU. Generally, the duty cycle of the pulse signal is about 0.3-0.4. The higher the motor speed, the greater the duty cycle.
2. Signal distribution. The induction stepper motors produced by our factory are mainly two-phase and four-phase motors. The working modes of two-phase motors are two-phase four-beat and two-phase eight-beat. The specific distribution is as follows: two-phase four-beat, the step angle is 1.8 degrees; two-phase eight-beat, the step angle is 0.9 degrees. There are also two working modes of four-phase motors. Four-phase four-beat is AB-BC-CD-DA-AB, the step angle is 1.8 degrees; four-phase eight-beat is AB-B-BC-C-CD-D-AB, (the step angle is 0.9 degrees).
3. Power amplification. Power amplification is the most important part of the drive system. The torque of the stepper motor at a certain speed depends on its dynamic average current rather than the static current (and the current on the sample is the static current). The larger the average current, the greater the motor torque. To achieve a large average current, the drive system needs to overcome the motor's back electromotive force as much as possible. Therefore, different driving modes are adopted in different occasions. So far, the driving modes generally include the following: constant voltage, constant voltage series resistance, high and low voltage drive, constant current, subdivision number, etc. In order to maximize the dynamic performance of the motor, the signal distribution and power amplification form the drive power supply of the stepper motor. The wiring diagram of the SH series two-phase constant current chopper drive power supply, the single-chip microcomputer and the motor is as follows:

Description:
CP connects to the CPU pulse signal (negative signal, low level is effective)
OPTO connects
to the CPU +5V FREE offline,
connected to the CPU ground line, the drive power supply does not work DIR direction control, connected to the CPU ground line, the motor reverses
VCC DC power supply positive terminal
GND DC power supply negative terminal
 A connects to the motor lead wire red
   wire connects to the motor lead wire green wire
 B
   connects to the motor lead wire yellow wire connects to the motor lead wire blue wire
Application of stepper motor: selection of stepper motor. Stepper motors are composed of three major elements: step angle (involving the number of phases), static torque, and current. Once the three major elements are determined, the model of the stepper motor is determined.
1. Selection of step angle: The step angle of the motor depends on the load accuracy requirements. The minimum resolution (equivalent) of the load is converted to the motor shaft, and each equivalent motor should move how many angles (including deceleration). The step angle of the motor should be equal to or less than this angle. At present, the step angles of stepper motors on the market are generally 0.36 degrees/0.72 degrees (five-phase motors), 0.9 degrees/1.8 degrees (two- and four-phase motors), 1.5 degrees/3 degrees (three-phase motors), etc.
2. Selection of static torque: The dynamic torque of a stepper motor is difficult to determine at once, so we often determine the static torque of the motor first. The basis for selecting the static torque is the load of the motor, and the load can be divided into two types: inertial load and friction load. A single inertial load and a single friction load do not exist. When starting directly (generally at low speed), both loads must be considered. When accelerating to start, the inertial load is mainly considered, and when running at a constant speed, only the friction load needs to be considered. In general, the static torque should be within 2-3 times of the friction load. Once the static torque is selected, the motor base and length can be determined (geometric dimensions).
3. Current selection: Motors with the same static torque have very different operating characteristics due to different current parameters. The motor current can be determined based on the torque-frequency characteristic curve (refer to the drive power supply and drive voltage).
4. Torque and power conversion: Stepper motors are generally used for speed regulation in a large range, and their power is variable. Generally, only torque is used to measure it. The torque and power conversion is as follows: P= Ω•M
        Ω=2π•n/60
       P=2πnM/60
, where P is power in watts, Ω is angular velocity per second in radians, n is speed per minute, and M is torque in Newton meters. P=2πfM/400 (half-step operation) where f is the number of pulses per second (PPS for short). In
summary, the following steps should be followed when selecting a motor: