What Are Stepper Motors?

Stepping motor is an open-loop control motor that converts electrical pulse signals into angular displacement or linear displacement. It is the main executive element in modern digital program control systems and is widely used. Under non-overload conditions, the speed and stop position of the motor only depend on the frequency and number of pulse signals, and are not affected by the load change. When the stepper driver receives a pulse signal, it drives the stepper motor according to The set direction rotates by a fixed angle, called "step angle", and its rotation runs step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve accurate positioning; at the same time, the speed and acceleration of motor rotation can be controlled by controlling the pulse frequency to achieve the purpose of speed regulation.

Stepping motor is also called pulse motor. Based on the most basic electromagnet principle, it is an electromagnet that can rotate freely. Its action principle is to rely on the change of air-gap permeability to generate electromagnetic torque. Its original model originated from year to year. At the beginning of this year, attempts to control were applied to the electrode transport mechanism of hydrogen arc lamps. This is considered the first stepper motor. In the early twentieth century, stepper motors were widely used in automatic telephone exchanges. As western capitalist powers vie for colonies, stepper motors have been widely used in independent systems such as ships and aircraft that lack AC power. The invention of the transistor in the late 1950s was also gradually applied to stepper motors, making digital control easier. After the 1980s, as inexpensive microcomputers appeared with a multifunctional attitude, the control methods of stepper motors became more flexible and diverse. ^[1]

Stepping motors can be divided into reactive stepping motors (Variable Reluctance, VR), permanent stepper motors (Permanent Magnet, PM), hybrid stepping motors (Hybrid Stepping, HS), and single-phase stepping. There are many types of stepping motors, planar stepping motors, etc. Among the stepping motors used in China, reactive stepping motors are the main types. The running performance of stepper motor is closely related to the control mode. From the control mode of stepper motor control system, it can be divided into the following three categories: open loop control system, closed loop control system, and semi-closed loop control system. Semi-closed-loop control systems are generally classified as open-loop or closed-loop systems in practical applications. ^[1]

Stepper motor and driver selection method:

Determine how much torque is needed: Static torque is the step of choice

Stepping motor is also called

1 PID control

PID control, as a simple and practical control method, has been widely used in stepper motor drive. It forms the control deviation e (t) according to the given value r (t) and the actual output value c (t). The proportional, integral and differential of the deviation form a control quantity by linear combination to control the controlled object. The literature uses integrated position sensors in two-phase hybrid stepping motors. Based on the position detector and vector control, an automatically adjustable PI speed controller is designed. This controller can be used under variable operating conditions. Provides satisfactory transient characteristics. According to the mathematical model of the stepper motor, the literature designs a PID control system for the stepper motor. The PID control algorithm is used to obtain the control amount, thereby controlling the motor to move to the specified position. Finally, simulations show that the control has good dynamic response characteristics. The PID controller has the advantages of simple structure, strong robustness and high reliability, but it cannot effectively deal with uncertain information in the system. ^[2]

Stepper motors convert pulse signals into angles

This module can be divided into the following 3 parts:

· Single-chip computer system: control stepper motor;

· Peripheral circuit: interface circuit between PIC microcontroller and stepper motor;

· PIC program: write the interface program of single-chip microcomputer to control stepping electric machine to realize the output function of triangle wave signal.

(1) Interface between stepping motor and single-chip microcomputer.

The single-chip microcomputer is a control processor with excellent performance. When controlling the operation of the stepper motor, the interface components must have the following functions.

Voltage isolation function.

The single chip microcomputer works at 5V, while the stepper motor works at tens of V or even higher. Once the voltage of the stepping motor is connected to the single-chip microcomputer, the single-chip microcomputer will be damaged; the signal of the stepping motor will interfere with the single-chip microcomputer, and may also cause the system to malfunction. Therefore, the interface device must have an isolation function.

Information transfer function.

The interface component should be able to pass the control information of the single-chip microcomputer to the stepper motor circuit to generate the control information required for work. Corresponding to different working modes, the interface component should be able to generate the corresponding work control waveform.

Generate different frequencies required.

In order to make the stepper motor work at different speeds to suit different purposes, the interface components should be able to produce different operating frequencies.

(2) Voltage isolation interface.

The voltage isolation interface is specially used to isolate the low-voltage part of the single-chip microcomputer and the high-voltage part of the stepper motor drive circuit to ensure their normal work.

The voltage isolation interface can use a pulse transformer or a photo-isolator. Basically, a photo-isolator is used. The output signal of the single-chip microcomputer can be sent to the base of the transistor through the TTL gate circuit, and then the light-emitting diode of the photoelectric coupling device is driven by the transistor.

The light from the light-emitting diode is irradiated onto the photosensitive tube inside the photoelectric coupling device, converted into an electric signal, and then drives the power amplifier circuit of the stepper motor. The current amplifier interface is a preamplifier circuit of the stepper motor amplifier circuit. Its role is to amplify the output signal of the opto-isolator in order to provide a sufficient driving current to the power amplifier circuit.

(3) Working mode interface and frequency generator.

To control a stepper motor with a single chip microcomputer, you need to control the stepper motor with three I / 0 lines on the input and output interface. At this time, the single chip microcomputer controls the three phases of the stepper motor with RA0, RAI, RA2 of the I / O port.

Stepper motors cannot be directly connected to the power frequency AC or DC power supply.

1. Can provide fast current rising and falling speed,

The stepping motor is composed of three major factors: the step angle (involving the number of phases), the static torque, and the current.

1. The stepper motor is used in low-speed occasions --- the speed per minute does not exceed 1000 rpm (6666PPS at 0.9 degrees), it is best to use between 1000-3000PPS (0.9 degrees), you can use the reduction device to make it work here, At this time, the motor has high working efficiency and low noise;

2. It is better not to use the full-step state for stepping motors, and the vibration during the full-step state is large;

3. For historical reasons, only 12V rated motors use 12V. The voltage of other motors is not the driving voltage. You can choose the driving voltage according to the driver (recommended: 57BYG uses DC 24V-36V, 86BYG uses DC 50V, 110BYG uses higher than DC 80V). Of course, 12V voltage can be used in addition to 12V constant voltage drive, but other drive power can be used, but temperature rise must be considered;

4. For the load with large moment of inertia, a large frame size motor should be selected;

5. When the motor is at a relatively high speed or a large inertia load, it generally does not start at the working speed, but gradually increases the frequency to increase the speed. One motor does not lose steps, and the second can reduce the noise and improve the positioning accuracy of the stop;

6. For high accuracy, it should be solved by mechanical deceleration, increasing the speed of the motor, or using a driver with a high number of subdivisions. A 5-phase motor can also be used, but the entire system is more expensive and there are fewer manufacturers. The saying is layman;

7. The motor should not work in the vibration zone. If necessary, it can be solved by changing the voltage, current or adding some damping;

8. If the motor works below 600PPS (0.9 degrees), it should be driven by small current, large inductance and low voltage;

9. The principle of selecting the motor first and then the drive should be followed.