A stepper motor driver is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called “step angle”) in the set direction, and its rotation runs step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses, so as to achieve the purpose of accurate positioning; at the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, so as to achieve the purpose of speed regulation and positioning.
A stepper motor and a stepper motor driver constitute a stepper motor drive system. The performance of the stepper motor drive system depends not only on the performance of the stepper motor itself, but also on the quality of the stepper motor driver. The research on the stepper motor driver is carried out almost simultaneously with the research on the stepper motor.
Stepper motors are classified by structure: stepper motors are also called pulse motors, including reactive stepper motors (VR), permanent magnet stepper motors (PM), hybrid stepper motors (HB), etc.
(1) Reactive stepper motor: also called induction, hysteresis or reluctance stepper motor. Both the stator and the rotor are made of soft magnetic materials. The evenly distributed large magnetic poles on the stator are equipped with multi-phase excitation windings. Small teeth and slots are evenly distributed around the stator and rotor. After electrification, the change of magnetic permeability is used to generate torque. Generally three, four, five, six phases; can achieve high torque output (large power consumption, current up to 20A, high driving voltage); small step angle (minimum 10′); power off There is no positioning torque; the internal damping of the motor is small, and the oscillation time of single-step operation (when the pulse frequency is very low) is long; the starting and operating frequency are high.
(2) Permanent magnet stepping motor: Usually the motor rotor is made of permanent magnet material, and the stator made of soft magnetic material has multi-phase excitation windings. There are no small teeth and slots around the stator and rotor. The stator current and magnetic field interact to generate torque. It is generally two-phase or four-phase; the output torque is small (the power consumption is small, the current is generally less than 2A, and the driving voltage is 12V); the step angle is large (such as 7.5 degrees, 15 degrees, 22.5 degrees, etc.); The holding torque; the starting and running frequency is lower.
(3) Hybrid stepping motor: also called permanent magnet reaction type, permanent magnet induction type stepping motor, which combines the advantages of permanent magnet type and reactive type. There is no difference between the stator and the four-phase reactive stepping motor (but the two magnetic poles of the same phase are opposite, and the N and S polarities generated by the windings on the two magnetic poles must be the same), and the rotor structure is more complicated (the inside of the rotor is a cylindrical permanent Magnet with soft magnetic material at both ends, with small teeth and grooves around it). Generally two-phase or four-phase; positive and negative pulse signals must be supplied; the output torque is larger than that of the permanent magnet type (the power consumption is relatively small); the step angle is smaller than that of the permanent magnet type (generally 1.8 degrees); Positioning torque; higher starting and operating frequency; a stepping motor with faster development.
A motor driver is an essential device that provides the required voltage and current to the stepper motor for smooth operation. A stepper motor is a stepping and rotating DC motor. It cannot be directly connected to a DC or AC power supply, and a dedicated drive power supply (stepper motor driver) must be used.
To design a stepper motor driver, it is very important to choose the right power supply, microcontroller and motor driver. It is well known that microcontrollers can be used to control rotating electrical machines, but when designing a drive, attention must be paid to voltage and current.
A single motor driver board can handle the current and voltage of the motor, while the stepper motor is turned precisely by using the controller by synchronizing the pulse signal with the help of the driver. This motor driver receives the pulse signal from the microcontroller and converts it into the motion of the stepper motor.
What is a stepper motor driver?
A motor driver that drives a motor to continuously rotate like a stepper motor by controlling precise position without using a feedback system is called a stepper motor driver. The driver of this motor mainly provides variable current control and multi-step resolution. Additionally, the stepper motor drivers include fixed converters, allowing the motor to be controlled with simple step and direction inputs.
Stepper motor drivers consist of different types of ICs and operate on less than 20V supply voltage. Low voltage and low saturation voltage ICs are best used in two-phase stepper motor drivers, which are used in different portable devices such as cameras, printers, etc.
Main parameters of stepper motor
The number of phases of the stepper motor: refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, and five-phase stepper motors are commonly used.
Number of beats: the number of pulses or conductive state required to complete a periodic change of the magnetic field, expressed in m, or the number of pulses required for the motor to rotate through a pitch angle.
Holding torque: refers to the moment when the stepper motor is energized but not rotating, the stator locks the rotor.
Step angle: corresponding to a pulse signal, the angular displacement of the motor rotor.
Positioning torque: The locking torque of the motor rotor itself when the motor is not powered.
Out of step: The number of steps that the motor runs when it is running is not equal to the theoretical number of steps.
Misalignment angle: The angle at which the rotor tooth axis deviates from the stator tooth axis. There must be an misalignment angle when the motor is running. The error caused by the misalignment angle cannot be solved by subdivision driving.
Running torque-frequency characteristics: The curve of the relationship between the output torque and frequency during the operation of the motor measured under certain test conditions.
Stepper motor drivers come in different voltage and current ratings. Therefore, it can be selected according to the requirements of the motor to be used. Most of these drives are available in 0.6 by 0.8 inches.
working principle
A stepper motor driver works by controlling the operation of a stepper motor by sending current in the direction of the motor using various pulse phases. Designers do not often use wave drive technology because it provides low torque, is inefficient, and can only use 1 phase of the motor at a time.
The basic components used today to drive stepper motors are controllers such as microprocessors/microcontrollers, driver ICs, and PSUs (power supply units), and other components such as switches, potentiometers, heat sinks, and connecting wires.
1. Controller
The first step is to select the microcontroller to design the driver. For stepper motors, this microcontroller should have at least four output pins. In addition, it also includes ADC, timer, serial port based on driver application.
2. Motor driver
Motor driver ICs are inexpensive and easy to implement in terms of design, which speeds up the overall circuit design time. The drive can be selected based on motor ratings such as voltage and current. The most popular motor drivers, such as the ULN2003, are used in non-H-bridge applications and are also suitable for driving stepper motors. The driver includes a Darlington pair and can handle a maximum current of up to 500mA and a maximum voltage of up to 50VDC. A stepper motor is an open-loop control motor that converts electrical pulse signals into angular displacement or linear displacement, also known as a pulse motor.
In the case of non-overload, the speed and stop position of the motor only depend on the frequency and pulse number of the pulse signal, and are not affected by the load change. When the stepper driver receives a pulse signal, it can drive the stepper motor to rotate a fixed angle in the set direction, which is called “step angle”. The rotation of the stepper motor 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 the motor can be controlled by controlling the pulse frequency. So as to achieve the purpose of speed regulation. Stepper motors are mostly used in peripheral equipment of digital computers, as well as devices such as printers, plotters, and disks.
The position and speed signals of the stepper motor are not fed back to the control system. If the position and speed signals of the motor are fed back to the control system, then it belongs to the servo motor. Compared with servo motors, the control of stepper motors is relatively simple, but it is not suitable for occasions with high precision requirements. The advantages and disadvantages of stepper motors are very prominent. The advantages focus on simple control and high precision. The disadvantages are noise, vibration and efficiency. It has no cumulative error, simple structure, convenient use and maintenance, and low manufacturing cost. The stepper motor has a large ability to drive the load inertia, and is suitable for small and medium-sized machine tools and places where the speed accuracy is not high. The disadvantages are low efficiency, high heat generation, and sometimes “out of step”. The pros and cons are listed below.
advantage:
1. The operation of the motor is easy to control by inputting the pulse signal to the motor;
2. No feedback circuit is required to return the position and speed information of the rotating shaft (open loop control);
3. Greater reliability due to no contact brushes.
shortcoming:
1. Need pulse signal output circuit;
2. When the control is not appropriate, there may be a loss of synchronization;
3. Heat is generated due to the current flowing after the rotating shaft stops.
The step driver can be divided into two parts, one is the ring distributor, and the other is the power amplifier.
Ring distributor: If it receives 3 kinds of signals, they are: pulse signal, direction signal and offline signal. Then the pulse signal is distributed to control the corresponding transistor of the power amplifier to be turned on, and then the coil of the stepping motor is energized. From here we can see that if the stepper motor is to run, it must input pulses. If there is no pulse, the stepper motor will not move, so we need a driver to energize the windings of the stepper motor in turn.
Direction signal: To control the phase sequence of AB energization, A-B clockwise, B-A counterclockwise
Off-line signal: When the stepping motor stops, one phase of the AB coil is energized, and the function of energization locks the rotor so that the rotor cannot move. When the power is completely cut off, the rotor is in a state of free rotation.
The principle of the stepper motor driver is powered by a unipolar DC power supply. As long as the phase windings of the stepping motor are energized according to the appropriate timing, the stepping motor can be rotated step by step.
Does the subdivision number of the subdivision driver represent the accuracy?
The subdivision technology of the stepper motor is essentially an electronic damping technology (please refer to the relevant literature). Its main purpose is to weaken or eliminate the low-frequency vibration of the stepper motor. Improving the running accuracy of the motor is only an incidental function of the subdivision technology. For example, for a two-phase hybrid stepper motor with a step angle of 1.8 degrees, if the subdivision number of the subdivision driver is set to 4, then the motor’s operating resolution is 0.45 degrees per pulse, and whether the motor’s accuracy can reach or approach 0.45 degrees, it also depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drivers from different manufacturers may vary greatly; the greater the subdivision number, the more difficult it is to control the accuracy.
What is a stepper motor driver?
What is the difference between the series connection method and the parallel connection method of the four-phase drive combined stepper motor and the driver?
The four-phase hybrid stepper motor is generally driven by a two-phase driver. Therefore, the four-phase motor can be connected into two phases by using a series connection method or a parallel connection method when connecting. The series connection method is generally used when the motor speed is relatively high. At this time, the required output current of the driver is 0.7 times of the phase current of the motor, so the motor generates less heat; the parallel connection method is generally used when the motor speed is higher (also known as high-speed connection method), and the required output current of the driver is the phase current of the motor. 1.4 times of that, so the motor heats up a lot.
