A stepper driver is an actuator that converts electrical pulses into angular displacement and is widely used in various automated control systems. It receives electrical pulse signals from the control system to control the speed, position, and direction of the stepper motor, thereby achieving precise angular displacement control.
A stepper motor, also known as a pulse motor, is based on the fundamental principles of electromagnetism. It is a freely rotating electromagnet that operates by generating electromagnetic torque through changes in the air gap's magnetic permeability. Its original model dates back to between 1830 and 1860. Around 1870, attempts at control-oriented applications began, using it in the electrode delivery mechanism of hydrogen arc lamps. This is considered the earliest stepper motor. In 1923, James Weir French invented the three-phase variable reluctance type, the precursor to the stepper motor. In the early 20th century, stepper motors were widely used in automatic telephone exchanges. Due to the Western capitalist powers' struggle for colonies, stepper motors were widely used in independent systems such as ships and aircraft lacking AC power. The invention of the transistor in the late 1950s gradually led to its application in stepper motors, making digital control easier. By the 1980s, the emergence of inexpensive, multifunctional microcomputers made stepper motor control methods even more flexible and diverse.
I. Types of Stepper Drivers
Stepper drivers can be classified into three types according to their structure: reactive, permanent magnet, and hybrid.
1. Reluctance Stepper Driver: Also known as inductive, hysteresis, or reluctance stepper driver. Its stator and rotor are both made of soft magnetic material, with small teeth and slots evenly distributed around their perimeters. When energized, it generates torque by utilizing changes in magnetic permeability. Typically three, four, five, or six phases, it can achieve high torque output (high power consumption, with current up to 20A and high drive voltage), small step angle (minimum 10'), no positioning torque when power is off, low internal motor damping, longer oscillation time during single-step operation (referring to very low pulse frequency), and higher starting and running frequencies.
2. Permanent Magnet Stepper Driver: Typically, the motor rotor is made of permanent magnet material, while the stator, made of soft magnetic material, has multi-phase excitation windings. Neither the stator nor the rotor has small teeth or slots around their perimeter. When energized, torque is generated by the interaction between the permanent magnet and the stator current's magnetic field. It is generally two-phase or four-phase, with low output torque (low power consumption, current typically less than 2A, drive voltage 12V), large step angle (e.g., 7.5 degrees, 15 degrees, 22.5 degrees, etc.), and a certain holding torque when de-energized. It also has a low starting and running frequency.
3. Hybrid Stepper Driver: Also known as permanent magnet reactive or permanent magnet induction stepper driver, it combines the advantages of permanent magnet and reactive stepper drivers. Its stator is no different from a four-phase reactive stepper driver (but the two magnetic poles of the same phase are opposite each other, and the N and S polarities generated by the windings on the two magnetic poles must be the same). The rotor structure is more complex (the rotor contains cylindrical permanent magnets, with soft magnetic material at both ends, and small teeth and slots around the perimeter). It is generally two-phase or four-phase, requires positive and negative pulse signals, has a larger output torque than permanent magnet stepper drivers (with relatively lower power consumption), a smaller step angle (generally 1.8 degrees), no positioning torque when power is off, and a higher starting and running frequency. It is a rapidly developing type of stepper driver.
II. Working principle of stepper driver
The working principle of a stepper driver is that when a stepper motor receives an electrical pulse signal, it rotates by a fixed angle (i.e., step size) in a set direction. This process controls the angle of rotation of the stepper motor by controlling the number of pulses. Simultaneously, the speed of rotation of the stepper motor is controlled by changing the frequency of the pulses.
A stepper motor contains a sophisticated control circuit. When it receives a pulse signal, the control circuit converts the signal into the required rotation angle and speed according to a pre-set algorithm. Then, it drives the motor to rotate to the designated position by transforming the electromagnetic field.
A stepper motor's step angle is reduced by a microstepping driver. For example, when the driver operates at 10 microsteps, its step angle is only one-tenth of the motor's inherent step angle. This is the basic concept of microstepping. The microstepping function is entirely generated by the driver precisely controlling the motor's phase current and is independent of the motor itself.
III. Application Scenarios of Stepper Drivers
Stepper motors, with their advantages of high precision, high response, and high efficiency, are widely used in various automated control systems, such as CNC machine tools, robots, and textile machinery. In these applications, stepper drivers can precisely control the motor's rotation angle and speed, thereby achieving high-precision machining and operation. Stepper drivers are important automated actuators that enable precise angular displacement and speed control. When used in conjunction with control systems, they can achieve various complex mechanical movements and control tasks.
