Views: 0 Author: Site Editor Publish Time: 2025-07-04 Origin: Site
In modern devices that require high-precision positioning and small step movements, micro stepper motors have become a key driving unit for many precision systems due to their unique open-loop control characteristics and compact size. From precision medical equipment to automated instruments, to various consumer electronic devices, micro stepper motors are quietly playing an important role. Understanding its core structure is the foundation for recognizing its outstanding performance and potential applications.
Micro stepper motor is a member of the stepper motor family specifically designed for miniaturization and lightweight applications. Its core features are:
Micro size: usually refers to motors with an outer diameter between 20mm and 60mm, or even smaller, with relatively low power (several watts to tens of watts).
Step characteristic: Accurately convert electrical pulse signals into mechanical rotations at a fixed angle (i.e., "step angle"). The position of the motor shaft is determined by the number of input pulses, and the speed is determined by the pulse frequency.
Open loop control: No additional sensors (such as encoders) are required to provide feedback on position information, simplifying the system structure and cost. The controller only needs to send the correct pulse sequence to accurately control the position and speed of the motor.
High precision positioning: It can easily achieve fine resolution (small step angle) and repeat positioning accuracy.
Maintain torque: Even when not powered (for permanent magnet or hybrid) or powered on, it can provide a certain torque locking position.
Its working principle is based on the basic principles of electromagnetic attraction and repulsion. The controller delivers current pulses to multiple windings (usually two-phase) inside the motor in a specific order. Each current pulse excites the corresponding winding, generating a magnetic field that attracts or repels the magnetic poles of the permanent magnets or magnetic teeth on the motor rotor, thereby driving the rotor to rotate precisely at a fixed angle (step angle).
The mainstream structural types of micro stepper motors include permanent magnet (PM), hybrid (HB), and variable reluctance (VR). Among them, hybrid is the most widely used in the micro field due to its excellent performance (high torque density, small step angle, smooth operation). Taking the two-phase hybrid micro stepper motor as an example, the internal structure is analyzed in detail
Structure: Composed of stacked high permeability silicon steel sheets, forming the fixed casing of the motor.
Teeth: A large number of protruding magnetic poles (usually 8, 12, or more) are evenly distributed on the inner circumference of the stator. These magnetic poles are key components for electromagnetic energy conversion.
Windings/Coils: Copper wire coils are wound around the stator poles. For a two-phase motor, all magnetic poles are divided into two sets of windings, A phase and B phase. The coils within each winding group are connected in series or parallel according to specific rules. After the winding is energized, alternating N/S magnetic fields are generated on the magnetic poles. The coils of micro motors are usually made of extremely fine enameled wire, which requires high winding accuracy.
Structure: Located inside the stator, it is the rotating part of the motor.
Permanent Magnet: The rotor core is an axially magnetized annular permanent magnet (usually a high-performance rare earth magnet such as neodymium iron boron). The magnet forms fixed N and S poles at both ends of the rotor.
Rotor Cups/End Caps: A toothed iron core (often referred to as a rotor cup) made of high permeability silicon steel sheets stacked tightly at each end (axial) of a permanent magnet.
Rotor Teeth: A large number of teeth are precisely machined on the outer circumference of each rotor cup (usually with a specific relationship to the number of stator poles, such as 50 teeth). The key point is that the teeth on the rotor cups at both ends are offset by half a tooth pitch in the circumferential direction. This misaligned tooth structure is the core design for achieving small step angles in hybrid stepper motors. The axial magnetic field generated by the permanent magnet is closed by the rotor teeth at both ends.
Support the rotor shaft to ensure smooth and low friction rotation within the stator bore. Micro stepper motors typically use precision ball bearings or oil containing sliding bearings (copper sleeves), with the former having a longer lifespan and lower noise, and the latter having lower costs.
Made of high-strength steel, extending from the center of the rotor as a mechanical power output end, connected to external loads.
Usually made of metal (such as aluminum) or engineering plastic, it is used to encapsulate fixed rotor components, secure bearings, and provide installation interfaces (such as flanges or threaded holes). The sealing performance of the end cap is important for certain applications, such as healthcare.
Connect the A-phase and B-phase (sometimes with a common wire) windings inside the motor to an external drive controller. Micro motors are commonly equipped with flexible wires for direct connection or micro connectors.
After understanding the structure, the following parameters directly affect the selection and application:
Dimensions: outer diameter, length (body length), shaft diameter, shaft length.
Step angle: The angle of rotation for each received pulse signal (such as 1.8 °, 0.9 °, 7.5 °). The smaller it is, the higher the resolution.
Phase number: commonly used two phases.
Voltage: Rated driving voltage (such as 5V, 12V, 24V).
Current: Rated value of phase current (such as 0.3A, 0.5A, 1.0A).
Maintain torque: The maximum torque (in N · cm or mN · m) that the motor can output when it is stationary (powered on). Measure the strength of the motor.
Positioning torque: The torque required to rotate the rotor when the motor is not powered (only for permanent magnet/hybrid).
Inductance and resistance: affect the electrical characteristics and high-speed performance of the motor.
Weight: Especially important for portable devices.
Temperature rise: The temperature increase during operation affects the lifespan and reliability.
Based on its structural characteristics, the micro stepper motor exhibits the following core advantages:
Ultra small size, space saving: The precise structural design allows it to work in extremely limited space.
Accurate positioning, open-loop controllability: precise angle and position control can be achieved without feedback.
Excellent start stop and reverse response: able to instantly start, stop or reverse, with flexible control.
Wide low-speed operating range: able to provide smooth torque even at low speeds or near zero speeds.
Good retention ability: able to maintain a stable position and resist disturbances when powered on.
Sturdy structure, high reliability: no vulnerable parts such as electric brushes, long service life.
Cost effectiveness: Compared to closed-loop servo systems with the same accuracy, it usually has a cost advantage.
The precise structure and excellent performance of micro stepper motors make them widely used in:
Medical equipment: infusion pump, insulin pump, ventilator valve control, endoscope drive, surgical robot joint, DNA sequencer.
Laboratory automation: pipette, sample sorter, microscope stage control, spectrometer slit adjustment.
Precision instruments and meters: pointer instrument drive, valve positioner, precision flow control, optical platform adjustment.
Office automation: Paper feed rollers, scanning head movement, and lens zoom for printers/copiers.
Consumer electronics: Camera autofocus (AF)/optical image stabilization (OIS), smartphone lift camera/rotation module, drone gimbal.
Industrial control: small valve control, micro feeding device, precision dispensing equipment, textile machinery yarn guide.
Robot technology: small robot joints, gripper drives, sensor scanning mechanisms.
When selecting a micro stepper motor, comprehensive consideration should be given to:
Load requirements: required torque (considering acceleration and deceleration), load inertia, motion mode (distance, speed, acceleration).
Accuracy requirements: step angle resolution, repeat positioning accuracy.
Space limitations: strict installation size constraints.
Environmental factors: temperature, humidity, dust, vibration, electromagnetic compatibility (EMC).
Power supply and driver: Matching the driving voltage and current capabilities, selecting the appropriate micro step driver can significantly improve operational stability and resolution.
Cost budget.
The micro stepper motor, a miniature power unit composed of precision stator windings, cleverly misaligned rotors, high-performance permanent magnets, and sturdy bearings, is an indispensable cornerstone in the field of modern high-precision micro motion control. Its unique open-loop control characteristics, excellent positioning accuracy, compact structural design, and high reliability make it continue to play a key role in a wide range of fields, from cutting-edge medical equipment to daily consumer electronics. A deep understanding of its internal structure and working principle is the key to fully realizing its performance potential and selecting the most suitable micro power solutions for various innovative applications. With the continuous growth of demand for miniaturization and intelligence, micro stepper motors and their driving technology will also continue to evolve, driving the precise pace of future technology.
