Linear stepper motors can directly perform linear motion or linear reciprocating motion. If a rotary motor is used as the power source and converted into linear motion, it requires mechanisms such as gears, cam structures, belts, or wires. This article first introduces the structure of an externally driven linear stepper motor, then introduces its basic principles and working principles, and finally elaborates on its advantages and applications.
Introduction to Linear Stepper Motors
The externally driven linear stepper motor ( LE series linear stepper motor) integrates the lead screw and motor rotor into one unit as the motor output shaft. The nut is located outside the motor and is connected to the drive mechanism. When the motor rotates, the nut moves linearly along the lead screw.
Structure of an externally driven linear stepper motor
The following diagram shows the basic structure of an externally driven linear stepper motor:
Compared to rotary motors, linear stepper motors can move directly in a straight line, which allows for smaller machines and simpler designs.
Basic principle of externally driven linear motor
The rotor of an externally driven linear stepper motor is a permanent magnet. When current flows through the stator windings, the stator windings generate a vector magnetic field. This magnetic field drives the rotor to rotate by a certain angle, aligning the direction of the rotor's magnetic field with that of the stator's magnetic field. When the stator's vector magnetic field rotates by an angle, the rotor also rotates by the same angle. Each input electrical pulse causes the rotor to rotate by an angle and move forward one step. Its output angular displacement is proportional to the number of input pulses, and its rotational speed is proportional to the pulse frequency. Changing the energizing sequence of the windings reverses the motor's rotation. Therefore, the rotation of the stepper motor can be controlled by adjusting the number and frequency of pulses and the energizing sequence of each phase winding.
The lead screw and motor rotor are integrated as a single unit, serving as the motor's output shaft. An external drive nut engages with the lead screw outside the motor, preventing relative rotation between the lead screw and nut, thus achieving linear motion. This significantly simplifies the design, enabling precise linear motion in many applications using externally driven linear stepper motors without the need for external mechanical linkages.
Advantages of externally driven linear stepper motors
Precision externally driven linear stepper motors can replace cylinders in certain applications, offering advantages such as accurate positioning, controllable speed, and high precision. Externally driven linear stepper motors are widely used in many high-precision fields, including manufacturing, precision calibration, precision fluid measurement, and precise position movement.
• High precision, with repeatability up to ±0.01mm
Externally driven linear stepper motors offer higher positioning accuracy, repeatability, and absolute accuracy than rotary motors with lead screws due to their simpler transmission mechanism, which reduces interpolation lag . Furthermore, they are easier to implement. Externally driven linear stepper motors with ordinary lead screws can achieve a repeatability of ±0.05mm , while those with ball screws can reach ±0.01mm .
• High speed, up to 300 m/min
In terms of speed and acceleration, externally driven linear stepper motors have a significant advantage. Externally driven linear stepper motors can reach speeds of up to 300 m/min with an acceleration of 10g , while ball screws achieve speeds of 120 m/min and accelerations of 1.5g . Furthermore, once the heat dissipation issue is successfully resolved, the speed of externally driven linear stepper motors can be further increased, while the speed of rotary servo motors and ball screws is limited and cannot be significantly improved.
• Long lifespan, simple maintenance
The externally driven linear stepper motor uses long-life, heavy-load bearings to ensure its effective service life. The nuts are made of high-polymer plastic, are self-lubricating, and easy to maintain.
