Stepper Motors: types, examples, and drives

Stepper motors_types, examples and drive

Stepper motors, also known as step motors, are DC synchronous electric motors named for their distinct type of rotation, divided into a specific number of steps. By dividing rotation into discrete steps, stepper motors provide precise positioning down to fractions of a degree, essential in fields like precision manufacturing and robotics. Their ability to produce high torque at low speeds while minimizing vibrations makes them ideal for applications requiring quick positioning over short distances.

Types of stepper motors

Steppers can be classified by construction type and the number of phases required for coil excitation. They include permanent magnet stepper motors (PM stepper motors) and variable reluctance stepper motors.

Permanent magnet stepper motors, as the name suggests, use permanent magnets to generate the magnetic field required for operation. This ensures a constant and high-torque magnetic flux, making these units particularly suitable for applications requiring high load and low speed, such as printers, plotters, woodworking machines, and industrial robots.

Variable reluctance stepper motors operate on a slightly different principle. In this case, the rotor is made of a material with high magnetic permeability but without permanent magnetism. The stator, on the other hand, has windings that generate a variable magnetic field. As the magnetic reluctance changes, the rotor is drawn to positions of lower reluctance, resulting in movement. These motors are known for their high energy efficiency and the ability to achieve high speeds. For this reason, they are often used in applications requiring high dynamics, such as industrial automation, collaborative robotics, and CNC machines.

Steppers are also categorized by their power supply type into unipolar, bipolar, or hybrid motors.

  • Unipolar stepper motors typically have four windings per phase and are easier to control, making them common in home automation devices and small robots.
  • Bipolar stepper motors operate with variable current direction and are used in precision applications like 3D printers and CNC machines.
  • Hybrid stepper motors combine features of both unipolar and bipolar motors, offering versatility and enhanced performance in resolution, reliability, torque, holding torque, and speed, making them preferable for a wide range of industrial applications.

 

Stepper motors: control advantages

By converting electrical pulses into mechanical movement, stepper motors offer numerous control advantages. Their operation is inherently “controlled” by the electrical pulses that the drive converts into current flowing through the motor windings. Each pulse corresponds to a motor “step.” This allows stepper motors to provide precise control of position and speed without the need for feedback devices, making the motor and drive combination a low-cost, precise, and simple control system.

For more reliable motor control—such as achieving high speeds while maintaining torque and the motor’s ability to hold the applied load—a closed-loop control system can be used. In this case, the system uses feedback to verify and correct any discrepancies between the desired and actual positions.

An advanced technique often employed in stepper motor control is called microstepping, which further divides the motor step, allowing for smoother and more precise movement. While traditional stepper motors have a fixed angle of rotation per step, microstepping further subdivides this angle, enabling higher precision and reducing vibrations and noise. Motion control can be integrated directly into the drive in various ways; from simple drives that fulfill classic low-cost applications with Step & Direction commands, to more advanced products with integrated motion control and the main communication buses such as EtherCat, Profinet, CANopen, Ethernet/IP, ModBus TCP or RTU.

Applications of stepper motors

Stepper motors are fundamental components in a wide range of industries. In industrial automation, they are used for the precise positioning of machinery and actuators due to their inherent ability to move in discrete increments. This capability allows for the accurate control of movements essential to ensure the quality and efficiency of production processes driven by industrial robots, CNC machines, and picking and packing systems. For similar reasons, steppers are highly valued in distribution applications requiring accurate service delivery, minimizing errors and interruptions, such as ATMs, beverage vending machines, and automatic drawers.

Notably, the textile industry makes extensive use of stepper motors, especially for controlling the movement of weaving, processing, and cutting machinery. The advantage lies in their ability to perform precise and repeatable movements, ensuring the quality and consistency of the finished product, reducing waste, and increasing production efficiency.

In professional lighting, stepper motors are used to adjust the direction and intensity of light in complex lighting systems. They can be employed in moving heads for stage lighting, architectural lighting systems, and security lights, allowing precise control of the light beam and head movements. Precision requirements also underlie inspection and optical applications: here, stepper motors enable the precise positioning of sensors and optical devices for analyzing and measuring objects. They are therefore used in quality control machines, artificial vision systems, and diagnostic equipment, ensuring high resolution and reliable reproducibility of measurements

In the medical and dental instrumentation sectors, stepper motors can become essential for controlling the movement of surgical instruments, scanners, and actuators in imaging devices. The level of precision and control allows operators to perform surgical interventions and diagnostic procedures with maximum accuracy and safety, minimizing patient risk.

 

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