Stepper Motors

About Stepper Motors

ABOUT STEPPER MOTORS

A stepper motor is a brushless DC electric motor characterized by the unique way its shaft rotates. Instead of rotating continuously like many other standard electric motors, a stepper motor’s shaft moves in a fixed number of degrees, or steps. It rotates at a precise angle one step at a time, with each step being the same size.

This characteristic allows them to transfer highly accurate movements to mechanical parts that need to be controlled precisely. When stepper motors are correctly sized to a given application in terms of speed and torque, they can be commanded to move and hold their position at one of these steps without any position sensor for feedback. Elinco JPC also offers value add services in encoder sourcing and assembly.

Stepper Motors Catalog

Types of Stepper Motors

A stepper motor's speed, resolution, and torque size are influenced by its construction. There are several stator and rotor configurations, step counts, shaft styles, and gearing options, each developed for a unique purpose. Out of all the types available, there are three primary types of stepper motors to be aware of: permanent magnet stepper motors, variable reluctance stepper motors, and hybrid stepper motors.

Permanent Magnet Stepper Motors

In this type, the rotor is a permanent magnet. It aligns with the magnetic field the stator circuit generates. Permanent magnet stepper motors guarantee a good and detent torque, meaning that it will resist changes in position regardless of whether or not the coil is energized. Even when all power is removed, the motor will hold the last position it was stepped to. Elinco JPC specializes in offering sub fractional horsepower hybrid stepper motors ranging from NEMA 8 to 34.

Variable Reluctance Stepper Motors

These stepper motors feature a non-magnetic, geared rotor made from soft iron. The rotor features teeth that are arranged so that they can be attracted to the stator’s magnetic field. Since the rotor is not magnetized, it can be made in any shape. However, since the teeth are attracted to energized fields with less force than permanent magnet stepper motors, variable reluctance motors provide less torque.

Hybrid Stepper Motors

Hybrid motors combine the beneficial characteristics of both previous stepper motor types. They have a toothed or geared rotor that allows for very small step angles as well as a permanent magnet that offers a small detent torque when the power is turned off. Their high-performance capabilities require a more complex construction than the other types. Hybrid stepper motors are capable of producing high torque at low speeds and are the most commonly used type.

Bipolar vs. Unipolar Windings

With stepper motors, there are two ways to supply current in the coil: bipolar or unipolar.

Bipolar

Bipolar stepper motors require only one winding per phase, and the current can flow in both directions in all coils. Although bipolar motors can be used for voltage drive, they are a better choice for current drive applications. In many situations, bipolar stepper motors can deliver higher torque than unipolar motors.

Unipolar

In unipolar stepper motors, the current always flows in the same direction, and each coil is dedicated to one current direction. Unipolar motors are a simple and cost-effective solution for voltage drive applications. However, they are not ideal for current drive applications, as they require complex electronic solutions for lower motor performance. At high speed in voltage drive, unipolar stepper motors can provide higher torque than bipolar stepper motors because the current can move quicker in the coil.
Bipolar vs. Unipolar Windings

Stepper Stack Length Increases

In general, larger frame sizes produce higher torque. However, within a given frame size, the motor length, or stack length, can vary and also affect torque. To create longer and more powerful stepper motors, several stators and rotors can be “stacked up.” This gives engineers the flexibility to match a stepper motor to a particular application.

The easiest way to differentiate the different stack lengths of a specific frame size is the think of the trade-offs. For example, smaller stack lengths offer less torque that persists at higher speeds, whereas larger stack lengths have higher torque that falls off rapidly as speed increases.

Stepper Stack Length Increases

Key Advantages of Stepper Motors

Compared to other types of motors, stepper motors provide many key advantages when used in the right application. With computer-controlled stepping, it’s possible to achieve highly precise speed control and positioning. This makes them an ideal solution for applications that require precision motion control. Since their speed is proportional to the frequency of their pulse inputs, they can achieve many rotational speeds.

They also offer maximum torque at low speeds, unlike normal DC motors, making them a great choice for low-speed, high-precision applications. In addition, since there are no contact brushes in the motor, stepper motors offer added reliability, with a minimized risk of mechanical failure and enhanced operational lifespan.

Some other notable advantages include:

  • When the windings are energized, the motor offers full torque at a stand-still
  • The motor's rotation angle is proportional to the input pulse
  • They offer excellent responses to starting, reversing, and stopping
  • Significantly more reliable than brushed DC electric motors, since there are fewer parts that can wear out and need replacement
  • Their lifespan is dependent on the life of the bearing alone since all moving parts are frictionless
  • A safer option than other types of motors, since they will stop if anything breaks
  • Ideal for applications requiring high precision and low speed
  • More cost-effective and readily available

Key Disadvantages of Stepper Motors

While they offer many benefits, stepper motors are not ideally suited to every application. Some disadvantages to be aware of include:

  • They offer lower speeds than servo motors
  • They operate at low efficiency, drawing substantial power regardless of torque
  • While their accuracy can be improved with micro-stepping techniques or added teeth, they offer lower accuracy overall compared to some other motor options
  • They cannot rotate at high speeds and feature a low torque to inertia ratio. For this reason, they cannot rapidly accelerate loads and can get hot in high-performance applications
  • At moderate to high speeds, they can be noisy and produce vibrations

Good alternatives to stepper motors include brushless DC (BLDC) motors, and value-add ons such as closed-loop encoder mounted solutions or gearboxes.

Stepper Motor Applications

Stepper motors are used throughout many commercial and industrial applications. In general, any application that requires speed control, highly accurate positioning, and low-speed torque would be suitable for a stepper motor. Some of the most common uses include:

Biotechnology & Medical Devices

Printers, analog clocks, air conditioning louvers, digital and phone camera zoom mechanisms, gaming machines

Robotics

Robotics

Bank ATMs, vending machines, rotating security cameras, ticket validation machines

Industrial

Industrial

Conveyor belts, small robotics and industrial robot joints, CNC milling machines and welding equipment, semiconductor wafer transfer machines, textile machines, 3D printing equipment, printing presses, and medical imaging machinery

Stepper motors are also useful for performing tasks like indexing operations over short distances, achieving high-speed reciprocating motion with minimal vibration, and indexing large inertial loads. They can perform closed-loop positioning, vertical positioning with power-off braking, and positioning within small spaces.

Stepper Motors by Elinco International

The cost and performance advantages that stepper motors provide have made them an essential electric motor variety for applications spanning many industries. Hybrid stepper motors, in particular, combine key characteristics of other types, making them a powerful solution for applications that require high torque, small step angles, and detent torque.

At Elinco International JPC, we have nearly 100 years of experience developing high-performance precision electric motors for demanding industries worldwide. Our stepper motors support the needs of medical technology, industrial automation, home automation, automotive, and more. We are ISO 9001:2015 certified and RoHS-compliant. To learn more about our stepper motor inventory, contact our team with any questions.