Stepper motors

Stepper motors can perform demanding positioning tasks with particularly high accuracy. They accelerate very quickly and reach their full power almost without delay. In addition, they hold their position even when the power supply is switched off and can be controlled precisely without an encoder. FAULHABER offers a uniquely broad range of different stepper motors in numerous sizes.

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With stepper motors, the rotor moves around its circular path in multiple individual steps. By switching the stator windings on and off in a targeted manner, it can be moved into specific positions. This mode of operation differentiates it in principle from conventional electric motors with continuous rotation.

When the power supply is switched off, the rotor remains in the most recent step position and its magnets provide a currentless static torque. This is particularly advantageous in many battery-driven applications. As the motor controller counts the steps completed, it also performs the function of an encoder. In general, an additional encoder is not required for operation.

The magnets of the stepper motor – whether positioned as individual small magnets or as pole pairs on a disk – are part of the rotor. The stator consists of two or more windings that are arranged in a circle. The windings are each assigned to one of two phases that are energized alternately. When the phases are energized one after the other, the alternating attraction and repelling of the magnetic fields being created produce the step-by-step circular movement of the rotor.

The sequence of the power supply is determined by the controller. Each current pulse generates a partial rotation of the shaft by a specific angle. If the phases are completely switched on and off, the rotor adjusts itself to the magnetic field of the current-carrying phase and completes a whole step with this angle. A full rotation is completed only when the maximum number of individual steps has been performed and the starting position has been reached again.

With simple switching on and off of the phases, the rotor moves in whole steps. However, rather than having a full voltage change from phase to phase, the power supply can be divided into smaller steps, resulting in the ebb and flow of the current on the windings. In this case, the power supply follows a graduated sine wave. The rotor then moves between the phases in substeps or microsteps. The micro-stepping operation makes the motor run more quietly and enables particularly high positioning accuracy.

The rotor responds to the changes of the magnetic fields with minimal delay. The small stepper motors achieve their full power almost immediately after switching on. They are therefore particularly well suited for applications that require frequent and fast changes of direction.

The stepper motors from FAULHABER are all two-phase devices and are designed as permanent or disc magnet motors. In the latter case, up to 25 pole pairs are arranged like pizza slices on the disc magnet of the rotor. The windings of the one- or two-piece stator are positioned perpendicular to the disc magnet. In permanent magnet motors, the rotor consists of a plastic sleeve that contains multiple small permanent magnets. The windings are housed in a two-piece stator. The rotor runs between the stator halves.

Regardless of their number and arrangement, the stator windings are energized alternately in two phases. With each phase, the rotor moves by one magnetic pole segment. Both stepper motor variants have a range of design-related strengths, in comparison with both conventional DC motors and the hybrid stepper motors that are used in large numbers in electronic mass products.

Conventional stepper motor technologies are generally optimized for one of several characteristics such as speed, torque or precision. However, the small stepper motors from FAULHABER achieve top values in multiple categories simultaneously. In terms of positional accuracy, they attain absolute peak values. For example, the maximum positional deviation when using a FAULHABER stepper motor with a lead screw can be less than two microns. Like all motors from FAULHABER, the steppers are also characterized by maximum power with the smallest volume.

For safety-relevant applications, the motors can be combined with an additional encoder. As the motor controller already outputs position data, position monitoring with the additional device is redundant. This use of an encoder as a safeguard is particularly common in laboratory diagnostics, laser technology and technical microscopy, medical technology and dentistry, as well as in the semiconductor industry.

Stepper motors have specific strengths that make them the optimal solution for certain applications. Compared to other motor technologies, in addition to a high torque, they offer a particularly high positioning accuracy, the highest acceleration values and the ability to change direction very quickly. They can be used without an encoder, without a brake and also as a direct drive without a gearhead, and therefore enable very compact solutions.

Basic parameters for selecting a small stepper motor:

• Speed profile of the application
• Friction torque and inertia
• Necessary resolution
• Available space
• Available power supply

Other criteria to consider when selecting a motor are the location and type of mounting points as well as the shaft diameter. The external conditions of use should also be taken into account. In the case of adverse environmental influences such as moisture, dust, negative pressure or extreme temperatures, a certain degree of protection, suitability for vacuum, or a particularly large temperature range may be required.

FAULHABER offers a uniquely wide range of stepper motors. Among the numerous product variants, you will find the optimal drive for the vast majority of applications. In addition, there is an extensive range of peripherals and accessories available, giving the industry's biggest selection of tailor-made combination options.

Our Drive Calculator enables you to quickly find the small stepper motor that best matches your requirements. We also offer our customers the bespoke manufacture of drives that are configured for a specific application.

You can find further information on stepper motors in our webinars and tutorials: