Engineers can implement stepper motor drives in numerous ways. Companies often produce pre-packaged drives that can run with a variety of microprocessors and motors. This means that that drive is prefabricated and the engineer has many decisions on where and how to use it. Beyond this, some companies even offer complete off-the-shelf boards. These combine the drive and microprocessor … so the engineer programs the unit with instructions on the angles to which the stepper motor must step. Designing a custom drive is also possible. In terms of price paid for upfront costs, this is often the cheapest option. Tip: consider more than just cost when implementing drives. Building drives takes much time and work and relies on in-house expertise. For complex systems, it is often better to buy than build.
During operation, drives receive step and direction commands from an indexer or control system. In most cases, the indexer must also provide and manage acceleration, steps per second, distance and deceleration controls. The indexer collects high-level commands from the host computer and generates the needed step and direction pulses. Some versions can also run as standalone controllers after downloading and storing data to non-volatile memory. Here, the drive translates control data into electrical signals that run the step motor.
Beyond this, stepper motors also require power supplies, logic sequencers, switching components and a clock pulse source. Many drives incorporate these already, but some more basic drives contain only the final power stage without any controller electronics to generate step sequences. These need power supplies to regulate output.
To determine what kind of drive to use, engineers must analyze the load, including determining friction and inertia loads, torque required and power consumption, and damping required. Next, engineers must determine what kind of motor-drive combination works best. Tip: here, use performance curves provided by manufacturers and compare them to the intended design requirements.
For more information, visit:
Omega Engineering’s technical page on stepper motors
AMETEK’s Haydon Kerk stepper-drive landing page
University of Texas at Austin PDF: Stepper motor and driver selection
Design World article: Building versus buying a stepper motor
Filed Under:Motion Control Tips,Drives (stepper) + amplifiers
