Servo motors offer an undeniable performance advantage. In terms of repeatability, however, stepper motors can be quite competitive. This point brings up a common misconception about stepper motors, which is the myth of lost motion. As we discussed previously, the mass-spring nature of a stepper motor may result in a few lost steps. Because the drive is commanding the stepper to move to an angular location, lost steps are not carried over from rotation to rotation, however. Rotation to rotation, stepper motors are highly repeatable. Look for a more detailed discussion of this topic in a future blog post.
The discussion above brings us to a final key differentiation between stepper axes and servo axes, which is cost. Stepper motors typically don’t require feedback, they use less expensive magnets, and they rarely incorporate gearboxes. Because of the high pole count and their ability to generate holding torque, they consume less power at zero speed. As a result, a stepper motor can be up to an order of magnitude less expensive than a comparable servo motor.
To summarize, stepper motors are good solutions for applications with low speed, low acceleration, and low accuracy requirements. Stepper motors also tend to be compact and inexpensive. This makes these motors a good fit for medical, biotech, security and defense, and semiconductor manufacturing applications. Servo motors are a better choice for systems requiring high speed, high acceleration, and high accuracy. The trade-off is a higher cost and complexity. Servo motors are typically used in packaging, converting, web processing, and similar applications.
When your application is forgiving but your budget is not, consider a stepper motor. If performance is the most important aspect, a servo motor will do the job but be prepared to pay more.
