Whether the given application is a systolic pump or a Petrie dish, the following step motor characteristics should be evaluated:
• Small Package
• High Accuracy
• Smooth Motion
• Low Noise
• High Quality & Reliability
Small Package
In terms of size, step motor manufacturers adhere to various NEMA frame sizes. These sizes range from the miniature NEMA 8 to the massive NEMA 42. For most medical applications, space constraints are a critical issue to deal with, so the smaller amount of space the motors takes up, the better. Although there are some drawbacks to going with a smaller motor (i.e. less torque), this is the way to go in most applications. The NEMA 8 for example, measures a mere 0.79" square while the NEMA 34 measures 3.39" square.
High Accuracy
When the issue of accuracy is concerned, it’s safe to say that several medical applications require extremely high accuracy within the step motor. A Laser Eye Surgery machine would be in great danger if the motors and machinery weren’t accurate during a surgical process. Step motors rotate in terms of degrees. All step motors will have some form of step error. Therefore, it’s a matter of choosing one that has the least amount of error. °.
Smooth Motion
Step motors are advantageous because they can stop at any location your program tells it to. But, as the name indicates, these motors take steps when moving. In order to move one revolution, the motor must take 200 steps for a 1.8° motor. Each step the motor takes, it takes a few microseconds to settle in that new position, creating a slight oscillation. If these oscillations continue to add up with each step the motor takes, this can cause jittery and unsmooth motion.
Low Noise
Smooth motion and low noise come hand in hand. But, noise from a motor can be a result of a few factors. Mechanical noise can be caused by an imbalance of inductance or resistance readings from phase to phase. Step motors generally have two phases where electrical characteristics must match. Other times, noise can be caused by poor design and manufacturing of each component in the step motor.
High Quality & Reliability
Medical applications run the risk of reliability in most situations. Therefore, searching for the right motor is not the only factor. Searching for the right motor manufacturer is just as important.
