Stepper Motor Applications and Advantages Disadvantages
• Lowest-cost solution
• A stepper motor will always offer the cheapest solution. If a stepper will do the job, use it.
Rugged and Reliable:
Steppers are mechanically very simple and apart from the bearings (like in servos) there is nothing to deteriorate or fail.
There are no brushes or other wearing parts requiring periodic checking or replacement.
Industry-standard ranges (Nema or metric):
Steppers are produced to standard flange and shaft sizes so finding a second source is not a problem.
Few environmental constraints:
A stepper may be used in just about any environment, including in a vacuum. Special magnets may be needed if there are very large magnetic fields around, e.g. in evaporation chambers.
Watch heat dissipation in a vacuum (there is no convection cooling).
There are no conceivable faults within the drive to cause the motor to run away. Since current must be continually switched for continuous rotation most faults cause the motor to stop rotating. A brush motor is internally-commutated and can run away if continuous current is applied. A brushless servo relies on the feedback signal. If the signal is damaged, or absent the motor will run away.
Not easily demagnetized by excessive current:
Owing to the perpendicular planes of the permanent magnet and alternating flux paths stepper motors will more often melt the windings before demagnetizing the permanent magnet, as would happen in a brushed motor.
Inherently stable at standstill:
With DC flowing in the winding, the rotor will remain completely stationary. There is no tendency to jitter around an encoder or resolver position. This is useful in applications using vision systems.
Can be stalled indefinitely without damage:
There is no increase in motor current as a result of a stall or jam as in a servo system. There is no risk of overdriving a stepper system due to large loads, or high speeds.
High continuous torque in relation to size:
Compared with brushed servos of the same size, a stepper can produce greater continuous torque at low speeds.
Only 4 leads required:
This minimizes the installed cost, particularly important in applications where connections are expensive (e.g. vacuum chambers).
Stepper Motor Drawbacks:
Ringing, resonance and poor low speed smoothness:
These are criticisms generally leveled at full-step drives. These problems may be almost wholly overcome by the use of a higher-resolution drive.
Undetected position loss in open loop:
This should only occur under overload conditions and in many applications it causes few problems. When position lost must not go undetected, a check encoder may be fitted which then results in a very secure system. The encoder is not needed for positioning, only for confirmation. If a positioning encoder is desired a servo system should be used.
Uses full current at standstill:
Since current is needed to produce holding torque, this increases motor heating at standstill.
Noisy at high speeds:
The 50-pole rotor has a magnetic frequency of 2.5 kHz at 3000 rpm. Magneto-striction causes a correspondingly high-pitched sound.
Excessive iron losses at high speed:
Again due to the high pole count, hysteresis and eddy current losses are higher than in a servo. A stepper is therefore not recommended for continuous operation at speeds approximately above 2000 rpm.