As mentioned, closed-loop stepper control with feedback for step-loss compensation uses algorithms to detect lost steps. The many different compensation algorithms used in industry have advantages and disadvantages:
These types of algorithms can be used in many point-to-point motion applications but are less useful for maintaining a profiled trajectory under varying load.
This type of control suffers from the main weakness of traditional stepper motor control: Once pullout torque is exceeded, torque delivered to the load plummets to zero and a recovery algorithm must fix the problem.
This control also suffers from the traditional problem of stepperresonance excitation. Algorithms abound to reduce the effects of stepper resonance but none completely eliminate the issue.Just like a traditional open-loop stepper, the motor can run hot because the control applies full current to the motor whenever it’s in motion.
Closed-loop stepper driver with load position control is similar to step-loss compensation as this drive scheme uses feedback and compensation algorithms to detect and address lost steps. This is a position-control scheme and dynamically controls and updates the output position when an error is present between commanded position and actual position. These compensation algorithms have advantages and disadvantages:
The algorithms are especially useful when a profiled trajectory must be maintained under varying load.
This type of control still suffers from the main weakness of traditional stepper motor control (that once pullout torque is exceeded the torque delivered to the load plummets).
This type of control also suffers from the stepperresonance problem.
Just like a traditional open-loop stepper, the motor can run hot because the control applies full current to the motor whenever it’s in motion.
It’s usually easy to determine when a drive implements closed-loop stepper servo control because the drive can control torque. Case in point: The ElectroCraft PRO Series drives run steppers like high-pole-count brushless motors, via closed-loop stepper servo control. The ability to control torque has advantages and disadvantages:
A wider variety of applications can use this type of control. In addition to point-to-point motion, the drive can execute profiled motion and coordinate axes.
Machine builders can use the motor’s full rated torque because this algorithm doesn’t experience pullout issues; full torque is maintained up to the maximum limit.
The drive can use the motor’s full torque, but the system delivers only as much torque as is required at any point in time. This reduces motor heating associated with traditional stepper drives and other closed-loop controls.This control method completely eliminates the stepper resonance issue because the motor is no longer operated as a stepper.The ability to control motor current is a more complex control scheme and does not come free. Generally these types of systems are more expensive than step-loss compensation systems.