Feedback Control

Ramp generation without feedback is called open-loop operation. The motion controller calculates acceleration and velocity with no communication to the motor. In contrast closed-loop operation receives motor status feedback and adjusts acceleration and velocity accordingly.

Open-Loop Operation

feedback control modes

Motion control without feedback assumes motors always behave as expected. Under common conditions, the motor position of the motor is deterministic and predictable. To cover uncommon conditions, the motor needs to be operated with safety margins, which can reduce efficiency and overall performance.

Open-Loop Operation

Closed-Loop Operation

Closed-loop operation or motion control with feedback is more complex. By measuring motor condition and behavior, closed-loop operation can deliver higher control reliability and flexibility. Feedback response, however, needs to be harmonized with applications and requires sophisticated control algorithms, otherwise systems can lapse into unstable conditions oscillation.

Closed-Loop Operation

Sources of Feedback

Magnetic or optical encoders are very common feedback sources and are available with different levels of precision and speed. These encoders are typically directly mounted to the motor axis so they can accurately measure mechanical movement.

Another option is to sense motor electrical behavior. Power consumption is directly related to axis load and motion control can respond if load exceeds certain limits.

Closed-Loop Stepper Control