Figure 1 illustrates the difference between open- and closed-loop speed control as different fans are driven to a target speed from the OFF condition.

Feedback control methods implemented using low-cost microprocessors enable significant gains for single-phase ac motor speed controls.

In motion control applications, you frequently hear all sorts of loops -- open, closed, current, torque, speed, voltage, and so on. Here, we define and explain these terms.

Open-loop vector (OLV) control is used for greater and more dynamic motor control. It independently controls motor speed and torque, much like DC motors are controlled.

Toshiba launches a three-phase brushless motor control pre-driver IC suited to high-velocity server fans, blowers and pumps.

[Misan] has the solution to this: closed loop control of DC motors for a 3D printer. Most printer firmwares use an open loop control system for moving their motors around.

Toshiba launches a three-phase brushless motor driver IC with a rotation speed control function, for application in small fans.

The control methods listed above utilize either an ‘open-loop’ control system or ‘closed-loop’ control system. In an open-loop system, a parameter is set, and the fan will operate at that speed ...

In this case, they’re being used to create a basic PWM motor controller. The trick is to set the 555 up in astable mode, and use diodes and a potentiometer in the charge/discharge loop.