In this post, we explain the difference between open loop and closed loop.

 

The difference between open vs. closed loop

The motor circuit can often be defined as either open loop or closed loop.

In an open circuit, there is no feedback, meaning that the speed of the motor is controlled at a fixed level, which can vary under different load conditions.

A closed loop contains feedback, which returns information to the entry point for self-adjustment. This means that if the speed of the motor is set at a specific level and the load changes, the controller will adjust the speed back to the set level.

The above describes speed control, and in addition to speed control, you can also control position and torque.

In position control, the controller regulates a defined position, usually involving feedback from an encoder or a stepper motor with/without feedback.

In torque control (also known as torque control), the output of the motor provides a defined torque, andtypically involves either a DC motor or a BLDC motor because stepper motors are less suitable for torque control.

Closed loop feedback or can we just use open loop?

Open loop is suitable for applications where the motor runs at the same speed (e.g. a regular DC motor) when power is applied. In applications like this, the speed of the motor will be reduced if the motor is loaded (e.g. on an electric pallet truck, where the speed slows down under heavy load).

If feedback is required, in 9 out of 10 cases we use hall sensors or incremental encoders in our development projects. This is because many customers want brushless DC (BLDC) motors, which are typically supplied with 3 hall sensors that send feedback to the motor controller. If the application requires even more precision, then the encoder can be a solution. Here, for example, you can get 1000 pulses per lap (as opposed to the 3 in the case of the Hall sensors), and thus more precise feedback.

Open vs. Closed loop

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