Difference between open-loop and closed loop controllers and working of PID controller

There is always need a control system in order to control the robot based on some parameters. Control systems are classified into two types like open loop and closed loop. The main difference between open-loop and closed-loop control system is, the required output within the open loop doesn’t depend on the input whereas, in closed-loop, the required output mainly depends on the input. This article discusses an overview of the difference between open-loop and closed-loop control systems. The open-loop system doesn’t have feedback, whereas the closed-loop system has feedback figure 3 and 4, depending on the feedback controller produce the output.

Open Loop System

Closed-Loop System.

To control the system, we used PID (proportional, integral and derivative), controller. see below figure

PID Controller

In this PID controller,

Term P is proportional term tried to reach the desired output of the system as soon as possible. we use “K” as gain. in general, we use “Kp” for proportional gain. In general Proportion, the term Kp  helps system to reach the desired output as fast as possible. if “Kp” is more then we have lots of oscillations as system overshoots and if we use less then the system takes a longer time to achieve goal.

Term D keeps an eye on the required output, as soon as the system reaches to desire output D term slowdowns the system and helps the system to avoid overshoots. Because of this, the system will not oscillate and remains stable. We used Kd for tuning the controller called a Derivative gain.

Due to these two factors some time the system goes up slightly duo to Kp and sometimes down due to Kd. To solve this problem and to keep the system more stable Integral Ki is added to the controller

Term I term is known for integral gain noted as “Ki” which perform based on past value obtained by the controller results and based on the error received it will try to eliminate the error between the desire output state of the system and present system state

References

1.       A Practical Multirobot Localization System” , T. Krajník, M. Nitsche, J. Faigl, P. Vaněk, M. Saska, L. Přeučil, T. Duckett, and M. Mejail, ,” Journal of Intelligent & Robotic Systems, 2014.

2.       External localization system for mobile robotics” , T. Krajnik, M. Nitsche, J. Faigl, T. Duckett, M. Mejail, and L. Preucil, ,” in Advanced Robotics (ICAR), 2013 16th International Conference on, 2013

3.       https://www.youtube.com/watch?v=6OH-wOsVVjg