Control Systems

       

 Blog: Control Systems

A branch of engineering that deals with the design of mechanical and electrical parts of a mechanical system is called the “Mechatronic System”. It is used in the majority of sectors, including healthcare, space exploration, and many instruments that make our daily jobs easier. This broad engineering sub-branch typically refers to the integration of mechanical systems, and telecommunications engineering, all of which typically involve micro-controlled systems.

 

A "control system" in the mechatronics discipline of engineering refers to a group of mechanical components that are connected in a way that may regulate, direct, or control other systems. Physical components of a control system include those that are mechanical, electrical, thermal, hydraulic, pneumatic, or biochemical.                             

                                                     

Control systems are very important to the development of engineering and science. The automatic control has become a crucial part of modern manufacturing and industrial processes. For example, numerical control of machine tools in the manufacturing sector, and control of flow, viscosity, temperature, and pressure in the process industry.

             A system is a collection of interconnected elements or components that work together to carry out a certain task. In a system when the output quantity is controlled by varying the input quantity, the system is called control system. The controlled variable or response is the output quantity, while the command signal or excitation is the input quantity.

There are two types of control systems:

1.    Open-loop Control Systems

2.    Close-loop Control Systems

 

1.    Open-loop Control System:

An open loop system, also known as a control system where the output quantity has no impact on the input quantity, is any physical system which does not automatically correct the fluctuation in its output. This indicates that the output is not a correctional feedback to the input.

   

 In open loop control system, the output can be varied by varying the input. But due to external disturbances, the system output may change. When the output changes due to disturbances, it is not followed by changes in input to correct the output. Open loop systems require manual input modifications in order to fix output changes.

Examples of open loop control systems:

1.    Automatic washing machine

2.    Traffic signal system

3.    Home heating system (without sensing, feedback and control)

 

Any non-feedback control system can be considered as a feedback control system if it is under the supervision of someone. These systems are simple in construction, stable and cost cheap. But these systems are inaccurate and unreliable.

As an example, let us consider a home furnace control system. This system must control the temperature in a room, keeping it constant. An open loop system usually has a timer which instructs the system to switch on the furnace for some time and then switch it off. Accuracy cannot be achieved as the system does not switch on/off based on the room temperature but it does as per the present value of time.

2.    Close-loop Control System:

Control systems in which the output has an effect upon the input quantity in order to maintain the desired output value are called closed loop systems. The provision of feedback automatically corrects the changes in output due to disturbances. Hence the closed loop system is also called automatic control system.

 

In a closed loop control system, the system's controlled variable (output) is sensed at each moment of time, fed back on, and compared to the desired input to produce an error signal. This error signal instructs the system's control components to make the appropriate adjustments so that the expected system output is produced. The feedback control system takes into account the disturbances also and makes the corrective action. These control systems are accurate, stable and less affected by noise. But these control systems are sophisticated and hence costly. They are also complicated to design for stability, give oscillatory response and feedback brings down the overall gain of the control system.

Examples of Close-loop Control System:

1.    Household examples: ACs, fridge, toaster

2.    Rocket launching system, radar tracking system, etc. 

Difference between Open-Loop Control System and Closed-Loop Control System:

 

Basis of Difference	Open Loop Control System	Closed Loop Control System
Definition	A control system in which there is no feedback path is provided is called an open loop control system.	The control system in which there is a feedback path present is called a closed loop control system.
Also called	Open loop control system is also called non-feedback control system.	Closed loop control system is also called a feedback control system.
Control action	In open loop control system, the control action is independent of the output of the overall system.	In closed loop control system, the control action is dependent on the output of the system.
Design complexity	The design and construction of an open loop control system is quite simple.	Closed loop control system has comparatively complex design and construction.
Main Components	The major components of an open loop control system are − controller and plant.	The main components of a closed loop control system are − Controller, plant or process, feedback element and error detector (comparator).
Response	Open loop control system has fast response because there is no measurement and feedback of output.	The response of the closed loop control system is slow due to presence of feedback.
Reliability	The reliability of open loop control system is less.	The closed loop control system is more reliable.
Accuracy	The accuracy of open loop control system depends upon the system calibration and therefore, may be less.	Closed loop control system is comparatively accurate because the feedback maintains its accuracy.
Stability (in terms of output)	The stability of open loop control system is more, i.e., the output of the open loop system remains constant.	Closed loop control system is comparatively less stable.
Optimization	The open loop control system is not optimized.	Closed loop control system is optimized to produce the desired output.
Maintenance	Open loop control system requires less maintenance.	Comparatively more maintenance is needed in closed loop control system.
Implementation	Open loop control system is easy to implement.	The implementation of a closed loop control system is relatively difficult.
Cost	Open loop control system is less expensive.	The cost of the closed loop control system is relatively high.
Noise	Open loop control system has more internal noise.	In closed loop system, the internal noise in the system is less.
Examples	Common practical examples of open loop control systems are − automatic traffic light system, automatic washing machine, immersion heater, etc.	Examples of closed loop control systems include: ACs, fridge, toaster, rocket launching system, radar tracking system, etc.

 

Advantages of Open loop control system: 

1.    Open loop systems are simpler and affordable.

2.    Open loop systems are easier to build.

3.    Open loop systems are typically stable.

 

Disadvantages of open loop systems:

1.    Open loop systems are unreliable and imprecise.

2.    The output changes brought on by disruptions from the outside are not automatically adjusted.

 

Advantages of closed loop systems:

1.    The closed loop systems are accurate.

2.    Even when non-linearities are present, closed loop systems are accurate.

3.    To make the system more stable, the sensitivity of the systems may be reduced.

4.    The closed loop systems are less affected by noise.

 

Disadvantages of closed loop systems:

1.    Closed loop systems are expensive and complicated.

2.    An oscillating response could result from the feedback in a closed loop system.

3.    The feedback reduces the overall gain of the system.

4.    A closed loop system's lack of stability is a serious issue, hence extra care must be taken while designing a reliable closed loop system.

 

Conclusion:

 

The most significant difference between open and closed loop control systems is that an open loop control system has no feedback path, while a closed loop control system has feedback path. Many automatic processes, including traffic lights, automatic washing machines, temperature control systems in refrigerators and air conditioners, etc., use both open loop and closed loop control systems.

 

References:

1.     Chole Kirner.(2022).“The Role of Controls in Mechatronic Systems.”

2.     Shunmathi M*.(2019). “Control System in Mechatronics -A Review.”

3.     Santhakumar Raja.(2020). “Control System in Mechatronics – Open loop, Closed loop Control System.”

Authors - 

Harsha Mamdyal

Vaishnavi Mane 

Pratham Matal 

Muthu Krishnan 

Shivani Padamwar