Flexible Manufacturing Systems

Closed-loop control process

A closed-loop control process has a feedback that is related to the output of the system. Take for example a flow control system, the system has as input a desired value, also known as setpoint, and this setpoint is received by a controller that acts on the process sending a control signal to a flow valve. So far we have described an open control loop where there is no feedback.

To close the loop, it is required a sensor that measures the flow that varies according to the position of the valve, in this way the flow sensor measurement represents the feedback of the system.

The system then calculates the error or difference between the flow set point (reference value) and the feedback value, also called process value, which is processed by the controller to again act on the valve which will simultaneously produce a variant of the flow. At the end the goal is that the difference or error between the reference and feedback is closest to zero.

Closed-Loop Control Process

In closed-loop control systems it is very important to determine the correct control equation and the gains or factors thereof to have a well-tuned control where the reference value is reached (error equal to zero) in a suitable time.

The measured variable from the sensor must send the signal back to the controller in real time, to have an acceptable response time.

By applying this closed-loop principle to different workstations that have a function into a manufacture, we obtain a computer integrated manufacture.


The computer integrated manufacture have the possibility to adapt the system according to the process requirements. This type of systems are also called flexible manufacturing systems (FMS).

Flexible Manufacturing Systems

Flexible manufacturing systems allow the system to adapt to changes easily. For example, the system can change to produce some new product easily or change the execution of manufacturing operations, this is known as machine flexibility.

The flexible manufacturing systems can offer redundancy of the process, where they allow to use different machines to generate the same product and thus to eliminate the dead times, or to change the capacity of production of the system, to adapt to the demands of the market, this is known as routine flexibility.

This flexibility of the system allows to adapt the factory to be more efficient, for example, the factory can change the process according to the availability and price of the raw material, as well as the demand of the product.

This flexibility makes the system more efficient, but it is also necessary to consider the cost of implementation and maintenance of the system because it is a more complex system.

Basically a flexible manufacturing system consists of three parts:

Workstations: Also known as CNC (Computer Numerical Control), which perform different functions on the parts, such as loading and unloading, assembly, inspections, formers, etc.

Automated material handling and storage system: These systems are used to transport parts between workstations and sometimes store them in warehouses once finished.

Control System: It is responsible for organizing the different tasks performed by the workstations and managing the automated system of handling and storage. Has control over each of the workstations. It can also monitor and generate reports.

Flexible Manufacturing System components

An example of FMS application is the automotive industry, where it is necessary to assemble different types of parts to produce different types of cars, using the same machinery.