A flexible manufacturing system (FMS) is a manufacturing system in which there is some amount of flexibility that allows the system to react in the case of changes, whether predicted or unpredicted. This flexibility is generally considered to fall into two categories, which both contain numerous subcategories.
The first category, machine flexibility, covers the system's ability to be changed to produce new product types, and ability to change the order of operations executed on a part. The second category is called routing flexibility, which consists of the ability to use multiple machines to perform the same operation on a part, as well as the system's ability to absorb large-scale changes, such as in volume, capacity, or capability.
Most FMS systems comprise of three main systems. The work machines which are often automated CNC machines are connected by a material handling system to optimize parts flow and the central control computer which controls material movements and machine flow.
The main advantages of an FMS is its high flexibility in managing manufacturing resources like time and effort in order to manufacture a new product. The best application of an FMS is found in the production of small sets of products like those from a mass production.
Industrial FMS Communication
An Industrial Flexible Manufacturing System (FMS) consists of robots, Computer-controlled Machines, Numerical controlled machines (CNC), instrumentation devices, computers, sensors, and other stand alone systems such as inspection machines. The use of robots in the production segment of manufacturing industries promises a variety of benefits ranging from high utilization to high volume of productivity. Each Robotic cell or node will be located along a material handling system such as a conveyor or automatic guided vehicle. The production of each part or work-piece will require a different combination of manufacturing nodes. The movement of parts from one node to another is done through the material handling system. At the end of part processing, the finished parts will be routed to an automatic inspection node, and subsequently unloaded from the Flexible Manufacturing System.
The FMS data traffic consists of large files and short messages, and mostly come from nodes, devices and instruments. The message size ranges between a few bytes to several hundreds of bytes. Executive software and other data, for example, are files with a large size, while messages for machining data, instrument to instrument communications, status monitoring, and data reporting are transmitted in small size.
There is also some variation on response time. Large program files from a main computer usually take about 60 seconds to be down loaded into each instrument or node at the beginning of FMS operation. Messages for instrument data need to be sent in a periodic time with deterministic time delay. Other type of messages used for emergency reporting is quite short in size and must be transmitted and received with almost instantaneous response.
The demands for reliable FMS protocol that support all the FMS data characteristics are now urgent. The existing IEEE standard protocols do not fully satisfy the real time communication requirements in this environment. The delay of CSMA/CD is unbounded as the number of nodes increases due to the message collisions. Token Bus has a deterministic message delay, but it does not support prioritized access scheme which is needed in FMS communications. Token Ring provides prioritized access and has a low message delay, however, its data transmission is unreliable. A single node failure which may occur quite often in FMS causes transmission errors of passing message in that node. In addition, the topology of Token Ring results in high wiring installation and cost.
A design of FMS communication protocol that supports a real time communication with bounded message delay and reacts promptly to any emergency signal is needed. Because of machine failure and malfunction due to heat, dust, and electromagnetic interference is common, a prioritized mechanism and immediate transmission of emergency messages are needed so that a suitable recovery procedure can be applied. A modification of standard Token Bus to implement a prioritized access scheme was proposed to allow transmission of short and periodic messages with a low delay compared to the one for long messages.
In the middle of the 1960s, market competition became more intense.
During 1960 to 1970 cost was the primary concern. Later quality became a priority. As the market became more and more complex, speed of delivery became something customer also needed.
A new strategy was formulated: Customizability. The companies have to adapt to the environment in which they operate, to be more flexible in their operations and to satisfy different market segments (customizability).
Thus the innovation of FMS became related to the effort of gaining competitive advantage.
First of all, FMS is a manufacturing technology.
Secondly, FMS is a philosophy. "System" is the key word. Philosophically, FMS incorporates a system view of manufacturing. The buzz word for today’s manufacturer is "agility". An agile manufacturer is one who is the fastest to the market, operates with the lowest total cost and has the greatest ability to "delight" its customers. FMS is simply one way that manufacturers are able to achieve this agility.
An MIT study on competitiveness pointed out that American companies spent twice as much on product innovation as they did on process innovation. Germans and Japanese did just the opposite.
In studying FMS, we need to keep in mind what Peter Drucker said: "We must become managers of technology not merely users of technology".
Since FMS is a technology, well adjusted to the environmental needs, we have to manage it successfully.
So, what is flexibility in manufacturing?
While variations abound in what specifically constitutes flexibility, there is a general consensus about the core elements. There are three levels of manufacturing flexibility.
(a) Basic flexibilities
* Machine flexibility - the ease with which a machine can process various operations
* Material handling flexibility - a measure of the ease with which different part types can be transported and properly positioned at the various machine tools in a system
* Operation flexibility - a measure of the ease with which alternative operation sequences can be used for processing a part type
(b) System flexibilities
* Volume flexibility - a measure of a system’s capability to be operated profitably at different volumes of the existing part types
* Expansion flexibility - the ability to build a system and expand it incrementally
* Routing flexibility - a measure of the alternative paths that a part can effectively follow through a system for a given process plan
* Process flexibility - a measure of the volume of the set of part types that a system can produce without incurring any setup
* Product flexibility - the volume of the set of part types that can be manufactured in a system with minor setup
(c) Aggregate flexibilities
* Program flexibility - the ability of a system to run for reasonably long periods without external intervention
* Production flexibility - the volume of the set of part types that a system can produce without major investment in capital equipment
* Market flexibility - the ability of a system to efficiently adapt to changing market conditions
2. Seeking benefits on flexibility
Today’s manufacturing strategy is to seek benefits from flexibility. This is only feasible when a production system is under complete control of FMS technology. Having in mind the Process- Product Matrix you may realize that for an industry it is possible to reach for high flexibility by making innovative technical and organizational efforts. See the Volvo’s process structure that makes cars on movable pallets, rather than an assembly line. The process gains in flexibility. Also, the Volvo system has more flexibility because it uses multi-skill operators who are not paced by a mechanical line.
So we may search for benefits from flexibility on moving to the job shop structures.
Actually, the need is for flexible processes to permit rapid low cost switching from one product line to another. This is possible with flexible workers whose multiple skills would develop the ability to switch easily from one kind of task to another.
As main resources, flexible processes and flexible workers would create flexible plants as plants which can adapt to changes in real time, using movable equipment, knockdown walls and easily accessible and re-routable utilities.
3. FMS- an example of technology and an alternative layout
The idea of an FMS was proposed in England (1960s) under the name "System 24", a flexible machining system that could operate without human operators 24 hours a day under computer control. From the beginning the emphasis was on automation rather than the "reorganization of workflow".
Early FMSs were large and very complex, consisting of dozens of Computer Numerical Controlled machines (CNC) and sophisticate material handling systems. They were very automated, very expensive and controlled by incredibly complex software. There were only a limited number of industries that could afford investing in a traditional FMS as described above.
Currently, the trend in FMS is toward small versions of the traditional FMS, called flexible manufacturing cells (FMC).
Today two or more CNC machines are considered a flexible cell and two ore more cells are considered a flexible manufacturing system.
Thus, a Flexible Manufacturing System (FMS) consists of several machine tools along with part and tool handling devices such as robots, arranged so that it can handle any family of parts for which it has been designed and developed.
* Faster, lower- cost changes from one part to another which will improve capital utilization
* Lower direct labor cost, due to the reduction in number of workers
* Reduced inventory, due to the planning and programming precision
* Consistent and better quality, due to the automated control
* Lower cost/unit of output, due to the greater productivity using the same number of workers
* Savings from the indirect labor, from reduced errors, rework, repairs and rejects
* Productivity increment due to automation
* Preparation time for new products is shorter due to flexibility
* Saved labor cost, due to automation
* Improved production quality, due to automation
o However, it is not always necessary that on increasing flexibility productivity also increases.
* Limited ability to adapt to changes in product or product mix (ex. machines are of limited capacity and the tooling necessary for products, even of the same family, is not always feasible in a given FMS)
* Substantial pre-planning activity
* Expensive, costing millions of dollars
* Technological problems of exact component positioning and precise timing necessary to process a component
* Sophisticated manufacturing systems