1.1 AUTOMATION DEFINED
Automation is a technology concemed with the application of
mechanical, electronic, and computer-based systems to operate and
control production. This technology includes :
- Automatic machine tools to process parts
- Automatic assembly machines
- Industrial robots
- Automatic material handling and storage systems
- Automatic inspection systems for quality control
- Feedback control and computer process control
- Computer systems for planning, data collection, and decision making to support manufacturing activities
The
scope of this text will be limited primarily to automated systems used
in discrete-product manufacturing. Examples of industries using these
types of systems include : metalworking, electronics, automotive,
appliances, aircraft, and many others.
Types of automation
For our purposes in this book, automated production systems can best be classified into three basic types :
For our purposes in this book, automated production systems can best be classified into three basic types :
- Fixed automation
- Programmable automation
- Flexible automation
Fixed
automation is a system in which the sequence of processing (or
assembly) operations is fixed by the equipment configuration, The
operations in the sequence are usually simple. lt is the integration and
coordination of many such operations into one piece of equipment that
makes the system complex. The typical features of fixed automation are :
- High initial investment for custom-engineered equipment
- High production rates
- Relatively inflexible in accommodating product changes
The
economic justification for fixed automation is found in products with
very high demand rates and volumes. The high initial cost of the
equipment can be spread over a very large number of units, thus making
the unit cost attractive compared to altemative methods of production.
Examples of fixed automation include mechanized assembly lines (starting
around 1913 - the product moved along mechanized conveyors, but the
workstations
along the line were manually operated) and machining transfer lines (beginning around 1924).
along the line were manually operated) and machining transfer lines (beginning around 1924).
ln
programmable automation, the production equipment is designed with the
capability to change the sequence of operations to accommodate different
product configurations. The operation sequence is controlled by a
program, which is a set of instructions coded so that the system can
read and interpret them. New programs can be prepared and entered into
the equipment to produce new products. Some of the features that
characterize programmable automation include :
- High investment in general-purpose equipment
- Low production rates relative to fixed automation
- Flexibility to deal with changes in product configuration
- Most suitable for batch production
Automated
production systems that are programmable are used in low and
medium-volume production. The parts or products are typically made in
batches. To produce each new batch of a different product, the system
must be reprogrammed with the set of machine instructions that
correspond to the new product. The physical setup of the machine must
also be changed over: Tools must be loaded, fixtures must be attached to
the machine table, and the required machine settings must be entered.
This changeover procedure takes time. Consequently, the typical cycle
for a given product includes a period during which the setup and
reprogramming takes place, followed by a period in which the batch is
produced. Examples of programmable automation include numerically
controlled machine tools (first prototype demonstrated in l952) and
industrial robots (initial applications around 1961), although the
technology has its roots in the Jacquard loom (1801).
Flexible
automation is an extension of programmable automation. The concept of
flexible automation has developed only over the last 15 or 20 years, and
the principles are still evolving. A tlexible automated system is one
that is capable of producing a variety of products (or parts) with
virtually no time lost for changeovers from one product to the next.
There is no production time lost while reprogramming the system and
altering the physical setup (tooling, fixtures, machine settings).
Consequently, the system can produce various combinations and schedules
of products, instead of requiring that they be made in separate batches.
The features of flexible automation can be summarized as follows :
- High investment for a custom-engineered system
- Continuous production of variable mixtures of products
- Medium production rates
- Flexibility to deal with product design variations
The
essential features that distinguish flexible automation from
programmable automation are : (1) the capacity to change part programs
with no lost production time, and (2) the capability to change over the
physical setup, again with no lost production time. These features allow
the automated production system to continue production without the
downtime between batches that is characteristic of programmable
automation. Changing the part programs is generally accomplished by
preparing the programs off-line on a computer system and electronically
transmitting the programs to the automated production system. Therefore,
the time required to do the programming for the next job does not
interupt production on the current job. Advances in computer systems
technology are largely responsible for this progamming capability in
flexible automation. Changing the physical setup between pans is
accomplished by making the changeover off-line and then moving it into
place simultaneously as the next part comes into position for
processing. The use of pallet fixtures that hold the parts and transfer
into position at the workplace is one way of implementing this approach.
For these approaches to be successful, the variety of pans that can be
made on a flexible automated production system is usually more limited
than a system controlled by programmable automation. Examples of
flexible automation are the llexible manufacturing systems for
perfonning machining operations that date back to the late l960s.
The
relative positions of the three types of automation for different
production volumes and product varieties are depicted in Figure 1.1.
Computer integrated manufacturing
The computer has had and continues to have a dramatic impact on the development of production automation technologies. Nearly all modem production systems are implemented today using computer systems. The term computer integrated manufacturing (CIM) has been coined to denote the pervasive use of computers to design the products, plan the production, control the operations, and perform the various business related functions needed in a manufacturing fimt. CAD/CAM (computer-aided design and computer-aided manufacturing) is another term that is used almost synonymously with CIM.
The computer has had and continues to have a dramatic impact on the development of production automation technologies. Nearly all modem production systems are implemented today using computer systems. The term computer integrated manufacturing (CIM) has been coined to denote the pervasive use of computers to design the products, plan the production, control the operations, and perform the various business related functions needed in a manufacturing fimt. CAD/CAM (computer-aided design and computer-aided manufacturing) is another term that is used almost synonymously with CIM.
FIGURE 1.1 Three types of production automation as a function of production volume and product variety.
Let
us attempt to define the relationship between automation and CIM by
developing a conceptual model of manufacturing. ln a manufacturing firm,
the physical activities related to production that take place in the
factory can be distinguished from the information-processing activities,
such as product design and production planning, that usually occur in
an office environment. The physical activities include all of the
manufacturing processing, assembly, material handling, and inspections
that are perfomied on the product. These operations come in direct
contact with the product during manufacture. They touch the product. The
relationship between the physical activities and the
information-processing activities in our model is depicted in Figure
1.2. Raw materials fiow in one end of the factory and finished products
fiow out the other end. The physical activities (processing, handling,
etc.) take place inside the factory. The information-processing
functions form a ring that surrounds the factory, providing the data and
knowledge required to produce the product successfully. These
information-processing functions include (1) certain business activities
(e.g., marketing and sales, order entry. customer billing, etc.), (2)
product design, (3) manufacturing planning, and (4) manufacturing
control. These four functions form a cycle of events that must accompany
the physical production activities but which do not directly touch the
product.
Now consider the difference between automation and CIM.
Automation is concemed with the physical activities in manufacturing.
Automated production systems are designed to accomplish the processing,
assembly, material handling, and inspecting activities with little or no
human participation. By comparison, computer integrated manufacturing
is concerned more with the information-processing functions that are
required to support the production operations. CIM involves the use of
computer systems to perfomi the four types of information-processing
functions. Just as automation deals with the physical activities, CIM
deals with automating the information-processing activities in
manufacturing. The growing applications of computer systems in
manufacturing are leading us toward thc computer-automated factory at
the future.
FIGURE
1.2 Model of manufacturing, showing (e) the factory as a processing
pipeline where the physical manufacturing activities are performed, and
(b) the information-processing activities that support manufacturing as a
ring that surrounds the factory.
We will return to our model of
manufacturing in Chapter 2 and to the topics of CIM, CAD/CAM, and the
future automated factory in the final chapters. For now let us consider some of the more general issues related to automation and computer-integrated manufacturing.
1 Komentar:
Are you Looking for Industrial Summer training on Automation System like PLC, SCADA? Then you can join DIAC Automation Technology. Call @9310096831.
Posting Komentar
Berlangganan Posting Komentar [Atom]
<< Beranda