Page 10 - Electric Drives and Electromechanical Systems

2 Electric Drives and Electromechanical Systems

1.1 Principles of automation

Automation is defined as the technology which is concerned with the application of
mechanical, electrical, and computer systems in the operation and control of a pro-
cesses. In general, an automated production process can be classified into one of three
groups: fixed, programmable, or flexible.

Fixed automation is typically employed for products with a very high production
rate; the high initial cost of fixed-automation plant can therefore be spread over a
very large number of units. Fixed-automation systems are used to manufacture
products as diverse as cigarettes and steel nails. The significant feature of fixed
automation is that the sequence of the manufacturing operations is fixed by the
design of the production machinery, and therefore the sequence cannot easily be
modified at a later stage of a product’s life cycle.
Programmable automation can be considered to exist where the production
equipment is designed to allow a range of similar products to be produced. The
production sequence is controlled by a stored program, but to achieve a prod-
uct change-over, considerable reprogramming and tooling changes will be
required. In any case, the process machine is a stand-alone item, operating
independently of any other machine in the factory; this principle of automation
can be found in most manufacturing processes and it leads to islands of auto-
mation. The concept of programmable automation has its roots in the Jacquard
looms of the nineteenth century, where weaving patterns were stored on a
punched-card system.
Flexible automation is an enhancement of programmable automation in which a
computer-based manufacturing system has the capability to change the
manufacturing program and the physical configuration of the machine tool or cell
with a minimal loss in production time. In many systems the machining programs
are prepared at a location remote from the machine, and they are then transmitted
as required over a computer-based local-area communication network.

The basic design of machine tools and other systems used in manufacturing pro-
cesses changed little from the eighteenth century to the late 1940s. There was a gradual
improvement during this period as the metal cutting changed from an art to a science as
there was an increased understanding of the materials used in cutting tools. However,
the first significant change to machine-tool technology was the introduction of
numerical-control (NC) and computer-numerical-control (CNC) systems.
To an operator, the differences between these two technologies are small, both
operate from a stored program, which was originally on punched tape, then computer
media such as magnetic tapes and discs, and currently stored centrally and distributed
over a network. The stored program in a NC machine is directly read and used to control
the machine; the logic within the controller is dedicated to that task. A CNC machine tool
incorporates a dedicated computer to execute the program. The use of the computer