Page 20 - Electric Drives and Electromechanical Systems

12 Electric Drives and Electromechanical Systems

1.2.4 Machining centres

The introduction of CNC systems has had a significant effect on the design of machine
tools. The increased cost of machine tools requires higher utilisation; for example,
instead of a manual machine running for a single shift, a CNC machine may be required
to run continually for an extended period. The penalty for this is that the machine must
be designed to withstand the extra wear and tear. It is possible for CNC machines to
reduce the non-productive time in the operating cycle by the application of automation,
such as the loading and unloading of parts and tool changing. Under automatic tool
changing several tools are stored in a magazine; the tools are selected, when they are
required, by a program and they are loaded into the machining head, and as this occurs
the system will be updated with changes in the cutting parameters and tool offsets.
Inspection probes can also be stored, allowing in-machine inspection. In a machining
centre fitted with automatic part changing, parts can be presented to the machine on
pallets, allowing for work to be removed from an area of the machine without stopping
the machining cycle. This will give a far better usage of the machine, including un-
manned operation. It has been estimated that seventy per cent of all manufacturing is
carried out in batches of fifty or less. With manual operation (or even with program-
mable automation) batches of these sizes were uneconomical; however, with the
introduction of advanced machining centres together with additive manufacturing, the
economic-batch size is equal to or approaching one.

1.3 Robotics

The development of the industrial robot can be traced to the work undertaken in the
United States at the Oak Ridge and Algonne National Laboratories into mechanical
teleoperated manipulators for handling nuclear material during the 1940’s. It was soon
realised that, by the addition of powered actuators and a stored program system, a
manipulator could perform the autonomous and repetitive tasks. Even with the
considerable advances in sensing systems, control strategies, and artificial intelligence,
the current range of industrial robots are not significantly different from the initial
concept. Industrial robots can be considered to be general-purpose reprogrammable
machine tools moving an end effector, which holds either components or a tool. The
functions of a robot are best summarised by considering the following definition of an
industrial robot as used by the Robotic Industries Association (Shell and Hall, 2000);

An industrial robot is a reprogrammabledevicedesignedtobothmanipulate
and transport parts, tools, or specialised manufacturing implements through
programmed motions for the performance of specific manufacturing tasks.

Since the early industrial robots, technology has advanced considerable with the
development of both static and mobile robots that include sensors (e.g. vision or tactile)