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PROCESS CHARTS:
The charting of work flows, working processes, systems and procedures is a
useful way of recording the essential features of a work situation for subsequent
analysis.
Process Charts are one of the simpler forms of workflow charting and are still
in regular usage but are less common than they once were (see Process Mapping).
This is unfortunate since it was the ubiquitous nature of the process chart
that made it a common "language" between different groups of people
and across different industries.
A variety of process charts has been designed to meet the needs of a particular
level or stage of analysis; they can be used at a detailed level (recording
activity at a specific work station or workplace), but also at the wider system,
process or procedure level.
The different kinds of process chart share a common core set of symbols, though
some have additional symbols for specific and specialised process steps. The
common symbols (of which there are only five) were first promulgated by the
American Society of Mechanical Engineers and have become known as the ASME symbols.
OPERATION : a main step, where the part, material or product is usually modified
or changed
INSPECTION : indicates a check for quality or quantity
TRANSPORT : the movement of workers, materials or equipment
STORAGE : controlled storage in which material is received into or issued from
a store, or an item is retained for reference purposes
DELAY or TEMPORARY STORAGE : indicates a delay in the process, or an object
laid aside until required
These symbols are simple linked together in a vertical chart representing the
key stages in a process; it is usual to place a commentary in an adjoining column
recording contextual/environmental information. e.g. against a Transport symbol
would be recorded, start of journey, end of journey, distance and mode of transport.
The simplest form of process chart is known as an outline process chart and
records an overview (or outline) of a process. Only those steps of a process
that can be represented by the ASME symbols of operation and inspection are
recorded. An outline process chart is often a useful first step to identify
key areas of concern before recording (part of) the process in more detail.
In a "full" process chart, where all symbols are used, it is common
to chart the process from the "viewpoint" of the material being processed,
the worker carrying out the work or, less commonly, a piece of equipment. Thus,
the same symbols can be used in different ways. As a simple example, a piece
of equipment can be represented on an equipment-type flow process chart as a
"delay" (because it is not in use) while a material-type flow process
chart (of the same process) would show the material being transported to the
next work station, and a man-type chart could show the operator involved in
another operation on another machine.
The chart to be used may be determined by the purpose of the investigation
or by the relative costs involved in the process - a highly capital-intensive
process may focus more attention on the equipment being used.
Process charts may also be used at a more micro level of analysis. An example
is the two-handed process chart which records the motions performed by both
hands during a task. The sequence of motion of each hand is charted using the
same symbols as before. There are slight changes to the meaning of the symbols,
however. The delay symbol is used to indicate that the hand is waiting to carry
out its next task. The storage symbol is used to indicate that the hand is holding
on to a piece of material or a document. Two-handed process charts are usually
drawn on a pre-formatted diagram. Their use has generally been superceded by
the analyses involved in the use of low level pre-determined motion times systems.
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