I originally presented this article, "Design for Robot Assembly", as a
guest speaker at the UK's 2nd National Conference on Production
Research ...
SUMMARY
The design of products and systems for robot assembly requires a new
approach to that used for manual and automatic assembly. Robot
assembly is only effective if the robot’s flexibility is used to best
advantage. Additionally, peripheral devices supporting the robot
must also be adaptable to handle a wide variety of products and product
parts. This is achieved by using equipment that is not designed
specifically to handle a particular type of part with minor
modifications to tooling, or the use of a different software
application, the robot assembly system can be quickly adapted to
assemble a different product or product style. By this method,
robot assembly can be economically justifiable in many situations where
it would otherwise have been precluded.
This article discusses the development of robot assembly systems and
describes how product design plays an important role in the design of
the equipment.
INTRODUCTION
There are three categories of system used in product assembly.
These are manual assembly, automatic assembly and robot assembly.
Whilst assembly can be classified in this manner, it is not uncommon to
find an assembly system consisting of two or all of these groups to
form a hybrid system. Manual assembly systems account for the
majority of applications. Automatic systems are used in
situations where the demand is high and there is no, or limited, change
in the product styles being assembled. Robots have yet to make a
significant impact in the field of assembly. It’s difficult to
technically justify the use of assembly robots as the operation time of
programmable devices is longer than that of dedicated automatic
equipment. The economic justification of assembly by robots is
equally difficult due to the characteristically small batch sizes for
which these systems are appropriate. This has the effect of
increasing the handling and insertion costs of the product being
assembled.
Manual assembly is still used for more than ninety per cent of all
assembly tasks. This is because many products are required in low
volumes and with a high degree of variety. Robot assembly could
account for more than fifty per cent of all assembly tasks if it could
be made to be economic for much smaller annual production volumes. This
could be achieved by assembling more than one family of products on one
system. For this approach to be effective, two major conditions
must be met. The proportion of re-usable, or general-purpose,
equipment must be high and the time taken to re-configure the system
for the assembly of the next product must be low.
Using existing technology, the industrial applications where robots can
readily be used have been filled. These applications include
paint spraying, spot welding and materials handling. Only a very
small proportion of existing robots are used for assembly.
Robot assembly system equipment is either general-purpose or
special-purpose. A robot assembly system should have a high
proportion of general-purpose equipment and a low proportion of
special-purpose equipment. The cost of a system, with a high proportion
of general-purpose equipment, can be amortised by all the products that
are being assembled by the robot. This is important when trying
to economically justify the use of robot assembly for products required
in low volumes. Under these conditions, many products or product
styles, each with a low annual volume, can be grouped together and
assembled on a single robot assembly station to obtain a high system
utilisation.
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