I originally published this article under the title, “The Presentation of Parts for Robot Assembly” in the book “Advances in Manufacturing Technology”, Kogan Page, London, ISBN 1.85091.3951 ...
The presentation of parts for robot assembly involves the selection of
the correct parts handling devices and it influences the robot degrees
of freedom required. The design of appropriate feeders is discussed,
with an emphasis on their flexibility. A classification system is
described that allows parts to be categorised by their design features
and physical properties. The performance of an automatic parts feeder
is shown to depend upon the design of the part that is being handled. A
selection procedure is described that enables the correct handling
device and robot configuration to be chosen for a particular
application. An expert system is shown to be the best method of
acquiring design information about the handle-ability of a part.
A software package that simplifies the selection of parts feeders and
robot configurations is described. The importance of knowledge transfer
between industrialists and researchers, in defining relevant handling
devices, is discussed. The development of an enhanced CAD system is the
subject of a further publication.
INTRODUCTION
The presentation of parts to a robot presents some of the most
difficult problems in robot assembly. Single cell robot assembly
systems may assemble a complete product consisting of several parts.
These parts have to be presented to the robot at the correct rate and
in a known orientation, or a limited number of known orientations. The
rate of supply of parts to the robot cell is seldom a problem because
cycle times are usually long. The orientation of the part, at the exit
of the parts feeding device, is critical because this influences many
other factors. The orientation of a particular design of part at
the feeder exit can be predicted using knowledge of handling device
design. Parts are classified according to size, geometry, etc. so that
feeding device performance can be qualified. Using a standard parts
coding system, feeder performance can be matched with that required for
a particular design of part. The orientation of the part, at the exit
of the automatic feeder, can be predicted and the need for extra robot
degrees of freedom can be determined. The presentation of parts for
robot assembly is a complex problem and it’s best carried out using a
software application.
PARTS PRESENTATION TECHNIQUES
A multitude of automatic feeders are available to handle a wide variety
of parts. However, only a small proportion of these automatic feeders
are economically viable for robot assembly. For robot assembly,
an automatic parts feeder must have a high general-purpose content and
a low special-purpose content, so that the flexibility of the robot is
not compromised by the inflexibility of its feeders. The vibratory
linear feeder has a low cost special-purpose feed track that is mounted
on a general-purpose drive unit and frame. The device is very
flexible because changeover is effected by removing the current feed
track and replacing it with a feed track for the next part. The
vibratory bowl feeder consists of medium cost special-purpose tooling
that is mounted around the periphery of a general-purpose bowl. The
feeder is generally inflexible and the time associated with part
changeover makes it unsuitable for many applications with small batch
sizes. The horizontal pallet transfer system has low cost
special-purpose pallets that move into, and out of, the work zone by a
general-purpose transfer system. Flexibility is achieved by using
different pallet configurations or by simply changing the pallet
contents. The 'Hitachi' type feeder works on a similar principle to the
vibratory bowl feeder, with the special-purpose tooling being replaced
by a vision system. Within certain geometrical and size limitations,
this device is highly flexible; using a vision system to identify part
orientations. The programmable belt feeder uses special-purpose pushers
and gates, activated by a vision system or sensors, mounted above a
general-purpose belt. Product changeover is achieved by using a
different vision system computer program or by replacing the pushers
and gates.
No comments:
Post a Comment