THE HANDLING OF PARTS FOR ROBOT ASSEMBLY
Handling device selection for a particular part depends on the size and
geometry of a part, as well as the rate at which the part is
required. Each handling device has its own performance
characteristics. This means that it is suitable for dealing with
a limited range of parts. Small to medium sized parts, with
features that can be seen in silhouette, can be handled by the most
common of devices, the vibratory bowl feeder. Parts with no
useful features for orientation purposes, or parts with adverse
physical properties, are expensive to feed automatically and require
special automatic feeding devices. These types of parts need to
be re-designed to reduce their cost for automatic feeding. There
are many properties of a part that would prevent it from being handled
by vibratory bowl feeders, such as flexibility and stickiness.
Parts with adverse properties such as these, and larger parts, must be
handled by other feeding devices like magazine systems or pallet
transfer systems.
The multi-part linear vibratory linear feeder can deliver different
parts to a robot assembly station. It consists of two straight
and parallel vibratory orientating tracks on a common drive unit.
The rejected parts fall into return tracks and are brought to the start
of the orientating tracks by a reciprocating elevator. The tracks
can be CNC machined from a database of designs that are identified by
an automated handling code for a particular part. Only the
orientating tracks are replaced to changeover this multi-part feeder to
handle other part types. The vibratory drive unit and
reciprocating elevator are completely re-usable and the cost of these
devices is divided between the different part types. The
orientating track for this multi-part feeder is straight and it is much
less expensive to produce than the curved orientating track of a
vibratory bowl feeder. Applications of this feeder are limited to
parts which require orientating devices simple enough to be produced in
one set-up on a horizontal machining centre.
Gravity feed track magazines are simply short lengths of track which
are loaded manually on-line or off-line. During off-line loading,
a full magazine is substituted for a magazine when it becomes
empty. These magazines are specifically designed for the
particular type of part type and cannot easily be re-used for different
types of parts. Although most of the gravity feed track magazine
is special-purpose, the cost of these devices is relatively low.
They are useful far feeding large parts and they provide an economic
alternative to palletisation. Parts that are to be handled by
this type of device must be stackable, for vertical magazines, and not
susceptible to damage when the part is slid into position by the pusher.
The pallet transfer system consists of a walking beam transfer device
to load a paternoster, an unload paternoster, and pallets. Full
pallets are elevated by the load paternoster and transferred to the
robot working zone by the walking beam transfer device. Parts are
picked from the pallet and the pallets are then indexed to present a
new pallet of parts to the robot. Empty pallets are offloaded
from the walking beam by an unload paternoster that produces a stack of
empty pallets. Virtually all of the pallet transfer system is
general-purpose, with only the vacuum-formed part retainers being
specific to a particular component. Pallets are loaded by
standard means. Filling of the pallets at the point of
manufacture is a very economic way of loading parts, although the cycle
time of most manufacturing operations makes it difficult to use this
method of loading. Parts are positively held in position on the
pallet by ensuring that they are sandwiched between the underside of
one pallet and the top of the one beneath.
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