Feeding
Challenges And
Solutions For Odd-Form Parts
Written
By:
Gregory Holcomb
Presented at Apex 2000
Abstract
The ready availability of parts feeders from different odd-form assembly
equipment suppliers may at first seem to make a purchase decision easy--just
select the low priced feeder that will handle the part. However things
are not always as simple as they seem, especially when it comes to selecting
reliable parts feeding solutions. Among the many issues to consider are
reliability, maintainability, flexibility, control method, and initial
cost. Equally important is the "true cost" which includes the real costs
of downtime, maintenance, parts inventory, and parts reloading. Finally,
a thorough and careful evaluation of the supplier's product history,
product quality, and verifiable reliability are needed to ensure a feeder
that can meet the special requirements of successful odd-form assembly.
Introduction
The demand for effective odd-form automation is greater today than ever before.
Since the advent of surface mount, the status of odd-form components,
both surface mount and thru-hole, has dramatically changed. As more thru-hole
components are converted to surface mount, the remaining "standard" thru-hole
components are becoming odd-form by "default" due to their decreased
ratio of use. And the true odd-form by "design" components have not diminished.
These two factors combined with a better understanding of the value of
automation are what is driving the growth of odd-form today. Ceeris International
has noted a marked increase in the number of clients requesting research
and market information on odd-form assembly equipment with observed growth
not just in North America, but Europe and Asia as well.
Odd-form
components remain the most challenging components in board assembly
due to the obvious need for true flexibility in the systems that
handle them. Because of their varying sizes and shapes, special
locating and handling methods are required and have been developed
to assemble them, each fulfilling a specific need.
The
first method is lead gripping. It is the most dedicated and least
flexible approach, requiring tool changes, which tend to nullify
any speed gains over the more flexible solutions, but works well
for low mix, high volume applications requiring minimum tool
changes. The second method is the use of vision systems. This
method is mechanically the most simple, but somewhat limited
in flexibility due to the complex algorithms required for some
applications, and difficulty of imaging certain component types.
The third method is 3-D compliant gripping which provides the
maximum flexibility. 3-D compliant gripping can be used for high
to low mix as well as high to low volume applications. Three-dimensional
compliance allows for both lead and body gripping, and the variable
grip technology also allows for reliable insertion in high-density
brick wall applications.
The
mix and volume of odd-form components to be assembled is an important
factor in determining the most effective handling method used,
and is also important in selecting the right feeders to most
efficiently supply parts to the system. Until the electronics
industry can agree and implement a set of packaging standards
for odd-form components, the feeding technology will continue
to require a high degree of flexibility, robustness, and reliability
to accommodate a wide range of component specs and feeding requirements.
Packaging
standardization may at first sound like a simple task, but it
has proven to be otherwise. There have been several industry
summits held over the last few years focused solely on the standardization
of packaging for odd-form components, and yet no substantial
progress has been made. Why has packaging standardization been
such a difficult task when there are so many interested in its
inception? The reasons include rapidly changing form factors,
a very large, fragmented pool of component suppliers, and a lack
of motivation globally to push for standardization. When you
consider all these variables and obstacles, the complexity of
this issue becomes clear. However the good news is, with or without
standardization there are reliable feeding solutions available.
The challenge then becomes one of finding the right feeding technology
for your budget and application.
How
Hard Can It Be?
A parts feeder seems so small and simple compared to many other system components
that you may think feeder design and technology are not as critical - but
think again. Your entire system is only as flexible and reliable as the feeders
that supply parts to it. There is no shortage of manufacturers who have automated
their odd-form assembly only to soon see parts being assembled manually again
due to lack of flexibility in their feeding systems. Many buyers who have
based their purchasing decision on price alone have struggled with their
feeders for years before finally scrapping and replacing them with feeders
of a more robust design.
So
how can this be avoided? Advances in feeding technology alone
have resulted in a wide array of price/performance solutions.
The market abounds with parts feeders from different vendors,
which makes for a great selection, but can also make the prospect
of finding the right feeders seem daunting. However with a little
knowledge and preparation, the search does not need to be complicated
- it just needs to be smart. Here are some of the most important
issues to consider when evaluating odd-form feeders and the vendors
who supply them.
Basic
Feeder Types
Basic styles of odd-form components are often classified by their packaging,
such as tubed components, taped radial components, taped axial components,
continuous pin header strip, components supplied in trays, bulk packaged
components fed from a bowl, and the GPAX tape system. Feeders are available
for all of these odd-form component styles as shown in Table 1. These feeder
types are offered by a variety of manufacturers, although the costs vary
substantially.
Table
1 - Basic Odd-Form Feeder Types
Tube
and tray feeders handle a wide range of components. Parts which
can be handled include DIP's, connectors, relays, hybrid SIP's,
headers, surface mounts, TO-220's, transformers, displays, etc.
Tube feeders actually perform two different functions, first
feeding tubes of parts through the feeder, and then taking parts
from a tube and positioning them in a locating nest.
While
some tube feeders place the tubes on an incline to feed the parts
out of the tube with the help of gravity, better performance
is obtained by feeders, which positively feed the parts. While
the incline design may have a less expensive feeding mechanism,
feeder inventory can be considerably lower than that of a feeder
that stacks the tubes horizontally. More importantly, gravity
is not very reliable for this job and may cause increased part
jamming. The greatest risk for feeder jamming or stoppage is
due to transitions and direction changes of parts as they move
through the feeder, and when utilizing an inclined tube for gravity
feeding, you have both. The part must transition from the inclined
tube to a horizontal track which also creates a change of direction
as the part exits the tube. To avoid this problem, the parts
must be positively fed, moving them in the same direction to
keep them under control at all times. A robust feeder design
honors the old adage, "Once you have control of the part, don't
lose it".
Axial
feeders can feed two leaded parts, such as resistors, diodes,
inductors, capacitors, etc. Axial feeders with cut and bend are
typically configured for only one part style and type. Some axial
feeders depend upon an integrated end effector to finish the
lead forming/cutting. This type of feeder/end effector combination
can have a negative effect on cycle time, especially if grippers
must be changed during a board build.
Radial
feeders are frequently used for capacitors, MOV's, LED's, crystals,
small transistors, etc. These feeders are a good example of an
odd-form feeder with a modular base and custom change tooling.
Typically, radial feeders have a reliable and proven mechanism
for tape feeding, and simple change parts for accommodating a
different lead spacing or sprocket hole spacing.
Continuous
pin header feeders cut headers to length from strip, and can
perform a pin pull operation for correct polarity during a later
assembly operation. The most flexible of these feeder types can
handle custom or nonstandard pin shapes as well as single and
dual row header without having to make any tool changes.
Parts
fed from a bowl must be robust enough to retain their shape and
form while being moved through the feeder. Bowl feeders have
a simple and sturdy standardized base and can handle a wide variety
of parts, however their operation and parts feeding rely entirely
on the skills and craftsmanship of the builder.
Cut/form
mechanisms can be installed on many types of feeders. On-line
lead cut/form can be effectively used to produce accurate lead
patterns. This virtually eliminates handling damage since the
lead form is produced on-line just prior to insertion, insuring
error free assembly.
Be
wary of feeders that cut carrier tape within the feeder itself
or within the workcell. Fiber dust tends to be spread from the
repeated cutting, and adhesive buildup may cause the cutting
mechanism to clog. Dust and particulate contamination will adversely
affect the mechanisms, optical sensors and vision systems.
Feeder
Reliability And Maintainability
Among
the most important issues for feeders is their reliability. Keeping
in mind that the feeder is one of the hardest worked components
of the system, it's easy to see that high reliability and good
performance required for continuous operation must be designed
and built in from the beginning. Re-engineering or rebuilding an
unreliable feeder is not a good solution for correcting a flawed
basic design. Adding "band-aid" sensors and guides to a feeder
will decrease the overall reliability, not improve it. The more
complex the feeder, the more likely failures will occur. Unreliability
is a factor that will cause more loss to your company than the
extra cost of more expensive but more reliable feeders. In most
automated production lines, even one feeder down can significantly
slow or even stop production.
Since
machines can and do fail, it is essential to investigate the
maintainability of the various feeders you are considering. Easy
access to mechanisms and controls allows for faster maintenance
and troubleshooting.
Parts
quality is an important issue and cannot be overlooked. A feeder
operating perfectly may jam when given parts out of spec. Ease
of clearing parts jams and resetting the feeder need to be considered.
The parts track should allow both inspection of parts on the
track and physical access to manually clear any possible jam
condition. Feeders need to be as robust and forgiving as possible
to accommodate marginal parts. This goal is best achieved through
solid tool design and thorough testing.
Feeder
Flexibility And Control Methods
As with all odd-form system components, the flexibility of the basic feeder
design is critical. The ability of the feeders to accommodate different part
styles will determine the flexibility, or the limitations, of the entire
system. Many feeder designs have a standard base or shell, with custom parts
added to handle the odd-form parts. Modular change parts allow the feeder
the flexibility to handle a new part style with ease of changeover. Some
feeders are more flexible than others; i.e. tube feeders with built-in adjustability
that can accommodate various tube designs without retooling.
Also
check into the feeder control system. A feeder that has mechanisms
controlled by flow controls and timers is bound to have reliability
problems as the mechanism parameters change. Such mechanisms
are typically set with some safety margin added to account for
parameter changes, and are therefore never running at the fastest
rate. Mechanisms controlled by closed loop are more robust, and
will perform at their maximum rate all of the time. In recent
years, programmable logic controller (PLC) controlled feeders
have become the industry standard. This allows customization
of the feeders operating characteristics while retaining a common
workcell interface. PLC's enable feeders to accommodate a variety
of control and sensor strategies on a single feeder platform.
Feeders without PLC control (often referred to dumb feeders),
are controlled directly by the workcell. Troubleshooting a dumb
feeder may require the use of the workcell to check sensor states
and toggle feeder inputs, thus holding up production; i.e. downtime.
Troubleshooting a PLC controlled feeder may only require a PC
with the appropriate PLC software and hardware interface. PLC
control allows a feeder to be programmed to interface to another
manufacturer's robotic workcell, whereas dumb feeders may require
rewiring.
Standardizing
Odd-Form Parts
Cost
savings can be achieved through the use of standardized components,
and should be carefully investigated. Consider standardizing tube
lengths, part styles, etc. Costs associated with using a multitude
of odd-form styles, feeder styles, manufacturers, and suppliers
can all be a factor. Standardization of styles and packaging methods
for parts can lead to cost savings through increased interchangeability
and flexibility of equipment. In some cases where parts are similar,
the same feeder can be used to feed different part types. Change
tooling can be used to locate the part while the feeding track
remains the same.
Initial
Feeder Cost: Pricing Variables
A wide range of factors may influence the cost of a feeder. In general, feeder
pricing will be most affected by the following:
Taking
into consideration all these factors, it's apparent that pricing
will vary dramatically from one feeder to another and one vendor
to another. When comparing quotes, don't automatically opt for
the lowest price, especially if it is substantially lower than
the others. This difference in pricing may be an honest miscalculation
on the supplier's part, or if the price is accurate, the supplier
may plan on using inferior materials or design, in which case
you would want to avoid them altogether. Comparative pricing
is a good idea as long as you are careful to identify and evaluate
actual value in relation to the cost.
Once
you have made a final purchasing decision, be sure to let the
other suppliers know. This is a common courtesy, and in fact
may help you later if for some reason your vendor of choice doesn't
work out, or if there is ever a future need for the other suppliers'
products.
True
Feeder Cost: The Price REALLY Paid
Although feeder pricing is very important, the "true" cost
of any feeder cannot be measured solely on its initial price.
Downtime, maintenance, performance,
parts inventory, and parts reloading must all be viewed as major cost considerations
as well. Downtime can easily cost many times over the initial feeder price
in a very short period of time. It is sadly not uncommon for manufacturers
to purchase inexpensive feeders, then find that they prove to be unreliable
and difficult to use or maintain requiring constant attention and troubleshooting.
The parts inventory a feeder carries can dramatically effect the overall
operation of the workcell. Make sure the feeder can be reloaded while in
operation, and find out how long loading the feeder will take. A feeder requiring
replenishment while the workcell is stopped will ultimately cost much more
in terms of production time and dollars.
Supplier
Evaluation
Just
as important as the feeder product itself is the supplier who provides
it. Is the supplier quality oriented? Can they show product history
and verified product reliability? Verified reliability means the
supplier should be able to provide data or guarantees for the reliability
of their feeders. Additionally, equipment suppliers should have
a proven track record with the feeder technology being evaluated
for your assembly line. Always check references and find examples
of long run production units to verify product performance. Any
supplier can make incredible claims and put together impressive
marketing materials, but are they actually able to offer proof
of these claims?
Talk
to the supplier and question any costs or terms you may not understand.
How well do you communicate with one another? Do you have the
same basic understanding of your needs? Now is the time to determine
whether you will be able to work well together. This may be as
important as any other factor in evaluating a supplier.
One
thing often overlooked is documentation. Ask to see representative
examples of manuals, spare parts lists and schematic drawings
for the feeders. If a supplier cannot show a copy of a manual,
it probably hasn't been written yet. A clear, concise and thorough
manual should be available for every piece of equipment that
a supplier offers.
Ask
for information from the supplier on the issues of feeder reliability,
maintenance, accessibility, mechanism control method, and feeder
replenishment. You should feel confident that the supplier is
able to provide this information clearly, and can offer the experience,
service and support to meet all your needs.
Putting
It All Together - Lessons Learned
Look for robust, reliable and proven equipment that maximizes the price to
performance relationship that is so critical to the bottom line. Use the
evaluation overview shown in Table 2 to help effectively evaluate different
feeder products. Be sure to take into consideration the true costs of operation,
not just the initial feeder price.
Table
2 - Odd-Form Feeder Evaluation
