Articles

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

Table 1

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:

  • Feeder base cost
  • Manufacturer's specialty
  • Modifications required to the standard feeder design
  • Part complexity and variance
  • Custom software/hardware interface
  • New feeder design
  • Cutting and forming requirements
  • Special functions (DIP rollover, sub-component assembly, and vision inspection)
  • Overall complexity

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

RELIABILITY:
  • Is feeder reliability verifiable? Is supplier able to provide data or guarantees for the reliability?
  • Does the feeder technology have a proven track record?
  • Can supplier provide references of other manufacturers using the feeder?
  • Can supplier provide examples of long run production units to verify product performance?
MAINTAINABILITY:
  • Is there easy access to mechanisms and controls for faster maintenance and trouble shooting?
  • Does the parts track allow both inspection of parts on the track and physical access to manually clear any possible jam conditions?
FLEXIBILITY:
  • Is the feeder designed specifically for odd-form assembly?
  • Is the feeder robust enough and forgiving enough to accommodate marginal parts?
  • What methods are used to provide feeder flexibility? (Modular change parts, adjustability, etc.)
  • What locating and handling method is being used? (Lead gripping, vision, or 3-D compliance)
  • Does this method take into consideration the mix and volume of odd-form components to be assembled?
  • Does this method provide enough flexibility to handle your current application as well as future system requirements?
CONTROL METHOD:
  • What is the method used to control this feeder? (Workcell control (dumb feeder), or PLC control (smart feeder)).
  • What type of feeder mechanism controls are used? (Flow controls, timers, closed loop control)
  • Do these control methods provide the reliability needed for this and future applications?
FEEDER PRICING:
  • Does the price quoted correlate to the factors most likely to affect feeder price? (base cost, manufacturer's specialty, required modifications, part complexity and variance, custom software/hardware interface, new design, overall complexity, cutting and forming requirements, and special functions).
  • How does the pricing compare to other vendors? (Don't automatically opt for lowest price, but rather examine the differences in products being careful to identify and evaluate actual value in relation to cost).
  • Besides the initial purchase price, determine what will be the "true" feeder cost. (This must include downtime, maintenance, performance, parts inventory, and parts reloading).

Finally, carefully evaluate the product quality, service and reputation of the equipment supplier as outlined in Table 3. Be sure you are able to communicate and work well with the supplier, and always ask for proof of feeder performance and reliability to substantiate claims before making a final purchase decision. By making use of this information, you can avoid the mistakes of others that have had to replace problem feeders, and purchase the right feeders for successful odd-form assembly the first time.

Table 3 - Supplier Evaluation Overview

PRODUCTS:

  • Are the supplier's products robust and quality oriented? Is there attention paid to design, ergonomics, aesthetics and detail?
  • Does the supplier specialize in odd-form products?
  • Can supplier show product history and verified product reliability?
  • Do the product sales and marketing claims actually match the product performance?

DOCUMENTATION:

  • Ask the supplier to provide you with representative examples of manuals, spare parts lists and schematic drawings.
  • A clear, concise and thorough manual should be available for every feeder a supplier offers.

REPUTATION:

  • Can supplier provide you with references and examples of long run productions?
  • Does supplier have a sound and stable company history and a good credit rating?
  • Does supplier have a strong background and experience in odd-form assembly?
  • How do other customers rate supplier's quality, service, support, experience and expertise?

COMMUNICATION:

  • Are you able to communicate comfortably and easily with the supplier?
  • Is the supplier willing to clarify all cost issues and other purchase terms?
  • Do they have a solid understanding of your needs?
  • Are they willing to openly discuss with you the issues of feeder reliability, maintenance, accessibility, handling and locating methods, mechanism and feeder control methods. and feeder replenishment? Will the supplier openly discuss all "true costs" such as downtime, parts inventory, maintenance, performance, etc.
  • Do you feel supplier and your company will work well together as a team, and the supplier is able and willing to meet all your needs?

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