Articles

The State of Odd-Form Equipment Technology

Written By:
Gregory Holcomb
Tawnya Henderson
Presented at ATE 2000

ABSTRACT

A highly diverse mix of various shaped and sized components, combined with limited component packaging standards, make the automation of odd-form assembly one of the more seemingly challenging tasks on the assembly line. In reality, with the commercial availability of odd-form automation equipment from several industry suppliers flexible enough to handle virtually all odd-form assembly requirements, odd-form automation is just as attainable and justifiable as other standard assembly automation processes.

Key to the success of odd-form automation are component locating and handling options flexible and robust enough to handle the wide variety of components typical to this type of assembly. In addition, solutions must adequately compensate for any board variances, body-to-lead variations, and lead-to-lead tolerance stack-ups to ensure accurate insertion/placement. To determine which locating and handling options are best suited to automate your odd-form assembly, you must first carefully evaluate the component mix, volume, part variance, and throughput requirements.

Key words: odd-form, automation, locating, handling.

INTRODUCTION
Although in the past the words "odd-form" put fear into the hearts of most manufacturers, today's odd-form assembly products are technically advanced enough to handle this challenge without difficulty. The question is no longer whether or not there is equipment capable of successfully automating odd-form assembly, but whether or not the proper assembly technology and equipment are matched to the required task. With careful assembly requirement evaluation, and knowledge of available technologies and equipment, total success in odd-form assembly can be achieved without the anxiety and risk, which often accompany an equipment purchase.

EVALUATION OF NEEDS
By being clear on your needs, both now and for the future, and working with your supplier to provide a complete assessment of those needs, you can determine how much accuracy, speed and flexibility are required. In doing so, you can match these requirements with the best suited locating and handling strategies, and in turn determine the optimal odd-form assembly equipment for the job.

There are two categories of information to be evaluated to best accomplish this; the application requirement information, and the production requirement information:

Application Specific Information:

  • What is the mix of components to be assembled? Is the mix low (1 - 3 part types), medium (4 -5 part types), or high (6 or more part types)?
  • Are you assembling similar types of components (such as a variety of DIPS), or are there many different styles of components which vary significantly in size and shape?
  • What is the range of variance in the body-to-lead and lead-to-lead geometry of the parts?
  • What percentage is surface mount and what percentage is through-hole?
  • What is the volume of odd-form components to be assembled? (low, medium, high.)
  • How many boards per panel? How many insertions/placements per board?
  • How many of each part number do you need to place or insert? Are the parts "balanced" or are there many more of some types which need to be placed/inserted than others?
  • Is lead cut/form or lead snap-in retention required? Is clinching of leads after insertion required?
  • Is pin-in-paste being used?

Production Specific Information:

  • How many shifts a day are you running?
  • What are your throughput requirements?
  • What type of packaging are you using?
  • What type of packaging is available?
  • How often do you need to change over to a new board?
  • What are your standards for the number of systems supported per operator?

It is very helpful to work with and communicate these issues with your supplier. By providing information on the number of boards you need and the number of parts you have, you can determine what kind of machine or machine combination is needed to achieve your desired throughput. By evaluating the component mix, you can then determine the best way to handle those parts. The part mix, part consistency, and part packaging will also determine your flexibility requirements.

An extremely important flexibility issue is the frequency of required board changeovers. For example, one automotive manufacturer runs its line three shifts a day using the exact same or very similar boards. They aren't extremely concerned about flexibility. Speed, accuracy and throughput requirements are obviously the priorities. On the other hand, a contract electronics manufacturer may change over boards several times a week. They require the greatest flexibility.

LOCATING AND HANDLING OPTIONS
Once you have carefully reviewed and evaluated your application and production needs, there are several viable locating and handling options available from industry suppliers, one or a combination of which will provide the maximum payback and productivity for your current and future application requirements.

ODD-FORM LEAD LOCATING TECHNOLOGIES:
Direct Lead Acquisition:
This method is used for through-hole odd-form parts and locates components by their leads with dedicated grip fingers. This more dedicated approach is highly suitable for lower mix applications and components requiring lead form or retention during insertion, such as splayed DIP's.



Figure 1. Illustration of a splayed DIP; an example of a component requiring lead retention during insertion.

Optical Lead Finding:
There are two general approaches to this method:

Vision: This approach typically uses upward viewing cameras to locate SMT part leads, and X-Y viewing cameras to locate through-hole part leads. Upward viewing cameras can be very effective for odd-form SMT applications (where the leads can be viewed in profile and a majority of the algorithms required have already been developed), but more limited for odd-form through-hole due to the great variety and difficulty of imaging the various lead tip configurations as illustrated in figure 2 below. Vision used to image the ends of through-hole leads creates issues with lighting and algorithms. Application specific algorithms must be developed for each new lead variation to accurately see the ends of leads due to the varying surface geometries of lead tips versus the simple lead profile of surface mountable parts. Profile (X -Y viewing) imaging can be easier to light and develop algorithms. Due to issues with shadowing and the need to obtain the X - Y coordinates of the lead pattern for insertion, use of profile imaging requires viewing in both the X and Y planes. Both upward and X - Y viewing cameras require passing parts through a vision station at the cost of cycle time.



Figure 2. Vision limitations when imaging through-hole component leads with an upward viewing camera only; difficulty verifying lead tip configurations.

Lead Scanning: This profile viewing technique is similar to the vision based X-Y viewing technology mentioned above. Using a laser rather than standard vision to image leads, this method has the same profile viewing benefits as the X-Y camera technology. It identifies and then compensates for variances between the expected and the actual offset of component leads. Similar to vision, the laser scanning technology requires passing the part through a viewing area, which may not meet the requirements of higher throughput applications.

Lead Registration in the Feeder:
This method physically locates through-hole part leads while the part is still in the feeder, and then the part is gripped by the body for placement/insertion. This is a simple approach which allows you to keep constant control of the part. In addition, the flexibility gained through use of body gripping allows for effective assembly of parts ranging from geometrically stable parts (using a simple handling strategy), to parts with greater geometric variance (using a more flexible, adaptive compliant handling strategy). When matched with a flexible handling strategy, picking a part by the body versus the leads provides greater agility, allowing it to handle component brickwalling and to meet other common odd-form assembly challenges.

ODD-FORM COMPONENT HANDLING TECHNOLOGIES:
The following handling technologies are available in many different types of heads or grippers (single, multi, compliant, etc.), as well as with automatic head, finger, and other tool changers. Tactile sensing must be included in all these technologies for successful insertion/placement detection. Vision can also be used with any of these handling technologies when needed.

Vacuum
Pneumatic vacuum picking is the handling of parts with a vacuum tip or quill which when placed on a flat surface of a component will pick up, move, and place the part using vacuum suction and release. This handling technology is most commonly used for placement of surface mount components which are more likely to have a flat surface to pick from.

Vacuum technology can be very cost effective as an add-on if you already have a surface mount machine and are using existing tools, or if you are only using these specific surface mount part types. However the technology is limited to parts that can be vacuum picked only, and many odd-form parts are not typically surface mount devices and do not necessarily lend themselves to vacuum picking. Parts not easily vacuum picked can be adapted by adding special flat surface pieces to each part which is then removed after part placement on the board.

Simple Pneumatic Actuated Fingers:
This technology makes use of air pressure to open and close gripper jaws, typically tooled with dedicated fingers. It is the most simple and least expensive type of handling technology, but limited due to the fact that gripper jaws controlled by air pressure alone are either completely open or completely closed. Although this is not a problem when picking a part from a feeder, placement on a densely populated board can be limited.

Servo Actuated Fingers:
Servo actuated technology is the handling of parts with jaws operated by a small electric motor in the grip which allows movement of the jaws to any pre-programmed point. It makes it possible to handle different sized parts on densely populated boards due to the programmable motorized movement of the jaws without having to open fully after placing/inserting a part. However with the advantage of the programmed movement comes the disadvantage of increased complexity of mechanical design and software programming.

Self-Adapting Fingers:
This technology handles parts with jaws operated by air pressure, but also has controlled opening and closing of the jaws by use of a specialized cylinder. The cylinder allows incremental movement of the jaws, as with servo-gripping, but without the need for electric motors and drives or the extent of software programming. In other words, adaptive technology combines the simplicity of simple pneumatic actuation with the flexibility of servo actuation.

The jaws have a grip release that automatically opens from any size or shape part within a few thousandths of an inch for insertion/placement into densely populated boards. There is no need for application specific programming for jaw positioning. Self-adapting tools easily accommodate high density and brickwall applications.

HANDLING IMPLEMENTATION STRATEGIES:
The handling technologies outlined above are integrated into many different physical forms for execution by different suppliers. Some are combined with, or in addition to others, and some overlap others, but the physical manifestation of these technologies generally falls into one of the implementation strategies outlined below. These strategies help to take the application and technology requirements we have defined to this point and match them with the physical performance levels needed to best handle the job.

Single-tool:
This strategy makes use of a single dedicated tool for handling odd-form components. It can also be equipped with automatic head and/or finger changers and used with vision location when required. Handling technologies used with single-tool strategies include:

  • Vacuum (for SMT or mixed technology applications)
  • Simple pneumatic fingers
  • Servo actuated fingers
  • Self-adapting fingers

A single-tool grip generally has the least weight so it can move quickly and is the least complex implementation choice, however it is also the least flexible and can therefore only be used for very low-mix applications. Automatic head or finger changers can generally be used to improve the flexibility, but with the cost of increased cycle time. Single-grip tool strategies are best used for applications requiring low flexibility with only one to three different part styles to be assembled, and with medium to high throughput.

Multi-tools:
This strategy makes use of several tools on one head, turret, or indexing wrist, which are then used to assemble several different part types simultaneously. Component "balance" is a huge issue with multi-tool handling and must be carefully evaluated to make this a viable option; even systems equipped with automatic head and jaw changers are subject to this problem. For example, if you are using a five-up tool and have six parts to be assembled, the gripper can only pick up five of them, and then must go back again to get the single left-over part. This causes loss of much of the speed advantage over other more flexible methods. In addition, depending on the part types, vision location may be required. Handling technologies used with multi-tools include:

  • Vacuum (for SMT or mixed technology applications)
  • Simple pneumatic fingers
  • Servo actuated fingers
  • Self-adapting fingers

If component assembly is "balanced", this strategy can provide more speed and more flexibility than a single-tool approach, and can typically handle up to six part types without the need to change heads or jaws. If more than six parts need to be assembled, head or jaw changes will likely be required. Tool changing can be more complex since jaws and grip modules must be matched as well as the combination of jaws and applications, and therefore this strategy is best used for applications with a well balanced, medium parts mix.

Compliant Tools:
This strategy consists of two general approaches:

  • Single-Plane Compliant Tools: This 2-D approach can accommodate a variety of through-hole and SMT odd-form component styles and lead variations. It normally does not require vision location if the part is geometrically consistent. The typical handling technologies used with this strategy are:
  • Servo actuated fingers
  • Self-adapting fingers.

While the single-plane compliant tool can accommodate a variety of odd-form parts without the need for vision, it cannot compensate for tilted parts such as Capacitors, SIP's, hybrid SIP's, Inductors, MOV's, TO-220's, and many others. Therefore this strategy is best used for applications with a lower parts mix which only require compensation for skewed or twisted parts, such as Connectors or other "precision" molded parts that are not tilted.

Adaptive Compliant Tool: This tool facilitates body gripping regardless of part geometry or condition and does not require lead find tools since control of lead location is never lost. Using this 3-D adaptive technology approach, the assembly head can fully comply with all six degrees of freedom, thus creating a totally flexible handling strategy able to accommodate virtually all odd-form through-hole and SMT component types. It can also handle all part tolerance variations, including tilted, skewed, and twisted parts, as illustrated in figure 3 (shown at end of paper). The handling technology typically used with this strategy is:

  • Self-adapting fingers

The adaptive technology combines the most flexible handling method with a simple mechanical design. It is capable of handling odd-form through-hole and surface mount components without head or finger changes, and is therefore best suited to applications requiring a medium to high mix of component types with varying tolerances and/or many board changeovers. Although the adaptive technology is much more flexible, a multi-tool used in a well-balanced application without the need for tool changes or retooling may be faster.

Mixed Technology Tools:
The mix-tech handling strategy uses two or more of the appropriate handling technologies and strategies listed above to handle both through-hole and a wider variety of SMT components on the same system. Handling technologies used with these tools include:

  • Vacuum
  • Simple pneumatic fingers
  • Servo actuated fingers
  • Self-adapting fingers

Mixed technology tools provide the necessary flexibility to handle both through-hole and SMT mixed technology applications, however the degree of flexibility and throughput achieved is dependant on the handling technology used. This range of capabilities provides many benefits, but the addition of more tools also adds more complexity to the system.

SUMMARY
Equipment solutions are easily identified when properly matched with the required odd-form tasks. Component mix, volume, and throughput requirements are the most important issues to consider when evaluating which locating and handling technologies are best utilized for the automation of your odd-form assembly process.

It is necessary to give weight to the importance of each issue as it relates to the ultimate productivity of your current and future assembly line requirements. Once you have established which requirements are the most critical to the success of your business, they can be matched to the most effective locating and handling technologies, and your odd-form automation solutions will become clear.

ADAPTIVE COMPLIANT
HANDLING


 
APPROACH
GRIP,
3-D ADAPTIVE
COMPLIANCE & LOCK
DEPART
ROLL:

REQUIRED FOR
TILTED PARTS
YAW:

REQUIRED FOR
TWISTED LEAD TO
BODY RELATIONSHIP
X-Y
TRANSLATION:


REQUIRED DUE TO
VARIATION IN LEAD
TO BODY CENTERLINE -
SKEWED PARTS
3-D
ADAPTIVE COMPLIANCE (ACT):


PITCH
, ROLL AND YAW
REQUIRED ON
CONFORMAL COATED
PARTS OR ANY PART
WITH UNEVEN
BODY SURFACES

Figure 3. Drawing illustrates an adaptive compliant assembly head compensating for body-to-lead and lead-to-lead variations in three dimensions (allowing for all six degrees of freedom).

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